M. NYSSANBEK et al.: ISOLATION OF MICROFIBERS IN THE PROCESSING OF POLYAMIDE FABRICS 623–627 ISOLATION OF MICROFIBERS IN THE PROCESSING OF POLYAMIDE FABRICS IZOLACIJA MIKROVLAKEN PRI PROCESIRANJU POLIAMIDNIH TKANIN Marzhan Nyssanbek 1,2 , Almas Mukhametov 3 , Abdugani Azimov 4* 1 Department of Textile Industry Technology and Materials Science, M.Kh. Dulaty Taraz Regional University, Taraz, Kazakhstan 2 Peoples’ Friendship University named after Academician A. Kuatbekov, Shymkent, Kazakhstan 3 Department of Technology and Safety of Food Products, Kazakh National Agrarian Research University, Almaty, Kazakhstan 4 Scientific Research Institute Natural and Technical Sciences, South Kazakhstan University named after M. Auezova, Shymkent, Kazakhstan Prejem rokopisa – received: 2022-07-18; sprejem za objavo – accepted for publication: 2022-09-26 doi:10.17222/mit.2022.621 In recent years, the problem of the release of polymer microparticles (the so-called microplastics) from textile products has been extensively investigated. The main reason of the release of a large number of plastic microfibers is considered to be machine washing of synthetic clothing. However, approaches aimed at reducing the amounts of detached microfibers (MFs) differ signifi- cantly. This paper reviews the existing approaches, presents a method for processing polyamide fabrics with a chitosan solution, and describes the experiments that confirm the feasibility of the proposed method. The formation of a chitosan film on the sur- face of polyamide fibers was evidenced with the results of scanning electron microscopy. The authors have shown that fabric surface treatment witha1%chitosan solution reduces the amount of microfibers released during washing by 60 %. A fluo- rescent analysis demonstrated that mechanical processing of polyamide fabrics with a higher surface density is associated with a release of a smaller number of microfibers (358 ± 24) MF/g as compared to less dense fabrics (533 ± 16) MF/g. The results ob- tained in the present study can be used in the development of a standard method for quantifying the amount of synthetic microfibers shed from textile materials during their washing. Keywords: microplastics, fiber, polyamide, chitosan, washing V zadnjem ~asu se raziskovalci zelo ukvarjajo s problemom spro{~anja polimernih mikrodelcev oziroma mikroplastike. Ugotavljajo, da je glavni razlog za spro{~anje velike koli~ine mikrovlaken strojno pranje sinteti~nih obla~il oziroma tekstila. Vendar pa se pristopi za re{evanje zmanj{anja koli~ine izlo~enih mikrovlaken (MF, angl.: microfibers) med seboj zelo razlikujejo. V tem ~lanku avtorji opisujejo pregled obstoje~ih pristopov in novo metodo procesiranja poliamidnih vlaken v hitozanski raztopini ter opisujejo preizkuse, ki potrjujejo izvedljivost predlagane metode. S presevnim elektronskim mikroskopom so dokazali tvorbo hitozanskega filma na povr{ini poliamidnih vlaken. Avtorji pri~ujo~ega ~lanka so dokazali, da obdelava tekstila z 1 %-no hitozansko raztopino zmanj{a vsebnost mikrovlaken med pranjem za pribli`no 60 %. S fluorescentno analizo so dokazali, da je mehansko procesiranje poliamidnih vlaken z ve~jo povr{insko gostoto povezano s spro{~anjem manj{ega {tevila mikrovlaken (358 ± 24) MF/g v primerjavi z manj gostimi tkaninami (533 ± 16) MF/g. Rezultati te {tudije se lahko uporabijo za razvoj oziroma izdelavo standardizirane metode za ovrednotenje koli~ine izlo~enih sinteti~nih vlaken iz tekstilnih materialov med njihovim pranjem. Klju~ne besede: mikroplastika, vlakna, poliamid, hitozan, pranje 1 INTRODUCTION 1.1 General The presence of microplastics (particles smaller than 5 mm) in almost all ecosystems presents a global prob- lem. 1 Microplastic particles have been found not only in wastewater, but also in coastal areas as well as in the or- ganisms of the species inhabiting rivers and seas. 2,3 Re- cent studies have shown that 73 % of fish caught in the northwestern Atlantic Basin have microplastics in their stomachs. 