L e s /W o o d , V o l . 70, No . 1, Ju n e 2021 1 • U v o d n ik . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Ed it o r ia l Jo ž e Kr o p i v š e k • N a s t a ja n je in s t r u k t u r a le s a in fl o e m a p r i n a v a d n i s m r e k i . . . . . . . . . . . . . . . . . . . . . . 5 Fo r m a ti o n a n d s t r u c t u r e o f w o o d a n d p h lo e m in N o r w a y s p r u c e Jo ž i c a G r i č a r , Ka t a r i n a Č u f a r , Pe t e r Pr i s l a n • A n a liz a r a z k r o je n e g a s m r e k o v e g a le s a , z a š č it e n e g a z b io c id n im p r o iz v o d o m CCB, p o 14 le ti h iz p o s t a v it v e n a p r o s t e m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 A n a ly s is o f d e c a y e d N o r w a y s p r u c e w o o d im p r e g n a t e d w it h CCB a ft e r 14 y e a r s o f o u t d o o r e x p o s u r e M i h a Hu m a r , B o š t j a n L e s a r , Da v o r Kr ž i š n i k , A n g e l a B a l z a n o • Ch e m ic a l a n d m e c h a n ic a l c h a r a c t e r iz a ti o n o f t h e r m a lly m o d ifi e d G m e lin a a r b o r e a w o o d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Ke m ijs k a in m e h a n s k a k a r a k t e r iz a c ija t e r m ič n o m o d ifi c ir a n e g a le s a v r s t e G m e lin a a r b o r e a M a x i d i t e A m a n k w a a h M i n k a h , Ko j o A g y a p o n g A f r i f a h , Dj e i s o n C e s a r B a ti s t a , Ho l g e r M i l i t z • U p o r a b n o s t le s n ih o s t a n k o v t u je r o d n ih in v a z iv n ih d r e v e s n ih v r s t z a p r o iz v o d n jo p e le t o v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 U s e f u ln e s s o f n o n -n a ti v e in v a s iv e t r e e s p e c ie s w o o d r e s id u e s f o r p e lle t p r o d u c ti o n Do m i n i k a G o r n i k B u č a r , Pe t e r Pr i s l a n , Pa v e l Sm o l n i k a r , Da r j a St a r e , Ni k e Kr a j n c , B o j a n G o s p o d a r i č • Fo r m a ti o n o f s ilv e r n a n o p a r ti c le s o n lig n in a n d t w o o f it s p r e c u r s o r s . . . . . . . . . . . . 59 T v o r b a s r e b r o v ih n a n o d e lc e v n a lig n in u in n je g o v ih d v e h p r e k u r z o r jih Se b a s ti a n Da h l e , L i e n h a r d W e g e w i t z , W o l f g a n g V i ö l , W o l f g a n g M a u s -Fr i e d r i c h s • T h e r m a l c o n d u c ti v it y o f d iff e r e n t b io -b a s e d in s u la ti o n m a t e r ia ls . . . . . . . . . . . . . . . 73 T o p lo t n a p r e v o d n o s t r a z lič n ih b io -iz o la c ijs k ih m a t e r ia lo v Se r g e j M e d v e d , Eu g e n i a M a r i a n a Tu d o r , M a r i u s C a t a l i n B a r b u , Ti m o t h y M . Y o u n g N o v ic e • O d d e le k z a le s a r s t v o s o d e lu je k o t p a r t n e r v c iljn e m r a z is k o v a ln e m p r o je k t u z a iz b o ljš a n je k o n k u r e n č n o s ti le s a lis t a v c e v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Ti n a Dr o l c • In m e m o r ia m : p r o f. d r. Jo ž e Ko v a č ( 1930– 2021). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Jo ž e Re s n i k • In m e m o r ia m : A lo jz Le b – s t a r o s t a s lo v e n s k e g a le s a r s t v a !. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 M i r k o G e r š a k • P r o f. d r. Ka t a r in a Č u f a r je p r e je la Je s e n k o v o n a g r a d o z a ž iv lje n js k o d e lo . . . . . . . . . . . . . . . . . . . . . 89 P r o f. Dr. Ka t a r in a Č u f a r r e c e iv e d t h e Je s e n k o Lif e ti m e A c h ie v e m e n t A w a r d M a r k o Pe t r i č , M i l a n Š e r n e k V S EBIN A / CO N T EN T S Le t n ik 70, š t e v ilk a 1 / V o lu m e 70, N u m b e r 1 L e s /W o o d , V o l . 70, No . 1, Ju n e 2021 2 Le s /W o o d Z a lo ž ila /P u b lis h e d b y Z a l o ž b a U n i v e r z e v L j u b l j a n i / U n i v e r s i t y o f L j u b l j a n a P r e s s Z a z a lo ž b o /F o r t h e P u b lis h e r Ig o r Pa p i č , r e k t o r U n i v e r z e v L j u b l j a n i / t h e R e c t o r o f t h e U n i v e r s i t y o f L j u b l j a n a Iz d a la /I s s u e d b y U n i v e r z a v L j u b l j a n i , B i o t e h n i š k a f a k u l t e t a , Od d e l e k z a l e s a r s t v o / U n i v e r s i t y o f L j u b l j a n a , B i o t e h n i c a l F a c u l t y , D e p a r t m e n t o f W o o d S c i e n c e a n d T e c h n o l o g y Z a iz d a ja t e lja /F o r t h e I s s u e r Na t a š a Po k l a r U l r i h , d e k a n j a B i o t e h n i š k e f a k u l t e t e U L / t h e D e a n o f t h e B i o t e h n i c a l F a c u l t y U L N a s lo v u r e d n iš t v a /E d it o r ia l O ffi c e A d d r e s s U n i v e r z a v L j u b l j a n i , B i o t e h n i š k a f a k u l t e t a , Re v i j a L e s /W o o d , Ja m n i k a r j e v a u l i c a 101, 1000 L j u b l j a n a , Sl o v e n i a Gla v n a u r e d n ic a /E d it o r - in - c h ie f Ka t a r i n a Č u f a r , Sl o v e n i j a , e -p o š t a : k a t a r i n a . c u f a r @ b f . u n i -l j . s i O d g o v o r n i u r e d n ik /M a n a g in g e d it o r Jo ž e Kr o p i v š e k , Sl o v e n i j a , e -p o š t a : j o z e . k r o p i v s e k @ b f . u n i -l j . s i T e h n ič n i u r e d n ik /T e c h n ic a l e d it o r A n t o n Z u p a n č i č , Sl o v e n i j a , e -p o š t a : a n t o n . z u p a n c i c @ b f . u n i -l j . s i U r e d n iš k i o d b o r /E d it o r ia l b o a r d C h r i s ti a n B r i s c h k e , Ne m č i j a / G e r m a n y A l a n C r i v e l l a r o , V e l i k a B r i t a n i j a / U n i t e d K i n g d o m Do m i n i k a G o r n i k B u č a r , Sl o v e n i j a / S l o v e n i a M i h a Hu m a r , Sl o v e n i j a / S l o v e n i a De n i s Je l a č i ć , Hr v a š k a / C r o a ti a L e o n Ob l a k , Sl o v e n i j a /S l o v e n i a Pr i m o ž Ov e n , Sl o v e n i j a / S l o v e n i a Kr i s h n a K. Pa n d e y , In d i j a / In d i a M a n u e l a Ro m a g n o l i , It a l i j a /I t a l y Ke v i n T. Sm i t h , Z DA / U S A M i l a n Š e r n e k , Sl o v e n i j a / S l o v e n i a Ru p e r t W i m m e r , A v s t r i j a / A u s t r i a Je z ik o v n i p r e g le d /P r o o f r e a d in g Da r j a V r a n j e k (s l o v e n s k o b e s e d i l o / S l o v e n e t e x t ) Pa u l St e e d (a n g l e š k o b e s e d i l o / E n g l i s h t e x t ) P r e lo m /L a y o u t DEC OP, d . o . o . , Ž e l e z n i k i T is k /P r in t Ti s k a r n a Ro b o p l a s t d . o . o . , L j u b l j a n a Na ti s n j e n o v j u n i j u 2021 v 100 i z v o d i h . / P r i n t e d i n J u n e 2 0 2 1 i n 1 0 0 c o p i e s . IS S N 0024-1067 (ti s k a n a v e r z i j a / p r i n t e d v e r s i o n ) IS S N 2590-9932 (s p l e t n a v e r z i j a / o n - l i n e v e r s i o n ) h tt p ://w w w .le s -w o o d .s i/ P e r io d ič n o s t /F r e q u e n c y Dv e š t e v i l k i l e t n o / T w o i s s u e s p e r y e a r Le s /W o o d je r e f e r ir a n v m e d n a r o d n ih b ib lio g r a f s k ih z b ir k a h L e s / W o o d is in d e x e d in t h e in t e r n a ti o n a l b ib lio g r a p h ic d a t a b a s e s A G RIS, C A B A b s t r a c t L e s /W o o d j e r e v i j a z o d p r ti m d o s t o p o m , k i i z h a j a p o d p o g o j i l i c e n c e C r e a ti v e C o m m o n s C C B Y -NC 4. 0. L e s / W o o d i s a n O p e n A c c e s s j o u r n a l p u b l i s h e d u n d e r t h e t e r m s o f t h e C r e a ti v e C o m m o n s C C B Y - N C 4.0 L i c e n s e . Iz d a j a n j e r e v i j e s o fi n a n c i r a Ja v n a a g e n c i j a z a r a z i s k o v a l n o d e j a v n o s t Re p u b l i k e Sl o v e n i j e (A RRS) T h e j o u r n a l i s c o - fi n a n c e d b y S l o v e n i a n R e s e a r c h A g e n c y ( A R R S ) L e s /W o o d , V o l . 70, No . 1, Ju n e 2021 3 U V O DN IK / EDIT O R IA L Od g o v o r n i u r e d n i k / M a n a g i n g e d i t o r Jo ž e Kr o p i v š e k p a n o g e i n d r u ž b e v c e l o ti . Ko n c e p t d i g i t a l i z a c i j e z n o v i m i t e h n o l o g i j a m i i n s t o r i t v a m i , k i s o v č a s u p a n - d e m i j e C o v i d -19 o m o g o č a l e , d a j e d r u ž b a b o l j a l i m a n j u č i n k o v i t o d e l o v a l a k l j u b (s k o r a j ) p o p o l n e m u z a p r t j u j a v n e g a i n g o s p o d a r s k e g a o k o l j a , š e v e d n o p r e d s t a v l j a z a p o d j e t j a (i n d r ž a v o ) p r e c e j š e n i z z i v . Na j v e č j i i z z i v s o d i g i t a l n e k o m p e t e n c e m a n a g e r j e v , z a p o s l e n i h i n v s e h l j u d i , k i s o k l j u č n e z a u v a j a n j e n o v i h d i g i t a l n i h t e h n o l o g i j i n k o n c e p t o v , k i s o v s o d - o b n i d r u ž b i n u j n i z a p r e ž i v e t j e i n n a d a l j n j i r a z v o j . Ra z v o j u l e -t e h j e n a m e n j e n e v r o p s k i p r o j e k t » A l l - V i e w « , k a t e r e g a c i l j j e d i g i t a l i z a c i j a i n p o e n o t e n j e i z - o b r a ž e v a l n i h p r o c e s o v n a v s e h n i v o j i h i z o b r a ž e v a n j a n a p o d r o č j u l e s a r s t v a , k i b o d o v k l j u č e v a l i d i g i t a l n e v s e b i n e z a r a z v o j d i g i t a l n i h k o m p e t e n c u č e č i h s e , i n b o d o t e m e l j i l i n a s o d o b n i , p a m e t n i p l a tf o r m i . Ra v n o p r o b l e m p o m a n j k a n j a d i g i t a l n i h z n a n j i n k o m p e t e n c v l e s a r s t v u p a j e b i l a s k u p n a u g o t o v i t e v o k r o g l e m i z e , k i j e s l e d i l a p r e d s t a v i t v a m p r o j e k t o v n a p r e j o m e n j e n e m 9. Ra z v o j n e m d n e v u g o z d n o -l e s n e g a s e k t o r j a . Da p a j e d i g i t a l i z a c i j a z e l o p r i s o t n a t u d i v l e s a r s t v u , s o n a t e m d o g o d k u n a p r i m e r i h d o b r e p r a k s e p o k a z a l i p r e d s t a v n i k i v e č p o d j e ti j . G l e d e n a i z k a z a n o r a z v o j n o m o č g o z d n o -l e s n e v e r i g e p r i r e v i j i L e s /W o o d t u d i v p r i h o d n j e u p a m o n a d o t o k z a n i m i v i h p r i s p e v k o v . Hv a l a v s e m , k i p o - m a g a t e p r i p r i p r a v i r e v i j e , š e p o s e b e j (a n o n i m n i m ) r e c e n z e n t k a m i n r e c e n z e n t o m , k i s t e n a m s s v o j i m a ž u r n i m i n k a k o v o s t n i m d e l o m p r i s k o č i l i n a p o m o č t u d i p r i p r i p r a v i t e š t e v i l k e r e v i j e L e s /W o o d . Pr e d v a m i j e n o v a š t e v i l k a r e v i j e L e s /W o o d , k i j e n a s t a j a l a v d r u g e m l e t u p a n d e m i j e C o v i d -19, k i j e k r o j i l a d o g a j a n j e t u d i v g o z d n o -l e s n i v e r i g i . Z n a n - s t v e n i p r i s p e v k i v t e j r e v i j i p r i k a z u j e j o n o v a s p o z n a - n j a o t e m , k a k o i n k d a j n a s t a j a k a s n i l e s p r i n a v a d n i s m r e k i , k a j s e d o g a j a z z a š č i t e n i m l e s o m s m r e k e n a p r o s t e m p o d a l j š e m č a s u i z p o s t a v i t v e i n k a j s e z g o d i s k e m i č n i m i i n m e h a n s k i m i l a s t n o s t m i p r i t e r m i č n i m o d i fi k a c i j i l e s a h i t r o r a s t o č e p l a n t a ž n e l e s n e v r s t e G m e l i n a a r b o r e a , k i j o u v a j a j o n a d e g r a d i r a n i h o b - m o č j i h v G a n i , d a b i o m e j i l i k r č e n j e g o z d o v . Na d a l j e p r i s p e v k i p r i k a z u j e j o m e h a n i z m e n a s t a n k a n a n o d e l - c e v s r e b r a n a l i g n i n u , u p o r a b n o s t l e s n i h o s t a n k o v i n v a z i v n i h d r e v e s n i h v r s t z a p r o i z v o d n j o p e l e t o v i n t o p l o t n o p r e v o d n o s t r a z l i č n i h b i o -i z o l a c i j s k i h m a t e - r i a l o v n a o s n o v i l e s n i h o s t a n k o v . V s e n a š t e t e t e m e s e d o b r o v k l a p l j a j o v r a z v o j n i k o n c e p t b i o g o s p o d a r - s t v a , k i j e p o s e b e j p o m e m b e n p r i z a g o t a v l j a n j u d o l - g o r o č n e j š e g a o b v l a d o v a n j a p o d n e b n i h s p r e m e m b i n p r e h o d a v n i z k o o g l j i č n o d r u ž b o . B i o g o s p o d a r s t v o k o t p o m e m b n a r a z v o j n a u s m e r i t e v t a k o v g o z d n e m d e l u g o z d n o -l e s n e v e r i g e k o t v p r e d e l a v i l e s a j e b i l o p o s e b e j i z p o s t a v l j e n o n a Dn e v i h s l o v e n s k e g a l e s a r - s t v a 2021 i n n a 9. Ra z v o j n e m d n e v u g o z d n o -l e s n e g a s e k t o r j a , k j e r j e b i l o v l e t u 2021 i d e n ti fi c i r a n i h k a r 59 a k t u a l n i h p r o j e k t o v , s o fi n a n c i r a n i h i z j a v n i h s r e d - s t e v Re p u b l i k e Sl o v e n i j e i n /a l i EU . To k a ž e n a i z - j e m n o r a z v o j n o m o č t e v e r i g e , k i j e k l j u č n a z a n j e n o d o l g o r o č n e j š o u s p e š n o s t , p o l e g k r a t k o r o č n i h o d z i - v o v p o d j e ti j n a s p r e m e m b e p o s l o v n e g a o k o l j a z u v a - j a n j e m n o v i h t e h n o l o g i j , p o s l o v n i h m o d e l o v i n k o n c e p t o v v s v o j a p o s l o v a n j a . Sk u p n e t e m e r a z v o j n i h u s m e r i t e v b i p o l e g b i o - g o s p o d a r s t v a l a h k o s t r n i l i š e v e n o k l j u č n o t e m o , t o j e d i g i t a l i z a c i j a o z . d i g i t a l n a t r a n s f o r m a c i j a p o d j e ti j , R a z v o jn o -r a z is k o v a ln e a k ti v n o s ti v le s a r s t v u v z n a m e n ju d ig it a liz a c ije in b io g o s p o d a r s t v a L e s /W o o d , V o l . 70, No . 1, Ju n e 2021 4 In f r o n t o f y o u i s a n e w i s s u e o f t h e j o u r n a l L e s /W o o d , w h i c h w a s c r e a t e d i n t h e s e c o n d y e a r o f t h e C OV ID-19 p a n d e m i c , w h i c h a l s o s h a p e d t h e e n - ti r e f o r e s t w o o d c h a i n . Th e s c i e n ti fi c a r ti c l e s i n t h i s j o u r n a l p r e s e n t n e w i n s i g h t s i n t o h o w a n d w h e n l a - t e w o o d i s f o r m e d i n s p r u c e , w h a t h a p p e n s t o p r o - t e c t e d s p r u c e w o o d o u t d o o r s a ft e r a l o n g e x p o s u r e p e r i o d , a n d w h a t h a p p e n s t o t h e c h e m i c a l a n d m e c - h a n i c a l p r o p e r ti e s o f t h e r m a l l y m o d i fi e d w o o d f r o m t h e f a s t -g r o w i n g p l a n t a ti o n s p e c i e s G m e l i n a a r b o - r e a , w h i c h i s b e i n g i n t r o d u c e d i n t o d e g r a d e d a r e a s i n G h a n a t o l i m i t d e f o r e s t a ti o n . In a d d i ti o n , t h i s i s s u e p r e s e n t s t h e m e c h a n i s m s o f t h e f o r m a ti o n o f s i l v e r n a n o p a r ti c l e s o n l i g n i n , t h e u s a b i l i t y o f w o o d r e s i d u e s f r o m i n v a s i v e t r e e s p e c i e s f o r t h e p r o d u c - ti o n o f p e l l e t s , a n d t h e t h e r m a l c o n d u c ti v i t y o f v a - r i o u s w o o d r e s i d u e -b a s e d b i o -i n s u l a ti o n m a t e r i a l s . A l l t h e s e t o p i c s fi t w e l l i n t o t h e d e v e l o p m e n t o f t h e c o n c e p t o f t h e b i o e c o n o m y , w h i c h i s o f p a r ti c u l a r i m p o r t a n c e f o r t h e l o n g -t e r m m a n a g e m e n t o f c l i - m a t e c h a n g e a n d t h e t r a n s i ti o n t o a l o w -c a r b o n so c i e t y . Th e b i o e c o n o m y a s a n i m p o r t a n t d e v e l o p - m e n t d i r e c ti o n i n t h e f o r e s t r y p a r t o f t h e f o r e s t - w o o d c h a i n , a s w e l l a s i n w o o d p r o c e s s i n g , w a s p a r ti c u l a r l y h i g h l i g h t e d a t t h e Da y s o f t h e Sl o v e n i a n W o o d Se c t o r 2021 a n d a t t h e 9t h De v e l o p m e n t Da y o f Fo r e s t -W o o d Se c t o r , w h e r e n o l e s s t h a n 59 c u r - r e n t p r o j e c t s s u p p o r t e d b y p u b l i c f u n d s o f t h e Re - p u b l i c o f Sl o v e n i a a n d /o r t h e EU w e r e i d e n ti fi e d . Th i s s h o w s t h e e x c e p ti o n a l d e v e l o p m e n t a l s t r e n g t h o f t h i s c h a i n , w h i c h i s c r u c i a l f o r i t s l o n g -t e r m s u c - c e s s , i n a d d i ti o n t o t h e s h o r t -t e r m r e a c ti o n s o f c o m - p a n i e s t o c h a n g e s i n t h e b u s i n e s s e n v i r o n m e n t b y i n t r o d u c i n g n e w t e c h n o l o g i e s , b u s i n e s s m o d e l s a n d c o n c e p t s i n t o t h e i r b u s i n e s s e s . In a d d i ti o n t o t h e b i o e c o n o m y , t h e c o m m o n t h e m e s o f t h e d e v e l o p m e n t o r i e n t a ti o n s c a n b e s u m m a r i s e d i n a n o t h e r k e y t h e m e , n a m e l y d i g i t a l i - s a ti o n o r t h e d i g i t a l t r a n s f o r m a ti o n o f c o m p a n i e s , i n d u s t r i e s a n d s o c i e t y a s a w h o l e . Th e c o n c e p t o f d i - g i t a l i s a ti o n w i t h n e w t e c h n o l o g i e s a n d s e r v i c e s , w h i c h e n a b l e d s o c i e t y t o o p e r a t e r e a s o n a b l y e ffi - c i e n t l y d e s p i t e t h e (a l m o s t ) c o m p l e t e c o m p a r t m e n - t a l i s a ti o n o f t h e p u b l i c a n d e c o n o m i c e n v i r o n m e n t d u r i n g t h e C OV ID-19 p a n d e m i c , c o n ti n u e s t o p o s e s i g n i fi c a n t c h a l l e n g e s f o r b o t h b u s i n e s s e s a n d t h e s t a t e . Th e g r e a t e s t c h a l l e n g e s l i e i n t h e d i g i t a l c o m - p e t e n c i e s o f m a n a g e r s , e m p l o y e e s , a n d t h e g e n e r a l p o p u l a ti o n . Th e s e c o m p e t e n c i e s a r e c r u c i a l f o r t h e a d o p ti o n o f n e w d i g i t a l t e c h n o l o g i e s a n d c o n c e p t s i n s o c i e t y , t o a i d b o t h i t s f u r t h e r d e v e l o p m e n t a n d u l ti m a t e s u r v i v a l . Th e Eu r o p e a n p r o j e c t "A l l V i e w " i s a i m e d a t t h e d e v e l o p m e n t o f t h e s e c o m p e t e n c i e s , w i t h t h e g o a l o f d i g i t a l i s a ti o n a n d u n i fi c a ti o n o f e d u - c a ti o n a l p r o c e s s e s a t a l l l e v e l s o f e d u c a ti o n i n t h e fi e l d o f w o o d , w h i c h i n c l u d e s d i g i t a l c o n t e n t f o r t h e d e v e l o p m e n t o f d i g i t a l c o m p e t e n c e s o f l e a r n e r s a n d i s b a s e d o n a n u p -t o -d a t e , s m a r t p l a tf o r m . Th e l a c k o f d i g i t a l k n o w l e d g e a n d c o m p e t e n c e s i n t h e w o o d s e c t o r w a s o n e o f t h e m a i n fi n d i n g s o f t h e r o u n d t a - b l e d i s c u s s i o n w h i c h f o l l o w e d t h e p r e s e n t a ti o n s o f p r o j e c t s a t t h e p r e v i o u s l y m e n ti o n e d 9t h De v e l o p - m e n t Da y o f t h e Fo r e s t -W o o d Se c t o r . Ho w e v e r , w i t h p r e s e n t a ti o n s o f c a s e s o f g o o d p r a c ti c e a t t h i s e v e n t , r e p r e s e n t a ti v e s o f s e v e r a l c o m p a n i e s s h o w e d t h a t d i g i t a l i s a ti o n i s a l r e a d y p r e s e n t i n t h e w o o d s e c t o r . Du e t o t h e p r o v e n d e v e l o p m e n t s t r e n g t h o f t h e f o r e s t -w o o d c h a i n , a n (i n c r e a s e d ) i n fl u x o f i n t e r e - s ti n g a r ti c l e s a t L e s /W o o d j o u r n a l c a n b e e x p e c t e d i n t h e f u t u r e . Ou r t h a n k s g o t o a l l t h o s e w h o c o n t r i - b u t e t o t h e p r e p a r a ti o n o f t h e j o u r n a l , e s p e c i a l l y t o t h e (a n o n y m o u s ) r e v i e w e r s w h o h e l p u s w i t h t h e i r u p -t o -d a t e a n d h i g h -q u a l i t y w o r k i n t h e p r e p a r a ti o n o f t h i s i s s u e o f L e s /W o o d . R &D a c ti v iti e s in w o o d w o r k in g in t h e s ig n o f d ig it a liz a ti o n a n d b io e c o n o m y 5 Les/Wood, Vol. 70, No. 1, June 2021 1 UVOD 1 INTRODUCTION Podnebne spremembe in z njimi povezani izredni vremenski dogodki kot so suše, veter, žled, vročinski valovi in pozebe, vplivajo na vrstno ses- tavo, vitalnost dreves, produkcijo in kakovost lesa v slovenskih gozdovih (IPCC, 2014; Krajnc, et al., 2021). V Sloveniji je trenutno gospodarsko najpo- UDK: 630*811.41/.42+630*811.7 Izvirni znanstveni članek / Original scientific article Prispelo / Received: 24. 5. 2021 Sprejeto / Accepted: 1. 6. 2021 Vol. 70, No. 1, 5-18 DOI: https://doi.org/10.26614/les-wood.2021.v70n01a06 Izvleček / Abstract Izvleček: Baze podatkov o nastajanju lesa in floema so pomembne za razumevanje vpliva podnebnih sprememb in izrednih vremenskih dogodkov na vrstno sestavo, vitalnost dreves, produkcijo ter kakovost lesa v slovenskih gozdovih. V tem članku predstavljamo najnovejše rezultate o debelinski rasti navadne smreke (Picea abies (L.) Karst.) z dveh rastišč v Sloveniji, na Panški reki (PAN – 400 m n. v.) in Menini planini (MEN – 1200 m n. v.) v letih 2009–2011. Pou- darek je bil na sezonski dinamiki nastajanja ranega in kasnega lesa ter ranega in kasnega floema. Ugotovili smo, da rastiščne razmere v veliki meri vplivajo na sezonsko dinamiko nastajanja lesa in floema, kar se odraža v širini in struk- turi prirastkov. Na višje ležečem rastišču MEN je bila rastna sezona približno mesec dni krajša (dolga slabe 4 mesece), posledično so bili letni prirastki ožji, in sicer v lesu za 39 % in v floemu za 15 %. Na MEN smo prehod iz ranega v kasni les v povprečju opazili le teden dni kasneje kot na PAN, medtem ko je prehod iz ranega v kasni floem nastopil v popre- čju 20 dni kasneje. Informacije o vplivu rastiščnih razmer na debelinsko rast smreke in kakovost lesa so pomembne za vse deležnike v gozdno-lesni verigi, saj so lahko v pomoč pri sprejemanju ustreznih ukrepov upravljanja za prilagoditev spremenjenim razmeram. Ključne besede: rani les, kasni les, rani floem, kasni floem, branika, kambij, navadna smreka-Picea abies Abstract: Wood and phloem formation databases are important for understanding the effects of climate change and extreme weather events on species composition, tree vitality, wood production and wood quality in Slovenian forests. In this paper, we present the latest results on the radial growth of Norway spruce (Picea abies (L.) Karst.) at two sites in Slovenia, Panška reka (PAN – 400 m a. s .l.) and Menina planina (MEN – 1200 m a. s .l.) in 2009–2011. The focus was on the seasonal dynamics of early and latewood, and early and late phloem formation. We found that site conditions greatly affected the seasonal dynamics of wood and phloem formation, which was reflected in the width and struc- ture of annual increments. At the higher elevation MEN site, the growing season was about a month shorter (about 4 months long), which resulted in 39% and 15% narrower wood and phloem increments, respectively. At MEN, the transition from early to latewood was observed on average only a week later than at PAN, while the transition from early to late phloem occurred on average 20 days later at MEN than at PAN. Information on the impact of site condi- tions on radial growth of spruce and wood quality is important for all stakeholders in the forest-wood value chain, as it can help to take appropriate management measures of adaptation to changing conditions. Keywords: earlywood, latewood, early phloem, late phloem, growth ring, cambium, Norway spruce = Picea abies NASTAJANJE IN STRUKTURA LESA IN FLOEMA PRI NAVADNI SMREKI FORMATION AND STRUCTURE OF WOOD AND PHLOEM IN NORWAY SPRUCE Jožica Gričar 1* , Katarina Čufar 2 , Peter Prislan 1 1 Gozdarski inštitut Slovenije, Večna pot 2, 1000 Ljubljana, SLO * e-pošta: jozica.gricar@gozdis.si 2 Univerza v Ljubljani, Biotehniška fakulteta, Oddelek za lesar- stvo, Jamnikarjeva 101, 1000 Ljubljana, SLO membnejša drevesna vrsta navadna smreka (Picea abies (L.) Karst.), ki je v letu 2019 predstavljala 30,4 % delež v lesni zalogi. Vse pogostejši izredni dogod- ki v zadnjih letih so resno ogrozili njeno odpornost in s tem povečali dovzetnost oslabljenih dreves za napad podlubnikov ali drugih škodljivcev (de Groot & Ogris, 2019), kar se odraža v povečanem obse- gu sanitarne sečnje v celotnem poseku v obdobju 2012–2017, ki znaša kar 62 % oziroma 9,4 mio m 3 (Zavod za gozdove Slovenije, 2020). Posledica inten- zivnih sanitarnih sečenj so velike količine dostikrat poškodovanega in manj vrednega lesa smreke na domačih in svetovnih trgih. Razlog za veliko zasto- 6 Les/Wood, Vol. 70, No. 1, June 2021 Gričar, J., Čufar, K., & Prislan, P .: Formation and structure of wood and phloem in Norway spruce panost smreke v slovenskih gozdovih je nekdanja gozdarska praksa, ki je pospeševala pogozdovanja s smreko, tudi v obliki monokulturnih nasadov na zanjo nenaravnih rastiščih in v nižinah. Njen poten- cialni naravni delež je ocenjen na 8 % (Krajnc et al., 2020a). Pričakujemo, da se bodo intenzivne sani- tarne sečnje nadaljevale tudi v prihodnje, obenem pa se bo nadaljevalo zmanjševanje deleža smreke v slovenski lesni zalogi. Podnebne spremembe zaradi naraščajočih temperatur negativno vplivajo na rast dreves na rastiščih na nižjih nadmorskih višinah. Hkrati šte- vilne dendroklimatološke študije kažejo, da lahko naraščanje temperature pozitivno vpliva na debe- linsko rast smreke na višje ležečih rastiščih (Levanič et al., 2009; Jevšenak et al., 2021). Podnebne spre- membe bodo tako verjetno različno vplivale na rast in preživetje dreves v različnih okoljih, pri čemer moramo upoštevati še vpliv izrednih vremenskih dogodkov, ki se lahko pojavijo na globalni, regional- ni ali lokalni ravni in praviloma negativno vplivajo na rast dreves. Informacije o časovni dinamiki sezonske debe- linske rasti dreves ter struktura lesa in floema lahko služijo kot kazalniki za odziv in prilagoditev dreves na dane rastiščne razmere in izjemne dogodke (Sass- -Klaassen et al., 2016). Raziskave sezonske dinami- ke debelinske rasti dreves so časovno zamudne, saj zajemajo odvzem vaskularnih tkiv v kratkih časovnih intervalih tekom rastne dobe ter nadaljnjo pripravo vzorcev v laboratoriju za opazovanje tkiv pod mi- kroskopom. Posebno dragocena, a redka so večletna opazovanja, ki prikazujejo razlike v vzorcih rasti med leti na istem rastišču v odvisnosti od različnih (zuna- njih) dejavnikov (Prislan et al., 2019). Zato so infor- macije o nastajanju lesa dokaj omejene, še redkejše pa so študije, ki vključujejo tudi nastajanje floema. V Sloveniji imamo večletne podatke o sezon- skem delovanju kambija ter nastajanju lesa in flo- ema za navadno smreko in navadno bukev (Fagus sylvatica L.) na dveh rastiščih (npr. Prislan et al., 2013, 2019; Gričar et al., 2014, 2021) ter za pu- hasti hrast (Quercus pubescens Willd.), črni gaber (Ostrya carpinifolia Scop.), mali jesen (Fraxinus or- nus L.) in črni bor (Pinus nigra Arn.) na Podgorskem krasu (Gričar et al., 2017, 2020). Za temeljite razi- skave zvez med debelinsko rastjo in podnebjem pri različnih drevesnih vrstah na globalni ravni pa razi- skovalci iz različnih laboratorijev po svetu intenziv- no sodelujejo, izmenjujejo znanje, usklajujejo me- todologijo raziskav in združujejo podatke v skupne baze (npr. Rossi et al., 2008; Cuny et al., 2015; Mar- tinez del Castillo et al., 2018; Huang et al., 2020). Širine letnih prirastkov (branik) v lesu so v tes- ni zvezi z njegovo strukturo, zato so informacije o vplivu rastiščnih razmer na gozdno produkcijo (de- belinsko rast) in kakovost lesa pomembne za vse deležnike v gozdno-lesni verigi. Za drevesne vrste zmernega pasu je značilno periodično delovanje kambija, ki je povezano z okoljskimi dejavniki, z izmenjavami hladnih in toplih ali pa sušnih in de- ževnih obdobij (Lachaud et al., 1999). Rast in razvoj dreves se v normalnih razmerah začne spomladi in zaključi pozno poleti ali zgodaj jeseni. Na vzorce rasti vplivajo številni dejavniki, kot so rastiščne razmere, drevesna vrsta, starost, vitalnost in socialni položaj drevesa (Larson, 1994). S periodičnim delovanjem meristemskih tkiv in diferenciacijo celic variira tudi količina produktov fotosinteze, hormonov in drugih signalnih molekul v drevesu, ki vplivajo na struktu- ro lesa. Spomladi nastajajo traheide ranega lesa, ki imajo velike lumne in tanke celične stene. V drugi polovici rastne sezone nastajajo traheide kasnega lesa, ki imajo majhne lumne in debele celične stene (Čufar, 2006). Razmejevanje med ranim in kasnim lesom navadno temelji na razmerju med radialno dimenzijo lumna in debelino tangencialne celične stene (Denne, 1988). Omenjene razlike med ranim in kasnim lesom narekujejo njihovo vlogo v dreve- su, pri čemer so traheide ranega lesa bolj učinkovi- te pri prevajanju vode, traheide kasnega lesa pa so pomembne za zagotavljanje mehanske trdnosti. Z vidika uporabe lesa so pomembne razlike v količi- ni stenskega materiala, saj narekujejo gostoto lesa, pri čemer ima kasni les do trikrat višjo gostoto od ranega lesa. Širine branik ter deleži ranega in kasne- ga lesa zato bistveno vplivajo na gostoto lesa, ki je eden glavnih kazalnikov lastnosti in kakovosti lesa (Panshin & de Zeeuw, 1980; Čufar, 2006; Gorišek, 2009). Zelo malo je znanega o času prehoda iz ra- nega v kasni les oziroma o času nastanka ranega in kasnega lesa, a imajo te informacije zaradi zgoraj omenjenih razlogov velik aplikativni pomen. V raziskavah debelinske rasti dreves je floem- ski prirastek dostikrat spregledan zaradi manjšega gospodarskega pomena tkiv skorje. Poleg tega so včasih domnevali, da na nastanek floema vplivajo predvsem notranji dejavniki (npr. Larson, 1994), 7 Les/Wood, Vol. 70, No. 1, June 2021 Gričar, J., Čufar, K., & Prislan, P .: Nastajanje in struktura lesa in floema pri navadni smreki novejše raziskave pa so pokazale, da je nastanek floema vsaj deloma podvržen rastiščnim razmeram, kar se odraža v njegovi strukturi, zato ga je smisel- no vključiti v ekofiziološke in dendroekološke štu- dije (Gričar et al., 2015, 2016, 2020). Nenazadnje je kambij bifacialen meristem, ki proizvaja celice na lesno in floemsko stran, zato je nujno, da je v razi- skavah delovanja kambija vključen tudi floemski del (Gričar, 2017). Podobno kot v lesu tudi v nekolabira- nem (prevodnem) floemu pri smreki lahko razloči- mo prirastne plasti (floemske branike), razmejene z letnicami. Znotraj floemskih branik razlikujemo rani in kasni floem, ki ju razmejuje bolj ali manj sklenjen tangencialni pas aksialnega parenhima (Gričar et al., 2005, 2006, 2014, 2015, 2016; Gričar, 2017). Si- taste celice ranega in kasnega floema se razlikujejo predvsem po radialni dimenziji lumnov. Osrednja naloga ranega floema je prevajanje asimilatov in drugih molekul iz listov po deblu proti koreninam do meristemskih in skladiščnih tkiv. Kasni floem, ki vsebuje aksialni parenhim, je pomemben za skla- diščenje nestrukturnih ogljikovih hidratov (Jyske & Hölttä, 2015). Sitaste celice so žive in opravljajo svojo nalogo eno do dve leti, nato odmrejo in ko- labirajo. Vsakoletni nastanek floemske branike je tako ključen za preživetje drevesa (Gričar, 2017). Namen prispevka je predstaviti nekaj najnovej- ših rezultatov o debelinski rasti navadne smreke z dveh rastišč v Sloveniji, na Panški reki (PAN – 400 m n. v.) in Menini planini (MEN – 1200 m n. v.) v letih 2009–2011. Raziskali smo: (a) kambijevo ce- lično produkcijo, z glavnimi fazami, ki vključujejo začetek, konec, trajanje in stopnjo produkcije celic lesa in floema; (b) prehod iz ranega v kasni les in iz ranega v kasni floem, ki je v splošnem slabo poznan ter (c) strukturo lesnih in floemskih prirastkov. 2 MATERIAL IN METODE 2 MATERIAL AND METHODS 2.1 RAZISKOVALNI PLOSKVI 2.1 STUDY SITES Raziskava je bila opravljena na rastiščih Panška reka PAN in Menina planina MEN v Sloveniji, ki se razlikujeta v nadmorski višini (PAN – 400 m n.v. in MEN – 1200 m n.v.) (slika 1). Rastišče PAN se nahaja v bližini Ljubljane, kjer rastejo značilni podgorski bu- kovi gozdovi (Hacquetio-fagetum typicum) s prev- ladujočimi vrstami navadna bukev (Fagus sylvatica L.), gorski javor (Acer pseudoplatanus L.) in navadna smreka (Picea abies (L.) H. Karst.). Višje ležeče ras- tišče MEN se nahaja na Menini planini, predalpski planoti v Kamniško-Savinjskih Alpah, za katerega je značilen predalpski visokogorski gozd jelke in bukve (Abieti fagetum prealpinum typicum) in prevladu- jejo vrste navadna bukev, navadna smreka in bela jelka (Abies alba Mill.). Vremenske podatke za rastišče PAN smo pri- dobili iz bližnje meteorološke postaje Agencije RS Slovenije za okolje (Ljubljana–Bežigrad 46°30´ N, 14°30´ E, 299 m n. v.). Na rastišču MEN smo za čas spremljanja debelinske rasti dreves namestili vre- mensko postajo Davis®, ki je v enournih intervalih beležila temperaturo in količino padavin. Namestili Slika 1. Zemljevid Slovenije in lo- kaciji rastišč Panška reka (PAN – 400 m n. v.) in Menina planina (MEN – 1200 m n. v.) (sliko prip- ravil D. Arnič). Figure 1. Map of Slovenia with locations of the selected sites Panška reka (PAN – 400 m a.s.l.) and Menina Planina (MEN – 1200 m a. s. l.) (figure prepared by D. Arnič). 8 Les/Wood, Vol. 70, No. 1, June 2021 Gričar, J., Čufar, K., & Prislan, P .: Formation and structure of wood and phloem in Norway spruce smo jo na jasi, približno 2 m nad tlemi v bližini iz- branih dreves. Letna količina padavin je bila na ras- tiščih primerljiva (PAN – 1384 mm in MEN – 1355 mm), razlike pa smo zabeležili v letni povprečni temperaturi (PAN 10,3 °C in MEN 7,4 °C). 2.2 IZB IRA DREVE S, IZVEDB A VZ OR ČENJ A IN PRIPRAVA VZORCEV 2.2 SELECTION OF TREES, TISSUE SAMPLING, AND SAMPLE PREPARATION Na obeh rastiščih smo izbrali šest dominantnih ali sodominantnih dreves smreke. Drevesa na PAN so bila stara 68 ± 8 let, s premerom na prsni višini 36 ± 5 cm in višino 30 ± 5 m. Na MEN so bila dre- vesa stara 102 ± 31 let, s premerom na prsni višini 34 ± 2 cm in višino 25 ± 1 m. V letih 2009, 2010 in 2011 smo med rastno sezono (t. j. od sredine marca do sredine oktobra) v tedenskih intervalih z uporabo orodja Trephor (Rossi et al., 2006) iz debel dreves jemali mikro izvrtke premera 1,8 mm in dol- žine približno 20 mm. Vzorce smo odvzeli po obodu drevesa na višini debla od 1,1 do 1,7 m nad tlemi tako, da smo sledili obliki vijačnice. V izogib vpliva poškodb na odvzeta tkiva na sosednjih vzorcih smo zaporedna mesta vzorčenja izbrali z razdaljo od 5 do 10 cm. Vsak mikro izvrtek je vseboval vsaj dve najmlajši lesni braniki, kambij in ličje (floem). Po- stopke priprave trajnih preparatov prečnih prere- zov mikro izvrtkov za opazovanje in izvedbo meritev pod mikroskopom smo podrobno opisali v Gričar et al. (2014). Rezine debele 10–12 μm za pregled pod svetlobnim mikroskopom smo narezali z rota- cijskim mikrotomom in jih obarvali z vodno meša- nico barvil safranin in astra modro ter jih vklopili v Euparal. Opazovanje in meritve nastajajočih lesnih (ksilemskih) in floemskih branik smo opravili s sve- tlobnim mikroskopom (svetlo polje in polarizirana svetloba) ter sistemom za analizo slike. 