Breathable, Antistatic and Superhydrophobic PET/Lyocell Fabric

Breathable, Antistatic and Superhydrophobic PET/Lyocell Fabric Seong Ok Kwon 1, Chung Hee Park 1, Jooyoun Kim, PhD 2 1 Seoul National University, Gwanak Gu, Seoul KOREA 2 Kansas State University, Department of Apparel, Textiles, and Interior Design, Manhattan, KS UNITED STATES Correspondence to: Jooyoun Kim email: jkim256@gmail.com ABSTRACT The objective of this study was to develop a breathable and antistatic superhydrophobic PET/lyocell fabric by simple finishing with polymeric fluorocarbon siloxane. To find an optimum concentration of the finish agent, four different concentrations of fluorocarbon finish agent were applied on three different types of fabrics; lyocell %, PET %, and PET/lyocell blend (50%/50%). Static water contact angle (WCA), shedding angle, and water repellency tests were measured to evaluate the wettability and hydrophobicity of treated fabrics. A PET/lyocell blend fabric treated with 40 g/l fluorocarbon finish agent exhibited superhydrophobic characteristics with WCA of 153.6 and shedding angle of 9.5 resulting from its lowed surface energy and multi-scale roughness. The effects of fluorocarbon finish on fabric moisture regain, electrostatic property, water vapor transmission rate (WVTR), and air permeability were evaluated as parameters for clothing comfort. PET/lyocell blend fabric treated with fluorocarbon exhibited significantly lower static electricity and higher moisture regain than the treated PET fabric. WVTR and air permeability were maintained after the finish. The blended fabric achieved noteworthy combination of antistatic and superhydrophobic properties. The functionality of finished PET and PET/lyocell fabrics, measured by WCA, shedding angle, and water repellency rate, was maintained until 10 washing cycles. Keywords: lyocell, breathable, antistatic, superhydrophobic, washing durability INTRODUCTION Superhydrophobic surface fabrication and its application to water repellent textiles are acquiring growing attention in the outdoor sportswear industry, where the level of water repellency, either as waterproof or water repellent, is tuned for a particular end use of the textile material [1]. Research of wetting behavior on a porous surface originated from Wenzel [2] and Cassie-Baxter [3] in 1940 s. The interest has evolved to the fabrication of superhydrophobic surface, which is often demonstrated by a static water contact angle greater than 150 and a contact angle hysteresis less than 10 [4]. Recently, superhydrophobic textile surface design is being actively studied as a way to impart self-cleaning performance in clothing. Water repellent fabrication can be achieved by a thin layer coating with low surface energy chemicals such as hydrocarbon-based hydrophobes, waxes, methyol compounds [5-6], silicone based polymers [7], and fluorocarbon based polymers [8-10]. Of particular interest in this study is fluorocarbon based water repellent finishing for its excellent water repellency and oil resistance with good adhesion to textile surfaces. To impart the superhydrophobicity on the fabrics, nanoparticles such as SiO 2, TiO 2, ZnO, and CNT [7, 11-14] can be introduced onto textile surfaces to create nano scale roughness in addition to low surface energy. However, application of nanoparticles has potential concerns about biotoxicity. Also, the fabrication process is often timeconsuming, costly, and difficult to be scaled up in large-scale manufacturing. Synthetic fibers such as polyethylene terephthalate (PET) and nylon are most commonly used fibers in active sportswear for their excellent mechanical durability, efficient sweat wicking, and fast drying [15]. However, high static electricity and low moisture regain that are attributed to the hydrophobic nature of synthetic fibers can cause a sense of discomfort, creating electric shock and attracting dust and soils in a dry environment. There was an attempt by Shyr et al. [9] to give PET fabric both the waterrepellency and anti-static property at the same time, and used PET fabric to give water repellency and Journal of Engineered Fibers and Fabrics 46 http://www.jeffjournal.org

