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VOLUME 65 • TEKSTILEC 3 2022 UDK 677 + 687 (05) SCIENTIFIC ARTICLES/ Znanstveni članki ISSN 0351-3386 (tiskano/printed) 160 Olga Semeshko, Yulia Saribyekova, Tatyana Asaulyuk, Sergey Myasnykov, Irina Kulish, Ihor Horokhov Study of the Influence of the Surface Roughness of Knitted Fabrics from Natural Fibres on the Light Fastness of Their Colours Študija vpliva površinske hrapavosti pletiv iz naravnih vlaken na barvno obstojnost proti sončni svetlobi 170 Mong Hien Thi Nguyen, My Duyen Thi Doan, Nhat Le Pham Designing Functional Clothing for People with Locomotor Disabilities Oblikovanje funkcionalnih oblačil za ljudi z motnjami gibanja 181 Katarina Krstović, Vesna Marija Potočić Matković, Ivana Salopek Čubrić, Goran Čubrić Physical-mechanical Properties of Aged Knitted Fabric for Swimsuits Fizikalno-mehanske lastnosti staranih pletiv za kopalke 194 Aulon Shabani, Majlinda Hylli, Ilda Kazani Investigating Properties of Electrically Conductive Textiles: A Review Raziskave lastnosti elektroprevodnih tekstilij: pregled 218 Jasminka Butorac, Ružica Brunšek, Milan Pospišil, Zvjezdana Augustinović The Influence of Water Hardness on the Agronomic Traits of Foreign Fibre Flax Varieties in the Republic of Croatia Vpliv trdote vode na agronomske lastnosti tujih sort vlaknatega lanu v Republiki Hrvaški 227 Akhtarul Islam Amjad Filtration in Pharmaceutical Industries and the Role of Textile Filtracija v farmacevtski industriji in vloga tekstila 160 Tekstilec, 2022, Vol. 65(3), 160–169 | DOI: 10.14502/tekstilec.65.2022035 Olga Semeshko, Yulia Saribyekova, Tatyana Asaulyuk, Sergey Myasnykov, Irina Kulish, Ihor Horokhov Kherson National Technical University, Berislav highway 24, 73008 Kherson, Ukraine Study of the Influence of the Surface Roughness of Knitted Fabrics from Natural Fibres on the Light Fastness of Their Colours Študija vpliva površinske hrapavosti pletiv iz naravnih vlaken na barvno obstojnost proti sončni svetlobi Original scientific article/Izvirni znanstveni članek Received/Prispelo 5-2022 • Accepted/Sprejeto 8-2022 Corresponding author/Korespondenčna avtorica: Tatyana Asaulyuk, PhD E-mail: tatisevna@gmail.com Tel. +380509932893 ORCID ID: 0000-0001-5961-6895 Abstract The article examines the influence of the surface properties of knitted fabrics from cotton and wool of various knitted structures on the light fastness of their colours. The surface properties of knitted fabrics of single plain, 1×1 rib and French piqué knitted structures were evaluated by determining their roughness using a non-contact optical method for processing digital images of the knitted fabric’s surface. The roughness profiles of the corresponding knitted fabric samples were obtained, and the main indicators of surface roughness were calculated: the profile height at ten points Rz and the arithmetic mean profile deviation Ra. Cotton knitted fabrics were dyed with the Bezaktiv Cosmos dye brand, which are bifunctional reactive dyes with monochlorotriazine / vinyl sulfone active groups, and wool knitted fabrics were dyed with acid dyes. The light fastness of the samples was evaluated after exposure to the Light Fastness Tester (Mercury-Tungsten Lamp) RF 1201 BS (REFOND) with a PCE-TCR 200 colorimeter. Colour measurements were averaged for each sample. Total colour difference (dE) was measured on the dyed cotton knitted fabrics samples after light exposure. According to the obtained roughness profiles of cotton and wool knitted fabrics, it can be concluded that the studied knitted fabrics are characterized by different roughness, which depends on their knitted structures. At the same time, a relationship was found between an increase in the roughness of knitted fabrics and the photodestruction of colours by reactive and acid dyes on cotton and wool knitted fabrics, respectively. The results show that the surface structure of knitted fabrics, that is the knitted structure, impacts the process of colour photodestruction and that the amount of dye that has undergone photodestruction increases with the increasing surface roughness of the knitted fabric. Keywords: knitted fabric, knitted structure, roughness, photodestruction, light fastness. Izvleček V članku je proučen vpliv površinskih lastnosti strukturno različnih bombažnih in volnenih pletiv na barvno obstojnost proti sončni svetlobi. Površinske lastnosti pletiv v enostavni levo-desni, 1x1 rebrasti in francoski vezavi piké so bile ovrednotene z določanjem hrapavosti z brezstično optično metodo za obdelavo površine pletiv na digitalnih slikah. Dobljeni so bili profili hrapavosti posameznih vzorcev pletiv in izračunani glavni kazalci površinske hrapavosti: višina profila v Time-Dependence of Stop Marks in Warp-Knitted Fabrics 161 desetih točkah, Rz, in aritmetična sredina odstopanja profila, Ra. Bombažna pletiva so bila barvana z bifunkcionalnimi reaktivnimi barvili znamke Bezaktiv Cosmos, z monoklorotriazinskimi oziroma vinilsulfonskimi aktivnimi skupinami. Volnena pletiva so bila barvana s kislimi barvili. Barvna obstojnost pletiv na svetlobi je bila ocenjena po izpostavitvi vzorcev osvetljevanju v aparatu Light Fastness Tester RF 1201 BS (REFOND), opremljenem z živosrebrno-volframovo žarnico, in kolorimetrom PCE-TCR 200. Meritve barve so bile povprečne za vsak vzorec. Skupna barvna razlika (dE) je bila izmerjena na vzorcih barvanih bombažnih pletiv po izpostavljenosti svetlobi. Glede na dobljene profile hrapavosti bombažnih in volnenih pletiv je bilo ugotovljeno, da imajo pletiva različno hrapavost, ki je odvisna od strukture pletiv. Hkrati je bila ugotovljena povezava med povečanjem hrapavosti pletiv in fotorazgradnjo barve bombažnih in volnenih pletiv, obarvanih z reaktivnimi in kislimi barvili. Dobljeni rezultati prikazujejo vpliv strukture površine pletiv na proces fotorazgradnje barve in kažejo, da količina, razgrajenega zaradi delovanja svetlobe, narašča z večanjem površinske hrapavosti pletiva. Ključne besede: pletivo, pletilske vezave, hrapavost, fotorazgradnja, svetlobna obstojnost 1 Introduction The roughness of fibrous materials is an important aspect of their quality and determines the surface properties and appearance of fabrics and knitted fabrics as well as products made from them [1, 2]. We have already examined the effect of the nature of the polymer matrix [3], preparation technologies [4, 5], chemical properties [6, 7] and dye concentration [8] on the light fastness of cotton and wool knitted fabrics colours. Despite the fact that the light fastness of colours largely depends on the chemical structure of dyes, in order to obtain comprehensive data, in this work, we planned to study the effect of structural characteristics of knitted fabrics from natural fibres on the light fastness of their colours. The irregularity of the surface of knitted fabrics of various knitted structures is proposed to be assessed by determining roughness indicators. The roughness of material is characterized by the parameters given in ISO 4287:1997. Geometrical Product Specifications – Surface texture: Profile method – Terms, definitions and surface texture parameters [9]. According to these parameters, surface roughness is a set of surface irregularities with a relatively small step that is usually determined by its profile (Figure 1), which is formed in the cross section of this surface by a plane perpendicular to the nominal surface. In this case, the roughness profile is considered along the length of the baseline and is used to highlight the irregularities and quantify the parameters. The assessment of surface roughness is based on the accepted reference system, in which the middle line of the profile serves as the baseline – this is the baseline m, which has the shape of a nominal profile and is drawn, so that the standard deviation of the profile to this line is minimal within the base length. The middle line of the profile is at the same distance from the lines of the peaks and valleys of the profile, which respectively pass through the highest and lowest points of the profile within the base length. The main characteristics of the roughness profile are the height of its peak y pm and the depth of its valley y vm. These are the distances from the midline of the profile to the highest point of the peak and the lowest point of the valley, respectively. To assess the surface roughness of fibrous materials, the height criterion R z is common – the height of the profile at ten points [9]. It is the sum of the average absolute values of the heights of the five largest peaks of the profile and the depths of the five largest valleys of the profile within the length of the profile. The criterion of the arithmetic mean deviations of the Ra profile, which is the arithmetic mean absolute value of profile deviations within the basic profile length [9, 10], is also significant for assessing surface roughness. Thus, to calculate the roughness parameters of knitted fabrics, it is necessary to obtain their roughness profiles. Figure 1: Roughness profile and its characteristics 162 Tekstilec, 2022, Vol. 65(3), 160–169 Studies aimed at measuring and evaluating the profile characteristics of the roughness of textile materials using various devices are presented in [11, 12, 13], where all methods are divided into contact and non-contact. Contact methods for determining roughness involve a direct measurement of the relief of a textile material using a multidirectional tribometer [12], an optical multidirectional roughness meter [14], the so-called “vibrating blade” [15], and an inductive sensor converting displacement into an electric stream [16]. Non-contact measurement of roughness is performed using a variety of optical profilometer systems: Talysurf CCI 6000 [17], Micro Measure 3D Station [18], MicroXAM-100 and MicroXAM-1200 [19], Puotech 0918 [20], helium-neon laser [21, 22], triangulated laser technology [23], and microscopy and confocal microscopy [22]. However, these devices are expensive and not widely available. The method for determining the roughness of textile materials using software products for processing scanned images, proposed in [24], does not require additional equipment and is available. Therefore, in this work, the determination of the roughness indicators of knitted fabrics was carried out in a non-contact way, that is by the optical method of processing digital images of the knitted fabrics surface in the JMicroVision 1.3.2 software environment. 2 Materials and methods In the work, cotton and wool knitted fabrics of various knitted structures and surface density were investigated. Their main characteristics are given in Table 1. Cotton knitted fabric was dyed with Bezaktiv Cosmos reactive dyes: Rot S-C, Blue S-C, Gold S-C, which are bifunctional reactive dyes with monochlorotriazine / vinyl sulfone active groups. Dyeing cotton knitted fabric was carried out using the exhaust dyeing method with a 1/50 solution rate. The mass of the knitted fabric sample was 1 g. The dye Table 1: Characteristics of knitted fabrics Raw material Knitted structure Surface density (g/m2) Single plain 150 1×1 rib 150 1×1 rib 280 Schematic representation of knitted structure Feed 4 100% cotton Feed 3 French piqué 170 Feed 2 Feed 1 100% wool Single plain 420 1×1 rib 380 1×1 rib 450 Time-Dependence of Stop Marks in Warp-Knitted Fabrics solution contained 1% dye and dyeing auxiliaries (30 g/l NaCl + 15 g/l Na 2CO3). The dyeing was performed for 60 min at 60 °C, followed by applying overflow cold, hot washing, boiling soaping and cold rinsing procedures [25]. For dyeing the wool knitted fabric, the following acid dyes were used according to the corresponding dyeing methods: Acid Red 150 (method I), Acid Blue 92 (method II), Acid Green 27 (method followed by chroming). Dyeing technologies with acid dyes depend on their chemical structure. Dyeing of wool knitted fabric was carried out with the exhaust dyeing method. Samples of wool knitted fabric with a mass of 1 g and a liquor to fabric ratio of 50:1 were used. The dyebath contained 1% owf dye, 10% owf sodium sulphate, 4% owf acetic acid 30% (method I) or 4% owf ammonium sulphate (method II). Sodium sulfate and an acid agent (acetic acid or ammonium sulfate) were introduced into the total volume of water, heated to 40 °C , and knitted fabric samples were immersed in the solution. The treatment was carried out for 10 min. Then, the samples were taken out, the dye was added to the solution and the knitted fabric was immersed again. Next, the dye bath was heated to boiling point for 30 min. and dyed for 45 min. The dyed samples were washed with cold water and dried [26, 27]. The technology of dyeing wool knitted fabric with chrome dyes was followed by chroming. The liquor to fabric ratio was 50:1. The dyebath contained 1% owf dye, 10% owf sodium sulfate, 4% owf acetic acid. 30% Sodium sulfate, acetic acid and knitted fabric were introduced into the total volume of water at 30−45 °C, heated to boiling point for 45 minutes. Then, concentrated sulfuric acid measuring 1% of weight of the knitted fabric was introduced into the bath and dyed for another 20 min until the dye was completely exhausted. Afterwards, the temperature was lowered to 80 °C by adding cold water and a solution of potassium dichromate was introduced Table 2: Indicators of light fastness of colours of the dyes used Reactive dyes Bezaktiv Cosmos Rot S-C Bezaktiv Cosmos Blue S-C Bezaktiv Cosmos Gold S-C Light fastness Acid dyes Light fastness 4−5 Acid Red 150 4 5−6 Acid Blue 92 4 6 Acid Green 27 6 163 in the amount of 1% of the weight of knitted fabric. Chroming was carried out at boiling point for 20 min. Afterwards, the dyed samples were washed with cold water and dried [26, 27]. Table 2 shows the light fastness of colours obtained by the reactive and acid dyes used in the work as declared by the manufacturers [25, 28−30]. The study of the surface roughness of knitted fabrics was conducted by obtaining roughness profiles of the corresponding knitted fabrics samples by processing digital images of the surface of knitted fabrics in the JMicroVision 1.3.2 software environment. Next, the main indicators of surface roughness were calculated: the profile height at ten points R z and the arithmetic mean profile deviation R a using formulas (1), (2), according to ISO 4287:1997 [9]. R! = ∑&$'( y"#$ + ∑&$'(|y%#$ | (1) 10 where ypmі is height of the ith largest peak of the profile and yvmш is depth of the ith largest valley of the profile. R! = % % $&' $&' 1 1 & y"#$ + &|y(#$ | (2) 2n 2n where n is the number of selected points on base length. The studied indicators were determined for samples of knitted fabrics walewise and coursewise. The light fastness of samples was evaluated after exposure to the Light Fastness Tester (MercuryTungsten Lamp) RF 1201 BS (REFOND) with a PCE-TCR 200 colorimeter. The exposure time of the dyed knitted fabric samples was 320 hours. Colour measurements were averaged for each sample. Total colour difference (dE) was measured on the dyed cotton knitted fabrics samples after light exposure. Colour difference was calculated according to CIE 1976 L*a*b* equation (3): dE = [(𝑑𝑑𝑑𝑑)! + (𝑑𝑑𝑑𝑑)! + (𝑑𝑑𝑑𝑑)! ]"/! (3) where dL is difference in lightness-darkness, da is difference in redness-greenness; db is difference in yellowness-blueness. 164 Tekstilec, 2022, Vol. 65(3), 160–169 3 Results and discussion The obtained profiles of the surface roughness of the cotton knitted fabrics samples of the studied knitted structures and surface density walewise and coursewise are shown in Figure 2. According to the obtained roughness profiles of cotton knitted fabric, it can be concluded that the studied knitted fabrics vary in roughness, depending on their knitted structures. Knitted fabric with a single plain knitted structure has a uniform roughness of low values in both directions. For the rib, there is an increase in roughness coursewise. Piqué knitted fabric is characterized by high levels of roughness both walewise and coursewise. Figure 3 depicts the roughness profiles of wool knitted fabric samples of the studied knitted structures and surface density. Figure 2: Roughness profiles of cotton knitted fabric samples: а) single plain; b) 1×1 rib 150 g/m2; c) French piqué; d) 1×1 rib 280 g/m2 Figure 3: Roughness profiles of wool knitted fabric samples: а) single plain; b) 1×1 rib 380 g/m2; c) 1×1 rib 450 g/m2 165 Time-Dependence of Stop Marks in Warp-Knitted Fabrics Table 3: Influence of knitted structure and surface density on the roughness characteristics of cotton and wool knitted fabrics Knitted fabric Knitted structure and surface density Single plain Cotton Wool Profile height by ten points, R z (μm) Arithmetic mean of profile deviations, Ra (μm) walewise coursewise mean walewise coursewise mean 0.018 3.09 4.08 3.58 0.018 0.018 2 0.029 0.122 0.076 6.39 6.36 6.38 1×1 rib, 280 g/m2 0.044 0.142 0.093 6.62 7.11 6.86 1×1 rib, 150 g/m French piqué 0.152 0.139 0.146 8.57 7.75 8.16 Single plain 0.030 0.047 0.039 7.12 7.25 7.19 1×1 rib, 380 g/m 2 0.068 0.087 0.078 6.97 8.39 7.68 1×1 rib, 450 g/m 2 0.089 0.099 0.094 7.56 9.12 8.34 The obtained surface roughness profiles of wool knitted fabric samples of plain and rib knitted structures, as in the case of cotton knitted fabrics, differ. The plain has a more uniform roughness walewise and coursewise on the canvas. The rib is characterized by a uniform surface walewise and an increase in roughness coursewise. For the rib, there is an increase in roughness coursewise, irrespective of the surface density of the knitted fabric. Based on the obtained roughness profiles, the main roughness characteristics were calculated: the profile height at ten points R z and the arithmetic mean profile deviation R a. The research results are presented in Table 3. The results of calculating the main roughness indicators R z and R a (Table 3), which characterize the unevenness of the knitted fabrics surface, show that the roughness of knitted fabrics from natural fibres depends on the knitted structure and increases in the series single plain < 1×1 rib < French piqué and with an increase in surface density. The plain knitted structure has a more uniform roughness walewise and coursewise compared to the rib knitted structure, but less uniformity compared to the plain knitted structure of cotton knitted fabric. Figure 4 depicts the study results of the colours’ photodestruction in knitted fabrics for 320 hours of insolation and the roughness indicators depending on the knitted fabrics’ knitted structures. The results presented in Figure 4 show that with an increase in the roughness of knitted fabrics, the photodestruction of dyes by reactive and acid dyes on cotton and wool knitted fabrics increases, respectively. Figure 5 presents the study results of the photodestruction of knitted fabrics colours for 320 hours of insolation and the roughness indicators depending on the surface density of knitted fabrics. Presented in Figure 5, the results indicate that with an increase in the surface density of knitted fabrics from natural fibres, the roughness increases and the photodestruction of reactive and acid dyes increases on cotton and wool knitted fabrics, respectively. The obtained results confirm the impact of the surface structure of knitted fabrics, that is the knitted structure and surface density, on the photodestruction process of colours and show that the amount of dye that has undergone photodestruction increases with an increase in the surface roughness of the knitted fabric. Taking into account the results of determining the surface roughness of knitted fabrics and the features of the photodestruction process of colours depending on their knitted structures, Figure 6 shows schematic images of the studied knitted fabrics and the mechanism of light exposure to them. Thus, the studies on the roughness of knitted fabrics make it possible to determine the relationship between the light fastness of colours and the structural properties of knitted fabrics. The relatively uniform surface of a single plain structure knitted fabric distributes energy evenly and reflects more incident light than knitted fabrics with an uneven rough surface of 1×1 rib and French piqué knitted structures. Knitted fabrics with a more uneven rough surface- 1×1 rib and French piqué reflect less light, the incident rays are refracted and again fall on the surface of the knitted fabrics, which leads to a greater photodestruction of its colours. 10 9 8 7 6 5 4 3 2 1 0 9 8 7,63 5,54 6,29 5,51 7 8,47 8,42 6 6,98 5,96 5,60 Height ( μm) Colour difference, dE Tekstilec, 2022, Vol. 65(3), 160–169 5 4 3 2 1 plain rib Knitted structure pique Bezaktiv Cosmos Rot S-C Bezaktiv Cosmos Blue S-C Bezaktiv Cosmos Gold S-C profile height by ten points, Rz (μm) 0 arithmetic mean of profile deviations, Ra (μm) 10 9 8 7 6 5 4 3 2 1 0 5,13 4,18 5,47 5,11 plain 5,92 5,95 rib 9 8 7 6 5 4 3 2 1 0 Height (μm) Colour difference, dE a) Knitted structure Acid Red 150 Acid Blue 92 Acid Green 27 profile height by ten points, Rz (μm) arithmetic mean of profile deviations, Ra (μm) b) 10 9 8 7 6 5 4 3 2 1 0 9 8 8,75 8,42 6,29 6,61 5,60 6,83 7 6 5 4 3 Height (μm) Colour difference, dE Figure 4: Influence of knitted structure on surface roughness and photodestruction of colours: а) cotton knitted fabrics dyed with reactive dyes; b) wool knitted fabrics dyed with acid dyes 2 1 rib 150 0 rib 280 Surface density (g/m2) Bezaktiv Cosmos Rot S-C Bezaktiv Cosmos Blue S-C Bezaktiv Cosmos Gold S-C profile height by ten points, Rz (μm) arithmetic mean of profile deviations, Ra (μm) 10 9 8 7 6 5 4 3 2 1 0 5,95 4,32 rib 380 6,32 5,27 Surface density (g/m2) 6,59 7,06 rib 450 Acid Green 27 Acid Red 150 Acid Blue 92 profile height by ten points, Rz (μm) 9 8 7 6 5 4 3 2 1 0 Height (μm) a) Colour difference, dE 166 arithmetic mean of profile deviations, Ra (μm) b) Figure 5: Influence of surface density on surface roughness and photodestruction of colours: а) cotton knitted fabrics dyed with reactive dyes; b) wool knitted fabrics dyed with acid dyes Time-Dependence of Stop Marks in Warp-Knitted Fabrics a) b) 167 c) Figure 6: Mechanism of action of light on knitted fabrics of different knitted structures: а) single plain; b) 1×1 rib; c) French piqué Therefore, on the basis of the obtained roughness profiles by calculating the main characteristics of roughness – the profile height at ten points R z and the arithmetic mean deviations of the profile Ra – it has been found that for the studied knitted fabrics, the photodestruction of colours increases with the increasing roughness in the series single plain < 1×1 rib < French piqué and with an increase in the surface density of knitted fabrics. Based on the conducted research, we can conclude that knitted fabrics with an uneven rough surface structure necessarily need light-protective treatment. 4 Conclusion Studies on the dependence of the light fastness of knitted fabrics from natural fibres on the structure of knitted fabrics have showed that the type of knitted structure and the surface density of knitted fabrics have a significant impact on their light fastness. The research of the effect of knitted structure and surface density on the photodestruction kinetics of colours of knitted fabrics from natural fibres showed that both for cotton and wool knitted fabrics, the light fastness of colours increases in the series French piqué < 1×1 rib < single plain and with a decrease in the surface density of the studied knitted fabrics. 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Available on World Wide Web: . 170 Tekstilec, 2022, Vol. 65(3), 170–180 | DOI: 10.14502/tekstilec.65.2022038 Mong Hien Thi Nguyen, My Duyen Thi Doan, Nhat Le Pham University of Technology, VNU-HCM, Faculty of Mechanical Engineering, Ho Chi Minh City, Vietnam Designing Functional Clothing for People with Locomotor Disabilities Oblikovanje funkcionalnih oblačil za ljudi z motnjami gibanja Original scientific article/Izvirni znanstveni članek Received/Prispelo 5-2022 • Accepted/Sprejeto 9-2022 Corresponding author/Korespondenčna avtorica: Mong Hien Thi Nguyen E-mail: ntmhien14719@hcmut.edu.vn ORCID: 0000-0002-5384-9775 Abstract This article presents a study on functional clothing for people with disabilities. The clothing items which were the subject of research, i.e. polo shirt, T-shirt, shirt, trousers and jeans, were designed for people with physical disabilities, namely for daily activities for people who often sit in wheelchairs. The study used the research method of anthropometric theory, pattern design, textile materials, and an actual survey to analyse and evaluate the reality of movement ability and perception of clothes to determine the requirements for people with disabilities. The authors proposed suitable materials and provided solutions to adjust the basic pattern to become more suitable for people with locomotor disabilities. Finished sewing products were tested and evaluated experimentally by people with leg disabilities at the Center for Sponsoring - Vocational Training and Employment Introduction of Ho Chi Minh City and the Association for the support of people with Disabilities and Orphans of Ho Chi Minh City according to the Likert scale with 5 rating levels for each criterion. The results showed that the Cronbach’s Alpha index was over 0.7. The research addressed the comfort of disabled people’s clothing, indicating promising further development of other functional clothing. Keywords: pattern design, functional clothes, locomotor disabilities, leg disability, bamboo fibre, pants, shirt Izvleček Članek predstavlja študijo funkcionalnih oblačil za osebe s posebnimi potrebami za dnevno nošenje, kot so polo majica, majica, srajca, hlače in kavbojke. Izdelki so na podlagi raziskav zasnovani tako, da so primerni za ljudi z motnjami v telesnem razvoju, predvsem za vsakodnevne aktivnosti ljudi, ki pogosto sedijo na invalidskih vozičkih. Na podlagi uporabljene raziskovalne metode antropometrične teorije, krojenja, izbire tekstilnih materialov in ankete so bile analizirane in ovrednotene realne gibalne zmožnosti in zaznavanje oblačil, da bi določili zahteve za kostumiranje oseb s posebnimi potrebami. Avtorji predlagajo materiale in rešitve za prilagoditev osnovnega vzorca, ki je primernejši za osebe z motnjami v gibanju. Oblačila so testirale in po Likertovi 5-stopenjski lestvici eksperimentalno individualno ocenile osebe z invalidnostjo stopal v Centru za poklicno podporo in ustvarjanje delovnih mest v mestu Ho Ši Minh in Centru za poklicno usposabljanje invalidov in otrok sirot v mestu Ho Ši Minh. Pokazalo se je, da je Cronbachov indeks alfa višji od 0,7. Raziskava, ki obravnava udobnost nošenja oblačil za invalide, je potencialno ustrezna tudi za nadaljnji razvoj drugih funkcionalnih oblačil. Ključne besede: krojenje, funkcionalna oblačila, gibalna oviranost, oviranost nog, bambusova vlakna, hlače, srajca Designing Functional Clothing for People with Locomotor Disabilities 1 Introduction Clothes, which protect our bodies, also enhance the beauty, hide the flaws of the wearer, and express their style and personality. In the world, there are about 600 million people with disabilities, accounting for about 10% of the population, most of them living in developing countries [1]. In Vietnam, there are about seven million people with disabilities [2]. The demand for clothes for people with mobility impairments is not small. However, the offer of the clothing market for people with disabilities in general and especially for people with locomotor disabilities is still limited, not focused, and needs the attention of designers and fashion brands. Research was conducted that focuses on people with hemiplegia, multiple sclerosis, other injuries, and on people with limited mobility who use a wheelchair. Physical characteristics of people with disabilities cause losing balance due to spinal trauma and change in body shape to disproportion [3]. The lack of blood circulation, low body temperature, physical inactivity of damaged body parts tend to impair muscle functions and lead to muscle atrophy in the extremities. To compensate for the loss of affected body parts, the unaffected body parts are forced to work more than normally; hence, people with lower extremity disabilities have stronger trunks and upper extremities. Using wheelchair leads to the development of related muscle groups of upper extremities [4, 5]. Clothing for people with disabilities should provide ergonomic comfort in sitting positions, improve the quality of life, be designed for everyone, and be suitable for the wearer’s physique and awareness. Adaptive or function clothing helps minimise joint movements and pain that patients face when dressing or undressing [6, 7]. In addition, apparel must also be suitable for the socio-cultural context and ensure the comfort of the outfit [8, 9]. Wheelchair users frequently experience difficulty when dressing, as studied by Pruthi and partners, since they feel pain in the upper extremities when putting on clothes and undressing, when undressing the inactive leg, due to incontinent motion, often lying in bed resulting from the loss of mobility, trauma from traction belt [10]. Research showed that the comfort of pants is influenced by four main areas, affected by pressure, i.e. waist (39.17%), knees (16.4%), crotch (13.96%) and calves (6.95%), while the pressure on the areas below the knees and calves does not significantly affect dressing. Comfort is ac- 171 ceptable if the pressure is as low as 20 kPa on hips, waist and crotch, and less than 10 kPa on the back of the thighs and knees. Research which was conducted in 2013 on 10 young women aged 18 to 38 with various disabilities found that design, form, function, self-expression and social identity are essential factors for choosing their clothes. Standing measurements are not applicable to sitting posture measurements due to anatomical variations and different defects [9, 10]. The proportion of people with disabilities tends to increase. The products on the market are not capable of meeting their needs. Therefore, it is extremely important to design and make a suitable garment for people with disabilities in the legs to bring the most convenience to them. This study proposes options for designing clothes for people with disabilities. The authors recommend suitable materials and, at the same time, provide solutions to adjust the basic pattern suitable for sitting posture and experiment with some designs. 