GLASILO SLOVENSKIH TEKSTILCEV • SLOVENE JOURNAL FOR TEXTILE AND CLOTHING TECHNOLOGY, DESIGN AND MARKETING tekstilec 2/2020-vol. 63-77-162 ISSN 0351-3386 (tiskano/printed) ISSN 2350 - 3696 (elektronsko/onllne) UDK 677 + 687 (05) http://www.tekstilec.si Časopisni svet/Publishing Council Barbara Simončič, predsednica/President Katja Burger, Univerza v Ljubljani Silvo Hribernik, Univerza v Mariboru Tatjana Kreže, Univerza v Mariboru Gašper Lesjak, Predilnica Litija, d. o. o. Nataša Peršuh, Univerza v Ljubljani Petra Prebil Bašin, Gospodarska zbornica Slovenije Melita Rebič, Odeja, d. o. o. Tatjana Rijavec, Univerza v Ljubljani Daniela Zavec, ZITTS Helena Zidarič Kožar, Inplet pletiva d. o. o. Vera Žlabravec, Predilnica Litija, d. o. o. 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VOLUME 63 • TEKSTILEC 2 • 2020 ISSN 0351-3386 (tiskano/printed) I6KSIII6C UDK 677 + 687 (05) SCIENTIFIC ARTICLES/ Znanstveni članki 80 Ekrem Gulsevincler, Mustafa Resit Usal, Demet Yilmaz Modular Jet-Ring Yarn Spinning System Modularni sistem za izdelavo curkovne prstanske preje 94 Akhtarul Islam Amjad, Rajiv Kumar Evaluation of Mechanical and Physical Characteristics of Eco blended Melange Yarns Vrednotenje mehanskih in fizikalnih lastnosti ekomelanžne preje 104 Tomasz Blachowicz, Tobias Böhm, Jacek Grzybowski, Krzysztof Domino, Andrea Ehrmann Analysis of AFM images of Nanofibre Mats for Automated Processing Analiza slik AFM nanovlaknatih kopren za samodejno obdelavo 113 Olena Kyzymchuk, Liudmyla Melnyk, Svitlana Arabuli Study of Elastic Warp Knitted Bands: Production and Properties Študija elastičnih snutkovnih pletenih trakov: izdelava in lastnosti 124 Nuredin Muhammed, Nalankilli Govindan Chemical Modification of Cotton Cellulose by Carbamation with Urea and its Dyeability with Reactive Dyes without the use of Electrolytes Kemična modifikacija bombaža s karbamiranjem s sečnino in njegova obarvljivost z reaktivnimi barvili brez uporabe elektrolita 138 Dinesh Bhatia, S.K. Sinha Thermo-physiological Properties of Structurally Modifi ed Wool/ Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics Lastnosti toplotne udobnosti ročno stkanih tkanin z votkom iz strukturno modifi cirane preje iz mešanice volna/poliester, izdelanim strojno in ročno 151 Ivana Bonic, Andrea Palac, Ana Sutlovic, Branka Vojnovic, Mario Cetina Removal of Reactive Black 5 dye from Aqueous Media using Powdered Activated Carbon - Kinetics and Mechanisms Odstranjevanje barvila Reactive Black 5 iz vodnih medijev z uporabo praškastega aktivnega oglja - kinetika in mehanizmi 80 Ekrem Gulsevincler1, Mustafa Resit Usal2, Demet Yilmaz3 1 Kastamonu University, Electric and Energy Department, Abana Sabahat Mesut Yilmaz Vocational School, 37970 Kastamonu, Turkey 2 Suleyman Demirel University, Department of Mechanical Engineering, Faculty of Engineering, 32260 Isparta, Turkey 3 Suleyman Demirel University, Department of Textile Engineering, Faculty of Engineering, 32260 Isparta, Turkey Modular Jet-Ring Yarn Spinning System Modularni sistem za izdelavo curkovne prstanske preje Original scientific article/Izvirni znanstveni članek Received/Prispelo 2-2020 • Accepted/Sprejeto 4-2020 Abstract In this study, a modular nozzle design was developed in which the twist chamber diameter, injector diameter, injector angle and the number of injectors of the nozzle can be optionally changed without the need of conventional manufacturing methods. The developed modular nozzle was compared with conventional nozzles taking into account both experimental and numerical analysis results. Experimental performance tests were conducted on the yarn quality achieved using air twist, which is the subject of the application of the nozzle. In the experimental study, conventional nozzles with the same structural configurations were produced to determine modular nozzle performance. In all jet-ring yarn productions, the air pressure was set at two different values: 75 kPa and 125 kPa (gauge). Yarn hairiness, irregularity and imperfection tests were carried out using an Uster Tester 3. Tensile properties (percentage of elongation and tenacity measured as cN/tex) tests were carried out using an Uster Tensorapid. In the numerical analysis, an Ansys CFX 18.0 computational fluid dynamics program was used for both conventional nozzle and modular nozzle configurations. All parametric study configurations were set separately using an SST turbulence model. Comparing the flow parameters of yarn hairiness (CFD analysis), it was found that increasing vorticity or helicity real eigen values reduced yarn hairiness. Keywords SST, swirling flow, swirl number, jet-ring, nozzle-ring, air nozzle Izvleček V študiji je bila razvita modularno zasnovana šoba za curkovno predenje prstanske preje, v kateri se lahko poljubno spreminjajo premer vijne komore, premer in kot injektorja. Število injektorjev v šobi se lahko spreminja brez potrebe po običajnih proizvodnih metodah. Razvita modularna šoba je primerjana z običajnimi šobami z upoštevanjem rezultatov eksperimentalne in numerične analize. Izvedeni so bili eksperimentalni preizkusi kakovosti preje, vitih z uporabo modularno zasnovane šobe. Za določitev uporabnosti modularne šobe so bile izdelane običajne šobe z enakimi strukturnimi konfiguracijami. V vseh primerih izdelave curkovne prstanske preje sta bili uporabljeni dve vrednosti zračnega tlaka, in sicer 75 kPa ter 125 kPa. Na Uster Testerju 3 so bile izvedene meritve kosmatosti in neenakomernosti preje ter količine napak v preji. Natezne lastnosti (pretržna napetost in pretržni raztezek) so bile določene na aparatu Uster Tensorapid. Za numerično analizo običajne konfiguracije šobe in modularne šobe je bil uporabljen računalniški program za računalniško dinamiko tekočin, Ansys CFX 18.0. Vse študije konfiguracijskih parametrov so bile izvedene ločeno z uporabo SST turbulentnega modela. Z analizo CFD, ki omogoča računalniško primerjavo parametrov dinamike tekočin, je bilo ugotovljeno, da povečanje vrtinčenja ali vijačenja realno zmanjša vrednosti kosmatost preje. Ključne besede: SST, vrtinčasti tok, vrtinčna številka, curek-prstan, obroč šobe, zračna šoba Corresponding author/Korespondenčna avtorica Dr. Ekrem Gulsevincler E-mail: egulsevincler@kastamonu.edu.tr ORCID: 0000-0002-4787-6275 Tekstilec, 2020, 63(2), 80-93 DOI: 10.14502/Tekstilec2020.63.80-93 Modular Jet-Ring Yarn Spinning System S1 1 Introduction Swirling flows are found in many areas of our lives and engineering. 'Swirling flow' [1] is defined as the rotating helical flow and can be seen in natural events, e.g. tornadoes, hurricanes, water vents, etc. Another example of swirling flows are the air-jet nozzles used in the textile industry on spinning machines. Swirling air flow is produced in an air nozzle depending on nozzle geometry and compressed air [2, 3]. The helical rotating flow in turbulent jets results in an increase in jet growth, drift speed and the decay rate of the jet. These effects also increase when helical rotation density increases. Swirling flows depend on different parameters, most of which were formulated and found as a result of studies. The most important parameter is the swirling number (Sri). The integral definition of the swirling number is expressed as the ratio of the axial flux of the angular momentum to the axial momentum flux and radius multiplication [1]. s Ax Angular Momentum _ GAng R ■ Axial Momentum RG Zo2n JR uzu m id) M m Figure 13: Conventional nozzle YZ plane velocity CFD result: a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° Figure 14: Conventional nozzle YZ plane velocity w (z axis) CFD result: a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° Tekstilec, 2020, 63(2), S0-93 SS Modular Jet-Ring Yarn Spinning System S1 Figure 15: Conventional nozzle YZ plane vorticity (velocity curl) CFD result: a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° Figure 16: Conventional nozzle YZ plane vorticity (velocity curl) CFD result (flow trajectories): a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° Figure 17: Conventional nozzle YZ plane helicity real eigen CFD result: a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° fa) lb) ft) Id) (e) (f) Figure 19: Modular nozzle YZ plane total pressure CFD result: a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° Figure 18: Conventional nozzle YZ plane helicity real eigen CFD result (flow trajectories): a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° fb) It) Id) (,) ft Figure 20: Modular nozzle YZ plane velocity CFD result: a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° Tekstilec, 2020, 63(2), S0-93 Modular Jet-Ring Yarn Spinning System S1 Figure 22: Modular nozzle YZ plane vorticity (velocity curl) CFD result: a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° Figure 23: Modular nozzle YZ plane vorticity (velocity curl) CFD result: (flow trajectories) a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° Figure 21: Modular nozzle YZ plane velocity w (z axis) CFD result: a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° Figure 24: Modular nozzle YZ plane helicity real eigen CFD result: a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° Tekstilec, 2020, 63(2), S0-93 90 Modular Jet-Ring Yarn Spinning System S1 the injector air inlet mass flow value was achieved from the fibre inlets of conventional nozzles. In modular nozzles, this coefficient was -0.05. In other words, in modular nozzles of the same structural configurations, air cannot be sucked in from the fibre inlet. Conversely, air is released the outside from this opening. According to the principle of mass conservation, the mass flow rates of the fiber and the air outlet are the difference between the mass flow of air from the injectors and the mass absorbed from the fibers, if any, or the amount of air ejected from the fiber inlet. In the conventional nozzle fiber inlet mass flow value is positive. In other words, air is discharged through this opening. In the modular nozzle, fiber inlet mass flow value is a negative. In this case, we understand that there is air suction from the environment to the twisting chamber. The air flow velocity value of the modular nozzle configurations and the velocity-dependent z-axis velocity, Reynolds number, vorticity and helical real eigen values were approximately one third of that of conventional nozzles. Although the swirl numbers (Sn) of the modular nozzle configurations given in Table 6 are lower than the conventional nozzles, the geometric swirl numbers (Sg) are relatively high compared to the conventional nozzles (Table 5). According to the calculations made in the plane in which the injectors are opened to the twisting chamber in the comparative structural configurations, the total pressure values of conventional nozzles are Table 5: CFD analysis results of conventional nozzles with twisting chamber diameter < = 3 mm, injector diameter < = 0.5 mm and three circumferential injectors (225 kPa absolute) Injector angle (degree) 20 25 30 35 40 Injector air inlet mass flow rate (kg/s) 0.000336 0.000343 0.000349 0.000358 0.000376 Fibre inlet mass flow rate (kg/s) 0.000217 0.000241 0.000267 0.000301 0.000332 Fibre and air outlet mass flow rate (kg/s) -0.000553 -0.000584 -0.000616 -0.000659 -0.000708 Swirl number (Sn) 3.38 3.175 2.908 2.626 2.308 Geometric swirl number (Sg) 4.166 3.746 3.333 2.903 2.597 Total pressure (Pa) 44161 42443 41943 41793 41972 Flow pressure (Pa) 6375 7625 8576 9075 9399 Reynolds number (Re) 39820 39047 39543 40456 41238 Velocity (m/s) 202.9 201.1 203.7 208.4 212.4 Velocity w (fibre axis) (m/s) 64.7 68.6 72.5 77.6 84.4 Vorticity 708257 687890 675408 675006 682107 Helicity real eigen 599981 574558 541261 537100 522006 Tekstilec, 2020, 63(2), S0-93 Figure 25: Modular nozzle YZ plane helicity real eigen CFD result (flow trajectories): a) colour scale, b) injector angle 20°, c) injector angle 25°, d) injector angle 30°, e) injector angle 35°, f) injector angle 40° Considering injector air inlet mass flow values, the modular nozzles with the same structural configurations and analysed at the same pressure (225 kPa absolute) consumed an average of 11.5% more air than conventional nozzles. Considering fibre inlet mass flow values, an average suction in the fibre inlet opening of 0.77 times (minimum 0.65 - maximum 0.88) Modular Jet-Ring Yarn Spinning System S1 Table 6: CFD analysis results of modular nozzle's with twisting chamber diameter ^ = 3 mm, injector diameter ^ = 0.5 mm and three circumferential injectors (225 kPa absolute) Injector angle (°) 20 25 30 35 40 Injector air inlet mass flow rate (kg/s) 0.000375 0.000394 0.000397 0.000397 0.000399 Fibre inlet mass flow rate (kg/s) -0.000049 -0.000018 -0.000011 -0.000024 0.000010 Fibre and air outlet mass flow rate (kg/s) -0.000326 -0.000375 -0.000386 -0.000374 -0.000410 Swirl number (Sn) 0.433 0.395 0.306 0.343 0.348 Geometric swirl number (Sg) 14.92 11.968 10.972 11.114 8.71 Total pressure (Pa) -493 1026 -428 -650 143 Flow pressure (Pa) -1036 72 -1934 -2539 -1390 Reynolds number (Re) 12552 14671 9359 11246 9666 Velocity (m/s) 64.6 75.6 48.2 57.9 49.8 Velocity w (fibre axis) (m/s) 14.2 10.1 21 16.6 24.2 Vorticity 225448 223036 197273 233608 230605 Helicity real eigen 172484 156333 138241 171569 171734 above 40 kPa, while the total pressure value in modular nozzles is just below or just above 0 kPa. Similarly, the flow pressure value of conventional nozzles is above 6 kPa, while the flow pressure value of modular nozzles is below 0 kPa. According to the graphical comparison of yarn hairiness of the modular nozzles and conventional nozzles in Figure 8, modular nozzles with a pressure of 125 kPa (225 kPa absolute) demonstrated the lowest yarn hairiness at injector angle configurations of 20°, 40°, 25° , 30° and 35°. According to the modular nozzle YZ plane vorticity CFD result in Figure 22, the order of vorticity from highest value to lowest value is seen at injector angle configurations of 20°, 25°, 30°, 35° and 40°. If the measurement at 40° in Figure 8 is not taken into account, the increase in the amount of vorticity resulted in a decrease in yarn hairiness. A similar situation was seen in the helicity real eigen CFD results in the YZ plane (Figure 24). According to the graphical comparison of yarn hairiness of the modular nozzles and conventional nozzles in Figure 8, conventional nozzles with a pressure of 125 kPa (gauge) demonstrated the lowest yarn hairiness at injector angle configurations of 20°, 40°, 25° , 30° and 35°. According to the modular nozzle YZ plane vorticity CFD result in Figure 15, the order of vorticity from highest value to lowest value is seen at injector angle configurations 40°, 35°, 30°, 25° and 20°. A similar situation was seen in the helicity real eigen CFD results in the YZ plane (Figure 17). 3.6 CFD verification The CFD validation process was addressed and validated in a study similar to this one [11]. 4 Conclusion and outlook • Comparing conventional jet-ring nozzles with modular jet-ring nozzles in terms of yarn hairiness value, modular jet-ring nozzles proved to be more successful in reducing yarn hairiness values. The main objective of jet-ring nozzles is to reduce yarn hairiness values. • When hairiness values are considered, conventional jet-ring nozzles and modular jet-ring nozzles form an antithesis relative to one another in terms of the injector angle structural parameter. In the 20° injector angle structural configuration, conventional jet-ring nozzles gave the best yarn hairiness values, while modular jet-ring nozzles gave the worst yarn hairiness values. In the 35° injector angle structural configuration, hairiness values were reversed. In other words, modular and conventional nozzles formed an antithesis with respect to one another in terms of yarn hairiness values according to their injector angle structural configurations. • In modular and conventional nozzles with generally known structural configurations, an increase in pressure led to an increase in yarn hairiness. • It is generally understood that the irregularity values of yarns produced using modular jet-ring Tekstilec, 2020, 63(2), S0-93 92 Modular Jet-Ring Yarn Spinning System S1 nozzles are higher than those produced using conventional jet-ring nozzles. • It is generally understood that the elongation values of the yarns produced using modular jet-ring nozzles are lower than those produced using conventional jet-ring nozzles. • When the air pressure was set to 75 kPa (gauge), yarn tenacity values were higher in the yarns produced using conventional jet-ring nozzles, and higher in the yarns produced in modular jet-ring nozzle when it was set to 125 kPa (gauge). • Comparing the flow parameters of yarn hairiness (CFD analysis), it was found that increasing vor-ticity or helicity real eigen values reduced yarn hairiness. Yarn hairiness can be minimised if both conventional nozzles and modular nozzles concentrate on structural configurations that can maximise vorticity or helicity real eigen values to reduce yarn hairiness. • According to the structural configurations that maximise vorticity or helicity real eigen values in conventional nozzles, the twisting chamber diameter should be at the lowest value (^ = 2 mm). • No significant correlation was found between other structural parameters and vorticity or helical real eigen values in conventional nozzles. However, in conventional nozzles, vorticity or helical real eigen values were high in the 35-40° injector angle configurations. • In modular nozzles, on the contrary, vorticity or helical real eigen values were high in the 20-25° injector angle configurations and low in the 35-40° injector angle configurations. • It is precisely for this reason that the yarn produced using modular nozzles demonstrated a low hairiness value when a low injector angle was set and a high hairiness value when a high injector angle was set, which can be explained logically when comparing vorticity or helicity real eigen values. Acknowledgement This work was supported by grants from the Unit of Scientific Research Projects of Isparta (Suleyman Demirel University) in Turkey [Project 4995-D1-17]. We would like to thank H. Husnu Isik, the owner of Adim Textile Industry and Trade Inc. 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The Journal of the Textile Institute, 2020 (in press), 1-11, doi: 10.1080/00405000.2020.1716527. 17. YILMAZ, Demet. Development and numerical modelling of plied yarn production process based on the usage of high velocity air. Ph.D. thesis. Isparta : Suleyman Demirel University, 2011. Tekstilec, 2020, 63(2), S0-93 94 Akhtarul Islam Amjad, Rajiv Kumar M L V Textile and Engineering College, Bhilwara, Department of Textile Engineering, Rajasthan, 311001, India Evaluation of Mechanical and Physical Characteristics of Eco blended Melange Yarns Vrednotenje mehanskih in fizikalnih lastnosti ekomelanžne preje Original scientific article/Izvirni znanstveni članek Received/Prispelo 2-2020 • Accepted/Sprejeto 5-2020 Abstract The production and consumption of melange yarns are gradually increasing due to natural multi-colours and strong 3D fashionable effects. The raw material and chemical processing influence the environmental and textile values of the melange yarn. Organic cotton and regenerated cellulose fibres are basic raw materials for eco-friendly production of yarns. In this study three different regenerated fibres are blended with organic cotton in three different ratios to manufacture the blended melange yarns of two different shade depths. Therefore, cotton-bamboo viscose, cotton-lyocell and cotton-SeaCell™ blended melange yarns with three blend combination 30/70, 50/50 and 70/30 are manufactured. All the dyed and grey components are mixed at the blow room. The aim of the study is to investigate impact of raw material and blend ratio on mechanical and physical characteristics of different shade depth blended melange yarns. Better yarn characteristics with respect to yarn evenness, imperfections, hairiness, tenacity, elongation, coefficient of friction and diameter are achieved for lower shade depth melange yarn. In cotton-rich blended melange yarns, elongation, hairiness, evenness, total imperfections and diameter are noticeably worse for all the combinations. Statistical analysis shows significant effect of blend type, blend ratio and shade depth on the all yarn properties. Keywords: bamboo viscose, TencelTM, SeaCellTM, shade depth, melange spinning Izvleček Proizvodnja in poraba melanžne preje se postopoma povečuje zaradi naravne večbarvnosti in zelo modnih 3D estetskih učinkov. Surovine in kemična obdelava vplivajo na okolje in tekstilne lastnosti melanžne preje. Organski bombaž in regenerirana celulozna vlakna so osnovne surovine za okolju prijazno proizvodnjo preje. Z namenom, da bi dosegli različne barvne nianse, so bile v študiji izdelane melanžne preje iz mešanic vlaken bombaž/bambusova viskoza, bombaž/liocel in bombaž/SeaCellTM, v razmerjih 30/70, 50/50 in 70/30. Barvane in surove komponente vlaken so bile mešane v fazah priprave prediva. Namen študije je bil raziskati vpliv razmerja surovin v mešanicah na mehanske in fizikalne lastnosti melanžnih prej. Boljše lastnosti prej glede enakomernosti, količine napak, kosmatosti, trdnosti, raztezka, koeficienta trenja in premera so bile dosežene pri melanžnih prejah s svetlejšim barvnim tonom. V melanžnih prejah z večjim deležem bombaža so bile pri vseh mešanicah ugotovljene slabše vrednosti raztezka, kosmatosti, enakomernosti, količine napak in premera. Statistična analiza je pokazala pomemben vpliv vrste mešanice, razmerja mešanice in globine barvnega tona na vse lastnosti preje. Ključne besede: bambusova viskoza, TencelTM, SeaCellTM, barvne nianse, izdelava melanžne preje Corresponding author/Korespondenčni avtor: Tekstilec, 2020,63(2), 94-103 Akhtarul Islam Amjad DŒ, m 14502/Tekstilec2020.63.94-103 E-mail: akh.textile@gmail.com ORCID: 0000-0002-9667-4012 Evaluation of Mechanical and Physical Characteristics of Eco blended Melange Yarns 95 1 Introduction The increase in global demand for clothing is expected to continue, not only due to an increase in the world's population, but also due to living standards, economic activities and developments. In the present era, clothing serves many purposes. It not only satisfies the basic needs of human beings, but is also used as a symbol to express wealth, status, occupation, leisure and eco-friendliness [1]. Fibre is one of the basic units for producing desirable clothes [2]. Biodegradable and sustainable fibres are being developed for environmental protection and providing a significant opportunity for sustainable textiles [3]. Cotton is considered the most eco-friendly, but the use of insecticides and pesticides in cultivation make it less sustainable. Organic cotton and regenerated cellulose fibres may serve as a substitute for polluted cotton [4]. Regenerated cellulose fibres, such as viscose rayon, bamboo rayon, modal rayon, lyocell