Removal of spandex from nylon/spandex blended fabrics by selective polymer degradation

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1 Original article Removal of spandex from nylon/spandex blended fabrics by selective polymer degradation Textile Research Journal 84(1) 16 27! The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalspermissions.nav DOI: / trj.sagepub.com Yunjie Yin 1,2, Donggang Yao 1, Chaoxia Wang 2 and Youjiang Wang 1 Abstract As the use of fabrics containing spandex for apparel applications is expanding, developing eco-friendly technologies to recycle the industrial as well as post-consumer waste for spandex blended fabrics becomes increasingly important. As is known in the industry and demonstrated in this study, spandex may be removed from blended fabrics by dissolving it in solvents such as N,N-dimethylformamide, but the use of such solvents is undesirable for economical and environmental reasons. The main focus of this study was to develop an alternative process for removing the spandex component in a nylon/spandex blended fabric (NSBF) by selective degradation so that the nylon component can be recovered for recycling. In this process, the fabric first underwent a heat treatment step, followed by a washing process. For the heat treatment, the effect of temperature, water-to-fabric ratio, and pressure were studied. Treatment at 220 C for 2 hours under atmospheric pressure was found to be very effective, allowing the degraded spandex residues to be readily washed off in ethanol, while the nylon component retained its original morphology. With the removal of spandex in NSBF, a decrease in -CON- absorption peaks in the Fourier transform infrared attenuated total reflectance spectra of the fabrics was observed. Keywords Waste recycling, selective degradation, blended fabrics, spandex, nylon 6 Spandex fibers exhibit superior stretch and elastic recovery ability, providing garments containing spandex fibers with good fitting and comfort characteristics. 1 3 The elongation to break of spandex fibers is typically over 200%, and more often in the range of %. Upon releasing the deforming stress, the fiber returns quickly to its original shape. 4 Because of their superior extensibility, elasticity, wrinkle recovery, dimensional stability, and simple care, fabrics containing spandex fibers find a wide range of applications, especially in garments such as sport cloths and swimwear. 4 6 However, the deficiencies of spandex in chemical resistance and temperature stability have to be managed during garment manufacture and wear to avoid excessive fiber degradation and loss of elasticity. 7,8 Nylon filaments, with good strength and chemical resistance but lower extensibility, are often combining with spandex to make blended fabrics that overcome the disadvantages associated with using one type of material on its own. Polymer waste consisting of a single type of nylon can be recycled into various products, such as automotive parts, and the recycling rate for such waste is quite high. However, waste of polymer blends is often discarded or incinerated unless the components can be economically separated. As the use of fabrics containing spandex for apparel applications is expanding, 1 School of Materials Science & Engineering, Georgia Institute of Technology, USA 2 Key Laboratory of Eco-Textile, Ministry of Education, School of Textiles and Clothing, Jiangnan University, China Corresponding author: Youjiang Wang, Georgia Institute of Technology, 801 Ferst Drive, Atlanta, GA 30332, USA. [email protected]