2 Materials and methodology The study included people with atrophy of legs, poor legs and those in wheelchairs. The survey locations were the Center for Sponsoring – Vocational Training and Employment ­Introduction of Ho Chi Minh City and the Association for the support of people with Disabilities and Orphans of Ho Chi Minh City. Gerber V9.0 software was used to design patterns [11]. IBM SPSS [12] software was used to evaluate the reliability of the fit and comfortable clothes through the Cronbach’s Alpha coefficient. In the study, a 2/1 twill weave (cf. Figure 1) and combined twill weave (cf. Figure 2) bamboo fabric was used. Bamboo fibres give the fabric antibacterial properties, which means that the garment does not leave body odour, it absorbs sweat and creates a soft feeling for the wearer. As it has superior properties, this material is widely used in the garment industry. Due to the fibre structure and constituent compounds, a bamboo fibre fabric has a soft surface and good hygroscopicity. It is also antibacterial, deodorising and UV resistant, making it environmentally friendly to meet the customers’ needs [13]. The selected fabric was of moderate strength since the product was intended for the disabled. If the strength is too high, the fabric is of high thickness or high cost, and both of these properties do not 172 Tekstilec, 2022, Vol. 65(3), 170–180 Figure 1: White bamboo fabric: surface of white bamboo fabric (left), performance of rapport 2/1 twill weave of white bamboo fabric (right) Figure 2: Blue bamboo fabric: surface of blue bamboo fabric (left), performance of rapport of white bamboo fabric (right) meet the criteria for our study. The fabric was basic in colour, easy to apply and suitable for clothing designs, objects and circumstances. Used accessories were zipper, button, elastic band and elbow pad. Zippers and buttons were arranged in appropriate positions, helping to expand the clothes for easier putting on and taking off. The elastic band helped keep the back of pants snug against the waist while still being easy to wear. Elbow pads, which are frequently used to support hands in wheelchairs or desks, were used as well. For the purpose of the study, we used theoretical research methods about anthropometric methods, and textile materials to design and sew complete products. The basic pattern set was designed according to the pattern design method of the ­document [14]. The experimental method was used in surveying, analysing and evaluating research results according to the Cronbach’s Alpha coefficient [12]. ting posture greatly influences their body shape (cf. Figure 3). Therefore, the design of clothes needs to be adjusted in several positions on the body for more comfort and convenience. Wheelchairs are assistive tools to help improve life, and create an optimistic spirit for users in general, especially people with disabilities. They use wheelchairs during most of their daily activities, especially for mobility, meaning that they need to use a lot their hands and 3 Results and discussion 3.1 Effects of wheelchairs on physical activity of people with leg disabilities People with leg disabilities often use their upper limbs and upper body musculoskeletal system in their daily activities. At the same time, their sit- Figure 3: Body shapes of people with disabilities are disproportionate and abnormal [15] Designing Functional Clothing for People with Locomotor Disabilities the upper body musculoskeletal system [16]. As a result of using a wheelchair for longer periods of time, the upper limb musculoskeletal system is much more flexible. At the same time, the lower limbs are weaker and the weight of the entire upper body is concentrated on lower limbs. People with leg disabilities are thus prone to losing balance and falling forward in cases of moving downhill with a sudden change in height [17]. Problems that wheelchair users experience with dressing are pain in the upper extremities when dressing and undressing, difficulty removing clothing from the inactive leg, problem with incontinence hygiene, injuries caused by belt pulling etc. [9, 10, 18]. 3.2 Plan for designing clothing Clothing for people with disabilities must be specially designed and adjusted to provide ergonomic comfort in the sitting position and functional requirements when worn, not causing health problems for the wearer, e.g. skin irritation, sores resulting from pressure, or blockage of blood flow [10, 19]. Garment products must also have an aesthetic and fashionable appearance to help people with disabilities integrate into the society [5]. The plan for the design of apparel products was divided into two groups from the base of the initial survey of 90 people with leg disabilities about clothes ergonomic (cf. Figure 4). In the first group, the pattern was 173 designed in some positions to suit body characteristics to provide the most comfort and convenience. For the pants, it was important to pay attention to the design at the back; the bottom ring was hence higher than that of standard clothes and more elastic at the waist for convenience. Due to the limited mobility in the legs, additional pleats were required at the knee position. In addition, there had to be an opening in the leg and pants for them to be easily put on or taken off. To avoid skin chafing due to seizures of the back and the wheelchair seat, pockets were not to be sewn on the back of the pants. At the same time, the pants’ door was opened wider by extending the length of the zipper fly. For the shirt, extra wide adjustments needed to be made at the neck position as most disabled people’s necks are more developed than those of non-disabled people. Moreover, the width of shoulders and armhole depth needed to be adjusted to make hand movements more flexible. Furthermore, in order not to sit on the shirt, its length had to be shorter than for an able-bodied person. The sleeves in the elbow area also had to be shaped according to the comfort principle. Sleeves had elbow pads added to increase the durability of the shirt and to make the wearer more comfortable when moving the wheelchair. In the second group, the pattern design, attention was paid to the manipulation required when using the clothes. Clothes Pants Techniques for designing Shirts Utilities for using Techniques for designing Utilities for using Waist: add back waistband, front elastic Front body: open waist down to front body Body length: shorten length Simple to wear over head Knee: make pleats Pants' legs: use zippers Elbow: add pads Body sides: use zippers Back: no pocket Inside arms: double layer Crotch depth: increase length Plus comfort across bust Figure 4: Plan for designing clothing 174 Tekstilec, 2022, Vol. 65(3), 170–180 3.3 Adjusting basic pattern to suit body shape The patterns for the T-shirt, shirt, trousers and jeans were designed according to the method basic block by Winifred Aldrich [14] with a non-disabled’s body dimensions. The unit of measurement was centimetre (cm). In line with section 3.2, the basic block was edited accordingly for the pattern to suit the disabled people’s body dimensions. 3.3.1 Adjusting basic trousers pattern The length of the front bottom pants was reduced, and the width of the front waistline was increased to create a comfortable sitting position for the waist and abdomen. In addition, a 4-cm ply fold was at the front knee to prevent the knee position from being stretched. In the back, the curvature of the buttocks and the height of the back was increased to best suit the sitting posture. The front of the pants was lower than the back by 0.5–1 cm (cf. Figure 5). In the knee-level position, it was open by 3–4 cm to arrange the pillow pleats. The back of the pants was extended by 4–5 cm, and the width of the buttocks was by 2–3 cm larger. The bottom was extended by 0.5–1 cm and by 0.5–1 cm down (cf. Figure 6). Figure 5: Trousers’ front pattern (left), adjustment position (middle), pattern after alterations (right) Figure 6: Trousers’ back pattern (left), adjustment position (middle), pattern after alterations Designing Functional Clothing for People with Locomotor Disabilities 3.3.2 Adjusting basic shirt pattern The neck was extended by 0.5–1 cm (cf. Figure 7). 2–3 cm were added to the length of shoulders and 175 1–2 cm to the length of lower armpit. The armpit ring was curled and the shirt length was reduced by 3–5 cm (cf. Figure 8). Figure 7: Pattern’s front: adjustment position (left), pattern after adjustment (right) Figure 8: Pattern’s back: adjustment position (left), pattern after adjustment (right) 3.4 Adjusting pattern design to support operation of people with disabilities From the analysed content, the research team experimented with four designs for people with leg disabilities according to the plan of assisting manipulation when using clothes. Figure 9 shows design 1, a polo shirt on a 100% cotton knit base with a side zipper, which makes it easier to put on or take off the shirt. In design 2, the inner ribs of the sleeves and body were sewn with a mesh fabric for ventilation. In addition, the shirt pillar was cut deeper than for a reg- ular shirt, making it easier for the wearer to put the shirt on through the head (cf. Figure 10). In design 3, a long-sleeved shirt from bamboo fabric (50% bamboo) was sewn with elbow pads (cf. Figure 11) to help support the lower arm for extended periods of time on a table or wheelchair armrest (cf. Figure 12). In design 4, pants which could be easily put on with no or less help from the caregiver were designed. The length of zippers was increased or zippers were used on the sides of pants’ pockets to make the pants wider (cf. Figure 13). Simultaneously, the back 176 Tekstilec, 2022, Vol. 65(3), 170–180 Figure 9: Descriptive drawing of polo with side zipper Figure 10: Drawing of T-shirt with mesh Figure 11: Double-layer long-sleeved shirt Figure 12: Shirt with sewn elbow patch Designing Functional Clothing for People with Locomotor Disabilities of the pants was raised, increasing the curvature of the buttocks and the ply at the knees was folded to suit the sitting position for a longer period of time. A teardrop zipper was added to the inner side of the bottom of trousers’ legs to widen the leg while still preserving the look of the pants (cf. Figure 14). Figure 13: Jeans with open zipper Figure 14: Trousers with inner side zippers People with severe disabilities need their caregiver’s support in dressing and personal activities. Therefore, the authors propose in design 5 models 177 of pants using a knit fabric and an elastic waistband with an open back, which make it easier when going to the restroom and provide comfort during wearing. Moreover, the pants’ design makes opening them easier, aiding their personal activities. In these samples, the authors still added length of the buttocks, waist of the pants (cf. Figure 15) and pleats at the knee (cf. Figure 16). Figure 15: Knit pants with elastic waistband and open front Figure 16: Knit pants with elastic waistband and open back 3.5 Testing and evaluating product feasibility The products were surveyed and tested on 76 people with leg disability to evaluate the feasibility of the study through the criteria according to the Likert 178 Tekstilec, 2022, Vol. 65(3), 170–180 scale in terms of material, design, convenience, colour, product cost and external assessment. Each criterion was evaluated on a scale from one to five, namely completely dissatisfied, unsatisfied, no idea, satisfied, completely satisfied. The survey was conducted in the Center for Sponsoring - Vocational Training and Employment Introduction of Ho Chi Minh City and the Association for the support of people with Disabilities and Orphans of Ho Chi Minh City. The survey results were analysed according to the Cronbach’s Alpha coefficient and showed that the majority of survey participants were satisfied with the given criteria. The survey also showed that the templates need certain changes. The external assessment of all products was acceptable. In design 1, some people had difficulties wearing the trousers. In design 2, a few people felt uncomfortable about the material as bamboo and jeans fabrics were not as soft as the cotton fabric. In design 3, the fabric’s colour was quite good. In design 4, the product’s shape was evaluated as appealing. However, the test results showed that all observed variables had a suitable total correlation coefficient (over 0.3). The Cronbach’s Alpha coefficient of the samples for designing were 0.776, 0.837, 0.807, 0.810 – all over 0.7. The results of the scale used were good in terms of reliability (cf. Table 1), which shows that the products would be highly applicable for people with disabilities. 4 Conclusion The study provides options for designing clothes and trousers suitable for the physical characteristics of people with disabilities, combined with actual surveys at vocational training centres for people with disabilities to come up with solutions. They Table 1: Evaluation of reliability through Cronbach’s Alpha coefficient Design Material Designs 0.78 0.750 0.728 0.756 2 (Figure 18) 0.795 0.828 0.822 3 (Figure 19) 0.804 0.771 0.797 4 (Figure 20) 0.801 0.761 0.786 1 (Figure 17) Convenience Colour Figure 17: Try-on shirt with double layers and trousers with inside zipper Cost External assessment Cronbach’s Alpha 0.756 0.671 0.776 0.833 0.812 0.766 0.837 0.761 0.784 0.737 0.807 0.799 0.787 0.745 0.810 Figure 18: Try-on shirt with elbow pads, and jeans with open waist down the front Designing Functional Clothing for People with Locomotor Disabilities 179 Figure 19: Try-on polo shirt with zipper at side and knit pants with elastic at the front and waist opening down the body with pleats at knees, and higher waistband at the back Figure 20: Try-on T-shirt with zipper at side and knit pants with open back shared their clothes requirements, proposed suitable materials and solutions to adjust the basic stamping design, suggested the direction to correct the pattern and experimented with some sewing samples for home T-shirts, front and back elastic waist pants. Furthermore, the authors designed shirts and trousers with zippers for use when going out. In each model, the authors paid attention to the manipulation of wearing and taking off the product easily in usual state as well as when needing to go to the toilet. The designs are suitable for people who are often in wheelchairs. The products were after being designed and sewn tested at two initial survey facilities. After analysing the reliability according to the Cronbach’s Alpha coefficient, all 4 outfits were over 0.7. The research opened up a new direction in functional apparel design. In the future, designs should be developed to be more diverse for people with disabilities to have more options for their fashion styles, and at the same time develop clothes for other types of disabilities. References Acknowledgments We would like to thank the Ho Chi Minh City University of Technology (HCMUT), VNU-HCM for their support, time and help in this study. 1. 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KABEL, A., DIMKA, J., MCBEE-BLACK, K. Clothing-related barriers experienced by people with mobility disabilities and impairments. Applied Ergonomics, 2017, 59(A), 165−169, doi: 10.1016/j.apergo.2016.08.036. Tekstilec, 2022, Vol. 65(3), 181–193 | DOI: 10.14502/tekstilec.65.2022048 181 Katarina Krstović, Vesna Marija Potočić Matković, Ivana Salopek Čubrić, Goran Čubrić University of Zagreb Faculty of Textile Technology, Prilaz baruna Filipovića 28a, Zagreb, Croatia Physical-mechanical Properties of Aged Knitted Fabric for Swimsuits Fizikalno-mehanske lastnosti staranih pletiv za kopalke Original scientific article/Izvirni znanstveni članek Received/Prispelo 7-2022 • Accepted/Sprejeto 9-2022 Corresponding author/Korespondenčna avtorica: Katarina Krstović, mag. ing. techn. text., asistent E-mail: katarina.krstovic@ttf.unizg.hr Tel. +38513712572 ORCID ID: 0000-0002-5095-1192 Abstract The physical and mechanical properties of knitted fabrics for sports swimsuits are analysed in this paper. The knitted fabrics were experimentally aged in seawater and exposed to the sun continuously for 100 hours. Data were processed for nine knitted fabrics with the same raw material composition, polyamide and elastane in different proportions. The physical-mechanical properties of all nine samples before and after aging, as well as the drying rate and water absorption capacity, were examined. The results show that the properties of the knitted fabric changed in all samples. The sample with a higher elastane content (59% PA and 41% EL) is less sensitive to changes in mass per unit area and thickness after aging (−0.89% and 0.40%). The results of maximum wetted radius absorption water on the top and bottom of the knitted fabric, spreading speed absorption and drying time are shown. The results show that the values of the maximum wetted radius of absorbed water and the spreading speed increase for all samples, while the drying time for the knitted fabrics show different results. Keywords: fabric, knitwear, physical-mechanical properties, swimwear, mechanical functionalization Izvleček V članku so analizirane fizikalne in mehanske lastnosti pletiv za športne kopalke. Pletiva so bila poskusno starana v morski vodi in neprekinjeno sto ur izpostavljena soncu. Meritve so bile izvedene za devet pletiv z enako surovinsko sestavo, poliamidom in elastanom v različnih razmerjih. Preučene so bile fizikalno-mehanske lastnosti vseh devetih vzorcev pred staranjem in po njem, hitrost sušenja in sposobnost vpijanja vode. Rezultati kažejo, da so se lastnosti pletiv pri vseh vzorcih spremenile. Vzorec z višjo vsebnostjo elastana (59 % PA in 41 % EL) je bil najmanj občutljiv na spremembe ploščinske mase in debeline po staranju (−0,89 % in 0,40 %). Prikazani so rezultati največjega omočenja na zgornjem in spodnjem delu pletiva (največji polmer kroga absorbirane vode), največje hitrosti vpijanja in časa sušenja. Vrednosti največjega omočenja in hitrosti vpijanja se povečajo za vse vzorce, čas sušenja za pletiva pa kaže različne rezultate. Ključne besede: ploskovna tekstilija, pletenina, fizikalno-mehanske lastnosti, kopalke, mehanska funkcionalizacija 1 Introduction The swimsuits used in sports today have undergone many transformations throughout history. From heavy woollen swimsuits to performance-enhanced sports swimsuits for competition. The first swimsuit manufacturers shifted their former underwear into the range of fashionable swimwear. The materials for swimsuits are knitted and, as such, are a relatively small, narrowly specialized manufacturing 182 Tekstilec, 2022, Vol. 65(3), 181–193 area in the textile industry. Thanks to technological innovations, swimwear manufacturing experienced revolutionary success in the 1980s and 1990s. In the late 1990s, new materials with a lower hydrodynamic resistance than shaved skin were developed. Reducing friction and hydrodynamic resistance has been a major issue recently. It is believed that the swimmer uses almost 90% of the energy to overcome hydrodynamic resistance during swimming. Swimsuit manufacturers invest a great deal of effort in developing new materials and cuts for swimsuits to reduce hydrodynamic resistance [1−4]. Flexibility, comfort, drying speed, high chlorine resistance and durability are desirable characteristics of knitwear for swimwear. Materials made from a mixture of polyamide and elastane, and often from 100% polyester fibres, are usually used to make swimsuits. Recently, swimsuits made of recycled materials have become popular, and sports swimsuits made of 100% recycled polyester can be found at well-known manufacturers. In sports swimwear, there is a classification of swimwear for competition, the so-called “fast suits” and training suits. Fashion swimsuits usually contain between 10% and 20% elastane, while in training swimsuits the most common blend is 68% PA and 32% EL. Competition swimsuits have an even higher percentage of elastane and have recently begun to contain carbon fibres, e.g. 65% PA/34% EL/1% carbon. Integrated carbon fibres, known for their strength and low density, work to apply compression before the fabric is fully stretched, giving the suit additional stretch capacity for excellent flexibility and mobility. Raw materials made from synthetic polymers are now an integral part of sportswear and equipment. Fast drying, lightness, perfect fit and resistance represent the characteristics and many advantages of these materials. Polyamide 6 and polyamide 6.6 are most commonly used to make swimwear because they have higher resistance to wear, chemicals and oils, as well as good mechanical properties. However, polyamides have the ability to absorb moisture, which affects their overall properties. Polyester is a synthetic material that also offers numerous advantages and has similar properties to polyamide but has lower water absorption, which makes it more difficult for bacteria to grow. These fibres are characterized by the fact that they are resistant to deterioration and seawater compared to natural fibres. The maintenance of such synthetic fibres is easy, they dry quickly, can be mixed with other fibres and are susceptible to dying. Today, however, a great deal of research relates to the degradation of synthetic polymers such as PES and PA and their impacts on the environment. Under the influence of UV radiation, polyamide and polyester decompose at the molecular level, which consequently affects the properties of the material, durability and comfort [5−8]. As mentioned above, polymers are combined with elastane in different proportions in the manufacture of swimsuits. Elastane has a wide range of applications and is used for fashion or functional clothing, which is intended to adhere to the body and at the same time provide comfort and dimensional flexibility. Invented in Germany in 1937, spandex has exceptional elasticity, i.e. a temporary stretch of more than 200%, and also recovers quickly after exposure to stress. These fibres have a rubber-like behaviour with a high reversible elongation of between 400% and 800% [9]. The decomposition of swimwear knitted fabric is influenced by several factors. The most important factors in aging swimsuits are chlorinated water, sweat in an aqueous medium and on dry land, and swimsuit maintenance and care after each workout. In the summer months, UV radiation, high temperature and seawater are important factors for swimsuit aging. Swimsuit knitwear is expected to be resistant to UV rays, seawater, and chlorinated water. The durability of the colour in the sun is also an important requirement for the longevity and successful performance of swimsuit materials. Previous studies have shown that the properties of materials made of polyamide, polyester and elastane change when exposed to aging conditions. The change in these properties also affects changes in the comfort and durability of the material. In the study by Salopek Čubrić et al [4], it was found that the aging of knitted fabrics made of a mixture of polyester or polyamide with elastane reduces resistance to tensile forces, and after prolonged exposure and the reduction of the mass per unit area of the knitted fabric. Due to a number of influential research parameters related to the comfort and durability of knitwear, they represent a major challenge but have been the focus of much research for many years. The physical and mechanical properties of nine swimwear knitted fabrics from commercial manufacturers were investigated in this paper. The selected ­k nitted Physical-mechanical Properties of Aged Knitted Fabric for Swimsuits fabrics were made from polyamide or polyester and elastane fibre blends in varying proportions and with different construction characteristics. The research presented in this paper is focused on the exposure of the knitted fabrics to external natural weather conditions during the summer. According to the manufacturer’s description, all knitted fabrics are intended for fashion swimsuits, while six of them are for sports swimsuits. They are described as knitted fabric with maximum comfort, stretchable in both directions, easy to clean, with UV protection, and resistant to chlorine and pilling. The purpose of this study was to determine the physical and mechanical changes in the fabric after 100 hours of exposure to seawater and sun. A protocol was developed for the aging of knitwear for swimwear. The target group of the research was cadets for whom a training regimen of 120 minutes, six times a week was set, with athletes spending 10 hours training in the water. In this work, training sessions over 10 weeks were taken into account, for a total of 100 hours (June to August) spent in a water medium outdoors. The test results before and after exposure of the knitted fabric to aging conditions were compared. of swimsuits and are characterized by durability, ­resistance to chlorine, elasticity in both main directions that allows high comfort, and medium-strong compression to support the muscles. The selected sample with the highest elastane content of 41% was designated as S5. Of the nine samples, three have the same polyamide and 80/20 elastane content (Table 1.) All samples are marked with the letter S (swimming) and an ordinal number. Aged samples are marked with a letter “X”. 