2.3 FENOLOGIJA KAMBIJEVE AKTIVNOSTI IN ANATOMIJA LESNIH IN FLOEMSKIH BRANIK 2.3 PHENOLOGY OF CAMBIAL ACTIVITY AND ANATOMY OF XYLEM AND PHLOEM INCREMENTS Začetek, konec in trajanje kambijeve celične produkcije lesne in floemske branike smo določili, kot opisuje prispevek Gričar et al. (2014). Na vseh preparatih smo prešteli število celic v nastajajoči lesni in floemski braniki v vsaj treh radialnih nizih ter na podlagi podatkov za vsako drevo izračunali Gompertzovo funkcijo, ki opisuje sezonsko dinami- ko nastajanja lesa in floema. Kambijevo produkcijo na lesni in floemski strani prikazujejo glavni mejni- ki: začetek, konec in trajanje nastajanja celic. Zače- tek kambijeve celične produkcije smo določili kot dan, ko smo opazili prve novo nastale lesne celice v fazi površinske rasti. Konec kambijeve celične pro- dukcije smo določili kot dan, ko lesnih celic v fazi površinske rasti nismo več zasledili ob kambiju, opazili pa smo traheide v poznih fazah diferencia- cije. Konec nastajanja lesa smo označili takrat, ko je bila lesna branika popolnoma oblikovana in je bil v vseh celicah proces diferenciacije zaključen. Ob- dobje maksimalne celične produkcije na lesni in flo- emski strani smo določili s pomočjo Gompertzove ali GAM funkcije (funkcije generaliziranih aditivnih modelov - Generalized additive models) (Gričar et al., 2021). Zabeležili smo datum prehoda iz ranega v kasni les in iz ranega v kasni floem in izračunali trajanje nastajanja ranega in kasnega ranega lesa ter ranega in kasnega floema. Vzorce, ki so bili odvzeti konec rastne sezone in so imeli dokončno izoblikovane lesne in floemske branike, smo uporabili za izdelavo traheidogramov (za traheide v lesu) in floemogramov (za sitaste ce- lice v floemu). To so grafi, ki prikazujejo variabilnost radialnih dimenzij celic in v primeru lesa tudi debe- lin celičnih sten znotraj branike. Meritve smo opra- vili v vsaj treh radialnih nizih. Povprečne vrednosti anatomskih spremenljivk za rani in kasni les ter rani in kasni floem smo izračunali ločeno za vsak niz ce- lic. Ker je bilo število celic v radialnih nizih znotraj branik lesa ali floema različno, smo standardizirali velikost vzorca, da smo lahko opravili tudi primerja- ve med drevesi, območji in leti. Zato smo uporabili „relativni položaj“ vsake celice znotraj radialnega niza branike (Gričar et al., 2015). Za razlikovanje med treheidami ranega in kasnega lesa smo upora- bili prvo interpretacijo, ki jo je predlagal Mork, po kateri imajo traheide kasnega lesa premer lumna, ki je manjši od dvakratne debeline celične stene (Denne, 1988). Datum prehoda iz ranega v kasni les smo izračunali s pomočjo predhodno izdelanih Gompertzovih oz. GAM funkcij (Gričar et al., 2021). Prehod iz ranega v kasni floem smo določili kot čas, ko smo na prečnih prerezih opazili prve celice aksi- alnega parenhima (Gričar & Čufar, 2008). 9 Les/Wood, Vol. 70, No. 1, June 2021 Gričar, J., Čufar, K., & Prislan, P .: Nastajanje in struktura lesa in floema pri navadni smreki 3 REZULTATI 3 RESULTS 3.1 KAMBIJEV A CELIČNA PR ODUK CIJ A IN DINAMIKA DEBELINSKE RASTI 3.1 CAMBIAL CELL PRODUCTION AND RADIAL GROWTH DYNAMICS Fenologijo kambijeve celične produkcije smre- ke prikazujemo za leta 2009, 2010 in 2011 ločeno za posamezno rastišče PAN in MEN ter ločeno za ksi- lem (les) in floem (ličje) (slika 2). Prikazani rezultati predstavljajo letna povprečja 6 dreves na rastišču, pri čemer smo opazili tudi precejšnjo variabilnost Slika 2. Zveza med fenologijo kambija (začetek, konec, trajanje) in številom celic v lesni in floemski braniki pri navadni smreki (Picea abies) na rastiščih Panška reka (PAN) in Menina planina (MEN) v letih 2009, 2010 in 2011. Tanjši del horizontalnih linij označuje obdobje nastajanja ranega lesa oz. ranega floema, debelejši pa obdobje nastajanja kasnega lesa oz. kasnega floema. Vertikalne linije označujejo dan maksimalne celič- ne produkcije. Rumena vertikalna črtkana črta označuje poletni solsticij. Sive črtkane črte predstavljajo zve- zo med začetkom in koncem celične produkcije ter končnim številom celic v (a) lesni in (b) floemski braniki: število celic v lesni braniki = 1,39 ∙ DOY (začetek) + 200,11, r 2 = 0,62, P < 0,039; število celic v lesni braniki = 1,72 ∙ DOY (konec) - 355,65, r 2 = 0,71, P < 0,022; število celic v floemski braniki = –0,051 ∙ DOY (začetek) + 15,60, r 2 = 0,67, P < 0,029; število celic v floemski braniki = 0,107 ∙ DOY (konec) - 14,52, r 2 = 0,48, P < 0,076. (DOY = dan v letu). Figure 2. Relationships between cambial phenology (onset, end, and duration) and the total number of xylem and phloem cells for Norway spruce (Picea abies) Panška reka (PAN) in Menina planina (MEN) in 2009, 2010 and 2011. Different thickness of the horizontal lines represents periods of formation of early (thinner line) and late (thicker line) increment parts. Vertical bars indicate the dates of maximal cell pro- duction. Yellow vertical dot-dashed lines denote the summer solstice. Grey dashed lines show relationships between onset and cessation of cambial cell production and final (a) xylem and (b) phloem ring cell number: Xylem ring cell number = 1.39 ∙ DOY (onset) + 200.11, r 2 = 0.62, P < 0,039; Xylem ring cell number = 1.72 ∙ DOY (end) – 355.65, r 2 = 0.71, P < 0.022; Phloem ring cell number = –0.051 ∙ DOY (onset) + 15.60, r 2 = 0.67, P < 0.029; Phloem ring cell number = 0.107 ∙ DOY (end) – 14.52, r 2 = 0.48, P < 0.076. (DOY – day of the year). 10 Les/Wood, Vol. 70, No. 1, June 2021 Gričar, J., Čufar, K., & Prislan, P .: Formation and structure of wood and phloem in Norway spruce med drevesi znotraj istega rastišča (Gričar et al., 2014, 2015). Ugotovili smo, da se je dinamika kam- bijeve celične produkcije med rastiščema na različ- nih nadmorskih višinah razlikovala. V splošnem je bilo trajanje kambijeve celične produkcije daljše na nižje ležečem rastišču PAN, in sicer zaradi zgodnej- šega začetka in kasnejšega zaključka celičnih deli- tev, pri čemer je slednja faza bolj variirala med leti (slika 2). Razlike med rastiščema smo zabeležili tudi v dinamiki nastajanja lesnih in floemskih letnih pri- rastkov, kar se je odrazilo v njihovi širini in strukturi. Na istem rastišču so bile razlike med proučevanimi leti manj izrazite in statistično neznačilne. Potrdili smo, da se je začetek in konec kam- bijeve celične produkcije lesnih in floemskih celic pri smreki začel sočasno, kar je značilnost iglavcev zmernega in hladnega pasu. Dinamika nastajanja lesne in floemske branike pa je različna (Gričar, 2017), zato v nadaljevanju podajamo rezultate lo- čeno za les in floem. V opazovanih letih smo na PAN začetek kambijeve celične produkcije zabeležili v prvi polovici aprila (dan 99–106), vrhunec produk- cije lesnih celic med 19. 5. in 12. 6. in zaključek v drugi polovici avgusta (dan 238–243). Kasni les je začel nastajati po poletnem sončnem obratu (sol- sticiju), med 22. 6. in 11. 7. Kambij je proizvajal les 138,4 ± 14,3 dni (t. j. slabih 5 mesecev), od tega je 74–86 dni nastajal rani les ter 51–71 dni kasni les. V povprečju je tako rani les nastajal 23,8 % dlje časa. Lesna branika je bila popolnoma oblikovana v za- četku oktobra (dan v letu 275,8 ± 13,3). Na MEN smo vse fenološke faze, razen zaključ- ka nastajanja lesa (t. j. zaključek kambijeve celične produkcije in diferenciacije zadnjih nastalih celic) zabeležili kasneje kot na PAN. Začetek kambijeve produkcije smo zabeležili med 18. 4. in 3. 5. (dan 108–123), maksimum med 19. 5. in 12. 6. in zaklju- ček med 13. 8. in 20. 8. (dan 225–232). Kasni les je začel nastajati od 4. 7. do 16. 7. Kambij je proizvajal les 109,9 ± 16,3 dni (t. j. slabe 4 mesece), od tega je 62–79 dni nastajal rani les ter 35–41 dni kasni les. V povprečju je tako rani les nastajal 46.1 % dlje časa. Lesna branika je bila popolnoma oblikovana do konca septembra (dan v letu 264 ± 10,2). Na floemski strani so se že pred začetkom kam- bijeve celične produkcije nediferencirane celice, ki so se nahajale na zunanjem robu kambija, začele oblikovati v sitaste celice ranega floema brez pred- hodnih delitev. Na PAN smo prve diferencirajoče celice floema zabeležili med 16. 3. in 20. 3. (dan 75–79), kar je 24–28 dni pred začetkom kambije- ve celične produkcije. Kasni floem je začel nastajati med 22. 4. in 6. 5. (dan 112–130), preden je kambi- jeva produkcija floemskih celic dosegla maksimum med 13. 5. in 6. 6. (dan 133–157). Na MEN so se vse faze nastajanja floema začele kasneje kot na PAN. Prve diferencirajoče celice flo- ema smo zabeležili približno en mesec kasneje kot na PAN, med 11. 4. in 24. 4. (dan 101–114), kar je 6–9 dni pred začetkom kambijeve celične produkci- je. Kasni floem je začel nastajati med 12. 5. in 2. 6. (dan 132–153), največjo produkcijo pa smo tudi na tem rastišču zabeležili v obdobju nastajanja kasne- ga lesa, in sicer med 14. 5. in 26. 5. (dan 134–146). Vsi omenjeni mejniki so na obeh rastiščih nastopili pred poletnim sončevim obratom. 3.2 STRUKTURA LESNIH IN FLOEMSKIH PRIRASTKOV 3.2 STRUCTURE OF XYLEM AND PHLOEM INCREMENTS Razlike med rastiščema v mejnikih in traja- nju kambijeve produkcije so se odražale v širini in strukturi lesnih in floemskih prirastkov (slika 3, 4). Na PAN je bila povprečna lesna branika v obdob- ju 2009–2011 široka 60,2 ± 8,0 (srednja vrednost ± standardna napaka) slojev celic. Širina ranega lesa je znašala 30–31 celic, kasnega lesa pa 24–27 celic v radialnih nizih. Delež ranega lesa je bil v splošnem v vseh primerih nekoliko večji od kasnega lesa in je v povprečju v treh letih znašal 51,9 %. Gledano po posameznih letih pa smo v letu 2009 zabeležili največji delež kasnega lesa (54,6 %). Deleža ranega in kasnega lesa sta prikazana glede na število ce- lic in ne glede na merjene širine prirastkov. Ker je radialna dimenzija traheid kasnega lesa približno 2–3-krat manjša od dimenzij traheid ranega lesa, bi bil delež kasnega lesa, preračunan glede na širino ranega in kasnega lesa v milimetrih, precej manjši. Na MEN je bila povprečna lesna branika v lesu široka 37,0 ± 7,4 slojev celic. Širina ranega lesa je znašala 23–24 celic, kasnega lesa pa 9–18 slojev ce- lic. Delež ranega lesa je bil na tem rastišču v vseh treh letih večji od kasnega lesa in je v povprečju znašal 64,6 %. Na obeh rastiščih je bil floemski prirastek ožji v primerjavi z lesnim, in sicer na PAN za 81 %, na MEN pa za 73 % (slika 4, 5). V obdobju 2009–2011 je bila 11 Les/Wood, Vol. 70, No. 1, June 2021 Gričar, J., Čufar, K., & Prislan, P .: Nastajanje in struktura lesa in floema pri navadni smreki Slika 3. Mikroskopska slika zgradbe lesne in floemske branike pri navadni smreki na Pan- ški reki (PAN) ob zaključku kambijeve celične produkcije (a) in na Menini planini (MEN) na začetku rastne sezone (b). XY – lesna brani- ka, EXY – rani les, LXY – kasni les, CC – kam- bij, Ph – floemska branika tekočega leta, EPh – rani floem, LPh – kasni floem, PPh – floemska branika preteklega leta. Figure 3. Microscopic image of the structu- re of the xylem and phloem growth ring of Norway spruce on PAN at the end of cam- bial cell production period (a) and on MEN at the beginning of the growing season (b). XY – xylem growth ring, EXY – earlywood, LXY – latewood, CC – cambium, Ph – phloem increment of the current year, EPh – early phloem, LPh – late phloem, PPh – phloem increment of the previous year. 12 Les/Wood, Vol. 70, No. 1, June 2021 Gričar, J., Čufar, K., & Prislan, P .: Formation and structure of wood and phloem in Norway spruce Slika 4. Širina in struktura lesnih in floemskih branik pri navadni smreki na Panški reki (PAN) in Menini planini (MEN) v obdobju 2009–2011. Delež ranega lesa in ranega floema je preračunan gle- de na število celic. Figure 4. Width and structure of xylem and phloem growth rin- gs in Norway spruce on Panška reka (PAN) and Menina planina (MEN) in the period 2009–2011. The proportion of earlywood and early phloem is calculated based on the number of cells. floemska branika na PAN v povprečju široka 11,7 ± 0,7 slojev celic, pri čemer je bil rani floem širok 3,9 ± 0,2 slojev celic, kasni floem pa 6,8 ± 0,6 slojev ce- lic. Pri smreki na PAN je bil delež celic ranega floe- ma v vseh primerih manjši od kasnega floema in je znašal 33,3 %. Na MEN je bila floemska branika v proučeva- nih letih v povprečju široka 10,0 ± 0,7. Širina ranega floema je znašala okoli 4,1 ± 0,3 slojev celic, širina kasnega floema pa je znašala 4,9 ± 0,6 slojev. Na tem rastišču je znašal delež celic ranega floema v povprečju 45,7 %. 13 Les/Wood, Vol. 70, No. 1, June 2021 Gričar, J., Čufar, K., & Prislan, P .: Nastajanje in struktura lesa in floema pri navadni smreki 4 RAZPRAVA 4 DISCUSSION Naše raziskave kažejo, da rastiščne razmere v veliki meri vplivajo na sezonsko dinamiko nastaja- nja lesa in floema, kar se odraža v širini in strukturi prirastkov. Na višje ležečem rastišču MEN je bila ra- stna sezona približno mesec dni krajša, posledično so bili letni prirastki ožji, in sicer v lesu 39 % in v floemu 15 % kot na PAN. Poleg trajanja kambijeve celične produktivnosti je bila tudi dinamika debe- linske rasti na proučevanih rastiščih različna. Za nastanek lesne branike sta bila na obeh rastiščih ključna meseca maj in junij, za nastanek floemske branike pa predvsem maj. Stopnja celičnih delitev je bila na lesni strani na MEN večja kot na PAN (Gričar et al., 2014), kar pomeni, da je kambij pri smreki na višje ležečem rastišču v krajšem času proizvedel večje število lesnih celic. Stopnja celičnih delitev poleg trajanja kambijeve celične produkcije vpliva na končno ši- rino branike (Skene, 1972). Rezultati so skladni z ugotovitvami drugih študij o prilagoditvi drevesih vrst danim okoljskim razmeram, kar kaže na nji- hovo veliko fleksibilnost in plastičnost (Gregory & Wilson, 1968; Alpert & Simms, 2002; Rossi et al., 2007). Gregory in Wilson (1968) sta ugotovila, da se je bela smreka (Picea glauca) na Aljaski s hitrej- šimi delitvami kambijevih celic prilagodila na krajšo rastno sezono. Posledično so bile širine lesnih bra- nik primerljive s širinami branik bele smreke, ki je rasla v Novi Angliji, kjer so bile razmere za rast bolj ugodne. Prehod iz ranega v kasni les smo na PAN zabe- ležili le kakšen teden prej kot na MEN, in sicer v ob- dobju od konca junija do prve polovice julija. Čeprav so bili lesni prirastki širši na PAN, pa je bil delež ce- lic ranega lesa večji na MEN, kar je v nasprotju s predhodnimi poročanji o pozitivni zvezi med širino branike in deležem ranega lesa (Dinwoodie, 1981). Na obeh rastiščih je bilo obdobje nastajanja ranega lesa daljše od nastajanja kasnega lesa, njuni deleži pa so se na rastiščih razlikovali, kar lahko pripiše- mo kombinaciji vpliva trajanja in stopnje kambijeve celične produkcije na širino prirastka, ki se tekom rastne sezone spreminja (Gričar et al., 2021). Na strukturo lesne branike in značilnosti celic ranega in Slika 5. Mikroskopska slika zgradbe floemske branike pri navadni smreki na PAN(a) in MEN (b). XY – les, CC – kambij, EPh – rani floem, LPh – kasni floem. Figure 5. Microscopic image of the structure of the phloem growth ring of Norway spruce on PAN (a) and MEN (b). XY – xylem, CC – cambium, EPh – early phloem, LPh – late phloem. 14 Les/Wood, Vol. 70, No. 1, June 2021 Gričar, J., Čufar, K., & Prislan, P .: Formation and structure of wood and phloem in Norway spruce kasnega lesa (t. j. velikost lumnov in debelina celič- ne stene) pa vpliva še proces diferenciacije traheid (Cuny et al., 2014). Kot že omenjeno, razlike v morfoloških značil- nostih traheid ranega lesa v smislu dimenzij in de- belin celičnih sten vplivajo na gostoto lesa. Srednja gostota absolutno suhega lesa smreke znaša 430 kg/m 3 , z razponom od 300 do 640 kg/m 3 (Grosser & Teetz, 1985). To variiranje gostote pripisujemo raz- ličnim deležem kasnega lesa, ki pri iglavcih s širino branike praviloma pada, posledično pada tudi go- stota (Dinwoodie, 1981). Zveze med širino branike ter deležem in strukturo kasnega lesa so komple- ksne, saj številni notranji (genetika, hormoni) in zu- nanji (abiotski in biotski) dejavniki različno vplivajo na sezonsko dinamiko kambijeve celične produkcije in celično diferenciacijo (Larson, 1994; Fonti et al., 2013). Zaradi tega bo za boljše razumevanje zvez v prihodnje potrebno opraviti še več tovrstnih analiz pri različnih iglavcih iz različnih okolij. Ker je gostota v tesni zvezi z mehanskimi lastnostmi lesa (trdnost in trdota) in ima velik vpliv tudi na druge lastnosti in kakovost lesa, imajo takšne študije velik aplikativni pomen (Krajnc et al., 2020b). Obdobje najintenzivnejše celične produkcije je nastopilo na floemski strani približno en mesec prej kot na strani lesa. Na strani lesa je bilo to obdob- je vedno v času nastajanja ranega lesa, pri floemu pa je bilo to povezano s širino letnega prirastka. Pri branikah, ožjih od 10 slojev celic, je bilo obdobje najintenzivnejše rasti v času nastajanja ranega flo- ema, v prirastkih, širših od 10 slojev celic, pa v času nastajanja kasnega floema. Na PAN je maksimum floemske rasti tako vedno zabeležen v obdobju nastajanja kasnega floema, pri smreki na MEN pa različno; v letih 2009 in 2010 v obdobju nastajanja ranega floema in v letu 2011 v obdobju nastajanja kasnega floema. Na floemski strani sta bila trajanje in stopnja celične produkcije večja na PAN kot na MEN, kar se je odražalo v širših prirastkih. Čeprav se je kambi- jeva celična produkcija pri smreki začela in končala na lesni in floemski strani istočasno, se je dinamika nastanka obeh prevodnih tkiv razlikovala. Na obeh rastiščih so bili lesni prirastki širši od floemskih, kar je skladno s predhodnimi raziskavami (Gričar et al., 2009), da je v normalnih razmerah kambijeva ce- lična produkcija na lesni strani intenzivnejša kot na floemski strani. V stresnih razmerah se lahko raz- merje obrne in je floemski prirastek lahko širši od lesnega (Gričar et al., 2009); priraščanje lesa lahko lokalno celo izostane (pojav manjkajočih branik na deblu drevesa) (Novak et al., 2016). Floemska bra- nika mora nastati vsako leto, kar je ključno za pre- živetje drevesa, saj sitaste celice po 1–2 letih delo- vanja odmrejo in kolabirajo, zato so za vzdrževanje prevodnega sistema v floemu potrebne nove celice (Esau, 1939). Poleg različne dinamike celične produkcije, ki vpliva na širino prirastkov, smo ugotovili tudi raz- ličen vzorec nastajanja lesa in floema. Nastanek lesne branike se je začel s kambijevo produkcijo lesnih celic, pri floemu pa z diferenciacijo celic, ki so nastale z delitvami v kambiju v predhodni se- zoni (slika 3b). Pred začetkom kambijeve celične produkcije so se torej nediferencirane celice, ki so se nahajale na zunanjem robu kambija, začele oblikovati v sitaste celice ranega floema brez pred- hodnih delitev, kar je v skladu z opažanji, ki sta jih objavila Alfieri in Evert (1973). Te celice, nastale v preteklem letu, so sestavljale inicialne celice rane- ga floema. Obdobje najintenzivnejše celične pro- dukcije je nastopilo na floemski strani približno en mesec prej kot na strani lesa. Širina in struktura ranega floema je bila pri smreki na obeh rastiščih primerljiva in manj variabilna v primerjavi s kasnim floemom. Rani floem je bil sestavljen iz 3–4 slojev sitastih celic z velikimi lumni. Prehod iz ranega v kasni floem je označeval bolj ali manj sklenjen pas aksialnega parenhima. Širina kasnega floema je bila večja na PAN. Sitaste celice kasnega floema so imele manjše lumne, prisoten je bil aksialni paren- him. Različna struktura ranega in kasnega floema podpira predhodne ugotovitve, da je njuna vloga v drevesu različna (Gričar et al., 2015). Razlike lahko pripišemo veliki plastičnosti debelinske rasti smre- ke na proučevanih rastiščih, kjer so razmere za nje- no rast ugodne. 5 SKLEPI 5 CONCLUSIONS Spremljanje sezonske dinamike nastanka lesa in podrobne lesno-anatomske analize je zelo pri- merno za oceno odziva in prilagoditve debelinske rasti dreves na okoljske razmere. Naše dolgoletne raziskave potrjujejo, da informacije o nastanku in strukturi floema pomembno dopolnjujejo znanja 15 Les/Wood, Vol. 70, No. 1, June 2021 Gričar, J., Čufar, K., & Prislan, P .: Nastajanje in struktura lesa in floema pri navadni smreki na tem področju. V drevesu sta osnovni funkciji lesa in floema povsem različni, vendar sta obe tkivi ključni za rast, razvoj in preživetje drevesa. Ker sta les in floem povezana preko trakov (Spicer, 2014), nekateri avtorji predlagajo, da bi se ju obravnava- lo kot enoten vaskularni sistem (Pfautsch et al., 2015). Navkljub številnim raziskavam o debelinski rasti dreves pa so podatki o času prehoda iz ranega v kasni les in še posebej iz ranega v kasni floem zelo redki, čeprav predstavljajo pomemben mejnik v ra- zumevanju vplivov variabilnosti fenologije kambija in celične diferenciacije na strukturo in lastnosti lesa. Nova spoznanja, prikazana v pričujoči študiji, so pomembna z vidika gostote lesa, ki v veliki meri vpliva na kakovost lesa, kar je zanimivo za različne deležnike gozdno-lesne verige. 6 POVZETEK 6 SUMMARY Norway spruce (Picea abies (L.) Karst.) is curren- tly the most economically important tree species in Slovenia, accounting for 30.4% of the wood stock in 2019. Increasingly frequent extreme events, mostly related to climate change, have seriously threate- ned its resilience and survival in recent years, espe- cially on sites at lower altitudes. Information on the temporal dynamics of wood and phloem formation can serve as indicators of tree response and adap- tation to site conditions and extreme events. In Slovenia, we have established long-term data on seasonal activity of the cambium and wood and phloem formation at two sites, Pan- ška reka (PAN – 400 m a.s.l.) and Menina planina (MEN – 1200 m a.s.l.) for Norway spruce (Gričar et al., 2014, 2015, 2021) and European beech (Fagus sylvatica L.) (e.g. Prislan et al., 2013, 2019). These studies were conducted according to an interna- tionally harmonized methodology and the results were included in international databases, which made it possible to answer important research qu- estions on tree growth at a global scale (e.g. Rossi et al., 2008; Cuny et al., 2015; Martinez del Castillo et al., 2018; Huang et al., 2020). Despite numerous studies on wood formation, data on the timing of the transition from early to latewood and especial- ly from early to late phloem are very scarce. The purpose of this article is to present some of the latest results on the growth of spruce from the two sites during three years in Slovenia. The study included analyses of: (a) production of cambium cells, with the beginning, end, duration and rate of production of wood and phloem cells; (b) the tran- sition from early to latewood and from early to late phloem, which is generally poorly known; and (c) structure of wood and phloem formed in each year. On two typical forest sites, PAN (400 m a.s.l.) and MEN (1200 m a.s.l.), six dominant or co-do- minant Norway spruce trees were selected for sampling. In the years 2009, 2010 and 2011, micro- cores of 1.8 mm in diameter were taken with the Trephor tool from the tree stems at weekly inter- vals during the growing season (i.e., mid-March to mid-October). The microcores were used to cut cross-sections of tissues prepared for observation and measurements under the microscope accor- ding to the established methodology proposed by Gričar et al. (2014). The beginning, end, and du- ration of cambium cell production of wood and phloem annual increments were determined as described by Gričar et al. (2014). On all cross secti- ons, we counted the number of cells in the forming wood and phloem along at least three radial rows and calculated the Gompertz function based on the data for each tree to describe the seasonal dynami- cs of wood and phloem formation. The period of maximum cell production of wood and phloem was determined using the Gompertz or GAM function (Gričar et al., 2021). We recorded the date of tran- sition from early to latewood and from early to late phloem, and calculated the duration of formation of early and latewood and early and late phloem. Samples collected at the end of the growing sea- son with fully formed current growth rings in wood and phloem were used to generate tracheidograms (for tracheids in wood) and phloemograms (for si- eve cells in phloem). Mork’s rule was used to di- stinguish between early and latewood tracheids (Denne, 1928). The timing of the transition from early to latewood was calculated using previously constructed Gompertz or GAM functions (Gričar et al., 2021). The transition from early to late phloem was defined as the time when the first cells of the axial parenchyma were observed on the cross secti- ons (Gričar & Čufar, 2008). In the study years 2009, 2010 and 2011, the beginning of cambium cell production on the PAN was recorded in the first half of April (DOY = day 16 Les/Wood, Vol. 70, No. 1, June 2021 Gričar, J., Čufar, K., & Prislan, P .: Formation and structure of wood and phloem in Norway spruce of the year 99-106), the maximum wood cell pro- duction between 19 May and 12 June, and the end in the second half of August (DOY 238-243). Latewood formation began after the summer sol- stice, between 22 June and 11 July. The cambium produced wood for 138.4 ± 14.3 days, of which the duration of earlywood formation was 74-86 days and latewood 51-71 days. The annual rings in the wood were fully formed at the beginning of October. At MEN, all phenological phases except the completion of wood formation (i.e., the com- pletion of cambium cell production and differen- tiation of the last formed cells) were recorded later than at PAN. The onset of cambium produ- ction was recorded between 18 April and 3 May (DOY 108-123), maximum production between 19 May and 12 June, and termination between 13 and 20 August (DOY 225-232). Latewood produ- ction began between 4 and 16 July. The cambium produced wood for 109.9 ± 16.3 days, of which earlywood production lasted 62-79 days and la- tewood 35-41 days. On the phloem side, undifferentiated cells lo- cated at the outer edge of the cambium began to differentiate into sieve cells of the early phloem without prior division and before the onset of cam- bium cell production. The first phloem differenti- ating cells were recorded at PAN between 16 and 20 March (DOY 75-79), 24-28 days before the onset of cambium cell production. Late phloem began to form between 22 April and 6 May (DOY 112-130), before cambium phloem cell production peaked between 13 May and 6 June (DOY 133-157). At MEN, all phases of phloem formation began later than at PAN. The first differentiating phloem cells were recorded about a month later than at PAN, between 11 and 24 April (DOY 101-114), 6-9 days before the onset of cambium cell production. Late phloem began to form between 12 May and 2 June (DOY 132-153), and maximum production was recorded at this site during the period of late phlo- em formation, between 14 and 26 May (DOY 134- 146). Maximum cell production and the transition from early to late phloem occurred at both sites before the summer solstice. May and June were critical months for wood and phloem increment formation. Differences between sites in milestones and duration of cam- bium production were reflected in the width and structure of wood and phloem annual rings (Figure 3, 4). At PAN, the average wood increment in 2009- 2011 was 60.2 ± 8.0 cell layers wide. Earlywood width was 30-31 cells and latewood width was 24- 27 cells per radial row. At MEN, the mean wood in- crement was 37.0 ± 7.4 cell layers wide. The width of the earlywood was 23-24 cells, and that of the latewood was 9-18 cell layers. In both sites, the phloem increment was narrower than the wood increment (Figs. 4, 5). In 2009-2011, the phloem increment at PAN was on average 10.7 ± 0.7 cell layers wide, with the early phloem consisting of 3.9 ± 0.2 and the late phloem consisting of 6.8 ± 0.6 cells. The presented study brings new information on the onset and duration of early and latewood formation, as well as early and late phloem, and in this way complements previous studies on wood formation at the same sites. It also places the for- mation of early and latewood and phloem in the broader framework of cambium production, diffe- rentiation and wood and phloem quality. Furthermore, the cell structure and ratios of early and latewood, which significantly influence wood density, are presented. Density is one of the main indicators of wood properties; therefore the results are important for wood quality assessment, which is interesting for stakeholders in the forest- -wood chain. Importantly, the study also provides new insights into the early and late phloem, which has been particularly poorly studied. ZAHVALA ACKNOWLEDGEMENT Za podporo na terenu in v laboratoriju se zah- valjujemo Marku Bebru (Zavod za gozdove Sloveni- je), Milku Detmarju (Metropolitana d.o.o.) ter Luki Kržetu, Maksu Mereli in Marku Željku (Univerza v Ljubljani, Biotehniška fakulteta, Oddelek za lesar- stvo). Za pomoč pri pripravi slike 1 se zahvaljujemo Domnu Arniču z Gozdarskega inštituta Slovenije. Pripravo prispevka so omogočili Javna agencija za raziskovalno dejavnost Republike Slovenije (ARRS), raziskovalna programa P4-0107 in P4-0015 ter pro- jekti V4-2017, V4-2016, V4-1419, J4-2541 in Z4- 7318. 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Journal of Experimental Botany, 65(7), 1829- 1848. DOI: https://doi.org/10.1093/jxb/ert459 Zavod za gozdove Slovenije. (2020). Poročilo zavoda za gozdove slo- venije o gozdovih za leto 2019. Ljubljana: 121 str. 19 Les/Wood, Vol. 70, No. 1, June 2021 UDK 630*84 Izvirni znanstveni članek / Original scientific article Prispelo / Received: 11. 12. 2020 Sprejeto / Accepted: 20. 1. 2021 Vol. 70, No. 1, 19-29 DOI: https://doi.org/10.26614/les-wood.2021.v70n01a01 Izvleček / Abstract Izvleček: Les na prostem je izpostavljen delovanju abiotskih in biotskih dejavnikov. Če hočemo njihovo delovanje upočasniti, moramo les zaščititi. V preteklosti je bil biocidni proizvod na osnovi bakrovih, kromovih in borovih spojin (CCB) ena najpomembnejših rešitev za zaščito lesa v ostrih pogojih izpostavitve. Kljub temu, da se CCB v EU praktično ne uporablja več, lahko služi kot referenca za vrednotenje novih biocidnih proizvodov. Na terenskem polju Oddelka za lesarstvo Biotehniške fakultete že 14 let poteka poskus v realnih pogojih, kjer so impregnirani vzorci izpostavljeni vremenskim vplivom v skladu z dvoslojnim testom. Pri zaščitenem lesu pogosto opažamo, da les propade hitreje kot je pričakovano. V okviru tega prispevka želimo na podlagi analize razkrojenega s CCB impregniranega lesa s terenskega polja Oddelka za lesarstvo ugotoviti, zakaj je prišlo do prezgodnjega razkroja. Rezultati kažejo, da ustrezno življenjsko dobo zagotavljata ustrezna retencija in penetracija aktivnih učinkovin v les. Ključne besede: les, zaščita lesa, CCB, impregnacija, razkroj, lesne glive Abstract: Wood in outdoor applications is exposed to abiotic and biotic factors. If we want to slow down the decay, the wood must be protected. In the past, biocidal products based on copper, chromium, and boron compounds (CCB) were one of the most important solutions for wood protection under extreme conditions. Although CCB is in practice no longer used in the EU, it can serve as a reference for the evaluation of new biocidal products. At the field test site of the Department of Wood Science and Technology, Biotechnical Faculty, an experiment has been carried out under real conditions for 14 years, in which impregnated samples are exposed to the weather according to a double-layer test. In the case of treated wood, we often find that the wood decays faster than expected. In this work we want to determine what contributes to decay based on the analysis of decayed impregnated wood from the field test site. The results show that sufficient retention and penetration of the active substances into the wood ensures the planned service life. Keywords: wood, wood protection, CCB, impregnation, decay, wood inhabiting fungi ANALIZ A RAZKR O JENE GA SMREK O VE GA LE S A , Z AŠČITENE GA Z BIOCIDNIM PROIZVODOM CCB, PO 14 LETIH IZPOSTAVITVE NA PROSTEM ANALYSIS OF DECAYED NORWAY SPRUCE WOOD IMPREGNATED WITH CCB AFTER 14 YEARS OF OUTDOOR EXPOSURE Miha Humar 1* , Boštjan Lesar 1 , Davor Kržišnik 1 , Angela Balzano 1 1 Univerza v Ljubljani, Biotehniška fakulteta, Jamnikarjeva 101, Ljubljana, Slovenija * e-mail: miha.humar@bf.uni-lj.si; +386 1 3203 638 1 INTRODUCTION 1 UVOD Les na prostem je izpostavljen delovanju biotskih in abiotskih dejavnikov. V našem pod- nebnem pasu glive sodijo med najpomembnejše vzroke za propadanje lesa na prostem. Na lesu iglavcev se najpogosteje pojavita glivi tramov- ka (Gloeophyllum sp.) in bela hišna goba (Fibro- poria sp.) (Schmidt, 2006). Če neodporen les ni zaščiten, se razkroj v našem podnebnem pasu pojavi že po prvem ali najkasneje drugem letu izpostavitve (Humar et al., 2019a). V naravi so razkrojni procesi zaželeni, ko les uporabljamo v gospodarske namene, želimo njegov razkroj upo- časniti. V preteklosti smo v ta namen praviloma uporabljali le biocidne proizvode (Preston, 2000). Za zaščito lesa v bolj izpostavljenih pogojih se v EU in ZDA najpogosteje uporabljajo biocidni proizvodi na osnovi bakrovih spojin (Freeman & Mcintyre, 2008). Bakrovi pripravki ostajajo ena izmed na- jpomembnejših sestavin biocidnih proizvodov za zaščito lesa tudi po implementaciji evropske zakonodaje s področja biocidov (EC, 2000). Glavni razlogi za uporabo bakrovih spojin so do- bra učinkovitost, nizka toksičnost za neciljne or- ganizme, ugodno razmerje med kakovostjo in ceno in veliko povpraševanje po poceni impreg- 20 Les/Wood, Vol. 70, No. 1, June 2021 Humar, M., Lesar, B., Kržišnik, D., & Balzano, A.: Analysis of decayed Norway spruce wood impregnated with CCB after 14 years of outdoor exposure niranem lesu (Humar, 2002). Poleg tega njihovo uporabnost povečuje dejstvo, da so v EU poleg kreozotnega olja edino bakrovi zaščitni pripravki primerni za zaščito lesa v četrtem razredu upora- be (les v stiku z zemljo) (Humar et al., 2018). Bak- rove učinkovine se za zaščito lesa ne uporabljajo samostojno, ker se iz lesa izpirajo (Humar et al., 2007) in nimajo insekticidnih lastnosti (Mbitnkeu Fetnga Tchebe et al., 2020). V preteklosti so bak- rovim pripravkom dodajali kromove spojine za izboljšanje vezave v les, tako da je še danes v uporabi relativno veliko lesa, impregniranega s pripravki na osnovi bakrovih in kromovih spojin (Eaton & Hale, 1993; Richardson, 1993; Freeman & Mcintyre, 2008). Danes biocidnih proizvodov na osnovi bakrovih in kromovih spojin v EU skoraj ne uporabljamo več. Glavni razlog je šestvalentni krom, ki je škodljiv za okolje in živa bitja (Humar et al., 2006). Kljub temu, da so bakrovi pripravki na trgu že več desetletij, mehanizem vezave teh pripravkov v les še ni v celoti pojasnjen. Poleg tega ne vemo, zakaj s temi pripravki impregniran les občasno propade hitreje kot smo načrtovali (Ribera et al., 2017). Ali so temu vzrok na bakrove pripravke tolerantne glive, ali so tolerantne glive okužile les po tem, ko se je iz njega izprala velika večina aktivnih učinkovin? Toleranca gliv razkro- jevalk na baker je povezana z izločanjem oksalne kisline, ki jo izločajo glive razkrojevalke (Takao, 1965). Oksalna kislina ima močno afiniteto na tvorbo kompleksov z bakrovimi spojinami. Bakrov oksalat je v vodi zelo slabo topen in zato za glive praktično nestrupen. Med glivami razkrojevalka- mi se toleranca najpogosteje pojavlja pri sivi hišni gobi (Serpula lacrymans), beli hišni gobi (Fibropo- ria vaillantii) in drugih glivah tega rodu (Steenk- jær Hastrup et al., 2005; Liew & Schilling, 2012; Karunasekera et al., 2017). Namen tega prispevka je raziskati lastnosti raz- krojenega lesa in izpiranje bakrovih spojin iz lesa v tretjem razredu uporabe. Kljub temu da pripravkov na osnovi bakra in kroma (CCB in CCA) v Sloveni- ji skoraj ne uporabljamo več, so ti podatki zelo pomembni za načrtovanje življenjske dobe lesa na prostem in za razvoj novih biocidnih proizvodov na osnovi bakra. 