and SeaCell™ are widely considered the most important for environmental aspects and often referred to as environmentally friendly [5]. Bamboo rayon is produced by wet spinning, while lyocell and SeaCell™ fibres are produced by solvent spinning. Bamboo rayon is naturally antibacterial, breathable, green, biodegradable, soft, flexible and strong, with a luxurious, shiny appearance [6]. Modal is a second generation regenerated cellulose fibre and is known for its softness [5]. Lyocell is a third-generation fibre. It is highly absorbent, soft, has a high wet or dry strength, and is wrinkle resistant [7]. SeaCell™ and smartcell are modified versions of third generation fibre. Their advantages include the environmental friendliness of processing, combined with their softness, drape and antibacterial properties [8-10]. In the production of SeaCell™ fibre, powdered seaweeds are firmly incorporated into a natural cellulose fibre. As a result, the positive properties of the seaweed are permanently preserved within the fibre, even after multiple washes [10, 11]. All regenerated cellulosic fibres have the same basic unit, but are quite different in degree of polymerisation, molecular arrangement, molecular mass, degree of orientation and crystallinity [12]. The lyocell and SeaCell™ have a circular cross section and a smooth longitudinal surface. On the other hand, bamboo rayon and viscose rayon possess an irregular and toothed cross section, micro-gaps and micro-holes with striated cracks distributed over the longitudinal surface [13, 14]. A single fibre yarn cannot offer all the desired characteristics. The blending of different types of fibres not only enhances the functional or mechanical performance, but also the aesthetic qualities of textile fabric. Blending is also practiced in industry for cost minimisation [15, 16]. Many researchers have investigated blended yarn properties and analysed their functional and mechanical attributes. Sowmya et al. [15] reported that yarn unevenness is affected by the blended ratio of cotton, polyester, and regenerated bamboo fibre. They also reported that the work of rupture and elongation at break of bamboo-cotton blended yarns are found to be lower than those of bamboo/polyester-blended yarns. Tyagi et al. [16] reported that Tencel™-polyester yarns yield more satisfactory results than Tencel™-cotton yarns in terms of tenacity, breaking elongation, mass regularity, imperfections and work of rupture for all spinning system. Increasing the Tencel™ content both in Tencel™-polyester and Tencel™-cotton fibre blends makes the yarn rigid and hairier. Kilic et al. [17] determined that yarn-to-yarn friction decreases, while yarn-to-metal and yarn-to-ceramic friction increases when the ratio of Tencel™ in Tencel™-cotton blended yarn is increased. Majum-dar et al. [6] reported that yarn diameter reduces as the proportion of bamboo fibre is increased in the blend of bamboo cotton fibre. Kili^ and Okur [14] found that unevenness, imperfections, diameter and roughness values decrease when the regenerated cellulosic fibre content in cotton-Tencel™ and cot-ton-paramodal blended yarns is increased, while increasing breaking force, elongation, density and shape values. Avik et al. [11] worked on the functional properties of SeaCell™ sock and summarise that SeaCell™ socks may be a good choice for people with foot problems such as fungus. SeaCell™ fibre has a more homogenous pore distribution, which in turn facilitates improved water transport. All of the above research was performed on the manufacturing of plain blended yarn. But there is another field where the blending/mixing of different colours or the dye affinities of fibres are performed for the production of fancy or melange yarns [18-19]. Melange yarns are fancy yarns consisting of a wavy effect, a wide range of colour tones and unique colour effects. They are manufactured to achieve higher rates due to the aesthetics and obsolescence of fashion [20]. Researchers reported that cotton fibres suffer from a decrease in strength Tekstilec, 2020, 63(2), 94-103 96 Evaluation of Mechanical and Physical Characteristics of Eco blended Melange Yarns and change in surface properties after being dyed due to the aggressive nature of chemicals and the removal of a large portion of the wax present on the surface of cotton fibres [21, 22]. The dyeing of fibres results in their greater entanglement and cohesion. The average length of dyed fibre decreases with a higher rate than that of undyed fibre after going through opening and mechanical processes. Various stages of spinning cause tip fibrillation, end rupture, transverse cracks, deep cracks, a saw-tooth effect and rippling damage. Dyed fibres are more prone to damage than undyed fibres [22, 23]. Fibre damage not only affects the efficiency of the spinning process, but also the mechanical properties of the final yarn and fabric. The quality of cotton melange yarn is affected significantly by the applied blending method [24, 25]. Conventional approaches used in the manufacturing of melange yarn are entirely dependent on cotton fibre in the melange yarn industry. None of the researchers mentioned above have focused on the properties of eco-friendly blended melange yarns. In this study, two different shade depth cotton blended melange yarns were produced using bamboo viscose, lyocell and SeaCell™ fibres in three different proportions that might be useful for the textile melange yarn industry in terms of exploring new applications for melange products. 2 Materials and methods 2.1 Materials for melange yarn production Dyed and grey H-4 organic combed cotton, bamboo viscose, lyocell and SeaCell™ fibres were used to produce 19.68 tex (30s Ne) melange yarns. The properties of the fibres that were used to produce the yarns are summarised in Tables 1a and 1b. The results presented in Tables 1a and 1b show that dyeing and opening have an adverse effect on the tensile and length properties of fibres. It was also observed that cotton fibres show incremental changes in short fibre content and neps/g after dyeing and opening. 2.2 Melange yarn production The mixing or blending of dyed and un-dyed (grey) fibres in predefined ratios results in melange yarns. Shade depth (%) is a common term used in melange yarn spinning to illustrate the percentage contribution of dyed fibre in a blend. In this study, the blending of fibres (dyed/un-dyed, cotton or regenerated cellulose) was performed in a blow room to achieve the perfect regularity of colour and structure. Figure 1 depicts the process flow of melange yarn spinning. Grey fibres for dyeing or mixing are prepared in the first stage. A predefined amount of grey fibres is dyed in the second stage, while the third stage involves the stack blending of grey and dyed fibres in the required ratio in the blow room. Cotton fibres Table 1a: Properties of combed grey and dyed cotton fibres Instruments Fibre quality HVI (HVI mode) AFIS Fineness Length Strength Elongation Short fibre Fibre neps (mic.) (mm) (g/tex) (%) content (%) (neps/g) Grey combed 4.23 29.3 29.37 6.14 18.02 14 Dyed combed 4.2 29.0 28.12 5.9 19.32 18 Dyed combed (after opening) 4.2 28.7 27.24 5.97 21.57 24 Type of fibre Bamboo viscose (BV) Lyocell (L) SeaCell™ (S) Grey Dyed Grey Dyed Grey Dyed Fineness (dtex) 1.56 1.56 1.56 1.56 1.67 1.67 Length (mm) 37.90 (38) 37.65 (38) 37.92 (38) 37.81(38) 37.9(38) 37.7(38) Strength (g/tex) 23.2 21.0 36.23 35.0 29.00 28.1 Elongation (%) 11.8 11.5 9.7 9.5 11.2 10.9 Table 1b: Properties of grey and dyed regenerated cellulose fibres Tekstilec, 2020, 63(2), 94-103 Evaluation of Mechanical and Physical Characteristics of Eco blended Melange Yarns 97 Washing StOUNPlß Washing When contribution (%) oT coll an fibre 1b leu then shad« depth (%} Sarntrao viscose, Lyoeell. Seacefl Combed fleece (grey) Ldp ioim^r a combef Dyeing Igi ra \ Draw trame Drying [a Carding Dveci fibres 1 1 f Blow room Mining/Binding 1/ [ fia^d totton □ law rgom Speed frame Ring frame Figure 1: Process flow of melange yarn manufacturing are preferred over the regenerated cellulose fibres for dyeing to achieve the proper shade depth (%). 2.3 Design of experiment Light and dark melange yarns were produced on a short staple spinning machine by blending three different fibres and blend compositions with cotton. All the process variables were kept constant. The aim of varying the factors was to investigate the interaction effect of fibre properties and composition with different shade depths. The design plan of the experiment is presented in Table 2. A total of 18 yarn samples were manufactured according to full factorial design. 2.4 Methods The yarn samples were conditioned at a standard tropical atmospheric condition of 65 ± 2% RH and 27 ± 2 °C temperatures for 24 hours. extension rate using a gauge length of 500 mm (ASTM D 2256). A total of 50 readings were taken for each sample. 2.4.2 Unevenness, thin, thick, neps and hairiness The unevenness, thin, thick, neps and hairiness were measured using an Uster Evenness Tester-5. Thin places (-50%), thick places (+50%) and neps (+200%) were considered to measure total imperfection in the melange yarn. 2.4.3 Yarn diameter The diameter of yarn was measured by an optical method using a Leica image analyser. At least 100 readings were taken for each sample. 2.4.4 Coefficient of friction An Uster Zweigle Friction Tester 5 was used to measure fibre to metal friction. The friction coefficient was calculated using the formula F2 = where F1 is constant force applied to produce a defined force on the yarn in a vertical direction and F2 is the force required to pull the yarn. 3 Results and discussion This paper includes an analysis of cotton blended melange yarn with varying parameters. In this study, parameters were assessed in terms of unevenness, total imperfections, hairiness, tenacity, elongation, yarn diameter and coefficient of friction of the melange yarns. An analysis of variance was carried out to determine the effect of different parameters on yarn properties. The ANOVA of the parameters is presented in Table 3. 2.4.1 Tensile testing of yarn An Instron universal testing machine was used to measure the breaking load and extension properties. The yarn samples were tested at 120 mm/min It is evident from Table 3 that the blend ratio has a significant impact on all the properties of the yarn, while blend type has a significant effect on all properties except unevenness. Table 2: Experiment design plan Sr. No. Factors Levels 1 Blend type Cotton/Bamboo viscose (C/BV) Cotton/Lyocell (C/L) Cotton/SeaCell™ (C/S) 2 Blend ratio 30/70 50/50 70/30 3 Shade depth (%) 20 (light); 70 (dark) 20 (light); 70 (dark) 20 (light); 70 (dark) Tekstilec, 2020, 63(2), 94-103 98 Evaluation of Mechanical and Physical Characteristics of Eco blended Melange Yarns Table 3: ANOVA results for yarn characteristics Factors Unevenness IPI Hairiness Tenacity Breaking Extension Diameter Coefficient of friction BT NS (0.19) S (0.000) S (0.0009) S (0.000) S (0.000) S (0.014) S (0.001) BR S (0.0003) S (0.000) S (0.0001) S (0.0001) S (0.0000) S (0.034)) S (0.0000) SD S (0.0001) S (0.000) S (0.001) S (0.029) S (0.0004) NS (0.450) S (0.006) BTxBR NS (0.5757) NS (0.172) NS (0.163) S (0.0004) S (0.0001) NS (0.283) NS (0.216) BTxSD NS (0.2813) S (0.0001) NS (0.792) S (0.002) S (0.013) NS (0.146) NS (0.444) BRxSD S (0.0226) S (0.045) NS (0.664) S (0.027) NS (0.18) NS (0.683) NS (0.500) BT - blend type, BR - blend ratio, SD - shade depth. Values in parenthesis are p-values, calculated at 95% statistical probability: p < 0.05 - result is statistically significant (S), p > 0.05 - result is not statistically significant (NS) 3.1 Tensile characteristics of melange yarn The tensile attributes of a staple fibre melange yarn are influenced by fibre characteristics. Tenacity and breaking extension are important properties for assessing the tensile behaviour of melange yarn. Blend type, blend ratio and shade depth have a significant impact on the tenacity and breaking extension of blended melange yarn (Table 3). Tenacity is the applied load with respect to fineness at which a specimen breaks. The effect of blend type and blend ratio on tenacity for different shade depth blended melange yarns is presented in Figure 2. 18 16 14 „ 12 K ED z 10 u i 6 o c CO tl C ai F 4 2 0 C tBV C/L C/S C/BV C/L C/S 20% Shade depth 70% Shade depth Samples ■ 30C/70 6V I 50 C/50 SV n7OC/30BV Figure 2: Effect of blend type and blend ratio on tenacity It is evident from Figure 2 that: - cotton-lyocell blended yarn shows the highest tenacity, followed by cotton-SeaCell™ and cotton-bamboo viscose blended yarns for both shade depths; - melange yarn tenacity increases with an increase in the cotton component in the case of bamboo viscose and SeaCell™-blended yarns, and decreases in lyocell-blended yarn; and - tenacity of melange yarn decreases with an increase in shade depth. Lyocell fibres have a high degree of polymerisation compared to bamboo viscose and SeaCell™ fibres due to their long molecular chains [13], so that the strength of the yarns produced from lyocell fibre showed a higher tenacity, followed by cotton-SeaCell™ and cotton-bamboo viscose blended yarn for both shade depths. The bamboo viscose fibre has a lower strength and higher amorphous region in the macromolecular structure than cotton fibre. Blended yarn with rich bamboo viscose fibre demonstrates a lower tenacity. SeaCell™ fibre possesses much higher elongation than cotton fibre. During the loading of cotton-SeaCell™ blended yarn, cotton fibres will resist further elongation and are expected to reach the breaking point earlier. The difference is marginal. Dyed fibres are weaker than undyed fibre (Table 1), while 70% shade depth melange yarn consists of more dyed fibre. Simultaneously dyeing causes entanglement, causes difficulties during opening and drafting, and ultimately leads to rupture. For these reasons, the load bearing capacity of survival fibres decreases and stress increases during tensile testing, causing a rupture to propagate faster across the cross section in high shade depth yarn. The effect of blend type and blend ratio on the percentage of elongation for different shade depth blended melange yarns is illustrated in Figure 3. It is evident from Figure 3 that: - cotton-bamboo viscose blended yarn shows the highest percentage of elongation, followed by cotton Tekstilec, 2020, 63(2), 94-103 Evaluation of Mechanical and Physical Characteristics of Eco blended Melange Yarns 99 Figure 3: Effect of blend type and blend ratio on breaking extension lyocell and cotton-SeaCell™ blended yarns for all type of samples; - the percentage of elongation decreases as the ratio of cotton increased; and - 70% shade depth melange yarn demonstrates the lowest percentage of elongation. Because fibre elongation properties directly affect yarn elongation, higher elongation values of regenerated fibres result in high elongation values in all 30/70 blended melange yarns. Cotton- lyocell blend yarns demonstrated the lowest percentage of elongation, while it is also evident from Table 1 that lyo-cell fibre showed a lower elongation than all regenerated fibres. It is evident that a high number of dyed fibres are present in the yarn cross section for high depth melange yarn and, similar to tenacity, they will reduce the percentage of elongation. 3.2 Unevenness of melange yarn Unevenness (U expressed in %) shows the mass irregularity per unit length in the yarn. No significant difference in unevenness is observed for the type of blend. This may be due to the almost identical production process and the dimensional properties of all three regenerated fibres. Blend ratio and shade depth had a significant impact on the unevenness of melange yarns (Table 3). Figure 4 illustrates in graphical form the effect of blend type and blend ratio on the unevenness of different shade depth blended melange yarns. Figure 4: Effect of blend type and blend ratio on un-evenness It is evident from Figure 4 that: - an increase of the cotton fibre contribution leads to the high unevenness of the yarn irrespective of other factors; and - unevenness of darker melange yarns is higher than that of low depth melange yarns. The arrangement of fibres and fibre properties influence yarn characteristics. Cotton is a naturally grown fibre, and is highly variable in terms of length and fineness relative to regenerated fibres. Cotton fibres are shorter in length than regenerated fibres (Table 1). Any variation in the fibres negatively affects the mechanical and physical properties of yarn. As the percentage of cotton increases, the availability of shorter fibres increases in the spinning system and decreases mean fibre length in the yarn structure, so that consolidation at the nip point during yarn manufacturing is lesser, which generates a greater amplitude of drafting waves. Mass irregularity thus increases. Opening difficulties are seen more in high shade depth melange blends, as they consist of more dyed fibres. These difficulties cause the uncontrolled and erratic movement of fibres in the drafting area and eventually result in increased yarn mass variation. 3.3 Total imperfection of melange yarn The imperfection index (IPI) consists of thin, thick and neps per unit length of yarn. Blend type, blend ratio and shade depth had a significant impact on Tekstilec, 2020, 63(2), 94-103 100 Evaluation of Mechanical and Physical Characteristics of Eco blended Melange Yarns the total imperfection of blended melange yarn (Table 3). Figure 5 illustrates in graphical form the effect of fibre blend type and blend ratio on total imperfection. Figure 5: Effect of blend type and blend ratio on total imperfection It is evident from Figure 5 that: • a higher percentage of cotton leads to an increase in the total imperfection level in blended melange yarn; • cotton-bamboo blend yarn demonstrates the highest and cotton-lyocell blended yarn the lowest total imperfection; and • total imperfection increases with an increase in shade depth irrespective of blend type and blend ratio. Regenerated fibres are known to have more a uniform shape and size in their longitudinal direction, while cotton fibres show a twisted structure. Simultaneously blended yarn with higher regenerated fibres consists of fewer shorter fibres and a higher mean fibre length, so that control over the movement of fibres is easy and imparts better association and orientation in yarn structure. Hence, higher cotton contribution leads to an increase in the total imperfection level in blended melange yarn. The proportions of dyed fibres are higher in the high shade depth melange yarns. Dyeing changes the surface properties of the fibres, damages the fibres and increases fibre-to-fibre friction due to the removal of natural wax [23]. High fibre-to-fibre friction causes difficulties in the opening and drafting of fibres, which ultimately leads to the poor arrangement and distribution of fibre in yarn. Thus, higher yarn imperfections are seen for darker shades. 3.4 Hairiness of melange yarn The hairiness of a yarn is the result of fibre protrusion from the yarn surface. Hairiness in spun yarn depends primarily on fibre properties such as the length, shape and bending rigidity of fibres. The effect of blend type, blend ratio and shade depth on the hairiness of melange yarn is significant (Table 3). C/BV CiL CIS CIBV C/L CIS 20% Shade depih 70% Shade depth Samples 130 C/70 BV : 50 C/50 BV 170 C/30 BV Figure 6: Effect of blend type and blend ratio on hairiness It is evident from Figure 6 that: - hairiness of melange yarn increases with an increase in the percentage of cotton in blended melange yarn; - cotton-lyocell and cotton-SeaCell™ blended yarns demonstrate a marginal difference, while cotton-bamboo viscose blended yarn shows the lowest hairiness; and - hairiness of melange yarn increases with an increase in shade depth. Bamboo viscose, lyocell and SeaCell™ fibres have a longer length than the cotton fibres. Moreover, short fibres are totally absent in the all three fibres. The flexural and torsional rigidity of all three fibres are also lower than that of cotton fibre. Regenerated fibres are thus wrapped and adhered with the internal structure of melange yarn in the twisting triangle. As a result, hairiness decreases with an increase in the proportion of regenerated fibres. Tekstilec, 2020, 63(2), 94-103 Evaluation of Mechanical and Physical Characteristics of Eco blended Melange Yarns 101 The cross-section of lyocell and SeaCell™ fibre is round and the surface is smooth, while bamboo viscose fibre has an irregular and toothed shape [13]. On the other hand, bamboo viscose fibre shows a lower torsional rigidity than lyocell and SeaCell™ fibre. These properties of bamboo viscose fibres cause higher inter-fibre friction, while a better consolidation of surface hair in the main yarn structure ensures low hairiness. The chemical and mechanical processing of fibres in melange yarn manufacturing causes rupture and high short fibre generation. Short fibres have a tendency to come out from the yarn body and do not wrap with the main body of melange yarn during twisting. Moreover, control over the short fibres is also difficult during drafting. High depth melange yarn consists of more such fibre, which results in a high level of hairiness. 3.5 Diameter of melange yarn The surface characteristics and appearance of a yarn influence the appearance of products made from that yarn. No significant difference in the diameter is observed for the shade depth. The type of fibre and blend ratio have a significant impact (see Table 3). Figure 7 illustrates in graphical form the effect of blend type and blend ratio on diameter for different shade depth blended melange yarns. It is evident from Figure 6 that: - diameter of melange yarn increases with an increase in the percentage of cotton in blended melange yarn; and - cotton-lyocell blended yarn shows the lowest diameter, followed by cotton-SeaCell™ and cotton-bamboo viscose blended yarn. Figure 7: Effect of blend type and blend ratio on diameter Yarn diameter steadily increases with an increase in the percentage of cotton in the yarn composition. As discussed, all of the regenerated fibres have a longer length (38 mm) than that of cotton fibres. Moreover, they have lower bending and torsional rigidity than cotton fibre. On the other hand, the non-circular cross-section of cotton does not allow close association. Thus, fewer cotton fibres in the cross section lead to closed packing in the melange yarn structure and high diameter in cotton-rich blends. Figure 8 is a microscopic image of blended melange yarns, which shows that lyocell-blended yarn has a compact internal structure and better integrity and thus a lower diameter. On the other hand, Blend type; shade depth Blend ratio 30/70 50/50 70/30 C/BV; 20% ^MMI C/BV; 70% HHPI WHBagj - m ^■BMÂÉ C/L; 20% - M 1^1 MMHHBÍ C/S; 20% :» ; : MJP ap^na^p HBttm ■AiMriÉI SSâÊÈËÉ^âUm Figure 8: Microscopic image of blended melange yarn Tekstilec, 2020, 63(2), 94-103 102 Evaluation of Mechanical and Physical Characteristics of Eco blended Melange Yarns bamboo-blended melange yarn has a more uniform surface and lesser protruding fibres from the main body, while the fibres are rather protruded on the surface in the case of lyocell- and SeaCell™-blended yarns. Bamboo viscose blended yarn thus shows low hairiness. 