2.2 Methods of measurement In the experimental part, the following physical and mechanical properties of the fabric were studied: horizontal and vertical density of the fabric, mass per unit area, thickness of the fabric, breaking forces, resistance to bursting forces, maximum wetting radius during absorption, the water spreading speed of the knitted fabric and drying rate. All measurements were performed on samples before and after aging in seawater. The horizontal and vertical densities of the knitted samples were measured using a Dino-Lite Pro AM7000 microscope at 200× magnification. The sample was placed on a flat surface and, after calibrating the microscope to the appropriate magnification, the loops in the measurement area were counted. The mass per unit area of the fabric was measured according to ISO 3801[10], method 5, where a circular sample for surfaces of 100 cm2 was cut and measured on an analytical balance with an accuracy of +/− 0.001 g. The sample thickness was measured as the distance between the reference plate and the parallel circular feet. During the test, a pressure of 1 kPa was applied to the surface of the 2 Materials and methods 2.1 Material selection Materials were selected to include knitted fabrics made from a blend of polyamide and elastane in varying proportions and mass per unit area, with one exception of PES and elastane. Selected materials are intended for use in the manufacture Table 1: Materials for swimwear Fabric sample 183 Fibre composition Yarn linear density PA (%) EL (%) PA (dtex) EL (dtex) S1 80 20 110/7 0.4/2 S2 80 20 62/7 0.6/2 S3 78 22 150/14 0.4/3 S4 78 22 150/14 0.4/3 S5 59 41 44/28 44/4 S6 73 27 33/28 33/3 S7 80 20 88/56 78/5 S8 72 28 44/28 44/4 S9 71 29 58/34 60/5 184 Tekstilec, 2022, Vol. 65(3), 181–193 test sample. This test was performed in accordance with EN ISO 5084: 1996 [11]. Tensile force at break was measured according to ISO 13934-1 [12]. Test samples measuring 20 cm × 5 cm were prepared in the direction of the courses and in the direction of the wales. The test samples were placed between the clamps of the dynamometer and subjected to a tensile elongation at a constant speed of 100 mm/minute. The test ­procedure was repeated for all fabrics in both directions with five test samples. The knitted fabric was stretched to break, and the values of breaking force and breaking elongation were determined. The resistance to bursting force was tested according to ISO 13938‑2 [13]. Circular samples ­measuring 50 mm in diameter were secured to the bursting test ring with two circular stainless-steel rings. The samples were exposed to a steel ball with a diameter of 2.45 cm, which stretched the material in a spherical shape, and the angle of application of the force and the surface of the material on which the force acts changed continuously during the testing of the material [14]. The values obtained by this method are the force required to burst the knitted fabric. The liquid moisture management of the fabric was measured according to the AATCC Test Method 195 [15]. This method evaluates and qualifies the moisture transfer properties of a particular knitted fabric. The instrument used for these measurements is the MMT (Moisture Management Tester) [16]. Samples measuring 8 cm × 8 cm were prepared for the test, and the test was repeated four times for each knitted sample. The values obtained and taken into account in this test were the maximum wetted radius for top and bottom surfaces, and the spreading speed for top and bottom surfaces of the knitted fabric [17]. Thermography was used as an additional method to observe liquid transport on the surface of s sample. It was used both to compare the values with the results obtained using the MMT and to describe this phenomenon in detail with regard to the parameters that were not observed using MMT, such as drying time and spreading in the x and y direction. This method has previously been used by investigators in different fields, including textiles, and authors have shown that this method is valuable in obtaining additional details that are used to observe the properties of materials [5,18]. An E6 infrared camera from Flir Systems Inc., USA was used for the measurements. The camera used has a measurement accuracy of ±2%, and thermal sensitivity of 0.06 °C. A square sample measuring 100 cm × 100 mm was prepared for the measurements. During the measurement, the sample was placed on a flat surface in a room with an air temperature of 20 °C ± 2 °C and relative humidity of 65% ± 3%. A solution of distilled water and artificial sweat (amount of 0.1 mL) was applied vertically with a pipette at a distance of 20 mm from the surface of the sample. A thermal imaging camera was placed vertically above the sample at a distance of 300 mm. It was used to detect the different phases of liquid transport and capture images, which were then used to measure the corresponding parameters. The experiment focused on the following parameters: • wetting time (determined as the time required to absorb the solution), • wetting area (the area of the wetted zone on the sample, determined from the image captured using the thermal camera), • spreading speed in x- and y-direction (the spreading radii in x- and y- direction were determined from the thermal image, and those values were further used to calculate the spreading speed taking into account the wetting time), and • drying time (after applying the solution to a sample, the temperature of the wetted zone changed, which can be seen as a colour change on a thermal image. Drying time was determined as the time taken from the moment of solution application until the moment when there was no longer a difference between the temperatures of the wetted and non-wetted zones). FLIR Thermal Studio Suite software was used to analyse the thermograms. The liquid transport on the sample was determined by observing the histograms of the thermal images. More precisely, the histogram of the image at the beginning of the measurement was compared to the histogram of the image during the drying process of the material. At the point when it was determined that there were no differences between the two histograms (i.e., when these two histograms were equal), the material was deemed dry. The total time that elapsed from the application of the liquid to the point where the two histograms were equal was measured and noted as the drying time. The total number of repetitions was five. Physical-mechanical Properties of Aged Knitted Fabric for Swimsuits 2.3 Aging method Aging conditions were defined by observing the training conditions of swimmers who trained for 120 minutes, six times a week, which means that they trained in the water for 10 hours a week, taking into account the washing of swimsuits after each training. The conditions of aging in seawater were taken into account in this work. The aging order of 100 hours of soaking in water in the sun was defined, followed by washing 10 times and air drying. All samples were immersed in seawater outdoors for a period of 100 hours during the summer in August 2021 in the Mediterranean climate zone in Dubrovnik. Maximum daily temperatures ranged from 32.2 °C to 33.5 °C, and the lowest from 27 °C to 28.3 °C, without precipitation with a mean daily relative humidity of 61% to 46%. Weather data was obtained from the Croatian Meteorological and Hydrological Service. After 100 hours of immersion in seawater, the samples were washed in a washing machine on a short program for 30 minutes at a temperature of 30 °C. ECE Formulation Non-Phosphate Reference Detergent (without optical brightener), manufactured by James Heal, was used to wash the samples, in a ratio of 5 g of detergent per 1 kg of textile. The samples were air dried in the shade and the washing procedure was repeated 10 times. 3 Results and discussion The results of the measurements of physical and mechanical properties before and after aging are shown in the table for all samples. Table 2 shows the mean values of horizontal and vertical knitted fabric 185 ­ ensity, mass per unit area and thickness of the nine d selected samples before the aging process. The results show that there are no significant differences in knitted fabric density for the first four samples (from S1 to S4), while the approximate values of mass per unit area range from 171 g/m2 for sample S2 to 209 g/m2 for sample S4. The thicknesses of these knitted samples are also very similar, ranging from 0.527 mm for sample S4 with the lowest knit density and the largest mass per unit area, to a thickness of 0.655 mm, which is the same for samples S1 and S2. Samples S1 and S2 are made with the same ratio of polyamide and elastane, 80%/20%, while S3 and S4 have a ratio of 78%/22%. Samples S5 to S9 have similar values for vertical and horizontal density, while the values for mass per unit area and thickness are very different. Sample S6 has a minimum thickness of 0.358 and a mass per unit area of 113 g/m2, while the vertical and horizontal densities are 28%/26%. The sample with the largest mass per unit area is sample S5 with 226 g/m2, while the maximum thickness of 0.655 mm was recorded for S1 and S2. After the aging procedure, the same tests were performed on the samples under the same conditions. The results show that all samples changed to a greater or lesser extent. The change in density of knitted fabrics is shown graphically and numerically in Figure 1. The coefficient of loop density, which is the ratio between the horizontal and the vertical density, was calculated using the formula: C = Dh/Dv(1) where Dh is horizontal knitting density and D v is vertical knitting density. Table 2: Results of measured density, mass per unit area and thickness of the knitted fabric samples before aging Vertical/horizontal loop density (1/cm) Mass per unit area (g/m2) Thickness (mm) S1 46/26 187 0.655 S2 42/26 171 0.655 S3 44/26 198 0.561 S4 42/25 209 0.527 S5 26/24 226 0.495 S6 28/26 113 0.358 S7 20/24 216 0.502 S8 28/26 160 0.404 S9 26/20 184 0.450 Fabric sample 186 Tekstilec, 2022, Vol. 65(3), 181–193 The coefficient of loop density C was calculated for the values before and after the aging of the knitted fabric. It can be noted that no or insignificant change occurred in samples S4, S5 and S6. The change in the coefficient of loop density shows that the relationship between horizontal and vertical density changed, i.e. that the knitted fabric shrank more in the horizontal or vertical direction than in the other direction. This change can be observed in samples S1, S7 and S9, which leads to the dimensional instability of the knitted fabric after aging and ultimately to a change in the shape of the swimsuit. The decrease in the coefficient of loop density in samples S1, S2 and S7 indicates that initial damage to the elastane occurred, which in other samples would occur after prolonged exposure to sun and sea. The change in mass per unit area and thickness is shown as a percentage in Table 3. Mass per unit area increased in most knitted fabrics, except in samples S4, S5 and S6, where the greatest mass loss occurred in sample S4 at 2.96%, while S5 and S6 recorded a smaller mass loss of 0.89%. The greatest change in mass per unit area was seen in sample S7, and the least in S5 and S6. A similar trend was observed for the change in thickness, with an increase in thickness for most samples except S4 and S6. The results show that the smallest change in thickness and mass per unit area occurred in sample S5 with the highest elastane content of 59% PA/41% EL, which gives it very good dimensional stability (Table 3). Swimsuits, and particularly swimsuits for sports, are expected to fit the body very tightly, ensuring faster body movement in the water. In other words, the knitted fabrics are expected to be more resistant to multiple stresses. Since the aging process leads to changes in tensile properties, data on bursting strength were processed using the bursting test method. This method is recommended for testing the resistance of knitted fabrics to the increasing penetration load because the knitted structure stretches simultaneously in all directions. The negative effect of UV rays and seawater on the resistance of knitted fabrics to breaking force is Change in the coefficient of loop density, c, (%) 1,4 1,2 1 0,8 0,6 0,4 0,2 0 begore aging S1 0.57 S2 0.62 S3 0.59 S4 0.60 S5 0.92 S6 0.93 S7 1.20 S8 0.93 S9 0.77 after aging 0.52 0.60 0.62 0.59 0.92 0.92 1.10 0.96 1.04 Samples Figure 1: Change in the coefficient of loop density before and after aging Table 3: Changes in mass and thickness, expressed in %, compared to non-aged materials Fabric sample Changes in mass per unit area (%) Change in thickness (%) S1 2.09 3.68 S2 6.56 1.34 S3 4.35 1.41 S4 −2.96 −1.74 S5 −0.89 0.4 S6 −0.89 −1.99 S7 9.62 3.65 S8 7.51 1.7 S9 2.13 3.43 Physical-mechanical Properties of Aged Knitted Fabric for Swimsuits 187 450 Breaking force (cN) 400 350 300 250 200 150 100 50 0 before aging S1 272.72 S2 302.15 S3 426.74 S4 349.24 S5 229.56 S6 184.43 S7 413.98 S8 247.21 S9 270.76 after aging 267.82 267.82 374.74 329.62 214.84 177.56 381.61 250.16 264.87 Samples Figure 2: Change in the breaking force (bursting test) after aging e­ vident from the results shown in Figure 2. Eight of the nine samples showed a decrease in breaking force, while sample S8 showed a slight increase of 1.18%. This sample also showed one of the largest mass per unit area increases (because of shrinkage), which led to a small increase in the breaking force, although it can be assumed that this material was also damaged under the influence of UV radiation and seawater. The percentage decrease in resistance ranged from 1.83% to 13.88%, with S3 showing the greatest sensitivity to aging conditions. The results of the knitted fabrics tensile strength test are shown in Figure 3a in the wale direction and 3b in the course direction. Eight samples showed a decrease in average breaking force in one of the directions, which is directly related to the lower stress tolerance. The highest percentage change was seen in S9-X with -27.07% in the wale direction and 600 Breaking force (cN) 500 400 300 200 100 0 before aging S1 291.13 S2 283.64 S3 406.41 S4 309.31 S5 287.5 S6 202.3 S7 528.74 S8 252.94 S9 362.97 after aging 244.3 261.83 425.96 318.42 210.2 192.45 496.65 258.48 322.04 S5 233.36 S6 138.16 S7 271.05 S8 197.07 S9 224.78 248.99 124.73 341.5 186.58 176.9 Samples a) 400 Breaking force (cN) 350 300 250 200 150 100 50 0 before aging S1 175.42 S2 173.8 S3 203.5 S4 201.12 after aging 158.95 173.15 246.3 192.03 Samples b) Figure 3: Change in the breaking force after aging (a) in the direction of wale (b) in the direction of course 188 Tekstilec, 2022, Vol. 65(3), 181–193 -12.71% in the course direction. This sample recorded the largest change in the density coefficient of wales and courses from 0.77 to 1.04, i.e. the dimensional instability of the knitted fabric after aging. The next largest changes in the compaction coefficient were observed in S7 (from 1.20 to 1.10) and S3 (from 0.59 to 0.62), which was also reflected in the unexpected behaviour with increasing resistance to tensile forces in the row direction. The influence of aging conditions was also reflected in the measured values of elongation at break, which gave the expected results of increasing elongation under the influence of aging. Of interest is sample S5, where the elongation at break was reduced in both observed directions. S5 is the sample with the highest mass per unit area and the highest percentage of elastane (Figure 4). In order to better understand the influence of aging conditions on the changes in fabric strength, the changes of the individual measured values are given in Table 4. Sports swimsuits are expected to absorb and ­retain less water, particularly in competitive swimsuits where water repellent finishes are used. The AATCC Test Method 195 and MMT tester test also evaluated the qualified moisture absorption capacity of aged and unaged samples. Figure 5 shows the results of the maximum wetted radius absorption on the top (a) and bottom (b) of the knitted fabric. These results suggest that the knitted fabric has a greater capacity to absorb water after aging, which is an undesirable characteristic for swimwear. Breaking elongation (%) 300 250 200 150 100 50 0 S1 before aging 275.43 after aging S2 S3 S4 251.07 242.84 202.77 S5 S6 S7 S8 255.22 185.02 158.09 224.83 S9 172.8 254.03 260.06 252.29 227.87 241.41 185.77 160.79 229.85 192.8 Samples a) 500 Breaking elongation (%) 450 400 350 300 250 200 150 100 50 0 S1 before aging 329.68 S2 291.93 after aging 322.92 311.54 262.26 412.94 277.32 293.18 326.22 282.19 342.1 S3 279.4 S4 240.95 S5 S6 S7 S8 446.47 281.06 288.92 347.92 S9 267.5 Samples b) Figure 4: Change in the breaking elongation after aging (a) in the direction of wale (b) in the direction of course 189 Physical-mechanical Properties of Aged Knitted Fabric for Swimsuits Table 4: Changes in breaking force and elongation, expressed in %, compared to non-aged materials Measured properties Breaking force (N) Fabric sample Bursting test Breaking elongation (%) Strip test/ course Strip test/wale Wale Course S1-X −1.83 −19.17 −10.36 −8.42 3.63 S2-X −12.82 −8.33 −0.38 3.46 9.6 S3-X −13.88 4.59 17.38 3.75 10.32 S4 -X −5.95 2.86 −4.73 11.02 8.13 S5 -X −6.85 −36.77 6.28 −5.72 −8.12 S6 -X −3.87 −5.12 −10.77 0.4 −1.35 S7-X −8.48 −6.46 20.63 1.68 1.45 S8-X 1.18 2.14 −5.62 2.18 −6.65 S9-X −2.22 −12.71 −27.07 10.37 5.21 Top max wetted radius (mm) 35 30 25 20 15 10 5 0 before aging S1 10 S2 5 S3 0 S4 7.5 S5 5 S6 17.5 S7 17.5 S8 5 S9 5 after aging 30 21.25 12.5 16.25 22.5 30 22.5 25 21.25 S5 5 S6 16.25 S7 17.5 S8 5 S9 5 22.5 30 25 26.67 22.5 Samples a) Bottom max wetted radius (mm) 35 30 25 20 15 10 5 0 before aging S1 10 S2 5 S3 5 S4 5 after aging 30 23.75 12.5 16.25 Samples b) Figure 5: Change in the wetted radius on the top (a), and bottom (b) on the knitted fabric As a result of the test, the spreading speed on the top and bottom side of the knitted fabric was also recorded. Figure 6 shows that the spreading speed increases after aging for all tested fabrics. The results show that the highest spreading speed after aging was recorded on S6 with the lowest mass per unit area and thickness. 190 Tekstilec, 2022, Vol. 65(3), 181–193 Top spreading speed (mm/s) 8 7 6 5 4 3 2 1 0 before aging S1 0.7198 S2 0.8092 S3 0 S4 0.8037 S5 0.7123 S6 0.7281 S7 0.7889 S8 0.2969 S9 0.4888 after aging 4.3154 2.2727 0.5258 2.2231 1.2447 6.6973 2.7316 1.5136 0.9294 S5 0.263 S6 0.7723 S7 0.7899 S8 0.4578 S9 0.4629 1.2447 6.6959 2.7604 1.4608 1.0865 Samples a) Bottom spreading speed (mm/s) 8 7 6 5 4 3 2 1 0 before aging S1 0.7317 S2 0.7717 S3 0.5561 S4 0.7711 after aging 4.3288 2.2672 0.5997 2.5907 Samples b) Figure 6: Change in the water spreading speed on the top (a), and bottom side (b) of the knitted fabric The results of measurements using the thermal camera are presented in Figure 7. Results relate to the wetting time, wetting area, spreading speed on the top of a sample (in both x and y direction) and drying time. a) b) Physical-mechanical Properties of Aged Knitted Fabric for Swimsuits c) 191 d) e) Figure 7: Results of measurement using the thermal camera: (a) wetting time, (b) wetting area, (c) spreading speed of the top of a sample in the x-direction, (d) spreading speed of the top of a sample in the y-direction and (e) drying time The wetting time of observed materials was in the range of 3 to 60 seconds, and decreased for all samples studied. The longest wetting time of both unaged and aged samples was recorded for S5, which stands out for its highest mass per unit area (226 g/m 2 , Table 2). The results of the measured wetting area were in accordance with the measured maximal wetted radius (measured using MMT, Figure 5). As can be seen from the presented graph (Figure 7 (b)), the wetting area also increases after aging for all samples studied. The increase is espe- cially prominent for samples S1, S2, and S5-S9. The results of the spreading speed measured using the thermal camera correspond to the results of top/ bottom spreading speed obtained using the MMT apparatus. For both spreading speeds (i.e. in x- and y- direction), the values increased due to aging. The most significant differences caused by aging were observed for S6 (the sample with the lowest mass per unit area and thickness among studied samples) and S1. It is interesting to note the results of the measured drying time. It can be observed from 192 Tekstilec, 2022, Vol. 65(3), 181–193 these results that the drying time was longer for the majority of samples after aging. A significant difference between the drying time of unaged and aged samples was clear for the samples with the highest initial thickness, i.e. samples S1 and S2 (both with a thickness of 0.655 g/m2). For those two samples, the drying time decreased due to aging for up to 40% of the original drying time. As previously noted, a shorter drying time is preferable for the final purpose of the studied materials, but only if other properties are not negatively affected by aging. more sensitive to tensile and breaking forces and had higher elasticity. The results show that the wetting time of observed materials decreased due to aging, while the wetting area and spreading speed increased. Fabrics showed different behaviours in terms if drying time. For the majority of fabrics, the aging process resulted in a slight increase in drying time, while that time decreased significantly for two out of nine fabrics. 4 Conclusion 1. POTOČIĆ M ATKOV IĆ, Vesna Ma rija, SALOPEK ČUBRIĆ, Ivana, KRSTOVIĆ Katarina. Characterization of physical-mechanical properties of functional fabrics for fashion and sports swimwear. In MATRIB 2021. Book of Proceedings. Edited by Danko Ćorić, Sanja Šolić and Franjo Ivušić. Vela Luka : HDMT – Hrvatsko društvo za materijale i tribologiju, 2021, 355–366. 2. CUNNINGHAM, Patricia A. From underwear to swimwear: branding at atlas and B.V.D. in the 1930s. The Journal of American Culture, 2009, 32(1), 38–52, doi: 1 0.1111/j.1542-734X.2009.00692.x. 3. MORIA, Hazim, CHWGHURY, Harun, ALAM, Firoz, SUBIC, Aleksandar, SMITS, Aleksander J., JASSIM, Rahim, BAJABA, Nasser S. Contribution of swimsuits to swimmer’s performance. Procedia Engineering, 2010, 2(2), 2505–2510, doi: 10.1016/j. proeng.2010.04.023. 4. MORALES, Alfonso T., FAJARDO, Javier A.T., GONZÁLEZ-GARCÍA, Higinio. High-speed swimsuits and their historical development in competitive swimming. Frontiers in Psychology, 2019, 10, 1–11, doi: 10.3389/fpsyg.2019.02639. 5. SALOPEK ČUBRIĆ, Ivana, ČUBRIĆ, Goran, POTOČIĆ MATKOVIĆ, Vesna M. Behavior of polymer materials exposed to aging in the swimming pool: focus on properties that assure comfort and durability. Polymers, 2021, 13(15), 1–19, doi: 10.3390/polym13152414. 6. HER R ERO, Mar ta, ROVIR A, Joaquim, ESPLUGAS, Roser, NADAL, MartÍ, DOMINGO, José L. Human exposure to trace elements, aromatic amines and formaldehyde in swimsuits: assessment of the health risks. Environmental Research, 2019, 181, 1–10, doi: 10.1016/j. envres.2019.108951. 7. ARHANT, Mael, LE GALL, Maelenn, LE GAC, Pierre-Yves, DAVIES, Peter. Impact of All knitted fabrics had a similar raw material composition, but in different proportions and with different yarn constructions, and as expected they showed different resistance to the effects of aging conditions. However, it can be clearly seen that there were more or less significant changes in the performance of knitted fabrics in all samples. Knitted fabrics with the same content of PA and EL (S1, S2 and S7) of 80%/20% intended for fashionable swimwear showed similar behaviour after aging, in the form of a decrease in the density coefficient and an increase in the mass per unit area and thickness of the knitted fabrics. Resistance to breaking force decreasesd and elongation at maximum force increased. The wetted radius of water absorption and water spreading speed increased. Samples S3 and S4 had different raw material compositions (polyamide and polyester) in the same proportion with elastane of 72%/28%. From the results, as in the previous three samples, the sample with polyamide recorded an increase in the mass per unit area and thickness of the knitted fabric, while the sample with polyester recorded a decrease in the mass and thickness of the knitted fabric. However, their tensile properties under force were the same. The sample with the highest percentage of elastane of 41% showed slight changes in the mass per unit area and thickness of the knitted fabric, but the largest changes were observed under force, which is to be expected given the elastane content in the knitted fabric. The last three samples of polyamide and elastane with very similar proportions (73%/27%, 72%/28% and 71%/29%) showed similar changes in mass per unit area and thickness, although it can be observed that the sample with the higher elastane proportion was References Physical-mechanical Properties of Aged Knitted Fabric for Swimsuits hydrolytic degradation on mechanical properties of PET - towards an understanding of microplastics formation. Polymer Degradation and Stability, 2019, 161, 175–182, doi: 10.1016/j. polymdegradstab.2019.01.021. 8. CIONEK, Caroline A., NUNES, Catia, FREITAS, Adonilson, HOMEM, Natalia, MUNIZ, Edvani, AMORIM, Teresa. Degradation study of polyester fiber in swimming pool water. Textile Research Journal, 2021, 91(1-2), 51–61, doi: 10.1177/0040517520934507. 9. SENTHILKUMAR, Mani, ANBUMANI, Natarajan, HAYAVADANA, J. Elastane fabrics – a tool for stretch applications in sports. Indian Journal of Fibre & Textile Research, 2011, 36(3), 300–307. 10. ISO 3801:1977. Textiles – Woven fabrics – Determination of mass per unit length and mass per unit area. Geneva : International Organization for Standardization, 1977, 1–4. 