2 MATERIALI IN METODE 2 MATERIALS AND METHODS 2.1 MATERIALI IN IZPOSTAVITEV VZORCEV 2.1 MATERIALS AND EXPOSURE Smrekove (Picea abies) vzorce dimenzij 2,5 cm × 5,0 cm × 50 cm smo pred impregnacijo tri tedne uravnovešali pri 20 °C in 65-odstotni re- lativni zračni vlažnosti (RH). Vzorci so bili polra- dialni, branike so z vzdolžno površino tvorile kot 45° ± 15°. Za impregnacijo smo uporabili biocid- ni proizvod CCB (Silvanol GBP , Silvaprodukt), na osnovi bakrovega(II) sulfata, kalijevega dikroma- ta(VI) in borove kisline (Richardson, 1993). Kon- centracija aktivnih učinkovin v pripravku je ustre- zala zahtevam za rabo v tretjem razredu uporabe (CEN, 2013). Predpisan suh navzem učinkovin biocidnega proizvoda CCB za uporabo v tretjem razredu uporabe je 4 kg/m 3 (Willeitner, 2001). Vzorce smo impregnirali v skladu s postopkom polnih celic. Postopek je sestavljen iz treh stopenj: 1 h pri tlaku -0,02 MPa, 2 h pri tlaku 1 MPa in 2 h namakanja pri normalnem tlaku. Po impregnaciji smo vzorcem gravimetrično določili mokri navzem in jih štiri tedne počasi sušili ter s tem omogočili redukcijo kroma iz Cr(VI) v Cr(III). Za primerjavo smo uporabili neimpregnirane smrekove vzorce (kontrola). Vzorce smo izpostavili vremenskim vplivom 7. 4. 2006 na terenskem polju Oddelka za lesarstvo v Rožni dolini v Ljubljani na pretežno senčni in zatiš- ni legi (310 m n.m.). Izpostavljeni so bili v tretjem razredu izpostavitve (nepokrito na prostem nad tlemi, pogosto močenje) (CEN, 2013). Za določanje odpornosti lesa smo v raziskavi uporabili dvoslojni test (ang. double layer test) (Rapp & Augusta, 2004; CEN, 2015). Pet enako obdelanih vzorcev smo zložili v spodnjo in pet v zgornjo vrsto. Vzorci v zgornji vrs- ti so bili za polovico vzorca zamaknjeni. Na ta način smo ustvarili vodno past, kjer je zastajala voda. S tem smo pospešili glivni razkroj (slika 1). Ocenjevanje vzorcev je potekalo vsako leto med petnajstim majem in petnajstim junijem. Vsak vzorec smo si natančno ogledali in ocenili stopnjo razkroja po standardu SIST EN 252 (CEN, 2015) (preglednica 1). Po 14 letih izpostavitve je propadel prvi zaščiten vzorec, ki smo ga podrobneje raziskali, da bi določili vzrok za razkroj. Vzorec smo prežagali na 12 mestih in z optičnim čitalcem preslikali preseke. 21 Les/Wood, Vol. 70, No. 1, June 2021 Humar, M., Lesar, B., Kržišnik, D., & Balzano, A.: Analiza razkrojenega smrekovega lesa, zaščitenega z biocidnim proizvodom CCB, po 14 letih izpostavitve na prostem Preglednica 1. Ocene razkroja vzorcev (CEN, 2015). Table 1. Decay ratings of samples (CEN, 2015). Ocena / Ra ting Raz vr s tit e v / Classific a tion Opis preizkušanca / De finition of c ondition 0 Ni znakov razkroja Na preizkušancu ni zaznavnih sprememb. 1 Neznaten razkroj Na vzorcu so vidni znaki razkroja, vendar razkroj ni intenziven in je zelo prostorsko omejen: - Spremembe, ki se pokažejo predvsem kot sprememba barve ali zelo površinski razkroj, mehčanje lesa je najpogostejši kazalec, razkroj sega do 1 mm v globino. 2 Zmeren razkroj Jasne spremembe v zmernem obsegu: - Spremembe, ki se kažejo kot mehčanje lesa 1 mm do 3 mm globoko na 1 cm 2 ali večjem delu vzorca. 3 Močen razkroj Velike spremembe: - Izrazit razkroj lesa 3 mm do 5 mm globoko na velikem delu površine (večje od 20 cm 2 ), ali mehčanje lesa globlje kot 10 mm na površini, večji od 1 cm 2 . 4 Propad Preizkušanec je močno razkrojen: - Ob padcu z višine 0,5 m se zlomi. Slika 1. Dvoslojni test Figure 1. Double-layer test 22 Les/Wood, Vol. 70, No. 1, June 2021 2.2 ELEMENTNA ANALIZA 2.2 ELEMENTAL ANALYSIS Lesene vzorce smo z dletom in krožnim žagal- nim strojem razdelili v tri sloje in odstranili čela (2,5 cm od roba). Posebej smo ločili čela, ki jih je mogo- če lažje impregnirati, ter zgornji, srednji in spodnji sloj. V nadaljevanju smo vzorce posameznih plas- ti zmleli (velikost sita = 1 mm) z rezalnim mlinom (Retsch SM 2000, Haan, Nemčija). Iz zmletega lesa smo s stiskalnico (Chemplex, Palm City, FL, Združe- ne države Amerike) izdelali vsaj pet tablet. Te table- te smo uporabili za elementno analizo, ki smo jo izvedli z rentgenskim fluorescenčnim spektromet- rom (TwinX, Oxford instruments, Velika Britanija) in določili delež Cu. Vse meritve smo izvedli s PIN detektorjem (U = 26 kV, I = 115 μA, t = 300 s). 2.3 MIKROSKOPSKA ANALIZA 2.3 MICROSCOPIC ANALYSIS Na razkrojenem impregniranem vzorcu smo opravili tudi morfološko in mikroskopsko analizo. Za morfološko analizo smo uporabili laserski konfokal- ni vrstični mikroskop (Olympus, Lext OLS 5000). Ta tehnika ne zahteva posebne priprave, zato je še posebej primerna za preiskave vlažnega in trhlega lesa (Humar et al., 2019b; Žigon et al., 2020). Ana- lizo smo izvedli na zgornji strani vzorca, na najmanj razkrojenem delu. Del vzorcev je bil analiziran tudi s klasično svetlobno mikroskopijo. Vzorce smo ob- rezali in jih vklopili v parafin. Pripravo rezin smo izvedli z rotacijskim mikrotomom (Leica, RM2245). Rezine so bile obarvane z barviloma safranin in astra-modro. Rezine so bile vklopljene v Euparal (Prislan et al., 2008). 3 REZULTATI IN RAZPRAVA 3 RESULTS AND DISCUSSION Gostota lesa je osnovni indikator, ki posred- no nakazuje na nekatere ključne lastnosti lesa. Povprečna gostota (r 12 ) vremenskim vplivom izpo- stavljenih impregniranih in neimpregniranih vzor- cev se med seboj značilno ne razlikuje (slika 3). Gos- tota lesa, impregniranega s CCB, je bila 488 kg/m 3 , gostota kontrolnih vzorcev 490 kg/m 3 . Te vrednosti so povsem v skladu z literaturnimi podatki za smre- kovino (Wagenfuhr, 2007), kar nakazuje, da je bil za raziskavo uporabljen reprezentativen material. Prve znake razkroja na nezaščiteni smrekovini smo opazili že po prvem letu izpostavitve. Šibek raz- kroj se je pojavil na dveh od desetih izpostavljenih vzorcev. V nadaljevanju je razkroj počasi napredo- val. Prvi kontrolni vzorec je propadel po štirih letih, polovica vzorcev je propadla po šestih, vsi kontrolni vzorci so propadli po osmih letih izpostavitve (slika 4A). To obdobje je relativno dolgo. Neimpregnira- ni smrekovi vzorci na terenskem polju v Ljubljani Slika 2. Prikaz vzorčenja z XRF analizo Figure 2. Sketch of the sampling for XRF analysis Humar, M., Lesar, B., Kržišnik, D., & Balzano, A.: Analysis of decayed Norway spruce wood impregnated with CCB after 14 years of outdoor exposure 23 Les/Wood, Vol. 70, No. 1, June 2021 navadno propadejo hitreje in sicer po 4 do 6 letih izpostavitve (Humar et al., 2019a; Humar et al., 2020). Impregnacija s CCB je bistveno upočasnila razkroj. Prvi znaki razkroja so se na smrekovini, impregnirani s CCB, pojavili po 10 letih testiranja. Razkroj je v povprečju potem počasi napredoval s povprečne ocene 0,3 po desetih letih na 1,1 po 14 letih izpostavitve (slika 4A). Kot je razvidno iz po- razdelitve ocen, je po 14 letih delovanja biotskih in abiotskih dejavnikov potek razkroja relativno nehomogen. Vzorci izpostavljeni v spodnji vrsti, so ostali nerazkrojeni, medtem ko smo intenziven raz- kroj opazili predvsem na vzorcih v zgornjem sloju (slika 4B). Dvoslojni test je zasnovan tako, da med vzorci zastaja voda, zato smo pričakovali, da se bo razkroj najprej razvil med obema slojema vzorcev. V na- sprotju s pričakovanji je analiza preseka impregnira- nega vzorca pokazala, da se je razkroj impregniranih vzorcev pričel z zgornje strani (slika 5). Očitno je, da so se na zgornji strani pojavile razpoke. V razpokah je zastajala voda in s tem so se vzpostavili ugodni pogoji za razvoj gliv (slika 8). Hrapavost izpostavl- jene površine (Sa) znaša kar 500 µm, hrapavost referenčne, vremenskim vplivom neizpostavljene impregnirane smrekovine znaša le 20 µm. Na podlagi barve razkrojenega lesa sklepamo, da so površino lesa razkrojile glive rjave trohno- be. Po 14 letih razkroja je bila površina močno razpokana, kar verjetno vodi v spiralo propada, v razpokah zastaja voda, zato so pogoji za razkroj ugodnejši skozi daljše časovno obdobje kot pri ne- razpokanih vzorcih. Profil površine na najmanj raz- krojenem delu vzorca je razviden na spodnji sliki (slika 6). Poleg tega se je na površini smrekovine, impregnirane s CCB, razvil intenziven biofilm (slika 7). Biofilm, pritrjen na podlago, je skupek mikro- organizmov in njihovih zunajceličnih izločkov, ki Slika 3. Gostota zračno suhega impregniranega (CCB) in neimpregniranega (Kontrola) smrekovega lesa Figure 3. Density of air dry impregnated (CCB) and non-impregnated (Control) wood Slika 4. (A) Potek razkroja na impregniranih (CCB) in neimpregniranih (Kontrola) vzorcih smrekovega lesa; (B) Distribucija ocen razkroja vzorcev, impregniranih z biocidnim proizvodom CCB, po 14 letih izpostavitve na prostem Figure 4. (A) Decay development on impregnated (CCB) and non-impregnated (Control) Norway spruce wood samples; (B) Distribution of decay ratings of wood impregnated with CCB preservative solution after 14 years of outdoor exposure Humar, M., Lesar, B., Kržišnik, D., & Balzano, A.: Analiza razkrojenega smrekovega lesa, zaščitenega z biocidnim proizvodom CCB, po 14 letih izpostavitve na prostem 24 Les/Wood, Vol. 70, No. 1, June 2021 delujejo kot povezovalni člen. Na podlagi CLSM analize sklepamo, da so se na površini razvile gli- ve modrivke, plesni in alge. Ta pojav je značilen za les, izpostavljen na prostem. Najpogostejša gliva (črna kvasovka) na površini lesa je Aureobasidium pullulans (Sailer et al., 2010). Biofilmi na prostem ne nastajajo le na lesu, temveč tudi na drugih ma- terialih, kot so beton ali polimerni materiali (Miao et al., 2019) in služijo kot substrat za kolonizaci- jo mikroorganizmov, ki tvorijo biofilme. Različne mikrobne združbe med mikroplastiko in obdajajočo vodo so bile dobro dokumentirane, kljub temu pa ni dovolj znanja o kolonizaciji plastičnih in neplastičnih substratov, kljub dejstvu, da se mikrobne združbe običajno pojavljajo na naravnih trdnih površinah. Biofilm pripomore k zadrževanju vode in ustvar- janju ugodnih pogojev za glivni razkroj. Biofilm na lesu, impregniranem s CCB, je tako debel, da pod biofilmom lesa sploh ni opaziti (slika 7). Analiza lesa s svetlobno mikroskopijo je po- kazala, da je na lesu opaziti razkroj, ki je značilen za glive mehke trohnobe (slika 7). Za glive mehke trohnobe je značilno, da z razkrojem celuloze in hemiceluloz ustvarijo vrzeli v S2 sloju sekundar- ne celične stene, v nadaljnjih stopnjah razkroja ta sloj povsem razgradijo (Reinprecht, 2016). Znači- len pojav mehke trohnobe je viden na vzorcu im- pregniranem s CCB. Kljub temu, da je mehka tro- hnoba značilna za okolja z zelo visoko vlažnostjo Slika 5. Presek vzorca, impregniranega z biocidnim proizvodom CCB po 14 letih izpostavitve na prostem Figure 5. Several cross-sections of wood impregnat- ed with CCB preservative solution after 14 years of outdoor exposure Slika 6. Profili površine vzorca, impregniranega z biocidnim proizvodom CCB po 14 letih izpostavitve na prostem Figure 6. Profile of the CCB-treated wood after 14 years of outdoor exposure Humar, M., Lesar, B., Kržišnik, D., & Balzano, A.: Analysis of decayed Norway spruce wood impregnated with CCB after 14 years of outdoor exposure 25 Les/Wood, Vol. 70, No. 1, June 2021 in vsebnostjo dušika, kot na primer les v vodnem okolju, se je ta trohnoba pojavila tudi na našem vzorcu, izpostavljenem v tretjem razredu upo- rabe. Po vsej verjetnosti so k temu pripomogle razpoke in biofilm, kar omogoča zastajanje vode. Tako se lahko tudi na lesu v tretjem razredu upo- rabe vzpostavijo ugodni pogoji za razkroj. Prisotni biocidi preprečujejo razvoj večine lesnih gliv. Na impregniranem lesu se lahko pojavijo na baker tolerantne glive. V tej skupini so tudi glive meh- ke trohnobe. K uspešnosti gliv mehke trohnobe pogosto pripomore dejstvo, da pogosto živijo v simbiozi z bakterijami, ki jim pomagajo razstrupiti impregniran les (Clausen, 1996). Eden od ključnih vzrokov, ki preprečuje razvoj gliv na lesu, je prisotnost biocidnih učinkovin. Suhi navzem aktivnih učinkovin v impregniranih vzorcih je razviden iz slike 8A. Za tretji razred uporabe je priporočeno, da mora les vsebova- ti vsaj 4 kg aktivnih učinkovin na kubični meter (Willeitner, 2001). Pri izpostavljenih vzorcih smo v povprečju to vrednost dosegli. Povprečni suhi navzem znaša 4,2 kg/m 3 , vendar je med vzorci opaziti velike razlike. Suhi navzem niha med 1,8 kg/m 3 in 7,0 kg/m 3 (slika 9A). Razloge za te razli- ke lahko pripišemo slabi impregnabilnosti smre- kovega lesa (CEN, 2016). Slaba impregnabilnost smrekovega lesa je med drugim povezana z aspi- racijo pikenj v procesu ojedritve. Najnižji navzem smo zabeležili pri vzorcu 6, ki je po 14 letih pro- padel. Ta vzorec je tudi predmet analize, opisane v tem članku. Poleg nizkega suhega navzema je k hitremu razkroju pripomoglo še dejstvo, da se je vzorec nahajal v zgornjem sloju dvoslojnega tes- ta, ki je bil bolj izpostavljen razkroju kot spodnji vzorci. Menimo, da navzem ni edini dejavnik, saj med navzemom aktivnih učinkovin in razkrojem nismo odkrili povezave. V nadaljevanju opisujemo natančnejšo anali- zo porazdelitve aktivnih učinkovin po vzorcu. Gle- de na to, da sta koncentraciji bakrovih in kromovih učinkovin v impregniranem lesu prisotni v enakem razmerju, v nadaljevanju opisujemo le prisotnost bakra. Baker je v biocidnem proizvodu prisoten kot ključna aktivna učinkovina, medtem, ko kromove spojine nimajo biocidnih lastnosti. Kromove spoji- ne v prvi vrsti omogočajo vezavo bakrovih spojin v les (Humar et al., 2004a). Rentgenska fluorescenč- na spektrometrija (XRF) je pokazala, da je najvišji navzem bakra mogoče opaziti v okolici čel (c Cu = 700 ppm). Biocidni proizvodi v les bistveno bolje prodirajo v aksialni smeri kot v tangencialni in ra- Slika 7. Biofilm na površini s CCB impregniranega vzorca po 14 letih izpostavitve na prostem. Na levi (A) je barvna slika, na desni (B) sliki je razvidna morfologija. (540 µm × 540 µm) Figure 7. Biofilm on the surface of CCB-treated wood after 14 years of outdoor exposure. On the left (A) there is a colour image, and on the right (B) the morphology is resolved. (540 µm × 540 µm) Humar, M., Lesar, B., Kržišnik, D., & Balzano, A.: Analiza razkrojenega smrekovega lesa, zaščitenega z biocidnim proizvodom CCB, po 14 letih izpostavitve na prostem 26 Les/Wood, Vol. 70, No. 1, June 2021 dialni, zato je ta rezultat pričakovan. Sredica vzor- ca je bila zelo slabo impregnirana, na kar nakazuje že nizek suhi navzem, zato je nizka koncentracija bakrovih učinkovin v sredini razumljiva (c Cu = 23 ppm). Zanimiva je velika razlika med koncentraci- jo aktivnih učinkovin v zgornjem (c Cu = 72 ppm) in spodnjem sloju vzorca (c Cu = 438 ppm). Ocenjuje- mo, da je koncentracija bakra v čelih in spodnjem sloju primerljiva s koncentracijo te aktivne učinko- vine v izhodišču. Po drugi strani je koncentracija bakra na zgornji površini skoraj šestkrat nižja od koncentracije bakra na spodnji strani. Menimo, da je k temu pripomoglo izpiranje zaradi kombina- cije abiotskih (padavine, UV …) in biotskih dejav- nikov (bakterije, glive). Bakterije in glive izločajo Slika 8. Prečni prerez s CCB impregniranega smrekovega vzorca (Picea abies) po 14 letih izpostavitve na prostem Figure 8. Cross-section of CCB-treated Norway spruce wood (Picea abies) after 14 years of outdoor exposure cel spekter organskih kislin (oksalna, metanojska, etanojska, hidroksi dikarboksilna butanojska …) (Takao, 1965). V kislem okolju so aktivne učinko- vine zaradi nastanka topnih kompleksov bolj top- ne in se izpirajo iz lesa (Humar et al., 2004b), kar prispeva k počasnemu razstrupljanju lesa in v na- daljevanju pripelje do razkroja. Ta proces se upo- rablja tudi za bioremediacijo odsluženega lesa za pridobivanje kovin z učinkovitimi biometalurškimi procesi iz jalovine, odpadne elektronike ipd. (Ilyas & Lee, 2015). Humar, M., Lesar, B., Kržišnik, D., & Balzano, A.: Analysis of decayed Norway spruce wood impregnated with CCB after 14 years of outdoor exposure 27 Les/Wood, Vol. 70, No. 1, June 2021 4 Z AKL JUČKI 4 CONCLUSIONS Na nezaščitenem smrekovem lesu se je kmalu po izpostavitvi zunanjim biotskim in abiotskim de- javnikom pojavil razkroj. Prisotnost biocidnih učin- kovin (CCB) v impregniranem lesu je uspešno upo- časnila razkroj. Kljub vsemu je prvi vzorec, zaščiten z biocidnim proizvodom CCB propadel po 14 letih. Vzorec je propadel zaradi delovanja gliv rjave in mehke trohnobe. Razkroj na dvoslojnem testu je hitrejši pri vzorcih, ki so bili v dvoslojnem testu na zgornji strani, izpostavljeni vremenskim vplivom, zato sam dvoslojni test ni imel izrazitega vpliva na dinamiko razkroja. Rezultati te raziskave nedvoumno kažejo, da je neodporen les smrekovine treba zaščititi, da mu zagotovimo ustrezno življenjsko dobo. Zaščita mora biti izvedena kvalitetno. Les mora biti prepojen po celotnem preseku, navzem mora ustrezati zahte- vam proizvajalca. V nasprotnem primeru tudi zašči- ten les lahko hitro propade. 5 POVZETEK 5 SUMMARY Wood in outdoor applications is exposed to abiotic and biotic factors. Fungi are the most im- portant reason for the failure of wooden construc- Slika 9. (A) Suhi navzem vzorcev, izpostavljenih na terenskem polju. Vzorec šest je bil uporabljen v tej študiji. (B) Koncentracija bakra v posameznih slojih vzorca 6, po 14 letih izpostavitve. Figure 9. (A) Retention of the wood specimens exposed in the field test site. Sample no 6 was used in the current study. (B) Copper concentration in sample 6 after 14 years of exposure. tions. If we want to slow down the decay, there are three possibilities: Using naturally durable wood, wood modification and wood preservation. Since most wood species in Europe do not have dura- ble wood and modification is quite expensive and not suitable for in ground exposures, impregnation with biocides remains the most commonly used al- ternative. In the past, biocidal products based on copper, chromium, and boron compounds (CCB) were one of the most important solutions for wood protection under extreme conditions. Today, these products have almost entirely been taken off the market in the EU. In order to assess the effective- ness of copper-based wood preservatives, a com- prehensive field test site has been set up at the Department of Wood Science and Technology, Bio- technical Faculty. For 14 years, field tests have been carried out under real conditions, in which impreg- nated samples are exposed to the weather in a dou- ble-layer test, with the samples assessed annually for decay. With treated wood, we often find that the wood decays faster than expected. In this work we wanted to determine what contributes to the decay based on an analysis of decayed impregnated wood from the field test site. The decayed sample was analysed by light and laser scanning confocal microscopy. Furthermore, the presence of copper in decayed wood was determined by X-ray fluo- Humar, M., Lesar, B., Kržišnik, D., & Balzano, A.: Analiza razkrojenega smrekovega lesa, zaščitenega z biocidnim proizvodom CCB, po 14 letih izpostavitve na prostem 28 Les/Wood, Vol. 70, No. 1, June 2021 rescence spectroscopy. The results show that the untreated control wood samples were completely degraded after eight years of exposure. In contrast, CCB-treated wood performed significantly better. The first signs of decay on CCB-treated wood were observed after 10 years of exposure. Decay is as- sociated with surface cracks, biofilm formation and insufficient retention and penetration. Sufficient retention and penetration of the active substances into the wood ensures the planned service life. 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DOI: https://doi.org/10.26614/les-wood.2020.v69n01a05 Humar, M., Lesar, B., Kržišnik, D., & Balzano, A.: Analiza razkrojenega smrekovega lesa, zaščitenega z biocidnim proizvodom CCB, po 14 letih izpostavitve na prostem 30 Les/Wood, Vol. 70, No. 1, June 2021 31 Les/Wood, Vol. 70, No. 1, June 2021 UDK 630*813:543 Original scientific article / Izvirni znanstveni članek Received / Prispelo: 10. 1. 2021 Accepted / Sprejeto: 15. 3. 2021 Vol. 70, No. 1, 31-44 DOI: https://doi.org/10.26614/les-wood.2021.v70n01a02 Abstract / Izvleček Abstract: Gmelina arborea (Roxb. ex. Sm.) wood samples were thermally modified at 180 °C, 200 °C and 220 °C for 3 h, by employing a process similar to ThermoWood®. The resulting effects on the basic chemical composition and mechanical properties were determined. The results were analyzed statistically with ANOVA, and Least Square Deviation was used to compare means. Generally, after the thermal modification (TM) process, the cellulose, hemi- celluloses and extractives content decreased significantly. By contrast, lignin proportions increased significantly. Un- treated wood and samples modified at 180 °C indicated comparable modulus of elasticity (MOE), modulus of rupture (MOR), degree of integrity (I), fine fraction (F) and resistance to impact milling (RIM). Noteworthy reductions however occurred at 200 °C and 220 °C. Significant increases in Brinell hardness (BH) took place at 180 °C, recording a high decrease at 220 °C. Gmelina arborea could be modified suitably at 180 °C for structural and other purposes. To take advantage of other improved properties, modification at 200 °C could be employed for non-structural uses. Keywords: High-Energy Multiple Impact (HEMI), Resistance to Impact Milling (RIM), Thermal modification, Static Bending Izvleček: Vzorce lesa vrste Gmelina arborea (Roxb. ex. Sm.) smo 3 ure termično modificirali pri 180 °C, 200 °C in 220 °C po postopku, ki je soroden ThermoWood® procesu. V nadaljevanju smo ocenili vpliv modifikacije na kemijsko sestavo in mehanske lastnosti. Rezultate smo testirali z analizo variance ANOVA, za primerjavo povprečij pa smo uporabili metodo najmanjših kvadratov. Na splošno se je delež celuloze, hemiceluloz in ekstraktivnih snovi v termično modificiranem lesu znatno zmanjšal. Nasprotno se je delež lignina v modificiranem lesu statistično značilno povečal. Neobdelani les, mod- ificiran pri 180 °C, je imel primerljivo upogibno trdnost (MOR) in modul elastičnosti (MOE), stopnjo integritete (I), delež fine frakcije (F) in odpornost proti udarnemu mletju (RIM). Pri modifikaciji pri temperaturah 200 °C in 220 °C je prišlo do znatnega poslabšanja omenjenih lastnosti. Trdota po Brinellu (BH) se je znatno povečala pri 180 °C, pri 220 °C pa se je močno zmanjšala. Les vrste G. arborea bi bilo za konstrukcijske namene primerno modificirati pri 180 °C. Da bi izkoristili druge izboljšane lastnosti, bi za les za nekonstrukcijske namene lahko uporabili modifikacijo pri 200 °C. Ključne besede: večkratni visokoenergijski udarci (HEMI), odpornost proti udarnemu mletju (RIM), termična modifi- kacija, statični upogib CHEMICAL AND MECHANICAL CHARACTERIZATION OF THERMALLY MODIFIED GMELINA ARBOREA WOOD KEMIJSKA IN MEHANSKA KARAKTERIZ A CIJ A TERMIČNO MODIFICIRANEGA LESA VRSTE GMELINA ARBOREA Maxidite Amankwaah Minkah 1* , Kojo Agyapong Afrifah 1 , Djeison Cesar Batista 2 and Holger Militz 3 1 Department of Wood Science and Technology, Kwame Nkrumah University of Science and Technology, P . O. Box PMB KNUST, Kumasi, Ghana. * e-mail: minkahmaxidite@yahoo.com 2 Department of Forest and Wood Sciences, Federal University of Espírito Santo, Avenida Governador Carlos, Lindenberg 316, Postal Code 29550-000, Jerônimo, Monteiro, Espírito Santo, Brazil. 3 Department of Wood Biology and Wood Products, University of Göttingen, Büsgenweg 4, D-37077, Göttingen, Germany. 1 INTRODUCTION 1 UVOD Wood is a very important environmentally friendly, renewable and accessible material, which is widely preferred around the globe. However, the sustainable supply of tropical timber on the world market is increasingly threatened (Boonstra, 2008). For instance, deforestation in Ghana has assumed alarming proportions, leading to massive reductions in the nation’s primary forest cover (FAO, 2006). In its 2016 report, the Forestry Commission (FC) of Ghana indicated that about 80% of the country’s forest re- sources under state management had been lost to illegal logging activities facilitated mainly by farm- ing, the chainsaw operations which supply most of the local lumber demand, and mining (FC, 2016a; 32 Les/Wood, Vol. 70, No. 1, June 2021 Minkah, M. A., Afrifah, K. A., Batista, D. C., & Militz, H.: Kemijska in mehanska karakterizacija termično modificiranega lesa vrste Gmelina arborea Hansen & Treue, 2008). Asiedu (2019) also record- ed a 60% increase in loss of primary forest cover in 2018 compared to 2017 in Ghana, with clearing for cocoa farming being a leading cause of deforesta- tion, while mining remains the biggest threat. To reduce over-exploitation of primary forests and ensure sustainable supply of timber on the local and export markets, Ghana has embarked on the es- tablishment of plantations, covering about 190,500 ha as of 2015. The FC further plans to cultivate 100,000 ha of plantations in the years 2016 – 2040. Among the many species to be cultivated is Gmeli- na arborea, which is an exotic species (FC, 2016b), indigenous to the Indo-Burma region of Southeast Asia (Nwoboshi, 1994). Over 5,000 ha of Gmelina ar- borea plantations have been established in Ghana, 2,000 ha of which was cultivated by the Subri Indus- trial Plantation Limited (SIPL), near Sekondi-Takoradi in the Western Region (Nwoboshi, 1994). Gmelina arborea has oven-dry density ranges of 390 – 599 kg/m 3 and good machining properties (Mitchual et al., 2018). It is rated as naturally non-durable and thus requires preservative treatment to prolong its service life (Owoyemi et al., 2011). Kasmudjo (1990) indicated that suitable uses of Gmelina arborea wood are fuelwood, pulp and paper, plywood, fur- niture, construction and matches. The researcher further suggested harvesting cycles of five years for fuel wood, 15 years for plywood and boards, 20 years for construction and eight years for uses such as boxes, toothpicks and matches. To complement the efforts of the FC there is the need to research the properties of these plan- tation species, in order to establish their suitabili- ty for furniture and other such applications. When thermally modified, Gmelina arborea could be used for applications exposed to the weather and humidity variations above ground, including clad- ding, garden furniture, windows and saunas, but could also be used for interior applications such as stairs, decorative panels, flooring, kitchen furni- ture, etc. (Sandberg & Kutnar, 2016). The current study aimed at redirecting the attention of wood industry stakeholders to plantation species like Gmelina arborea and encouraging its use. Thermal modification (TM) of wood is one im- portant method for improving wood properties, including dimensional stability, natural durability and hygroscopicity. Wood retains its environmen- tally friendly nature after this process. TM of wood is less costly compared to wood preservation using biocidal treatment (Esteves et al., 2014). However, TM may cause a reduction in mechanical strength. The extent of the effect of TM on the properties of wood depends on species and process conditions (Esteves & Pereira, 2009). Differences in wood spe- cies’ response to TM treatments are due to varia- tions in chemical, anatomical and physical proper- ties (Ranin, 2004). Vẏbohová et al. (2018) analysed the effect of TM intensity at the temperatures of 160 °C, 180 °C and 200 °C under atmospheric pres- sure in the presence of air for durations of 3, 6, 9, and 12 h on ash wood. The researchers reported that the extractives content initially increased up to 200 °C and 3 h, which decreased with extend- ed treatment duration. Hemicellulose monosac- charide (D-xylose) degraded under all treatment conditions, which resulted in a decrease in holo- cellulose content. Lignin content also increased at temperatures of 180 °C and 200 °C. Bekhta and Niemz (2003) indicated that the MOR of spruce (Pi- cea abies (L.) Karst.) decreased by 44% to 50% as the modification temperature was raised from 100 °C to 200 °C, while temperature had no effect on MOE. Korkut et al. (2008) reported that the surface hardness, MOE and MOR in the radial direction of Scots pine (Pinus sylvestris L.) decreased by 27%, 32% and 33%, respectively at 180 °C for 10 h. To reduce the focus on traditional primary tim- ber species in order to curb deforestation in Ghana, it is necessary to promote lesser used species (LUS) like Gmelina arborea on both local and export mar- kets. Successful adoption of Gmelina arborea for utilization will depend on its properties. This study therefore aimed to investigate the impact of the TM process applied to enhance the properties of Gmelina arborea wood from Ghana with regard to its basic chemical and mechanical properties. 2 MATERIALS AND METHODS 2 MATERIAL IN METODE 2.1 MATERIALS 2.1 MATERIAL 2.1.1 Sour ce of Ma t erial and Pr epar a tion 2.1.1 Iz v or ma t eriala in prip r a v a Four Gmelina arborea trees with diameter at breast height (DBH, 1.3 m above ground) of 35 – 33 Les/Wood, Vol. 70, No. 1, June 2021 Minkah, M. A., Afrifah, K. A., Batista, D. C., & Militz, H.: Chemical and Mechanical Characterization of Thermally Modified Gmelina arborea Wood 55 cm were obtained from a 40-year old plantation of the Centre for Scientific and Industrial Research – Forestry Research Institute of Ghana’s (CSIR – FORIG) research plot at Abofour, Offinso District in the Ashanti Region of Ghana. Abofour is located within the moist Semi-Deciduous Forest Zone with average annual rainfall of 1,400 mm. It lies 7°8”0’ N and 1°45”0’ W and it is about 60 km from the Ashanti regional capital, Kumasi. Trees were bucked into 2.5 m length bolts with a chainsaw, which were further processed using a portable Wood-Mizer sawmill (LT 30) into boards of 25 mm thickness at the CSIR – FORIG wood workshop at Fumesua, Kumasi. The boards were air-dried for at least 12 months until a mois- ture content (MC) below 20% was achieved. Boards were randomly selected from within 15 cm radius of the pith to assure the use of heartwood. These boards were further processed into test slats of di- mensions 20 x 50 x 650 mm 3 (radial (r) × tangential (t) × longitudinal (l)) for the TM process. The slats were sorted according to weight and those in the range of 300 to 400 g were used for the study. This pre-sorting was necessary for the homogenization of the lot and to minimize the effect of the initial density on the results. 2.2 METHODS 2.2 METODE 2.2.1 Thermal Modific a tion 2.2.1 T ermična modifik acija The open system TM similar to the Ther- moWood® process (Mayes & Oksanen, 2002) was employed, using a 65 L capacity laboratory scale reactor. Firstly, the temperature in the ves- sel was raised at 12 °C/h to 100 °C and then 4 °C/h to 130 °C to allow high temperature drying of slats to nearly 0% MC. Secondly, the tempera- ture was again increased at 12 °C/h until reaching the peak temperatures of 180, 200 and 220 °C. Each peak temperature was held for 3 h. Finally, the temperature was decreased at 20 °C/h until reaching 65 °C, at which the vessel was opened and the slats removed. Eventually, the thermally modified wood samples at the three peak tem- peratures resulted in three treatments with the untreated wood as control. The wood samples were assessed for selected chemical and mechan- ical properties. 