3.6 Surface friction Basic yarn properties such as linear density, evenness and strength do not fully account for processing performance and/or fabric quality. Friction plays vital role in expressing interactive behaviour for fibre-to-yarn and yarn-to-fabric modelling. The resistance to movement, characterised by the coefficient of friction, is dependent on the nature of the two contacting surfaces and their actual area of contact. Figure 9 illustrates in graphical form the effect of blend type and blend ratio on the coefficient of friction for different shade depth blended melange yarns. It is evident from Figure 9 that: - increase in the percentage of cotton leads to lower value of coefficient of friction; - cotton-bamboo viscose blended melange yarn shows the highest coefficient of friction, while the differences between cotton-SeaCell™ and cotton-lyocell blended yarns are not significant; and - the value of the coefficient of friction is marginally higher for high depth melange yarn. As discussed, increasing the percentage of cotton in the blended melange yarn structure leads to high hairiness values. The same is also evident from Figure 8. On the other hand, cotton fibres have a natural wax that serves as a lubricant when they come in contact with other surfaces. Hence, cotton-rich blended varn shows a lower coefficient of friction. 0.2 0.15 0.1 £ 0 05 0> o o C/BV C/L CI S C/BV C/L C / 5 20% Shade depth 70% Shade depth Samples □ 30 C/7Û BV "SO C/5Û 6V a 70 C/30 BV Figure 9: Effect of blend type and blend ratio on coefficient of friction The frictional characteristics of parent fibres have an impact on the frictional characteristics of blended yarn. Microscopic images show that the surface of bamboo-blended yarn is more uniform and less hairy than SeaCell™- and lyocell-blended yarns (Figure 8). Due to their yarn structure, bamboo-blended yarns show a high coefficient of friction. In dyeing process, cotton fibre is subject to a scouring process that removes the lubricating layer. The removal of cotton wax increases the coefficient of friction due to underlying rough surface of the layer. On the other hand, the presence of short fibres increases the voluminous of the high depth melange yarn, making the yarn bulkier, which is also evident from Figure 8. Bulkier yarn is more compressible and flattens easier, so the scope of flattening increases when passed over any surface. Hence, higher coefficient of friction values are demonstrated by darker melange yarn. 4 Conclusion The analysis of the study presents an overview of cotton-bamboo viscose, cotton-lyocell and cotton-SeaCell™ blended melange yarn characteristics, such as strength, elongation, unevenness, hairiness, diameter and friction. The following conclusion can be reached from the experiments: • Type of blend, blend ratio and shade depth have a significant affect on blended melange yarn quality. An evaluation of the effect of shade depth on blended melange yarns shows a reduction in strength and elongation. The dyeing and opening of bamboo viscose fibres causes a reduction in strength of up to 9.48%. The lower depth melange yarn contributes to the production of good quality yarns with significantly reduced hairiness and improved mechanical and frictional characteristics. • Cotton-rich blended yarns show lower friction and elongation, and higher hairiness, total imperfection and unevenness, irrespective of the type of blend. Increasing the cotton content in bamboo- and SeaCell™-blended melange yarns increased tenacity. However, lyocell-blended yarns show the opposite trend. • Cotton-bamboo blended yarns show the highest diameter and lowest hairiness in all the combination of yarn samples. Cotton-lyocell 30/70 blended yarn gives the strongest blended melange yarn among the studied yarn samples. Tekstilec, 2020, 63(2), 94-103 Evaluation of Mechanical and Physical Characteristics of Eco blended Melange Yarns 103 References 1. ERYURUK, S. H. Greening of the textile and clothing industry. Fibres and Textiles in Eastern Europe, 2012, 95(6), 22-27. 2. SHABBIR M., MOHAMMAD, F. Sustainable production of regenerated cellulosic fibres. In Sustainable Fibres and Textiles. Edited by Subra-manian Senthilkannan Muthu. Cambridge : Woodhead Publishing, 2017, 171-189. 3. BLACKBURN, R. S. Introduction. In Biodegradable and Sustainable Fibres. Cambridge : Wood-head Publishing, 2005, pp. xiv-xxii. 4. YU, M., WAN, J. Environmental friendly development of regenerated cellulose fiber production. In Asia-Pacific Engineering and Technology Conference (APETC 2017), 2017, 760-765. 5. MARWAHA, S. V. Eco-friendly fibres. Asian Textile Journal, 2006, 15(5), 58-62. 6. MAJUMDAR, A. MUKHOPADHYAY, S. YA-DAV, R., MONDAL, A. K. Properties of ring-spun yarns made from cotton and regenerated bamboo fibres. Indian Journal of Fibre & Textile Research, 2011, 36(1), 18-23. 7. BASIT, A. LATIF, W. BAIG, S. A. AFZAL, A. The mechanical and comfort properties of sustainable blended fabrics of bamboo with cotton and regenerated fibres. 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Structure and thermal properties of bamboo viscose, Tencel™ and conventional viscose fiber. Journal of Thermal Analysis and Calorimetry, 2007, 89(1), 197-201, doi: 10.1007/s10973-005-7539-1. 14. KILIg, M. OKUR, A. The properties of cotton-Tencel and cotton-promodal blended yarns spun in different spinning systems. Textile Re- search Journal, 2011, 81(2) 156-172, doi: 10. 1177/0040517510377828. 15. SOWMYA, R. VASUGI RAAJA N., PRAKASH C. Investigation of relationship between blend ratio and yarn twist on yarn properties of bamboo, cotton,polyester, and its blends. Journal of Natural Fibres, 2016, 14(2), 228-238, doi: 10. 1080/15440478.2016.1193087. 16. TYAGI G. K. GOYAL A., CHATTOPADHYAY, R. Physical characteristics of tencel-polyester and tencel-cotton yarns produced on ring, rotor and air-jet spinning machines. Indian Journal of Fibre & Textile Research, 2013, 38(3), 230-236. 17. KILIC, G.B., VILDAN, S. Frictional properties of cotton-Tencel yarns spun in different spinning systems, Textile Research Journal. 2012, 82(8), 755-765, doi: 10.1177/0040517511429610. 18. ERDUMLU, N. OZIPEK, B. Investigation of regenerated bamboo fiber and yarn characteristics. Fibres & Textiles in Eastern Europe, 2008, 16(4), 43-47. 19. REGAR, M. L. AMJAD, A.I. AIKAT, N. Studies on the properties of ring and compact spun melange yarn. International Journal of Advance Research and Innovative Ideas in Education, 2017, 3(2), 476-483. 20. LIU, Y. ZHU, L. ZHANG, C. REN, F. HUANG, H, LIU, Z. Life cycle assessment of melange yarns from the manufacturer perspective. The International Journal of Life Cycle Assessment, 2019, 25(3), 588-599, doi: 10.1007/s11367-019-01705-8. 21. MEMON, H. KHOSO, A. N. MEMON, S. Effect of dyeing parameters on physical properties of fibres. International Journal of Applied Sciences and Engineering Research, 2015, 4(4), 401-407. 22. MOGHASSEM, Abdolrasool. Damaging of dyed cotton fibres with direct dye in spinning processes and its effect on the properties of cotton mélange yarn. International Journal of Engineering - Transactions B: Applications, 2007, 20(2), 203-210. 23. KARBALAIKARIM, S. Karim, GHAREHAG-HAJI, A.A., TAVANAIE, H. A study of the damage caused to dyed cotton fibres and its effects on the properties of rotor- and ring-spun melange yarns. Fibres and Textiles in Eastern Europe, 2007, 15, 3(62), 63-67. 24. RAY, S., GHOSH, A., BANERJEE, D. Effect of blending methodologies on cotton mélange yarn quality. Fibres and Textiles in Eastern Europe, 2018, 26(5), 41-46, doi: 10.5604/01.3001. 0012.2529. 25. HABIBA H. GONG, T., KALEEM, K. Real-time quality assessment of neppy mélange yarn manufacturing using macropixel analysis. Tekstilec, 2019, 62(4), 242-247, doi: 10.14502/Tekstilec2019. 62.242-247. Tekstilec, 2020, 63(2), 94-103 104 Tomasz Blachowicz1, Tobias Bohm2, Jacek Grzybowski1, Krzysztof Domino3, Andrea Ehrmann2 1 Silesian University of Technology, Institute of Physics - Centre for Science and Education, 44-100 Gliwice, Poland 2 Bielefeld University of Applied Sciences, Faculty of Engineering and Mathematics, 33619 Bielefeld, Germany 3 Institute of Theoretical and Applied Informatics, Polish Academy of Sciences, 44-100 Gliwice, Poland Analysis of AFM images of Nanofibre Mats for Automated Processing Analiza slik AFM nanovlaknatih kopren za samodejno obdelavo Original scientific article/Izvirni znanstveni članek Received/Prispelo 4-2020 • Accepted/Sprejeto 5-2020 Abstract The image processing of pictures from fibres and fibrous materials facilitates the investigation of diverse geometrical properties, such as yarn hairiness, fibre bifurcations or fibre lengths and diameters. Such irregular sample sets are naturally suitable to the statistical examination of images, using a random-walk algorithm. This results in the calculation of the so-called Hurst exponent, which is the asymptotic scaling exponent of the mean squared displacement of the walker's position. Previous investigations have proven the appropriateness of this method for examinations of different fibres, yarns and textile fabrics. In a recent study, we used AFM (atomic force microscopy) images, split into different greyscales, to analyse and quantify differences between various nanofibre mats created from polyacrylonitrile. In addition to the strong influence of the nanofibre diameters, a certain impact of the AFM settings was also seen and must be taken into account in future research. Keywords: electrospinning, polyacrylonitrile (PAN), nanofibrous mat, atomic force microscopy (AFM), Hurst exponent, random walk Izvleček Obdelava slik vlaken in vlaknastih materialov omogoča raziskovanje različnih geometrijskih lastnosti, kot so kosmatost preje, bifurkacija vlaken ali dolžine in premera vlaken. Takšni vzorčni seti z nepravilnostmi so naravno primerni za statistični pregled slik z algoritmom slučajnega hoda. Pri tem izračunamo ti. Hurstov eksponent, ki je asimptotični skalirni eksponent srednjega kvadratnega premika položaja sprehajalca. Dosedanje raziskave so dokazale ustreznost metode za oceno različnih vlaken, prej in ploskovnih tekstilij. V nedavni študiji smo uporabili slike AFM (mikroskopije na atomsko silo), razdeljene glede na različne sive odtenke, za analizo in količinsko določitev razlik med različnimi nanovlaknatimi koprenami iz poliakrilonitrila. Poleg močnega vpliva premera nanovlaken je bil viden tudi določen vpliv nastavitev AFM, ki jih je potrebno upoštevati v prihodnjih raziskavah. Ključne besede: elektropredenje, poliakrilonitril (PAN), nanovlaknata koprena, mikroskop na atomsko silo (AFM), Hurstov eksponent, slučajni hod Corresponding author/Korespondenčna avtorica: Tekstilec, 2020,63(2), 104-112 Prof. Dr. Dr. Andrea ttmann D0L. m 14502^^2020.63.104-112 E-mail: andrea.ehrmann@fh-bielefeld ORCID: 0000-0003-0695-3905 Analysis of AFM images of Nanofibre Mats for Automated Processing 105 1 Introduction Electrospinning can be used to prepare nanofibres or nanofibrous mats from diverse polymers or polymer blends [1-5], even in combination with metallic [6-8], semiconducting [9-11] or other nanopar-ticles. Subsequent thermal treatment can be used to stabilise the nanofibrous mats chemically [12-14], followed by carbonisation [15-17], or to use a calcination step instead to evaporate the polymer and sinter the residual inorganic material [9, 14, 18]. To describe such electrospun nanofibres or nanofi-brous mats quantitatively, usually the fibre diameter distribution is given [19, 20], as well as the fibre orientation [21, 22]. There are, however, many more interesting parameters, e.g. the pore size or general porosity, which is sometimes measured by sophisticated instruments [23, 24], but hard to define from a microscopic image, even if the resolution is high enough. Such questions are also important, particularly for the application of such nanofibrous mats as filters [25, 26]. Using only high-resolution images as the basis for a quantitative description of a nanofibre mat may be possible by different mathematical methods. Some of them are the fractal dimension, which is often used as an indicator of the roughness of surface coatings or finishings [27] or for the detection of irregularities in the form of fabric defects [28-31], including the topothesy fractal dimension, which is less affected by scale variations and thus assumed to be a good instrument to measure surface roughness [32-34]. Other methods are calculations of the lac-unarity, which describes spatial features of multi-fractal or non-fractal surfaces [35-37], or sometimes the succolarity, which measures the degree of percolation of an image [38, 39]. Another parameter that can be used is the so-called Hurst exponent. This value is calculated by performing random walks on the parts of an image where the sample is visible. This is how spatially adjacent areas of a sample in a certain image are defined. Hurst exponent evaluations of textile fabrics were performed by our group [40-42] and several other researchers [43]. In our previous investigations, we concentrated on microscopic images of knitted fabrics to evaluate fabric hairiness. This article presents a study of atomic force microscopy (AFM) images taken on different electro-spun nanofibre mats, focusing mainly on the influence of the AFM control parameters on the resulting image and the corresponding Hurst exponents. 2 Materials and methods Sample preparation A needleless Nanospider Lab electrospinning machine (Elmarco Ltd., Liberec, Czech Republic) was used for sample preparation. The following spinning parameters were chosen: voltage of 80 kV (or 65 kV), nozzle diameter of 0.9 mm (or 1.5 mm), carriage speed of 200 mm/s, bottom electrode/substrate distance of 240 mm, ground electrode/substrate distance of 50 mm, chamber temperature of 22 °C, and relative humidity in the chamber of 32%. Electrospinning was performed using a polypropylene (PP) nonwoven as a substrate. The spinning solution contained 16% (or 20%) PAN (X-PAN, Dralon GmbH, Lingen, Germany), dissolved in dimethyl sulfoxide (DMSO, min. 99.9%, S3 Chemicals, Bad Oeynhausen, Germany). Measurements Investigations of the sample morphology were performed with an atomic force microscope (AFM, FlexAFM by Nanosurf, Liestal, Switzerland), using SHR 300 and TAP190Al-G AFM probes as cantilevers, which work in dynamic mode and have tip diameters of 1 nm and 20 nm, respectively. The AFM settings (proportional (P), integral (I), differential (D) control and setpoint) were either optimised to get a sharp image or, in the second part of the study, varied around the optimum. While P, I and D describe the values of a common PID controller, the setpoint defines the oscillation amplitude of the cantilever in the dynamic mode. Random walk and Hurst exponent In the simplest case, a colour image or, in the case of an AFM image, a greyscale image has to be transferred into a black-and-white image. Often the black parts define the sample area, while the white parts define the pores or the open areas between sample parts, e.g. between the yarns of a knitted fabric [40-42]. The black area can be more or less connected, depending on the sample under examination, starting from a completely black square as one extremum to tiny black spots as another extremum. Next, a so-called random walk is performed on the black parts of the sample only. A random walk can be described as follows: an arbitrary pixel inside the black part of the sample is chosen. Then, a step in an arbitrary direction - one pixel left, right, up or Tekstilec, 2020,63(2), 104-112 106 Analysis of AFM images of Nanofibre Mats for Automated Processing down - is performed, followed by another arbitrary step, etc. Finally, after a defined number of steps -e.g. 100, 1,000 or 10,000 - the distance between the original pixel and the final pixel (the displacement vector) is calculated. If this process is repeated several times, the average displacement vector vanishes, since the final pixel will sometimes be located on the upper left of the original pixel, sometimes on the lower right, etc. What does not vanish, however, is the squared displacement vector. For a completely black square, i.e. a large area without any restrictions of the random walk path, the squared average displacement vector can be assumed to be proportional to the number of experiments n: = Cn (1) with the displacement r and a constant C, which is only necessary for mathematical reasons and has no physical relevance. This formula must be modified as follows for a not completely black area, but rather a complex image with partly black areas, on which the random walk can be performed, and white areas that limit the possible walk directions, especially in fine black structures whose border must not be crossed: = Cn2h (2) where h represents the aforementioned Hurst exponent (see for example [46] for some mathematical justifications). Comparing both formulas, we see that for a completely black area h can be expected to be approximately 0.5 to make both formulas identical. For a fractured black area, the possible ways of the random walk are limited by the white areas in between, making the possible distance between the starting and ending points smaller and thus reducing h. Indeed, the values of h are reduced for smaller structures, especially for the aforementioned small black dots in a white matrix that do not allow for moving from one black dot to another, thus strongly limiting possible movements. Such a random walk would result in a single value of the Hurst exponent. Since this is a statistical method, it makes sense to use more than one test. Typically, approximately 100-1,000 starting points on a given image are chosen on which random walks with 100, 10,000 or 1,000,000 steps are performed. In this way, a large number of Hurst exponents is calculated, resulting in a Hurst exponent distribution being characteristic for an image, as will be shown in the next section. It should be mentioned that in this description we started by transforming an original image into a single black-and-white representation. This may, however, not always be sufficient. Here we will also discuss the possibility of splitting one original image into several grey-channel sub-images, for example, labelled with numbers between 0 (black) and 31 (white) representing 256 grey channels. Importantly, this is analogous to the analysis of multi-colour (multi-spectral) or hyper-spectral images, where various wavelengths are split into spectral channels. It is worth mentioning that other image processing methods were not used as pretreatments of the AFM images. To exclude the possible influence of typical AFM image processing routines, using dedicated optimisation software, the original AFM images with line fit applied were used as the basis of this study. The influence of image processing with specific AFM software, especially for sharpening purposes, will be investigated in a future study. 3 Results and discussion Figure 1 depicts an exemplary Hurst exponent distribution measured for a PAN nanofibre mat elec-trospun with a voltage of 65 kV. The area of investigation, as depicted in the orange inset, has a dimension of 25 ¡um x 25 um. The second image shows the corresponding black-and-white image. The relatively large Hurst exponent of h ~ 0.43 can be attributed to relatively large fibre areas, here defined as the white areas, while the black areas are correlated with borders between neighbouring fibres so that their evaluation would not be related to a physically meaningful property. This number alone is not very meaningful, so we next tested how strongly Hurst exponents vary for completely different treatments. Figure 2 illustrates a surface showing broken polishing lines on a metallic coating (Figure 2a), as well as a lithography resist (Figure 2b) on atomically smooth substrates. The Hurst exponent distribution on the dark features in Figure 2a results in a smaller Hurst exponent due to the much narrower and additionally Tekstilec, 2020,63(2), 104-112 Analysis of AFM images of Nanofibre Mats for Automated Processing 107 fractured lines, but only with a small difference to the nanofibre image (Figure 1). 90 30 70 60 »50 §40 o 30 20 10 (a) h - 0.4201 +0.0014 Jj_"nip' I liiiiiil (non-Gaussian), since cases h > 0.5 are not expected in image processing analysis of this type. Thus, the presented results differ and allow for a quantitative differentiation between the different images. Nevertheless, the differences, especially between the na-nofibre mat depicted in Figure 1 and the scratched substrate in Figure 2a, are not very clear due to the non-Gaussian character of the distributed data. Figure 3 shows the results of a Hurst evaluation of another PAN nanofibre mat, this time produced with 20% PAN dissolved in DMSO, electrospun with a nozzle diameter of 1.5 mm using a voltage of 65 kV to obtain significantly thicker fibres, as visible Figure 1: Hurst exponent distribution measured for a PAN nanofibre mat electrospun with a voltage of 65 kV, using a nozzle diameter of 0.9 mm and a polymer solution with 16% PAN. The insets show the original AFM amplitude image with line fit applied (orange), as well as the corresponding black-and-white image on whose white areas the Hurst exponent evaluation was performed. The red line is the Lorentz line fit to the distribution. The Hurst exponent distribution calculated for the lithography resist (Figure 2b), on the other hand, shows large connected areas and thus suggests a larger Hurst exponent, which is clearly the case. The standard deviations (cf. insets in Figures 1 and 2) are very small, as derived from Lorentz line fits to the obtained histograms, which are not symmetrical Figure 3: Hurst exponent distribution measured for a PAN nanofibre mat electrospun at 65 kV with 20% PAN through a nozzle of diameter 1.5 mm. The insets show the original AFM amplitude image with line fit applied (orange), as well as the corresponding black-and-white image on whose white areas the Hurst exponent evaluation was performed. 