11. ISO 5084:1996. Textiles – Determination of thickness of textiles and textile products. Geneva : International Organization for Standardization, 1996, 1–5. 12. ISO 13934-1. Textiles – Tensile properties of fabrics — Part 1: Determination of maximum force and elongation at maximum force using the strip method. Geneva : International Organization for Standardization, 2013, 1–24. 193 13. ISO 13938-2:2019. Textiles – Bursting properties of fabrics – Part 2: Pneumatic method for determination of bursting strength and bursting distension. Geneva : International Organization for Standardization, 2019, 1–6. 14. POTOČIĆ M ATKOV IĆ, Vesna Ma rija, SKENDERI, Zenun. Mechanical properties of polyurethane coated knitted fabrics. Fibres and Textiles in Eastern Europe, 2013, 100(4), 86–91. 15. AATCC TM195-2021. Test Method for Liquid Moisture Management Properties of Textile Fabrics. Englewood : American Association of Textile Chemists and Colorists (AATCC), 2000, 1–5. 16. M290 Moisture Management Tester, Instruction Manual, Rev. 1.4 (06/18), SDL Atlas 17. SALOPEK ČUBRIĆ, Ivana, ČUBRIĆ, Goran, KATIĆ KRIZMANČIĆ, Ines, KOVAČEVIĆ, Monika. Evaluation of changes in polymer material properties due to aging in different environments. Polymers, 2022, 14(9), 1–23, doi: 10.3390/ polym14091682. 18. DEMA, Mesfin, TURNER, Chris, SARI-SARRAF, Hamed, HEQUET, Eric. Machine vision system for characterizing horizontal wicking and drying using an infrared camera. IEEE Transactions on Industrial Informatics, 2016, 12(2), 493–502, doi: 10.1109/TII.2016.2516441. 194 Tekstilec, 2022, Vol. 65(3), 194–217 | DOI: 10.14502/tekstilec.65.2022045 Aulon Shabani 1, Majlinda Hylli 2, Ilda Kazani 2 1 Polytechnic University of Tirana, Department of Electrotechnics, Mother Teresa Square No. 1, Albania 2 Polytechnic University of Tirana, Department of Textile and Fashion, Mother Teresa Square No. 1, Albania Investigating Properties of Electrically Conductive Textiles: A Review Raziskave lastnosti elektroprevodnih tekstilij: pregled Original Scientific Article/Izvirni znanstveni prispevek Received/Prispelo 6-2022 • Accepted /Sprejeto 9-2022 Corresponding author/Korespondenčni avtor: Dr. Aulon Shabani E-mail: aulon.shabani@fie.upt.al ORCID ID: 0000-0003-4368-6156 Abstract Electro-conductive textiles are mostly fabrics that have conductive elements or electronics integrated into them to achieve electrical characteristics. They have acquired considerable attention in applications involving sensors, communications, heating textiles, entertainment, health care, safety etc. To produce electro-conductive textiles, several techniques, e.g. chemical treating with conductive polymers on various textile materials, or using different technologies, e.g. knitting, weaving, embroidery techniques to include conductive threads into fabric interconnections etc., are being used. Electro-conductive fabrics are flexible enough to be adapted to quick changes in any particular application, beginning with wearable purposes and sensing needs as specified by many different groups. The ability of electro-conductive textiles to conduct electricity is the most essential property they must possess. In addition, the applications that may be worn should have stable electrical, thermal and mechanical qualities. The most recent developments in the field of electro-conductive textiles represent the aim of this review, which analyses these properties, including the investigation of methods that are used to obtain conductive textiles, their electrical properties, thermal properties, and beyond that, the scientific methods that are used to measure and investigate electro-conductive textiles. We also focused on the textile materials used in studies, as well as the technologies used to make them conductive, which may be a guide for different interested groups for use in a variety of smart applications. Keywords: electro-conductive textiles, electrical resistivity, electro-thermal behaviour Izvleček Elektroprevodne tekstilije so večinoma tekstilije, v katere so vgrajeni prevodni elementi ali elektronika za doseganje električnih lastnosti. Veliko pozornosti so pridobili v aplikacijah, ki vključujejo senzorje, komunikacije, grelne tekstilije, zabavo, varovanje zdravja in varnost. Za izdelavo elektroprevodnih tekstilij se uporabljajo številne tehnike, kot je kemična obdelava s prevodnimi polimeri na različnih tekstilnih materialih ali uporaba različnih tehnologij, kot so pletenje, tkanje, tehnike vezenja za vključevanje prevodnih niti v strukturo ploskovnih tekstilij idr. Elektroprevodne ploskovne tekstilije so dovolj upogibljive, da se lahko prilagodijo hitrim spremembam v kateri koli posebni aplikaciji, začenši z namenom nošenja in potrebami zaznavanja, ki jih določajo različne skupine. Sposobnost elektroprevodnega tekstila za prevajanje električnega toka je najpomembnejša lastnost, ki jo mora ta imeti. Poleg tega morajo aplikacije, ki so nosljive, imeti stabilne električne, toplotne in mehanske lastnosti. Namen tega pregleda je podati analizo najnovejšega razvoja na področju elektroprevodnih tekstilij, vključno z raziskavo metod, ki se uporabljajo za pridobivanje prevodnih tekstilij, njihovih električnih lastnosti, toplotnih lastnosti in poleg tega znanstvenih metod, ki se uporabljajo za mer- Investigating Properties of Electrically Conductive Textiles: A Review 195 jenje in raziskovanje elektroprevodnih tekstilij. Pregled se osredinja tudi na tekstilne materiale in tehnologije, ki so jih avtorji uporabili za dosego prevodnosti, kar je lahko vodilo različnim zainteresiranim skupinam za uporabo v različnih pametnih aplikacijah. Ključne besede: elektroprevodne tekstilije, električna upornost, elektrotoplotno obnašanje 1 Introduction Over the last decades, smart textiles have become popular as a concept. In order to manufacture wearable textile systems, electro-conductive textiles are needed. These textiles are materials which can conduct electric current [1]. They are made by means of different methods, e.g. using conductive fibres, yarns, coatings, polymers or inks, with the most common manufacturing techniques (cf. Figure 1) [2–4]. Furthermore, Figure 2 depicts the percentage of e-textile players who use various types of textile material. Different conductive yarn manufacturers can be found on the market, and their growth and development have followed a traditional path. As new electro-conductive materials have become available on the market, manufacturers have found different ways of developing and improving the properties of conductive fibres and yarns [5–7]. As a building block for intelligent textile components, electrically conductive yarns must offer stable and reliable electrically conductive properties while maintaining textile properties, which ensure good processing and pleasant wearing comfort. The reliability and stability requirements may vary depending on the application. Electro-conductive textiles can be made using traditional techniques, e.g. knitting, weaving, sewing and embroidering. When it comes to smart textiles that monitor vital functions and also need to be close to the human body, like a second skin, the knitting technology can be chosen [9–12]. The latter can provide a textile structure that can conform to the shape of our body by giving the wearer a comfortable feeling while moving freely. In this way, a knitted fabric can be stretched when subjected to a force and return to its original shape when the force is removed. When this technology combines textiles with electrically conductive materials, it is Figure 1: Different manufacturing techniques of conductive textiles: a) knitting, b) weaving, c) embroidery, d) coating methods, d) screen printing, e) magnetron sputtering 196 Tekstilec, 2022, Vol. 65(3), 194–217 Figure 2: Percentage of e-textile players using different types of material (Image source: E-Textiles 2021–2031, IDTechEx Research [8]) important that the knitted fabric is combined with elastic yarn without loop formation during its use. The second method to obtain conductive textiles is to chemically treat the fibres/yarns/fabrics to make them conductive. This can be achieved by coating them in different processes, e.g. electroless deposition, electroplating, physical vapour deposition (PVD), chemical vapour deposition (CVD) and conductive polymer coating, the latter being used more on textiles, which is the focus of this article. Conductive polymers, e.g. polypyrrole, polyaniline or polythiophene, are applied to textile surfaces with in situ polymerisation. The first electronic textile introduced to the market was the ICD+ (Industrial Clothing Design Plus) jacket in 2000 by Levi Strauss & Co. and Philips Research Laboratories [13], which could house an MP3 player and a mobile phone. When the jacket goes into the washing machine for maintenance, all appliances and cords must be removed. From the textile point of view, the challenge for researchers (even nowadays) is to produce as many components as possible from textile materials. Therefore, it was necessary to develop electro-conductive textiles that can be obtained in several ways, e.g. by integrating conductive fibres or yarns, by applying conductive coatings or by using conductive inks [2, 4, 14]. Electro-conductive textiles have emerged as a new trend in recent decades. Based on the above, we study electrical and thermal properties of conductive textiles obtained with various chemical processes, in particular polymerisation, carbon-based technologies, or technologies such as knitting, weaving, embroidery, sewing and needle felting. It is of crucial importance to study the properties of textile materials to predict their future applications, human comfort and lifespan due to aging factors. Table 1 shows a chronological overview of published work focusing on the properties of conductive textiles and their applications. The overview continues with the analysis of conductive fabrication process, methods of measuring electrical resistance, thermo-mechanical properties and modelling techniques as an approach to simulate the electrical behaviour of conductive textiles. In the end, the applications of conductive textiles as electrical devices, e.g. sensors and antennas, are mentioned. Investigating Properties of Electrically Conductive Textiles: A Review 197 Table 1: Chronological overview of papers published on electro-conductive textiles First author, Journal/ Conf. Title published year, ref. Hersh, S. P. Textile Research Electrical Resistance 1952 [15] Journal Measurements on Fibres and Fibre Assemblies Azoulay, J. 1988 [16] Berberi, P. 1998 [17] Meoli, D. 2002 [18] Tappura, K. 2003 [19] Kaynak, A. 2003 [20] Xue, P. 2004 [21] Dhawan, A. 2004 [22] Wu, J. 2005 [23] Varesano, A. 2005 [24] Kim, B. 2006 [25] Gasana, E. 2006 [14] Conductive type Methodology Poorly conducting hydrophobic synthetic fibres, such as nylon, Dynel and Dacron 2/1 warp-faced twill fabric containing 10% new conductive fibre Static electricity, resistance measurement Textile assemblies Electrical resistivity, volume resistivity Journal of Textile and Apparel, Technology and Management Journal of Computational modeling Electrostatics of charge dissipation of fabrics containing conductive fibres Polymer Effect of synthesis International parameters on the electrical conductivity of polypyrrolecoated poly(ethylene terephthalate) fabrics Textile Research Electromechanical Journal Behavior of Fibres Coated with an Electrically Conductive Polymer Smart fabrics, interactive textiles Review the possibilities to develop smart textiles Textile Research Woven Fabric-Based Journal Electrical Circuits: Part I: Evaluating Interconnect Methods Synthetic Conducting polymer Metals coated lycra Fabric-based electrical circuits, woven textile structures Polymer Degradation and Stability Wool fibres coated with electrically conducting polypyrrole (PPy) In situ polymerisation process is used to produce conductive polymer nylon lycra Electrical conductivity stability due to dry cleaning and other factors Conductive polymer and polyethylene terephthalate (PET) yarns, polyaniline (PANI) Electrical, mechanical, and electro-mechanical properties of PET conductive yarns IEEE Transactions on Electrical Insulation Textile Research Journal Anisotropy in Electric Properties of Fabrics Containing New Conductive Fibres A New Method for Evaluating Electrical Resistivity of Textile Assemblies Interactive electronic textile development: A review of technologies A study on the electrical conductivity decay of polypyrrole coated wool textiles Journal of Polyaniline-coated PET Applied conductive yarns: Study Polymer Science of electrical, mechanical, and electro-mechanical properties Surface and Electroconductive textile Coatings structures through Technology electroless deposition of polypyrrole and copper at polyaramide surfaces Surface resistance measurement, anisotropy Twenty different fabrics with base fabric cotton and polyester Analyse electrostatic properties in conductive fibres and discharging properties Coated fabrics polypyrrole, Conductive resistance poly(ethylene terephthalate) measurement, (PET) temperature affection on conductivity Polymer fibres coated with conductive polymer, polypyrrole (PPy). PPycoated PA6 fibres and PPycoated Lycra fibres Conducting polymer using pyrrole, nylon lycra Electrochemical behaviour, electrical resistance, electromechanical model, resistance as function of strain, damage level, relative humidity, air temperature. Develop fabric-based electrical circuits Polyaramide fabrics, metal Polymerisation of coated textile fibres, pyrrole polyaramide textile monomer structures using polypyrrole combined with copper metallisation 198 Tekstilec, 2022, Vol. 65(3), 194–217 First author, Journal/ Conf. Title published year, ref. Wang, J. Journal of the Thermal conductivity 2006 [26] Textile Institute studies on wool fabrics with conductive coatings Asanovic, K. 2007 [27] Locher, I. 2008 [28] Banaszczyk, J. 2009 [29] Banaszczyk, J. 2009 [4] Conductive type Surface resistivity measurements, thermal conductivity measurements, investigation the relation between electrical conductivity and thermal conductivity Journal of Investigation of the Textiles, wool, hemp, cotton, Electrical behaviour, Electrostatics electrical behavior of pan, flax, jute dielectric loss tangents some textile materials and relative dielectric permeabilities Textile Research Enabling Technologies Woven fabric with Electrical proprieties, Journal for Electrical Circuits on embedded copper wires frequency transmission, a Woven Monofilament transmission lines, Hybrid Fabric electronic circuits Quantitative InfraRed Thermography Journal FIBRES & TEXTILES in Eastern Europe Wool fabrics, PPy-coated, Anthraquinone-2-sulfonic acid (AQSA) sodium salt monohydrate 97% was the dopant and iron chloride hexahydrate (FeCl3·6H2O) as the oxidising agent Infrared thermography of electroconductive woven textiles Woven stainless steel sheet (Bekintex) Current distribution modelling, anisotropy, IR thermography Current Distribution Modelling in Electroconductive Fabrics Electro-conductive textile yarns Woven electroconductive textiles sheets Model current distribution of woven conductive textiles using resistive networks Manufacturing process of electro-conductive yarns Latifi, M. 2010 [30] Technical Textile Yarns Gu, J. F. 2010 [31] Smart Materials Soft capacitor fibres and Structures using conductive polymers for electronic textiles Surface and Gold coated para-aramid Para-aramid yarns, (Teijin Coatings yarns through electroless Aramid). polypyrrole PPy Technology deposition and copper coatings Schwarz, A. 2010 [3] Li, L. 2010 [32] Ding, Y. 2010 [33] Kazani, I. 2011 [34] Yoon, B. 2011 [35] Methodology Textile Research A Resistive Network Journal Model for Conductive Knitting Stitches ACS Applied Conductivity trends Materials and of PEDOT-PSS Interfaces impregnated fabric and the effect of conductivity on electrochromic textile Textile Research Van Der Pauw Journal method for measuring resistivities of anisotropic layers printed on textile substrates Fibres and Designing waterproof Polymers breathable materials based on electrospun nanofibres and assessing the performance characteristics Electro-conductive yarn, metallic fibre, electroconductive polymers, composite fibres Conductive polymer-based fibre Conductive knitting yarn High capacitance fibres frequency analysation Gold, polypyrrole and copper coated para-aramid yarns proved to offer good electroconductive properties and endurable due to washing Resistance of knitting yarn, electrical modelling Stretchable fabric (SPANDEX), cotton, polyester, Lycra, rayon were treated with PEDOT-PSS conductive polymer Woven textile substrates, screen printed Electrical conductivity measurements Layered fabric structures based on electrospun nanofibre Examine waterproofness and breathability performances Van Der Pauw method for electrical resistance measurement Investigating Properties of Electrically Conductive Textiles: A Review 199 First author, Journal/ Conf. Title published year, ref. Petersen, P. Textile Research Electronic textile 2011 [36] Journal resistor design and fabric resistivity characterization Kacprzyk, R. Fibres and Measurements of the 2011 [37] Textiles in volume and surface Eastern Europe resistance of textile materials Patel, P. C. IEEE Applications of 2012 [38] International electrically conductive Conference on yarns in technical Power System textiles Technology, POWERCON Tokarska, M. Indian Journal Measuring resistance of 2013 [39] of Fibre textile materials based and Textile on Van der Pauw method Research Yen, R. H. International Numerical study of 2013 [40] Journal of anisotropic thermal Numerical conductivity fabrics with Methods for heating elements Heat and Fluid Flow Hamdani, S. Materials Thermo-mechanical 2013 [41] behavior of textile heating fabric based on silver coated polymeric yarn Tokarska, M. Journal of Electrical properties of 2013 [42] Materials flat textile material as Science: inhomogeneous and Materials in anisotropic structure Electronics Odhiambo, S. Mixed Design Comparison of 2013 [43] of Integrated Commercial Brands of Circuits and PEDOT : PSS in Electric Systems “Capattery” Integrated in Textile Structure Stoppa, M. Sensors Wearable electronics and 2014 [44] smart textiles: A critical review Conductive type Methodology Highly conductive metallic coated thread knitted into fabric Electrical resistance characterisation for different knitting methods Surface and volume resistance measurement Wegene, J. 2014 [45] Conductive leather Capineri, L. 2014 [46] Tokarska, M. 2014 [47] Industrial and Engineering Chemistry Research Procedia Engineering Conducting leathers for smart product applications Resistive sensors with smart textiles for wearable technology: From fabrication processes to integration with electronics Autex Research Determination of fabric Journal surface resistance by Van der Pauw method in case of contacts distant from the sample edge Textile materials High conductive fibres, metal fibres, electroconductive yarns etc. Electromechanical properties of conductive yarns and fibres Electro-conductive Shieldex® fabric Van Der Pauw resistance measurement, surface resistance measurement, anisotropy Numerical analysis, temperature control, temperature uniformity Electrically conductive yarns Conductive silver yarn Electro-conductive plainweave polyester woven fabric PEDOT:PSS are used in making “capatteries” and Ag coated yarns and stainless steel filament yarn used as electrodes Conductive fabrics, Smart textiles Heating of conductive textiles, thermography of conducting elements, heating due to knitting methodology Electrical resistance as function of electrode placement, electrode properties Measuring discharging characteristics of capattery Conductive fabrics using copper wire, steel wire Reviewing materials, methods of manufacturing, energy consumption, ergonomics etc. Infrared spectroscopy, Fourier transform, electron microscopic analysis Fabrication of smart textiles, sensors Antioxidant silver fibre shielding rip-stop fabric, silver fibre shielding canvas fabric Surface resistance measurement, Van der Pauw, electrode placement 200 Tekstilec, 2022, Vol. 65(3), 194–217 First author, Journal/ Conf. published year, ref. Usma, C. Procedia 2015 [48] Technology Vásquez Quintero, A. 2015 [49] Procedia Engineering Arogbonlo, A. 2015 [50] Procedia Technology Felczak, M. 2015 [51] Fibres and Textiles in Eastern Europe Lipol, L. 2016 [52] European Scientific Journal Karim, N. 2017 [53] Bahadir, S. 2017 [54] Ryan, J. D. 2017 [55] Alhashmi A., F. 2017 [56] Nuramdhani, I. 2017 [57] Chaves, F. A. 2018 [58] Title Conductive type Methodology Fabrication of Force Sensor Circuits on Wearable Conductive Textiles Capacitive strain sensors inkjet-printed on PET fibres for integration in industrial textile Design and Fabrication of a Capacitance Based Wearable Pressure Sensor Using E-textiles Lateral and perpendicular thermal conductivity measurement on textile double layers The Resistance Measurement Method of the Conducting Textiles Sn-Ag-Cu (SAC) plated Nylon fabric Fabrication possibilities of pressure sensors based on conductive textiles PET fibres Printed strain sensors, sensor measurement Zell sensor; a Tin/Copper over Silver (Sn/Cu/Ag)(SAC) plated Nylon Fabric – Shieldex – U.S Fleece produced from blends of 40% flax, 40% steel and 20% polyester Analysis of design parameters for pressure sensor Thermographic measurements, theoretical model and experimental measurements Two and four probe resistance measurements Conductive threads through adding: Metal, Carbon, Polyaniline (PANi) – Poly (3, 4-ethylenedioxythiophene) (PEDOT) – Polypyrrole (PPy) ACS Nano Scalable Production Conductive graphene Sheet resistance and of Graphene-Based textiles electrical proprieties due Wearable E-Textiles to different factors such as washing, mechanical stability analysis Textile Research Modelling of Conductive textile yarns, Temperature Journal surface temperature stainless steel, Silver plated distributions modelling, distributions on powered PA artificial neural network e-textile structures using an artificial neural network ACS Applied Machine-Washable Degummed silk yarn and Produced and tested a Materials and PEDOT:PSS Dyed Silk cotton yarn were treated high conductive silk yarn Interfaces Yarns for Electronic with water dispersion of which was durable to Textiles PEDOT:PSS washing and dry cleaning Journal of Alloys and Compounds A simple method for fabricating highly electrically conductive cotton fabric without metals or nanoparticles, using PEDOT:PSS Materials Electrochemical impedance analysis of a PEDOT: PSS-based textile energy storage device Nanotechnology Mechanical, in-situ electrical and thermal properties of wearable conductive textile yarn coated with polypyrrole / carbon black composite Cotton fabric treated with PEDOT:PSS Investigating conductive fabric surface morphology, electrical resistance measured using four line probe Textile-based energy storage device treated with PEDOT:PSS stainless-steel electro-conductive yarn as the electrodes Bare and coated cotton yarn using polypyrrole/carbon black composite Cyclic Voltammetry, electrochemical impedance analysis, equivalent electric circuit model simulation Electrical properties measured with a source meter in conjunction with the KickStart Software to obtain resistance, resistivity, and conductivity, thermal conductivity was measured using Transient Hot Bridge Investigating Properties of Electrically Conductive Textiles: A Review 201 First author, Journal/ Conf. published year, ref. Lund, A. Materials 2018 [59] Science and Engineering R: Reports Title Conductive type Methodology Electrically conducting fibres for e-textiles: An open playground for conjugated polymers and carbon nanomaterials Fibres and yarns treated to be conductive using conjugated polymers and carbon materials Reviewing possible technologies, methods and properties of conductive textiles treated with conjugated polymers and carbon materials including areas of application Hughes-Riley, T. 2018 [60] Fibers A historical review of the development of electronic textiles Electronic textiles, smart textiles Chronological review of e-textiles and their applications, mainly sensors and technological approaches Chatterjee, K. 2019 [61] Fibres Electrically conductive coatings for fibre-based E-Textiles Conductive polymers Fabrication process of electrically conductive textiles Mohamed, A. A. 2019 [62] Journal of Suitability of conductive Textile and knit fabric for sensing Apparel, human breathing Technology and Management Silver coated Polyamide (Nylon) Fibre (Ag/ Nylon); yarn count 70 denier ratio of silver to Nylon is 20%–80 % Electrical resistance measurement, human breathing simulator design Shabani, A. 2019 [63] Textile & leather review Resistivity behavior of leather after electroconductive treatment White sheep crust leather coated pyrrole, ferric chloride, anthraquinone –2-sulfonic acid sodium salt monohydrate Volume resistance measurement, relation of resistivity and air humidity Shabani, A. 2019 [64] Textile & leather review The anisotropic structure of electro conductive leather studied by Van Der Pauw method White sheep crust leather coated pyrrole, ferric chloride, anthraquinone – 2-sulfonic acid sodium salt monohydrate Surface resistance measurement, Van Der Pauw, anisotropy Akbarpour, H. 2019 [65] Journal of Nanostructure in Chemistry Comparison of the conductive properties of polyester/viscose fabric treated with Cu nanoparticle and MWCNTs Polyester/viscose fabric treated with nanoparticles MWCNT and Cu Treated fabrics using nanoparticles, conductivity test, electrical resistance, strength and voltametric charts Hardianto, H. 2019 [66] Journal of Engineered Fibres and Fabrics Textile yarn Nickel-coated carbon fibre thermocouples for use in adding stainless steel yarn, fabrics polypyrrole-coated carbon fibre, or carbon fibre Kamyshny, A. 2019 [67] Chemical Conductive Society Reviews nanomaterials for 2D and 3D printed flexible electronics Printed nanomaterials, inkbased metal nanoparticles Reviewing materials and methods used to incorporate into 2D and 3D printed electronic textiles Nuramdhani, I. 2019 [68] Polymers Charge-discharge characteristics of textile energy storage devices having different PEDOT:PSS ratios and conductive yarns configuration Twill woven polyestercotton fabric treated with PEDOT:PSS, two types of conductive yarn, firs is pure stainless steel and silvercoated polybenzoxazole (Ag-PBO) used as electrodes Electrical characterisation charge and discharge measured using microcontroller Lund, A. 2020 [69] Journal of Power Sources A polymer-based textile thermoelectric generator for wearable energy harvesting Wool fabrics treated with conducting polymer: polyelectrolyte complex poly(3,4ethylenedioxy­ thiophene): poly(styrene sulfonate) (PEDOT: PSS) Electrical conductivity measurements, thermal resistance, design thermoelectric generators Different conductive textile yarns were tested to use as thermocouple and thermopile 202 Tekstilec, 