2.2.2 Mass loss 2.2.2 Iz guba mase The mass loss of each slat after the thermal modification process was calculated as described by Metsä-Kortelainen et al. (2006). Each air-dried slat was weighed before and after the thermal modification process. Moisture content was then determined for the slats before and after the ther- mal modification process, in order to determine the mass loss. Mass loss% (ML%), was thus calculated as in Equation 1. [%] (1) Where m 1 is the dry mass of the sample before the thermal modification, in g; m 2 is the dry mass of the sample after the thermal modification, in g. Dry mass (g), mdry, was calculated as follows (Equa- tion 2). [g] (2) where m u is the mass of the sample at moisture content u%, in g. 2.2.3 Chemic al Analysis 2.2.3 K emijsk a analiz a Slats were randomly selected per treatment for the analysis. Two samples of the dimensions 20 × 20 × 20 mm 3 (r × t × l) were cut from both ends of each slat to make up six parts. The parts of the slats were reduced manually and ground in a cutting mill (Retsch, model SM 2000, Haan, Germany) with a sieve of 1 mm diameter, resulting in a compound sample per treatment. The powder was screened in a vibratory sieve shaker (Retsch, model KS 1000, Haan, Germany), operating at 200 rotations min -1 for four minutes. The chemical analysis was done on the fraction remaining on the 40-mesh sieve. All chemical analyses were carried out in triplicate for each TM treatment. The extractives content was determined in ac- cordance with the hot water solubility method, de- ML= − () × mm m 12 100 1 mdry   = × + 100 100 mu u 34 Les/Wood, Vol. 70, No. 1, June 2021 Minkah, M. A., Afrifah, K. A., Batista, D. C., & Militz, H.: Kemijska in mehanska karakterizacija termično modificiranega lesa vrste Gmelina arborea scribed in the standard T 207 cm-99 (TAPPI, 1999b). The insoluble lignin was determined using 72% sul- furic acid, following the method used by Sluiter et al. (2008). Holocellulose was prepared using a solu- tion of sodium chlorite and acetic acid according to the method of Wise et al. (1946). The filtered frac- tion from the holocellulose analysis was used in the α-cellulose analysis, which was carried out with a solution of sodium hydroxide (17.5%), according to the standard T-203 cm-99 method (TAPPI, 1999a). The amount of hemicelluloses was calculated by difference [holocellulose - α-cellulose]. 2.2.4 St a tic Bending 2.2.4 St a tični upogib A three-point bending test based on the DIN 52186 (1978) test norm was performed on a univer- sal testing machine (Zwick Roell Z010, Zwick, Ulm, Germany) using the central loading method and 30 samples per treatment, measuring 10 × 10 × 180 mm 3 (r × t × l). For each TM treatment, three slats were used with each providing 10 samples. All the samples were conditioned at 20 °C and 65% relative humidity for seven days until constant weight. This ensured that the moisture content and tempera- ture, which affect the strength of wood, were main- tained to enhance comparability of the results. The loading heads moved at constant speeds of 3 mm/ min for untreated wood, 3 mm/min, 2 mm/min and 1 mm/min for samples thermally modified at 180 °C, 200 °C and 220 °C, respectively. Loading head speed was varied for each modification to be able to cause the failure of the samples within 90 ± 30 s. The test samples were supported at the ends by rotating supports with the diameter of 15 mm. The distance between the supports was 160 mm. At the point of failure the modulus of elasticity (MOE) and modulus of rupture (MOR) generated by the uni- versal testing machine and displayed on a monitor were recorded. MOE and MOR were determined according to Equations 3 and 4, respectively: [N/mm 2 ] (3) Where ΔF is the force difference in N (Newton) in the elastic deformation range of the specimen; Δf is the deflection, corresponding to the force differ- ence ΔF, in the middle of the specimen in mm; l is distance between the supports (span) in mm; b is width of the sample in mm; and h is height of the sample in mm. [N/mm 2 ] (4) Where P is the breaking (maximum) load in N; l and h are the span and height of the samples, respec- tively. 2.2.5 High Ene r gy Multiple I mpact (HEMI-t es t) 2.2.5 Visok oener gijski v ečkr a tni udar (HEMI-t es t) The HEMI-test was carried out according to the procedure presented by Brischke (2017). For each treatment, the test was replicated five times. Each replicate was made up of 20 oven-dry samples of 10 × 10 × 10 mm 3 (r x t x l). In all, a total of 100 samples from four slats were assessed for each TM treatment. Each of the 20 samples was placed into a bowl of 140 mm inner diameter of a heavy impact ball mill (Her- zog HSM 100, Osnabrück, Germany), together with one steel ball of 35 mm diameter, three steel balls of 12 mm diameter, and three steel balls of 6 mm diameter. The bowl was shaken for 60 s with a rotary frequency of 23.3 s -1 and a stroke of 12 mm. The frag- ments of the 20 samples were fractionated on a slit sieve with a slit width of 1 mm using an orbital shaker at an amplitude of 25 mm and a rotary frequency of 200 min -1 for 1 min. The following values were calcu- lated using Equation 5, Equation 6, and Equation 7: [%] (5) Where the degree of integrity (I) is the ratio of the mass of the 20 biggest fragments (m 20 ) to the mass of all fractions (m all ) after the crushing process. [%] (6) Where the fine fraction (F) is the ratio of the mass that is sieved and has a diameter of less than 1 mm (m <1mm ) to the mass of all fractions (m all ). MOE l bh F f = Δ Δ 3 4 3 ** * MOR Pl bh = 15 2 .* * * I m m all =       × 20 100 F m m mm all =       × <1 100 35 Les/Wood, Vol. 70, No. 1, June 2021 Minkah, M. A., Afrifah, K. A., Batista, D. C., & Militz, H.: Chemical and Mechanical Characterization of Thermally Modified Gmelina arborea Wood [%] (7) Where RIM is the resistance to impact milling and represents the value of the measure for the struc- tural integrity of the material. 2.2.6 Brinell har dness 2.2.6 T r dot a po Brinellu The Brinell hardness (static hardness) perpen- dicular to the grain on the radial face was measured according to DIN EN 1534 (2011) with a universal testing machine (Zwick Roell Z010, Zwick, Ulm, Ger- many). Ten samples obtained from five slats (i.e. two samples per slat) were used per treatment. The samples were conditioned at 20 °C/ 65% RH for 14 days until constant weight. A maximum force of 500 N was exerted using a steel ball with a diameter of 10 mm applied for 25 seconds on the samples with dimensions of 20 × 50 × 200 mm 3 (r × t × l). The di- ameters of the residual impressions at three points on a face of each sample, with any two points being at least 50 mm apart, were automatically deter- mined by the testing machine. The Brinell hardness was then calculated according to Equation 8: [N/mm 2 ] (8) Where BH is the Brinell hardness (N/mm 2 ), F is the maximum force used (N), D is the diameter of the steel ball (mm) and d is the diameter of the imprint on the sample (mm). 2.2.7 Da t a Analy sis 2.2.7 Obdela v a poda tk o v Descriptive statistics comprising means with standard deviations were presented for each treat- ment and test. A comparison of the results from the treatments was made using Analysis of Vari- ance (ANOVA). The Least Square Deviation test was used to compare means at α = 0.05, when ANO- VA revealed significant differences. The Statistical Package for Social Sciences (IBM Statistics) version 26 was used for the analyses. 3 RESULTS AND DISCUSSIONS 3 REZULTATI IN DISKUSIJA 3.1 MASS LOSS 3.1 IZGUBA MASE Table 1 presents the mass loss, proportions of cellulose, hemicelluloses, lignin and extractives in the thermally-modified Gmelina arborea wood. Most properties of thermally modified wood de- pend to a large extent on the mass loss (Bal, 2013). This indicates that high mass loss results in more T r ea tmen t Mass Loss [%] α-Cellulose [%] Hemicelluloses [%] Lignin [%] Extr activ es [%] Un tr ea t ed 0.00 55.93 a 19.16 a 34.86 a 7.87 a (0.00) (0.98) (1.13) (1.09) (0.20) 180 °C 5.44 a 51.50 b 18.08 a 39.62 b 6.35 b (0.86) (0.55) (0.43) (0.98) (0.34) 200 °C 10.08 b 53.20 ab 10.56 b 40.50 bc 9.11 a (0.95) (0.14) (0.88) (0.64) (0.23) 220 °C 15.13 c 52.45 b 6.63 c 44.16 c 6.35 b (2.17) (0.52) (0.23) (0.62) (0.40) RIM IF  *  = −+ () 3 300 4 Means followed by the same letter are not significantly different at α = 0.05 Standard error values are shown in parentheses Table 1. Mass loss, proportions of cellulose, lignin, hemicelluloses and extractives per treatment. Preglednica 1. Rezultati izgube mase in deleži celuloze, lignina, hemiceluloz in ekstraktivov glede na upo- rabljen postopek termične modifikacije BH FD DD d =− √ ()     2 22 ./ . π BH FD DD d =− √ ()     2 22 ./ . π 36 Les/Wood, Vol. 70, No. 1, June 2021 Minkah, M. A., Afrifah, K. A., Batista, D. C., & Militz, H.: Kemijska in mehanska karakterizacija termično modificiranega lesa vrste Gmelina arborea pronounced changes in wood properties, including chemical and mechanical properties (Militz, 2002; Hill, 2006; Esteeves & Pereira, 2009). Mass loss in- creased with the modification temperature, from 5.44% at 180 °C to 15.17% at 220 °C. Esteeves and Pereira (2007) reported that mass loss is primarily due to thermal degradation of hemicelluloses and volatilization of extractives. This is evidenced in Table 1, where the hemicelluloses and extractives contents decreased from 19.16% and 7.87% in untreated wood to 6.63% and 6.35% at 220 °C, re- spectively. The influence of the reduced hemicellu- loses content on mass loss is more pronounced (R 2 = 0.9197) than that of the extractives content (R 2 = 0.0369) (Fig. 1). 3.2 CELLULOSE AND HEMICELLULOSES CONTENT 3.2 VSEBNOST CELULOZE IN HEMICELULOZ Variations in the cellulose concentrations at 180 °C and 220 °C were not significantly different, with both differing significantly from untreated wood. Yildiz et al. (2006) and Esteves et al. (2008) noted that cellulose is less affected by TM in com- parison to hemicelluloses in an atmosphere with- out oxygen. Degradation of amorphous cellulose is principally what takes place, making the resulting cellulose more crystalline and causing a reduc- tion of cellulose content in TM woods (Boonstra & Tjeerdsma, 2006). The hemicelluloses content de- creased significantly from 19.16% when untreated Figure 1. Relationship between mass loss and hemicellu- loses (A) and extractives (B) contents [%]. Slika 1. Zveza med izgubo mase in vsebnostjo hemice- luloz (A) in ekstraktivnih snovi (B) [%]. 37 Les/Wood, Vol. 70, No. 1, June 2021 Minkah, M. A., Afrifah, K. A., Batista, D. C., & Militz, H.: Chemical and Mechanical Characterization of Thermally Modified Gmelina arborea Wood to 6.63% at 220 °C modification temperature (Table 1). According to Sivonen et al. (2002) and Nuop- ponen et al. (2004), hemicelluloses are the first wood structural component to be affected during TM. They pointed out that deacetylation and the released acetic acid act as a depolymerization cat- alyst that further facilitates polysaccharide degra- dation, in line with the observations made in this study. The hemicelluloses content decreased with increased modification temperature, showing the highest reduction of 65.40% at 220 °C. On the other hand, cellulose decreased by a maximum of 8.60% at 180 °C. As such, cellulose is less degraded than hemicelluloses when wood is thermally modified. 3.3 LIGNIN CONTENT 3.3 DELE Ž LIGNINA Table 1 shows that the lignin content increased significantly and consistently from 34.86% for un- treated wood to 44.16% for a modification tem- perature of 220 °C. Similar results were obtained by Zaman et al.,(2000) in their study of Scots pine (Pinus sylvestris L.) and birch (Betula pendula Roth Tent. fl. Germ.) thermally modified at 205 °C and 230 °C with respective holding times of 4 and 8 hours. They recorded increased lignin content from 24.5% to 38.7% and from 21.8% to 35.8%, respec- tively. Several researchers have suggested that an increase in lignin content after TM could be due to polycondensation reactions of lignin with other cell wall components (Tjeerdsma & Militz, 2005; Boon- stra & Tjeerdsma, 2006). This results in cross-link- ing of lignin, leading to an increase in lignin con- tent. Other reports have also indicated that lignin degrades at the beginning of the modification pro- cess, although the rate of degradation is slower than that seen with polysaccharide (hemicellulose) degradation (Windeisen et al., 2007). Therefore, the higher decrease in polysaccharide content gives the apparent observed increase in lignin content. 3.4 EXTRACTIVES CONTENT 3.4 DELE Ž EK S TRAKTIV O V Generally the extractives content (EC) was significantly reduced after TM. It decreased from the initial content of 7.87% for untreated wood to 6.35% for modification temperatures of 180 °C and 220 °C (Table 1). A spike in EC of 9.11% was, however, recorded at a modification temperature of 200 °C. Similarly, Esteves et al. (2008) reported a substantial increase in EC with increased modi- fication temperature followed by a decrease with a further increase in temperature. Esteves and Pereira (2009) explained that although EC gener- ally decreases with increased modification tem- peratures, new extractable compounds released at certain temperatures from polysaccharide deg- radation, such as water and ethanol, may cause it to increase. Esteves et al. (2008) indicated that the composition of the extractives changed as the orig- inal extractives disappeared and new compounds were formed in their place. In the present study, part of the inherent extractives may have been re- moved at 180 °C resulting in the observed decrease in EC. In contrast, the increased EC at 200 °C could have been contributed by degradation products of polysaccharides or hemicelluloses at that tempera- ture. A further increase in temperature to 220 °C resulted in increased removal of extractible materi- als leading to the decreased EC and the significant mass loss observed. Consequently, the composition of the extractives may also vary from the original. 3.5 MODULUS OF ELASTICITY IN STATIC BENDING 3.5 MODUL ELAS TIČNOS TI IZ S T A TIČNE GA UPOGIBA Table 2 presents results of mechanical tests of thermally modified Gmelina arborea wood. Gener- ally, a decreasing trend was observed in the Modulus of Elasticity (MOE) of the thermally modified wood with an increase in temperature. At 220 °C a sig- nificant reduction of 25.71% in MOE was observed compared to the untreated wood. Despite the mar- ginal increase of 6.89% at 180 °C and a decrease of 3.50% at 200 °C compared to the untreated wood’s MOE, the differences were not statistically signifi- cant. The initial marginal increase or relatively sta- ble MOE at 180 °C (mass loss of 5.44% (Table 1)) was mainly due to crystallization of cellulose and condensation of lignin resulting from cross-linking reactions with furfurals produced from the thermal degradation of hemicelluloses (Bal & Bektas, 2013; Wang et al., 2018). However, it is noteworthy that comparing the MOE’s for the various modification temperatures shows that there were significant reductions with an increase in temperature (Table 2). A similar observation has been made by other researchers. Esteves and Pereira (2007) and Inoue 38 Les/Wood, Vol. 70, No. 1, June 2021 Minkah, M. A., Afrifah, K. A., Batista, D. C., & Militz, H.: Kemijska in mehanska karakterizacija termično modificiranega lesa vrste Gmelina arborea et al. (1993), for example, observed an increase in MOE at about 4.0% mass loss, which decreased subsequently at higher mass losses or modification temperatures. Xu et al. (2019) reported an initial increase in MOE from 9230 N/mm 2 in the control samples to 10840 N/mm 2 of TM white oak (Quer- cus alba L.) at 160 °C which decreased to 7640 N/ mm 2 at TM temperature of 200 °C and 9 h holding times. Hidayat et al., (2016) also obtained signifi- cant reductions in the MOE for thermally modified wood of Cylicodiscus gabunensis (Harms). 3.6 MODULUS OF RUPTURE IN STATIC BENDING 3.6 TRDNOS T PRI S T A TIČNEM UPOGIBU Modulus of rupture (MOR) is one of the me- chanical properties most affected by wood TM, and it decreases with increasing modification tempera- ture (Esteves & Pereira, 2009). The MOR of Gmelina arborea wood was significantly reduced after TM, from 85.85 N/mm 2 when untreated to 38.76 N/ mm 2 at 220 °C (Table 2). Decreased MOR could be caused by degradation of wood structural compo- nents, specifically cellulose and hemicelluloses. The hemicelluloses content gets degraded much more than cellulose (Table 1). When amorphous hemicel- luloses are degraded, the remaining and dominant cellulose becomes more crystalline (Boonstra & Tjeerdsma, 2006). Wood then becomes increasing- ly brittle with increased modification temperature, lowering its MOR. One of the functions of hemi- celluloses is to absorb stress transferred in wood by reinforcing cellulose microfibrils in the wood cell wall. Removal of hemicelluloses thus leads to the distribution of stress over less cell wall materi- al which is brittle, resulting in failure with minimal stress (Winandy & Lebow, 2001). 3.7 DE GREE OF INTE GRITY ( I), FINE FRA C TION (F) AND RE SIS T ANCE T O IMP A C T MILLING (RIM) 3.7 S T OPNJ A INTE GRITETE (I), DR OBNA FRAK CIJ A (F) IN ODPORNOS T NA UD ARNO MLET JE (RIM) The degree of integrity of Gmelina arborea decreased significantly from 55.30% for untreat- ed wood to the lowest value of 42.92% at 220 °C modification temperature. The fine fraction, which shows greater discrimination between untreated and modified wood, generally increased signifi- cantly when wood was modified, from 1.32% in un- treated wood to 8.17% at 220 °C (Table 2). Overall, a significant reduction in RIM was recorded between untreated and modified wood. Untreated wood re- corded RIM of 87.84% reaching a lowest value of 79.60% at 220 °C (Table 2). The reduction in RIM as a result of increased modification temperature T r ea tmen t MOE [N/mm 2 ] MOR [N/mm 2 ] I [%] F [%] RIM [%] BH [N/mm 2 ] Un tr ea t ed 9562.73 ab 85.85 a 55.30 a 1.32 a 87.84 a 17.39 ab (125.60) (2.00) (0.78) (0.08) (0.16) (0.49) 180 °C 10221.82 a 82.56 a 53.85 a 1.19 a 87.57 a 20.65 c (250.97) (2.11) (0.67) (0.11) (0.22) (0.57) 200 °C 9227.88 b 56.45 b 47.19 b 3.66 b 84.05 b 19.18 ac (177.32) (1.76) (0.72) (0.17) (0.26) (0.52) 220 °C 7103.94 c 38.76 c 42.92 c 8.17 c 79.60 c 15.90 bd (178.34) (1.13) (2.01) (0.35) (0.45) (0.53) Means followed by the same letter are not significantly different at α = 0.05 Standard error values are shown in parentheses MOE: Modulus of Elasticity, MOR: Modulus of Rupture, I: Integrity, F: Fine fraction, RIM: Resistance to Im- pact Milling, BH: Brinell Hardness. Table 2. Results of static bending, HEMI-test and Brinell hardness per treatment. Preglednica 2. Rezultati statičnega upogiba, HEMI-testa in trdote po Brinellu glede na postopek obdelave. 39 Les/Wood, Vol. 70, No. 1, June 2021 Minkah, M. A., Afrifah, K. A., Batista, D. C., & Militz, H.: Chemical and Mechanical Characterization of Thermally Modified Gmelina arborea Wood could be ascribed to the reduced microstructural integrity which underlies the recorded increase in fragmentation and decrease in fragment size (Rapp et al., 2006; Welzbacher, et al., 2011). The decline in microstructural integrity occurred as a result of reductions in hemicelluloses content (Table 1) and increased cellulose crystallinity at higher modifica- tion temperatures leading to increased wood brit- tleness. 3.8 BRINELL HARDNESS 3.8 TRDOTA PO BRINELLU Table 2 shows that Brinell hardness parallel to the grain increased from 17.39 N/mm 2 up to 20.65 N/mm 2 and 19.18 N/mm 2 as Gmelina ar- borea wood was thermally modified at 180 °C and 200 °C, respectively. It reduced to a minimum of 15.90 N/mm 2 at 220 °C modification tempera- ture. Wood hardness increased with modification temperature in the instance of 180 °C and 200 °C, due to increased cellulose crystallinity as the mod- ification temperature increased. However, the sig- nificant decrease observed at 220 °C could be due to enhanced degradation of hemicelluloses (Table 1), which reduced the wood’s ability to withstand stresses (Winandy & Lebow, 2001). A similar trend was recorded in ash (Fraxinus spp. L.) and tali (Erythrophleum ivorense A. Chev.), each thermally modified at 180 °C for 1.5 h and 210 °C for 2 h. The Brinell hardness increased from 6.79 N/mm 2 and 4.51 N/mm 2 in untreated wood to 7.01 N/mm 2 and 10.81 N/mm 2 at 180 °C and subsequently reduced to 6.95 N/mm 2 and 9.19 N/mm 2 at 210 °C (Sivrikaya et al., 2015). 4 CONCLUSIONS 4 Z AKL JUČKI The research focused on the effects of ther- mal modification at temperatures of 180 °C, 200 °C and 220 °C on chemical and mechanical chang- es in Gmelina arborea wood. Generally, the cel- lulose and hemicelluloses content decreased significantly after TM, with only lignin recording a significant increase with TM temperature. Ad- ditionally, MOE, MOR, I, and RIM decreased with increased modification temperature, recording the highest decreases of 26.13%, 58.30%, 83.69%, 22.37%, and 9.38%, respectively, at 220 °C. The fine fraction and Brinell hardness increased up to 518.94% at 220 °C and 18.75% at 180 °C, respec- tively. The closely comparable strength properties between untreated wood and that modified at 180 °C makes this particular temperature accept- able for modification of this species, especially when used for structural purposes and other such applications, where the strength properties are critical. However, for purposes other than struc- tural ones a modification temperature of 200 °C could be adopted to offer the added advantage of other improved wood properties. The results obtained in this study are generally useful as a reference for applications of thermally-modified Gmelina arborea wood. 5 SUMMARY 5 POVZETEK Wood is a very important environmental- ly friendly, renewable and accessible material, which is widely preferred around the globe. How- ever, the sustainable supply of tropical timber on the world market is increasingly threatened (Boonstra, 2008). In its 2016 report, the Forestry Commission (FC) of Ghana indicated that about 80% of the country’s forest resources under state management had been lost to illegal logging ac- tivities (FC, 2016a). To reduce over-exploitation of primary forests and ensure a sustainable supply of timber on local and export markets, Ghana has embarked on the establishment of plantations covering about 190,000 ha as of 2015. The FC fur- ther plans to cultivate 100,000 ha of plantations from 2016 – 2040. Among the many species to be cultivated is Gmelina arborea, which is an exotic species (FC, 2016b). To complement the effort of the FC to curb deforestation in Ghana and reduce the focus on traditional primary timber species, there is a need to research the properties of the plantation species to establish their suitability for furniture and other such applications. Successful adoption of plantation species such as G. arborea for utilization on both local and export markets will depend on their properties. This study there- fore investigated the impact of TM applied to en- hance the properties of G. arborea wood from Ghana with regard to its basic chemical and me- chanical properties. 40 Les/Wood, Vol. 70, No. 1, June 2021 Minkah, M. A., Afrifah, K. A., Batista, D. C., & Militz, H.: Kemijska in mehanska karakterizacija termično modificiranega lesa vrste Gmelina arborea Four Gmelina arborea trees were bucked into 2.5 m length bolts with a chainsaw, which were fur- ther processed using a portable Wood-Mizer saw- mill (LT 30) into boards of 25 mm thickness. The boards were air-dried until moisture content (MC) below 20% was achieved. Boards were selected from within 15 cm radius of the pith to ensure the use of heartwood. These boards were further pro- cessed into slats of dimension 20 × 50 × 650 mm 3 for the TM process. The slats were sorted according to weight and those in the range of 300 – 400 g were used for the study. The pre-sorting was neces- sary to homogenize the lot and minimize the effect of the initial density on the results. An open TM system similar to the Ther- moWood® process (Mayes & Oksanen, 2002) was employed. Peak temperatures of 180, 200, and 220 °C were adopted. Each peak temperature was held for 3 h. The mass loss of the wood slats after the TM process was determined according to Metsa-Korte- lainen et al. (2006). The chemical composition of the wood was also conducted based on TAPPI and Wise et al. (1946). Static bending (MOE and MOR) was determined in accordance with DIN 52186 (1978). High Energy Multiple Impact (HEMI) testing was performed using methods outlined by Brischke (2017). The degree of integrity (I), fine fraction (F) and resistance to impact milling (RIM) were deter- mined. Brinell (static) hardness were also carried out according to DIN EN 1534 (2011). Descriptive statistics comprising means with standard devia- tions were presented for each treatment and test. Comparison of the results from the treatments was made using Analysis of Variance (ANOVA). Least Square Deviation was used to compare means at α = 0.05 when ANOVA revealed significant differenc- es. The Statistical Package for Social Sciences (IBM Statistics) version 26 was used for the analysis. Table 1 presents the mass loss, proportions of cellulose, hemicelluloses, lignin and extractives in the thermally modified Gmelina arborea wood. Mass loss increased along with the TM tempera- ture from 5.44% at 180 ºC to 15.17% at 220 ºC. According to Esteves and Pereira (2007), mass loss is primarily due to thermal degradation of hemi- celluloses and volatilization of extractives (Fig. 1). Variations in the cellulose concentrations at 180 °C (51.50%) and 220 °C (52.45%) were not significant- ly different, with both differing significantly from untreated wood (55.93%). Hemicelluloses content decreased significantly from 19.16% when untreat- ed to 6.33% at 220 °C (Table 1). Esteves et al. (2008) noted that cellulose is less affected by TM in com- parison to hemicelluloses. According to Sivonen et al. (2002) and Nuopponen et al. (2004), hemicel- luloses are the first wood structural component to be affected during TM. The highest reductions in cellulose and hemicelluloses were 8.60% at 180 °C and 65.40% at 220 °C respectively. Lignin content increased consistently from 34.86% for untreated wood to 44.16% for a modification temperature of 220 °C. Windeisen et al. (2007) reported that lig- nin degrades at the beginning of the modification process, but the rate of degradation is slower than polysaccharide (hemicelluloses) degradation, giv- ing the apparent observed increase in lignin con- tent. Generally, the extractive content (EC) was significantly reduced after TM. It decreased from the initial content of 7.87% for untreated wood to 6.35% at 180 °C and 220 °C (Table 1). Table 2 presents the results of mechani- cal tests of thermally modified Gmelina arborea wood. Generally, a decreasing trend was ob- served in the modulus of elasticity (MOE) with an increase in temperature. At 220 °C, a significant reduction of 25.71% in MOE was observed com- pared to untreated wood. In spite of the mar- ginal increase of 6.86% at 180 °C and decrease of 3.50% at 200 °C compared to the untreated wood’s MOE, the differences were not statistical- ly significant. The modulus of rupture (MOR) is one of the mechanical properties that are most affected by wood TM and decreases with increas- ing modification temperature (Esteves & Pereira, 2009). The MOR of Gmelina arborea wood was significantly reduced after TM, from 85.85 N/ mm 2 when untreated to 38.76 N/mm 2 at 220 °C (Table 2). When amorphous hemicelluloses are degraded, the remaining and dominant cellulose become crystalline (Boonstra & Tjeerdsma, 2006). Removal of hemicelluloses thus leads to the distri- bution of stress over less cell wall material which is brittle, resulting in failure with minimal stress (Winandy & Lebow, 2011). The degree of integ- rity (I) of Gmelina arborea decreased significant- ly from 55.30% for untreated wood to a low of 42.92% at 220 °C modification temperature. The fine fraction, which shows greater discrimination 41 Les/Wood, Vol. 70, No. 1, June 2021 Minkah, M. A., Afrifah, K. A., Batista, D. C., & Militz, H.: Chemical and Mechanical Characterization of Thermally Modified Gmelina arborea Wood between untreated and modified wood, generally increased significantly when wood was modified, from 1.32% in untreated wood to 8.17% at 220 °C (Table 2). Overall, a significant reduction in RIM was recorded between untreated and modified wood. Untreated wood recorded RIM of 87.84% reaching a lowest value of 79.60% at 220 °C (Table 2). The reduction in RIM as a result of increased modification temperature could be ascribed to the reduced microstructural integrity which un- derlies the recorded increase in fragmentation and decrease in fragment size (Rapp et al., 2006; Welzbacher et al., 2011). Brinell hardness parallel to the grain increased from 17.39 up to 20.65 and 19.18 N/mm 2 as Gmelina arborea wood was ther- mally modified at 180 °C and 200 °C, respectively. It fell to a minimum of 15.90 N/mm 2 at 220 °C. Generally, the cellulose and hemicelluloses contents decreased significantly after TM, with only lignin recording a significant increase with TM temperature. Additionally, MOE, MOR, I, and RIM decreased with increased modification tempera- ture, recording the highest decreases of 26.13%, 58.30%, 83.69%, 22.37%, and 9.38%, respectively, at 220 °C. The fine fraction and Brinell hardness saw increases of up to 518.94% at 220 °C and 18.75% at 180 °C, respectively. Closely compara- ble strength properties between untreated wood and those modified at 180 °C, makes this partic- ular temperature acceptable for modification of this species, especially for structural purposes and other such applications, where the strength prop- erties are critical. However, for purposes other than structural ones a modification temperature of 200 °C could be adopted to offer the added ad- vantage of other improved wood properties. The results obtained in this study are generally useful as a reference for applications of thermally modi- fied Gmelina arborea wood. Les je pomemben okolju prijazen, obnovljiv, dostopen in priljubljen material po vsem svetu. Trajnostna ponudba tropskega lesa je na svetov- nem trgu vse bolj ogrožena (Boonstra, 2008). V svo- jem poročilu za leto 2016 je gozdarska komisija (FC) iz Gane navedla, da je bilo okoli 80 % državnih gozd- nih virov izgubljenih zaradi nezakonite sečnje (FC, 2016a). Da bi zmanjšala prekomerno izkoriščanje primarnih gozdov in zagotovila trajnostno oskrbo z lesom za porabo doma in za izvoz, je Gana v letu 2015 zasnovala nasade v obsegu približno 190.000 ha. FC nadalje načrtuje gojenje lesa na 100.000 ha nasadov v obdobju 2016–2040. Med številnimi vrstami, primernimi za gojenje, je Gmelina arbo- rea, ki na območju predstavlja eksotično vrsto (FC, 2016b). Da bi dopolnili prizadevanja FC, omejili kr- čenje gozdov v Gani in zmanjšali prekomerno izko- riščanje tradicionalnih primarnih lesnih vrst, želijo raziskati lastnosti lesa plantažnih vrst in njihovo pri- mernost za pohištvo in podobne namene. Uspešno uvajanje plantažnih vrst, kot je G. arborea, za upo- rabo doma in za izvoz, bo odvisno od lastnosti lesa. Ta študija zato vključuje raziskave vpliva postopka termičnega modificiranja (TM), ki se uporablja za izboljšanje relevantnih lastnosti lesa G. arborea iz Gane, in vpliva na njegove osnovne kemijske in mehanske lastnosti. Štiri drevesa vrste Gmelina ar- borea so bila z motorno žago razžagana na hlode dolžine 2,5 m, ki so bili nato s prenosno žago Wo- od-Mizer (LT 30) razžagani v deske debeline 25 mm. Deske smo osušili na zraku, do lesne vlažnosti (MC) pod 20 %. V nadaljevanju smo izbrali deske znotraj polmera 15 cm od stržena na območju jedrovine in jih razžagali na letve dimenzij 20 mm × 50 mm × 650 mm za postopek TM. Letve smo sortirali glede na maso lesa in za raziskavo uporabili tiste z maso od 300 do 400 g. Predhodno razvrščanje je bilo potreb- no za homogenizacijo vzorca in zmanjšanje učinka gostote lesa na rezultate. Uporabili smo odprti sistem termične modifikacije, podoben postopku ThermoWood® (Mayes & Oksanen, 2002). Najvišje temperature tretiranja so bile 180, 200 in 220 °C, trajanje delovanja vsake od navedenih temperatur pa je bilo 3 ure. Izguba mase lesa je bila po TM do- ločena v skladu z Metsa-Kortelainen et al. (2006). Kemijsko sestavo lesa smo določili na podlagi TAPPI in Wise et al. (1946). Statično upogibno trdnost in modul elastičnosti (MOR in MOE) smo določili v skladu z DIN 52186 (1978). Preskus večkratnih viso- koenergijskih udarcev (HEMI) je bil izveden z upora- bo metod, ki jih je opisal Brischke (2017). Določena je bila stopnja integritete (I), drobne frakcije (F) in odpornost na udarno mletje (RIM). (Statična) trdo- ta po Brinellu je bila določena v skladu z DIN EN 1534 (2011). Za rezultate posamičnega postopka in testiranja smo izračunali osnovno statistiko, srednje vrednosti s standardnim odklonom. Primerjavo re- zultatov po postopkih smo ocenili z analizo variance 42 Les/Wood, Vol. 70, No. 1, June 2021 Minkah, M. A., Afrifah, K. A., Batista, D. C., & Militz, H.: Kemijska in mehanska karakterizacija termično modificiranega lesa vrste Gmelina arborea (ANOVA). LSD test mnogoterih primerjav smo upo- rabili za primerjavo povprečij pri stopnji zaupanja α = 0,05, ko je ANOVA pokazala statistično značilne razlike. Za analize smo uporabili Statistični paket za družbene vede (IBM Statistics) različice 26. V preglednici 1 so predstavljeni deleži celuloze, hemiceluloz, lignina, ekstraktivnih snovi in izgube mase v termično modificiranem lesu vrste G. ar- borea. Razlike v deležih celuloze pri 180 °C (51,50 %) in 220 °C (52,45 %) niso bile statistično značilne, v obeh primerih pa smo zabeležili bistvene zman- jšanje deleža celuloze v primerjavi z neobdelanim lesom (55,93 %). Vsebnost hemiceluloz se je znatno zmanjšala z 19,16 % (neobdelan les), na 6,33 % pri 220 °C (preglednica 1). Esteves et al. (2008) so ugo- tovili, da TM bolj zmanjšuje delež hemiceluloz kot celuloze. Sivonen et al. (2002) in Nuopponen et al. (2004) so objavili, da TM najbolj vpliva na deleže hemiceluloz. Najvišje znižanje deležev celuloze in hemiceluloz je bilo 8,60 % pri 180 °C in 65,40 % pri 220 °C. Vsebnost lignina se je sistematično poveča- la s 34,86 % pri neobdelanem lesu na 44,16 % pri lesu, obdelanem pri temperaturi 220 °C. Windeisen et al. (2007) so poročali, da se lignin razgrajuje na začetku postopka modifikacije, vendar je stopnja razgradnje počasnejša od razgradnje polisaharidov (hemiceluloze), kar ima za posledico znatno pove- čanje vsebnosti lignina. Na splošno se je vsebnost ekstraktivnih snovi (EC) po TM znatno zmanjšala. Z začetne vsebnosti 7,87 % v neobdelanem lesu se je zmanjšala na 6,35 % pri 180 °C in 220 °C (pregled- nica 1). Izguba mase se je povečala s povečanjem temperature TM za 5,44 % pri 180 °C do 15,17 % pri 220 °C. Esteves & Pereira (2007) poročata, da je izguba mase predvsem posledica toplotne raz- gradnje hemiceluloz in hlapenja ekstraktivnih snovi (slika 1). V preglednici 2 so predstavljeni rezultati me- hanskih preskusov toplotno modificiranega lesa vrste G. arborea. Na splošno smo opazili trend zniževanja modula elastičnosti (MOE) z višanjem temperature. Pri 220 °C smo opazili znatno zmanj- šanje MOE za 25,71 % v primerjavi z neobdelanim lesom. Kljub mejnemu povečanju 6,86 % pri 180 °C in 3,50 % pri 200 °C v primerjavi z MOE neobdel- anega lesa razlike niso bile statistično pomembne. Upogibna trdnost (MOR) je ena od mehanskih last- nosti, ki se najbolj zmanjša pri TM v odvisnosti od naraščanja temperature (Esteves & Pereira, 2009). Upogibna trdnost lesa vrste G. arborea se je po TM znatno zmanjšala, in sicer s 85,85 N/mm 2 pri neob- delanem, na 38,76 N/mm 2 pri lesu, obdelanem pri temperaturi 220 °C (preglednica 2). Ko se amorfne hemiceluloze razgradijo, postane preostala celulo- za bolj kristalinična (Boonstra & Tjeerdsma, 2006). Odstranjevanje hemiceluloz vodi do porazdelitve stresa po manjši količini materiala celične stene, ki je krhek, kar povzroči porušitev že pri nizki nape- tosti (Winandy & Lebow, 2011). Stopnja integritete (I) lesa G. arborea se je znatno zmanjšala s 55,30 % pri neobdelanih do 42,92 % pri 220 °C. Drobna frakcija, ki kaže večje razlike med neobdelanim in modificiranim lesom, se je na splošno znatno po- večala z modifikacijo, od 1,32 % v neobdelanem lesu na 8,17 % pri 220 °C (preglednica 2). V glav- nem je bilo zabeleženo znatno zmanjšanje RIM med neobdelanim in modificiranim lesom. Ne- obdelani les je imel RIM 87,84 %, ki je pri 220 °C padel na 79,60 % (preglednica 2). Zmanjšanje RIM zaradi povečane temperature modifikacije bi lahko pripisali zmanjšani mikrostrukturni celovitosti, ki je podlaga za povečanje fragmentacije in zmanjšan- je velikosti delcev (Rapp et al., 2006; Welzbacher et al., 2011). Trdota po Brinellu vzporedno s po- tekom aksialnih elementov se je povečala s 17,39 na 20,65 oz. 19,18 N/mm 2 , po toplotni modifikaciji pri 180 °C oziroma 200 °C. Trdota se je znižala na 15,90 N/mm 2 pri 220 °C. Na splošno se je vsebnost celuloze in hemiceluloz po TM znatno zmanjšala, le delež lignina se je znatno povečal s temperaturo TM. Poleg tega so se MOE, MOR, I in RIM zniža- li s povišano temperaturo modifikacije, pri čemer smo zabeležili njihova najvišja znižanja za 26,13 %, 58,30 %, 83,69 %, 22,37 % in 9,38 % pri 220 °C. Drobna frakcija in trdota po Brinellu sta se pove- čali do 518,94 % pri 220 °C in 18,75 % pri 180 °C. Majhna izguba trdnosti po obdelavi pri 180 °C na- kazuje, da je ta temperatura sprejemljiva za modi- fikacijo lesa proučene vrste, zlasti kadar jo želimo porabiti za konstrukcijske in podobne namene, kjer so trdnostne lastnosti zelo pomembne. Za uporabo lesa za nekonstrukcijske namene pa bi bila lahko sprejemljiva tudi temperatura modifikacije 200 °C, da bi dosegli dodatno izboljšanje drugih lastnosti lesa. Predstavljeni rezultati te študije bodo po pri- čakovanju splošno uporabni kot referenca za upo- rabo toplotno modificiranega lesa pogoste plan- tažne vrste Gmelina arborea. 