298 Nina Logar1, Danijela Klemenčič2, Brigita Tomšič1, Alenka Pavko Čuden1, Barbara Simončič1 'University of Ljubljana, Faculty for Natural Sciences and Engineering, Department of Textiles, Graphic Arts and Design, 1000 Ljubljana, Snežniška 5, Slovenia 2LISCA, d. d., Sevnica, Slovenia Tailoring of a Dual-active Antibacterial Coating for Polylactic Acid Fibres Izdelava protibakterijske apreture z dvojno aktivnostjo za vlakna iz polimlečne kisline Original Scientific Article/Izvirni znanstveni članek Received/Prispelo 09-2016 • Accepted/Sprejeto 10-2016 Abstract The aim of this research was to develop a new, dual-active antibacterial coating for fibres made from polylactic acid and, consequently, to increase the possibility of their use for a variety of technical textiles. The process of finishing was performed on a knitted fabric in three stages by applying silver chloride and 3-(trimethoxysilyl)-propyldimethyltetradecyl ammonium chloride, which provided simultaneous dual antibacterial activity based on the mechanisms of controlled release and bio-barrier formation. The presence of the coating on the fibres was confirmed by scanning electron microscopy with energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectroscopy and a test with bromophenol blue. The results of microbiological tests confirmed the excellent bactericidal activity of the coating, with a 99.99% reduction in the gram-positive bacteria Staphylococcus aureus and the gram-negative bacteria Escherichia coli. Application of the coating reduced the lightness and increased the yellowing of the fibres from polylactic acid, which were disadvantages. Keywords: fibres from polylactic acid, antibacterial coating, dual antimicrobial activity, silver, trialkoxysilane with quaternary ammonium group Izvleček Namen raziskave je bil razviti novo protibakterijsko apreturo z dvojno aktivnostjo na vlaknih iz polimlečne kisline in s tem povečati možnost njihove uporabe za različne tehnične tekstilije. Apreturni postopek je bil izveden na pletivu v treh stopnjah z nanosom srebrovega klorida in 3-(trimetoksisilil)-propildimetiltetradecilamonijevega klorida (Si-QAC), ki sta zagotovila dvojno hkratno protibakterijsko aktivnost po mehanizmih nadzorovane sprostitve in tvorbe bioba-riere. Prisotnost apreture na vlaknih smo potrdili z vrstično elektronsko mikroskopijo z energijsko-disperzijsko spektroskopijo rentgenskih žarkov, masno spektroskopijo z induktivno sklopljeno plazmo ter testom z bromofenol modrim reagentom. Rezultati mikrobioloških testov so potrdili baktericidno delovanje apreture z 99,99-odstotno bakterijsko redukcijo za grampozitivno bakterijsko vrsto Staphylococcus aureus in gramnegativno bakterijsko vrsto Escherichia coli. Nanos apreture je zmanjšal belino in povečal porumenitev vlaken iz PLA, kar je njena pomanjkljivost. Ključne besede: vlakna iz polimlečne kisline, protibakterijska apretura, dvojna protimikrobna aktivnost, srebro, tri-alkoksisilan s kvarterno amonijevo skupino 1 Introduction Fibres from polylactic acid (PLA) constitute an important group of non-toxic, biodegradable and bio- Corresponding author/Korespondencna avtorica: Prof DrSc Barbara Simoncic Tel. +386 1 200 32 31 E-mail: barbara.simoncic@ntf.uni-lj.si compatible polyester textile fibres made from renewable resources. Due to their thermoplasticity, which enables melt spinning, as well as their chemical resistance and good mechanical and barrier Tekstilec, 2016,59(4), 289-297 DOI: 10.14502/Tekstilec2016.59.289-297 41 Tailoring of a Dual-active Antibacterial Coating for Polylactic Acid Fibres properties, PLA fibres have become one of the most promising alternatives for polymer fibres derived from