2022, Vol. 65(3), 194–217 First author, Journal/ Conf. published year, ref. Title Conductive type Methodology Afroj, S. 2020 [70] Advanced Functional Materials Highly Conductive, Scalable, and Machine Washable GrapheneBased E-Textiles for Multifunctional Wearable Electronic Applications Graphene-based e-textiles Analysation for electronic applications Tseghai, G. B. 2020 [71] Sensors PEDOT:PSS-based conductive textiles and their applications PEDOT:PSS and composites Analysing possible applications of PEDOT:PSS conductive textiles, methods of treatment for producing conductive textiles Hylli, M. 2020 [72] IOP Conference Series: Materials Science and Engineering The color fastness properties of conductive leather improved by the use of mordants Leather samples using mordant FeSO4, Na2SO4 × 10 H2O Colour fastness, Surface resistance, dry rubbing Krifa, M. 2021 [73] Textiles Electrically Conductive Textile Materials— Application in Flexible Sensors and Antennas In situ polymerisation of aniline on nylon, Electrospun doped PANi, PPy/PPTA fibres Electrical conductivity, application-based textiles antennas Angelucci, A. 2021 [74] Sensors Smart textiles and sensorized garments for physiological monitoring: A review of available solutions and techniques Conductive fibres and filaments Reviewing applications of smart textiles to different wearable sensor applications Jin, I. S. 2021 [75] Polymers A facile solution engineering of PEDOT: PSS-Coated conductive textiles for wearable heater applications Microfibre fabric (Welcron, nylon/polyester splitting yarn) was treated using PEDOT:PSS Electrical sheet resistance was measured using four probe method, temperature distribution was measured using the thermal camera, crystalline properties were measured by an X-ray diffraction instrument Shakeri V. 2021 [76] Journal of Industrial Textiles Highly stretchable conductive fabric using knitted cotton/lycra treated with polypyrrole / silverNPs composites post-treated with PEDOT:PSS Cotton/lycra stretchable fabric is treated polypyrrole (PPy), silver nanoparticles (SNPs) composites, and post-treating PEDOT:PSS Linear four probe method was used to measure electrical resistance, morphology of fabrics and fibres cross-section observed with a field emission scanning electron microscopy Rogale, S. 2021 [77] Materials Measurement method for the simultaneous determination of thermal resistance and temperature gradients in the determination of thermal properties of textile material layers M3 Fabric upper-side: 100% polyester; membrane: polytetrafluoroethylene; fabric inner-side: 100% polyester fleece M4 (100% polyester) M5 (lining: 100% polyester; membrane: 100% polypropylene; padding: 100% polypropylene) M6 (100% polyester micro-fleece) Thermal proprieties, electrical resistance, temperature gradients Investigating Properties of Electrically Conductive Textiles: A Review First author, Journal/ Conf. published year, ref. Kaynak, A. Materials 2021 [78] Title Conductive type Methodology Electrothermal modeling and analysis of polypyrrole-coated wearable e-textiles Utilization of Nanomaterials in Conductive SmartTextiles: A Review Fabrication of durable and conductive cotton fabric using silver nanoparticles and PEDOT:PSS through mist polymerization Fabrication of Electroconductive Textiles Based Polyamide/ Polyurethan Knitted Fabric Coated with PEDOT:PSS/Nonoxidized Graphene Heat as a Conductivity Factor of Electrically Conductive Yarns Woven into Fabric Polypyrrole coated fabric Thermal modelling, surface resistivity Effect of Stretching on Thermal Behaviour of Electro-Conductive Weft-Knitted Composite Fabrics Overview of the Influence of Silver, Gold, and Titanium Nanoparticles on the Physical Properties of PEDOT:PSS-Coated Cotton Fabrics Improving thermal conductivities of textile materials by nanohybrid approaches Weft-knitted composite fabrics with silver coated polyamide multifilament yarns Tokarska, M. 2022 Materials [86] A Mixing Model for Describing Electrical Conductivity of a Woven Structure Abou Taleb, M. 2022 [87] Facile development of electrically conductive comfortable fabrics using metal ions Polyamide woven fabric; nickel and copper metalized, polyester woven fabric; nickel metalized and polyester woven fabric; nickel metalized Wool, polyester, and wool/ polyester fabrics were treated with two metal salt solutions, 0.005 M CuSO45H2O and 0.005 M AgNO3 and 0.01 M nano-ZnO Adak, B. 2021 [79] Journal of Textile Science & Fashion Technology Wang, P. 2022 [80] Luo, Y. 2022 [81] Journal of the Korean Society of Clothing Industry Penava, Ž. 2022 [82] Materials Repon, R. 2022 [83] Polymers Alamer, F. 2022 [84] Nanomaterials Kalaoglu-Altan, O. iScience 2022 [85] Journal of Industrial Textiles 203 Conductive textiles, Review of nanomaterials Graphene, MXene, Polymer used in conductive nanocomposite textiles Cotton fabrics are coated using silver nanoparticles and PEDOT:PSS Surface electrical resistance measured according to the AATCC-76–2005 Knitted fabric treated with PEDOT:PSS/Non-oxidised Graphene Four probe method was used to measure sheet electrical resistance, tensile properties were evaluated Silver-coated conductive yarns were weaved in woven fabric using different techniques Sample heat dissipation was investigated as function of applied voltage and also it was investigated the change of electrical resistance influenced by temperature change Temperature measures as function of stretching, applied voltage as function of time Cotton fabrics coated with PEDOT:PSS Reviewing applications and technologies used in e-textiles formed by PEDOT:PSS coatings of cotton Passive conductive textiles Reviewing methods for producing passive conductive textiles to improve thermal conductivity Investigating Archie’s law as it can be used to describe electrical conductivity of woven textiles Scanning electron microscopy, energy dispersive X-ray, Fourier transform infrared and atomic absorption spectroscopy, AC electrical conductivity, air and water permeability 204 Tekstilec, 2022, Vol. 65(3), 194–217 2 Electro-conductive textiles Conductive textiles can be made by using conductive fibres, yarns, coatings, polymers or by applying inks to textiles. All smart textile components require to some extent electro-conductive materials, which can be conductive yarns or fabrics. These conductive yarns serve as a functional material forming the basis for the functionality of the whole smart textile system. Electro-conductive fibres/yarns can be divided into two main groups: a) Fibres/yarns which are applied in forms such as conductive wires These can be pure metals, mainly silver, copper and stainless steel, produced with methods such as wire drawing, bundled wire drawing, cutting production, melt spinning and melt extraction [88]. Metal fibres have several advantages, including their strength, composition, biological inertness and immediate availability in textile form at low production costs. They are unaffected by washing or sweating due to its inertness. However, they are unable to deliver homogeneous heating and their brittle nature can cause long-term damage to the spinning machinery [44]. b) Fibres/yarns chemically treated to be conductive Metal-based fibres, as mentioned above, have highest conductivity, but are not stretchable enough and by using more elastic interconnects, conductivity decreases. The second group of fibres/yarns is coated using conventional conductive polymers, galvanic substances or metallic salts. The most commonly used coating processes are electroless plating, evaporative deposition, sputtering and coating with conductive polymers. Although conductive textiles can be obtained also by treating the surface of traditional textiles, which can be achieved by coating them with polymers such as polypyrrole [4], deposited onto the surface of textile substrates or by printing with conductive inks and forming a conductive layer. Polypyrrole (PPy) is an organic conductive polymer formed with a chemical or electrochemical polymerisation of pyrrole. The polymerisation solution contains a monomer, dopant and oxidising agent to start the polymerisation of monomers. Different textile materials have been used to produce polypyrrole-coated textiles obtained with chemical reaction, e.g. polyester [89], polyamide [20, 90] cotton [91] and wool [92]. Different methods follow in chemical polymerisation. While often a twostep polymerisation has been the method of choice [23, 90, 91, 93], in situ polymerisation [73, 94] and emulsion polymerisation [95] are applied as well. Polyaniline has been applied as a coating on polyester and polyamide fabrics via in situ polymerisation [96]. Moreover, a two-step polymerisation of aniline on fabrics is commonly used [97]. Possible techniques are also a chemical coating with conducting polymers [98] or a reinforcement of polymeric materials with conductive compounds via spinning [99]. Furthermore, one of the most explored conventional conductive polymers is also polystyrene sulfonate (PEDOT:PSS). This polymer was used by Ding et al. [33] to treat stretchable fabrics by soaking them into a conductive polymer, resulting in the concentrate being homogeneously dispersed on the fabrics. Stretchable cotton textiles post-treated with PEDOT:PSS were investigated in [76]. Moreover, Ryan et al. [55] tested PEDOT:PSS to produce high conductive silk yarns, which were good for e-textile used in different applications, retaining conductive properties also after several washing cycles. In addition, the washing durability of conductive textiles treated with PEDOT:PSS was investigated in [100]. Furthermore, cotton fabrics have been treated using PEDOT:PSS to produce electrically conductive textiles by various authors [56, 69, 80, 84]. The applications of commercially available PEDOT:PSS as a potential to produce energy storage and capacitors from electro-conductive textiles were studied [43]. The energy storage devices gained from textiles treated with PEDOT:PSS were the subject of research in [57, 68], where the obtained devices acted as capacitors and their electrical characteristics in charging and discharging were studied. Tseghai et al. [71] offered a comprehensive overview of most state-of-the-art applications, of electro-conductive textiles, which are treated with PEDOT:PSS and their composites, and also an overview of treatment methods. – Carbon-based conductive materials Traditional conductive fabrics like metallic filaments and conducting polymers have several drawbacks. Different research groups have combined carbon-based conductive materials with textile materials, as it will be described below. Due to its high electrical conductivity, enhanced mechanical qualities, environmental stability and Investigating Properties of Electrically Conductive Textiles: A Review potential for low-cost manufacture, the most widely used carbon-based material for electro-conductive textiles is graphene. Graphene was used in [101], where the authors investigated graphene-coated cotton fabrics to obtain low-cost and high conductive cotton-based homogenous nano sheets for further use in smart textile applications. Furthermore, cotton-based fabrics were analysed in [102], where they were treated with graphene oxide (GO) and reduced graphene oxide (rGO) to produce antibacterial electro-conductive textiles. This resulted in Ag 0/rGO-coated samples not developing bacterial growth. Recently, there has been a surge of interest in producing conductive smart textiles by incorporating active conductive nanoparticles into textiles. Due to their high electrical and thermal conductivity, particular emphasis has been placed on carbon-based nanomaterials, i.e. carbon nanotubes (CNTs). These are found in a variety of diverse and critical applications, including nano-electronic devices, nano-scale structural materials, actuators and sensors, functional fabric and e-textiles etc., which is due to their exceptional properties, i.e. mechanical, thermal and electrical behaviours. In the textile industry, CNTs are used in the production of conductive fibres and yarns with different techniques [30], e.g. electro-spun fibre [103, 104], electrophoretic spun fibre [105], recondensed fibre [106], solution spun fibre [107], melt spun fibre [108]. Another common conductive material is also carbon black, which is a low-cost material easy to fabricate [109]. Gültekin et al. [110] investigated the electrical and thermal properties of carbon black coated cotton fabric by achieving conductivity increase. Besides, carbon black and PPy were used together to coat cotton fabrics by Chaves et al. [58], where they investigated mechanical and electrical properties focusing on the production of durable samples for use in real world applications. An outstanding review of fabrication procedures of common carbon-based electronic materials and relevant applications was presented in [109]. Moreover, carbon-based nanomaterials applied in e-textiles were reviewed in [59, 79, 111, 112]. – Conductive inks printed on textile surface Printing using conductive inks is another method, which has found usage in a variety of applications in the electronics area – not only at the beginning of smart/intelligent textiles, but this technique 205 was also used to produce conductive fabrics. There are different textile printing methods that can be used, e.g. rotogravure, offset lithography, flexography, screen and inkjet printing technologies [18, 73]. Printing electrical traces directly on a fabric is a versatile method that occasionally displays its shortcomings, e.g. the thickness of the silver paste during the printing is one of its limits. Most of the applications, especially on textiles, are limited to screen and inkjet printing as they are very good for low volume and high-precision work. Although inkjet printing offers greater design versatility and production flexibility, screen printing is more economic and covers a huge range of products. 3 Resistance measurement methods The electrical resistance of materials is related to other electrical properties like voltage and current, while the surface resistivity is the resistance to current leakage along the surface of an insulating material. The most common method to measure the resistance is the two probe method as shown in Figure 3a, where the voltage drop between two electrodes is measured as an effect of the applied known current. However, this method has drawbacks due to neglecting the contact resistance of electrodes. Consequently, four probe techniques come into play. There are two types of these techniques, i.e. linear placement and peripheral placement. Wenner [113] found and resolved the issue of neglecting contact resistance by proposing an inline four probe geometry technique to decrease the electrode contact resistance, as it can be seen in Figure 3b. The method using four probes circumferentially along the sample was proposed by Van Der Pauw [114]. Initially, this method was devoted to any arbitrary shape surface resistance measurement, while later, this method was adopted by many authors in order to measure electrical resistance of conductive textiles, as given in Figure 3c. An improvement of the measurement accuracy can be achieved by applying a correction factor to asymmetrical samples. The problem of measuring electrical resistance of textiles began with issues caused mostly by the static electricity, this leading to many problems, even when the processed fibres were natural, e.g. cotton, wool, silk and flax, which are hydrophilic and have moderate conductivity. With the advent of poorly conducting hydrophobic synthetic fibres, e.g. nylon, 206 Tekstilec, 2022, Vol. 65(3), 194–217 Figure 3: Surface resistance measurement methods: a) two probes, b) linear four probes, c) Van Der Pauw Dynel and Dacron, the effects of static electricity changed from a minor to a major problem, as described by Hersh and Montgomery [15]. They used a novel apparatus to study the electrical resistance of a textile fibre and fibre assemblies to investigate the effects of static electricity in fibrous materials. Electrostatic properties of natural fibres were investigated under various environmental conditions, discovering that the electrical properties of those fibres are highly dependent on the moisture content of the material. Volume resistivity is the resistance to the flowing current through the body of an insulating material, and in the case of textile materials with a very rich structure and highly developed surface, measurements of volume and surface resistances (measured in a two-electrode system) should correlate with each other. The basis for such a correlation may be the assumption that a conduction current (volume or surface), measured in a two-electrode system, flows through the bulk material [115]. Another novel method for evaluating the electrical properties of textile assemblies was proposed by Berberi [17], where the proposed idea was a novel multi-step method for assessing electrical resistance. He has developed a novel probe for measuring resistance that makes use of the material’s volume fraction properties. Also, this novel probe was used to measure the electrical properties of electro-conductive leather and by applying this multi-step method, it was concluded that the electrical properties of conductive leather were not influenced by the sample form [63]. The measurement of surface and volume resistance of textile materials was discussed by Kacprzyk et al. [37], who compared various electrode placement systems in order to measure the resistance. The methods mentioned above focused on the electrical properties of textile fibres; however, most of the existing researches measure surface resistance due to their application purposes. Furthermore, the conductivity of threads was studied by Dhawan et al. [22] and they developed efficient conductive threads by interconnecting them orthogonally. The aim of their research was to reduce the DC resistance associated with interconnections, which was achieved by trying different materials and a specific bonding/welding procedure. The interconnecting resistance was measured using a DC multimeter. They found that the welding procedure was the most effective in producing efficient and uniform interconnections. On the other hand, determining the electrical resistance of textile samples with various forms and raw material compositions was challenging for Asanovic et al. [27], who developed a measuring device based on direct current measurement through textile samples. Dielectric loss tangents and relative dielectric permeability for textile samples were measured by using specially capacitance cells. Their study results showed that the resistance of textile materials was strongly dependent on their absorbed moisture. On the other hand, the ageing of conductive fibres coated with electrically conducting doped polypyrrole (PPy) plays an important role in electrical and thermal characteristics, which was investigated by Varesano et al. [24], who used simulated ageing tests. They evaluated performance decay during the processing stages and final product used, and their findings indicated that the fabrics made of PPy coated wool fibres had acceptable conductivity decay. Similarly, hybrid yarns were in focus of various publications, e.g. Šafářová et al. [115] tried to develop models that describe the dependence of electrical resistivity R on wire length L. They concluded that this behaviour was highly nonlinear and in contradiction with metals. As already mentioned, the most commonly used resistance measurement methods are the two and four probe. Lipol et al. [52] investigated two and four Investigating Properties of Electrically Conductive Textiles: A Review t­ erminal methods for the novel conducting threads, concluding that the two terminal method was more informative than the four terminal method, and that the latter had no advantage over the former. Another method for measuring sheet resistance is the so-called Van Der Pauw method, which was used in the case of electro-conductive textiles by various researchers [34, 39, 47, 64, 116, 117]. Tokarska et al. [39] investigated the contact diameter of electrodes and their arrangement on sample edges, while their main focus was the proper placement of electrodes. This research was extended and exploited more by this group [42], as they conducted a multivariant research on electrical properties of woven fabrics. Furthermore, the Van Der Pauw method was used to investigate the electrical properties of conductive woven fabrics, analysing the effect of electrode placement on resistance measurements, concluding that surface resistance was a function of electrode placement. During the investigation of surface resistance by applying the Van Der Pauw method, authors also investigated homogeneity and anisotropy. Anisotropy was also studied by Azoulay et al. [16], who focused on the electrical properties of textile fabrics and measured the surface resistivity in various directions, revealing an anisotropy effect attributed to the sample weave pattern. The anisotropy structure of screen printed textiles was studied by Kazani et al. [34], who measured the electrical surface resistance of screen printed textiles by using the Van Der Pauw’s method, which showed the anisotropic behaviour of electro-conductive textiles. Apart from the conductive textile materials mentioned above, Shabani et al. [64] recently focused on electro-conductive leather, where the Van Der Pauw method was used to measure the electro-conductive properties. It was concluded that a different electrode placement along the sample circumference revealed the anisotropic structure of samples. The anisotropy behaviour of conductive textiles together with other properties, e.g. electrical or thermal, was studied by various groups [29, 37, 40, 51, 63, 104, 109, 118]. 4 Electro-thermal proprieties Conductive textiles are widely used to provide comfort to humans, from heating to life monitoring functions. Thus, investigating the electro-thermal 207 properties of conductive textiles plays an important role in their applicability. Many research groups that have investigated conductive textiles have found a strong relation of thermal conductivity with electrical conductivity. Similarly, Wang et al. [26] evidenced that increasing electrical conductivity by coating a wool fabric with PPy led to an increase in thermal conductivity. The correlation between the heat conductivity and electrical conductivity of PPy-coated wool textiles was investigated, demonstrating that when these materials were coated with conductive PPy to create electro-conductive textiles, their thermal conductivity improved. Meanwhile, the heat dissipation caused by an electric current flow at certain voltages was studied by Penava et al. [82], observing how heat influences the changes in the electrical resistance of electro-conductive yarns. It was concluded that the temperature change in conductive yarns resulted due to the contribution of an external source or due to the passing electric current in a linear change in the resistance of conductive yarns. Moreover, the temperature distribution and heat generation for stretchable conductive textiles used for medical purposes was investigated in [83]. The research revealed that the required temperature of 40 °C was achieved within 2–3 minutes, but the increase of sample surface had a negative impact on heat generation. The thermal properties of knitted structures, their manufacturing methods and the effect of contact pressure at structural binding points on the degree of heating were analysed by Hamdani et al. [41]. They were interested in analysing generated heat as a function of distance between the supply terminals and yarn decay properties due to the heating. By taking thermographic images, they discovered that knitted fabrics, with silver and elastomeric yarn, can generate enough heat to warm the body. Moreover, the thermography was used to analyse the woven conductive textiles for the non-homogeneity and anisotropy, using the modelling and infrared thermography to analyse the contact resistance [29]. Furthermore, the temperature distribution was investigated by Felczak et al. [51] for a double-layered fleece textile by studying the thermographic measurements. They developed a theoretical model and compared it to experimental data. Designing technically comfortable electro-thermal textiles has been a challenging task due to the lack of adequate measurement devices and methods. 208 Tekstilec, 2022, Vol. 65(3), 194–217 Consequently, Rogale et al. [77] developed a new measuring device and method for simultaneous measurements to determine the thermal resistance in one or more textile material layers, e.g. multilayer composite clothing, where the temperature gradients of textile material layers, as well as the theoretical principles of operation and practical results were presented. The analysis of electrical properties sensing behaviour and the mechanical analysis of polymer fibres coated with an intrinsically conductive polymer, and their electromechanical behaviour under tensile load was performed experimentally by Meoli et al. [18]. The investigated electromechanical behaviour of these conductive fibres showed a correlation of various mechanical and environmental factors with electrical resistance. The heat transfer properties of anisotropic conductive textiles analysed by Yen et al. [40], revealed that by employing non-electric high effective thermal conductive yarns perpendicularly to the electro-conductive yarns increases temperature distribution uniformity. In order to analyse the heating fabric, a numerical program based on a spectral element method was used. The investigation of textiles does not focus only on electro-thermal properties. Reiners et al. [119] also considered cutting resistance. Meanwhile, for the textiles such as tarpaulin fabrics used to protect against vandalism, it was determined based on the analysis that in addition to cutting resistance, the tearing strength and the seam slippage should be tested. Prior to experimentally analysing the thermal distribution of conductive textiles, the temperature distribution in textile materials was modelled as an effect of single laser pulse treatment using simulation software. The surface heat sources were modelled for different shapes in Comsol Multiphysics to verify experimental results [120]. Similarly, the modelling was used by Banaszczyk et al. [4] to analyse current distribution in conductive textiles. They used a large electrical resistor network to investigate contact resistance, surface resistance and also homogeneity of the structure. The research results showed that this method was able to measure current distribution using modelled prototype, as it was difficult for direct measurements. A similar methodology was used, again by Banaszczyk et al. [29], where the modelling method was compared with the four probe method to measure the contact resistance of conductive textiles. The results gained from both methods were complementary to each other. Moreover, Wai et al. [32] developed a resistive network to analyse the electrical resistance of knitting stitches, concluding in simulated results being comparable with experimental results. The modelling methods mentioned above were based on software or electrical modelling, while Bahadir et al. [54] applied Artificial Neural Networks to derive surface temperature distribution of conductive textiles. Based on this research, not only that the temperature distribution can be analysed, but also the sample temperature distribution can be predicted. Conductive fibres can cause problems due to the electrostatic charge. To analyse these behaviours, theoretical modelling was applied by Tappura et al. [19], showing that the induced charge was a strong correlation of base material conductivity and dielectric properties. Passive electro-conductive textiles were investigated in [85], where an overview of most commonly used methods and materials used to improve the thermal conductivity of samples was presented. 