1 As for the impact of microfibers (MFs) on human health, it will depend on the cumulative impact of diffuse terrestrial sources. There is evidence for the presence of microfibers in a wide range of foods and beverages such as seafood, drinking water, beer, salt and sugar. 4 There is no doubt that some degree of chronic exposure is now an integral part of human life. 5 According to the Friends of the Earth International, 6 about 64 % of all textile products are made of plastic. The polyester fiber (PEF) segment leads the synthetic fi- ber market, accounting for a share of about 84 %, fol- lowed by the nylon, acrylic and polypropylene seg- ments. 3 Synthetic fibers are considered to be cheap and versatile. They are comfortable and breathable for sportswear, warm and durable for winter apparel. How- ever, microfibers are not as good in terms of bio- degradability. It takes one month for 82 % of cotton to decompose, whereas polyester fibers do not decompose during this period at all. 3 Given the growing demand for synthetic textiles in various industries, the growth of the world population and the rise in living standards, the market for synthetic fibers is constantly expanding. As estimated by analysts, Materiali in tehnologije / Materials and technology 56 (2022) 6, 623–627 623 UDK 677.494.675:648.23 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 56(6)623(2022) *Corresponding author's e-mail: abduganiazimov@rambler.ru (Abdugani Azimov) the global production of synthetic materials increases by more than 9 million tons each year and will reach 80 million tons by 2025. 3 As of 2017, the volume of synthetic fibers produced in Russia was 377.5 thousand tons, of which the produc- tion of synthetic textile accounted for 53.6 thousand tons. The global trend is also observed in the Russian market, as the production of polyester fibers predomi- nates over the production of other synthetic fibers. 7 1.2 Literature review Scientists assume that MF shedding occurs at all stages of the synthetic fabric production, from the raw material processing to MF disposal. 4,7–11 The Interna- tional Union for Conservation of Nature reports that about 35 % of all primary microplastics are generated from washing synthetic materials, 12 since washing ma- chine filters and wastewater treatment plants do not re- move such fibers. 13 Thus, freshwater ecosystems are at considerable risk, since they receive not only domestic, but also industrial wastewater, including the wastes dumped by textile factories. 14 Given the growing environmental concern and the continuous growth of the synthetic textile market, active research is being carried out in the area of MF shedding. It is dedicated to the development of measures intended to reduce the amount of MFs generated during machine washing and subsequently released into the environ- ment. 4,11,14–18 While developing sufficiently effective methods aimed at the prevention of harmful effects asso- ciated with this source of pollution, many researchers fo- cus on the optimization of washing parameters, including the temperature and cycle time, the presence of deter- gents and conditioners, the amount of water used, the number of revolutions during spinning, etc. 13,19–22 There are contradictory findings concerning the ex- posure to detergents. Notably, a group of investi- gators 2,18,23 showed that the use of detergents promotes the release of microfibers during washing. Other authors concluded that the use of detergents decreases the num- ber of microfibers released from synthetic clothing dur- ing machine washing. 