petroleum [1-4]. Their use has already been extended to the field of technical textiles. They are particularly suitable for single-use products, such as sanitary materials, specific medical textiles and textile filters [5, 6]. For this type of textile products, a functional antimicrobial protection provides high added value and is therefore of great technological and economical importance. When preparing the antimicrobial protection for textiles, two groups of antimicrobial agents can generally be used, which vary according to the mechanism of antimicrobial activity [7-9]. The first group comprises antimicrobial agents that act by the mechanism of controlled release. Because most of these agents are bound to the fibres with physical forces, they can be slowly released from the fibres into the surrounding area in the presence of a sufficient amount of moisture where they wholly destroy or inhibit the growth of microorganisms. An important weakness of physically bonded agents is the lowering of their concentration in the fibres due to leaching, eventually falling below the limit of efficiency. The second group includes agents that operate on the principle of bio-barrier formation. In this case, agents are chemically bonded to the textile fibres where they create a biological obstacle for the microorganisms that come in contact with the fibres. Because they do not leach from the fibres, their concentration does not change with time. However, chemical bonding cannot ensure the permanent antimicrobial activity of agents because the settling of dead microorganisms on the bio-barrier can greatly reduce or even eliminate their effectiveness. To eliminate the problems related to the mode of antimicrobial action and thereby to increase the effectiveness of antimicrobial protection, the research work in recent years has been oriented towards finding new approaches for the preparation of antimicrobial coating preparations. One such approach is the tailoring of antimicrobial coatings to obtain dual activity. To this end, combinations have been used, consisting of antimicrobial agents that operate by the mechanism of controlled release and those that form a biological barrier [10-15]. These results have encouraged us to develop a novel, dual-active antimicrobial coating for the textile fibres from PLA, which would also be appropriate for chemical modification of other hydrophobic and low-adhesive fibres. The previous research on the PLA fibres or PLA films has been mostly directed towards the preparation of monocomponent antimicrobial coatings exhibiting either the controlled release of essential oils, antibiotics, silver nanoparticles, or zinc oxide, [16-20], or the formation of the chitosan bio-barrier [21, 22]. For the preparation of an antimicrobial coating with dual antimicrobial activity, we chose silver as a representative agent for the controlled-release mechanism of action, and an organic-inorganic hybrid sol-gel precursor with a quaternary ammonium functional group as a representative agent with the bio-barrier-forming antimicrobial mechanism. Assuming that because of their morphological and chemical structure, PLA fibres have insufficient adhesive ability for silver, we decided to create a silica matrix on the fibre surface to increase their adsorption capacity. In fact, it was found that the silica matrix significantly increases the concentration of the adsorbed silver, resulting in more uniform distribution as well as the reduced size of silver particles [23, 24]. Thus, we have developed a three-stage finishing procedure that includes the following stages: (i) the creation of a silica matrix, (ii) the in situ synthesis of AgCl and (iii) the