5 Smart applications of electro-conductive textiles Smart textiles, known as electronic textiles (e-textiles), incorporate electronic components in order to perform different functions. Thereby, using electrical, thermal, mechanical, chemical, magnetic, and other inputs and outputs, they can perform the following functions: – Passive smart textiles: they can sense sensor outputs from user or environment. – Active smart textiles: they can integrate a sensing device to control actuator behaviour. – Very smart textiles: they can react and adapt behaviour to given circumstances. In this section, we are going to highlight smart textile applications of electro-conductive textiles, which are used to produce resistive sensors, where different etching techniques revealed the possibility of obtaining customised wearable sensors [48]. The fabrication of resistive sensors was analysed by Capineri et al. [46], who applied conductive textiles to obtain pressure and temperature sensors for use in measuring human interaction parameters, e.g. step measurements. Moreover, conductive wires were used by Uzun et al. [88] to produce smart textiles for the purpose of protection, and Investigating Properties of Electrically Conductive Textiles: A Review also to be able to install various sensors for measuring life body parameters. In this way, by using different yarn production techniques, they analysed the effectiveness of smart textiles. The production of smart sensors, using textiles and screen printed technology, was studied by Khan et al. [121]. The used technology revealed the possibility of using screen printing to produce pressure sensors. A further investigation is to follow to improve this idea. Moreover, obtaining capacitive sensors from PET conductive fibres through printing on them was the focus of Vásquez Quintero et al. [49]. These sensors were integrated into industrial textiles, mainly used in the automotive industry. Moreover, Lee et al. [122] integrated a fibre-based pressure sensor into textiles to monitor human body parameters. Recently, conductive textiles were integrated with temperature measurement technology, more specifically by using thermocouples, where Hardianto et al. [66] integrated the thermocouples for measuring body temperature and this temperature was then used to generate low power electricity used for portable electronic devices. The idea of energy harvesting by integrating thermocouples into wearable textiles was elaborated by Lund et al. [69]. Furthermore, Root et al. [123] analysed related work in order to observe human comfort when sensory technology and textiles are integrated together. It was observed that combining the conductivity of metal coatings with flexibility, low weight and stretch of a fabric may lead to significant advancements in miniaturised textile thermocouple fabrication. Based on the literature review, it was established that until now, the used smart textile sensors were fabricated from incorporated metal-based technologies, whereas Afroj et al. [70]current reduced graphene oxide (rGO applied graphene-based textiles. They developed washable electronic textiles intended for ultraflexible supercapacitors. Furthermore, smart textiles have been fabricated not only from fabrics, but also from leather. Conductive leather for smart applications was investigated by Wegene et al. [45], where it was proposed to use conductive leather for gloves to operate on touch-screen technologies. Moreover, a screen printed technology on conductive textiles was used in [124] to produce a piezoresistive sensor from graphene nanoplates. Conductive textiles based on PEDOT:PSS that have been used in the development of sensors, actuators, 209 energy harvesting and storage devices were reviewed in [71]. Similarly, conductive leather was investigated by Hylli et al. [72], revealing that after the treatments with mordants and polymerisation, the colourfastness of dyed leather increased and also, the ability to maintain their conductive properties remained. The authors were able to obtain coloured electro-conductive samples. A wide variety of applications of smart textiles encouraged many researchers to devote the focus of their work on the areas of textile sensors. Krifa et al. [73] reviewed the application of smart fabrics in wearable technology with the focus on sensors and antennas. Another review, a review of applications of smart sensors for psychological monitoring, was described by Angelucci et al. [74]. The combination of electronics with textiles, and the possible techniques and their solutions was reviewed by Stoppa et al. [44]. Cho et al. [125] reviewed wearable e-textiles used for sensing, their methods being construction, used materials and applications. Furthermore, the application of textile-based sensors was conducted in [126], where they had in focus the recent developments in the field of electrochemical sensors and biosensors. A historical overview of how electronic textiles have evolved, their areas of applications, especially sensors and wearable textiles, was elaborated in [60]. This paper discussed various strategies for making smart fabrics, a very interesting and promising area also being 3D printing approaches. Direct 3D printing of polymers into textile fibres with the purpose of developing wearable electronic textiles was studied in [127]. Mellin et al. [128] used the 3D printing technology to produce the metal-based nanosized metal powders for use in electro-conductive textiles. 6 Conclusion The incorporation of conductive elements into textiles has produced the so-called electrically conductive textiles, which enable the production of interactive electronic textiles (smart textiles). As the wearable systems have become more feasible in the recent years due to the advancements in textile technologies, innovative materials, nanotechnology and miniaturised electronics, the most important factor for the user acceptance of wearable devices is the fit comfort. Moreover, we are convinced that 210 Tekstilec, 2022, Vol. 65(3), 194–217 certain requirements must be satisfied for their usage in these applications, including electrical characteristics, thermal characteristics, comfort, and durability to different environmental and mechanical influences. In this paper, we briefly described the most common processes and materials for obtaining conductive materials, beginning with conducting metals (most often silver, copper and stainless steel) integrated into textiles, continuing with carbon conductive nanotube utilised to generate conductive yarns, and techniques for processing textiles, e.g. chemical treatment with electrically conductive polymers employing in situ polymerisation. Based on the studies, polypyrrole was the most often employed, as well as the PEDOT:PSS applications. In addition to the use of nanoparticles, the printing of textiles employing ink was another form of textile processing. All of these methods used to produce electro-conductive textiles served as the starting point in the development of smart wearable textiles, making the exploration of electrical characteristics the central focus of this article. Moreover, the two probe, four probe and Van Der Pauw resistance measurement methods were explored, where the Van Der Pauw method was proven to be the most practical one, since it was dedicated to measuring the resistance of flat and arbitrary-shaped materials. The primary purpose of electro-conductive fabrics is their use in wearable technology, where they must fulfil comfort standards necessary to provide the warmth for the body, or in a wide variety of other applications. Therefore, the thermal features, e.g. temperature distribution, were researched in order to bring many study results into the focus. Nonetheless, it should be highlighted that the usage of conductive materials is going to increase, as will their capacity to meet the comfort criteria. 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A Method of Measuring Earth Resistivity, National Bureau of Standards, Scientific Paper, 12(4), p. 469, 1916, doi: 10.6028/ bulletin.282. 218 Tekstilec, 2022, Vol. 65(3), 218–226 | DOI: 10.14502/tekstilec.65.2022031 Jasminka Butorac1, Ružica Brunšek 2, Milan Pospišil 3, Zvjezdana Augustinović 4 1 University of Zagreb, Faculty of Agriculture, Department of Field Crops Forage and Grassland, Svetošimunska cesta 25, 10000 Zagreb, Croatia 2 University of Zagreb, Faculty of Textile Technology, Department of Materials, Fibres and Textile Testing, Prilaz baruna Filipovića 28a, 10000 Zagreb, Croatia 3 University of Zagreb, Faculty of Agriculture, Department of Field Crops Forage and Grassland, Svetošimunska cesta 25, 10000 Zagreb, Croatia 4 College of Agriculture at Križevci, Milislava Demerca 1, 48260 Križevci, Croatia The Influence of Water Hardness on the Agronomic Traits of Foreign Fibre Flax Varieties in the Republic of Croatia Vpliv trdote vode na agronomske lastnosti tujih sort vlaknatega lanu v Republiki Hrvaški Original Scientific Article/Izvirni znanstveni članek Received/Prispelo 4-2022 • Accepted /Sprejeto 9-2022 Corresponding author/Korespondenčna avtorica: Assoc. Prof. Ružica Brunšek, Ph.D. Phone: +385 1 3712 566 E-mail: ruzica.brunsek@ttf.unizg.hr ORCID ID: 0000-0003-4859-6088 Abstract The amount and quality of fibres depend on a whole range of factors, the most important being variety, agroecological conditions, agrotechnics and the degree of fibre flax plant maturity, the purpose for which flax is grown, retting and processing. The retting of fibre flax is the most complex stage in the processing of flax into fibre. The aim of this study was to gain knowledge about the acclimatization ability of foreign varieties that can potentially be adapted to climatic in Republic Croatia. Therefore, this paper presents the results of achieved agronomic traits (dry stem yield, dry stem after retting, total fibre yield, long fibre yield, share of total fibre and share of long fibre) of five foreign varieties of fibre flax. The selected varieties were retted in very soft, medium hard and hard water. Variety trials with fibre flax were set up over three years (2012–2014) at two locations (Zagreb) on anthropogenized eutric cambisol and (Križevci) on pseudogley on level terrain. The trials were carried out according to the RCBD in four replications. According to the results of the three-year research into the agronomic traits of fibre flax, significant differences were identified among the varieties studied. The varieties Agatha, Viola and Electra recorded the highest values of studied traits. Statistically significant differences were only recorded among different water hardness for long fibre yield in 2012 and share of total fibre in 2013 in Zagreb. The highest yields and share of fibres were recorded when the fibre flax was retted in very soft water. Keywords: agronomic traits, fibre flax, varieties, water hardness Izvleček Količina in kakovost vlaken iz vlaknatega lana sta odvisni od vrste dejavnikov, med katerimi so najpomembnejši sorta, agroekološke razmere, agrotehnika, stopnja zrelosti stebel, namen uporabe, godenje in predelava. Godenje stebel vlaknatega lana je najzahtevnejša faza v celotnem procesu predelave stebla v vlakno. Cilj teh študij je pridobiti znanje o aklimatizacijskih sposobnostih tujih sort, ki se potencialno lahko prilagodijo podnebnim razmeram Republike The Influence of Water Hardness on the Agronomic Traits of Foreign Fibre Flax Varieties in the Republic of Croatia 219 Hrvaške. V tem članku so zato predstavljeni rezultati doseženih agronomskih lastnosti (pridelek suhih stebel, suhih stebel po namakanju, skupni pridelek vlaken, pridelek dolgih vlaken, delež vseh vlaken in delež dolgih vlaken) petih tujih sort lanu, namenjenih za pridobivanje vlaken. Stebla izbranih sort so bila namakana v zelo mehki, srednje trdi in trdi vodi. V raziskavo so bili zajeti sortni poskusi iz treh let (2012−2014) na dveh lokacijah, in sicer na antropogeni evtrični rjavi prsti v Zagrebu in na psevdogleju na ravnih terenih v Križevcih. Poskusi so bili izvedeni v naključnih blokih v štirih ponovitvah. Glede na rezultate triletnega raziskovanja agronomskih lastnosti lanu so bile med obravnavanimi sortami ugotovljene pomembne razlike. Najboljše preiskovane lastnosti so zabeležili pri sortah Agatha, Viola in Electra. Statistično značilne razlike so bile zabeležene med različnimi trdotami vode le za donos dolgih vlaken v letu 2012 in v deležu vseh vlaken v letu 2013 v Zagrebu. Največji pridelek in največji delež vlaken sta bila zabeležena pri namakanju lanenih stebel v zelo mehki vodi. Ključne besede: agronomske lastnosti, lan za vlakna, sorte, trdota vode 1 Introduction A review of available literature covering the fields of textiles and agriculture showed insufficient cooperation among researchers, particularly with a focus on flax and flax fibres. There is thus a need for an interdisciplinary approach to research, taking into account agricultural and textile knowledge. Twenty years ago, collaboration between researchers at the Faculty of Agriculture and Faculty of Textile Technology, University of Zagreb, was established with the aim of reviving flax production in Republic Croatia, and defining and improving the quality of flax fibres. Setting the yield and quality parameters of fibre flax depends on many factors, such as soil-climatic, breeding-genetic and anthropogenic factors. Furthermore, the quality of fibres depends on a combination of a number of properties that in turn depend on the variety characteristics of plants, their growing conditions, harvesting technology and retting process, and raw material processing methods. One of the most important factors that determines the quality of long flax fibres is the retting process. Traditional retting methods include dew retting and water retting. Alternative methods include mechanical decortication, and chemical, heat, and enzymatic treatments [1]. In addition, ultrasound retting has been used for fibre flax in recent years [2]. Water retting is one of the best but also one of the most expensive flax fibre production methods. In principle, the method is analogous to stream retting but the flax stems are retted for four to seven days depending on the quality of the flax in heated tanks or pits maintained at 40 °C. Warm water retting, which can be used all year round, normally results in finer fibres of better quality than those produced by dew retting [3]. The advantage of water retting over dew retting is that it is more easily controlled and avoids the risk of the crop being spoilt by inclement weather during the weeks that it lies on the ground [4]. However, it also has serious disadvantages. The main disadvantage is that the water in which the straw has been steeped is highly polluted and in Europe must be treated before being discharged as wastewater. It has almost completely disappeared in Western Europe and in most Eastern European countries, but is still widely practised in China and Egypt. It also requires high water treatment maintenance and the costs are very high. In Croatia, after the fibre flax pulling during July, the weather conditions (warm and dry) are not suitable for dew retting. Therefore, the fibre flax was traditionally retted in Croatia in rivers, lakes and ponds until the Second World War, and after the war in pools and tanks with cold or warm water. Today, small quantities of water-retted flax are still produced in Croatia. According to Pasković, [5] the quality and yield of fibre depends on water hardness, while bleaching also affects the colour and the characteristics of flax fibres. If the water is softer, the retting of flax fibres is faster and produces the highest quality, characterized by good fineness, strength, softness and whiteness. In the lowland continental area of Croatia, where fibre flax is grown, the natural water that is used for retting is medium hard to hard. In Croatia, there are only a few studies dealing with the retting of fibre flax in different water hardnesses [2, 6, 7]. The commercial breeding of fibre f lax started in Europe at the end of the 19th century. Before Western European varieties became available, European varieties of seeds were imported from Russia. Cross breeding is still the main breeding method for fibre flax [8]. The main task of the breeding programme is to develop flax genotypes that are 220 Tekstilec, 2022, Vol. 65(3), 218–226 highly productive (both fibre and seeds) and highly adaptable to changing environmental conditions [9]. Standard European varieties are spring varieties adapted to the coastal climate and long days. At the beginning of the growth cycle, the flax plant does not tolerate negative temperatures, while excessively high temperatures accelerate the maturation of flax plants and there is no elongation of fibres, which ultimately reduces the quality of fibres. According to Rossini and Casa, [10] warm and dry weather conditions, predominant from late spring onwards, cause the excessive shortening of the growing cycle of spring crops, which results in lower yield and poorer seed and fibre quality. The environment has a strong influence on crop success, with some varieties showing more year-to-year stability than others [11]. According to the Liebieg’s law, weather conditions (precipitation) represent the main limiting factor that frequently affects flax yield in many regions of Europe [12]. Fibre flax is traditionally cultivated in most parts of Croatia. In the lowland continental area of the country, flax is sown around the end of March, while the growth stage of flowering starts at the end of May [13]. The Croatia has no indigenous fibre flax varieties [14, 15]. Introduced varieties are from Western Europe and are less suitable for the climatic conditions of Croatia (yields and quality are usually lower) [16–24]). The aim of these studies was to determine the agronomic traits (dry stem yield, dry stem yield after retting, total fibre yield, share of total fibre, long fibre yield and share of long fibre) of five fibre flax varieties that were retted in very soft, medium hard and hard water over three years at two locations. The obtained results will be of great importance for gaining knowledge about the acclimatization ability of foreign varieties that can potentially be adapted to the climatic conditions of Croatia. 2 Materials and methods Variety trials with fibre flax were carried out in the experimental fields of the University of Zagreb Faculty of Agriculture (45°49’26” N, 16°02’07” E) on anthropogenized eutric cambisol, and of the College of Agriculture in Križevci (46°02’23” N, 16°54’62” E) on pseudogley on level terrain from 2012 to 2014. The trials involved five varieties: Viking (Cooperative Liniere de Fontaine Cany, France), Viola (Van de Bilt Zaden, Netherlands), Venica (Agritec, Czech Republic), and Agatha and Electra (Cebecco Seed, Netherlands). The content of the nutrients in the soil and pH values for both locations are given in Table 1. Weather conditions were also monitored during the flax growing season for all the years and both locations (Tables 2 and 3). Fertilization with100 kg/ha P (as superphosphate) and 150 kg/ha K (potassium salt) was carried within basic tillage for both locations. A total of 30 kg of N/ha (nitrogen) was added before sowing, as well as 30 kg/ha in a single fertilizer application at the average plant height of 0.1 m. The trials were designed according to the randomized complete block design (RCBD) with four replications. The main trial plot size was 10 m2 (10 rows × 0.1 m row spacing × 10 m length). Sowing was carried out using a plot seeder (Wintersteiger, Austria). Fibre flax seeding was performed on 28 March 2012, 12 April 2013 and 14 April 2014. Sowing density was 2,500 germinable seeds/m2. The agronomic traits studied were dry stem yield, dry stem yield after retting, total fibre yield, share Table 1: Content of nutrients in soils and pH Year Location P2O5 (mg/100 g) K 2O (mg/100 g) Total nitrogen (%) pH - 1M KCl (1:2.5) 2012 Zagreb 32.20 27.0 0.13 7.31 2013 Zagreb 34.54 25.0 0.11 6.20 2014 Zagreb 37.03 16.2 0.12 7.09 2012 Križevci 28.39 19.05 0.10 5.42 2013 Križevci 21.47 16.67 0.12 4.84 2014 Križevci 29.19 25.31 0.10 6.05 P2O5, K 2O – Al method; Total nitrogen – HRN ISO 13878:2004; pH – HRN ISO 10390:2004 The Influence of Water Hardness on the Agronomic Traits of Foreign Fibre Flax Varieties in the Republic of Croatia 221 Table 2: Mean monthly absolute minimum and maximum air temperatures (°C) and mean monthly precipitation amounts (mm) for 2012, 2013 and 2014 for Zagreb (Meteorological and Hydrological Services of the Republic of Croatia) Year 2012 2013 2014 Month Mean monthly air temperature (°C) Absolute minimum air temperature (°C) Absolute maximum air temperature (°C) March April May June March April May June March April May June 9.4 12.5 16.7 22.0 4.9 13.0 16.3 20.0 10.8 13.3 16.2 20.2 −3.1 −2.3 3.3 7.0 −4.8 −1.2 6.8 8.4 0.3 2.5 3.2 8.8 23.9 30.5 29.3 35.3 17.9 29.2 28.9 33.6 23.6 25.0 29.0 33.9 Mean monthly precipitation amounts (mm) 4.5 51.3 81.8 127.9 121.7 56.1 94.0 48.7 21.0 70.4 145.0 147.0 Table 3: Mean monthly absolute minimum and maximum air temperatures (°C) and mean monthly precipitation amounts (mm) for 2012, 2013 and 2014 for Križevci (Meteorological and Hydrological Services of the Republic of Croatia) Year 2012 2013 2014 Month Mean monthly air temperature (°C) Absolute minimum air temperature (°C) Absolute maximum air temperature (°C) Mean monthly precipitation amounts (mm) March 9.2 −4.1 23.0 2.4 April 12.2 −4.0 29.6 34.6 May 16.1 1.4 29.5 99.4 June 21.5 5.4 34.6 65.6 March 4.2 −6.0 17.5 132.1 April 12.3 −0.9 28.1 47.1 May 15.8 5.9 29.1 108.2 44.4 June 19.5 7.5 34.2 March 10.3 −3.1 23.3 14.7 April 12.7 1.9 24.4 56.5 May 15.4 3.0 29.3 118.3 June 19.8 9.2 34.1 99.4 of total fibre, long fibre yield and share of long fibre [13]. Manual harvest by hand pulling was carried out at yellow-green ripening and an area of 1 m 2. Dry stem yield was determined after de-seeding. Flax stems were then placed in a tank of water (very soft, medium hard and hard – Table 2) at 32 °C for three days (72 hours) under controlled conditions. Retted stems were then removed from the tank. They were dried at 60 °C for 30 hours and weighed. A scutching machine was used to separate straw (woody matter) from fibre, where the yields of total and long fibres (using a set of hackling pins), and their respective share, were estimated. The water hardness is expressed in German degrees of hardness (°dH) and in ppm (determination by 222 Tekstilec, 2022, Vol. 65(3), 218–226 t­ itration with 0.1 M HCl with methyl orange indicator) (Table 4). Table 4: Hardness of water retting Water German degrees of hardness (°dH) ppm Very soft 0.8–1.5 14–26 Medium hard 5.2–5.7 88–98 Hard 15.5–21 263–357 Data regarding all of the traits studied were statistically processed using analysis of variance (two-factor trial – variety and water hardness) separately for each year and each location. Differences between mean values were analysed using Duncan’s multiple range test [25]. 3 Results and discussion Statistically significant differences were recorded among the varieties for the studied traits of fibre flax, except for total fibre yield, share of total and long fibre in 2014 in Zagreb, share of total fibre in 2012 and 2014 in Križevci, all studied traits in 2013 in Križevci and dry stem yield in 2014 in Križevci (Tables 5 and 6). In addition, statistically significant differences were only recorded among different water hardnesses for long fibre yield in 2012 and share of total fibre in 2013 in Zagreb (Tables 7 and 8). No significant interaction was recorded for any traits or any location, so interactions were not included in the factors shown here and were not discussed any further. Accordingly, the factors affected the studied traits independently. The highest dry stem yield was achieved by the varieties Viola in 2012 and 2013 in Zagreb, Venica in 2013 in Križevci and Agatha in 2014 at both locations (Tables 5 and 6). Viola gave the highest dry stem yield after retting in two years in Zagreb and Križevci, and Electra in one year in Zagreb. The highest total fibre yield was achieved by the varieties Viola in 2012 at both locations, in 2013 in Zagreb, and Agatha in 2014 in Križevci and Electra in Zagreb. Also, Viola gave the highest long fibre yield in 2012 and 2013 in Zagreb and Agatha in 2012 in Zagreb, and in three years in Križevci. However, Venica gave the highest share of total fibre in two years in Zagreb and one year in Križevci. The highest share of long fibre was achieved by the variety Agatha in 2012 in Zagreb, in 2013 at both locations and in 2014 in Križevci. Comparing locations, all varieties achieved higher values of dry stem yield, dry stem yield after retting, total fibre yield, share of total fibre and long fibre yield in two years at Križevci. The higher values in Križevci were also the result of flax production on heavier soil (pseudogley on level terrain), in which some winter moisture remained available in April and at the beginning of May (Tables 2 and 3). According to previous studies of these varieties, dry stem yields after retting ranged between 4.5 and 9.0 t/ha, total fibre yield between 1.5 and 3.8 t/ha, share of total fibre between 25 and 45%, long fibre yield between 1.3 and 2.0 t/ha, and share of long fibre between 20 and 25%, depending on climatic conditions [11, 26–32]. The growth of flax plant is usually monitored in terms of accumulated temperature or effective cumulative temperature [33]. It was determined that optimum fibre richness is reached around an accumulated temperature of 850-1100 °C, which is a ­favourable condition for harvest. Higher accumulated temperatures (> 1100 °C) were found to be ineffective for the improvement of fibre richness. Higher accumulated temperatures cause lignin generation within the plant, and pose problems during the retting and mechanical separation of fibres. In our studies (Tables 2 and 3), excessively high temperatures in some years at the end of April and at the beginning of May in the intensive flax growth stage (absolute maximum temperature was recorded in April in Zagreb (30.5 °C) and in May in Zagreb (29.3 °C) accelerated the maturity of flax, and the elongation of fibre did not appear and the yield and quality was reduced. The annual precipitation also influenced the growth of fibres. It has been suggested that precipitation should be about 110-150 mm [28] during the growing period. The below-mean values for dry stem yield after retting, total fibre yield, long fibre yield and share of long fibre in 2012 and 2014 in Zagreb and in 2013 in Križevci were influenced by plant lodging due to poor climatic conditions and strong winds at the end of May (in 2014 in Zagreb and in 2013 in Križevci) and at the beginning of June (in 2012 and 2014 in Zagreb), and excessive precipitation in May (in 2014 in Zagreb (145.0 mm); in 2013 in Križevci (108.2 mm) and in June (in 2012 and 2014 in Zagreb (127.9 mm and 147.0 mm) (Tables 2 and 3). 