14 A team of researchers confirmed the selective action of biodetergents (detergents contain- ing enzymes): in some cases, their use promotes the fiber loss, while under other circumstances it may decrease the number of fibers released or have no significant ef- fect at all. 24 Similar discrepancies have been identified in studies investigating the effects of fabric softeners or, as they are also called, fabric conditioners. 13,23–25 The authors of one paper note that the use of fabric softeners can enhance the release of microfibers under certain conditions. 23 However, these findings contradict the results obtained by other researchers, 24 who concluded that these prod- ucts can reduce the release of microfibers by more than 35 %. Some researchers have shown that clothes shed more microfibers in the first wash than in subsequent washing cycles. 10,13,20 However, there are authors who state that the number of released microfibers does not depend on the number of washing cycles. 23 Summing up the literature review, one promising, rel- atively inexpensive and simple method of chemical treat- ment of polyamide fabrics should be mentioned, which is their pre-treatment with an accessible and natural reagent – chitosan. 26,27 This method enables increasing the strength of synthetic fibers and, consequently, reduces the number of MFs released. Thus, the purpose of the present paper is to elucidate the effects of chitosan treatment of polyamide fabrics on the release of microfibers during the washing of fabrics of different densities. To achieve this purpose, the re- searchers should accomplish several objectives. Firstly, they are to develop a procedure for the treatment of fab- rics with chitosan. Secondly, the researchers intend to identify the effects of treatment on the number and char- acteristics of microfibers released before and after wash- ing, and to analyze the results obtained in comparison with the data presented in the literature. 2 EXPERIMENTAL PART 2.1 Materials Samples of two polyamide fabrics, used for tailoring, where chosen for the experiment. According to the man- ufacturer’s specification, the surface densities of the samples were 92 MF/g and 200 MF/g. Polyamide fabric is a synthetic textile made of petroleum-based plastic polymers. To prepare the treatment solution, the investigators used chitosan with a molecular weight of 200 kDa and a degree of deacylation of 82 %, and acetic acid of chemi- cally pure grade. Distilled water was used in all experi- ments. Chitosan is a natural cationic polysaccharide com- posed of randomly distributed (1–4)-linked N-acetyl- glucosamine and glucosamine. This polymer has been used as a textile finishing substance, conferring antibac- terial properties, as an adsorbent of anionic dyes or a as shrink-resist agent in wool, among other applications. 28 2.2 Experiment A sample of chitosan was dissolved ina2%acetic acid solution during 24 h at room temperature. The con- centration of the resulting chitosan solution was 1 %. Tissue samples, which had been previously cut into squares of (500 × 500) mm, were placed in the prepared solution for one hour and completely dried at a tempera- ture of 125 °C. 29 Samsung WF8590NLW9 was chosen for the study. The washing mode was chosen according to the recom- mendations of the polyamide-fabric manufacturers (deli- M. NYSSANBEK et al.: ISOLATION OF MICROFIBERS IN THE PROCESSING OF POLYAMIDE FABRICS 624 Materiali in tehnologije / Materials and technology 56 (2022) 6, 623–627 cate wash, 30 °C, spinning with a minimum number of revolutions). The amount of the bleach-free laundry de- tergent used corresponded to the amount indicated by the manufacturer for washing machines of the given class. No fabric softener was used. Each experiment lasted 30 min and was performed in triplicate. After the end of the washing cycle, the drainage water was filtered through a laboratory sieve with a pore size of 100 μm. The fibers captured by the filter were washed with dis- tilled water into a beaker, dried in a desiccator, and tested. 