43 Les/Wood, Vol. 70, No. 1, June 2021 ACKNOWLEDGEMENT ZAHVALE The authors are grateful to the Staff of the Department of Wood Biology and Wood Products, Georg – August University (Germany) for making their wood workshop and laboratories available for the study. We are also thankful to the CSIR-For- estry Research Institute of Ghana for the provision of Gmelina arborea trees from their plantations at Abofour - Offinso, Ghana. REFERENCES VIRI Asiedu, K. G. (2019). Ghana is losing its rainforest faster than any other country in the world. World Economic Forum. Bal, B. C., & Bektas, I. (2013). 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C., & Militz, H.: Kemijska in mehanska karakterizacija termično modificiranega lesa vrste Gmelina arborea 45 Les/Wood, Vol. 70, No. 1, June 2021 UDK 630*839.813:662.71 Izvirni znanstveni članek / Original scientific article Prispelo / Received: 14. 5. 2021 Sprejeto / Accepted: 25. 5. 2021 1 UVOD 1 INTRODUCTION Vse večja skrb za čisto okolje in zmanjševanje emisij toplogrednih plinov ter hkrati vse večje po- trebe po energiji se kažejo v povečani rabi obnovl- jivih virov energije. Proizvodnja in poraba lesnih peletov iz leta v leto narašča tako v svetovnem kot tudi evropskem merilu in po podatkih European Vol. 70, No. 1, 45-58 DOI: https://doi.org/10.26614/les-wood.2021.v70n01a04 Izvleček / Abstract Izvleček: Na laboratorijski peletirni napravi smo izdelali pelete iz petih izbranih tujerodnih invazivnih drevesnih vrst, ki rastejo na območju Slovenije in sicer: divjega kostanja (Aesculus hippocastanum), amerikanskega javora (Acer negundo), robinije (Robinia pseudoacacia), trnate gledičevke (Gleditsia triacanthos) in velikega pajesena (Ailanthus altissima) ter mešanic surovine omenjenih tujerodnih invazivnih vrst s smrekovino (Picea abies) v razmerjih 70 : 30 in 50 : 50. Pod enakimi proizvodnimi pogoji smo skupno izdelali 15 različnih vrst peletov. Izdelanim peletom smo določili pomembnejše fizikalne in mehanske lastnosti (vsebnost vode, gostoto nasutja, mehansko obstojnost in vseb- nost pepela). Rezultate smo primerjali z mejnimi vrednostmi, opredeljenimi v standardu SIST EN ISO 17225-2:2014. Vsebnost vode in gostota nasutja vseh izdelanih vrst peletov sta zadostili zahtevam standarda za razvrstitev v najvišji kakovostni razred A1. Mehanske obstojnosti izdelanih peletov niso dosegale zahtev standarda in niso presegale 96,5% (kar je mejna vrednost za B razred). Rezultati kažejo, da imajo med izbranimi tujerodnimi invazivnimi drevesnimi vrstami največji potencial za nadaljnjo optimizacijo peletirnega postopka robinija, trnata gledičevka in visoki pajesen. Ključne besede: lesni ostanki, trdna biogoriva, tujerodne invazivne drevesne vrste, peletiranje, kakovost peletov Abstract: We produced pellets from five invasive non-native tree species growing in Slovenia on a laboratory pelle- ting device, namely: wild chestnut (Aesculus hippocastanum), boxelder maple (Acer negundo), black locust (Robinia pseudoacacia), thorny locust (Gleditsia triacanthos) and tree of heaven (Ailanthus altissima), as well as mixtures of the raw material from the above non-native invasive species and spruce (Picea abies) in the ratios 70:30 and 50:50. Under the same production conditions, we produced a total of 15 different types of pellets. The most important phy- sical and mechanical properties (water content, bulk density, mechanical stability and ash content) were determined for the pellets produced. The results were compared with the limits defined in the standard SIST EN ISO 17225-2:2014. The water content and bulk density of all produced pellet types met the requirements of the standard for the highest quality class A1. The mechanical durability of the pellets produced did not meet the requirements of the standard and did not exceed 96.5% (which is the limit value for quality class B). The results suggest that black locust, thorny locust and tree of heaven have the highest potential for further optimization of the pelleting process. Keywords: wood residues, solid biofuels, non-native invasive tree species, pelleting, pellet quality UPORABNOST LESNIH OSTANKOV TUJERODNIH INVAZIVNIH DREVESNIH VRST ZA PROIZVODNJO PELETOV USEFULNE SS OF NON-NA TIVE INV ASIVE TREE SPE CIE S W OOD RESIDUES FOR PELLET PRODUCTION Dominika Gornik Bučar 1* , Peter Prislan 2 , Pavel Smolnikar 1 , Darja Stare 2 , Nike Krajnc 2 , Bojan Gospodarič 1 1 Univerza v Ljubljani, Biotehniška fakulteta, Oddelek za lesarstvo, Rožna dolina, Cesta VIII/34, 1000 Ljubljana, SLO * e-pošta: dominika.gornik@bf.uni-lj.si 2 Gozdarski inštitut Slovenije, Večna pot 2, 1000 Ljubljana, SLO Pellet Council je proizvodnja peletov v EU-28 v letu 2019 za 5 % presegla proizvodnjo v letu 2018 in je tako dosegla 18 milijonov ton (EPC, 2021). Po po- datkih Gozdarskega inštituta Slovenije konstantno narašča tudi letna proizvodnja peletov v Sloveniji in se je med letom 2010 in 2019 povečala iz 60.000 ton na 134.000 ton (GIS, 2021). Zaradi vse večjega obsega proizvodnje in rabe peletov se bo tudi v prihodnjih letih potreba po vhodni surovini konstantno povečevala (Stelte et al., 2012; Lauri et al., 2014; Puig-Arnavat et al., 2016; Whittaker & Shield, 2017; Garcίa, 2019; Picchio et al., 2020), kar ima vpliv tudi na ceno vhodne suro- 46 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Usefulness of non-native invasive tree species wood residues for pellet production vine. Zato je potrebno raziskati dodatne možnosti uporabe in potenciale različnih lesnih kot tudi ne- lesnih virov biomase. Zelo podroben pregled razis- kav o kakovosti peletov, izdelanih iz različnih virov gozdno-lesne in kmetijske biomase iz obdobja zad- njih petih let, podajajo Picchio et al. (2020). Težave, povezane z rabo biomase za proizvod- njo peletov v energetske namene, se nanašajo na neprimerno obliko vstopne surovine, nizko nasutno gostoto in visoko vlažnost, kar povzroča probleme v obdelavi in lahko privede do degradacije med transportom in skladiščenjem ter posledično viš- je stroške proizvodnje (Puig-Arnavat et al., 2016). Na gospodarnost izdelave trdnih biogoriv ključno vpliva tudi razpršenost virov surovin, zato je nuj- no učinkovito in okolju prijazno obvladovanje sicer kompleksne biomasne oskrbovalne verige (Puig-Ar- navat et al., 2016). S procesom peletiranja ali zgoščevanja bio- mase dosegamo homogeno trdno gorivo z visoko gostoto, nizko vsebnostjo vlage in povišano kurilno vrednostjo. Enostaven transport, manjši skladiščni prostor, enostavna uporaba (ogrevanje s peleti je popolnoma avtomatizirano) so dodatne prednos- ti peletov. Med trdnimi biogorivi je povpraševanje po lesnih peletih največje. Uporabljajo se tako v industrijskih napravah za proizvodnjo toplotne in električne energije, termičnih napravah za toplot- no uplinjanje, kot tudi za neindustrijsko rabo v gos- podinjstvih v majhnih kurilnih napravah (Stelte et al., 2012). Pri neindustrijski rabi morajo peleti imeti najvišjo kakovost. Na končno kakovost peletov odločilno vpliva- jo vrsta in lastnosti vhodne surovine (npr. kemij- ska sestava, vlažnost, velikost gradnikov in njihova porazdelitev); način priprave surovine in pogoji pri proizvodnji peletov (npr. temperatura matrice, di- menzije matrice, podajalna hitrost, tlak pri peleti- ranju, itd.) (Obernberger & Thek, 2010). Proces proizvodnje lesnih peletov lahko v gro- bem razdelimo na tri dele in sicer: (I) dobava in priprava vhodne surovine, (II) izdelava peletov in (III) distribucija proizvoda (GIS, 2020). Vsi deli ima- jo svoje značilnosti, ki jih je za doseganje ustrezne kakovosti potrebno poznati, obvladovati in dosled- no upoštevati. Obdelavo oz. postopek izdelave peletov razdelimo na več faz (npr. mletje, sušenje, kondicioniranje, stiskanje oz. peletiranje, hlajenje, sejanje in embaliranje), katerih zaporedje je odvis- no predvsem od vrste in oblike uporabljene vhod- ne surovine za proizvodnjo peletov (npr. hlodovina slabe kakovosti, sečni ostanki, kosovni ostanki iz predelave lesa, žagovina, lesni ostružki, oblanci, lesni sekanci …). V proizvodnji peletov se danes največ upo- rablja les oziroma lesni ostanki iz žagarske in lesno- predelovalne industrije (npr. lesni prah, žagovina in drobni oblanci), saj je takšen les neoporečen in kemijsko neobdelan. Za žagovino so značilni majhni delci lesa, zato priprava surovine za nadaljnje pele- tiranje ni energetsko potratna. Velikokrat je žagovi- na iz žagarskih obratov brez lubja (ali drugih nečis- toč), kar omogoča proizvodnjo visokokakovostnih peletov. Uporaba manj znanih drevesnih vrst za proizvodnjo peletov je povsem smiselna, pri čemer je ključno doseganje podobne ravni kakovosti pe- letov kot jo imajo peleti, izdelani iz lesnih vrst, ki se običajno uporabljajo v Evropi (npr. smreka, jelka, bukev) (Castellano et al., 2015). Tujerodne invazivne drevesne vrste (TIDV) in grmovne vrste predstavljajo določen potencial za izdelavo peletov, še posebej tiste, ki so rasle v ur- banem okolju (npr. mestni parki, drevoredi, vrtovi …) in imajo zaradi rastiščnih pogojev pogosto nižjo kakovost lesa in s tem omejeno področje uporabe. Cilj pričujoče študije je oceniti primernost manjvrednih lesnih ostankov izbranih tujerodnih in- vazivnih drevesnih vrst za peletiranje. Čistim lesnim ostankom divjega kostanja, amerikanskega javora, robinije, trnate gledičevke in velikega pajesena smo določili gostoto, jih zmleli in kondicionirali na ciljno vlažnost, primerno za peletiranje v laboratorijskih pogojih. Pelete smo izdelali tako iz omenjenih tu- jerodnih invazivnih drevesnih vrst kot tudi meša- nic TIDV in smreke v razmerjih 70 : 30 in 50 : 50. Vse postopke priprave surovine in peletiranja smo izvedli pod enakimi pogoji in parametri. Izdelanim peletom smo izmerili pomembnejše kazalnike ka- kovosti, ki jih določa standard SIST EN ISO 17225- 2:2014 in sicer mehansko obstojnost, vsebnost vode, gostoto nasutja in vsebnost pepela. Postavili smo tri hipoteze; (I) lastnosti surovine se razlikuje- jo glede na izbrane TIDV in mešanice, (II) lastnosti izdelanih peletov se med izbranimi vrstami in me- šanicami razlikujejo, (III) peleti, izdelani iz mešanice tujerodnih invazivnih drevesnih vrst in smrekovine bodo imeli boljše lastnosti kot peleti, izdelani izkl- jučno iz lesa tujerodne invazivne drevesne vrste. 47 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Uporabnost lesnih ostankov tujerodnih invazivnih drevesnih vrst za proizvodnjo peletov 2 MATERIALI IN METODE 2 MATERIALS AND METHODS 2.1 VHODNA SUROVINA 2.1 RAW MATERIALS V raziskavi smo uporabili kosovne ostanke izbranih tujerodnih invazivnih drevesnih vrst, ki so bile proučevane v okviru projekta Applause (UIA02- 228). Kot surovino za izdelavo peletov smo upora- bili les divjega kostanja (Aesculus hippocastanum), amerikanskega javora (Acer negundo), robinije (Robinia pseudoacacia), trnate gledičevke (Gledit- sia triacanthos) velikega pajesena (Ailanthus altis- sima) in smrekovine (Picea abies). Značilnosti lesa uporabljenih drevesnih vrst so opisane v literaturi (Torelli, 2002; Gorišek et al., 2018; Gorišek et al., 2019; Merhar et al., 2020; Smolnikar, 2020). Lesne ostanke smrekovine smo uporabili za pripravo me- šanic TIDV v dveh razmerjih. 2.2 PRIPRAVA SUROVINE 2.2 SAMPLE PREPARATION Ostanke masivnega lesa brez lubja vseh na- štetih vrst smo razžagali na kose okvirnih dimenzij 20 mm × 20 mm × 30 mm in jih zmleli v dveh kora- kih (slika 1). Po opravljenem grobem mletju na la- boratorijskem mlinu CONDUX CSK 350/N1 smo fino mletje izvedli na mlinu Retsch SM200. Pri finem mletju smo uporabili 2 mm sito za 2/3 volumna in 4 mm sito za 1/3 volumna vsake drevesne vrste. Me- šanice tujerodnih invazivnih drevesnih vrst in smre- kovine smo pripravili v dveh različnih volumskih razmerjih (50 % TIDV / 50 % smrekovine in 70 % TIDV / 30 % smrekovine) (preglednica 1). V nadalje- vanju navajamo mešanice glede na delež tujerodne invazivne drevesne vrste. Mešanje zmlete surovine TIDV in smrekovine je potekalo ročno, v 10 l plastič- nih vedrih. V vseh mešanicah smo uporabili enako volumsko razmerje velikosti gradnikov. Vsem preučevanim TIDV smo volumetrično do- ločili gostoto v absolutno suhem stanju pred fazo mletja na desetih naključno izbranih vzorcih in po- dali rezultat kot povprečje meritev. Analizo vsebnosti pepela v pripravljenih mešani- cah (preglednica 1) smo izvedli skladno s SIST EN ISO 14775:2010 z uporabo peči Nabertherm LE 14/22 B 300. Segrevanje vzorcev smo izvedli po naslednjem temperaturnem režimu: 50 min enakomerno segre- vanje do 250 °C, 60 min gretje na 250 °C, enakomerno povišanje temperature na 500 °C v 30 min intervalu in vzdrževanje temperature 500 °C nadaljnjih 120 min. Za vsako mešanico smo naredili po štiri meritve in podali povprečje meritev deleža pepela. Pripravljenim kombinacijam surovin smo do- ločili vsebnost vode na merilniku vlažnosti BEA- MA110-1 in po potrebi surovino navlažili do ciljne vsebnosti vode med 13 % in 15 %, kar je optimal- na vrednost za peletiranje na uporabljeni peletirni napravi. Pred izdelavo peletov smo izvedli tudi fazo Slika 1. Vzorci tujerodnih invazivnih drevesnih vrst po grobem in finem mletju. Figure 1. Chipped and ground samples of non-native invasive tree species. 48 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Usefulness of non-native invasive tree species wood residues for pellet production kondicioniranja in sicer tako, da smo mešanice 20 min pred peletiranjem enakomerno poškropili z vodo, jih temeljito ročno premešali in tako dosegli navlažitev površine gradnikov. 2.2 PROIZVODNJA PELETOV 2.2 PELLET PRODUCTION Pelete smo izdelali na laboratorijski peletir- ni napravi Kahl 14-175 (slika 2a) z matrico v obliki diska (plošče), s kanali premera 6 mm, dolžine 22 mm, oziroma s stiskalnim razmerjem 0,27 (slika 2b). Podroben postopek peletiranja je opisal Smol- nikar (2020). Med peletiranjem smo natančno bele- žili pogoje peletiranja (temperaturo matrice, vrtilno hitrost dozirnega polža in maso izdelanih peletov v časovnih intervalih). Pelete smo po vsakem stiskan- ju ohladili na rešetki (slika 2c). 2.3 ANALIZA PELETOV 2.3 ANALYSIS OF PELLETS Vsem izdelanim peletom smo skladno s stan- dardom SIST EN ISO 17225-2:2014 določili nasled- nje lastnosti: • Vsebnost vode po standardni gravimetrični metodi, opredeljeni v standardu SIST EN ISO 18134-1:2015 ter z merilnikom vlažnosti BEA- MA110-1. • Gostoto nasutja, skladno s postopkom, opre- deljenim v standardu SIST EN ISO 15103:2010, s tem, da smo namesto 5 l posode uporabili posodo z volumnom 0,5 l. • Mehansko obstojnost skladno s standardom SIST EN ISO 15210:2010. Postopek določanja mehanske obstojnosti temelji na kontrolira- ni obrabi pelet. Med testiranjem peleti trkajo Lesna vr s t a / Species T ujer odna in v azivna vr s t a : Smr ek o vina / Non-na tiv e in v asiv e Species: Spruce 100 % : 0 % 70 % : 30 % 50 % : 50 % Veliki pajesen / Tree of heaven Divji kostanj / Horse chestnut Trnata gledičevka / Thorny locust Robinija / Black locust Amerikanski javor / Boxelder maple Preglednica 1. Surovinska sestava peletov. Table 1. Raw material composition of pellets. Slika 2. Laboratorijska peletirna naprava Kahl 14-175 (a), proizvodnja peletov (b) in ohlajevanje peletov (c). Figure 2. Laboratory pellet press Kahl 14-175 (a), pellet production (b) and cooling of the pellets (c). 49 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Uporabnost lesnih ostankov tujerodnih invazivnih drevesnih vrst za proizvodnjo peletov drug ob drugega ter ob stene testirne naprave, katere delovanje in oblika je natančno opre- deljena v standardu SIST EN ISO 15210-1:2010. Manjša obraba peletov pomeni manjšo koli- čino nastalih finih delcev in posledično boljšo mehansko obstojnost. Za vsako vrsto (meša- nico) peletov (preglednica 1) smo mehansko obstojnost določili dvema vzorcema, in sicer peletom, ki smo jih izdelali po približno 10 min peletiranja, in peletom, ki smo jih naredili na koncu peletiranja. Rezultati mehanske obstoj- nosti za posamezno mešanico so podani kot povprečje obeh meritev. 3 REZULTATI IN RAZPRAVA 3 RESULTS AND DISCUSSION V raziskavi smo ugotavljali, ali so lesni ostanki tujerodnih invazivnih drevesnih vrst primerni za pe- letiranje in kakšna je kakovost peletov, če ne spre- minjamo pogojev priprave surovine in peletiranja glede na drevesno vrsto. Peletiranje smo izvajali v laboratorijskih pogojih na laboratorijski peletirni napravi in kakovost peletov določali s standardnimi metodami. 3.1 LASTNOSTI IN PRIPRAVA VHODNE SUROVINE 3.1 PROPERTIES AND PREPARATION OF RAW MATERIALS Eden ključnih dejavnikov, ki vplivajo na kako- vost peletov, je homogena in ustrezno pripravljena vhodna surovina. V raziskavi smo različne oblike lesnih ostankov tujerodnih invazivnih drevesnih vrst razžagali na enotne kose in jih nato v dveh ko- rakih zmleli do želene velikosti gradnikov. S sejalno analizo smo določili velikostne razrede gradnikov, kar je predstavil Smolnikar (2020). Ciljna velikost gradnikov je odvisna od načina peletiranja oziroma izvedbe matrice in peletirne naprave (Obernberger & Thek, 2010; Döring, 2013). V naši raziskavi so bile ciljne dimenzije gradnikov v velikostnem razredu med 2 mm in 4 mm. V raziskavi smo izdelali pelete iz 15 različnih vhodnih surovin oziroma mešanic (preglednica 1). Za vsako mešanico smo pripravili cca 16 dm 3 surovi- ne s ciljno vsebnostjo vode 13 % (realno izmerjene med 13 % in 15 %) in ustrezno sestavo gradnikov ter s temeljitim mešanjem in uravnovešanjem za- gotovili homogenost vzorca. Različni raziskovalci navajajo različne ciljne vlažnosti za različne vrste vstopne surovine: med 8 % - 12 % (Obernberger & Thek, 2010) med 6 % - 13 % (Whittaker & Shield, 2017), Lehtinkangas (2001) navaja za smrekovino vlažnost med 13 % - 15 %. Optimalno vlažnost je potrebno določiti za vsako vrsto vhodne surovine, saj pomembno vpliva na lastnosti izdelanih peletov kot je npr. mehanska obstojnost. Višja vlažnost su- rovine namreč zmanjšuje trenje v procesu peleti- ranja in povečuje relaksacijo peletov po izdelavi in s tem negativno vpliva na mehansko obstojnost. Po drugi strani pa višja vlažnost znižuje temperaturo steklastega prehoda (Tg) lignina, kar pospešuje po- vezovanje gradnikov. Glede na dejstvo, da je Tg pri listavcih na splošno nekoliko višja kot pri iglavcih, ima višja vlažnost surovine lahko pozitiven vpliv na mehansko obstojnost peletov (Stelte, 2011), kar smo upoštevali v naši raziskavi. Raziskali smo tudi vpliv gostote lesa na potek peletiranja. Variabilnost gostote med izbranimi in- vazivnimi vrstami je razmeroma velika, najvišje gos- tote so imeli vzorci robinije (726 kg/m 3 ), najnižje pa divjega kostanja (490 kg/m 3 ) (slika 3). Vpliv gostote lesa na hitrost doziranja in temperaturo matrice ko- mentiramo v poglavju 3.2. Rezultati analize vsebnosti pepela v pripravl- jeni surovini za izdelavo peletov kažejo, da imajo najnižjo vsebnost pepela peleti, izdelani iz 100 % lesa robinije (delež pepela je 0,30 %) ter njeni 70 % in 50 % mešanici s smrekovino (slika 4). Omen- jeni peleti izpolnjujejo kriterije standarda za uvrs- titev v najvišji kakovostni razred A1, ki predpisuje zgornjo mejo 0,7 %. Najvišjo vsebnost pepela pa imajo peleti, izdelani iz lesa amerikanskega ja- vorja, in sicer 1,35 % ter njegova 70 % mešanica s smrekovino (slika 4). 3.2 ANALIZA POGOJEV PELETIRANJA 3.2 CONDITIONS OF PELLET ANALYSIS Za kakovost peletov je ključnega pomena ustrezna hitrost peletiranja, ki jo uravnavamo s hit- rostjo doziranja vhodne surovine in vrtilno hitrostjo gnanih valjev. Vrtilna hitrosti valjev na matrici je bila v naši raziskavi konstantna, spreminjali pa smo vrtilno hitrost dozirnega polža. To smo konstantno nadzoro- vali in jo prilagajali glede na potek peletiranja. Vrtil- no hitrost dozirnega polža smo postopno povečevali iz začetnih 50 vrt/min po 10 vrt/min do končnih 260 vrt/min. V primeru, da je poraba električnega toka 50 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Usefulness of non-native invasive tree species wood residues for pellet production Slika 4. Vsebnost pepela v peletih izbranih TIDV in mešanicah. Figure 4. Ash content in pellets of selected non-native invasive species in mixtures. Slika 3. Gostote lesa izbranih tujerodnih invazivnih drevesnih vrst. Figure 3. Density of selected non-native invasive tree species. 51 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Uporabnost lesnih ostankov tujerodnih invazivnih drevesnih vrst za proizvodnjo peletov presegla normalno (nazivno) vrednost, smo vrtilno hitrost dozirnega polža zmanjšali in na ta način pre- prečili zabitje matrice. Povprečne hitrosti doziranja pri posameznih mešanicah prikazuje slika 5. Pri 100 % TIDV je prišlo do najvišje povprečne vrtilne hitros- ti dozirnega polža pri divjem kostanju, kar bi lahko pripisali nizki gostoti surovine. Po zgornji trditvi bi pričakovali, da bo vrtilna hitrost z večanjem deleža smreke v mešanicah (70 % in 50 %) višja, kar lahko potrdimo pri mešanicah lesnih vrst divjega kostanja, trnate gledičevke in amerikanskega javorja. Na sliki 6 je prikazana količina proizvedenih peletov v odvisnosti od časa, kar smo v naši ra- ziskavi opredelili kot hitrost peletiranja različnih vrst surovine. Ta parametra nam lahko služita za kvalitativno primerjavo poteka peletiranja različ- nih surovin (Gornik Bučar et al., 2019). Iz vsake mešanice surovine smo naredili med 2,5 in 4,5 kg peletov. Hitrost peletiranja je vsekakor odvisna od uporabljene peletirne naprave, značilnosti vstop- ne surovine in pogojev peletiranja, in nikakor ne sme biti razumljena kot absolutna vrednost. Na podlagi hitrosti peletiranja lahko sklepamo o »enostavnosti« oziroma »težavnosti« peletiran- ja določene surovine. Če smo pri določeni vrtilni hitrosti dozirnega polža zaznali preobremenitve elektromotorja gnanih valjev, smo dotok surovine zmanjšali in s tem preprečili zamašitev matrice, kar je vplivalo tudi na količino proizvedenih pele- tov v določenem časovnem intervalu. Pri peleti- ranju čiste (100 % TIDV) surovine (slika 6a), smo najvišjo hitrost peletiranja (proizvedena masa peletov v enoti časa) dosegli pri divjem kostanju (167 g/min) najnižjo pa pri robiniji (78 g/min), kl- jub temu, da ima največjo gostoto med izbranimi vrstami. V primeru peletiranja 70 % mešanic (slika 6b) je bila največja hitrost peletiranja pri visokem pajesenu (160 g/min), sledi divji kostanj, najnižjo pa ima amerikanski javor (104 g/min), ki odstopa od ostalih. Zanimivo je, da je ob mešanju TIDV s smrekovino pri nekaterih primerih prišlo do povi- šanja hitrosti peletiranja (visoki pajesen, robinija in amerikanski javor) pri nekaterih pa do znižanja (divji kostanj in trnata gledičevka). Podobna opa- Slika 5. Povprečna vrtilna hitrost dozirnega polža pri peletiranju izbranih TIDV in mešanicah. Figure 5. Average speed of feeding system for pelleting of selected non-native invasive tree species inmixtures. 52 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Usefulness of non-native invasive tree species wood residues for pellet production žanja kot pri 70 % mešanicah opazimo tudi pri 50 % mešanicah (slika 6c). Najvišjo hitrost peletiranja ima ponovno veliki pajesen (160 g/min), najnižjo pa amerikanski javor (100 g/min). Med peletiranjem oz. zgoščevanjem (ang. densification) biomasne surovine se med gradniki in stenami matrice zaradi trenja generira toplota, ki je ključnega pomena za kakovost peletov. Opti- malna temperatura, ki omogoča izdelavo najkako- vostnejših peletov, je odvisna od vrste biomase in načina priprave biomase, njene kemijske sestave in vsebnosti vode kot tudi značilnosti peletirne napra- ve. Zgoščevanje biomase je torej zelo kompleksen proces, na katerega imajo vpliv številni dejavniki, ki se v večini primerov določajo s poskušanjem (ang. »Trial and error«) in izkustvenimi spoznanji, kar je časovno zelo potratno (Pugi-Arnavat, 2016). Tem- perature peletiranja se glede na vrsto biomase in peletirne naprave gibljejo v širokem območju med 20 o C in 120 o C (Pugi-Arnavat, 2016). Kot je razvid- no iz slike 7, se je povprečna temperatura matrice oz. peletiranja v naši raziskavi gibala med 50 o C in 67 o C, kar se odraža tudi v relativno nizki mehanski obstojnosti peletov (slika 11). Naj pri tem pouda- rimo, da je raziskava preliminarna in da smo želeli proizvesti pelete iz različnih TIDV oziroma mešanic, pod kar se da enakimi pogoji, tako pri pripravi su- rovine kot peletiranju. Glede na to bi bilo smiselno v nadaljnjih raziskavah izvajati peletiranje pri višjih temperaturah matrice. 3.3 LASTNOSTI PELETOV 3.3 PROPERTIES OF PELLETS Pri lesni biomasi se vlažnost običajno poda- ja kot voda v lesu (preračunana glede na mokro maso), kar pomeni, da govorimo o absolutni vlaž- nosti (Prislan et al., 2020). Vsebnost vode odločil- no vpliva na potek peletiranja kot tudi na kalorične vrednosti peletov. Vsi izdelani peleti (slika 8) so ime- li povprečno vsebnost vode pod 10 % (slika 9), kar izpolnjuje kriterije standarda za uvrstitev v najvišji kakovostni razred peletov A1. Meritve povprečne vsebnosti vode, izmerjene po metodi, opisani v standardu SIST EN ISO 18134-1:2015, se gibajo med 5,8 % in 7,8 %. Najnižjo vsebnost vode smo izmerili za čisto mešanico trnate gledičevke, najvišjo pa pri 50 % mešanici robinije. Povprečne gostote nasutja izdelanih peletov (slika 10) variirajo od 611 kg/m 3 do 703 kg/m 3 in ustrezajo zahtevam za kakovostni razred pelet A1, kot je določeno v standardu SIST EN ISO 17225- 2:2014, ki navaja mejno vrednost 600 kg/m 3 . Naj- višjo gostoto nasutja je imela 70 % mešanica trnate gledičevke, najnižjo pa 70 % mešanica amerikan- Slika 6. Količina proizvedenih peletov, izdelanih iz: (a) 100 % lesa TIDV, (b) 70 % mešanic in (c) 50 % mešanic. Figure 6. Quantity of produced pellets during pelletization produced from: (a) 100% of non-native invasive tree species, (b) 70% of non-native invasive tree species and (c) 50% of non-native invasive tree species. 53 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Uporabnost lesnih ostankov tujerodnih invazivnih drevesnih vrst za proizvodnjo peletov Slika 7. Povprečna temperatura matrice med peletiranjem izbranih TIDV in mešanic. Figure 7. Average die temperature for pelleting of selected non-native invasive species and mixtures. Slika 8. Peleti, izdelani iz izbranih tujerodnih invazivnih drevesnih vrst. Figure 8. Pellets from selected non-native invasive tree species. Manjka slika 7! skega javorja. Gostota nasutja peletov je odvisna tako od gostote peletov kot tudi velikosti vmesnih prostorov med posameznimi peleti. Večja kot je gostota nasutja peletov, večja je količina akumulira- ne energije na prostorninsko enoto, posledično pa so transportni in skladiščni stroški nižji (Obernber- ger & Thek, 2010). Mehanska obstojnost je eden ključnih kako- vostnih kazalcev peletov. Na mehansko obstojnost ima odločilen vpliv tako vhodna surovina, njena sestava in priprava kot tudi postopek peletiranja. Najvišjo povprečno mehansko obstojnost, ki je znašala 95 %, so dosegli peleti iz čiste (100 %) su- rovine trnate gledičevke, odstotek nižjo pa peleti, 54 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Usefulness of non-native invasive tree species wood residues for pellet production izdelani iz velikega pajesena. Najslabšo mehansko obstojnost (46 %) so imeli peleti, izdelani iz 70 % mešanice amerikanskega javorja (slika 11). Me- hanska obstojnost mešanic s smrekovino je bila v primeru velikega pajesena in trnate gledičevke z večanjem deleža smrekovine manjša; v primeru divjega kostanja in robinije pa večja kot pri čisti surovini. Takšni rezultati mehanske obstojnosti kot enega ključnih kazalnikov kakovosti peletov potrjujejo navedbe raziskovalcev (Stelte, 2011; Puig-Arnavat et al., 2016; Picchio et al., 2020), da je peletiranje zelo kompleksen proces, na ka- terega imajo vpliv tako surovina kot postopek, in mora biti optimiziran za posamezno vrsto biomas- ne surovine. Nizka mehanska obstojnost vodi do številnih nezaželenih dogodkov že med samo pro- izvodnjo peletov kot tudi med distribucijo, trans- portom, skladiščenjem in uporabo. Velike emisije prahu tako povzročajo moteno delovanje avtoma- tiziranih sistemov kot tudi nevarnost požara in ek- splozije med prevozom ter skladiščenjem in imajo negativen vpliv na zdravje. Relativno nizko doseže- no mehansko obstojnost izdelanih peletov lahko pripišemo tudi relativno nizki temperaturi matrice pri peletiranju, saj se med postopkom zgoščevanja ni generirala zadostna toplota, ki bi pozitivno vpli- vala na tvorjenje vezi med delci. Predvidevamo, da bi višja temperatura peletiranja imela pozitiven vpliv na mehansko obstojnost peletov. Izboljšanje mehanske trdnosti bi poleg povišane temperature peletiranja najverjetneje dosegli tudi z optimiza- cijo vrtilne hitrosti gnanih valjev in stiskalnim raz- merjem, ki bi ga dosegli z izbiro druge debeline matrice. Slika 9. Povprečna vsebnost vode v peletih izbranih TIDV in mešanicah. Figure 9. Average water content of pellets of selected non-native invasive species and mixtures. 55 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Uporabnost lesnih ostankov tujerodnih invazivnih drevesnih vrst za proizvodnjo peletov Slika 10. Povprečna gostota nasutja peletov izbranih TIDV in mešanic. Figure 10. Average bulk density of pellets of selected non-native invasive species and mixtures. Slika 11. Povprečna mehanska obstojnost peletov izbranih TIDV in mešanic Figure 11. Average mechanical durability of pellets made from selected non-native invasive species and mixtures. 