223 The Influence of Water Hardness on the Agronomic Traits of Foreign Fibre Flax Varieties in the Republic of Croatia Table 5: Means of agronomic traits of fibre flax, depending on the varieties in Zagreb (2012, 2013 and 2014) Year 2012 2013 2014 Varieties Dry stem yield (t/ha) Dry stem yield after retting (t/ha) Total fibre yield (t/ha) Share of total fibre (%) Long fibre yield (t/ha) Share of long fibre (%) Viking 4.20b 3.20b 1.13b 35.27b 0.38b 11.71ab Viola 4.73a 3.86a 1.55a 40.18ab 0.50a 13.07ab Venica 4.27a 3.31b 1.35ab 41.14a 0.41ab 12.54ab Agatha 4.51a 3.39b 1.38ab 40.52ab 0.50a 14.81a Electra 4.71a 3.94a 1.53a 38.85ab 0.43ab 11.12b Viking 8.65b 6.23d 1.99b 32.34b 0.58c 9.42c Viola 12.77a 10.36a 3.66a 35.43b 1.41a 13.77b Venica 8.81b 6.69cd 2.31b 35.14b 0.93b 14.32ab Agatha 9.08b 7.76bc 3.29a 42.78a 1.40a 18.13a Electra 11.98a 8.92b 3.33a 37.70b 1.22ab 13.61b Viking 6.06b 3.70b 1.12a 30.65a 0.33c 9.10a Viola 8.65a 5.45a 1.36a 25.30a 0.54a 10.03a Venica 6.26b 3.73b 1.21a 32.76a 0.44b 11.96a Agatha 8.84a 4.21b 1.28a 31.53a 0.49ab 12.26a Electra 7.88ab 4.58ab 1.45a 32.65a 0.55a 12.47a Values with the same letter are not significant at a level of 5%. As the significance values decrease, the letters descend, as they are in alphabetical order. Table 6: Means of agronomic traits of fibre flax dependent on the varieties in Križevci (2012, 2013 and 2014) Year 2012 2013 2014 Dry stem yield (t/ha) Dry stem yield after retting (t/ha) Total fibre yield (t/ha) Share of total fibre (%) Viking 8.43b Viola 11.21a 5.63b 1.63b 29.43a 0.47c 8.43b 8.10a 2.46a 31.63a 0.80a 10.35ab Venica 8.47b 5.55b 1.80b 32.58a 0.66ab 12.00a Agatha 9.68ab 6.86ab 2.18a 31.96a 0.82a 11.92a Electra 11.27a 7.68ab 2.43a 31.97a 0.55bc 7.35b Viking 4.94a 4.33a 1.84a 44.42a 0.47a 10.68a Viola 5.05a 4.36a 1.87a 43.62a 0.61a 14.04a Venica 5.33a 4.50a 1.89a 44.79a 0.60a 13.74a Agatha 4.92a 4.08a 1.83a 45.47a 0.67a 15.91a Electra 4.78a 4.05a 1.83a 47.53a 0.52a 12.89a Viking 9.18a 4.91b 1.93b 39.63a 0.57d 11.94d Varieties Long fibre yield (t/ha) Share of long fibre (%) Viola 9.52a 6.54a 2.30ab 35.62a 1.15b 17.74bc Venica 9.39a 5.41ab 2.05ab 38.35a 0.75c 14.25cd Agatha 10.41a 6.08ab 2.49a 41.36a 1.33a 22.15a Electra 9.85a 6.20ab 2.43a 39.43a 1.30a 21.17ab Values with the same letter are not significant at a level of 5%. As the significance values decrease, the letters descend, as they are in alphabetical order. 224 Tekstilec, 2022, Vol. 65(3), 218–226 The highest values for all studied traits (Tables 7 and 8) were achieved when the plants were retted in very soft water. This does not apply for dry stem yield in 2013 and 2014 and dry stem yield after retting in 2013 in Zagreb, and share of total fibre in 2012, dry stem yield, long fibre yield and share of long fibre in 2013 in Križevci. These values were not significantly higher than the values when plants were retted in very soft water. During retting, it was observed that the maceration process was faster in softer water. This is consistent with previous studies reported in the literature [2, 5−7]. 4 Conclusion On the basic of the results obtained, the following conclusions can be drawn: – Statistically significant differences were recorded among the varieties for the studied traits of fibre flax, except for total fibre yield, share of total and long fibre in 2014 in Zagreb, share of total fibre in 2012 and 2014 in Križevci, all studied traits in 2013 at Križevci and dry stem yield in 2014 in Križevci. – Statistically significant differences were only recorded among different water hardnesses for long fibre yield in 2012 and share of total fibre in 2013 in Zagreb. Table 7: Means of agronomic traits of fibre flax, depending on water hardness in Zagreb (2012, 2013 and 2014) Year 2012 2013 Water hardness Very soft Dry stem yield (t/ha) 4.50a Dry stem yield after retting (t/ha) 3.61a Total fibre yield, t/ha 1.45a Share of total fibre (%) 40.12a Long fibre yield (t/ha) 0.49a Share of long fibre (%) 13.72a Medium hard 4.45a 3.54a 1.37a 39.03a 0.45a 12.92a 4.49a 10.01a 3.47a 7.86a 1.33a 3.08a 38.43a 39.67a 0.39b 1.12a 11.31a 14.39a 10.37a 7.85a 2.82a 36.03a 1.11a 14.28a Hard Very soft Medium hard Hard 10.40a 8.27a 2.85a 34.54b 1.08a 12.88a Very soft 7.58a 4.44a 1.37a 32.01a 0.49a 11.60a Medium 7.64a 4.35a 1.25a 29.71a 0.47a 11.00a 2014 hard Hard 7.40a 4.22a 1.23a 30.02a 0.45a 10.89a Values with the same letter are not significant at a level of 5%. As the significance values decrease, the letters descend, as they are in alphabetical order. Table 8: Means of agronomic traits of fibre flax dependent on the water hardness in Križevci (2012, 2013 and 2014) Year 2012 2013 Water hardness Very soft Dry stem yield (t/ha) 10.07a Dry stem yield after retting (t/ha) 6.89a Total fibre yield, t/ha 2.17a Share of total fibre (%) 31.63a Long fibre yield (t/ha) 0.70a Share of long fibre (%) 10.45a Medium hard 9.74a 6.84a 2.12a 31.64a 0.66a 10.13a 9.63a 4.96a 6.56a 4.49a 2.00a 1.95a 31.27a 45.80a 0.61a 0.57a 9.45a 12.68a 5.05a 4.21a 1.79a 44.40a 0.59a 14.22a Hard Very soft Medium hard Hard 5.01a 4.10a 1.81a 45.30a 0.56a 13.46a Very soft 9.75a 5.96a 2.33a 39.66a 1.06a 17.62a Medium 2014 9.61a 5.84a 2.23a 38.66a 1.02a 17.40a hard Hard 9.66a 5.69a 2.15a 38.32a 0.99a 17.33a Values with the same letter are not significant at a level of 5%. As the significance values decrease, the letters descend, as they are in alphabetical order. The Influence of Water Hardness on the Agronomic Traits of Foreign Fibre Flax Varieties in the Republic of Croatia – No significant interaction was recorded for any traits or any location. – The varieties Agatha, Viola and Electra recorded the highest values of studied traits. – Comparing locations, all varieties achieved higher values of dry stem yield, dry stem yield after retting, total fibre yield, share of total fibre and long fibre yield in two years in Križevci. – The highest values for all studied traits were achieved when the plants were retted in very soft water. This does not apply for dry stem yield in 2013 and 2014 and dry stem yield after retting in 2013 in Zagreb, and share of total fibre in 2012, dry stem yield, long fibre yield and share of long fibre in 2013 in Križevci. – Croatia has extremely hard water, and it would be most economically advantageous to use hard water for flax retting. The results obtained in this research show that the retting process was faster in softer water, making that process a little more expensive. The presented research will therefore be continued and expanded. – The obtained results are of great importance because they provided valuable knowledge about the acclimatization ability of foreign cultivars that can be potentially adapted to the climatic conditions of Croatia, which will ensure raw materials for making ecologically valuable products. References 1. TAHIR, Paridah; AMEL, B. Basher; SYEED SAIFUL, Azry and ZAKIAH, Ahmed. Retting process of some bast plant fibres and its effect on fibre quality: A review. Bioresurces, 2011, 6(4), 5260-5281. doi: https://doi.org/10.15376/ BIORES.6.4.5260-5281. 2. BRUNŠEK, Ružica; ANDRASSY, Maja and BUTORAC, Jasminka. Retting of f lax and ­characterization of fibres. In Proceedings of 14th AUTEX World Textile Conference 2014, Bursa, Turkey. Edited by Recep Eren, 2014, 1-6. 3. SHEKHAR SHARMA, H. 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New varieties – Venica. Czech Journal of Genetics and Plant Breeding, 2001, 37, 103-104. 33. BERT, F. Lin Fibre: Culture Et Transformation. Arvalis-Institut du Vegetal Paris, France, 2013. Tekstilec, 2022, Vol. 65(3), 227–241 | DOI: 10.14502/tekstilec.65.2022036 227 Akhtarul Islam Amjad National Institute of Fashion Technology, Panchkula, Haryana, 134116, India Filtration in Pharmaceutical Industries and Role of Textile Filtracija v farmacevtski industriji in vloga tekstilij Original scientific article/Izvirni znanstveni članek Received/Prispelo 5-2022 • Accepted/Sprejeto 9-2022 Corresponding author/Korespondenčni avtor: Assist Prof Dr. Akhtarul Islam Amjad E-mail: akh.textile@gmail.com Tel. +91-8209015640 ORCID ID: 0000-0002-9667-4012 Abstract Filtration is considered the keystone for clarification and control of contamination in pharmaceutical and biopharmaceutical manufacturing. From production to in-process to chemical and research laboratories to the purification of water for sterile and nonsterile products, all of which involve some form of filtration in order to achieve a good manufacturing practice (GMP). Textile materials possess a significant contribution to the pharmaceutical filtration system. Textile material in pharmaceutical filtration is used in the form of filter media or medium. Flexible in nature, large pore distribution and non-metallic properties of textile materials have led to widespread use as filter media for many years. In filtration processes, a proper selection of filter media/ membrane material is usually the most critical aspect for ensuring efficient separation. Generally, solid-liquid and solid-gas separation is done by the filter media. This paper emphasises solid-liquid filtration. Moreover, this paper reviews the water requirement, filtration processes and the role of textile in the filtration system of pharmaceutical industries. This paper also offers insight into the current market trend and COVID-19 impact on the pharmaceutical filtration industry. Furthermore, gathered information may be helpful to those studying and working in pharmaceutical engineering, filtration technology, and wastewater treatment and can get knowledge about filtration systems. Keywords: liquid filtration, textile filter media, water treatment, pharmaceutical filtration, COVID-19 impact Izvleček Filtracija velja za temeljni kamen čiščenja in nadzora kontaminacije v farmacevtski in biofarmacevtski proizvodnji. Od proizvodnje do medprocesnih, kemijskih in raziskovalnih laboratorijev čiščenja vode za sterilne in nesterilne izdelke vsi vključujejo določeno obliko filtracije, da dosežejo dobro proizvodno prakso. Tekstilni materiali prispevajo pomemben delež k farmacevtskemu filtracijskemu sistemu. V farmacevtski filtraciji se uporabljajo v obliki filtrnega medija ali medija. Gibka narava, porazdelitev velikih por in nekovinske lastnosti tekstilnega materiala že vrsto let vodijo v široko uporabo filtracije kot filtrnega medija. Pri postopkih filtracije je pravilna izbira filtrnega medija/membranskega materiala po navadi najbolj kritičen vidik zagotavljanja učinkovitega ločevanja. Na splošno se ločevanji trdno-tekoče in trdno-plin izvajata s filtrirnimi mediji. Ta članek obravnava filtracijo trdno-tekoče. Poleg tega obravnava potrebe po vodi, postopke filtracije in vlogo tekstilij v filtrnem sistemu farmacevtske industrije. Daje tudi vpogled v trenutni tržni trend in vpliv COVID-a na filtracijo v farmacevtski industriji. Znanja o filtrnih sistemih so lahko koristna vsem, ki študirajo in delajo na področju farmacevtskega inženirstva, filtracijske tehnologije in čiščenja odpadne vode. Ključne besede: filtracija tekočin, tekstilni filtrni mediji, priprava vode, farmacevtska filtracija, vpliv covida 228 Tekstilec, 2022, Vol. 65(3), 227–241 1 Introduction Filtration is the separation of solid particles suspended in a liquid or gas using a porous medium that traps the solids while allowing the fluid to flow through. When the amount of solids in a liquid is reduced, this is called clarification [1]. In the pharmaceutical sector, filtering is a common and wellknown activity. Filtration is used to make sterile goods, bulk pharmaceuticals, liquid oral formulations, and wastewater treatment plants (WWTPs) and their effluent receivers [2]. A porous material used to hold particles is known as filter media. There is a variety of materials that may be utilised in the filter medium to satisfy the users’ demands. A proper selection of filter media/membrane material in filtering procedures is frequently the most critical aspect for ensuring efficient separation [3]. Cotton, polyester, wool, linen, polypropylene, glass fibre, porous carbon, metals and rayons are some of the materials used to manufacture filter media [4]. New polymeric materials have recently been utilised in filtering processes to purify medications, fluids and wastewaters in the pharma industry, both separately and/or mixed [5]. Surface filtration relies heavily on textile materials and membranes. Textiles such as nonwoven textiles and natural or synthetic fibres may be selected for their ease of installation on the filter tank/module [6]. Apart from the nonwoven structure, metal glands may be installed in the weaving medium in specific situations, cartridge and wax filter can also be incorporated with a woven fabric. The usage of different chemicals (e.g. polymer blends) in the manufacturing of the filter material, as well as the addition of the base material (e.g. nanoparticles, nanotubes) may modify the surface of the existing material and can work as a highly efficient filter [7]. In recent years, textile nanofibers have gained popularity in liquid filtration due to their unique characteristics such as high aspect ratio, cohesiveness, high specific surface area, exclusive physicochemical properties, and the design flexibility for chemical/physical surface functionalisation. They are continually gaining popularity in the pharmaceutical industry as a filter material in liquid and gas filtration [2, 8]. Apart from the general production of drugs, sterile and non-sterile products, the current COVID-19 outbreak impacted the production trend of vaccines, and there has been a sudden rise in demand. Thus, filtration-based technologies are also gaining momentum in vaccine clarification [9]. 2 Filtration mechanism used in industry The pharmaceutical industry needs different filtration methods depending on what sort of chemical solution is being used. Generally, the pharmaceutical industry has three major types of filtration systems (surface, depth and crossflow filtration) [7, 8, 10]. Figure 1 depicts various mechanisms of filtration. Surface filtration, which operates with direct interception, separates the substance from the medium through which it may travel more readily than other materials in the same environment. The separation is caused by the size of holes in the filter, since the screen enables particles of specific size to pass through but traps molecules which are too big to fit through the pores. The technology is also known as membrane filtration, since it occasionally uses a porous membrane [8, 10, 64]. Deep-bed filters (also known as depth filtration) have been utilised in water and wastewater treatment for over a century. The creation of wells or springs in nature, which are drained from porous media such as rocks and sand, is similar to the principle of deep-bed filtration. Depth filtration holds particle matter further down from the surface than surface filtration [7, 11]. Its primary function is to clarify solutions. Ceramicfilter, sintered filters and nonwoven textile filters are the most frequently used in depth filtering. Recent advances in sintered metal filters include electrostatic precipitators, cyclones and disposable filters that were once highly used in the pharmaceutical industry [12]. Nanofiltration, also known as crossflow filtration, is a recently created device used by pharmaceutical industries seeking a solution of polyvalent cation removal in a low total dissolved solids water (surface or fresh ground water). The term nanofiltration refers to using a filtration membrane with holes that are one nanometre in diameter or smaller. It is comparable to reverse osmosis; however, the trans-membrane pressure required for functioning is much lower. As a result, the procedure is more cost-effective. Nevertheless, nanofiltration has flaws, e.g. the possibility of fouling and scaling on nanofiltration membranes [10, 13]. 229 Filtration in Pharmaceutical Industries and Role of Textile Filter media Particles Particles Fluid feed Fluid feed Fluid feed Retentate Permeate a) Surface filtration b) Depth filtration c) Cross flow filtration Figure 1: Filtration mechanism [8–13] 3 Water quality and filtration in pharmaceutical industries Water is an essential component in pharmaceutical and life science processes. Water is utilised as a raw material in the processing, formulation, and production of various pharmaceutical products and active pharmaceutical ingredients (API). Most pharmaceutical industries rely heavily on surface water and groundwater supplies. Water from these sources is contaminated in its natural condition and must be filtered before being used for pharmacological purposes [14]. For pharmaceutical use, water must be treated according to established protocols. Distillation and deionisation are used in this water purification procedure to lower the number of polluted particles, parasites, bacteria, algae, viruses and fungi [15]. Medicinal water systems of varying quality are required depending on the mode of administration of the pharmaceutical medication. Numerous types of water used for medicinal applications are listed below, based on water quality. Water standards are included in pharmacopoeias for both bulk and dosage forms of water [16]. National, regional and worldwide pharmacopoeias specify the pharmacopeial requirements or guidelines for WPU (water for pharmaceutical use), and limits for specific impurities or groups of impurities are either stated or suggested [17]. Companies that want to serve several markets create specifications that match the most stringent criteria of each pharmacopeia [18]. 3.1 Drinking water Potable water is the best way to describe drinking water. Drinking water should be available under constant positive pressure in a plumbing system that is devoid of any flaws that might lead to product contamination. The minimal quality of water should be used to manufacture drugs and other bulk pharmaceutical compounds in drinking water [19]. After assessing the source water’s condition, the treatment necessary to make it safe for human consumption is decided. Except for a minor treatment of water drawn from a natural or stored source, drinking water is unaltered [20]. 3.2 Bulk purified water (BPW) In preparing non-parenteral dosages and other pharmaceutical uses, bulk purified water is mainly employed as an excipient. Non-parenteral is most usually used to refer to the route through which oral drugs are taken; consequently, it is critical that the water used in non-parenteral preparations meet the ionic and organic chemical purity criteria [20, 21]. As feedwater for this should be at least a drinking-water source or filtered water which has at least the parameters equalling the drinking water. It must meet the applicable pharmacopeial requirements for chemical and microbiological purity, as well as action and warning limitations. It should also be protected from microbial multiplication and recontamination. A combination of reverse osmosis (RO), RO/electro-deionisation (EDI) and vapour compression can be used to make BPW [22]. 3.3 Bulk highly purified water (BHPW) BHPW is a unique water specification available only in the European Pharmacopoeia. Drinking water should be utilised as an input water source for the preparation of BHPW. This water grade must meet the same quality standards as water for injections (WFI), including endotoxin limits. In combination with other required processes, e.g. ultrafiltration 230 Tekstilec, 2022, Vol. 65(3), 227–241 and deionisation, double-pass RO is one of current manufacturing methods. BHPW can be made in various ways, including RO, ultrafiltration and deionisation. Highly cleansed water needs to be protected from recontamination and microbiological multiplication [18, 19, 23]. 3.4 Bulk water for injections (BWFI) BWFI is a common excipient in the production of parenteral and other pharmaceutical preparations where endotoxin is a concern. BWFI should be prepared with drinking water or filtered water as minimum quality feed water [21]. For pharmaceutical companies, chemical purity in BWFI is a crucial issue. The microbiological quality of the water should be consistent in testing and meet the standards for bacterial endotoxins, which are less than 0.25 IU per ml. Multi-effect distillation is the sole method for obtaining consistent BWFI. It is still the only official way of manufacturing BWFI. BWFI is not sterile water and is not intended to be used as a final dose form. BWFI is an intermediate bulk product that can be used as a component in a recipe. Sterlite water for injection (SWFI) is used for vials. The most outstanding quality of pharmacopeial WPU is BWFI. As a part of the BWFI definition, certain pharmacopoeias set restrictions on the allowed purification processes. Only distillation is permitted as the last purification stage in the International Pharmacopoeia and the European Pharmacopoeia [21–23]. Chemical and microbiological purity (including endotoxin) should be met by BWFI, with appropriate action and warning limits. BWFI should also be safeguarded from microbial multiplication and recontamination [23]. 4 Textile materials for pharmaceutical filtration Pharmaceutical filtration is divided into two-step prefiltration and main filtration. Prefiltration is any filtration procedure that takes place before the final filtration in the manufacturing process [19, 24]. The main goal is to achieve adequate particle removal. The filtration rate and throughput are other factors to consider. Fibre, yarn and fabrics (woven and nonwoven) are the basic textile products. All these textile products are used as filter media for liquid filtration. Textile fibres can be natural or manmade. Table 1 shows the properties of various textile fibres which are frequently used in liquid filtration. The aspect ratio (length and breadth or diameter) of textile fibres made them most suitable for the filter Table 1: Fibres used in pharmaceutical filtration and characteristics [6, 10, 13] No. Fibre category Fibre name Maximum service temp (°C) 1 Cellulosic Cotton, viscose, jute 90 2 Polyamide Nylon 100 3 Polyester Decron, Trevira 150 4 PTFE (Polytetrafluoroethylene) Teflon, Rastex 200 5 Polypropylene Moplefan (trol) 90 (120) 6 Copolymer Acrylic Dynel, Orlon 120 7 Polypeptide Wool 110 8 Silicate Glass fibre 250 Principal properties good abrasion and very good alkali resistance, poor acid resistance, inexpensive excellent abrasion and alkali resistance, poor acid resistance, high strength or flexibility very good abrasion, good acid resistance, poor alkali resistance, easy cake discharge, long life fair abrasion, excellent acid resistance, excellent alkali resistance, extreme, excellent cake discharge good abrasion, excellent acid resistance, excellent alkali resistance, low moisture absorption good abrasion, good acid resistance, and fair alkali resistance good abrasion, good acid resistance, poor alkali resistance poor abrasion, fair acid resistance, poor alkali resistance, suitable for a wide range of chemical solutions Filtration in Pharmaceutical Industries and Role of Textile ­ edia. Strand in the form of sliver, roving or yarn m is also used for the filter media. Fabrics, woven or nonwoven are the largest used textile products as filter materials. The number of pores, pore size, yarn count and weave type define the fabric filter media. More yarns and a finer yarn count result in smaller pores and a greater number of pores in the woven fabric. Nonwoven filter media is manufactured directly from the fibre and can be used in a variety of liquid filtering systems, including filter presses, horizontal disc filters and rotary drum vacuum filters. Due to the mechanical, chemical and thermal treatments, individual fibres in nonwoven filter media are often interconnected. To preserve the filter media, loose woven materials can be utilised on both sides of the filter [6, 10, 31]. The cellulose textile fibre-based depth filter, which comes in sheet or lenticular cartridge type, is one of the most prevalent prefilters used in biopharmaceutical processes. These prefilters are particularly cost-effective due to comparatively inexpensive raw materials used in their construction, and the thickness and structure of the filter matrix created during the manufacturing process [6]. Cellulose or manufactured textile fibres, inorganic filter aid, fabrics and a polymeric wet-strength resin are the main raw components utilised to make these filters. By refining the fibres, void volume and particle retention capacity of the fibre component of the filter can be adjusted [2–6, 24]. The filter aid is the second most crucial part of the filter sheet. Perlite is volcanic ash with a smooth, glass-like texture and is also used with a mixture of cellulose fibre matrix. The particles of Perlite have a somewhat uniform shape and form thickly within the cellulose fibre matrix. The powder comes in various particle sizes, allowing for a wide range of porosity [3]. Instead of cellulosic prefilters, glass fibres are also used, especially in serum filtrations. These may be borosilicate glass or glass fibres with special coatings such as nitrocellulose polymers. The adsorption of process contaminants, particularly protein-like materials and lipids, is quite successful with these coatings. The adsorptive elimination of pollutants with a nitrated polymer is most likely accomplished through hydrogen bonding. Polypropylene fibres are also a common material for filter media [3, 25]. To limit or eliminate media movement, they can be shaped into fleeces and mats of varying fibre diam- 231 eters bound together and permanently crosslinked by heat, then bonded by melting. The adhesives and mechanical manipulations of older and less effective sheet creation methods replaced the melt-spinning way of permanently connecting the fibres. Varying the mean fibre size during the fleece formation enables the mat pore size to change progressively [3, 6, 25]. Due to this filtration, the effect will be like a series of prefilters combined into a single prefilter composite. Due to the effectiveness of thinner fibres, the asymmetric morphology provides less resistance to flows, requires lower differential pressures in their operations, can accommodate higher particle loadings and delivers more particle removal. Fibres with mean diameters as tiny as 0.3 μm are capable of retaining particles as small as 1 μm in diameter from a fluid stream. A smaller pore size is created by shrinking fibre diameters rather than tightening mat packing density. This improves filter porosity while allowing for lower operational differential pressures and bigger load capacities [25, 26]. 