creation of a bio-barrier. An important objective of our study was to determine the effectiveness of the antibacterial coating as well as to determine the influence of the coating on the colour of PLA fibres, which is an important feature of the product from an aesthetic point of view. 2 Experimental 2.1 Materials We used a double weft knitted fabric in 1 x 1 rib structure made from 100% PLA multifilament (10 capillaries) with linear density of 11.1 dtex, breaking force of 40.7 N and breaking elongation of 31.8%. The PLA multifilament was kindly supplied by Applied Polymer Innovations BV (Emmen, Netherlands). The thickness and weight of the fabrics were 5.2 mm and 428.3 g/m2, respectively. The commercial products 3-(trimethoxysilyl)-pro-pyldimethyltetradecyl ammonium chloride (Si-QAC), namely, Sanitized T 99-19 (Sanitized, Switzerland) and silver chloride (AgCl), prepared from silver nitrate (AgNO3; Sigma-Aldrich) and sodium chloride (NaCl; Carlo Erba) were selected as the antimicrobial agents. To create a silica matrix, we used the commercial Tekstilec, 2016,59(4), 289-297 Tailoring of a Dual-active Antibacterial Coating for Polylactic Acid Fibres 42 product iSys MTX (CHT, Germany), which is a water-borne Si- and Zr-based sol-gel precursor (RV), in combination with Kollasol CDO (CHT, Germany), which is an anti-foaming and wetting agent. All solutions were prepared in bidistilled water. 2.2 Finishing Chemical modification of the PLA samples was accomplished in a three-stage finishing procedure. In the first stage (1S), the samples were immersed in 100.0 g/L RV and 10.0 g/L Kollasol CDO for 10 minutes at room temperature, followed by wringing via squeezing on a two-roll padder with a pick-up of 80 ± 5%, and drying in an oven at a temperature of 110 °C for 5 minutes. After drying, the samples were left for 7 days at standard atmospheric conditions to allow complete crosslinking of iSys MTX. In the second stage (2S), the in situ synthesis of AgCl on the RV-treated samples was performed in the Gyrowash 815 (James Heal, UK) apparatus at room temperature, with occasional stirring, as follows: the specimens were immersed for 10 minutes in a 0.5 mM solution of AgNO3 with a liquor ratio of 50:1 and then subsequently immersed for 10 minutes in a NaCl solution of the same concentration and liquor ratio. The procedure was repeated twice. Then, the samples were washed in bidistilled water to remove the excess chemicals and dried at room temperature. In the third stage (3S), Si-QAC was applied to the samples by the pad-dry-cure method, with full immersion of the samples in a 100 g/L solution of Si-QAC, followed by squeezing on a two-roll padder with a pick-up of 80 ± 5% and drying in an oven at temperature of 110 °C for 5 minutes. After drying, the samples were left for 7 days at standard atmospheric conditions to allow complete crosslinking of iSys MTX. The three-stage finishing procedure is schematically presented in Figure 1. For comparison, the two- and one-step application procedures were also performed with the same antimicrobial agents under the same conditions as in the three-stage procedure. Accordingly, in the two-step procedure, RV was applied as in 1S, followed by the application of AgCl as in 2S. In the one-stage procedure, AgCl and Si-QAC were applied to the PLA samples as in 2S and 3S, respectively. The sample codes in relation to the application procedures are summarized in Table 1. Figure 1: Schematic presentation of the three-stage procedure of antimicrobial finishing Table 1: Application procedures, sample codes and sol concentrations Finishing procedure Sample code Sol concentration No treatment PLA-N / Three-stage