2.3 Testing methods To assess the effectiveness of the developed process we used scanning electron and fluorescence microscopy. In the course of scanning electron microscopy, the fi- ber surface morphology was analyzed. The tests were performed before and after the fabric treatment with chitosan using a Philips XL30 scanning electron micro- scope (a 2.0 nm resolution at a voltage of 30 kV and a 1000× magnification). Fluorescence microscopy was undertaken to evaluate the amount of generated MFs. A 10 mg/L solution of Nile red in n-hexane was used. The test samples were prepared according to the prescribed procedure. 30 The samples were analyzed in the green part of the visible spectrum since a wavelength of 510–560 nm is the most illustrative for the visual examination of polyamide fi- bers stained with Nile red. 30 3 RESULTS The results of the surface morphology analysis are shown in Figure 1. The fibers of the sample that was pretreated with a 1 % chitosan solution (Figure 1b) are šglued’ together as compared to the control sample (untreated fabric, Fig- ure 1a). The chitosan solution is likely to bind individual fibers. The results obtained during a fluorescence analysis after washing the untreated control sample (Figure 2a) and the sample that had been treated with the 1 % chitosan solution (Figure 2b) confirm the above assump- tion. The researchers calculated that the amount of micro- fibers in the control sample was (893 ± 41) MF/g, and the amount of microfibers in the pre-treated sample was (358 ± 24) MF/g. The values are presented as arithmetic means, calculated based on the number of fibers released after each of the three experiments, plus or minus stan- dard deviation. When examining the samples under a microscope, no agglomeration of fibers was observed. These results are consistent with the assertion that household washing ma- chines cannot trap microfibers as they are not equipped with special devices. 13 To determine how the surface density of a polyamide fabric affects the process of MF release, two samples were compared. As mentioned in Section 2.1 and pro- vided in the manufacturer’s specification, the surface density of the first sample (O1) was 92 g/m 2 and the sur- face density of the second sample (O2) was 200 g/m 2 . Control (untreated) samples were labeled as KO1 and KO2, respectively. The results of the experiments are presented in Table 1. Table 1: Number of MFs shed from the untreated and chitosan-treated polyamide fabric samples Sample Fabric surface density (g/m 2 ) Number of MFs (MF/g) Reduction in MF shedding (%) KO1 92 1 346 ± 34 60.4 O1 92 533 ± 16 KO2 200 893 ± 41 60.1 O2 200 358 ± 24 As expected, a smaller amount of MFs was released from denser fabric samples (1 346 ± 34) MF/g for KO1 and (893 ± 41) MF/g for KO2. The tendency did not M. NYSSANBEK et al.: ISOLATION OF MICROFIBERS IN THE PROCESSING OF POLYAMIDE FABRICS Materiali in tehnologije / Materials and technology 56 (2022) 6, 623–627 625 Figure 2: Fibers detached from the polyamide fabrics with a surface density of 200 g/m 2 : a) untreated, b) chitosan-treated Figure 1: Surfaces of the polyamide fabrics with a surface density of 200 g/m 2 visualized during a SEM analysis (a magnification of 1000×): a) untreated surface, b) chitosan-treated surface change after the fabric treatment with chitosan (533 ± 16) MF/g for O1 and (358 ± 24) MF/g for O2. 4 DISCUSSION 4.1 Rationale for the choice of study material Some authors focused their attention on testing fabric samples and non-woven materials (e.g., microfleece), 2 new finished products and those that had been artificially aged. 23 The choice of textile for the present study is justi- fied by the fact that polyamide is characterized by high strength, high impact and wear resistance. The authors of this paper assumed that the same type of fabric with different surface densities releases differ- ent amounts of MFs. The experimental data presented in Table 1 confirm this assumption. The higher the fabric density, the lower is the amount of microfibers released (358 ± 24) MF/g and (533 ± 16) MF/g for O2 and O1, respectively. 