90 80 70 60 « 50 c = 40 o 30 20 10 0.0 0.1 0.5 MTfflfl (1 = 0.4785 + 0.0003 0 0.0 i - -■.trtWwn afoi A CE 0.92 LU 0.90 Û ) ■¿r 250 280 310 340 370 Pre-elongatior> (%) 33.4 te* 66.8 te* 100.2 lex b) 400 Figure 6: Effect of pre-elongation e of elastomeric threads on stretch properties: a) full deformation and b) elastic deformation contribution by 17% with triple density (100.2 tex) weft threads. The mass per unit area of the warp knitted band increased by 5-7% with an increase in of the pre-elon-gation of the elastomeric threads, which was mainly due to the vertical increase of the stitch density. An investigation of the stretchability of elastic warp knitted fabrics was carried out by stretching the band walewise, i.e. in the direction of the inlaid elastomeric filament. Three parallel measurements were performed for each variant. The obtained results Table 4: Samples photos within stretching showed a good convergence, which confirms their accuracy. The results of full deformation and its components calculations are presented in Table 3. As a result, it was established that the full deformation of the elastic warp knitted band (Figure 6a) was from 115% to 140%, which facilitates their use in medical binders and other support products. The full deformation of the investigated variants was directly proportional to the pre-elongation of the elastomeric filaments. Increasing the linear density of the weft Fabric elongation (%) Liner density of weft yarn (tex) 33.4 66.8 100.2 0 SHI HÜ HÜ 20 IIS HÜ WÊË 40 1 ] ; f\ ¡¡HI 60 ä 1 ill: 1111 Tekstilec, 2020, 63(2), 113-123 121 Study of Elastic Warp Knitted Bands: Production and Properties inlay yarn resulted in a slight (within 10%) decrease of deformation. The dependence of the full deformation on the pre-elongation of the elastomer filament can be expressed as (R2 = 0.8): ef = 94.1 + 0.1 £. The elastic component of the full deformation of warp knitted band had the highest content (> 0.93). Its value increased with the pre-elongation level of the elastomeric filament (Figure 6b), which confirmed the conclusions made by the authors in a previous study [22]: increasing the pre-elongation of elastomeric yarn leads to an increase in the yarn strain. As a result, the relaxation processes in the fabric structure are faster. The knitted band with 33,4 tex weft threads demonstrated the smallest level of elastic deformation. It should be noted that the residual deformation of the elastic warp knitted bands was insignificant (did not exceed 1.7%) and therefore will not affect the quality of the medical and prophylactic products for which this elastic fabric is designed. It is obvious that the residual component of full deformation was near zero for the elastic band with 100.2 tex weft threads. When using elastomeric yarn without any wrapping, the comfort of the fabric may be degraded. An elastomeric yarn should not be placed at the surface of the knitted structure as in the initial state as well as in a stretched state. Studies of the coverage degree of the elastomeric threads by transverse weft threads were carried out by taking a photo of knitted samples at different elongation levels (Table 4). A specimen was fixed in the clamps of the tensile testing machine; the camera was located to fix the middle part of the specimen. Samples were stretched to a certain elongation (10%, 20%, 30% ... 100%) at a constant speed (50 mm/minute) of the lower clamp. The machine was stopped and a photo was taken. Obviously, at the initial state (elongation 0%), the transverse weft threads completely covered the elastomer, preventing it from reaching the surface in all samples. For samples with a 33.4 tex transverse weft thread, the elastomer was visible even at 20% elongation. For samples with a 100.2 tex, the transverse weft thread visibility of the elastomer was observed at 60% or higher elongation. 4 Conclusion An elastic warp knitted band for use as a fixing element in rehabilitation and prophylactic products has been developed. It is proposed that the elastic thread should not be inlaid in every wale and the guide bar threaded according to repeat 2: 1 in order to reduce the material consumption and product's weight. This results in a 20% reduction in the mass per unit area of the warp knitted band, while maintaining relaxation characteristics within the relevant requirements for rehabilitation and prophylactic products. Based on the two-factor experiment planned and conducted in the work, the following was concluded: - the linear density of the weft yarn (X1) affected the thickness, vertical density and surface density of the knitted material, and, to a lesser extent, the content of the elastic component in full deformation; and - the pre-elongation of the elastomeric threads before the knitting zone had a significant effect on the vast majority of the investigated properties: an increase in pre-elongation from 280% to 395% which led to - an increase in the number of courses per 100 mm by 15-27%, mass per unit area by 7-10% and full deformation and its elastic component by 15%, and - a decrease in the length of the elastomer filament per stitch by 10%, as well as the residual component of the full deformation. From the result of our studies, it was found that the use of 100.2 tex transverse weft threads guarantees full coverage of the elastomer within the elastic band's elongation of up to 60%. 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Tekstilec, 2020, 63(2), 113-123 124 Nuredin Muhammed, Nalankilli Govindan Bahir Dar University, Ethiopian Institute of Textile and Fashion Technology, Textile Chemistry Research and Innovation Centre, 1037, Bahir Dar, Ethiopia Chemical Modification of Cotton Cellulose by Carbamation with Urea and its Dyeability with Reactive Dyes without the use of Electrolytes Kemična modifikacija bombaža s karbamiranjem s sečnino in njegova obarvljivost z reaktivnimi barvili brez uporabe elektrolita Original scientific article/Izvirni znanstveni članek Received/Prispelo 3-2020 • Accepted/Sprejeto 5-2020 Abstract Cotton cellulose is primarily dyed with reactive dyes that form a strong covalent bond with the substrate. The reactive dyeing process requires a high amount of salt and alkali. Studies have been conducted to improve exhaustion and reduce the use of a high amount of salt and alkali through the cationisation of the substrate. This study focuses on the carbamation of mercerised cotton cellulose for the purpose of preparing an alternative way of dyeing cotton fabric with reactive dye in the absence of electrolytes. The effect of carbamation was shown qualitatively using FTIR spectroscopy where the optimal results were achieved using a urea concentration of 400 g/l, a temperature of 135 °C and a time of 5 minutes. The carbamated cotton demonstrated a lower decomposition temperature than that of native cotton. Colour strength, exhaustion, fixation and total dye utilisation studies demonstrated good results compared to the dyeing of conventional cotton fabric. Keywords: cotton, carbamation, urea, pad-dry-cure technique, dyeing, Reactive Red HE3B, adsorption isotherm Izvleček Barvanje bombažne celuloze poteka večinoma z reaktivnimi barvili, ki tvorijo močno kovalentno vez s substratom. Proces barvanja z reaktivnim barvilom zahteva veliko količino soli in alkalij. Opravljene so bile raziskave s kationi-zacijo substrata za izboljšanje izčrpanja in zmanjšanje uporabe velikih količin soli in alkalij. Študija se osredotoča na karbamiranje mercerizirane bombažne celuloze z namenom priprave alternativnega načina barvanja bombažne tkanine z reaktivnim barvilom v odsotnosti elektrolita. Učinek karbamiranja je bil kvalitativno viden na spektrih FTIR, kjer so bili optimalni rezultati doseženi pri koncentraciji sečnine 400 g/l, temperaturi 135 °C in času 5 min. Kar-bamirani bombaž je imel nižjo temperaturo razgradnje od nemodificiranega bombaža. Jakost obarvanja, izčrpanje, fiksiranje in celotna uporaba barvil je pokazala dobre rezultate v primerjavi z barvanjem konvencionalne bombažne tkanine. Ključne besede: bombaž, karbamiranje, sečnina, impregnirno-fiksirni postopek, barvanje, Reactive red HE3B, ad-sorpcijska izoterma Corresponding author/Korespondenčni avtor: Prof. Dr. Nalankilli Govindan E-mail: gnalankilli@yahoo.com Phone: +251 984624403 ORCID: 0000-0001-9836-0925 Tekstilec, 2020, 63(2), 124-137 DOI: 10.14502/Tekstilec2020.63.124-137 Chemical Modification of Cotton Cellulose by Carbamation with Urea 125 and its Dyeability with Reactive Dyes without the use of Electrolytes 1 Introduction Cellulose is a chemically homogeneous linear polymer of up to 10,000 anhydroglucose units that are connected by (3-1,4 bonds [1]. Each glucose unit is tilted by 180° towards its neighbour. The structural subunit of cellulose is cellobiose. Chemical uniformity facilitates the spontaneous crystallisation of cellulose molecules. Hydrogen bonding within and between multiple layers of parallel molecules results in the formation of tightly packed microfibrils. It has been reported that, in the manufacturing of cellulose carbamate, urea first decomposes into ammonia and isocyanic acid at approximately 135 °C [2], while Fu et al. reported that the decomposition of urea starts above its melting temperature of 132.7 °C [3]. Isocyanic acid (-HNCO-) reacts with cellulose hydroxyl (-OH) groups to form cellulose carbamate. The car-bamate groups are substituted in the hydroxyl groups of the cellulose chain [4-7]. Reaction efficiency depends, inter alia, on the amount of urea, reaction conditions and raw material properties [8, 9]. The processes for synthesizing carbamated cellulose materials are explained in the following sections. Solventless carbamation has been reported by heating (in an oven or oil bath) urea with a mercerised, carbamated cotton/cellulose (MCC) or alkali-swollen cotton linters in the temperature range of 110— 185 °C for 3-9 hours, with an urea/cellulose weight ratio of 1.5-4.0, followed by microwave heating (255 W power) for 2-5 minutes [9]. Cellulose car-banilation performed through the reaction of cellulose, with phenyl isocyanate mostly in dimethyl sulfoxide (DMSO) or pyridine as the solvents, has been used widely for determining the analytical parameters of celluloses through gel permeation chromatography (GPC) in organic solvents, such as tet-rahydrofuran (THF) or N,N-dimethylacetamide (DMAc) [10]. Carbanilation was performed using native cellulose or its alkali-activated counterpart. Many of these reactions start heterogeneously (suspension) and turn homogeneously. Hearon et al. carried out work through the suspension of cotton linters in refluxing pyridine, while reaction was conducted using phenyl isocyanate or a-naphthyl isocyanate to give the corresponding tricarbani-lates. The reaction mixture became homogeneous after 36 and 40 hours, respectively. The CC was precipitated from the reaction mixture [11]. Cellulose tricarbanilate was obtained through the reaction of a suspension of biopolymer in DMF, using phenyl isocyanate in the presence of triethylenediamine as a catalyst at 95-100 °C. The suspension turned homogeneous within 30-60 minutes CC films were cast directly from the reaction mixture [12]. The reaction of cellulose with phenyl isocyanate in pyridine at 80 °C for 2 days produced a clear solution (MCC) or was incomplete (a pulp). The precipitation of CC in methanol resulted in the loss (5-26% (w/w)) of a low molecular weight fraction, while precipitation in water/methanol mixture (volume ratio 30/70) resulted in less [13] or no product fractionation [14]. Incomplete carbanilation of fibrous cellulose (bisulfite pulp; 86.3-97.1% a-cellulose; de-crystallized cotton linters) was later avoided through the pretreatment (activation) of the biopolymer with liquid ammonia. The reaction was carried out for 2 days at 80 °C in pyridine, DMF or DMSO. Clear solutions of cellulose tricarbanilate were obtained in all cases [4]. Kenaf core cellulose was suspended in urea solutions [0.9-4.5% (w/w)] and the mixture was stirred under normal and then reduced pressure, the latter to enhance urea penetration within the biopolymer fibres. The reaction was induced by MW heating (380 W power) for 10-30 minutes. The N% in the purified CC increased as a function of increasing the urea concentration in the solution and the reaction time [15]. Cellulose derivatisation can be better controlled, and the reaction temperature reduced, e.g. to 100-130 °C, where an activated biopolymer was employed and carbanilation was carried out in the presence of a solvent. Another approach to obtaining CC under heterogeneous conditions is to use SC-CO2 as a solvent to introduce urea into the biopolymer fibres [16]. The simplest approach to prepare CC under homogeneous conditions is to derivatise the hydroxyl groups of the AGU of a cellulose derivative. Cellulose tricarbamate from MCC, cotton linters, sulfate pulp, and cellulose obtained from wheat straw and hardwood by steam explosion was obtained through the reaction of phenyl isocyanate with the biopolymer dissolved in DMAc/ LiCl for 2 hours, at 60-80 °C, in the presence or absence of a pyridine catalyst [14]. The conditions employed for carbamate formation under homogeneous conditions may lead to the formation of by-products [17, 18]. The formation of these by products was avoided by using anhydrous reaction conditions, a low reaction temperature Tekstilec, 2020, 63(2), 124-137 126 Chemical Modification of Cotton Cellulose by Carbamation with Urea and its Dyeability with Reactive Dyes without the use of Electrolytes 60-70 °C and a longer time period of 24-48 hours, and by using di(l-butyl) tin dilaurate as catalyst, a controlled amount of isocyanate (phenyl- and 1-butyl) and product workup that did not include quenching using an alcohol. The reaction of MCC, cotton linters or partially silylated cellulose in DMAc started heterogeneously and then turned homogeneously. Good to high yields (65-94%) of products with DS of carbamate from 1.74 to 3.0 were obtained [19]. Chemical modifications to cati-onise cotton have been reported to have beneficial effects in dyeing with reactive dyes [20-23]. In cellulose carbamate, the hydroxyl groups in the cellulose repeating unit are partially substituted with carbamate groups. The degree of substitution indicates the average amount of substituted hy-droxyl groups per anhydroglucose unit. The theoretical maximum DS is thus 3.0 [2]. Properties that are affected most by the degree of substitution are solubility, swelling and plasticity. One of the key factors governing the substitution of the prepared cellulose carbamate is the amount of urea in the manufacturing process [24]. The nitrogen content of cellulosic material is often used to describe the substitution degree of cellulose carbamates. However, nitrogen content only indicates the amount of nitrogen in the sample, not the exact degree of substitution. Moreover, the uniformity of the product and the evenness of the carbamate groups in the cellulose chains are significant factors in determining cellulose carbamate quality and properties. However, researchers have reported that it is challenging to determine the uniformity of the substituted cellulose[11, 25]. Guo et al. and Yin et al. reported that the carbamate group is stable in acidic media, but that hydrolysis can take place in alkaline media. In alkaline media, the carbamate groups are irreversibly decomposed to carbonate and ammonia at a rate dependent on NaOH concentration and temperature [6, 17]. 2 Materials and methods 2.1 Materials Plain weave cotton fabric (half-bleached) with a warp density of 26 ends/cm, a weft density of 22 picks/cm, mass per unit area of 150 g/m2, warp and weft-way tensile strength of 319N and 228N respectively, and a warp and weft yarn count of 50 tex (20 Ne) were used throughout the work. Urea extra pure (Loba Chemie Pvt. Ltd., India), which decomposes at temperature above its melting temperature as a source for isocyanic acid, sodium hydroxide pellets, which is a strong alkali for mercerising, sodium carbonate powder to fix the reactive dye to the fibre, acetic acid to neutralise the fabric after mercerising, sodium sulphate for exhaustion in the conventional reactive dyeing of cotton (Alpha Chemika, India) and reactive dye of the class of HE (Reactive Red HE3B) for dyeing were utilised throughout this study. The following instruments were used in this study: Perkin Elmer TGA instruments to study the thermal decomposition properties of the carbamated material, a Perkin Elmer FTIR spectrometer to identify the molecular fingerprint of the carbamat-ed fabric and a Tensolab 100 (Mesdan Lab, Italy) to evaluate the mechanical strength of the carbamated fabric. Also used were: a crock meter (Mesdan Lab, Italy) to evaluate the resistance to fading of the dyed carbamated fabric to dry or wet rubbing, a lightfast-ness solar box (Mesdan Lab, Italy) to evaluate the resistance to fading of the dyed carbamated fabric while exposed to light and Laundr-o-meter (Mes-dan Lab, Italy) to evaluate the resistance to fading of the dyed carbamated fabric to wet washing. A Gre-tagmacbeth Colour Eye 310 was used to evaluate colour strength, while a UV/VIS spectrometer (Perkin Elmer Lambda 25, Singapore) was used to determine dye absorbance. The machines used in this study were an eco-IR dyeing machine for dyeing (Ahiba, US), a Padder Lab 300 (Mesdan Lab, Italy) for the application of treatments application to the mercerised fabric and an oven dryer (Mesdan Lab, Italy) for drying and curing purposes. The Kjeldahl method was used to determine the nitrogen content in the carbamated fabric to determine the degree of carbamation. 2.2 Methods The experimental part of this study was divided into three main sections. i. First, the carbamation of the cotton cellulose (i.e. the initial pre-treatment of half-bleached fabric through mercerization for the purpose of enhancing the accessibility of the functional groups in cotton cellulose) was carried out with the objective of optimisation. The main variables during the manufacturing of cotton cellulose carbamate were temperature, time and the concentration of Tekstilec, 2020, 63(2), 124-137 Chemical Modification of Cotton Cellulose by Carbamation with Urea 127 and its Dyeability with Reactive Dyes without the use of Electrolytes urea. The properties of the cotton cellulose car-bamate were studied, with major responses being the degree of substitution and the tensile strength (warp and weft direction) of the fabric. The optimised fabric was analysed using FTIR to determine the molecular fingerprint of the product, while TGA studies were also performed. ii. Secondly, the optimised carbamated and uncar-bamated cotton was dyed using reactive dyes (i.e. Reactive Red HE3B dye). The properties of the dyed cotton cellulose carbamate were evaluated against the dyed uncarbamated cotton fabric. The tests carried out were: the degree of exhaustion, fixation, colour strength (K/S), fastness to washing, fastness to light and rubbing fastness. iii. Thirdly, the modelling of an adsorption isotherm experiment was performed using Langmuir and Freundlich adsorption isotherms to find the best method to express the property of the carbama-ted cotton cellulose for dye adsorption. b. Carbamation The mercerised cotton fabric (barium activity number = 141.2 ± 1.0) was subjected to carbamation using 100 g/l, 250 g/l and 400 g/l amounts of urea by following pad-dry-cure method. The prepared cotton fabric was impregnated using a padding liquor in a laboratory padding mangle. The samples were then pre-dried for 5 minutes at 60 °C using an oven dryer, and then cured at 135 °C, 160 °C and 185 °C for 1, 3 and 5 minutes. The prepared carbamated samples were washed thoroughly with distilled water to purify them from the remains of urea and finally air dried. The experiment and optimisation were carried out using the response surface methodology (i.e. three-level factorial), with the major responses being the degree of substitution of carbamate groups in place of hydroxyl groups, warp- and weft-way tensile strength. Preparation of cellulose carbamate derivatives a. Mercerisation The mercerisation of half-bleached cotton fabric (i.e. sinking time < 3 seconds) was performed manually using a setup of a non-adjustable pan and frame. A piece of fabric was fixed to the pins of the steel frame with a tension of 3% and submerged into the concentrated (300 g/l) NaOH solution for 60 seconds with a mercerising temperature of 20-25 °C. The frame with the fabric still attached was then transferred to a sink and rinsed with running water to remove the majority of the alkali. After detaching the fabric from the frame, was rinsed, neutralised with dilute acetic acid, rinsed/washed with water and air dried. As an indicator of the degree of mercerisation, the barium number of the mercerised cotton fabrics was determined according to the AATCC test method 89-2003 [26]. Dyeing of uncarbamated and carbamated cotton Dyeing of untreated (uncarbamated) and carbamat-ed cotton fabrics was carried out using a laboratory eco-IR dyeing machine. Dyeing of uncarbamated cotton with Reactive Red HE3B (Figure 1) dye was performed according to the procedure recommended by the manufacturer, in which a shade (% o.w.f.) of Reactive Red HE3B (C.I. Reactive Red 120) dye was added to a room temperature dyebath. The fabric samples were then added and each bath was heated to 80 °C at a rate of 1.5 °C/minute. Before reaching 80°C, electrolyte (Na2SO4) of 40 g/l was added in two instalments at 55 °C and 65 °C to each bath. After holding the temperature at 80 °C for 10 minutes, 10 g/l of sodium carbonate was added. The bath was then held at 80 °C for 50 minutes, cooled to 60 °C at a rate of 2.5 °C/minute and then discarded (Figure 2 (a)) [27]. Figure 1: Reactive Red HE3B Tekstilec, 2020, 63(2), 124-137 128 Chemical Modification of Cotton Cellulose by Carbamation with Urea and its Dyeability with Reactive Dyes without the use of Electrolytes a) 30 Time (min) 105 b) 30 Time (min) 105 Figure 2: Dyeing cycle of (a) uncarbamated cotton fabric, (b) carbamated cotton fabric The procedure for dyeing the carbamated cotton was the same as that for uncarbamated cotton, except that the dyeing of carbamated cotton was done in the absence of electrolytes (Na2SO4), with the bath buffered at pH 6 using acetic acid (Figure 2 (b)). Dye uptake of both the carbamated cotton without sodium sulphate and uncarbamated cotton with sodium sulphate, was measured by sampling the dye bath before and after the dyeing process. The absorbance of the diluted dye solution was measured at the wavelength of the maximum absorption (2max = 560) of the dye using a UV-visible spectrophotometer. Percent dye bath exhaustion E% was determined using equation 1. values of the dyed samples taken before and after soaping, from which the extent of dye fixation was calculated using equation 3 and 4. F = Ç2 C 100 (%) T = E C2 (%) (3), (4), E = 100 (1 A A0 (%) (1), where A0 represents the absorbance of the dye solution before dyeing and Aj represents the absorbance of the dye solution after dyeing. The colour strength of the dyed samples was determined as the K/S value calculated from the sample reflectance (R) (equation 2): where T represents total dye fixed (%), C} represents the K/S value of dyed sample before soaping, C2 represents the K/S value of dyed sample after soaping and F represents the degree of fixation of absorbed dye. Determination of the degree of substitution The percentage of nitrogen present in the cotton fabric was measured in duplicate and used as an indicator of the level of carbamation. The analysis was conducted according to the Kjeldahl method using a sample mass of 10 mg ± 2 mg. The degree of substitution (DS) was determined using equation 5 below: DS = 162 x N K = (1 - R)2 S 2R (14 x 100) - (43 x N) (5), (2) The extent of the dye fixation of the reactive dyes on all the carbamated and uncarbamated cotton fabrics were determined using measurements of the K/S where N represents specimen nitrogen content (%), 162 represents the molar mass (g/mol) of an anhy-droglucose unit (AGU), 14 represents the molar mass of nitrogen (g/mol) and 43 represents the net increment in molar mass (g/mol) of an AGU on Tekstilec, 2020, 63(2), 124-137 Chemical Modification of Cotton Cellulose by Carbamation with Urea 129 and its Dyeability with Reactive Dyes without the use of Electrolytes substitution of a hydroxyl (-OH) by a carbamate (-OCONH2) group. Tensile strength and fastness testing Tensile strength was tested according to the ASTM D5034 textile grab method [28], colourfastness to laundering according to the AATCC test method 61-2007 [26], colourfastness to light in accordance with the ISO 105-B02:1994, and colourfastness to rubbing in accordance with the AATCC test method 8-2007 (AATCC, 2010). B:Tanpaalre{C) Fxtot Cniq: Actual DS O > . : : i. \:l v.