56 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Usefulness of non-native invasive tree species wood residues for pellet production 4 Z AKL JUČKI 4 CONCLUSIONS Raba lesne biomase v energetske namene še vedno predstavlja določen izziv, tako iz okoljskega kot tudi gospodarsko-ekonomskega stališča. Z zgoš- čevanjem lesne biomase (peletiranjem) dosegamo večjo gostoto energije, izboljšamo pa tudi enostav- nost transporta, skladiščenja in rokovanja s trdnim gorivom. Pri izdelavi peletov je nujno upoštevati pogoj, da se za ta namen uporabi samo lesna masa, ki nima druge možnosti uporabe, kajti raba v druge namene podaljšuje krožni gospodarski cikel (Zule et al., 2017), poleg tega pa je potencialna dodana vrednost v nadaljnjih predelavah v primeru rabe lesa kot energenta nizka (Kropivšek & Gornik Bučar, 2017). Zaradi vse večje rabe peletov, katerih vstop- na surovina je les in pa ostanki iz lesnopredelovalne industrije, se iščejo možnosti uporabe različnih dre- vesnih in grmovnih lesnih vrst, saj povečana raba lesa v energetske namene negativno vpliva tudi na ceno vhodne surovine. Eden od potencialnih virov je tudi manjvreden les tujerodnih invazivnih dre- vesnih vrst, ki rastejo predvsem v urbanem okolju in ima zaradi rastiščnih pogojev in slabše kakovo- sti omejeno področje uporabe. Tovrstna raba lesa TIDV bi lahko imela tudi pozitiven vpliv na omejeva- nje intenzivnosti širjenja le-teh, ker ogrožajo avtoh- tone drevesne vrste. V laboratorijskih pogojih smo izdelali pelete iz izbranih tujerodnih invazivnih drevesnih vrst: divjega kostanja (Aesculus hippocastanum), ameri- kanskega javora (Acer negundo), robinije (Robinia pseudoacacia), trnate gledičevke (Gleditsia tria- canthos) in velikega pajesena (Ailanthus altissima) ter avtohtone smreke (Picea abies), ki smo jo do- dajali TIDV v različnih razmerjih. Izdelanim peletom smo določili nekatere pomembnejše fizikalne in mehanske lastnosti (vsebnost vode, nasipno go- stoto, vsebnost pepela in mehansko obstojnost). Na osnovi rezultatov lahko zaključimo, da imajo od preučevanih tujerodnih invazivnih drevesnih vrst potencial za energetsko izrabo v obliki peletov predvsem robinija, trnata gledičevka in veliki paje- sen. Ugotavljamo, da se nekatere uporabljene vrste »lažje« peletirajo (t.j. z višjo hitrostjo peletiranja ob nižjih temperaturah) in da to ni odvisno od gostote lesne vrste. Tako lahko na osnovi rezultatov prvo in drugo zastavljeno hipotezo potrdimo. Za potrditev oziroma zavrnitev hipoteze, da imajo peleti, izdela- ni iz lesnih ostankov izbranih tujerodnih invazivnih drevesnih vrst in smrekovine boljše lastnosti kot iz- delani samo iz lesa TIDV, bi morali izvesti obsežnej- šo raziskavo in optimizirati postopke izdelave. Ker smo nekatere uporabljene tujerodne in- vazivne drevesne vrste za izdelavo pelet uporabili prvič in tudi v nam dostopni literaturi nismo našli podatkov o rabi v tovrstne namene, smo želeli pri- dobiti okvirne informacije o možnosti rabe izbranih TIDV za proizvodnjo peletov. Raziskava je prelimi- narna, zato naš cilj ni bil proizvesti peletov, ki iz- polnjujejo zahteve standardov, kar tudi pomeni, da postopkov priprave surovine in peletiranja nismo optimizirali. Dobljeni rezultati in pridobljene izku- šnje so zagotovo dragocene za nadaljnje raziskova- nje možnosti rabe tovrstnega vira lesnih ostankov za proizvodnjo peletov. 5 POVZETEK 5 SUMMARY The energetic use of wood biomass remains a challenge, both from an ecological and economic point of view. With the densification of wood bio- mass (pelletization), a higher energy density can be achieved, which can lead to optimized transport, storage and handling conditions of solid fuels. It should be emphasized that only low-quality wood biomass should be considered for this purpose in order to meet the requirements of a sustainable circular economy. As the use of pellets continues to increase, the possibility of using various tree and shrub wood species is being explored in addition to traditional sources of raw materials such as the wood proces- sing industry. One of the potential sources is also low-quality wood of invasive tree species, growing mainly in urban environments. The objective of this preliminary study is to evaluate the suitability of low-quality wood resi- dues from invasive non-native tree species for pel- leting. We produced pellets from five selected inva- sive non-native tree species growing in Slovenia on a laboratory pelleting device, namely: wild chest- nut (Aesculus hippocastanum), boxelder maple (Acer negundo), black locust (Robinia pseudoaca- cia), thorny locust (Gleditsia triacanthos) and tree of heaven (Ailanthus altissima), as well as mixtures of the raw materials from the above invasive alien 57 Les/Wood, Vol. 70, No. 1, June 2021 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Uporabnost lesnih ostankov tujerodnih invazivnih drevesnih vrst za proizvodnjo peletov species and spruce (Picea abies) in the ratios 70:30 and 50:50. Raw material preparation and pelleting procedures were carried out under the same con- ditions and parameters. The laboratory Kahl press (flat die with 0.27 press ratio) was used for pelle- ting, and the feed rate as well as the temperature at the die were continuously recorded during the pelleting process. The main quality parameters of the pellets produced were measured (i.e., water content, bulk density and mechanical durability). The methods and procedures for determining the properties of the pellets were carried out according to the rele- vant standards. The results of the tested pellet properties were compared with the limits for quality class A1, A2 and B defined in the international standard SIST EN ISO 17225-2:2014. All types of pellets produced met the requirements of the standard for classifi- cation in the highest quality class A1 in terms of water content and bulk density. The mechanical durability of the pellets did not meet the require- ments of the standard and did not exceed 96.5% (which is the limit for class B). We conclude that the reason for the low mechanical durability is the relatively low temperature of the die during pelle- ting. We find that the type of input raw material and the pelleting conditions affect the quality of the pellets, especially the mechanical durability. The results suggest that black locust, thorny locust and tree of heaven have the highest potential for further optimization of the pelleting process. We have observed that some of the wood species stu- died have a higher pelletization rate at lower tem- peratures, but this is not related to the density of the wood species. Since we used some of the non-native invasive tree species for the first time for pellet production and did not find data on their use in the relevant literature, we evaluated the possibility of using se- lected invasive species for pellet production. As this is a preliminary study, it was not our aim to produ- ce pellets that meet the requirements of the stan- dards, which also means that we have not optimi- zed the raw material preparation and the pelleting process. The results obtained and the experience gained are certainly valuable for further research into the possibilities of using such a source of wood residues for pellet production. ZAHVALA ACKNOWLEDGEMENTS Izvedbo raziskave je omogočila Javna agenci- ja za raziskovalno dejavnost Republike Slovenije (ARRS), Programske skupine P4-0015 Les in lig- nocelulozni kompoziti, P4-0107 Gozdna biologija, ekologija in tehnologija in P2-0182 Razvojna vred- notenja, projekti V4-2016, ki ga financirata ARRS in Ministrstvo za kmetijstvo, gozdarstvo in prehrano (MKGP), Applause (UIA02-228), ki nam je prijazno odstopil ostanke tujerodnih invazivnih drevesnih vrst in LIFE ARTEMIS (LIFE15 GIE/SI/000770). 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DOI: https://doi.org/10.1016/j. rser.2016.12.119 Gornik Bučar, D., Prislan, P ., Smolnikar, P ., Stare, D., Krajnc, N., & Gospodarič, B.: Usefulness of non-native invasive tree species wood residues for pellet production 59 Les/Wood, Vol. 70, No. 1, June 2021 UDK 665.947.4:543.428.4 Original scientific article / Izvirni znanstveni članek Received / Prispelo: 19. 1. 2021 Accepted / Sprejeto: 24. 2. 2021 Vol. 70, No. 1, 59-72 DOI: https://doi.org/10.26614/les-wood.2021.v70n01a03 Abstract / Izvleček Abstract: Metastable Induced Electron Spectroscopy, Ultraviolet Photoelectron Spectroscopy (He I and He II), X-ray Photoelectron Spectroscopy, and Atomic Force Microscopy were employed to study the interaction of silver with lignin as well as with two of its natural precursors, coniferyl alcohol and sinapyl alcohol. For all three of them, no chemical interaction between the adsorbed silver and the organic substrate was found before contact with air. Nevertheless, silver nanoparticles were found in all three cases after contact with air. Thus, a process of silver nanoparticle formation during the decomposition of the organic molecules is suggested, similar to the previously found catalytic decomposition of cinnamyl alcohol by water in the presence of silver atoms. Keywords: Coniferyl Alcohol; Lignin; Metastable Induced Electron Spectroscopy; Nanoparticle; Silver; Sinapyl Alcohol; Ultraviolet Photoelectron Spectroscopy; X-Ray Photoelectron Spectroscopy; Atomic Force Microscopy Izvleček: Za preučevanje interakcije srebra z ligninom ter z njegovima naravnima prekurzorjema koniferil alkoho- lom in sinapil alkoholom smo uporabili metastabilno elektronsko spektroskopijo, ultravijolično fotoelektronsko spek- troskopijo (He I in He II), rentgensko fotoelektronsko spektroskopijo in mikroskopijo na atomsko silo. V vseh treh prim- erih nismo ugotovili kemijske interakcije med adsorbiranim srebrom in organskim substratom. Kljub temu pa smo v vseh treh primerih po stiku z zrakom detektirali nanodelce srebra. Na podlagi teh opažanj smo predlagali proces tvorbe srebrovih nanodelcev med razgradnjo organskih snovi, ki je podoben predhodno ugotovljenemu katalitskemu razkroju cinamil alkohola z vodo v prisotnosti atomov srebra. Ključne besede: koniferil alkohol; lignin; metastabilna elektronska spektroskopija; nanodelci; srebro; sinapil alkohol; ultravijolična fotoelektronska spektroskopija; rentgenska fotoelektronska spektroskopija; mikroskopija na atomsko silo FORMATION OF SILVER NANOPARTICLES ON LIGNIN AND TWO OF ITS PRECURSORS TVORBA SREBROVIH NANODELCEV NA LIGNINU IN NJEGOVIH DVEH PREKURZORJIH Sebastian Dahle 1* , Lienhard Wegewitz 2 , Wolfgang Viöl 3 , Wolfgang Maus-Friedrichs 4 1 UVOD 1 INTRODUCTION The preservation of wood structures against all kinds of aging and degradation is a highly top- ical area of research around the world. The im- provement of hitherto existing processes and the development of new ones with higher efficien- cies and better sustainability are currently being investigated, employing a variety of chemical and physical means. Numerous novel materials (Mag- gini et al., 2012), different forms of modifications 1 University of Ljubljana, Biotechnical Faculty, Department of Wood Science and Technology, Jamnikarjeva ulica 101, 1000 Ljubljana, Slovenia * e-mail: sebastian.dahle@bf.uni-lj.si 2 Clausthal University of Technology, Clausthal Centre for Material Technology, Agricolastr. 2, 38678 Clausthal-Zellerfeld, Germany 3 University of Applied Sciences and Art, Faculty of Engineering and Health, Von-Ossietzky-Straße 99, 37085 Göttingen, Germany 4 Clausthal University of Technology, Institute of Energy Research and Physical Technologies and Clausthal Centre for Material Technology, Leibnizstr. 4, 38678 Clausthal-Zellerfeld, Germany like thermal treatment (Calonego et al., 2012) or chemical bonding (Namyslo & Kaufmann, 2009), as well as the use of nanostructures, were al- ready studied and presented in the literature (Ding et al., 2011). Even though the classic pres- ervation approach using chromated copper arse- nate (CCA) or copper chrome boric acid (CCB) is designated hazardous, similar approaches with reduced leaching (Treu et al., 2011; Lesar et al., 2011) and reutilization (Humar et al., 2011) have been investigated. 60 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Tvorba srebrovih nanodelcev na ligninu in njegovih dveh prekurzorjih The modification of inorganic materials em- ploying silver is carried out for many applications, like corrosion protection, RF shielding, reflective coatings and many more. Silver nanoparticles have drawn special interest due to additional features like enhancing the efficiency of organ- ic light emitting devices (Yang et al., 2009) and photocatalytic reaction rates on TiO 2 nanopar- ticles (Kato et al., 2005; Chuang & Chen, 2009), as well as their antibacterial properties (Lok et al., 2006; Ilic et al., 2010). The last one may be particularly useful for the preservation of wood surfaces against the attack of microorganisms like bacteria and fungi, which are part of the main mechanisms of wood aging and degrada- tion. Furthermore, a silver nanoparticle based functionalization may be much more sustainable than current procedures such as lacquering or impregnation. The presented investigation is part of a re- search project concerning the interaction of metals (Ag, Ti) with wood surfaces. Based on the results obtained here, we will come closer to un- derstanding such complex systems as the inter- actions of metals and wood. Furthermore, the reactions with atmospheric gases as well as typ- ical volatile organic compounds are investigated, with a view to future applications. A fundamen- tal understanding of the interactions between Ag and wood surfaces is developed, using mea- surements on the major compounds of wood, i.e. lignin and cellulose. While starting with lignin, several model systems are used which resemble the organic groups of lignin. The natural precur- sors of lignin are mainly the two monolignols co- niferyl alcohol and sinapyl alcohol (Klarhöfer et al., 2007; Klarhöfer et al., 2008; Klarhöfer et al., 2010). Since these two are derived from cinnam- yl alcohol (also known as phenylallyl alcohol), we have also used this less complex molecule as an additional model system for lignin in preliminary investigations (Dahle et al., 2012). The adsorbed silver was first found to be chemically inert, while nanoparticles were found after contact with air. Bringing the cinnamyl alcohol into contact with water after the adsorption of silver was then dis- covered to yield the decomposition of the cin- namyl alcohol (Dahle et al., 2014). Furthermore, the decomposition reaction has been proven to include the catalytical influence of silver atoms at their distinctive adsorption sites (Dahle et al., 2014). The effect of plasma treatment on the presented molecules was also studied previously (Klarhöfer, 2009). 2 MATERIALS AND METHODS 2 MATERIALI IN METODE An ultra-high vacuum (UHV) apparatus with a base pressure of 5 × 10 -11 hPa, which has been de- scribed in detail previously (Klarhöfer et al., 2008; Dahle et al., 2012), is used to carry out the experi- ments. All measurements were performed at room temperature. Electron spectroscopy is performed using a hemispherical analyser (Leybold EA 10) in combi- nation with a source for metastable helium atoms (mainly He* 3 S 1 ) and ultraviolet photons (HeI line). A commercial non-monochromatic X-ray source (Fisons XR3E2-324) is utilized for XPS. During XPS, X-ray photons hit the surface under an angle of 80° to the surface normal, il- luminating a spot of several mm in diameter. For all measurements presented here, the Al K α line with a photon energy of 1486.6 eV is used. Elec- trons are recorded by the hemispherical analyser with an energy resolution of 1.1 eV for detailed spectra and 2.2 eV for survey spectra, respec- tively, under an angle of 10° to the surface nor- mal. All XPS spectra are displayed as a function of binding energy with respect to the Fermi level. For quantitative XPS analysis, photoelectron peak areas are calculated via mathematical fitting with Gauss-type profiles using CasaXPS (Casa Soft- ware Ltd., Florida, USA) with a Shirley-type back- ground, which applies Levenberg-Marquardt al- gorithms to achieve the best agreement between experimental data and fit. To optimize our fitting procedure, Voigt profiles have been applied to various oxidic and metallic systems but for most systems the Lorentzian contribution converges to 0. Therefore all XPS peaks are fitted with Gauss- ian shapes. When calculating stoichiometries, the following variables are taken into account: pho- toelectric cross sections, as calculated by Scofield (1976) with asymmetry factors after Powell and Jablonski (2010a), taking into account asymme- try parameters after Reilman et. al. (1976) and 61 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Formation of silver nanoparticles on lignin and two of its precursors Jablonski (1995), as well as inelastic mean free paths from the NIST database (Powell & Jablons- ki, 2010b) (using the database of Tanuma, Powell and Penn for elementary contributions and the TPP-2M equation for molecules), and the energy dependent transmission function of our hemi- spherical analyser. As a quantitative measure, lay- er thicknesses d ox were calculated for each step of preparation from the attenuation of the inten- sities of peaks of the material covered below the adlayer with the inelastic mean free paths in the adlayer λ taking into account the angle between surface normal and the direction of the emitted electrons θ = 10°, using the following formula (Ertl & Küppers, 1985) MIES and UPS were performed applying a cold cathode gas discharge via a two-stage pumping sys- tem. A time-of-flight technique is employed to sep- arate electrons emitted by He* (MIES) from those caused by HeI (UPS) interaction with the surface. The combined He*/HeI beam strikes the sample surface under an angle of 45° to the surface normal and illuminates a spot of approximately 2 mm in diameter. The spectra are recorded simultaneously by the hemispherical analyser with an energy res- olution of 220 meV under normal emissions within 140 seconds. MIES is an extremely surface sensitive tech- nique probing solely the outermost layer of the sample, because the He* atoms typically interact with the surface 0.3 to 0.5 nm in front of it. This may occur via a number of different mechanisms depending on surface electronic structure and work function, as is described in detail elsewhere (Harada et al., 1997; Morgner, 2000; Ertl & Küppers, 1985). Only the processes relevant for the spectra presented here shall be discussed below, namely Auger Deexcitation and Auger Neutralization. During Auger Deexcitation (AD), an electron from the sample fills the 1s orbital of the impinging He*. Simultaneously, the He 2s electron is emitted carrying the excess energy. The resulting spectra re- flect the Surface Density of States (SDOS) directly. AD-MIES and UPS can be compared and allow a dis- tinction between surface and bulk effects. AD takes place for all organic systems shown here. Auger Neutralization (AN) occurs on pure and partly oxidized metal surfaces with work functions beyond about 3.5 eV, like silver surfaces, as long as the surface shows a metallic behaviour. As a result the impinging He* atom is ionized in the vicinity of the surface by resonant transfer (RT) of its 2s electron into unoccupied metallic surface states. Afterwards, the remaining He + ion is neutralized by a surface electron thus emitting a second surface electron carrying the excess energy. The observed electron spectrum is rather structureless and origi- nates from a self-convolution of the surface density of states (SDOS). All MIES and UPS spectra are displayed as a function of the electron binding energy with respect to the Fermi level, thus being able to compare MIES and UPS spectra more easily. Obviously, the binding energy scale is only valid for the AD process. Never- theless, all spectra including structures originating in the AN process have also been displayed in this particular manner. The surface work function can be determined from the high binding energy onset of the MIES or the UPS spectra with an accuracy of ± 0.1 eV. Atomic force microscopy (AFM) is applied to study the surface topography of the samples af- ter silver adsorption and determine the size of the silver nanoparticles on lignin films. A Veeco Dimension 3100 SPM is used to perform the AFM measurements in tapping mode. Silicon cantilevers (NSC15 with Al backside coating from Micromasch) with resonance frequencies of about 325 kHz and spring constants in the range of 40 N/m are used. All images are recorded with a line-scan frequen- cy of 1 Hz consisting of 512 × 512 pixels. SPIP (Im- age Metrology A/S) is employed for the depiction of the AFM images and the determination of the particle size. The RMS roughness calculations are performed according to ISO 4287/1. The experiments on coniferyl alcohol and sina- pyl alcohol were carried out on inert Au(111) sub- strates (Goodfellow, 99.999 %). These substrates were cleaned prior to the experiments by Ar + sput- tering at 4 kV for 20 min and subsequent heating up to 1000 K. Coniferyl alcohol (Sigma-Aldrich Co., 98.0 %) and sinapyl alcohol (Sigma-Aldrich Co., technical grade 80.0 %) were evaporated in a preparation chamber (base pressure < 10 -9 hPa) using a tem- 62 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Tvorba srebrovih nanodelcev na ligninu in njegovih dveh prekurzorjih perature controlled evaporator (Kentax TCE-BS). The preparation chamber is directly connected to the UHV chamber separated by an UHV valve. During the experiments, coniferyl alcohol has been evaporated at 75 °C for 5 min, leading to a film with a thickness of about 3 nm (Klarhöfer, 2009), where- as sinapyl alcohol has been evaporated at 60 °C for 5 min, leading to a film with a thickness of about 4 nm (Klarhöfer, 2009). For the experiments on lignin, an Au/Mica sub- strate (Sigma-Aldrich, 200 nm Au 99.999 % layer on mica) was used to most closely reproduce the protocol according to Klarhöfer (2009). The Au/ mica substate was etched using peroxymonosul- furic acid (from sulphuric acid ≥97% and hydrogen peroxide 30%, both Sigma-Aldrich) and rinsed with distilled water prior to the film preparation. Lignin (Sigma-Aldrich, organosolv lignin) was dissolved in dimethyl sulfoxide (DMSO, Sigma-Aldrich, ≥99.9 %), dispersed using an ultrasonic cleaning system and afterwards spin-coated for 120 s at 17500 rpm. Silver (Sigma-Aldrich, 99%) was evaporat- ed with a commercial UHV evaporator (Omicron EFM3) onto the samples. On a clean Si(100) tar- get (Sigma-Aldrich, Si wafer, single-side polished, N-type with phosphorous dopant), oxide-free me- tallic silver films grow at a rate of 0.23 nm min -1 at room temperature when evaporated with an Ag + ion flux of 1 µA at the fluxmeter of the EFM3. This flux is a measure for the number of Ag atoms moving towards the sample per second. The film growth rate for Ag has been estimated from the Si 2p peak attenuation in XPS, while the growth mode has been verified to be of the Frank-van der Mer- we-type via AFM measurements. 3 RESULTS AND DISCUSSION 3 REZULTATI IN RAZPRAVA The experiments on the interaction of silver with the three molecules described in the intro- duction, i.e. coniferyl alcohol, sinapyl alcohol and lignin, are presented following the increasing mol- ecule size. The spectroscopic results are directly followed up with the corresponding microscopic images, whereas the discussion is done afterwards for the entire set of results. The silver films were prepared with 8 min of evaporation, leading to a film thickness of about 1.8 nm (Dahle et al., 2012). The only exception was made for lignin, where ad- ditionally a film of about 9 nm after 40 min of evap- oration was produced according to the growth rate determined earlier (see sect. 2). 3.1 ADSORPTION OF SILVER ON CONIFERYL ALCOHOL 3.1 ADSORPCIJA SREBRA NA KONIFERIL ALKOHOL Fig. 1 shows the MIES (left), UPS He I (middle) and UPS He II (right) spectra of a coniferyl alcohol film before (black lines) and after silver adsorption (red lines). The shoulder between 2 eV and 5 eV cor- responds to p states of the ring system, which can most clearly be seen in the UPS He II spectrum. The intensity between 6 eV and 8 eV is mainly related to hydroxyl groups, whereas methoxyl groups cause multiple peaks between 6 eV and 12 eV (Kimura et al., 1981; Klarhöfer et al., 2008; Klarhöfer, 2009). These features are severely broadened in the MIES and UPS He I spectra, and can most clearly be seen in the UPS He II spectrum, again. For comparison, the corresponding molecular orbitals in benzene and phenol have been summarized in tab. 1 to- gether with the respective binding energies in the valence band spectrum and the noted markings provided in the MIES and UPS spectra. The phenol molecular orbitals 14a’ through 21a’ are equal to the respective MOs in benzene, and are expected to remain similar through larger molecules includ- ing lignin. Moreover, MO 14a’ in the marked region (d) includes phenolic hydroxyl groups, as opposed to those hydroxyl groups attached to aliphatic chains, which are more commonly found at lower binding energies. The adsorption of silver onto the coniferyl al- cohol film leads to a decrease in the work function from 4.5 eV to 4.1 eV and thus an increase of the background noise. With regard to this background signal, no significant change in the valence band states of the hydroxyl and methoxyl groups is vis- ible. The increased intensity below 5 eV binding energy most probably does not belong to a change corresponding to the p states of the ring system, but can rather be attributed to silver structures originating from an AN process as described in sect. 2. The AN structure at 2.8 eV involves two electrons from the Ag 5s orbital during the deexcitation pro- cess (Dahle et al., 2012), whereas the structure around 7 eV involves one electron each from the 63 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Formation of silver nanoparticles on lignin and two of its precursors Ag 4d and Ag 5s states (Stracke et al., 2001). The UPS spectra reveal a double peak at 4.9 eV and 6.4 eV, which corresponds to the Ag 4d orbital (Dahle et al., 2012). The previous features from the co- niferyl alcohol are still present, and except for slight broadening and attenuation the structures appear unaffected by the silver adsorption. Fig. 2 depicts the XPS spectra of the C 1s region (left), the O 1s region (middle) and the Ag 3d region (right) of a coniferyl alcohol film before (black lines) and after silver adsorption (red lines). The C 1s re- gion resembles the known spectrum for coniferyl alcohol (Klarhöfer, 2009). The intensity gets atten- uated upon silver adsorption, following the signal of the underlying gold substrate (not shown). The shape of the C 1s feature does not change nota- bly, which indicates the coniferyl alcohol to remain unaffected by the silver in the first place. The O 1s peak remains nearly unchanged in both, the shape and intensity. The Ag 3d feature is exactly like the Figure 1. MIES (left), UPS He I (middle) and UPS He II (right) spectra of a coniferyl alcohol film before (black lines) and after silver adsorption (red lines). Slika 1. MIES (levo), UPS He I (sredina) in UPS He II (desno) spektri filma koniferilnega alkohola pred (črne črte) in po adsorpciji srebra (rdeče črte). Table 1. Binding energies of valence structures for molecular orbitals (MO) in benzene and phenol (Klar- höfer, 2009; Kimura et al., 1981). Preglednica 1. Energije vezave valentnih struktur za molekularne orbitale (MO) v benzenu in fenolu (Klar- höfer, 2009; Kimura et al., 1981). Mark B inding ener gy MO in benz ene MO in phenol (a) 4.4 eV 1e 1g (πCH) 3a”, 4a” (b) 7.0 eV 3e 2g (σCH) 1a 2u (πCH) 21a’, 20a’, 19a’ 2a” (c) 8.5 – 10.5 eV 3e 1u (σCH) 1b 2u (σCC) 2b 1u (σCH) 1a“, 18a‘, 17a‘, 16a‘ (d) 11.7 eV 3a 1g (σCH) 15a’, 14a’ 64 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Tvorba srebrovih nanodelcev na ligninu in njegovih dveh prekurzorjih shape of metallic silver (Dahle et al., 2012), point- ing out the absence of any complexation processes or other chemical interactions with the coniferyl al- cohol film. The film thickness evaluation from the attenuation of the Au substrate’s intensity yields an organic adlayer thickness of 1.3 nm, whereas a silver adlayer thickness of 0.8 nm can be calculat- ed from the attenuation of the coniferyl adlayer’s intensity. The silver adlayer thickness is in discrep- ancy with the calibrated evaporation amounts. Fur- ther potential influences are a difference in sticking coefficients as well a possible desorption of organic material induced by the absorption of the silver at- oms. An absorption of silver into the organic film is further sustained by a change in C/O ratio from 3.2 before silver adsorption to 2.1 afterwards, where- as the conservation of peak shapes for both C 1s and O 1s indicate no chemical change of the mate- rial. Thus, a geometrical rearrangement of the or- ganic film upon silver adsorption can be deduced. The stoichiometries of the samples, C/O ratios and calculated film thicknesses are provided in tab. 2, Sample s y s t em Carbon O xy g en Silver C/O r a tio Adla y er thickness Coniferyl alcohol 75.9 % 24.1 % - 3.16 1.3 nm Silver on Coniferyl alc. 51.1 % 24.8 % 24.1 % 2.06 0.8 nm Sinapyl alcohol 75.7 % 24.3 % - 3.11 0.4 nm Silver on Sinapyl alc. 51.4 % 9.8 % 38.8 % 5.22 0.6 nm Lignin 77.1 % 22.9 % - 3.37 - Silver on Lignin 69.1 % 18.5 % 12.4 % 3.73 0.7 nm Silver on Lignin 46.9 % 9.1 % 44.0 % 5.15 0.9 nm Figure 2. XPS spectra of the C 1s region (left), the O 1s region (middle) and the Ag 3d region (right) of a coniferyl alcohol film before (black lines) and after silver adsorption (red lines). Slika 2. XPS spektri območja C 1s (levo), območja O 1s (sredina) in območja Ag 3d (desno) filma koniferilne- ga alkohola pred (črne črte) in po adsorpciji srebra (rdeče črte). Table 2. Sample stoichiometries and film thicknesses evaluated from XPS survey spectra. Preglednica 2. Vzorčne stehiometrije in debeline filma, ovrednotene iz XPS anketnih spektrov. 65 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Formation of silver nanoparticles on lignin and two of its precursors Figure 3. AFM image (500 × 500 nm 2 ) of a coniferyl alcohol film on Au(111) after silver adsorption and air contact. Slika 3. AFM-slika (500 × 500 nm 2 ) filma koniferil- nega alkohola na Au (111) po adsorpciji srebra in stiku z zrakom. whereas the complete set of original and analysed data are made openly available online (Dahle et al., 2021). Fig. 3 shows an AFM image of adsorbed silver on a film of coniferyl alcohol, which has been ex- posed to ambient air. The surface is very smooth (R q = 0.34 nm) except for sporadic particles, prob- ably representing silver clusters. Those islands ex- hibit a wide size distribution with a mean value of (30 ± 5) nm in diameter and 1.2 nm in height. 3.2 ADSORPTION OF SILVER ON SINAPYL ALCOHOL 3.2 ADSORPCIJA SREBRA NA SINAPIL ALKOHOL Fig. 4 shows MIES (left), UPS He I (middle) and UPS He II (right) spectra of a sinapyl alcohol film before (black lines) and after silver adsorption (red lines). The valence band states of the sinapyl alco- hol contribute in the same binding energy ranges as coniferyl alcohol (see sect. 3.1), as discussed by Klarhöfer (2009). The work function decreases from 4.2 eV to 4.1 eV upon silver adsorption, while the background noise decreases, too. The sinapyl alco- hol valence band features are significantly broad- ened after silver adsorption, especially in the MIES Figure 4. MIES (left), UPS He I (middle) and UPS He II (right) spectra of a sinapyl alcohol film before (black lines) and after silver adsorption (red lines). Slika 4. MIES (levo), UPS He I (sredina) in UPS He II (desno) spektri filma sinapilnega alkohola pred (črne črte) in po adsorpciji srebra (rdeče črte). 66 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Tvorba srebrovih nanodelcev na ligninu in njegovih dveh prekurzorjih spectrum. No silver AN contributions are visible in the MIES spectrum (reference positions marked by red arrows), whereas UPS reveals the presence of peaks corresponding Ag 4d states. Fig. 5 contains XPS spectra of the C 1s region (left), the O 1s region (middle) and the Ag 3d region (right) of a sinapyl alcohol film before (black lines) and after silver adsorption (red lines). The C 1s spectrum is similar to the spectra in the literature (Klarhöfer, 2009) and gets just attenuated after sil- ver adsorption without any change in shape. The O 1s structure consists of two peaks, the main feature at 535.5 eV and a shoulder at 533.5 eV. The fea- ture at a higher binding energy is erased after the silver adsorption, whereas the shoulder gets atten- uated similar to the C 1s structure. The Ag 3d peak yields no signs of any other chemical state than the pure metal. The calculated film thicknesses amount to 0.4 nm of sinapyl alcohol as well as to an addi- tional silver adlayer thickness of 0.6 nm. Similar to coniferyl alcohol, this is most likely due to an ab- sorption of the metal into the organic film. The C/O ratio changed from 3.1 before silver adsorption to 5.2 afterwards, thus again indicating a restructuring Figure 5. XPS spectra of the C 1s region (left), the O 1s region (middle) and the Ag 3d region (right) of a sinapyl alcohol film before (black lines) and after silver adsorption (red lines). Slika 5. XPS spektri območja C 1s (levo), območja O 1s (sredina) in območja Ag 3d (desno) filma sinapilnega alkohola pred (črne črte) in po adsorpciji srebra (rdeče črte). Figure 6. AFM image (500 × 500 nm 2 ) of a sinapyl alcohol film on Au(111) after silver adsorption and air contact. Slika 6. AFM slika (500 × 500 nm 2 ) filma sinapilnega alkohola na Au (111) po adsorpciji srebra in stiku z zrakom. 67 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Formation of silver nanoparticles on lignin and two of its precursors or rearrangement of the film during the silver ab- sorption. The stoichiometries of the samples, C/O ratios and calculated film thicknesses are provided in tab. 2, whereas the complete set of original and analysed data are made openly available online (Dahle et al., 2021). Fig. 6 depicts the AFM results concerning a sinapyl alcohol film after silver adsorption and air exposure. The smooth surface (R q = 0.16 nm) ex- hibits only a few randomly distributed bumps with diameters ranging from 40 nm to 70 nm and an av- erage height of approximately 0.5 nm. 3.3 ADSORPTION OF SILVER ON LIGNIN 3.3 ADSORPCIJA SREBRA NA LIGNIN Fig. 7 shows the MIES (left left), UPS He I (left middle) and UPS He II (left right) spectra of a pris- tine lignin film (black lines), after adsorption of 1.8 nm silver (red lines) and after adsorption of 9 nm silver (green lines). A shoulder at the high binding energy side for the lignin spectra, which is due to electrical charging through the lignin film, prevents the analysis of the work functions. The spectra of the pristine lignin film resemble the spectra from the literature quite well (Klarhöfer et al., 2008; Haensel et al., 2012), even though peak broadening conditioned by charging compli- cates the distinction of the different states. The adsorption of 1.8 nm silver leads to a reduction of the charging induced broadening as well as the shoulder at the high binding energy side of the secondary electron peak. Furthermore, the back- ground noise of inelastic scattered electrons gets reduced significantly after the adsorption of silver. Both UPS spectra, He I and He II, already exhibit a considerable conduction band. Nevertheless, no silver contributions can clearly be distinguished in the He I spectrum, while the He II spectrum con- tains a large Ag 4d structure. Further adsorption of silver up to a total amount of 9 nm leads to an increase in intensity of the Ag 4d structure in the He II spectrum, whereas the lignin contributions are diminished. After the adsorption of such an amount of silver, the UPS He I spectrum also clear- ly exhibits the same silver state. The MIES spec- trum shows a further reduction of the charging effects, but also exhibits some intensity due to the silver AN process. Figure 7. MIES (left left), UPS He I (left middle) and UPS He II (left right) spectra of a pristine lignin film (black lines), after adsorption of 1.8 nm silver (red lines) and after adsorption of 9 nm silver (green lines). Slika 7. MIES (levo levo), UPS He I (levo sredino) in UPS He II (levo desno) spektri neokrnjenega ligninskega filma (črne črte), po adsorpciji 1,8 nm srebra (rdeče črte) in po adsorpciji 9 nm srebra (zelene črte). 