4.2 Chemical treatment of polyamide fabrics The formation of chitosan films is known to be sig- nificantly affected by the polymer molecular weight and structure, the origin of chitosan, the degree of chitosan deacetylation, the presence of free amino groups, and the type of solvent. 32 In most cases, acetic acid is used as the standard solvent to form chitosan films. The use of other acids (formic, lactic, citric, glycolic ones) results in a de- terioration of the mechanical properties of chitosan films as compared to the films obtained with the use of acetate solutions. 33 Therefore, 2 % acetic acid was chosen as the solvent by the researchers. A 1 % chitosan solution was used in the process of developing the described method. This concentration of chitosan was chosen based on the results published by other investigators. 34,35 It is a well-known fact that the rigidity and stability of the highly ordered structure of chitosan are supported by a system of hydrogen bonds. Hydroxyl groups, oxy- gen atoms of the pyranose ring and glycosidic bond, and amino groups are involved in their formation. 34 If the de- gree of protonation is low, the unprotonated amino groups remain hydrogen bonded, maintaining the rigidity of the chitosan molecule. In case of a critical increase in protonation, a change in the macromolecule configura- tion occurs caused by the destruction of hydrogen bonds. Such a change leads to an increase in the macromolecule flexibility. 35 5 CONCLUSIONS In order to reduce the formation of plastic micro- fibers (the so-called microplastics), a method for treating polyamide fabrics with a 1 % chitosan solution was de- veloped. The formation of a chitosan film on the fabric surface was confirmed with spectral scanning micros- copy. The researchers have suggested that the film forms due to hydrogen bonds, which form spatial structures. The amount of microfibers shed from textiles during washing can be reduced by more than two times in case of a textile pretreatment with chitosan. To illustrate, the amount of microfibers in the untreated sample was (893 ± 41) MF/g, and the amount of microfibers in the sample pre-treated with chitosan was (358 ± 24) MF/g. The results of the experiment confirm that the surface density of a fabric has a significant impact on the amount of MFs generated. Fabrics with a higher surface density (200 g/m 2 ) released (358 ± 24) MF/g, while fabrics with a two-times lower surface density (92 g/m 2 ) released (533 ± 16) MF/g. The findings described in this paper were compared with the data provided by other authors. Based on the results of this comparison, the developed method is considered to be promising. Further detailed studies are required in this area. However, the data avail- able today may already be used for the development of a standard method for quantifying the microfibers shed from synthetic fibers during washing. 6 REFERENCES 1 A. H. Anik, S. Hossain, M. Alam, M. B. Sultan, M. T. Hasnine, M. M. Rahman, Microplastics pollution: a comprehensive review on the sources, fates, effects, and potential remediation, Environ. Nano- technol. Monit. Manag.,16 (2021), 100530, doi:10.1016/j.enmm. 2021.100530 2 B. M. Carney Almroth, L. Åström, S. Roslund, H. Petersson, M. Johansson, N. K. Persson, Quantifying shedding of synthetic fibers from textiles; a source of microplastics released into the environ- ment, Environ. Sci. Pollut. Res., 25 (2018), 1191–1199, doi:10.1007/s11356-017-0528-7 3 