5 Continuous filtration for pharmaceutical industries Pharmaceutical water system operators strive to create bacteria-free water that meets or exceeds purity standards. To safeguard system components and ensure that the water distributed for use is free of bacteria and most other particle pollutants, water systems employ several filters [27]. Figure 2 depicts a continuous filtration system used in pharmaceutical industries. Particle filtration and bacterial elimination are the two main filtration products used in pharmaceutical water systems [2]. Before the reverse osmosis (RO) unit, filters are used to reduce or remove particle contaminants, whereas filters after the RO unit are used to decrease or eliminate bacterial contamination. The use of filtration products in pharmaceutical water systems generally falls into two categories, i.e. particle filtration and bacterial removal. Filtration products located before the reverse osmosis (RO) unit reduce or remove particle contaminants, while the filters following the RO unit are intended to reduce or remove bacterial contaminants. Additional filters may be necessary if the water supply includes chemicals that, if not treated, could cause early filter blocking or fouling of RO membranes [2, 25, 28]. 232 Tekstilec, 2022, Vol. 65(3), 227–241 Multi-media filter (sand filtration) Deep filter (particle trap) Reverse osmosis Deionisation system (DI) Depth filter (resin trap) Still tank with vent filter Distillation unit Bioburden reduction (sterilising filter) Carbon filter Depth filter (carbon fine trap) Water softener Depth filter (resin trap) Bulk purified water tank with vent filter Bioburden reduction (sterilising filter) UV light Bulk water for injection Endotoxin filter UV light RO prefilter Bulk purified water (BPW use) Bulk water for injection (BWFI use) Figure 2: Filtered water system for pharmaceutical use [2, 21, 24, 25, 27, 28] 5.1 Before reverse osmosis (RO) unit Coarse filtration is commonly used as the first step in water treatment to remove bigger particulates like sediment and silt. Figure 2 depicts a multimedia (sand) filter followed by a depth filter to remove the particles emitted by the multimedia filter. Both filters can be merged into a single particle filter housing in smaller systems [10, 27, 28, 64]. There are two types of depth media for cartridge filters. Self-supporting tubes consist of a polymer, most commonly made of polypropylene or nylon. The melt-blown or nano-spun process is used to create the tube. Pleated flat sheet media, most commonly made of polypropylene or fiberglass, is used in the other type of depth filter [10, 11]. Although polypropylene is the most frequently used material for water and chemical filtration, fiberglass offers a greater filter efficiency. It allows for higher flows and throughput in most applications than polypropylene. Through the thickness of the media, standard depth filters will catch a range of particle sizes. Pleated media filters have a larger surface area than ordinary depth filters and may hold a more significant number of particles on that surface. These items can hold a lot of silt or sediment before they need to be replaced. Yarn wound filters are also used; however, these filters add extractable surfactants to the water when they are installed [3, 6, 25]. Melt-blown and nano-spun polypropylene filters are available in a wide variety of configurations to fit the existing housings. Pleated filtration devices, such as commercial-grade pleated polypropylene (CPF) depth filters, can remove up to three times as much sediment and silt as melt-blown or nano-spun filters. However, pleated filters are more expensive; however, longer life and higher dirt holding capacity and labour savings from less frequent filter changes make pleated filters economically advantageous [2, 6, 29]. The activated carbon filter depicted in the Figure 2 is a granular carbon filter that eliminates chlorine, chloramine and other dissolved organic compounds from the water supply. Cartridges include activated carbon that is immobilised within the filter matrix. It is also possible to employ activated zeta plus carbon. It is made up of activated carbon, cellulose and a positively charged crosslinking polymer, and is designed to deliver the best filtering and purification results for a wide range of fluid issues. This prevents the oxidation of downstream treatment components, particularly RO membranes. Unfortunately, all carbon filters produce carbon fines, and fine carbon particles must be removed with depth/particulate to safeguard downstream equipment. Again, CPF melt-blown or nano-spun polypropylene depth filters and yarn wound filters can be used for carbon fines removal [2, 6, 30]. With Filtration in Pharmaceutical Industries and Role of Textile their excellent dirt holding ability, pleated filters could also be used in this situation. Water softening and deionisation are two resin-based treatment procedures depicted in the system diagram. These resin-based techniques will be used in small and big pharmaceutical water systems. Polishing is the term used to describe this process [30, 31]. These resin beds can be blended or separated. They are highly dependable when it comes to creating USP (US pharmacopeia) grade water; however, they do require regeneration once they are depleted. Onsite or off-site regeneration is possible [32]. Before the regeneration, the resin must be separated if utilising a mixed bed. On-site regeneration capabilities are obviously more expensive in terms of capital, but they are cheaper for long-term maintenance. Continuous electro-deionisation is the advanced polishing method. Ion exchange resins in a stack remove cation and anion pollutants from the feedwater, and an electrical current runs through the stack to regenerate the resin continually [33]. The continuous regeneration eliminates the need for traditional ion exchange equipment to be shut down and regenerated regularly, allowing for the production of high-quality water [31–33]. The resin beads used to purify the water in both cases will break down over time and may release resin particles into the water supply. To remove these resin particulates from the water, textile-based depth filters must be fitted once again [34]. 5.2 Reverse osmosis unit The reverse osmosis process is supported by an RO prefilter, as illustrated in Figure 2, which protects the high-pressure RO pump and keeps the membranes from fouling due to particles. Protecting the RO membranes from particles is critical for extending membrane life. To safeguard the RO membranes, CPF offers melt-blown polypropylene, polyester filters, nano-spun polypropylene filters, pleated polypropylene, and nylon filters may be used. Though melt-blown or nano-spun cartridges may cost each less than a pleated cartridge, pleated filters may be desirable due to the lower number of filters and potentially longer filter life [2, 3, 36]. RO systems are the most common method for removing salt and organic material and inorganic and organic pollutants, colloids, microorganisms and endotoxins. Since it effectively removes inorganic/ organic impurities (excluding gases), has relatively 233 low operating costs, and is very reliable when pretreatment equipment is appropriately maintained, RO is the primary process for water purification [37]. 5.3 After reverse osmosis (RO) unit Vent filters are utilised at two points in the illustration. These are employed to filter the air directly in touch with the purified water or water for injection storage tanks and protect the water from bacterial and particle contamination. The air inside the tank must be allowed to go out as the tank fills, and when the tank is emptied, air (or a process gas like nitrogen) must be allowed to enter to replace the lost liquid volume [25, 35, 39]. Particle and bacterial contaminants must be eliminated from the tank’s air or gas. The filter media must be dry for air to travel freely through it. Almost all vent filters used in biopharmaceutical manufacturing are hydrophobic membranes with pore sizes of 0.22 µm. A hydrophobic membrane such as polypropylene or PTFE is commonly used as such a membrane resists the water vapour [40]. Sterilising grade polypropylene melt-blown media (PPM) or PTM cartridges or capsules is used for ambient temperature storage tanks since most WFI storage tanks are kept at high temperatures [27, 40]. Different particle and bioburden loading are encountered in each biopharmaceutical process. Outside materials can be the path for such particles and organisms into processes. Organisms may be prevalent in the plant atmosphere, like moulds and yeasts, and can enter into the processes during mixing or are introduced through normal handling of ingredients and equipment [41]. Operators may opt to remove the majority of organisms before the sterilising filter or all of them, depending on the nature and amount of organisms. Membrane-based filters handle almost all bioburden reduction filtration [35]. However, high-efficiency pleated depth media filters can remove some big microorganisms, e.g. moulds and yeasts. Using pleated flat sheet media, polypropylene or fiberglass cartridge filters may remove organisms as minor as 1 µm in size. Most moulds and yeasts, as well as spores like Bacillus subtilis, fall into this category. Membrane filters for bioburden reduction come in various materials, with pore sizes ranging from 0.85 µm to 0.22 µm [25]. The filter material and pore size will be determined by the type of fluid being filtered, and the size and number of organisms present. If the fluid 234 Tekstilec, 2022, Vol. 65(3), 227–241 contains a more significant number of bacteria, a sub-micron-rated membrane filter with a pore size of 0.65 µm or 0.45 µm will remove the majority of the bacteria [6, 25]. It is crucial to find out how many and what size organisms there are to remove enough to prevent processes and the sterilising filter from being damaged [42]. The final filtration and point of use filtration WFI systems utilising distillation coupled with storage and distribution systems kept at elevated temperatures need no extra filtration since the water has been sterile and is preserved in a sterile state with heat [38, 43]. Due to the multitude of bacterial entry points into the system, the final filtration utilising “sterilising grade” membrane filters is regularly used as the final bacterial removal process in most ambient temperature pharmaceutical water systems [40]. Sterilising grade filters are typically rated to remove at least 100,000 bacterial colonies per ml without passing through to the product side of the filter. Filters not meeting these removal criteria are considered bioburden reduction filters rather than sterilising grade filters [41, 43]. Typical sterilising grade filters utilised in pharmaceutical water systems are rated to remove particles and bacteria that are 0.22 micron or 0.1 µm or larger in size; however, coarser filters are available as well [38, 42]. In the past, the standard was 0.22 µm. Now, one organism (Acholeplasma laidlawii) has been found to pass through these filters; therefore, manufacturers have developed a finer, 0.1-micron filter to remove this organism [42, 45, 46]. To remove endotoxins (cell fragments), ultrafiltration or charge modified filter media are utilised. Pleated nylon 6,6 membrane and single-layer charge modified nylon 6,6 membrane filter cartridge provides superior microorganism reduction while substantially increasing the life of downstream sterilising grade filters. This filter offers enhanced particle and pyrogenic removal via an electrostatic charge on the membrane [46, 47]. 6 Ultrafiltration in pharmaceutical industries Ultrafiltration (UF) is a pressure-driven membrane transport technology that has been used both in the lab and in the industry. UF is used in industries such as chemical and pharmaceutical manufacturing, food and beverage processing, and wastewa- ter treatment to recycle flow or add value to later products [48]. The capacity of UF to purify, isolate and concentrate target macromolecules in continuous systems is its key selling point. Permeate is the solvent and other dissolved components that flow through the membrane. Retentate components are those that do not pass through [49]. UF is a separation technology that allows labile biopolymer streams (proteins, nucleic acids and carbohydrates) to be processed cost-effectively, even on a large scale, without using high temperatures, solvents or other chemicals. Low shear (e.g. positive displacement) pumps can help reduce shear denaturation. Infusion solvents, serum, vaccines and plasma are just a few of the pharmaceutical industry’s products that are manufactured to the highest quality and purity standards [35,50]. UF provides solutions that have been designed to meet the needs of the pharmaceutical and biotechnology industries for a variety of applications [48, 51]. 6.1 Wastewater treatment in pharmaceutical industries with ultrafiltration Ultrafiltration plant for pharmaceutical sector is responsible for water treatment in the pharmaceutical industry [52]. This plant is utilised in the RO prefiltering stage. It helps reverse osmosis membranes by lowering the water’s silt density index and removing particles. UF membranes improve RO performance and are widely utilised in desalination systems, pharmaceutical manufacturing and other industries. UF is a multi-skilled system that gives a reliable solution to wastewater problems or clean, reusable water after a complete treatment. The water produced as a result of this treatment can be used for various reasons. This method has water of such high quality that it can also be used for drinking [29]. UF utilises an air-sourced mechanism and provides excellent performance in the elucidation of wastewater. It addresses water scarcity and other water-related issues in enterprises. These systems are meant to eliminate bacteria and other microbiological debris from the water and meet the needs of enterprises across India [29, 53]. 6.2 Recent and developing application of ultrafiltration Ultrafiltration is becoming a potent separating tool for the constantly expanding biotechnology industry. Cell harvesting, depyrogenation of injectable Filtration in Pharmaceutical Industries and Role of Textile medicines and enzyme purification are only a few examples. UF has a number of advantages over centrifugation when it comes to bacteria collection. Owing to these advantages, UF membranes are less prone to clogging by cells and debris than microporous filters due to their asymmetric nature. Another possible application of UF is plasma product processing [54]. When human plasma is fractionated using the Cohn process or other novel technologies, there is a requirement to concentrate the essential protein fractions (albumin and globulins) or remove alcohol and salt. UF is a convenient way to accomplish this [24, 55]. 7 Selection and options of filter media The heart of any filtration process is considered the filter media. While the solids to be retained are concentrated on the membrane’s feed side, the liquid component is forced to pass through and delivered to the membrane’s other side. A filter medium is not uniform by nature, and its dimensions and geometries are derived from irregular pores. The distribution of these pores on the membrane surface may also be uneven. The microfluidic velocity within the holes can produce considerable changes on the filter surface since the flow in the environment only occurs through the pores [56]. This implies that the top layers of the filter cake created on the membrane surface are not uniform and are shaped by the filter medium’s composition and qualities. The basic structure of the cake is firmly related to the structure of initial layers since the number of channels in the filter cake is greater than the number in the filter media. This indicates that the filter crayon and the filter material influence one another [57]. In the pharmaceutical sector, various types of filters are employed. When it comes to choosing a suitable filter medium, it is worth considering two things. The first is the fluid’s substance, which includes viscosity, the nature of the solids (particle size, shape, size distribution etc.) and the concentration of solids in suspension [42, 44, 46]. The second factor are the equipment and process-related issues, e.g. flow rate, particle size restriction for passing through the filter, sterilisation by heat, radiation or gas, and cost. Solid particles smaller than the narrowest cross-section of the route can be caught by the pores having channels extending along with the filter me- 235 dia. Particle bridging or, in rare situations, physical adsorption is commonly used to explain particle retention. Different filter media are employed depending on the intended use [57–58]. Sand, diatomite, coal, cotton or wool fabrics, fibres, yarn, metal wire cloth, porous quartz plates, chamotte, sintered glass, metal dust and powdered ebonite are some of the most often used filter media [59]. The size and shape of each element from which the filter material is made determine the average pore size and configuration (including tortuosity and connectivity). The average pore size and shape are also influenced by the filter material’s manufacturing procedure. Pore characteristics are also influenced by the fibre qualities of the woven fabric or the sintering procedures used for glass and metal powders [26]. In addition, some filter media, particularly fibrous layers, experience substantial compression when exposed to common pressures used in industrial filtration operations. Under the same operating circumstances, other filter materials such as sintered ceramic plates, glass and metal powders are stable. The filtration/separation process also influences pore characteristics. Since the effective pore size decreases as filtering progresses, flow resistance rises. This is due to the particles penetrating the filter media’s pores. Filtration is a complicated method for separating solid particles from liquid. The larger pore size in comparison to particle size can also be used. However, the chosen filter medium must be able to adsorb solids and have significant enough cohesive forces between the particles to cause particle aggregation around the pore holes [60]. The utilisation of various water filters and common recommendations are given in Table 2. In the chemical and pharmaceutical industry, a belt filter is an industrial machine used for solid/liquid separation processes, particularly sludge dewatering. Filtration is accomplished principally by passing the solid for dewatering from a pair of filtering cloths and belts through a roller system. Filter bags are another option for filtration [8]. Filter bags are composed of felt, which has the advantage of being a three-dimensional filter media that provides both surface and depth filtering. They are available in different sizes and types of filter media with different ratings [25, 40]. Polypropylene filter bags are chemically compatible and can be used in various applications. Polyester filter bags can withstand extreme temperatures and are compatible with acids and petroleum-based fluids. Filter bags 236 Tekstilec, 2022, Vol. 65(3), 227–241 Table 2: Water filter application and recommendation for pharmaceutical industries [2, 6, 21, 28, 48, 61] No. Water filter application Function of filtration Recommended filter media 1 Particulate Reduction and Trap Filtration 2 RO Prefiltration Removal of larger particles and fractured softener or deionisation resin beads before further treatment or use Protect reverse osmosis membranes from premature fouling by removing particles larger than 1 micron in size Polypropylene melt-blown media, nanospun polypropylene media, polypropylene pleated depth media Polypropylene melt-blown media, nanospun polypropylene media, polypropylene pleated depth media Polyethersulfone (PES) membrane – nylon 6,6 membrane, positively charged nylon 6,6 membrane, high capacity hydrophilic (PVDF) membrane, high capacity polyethersulfone membrane 3 Bioburden Reduction Used in water distribution systems to remove larger organisms and protect final filters that remove all bacteria 4 Bacteria Removal, Sterilising Filtration Protect water quality for the patient, consumer or end use; remove all bacteria; may remove viruses and mycoplasma Polyethersulfone (PES) membrane – nylon 6,6 membrane, positively charged nylon 6,6 membrane, 5 Ultra-Fine Particle Removal Prevent sub-micron particles from reaching processes requiring ultra-pure water, such as semiconductor fabrication Polyethersulfone (PES) membrane – nylon 6,6 membrane, positively charged nylon 6,6 membrane. 6 Tank Vent Filtration Prevent airborne bacteria and fine particles from contaminating process or product water as it is held in tanks PTFE membrane, polypropylene membrane, high capacity hydrophobic PVDF membrane are commonly used to prepare adhesives, syrups, fruit juices, petroleum compounds and fluids with high viscosity [6, 25, 61]. Various filter forms used in the filtration system are shown in Figure 3. The filters are cleaned using various methods, including manual, mechanical and self-cleaning filter systems. Cleaning is done manually with a water jet. The filters may need to be soaked in chlorine or detergent on occasion. Brushes or knives are used for a) mechanical cleaning. Disposable trash and labour costs are reduced as a result of automation. Product loss is reduced by using a self-cleaning filter system that requires little user effort. Some examples are magnetically connected industrial filters, self-cleaning filters and tubular backwashing filters, e.g. clearamine and reactogard filters, and piezoelectric ceramic membrane (PCM) [62]. b) Figure 3: Filter forms used in filtration system: a) cartridge of polypropylene and b) carbon filter sheet and cartridge [3, 6, 10, 29, 30] Filtration in Pharmaceutical Industries and Role of Textile 8 Current market of pharmaceutical filtration and impact of COVID-19 According to the latest market research report “Pharmaceutical Filtration Market” published by Markets™, the global Pharmaceutical Filtration Market is projected to reach 29.7 billion USD by 2027 from 10.9 billion USD in 2022, a CAGR of 17.0% during the forecast period of 2022 to 2027 [63]. This growth can be attributed to the growing biopharmaceutical industry, advanced research, increasing adoption of single-use technologies, increasing the new product, high purity requirements in end-user segments and advances in nanofibre technology [25, 63]. The pharmaceutical filtration market covers filters, systems and other filtration products. The filters used in the current time are membrane filters and depth filters. Polyethersulfone (PES), polyvinylidene difluoride (PVDF), nylon, polytetrafluoroethylene (PTFE), mixed cellulose ester & cellulose acetate (MCE & CA), polycarbonate tracked etched (PCTE), polypropylene (PP), cellulose nitrate (CN), regenerated cellulose (RC) are commonly used membranes [9, 25, 40, 63]. COVID-19, a worldwide epidemic, has affected people and businesses in practically every field. It is an infectious disease caused by a new coronavirus that has only recently been discovered [65]. As the World Health Organisation named the COVID-19 outbreak a pandemic, several prominent pharmaceutical and biopharmaceutical businesses ramped up research and production efforts to create and distribute SARS-CoV-2 viral test kits, vaccines and treatments. The pandemic’s economic and social costs have spurred governments worldwide to increase funding for vaccine development and production, resulting in a rise in the use of pharmaceutical filtration products in COVID-19 research and production. Pharmaceutical filtration goods are employed in the production process of vaccines and other therapeutic medications; therefore, demand has increased as government backing, research activities and mass production of vaccines after approvals have increased [9, 64–66]. Removing suspended particles from a fluid medium during vaccine clarification is an important step that affects product recovery and downstream purification. Biopharmaceutical companies are using various filtration techniques and materials to help the downstream process (including filtration and purification) of vaccine production. Merck Millipore 237 has donated USD 0.086 million in research apparatus and supplies to Indonesia’s Eijkman Institute for Molecular Biology to speed up vaccine development. Merck has contributed water purification equipment with integrated reverse osmosis membranes for pretreatment and high performance that generate high-quality type-3 clean water. Pall Corporation, a Danaher subsidiary, has provided syringe filters, membrane filters, air filters, and water filters for vaccine and medicine manufacture, and research and development [9, 63]. In addition, the pandemic has provided possibilities for filtration companies to expand their production facilities. In the pharmaceutical filtration industry, the impact of the coronavirus crisis on supply chains, manufacturing and shipments to consumers has been controllable, with positive organic growth. Short- and medium-term predictability is severely limited and has little impact [62, 63, 66]. 9 Conclusion In the pharmaceutical sector, filtration is a crucial process. There is not a single aspect of the pharmaceutical industry that is not touched by filtration. For the pharmaceutical industry, drinking water, purified water and water for injection are required and obtained by different filtration methods. Despite the negative effects of the COVID-19, the market for pharmaceutical filtrations continues to grow. Textile materials in any form play an important role in the pharmaceutical filtration system. The innovative applications of textile filtration fabrics have been widely accepted in the pharmaceutical industry in the process of separation and purification of liquids. Due to their unique characteristics, textile filtration materials help maintain the high level of separation of particles from the fluids. A variety of filters media made from textile products (fibre, yarn, fabric, pleated polypropylene, charged nylon, polyester, nanofibers etc.) is often used in the filtration systems of pharmaceutical industries. In the pharmaceutical industry, the use of novel technology, new polymeric materials, and commercially available patent filters in bag and cartridge forms results in shorter filtration times and higher product quality. Multimedia filter, carbon filter, resin filter, reverse osmosis, distillation and UV lights may be utilised for contamination and particulate removal, and bacteria control. 238 Tekstilec, 2022, Vol. 65(3), 227–241 References 1. SUTHERLAND, K. Profile of the international filtration & separation industry. Elsevier Science, 2004, 11–67, doi: 10.1016/b978-185617448-0/50004-x. 2. MAJEKODUNMI, S.O., OLORUNSOLA, E.O. 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