2 Yin et al. 17 the waste disposal problem for the garment manufacturing process as well as post-consumer textiles needs to be addressed. Nylon in a nylon/spandex blended fabric (NSBF) represents the main component, whereas spandex represents a small portion in NSBF. It is therefore logical to focus on the recovery of nylon from NSBF waste so as the recovered nylon can be processed into engineered plastics by melt processing or into virgin-quality monomers by depolymerization, if nylon can be recovered from the waste steam with reasonable purity. Currently, there is no suitable technology to recycle NSBF waste other than by solvent extraction using, for example, N,N-dimethylformamide (DMF). Although solvent extraction of spandex from NSBFs with DMF or N,N-dimethylacetamide (DMA) is technically feasible, environmental and economic concerns limit its use in commercial applications. The spandex fiber is usually produced by the dry spinning process, in which the polymers are prepared via polytetramethylene glycol (PTMG) with -CONend-groups reacting with diamine in DMF or DMA. 9 Spandex is a polyurethane polyurea copolymer, 8,10,11 in which the polyurea component synthesized from diisocyanate and diamine contains a urea linkage that is easier to depolymerize than the amino linkage in nylon by hydrolytic actions Therefore, in this study the main focus is to find conditions that selectively degrade spandex by hydrolysis without significantly affecting the nylon component. A reaction chamber capable of heating water to 250 C was used for the heat treatment of NSBF, and the process variables studied included temperature, water-to-fabric ratio (WFR), and pressure. After the heat treatment, the treated fabrics were washed with solvents such as water, ethanol, and acetone. Direct solvent extraction of spandex from NSBF was also carried out to determine the mass ratio of spandex as well as to demonstrate its feasibility for recycling NSBF. Experimental details Materials NSBF (223.8 g/m 2, knitted, brown), nylon 6 (polyamide 6) fiber and spandex fiber obtained from Aquafil USA, Inc., were used in this experiment. Ethanol, acetone, and DMF were analytical reagent grade and supplied by Sigma-Aldrich Co. LLC. Solvent extraction of spandex Nylon, spandex, and NSBF samples were pre-washed with deionized water, and then dried at 50 C for 24 h. Samples containing 2 g of fibers or fabric were treated in DMF solvent (40 g) at 70 C for 4 h. After washing with deionized water and drying at 50 C for 24 h, the samples were weighed and the weight losses were calculated. Heat treatment A pressure vessel is needed in order to heat liquid water to a temperature range of C. In this study, a simple pressure vessel was constructed to be used with a 4-ton press, as illustrated in Figure 1. The press controlled the heating profile of the test vessel, which had a cavity of 10 cc. NSBF and fiber samples were washed with deionized water, and then dried in a vacuum dryer at 60 C for 24 h to allow for accurate measurement of sample weights. The stainless steel reaction chamber was first heated to the preset temperature, and then the pre-washed fabric sample was placed in the reaction chamber with predetermined amount of deionized water. The WFR varied from 0 to 4, and the test chamber was either closed or open during the heat treatment, as follows. 1. WFR ¼ 4: the chamber was filled with water after placing the samples inside to obtain an approximate Figure 1. Schematic of test apparatus for heat treatment.

3 18 Textile Research Journal 84(1) WFR of 4:1. The valve was closed during heat treatment to allow internal pressure to build up as the vessel was heated. 2. WFR ¼ 1: 2 g of water was added to the chamber after placing a 2 g fabric sample inside, and the valve was closed during heat treatment. 3. WFR ¼ 0 (Closed): no water was added to the chamber after placing the samples inside, and the valve was closed during heat treatment. 4. WFR ¼ 0 (Open): no water was added to the chamber after placing the samples inside, and the valve was kept open during heat treatment, at atmospheric pressure. After a series of extensive trials with different temperatures and time durations, a temperature range of C was selected in this study, and the treatment duration was kept at 2 h, which included time needed to bring the test vessel to the desired temperature. Figure 2 shows the internal pressure profile during the test when no water was added and the chamber was closed. The internal pressure directly correlated with the actual temperature inside the chamber. For an ideal gas in an enclosed chamber, the pressure is related to the temperature change by the ideal gas law. Starting from room temperature (T 1 ) and atmospheric pressure (P 1 ), the internal pressure P 2, measured by gage pressure, should increase with the internal temperature T 2 as follows: P 2 ¼ P 1 ðt 2 =T 1 1Þ ð1þ At 200 C (473 K), the internal pressure is expected to rise to 0.6 atm (61 kpa). This value was much lower than what was actually observed (441 kpa) for testing NSBF under the WFR ¼ 0 (Closed) condition, due to the presence of moisture in the chamber. Although no water was added to the chamber under the last two conditions, the fiber/fabric samples were expected to contain some moisture at the beginning of the test due to moisture regain. Sample cleaning after treatment After the fiber/nsbf sample was heat treated, it was weighed and washed at 60 C for 30 min with magnetic stirring in 40 ml water, ethanol, or acetone, respectively. The treated fabric sample was then washed with deionized water three times before it was dried at 60 C for 24 h for further testing. Characterization The treated fiber and fabric samples after washing and drying were analyzed for weight loss and change in appearance using an optical microscope. A Thermo Nicolet Nexus Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectrophotometer (Thermo Electron Co., MA, USA) equipped with an OMNI-Sampler was used to study the chemical structure of the fiber and fabric samples. Figure 2. Internal pressure of the sealed reaction chamber versus time, WFR ¼ 0 (Closed).