antistatic, though the result showed that the antistatic property decreased over the repeated washings. Lyocell is a regenerated man-made cellulose fiber which is produced using N-methylmorpholine-Noxide monohydrate (NMMO) as a solvent for direct dissolution of cellulose [16]. For its mechanical durability, soft hand, and good moisture management properties with the environmental credentials for its biodegradability, biocompatibility, and closed loop manufacturing process [17], the application of lyocell fiber as clothing material is continuously growing. Also, its unique fibril structure [18] helps quickly absorb and wick moisture over a large surface [19], and for such desirable properties, lyocell is often blended with hydrophobic fibers to give moisture absorbency [20]. Due to high crystalline structure in fibrils and rather weak bonding between fibrils, standard type of lyocell fibers have strong fibrillation tendency under mechanical stress especially in the wet state such as scouring and dyeing process [21]. Manufacturing efforts have been made to control the fibrillation by the enzyme treatment as it has been major issue regarding finishing of lyocell fabric. In this study, the unique fibril structure that a lyocell fiber inherently holds was utilized as to make up of a dual level roughness in achieving the superhydrophobic property. It is well known that surface roughness and low surface energy are two governing factors required for superhydrophobic surface. Liu et al. [22] developed superhydrophobic cotton fabric by a simple fluoropolymer foam coating method. This is possible because cotton fabric is made of inherently rough staple fibers and has complex surface structure. Lyocell fiber was thought to provide a higher level of roughness than cotton fiber for its fibrillation tendency, thus making the lyocell fabric an excellent candidate for a substrate for superhydrophobic fabrication. However, most of the superhydrophobic textile studies were conducted with cotton and PET fibers because of their representativeness in industry, and little study was performed with lyocell fabrics, probably due to their relative newness in fiber history. Many of the previous studies focused on fabrication of superhydrophobic textiles and evaluation of functional properties by means of contact angle and roll-off angle measurements; however, few studies evaluated the comfort related properties such as moisture absorption, water vapor transmission rate (WVTR), and antistatic property though wear comfort should be considered as an important subject for clothing materials. In this study, PET and lyocell fibers were used to develop a breathable, antistatic and superhydrophobic textile by simple fluorocarbon finishing. First, the effect of fluorocarbon siloxane finish on water repellency was investigated with the varied finish agent concentrations. Three different fabric blends were used; lyocell %, PET %, and PET/lyocell blend (50%/50%). Secondly comfort properties in terms of air permeability, WVTR, static electricity were evaluated as parameters of clothing comfort. Finally, washing durability of the treated fabric was assessed to examine the feasibility of practical applications. EXPERIMENTAL Materials % PET fabric made of PET filament, % lyocell fabric (TENCEL ) made of lyocell spun yarn, and PET/lyocell blend (50%/50%) fabric made of PET filament in warp and lyocell spun yarn in weft were used (Shinjintex, Korea). Fabrics were received as bleached and enzyme finished. Specifications of the fabrics are given in Table I. To remove any insoluble impurities, fabrics were prepared by soxhlet extraction in a 2:1 mixture of benzene and ethanol for eight hours. Although it is desirable to have the same count yarns for lyocell and PET for the convenient comparison, the finest available lyocell yarn was twice as coarse as the PET yarn used; due to the availability of the yarn size, the fabrics with different yarn sizes were used in the experiments. Therefore, the comparison between % lyocell and % PET should be made with limitation. P PET % L Lyocell % TABLE I. Specifications of the fabrics. Code Fiber Content Yarn & fiber Count/ warp and weft, 5.6 tex yarn with 0.4dtex filaments DTY warp and weft, 11.8 tex yarn (Ne60) with 0.9dtex staple fiber No. of Warp Weft (cm2) Weight (g/m2) 67 47 74.5 0.12 55 41 109.6 0.184 warp: PET 5.6 tex yarn with 0.4dtex filament DTY, P/L PET 50% /Lyocel 67 39 91.4 weft: lyocell 11.8 tex yarn (Ne60) with 0.9dtex staple fiber Note: DTY indicates drawn textured yarn. Thickness (mm) As water repellent finishing agent, Nuva TTC (Clariant AG, Switzerland) was used. The chemical structure of the polymeric fluorocarbon siloxane is shown in Figure 1. The proprietary chemical consists of 8 % of the fluorocarbon siloxane, 70% water, and 22% of additives including resin, binder, and surfactants. 0.195 Journal of Engineered Fibers and Fabrics 47 http://www.jeffjournal.org