PLA-RV-Ag-SiQAC (1S): 100.0 g/L RV, 10.0 g/L Kollasol CDO (2S): 0.50 mM AgNO3 + 0.50 mM NaCl (3S): 100.0 g/L Si-QAC Two-stage PLA-RV-Ag (1S): 100.0 g/L RV, 10.0 g/L Kollasol CDO (2S): 0.50 mM AgNO3 + 0.50 mM NaCl One-stage PLA-Ag (2S): 0.50 mM AgNO3 + 0.50 mM NaCl PLA-SiQAC (3S): 100.0 g/L Si-QAC Tekstilec, 2016,59(4), 289-297 43 Tailoring of a Dual-active Antibacterial Coating for Polylactic Acid Fibres 2.3 Analytical methods Fourier transform infrared spectroscopy (FT-IR) FT-IR spectra were obtained on the Spectrum GX (Perkin - Elmer, UK) spectrophotometer equipped with a diamond cell. The spectra were recorded over the range of 4,000-600 cm-1, with a resolution of 4 cm-1 and an average set of 32 spectra per sample. Before the measurements, the samples were dried to a constant weight. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) SEM was conducted on the Jeol JMS 6060LV and Jeol JSM 5610 microscopes, equipped with an Oxford-Link ISIS 300 EDS system with an ultra-thin window Si(Li) detector. Prior to performing the SEM and EDS analyses, we applied a 20-nm-thick carbon layer to each fabric sample to ensure sufficient electrical conductivity and to avoid charging effects. SEM micrographs were recorded using the secondary electron (SE) and backscattered electron (BSE) imaging modes. The BSE compositional contrast (Z-contrast) was applied to accentuate the differences between the added particles and the fibre matrix. Two parallel assessments were performed for each coated fabric sample, and the corresponding atomic concentration was reported as the mean value. Inductively coupled plasma mass spectroscopy (ICP-MS) ICP-MS was performed on the Perkin Elmer SCI-ED Elan DRC spectrophotometer. The fabric samples (0.5 g) were prepared in a Milestone microwave system by acid decomposition, using 65% HNO3 and 30% H2O2. Three measurements were taken for each sample, and the Ag concentrations were reported as the mean values. Test with bromophenol blue (BPB) reagent Qualitative determinations of Si-QAC on the coated samples were performed by using the BPB reagent, which is an alkaline dilution of the sodium salt 3'-3"-5'-5"-tetrabromophenolsulfonphtalein. The test was based on the formation of a complex between the BPB reagent anion and the quaternary ammonium group of Si-QAC on the surface of the fabric. Due to the formation of the complex, the samples were coloured blue. For the BPB test, 1 g of sample was immersed in 50 mL of 0.005% BPB reagent diluted in water and stirred vigorously for 20 min. The samples were subsequently removed from the BPB solution, thoroughly rinsed with cold tap water and dried at room temperature. The intensity of the blue coloration on the samples was assessed by the reflectance, R, measurements of the samples on the Datacolor Spectraflash SF 600 spectrophotometer, using D 65/10° light. Before these measurements, the samples were conditioned at relative humidity of 65 ± 2% and temperature of 20 ± 1 °C for 24 hours. For each sample, ten measurements of the R value were obtained, and the corresponding K/S values were calculated according to the Kubelka-Munk equation: K = (1 - R)2 S 2R (1), where K/S is the ratio of the coefficient of light absorption (K) to the coefficient of light scattering (S), and R the reflectance at the maximum absorption wavelength, determined at 610 nm. Afterwards, the mean K/S value was determined. Antibacterial activity The antibacterial activity was examined by a modified AATCC standard method 100-1999 for the bacteria Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 6538). In aseptic conditions, the sample was placed into a 250-mL container and inoculated with 400 ^L of a nutrient