4 Yin et al. 19 Results and discussion Spandex removal by solvent extraction Spandex was removed by solvent extraction in DMF to determine the content of spandex in NSBF, and the results are given in Table 1. After treatment in DMF, there was no noticeable weight loss or change in appearance for the nylon fibers. In contrast, the spandex fibers disappeared and were completely dissolved in DMF. The weight loss for the NSBF sample was 23.86%, which corresponded to loss of the spandex component in the fabric. In addition, the elasticity of the treated fabric decreased significantly when stretched by hand. From the dissolubility of nylon and spandex in DMF, the content of spandex in NSBF was estimated at 23.86%. When Table 1. Effect of treatment in N,N-dimethylformamide (70 C, 4h) Sample Weight loss Observation Nylon 0.22% No change in appearance Spandex 100% Spandex was completely dissolved NSBF 23.86% The elasticity of the treated fabric decreased significantly NSBF: nylon/spandex blended fabric. the DMF solvent containing dissolved spandex was allowed to evaporate, a spandex film was recovered whose weight matched that of the weight loss of the original sample. Besides being an effective method to determine the spandex content in NSBF, solvent extraction with DMF and other chemicals could also be used to obtain high-purity nylon from the blended fabrics. Effect of heat treatment on fabric structure After NSBF samples were heat treated under the four conditions at 220 C for 2 h, their appearances were examined under a microscope (Figure 3). From Figure 3(a) and (b), it can be observed that the fiber/ fabric structure of the fabric samples was destroyed when liquid water was added to the test chamber for the heat treatment. In contrast, the NSBF samples treated without added liquid water remained in fabric form (Figure 3(c) and (d)), and they exhibited reduced elasticity. The weight losses of fabric samples before and after heat treatments are shown in Figure 4. The weight losses corresponding to the four conditions (WFR ¼ 4, 1, 0 (Closed), and 0 (Open)) were 5.82%, 4.88%, 1.34%, and 1.83%, respectively. There were negligible weight losses (<2%) for treatments without added liquid water. A moderate weight loss Figure 3. Appearances of nylon/spandex blended fabric after heat treatment at 220 C for 2 h under the four conditions: (a) WFR ¼ 4; (b) WFR ¼ 1; (c) WFR ¼ 0 (Closed); and (d) WFR ¼ 0 (Open).

5 20 Textile Research Journal 84(1) Figure 4. Weight losses of fabrics after heat treatment under the four conditions. Figure 5. Weight losses after washing in solvents. (about 5 6%) was observed for treatments when liquid water was added, and this loss was mainly due to the disintegration of the fabric structure causing some small particles to be lost when water was removed after heat treatment. Effect of washing after heat treatment The spandex macromolecule was degraded into some short-chain residue after heat treatment at 220 C for 2 h. The residue was not an integral part of the fabric structure, but adsorbed or adhered to the surface of nylon fibers. Three solvents (water, ethanol, and acetone) were used to remove the spandex residue by a washing process, and the amount of weight reduction after washing is reported in Figure 5. Water appeared to be an ineffective solvent to remove the spandex residual, and the weight losses were lower than 8% for samples treated under all the four conditions. This was likely because most of the spandex residue was insoluble in water after the heat treatment.