FIGURE 1. Chemical structure of the polymeric fluorocarbon siloxane, Nuva TTC: X indicates a functional group prescribed by the supplier. Water Repellent Finishing Fabrics were treated with Nuva TTC at four different concentrations by a laboratory scale paddry-cure process. 25 cm 30 cm size fabrics were soaked in a bath containing 10 g/l, 20 g/l, 30 g/l and 40 g/l of the finishing agent respectively at ph around 5 adjusted by addition of acetic acid. After the immersion, fabrics were padded through two rollers at 19 rpm and 4 bar, dried at 110 C, and then cured at 170 C for 40 seconds. The pick-up rate was 40% for PET and 85% for lyocell and PET/lyocell blends. Surface Morphology Dimension of fibrils in lyocell fabrics and morphological changes after finishing was observed by field-emission scanning electron microscope (JSM-7600, JEOL, Japan) operating at 5kV accelerating voltage. The energy dispersive X-ray spectrometer (Aztec, Oxford Instrument, UK) was conducted for surface elemental analysis of the specimens. Water Repellent Properties Static Water Contact Angle: Static water contact angle was measured using Theta Lite (Attension, BiolinScientific, Sweden) at room temperature. The fabric sample was mounted on a slide glass and placed on the sample stage. For each measurement, 3.5±0.5 μl drop of deionized water was placed on different spots of fabric surface, and the contact angle was measured after 5 seconds. Shedding Angle: The angle at which a 12.5 ± 0.1 μl size water droplet rolls off in 2 cm-distance or greater on the substrate was measured as shedding angle. The distance between the syringe tip and the fabric was fixed at 1 cm [23]. All measurements for the contact angle and the shedding angle were conducted at five different spots in specimen, and the average of five measurements was used. Water Repellent Rating: According to the AATCC test method: 22-2010 spray test standard [24], surface wetting resistance levels were rated as 0, 50, 70, 80, 90, and grades. The highest rating indicates no wetting of the specimen, while 0 indicates the complete wetting of the entire face of the specimen. Three readings for each specimen were taken separately. Comfort Properties Moisture Regain: Moisture regain of pristine and fluorocarbon treated fabrics was measured. Fabric weight, after placing the specimen at 20 C, 65% RH for 24 hours, was measured as conditioned weight; also, dry weight of fabric was measured after placing the specimen into an oven for 24 hrs at C. The moisture regain was obtained as in the following. (1) Air Permeability: Air permeability was measured in accordance with ASTM: D737-75 [25], by the Frazier differential pressure air permeability tester (FX3300, Switzerland), where the air permeability is expressed as the quantity of air in cubic centimeters, passing through a square centimeter of fabric per second (cm 3 /sec cm 2 ). Fabric specimens were conditioned for 24 hours at 20±2 C, 65±5% RH prior to testing. The average of five measurements was used for comparison. Water Vapor Transmission Rate (WVTR): The rate of water vapor transmission through the fabric, expressed in unit of g/m 2 24h, was determined using a dish assembly according to ASTM E96-80 [26]. A test specimen with a diameter of 7 cm was placed on a cup containing 33 g of anhydrous calcium chloride with an air gap of 3 mm in a conditioned chamber at 40±2 C, 90±5% RH for one hour for conditioning and another one hour for measuring the weight change. The average of three readings was taken for each specimen. Antistatic Property: Electric potential was measured by JIS L1094 [27], rubbing the specimen against cotton and wool fabric respectively for 60 seconds at the speed of 565 cm/sec by the Kyodai Kagen type rotary static tester (Koa Shokai Co., Ltd., Kyoto, Japan). The average of six readings, three in warp direction and three in weft direction, were recorded. Journal of Engineered Fibers and Fabrics 48 http://www.jeffjournal.org

P Washing Durability of the Finish To assess the fastness of finishing, ten laundering cycles were carried out in a drum washing machine (SEW-5HW146A, Samsung, Korea) at 30 C. 40 g/l of detergent (Persil, USA) concentration was used, as recommended by the manufacturer. Each washing cycle ran for 36 min, followed by 20 min of rinsing and spin-drying. Static water contact angle and water repellency grade were measured after washings to evaluate the change in surface hydrophobicity of the treated fabrics The EDS results in Figure 3 revealed that the untreated P/L fabric consists of only C and O whereas 40 g/l fluorocarbon treated P/L fabric contained 0.43% of fluorine on the surface. The results confirm that the fluorocarbon chemical is chemically bonded to the fabric surface. RESULTS AND DISCUSSION Surface Characterization Surface morphology of lyocell (L), PET/lyocell (P/L) and PET (P) fabrics after 40g/L water repellent finish is presented in Figure 2. Fibrils on lyocell fibers were found in both L and P/L fabrics. On the other hand polyester fiber surface was smooth