broth culture containing 1-2 x 105 colony-forming units of bacteria. After incubation at 37 °C for 24 hours, the bacteria were eluted from the swatches by shaking in 100 mL of neutralizing solution for 1 minute. After preparing serial dilutions in sterilised water, the suspensions were plated on nutrient agar and incubated at 37 °C for 24 hours. The number of bacteria was counted, and the reduction of bacteria, R, was calculated as follows: R = (B - A) B 100 (%) (2), where A is the number of bacteria recovered from the inoculated swatch of the cotton sample in the jar incubated for the desired contact period (24 hours), and B is the number of bacteria recovered from the inoculated swatch of the cotton sample in the jar immediately after inoculation (at "0" contact time). For each fabric sample, four parallel assessments were performed and the mean value was determined. Tekstilec, 2016,59(4), 289-297 Tailoring of a Dual-active Antibacterial Coating for Polylactic Acid Fibres 44 Whiteness and yellowing index The whiteness of the samples was determined on the basis of the measurements of the CIE colour values using the Spectraflash 600 PLUS-CT spectrophotometer (Datacolor, Switzerland). The measurements were performed at the following conditions: 20 mm size of the measuring aperture, standard light D65 and T = 6500 K, using D65/10° with an excluded specular as an observer. The whiteness, W10, was calculated from the following equation: W10 = Y10 + 800(0.3138 - x10) + 1700(0.3310 - y10) (3), where Y10 is the standardized colour value of the sample, and x10 and y10 are the standardized colour portions of the sample. The yellowing index, YI, was calculated from the following equation: YJ = 100(1.3013 X - 1.1498 Z) Y (4), characteristic of amide II, which shows a strong absorption in the spectral region between 1570 and 1515 cm-1 [25]. In this spectral region, high intensity absorption peaks can be detected in the spectrum of RV, which suggests the presence of this group in the structure of RV. However, because RV is a commercial product, its exact structure is not evaluable by the producer. In the spectrum of the PLA-RV-Ag-SiQAC sample, the absorption peaks at the wavelengths 1129, 1083 and 1043 cm-1, which are characteristic of the asymmetric stretching vibration of the Si-O-Si group in the polysi-loxane network [25, 26], are overlapped by the peaks characteristic of the fingerprint of PLA. Silver could also not be detected in this spectrum. where X, Y and Z represent the values in the CIE colour space. Before these measurements, the samples were conditioned at relative humidity of 65 ± 2% and temperature of 20 ± 1 °C for 24 hours. For each sample, ten measurements of Y10 and YI were obtained and the mean values were calculated. 3 Results and discussion The ATR spectra of PLA-N and PLA-RV-Ag-SiQAC samples (Figure 2) show that the application of the antimicrobial coating caused chemical changes in the PLA fibres, resulting in the increase of the intensity of the absorption peaks at wave-numbers 2927 and 2856 cm-1, which are characteristic of asymmetric and symmetric stretching of the C-H bond in aliphatic alkyl groups [25]. This can be attributed to the tetradecyl groups in the structure of the Si-QAC film. Furthermore, the application of the coating caused a reduction in the intensity of the absorption peak at the wavenumber of 1759 cm-1, which is characteristic of the C=O stretch of ester groups in the macromolecules of PLA. This result indicates that the antimicrobial polymeric film coated the PLA fibres, which resulted in partial shading of the peaks characteristic of the fibre structure. Furthermore, a broad absorption peak appeared at the wavelength of 1565 cm-1 in the spectrum of the finished PLA fibres, which is 4000 3500 3000 1800 1600 1400 1200 1000 800 600 Wavenumber [cm-1] Figure 2: ATR spectra of PLA-N (a) and PLA-RV-Ag-SiQAC (b) samples Therefore, to prove the presence of Si-QAC in the coating, the BPB test was used, and the results are presented in Figure 3. Blue colour in the samples indicated the binding of the BPB anions to the cation-ic nitrogen atoms of the quaternary ammonium groups of Si-QAC via electrostatic attractive interactions. Accordingly, the K/S values, determined for the samples after shaking in the solution of BPB, highly increased from 0.2 for the PLA-N sample without Si-QAC to 10.2 and 11.4 for the PLA-SiQAC and PLA-RV-Ag-SiQAC samples, respectively. The presence of the antimicrobial coating on the PLA fibres was also confirmed by the SEM and EDS analysis. The SEM/BSE images of the PLA-N, PLA-Ag, PLA-RV-Ag and PLA-RV-Ag-SiQAC samples (Figure 4) revealed that spherical silver particles, visible as bright spots, were formed over the entire surface of the fibres in the in situ Tekstilec, 2016,59(4), 289-297 294 Tailoring of a Dual-active Antibacterial Coating for Polylactic Acid Fibres Figure 3: Photos of PLA samples after shaking in the solution of the BPB reagent synthesis of AgCl (Figure 4b). The presence of AgCl was also confirmed by the EDS analysis, from the peaks of Ag-La and Cl-Ka (Table 2). The application of RV and Si-QAC greatly increased the roughness of the fibres, confirming the forma- tion of the polymer coating from the sol-gel precursors (Figures 4 c and d). In these images, the presence of AgCl is not clearly perceptible. In addition, the Si-Ka peaks and Zr-La belong to the RV and Si-QAC silica matrix, while the C-Ka and Figure 4: SEM/EDS images of PLA-N (a), PLA-Ag (b), PLA-RV-Ag (c) and PLA-RV-Ag-SiQAC (d) samples Table 2: Elemental composition of the coated samples obtained by EDS analysis Sample code Atomic concentration of element [%] Ag-La Cl-Ka Si-Ka Zr-La Na-Ka C-Ka O-Ka PLA-Ag 0.275 7.988 0.000 0.000 2.936 74.000 1.145 PLA-RV-Ag 1.340 0.416 1.556 2.159 0.000 80.430 16.240 PLA-RV-Ag-SiQAC 0.636 3.649 2.595 1.919 0.000 83.004 8.198 Tekstilec, 2016,59(4), 289-297 Tailoring of a Dual-active Antibacterial Coating for Polylactic Acid Fibres 295 Table 3: Concentration of silver, cAg, on the finished samples and the bacterial reduction, R, against bacteria E. coli in S. aureus Sample code cAg [mg/kg] R [%] E. coli S. aureus PLA-N 0.0 - - PLA-Ag 9.2 ± 1.8 50.5 59.2 PLA-SiQAC 0.0 67.5 78.1 PLA-RV-Ag 140 ± 28 100 100 PLA-RV-Ag-SiQAC 53 ± 11 100 100 O-Ka peaks belong to the silicon matrix as well as to the PLA fibres. The peak for nitrogen in the structure of Si-QAC could not be determined on a PLA-RV-Ag-SiQAC sample because it was overshadowed by the much more intense peaks of carbon and oxygen. Table 3 shows that different samples absorbed different amounts of silver, namely: PLA-Ag = 9 6 3 0 15,12 16,58 10,23 3,23 7,84 1SE PLA-N PLA-RV PLA- PLA-RV- PLA-RV-SiQAC Ag Ag-SiQAC Sample Figure 6: Yellowing index, YI, of untreated and finished samples 4 Conclusion In this study, we have successfully developed a new three-stage procedure to tailor a dual-active antimicrobial finishing for the PLA fibres, using AgCl and Si-QAC. The procedure included the following steps: - the application of RV with the aim to create a silica matrix on the surface of the fibres, which was important for increasing the adhesive ability of the fibres; - the in situ synthesis of silver in a silica matrix with two sequential immersions of the PLA samples in the solutions of AgNO3 and NaCl to create an antimicrobial coating with physically incorporated silver particles, which can be released into the environment in a controlled manner, acting as a poison for microorganisms; - the application of Si-QAC with quaternary ammonium groups with the aim to create a polymer film on the fibre surface, which could act as a biological barrier and destroy microorganisms that come in contact with the fibres. The mode of preparation of the coating allows its application to other hydrophobic fibres, such as polyethylene tereph-thalate, polypropylene, and polyamide fibres. Acknowledgements The study was financially supported by the Research Agency RS under the programme P2-0213 Textiles and Ecology, and the Research Infrastructure Centre RIC UL NTF. The authors thank Andrej Vilar for his help in preparing the knitted fabric. References 1. FARRINGTON, D. W., LUNT, J., DAVIES, S., BLACKBURN, R. S. Poly(lactic acid) fibres, In: Biodegradable and sustainable fibres. Edited by Blackburn, R. S. Cambrige, England : Woodhead Publishing, ISBN 1-85573-916-x, 2005, pp. 389-440. 2. GUPTA, Bhuvanesh, REVAGADEA, Nilesh, HILBORN, Jons. Poly(lactic acid) fiber: an overview. Progress in Polymer Science, 2007, 32, 455482, doi: 10.1016/j.progpolymsci.2007.01.005. 3. RIJAVEC, Tatjana, BUKOSEK, Vili. Novel fibres for the 21st century. Tekstilec, 2009, 52(10/12), 312-327. 4. RASAL, Rahul M., JANORKAR, Amol V., HIRT, Douglas E. Poly(lactic acid) modifications. Progress in Polymer Science, 2010, 35(3), 338-356, doi: 10.1016/j.progpolymsci.2009.12.003. 5. GOETZENDORF-GRABOWSKA, Bogna, PO-LUS, Zenon, KIWALA, Magdalena, KARASZE-WSKA, Agnieszka, KAMINSKA, Irena, MACZ-KA, Iwona. Antibacterial air filter nonwovens modified by poly(lactide) microspheres containing triclosan. Fibres and Textiles in Eastern Europe, 2015, 23(1), 114-119. 6. URBANIAK-DOMAGALA, Wieslawa, KRUCIN-SKA, Izabella, WRZOSEK, Henryk, KOMISARC-ZYK, Agnieszka, CHRZANOWSKA, Olga. Plasma modification of polylactide nonwovens for dressing and sanitary applications. Textile Research Journal, 2016, 86(1), 72-85, doi: 10.1177/ 0040517515581586. 7. GAO, Yuan, CRANSTON, Robin. Recent advances in antimicrobial treatments of textiles. Textile Research Journal, 2008, 78(1), 60-72, doi: 10.1177/0040517507082332. 8. VIGO, Tyrone L. Protection of textiles from biological attack. In Functional finishes, Part A, Chemical processing of fibres and fabrics. Handbook of fiber science and tehnology. Vol. II. Edited by Menachem SELOand Stephen B. SELLO., pp. 367-426. New York, Basel : Marcel Dekker, 1983. 9. ABIDI, Noureddine, KIEKENS, Paul. Chemical functionalisation of cotton fabric to impart multifunctional properties. Tekstilec, 2016, 59(2), 156-161, doi: 10.14502/tekstilec2016.59.156-161, doi: 10.14502/tekstilec2016.59.156-161. 10. LI, Zhi, LEE, Daeyeon, SHENG, Xiaoxia, COHEN, Robert E., RUBNER, Michael F. Two-level antibacterial coating with both release-killing Tekstilec, 2016,59(4), 289-297 Tailoring of a Dual-active Antibacterial Coating for Polylactic Acid Fibres 297 and contact killing capabilities. Langmuir, 2006, 22, 9820-9823, doi: 10.1021/la0622166. 11. MOHAMED, Riham R., SABAA Magdy W. Synthesis and characterization of antimicrobial crosslinked carboxymethyl chitosan nanoparti-cles loaded with silver. International Journal of Biological Macromolecules, 2014, 69, 95-99, doi: 10.1016/j.ijbiomac.2014.05.025. 12. POUSHPI, D., NARVI, S. S., TEWARI, R. P. Coating made from Pseudotsuga menziesii phy-tosynthesized silver nanoparticles is efficient against Staphylococcus aureus biofilm formation. Nano LIFE, 2015, 5, 1540006, doi: 10.1142/ S1793984415400061. 13. WANG, X. H., DU, Y. M., FAN, L. H., LIU H., HU, Y. Chitosan-metal complexes as antimicrobial agent: synthesis, characterization and structure-activity study. Polymer Bulletin, 2015, 55, 105-113, doi: 10.1007/s00289-005-0414-1. 14. El SHAFEI, A., ABOU-OKEIL, A. ZnO/car-boxymethyl chitosan bionano-composite to impart antibacterial and UV protection for cotton fabric. Carbohydrate Polymers, 2011, 83, 920925, doi: 10.1016/j.carbpol.2010.08.083. 15. KAUR, Pawan, THAKUR, Rajesh, BARNELA, Manju, CHOPRA, Meenu, MANUJA, Anju, CHAUDHURY, Ashok. Synthesis, characterization and in vitro evaluation of cytotoxicity and antimicrobial activity of chitosan-metal nanocomposites. Journal of Chemical Technology and Biotechnology, 2015, 90, 867-873, doi: 10.1002/jctb.4383. 16. WEN, Peng, ZHU, Ding-He: FENG, Kun, LIU, Fang-Jun, LOU, Wen-Yong, LI, Ning, ZONG, Min-Hua, WU, Hong. Fabrication of electro-spun polylactic acid nanofilm incorporating cinnamon essential oil/beta-cyclodextrin inclusion complex for antimicrobial packaging. Food Chemistry, 2016, 196, 996-1004, 10.1016/j. foodchem.2015.10.043. 17. EREM, A. Dural, OZCAN, G., EREM, H.H., SKRIFVARS, M. Antimicrobial activity of poly (L-lactide acid)/silver nanocomposite fibers. Textile Research Journal, 2013, 83(20), 21112117, doi: 10.1177/0040517513481875. 18. CHITRATTHA, Sasiprapa, PHAECHAMUD, Thawatchai. Porous poly(DL-lactic acid) matrix film with antimicrobial activities for wound dressing application. Materials Science and Engineering C-Materials for Biological Applications, 2016, 58, 1122-1130, doi: 10.1016/j.msec.2015. 09.083. 19. DE SILVA, Rangika T., PASBAKHSH, Pooria, MAE, Lee Sui, KIT, Aw Yoong. ZnO deposited/ encapsulated halloysite-poly (lactic acid) (PLA) nanocomposites for high performance packaging films with improved mechanical and antimicrobial properties. Applied Clay Science, 2015, 111, 10-20, doi: 10.1016/j.clay.2015.03.024. 20. BILBAO-SAINZ, Cristina, CHIOU, Bor-Sen, VALENZUELA-MEDINA, Diana, DU, Wen-Xi-an, GREGORSKI, Kay S., WILLIAMS, Tina G., WOOD, Delilah F., GLENN, Greg M., ORTS, William J. Solution blow spun poly(lactic acid)/ hydroxypropyl methylcellulose nanofibers with antimicrobial properties. European Polymer Journal, 2014, 54, 1-10, doi: 10.1016/j.eurpol-ymj. 2014.02.004. 21. STOLERU, Elena, DUMITRIU, Raluca Petrone-la, MUNTEANU, Bogdanel Silvestru, ZAHA-RESCU, Traian, TANASE, Elisabeta Elena, MI-TELUT, Amalia, AILIESEI, Gabriela-Liliana, VASILE, Cornelia. Novel procedure to enhance PLA surface properties by chitosan irreversible immobilization. Applied Surface Science, 2016, 367, 407-417, doi: 10.1016/j.apsusc.2016.01.200. 22. ZHANG, C. Y., ZHANG, C. L., WANG, J. F., LU, C. H., ZHUANG, Z., WANG, X. P., FANG, Q. F. Fabrication and in Vitro investigation of nanohy-droxyapatite, chitosan, poly(L-lactic acid) ternary biocomposite. Journal of Applied Polymer Science, 2013, 127(3), 2152-2159, doi: 10.1002/app.37795. 23. JEON, H. J., YI, S. C., OH, S. G. Preparation and antibacterial effects of Ag-SiO2 thin films by solgel method. Biomaterials, 2003, 24, 4921-4928, doi: 10.1016/s0142-9612(03)00415-0. 24. MAHLTIG, B., FIEDLER, D., FISCHER, A. Antimicrobial coatings on textile-modifications of sol-gel layers with organic and inorganic bio-cides. Journal of Sol-Gel Science and Technologies, 2010, 55, 269-277, doi: 10.1007/s10971-010-2245-2. 25. SOCRATES, George. Infrared and Raman characteristic group frequencies. New York : John Wiley & Sons, 2001. 26. JERMAN, Ivan, SURCA, Angelja Kjara, KOŽELJ, Matjaž, ŠVEGL, Franc, OREL, Boris. Influence of amino functionalised POSS additive on the corrosion properties of(3-glycidoxypro-pyl)trimethoxysilane coatings on AA 2024 alloy. Progress in Organic Coatings, 2011, 72(3), 334342, doi: 10.1016/j.porgcoat.2011.05.005. Tekstilec, 2016,59(4), 289-297