6 Yin et al. 21 When ethanol and acetone were used for washing, the weight loss for samples heat treated with liquid water (WFR ¼ 1 and 4) was lower than that for samples treated without liquid water (WFR ¼ 0; Closed or Open). There were two main reasons for the lower mass loss after washing for the liquid water treated samples. Firstly, some of the degraded spandex residue was already removed by the liquid, which was reflected by the 5 6% weight loss after the heat treatment. Secondly, due to the disintegration of the fabric structure, the fabric became clumps, causing some degraded spandex residue to be trapped inside the clump, making it difficult to wash away. It was therefore concluded that heat treatment conditions with liquid water (WFR ¼ 1 and 4) were not as effective as those without liquid water. Comparing the weight losses after washing in acetone and ethanol (Figure 5), the two solvents showed nearly identical results for samples treated without liquid water, all about 22%. Based on the content of spandex in the NSBF (about 23.86%; Table 1) and a weight loss of % after the heat treatment (Figure 4), these results show that the spandex component was essentially fully removed by heat treatment without liquid water followed by washing with ethanol or acetone. For economical and environmental reasons, ethanol was clearly the preferred choice. For effectiveness, simplicity, and lower operating cost, heat treatment at atmospheric pressure (Open condition) was found to be a desirable processing method. Therefore, further studies were only carried out at atmospheric pressure and using ethanol as the washing solvent. Effect of heat treatment temperature Figure 6 shows photographic images of fabric samples after heat treatment for 2 h at atmospheric pressure and at temperatures from 180 C to 230 C. The structure of the original NSBF was tight with good elasticity. The appearance of the spandex fiber showed no obvious change after being treated at 180 C. It showed some slight change when the treatment temperature was increased to 190 C, revealing open spaces among the yarns (Figure 6(b)). From Figure 6(c), much irregular spandex residue on the nylon fiber surface was visible for samples treated at 200 C. In samples treated at 210 C or 220 C, the size of the spandex residue, adhered to the knots of the yarns, was decreased. Further increasing the temperature to 230 C, the nylon component in the NSBF was seen to be damaged, and the fabric became hard with a total loss of elasticity. Comparing the effect of treatment at these temperatures, a heat treatment temperature of 220 C was found to be the preferred condition. In order to analyze the changes of the appearances of nylon and spandex fibers in detail, these fibers were treated at 220 C for 2 h. From Figure 7(a) and (c), the appearances of nylon fibers before and after the treatment were identical. However, the spandex fibers changed significantly after the treatment (Figure 7(b) and (d)). The spandex had degraded into a wax-like short-chain spandex residue, and this made it easily removed from the remaining nylon structure of the fabric. Effect of washing with ethanol After the NSBF samples were heat treated at C for 2 h at atmospheric pressure, the samples were washed with ethanol at 60 C for 30 min. Weight reduction due to washing was found to increase with the heat treatment temperature (Figure 8). It was noted that the washing loss was 24.65% for the sample treated at 230 C, higher than the spandex content. This was caused by the disintegration of nylon fibers such that some brown nylon fragments were left in the ethanol solvent after the washing process, making it difficult to separate the nylon and spandex at the 230 C treatment temperature. Overall, treatment at 220 C was found to be most effective, yielding a weight loss after washing closely matching the spandex content in NSBF. Figure 9 shows photographic images of fabric samples washed with ethanol after heat treatment for 2 h at atmospheric pressure and at temperatures from 180 C to 230 C. Figure 9(a) reveals no change in the fabric structure after washing in ethanol for the untreated NSBF. This is not unexpected, since both the nylon and the spandex would not dissolve in ethanol under the condition for washing. When the NSBF was treated at 180 C and 190 C, respectively, the fabric showed some slight change in appearance after washing with ethanol (Figure 9(b) and (c)). Although the spandex fibers were still visible in the yarns, the elasticity of the fabric decreased and the fabric became less dense. After being heat treated at 200 C and 210 C followed by washing with ethanol, most of the spandex fibers disappeared and only some residue on the nylon fiber yarns was visible (Figure 9(d) and (e)). Heat treatment at 220 C allowed the spandex residue to be washed off completely while retaining the fabric structure of nylon yarns (Figure 9(f)). When the heat treatment temperature was raised to 230 C, the treated NSBF became brittle and fragmented (Figure 9(g)), with many small pieces and fiber segments besides the main remnant pieces. This observation confirms again that heat treatment at 220 C provides the best effect of removing spandex from NSBF. The NSBF samples after heat treatment and washing were further analyzed at a higher magnification with a