and clean. The treated polyester fabric had partially coagulated fibers. The physical presence of fluorocarbon polymer on the fibers had little influence on the interyarn spaces of the fabric. The size of lyocell fibrils ranged from 210 nm to 2 µm and the diameter of lyocell fibers were measured as 8.8-9.5 µm. Although the geometric feature of roughness differ between lotus leaf and the fibrillated lyocell fibers, the level of roughness on lyocell fibers are quite similar to that of lotus leaf which has 200 nm to 1 µm of fine scale bumps on the coarse scale asperities (~20 µm) [28]. Fibrillated lyocell could have substantially rougher surface than cotton and the PET fibers (3.7±0.5 µm). FIGURE 2. Surface morphology of lyocell, PET/lyocell and PET observed by SEM; 40 g/l fluorocarbon treated ( 1,000 magnifications). FIGURE 3. Surface chemical composition of PET/lyocell before (above) and after 40 g/l fluorocarbon treatment (below). Water Repellent Properties Wetting Properties: In Figure 4, wetting behavior of untreated and treated for three types of fabrics were observed. Untreated fabrics for all P, L, and P/L were completely wet within five sec. It is interesting to note that, when a water drop was placed onto a specimen, different shapes of water droplets were observed for untreated P, L, and P/L; that is, water drop on L hardly formed the spherical shape, exhibiting very low contact angle upon contact. The water drop was absorbed and wet very swiftly through L for the fabric s high water absorption capacity. However, water repellentfinished fabrics held a water droplet for more than 30 min without causing wicking regardless of fiber types, confirming effectiveness of the finish. Journal of Engineered Fibers and Fabrics 49 http://www.jeffjournal.org

FIGURE 4. Wetting behavior of P, L, and P/L with 40 g/l of fluorocarbon treatment. Figure 5 shows the effect of repellent concentration on static water contact angle on substrates. L showed the lowest contact angle among the fabric types tested, in less than 140 whereas it required higher concentration of the finishing agent (40 g/l) to obtain the same level of contact angle for P and P/L (10~20 g/l). It was speculated that because of the hydrophilic nature of lyocell fiber and more porous structure of tested fabric, % lyocell required greater amount of finishing agent to be equally effective on the fabric surface as P or P/L. For all fabrics, 10 g/l fluorocarbon treatment significantly increased the contact angle compared to that of untreated specimens. Interestingly, repellent treated P/L showed the highest level of hydrophobicity measured in static contact angle (144.0 ~153.6 ); this is higher than PET treated for all fluorocarbon chemical concentrations. The contact angle of hydrophobic fabric surface can be predicted by the following formula developed by Cassie-Baxter [3] and modified by Michielsen [29] and Marmur [30]. (2) R, R+d of P estimated from the SEM image projection was 30 and 53 µm, respectively, giving the estimatedθ CB as 141 ; and this estimated value matched with the actual measurement. However, the estimated WCAs for P/L and L were not well fit with the actual measurements; measured WCA of P/L was considerably higher (153 ) than the predicted value (137 ) based on R (42 µm), R+d (60 µm). It seemed that multi-scale roughness of the blended fabric that had fibrillated lyocell fibers and DTY PET yarns contributed to the surface hydrophobicity. % Lyocell, with R and R+D being 52 µm and 140 µm respectively, showed lower actual WCA (140 ) than the predicted value (149 ) probably due to the fact that porous structure of L resulting from the low fabric density (Table I) affected the wettability. L and P/L showed gradual increase of hydrophobicity with the increased amount of fluorocarbon finish agent while it was rather steady for PET. It is speculated that in the presence of lyocell fibers, the fluoro chemical is absorbed more into the fibers, enhancing repellency with the increased concentration of finish agent. Both L and PET did not achieve higher contact angle than 140 even at the highest concentration. FIGURE 5. Static water contact angle with fluorocarbon treatment concentrations. Shedding angle, as another indicator of surface hydrophobicity, is presented in Figure 6. P/L exhibited the lowest shedding angle of the tested fabrics. When P/L was treated with 40 g/l agent, the contact angle and shedding angle were 153.6±2.1 and 9.5±0.5 respectively, fulfilling superhydrophobic characteristic [29-31]. P/L, with filaments and staple fibers in different sizes, would have held a higher level of micro scale roughness at the surface, contributing to the enhanced hydrophobicity and lowered shedding angle. It is interesting to note that P showed the highest shedding angle around 20 among the treated fabrics, indicating the lowest level of hydrophobicity. The implication given by the shedding angle result differs from that given by WCA, where P showed slightly higher contact angle than L. It is speculated that the surface roughness contributes more to the shedding angle than to the static contact angle. Though both WCA and shedding angle serve as indicators for surface hydrophobicity, WCA measurement may not well represent the roll-off effect or self-clearing characteristics. Based on the WCA (Figure 5) and Journal of Engineered Fibers and Fabrics 50 http://www.jeffjournal.org

shedding angle results (Figure 6), 40 g/l treatment which showed the highest hydrophobicity was chosen for further evaluation of comfort related properties and washing durability. FIGURE 6. Shedding angle with fluorocarbon treatment concentrations. Comfort Properties Moisture Regain Moisture regain of lyocell and PET is known to be 11% and 0.4% from the literatures [32, 33]. The results (Figure 7) are in good agreement with the literature data. From the test result to see effect of blending and fluorocarbon treatment on moisture regain of the fabric, it was revealed that blended fabric possessed average moisture regain of P and L. Moisture regain of P, L, P/L was 0.4%, 9.9% and 4.8% respectively. After WR treatment the moisture regain was reduced by around 24%-37%. It is noteworthy that P/L kept 13 times higher moisture regain than PET and maintained the level of moisture regain difference even after the fluorocarbon treatment. The results are meaningful as it proves that a fabric containing hydrophilic fibers can maintain its hygroscopic property by attracting water molecules into the fibers even after the fabric become totally repellent to liquid water. TABLE II. Water repellency rate with different repellent concentrations. P L P/L Untreated 10 g/l 20 g/l 30 g/l 40 g/l 0 0 0 0 50 50 80 0 50 90 70 0 50 80 90 90 0 0 0 Water Repellent Rating To evaluate the fabric water repellency, a spray test was performed as a quick visual assessment of fabric resistance to wetting. Table II presents three measurements of untreated and treated fabrics, where the treated P and P/L showed significantly higher water repellency grades than those of treated L. P and P/L exhibited grade at 10 g/l finishing concentration. By contrast, L gave the rating of 50 grade at 10 g/l, and improved the water repellency with the increased concentration, reaching grade at 40 g/l. The water repellency rating presented the similar information as the contact angle results, confirming that L required higher amount of repellent agent to achieve the same level of water repellency as P and P/L. At the same amount of fluorocarbon treatment, it is speculated that L would have thinner layer of fluorocarbon material on the surface than P because of high absorbency and porosity of the fabric. P/L showed the same level of water repellency for all concentration as P. FIGURE 7. Effect of fluorocarbon treatment on moisture regain of the fabrics Antistatic Property Static charge on fabrics can create an unpleasant experience in dry environment, making fabrics cling to the body, generating electric shock, and attracting dust [34]. Charge can be generated when fabrics are rubbed against each other and the electrons transfer between layers. When fabrics that do not conduct electricity well, a discharge can occur to generate electric shock or spark. From a charge of 1,800 V and higher, a noticeable spark can appear [35]. As another comfort parameter of clothing materials, static electric charge was evaluated by JIS L1094 method using cotton and wool as the counterpart fabrics rub against the treated specimens [27]. From Figure 8, P presented electrical charges from 714~1,226 V while L generated 38~63 V. The static electric charge of P/L was 123~263 V. The fluorocarbon treatment hardly affected the antistatic Journal of Engineered Fibers and Fabrics 51 http://www.jeffjournal.org