68 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Tvorba srebrovih nanodelcev na ligninu in njegovih dveh prekurzorjih Fig. 8 exhibits XPS spectra of the C 1s region (left), the O 1s region (middle) and the Ag 3d re- gion (right) of a pristine lignin film (black lines), af- ter adsorption of 1.8 nm silver (red lines) and after adsorption of 9 nm silver (green lines). The O 1s structure reveals two peaks as previously found for sinapyl alcohol. Without any change in the shape, the intensity of the O 1s structure is attenuated according to the amount of adsorbed silver. Cor- respondingly, the intensity of the Ag 3d structure increases while resembling the peak shapes of pure metallic silver (Dahle et al., 2012). The C 1s structure decreases similarly to the O 1s structure upon silver adsorption. The peak shape after the adsorption of 9 nm silver matches the shape of the pristine lignin. There against, the peak shape after adsorption of 1.8 nm silver yields an asymmetri- cally larger contribution at the high binding energy side. This might indicate a momentary adsorption of carbon oxide within the lignin film. The C/O ratio changed from 3.4 before silver adsorption to 3.7 after adsorption of small amounts of silver, and fur- ther to 5.2 after further silver adsorption. The film thickness of the spin-coated lignin film cannot be Figure 8. XPS spectra of the C 1s region (left), the O 1s region (middle) and the Ag 3d region (right) of a pristine lignin film (black lines), after adsorption of 1.8 nm silver (red lines) and after adsorption of 9 nm silver (green lines). Slika 8. XPS spektri območja C 1s (levo), območja O 1s (sredina) in območja Ag 3d (desno) neokrnjenega lig- ninskega filma (črne črte), po adsorpciji 1,8 nm srebra (rdeče črte) in po adsorpciji 9 nm srebro (zelene črte). Figure 9. AFM image (500 × 500 nm 2 ) of a lignin film on Au/Mica after adsorption of 9 nm silver and subsequent air contact. Slika 9. AFM slika (500 × 500 nm 2 ) ligninskega filma na Au/sljuda po adsorpciji 9 nm srebra in nadaljn- jem stiku z zrakom. 69 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Formation of silver nanoparticles on lignin and two of its precursors evaluated from peak attenuation. For the silver ad- sorption, film thicknesses over the lignin of 0.7 nm and 0.9 nm are calculated. This is consistent with the absorption of the metal into the organic film, similar to the results above for coniferyl and sina- pyl alcohol. The stoichiometries of the samples, C/O ratios and calculated film thicknesses are pro- vided in tab. 2, whereas the complete set of orig- inal and analysed data are made openly available online (Dahle et al., 2021). Fig. 9 shows an AFM image of a spin-coated lignin film on Au/Mica. The surface has been cov- ered with the equivalent of 9 nm silver by evapo- ration and exposed to ambient air, resulting in an RMS-roughness of 0.52 nm. A dense layer of parti- cles covers the surface. Their diameters vary from 11 nm to 45 nm (d average = 23.4 nm), the average height is 1.3 nm. 4 CONCLUSIONS 4 SKLEPI All MIES and UPS valence band spectra reveal a work function of 4.1 eV after silver adsorption for all organic films. The values in the literature for the work function of silver vary between 4.1 eV (Chelvayohan & Mee, 1982) and 4.7 eV (Dweydari & Mee, 1975). The very low value found for the silver-coated organic systems may hence be due to the rough surface structure (Wan et al., 2012), due to a weak surface atom density of the silver with the work function following the Smoluchows- ki correlation (Dweydari & Mee, 1975), or due to an Ag(110)-oriented crystal face at the top of the nanoparticles (Chelvayohan & Mee, 1982). The va- lence band features of the organic molecules did not get modified upon silver adsorption for all three systems. The silver structures just slightly appeared in the MIES spectra directly after the adsorption, while the Ag 4d structure and the conduction band already became clearly visible in the UPS spectra. Thus, the silver seems to occupy adsorption sites closely beneath the surface of the organic film, where they are mostly screened by protruding or- bitals of the organic films. The XPS C 1s and O 1s results resembled the molecule spectra from the literature quite well, and the peak shapes did not change notably upon silver adsorption, while their intensities get attenuated by the adlayer. The Ag 3d feature well resembles the reference and literature results for pure metal- lic silver without any sign of chemical interactions between the adsorbed silver and the organic mole- cule films. However, a notable change in C/O ratios for all three organic films despite the unchanged peak shapes indicates a restructuring or rearrange- ment of the organic films upon silver adsorption. This further supports the interpretation of the va- lence spectra such that the silver for the most part is adsorbed within the organic films. Furthermore, this is sustained by the calculation of adlayer thick- nesses of silver over the organic layer, which is much too low for the amount of deposited materi- al. These findings are well in line with the results for cinnamyl alcohol and support the interpretation of those results published earlier (Dahle et al., 2012). The AFM images reveal structures of agglom- erated silver after the sample got in contact with air. The statistical evaluation yielded average di- ameters of about 30 nm for coniferyl alcohol, 23 nm for sinapyl alcohol and 28 nm for lignin at an average height of 1.2 nm for coniferyl alcohol, 0.5 nm for sinapyl alcohol and 1.3 nm for lignin. This is comparable to the results for cinnamyl alcohol, where nanoparticles with an average diameter of 12 nm at a height of 1.8 nm were found (Dahle et al., 2012). The results from more in-depth investigations on the interactions of the silver-coated cinnamyl alcohol films with gas molecules revealed a catalyt- ic decomposition of the organic film upon the first contact with oxidizing gases like water or oxygen (Dahle et al., 2014). Furthermore, these investiga- tions yielded strong evidence for this decomposi- tion reaction to be responsible for or at least pro- ceeding simultaneously with the formation of the nanoparticles. A plasma treatment of the cinnamyl alcohol preliminary to the silver adsorption did not influence the formation of the nanoparticles at all (Dahle et al., 2012), even though it caused the at- tached propylenol chain to be oxidized or reduced according to the chosen process gas. Therefore, the initial adsorption site of the silver atoms within the organic film must be related to the benzene ring rather than the attached chain. As such, a similar decomposition is suggested to be responsible for the nanoparticle formation upon air contact analo- gous to the findings for cinnamyl alcohol. 70 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Tvorba srebrovih nanodelcev na ligninu in njegovih dveh prekurzorjih In summary, the adsorption of silver on coniferyl alcohol, sinapyl alcohol and lignin yielded chemically inert silver atoms occupying adsorption sites closely beneath the surface of the organic film. No chemical interaction was measurable, but a structural rear- rangement of the organic films upon absorption of silver is apparent from the spectra. After the sam- ples were brought into contact with air, nanoparti- cles with an average diameter between 20 nm and 30 nm were found on all organic films. Due to all of the similarities, the adsorption process is proposed to proceed in a similar manner as to that on cinnam- yl alcohol (Dahle et al., 2012; Dahle et al., 2014). 5 SUMMARY 5 POVZETEK Vsi spektri valentnega pasu MIES in UPS razkri- vajo delovno funkcijo 4,1 eV po adsorpciji srebra za vse organske filme. Vrednosti v literaturi za delovno funkcijo srebra se gibljejo med 4,1 eV (Chelvayohan & Mee, 1982) in 4,7 eV (Dweydari & Mee, 1975). Zelo nizka vrednost, ugotovljena za srebrno prev- lečene organske sisteme, je zato lahko posledica grobe površinske strukture (Wan et al., 2012), zara- di šibke površinske gostote atomov srebra z delovno funkcijo po korelaciji Smoluchowskega (Dweydari & Mee, 1975) ali zaradi kristalne površine, usmer- jene v Ag (110) na vrhu nanodelcev (Chelvayohan & Mee, 1982). Značilnosti valentnega pasu organskih molekul se pri adsorpciji srebra za vse tri sisteme niso spremenile. Signali struktur srebra so bili na spektrih MIES komaj zaznavni, neposredno po ad- sorpciji, medtem ko sta struktura Ag 4d in prevodni pas že postala jasno vidna v spektrih UPS. Zdi se, da srebro zaseda mesta adsorpcije blizu pod površino organskega filma, kjer jih večinoma pregledujejo štrleče orbitale organskih filmov. Rezultati XPS C 1s in O 1s so bili precej podob- ni molekularnim spektrom iz literature in oblike vrhov se pri adsorpciji srebra niso bistveno spre- menile po obliki, medtem ko njihovo intenzivnost oslabi adsorbirana plast. Funkcija Ag 3d je zelo podobna referenčnim in literaturnim rezultatom za čisto kovinsko srebro brez kakršnih koli znakov kemičnih interakcij med adsorbiranim srebrom in filmi organskih molekul. Vendar opazna spremem- ba razmerja C / O za vse tri organske filme kljub ne- spremenjeni obliki vrhov kaže na prestrukturiranje ali prerazporeditev organskih filmov po adsorpciji srebra. To nadalje podpira razlago valenčnih spek- trov na osnovi večinske adsorbcije v organske filme. Poleg tega to potrjujejo tudi izračuni debeline ad- sorbirane plasti srebra nad organsko plastjo, ki je bistveno prenizka za količino naloženega materiala. Te ugotovitve se popolnoma ujemajo z rezultati o cinamil alkoholu in podpirajo razlago prej objavl- jenih rezultatov (Dahle et al., 2012). Slike AFM razkrivajo strukture aglomeriranega srebra, ko je vzorec prišel v stik z zrakom. Statistična ocena je dala povprečni premer približno 30 nm za koniferilni alkohol, 23 nm za sinapilni alkohol in 28 nm za lignin pri povprečni višini 1,2 nm za koniferil- ni alkohol, 0,5 nm za sinapilni alkohol in 1,3 nm za lignin. To je primerljivo z rezultati na cinamil alko- holu, kjer so našli nanodelce s povprečnim prem- erom 12 nm na višini 1,8 nm (Dahle et al., 2012). Rezultati poglobljenih raziskav interakcij posre- brenih filmov cinamil alkohola z molekulami plinov so pokazali katalitično razgradnjo organskega filma ob prvem stiku z oksidativnimi plini, kot sta voda ali kisik (Dahle et al., 2014). Poleg tega so te preiskave dale trdne dokaze, da je bila ta reakcija razgradn- je odgovorna za nastanek nanodelcev ali pa je vsaj potekala hkrati z njo. Obdelava cinamil alkohola s plazmo pred adsorpcijo srebra sploh ni vplivala na tvorbo nanodelcev (Dahle et al., 2012), čeprav je povzročila, da se pritrjena veriga propilenolov ok- sidira ali zmanjša glede na izbrani procesni plin. Zato mora biti začetno adsorpcijsko mesto atomov srebra v organskem filmu povezano z benzenskim obročem in ne s pritrjeno verigo. Na osnovi tega ugotavljamo, da je podoben razkroj odgovoren tudi za tvorbo nanodelcev ob stiku z zrakom, analogno ugotovitvam o cinamil alkoholu. Ugotavljamo, da so pri adsorpciji srebra na koniferilnem alkoholu, sinapilnem alkoholu in lign- inu nastali kemično inertni atomi srebra, ki so za- sedli mesta adsorpcije blizu površine organskega filma. Z meritvami ni bilo mogoče izmeriti nobene kemične interakcije, vendar je iz spektrov razvid- na strukturna preureditev organskih filmov po ab- sorpciji srebra. Ko so prišli vzorci v stik z zrakom, smo na vseh organskih filmih zaznali nanodelce s povprečnim premerom med 20 nm in 30 nm. Zaradi vseh podobnosti naj bi postopek adsorpcije potekal na podoben način kot pri cinamil alkoholu (Dahle et al., 2012; Dahle et al., 2014). 71 Les/Wood, Vol. 70, No. 1, June 2021 Dahle, S., Wegewitz, L., Viöl, W., & Maus-Friedrichs, W.: Formation of silver nanoparticles on lignin and two of its precursors ACKNOWLEDGEMENTS ZAHVALA We thankfully acknowledge Dana Schul- te genannt Berthold for her technical assistance and the Deutsche Forschungsgemeinschaft (DFG) for financial support under project numbers MA 1893/18-1 and VI 359/9-1. Avtorji se zahvaljujemo Dani Schulte genannt Berthold za njeno tehnično pomoč in Deutsche For- schungsgemeinschaft (DFG) za finančno podporo v okviru projektov MA 1893/18-1 in VI 359/9-1. 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Young 4 1 UVOD 1 INTRODUCTION One of the important advantages of wood and wood-based industry is its ability to utilize the whole potential of this material created by nature. Trees are perennial plants with roots, stems and branches, and the wood that we get from tree stems is one of the best materials for sustainable development. But when considering sustainable development, the circular economy and zero waste society, there is still much more we can do with wood, as a significant amount of the tree stays unused or its usability is limited, 1 Univerza v Ljubljani, Biotehniška fakulteta, Oddelek za le- sarstvo, Jamnikarjeva 101, 1000 Ljubljana, SLO * e-mail: sergej.medved@bf.uni-lj.si 2 Forest Products Technology and Timber Construction De- partment, Salzburg University of Applied Sciences, Kuchl, Austria; Transilvania University of Brasov, Brasov, Romania; 3 Forest Products Technology and Timber Construction De- partment, Salzburg University of Applied Sciences, Kuchl, Austria; Transilvania University of Brasov, Faculty of Furni- ture Design and Wood Engineering, Brasov, Romania 4 The University of Tennessee Institute of Agriculture, Depart- ment of Forestry, Wildlife and Fisheries, Center for Renewa- ble Carbon, Knoxville, Tennessee, USA Abstract: To achieve the zero-waste goal as well as sustainability, the use of the raw materials, especially those from nature, and wood in particular, has to be smart, meaning that the resource has to be used to its full potential. Since wood-based industry is associated with high intensity and the generation of a relatively large amount of residues, those residues should be used for the production of useful products, otherwise they will easily be classified as waste and afterwards used as a source of energy. To present a possible solution for wood residues like wood chips, wood particles and bark, we investigated the possibility of using wood and bark residues as constituents for the production of single layer insulation panel with a target thickness of 40 mm and target density of 0.2 g∙cm -3 . Thermal conduc- tivity was determined using the steady state principle at three different temperature settings. The average thermal conductivities were determined between 49 mW∙m -1 ∙K -1 and 74 mW∙m -1 ∙K -1 . The highest values were determined at boards made from bark, which also had the highest density (0,291 g∙cm -3 ), while the lowest thermal conductivity was observed for boards made from spruce wood particles. Keywords: thermal conductivity, insulation, particleboard, wood particles, bark Izvleček: Doseganje cilja „nič odpadkov“ in načela trajnostne rabe je kompleksen proces, ki zahteva učinkovito rabo surovine, še posebej naravne, zlasti lesa. Pomembno je, da je raba surovine celostna, da se uporabi v celoti za izdelavo trajnostnih produktov. Lesnopredelovalna industrija je visoko intenzivna proizvodnja, kar pomeni, da pri tem nasta- nejo tudi velike količine ostankov, primernih za izdelavo uporabnih proizvodov. V primeru, ko ostankov ne bi smotrno uporabili, pa se to surovino opredeli kot odpadek in uporabi za proizvodnjo energije (kar pa ni najbolj trajnostna in tudi optimalna rešitev). S ciljem predstavitve možne uporabe lesnih ostankov, kot so npr. sekanci, iveri in skorja, smo raziskali možnost njihove uporabe za izdelavo enoslojnih izolacijskih plošč ciljne debeline 40 mm in gostote 0.2 g∙cm -3 . Toplotno prevodnost smo določili pri treh različnih temperaturnih pogojih. Ugotovljene vrednosti povprečne toplotne prevodnosti so bile med 49 mW∙m - 1∙K -1 in 74 mW∙m - 1∙K -1 . Najvišje vrednosti so bile izmerjene pri ploščah iz skorjete so imele tudi najvišjo gostoto (0.291 g∙cm -3 ), najnižje pa so izmerili na ploščah iz smrekovih iveri. Ključne besede: toplotna prevodnost, izolativnost, sekanci, iveri, skorja 74 Les/Wood, Vol. 70, No. 1, June 2021 Medved, S., Tudor, E. M., Barbu, M. C., & Young, T. M.: Toplotna prevodnost različnih bio-izolacijskih materialov and thus is wasted or burned, with the latter cau- sing the emission of greenhouse gasses, and thus pollution. Particleboard made from wooden particles can be classified as a thermal insulating material. Sonderegger and Niemz (2009) reported a thermal conductivity value for three-layer particleboard be- tween 99 mW∙m -1 ∙K -1 and 118 mW∙m -1 ∙K -1 (density between 0.62 and 0.76 g∙cm -3 ). The availability of reports on the usability of wood chips for thermal insulation is limited. Wang and Fukuda (2016) presented the possibility of using vinyl packed wood chips as “loose-fill” insu- lation material for roofs. Skogsberg and Lundberg (2005) showed the positive impact of wood chips in order to prevent snow melting when snow is used as a cooling agent. The most unused part of a tree is also the part that is most visible, the bark, which serves as a protective barrier for wood. Bark consti- tutes between 10% and 20% of total tree mass, although this varies regarding wood species and age of tree. Bark is the outer part of a tree oc- curring outside of the vascular cambium and can be divided into outer bark (dead tissue) and inner part (tissue with living cells). The majori- ty of harvested bark is currently used for ener - gy, which is, according to Deppe and Hoffmann (1972) and Gupta et al. (2011), not the best solu- tion due its low calorific value and high CO 2 emis- sions. A smaller amount of bark is used in special applications like horticulture (for landscaping), in pharmacy (Miranda et al., 2012), for leather tanning (Pizzi, 2008), for insulation panels (Kain et al., 2014), foams (Tondi & Pizzi, 2009; Čop et al., 2015), decorative panels for flooring (Tu- dor et al., 2018), or as a substance to produce fire-resistant wood-based composites for con- struction purposes (Tondi et al., 2014). Most of the bark obtained in the debarking process in the forest or at a sawmill is unused, however, which creates an industrial and environmental prob- lem. The complex structure of bark presents a problem when considering its usage, but it also opens wide range of possible approaches. In the literature some information can be found about utilizing bark for particleboards, with such work presented by Dost (1971), Deppe and Hoffman (1972), Maloney (1973), Lehmann and Geimer (1974), Place and Maloney (1977), Muszynski and McNatt (1984), Suzuki et al. (1994), Blan- chet et al. (2000), Nemli and Colakoglu (2005), and Yemele et al. (2008). Despite the use of dif - ferent adhesives, they determined that excessive bark content in the particleboard lowers me- chanical properties and resistance against water (increases thickness swelling and water uptake). Ružiak et al. (2017) used bark as a filler (a flour substitute) and also determined its influences on thickness swelling. The main reason for such behaviour was due to differences in the size of constituents and the chemical structure of bark compared to wood. The chemical composition of bark shows that it contains a higher content of ash, extractives and lignin, and a lower content of polysaccharides cellulose and hemicelluloses (Antonović et al., 2010; Antonović et al., 2018). Due to the presence of phenol like components in bark, which react with formaldehyde (Camer- on & Pizzi, 1985; Prasetya & Roffael, 1991; Nemli & Çolakoğlu, 2005; Takano et al., 2008; Medved et al., 2019), the addition of bark resulted in lower formaldehyde emissions. Bark, although an underutilized bio- or lignocellulose-based re- source, is also a very interesting material, which has a versatile role in the tree. As summarized by Rossel et al. (2014), the main functions of bark are protection, transportation and storage of nutrients, insulation, and mechanical support of the stem. Due to undesired particle morphology and the fact that a lot of dirt, stones, and other unwanted contaminants, picked up during log- ging, can have a negative impact on processing, bark has generally been of low interest for wid- er industrial use, especially for the production of wood-based panels (Deppe & Hoffman, 1972; Pásztory et al., 2016). The utilization of bark relies mostly on its phys- ical and chemical properties, hence it is no surprise that the majority of reports in last decade(s) are fo- cused on using bark as insulation material (Martin, 1963; Suzuki et al., 1994; Sato et al., 2009; Kain et al. 2014). Martin (1963) determined that dry bark has almost 20% better insulation properties than solid wood at the same density, and that the conductiv- ity of boards made from bark was lower than that obtained for boards made from wood. 75 Les/Wood, Vol. 70, No. 1, June 2021 Medved, S., Tudor, E. M., Barbu, M. C., & Young, T. M.: Thermal conductivity of different bio-based insulation materials The usage of low quality wood is nowadays mostly related to particleboard and fibreboard pro- duction, and also with energy production, while bark is used mostly for energy. In the present in- vestigation we focus on an important wood proper- ty, on its thermal insulation ability. Wood and bark residues created by the wood processing industry are mostly in already crushed shape, meaning they are either in shape of particles or chips. The aim of this paper is thus to present the possibility to us- ing wood and bark residues for the production of boards with low thermal conductivity. 2 MATERIALS AND METHODS 2 MATERIALI IN METODE DELA To carry out this study Norway spruce (Picea abies Karst.) residues and a mixture of coniferous barks were used. Solid wood and bark were pro- cessed in a laboratory using a Prodeco M-0 chipper (Figure 1) with an output screen with openings of 25 mm in diameter, along with a Condux CSK 350/ N1 ring chipper (Figure 2), with the gap between the blade and beating bar of 1.25 mm. A ring chipper was used only to obtain wood particles (Figure 3a), while a chipper was used for the primary breakdown of wood (Figure 3b) and bark (Figure 3c). The resulting constituents were dried at 70°C for 16 hours to achieve a moisture content below 4 %. After drying, an appropriate mass of particles was put into a blending machine, where the par- ticles were blended with melamine-urea-formal- dehyde adhesive (blending ratio 15%, solid/solid ratio) produced by Melamin Kočevje, Slovenia. The total blending time was 10 minutes (5 minutes ad- hesive spraying and mixing + 5 minutes only mix- ing). Blended particles were then hand formed into Figure 1. Prodeco M-0 chipper Slika 1. Prodeco M-0 sekirostroj 76 Les/Wood, Vol. 70, No. 1, June 2021 Medved, S., Tudor, E. M., Barbu, M. C., & Young, T. M.: Toplotna prevodnost različnih bio-izolacijskih materialov a frame with the dimensions 500×500 mm 2 (Figure 4), which was placed on a steel plate. The target density of the produced panels was 0.2 g∙cm -3 , with a thickness of 40 mm. The mat was pressed at 180°C and a pressure of 2 N∙mm -2 . The pressing time was set to 9 minutes followed by a 1 minute degassing phase. Three boards per composition were made. The boards were then left at room conditions to cool down (for 60 minutes), and later placed in Figure 2. Condux CSK 350/N1 ring chipper Slika 2. Condux CSK 350/N1 obročasti iverilnik Figure 3. Constituents used in the investigation (spruce wood particles (3a), spruce wood chips (3b) and coniferous bark (3c)) Slika 3. Gradniki, uporabljeni v raziskavi (iveri lesa smreke (3a), sekanci lesa smreke (3b) in skorja iglavcev (3c)) 3a 3b 3c 77 Les/Wood, Vol. 70, No. 1, June 2021 Medved, S., Tudor, E. M., Barbu, M. C., & Young, T. M.: Thermal conductivity of different bio-based insulation materials a climate chamber at a temperature of 23±1°C and 55±5% relative air humidity. After 21 days the ther- mal conductivity of the boards was measured. Thermal conductivity was determined ac- cording to EN 12667, 2002 in an LM.305 heat flow meter (Stirolab, Sežana, Slovenia). The tech- nique used is based on the measuring of the heat conductivity in the heating chamber until steady state conditions are achieved. The measuring area was 290×260 mm 2 . The measurements were conducted at three different conditions, as shown in Table 1. The determination of heat conductivity lasted 240 minutes. Thermal conductivity λ in W∙m -1 ∙K -1 was calculated according to equation 1. [1] where t is the thickness of sample in m, Q is the generated heat flow in W (for upholding steady state conditions – linear temperature gradient), S is the sample surface area in m 2 and ΔT is the temper- ature difference between hot and cold sides in K. 3 RESULTS AND DISCUSSION 3 REZULTATI IN RAZPRAVA The thickness and density of the produced boards depends on the board composition (Table 2). Even though all boards had same target den- sity and thickness it can be observed that there were differences between the boards. The differ- ences in thickness and density between boards made from wood chips and wood particles are due the differences in the compressibility of the constituents (bigger constituents, i.e. chips, being less compressible, and hence a higher thickness and lower density). The higher density and low- er thickness of bark board could be the result of the reaction during compression, and thus it can be assumed that bark constituents were damaged (crushed and broken) during pressing, which ena- bled repositioning of the crushed parts into voids, hence creating a higher density. This higher den- sity bark board also resulted in higher thermal conductivity, and so lower resistance against heat conductivity (Figure 5). Comparing the density values (Table 2) and thermal conductivity (Figure 5) reveals a correla- tion, and namely that an increase in density causes Figure 4. Wood and bark mat before pressing Slika 4. Natreseni gradniki lesa in skorje pred stiskanjem 4a 4b 4c Lo w er pla t e / Spodnja plošč a Upper pla t e / Zg ornja plošč a A v er ag e t emper a tur e / P o vpr ečna t emper a tur a T emper a tur e diff er ence / T emper a turna r azlik a °C °C °C K Se t 1 / Območje 1 10 20 15 10 Se t 2 / Območje 2 10 35 22.5 25 Se t 3 / Območje 3 10 50 30 40 tQ ST λ × = ×∆ Table 1. Thermal conductivity measurements settings Preglednica 1. Merilna območja za določanje toplotne prevodnosti 78 Les/Wood, Vol. 70, No. 1, June 2021 Medved, S., Tudor, E. M., Barbu, M. C., & Young, T. M.: Toplotna prevodnost različnih bio-izolacijskih materialov an increase in thermal conductivity. The increase in thermal conductivity of denser materials is re- lated to the higher number of constituents in con- tact with each other and lower number of “air” filled voids, which present a barrier to heat con- ductivity, while constituents in contact conduct heat from hot towards cold areas. Heat transfer will occur when the area in question reaches the maximum potential (with regard to neighbouring conditions), and the area next to it is cooler and able to accept the energy. When all areas are heat- ed to maximum potential (according to available conditions) permanent heat flow occurs, and that flow also means a loss in energy. Higher thermal conductivity was also observed in the board made of wood chips (compared to wood particles), Table 2. Thickness and density of the produced boards Preglednica 2. Debeline in gostote izdelanih plošč Thickness / Debelina Density / Gos t ot a mm g·cm -3 W ood chip s / Lesni sekanci 42.42 0.232 W ood particles / Lesne iveri 42.01 0.252 Bark / Sk orja 37.06 0.291 Figure 5. Average thermal conductivity with regard to the board composition (numbers in parentheses represent standard deviation values) Slika 5. Povprečne vrednosti toplotne prevodnosti glede na zgradbo plošče (vrednosti v oklepajih so vrednosti standardnih odklonov) 79 Les/Wood, Vol. 70, No. 1, June 2021 Medved, S., Tudor, E. M., Barbu, M. C., & Young, T. M.: Thermal conductivity of different bio-based insulation materials which could be related to the constituents’ mor- phology. Although “stacking” bigger constituents leaves larger voids, those larger voids do not help much in lowering thermal conductivity. This is be- cause bigger constituents enable the creation of bigger contact areas between constituents, which results in more efficient heat transfer. A detailed analysis of the boards’ behaviour at different settings shows more clearly the differ - ence, especially between boards from wood-based constituents (Figure 6). In all boards, the increase in average tem- perature/temperature differences resulted in an increase in thermal conductivity, but when com- paring the relations related to board composition it reveals that boards made from wood chips are less influenced by the change in temperature con- ditions, while bark boards show higher sensitivity towards an increase in temperature. Since heat resistance is determined as the re- lation between thickness and thermal conductivity, there is no surprise that the lowest resistance was recorded in boards containing bark (Table 3), sup- porting the earlier observations that bigger con- stituents and higher density offer lower heat flow resistance. Table 3. Heat resistance of the produced boards (the numbers in parentheses represent standard deviation values) Preglednica 3. Toplotna upornost izdelanih plošč (v oklepajih so vrednosti standardnih odklonov) Hea t r esis t ance / T oplotna upornos t m 2 ·K· W -1 W ood chip s / Lesni sekanci 0.84 (0.047) W ood particles / Lesne iveri 0.88 (0.084) Bark / Sk orja 0.55 (0.033) Figure 6. Thermal conductivity with regard to board composition and testing conditions Slika 6. Toplotna prevodnost glede na zgradbo plošče in pogoje določanja toplotne prevodnosti 80 Les/Wood, Vol. 70, No. 1, June 2021 Medved, S., Tudor, E. M., Barbu, M. C., & Young, T. M.: Toplotna prevodnost različnih bio-izolacijskih materialov 4 CONCLUSIONS 4 SKLEPI An analysis of the different residues (chips, particles, bark) shows that it is possible to make a stable board with densities between 0.23 g∙cm -3 and 0.29 g∙cm -3 for insulation purposes. The highest thermal conductivity values and the lowest heat re- sistance were determined in bark boards. The high- est insulation effect was found when wood (spruce) particles were used, but the sensitivity towards the testing conditions was lowest in boards made from wood (spruce) chips. 5 SUMMARY 5 POVZETEK Pomembna prednost lesnopredelovalne in- dustrije je sposobnost izkoriščanja celostnega potenciala lesa kot dragocene naravne surovine. Celostna raba naravnih virov je pomemben vid- ik krožnega gospodarstva, nizkoogljične družbe in družbe z „nič odpadki“. Čeprav je področje rabe lesa zelo široko, od različnih proizvodov iz masivnega lesa do različnih lesnih ploščnih kom- pozitov, pa vseeno opažamo, da relativno velika količina lesa ostane neuporabljenega oz. njegov celotni potencial ni izkoriščen. Številne raziskave pričajo o možnostih rabe lesnih ploščnih kom- pozitov ne samo za izdelavo pohištva ali nosilnih konstrukcijskih elementov ampak tudi za izdela- vo izolacijskih materialov (Sonderegger & Niemz, 2009; Wang & Fukuda, 2016; Skogsberg & Lund- berg, 2005), pri čemer so bile plošče oz. izolatorji izdelani iz iveri ali pa iz sekancev. Skupina avtorjev pa je za izdelavo izolatorjev uporabila tudi skor- jo (Martin, 1963; Suzuki et al., 1994; Sato et al., 2009; Kain et al., 2014). Uporaba lesne surovine slabše kakovosti je danes omejena predvsem na izdelavo ivernih in vlaknenih plošč oz. na proizvodnjo energije, med- tem ko se skorja uporablja predvsem kot ener- gent. Ker se tako les kakor tudi skorja nahaja že v zdrobljeni obliki (sekanci, iveri), je cilj pričujoče ra- ziskave predstaviti možnost rabe takšne surovine za izdelavo izolacijskih plošč. Za izdelavo izolacijskih plošč smo uporabili le- sne ostanke navadne smreke (Picea abies Karst.) in skorjo iglavcev, ki smo jo predelali v sekance oz. iv- eri na laboratorijskem sekirostroju Prodeco M-0 in laboratorijskem obročastem iverilniku Condux CSK 350/N1. Izdelane gradnike smo nato pri tempera- turi 70 °C posušili do vlažnosti pod 4 %, čemur je sledilo oblepljanje z melamin-urea-formaldehidnim lepilom (delež lepila 15 %). Oblepljene gradnike smo nato ročno natresli v lesen okvir z dimenzijami 500 × 500 mm 2 . Ciljna debelina plošč je bila 40 mm, ciljna gostota pa 0.2 g∙cm -3 . Stiskali smo 9 minut pri temperaturi 180 °C in tlaku 2 N∙mm -2 . Po 21dnevni klimatizaciji pri normalnih pogojih (temperaturi 23±1 °C in 55±5 % relativni zračni vlažnosti) smo določili toplotno prevodnost plošč po standardu EN 12667, 2002. Toplotno prevodnost smo določili pri treh različnih pogojih in sicer: - ΔT10: temperatura spodnje plošče 10 °C, temperatura zgornje plošče 20 °C - ΔT25: temperatura spodnje plošče 10 °C, temperatura zgornje plošče 35 °C - ΔT40: temperatura spodnje plošče 10 °C, temperatura zgornje plošče 50 °C Meritev je trajala 240 minut. Debelina izdelanih plošč je bila 37,06 mm (skorja), 42,01 mm (iveri) oz. 42,42 mm (sekan- ci), gostota pa 0.232 g∙cm -3 (sekanci), 0.252 g∙cm - 3 (iveri) oz. 0.291 g∙cm -3 (skorja) (preglednica 2). Tudi toplotna prevodnost je odvisna od zgradbe plošče oz. velikosti uporabljenih gradnikov. Pri plošči, izdelani iz smrekovih sekancev, je bila pov- prečna toplotna prevodnost 51.35 mW∙m -1 ∙K -1 (44.23 mW∙m -1 ∙K -1 pri ΔT10; 55.12 mW∙m -1 ∙K -1 pri ΔT25 in 54.76 mW∙m -1 ∙K -1 pri ΔT40), iz smrek- ovih iveri 49.73 mW∙m -1 ∙K -1 (33.43 mW∙m -1 ∙K -1 pri ΔT10; 53.30 mW∙m -1 ∙K -1 pri ΔT25 in 55.91 mW∙m - 1 ∙K -1 pri ΔT40) in pri skorji 74.05 mW∙m -1 ∙K -1 (47.13 mW∙m -1 ∙K -1 pri ΔT10; 82.37 mW∙m -1 ∙K -1 pri ΔT25 in 92.66 mW∙m -1 ∙K -1 pri ΔT40). Ugotovili smo, da je toplotna prevodnost odvisna od velikosti upora- bljenih gradnikov (manjša pri manjših gradnikih) ter gostote (večja pri ploščah z večjo gostoto). Raziskava je pokazala, da je mogoče iz različnih ostankov (lesnih sekancev, lesnih iveri in skorje) izdelati stabilne plošče z gostoto med 0.23 g∙cm -3 in 0.29 g∙cm -3 , ki se lahko uporabijo kot izolaci- jske plošče, saj je toplotna prevodnost nižja od 75 mW∙m -1 ∙K -1 . 