7 22 Textile Research Journal 84(1) Figure 6. Photographs of nylon/spandex blended fabric samples heat treated for 2 h at atmospheric pressure and different temperatures: (a) before treatment; (b) 180 C; (c) 190 C; (d) 200 C; (e) 210 C; (f) 220 C; and (g) 230 C. focus on the appearance of the spandex residue, as shown in Figure 10 where the spandex residue appeared as brown clumps. The size of the spandex residue clumps decreased as the heat treatment increased, making it easier to be washed off with ethanol. When heat treated at 220 C, the spandex residue was fully removed by washing, and no spandex residue clumps could be seen in the images of the treated fabric (Figure 10(e)). When the treatment temperature was increased to 230 C, many fragmented nylon fiber ends could be seen (Figure 10(f)). The degradation of nylon fiber is undesirable, as it interferes with full removal of spandex residue, makes it difficult to handle in recycling the nylon component, and makes the nylon unsuitable for further melt processing.

8 Yin et al. 23 Figure 7. Appearances of nylon and spandex fibers: (a) nylon and (b) spandex before treatment; (c) nylon and (d) spandex after treatment at 220 C for 2 h at atmospheric pressure. Figure 8. Weight losses after washing in ethanol at 60 C for 30 min for nylon/spandex blended fabric samples treated at different temperatures.

9 24 Textile Research Journal 84(1) Figure 9. Photographs of nylon/spandex blended fabric samples heat treated for 2 h at atmospheric pressure and different temperatures and washed with ethanol: (a) before treatment; (b) 180 C; (c) 190 C; (d) 200 C; (e) 210 C; (f) 220 C; and (g) 230 C. Spectra analysis with FTIR-ATR Nylon fiber and NSBF samples after heat treatment at 220 C for 2 h at atmospheric pressure were analyzed by FTIR-ATR spectra analysis. From Figure 11, the main absorption peaks of nylon fibers before and after heat treatment were nearly the same, and there were no new peaks or fading peaks. This confirmed that the molecular structure of nylon was not changed by heat treatment at 220 C. The FTIR-ATR spectra of the original NSBF presented strong absorption peaks at 1650 and 1720 cm 1 (Figure 12, curve a), corresponding to the -CONgroup, which was part of the urethane and urea linkages in spandex and the amide linkage in nylon. After NSBF was heat treated at 220 C for 2 h, the absorption peaks of -CON- of the sample decreased in intensity, and this was likely caused by damages to the amino group in spandex molecules as they were degraded into oligomers. The weakened absorption peaks of

10 Yin et al. 25 Figure 10. Photographs of nylon/spandex blended fabric fragments (magnification 50) heat treated for 2 h at atmospheric pressure and different temperatures and washed with ethanol: (a) 180 C; (b) 190 C; (c) 200 C; (d) 210 C; (e) 220 C; and (f) 230 C. Figure 11. Fourier transform infrared attenuated total reflectance spectra of nylon fiber.