property. The static charge of P was measured unstable and had large deviation in measurements. The static charge in this test can be influenced by two factors; moisture regain or conductivity of a fiber and the contact potential difference between the fabric of interest and the rubbing fabric (for example, L vs. wool). The contact potential difference between P and cotton is smaller than that between P and wool, which would result in smaller static charge creation of P on cotton than P on wool [36]. In both case, P will be negatively charged and the rubbing fabrics will be positively charged creating high static charge after rubbing. Polyester fiber has high surface-resistivity over 1 10 5 (Ω) and it takes 2,600 sec to decrease the resistance by 50% [37] because P has only 0.4% of moisture regain. On the other hand, L generated significantly lower static charge when rubbed by cotton or wool. This is because high moisture content in the L fabric acts as an electric conductor dissipating the static in less than 0.05 sec. to outside in exchange of air [38]. This property is influenced by the fabric structure such as fiber cohesion, yarn structure, fabric construction, thickness, density, and porosity. In Figure 9, the air permeability of L was considerably larger than that of P or P/L, probably due to the lower fabric density of L (55 41 in cm 2 ) over those of P (67 47 in cm 2 ) and P/L (67 39 in cm 2 ) and more pores existing in L fabric consisted of staple fibers. For the same reason, P/L showed relatively higher air permeability than P. Air permeability after the repellent finishing equaled or slightly exceeded in P and P/L. However, air permeability slightly decreased in L fabric after repellent treatment. While P/L is equally blended 50/50, the static charge was much closer to that of L. The effectiveness static charge reduction of P/L (50/50) can be attributed to higher moisture regain of P/L than P. The presence of hydrophilic L helped reducing the static charges considerably, with and without repellent finish. Static charge of P was 18-20 times higher than L and 5 times higher than P/L. This will cause a big difference in comfort when the garments are worn in a dry environment. FIGURE 9. Effect of fluorocarbon treatment on air permeability. FIGURE 8. Effect of fluorocarbon treatment on static electricity against cotton and wool. Air Permeability Air permeability is regarded as an important parameter for thermal comfort when heat and perspiration are generated from body and transferred Water Vapor Transmission Rate (WVTR) Water vapor transmission of fabric is another factor to gauge the clothing comfort, especially during the vigorous activities under hot climatic conditions. A textile with low WVTR can give an unpleasant feeling as the perspiration from the body is limited to pass through the clothing. In Figure 10, all fabrics showed WVTR higher than 5,000 g/m 2 24h, and WVTR after repellent finish was not decreased, as the similar observation was reported in the earlier literature [39]. It was reported that a vigorously exercising person produces an average of 2,880 g/m 2 24h perspiration at 20 C [40]. The fabrics treated in this study can be regarded as comfortable in a high-pace working condition at 30 C. Journal of Engineered Fibers and Fabrics 52 http://www.jeffjournal.org

Water vapor transmission through the fabric can occur by two mechanisms [41]; 1) water vapor transmits through pores, 2) water vapor gets absorbed by the fabric then is evaporated from the fabric surface. In other words, WVTR is influenced by both the fabric pores that can be presented by air permeability, and the hydrophilicity of the fiber. From Figure 10, the difference of WVTR between P and L was much smaller than what was shown in air permeability (Figure 9). It can be concluded that the water repellent finish allowed water vapor to be transmitted through the fabric while effectively preventing liquid water penetration. FIGURE 11. Static contact angle and shedding angle after 10 washing cycles: fabrics treated with 40 g/l fluorocarbon chemical. Because of the lower fabric density for L over P and P/L, L fiber surfaces may experience more physicochemical and mechanical actions during washing, allowing faster elimination of repellent coating. While L showed the deteriorated hydrophobicity after repeated washing, P/L maintained the superhydrophobic characteristic even after 10 washing cycles. It is inferred that there is an optimal surface structure in roughness and fabric density that can maintain the high level of hydrophobicity with repeated washing. FIGURE 10. WVTR with fluorocarbon treatment concentrations. Washing Durability of the Finish Figure 11 showed the static contact angle before and after 10 cycles of washing. P and P/L maintained the high contact angle after 10 washing cycles, while L showed deterioration of hydrophobicity after washing. From Table III, the water repellency rating of P/L was not affected by the washing process while that of L was severely deteriorated. The fluorinated polymers with long perfluorinated side chains undergoes side-chain crystallization upon curing to form a tight packing on top of the surface layer allowing water repellency. When the treated fabric gets agitated in detergent solution, the side chains at the top layer could get more mobility and undergo partial disorientation, possibly deteriorating the water repellent property [42, 43]. TABLE III. Water repellency rating with 10 washing cycles for the fabrics treated with 40 g/l fluorocarbon chemical. Specimen P L P/L Before washing 90 After 10 washing cycles 90 90 70 80 70 CONCLUSION Water-repellency is generally considered to be incompatible with the hygroscopic property and antistatic property. Superhydrophobic or water repellent surface must have low surface energy in order to provide the water-repellency for the textiles. Journal of Engineered Fibers and Fabrics 53 http://www.jeffjournal.org

Conventional water-repellent polyester fabrics are not hygroscopic and tend to generate a serious amount of static electricity. It is challenging to impart a textile with excellent water-repellency, hygroscopic property and antistatic property at the same time. In this study, P, L, and P/L were treated with polymeric fluorocarbon siloxane by pad-dry-cure process to produce superhydrophobic water repellent and having antistatic property. Among three fabric types, the highest level of water repellency, represented in static contact angle, shedding angle, and water repellent grade, was achieved from P/L. For P/L, the highest static contact angle of 153.6 and lowest shedding angle of 9.5 were obtained with 40 g/l of concentration of fluorocarbon finishing. Superhydrophobicity was achieved by the multi-scale roughness inherently present in P/L fabric. The treated P/L fabric exhibited 4% of moisture regain with the improved antistatic property; that is, treated P/L showed 13 times less static electric charges compared to that of water repellent polyester fabric. The comfort properties, evaluated by air permeability, WVTR were not deteriorated after the water repellent treatment. The superhydrophobic P/L was durable for washing up to 10 washing cycles, while finishing of L was not as durable as those. This study demonstrated a benefit of blending lyocell with PET in fabricating a superhydrophobic fabric without compromising comfort properties much, by the simple finishing process of polymeric fluorocarbon siloxane. ACKNOWLEDGMENT This research was supported by the SRC/ERC program of MOST/KOSEF [R11-2005-065] and National Research Foundation of Korea (NRF) Grant funded by the Korean Government [2011-0014765]. REFERENCES [1] Ozcan, G. Performance evaluation of water repellent finishes on woven fabric properties, Textile Research. Journal, 2007, 77(4), 265-270. [2] Wenzel, R.N. Resistance of solid surfaces to wetting by water, Industrial Engineering Chemistry, 1936, 28(8), 988-994. [3] Cassie, A.B.D.; Baxter, S.S. Wettability of porous surfaces, Transaction of Faraday Society, 1944, 40, 546-551. [4] Zhao, Y. et al. Superhydrophobic cotton fabric fabricated by electrostatic assembly of silica nanoparticles and its remarkable buoyancy, Applied Surface Science, 2010, 256(22), 6736-6742. [5] Bullock, J.B.; Welch, C.M. Cross-linked silicone films as wash-wear, water-repellent finishes for cotton, Textile Research Journal, 1965, 35(5), 459-471. [6] Abo-Shosha et al. Paraffin wax emulsion as water repellent for cotton/polyester blended fabric, Journal of Industrial Textiles, 2008, 37(4), 315-325. [7] Roe, B.; Zhang, X. Durable hydrophobic textile fabric finishing using silica nanoparticles and mixed silanes, Textile Research Journal, 2009, 79(12), 1115-1122. [8] Castelvetro, V. et al. Evaluating fluorinated acrylic lattices as textile water and oil repellent finishes, Textile Research Journal, 2001, 71(5), 399-406. [9] Shyr, T.W.; Lien, C.H.; Lin, A.J. Coexisting antistatic and water-repellent properties of polyester fabric, Textile Research Journal, 2011, 81(3), 254-263. [10] De, P. et al. UV-resist, water-repellent breathable fabric as protective textiles, Journal of Industrial Textiles, 2005, 34(4), 209-222. [11] Xu, L. et al. Fabrication of superhydrophobic cotton fabrics by silica hydrosol and hydrophobization, Applied Surface Science, 2001, 257, 5491-5498. [12] Zhao, Y. et al. Superhydrophobic cotton fabric fabricated by electrostatic assembly of silica nanoparticles and its remarkable buoyancy, Applied Surface Science, 2010, 256, 6736-6742. [13] Yeeyee, K.; Yuyang, L.; John H.X. Fabrics with self-adaptive wettability controlled by light-and-dark, Journal of Materials Chemistry, 2011, 21, 17978-17987. [14] Shim, M.H.; Kim, J.; Park, C.H. The effects of surface energy and roughness on the hydrophobicity of woven fabrics, Textile Research Journal, 2014, online first publication, doi: 10.1177/0040517513495945. [15] Troynikov, O.; Wardiningsih, W. Moisture management properties of wool/polyester and wool/bamboo knitted fabrics for the sportswear base layer, Textile Research Journal, 2011, 81(6), 621-631. Journal of Engineered Fibers and Fabrics 54 http://www.jeffjournal.org