Y. Q. Zhang, M. Lykaki, M. T. Alrajoula, M. Markiewicz, C. Kraas, S. Kolbe, K. Klinkhammer, M. Rabe, R. Klauer, E. Bendt, S. Stolte, Microplastics from textile origin – emission and reduction measures, Green Chem., 23 (2021), 5247–5271, doi:10.1039/D1GC01589C 4 V. N. Kondakova, K. V. Pankratova, A. A. Pomortseva, G. B. Pospekhov, Analysis of the problem of classification of mining wastes, Conf. Proc. Engineering and Mining Geophysics 2020, Euro- pean Association of Geoscientists & Engineers, 2020, 1–8, doi:10.3997/2214-4609.202051139 5 B. Henry, K. Laitala, I. Grimstad Klepp, Microfibres from apparel and home textiles: prospects for including microplastics in environ- mental sustainability assessment, Sci. Total Environ., 652 (2019) 483–494, doi:10.1016/j.scitotenv.2018.10.166 6 P. Byrne, Microfibres: the plastic in our clothes, Friends of the Earth, 2018, https://friendsoftheearth.uk/plastics/microfibres-plastic-in- our-clothes, 20.12.2021 7 E. M. Eisenstein, Chemical fibers in Russia and worldwide, Neftegaz.RU, 8 (2018), 112–124 8 H. Deng, R. Wei, W. Luo, L. Hu, B. Li, H. Shi, Microplastic pollu- tion in water and sediment in a textile industrial area, Environ. Pollut., 258 (2020), 113658, doi:10.1016/j.envpol.2019.113658 9 M. R. Kelly, N. J. Lant, M. Kurr, J. G. Burgess, Importance of wa- ter-volume on the release of microplastic fibers from laundry, Envi- ron. Sci. Technol., 53 (2019), 11735–11744, doi:10.1021/acs.est. 9b03022 10 M. Volgare, F. De Falco, R. Avolio, R. Castaldo, M.E. Errico, G. Gentile, V. Ambrogi, Washing load influences the microplastic re- lease from polyester fabrics by affecting wettability and mechanical stress, Sci. Rep., 11 (2021), 19479, doi:10.1038/s41598-021-98836-6 M. NYSSANBEK et al.: ISOLATION OF MICROFIBERS IN THE PROCESSING OF POLYAMIDE FABRICS 626 Materiali in tehnologije / Materials and technology 56 (2022) 6, 623–627 11 J. Liu, J. Liang, J. Ding, G. Zhang, X. Zeng, Q. Yang, B. Zhu, W. Gao, Microfiber pollution: an ongoing major environmental issue re- lated to the sustainable development of textile and clothing industry, Environ. Dev. Sustain., 23 (2021), 11240–11256, doi:10.1007/ s10668-020-01173-3 12 J. Boucher, D. Friot, Primary microplastics in the oceans: A global evaluation of sources, IUCN, Gland, Switzerland, 43 (2017), dx.doi.org/10.2305/IUCN.CH.2017.01.en 13 F. S. Cesa, A. Turra, H. H. Checon, B. Leonardi, J. Baruque-Ramos, Laundering and textile parameters influence fibers release in house- hold washings, Environ. Pollut., 257 (2020), 113553, doi:10.1016/ j.envpol.2019.113553 14 C. Gaylarde, J. A. Baptista-Neto, E. M. da Fonseca, Plastic micro- fibre pollution: how important is clothes’ laundering?, Heliyon, 7 (2021) 5, e07105, doi:10.1016/j.heliyon.2021.e07105 15 L. Tiffin, A. Hazlehurst, M. Sumner, M. Taylor, Reliable quantifica- tion of microplastic release from the domestic laundry of textile fab- rics, J. Text. Inst., 113 (2021) 4, 558–566, doi:10.1080/00405000. 2021.1892305 16 N. J. Lant, A. S. Hayward, M. M. Peththawadu, K. J. Sheridan, J. R. Dean, Microfiber release from real soiled consumer laundry and the impact of fabric care products and washing conditions, PLOS ONE, 15 (2020), e0233332, doi:10.1371/journal.pone.0233332 17 C. Jönsson, O. Levenstam Arturin, A. C. Hanning, R. Landin, E. Holmström, S. Roos, Microplastics shedding from textiles – develop- ing analytical method for measurement of shed material representing release during domestic washing, Sustainability, 10 (2018) 7, 2457, doi:10.3390/su10072457 18 L. Yang, F. Qiao, K. Lei, H. Li, Y. Kang, S. Cui, L. An, Microfiber release from different fabrics during washing, Environ. Pollut., 149 (2019), 136–143, doi:10.1016/j.envpol.2019.03.011 19 P. Pfohl, C. Roth, L. Meyer, U. Heinemeyer, T. Gruendling, C. Lang, N. Nestle, T. Hofmann, W. Wohlleben, S. Jessl, Microplastic extrac- tion protocols