81 Les/Wood, Vol. 70, No. 1, June 2021 Medved, S., Tudor, E. M., Barbu, M. C., & Young, T. 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(EN 12667: 2002) 83 Les/Wood, Vol. 70, No. 1, June 2021 Les/Wood Novice/News Oddelek z a lesar s tv o sodeluje k ot partner v ciljnem r azisk o v alnem pr ojek tu z a izboljšanje k onk ur enčnos ti lesa lis t a v ce v Tina Drolc Ciljni raziskovalni projekt (CRP) z naslovom »Možnosti rabe lesa listavcev v slovenskem bio- gospodarstvu«(LesGoBio) v okviru vodilne inšti- tucije, Gozdarskega Inštituta Slovenije vodi dr. Peter Prislan. Partner v projektu je tudi Bioteh- niška fakulteta Univerze v Ljubljani. Koordinator projekta izr. prof. dr. Aleš Straže s Katedre za te - hnologijo lesa na Oddelku za lesarstvo je pove - dal: »Projekt naslavlja aktualna vprašanja glede možnosti širjenja in izboljšanja rabe lesa listav- cev, razvoja novih tehnologij ter tržnih in makro- ekonomskih posledic. Posebej izpostavlja pomen opredelitve obetavnih, okoljsko sprejemljivih in ekonomsko izvedljivih postopkov obdelave in predelave in presojo sodobnih inovativnih les- nopredelovalnih tehnologij. Pomemben cilj pro- jekta je razviti scenarije in strateška priporočila za implementacijo sodobnih tehnologij za proi- zvodnjo izdelkov z visoko dodano vrednostjo, ki bi omogočale racionalno in trajnostno rabo lesa listavcev.« V projektu se bodo raziskave osredotočale na najbolj zastopane domače lesove listavcev kot so bukovina, hrastovina in javorovina ter ostale bolj zastopane, kot so topolovina, gabrovina in bre - zovina. Širši cilj projekta je spodbuditi proizvodnjo izdelkov z višjo dodano vrednostjo, kar navadno z narodnogospodarskega vidika pomeni v prihodnje pozitivno prestrukturiranje lesnopredelovalne in- dustrije, s tem pa vzporedno spremembo strukture porabljenih virov za proizvodnjo. Projekt v vrednosti 170.000 EUR financirata Ministrstvo za kmetijstvo, gozdarstvo in prehrano Republike Slovenije (MKGP) in Javna agencija za raziskovalno dejavnost Republike Slovenije (ARRS), izvajal pa se bo 3 leta, od novembra 2020 do 2023. Dodatne informacije o CRP projektu »Les- GoBio« V4-2016: dr. Peter Prislan, e-pošta pe t er . prislan@g o z dis.si ali izr. prof. dr. Aleš Straže, e-poš- ta ales.s tr az e@b f .uni-lj.si 84 Les/Wood, Vol. 70, No. 1, June 2021 Les/Wood Novice/News In memoriam: pr of . dr . Jo ž e K o v ač (1930–2021) prof. dr. Jože Resnik, zaslužni profesor v pokoju Biotehniška fakulteta UL, Oddelek za lesarstvo Konec januarja 2021 se je v enaindevetdese- tem letu poslovil prof. dr. Jože Kovač, priznan stro- kovnjak tako v lesni industriji kot v univerzitetnem izobraževanju na področju lesarstva. Prof. dr. Jože Kovač je bil rojen v Ljubljani 18. marca 1930. Leta 1949 je z odliko končal gimnazijo v Ljubljani. Študij na gozdarskem oddelku takratne Fakultete za agro- nomijo, gozdarstvo in veterino Univerze v Ljubljani je zaključil leta 1956. Za diplomsko delo z naslovom Upoštevanje naravne dediščine pri gospodarjenju z gozdovi v krajinskem parku Zgornja Idrijca je prejel fakultetno Prešernovo nagrado. Po koncu študija se je kot pripravnik zapos- lil na Okrajni upravi za gozdarstvo OLO Ljubljana, leta 1958 pa kot asistent na Agronomsko-gozdarski fakulteti na gozdarskem oddelku, kjer je ostal do leta 1961. Nato je kot upravitelj gozdnega obrata Kamniška Bistrica delal v Silva-gozdnem in lesnem gospodarstvu Agronomske in gozdarske fakultete v Ljubljani, od leta 1963 pa kot referent za napredek proizvodnje v Gozdnem gospodarstvu Ljubljana. Po- membna sprememba se je zgodila v letu 1968, ko je postal generalni direktor v Lesnem podjetju Hoja v Ljubljani. V času njegovega vodenja je podjetje Hoja vidno napredovalo. Organizacijsko je združeval les- ne obrate in jih selil v industrijsko cono Vič, kar je poleg drugih prednosti omogočalo bolj optimalen razvoj podjetja in bolj ekonomično poslovanje, ki se je kazalo tudi v višanju plač zaposlenih v primerjavi s plačami v slovenskem gospodarstvu. Zaposlitev v podjetju Hoja je prekinil leta 1974 in se isto leto zaposlil na Biotehniški fakulteti kot predavatelj na gozdarsko-lesarskem oddelku Univerze v Ljubljani, kjer je ostal do upokojitve leta 1994. Leta 1976 je na Gozdarski fakulteti Univerze v Zagrebu uspešno zagovarjal doktorsko delo z na- slovom Proučevanje zastojev v avtomatiziranem delovnem procesu proizvodnje lesno-cementnih gradbenih plošč in istega leta postal izredni, leta 1982 pa redni profesor za organizacijo proizvodnih procesov v lesarstvu. Njegove organizacijske spo- sobnosti potrjuje tudi funkcija prvega predstojnika novoustanovljenega VTOZD-a za lesarstvo (1975– 1979). Veliko truda je vlagal v nadgradnjo razisko- valnega in pedagoškega delovnega področja ter optimalne in učinkovite organizacije proizvodnje v lesni industriji. V tem okviru je izdal več študijskih gradiv za področje, ki se je pričelo z njegovim pre- vzemom strokovno in znanstveno oblikovati. Us- pešnost njegovega pedagoškega dela na področju lesne proizvodnje v praksi potrjujejo tudi številna diplomska dela s tega področja. Kot zunanji sode- lavec-svetovalec je neposredno sodeloval tudi pri oblikovanju organizacijskih razvojnih politik v po- membnih lesnih tovarnah tistega časa, kot so bile Hoja Ljubljana, Bor Laško, Stilles Sevnica, Meblo Nova Gorica, Novoles Novo mesto in Savinja Cel- je. Bogate izkušnje iz dela v gozdarstvu in lesni in- dustriji je znal prenesti v pedagoški proces in delo s študenti in študentkami, v izbiro tem diplomskih del in raziskovalnih tematik. Seveda smo iz tako ce- lovitega znanja in dodanih praktičnih izkušenj veli- ko pridobili tudi njegovi sodelavci in sodelavke. V zgodovino razvoja Oddelka za lesarstvo Bio- tehniške fakultete UL se je zagotovo zapisal kot izku- šen poznavalec organizacije in pogojev za uspešen razvoj neke dejavnosti, kar zelo nazorno potrjuje njegovo prizadevanje za ustanovitev samostojnega Oddelka za lesarstvo na Biotehniški fakulteti UL leta 85 Les/Wood, Vol. 70, No. 1, June 2021 Les/Wood Novice/News 1975, vodenje študijskega predmeta organizacija poslovanja v lesarstvu, bogata in obširna bibliogra- fija ter mentorstva dodiplomskim in podiplomskim študentom in študentkam magistrskega in doktor- skega študija na tem področju. Bil je mentor pri dvainsedemdesetih diplomskih delih, dveh magis- trskih delih in dveh doktorskih disertacijah. Bil je avtor in soavtor številnih znanstvenih, stro- kovnih in poljudnih člankov ter prispevkov na doma- čih in mednarodnih strokovnih konferencah, posvetih in stanovskih srečanjih. Med njegovimi uredniškimi deli velja izpostaviti Spominski zbornik Biotehniške fakultete Univerze v Ljubljani 1988–1992. Prof. dr. Jože Kovač je pustil neizbrisen pečat tudi kot predsednik Odbora za izgradnjo 1. faze Od- delka za lesarstvo v letih od 1974 do 1984. Deset- letno delo, o katerem je bila izdana posebna publi- kacija, je bilo zelo zahtevno, saj se je ves čas soočal s številnimi formalnimi, organizacijskimi in izvedbe- nimi težavami. Posebno priznanje mu je bilo izkazano tudi s strani Biotehniške fakultete in Univerze v Ljubljani, ko mu je bilo v letih 1992–1994 zaupano vodenje Habilitacijske komisije Univerze v Ljubljani. Prof. dr. Jože Kovač je prejel decembra 1993 Svečano listino in zlato plaketo Univerze v Ljubljani za področje vzgojno-izobraževalnega in znanstve- noraziskovalnega dela. Leta 1994 je prejel Jesenko- vo priznanje Biotehniške fakultete UL za pomemb- ne zasluge, kot je bilo prizadevanje za ustanovitev samostojnega Oddelka za lesarstvo leta 1975, vo- denje študijskega predmeta organizacija poslo- vanja v lesarstvu, bogata bibliografija, mentorstvo bodočim magistrom in doktorjem znanosti ter predsedovanje odboru za izgradnjo novih pedago- ških in raziskovalnih prostorov na Oddelku za lesar- stvo BF UL. Uspešno je bilo tudi njegovo vodenje Biotehniške fakultete, kjer je bil dekan v letih od 1989 do 1992, v čas katerega sodijo tudi zaključne potrditve o selitvi Dekanata in dela prostorov za pe- dagoški proces s Krekovega trga v centru Ljubljane na Jamnikarjevo 101. Omeniti je potrebno tudi njegovo vseskozi ak- tivno in prizadevno sodelovanje pri delovanju posa- meznih delov strokovnih društev in revij. Tako je bil v letih od 1975 do 1977 predsednik Zveze društev inženirjev in tehnikov gozdarstva in lesarstva Slove- nije, leta 1978 je bil imenovan za njenega zasluž- nega, leta 1991 pa za častnega člana. Od leta 1982 je petnajst let vodil uredniško politiko uveljavljene strokovne in znanstvene revije LES, pri čemer je bil prvih deset let tudi njen glavni in odgovorni ured- nik. Pod njegovim vodstvom je revija pomembno izboljšala svoje mesto med tovrstnimi mednarodni- mi strokovnimi in znanstvenimi revijami. Prof. dr. Jože Kovač je bil velik ljubitelj in pozna- valec narave, posebno gozdnih območij Slovenije. Morda je tudi zato postal vnet pohodnik, ki je z ve- seljem predajal svoje znanje in krepil spoštovanje do narave. To so bile vedno posebne učne ure o naravi, različnih rastlinah in gozdu v njej, za kar smo mu vsi, ki smo ga spremljali na teh poteh, globoko hvaležni. Prof. dr. Jože Kovač je bil velik ljubitelj in pozna- valec narave, posebno gozdnih območij Slovenije. Morda je tudi zato postal vnet pohodnik, ki je z ve- seljem predajal svoje znanje in krepil spoštovanje do narave. To so bile vedno posebne učne ure o naravi, različnih rastlinah in gozdu v njej, za kar smo mu vsi, ki smo ga spremljali na teh poteh, globoko hvaležni. 86 Les/Wood, Vol. 70, No. 1, June 2021 Les/Wood Novice/News In memoriam: Alojz Leb – s t ar os t a slo v ensk eg a lesar s tv a! Mirko Geršak Alojz (uradno Alojzij) Leb se je rodil leta 1929 na Kapli na Kozjaku. Učil se je za mizarja in tesarja. Kot tesar je delal pri graditvi Litostroja. Pot ga je vodila mimo šole na Aškerčevi, vstopil je iz radovednosti in se nato vpisal na novoustanovljeni Lesnoindustrij- ski odsek Tehniške šole za kemijsko, metalurško, rudarsko, lesno in papirno stroko v Ljubljani (šolsko leto 1949/50). Izobraževanje je nadaljeval na Ekonomski fa- kulteti, kjer je leta 1962 diplomiral. Naredil je tudi vse izpite za magistrski študij. Magistriral ni zato, ker je mentor vztrajal, da v nje- govi diplomski nalogi ugotovitve niso v skladu s Kardeljevo socialistično doktrino. Alojz Lep pa jih ni hotel spremeniti. V svoji 41-letni karieri je opravljal različna dela. Bil je mizar, tesar, sušilničar (Kopitarna Sevnica), laborant, vodja oddelka za pospeševanje proizvod- nje (Stol Kamnik), tehnolog, tehnični vodja in v.d. direktorja (Melodija Mengeš). Bil je direktor Biroja za lesno industrijo, direktor organizacijsko-kadrov- skega sektorja v ljubljanski Lesnini, svetnik general- nega direktorja Slovenijalesa in sekretar Splošnega združenja lesarstva Slovenije. Privlačilo ga je tudi pedagoško delo, zato je za hobi poučeval tudi na poklicnih in vajeniških šolah na Duplici, Mengšu in Domžalah. Nekaj časa je honorarno učil tudi na Srednji tehniški šoli v Ljubljani in na višji šoli Lesar- skega oddelka Biotehniške fakultete. Kasneje je na Zavodu za šolstvo RS nadzoroval delovanje poklic- nih lesarskih šol, zastopal Gospodarsko zbornico Slovenije v Svetu za šolstvo RS in sodeloval pri re- formah v šolskem sistemu, še posebej, ko se je uva- jalo t.i. usmerjeno izobraževanje. Opravljal je delo tajnika Posebne izobraževalne skupnosti lesarstva v Sloveniji. Kot sekretar Splošnega združenja lesar- stva Slovenije ima precejšnje zasluge za gradnjo objekta Oddelka za lesarstvo Biotehniške fakultete Univerze v Ljubljani. Bil je izredno plodovit pisec, saj je napisal šte- vilne strokovne članke s področja lesarstva. Zapisal: M. Geršak s pomočjo Zbornika ob 120-letnici Srednje lesarske šole v Ljubljani 87 Les/Wood, Vol. 70, No. 1, June 2021 PR OF . DR . KA T ARINA ČUF AR JE PREJELA JE SENK O V O NA GRADO Z A ŽIVL JENJSK O DEL O PR OF . DR . KA T ARINA ČUF AR RE CEIVED THE JE SENK O LIFETIME ACHIEVEMENT AWARD Marko Petrič 1* , Milan Šernek 1 Vol. 70, No. 1, 87-93 DOI: https://doi.org/10.26614/les-wood.2021.v70n01a10 Izvleček / Abstract Izvleček: Prof. dr. Katarina Čufar je v marcu 2021 prejela Jesenkovo nagrado za življenjsko delo, ki je najprestižnejše priznanje Biotehniške fakultete Univerze v Ljubljani. To je tretja nagrada za Katarino Čufar v kratkem času, saj je konec leta 2020 prejela tudi Zlato plaketo Univerze v Ljubljani in Zoisovo priznanje Republike Slovenije za pomembne znan- stvenoraziskovalne dosežke in uspešno pedagoško delo. Ključne besede: Jesenkova nagrada, življenjsko delo, Biotehniška fakulteta, Univerza v Ljubljani Abstract: In March 2021, Prof. Dr. Katarina Čufar received the Jesenko Lifetime Achievement Award, the most presti- gious prize of the Biotechnical Faculty, University of Ljubljana. This is the third award for Katarina Čufar within just a few months, as at the end of 2020 she also received the Golden Plaque from the University of Ljubljana and the Zois Prize of the Republic of Slovenia for significant scientific achievements and exemplary teaching. Keywords: Jesenko Award, lifetime achievement, Biotechnical Faculty, University of Ljubljana Prof. dr. Katarina Čufar je v marcu 2021 preje- la Jesenkovo nagrado za življenjsko delo, ki je naj- prestižnejša nagrada Biotehniške fakultete Univer- 1 Univerza v Ljubljani, Biotehniška fakulteta, Oddelek za lesar- stvo, Jamnikarjeva 101, 1000 Ljubljana, SLO * e-pošta: marko.petric@bf.uni-lj.si Slika 1. Jesenkovo nagrado za življenjsko delo je nagrajenki prof. dr. Katarini Čufar podelila prva dekanja Biotehniške fakultete prof. dr. Nataša Poklar Ulrih. Figure 1. Presentation of the Jesenko Lifetime Achievement Award to Prof. Dr. Katarina Čufar by the first female Dean of the Biotechnical Faculty, Prof. Dr. Nataša Poklar Ulrih. ze v Ljubljani (Slika 1, 2). To je že tretja nagrada za prof. dr. Katarino Čufar v kratkem času, saj je v letu 2020 prejela tudi Zlato plaketo Univerze v Ljubljani za zgledno znanstvenoraziskovalno in pedagoško delo in Zoisovo priznanje Republike Slovenije za po- membne znanstvenoraziskovalne dosežke (Vrhunci …, 2020; Slaček, 2021). Dosežke, na osnovi katerih 88 Les/Wood, Vol. 70, No. 1, June 2021 Petrič, M., & Šernek, M.: Prof. Dr. Katarina Čufar received the Jesenko Lifetime Achievement Award je nagrajenka prejela Zlato plaketo in Zoisovo pri- znanje, sta v tej reviji predstavila prof. dr. Milan Šernek in prof. dr. Marko Petrič (Šernek & Petrič, 2020), tokrat pa na kratko povzemamo še nekaj poudarkov, ki dopolnjujejo sliko nagrajenkinega življenjskega dela. Prof. dr. Katarina Čufar je redna profesorica na Biotehniški fakulteti Univerze v Ljubljani. Kot Katarina Pleško je bila rojena v Ljubljani, kjer je obiskovala tudi osnovno šolo in gimnazijo Šentvid. Na Oddelku za lesarstvo Biotehniške fakultete je zaključila univerzitetni, magistrski in doktor- ski študij, vse pod mentorstvom prof. dr. dr. h. c. Nika Torellija. Po diplomi se je leta 1981 zaposlila na Biotehniški fakulteti, Oddelku za lesarstvo kot stažistka-raziskovalka ter delovala kot asistentka in nato visokošolska učiteljica, od leta 2008 redna profesorica (Velušček, 2021). Prof. dr. Katarina Čufar se kot vrhunska znan- stvenica na področju lesarstva posveča znanosti o lesu, dendrokronologiji ter vsestranskim raziska- vam lesa kot tkiva živih dreves in materiala v ob- jektih kulturne dediščine in arheologije. Na Bio- tehniški fakulteti je vzpostavila novo znanstveno področje dendrokronologije, s podpodročji den- droarheologije, dendroekologije in dendroklimato- logije. V Katedri za tehnologijo lesa, ki jo vodi, skrbi za razvoj laboratorijev, uvajanje novih metod in nji- hovo uporabo za raziskovalno in strokovno delo. S sodelavci razvija vsestranske raziskave lesa od nje- govega nastanka v drevesu in gozdu preko njego- ve predelave v industriji in uporabe kot naravnega obnovljivega materiala. Sistematično dolgoletno raziskovalno delo je posvetila tudi lesu v kulturni dediščini in arheologiji, pri čemer so najbolj od- mevne in sistematične raziskave prazgodovinskih kolišč na Ljubljanskem barju. Prof. Čufarjeva se tudi na tem področju povezuje s številnimi skupinami na Biotehniški fakulteti in na drugih institucijah (Slika 3, 4). Tako je vzpostavila in razvila sodelovanje z In- štitutom za arheologijo ZRC SAZU, enotami in centri Zavoda za varstvo kulturne dediščine Slovenije ter z muzeji nacionalnega in lokalnega pomena. Nagrajenkino bogato znanstvenoraziskovalno delo se kaže v številnih objavah v vrhunskih medna- rodnih revijah in na konferencah. Je avtorica preko 175 originalnih znanstvenih člankov v najprestižnej- ših znanstvenih revijah, med katerimi so npr. tudi revije Nature Communications, Science Advances, Nature Plants in številne druge z visokimi faktor- ji vpliva (COBISS …, 2021; Orcid …, 2021; RUL …, 2021). Bila je v organizacijskih odborih več kot 10 konferenc (posebej Eurodendro in World Dendro) ter na mednarodnih srečanjih sodelovala s števil- nimi vabljenimi plenarnimi predavanji. Prav tako je članica uredniških odborov več mednarodnih revij. Trenutno deluje predvsem kot zunanja urednica re- vije Tree-Ring Research in je glavna urednica revije Les / Wood, ki je pomembna za razvoj stroke v Slo- veniji in slovenske strokovne terminologije. Prof. dr. Katarina Čufar je izrazito vpeta v med- narodno raziskovalno in akademsko pedagoško okolje. Od leta 2016 je izvoljena članica IAWS (Inter- national Academy of Wood Science), kamor izvolijo vodilne znanstvenike s področja lesarstva in kjer je bila izvoljena kot prva članica iz Slovenije. Pedago- ško je redno gostovala na tujih univerzah, večinoma v okviru programa SOCRATES / ERASMUS. Katedra, kjer deluje, redno gosti uveljavljene raziskovalce in doktorske in dodiplomske študente različnih smeri z vsega sveta. Bila je mentorica več študentom iz tujine in je koordinirala izmenjave študentov z Bio- tehniške fakultete. Prof. dr. Katarina Čufar je izjemna pedago- ginja, ki je v bogati pedagoški karieri poučevala predmete na področju anatomije in zgradbe ter bioloških lastnosti lesa. Med študenti je izjemno priljubljena, zato ne preseneča dejstvo, da je bila mentorica ali somentorica skoraj 100 diplomant- kam in diplomantom, 4 doktorandkam in 1 dok- torandu. Šest njenih diplomantk in diplomantov je prejelo fakultetno Prešernovo nagrado. Bila je članica komisije za zagovor pri več kot 15 dokto- ratih na univerzah Zagreb, Hamburg, Praga, Du- naj, Brno, Innsbruck, Padova, Neapelj, Montpel- lier, Alicante in Zaragoza. Trenutno je mentorica podoktorskemu kandidatu in mladi raziskovalki na doktorskem študiju. Zaradi svojega zglednega pedagoškega dela je prof. Čufar dvakratna prejem- nica pohvale Biotehniške fakultete za najboljšo pe- dagoško delavko na Oddelku za lesarstvo. Snova- la in oblikovala je različne študijske programe in aktivno sodelovala pri bolonjski prenovi študijskih programov lesarstva. Več kot deset let je oddelčna predsednica komisije za dodiplomski študij. Prof. dr. Katarina Čufar je od leta 1999 vodja raziskovalne skupine Tehnologija lesa in Katedre za tehnologijo lesa. Bila je prodekanja za področje 89 Les/Wood, Vol. 70, No. 1, June 2021 Petrič, M., & Šernek, M.: Prof. dr. Katarina Čufar je prejela Jesenkovo nagrado za življenjsko delo lesarstva, trenutno pa je že četrti mandat namest- nica prodekana za pedagoško dejavnost. Več man- datov je bila in še vedno je članica Senata Bioteh- niške fakultete. Je članica Komisije za dodiplomski študij Biotehniške fakultete, kjer je bila 2 mandata predsednica. Vrhunsko raziskovalno in pedagoško delo prof. dr. Katarine Čufar je že bilo prepoznano tako na Univerzi v Ljubljani kot tudi izven nje. Je dobitnica priznanja Biotehniške fakultete ob 50-letnici delo- vanja fakultete (1997), priznanja Biotehniške fa- kultete za zgledno pedagoško in raziskovalno delo (2013) ter priznanja Društva lesarjev Slovenije za prispevek pri povezovanju članov in uspešno vo- denje ALUMNI kluba (2017), ter častnega priznanja Fakultete za gozdarstvo in tehnologijo lesa Univerze Mendel v Brnu, Republika Češka ob 100 letnici usta- novitve fakultete v letu 2019 (Drolc, 2019). V zad- njem obdobju še posebej odmeva, da je v letu 2020 prejela kar dve prestižni nagradi: Zoisovo priznanje in Zlati znak Univerze v Ljubljani. Nagrajenka je izjemno izobražena, razgledana in modra profesorica, ki s svojim delom, vzgledom in vrednotami pozitivno vpliva tako na študente in študentke kakor tudi na sodelavke in sodelavce ter jih s svojo energijo in raziskovalno navdušenostjo spodbuja ter motivira pri delu. Poklic profesori- ce in znanstvenice na univerzi jemlje kot posebno poslanstvo, kar je ključno pri uspešnem izobraže- vanju in vzgoji študentk in študentov ter pri razvoju znanosti in raziskovalne odličnosti. Hkrati je njeno delovanje velik navdih za vse nas, ki imamo privile- gij, da s profesorico tako ali drugače sodelujemo na svojih poteh. Na osnovi navedenega ji je na predlog kolegic in kolegov z Oddelka za lesarstvo in po izboru ko- misije prva dekanja Biotehniške fakultete, prof. dr. Nataša Poklar Ulrih (pred tem so fakulteto vodili le dekani), v marcu 2021 podelila Jesenkovo nagrado za življenjsko delo. Za slovesnost podelitve je bil o nagrajenki posnet tudi kratek film, kjer je na kratko povzela in predstavila svoje raziskovalno delo in se Slika 2. Zahvalni nagovor ob podelitvi. Figure 2. Acknowledgement speech at the award ceremony. 90 Les/Wood, Vol. 70, No. 1, June 2021 Petrič, M., & Šernek, M.: Prof. Dr. Katarina Čufar received the Jesenko Lifetime Achievement Award zahvalila vsem za sodelovanje in podporo (Katarina Čufar - Jesenkova …, 2021), predstavljena pa je bila tudi v Raziskovalnih novicah Univerze v Ljubljani (Z raziskovanjem lesa …, 2021). Nagrajenka se je ob podelitvi zahvalila sode- lavkam in sodelavcem, ki so njene dosežke prepo- znali, jo predlagali in izbrali, predvsem pa vsem, ki so z njo sodelovali in še sodelujejo. V prepričanju, da priznanje za življenjsko delo temelji na rezultatih skupnega dela, se je za sodelovanje in vsestransko podporo posebej zahvalila sodelavkam in sode- lavcem ter kolegicam in kolegom doma in v tujini, vsem ki so jo učili in se od nje učili, ter ožji in širši družini za nenehno spodbudo in podporo. Pouda- rila je, da je hvaležna za uspehe in izkušnje ter da si želi, da bi lahko svoje znanje, povezave in dobre prakse še naprej izmenjevala z vsemi, ki jih veselijo les, znanje o lesu, znanost in pomembne življenjske teme. Vsi, ki smo imeli in še imamo čast sodelovati s prof. dr. Katarino Čufar, niti najmanj ne dvomimo v to, da bomo pri njej vedno dobrodošli, ko bomo po- trebovali znanstveni ali strokovni nasvet s področja njenega delovanja, pa tudi kak bolj splošen nasvet ali mnenje, ki temelji na njenih bogatih znanstveno- raziskovalnih izkušnjah in življenjski modrosti. Pr of . Dr . K a t arina Čuf ar r eceiv ed the Jesenk o Lif e time Achie v emen t Aw ar d Prof. Dr. Katarina Čufar is the recipient of the Jesenko Lifetime Achievement Award 2021, the most prestigious award of the Biotechnical Faculty at the University of Ljubljana. This is the third award she has received in just a few months, as at the end of 2020 she also received the Golden Plaque of the University of Ljubljana and the Zois Prize of the Republic of Slovenia for significant scientific achie- vements as a researcher and teacher (Figure 1, 2). Her research was recently presented in this journal (Šernek & Petrič, 2020), but here we briefly sum- marise some of the highlights that complete the picture of the laureate‘s life work. The laureate was born Katarina Pleško in Ljubl- jana, where she also graduated at elementary and secondary school and completed her studies at the Biotechnical Faculty, Department of Wood Scien- ce and Technology at the Bachelor‘s, Master‘s and PhD levels with theses supervised by Prof. Niko Torelli, Dr. Dr. h. c. In 1981 she was employed as a young researcher at the Biotechnical Faculty and worked as a teaching assistant, then as a university lecturer, becoming a full professor in 2008. Prof. Dr. Katarina Čufar, is recognised as the top scientist in the field of wood research. She is dedicated to wood science, dendrochronology and general research of wood as a tissue of living trees and widely used material in numerous products, including objects of cultural heritage and archae- ology. At the Biotechnical Faculty she introduced the new scientific field of dendrochronology with its subfields of dendroarchaeology, dendroecology and dendroclimatology. At the Chair of Wood Tech- nology, which she heads, she helped to set up the laboratories, introduced new methods and their application for research and applied work. With her team, she researches wood from its origin in the tree, through its selection and processing in in- dustry, to its use as a natural, renewable material. She has also devoted many years to the systematic study of wood in cultural heritage and archaeolo- gy, especially and systematically the prehistoric pile dwellings in the Ljubljansko barje, which existed more than 4,500 years ago. Prof. Čufar cooperates actively with research teams at the Biotechnical Faculty and other institutions in Slovenia and worl- dwide (Figure 3, 4). The rich scientific and research work of the awardee is reflected in numerous publications in top scientific journals, where she has (co-)authored over 175 original scientific articles, among them Nature Communications, Science Advances, Nature Plants and other journals with high impact factors (CO- BISS..., 2021; Orcid..., 2021; RUL..., 2021). She has presented her work at numerous conferences and was a member of the scientific and organisational committees of more than 10 conferences, especially Eurodendro and World Dendro. She has served on the editorial boards of several journals. Currently she serves in the editorial board of Tree-Ring Rese- arch and as the editor-in-chief of Les/Wood, which is important for the development of wood science and of Slovene professional terminology. Prof. Dr. Katarina Čufar is heavily involved in the international research and academic teaching environment. She has regularly been a guest tea- cher and researcher at foreign universities, mainly in the frame of the SOCRATES / ERASMUS program- 91 Les/Wood, Vol. 70, No. 1, June 2021 Petrič, M., & Šernek, M.: Prof. dr. Katarina Čufar je prejela Jesenkovo nagrado za življenjsko delo me. The research group she leads regularly hosts international guests, including renowned resear- chers and graduate and undergraduate students from around the world. She has been a mentor for numerous outgoing and incoming students in the framework of mobility programmes, and coordina- ted studies at foreign universities for students from the Biotechnical Faculty. Slika 3. Življenjsko delo temelji na sodelovanju in medsebojni podpori. Na slikah Prof. Dr. Katarina Čufar s sodelavkami in sodelavci z Oddelka za lesarstvo (a, d), Gozdarskega inštituta Slovenije (b), Inštituta za arheologijo ZRC SAZU (c) in Univerze Zaragoza (b, d). Figure 3. A life time of successful work is based on the good cooperation and mutual support of colleagues on national and international levels. In the pictures Prof. Dr. Katarina Čufar with researchers from the De- partment of Wood Science and Technology (a, d), Slovenian Forestry Institute (b), Institute of Archaeology of the ZRC SAZU (c), and University Zaragoza (b, d). d b c a 92 Les/Wood, Vol. 70, No. 1, June 2021 Prof. Dr. Katarina Čufar is an excellent teacher who has taught courses on wood anatomy, struc- ture and biology during her teaching career. She is extremely popular among students. She has been (co-)supervisor of nearly 100 graduation thes- es and five doctoral dissertations. She has been a member of the defence committees of about 15 PhD theses at universities in Zagreb, Hamburg, Prague, Vienna, Brno, Innsbruck, Padova, Napoli, Montpellier, Alicante and Zaragoza. She is currently mentoring a postdoctoral researcher and a young researcher-doctoral student. Due to her exemplary work, Prof. Čufar has twice received the award for the best teacher of the year in the Department of Wood Science, Biotechnical Faculty. She has desig- ned and developed various study programmes. For more than ten years she has been the department chairperson of the committee for Student Affairs. Since 1999, Prof. Dr. Katarina Čufar has been the head of the Chair of Wood Science. She has been Vice-Dean for Wood Science and Technology and is currently in her fourth term as Deputy Vi- ce-Dean for Teaching Affairs. She has been a mem- ber of the Senate of Biotechnical Faculty for several Slika 4. Nagrajenka s študenti Oddelka za lesarstvo (a, b) in z mednarodnimi udeleženkami in udeleženci srečanja Historical Wood Utilization v Sloveniji. Figure 4. With colleagues and students of the Department of Wood Science and Technology (a, b) and with international participants of the meeting Historical Wood Utilisation in Slovenia. a b Petrič, M., & Šernek, M.: Prof. Dr. Katarina Čufar received the Jesenko Lifetime Achievement Award 93 Les/Wood, Vol. 70, No. 1, June 2021 terms. She is the member of the Undergraduate Studies committee of the Biotechnical Faculty, where she has been chair for two terms. Prof. Dr. Katarina Čufar's outstanding resear- ch and teaching activities have already been re- cognised both inside and outside the University of Ljubljana. Furthermore, she has been an elected member of IAWS (International Academy of Wood Science) since 2016 and a member of the IAWS Board since 2018. She received the Biotechnical Faculty Award on the occasion of the 50th anni- versary of the Faculty (1997), the Biotechnical Fa- culty Award for exemplary teaching and research (2013), the Slovenian Woodworkers‘ Association‘s Award for her contributions to member networ- king and successful leadership of the ALUMNI Club (2017), and the Honorary Award of the Faculty of Forestry and Wood Technology of Mendel Uni- versity of Brno, Czech Republic, on the occasion of the 100th anniversary of the Faculty‘s foundation (2019). As mentioned above, she received two prestigious awards in 2020: the Zois Prize and the Golden Plaque of the University of Ljubljana. Prof. Dr. Katarina Čufar is an exceptionally knowledgeable, insightful and wise professor who positively influences both students and colleagues through her work, example and values, encoura- ging and motivating them in their work with her energy and enthusiasm for research. She sees the profession of professor and scientist at the Uni- versity as a special mission that is crucial for the successful education of students and for the de- velopment of teaching and research excellence. At the same time, her work is a great inspiration to all of us who have had, and continue to have, the privilege of working with her in one way or another on our own journeys. Prof. Dr. Katarina Čufar received the Jesenko Li- fetime Achievement Award in March 2021 from the first female Dean of the Biotechnical Faculty, Prof. Dr. Nataša Poklar Ulrih. The short documentation (in Slovenian) briefly summarised her life‘s work (Katarina Čufar - Jesenkova..., 2021). At the award ceremony, she thanked all those who had recognised her achievements, nominated her and awarded her. She gave special thanks to all her colleagues, teachers, students and her fami- ly, as she believes that the Lifetime Achievement Award is based on the results of cooperation and mutual support. All of us who have the privilege of working with Prof. Dr. Katarina Čufar believe that we will conti- nue to meet with her, whether for professional or general discussions or opinions, or just for fun. VIRI REFERENCES Šernek, M., & Petrič, M. (2020). Prof. dr. Katarina Čufar – prejemni- ca Zoisovega priznanja za pomembne dosežke in Zlate plakete Univerze v Ljubljani - Prof. Dr. Katarina Čufar received the Zois Prize for important achievements and the Golden Plaque of the University of Ljubljana. Les / Wood 69, 2, 117-124. Drolc T. (2019) Prof. dr. Katarina Čufar prejela častno priznanje Fakul- tete za gozdarstvo in tehnologijo lesa Univerze Mendel v Brnu. Les / Wood (Novice), 68, 2, 85. In t erne tni viri W eb sour ces COBISS, Kooperativni online bibliografski sistem Osebna bibliogra- fija Katarina Čufar za obdobje 1981-2021. (9.6.2021). http:// splet02.izum.si/cobiss/bibliography?code=02937 Katarina Čufar - Jesenkova nagrajenka za življenjsko delo (9.6.2021). [Video]. 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Ljubljana, Znanstvenoraziskovalni center SAZU Slovenska akademija zna- nosti in umetnosti, 2013-. Vrhunci slovenske znanosti v luči nagrajencev za izjemne dosežke 2020 - dokumentarni film. (3.6.2021). https://www.rtvslo. si/4d/arhiv/174736192?s=tv Z raziskovanjem lesa lahko proučujemo vpliv klime na rast dreves. Raziskovalne novice, Univerza v Ljubljani (23.04.2021) https:// www.uni-lj.si/raziskovalno_in_razvojno_delo/raziskovalne_ novice/2021040609232512/ Petrič, M., & Šernek, M.: Prof. dr. Katarina Čufar je prejela Jesenkovo nagrado za življenjsko delo 94 Les/Wood, Vol. 70, No. 1, June 2021