[16] Rosenau, T. et al. The chemistry of side reaction and by product formation in the system NMMO/cellulose (Lyocell process), Progress in Polymer Science, 2001, 26, 1763-1837. [17] Široký, J. et al. Attenuated total reflectance Fourier-transform Infrared spectroscopy analysis of crystallinity changes in lyocell following continuous treatment with sodium hydroxide, Cellulose, 2010, 17(1), 103-115. [18] Abu-Rous, M. et al. New method to visualize and characterize the pore structure of TENCEL (Lyocell) and other manctionmade cellulosic fibres using a fluorescent dye molecular probe, Journal of Applied Polymer Science, 2007, 106(3), 2083-2091. [19] Männer, J. et al. Higher performance with natural intelligence, Lenzinger Berichte, 2004, 83, 99-110. [20] Firgo, H.; Suchomel, F.; Burrow, T. TENCEL high performance sportswear, Lenzinger Berichte, 2006, 85, 44-45. [21] Nemec, H. Fibrillation of cellulosic materials- Can previous literature offer a solution?, Lenzinger Berichte, 1994, 74, 69 72. [22] Liu, Y.; Xin, J.H.; Choi, CH. Cotton fabrics with single-faced superhydrophobicity, Langmuir, 2012, 28, 17426-17434. [23] Zimmermann, J.; Seeger, S.; Reifler, F.A. Water shedding angle: A new technique to evaluate the water-repellent properties of superhydrophobic surfaces, Textile Research Journal, 2009, 79(17), 1565-1570. [24] AATCC 22-2010, Water repellency spray test standard (2010). [25] ASTM D737-75, Standard Test Method for Air Permeability of Textile Fabrics (2012). [26] ASTM E96, Standard Test Method for Water vapour transmission of materials (2010). [27] JIS L1094, Testing methods for electrostatic propensity of woven and knitted fabrics (2008). [28] Neelesh, A.P. Mimicking the lotus effect: Influence of double roughness structures and slender pillars, Langmuir, 2004, 20, 8209-8213. [29] Michielsen, S.; Lee, H.J. Design of a superhydrophobic surface using woven structures, Langmuir, 2007, 23, 6004-6010. [30] Marmur A. Wetting on hydrophobic rough surfaces: To be heterogeneous or not to be?, Langmuir, 2003, 18, 8343-8348. [31] Wang, S.; Jiang, L.; Definition of superhydrophobic states, Advances Material, 2007, 19(21), 3423-3424. [32] Li, X.M.; Reinhoudt, D.; Crego-Calama M. What do we need for a superhydrophobic surface? A review on the recent progress in the preparation of superhydrophobic surfaces, Chemical Society Review, 2007, 36, 1350-1368. [33] Bravo, J. et al. Transparent superhydrophobic films based on silica nanoparticles, Langmuir, 2007, 23(13), 7293-7298. [34] Okubayashi, S.; Griesser, U.J.; Bechtolda, T. A kinetic study of moisture sorption and desorption on lyocell fibers, Carbohydrate Polymers, 2004, 58, 293 299. [35] Sanders, E.M.; Zeronian, S.H. An analysis of the moisture-related properties of hydrolyzed polyester, Journal of Applied Polymer Science, 1982, 27(11), 4477 4491. [36] Li, C. et al. Improving the antistatic ability of polypropylene fibers by inner antistatic agent filled with carbon nanotubes, Composites Science and Technology, 2004, 64(13), 2089-2096. [37] Wilson, N. Static Electricity and Textiles, Shirley Institute, 1987, 18. [38] Ballou, J.B. Static electricity in textiles, Textile Research Journal, 1954, 24, 146-155. [39] Wilson, D. The electrical resistance of textile materials as a measure of their anti-static properties, Journal of the Textile Institute, 1963, 54(3), T97-105. [40] Lee, S.W.; Cho, K.S.; Choi, J.H. Clothing and Environment, 7 th ed., Korea National Open University Press, Seoul, 2003, 97. [41] Bagherzadeh, R. et al. Evaluation of comfort properties of polyester knitted spacer fabrics finished with water repellent and antimicrobial agent, Fibers & Polymers, 2007, 8(4), 386-392. [42] Yoo, S.J.; Kim, E.A. Assessment techniques of waterproof breathable fabrics, Fiber Technology and Industry, 2004, 8, 271-285. [43] Lee, S.; Obendorf, S.K. Statistical modeling of water vapor transport through woven fabrics, Textile Research Journal, 2012, 82(3), 211-219. [44] Schindler, W.D.; Hauser, P.J. Chemical Finishing of Textiles, Cambridge, Woodhead Publishing Ltd, UK, 2004, 81. [45] Guo, J. et al. Alternative fluoropolymers to avoid the challenges associated with perfluorooctanoic acid, Industrial & Engineering Chemistry Research, 2008, 47(3), 502-508. Journal of Engineered Fibers and Fabrics 55 http://www.jeffjournal.org

AUTHORS ADDRESSES Seong Ok Kwon Chung Hee Park Seoul National University 1 Gwanak ro Gwanak gu, Seoul 151-742 KOREA Jooyoun Kim, PhD Kansas State University Department of Apparel, Textiles, and Interior Design 220 Justin Hall Manhattan, KS 66506 UNITED STATES Journal of Engineered Fibers and Fabrics 56 http://www.jeffjournal.org