-'k _ 03052 A: Concentration (gfl) XI = A: Cunœnhatiun X2 = ttTefrperat«R Acturi Factor c.r™=5 a) s 1 185 175" 165 B: Temperature (C) Tensile strength wen IN) O Design points above predicted value O Design points below predicted value 160 A: Concentration (g/l) XI - A. Concentration X2 = B: Temperature Actual Factor C: Time = 5 3 Results and discussion 3.1 Optimisation of the carbamation The response surface methodology (RSM) was used to evaluate the degree of the carbamate group that has been substituted in place of the hydroxyl group of cotton cellulose, with less effect on the weft- and warp-way tensile strength. The design was also used to study the relationship between the variables (urea concentration, curing temperature and curing time) and the responses (degree of substitution and tensile B: Temperature (C) A: Concentration (g/l) Design-Expert® Software Factor Coding: Actual Tensile Strength warp (N) Q Design points above predicted value O Design points below predicted value 216 K ' ft }16 XI = A: Concentration X2 = B: Temperature Actual Factor C: Time = 5 b) c) Figure 3: Response for (a) optimum carbamation, (b) weft-way tensile strength and (c) warp-way tensile strength strength). Analysis of variance (ANOVA) was used to test whether the variables (urea concentration, curing temperature and curing time) significantly affect the response values (degree of substitution, warp-way tensile strength and weft-way tensile strength). The results are presented in Figure 3. The effects of the factors are concentration, curing temperature and curing time, while responses are the degree of substitution, DS and tensile strength. It could be understood from the results that DS increased significantly by increasing the concentration of urea and increasing time, while there was no significant change in DS due to the varying of temperature. Tensile strength in the warp direction was affected significantly by increasing the temperature, while there was no significant change due to increment in concentration and curing time. Tensile strength in the weft direction was affected significantly by all the factors (concentration, temperature Tekstilec, 2020, 63(2), 124-137 130 Chemical Modification of Cotton Cellulose by Carbamation with Urea and its Dyeability with Reactive Dyes without the use of Electrolytes and time). The desired results were found to be: DS of 0.283, tensile strength in warp of 285.98 N and weft of 203.82 N. Under these conditions, the warp tensile strength decreased by 10.35%, while the weft tensile strength decreased by 10.61% relative to the control half-bleached fabric. 3.2 FTIR analysis Bands due to the stretching of OH groups of crystalline and amorphous modifications of cellulose in terms of celluloses I and II on account of merceri-sation and carbamation have been reported in literature [3, 31]. Because the properties of cotton cellulose carbamate material are one of the significant factors that contribute to the dyeability of material, differences between the mercerised cotton cellulose carbamate sample and mercerised, uncarbamated cotton were evaluated to understand the chemical change that took place in carbamation (Figure 4). Carbamates of cotton cellulose were characterised by means of FTIR to confirm the reaction of hy-droxyl groups with urea. A typical loss in the trans-mittance band for the carbamated cotton was observed in the range of 3600 cm-1 to 3300 cm-1, which is assigned to the (-NH2) [31] of the car-bamate group. The stretch is not as broad or strong as it appeared in the uncarbamated cotton (-OH stretch) in this region. The transmittance band from 3300 cm-1 to 3000 cm-1 is very broad in the uncarbamated cotton, which indicates the large numbers of -OH groups in the cotton [3, 31], while this band is not as broad in the carbamated cotton, which indicates a reduction in -OH groups that are replaced by the carbamate group. The transmittance peak at around 1100 cm-1 observed on uncarbamated cotton disappeared on the carbamated cotton. This can be attributed to the loss of -OH vibration in the carbamated cotton fabric. The reduction of hydroxyl peak at 3250 cm-1 represents strong evidence for the reaction of urea with the cotton samples. 3.3 Thermogravimetric analysis The TG curves of the mercerised cotton cellulose and its carbamate derivatives with DS of 0.2829 are shown in the Figure 5. The TG curves were separated into three sections. At the initial stage, the weight loss observed in the temperature range of 100 °C to 150 °C could be attributed to the evaporation of water and gas absorbed by the cellulose. In the range of 150 °C to 250 °C, there appeared a minor thermal decomposition of residues. In the TG curves, it was found that all the major decompositions are located in the range of 300 °C to 400 °C and 300 °C to 375 °C for control cotton cellulose and carbamated cotton cellulose, respectively. When comparing the samples, it was discovered that the major decomposition temperature of control cotton fabric was higher than car-bamated cotton cellulose. From the FTIR (Figure 4), it was observed that the carbamation of cotton showed the diminished intensity of hydrogen bonding in the range of 3600 cm-1 to 3300 cm-1, as the decrease in intensity had a visible effect on 2500 2000 1500 Wave number cm-1 Figure. 4: FTIR spectra of carbamated and control fabric Tekstilec, 2020, 63(2), 124-137 Chemical Modification of Cotton Cellulose by Carbamation with Urea 131 and its Dyeability with Reactive Dyes without the use of Electrolytes 3.4 Dyeing results Exhaustion, fixation and dye utilised The results of exhaustion, fixation and dye utilised are presented in Table 1. Exhaustion was determined by measuring the absorbance of the dye bath before and after the dyeing process at the wave length of maximum absorption (2max = 543 nm). The exhaustion percentage of the carbamated and mercerised cotton was higher than that of the control half-bleached fabric. For all fabrics, the exhaustion decreased by increasing the initial dye bath concentration. This can be attributed to the increment in affinity of the dye to the fibre. The dye utilisation of Reactive Red HE3B on all the control, mercerised and carbamated samples decreased by increasing the dye bath concentration. The exhaustion and dye utilisation are presented in Figures 6 and 7. The change percentage in dye utilisation was 12%, 13%, 7%, 15%, 14% and 10% for the shade depths of 0.5%, 1%, 2%, 3%, 4% and 5%, respectively, between the control and carbamated fabric. Table 1: Summary of the dyeing properties of Reactive Red HE3B for carbamated, mercerised and control samples Shade (%) Absorbance of dye solution before dyeing (A1) Material type Absorbance of dye solution after dyeing (A2) K/S value Exhaustion (%) Fixation (%) Total dye utilised (%) Before washing (C1) After washing (C2) 0.5 6.2 Ta) 0.80 3.80 3.44 87.10 90.48 78.81 UTb) 1.30 1.38 1.21 79.03 87.51 69.16 Mc) 0.90 3.90 3.50 85.48 89.74 76.72 1 8 T 1.90 5.27 4.78 76.25 90.58 69.06 UT 2.80 2.02 1.88 65.00 92.93 60.40 M 2.10 5.34 4.54 73.75 85.08 62.75 2 8.7 T 3.40 6.98 6.48 60.92 92.90 56.59 UT 3.80 2.30 2.14 56.32 93.14 52.46 M 3.50 7.17 6.83 59.77 95.29 56.96 3 9.3 T 4.10 7.59 7.19 55.91 94.68 52.94 UT 4.70 3.39 3.07 49.46 90.59 44.81 M 5.00 7.46 7.08 51.46 94.84 48.80 4 9.9 T 5.60 7.89 7.25 43.43 91.90 39.92 UT 6.20 3.93 3.62 37.37 92.15 34.44 M 7.54 7.68 7.35 36.64 95.70 35.06 5 10.8 T 6.30 8.00 7.37 41.67 92.07 38.36 UT 6.80 4.38 4.09 37.04 93.43 34.60 M 8.23 7.91 7.35 35.70 92.92 33.18 a)carbamated, b)control half-bleached fabric, c)mercerised fabric the TG curve (Figure 5) and on the decomposition temperature of the materials. Figure 5: TG curves of cotton cellulose and carbamat-ed cotton Tekstilec, 2020, 63(2), 124-137 132 Chemical Modification of Cotton Cellulose by Carbamation with Urea and its Dyeability with Reactive Dyes without the use of Electrolytes Figure 6: Percent exhaustion of Reactive Red HE3B on carbamated, mercerised and control fabric generation of positive charges, while the treatment fabric before carbamation (i.e. caustic mercerised) could also affect the dye adsorption, with the car-bamate groups introduced. Very good levelling on the carbamated cotton cellulose samples was visually confirmed in this study. Figure 7: Total dye utilisation of carbamated, mercerised and control samples Colour intensities (K/S) were employed to express the reduction ratio of light owing to absorption and scattering achieved based on reflectance. Figure 8 shows that the colour strength of the carbamated cotton dyed without sodium sulphate was much higher than that of the control half-bleached fabric. The carbamated cotton cellulose fabric was dyed with Reactive Red HE3B without using electrolytes; pH was instead made slightly acidic (pH = 6) through the addition of acetic acid. The improved dye uptake of carbamated cotton fabric may be attributed to the Figure 8: K/S values of carbamated, mercerised and control dyed samples In the dyeing of carbamated cotton samples using an acid bath, it was confirmed that there was a strong attraction between the cationic dye sites on the car-bamated cotton and the anionic Reactive Red HE3B dyes, which led to the achievement of higher exhaustion rates, without the addition of electrolytes to the dye bath. An enhancement of the colour strength is expected when the dye concentration is increased, as a greater number of dye molecules would be available in the vicinity of the cotton cellulose at higher concentrations. Unlike uncarbamated cotton, however, the dye build-up on the carbamated cotton is limited by its saturation adsorption value, which could be related to the amount of nitrogen introduced during pretreatment. The colour strength of the carbamated cotton increased by increasing the dye concentration, but the difference was very small at a 4% shade. This indicates that the fibre reached its saturation point, while the control half-bleached fabric colour strength increased in a fairly linear fashion. Looking at the results, the colour strength achieved by using a 5% shade of Reactive Red HE3B on the control half-bleached fabric could be obtained by using a 1% shade on the carbamated cotton fabric, Tekstilec, 2020, 63(2), 124-137 thus increasing the dye utilisation. Moreover, excellent levelness was visually observed on the dyed car-bamated cotton fabric. Fastness properties The overall result of dyeing properties in terms of the fastness of Reactive Red HE3B towards car-bamated cotton and control half-bleached fabric is summarised in Table 2. The result shows that wash fastness and rub fastness were not affected significantly. This may be due to the formation of a strong ionic bond between the fibre and the dye because it is equally good as the covalent bond that normally links the dye and the fibre. Adsorption isotherm analysis In order to study the adsorption property of Reactive Red HE3B dye on the carbamated cotton at a constant temperature, a sample of fabric was placed in a dye bath buffered at pH 6 and dyed for two hours at the temperature recommended by the dye manufacturer (i.e. 80 °C) [25]. The adsorption of Reactive Red HE3B dye by mercerised, carbamated Table 2: Summary of colourfastness results Con (%). Material type Wash fastness Rubbing fastness Light fastness Colour change Staining on white CA CO PA PES PAN WO Dry Wet 0.5 Control 4-5 4-5 4 4-5 5 4-5 5 5 4-5 4 CCCa) 4-5 4 3-4 4-5 5 4-5 5 5 4-5 4 Mb) 4-5 4-5 4 4-5 5 4-5 5 5 4-5 5 1 Control 4-5 4-5 4 4-5 5 4-5 4-5 5 4-5 4 CCC 4-5 4 3-4 4 5 4-5 4-5 4-5 4-5 4 M 4-5 4-5 4 4-5 5 4-5 4-5 5 4-5 5 2 Control 4-5 4-5 4 4-5 5 4-5 4-5 5 4-5 5 CCC 4 4 3-4 4 4-5 4-5 4-5 4-5 4-5 5 M 4-5 4-5 4 4-5 5 4-5 4-5 5 4-5 5 3 Control 4-5 4-5 4 4 4-5 4-5 4-5 4-5 4-5 5 CCC 4 4 3-4 3-4 4-5 4 4 4 4 5 M 4-5 4-5 4 4 4-5 4-5 4-5 4-5 4-5 5 4 Control 4 4-5 4 4 4-5 4-5 4-5 4-5 4-5 5 CCC 3-4 4 3-4 3-4 4-5 4 4 4 4 5 M 4 4-5 4 4 4-5 4-5 4-5 4-5 4-5 5 5 Control 4 4 3-4 3-4 4-5 4-5 4 4 4 5 CCC 3-4 3-4 3 3-4 4 3-4 3-4 4 4 5 M 4 4 4 4 4-5 4-5 4 4 4 5 a) carbamated cotton cellulose; b)mercerised; CA: acetate; CO: cotton; PA: nylon, PES: polyester; PAN: acrylic; WO: wool Tekstilec, 2020, 63(2), 124-137 Chemical Modification of Cotton Cellulose by Carbamation with Urea 133 and its Dyeability with Reactive Dyes without the use of Electrolytes cotton as a function of concentration is shown in Figure 9. It was observed that the initial dye adsorption was fast, and decreased with a subsequent increase in the concentration the dye. 0.0323 0.118S 0,3908 0.6614 1,1314 Ce (gJl) Figure 9: Effect of concentration on the adsorption of Reactive Red HE3B: temperature 80 °C; pH 6; amount is 5 g; time is 2 hours 134 Chemical Modification of Cotton Cellulose by Carbamation with Urea and its Dyeability with Reactive Dyes without the use of Electrolytes The profile obtained (Figure 9) from the study was utilised to plot Langmuir and Freundlich adsorption isotherms using well-known adsorption isotherm equations. In both the cases, linear plots were obtained and reveal the applicability of these isotherms on the ongoing adsorption process. Figures 10 (a) and 10 (b) illustrate Freundlich and Lang-muir plots respectively for the adsorption of Reactive Red HE3B on mercerised carbamated cotton, while different Freundlich and Langmuir constants derived from these plots are presented in Table 3. However, the best fit for the system is found with a Freundlich adsorption isotherm with an R2 value of 0.987 (Figure 10 (a)), while with Langmuir, the fit obtained is R2 = 0.963 (Figure 10 (b)). It can thus be concluded that the dyes are not only attached to the available carbamate groups, but that they also form layers. In normal situations, with the dye used, the formation of layers is not particularly surprising because the dye molecule is essentially linear, similar to a direct dye. It would, therefore, be expected to show a tendency to form layers, with hydrogen bonding between appropriately placed groups on the dye and the fibre, and between dye molecules and other dye molecules. In this study, however, this kind of result was not expected because the carbamate groups that ionize (positively) should attract the negatively ionized Reactive Red HE3B dyes, while the remaining -OH were not expected to adsorb, as the hydroxyl group and the dye are negatively ionized and should thus repel one anoth- log [0}f Rs = 0,9873 er. However, from the results, the adsorption was mostly explained with the Freundlich adsorption isotherm, which assumes that the dye adsorption is not limited to the functional groups available in the material to be dyed. The assumption was therefore made that the introduced functional groups play the role of attracting not only a single molecule, but rather many molecules that could be adsorbed on the hydroxyl groups. Table 3: Freundlich and Langmuir constants of Reactive Red HE3B over carbamated cotton: temperature 80 °C; pH 6; amount 5 g; time 2 hours Freundlich constants n 0.407 K 1.254 Langmuir constants [S]f (g/l) 15.97 K (l/g) 0.0056 Figure 11 shows the SEM image of half-bleached control, mercerised and carbamated fabrics. It is evident that surface roughness increased after car-bamation, better than the deconvoluted, swollen and circular cross section of mercerised fibres. The fibres in the half-bleached control fabric are convoluted; surface roughness is not visible up to a mag-nifi cation of 500-x. Surface roughness may have improved the adsorption property of the carbamated fabric, since it is expected that only the carbamate groups will be involved in the adsorption of the Reactive Red HE3B dye. The fact that most studies 0,25 R? = 0.9637 0,2 0,15 0,1 0,05 10 a) b) 20 VCe 30 40 Figure 10: Adsorption isotherm for Reactive Red HE3B carbamated cotton system: temperature of 80 °C; pH 6; amount is 5 g; time is 2 hours; (a) Freundlich; (b) Langmuir Tekstilec, 2020, 63(2), 124-137 Chemical Modification of Cotton Cellulose by Carbamation with Urea 135 and its Dyeability with Reactive Dyes without the use of Electrolytes a) b) Figure 11: SEM image of (a) carbamated; (b) control and (c) mercerised fabric c) [29-31] of adsorption isotherm on cationised cotton provide a better explanation of the Langmuir adsorption isotherm (which is not the case in this study) might be because the surface roughness of the carbamated cotton fibre increased. The experimental data were fitted to the Langmuir model, with the linearised form presented in Figure 10 (b), which had high correlation coefficient (R2 = 0.963), and demonstrated a very good correlation with the aforementioned model. The correlation coefficients also indicated a good correlation between parameters, and confirmed the functional adsorption of Reactive Red HE3B dye onto the carbamated fabric. Interestingly, the carbamated cotton with the selected dye fits the Freundlich model of adsorption isotherm, showing an even better correlation (R2 = 0.987), as indicated in Figure 10 (b). A conclusion concerning a Langmuir-type interaction between anionic dyes and aminised cotton was already reported by Porter [32]. It was described that the sorption of dye from dye baths can be stopped when the amino groups of fibres have been saturated with dye molecules. According to the results obtained (which a Freundlich type of interaction explains better), the process could be because of the interaction between the anionic Reactive Red HE3B dye and a positive functional site (-NH3+) of the cotton fabric, which first causes the sorption of more dye molecules on the carbamated cotton. After the dyeing sites are fully saturated, dyes might begin to be adsorbed on the surface by weak bonds. The dyeing process will thus be improved with the mechanism explained, while the surface roughness of the carbamated cotton might play a crucial role. 4 Conclusion The problem of reactive dyes requiring a large amount of electrolytes could be mitigated through an additional pretreatment process after mercerisation using urea to introduce a carbamate group in place of hydroxyl groups to make the cotton fabric positively charged. This makes the Reactive Red HE3B dye, which is negatively charged, highly attracted to the fibre. It can be concluded from the investigated report that urea, pad-dry-cure modification (i.e. carbama-tion) can improve the dyeability of cotton fibre. The treatment of carbamation allowed the adsorption of Reactive Red HE3B dye molecules onto cotton fibres and the reaction between the dye molecule and the cotton fibre without the utilisation of electrolytes. The procedure for optimum carbamation appeared to be at a urea concentration of 400 g/l for a curing time of 5 minutes at 135 °C. The degree of substitution was 0.2829, while warp- and weft-way tensile strengths were affected significantly. Dyeing studies show very good results with DS of 0.2829, The method would have great potential for industrial application, as pad-dry-cure is a relatively clean, environmentally friendly technique, with less energy, water, time and resources required, as the liquor could be reused. An entirely new system is required on curing equipment, which can collect the ammonia gas released during the decomposition of urea (which could be considered an advantage and could be used as a pre-activat-ing agent for cotton cellulose, replacing caustic mer-cerisation, or as a raw material for different chemical reactions), while care must be given during the production of cotton cellulose carbamate. The thermal analysis showed carbamated cotton fabrics have a very rapid degradation property above a temperature of 300 °C up to 370 °C, where the control half-bleached fabric starts at the same temperature of 300 °C and goes up to 400 °C. The dyeing results were good, with satisfactory fastness properties. The visual levelness of the dyed fabric was also good. The exhaustion, fixation and total dye utilisation percentage showed improvement compared with control half-bleached fabric. The change in total dye utilisation was in the range of 7-15% than that of control half-bleached fabric. Tekstilec, 2020, 63(2), 124-137 136 Chemical Modification of Cotton Cellulose by Carbamation with Urea and its Dyeability with Reactive Dyes without the use of Electrolytes Dyeing basically happens between the negatively charged Reactive Red HE3B dye and the positively charged cotton cellulose due to the replacement of the hydroxyl group with the carbamate group. 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Coloration Technology, 2002, 118(5), 238-243, doi: 10.1111/ j.1478-4408.2002.tb00106.x. Tekstilec, 2020, 63(2), 124-137 138 Dinesh Bhatia 1 2, S.K. Sinha2 1 Jawahar Lal Nehru Govt. Engineering College, Department of Textile Engineering, Sundernagar (Himachal Pradesh), India 2 Dr. B.R. Ambedkar National Institute ofTechnology, Department ofTextile Technology, Jalandhar (Punjab), India Thermo-physiological Properties of Structurally Modified Wool/Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics Lastnosti toplotne udobnosti ročno stkanih tkanin z votkom iz strukturno modificirane preje iz mešanice volna/poliester, izdelanim strojno in ročno Original scientific article/Izvirni znanstveni članek Received/Prispelo 4-2020 • Accepted/Sprejeto 5-2020 Abstract An attempt was made to compare the combined desirability value for a treated and untreated handloom fabric using machine-spun and hand-spun blended yarns as weft. The experimental plan included the preparation of both hand-spun and machine-spun yarns at different blend compositions according to a mixture design prepared on Design-Expert software, followed by the preparation of fabric on a handloom. The dissolution of one component using a suitable chemical treatment was then performed on both fabrics made from hand-spun and machine-spun yarn by taking into account an expected significant change in the arrangement of constituent fibres that ultimately enhance performance in terms of the thermo-physiological behaviour of fabrics. All properties viz air permeability, compressibility, thermal resistance, water vapour permeability, bending rigidity and drying capacity showed significant differences for both type of fabrics. Fabrics with hand-spun yarn as a weft demonstrated higher values of thermal resistance, compressibility, water vapour permeability and drying capacity due to the voluminous and soft structure of hand-spun yarn compared to fabric with machine-spun yarn as a weft. In general, after the dissolution of the polyvinyl alcohol component, both types of fabrics exhibited higher values of thermal resistance, compressibility, drying capacity and water vapour permeability, while values for air permeability and bending rigidity were lower for untreated fabrics. The results of the optimisation of treated fabrics with machine-spun yarn as weft demonstrated the highest desirability value (0.73), as well as a lower percentage of wool fibres (55%), followed by treated fabrics with hand-spun yarn as weft, which demonstrated a desirability value of 0.66 and a percentage of wool fibres of 60% in the blend composition. Untreated fabrics (both machine-spun and hand-spun) exhibited a similar desirability value and at same blend composition (20% polyester, 70% wool and 10% polyvinyl alcohol). Keywords: desirability, optimisation, blend composition, PVAL, handloom, thermal resistance Izvleček Neobdelane in obdelane ročno stkane tkanine z votkom iz strojno in ročno izdelanih mešanih prej so bile primerjane z vidika kombiniranega indeksa zaželenosti. Eksperimentalni načrt vključuje pripravo ročno in strojno spredene preje iz mešanic različne sestave glede na načrt, zasnovan s pomočjo programskega orodja Design-Expert, ki mu je sledila izdelava tkanin na ročnih statvah. Obe vrsti tkanin, izdelanih z ročno oziroma strojno spredeno prejo v votku, so bile kemično obdelane, pri čemer se je raztopila ena komponenta, da bi dosegli pričakovano spremembo razporeditve Corresponding author/Korespondenčni avtor: Tekstilec, 2020,63(2), 138-150 Dr. S.IC Smta DOI: 10.14502/Tekstilec2020.63.138-150 E-mail: sinhask@nitj.acin ORCID: 0000-0003-0871-3948 Thermo-physiological Properties of Structurally Modified Wool/ 139 Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics vsebovanih vlaken, ki znatno izboljšajo toplotno udobje tkanin pri nošenju. Vse lastnosti, tj. zračna prepustnost, stislji-vost, toplotni upor, prepustnost vodne pare, upogibna togost in kapaciteta sušenja, kažejo na velike razlike med obema vrstama tkanin. Zaradi voluminozne in mehke strukture ročno spredene votkovne preje so imele tkanine, ki so to prejo vsebovale, višje vrednosti toplotnega upora, stisljivosti, prepustnosti vodne pare in so se sušile hitreje v primerjavi s tkaninami, ki so vsebovale strojno spredeno votkovno prejo. Na splošno sta po raztopitvi komponente polivinilne-ga alkohola obe vrsti tkanin pokazali višje vrednosti toplotnega upora, stisljivosti, sposobnosti sušenja in prepustnosti vodne pare in nižje vrednosti zračne prepustnosti in upogibne togosti v primerjavi z neobdelanimi tkaninami. Rezultati optimizacije za obdelane tkanine, ki so vsebovale strojno spredeno votkovno prejo, kažejo najvišjo indeks zažele-nosti (0,73) pri najnižji vsebnosti volne (55 %), sledijo obdelane tkanine z ročno spredeno prejo v votku (0,66) in 60 % volnenih vlaken v mešanici. Neobdelane tkanine (s strojno in ročno spredeno votkovno prejo) so imele skoraj podobni indeks zaželenosti in enako mešanico (20 % poliestra, 70 % volne in 10 % polivinil alkohola). Ključne besede: zaželenost, optimizacija, sestava mešanice, PVAL, ročne statve, toplotni upor 1 Introduction The handloom industry is one of the oldest and largest cottage industry in India,which represents and preserves the vibrant culture of India. Due to the use of less capital and power, their eco-friendly behaviour and their suitability for innovation and transformation with respect to market requirements, handloom fabrics provide a broader scope for research and innovation. Comfort is considered one of the fundamental properties for evaluating any textile material. Comfort is defined as "the absence of unpleasantness or discomfort" or "a natural state compared to the mere active state of pleasure". Handloom fabrics are more comfortable due to the specific behaviour of handloom fabric and the structure of hand-spun yarn because the structure of yarn and fabric plays an important role in the comfort of any fabric. Thermo-physiological wear comfort, which relates to the heat and moisture transport properties of clothing and the way that clothing helps to maintain the heat balance of the body during various activities, is one of the basic and necessary properties of a fabric. Any change in the structure of yarn and fabric helps to improve comfort in terms of heat and moisture, as it plays important role in the comfort of any fabric. Thus, many researchers attempt to identify different methods by which the structure of yarn and fabric can be altered to improve comfort properties. The nature, composition and arrangement of constituent fibres, through the dissolving of one component, can influence the structure, properties and performance of yarn, which may ultimately influence fabric comfort properties [1-6]. Mixture experiments are a special class of response surface experiments in which the product under investigation is made up of several components or ingredients [7]. This design is thus suitable in a situation where the response is a function of the proportions of the different ingredients in the mixture [8]. During the twenty-first century, clothing markets have become highly competitive due to high demand and changing fashion. The textile and clothing industries are searching for competitive advantages by understanding and meeting consumer needs and desires in order to survive on the rapidly changing, highly competitive clothing market. Different statistical techniques are developed by researchers to satisfy the needs of industries. These include response surface methodology and various optimisation algorithms, e.g. the desirability function-based approach [9-10], multiple regression and linear programming-based approaches [11], and utility function-based approach [12]. Among the above, the desirability function-based approach has gained the most popularity in solving optimisation problems. Ghosh et al. [13] optimised different comfort and safety properties using the desirability function to achieve an overall desirability varying from zero to one. Gupta et al. [14] used the desirability approach to optimise carpet durability by considering abrasion loss, compression and compression recovery as a single objective. Knitted fabric properties, such as areal density, bursting pressure, extensibility, dimensional stability and abrasion resistance, were optimised using the desirability function [15]. Asim et al. [16] estimated the fixation of reactive printing and crease-resistant finishing using the desirability function. The disappearance of traditional textiles, through globalisation due to a lack of seriousness in this Tekstilec, 2020, 63(2), 138-150 140 field, has again prompted researchers to improve the quality of these fabrics through different product development to compete on the highly competitive market of power loom fabrics. The present work involved a detailed study of all the important fabric comfort properties of handloom fabrics made of the same warp yarn and different filling (for both machine- and hand-spun), which were produced according to a mixture design from different percentages of wool, polyester and PVAL. The optimisation of different fabric properties was preformed using the desirability function. 2 Experimental 2.1 Materials Merino wool (19.5 ^m, 70 mm), polyester (2 dtex, 52 mm) and polyvinyl alcohol (PVAL; 1.44 dtex, 44 mm) fibres were blended on a gill box in different proportions according to a mixture design. Table 1: Levels and factors are given below Table 2: Mixture design used to produce different blend proportions of yarn Thermo-physiological Properties of Structurally Modified Wool/ Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics Twelve wool/polyester/PVAL blended yarn samples, with a nominal linear density 50 tex (20 Nm), were prepared on a worsted spinning system. Another set of twelve yarns of the same linear density were also prepared on charkha (hand-spun yarns). A mixture design (Table 2) was used to investigate the proportion of different fibres on various properties of yarn. The idea of using a mixture design is to study the effect of the proportion of different fibres, and to set the proportion of the fibres according to the end-product with limited numbers of samples. The levels and percentages of different fibres are presented in Table 1. 2.2 Fabric formation Twenty-four fabric samples were prepared on a han-dloom by varying weft yarns (twelve from machine-spun and twelve from hand-spun yarn) and keeping warp yarn constant for all the fabrics. BT and BTH denote fabrics before treatment with machine-spun and hand-spun weft yarn respectively, while AT and ATH denote fabrics after treatment with machine-spun and hand-spun weft yarn respectively. 2.3 Dissolution of PVAL fibre on fabric stage After the production of fabrics, PVAL was removed by treating the fabrics (that contain PVAL in their filling yarn) with 0.5% formic acid at 90 °C for 60 minutes, followed by a hot wash. All fabric samples were then dried in an oven, followed by conditioning for 24 hours under standard atmospheric conditions to achieve standard moisture conditions. 2.4 Test methods The prepared samples were conditioned and tested for different fabric properties according to the standard mentioned below. Air permeability was measured using a TEXTEST FX 3300 air permeability tester according to the BS 5636 standard. Water vapour permeability (WVP) was measured according to the BS 7209 standard. Permeability was calculated using equation 1. WVP = (g m-2 24-1 h-1) (1), A x t where, m represents loss in mass (g), A represents the open area of the dish (m2) and t represents the time between weighing (h). For the purpose of testing drying capacity, 12 circular specimens per sample were cut using a round-shaped S. No. Polyester (%) Merino wool (%) PVAL (%) S1 35 45 20 S2 20 60 20 S3 20 65 15 S4 20 70 10 S5 55 30 15 S6 40 50 10 S7 60 30 10 S8 40 50 10 S9 20 70 10 S10 60 30 10 S11 60 30 10 S12 50 30 20 Factors Low Medium High Polyester (%) 20 40 60 Merino wool (%) 30 50 70 PVAL(%) 10 15 20 Tekstilec, 2020, 63(2), 138-150 cutter, each with an area of 100 cm2. Specimens were conditioned at a standard atmosphere for 6 hours as per ASTM D 1776 and the weight of each sample (W1) was recorded. The samples were dipped in distilled water to a depth of around 10 cm with the help of a wire sinker. After 6 hours, the specimens were taken out and kept on a sponge sheet to dry in a closed room where there was no air movement. A tropical atmosphere room temperature (27 °C ± 2 °C) and relative humidity (65% ±2 %) were maintained during the test. All fabrics were kept under the same conditions and the face side of the specimens was kept up. After a fixed time (i.e. 10 hours), the weight (W2) of specimens was taken for all samples. Drying capacity was calculated by using equation 2. Drying capacity = = (W2 - W1) x 100 (g m-2 10- h-1) (2), Thermo-physiological Properties of Structurally Modified Wool/ 141 Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics G = 9.807 x 10-6 Wc3 (3), where, G represents the fabric bending rigidity (wNm) and W represents the mass per unit area (g m-2), while the bending length c is equal to half the length of the overhang (mm). Go=(GwGp (4), where, Go represents the overall fabric bending rigidity, Gw represents the warp bending rigidity and Gf represents the weft bending rigidity. To measure compressibility, the thickness of the fabric was measured using a thickness gauge at pressures of 20 g cm-2 and 50 g cm-2. The compressibility of the fabric was then calculated using equation 5: T - T Compressibility = 20 50 x 100 (%) I- T20 -I (5), where W1 represents the weight of the specimen (g) and W2 represents the weight of water (g) dried from the fabric per 100 cm2 in 10 h. The test to determine fabric stiffness was carried out according to ASTM D1388-33 using a stiffness tester. Before the tests, the samples were conditioned under laboratory conditions (27 ± 2 °C, 65 ± 2% relative humidity (RH)). The tests were performed on each fabric sample at five replicas in both the warp and weft directions. Equation 3 given below was used to calculate the bending rigidities in the warp and weft directions. Overall fabric bending rigidity was calculated using equation 4. where T20 and T50 represent the thickness of fabric measured using a thickness gauge at pressures of 20 g cm-2 and 50 g cm-2 respectively. The thermal resistance of fabric was measured on a Testex guarded hot plate thermal conductivity tester. A minimum of three observations were carried out to determine the average CLO value. 3 Results and discussion 3.1 Observed structural changes SEM images of untreated and treated fabric are shown in Figures 1-4. Figure 1 and Figure 3 show a a) Figure 1: Scanning electron microscope images: a) S4 BT and b) S4 AT b) Tekstilec, 2020, 63(2), 138-150 142 Thermo-physiological Properties of Structurally Modified Wool/ Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics Figure 3: Scanning electron microscope images: a) S7 BT and b) S7 AT mm Figure 4: Scanning electron microscope images: a) S7 ATH and b) S7 BTH Tekstilec, 2020, 63(2), 138-150 fabric with maximum wool content with machine-spun and hand-spun yarn as a weft respectively, while Figure 2 and Figure 4 show a fabric with maximum polyester content with machine-spun and hand-spun yarn as a weft respectively. The following observations can be made from the images: (a) The removal of the PVAL component led the creation of voids in the structure of fabric. (b) The treatment of fabric with hand-spun yarn as a weft created more voids than fabric with machine-spun yarn as a weft. (c) More voids were observed in fabric with weft yarn with a higher percentage of wool after the dissolution of the PVAL component than in fabric with weft yarn with a lower wool content. The creation of voids after the dissolution of the PVAL component influences the arrangement and configuration of fibres in yarns. This change in the arrangement and configuration of fibres in yarn and fabric ultimately influences the thermo-physiologi-cal characteristics of fabric. 3.2 Properties of fabrics Table 3 shows the physical properties of fabrics, such as the weight per unit area, thickness, thread density and yarn linear density of both treated and untreated fabrics for hand-spun and machine-spun yarns as weft. Thermo-physiological Properties of Structurally Modified Wool/ 143 Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics Table 4 shows properties related to the thermo-physiological behaviour of both treated and untreated fabrics with machine- and hand-spun yarns as a weft. Thermal resistance The experimental results of thermal resistance (CLO value) are presented in Table 4 for both treated and untreated fabrics containing both hand- and machine-spun yarns as a weft at different blend compositions. It is evident from Figure 5 that the CLO value is higher for fabrics containing hand-spun yarn than for fabrics that contain machine-spun yarn as a weft. Air entrapment is one of the major reasons for the enhancement of the thermal resistance of any fabric. Hand-spun yarn is voluminous and soft, which helps to make bulkier fabric than machine-spun yarn, which helps to entrap more air, resulting in a higher value of thermal resistance in terms of a higher CLO value. As shown in Figure 5, the thermal resistance of treated fabric (for both machine- and hand-spun yarn) is higher than that of untreated fabric. After the dissolution of the PVAL component, the diameter of the yarn increased causing the creation of pores in the structure, which helps in the entrapment of air, resulting in a higher CLO value for treated fabrics than for untreated fabrics. Table 3: Physical properties of fabrics before and after treatment (weft from both hand- and machine-spun yarns) Seq. no Mass per unit area (g m-2) Thickness (mm) EPI/PPI Linear density (Nm) warp/weft yarns BT AT BTH ATH BT AT BTH ATH BT AT BTH ATH BT BTH S1 190 180 185 178 0.58 0.62 0.59 0.64 48/50 46/48 48/51 46/48 30.2/20.5 30.2/20.4 S2 175 170 174 168 0.64 0.67 0.65 0.70 49/51 47/49 49/51 47/49 30.2/20.4 30.2/20.5 S3 178 170 173 165 0.67 0.69 0.65 0.70 50/51 46/47 50/51 46/47 30.2/20.4 30.2/20.4 S4 170 159 168 154 0.66 0.69 0.64 0.70 48/53 47/48 48/52 47/48 30.2/20.3 30.2/20.4 S5 176 164 174 163 0.55 0.59 0.57 0.61 50/52 47/50 50/52 47/50 30.2/20.3 30.2/20.4 S6 183 175 182 173 0.57 0.60 0.59 0.63 48/53 47/51 48/53 47/51 30.2/20.4 30.2/20.3 S7 182 172 180 172 0.55 0.58 0.57 0.59 50/49 48/47 50/49 48/47 30.2/20.4 30.2/20.4 S8 185 179 180 172 0.57 0.59 0.59 0.63 53/52 51/51 53/52 51/51 30.2/20.2 30.2/20.3 S9 168 160 165 158 0.65 0.68 0.67 0.71 48/52 47/51 48/52 47/51 30.2/20.2 30.2/20.4 S10 182 174 178 170 0.55 0.57 0.56 0.60 50/51 50/49 49/51 50/49 30.2/20.3 30.2/20.4 S11 181 172 178 171 0.54 0.57 0.56 0.60 50/51 49/50 50/51 49/50 30.2/20.4 30.2/20.3 S12 180 169 178 168 0.55 0.57 0.58 0.61 50/51 49/50 49/51 49/50 30.2/20.5 30.2/20.4 Tekstilec, 2020, 63(2), 138-150 144 Thermo-physiological Properties of Structurally Modified Wool/ Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics Table 4: Fabric properties before and after treatment (weft from both hand- and machine-spun yarns) S. No. Thermal resistance (CLO) Compressibility (%) Air permeability (cm3 cm-2 s-1) BT AT BTH ATH BT AT BTH ATH BT AT BTH ATH S1 0.14 0.20 0.16 0.21 16.27 25.34 20.24 27.78 35.12 28.14 32.12 25.14 S2 0.16 0.21 0.18 0.22 18.98 26.62 22.41 28.24 36.01 29.12 34.11 28.47 S3 0.16 0.21 0.18 0.22 19.14 27.22 23.14 29.45 36.92 30.22 33.45 29.15 S4 0.17 0.20 0.18 0.21 20.94 28.05 24.20 30.25 38.25 31.25 35.21 29.78 S5 0.14 0.18 0.16 0.19 13.23 17.95 17.25 20.10 27.35 20.95 24.78 20.12 S6 0.15 0.18 0.16 0.20 15.67 22.46 19.47 24.58 30.66 25.16 27.22 24.14 S7 0.14 0.19 0.16 0.21 12.75 16.62 16.78 18.89 26.02 19.22 23.92 19.14 S8 0.15 0.18 0.17 0.19 17.27 22.81 21.62 24.78 32.41 25.51 29.33 24.18 S9 0.16 0.19 0.18 0.20 20.13 26.94 24.18 28.45 36.22 29.92 33.62 28.46 S10 0.14 0.18 0.16 0.20 12.71 16.34 16.98 18.78 26.3 19.3 23.14 19.13 S11 0.14 0.18 0.16 0.20 12.56 15.98 16.89 18.90 25.22 18.92 22.7 18.27 S12 0.14 0.20 0.16 0.21 11.48 18.67 15.24 17.49 27.97 21.77 24.87 20.47 This study also found that treated fabric shows a higher compression than untreated fabric, for both fabrics with machine- and hand-spun yarn as a weft, as shown in Figure 6. After the dissolution of the PVAL component, pores developed in the yarn structure, which ultimately led to a reduction in the compactness of fabric. Thus, the compression of treated fabric increased after the dissolution of the PVAL component. at a" Figure 5: Thermal resistance of fabrics Compressibility The compressibility of any fabric is influenced by its bulkiness and thickness. Bulkier and thicker fabric compresses more easily than less bulky and thinner fabric. Figure 6 shows the compressibility for all fabrics in the treated and untreated stages. It was determined that fabric with hand-spun yarn compresses more easily than fabric with machine-spun yarn as a weft. Due to the structural differences and higher bulk of hand-spun yarn, the fabrics are spongier that fabrics with machine-spun yarn as a weft. Thus, fabrics from hand-spun yarn are bulkier, which leads to the higher compression value of the fabric. Figure 6: Compressibility of fabrics Air permeability The air permeability of fabric depends on the inter and intra yarn pores, and the hairiness of the yarn used in a fabric. Hand-spun yarns are voluminous Tekstilec, 2020, 63(2), 138-150 Thermo-physiological Properties of Structurally Modified Wool/ 145 Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics Water vapour permeability (g m-2 24-1 h-1) Bending rigidity (wNm) Drying capacity (g m-2 10-1 h-1) BT AT BTH ATH BT AT BTH ATH BT AT BTH ATH 1425.5 1621.2 1220.34 1410.12 204.42 181.34 200.23 178.98 187 294 200 300 1617.2 1720.2 1410.21 1547.27 213.43 187.78 204.45 184.22 211 303 228 307 1635.3 1789.9 1420.10 1549.22 215.67 187.67 210.26 183.26 211 305 226 310 1712.2 1821.4 1545.23 1658.47 203.78 194.89 199.32 190.78 223 293 235 300 1454.7 1659.5 1245.10 1469.20 183.89 169.21 178.96 161.45 190 273 205 280 1522.2 1728.6 1322.89 1536.23 188.45 161.66 180.23 155.58 197 278 211 288 1410.5 1578.7 1245.55 1389.36 192.67 170.67 185.69 162.24 191 278 208 280 1534.4 1789.9 1332.45 1589.36 187.67 172.73 180.23 165.89 197 277 215 282 1693.8 1822.4 1489.59 1635.78 201.89 193.90 195.78 184.78 207 283 219 288 1456.9 1547.2 1278.36 1345.25 191.34 168.45 182.36 162.45 190 275 204 281 1447.1 1549.4 1274.32 1345.89 192.43 170.23 183.54 161.23 189 272 202 278 1456.3 1687.3 1233.36 1458.36 206.22 172.56 198.58 189.22 191 296 204 302 the fabric due to yarn compressibility. After the dissolution of the PVAL component, there was an increase in both yarn and fabric compressibility, which might have led to yarn flattening or fabric deformation. This ultimately reduced the air permeability of treated fabric. Water vapour permeability It is evident from Figure 8 that fabric containing hand-spun yarn as a weft exhibited lower water vapour permeability than fabric with machine-spun yarn as a weft. The water vapour permeability of fabric depends on the rate of diffusion. The irregular structure of hand-spun yarn could lead to a reduction in the diffusion rate, resulting in the reduced water vapour permeability of fabric. Experimental results for the water vapour permeability of fabrics before and after treatment are presented in Table 4, which shows that, after the dissolution of the PVAL component, treated fabric exhibited a higher water vapour permeability than untreated fabric. The transfer of vapour through fabric depends on diffusion. The rate of diffusion from fabric depends on the pores/voids created in the structure by the dissolution of the PVAL component from a blended yarn. After the dissolution of the PVAL component, pores were created in the yarn structure, which resulted in the better transfer of water vapours through the diffusion process from one side of fabrics to other and can easily flatten, thereby reducing both inter and intra yarn porosity. Moreover, any increase in hairiness will cause air permeability to decrease. The hairiness of hand-spun yarn was higher than that of machine-spun yarn, resulting in the higher air permeability of fabric with machine-spun yarn as a weft. Table 4 illustrates that the dissolution of one component resulted in a lower value of air permeability for treated fabrics than for untreated fabric. The air permeability of fabric was closely correlated with inter yarn porosity. Both intra and inter yarn porosity was affected by yarn flattening or deformation in Figure 7: Air permeability of fabrics Tekstilec, 2020, 63(2), 138-150 146 through pores within the structure, resulting in a higher value of water vapour permeability for treated fabric. BI O AT -Ar- 3TH —T- ATH Figure 8: Water vapour permeability of fabrics Bending rigidity Fabric bending rigidity is an important parameter that can influence the handling and comfort of textile material. It is evident from Figure 9 that fabric with hand-spun yarn as a weft exhibited a lower bending rigidity than fabric with machine-spun yarn as a weft. Hand-spun yarn is softer and more pliable than machine-spun yarn. Fabric from machine-spun yarn is thus stiff. Experimental results shown in Table 4 for untreated and treated fabric show a reduction in bending rigidity after the removal of the PVAL component Thermo-physiological Properties of Structurally Modified Wool/ Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics for both type of fabrics. This may be due to the creation of pores after the dissolution of the PVAL component, which ultimately enhanced fabric flexibility. Drying capacity It is evident from Figure 10 that the drying capacity of fabrics with hand-spun yarn as a weft is higher than that of fabric with machine-spun yarn as a weft. The porous nature of hand-spun yarn, which helps to absorb higher water content, resulted in a higher value of drying capacity than that of fabric with machine-spun yarn as a weft. Results from Table 3 shows that the drying capacity value increased after the dissolution of the PVAL component, meaning that treated fabric will take more time to dry than untreated fabric. A structure that can absorb a larger mass of water will have a high drying capacity value, i.e. it will take longer to dry. Figure 9: Bending rigidity of fabrics Figure 10: Drying capacity of fabrics 3.3 Optimisation of fabric properties through desirability function Today, multi-response optimisation is a suitable method for overcoming the problem of conflicting responses of single response optimisation. Under this optimisation technique, the desired weight is given to all responses (equal weight in the present study) for varying values of input parameters to calculate the combined impact of all desirability responses. Parameters are set to enhance fabric quality according to customers' demands. Figures 11-14 show the curves of various factors (all six responses Tekstilec, 2020, 63(2), 138-150 Thermo-physiological Properties of Structurally Modified Wool/ 147 Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics are given equal weights) for untreated fabric with machine-spun yarn as a weft, treated fabric with machine-spun yarn as a weft, untreated fabric with hand-spun yarn as a weft and treated fabric with hand-spun yarn as a weft respectively. The parameters required to maximise overall desirability involve the percentages of fibres presented in Table 5 for different treated and untreated fabrics with machine-spun and hand-spun yarn as a weft. The illustrations above (Figure 15 a-d) show the overall desirability for BT, AT, BTH and ATH fabrics respectively. Harrington's rating system was used to interpret desirability values. The overall desirability value for BT fabric was 0.65 (Figure 15 a) and 0.73 for AT fabric (Figure 15 b). It means that after the dissolution of PVAL, there was an improvement in overall desirability for fabric with machine-spun yarn as a weft, while in the case of fabric with hand-spun yarn as a weft, the overall desirability value remained approximately the same (0.66 and 0.67 for BTH and ATH respectively) as shown in Figure 10 c and d respectively. According to the Harrington standard, this threshold indicates that product quality is acceptable with regard to the specifications for BT, AT, BTH and ATH fabrics. The overall desirability bar graph for BT fabric (Figure 15 a) indicates that all responses are acceptable, but that the individual desirability values of bending rigidity (0.42) and drying capacity (0.25) require some improvement. Effectively, for AT fabric, the individual desirability value for all responses was good, except for thermal resistance, which requires a small improvement according to the Harrington standard, as shown in Figure 15 b. As evident in Figure 15 c, the individual desirability values for BTH fabric for different properties, such as air permeability, water vapour permeability, bending rigidity and compressibility, are 0.72, 0.79, 0.66 and 0.74 respectively, and are also acceptable according to the Harrington standard, while the individual desirability values for thermal resistance and drying capacity were 0.51 and 0.57, which are also acceptable but still require some improvement. Table 5: Percentage of fibres in weft with maximum desirability for different types of fabrics Fabric Fibres content in weft Polyester (%) Merino wool (%) PVAL (%) BT fabric 20 70 10 AT fabric 35 55 10 BTH fabric 20 70 10 ATH fabric 30 60 10 20.00 60.00 30.00 70.00 10.00 20.00 A:Polyester - 20.00 0.14 0.17 0.17 B:W00l = 70.00 1712 1410.5 1712.2 C:PVAL = 10.00 183.8S 183.83 215.67 Thermal Resistance = 0.164175 20.94 WVP = 1700.76 Desirability = 0.651 Bending Rigidity = 202.387 11.48 20.94 WVP - water vapour permeability Compressibility = 20.5595 Figure 11: Curves of various factors for untreated fabric with machine-spun yarn as a weft Tekstilec, 2020, 63(2), 138-150 148 Thermo-physiological Properties of Structurally Modified Wool/ Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics -O- -O- 20.00 60.00 30.00 70.00 10.00 20.00 A:Polyester = 35.00 0.1 S 0.21 0.21 B:Wool = 55.05 1S00 C: F'VA L - 10.00 165 161.66 194.89 Thermal Resistance = 0.192588 2S.05 WVP = 1762.14 Desirability = 0.729 Bending Rigidity = 172.31 S r 15.98 28.05 WVP - water vapour permeability Compressibility = 25.1495 Figure 12: Curves of various factors for treated fabric with machine-spun yarn as a weft 20.00 60.00 30.00 70.00 10.00 20.00 A:Polyester = 20.00 0.16 0.18 0.18 B:Wool = 70.00 1220.34 1545.23 1545.23 C:PVAL = 10.00 1 78.96 178.96 210.26 TR = 0.179968 WVP= 1519.55 Desirability = 0.667 Bending Rigidity = 196.186 TR - thermal resistance; WVP - water vapour permeability Figure 13: Curves of various factors for untreated fabric with hand-spun yarn as a weft It is evident from Figure 15 d that all responses 4 Conclusion for ATH fabric exhibited excellent individual desirability values, except bending rigidity (0.49), This study addressed the effect of hand-spun and ma-which requires some improvement, and drying chine-spun weft yarns, before and after treatment, on capacity (0.29), which requires more improve- different properties that influence the thermo-physio-ment. logical behaviour of fabric. A fabric with hand-spun Tekstilec, 2020, 63(2), 138-150 Thermo-physiological Properties of Structurally Modified Wool/ 149 Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics 20.00 60.00 30.00 70.00 10.00 20.00 A: Polyester = 30.00 0.19 0.22 0.22 B:W00l = 60.00 r 1345.25 1658.47 1658.47 C:PVAL = 10.00 155.58 155.58 190.78 TR = 0.205512 30.25 WVP = 1595.39 Desirability = 0.663 Bending Rigidity = 167.34 17.49 30.25 Compressibility = 26.9863 TR - thermal resistance; WVP - water vapour permeability Figure 14: Curves of various factors for treated fabric with hand-spun yarn as a weft A:Poiyester B:Wool C:PVAL Air permeability TR WVP Bending Rigidity Drying Capacity Compressibility Combined a) o.ooo A:Polyester B:Wool G:PVAL Air permeability TR WVP Bending Rigidity Drying Capacity Compressibility Combined c) a.ooo ArPolyester B:Wool C: PVAL Air permeability TR WVP Bending Rigidity Drying Capacity Compressibility Combined 1 ^ ' 1 1 .724299 ¡922 0.744222 (33 b) i TjO APolyester B:Woot C:PVAL Air permeability TR WVP Bending Rigidity Drying Capacity Compre5siblifty Combined 0.755208 1.734049 0.759696 .72912 1.000 —Ï 1 1 ?658 0.99839 0971 d) TR - thermal resistance; WVP - water vapour permeability Figure 15: Overall desirability: a) BT, b) AT, c) BTH and d) ATH yarn as a weft exhibited higher values of thermal re- with machine-spun yarn as a weft. After the dissolu- sistance, bending rigidity, compressibility and dry- tion of the PVAL component, thermal resistance, ing capacity, while air permeability and water va- compressibility, water vapour permeability and dry-pour permeability values were lower than fabrics ing capacity increased due to the creation of pores in Tekstilec, 2020, 63(2), 138-150 150 the structure of both AT and ATH fabrics. Optimisation using a multi-response technique was also performed to identify the suitable percentage of fibres to achieve maximum desirability for customers for different fabric properties. Results for optimisation indicate that the same desirability (0.65) can be achieved for both fabrics, either machine-spun or hand-spun, in the same blend composition. After the dissolution of PVAL, fibres in the case of AT fabrics exhibited an improved desirability value (0.73), as well as a change in the percentage of wool (55%) in the blend composition relative to BT fabric (70%). After the treatment of fabric with hand-spun yarn as weft, there was no change in desirability values, but there was a reduction in the percentage of wool (60%) in the blend composition relative to BTH fabric (70%). References 1. SHARMA, N., KUMAR, P., BHATIA, D., SIN-HA, S.K. Moisture management behaviour of knitted fabric from structurally modified ring and vortex spun yarn. Journal of The Institution of Engineers (India): Series E, 2016, 97(2), 123-129, doi:10.1007/s40034-015-0075-z. 2. BHATIA, D., MALHOTRA, U., MALHOTRA, A. Impact on properties of woven fabric from structurally modified shoddy/wool blended worsted yarn. Journal of Fashion Technology & Textile Engineering, 2016, 4(1), 1-6, doi: 10. 4172/2329-9568.1000128. 3. SINHA, S.K., KUMAR, P., GHOSH, S. Study on the packing density of structurally modified ring spun yarn. Fibres and Polymers, 2016, 17(11), 1898-1907, doi:10.1007/s12221-016-5940-y. 4. DAS, A., ISHTIAQUE, S.M., SINGH, R.P. Packing of micro-porous yarns. Part II : Optimization of fabric characteristics. Journal of the Textile Institute, 2009, 100(3), 207-217, doi:10.1080/ 00405000701559917. 5. CHANDRASEKARAN, V., SENTHILKUMAR, P., KARTHIK, T. Optimization of spinning parameters influencing the characteristics of structurally modified viscose yarn. Journal of the Textile Institute, 2016, 107(1), 50-63, doi:10.108 0/00405000.2014.1000017. 6. GHAREHAGHAJI, A.A., MOGHASSEM, A.R. Redistribution of fibres in the structure of hollow ring spun yarn. International Journal of En- Thermo-physiological Properties of Structurally Modified Wool/ Polyester Blended Machine and Hand-Spun Yarns as a Weft in Handloom Fabrics gineering, Transactions B: Applications, 2009, 22(2), 197-204. 7. ERIKSSON, L., JOHANSSON, E., KETTANEH-WOLD, N., WIKSTROM, C., WOLD, S. Design of experiments : principles and applications. Umeâ : Umetrics Academy, 2000. 8. BAYKAL, P.D., BABAARSLAN, O., EROL, R. Prediction of strength and elongation properties of cotton/polyester-blended OE rotor yarns. Fibres & Textiles in Eastern Europe, 2006, 14(1), 18-21. 9. PAL, S., GAURI, S.K. A desirability functions-based approach for simultaneous optimization of quantitative and ordinal response variables in industrial processes. International Journal of Engineering, Science and Technology (IJEST), 2018, 10(1), 76-87, doi:10.4314/ijest.v10i1.6. 10. DERRINGER, G., SUICH, R. Simultaneous optimization of several response variables. Journal of Quality Technology, 1980, 12(4), 214-219. doi: 10.1080/00224065.1980.11980968. 11. VINING, G.G., MYERS, R.H. Combining tagu-chi and response surface philosophies : a dual response approach. Journal of Quality Technology, 1990, 22(1), 38-45, doi:10.1080/00224065.1990. 11979204. 12. KUMAR, P., BARUA, P.B., GAINDHAR, J.L. Quality optimization (multi-characteristics) through Taguchi's technique and utility concept. Quality and Reliability Engineering International, 2000, 16(6), 475-485, doi: 10.1002/1099-1638-(200011/12)16:6<475::AID-QRE342>3.0.œ;2-0. 13. GHOSH, A., MAL, P., MAJUMDAR, A., BA-NERJEE, D. Optimization of knitted fabric comfort and UV protection using desirability function. Journal of Engineered Fibers and Fabrics, 2016, 11(4), 20-28, doi:10.1177/155892501601100404. 14. GUPTA, S.K., GOSWAMI, K.K., MAJUMDAR, A. Optimization of durability of Persian handknotted wool carpets by using desirability functions. Textile Research Journal, 2018, 88(1), 89-98, doi:10.1177/0040517516676056. 15. HADJ TAIEB, A., MSAHLI, S. Optimization of the knitted fabric quality by using multicriteria phenomenon tools. International Journal of Fiber and Textile Research, 2013, 3(4), 66-77. 16. ASIM, F, MAHMOOD, M, SIDDIQUI, M, A. Optimization of process parameters for simultaneous fixation of reactive printing and crease resistant finishing using desirability function. Journal of Textile and Apparel, Technology and Management, 2012, 7(3), 1-12. Tekstilec, 2020, 63(2), 138-150 151 Ivana Bonic1, Andrea Palac1, Ana Sutlovic2, Branka Vojnovic1, Mario Cetina1 1 University of Zagreb, Faculty of Textile Technology, Department of Applied Chemistry, Prilaz baruna Filipovica 28a, HR-10000 Zagreb, Croatia 2 University of Zagreb, Faculty of Textile Technology, Department of Textile Chemistry and Ecology, Savska c. 16/9, HR-10000 Zagreb, Croatia Removal of Reactive Black 5 dye from Aqueous Media using Powdered Activated Carbon - Kinetics and Mechanisms Odstranjevanje barvila Reactive Black 5 iz vodnih medijev z uporabo praškastega aktivnega oglja - kinetika in mehanizmi Original scientific article/Izvirni znanstveni članek Received/Prispelo 3-2020 • Accepted/Sprejeto 5-2020 Abstract The textile industry is considered one of the major environmental polluters, primarily due to the quantity and composition of wastewater. It is therefore important to examine its different treatment methods. For this purpose, the isothermal adsorption of Reactive Black 5 dye on powdered activated carbon at 25(±1) °C and 45(±1) °C was carried out to determine the effect of initial dye concentration, contact time and temperature on the adsorption process. In order to investigate the mechanism of adsorption of Reactive Black 5 dye on activated carbon, kinetic studies have also been carried out. Experimental data were analysed using a pseudo-first-order and pseudo-second-order kinetic models, as well as an intraparticle diffusion model. Standard Gibbs free energy values of the adsorption process were also calculated, while the morphological analysis of activated carbon before and after adsorption was performed using a scanning electron microscope. The efficiency of activated carbon as an adsorbent for Reactive Black 5 dye is evidenced by the fact that more than 60% of dye is adsorbed after 30 minutes regardless of initial concentration and temperature. The experimental data also showed that adsorption is kinetically controlled assuming a pseudo-second-order process, and that intraparticle diffusion is not the only process that influences the adsorption rate. Negative values of standard Gibbs free energy indicate that the adsorption reaction is spontaneous, while a higher negative value for temperature of 45 °C compared to 25 °C shows that a higher temperature is more energetically favourable for the adsorption of Reactive Black 5. Keywords: adsorption, activated carbon, Reactive Black 5, kinetics, intraparticle diffusion Izvleček Tekstilna industrija velja za eno glavnih onesnaževalk okolja, predvsem zaradi količine in sestave odpadnih voda, zato je pomembno preučiti različne metode njihove obdelave. V ta namen je bila izvedena izotermična adsorp-cija barvila Reactive Black 5 na praškasto aktivno oglje pri 25 °C ± 1 °C in 45 °C ± 1 °C, da bi ugotovili vpliv začetne koncentracije barvila, časa stika in temperature na postopek adsorpcije. Za preučitev mehanizma adsorpci-je barvila Reactive Black 5 na aktivno oglje so bile izvedene tudi študije kinetike. Eksperimentalni podatki so bili analizirani s kinetičnimi modeli psevdo prvega in psevdo drugega reda, kot tudi z modelom difuzije delcev snovi. Za proces adsorpcije je bila določena standardna Gibbsova prosta energija. Morfološka analiza aktivnega oglja je bila izvedena z rastrskim elektronskim mikroskopom. Učinkovitost aktivnega oglja kot adsorbenta za barvilo Reactive Black 5 je razvidna iz dejstva, da se je več kot 60-odstotkov barvila adsorbiralo po 30 minutah, ne glede na začetno koncentracijo in temperaturo. Eksperimentalni podatki so pokazali tudi, da je adsorpcija Corresponding author/Korespondenčni avtor: Tekstilec, 2020,63(2), 151-161 prof. dr. Mario Cetina doI: 10.14502/Tekstilec2020.63.151-161 E-mail: mario.cetina@ttf.unizg.hr ORCID: 0000-0001-7524-5828 152 Removal of Reactive Black 5 dye from Aqueous Media using Pow dered Activated Carbon - Kinetics and Mechanisms kinetično nadzorovana, pri čemer se predpostavlja proces psevdo drugega reda in da difuzija delcev ni edini proces, ki vpliva na hitrost adsorpcije. Negativne vrednosti standardne Gibbsove proste energije nakazujejo, da je reakcija adsorpcije spontana, višja negativna vrednost pri temperaturi 45 °C v primerjavi s 25 °C pa kaže, da je višja temperatura energijsko ugodnejša za adsorpcijo barvila Reactive Black 5. Ključne besede: adsorpcija, aktivno oglje, Reactive Black 5, kinetika, difuzija delcev 1 Introduction At the end of the 20th century, with all of the inventions and technical aids used every day, the relationship between man and nature was disrupted, and the Earth's ecosystem broken. Due to human knowledge and creativity over the last 250 years, a modern way of life, industrial development, advancing technology and agriculture, the use of large amounts of energy and natural resources, as well as the pursuit of a better and more comfortable life have led to the emergence of environmental hazards and their consequences (i.e. acid rain, desertification, ozone depletion, climate change and other harmful phenomena). A great deal of attention worldwide has been given to environmental protection, the effect of harmful substances on human health and the entire ecosystem. Particular attention is given to industry, as it is no longer possible to continue expanding production and waste accumulation without inflicting permanent damage to nature. The textile industry is one of the major environmental polluters. It uses significant quantities of water [1], which is eliminated as wastewater after being processed. Taking into account total industrial water pollution, textile finishing is considered one of the largest water consumption and pollution processes. The quantity and composition of waste-water depend on the type of basic raw material being processed (cotton, wool, flax, silk, synthetic fibres, blends, etc.) and textile finishing process used (laundering, bleaching, dyeing, printing, etc.), i.e. the type of chemicals used during some processes and the number of consecutive processes during production. In addition, the use of certain special finishing agents often results in specific and greater pollution of wastewater. Textile industry wastewa-ter has a wide range of pH values and temperatures, it may be coloured and mainly contains various types of pollutants, most commonly dyes, surfactants, pesticides, oils, fats, solvents, heavy metals, inorganic salts, waste fibres, etc. [2]. Special attention is given to dyes and pigments because they are highly visible materials so that even the minimum amount released into the environment may cause the appearance of colour in open waters. Besides being aesthetically deficient, coloured water prevents the penetration of light into natural water, which negatively affects the entire natural water ecosystem, i.e. organisms depending on water quality. There are more than 100,000 commercially available dyes with over 700,000 tonnes produced annually. Wastewater stream from the textile dyeing process contains unutilised dyes (about 8-20% of the total pollution load due to incomplete dye exhaustion) and auxiliary chemicals [3]. Besides, some dyes have been proven to have allergenic, toxic and/or carcinogenic properties that make them not only dangerous or potentially harmful to the environment, but also to human health in contact with human skin [4]. The continuous monitoring of dye content in wastewaters should therefore be an integral part of the technological process of textile materials and permitted concentrations regulated by law. Dyeing and printing should be carried out by achieving the maximum effect using a minimum amount of dye, not only for ecological reasons (reduced quantity of unused textile auxiliaries in wastewater), but also for economic reasons. Taking all of the above-mentioned facts into consideration, it is necessary to treat the wastewater by reducing the amount of harmful substances to legally limited concentrations. There are numerous methods for the treatment and disposal of textile industry wastewater: coagulation and flocculation, chemical oxidation, biological treatment, membrane separation, reverse osmosis, etc. [3, 5, 6]. Although high quality effluents can be obtained through water treatment with each of the previously mentioned processes, some of them have limitations/disadvantages, such as the use of excess chemicals, the formation of larger amounts of sludge that needs adequate care, and the incomplete removal of colour. Removal of dyes from wastewater is generally difficult. They are usually non-biodegradable, resistant to aerobic digestion, Tekstilec, 2020,63(2), 151-161 Removal of Reactive Black 5 dye from Aqueous Media using Pow 153 dered Activated Carbon - Kinetics and Mechanisms and stable to light, heat and oxidising agents. One of the most commonly used and effective treatment methods for coloured water is adsorption, which is based on the accumulation of the substance from the solution in a solid phase. Adsorption is one of the best treatment methods due to its flexibility, simplicity of design, and sensitivity to toxic pollutants. Furthermore, adsorption generally does not result in the formation of harmful substances [3, 7-9]. Activated carbon is the most popular adsorbent used for wastewater treatment due to its adsorption efficiency and great capacity, although some other adsorbents are less expensive and easily available. It is efficient in the removal of different types of dyes, including reactive dyes [10-15]. It is known that adsorption is a time-dependent process, and it is therefore necessary to know the adsorption rate for removal of dyes from wastewater. The most important factor in the design of adsorption systems is thus prediction of the rate of adsorption for a given system. This paper aims to present adsorption efficiency of commercial activated carbon for the removal of Reactive Black 5 dye (RB5). The effect of contact time, initial dye concentration and temperature on adsorption were monitored. The pseudo-first-order and pseudo-second-order models were used to correlate the adsorption kinetic data, while intraparticle diffusion was used to evaluate the diffusion mechanism of the adsorption process. Activated carbon was also characterised before and after the adsorption of RB5 using a scanning electron microscope. 2 Materials and methods 2.1 Materials Reactive Black 5 dye (Drimarene Black R-3B, supplied by Clariant GmbH, C.I. 20505, chemical formula: C26H21N5Na4O19S6, Mr = 991.82), was used for the adsorption experiment. The chemical structure of the dye prepared by the Accelrys Draw program is shown in Figure 1. One thousand milligrams per litre stock solution of dye was prepared by dissolving the required amount of dye in deion-ised water. The solutions of appropriate concentrations were prepared by diluting the stock solution with deionised water. Powdered activated carbon was purchased from the Croatian company Kemika. Adsorbent was dried in an oven at 105 °C for 24 hours and stored in a desiccator until it was used. O NHjOH __ O 1 L I NsOjS'' Figure 1: Chemical structure of Reactive Black 5 2.2 Batch mode adsorption studies Adsorption studies were conducted by contacting 50 ml of dye solution of different initial concentrations (c0 = 300, 500 and 700 mg/dm3) with 0.2 g of activated carbon in glass bottles. The experiments were repeated three times under identical conditions to confirm their repeatability. Experimental points presented in figures are the average values of three the repetitions. Suspensions were shaken at different contact times (15, 30, 45, 60, 90, 120, 180, 240 and 360 minutes and 16 hours until equilibrium was reached) with an impeller speed of 250 rpm at 25(±1) °C and 45(±1) °C (Heidolph Unimax 1010 with Incubator 1000). Experiments after 360 minutes for initial concentration of c0 = 300 mg/dm3 were not performed due to extremely low dye concentration after an adsorption time of 240 minutes. Suspensions were filtered after agitation through filter-paper blue ribbon. The residual liquid-phase dye concentration after adsorption was determined spectrophotometri-cally by monitoring the absorbance using a UV-Vis spectrophotometer (Lambda 20, Perkin Elmer) at a maximum absorbance wavelength (^max = 598 nm). The calibration graph of absorbance versus concentration followed a linear Beer-Lambert relation. The amount of adsorbate adsorbed at any time t, qt (mg/g), and the amount of adsorbate adsorbed at equilibrium, qe (mg/g), were calculated using the following equation: q v • (co " ct) (1), where c0 (mg/dm3) represents the initial dye concentration, ct (mg/dm3) represents the dye concentration in the liquid phase after appropriate time of adsorption and when equilibrium is reached (t = 16 hours), V represents the volume of the liquid phase (dm3), and m represents the mass of the adsorbent (g). Percentage of adsorbed dye (% ads.) is calculated using the equation: % ads. = x 100 (2), where cs (mg dm 3) represents the concentration of the adsorbed dye in a solid phase (cs = c0 - ct). c 0 Tekstilec, 2020,63(2), 151-161 154 Removal of Reactive Black 5 dye from Aqueous Media using Pow dered Activated Carbon - Kinetics and Mechanisms 2.3 Morphological analysis of adsorbent and dye-adsorben t samples A field emission scanning electron microscope (Mira, Tescan) was used for visualization of the adsorbent's morphology before and after adsorption. The accelerating voltage was 10.00 kV, while scanning was performed in situ on a sample powder. Samples were pre-coated with gold/palladium in a sputter coater. Optical micrographs were recorded using a Nikon Elipse E 400 microscope. 3 Results and discussion 3.1 Effect of contact time, temperature and initial dye concentration on the adsorption process The objective of this work was to assess the effectiveness of activated carbon for the treatment of Table 1: Percentage of adsorbed RB5 (% ads.) and amount of adsorbed RB5 at any time t (qt) for three initial dye concentrations (c0) at both temperatures T t c0 = 300 mg/dm3 c0 = 500 mg/dm3 c0 = 700 mg/dm3 (oC) (min) % ads. qt (mg/g) % ads. qt (mg/g) % ads. qt (mg/g) 15 74.9 56.2 59.0 73.8 53.2 93.1 30 79.5 59.6 68.0 85.0 60.9 106.6 45 87.4 65.6 73.9 92.3 63.3 110.8 60 89.6 67.2 76.9 96.2 67.0 117.2 25 90 93.7 70.3 78.3 97.9 71.2 124.7 120 97.5 73.1 83.9 104.8 73.2 128.1 180 97.7 73.3 89.7 112.1 80.4 140.7 240 96.5 72.4 93.9 117.4 85.1 148.9 360 a --- — 96.1 120.2 91.7 160.4 960 98.8 74.1 98.2 122.7 98.6 172.6 15 83.8 62.8 61.2 76.5 64.2 112.5 30 95.4 71.6 76.9 96.1 71.2 124.6 45 96.6 72.5 84.1 105.1 80.0 140.0 60 98.1 73.6 90.4 113.1 82.5 144.4 45 90 98.7 74.0 95.4 119.3 88.2 154.3 120 98.7 74.0 97.2 121.5 90.7 158.7 180 99.0 74.2 98.2 122.8 95.9 167.8 240 98.7 74.0 98.8 123.6 98.0 171.5 360 a) — — 99.3 124.1 98.9 173.2 960 98.7 74.0 99.4 124.3 99.2 173.6 a)Due to extremely low dye concentration after the adsorption time of 4 hours, an adsorption experiment after 6 hours for initial concentration of c0 = 300 mg/ dm3 was not performed Tekstilec, 2020,63(2), 151-161 200 40 20 0 0 120 240 360 4S0 600 720 840 960 11 min Figure 2: Effect of initial concentration and temperature on the amount of adsorbed RB5 on activated carbon after appropriate time (initial concentrations, c0: ® 300 mg/dm3, © 500 mg/dm3, ® 700 mg/dm3; temperatures: a) 25 °C, b) 45 °C) Removal of Reactive Black 5 dye from Aqueous Media using Pow 155 dered Activated Carbon - Kinetics and Mechanisms dye-rich textile wastewater with special focus on the reduction of colour polluters. The initial concentration of RB5 varied from 300 to 700 mg/dm3, which is a possible range of dye concentration in textile industry wastewater after the process of dying. The dependence of the amount of adsorbate adsorbed after appropriate time (qt) versus time (t) is presented in Figure 2, while data are given in Table 1. It is evident from Figure 2 that a higher initial concentration of the dye increases the adsorption capacity and that the amount of adsorbed RB5 is higher at higher temperature for all concentrations. As equilibrium for the initial concentration c0 = 300 mg/dm3 was reached very quickly, the amount of adsorbate adsorbed was monitored from 15 minutes to 4 hours, while for the other two initial concentrations were monitored from 15 minutes to 6 hours. The plots can be approximately divided into three regions. The first region includes a very fast initial adsorption, probably governed by a rapid external diffusion process, which mainly includes adsorption of dye on the surface of activated carbon. After this step follows the second region, with a milder and gradual increase of adsorbed dye, and the third region where a state of equilibrium was almost reached. The sorption capacity at equilibrium at both temperatures increased from ca. 74 to ca. 173-174 mg/g with an increase of the initial dye concentration from 300 to 700 mg/dm3 (Table 1). Initially, differences in adsorbed RB5 between two temperatures for the same initial dye concentration were more significant, while after a longer period of adsorption, quantities of adsorbed RB5 became very similar. Also, as expected, less time was needed to obtain high dye adsorption percentage values for lower concentra- tions of dye (Figure 3). Thus, approximately 90% of RB5 was adsorbed at 25 °C for initial concentrations of c0 = 300, 500 and 700 mg/dm3 after 1, 3 and 6 hours, respectively (Table 1). At 45 °C, these times are significantly shorter, and they were between 15 and 30 minutes for c0 = 300 mg/dm3, 1 hour for c0 = 500 mg/dm3 and 2 hours for c0 = 700 mg/dm3. The efficiency of activated carbon for the adsorption of RB5 is also evidenced by the fact that more than 60% of dye is adsorbed after 30 minutes, regardless of initial concentration and temperature. 3.2 Kinetics of adsorption Kinetic studies were performed in order to investigate the mechanism of adsorption and potential rate controlling steps. Kinetic study is important to an adsorption process because it depicts the uptake rate of the adsorbate and controls the residual time of the whole adsorption process for a given system. The experimental data were analysed using three kinetic models: pseudo-first-order and pseudo-second-order kinetic models, and an intraparticle diffusion model. The pseudo-first-order and pseudo-second-order models are used most frequently for determining of kinetic parameters. Pseudo-first-order kinetic model Lagergren [16] proposed a rate equation for the sorption of solute from a liquid solution based on solid capacity. The kinetic model of this the most widely used rate equation is expressed using the following equation: dqL dt - ki (qe - qt) (3), where k1 represents the rate constant of the pseudofirst-order (min-1). (a) (b) Figure 3: Effect of initial concentration on percentage of adsorbed RB5 (% ads.) at temperatures of (a) 25 °C and (b) 45 °C (initial concentrations, c0: © 300 mg/dm3, © 500 mg/dm3, © 700 mg/dm3) Tekstilec, 2020,63(2), 151-161 156 Removal of Reactive Black 5 dye from Aqueous Media using Pow dered Activated Carbon - Kinetics and Mechanisms Integrating this equation for the boundary conditions t = 0 to t = t and qt = 0 to qt = qt results in: Mqe - qt) = In qe - k1 ■ t (4). The kinetic constant k1 can be determined by plotting ln(qe-qt) against time (t), and if the first-order equation is applicable, the plot should give a linear relationship, and facilitates the calculation of the rate constant of pseudo-first-order (k1) from the slope and amount of adsorbate adsorbed at equilibrium (qecalc) from the intercept. The values of the constants of the pseudo-first-order model for adsorption of RB5 onto activated carbon are given in Table 2. The values of the correlation coefficient (R2) obtained from the linear plot (Eq. 4) are relatively high (from 94.6% to 99.8%), the exception being the initial concentration of c0 = 300 mg/dm3 at 25 °C (71.1%). However, for all concentrations and at both temperatures, there is considerable disagreement between the 3,5 3 2,5 2 O- ^ 1,5 1 0,5 60 120 180 240 11 min 300 (a) experimental and calculated values of the amount of adsorbed RB5 at equilibrium (qeexp and qecalc). This suggests that this sorption system is not a first-order reaction and that a pseudo-second-order model might provide a better correlation of the data. Pseudo-second-order kinetic model Ho and McKay [17, 18] developed a second-order equation based on adsorption capacity. This kinetic model is illustrated by the following equation: dqt dt - k2 (qe - qt)2 (5), where k2 represents the rate constant of the pseudo-second-order (g mg-1 min-1). Integrating the equation (5) for the same boundary conditions used for the first-order results in the equation presented below in the linear form: t qt 1 - +1 ■ t k2 ■ q2 qe (6). 3,5 3 2,5 ~ 2 oi 1,5 1 0,5 360 60 120 130 240 tl min 300 360 (b) Figure 4: Pseudo-second-order kinetic model for three initial concentrations of RB5 at temperatures of (a) 25 °C and (b) 45 °C (initial concentrations, c0: © 300 mg/dm3, © 500 mg/dm3, © 700 mg/dm3) Table 2: Kinetic parameters for the effect of initial dye concentration on adsorption at temperatures of 25 °C and 45 °C T (oC) co (mg/dm3) qe,exp (mg/g) Pseudo-first-order model Pseudo-second-order model qe,calc (mg/g) R2 ki (min-1) qe,calc (mg/g) R2 k2 (g mg-1 min-1) h (mg g-1 min-1) 25 300 74.1 14.3 0.7108 0.0129 74.6 0.9995 0.002295 12.77 500 122.7 48.6 0.9888 0.0085 125.0 0.9983 0.000463 7.23 700 172.6 79.4 0.9948 0.0052 166.7 0.9944 0.000252 7.00 45 300 74.0 26.1 0.9656 0.0674 74.6 0.9999 0.009075 50.51 500 124.3 32.5 0.9463 0.0154 128.2 0.9998 0.000935 15.36 700 173.6 72.9 0.9975 0.0145 178.6 0.9997 0.000437 13.95 Tekstilec, 2020,63(2), 151-161 Removal of Reactive Black 5 dye from Aqueous Media using Pow 157 dered Activated Carbon - Kinetics and Mechanisms If the pseudo-second-order equation is applicable, the plot of t/qt against time t should give a linear relationship and facilitates the calculation of the amount of adsorbate adsorbed at equilibrium (qe calc) from the slope, and then the rate constant of the pseudo-second-order (k2) from the intercept. The values are given in Table 2, while linear plots are presented in Figure 4. Based on this model, calculated qe values (qecalc) and experimental equilibrium values (qeexp) demonstrate a much better correlation (Table 2). Moreover, the values of correlation coefficients are very close to 1 (higher than 99.4%) for all initial dye concentrations and at both temperatures. Figure 5 shows the good correlation of the data with the pseudo-second-order equation. The experimental points are shown together with the theoretically generated lines, and they fit nicely for all concentrations and at both temperatures, although slightly better for the temperature of 45 °C. The adsorption of RB5 dye on commercial activated carbon is thus kinetically controlled assuming a pseudo-second-order rather than a pseudo-first-order process. The pseudo-second-order model assumes chemical sorption or chemisorption as the rate-limiting process. Maximum k2 values were obtained for the smallest initial dye concentration (c0 = 300 mg/dm3), while values for temperature of 45 °C are approximately 2-4 times higher than those for 25 °C. Also, as time approaches zero, according to the pseudo-second-order model, the initial adsorption rate h (mg g-1 min-1) can be calculated using the following equation [18, 19]: h = k2 ' ql,calc (7). The obtained h values are also presented in Table 2. As for k2, values of the initial adsorption rate increase with a decrease of initial dye concentration, and increase with an increase in temperature. Intraparticle diffusion model We used an intraparticle diffusion model to evaluate the diffusion mechanism for adsorption of RB5 on activated carbon. Most adsorption reactions are carried out using a multistep mechanism and involve several steps: (i) external mass transfer of the adsorbate from the solution to the adsorbent surface; (ii) adsorption at a site on the adsorbent surface; and (iii) intraparticle diffusion of the adsorbate in the pores of the adsorbent and adsorption on the site. Step (ii) is often assumed to be very fast, and thus cannot be treated as a rate limiting step. Generally, the rate of adsorption is limited by external mass transfer for a system with poor mixing, low adsorbate concentration, its high affinity to the adsorbent and the small adsorbents particles. The adsorption of large molecules, for which longer contact time is needed to reach equilibrium, is always considered to be diffusion controlled by external film resistance and/or internal diffusion mass transport or intraparticle diffusion [20]. Theoretical treatments of intraparticle diffusion yield complex mathematical relationships that differ in form as functions of the geometry of the adsorbent particle. The intraparticle diffusion model is based on the following equation [19, 20]: qt = kt ■ to-5 (8), where ki represents the intraparticle diffusion rate constant (mg g_1 min-0-5). 120 240 360 480 600 f I min (a) 180 160 140 120 O) 100 Ul E 80 ii 60 40 20 0 720 840 960 -ii.'- 120 240 360 480 600 tl min (b) 720 840 960 Figure 5: Fitting of pseudo-second-order kinetic model with experimental data at temperatures of (a) 25 °C and (b) 45 °C (initial concentrations, c0: © 300 mg/dm3, © 500 mg/dm3, © 700 mg/dm3) Tekstilec, 2020,63(2), 151-161 Removal of Reactive Black 5 dye from Aqueous Media using Pow 158 dered Activated Carbon - Kinetics and Mechanisms 200 200 180 180 . fTl 160 ■ - 160 . . 140 • 140 Cg) * 120 tj u 120 • . * 1 oi mo . 4, 4 * o) ioo 5. so CD . E 80 '....... CD If 60 , <" 60 * 40 10 20 20 0 0 0 4 8 12 16 20 24 28 32 0 4 8 12 16 20 24 23 32 f o.5 i m ¡n°s (i s imin0'5 (a) (b) Figure 6: Root time plots for the adsorption of RB5 for three initial dye concentrations (c0: © 300 mg/dm3, © 500 mg/dm3, ® 700 mg/dm3) at temperatures of (a) 25 °C and (b) 45 °C If the intraparticle diffusion is a rate limiting step of adsorption, i.e. intraparticle diffusion controls the rate of adsorption, then plot qt versus t05 should be linear and pass through the origin. If the plot of qt versus t05 exhibit multi-linearity, this indicates that two or more rate controlling steps occur in the adsorption processes [20-22]. Figure 6 shows the root time plots for the adsorption of RB5 onto activated carbon at temperatures of 25 and 45 °C. It is evident from the above figure that the plots are not linear, i.e. that they exhibit multi-linearity with several sections. It can thus be concluded that in-traparticle diffusion is not the only process that influences the adsorption rate and that multiple steps took place during the adsorption process. Few stages can be distinguished during the dye adsorption. The adsorption rate is initially higher and corresponds to instantaneous adsorption, probably due to an electrostatic attraction between the dye and the external surface of the adsorbent. The amount of adsorbed substance on the adsorbent and diffusion decreases over time, and represents a gradual adsorption stage where diffusion rates decreased by increasing the contact time. This process usually includes the intraparticle diffusion of the molecules through the pores of the adsorbent. That stage is followed by the equilibrium stage when dye molecules occupy all active sites of the adsorbent [19]. Diffusion in the pores of the adsorbent is usually determined by the fact that there are several different pore sizes in the adsorbent, and that controlling regions correspond to the dye diffusion to the activated carbon pores of different dimensions. Since the dye molecules diffuse into the inner structure of the adsorbents, the pores for diffusion become smaller and thus the free path of the molecules in the pore decreases. 3.3 Thermodynamics Standard Gibbs free energy (AG0, kJ/mol) values of the adsorption process can be calculated using the equation: AG0 = -RT ln (K) (9), Table 3: Standard Gibbs free energy changes (AG0, kJ/mol) for the adsorption of Reactive Black 5 on activated carbon co T Kc AG0 (mg/dm3) (K) (mg/dm3) (kJ/mol) 300 298 3.7 80.1 -10.86 318 4.0 74.0 -11.38 500 298 9.2 53.3 -9.86 318 2.8 177.6 -13.70 700 298 9.6 71.9 -10.60 318 5.8 119.7 -12.66 Tekstilec, 2020,63(2), 151-161 Removal of Reactive Black 5 dye from Aqueous Media using Pow 159 dered Activated Carbon - Kinetics and Mechanisms where R represents the universal gas constant and T represents temperature. Kc represents the equilibrium constant calculated from the concentration of the dye adsorbed on the solid at equilibrium (cs / mg/dm3) and the concentration of the dye when equilibrium is reached in the liquid phase (ce / mg/dm3) [23]: Kc = ^ (10). Ce The negative values of AG0 indicate that the adsorption reaction is spontaneous. Thus, AG0 values given in Table 3 reflect the feasibility of the process, and that the adsorption of RB5 onto activated carbon was a spontaneous process in nature, in which no energy input from outside of the system was required. The higher negative value reflects a more energetically favourable adsorption. It can thus be concluded that adsorption at 45 °C is energetically more favourable than at 25 °C. 3.4 Morphological analysis of the adsorbent and dye-adsorbent samples In order to perform a morphological analysis of activated carbon before and after adsorption, photographs were taken using scanning electron microscopy (SEM). It is evident from recorded photographs of activated carbon that the particles differ morphologically and have different pore sizes, as assumed by the results of the intraparticle diffusion model (Figure 7). (a) (b) Figure 7: SEM images of activated carbon surface enlarged (a) 15000 x and (b) 20000 x Figure 8 shows the appearance of activated carbon after the adsorption of RB 5 (adsorption time of 4 hours at a temperature 45 °C) for initial dye concentrations of c0 = 300 mg/dm3 (Figure 8a) and c0 = 700 mg/dm3 (Figure 8b). It is evident from the images that dye is adsorbed on the surface of activated carbon. For the initial concentration c0 = 300 mg/dm3, some parts of the surface are almost completely straight, while the other parts are uneven. The activated carbon surface for the initial dye concentration of c0 = 700 mg/dm3 is flatter on most parts, an indication that activated carbon is almost completely covered with dye molecules. From this it can be assumed that, for a higher initial concentration, a certain amount of dye is further adsorbed on activated carbon. (a) (b) Figure 8: SEM images of activated carbon after the adsorption of dye enlarged 15000 x for initial dye concentrations of (a) c0 = 300 mg/dm3, and (b) c0 = 700 mg/dm3 4 Conclusion According to the results achieved, the adsorption of Reactive Black 5 onto activated carbon was very fast. This study also confirmed that activated carbon is a very efficient adsorbent and that adsorption at higher temperature is greater. For all initial concentrations, approximately 90% of RB5 was adsorbed at 25 °C after 1 to 6 hours. On the other hand, these times are significantly shorter at a temperature of 45 °C, with the maximum value of 2 hours for the initial concentration of c0 = 700 mg/dm3. Furthermore, the adsorption of RB5 dye on commercial activated carbon was kinetically controlled assuming a pseudo-second-order rather than a pseudo-first-order process. This study also revealed that intraparticle diffusion was not the only process that influenced the adsorption rate and that multiple steps took place during the adsorption process. Finally, the negative values of AG0 indicate that the adsorption reaction was spontaneous in nature and that adsorption at 45 °C was energetically more favourable than at 25 °C. The adsorption of Reactive Black 5 dye on activated carbon was also confirmed by scanning electron microscopy. Tekstilec, 2020,63(2), 151-161 160 Removal of Reactive Black 5 dye from Aqueous Media using Pow dered Activated Carbon - Kinetics and Mechanisms Acknowledgements Authors would like to thank Zorana Kovacevic from Faculty of Textile Technology for SEM images recording. References 1. SAVIN, Irina-Isabella, BUTNARU, Romen. Wastewater characteristics in textile finishing mills. Environmental Engineering and Management Journal, 2008, 7(6), 859-864, doi: 10.30638/ eemj.2008.113. 2. BISSCHOPS, I., SPANJERS H. 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