can impact the polymer structure, Micropl. Nanopl., 1 (2021) 8, doi:10.1186/s43591-021-00009-9 20 N. Kärkkäinen, M. Sillanpää, Quantification of different microplastic fibres discharged from textiles in machine wash and tumble drying, Environ. Sci. Pollut. Res., 28 (2021), 16253–16263, doi:10.1007/ s11356-020-11988-2 21 F. De Falco, G. Gentile, E. Di Pace, M. Avella, M. Cocca, Quantifi- cation of microfibres released during washing of synthetic clothes in real conditions and at lab scale, Eur. Phys. J. Plus, 133 (2018), doi:10.1140/epjp/i2018-12123-x 22 E. Hernandez, B. Nowack, D. M. Mitrano, Polyester textiles as a source of microplastics from households: a mechanistic study to un- derstand microfiber release during washing, Environ. Sci. Technol., 51 (2017) 12, 7036–7046, doi:10.1021/acs.est.7b01750 23 I. E. Napper, R. C. Thompson, Release of synthetic microplastic plastic fibres from domestic washing machines: effects of fabric type and washing conditions, Mar. Pollut. Bull., 112 (2016) 1–2, 39–45, doi:10.1016/j.marpolbul.2016.09.025 24 F. De Falco, M. P. Gullo, G. Gentile, E. Di Pace, M. Cocca, L. Gelabert, M. Brouta-Agnésa, A. Rovira, R. Escudero, R. Villalba, R. Mossotti, A. Montarsolo, S. Gavignano, C. Tonin, M. Avella, Evalua- tion of microplastic release caused by textile washing processes of synthetic fabrics, Environ. Pollut., 236 (2018), 916–925, doi:10.1016/j.envpol.2017.10.057 25 Z. Samicho, A. Ramli: Extraction of chitosan & its film-forming properties: a review, 2011 IEEE symposium on business, engineering and industrial applications (ISBEIA), IEEE, Langkawi, Malaysia, 2011, 576–580 26 K. Koo, S. S. Kim, Y. M. Park, J. Y. Yu, B. S. Koo, S. C. Yoo, Physicochemical characterization of PET fabrics treated with chitosan after exposure to O2 low temperature plasma – especially by KES evaluation, Text. Color. Finish., 17 (2005) 5, 26–36 27 J. Sole, S. Vilchez, N. Montanya, M. J. Garcia-Celma, M. Ferrandiz, J. Esquena, Polyamide fabric coated with a dihydroxyacetone-loaded chitosan hydrogel for a cosmeto-textile application, J. Ind. Text., 50 (2020) 4, 526–542, doi:10.1177/1528083719835762 28 K. E. Perepelkin, Physical and chemical basis for the formation of chemical fibers, Chemistry, Moscow 1978 29 E. V. Ivanova, A. V. Guzeva, A. E. Lapenkov, Sh. R. Pozdnyakov, L. L. Kapustina, G. G. Mitrukova, D. A. Tikhonova, The aspects of us- ing Nile red for the detection of plastic particles in environment (in Russian), J. Appl. Ecol., 4 (2020), 36–41, https://cyberleninka.ru/ar- ticle/n/osobennosti-primeneniya-krasitelya-nilskiy-krasnyy-dlya- identifikatsii-chastits-plastika-v-prirodnyh-obektah/viewer 30 M. N. R. Kumar, A review of chitin and chitosan applications, React. Funct. Polym., 46 (2000) 1, 1–27, doi:10.1016/S1381-5148(00) 00038-9 31 K. M. Kim, J. H. Son, S. K. Kim, C. L. Weller, M. A. Hanna, Prop- erties of chitosan films as a function of pH and solvent type, J. Food Sci., 71 (2006) 3, E119–E114, doi:10.1111/j.1365-2621.2006. tb15624.x 32 S. Y. Park, K. S. Marsh, J. W. Rhim, Characteristics of different mo- lecular weight chitosan films affected by the type of organic solvents, J. Food Sci., 67 (2002) 1, 194–197, doi:10.1111/j.1365-2621. 2002.tb11382.x 33 E. N. Fedoseeva, L. A. Smirnova, V. B. Fedoseev, Viscosity and reac- tivity of chitosan solutions, Bull. N. I. Lobachevsky State Univ. of Nizhny Novgorod, 4 (2008), 59–64, http://www.unn.ru/pages/e-li- brary/vestnik/99999999_West_2008_4/9.pdf 34 M. Alekseeva, E. Fedoseeva, V. Frolov, V. Nistratov, L. Smirnova, The strength of chitosan films. The role of molecular weight, the de- gree of order, the nature of contre-ion, Prog. Chem. Appl. Chitin Deriv., 14 (2009), 65–74 M. NYSSANBEK et al.: ISOLATION OF MICROFIBERS IN THE PROCESSING OF POLYAMIDE FABRICS Materiali in tehnologije / Materials and technology 56 (2022) 6, 623–627 627