11 26 Textile Research Journal 84(1) Figure 12. Fourier transform infrared attenuated total reflectance spectra of nylon/spandex blended fabric samples. -CON- were due to the amino group in the nylon and in the spandex residue. When the spandex residue was removed by washing with ethanol, the absorption peaks at 1650 and 1720 cm 1 decreased further (Figure 12, curve c). Conclusions Effective and environmentally friendly methods to remove the spandex component in a NSBF were studied to enable the recovery of nearly pure nylon for further processing. The study showed that spandex separation via selective degradation was a promising route, which involved heat treatment of the fabric followed by a washing process. The samples were examined by weight loss analysis comparing with the spandex content in the blended fabric, appearance analysis using an optical microscope, and FTIR spectra analysis. For the heat treatment, the effect of temperature, WFR, and pressure were studied. The presence of liquid water in a sealed chamber for the heat treatment at elevated temperatures disintegrated the fabric structure and made removal of spandex difficult. Heat treatments in a sealed chamber and in an open chamber yielded similar results in spandex degradation when no liquid water was added to the chamber in the process. Without added liquid water, heat treatment at a temperature of 220 C, just below the nominal melting temperature of nylon 6, was found to have little effect on the nylon fiber but was effective to cause sufficient spandex degradation for the spandex residue to be readily washed off. Removing the degraded spandex residue after heat treatment was accomplished by a washing process. Among water, acetone, and ethanol, ethanol was found to be the most desirable washing solvent for its effectiveness and being environmentally benign. A simple process using only heat and ethanol was found to be the most effective, which involved heat treatment at 220 C for 2 hours under atmospheric pressure followed by a washing process with ethanol. The process was able to remove essentially all the spandex component from the blended fabric, resulting in a fabric containing nylon yarns only. As the spandex in the blended fabric was removed, a decrease in -CONabsorption peaks was observed in the FTIR-ATR spectra of the heat-treated and washed fabrics. This selective degradation method provides an effective pathway to recycle NSBF waste. Further study is underway to investigate the melt processing characteristics and thermal and mechanical properties of the recovered nylon from NSBFs. Funding This work was supported by Aquafil USA, and also the Business Doctoral Innovation Project of Jiangsu Province in China (BK ), the Graduate Students Innovation Project of Jiangsu Province in China (CX08S_016Z), and the Excellent Doctoral Cultivation Project of Jiangnan University. References 1. Zhang HX, Xue Y and Wang SY. Effects of twisting parameters on characteristics of rotor-spun composite yarns with spandex. Fiber Polym 2006; 7: Hicks EM, Ultee AJ and Drougas J. Spandex elastic fibers: development of a new type of elastic fiber stimulates

12 Yin et al. 27 further work in the growing field of stretch fabrics. Science 1965; 147: Niesten M, Krijgsman J, Harkema S, et al. Melt spinnable spandex fibers from segmented copolyetheresteraramids. J Appl Polym Sci 2001; 82: Tezel S and Kavusturan Y. Experimental investigation of effects of spandex brand and tightness factor on dimensional and physical properties of cotton/spandex single jersey fabrics. Textil Res J 2008; 78: Adeli B, Ghareaghaji AA and Shanbeh M. Structural evaluation of elastic core-spun yarns and fabrics under tensile fatigue loading. Textil Res J 2011; 81: Beceren Y, Candan C, Cimilli S, et al. Properties of plain knits from siro-spun viscose/spandex yarns. Fibres Textil East Eur 2010; 18: Kakvan A, Najar SS, Saidi RG, et al. Effects of draw ratio and elastic core yarn positioning on physical properties of elastic wool/polyester core-spun ring yarns. J Textil Inst 2007; 98: Kim SH, Oh KW and Bahk JH. Electrochemically synthesized polypyrrole and Cu-plated nylon/spandex for electrotherapeutic pad electrode. J Appl Polym Sci 2004; 91: Han KQ, Li WJ, Wu CX, et al. Study on hyperbranched polyesters as rheological modifier for Spandex spinning solution. Polym Int 2006; 55: Lee HS, Ko JH, Song KS, et al. Segmental and chain orientational behavior of spandex fibers. J Polym Sci B Polym Phys 1997; 35: Lee CG. Changes of pulling-out length and shrinkage ratio in polyester/spandex power net warp knitted fabrics. Fiber Polym 2006; 7: Griffith AT, Park Y and Roberts CB. Separation and recovery of nylon from carpet waste using a supercritical fluid antisolvent technique. Polym Plast Technol Eng 1999; 38: Tokoro T and Hackam R. Loss and recovery of hydrophobicity, surface energies, diffusion coefficients and activation energy of nylon. IEEE T Dielect El I 1999; 6: Lozano-Gonzalez J, Rodriguez-Hernandez T, Los Santos E, et al. Physical-mechanical properties and morphological study on nylon 6 recycling by injection molding. J Appl Polym Sci 2000; 76: