spandex recycling

Original article

Removal of spandex from nylon/spandexblended fabrics by selective polymerdegradation

Yunjie Yin1,2, Donggang Yao1, Chaoxia Wang2 andYoujiang Wang1

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 220C for2 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 infraredattenuated total reflectance spectra of

the fabrics was observed.

Keywords

Waste recycling, selective degradation, blended fabrics, spandex, nylon 6

Spandex fibers exhibit superior stretch and elasticrecovery ability, providing garments containing span-dex fibers with good fitting and comfort characteris-tics.13 The elongation to break of spandex fibers istypically over 200%, and more often in the range of400800%. Upon releasing the deforming stress, thefiber returns quickly to its original shape.4 Becauseof their superior extensibility, elasticity, wrinklerecovery, dimensional stability, and simple care, fab-rics containing spandex fibers find a wide range ofapplications, especially in garments such as sportcloths and swimwear.46 However, the deficienciesof spandex in chemical resistance and temperaturestability have to be managed during garment manu-facture and wear to avoid excessive fiber degradationand loss of elasticity.7,8 Nylon filaments, with goodstrength and chemical resistance but lower extensibil-ity, are often combining with spandex to makeblended fabrics that overcome the disadvantages

associated with using one type of material onits own.

Polymer waste consisting of a single type of nyloncan be recycled into various products, such as auto-motive parts, and the recycling rate for such waste isquite high. However, waste of polymer blends is oftendiscarded or incinerated unless the components canbe economically separated. As the use of fabrics con-taining spandex for apparel applications is expanding,

1School of Materials Science & Engineering, Georgia Institute of

Technology, USA2Key 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: [email protected]

Textile Research Journal

84(1) 1627

! The Author(s) 2014

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DOI: 10.1177/0040517513487790

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the waste disposal problem for the garment manufac-turing process as well as post-consumer textiles needsto be addressed. Nylon in a nylon/spandex blendedfabric (NSBF) represents the main component,whereas spandex represents a small portion inNSBF. It is therefore logical to focus on the recoveryof nylon from NSBF waste so as the recovered nyloncan be processed into engineered plastics by melt pro-cessing or into virgin-quality monomers by depoly-merization, if nylon can be recovered from thewaste steam with reasonable purity. Currently, thereis no suitable technology to recycle NSBF wasteother than by solvent extraction using, for example,N,N-dimethylformamide (DMF). Although solventextraction of spandex from NSBFs with DMF orN,N-dimethylacetamide (DMA) is technically feasible,environmental and economic concerns limit its use incommercial applications.

The spandex fiber is usually produced by the dryspinning process, in which the polymers are preparedvia polytetramethylene glycol (PTMG) with -CON-end-groups reacting with diamine in DMF or DMA.9

Spandex is a polyurethanepolyurea copolymer,8,10,11

in which the polyurea component synthesized from dii-socyanate and diamine contains a urea linkage that iseasier to depolymerize than the amino linkage in nylonby hydrolytic actions.1214 Therefore, in this study themain focus is to find conditions that selectively degradespandex by hydrolysis without significantly affectingthe nylon component. A reaction chamber capable ofheating water to 250C was used for the heat treatmentof NSBF, and the process variables studied includedtemperature, water-to-fabric ratio (WFR), and pres-sure. After the heat treatment, the treated fabricswere washed with solvents such as water, ethanol, andacetone. Direct solvent extraction of spandex fromNSBF was also carried out to determine the massratio of spandex as well as to demonstrate its feasibilityfor recycling NSBF.

Experimental details

Materials

NSBF (223.8 g/m2, knitted, brown), nylon 6 (poly-amide 6) fiber and spandex fiber obtained fromAquafil USA, Inc., were used in this experiment.Ethanol, acetone, and DMF were analytical reagentgrade and supplied by Sigma-Aldrich Co. LLC.

Solvent extraction of spandex

Nylon, spandex, and NSBF samples were pre-washedwith deionized water, and then dried at 50C for 24 h.Samples containing 2 g of fibers or fabric were treatedin DMF solvent (40 g) at 70C for 4 h. After washingwith deionized water and drying at 50C for 24 h, thesamples were weighed and the weight losses werecalculated.

Heat treatment

A pressure vessel is needed in order to heat liquid waterto a temperature range of 200250C. In this study, asimple pressure vessel was constructed to be used with a4-ton press, as illustrated in Figure 1. The press con-trolled the heating profile of the test vessel, which had acavity of 10 cc. NSBF and fiber samples were washedwith deionized water, and then dried in a vacuum dryerat 60C for 24 h to allow for accurate measurement ofsample weights. The stainless steel reaction chamberwas first heated to the preset temperature, and thenthe pre-washed fabric sample was placed in the reactionchamber with predetermined amount of deionizedwater. The WFR varied from 0 to 4, and the test cham-ber was either closed or open during the heat treatment,as follows.

1. WFR 4: the chamber was filled with water afterplacing the samples inside to obtain an approximate

Figure 1. Schematic of test apparatus for heat treatment.

Yin et al. 17

WFR of 4:1. The valve was closed during heat treat-ment to allow internal pressure to build up as thevessel was heated.

2. WFR 1: 2 g of water was added to the chamberafter placing a 2 g fabric sample inside, and thevalve was closed during heat treatment.

3. WFR 0 (Closed): no water was added to the cham-ber after placing the samples inside, and the valvewas closed during heat treatment.

4. WFR 0 (Open): no water was added to the cham-ber after placing the samples inside, and the valvewas kept open during heat treatment, at atmosphericpressure.

After a series of extensive trials with different tempera-tures and time durations, a temperature range of 180230C was selected in this study, and the treatmentduration was kept at 2 h, which included time neededto bring the test vessel to the desired temperature.Figure 2 shows the internal pressure profile during thetest when no water was added and the chamber wasclosed. The internal pressure directly correlated withthe actual temperature inside the chamber. For anideal gas in an enclosed chamber, the pressure is relatedto the temperature change by the ideal gas law. Startingfrom room temperature (T1) and atmospheric pressure(P1), the internal pressure P2, measured by gage pres-sure, should increase with the internal temperature T2as follows:

P2 P1 T2=T1 1 1

At 200C (473K), the internal pressure is expected torise to 0.6 atm (61 kPa). This value was much lowerthan what was actually observed (441 kPa) for testingNSBF under the WFR 0 (Closed) condition, due tothe presence of moisture in the chamber. Although nowater was added to the chamber under the last twoconditions, the fiber/fabric samples were expected tocontain some moisture at the beginning of the testdue to moisture regain.

Sample cleaning after treatment

After the fiber/NSBF sample was heat treated, it wasweighed and washed at 60C for 30min with magneticstirring in 40mL water, ethanol, or acetone, respect-ively. The treated fabric sample was then washed withdeionized water three times before it was dried at 60Cfor 24 h for further testing.

Characterization

The treated fiber and fabric samples after washingand drying were analyzed for weight loss andchange in appearance using an optical microscope.A Thermo Nicolet Nexus Fourier transform infra-redattenuated total reflectance (FTIR-ATR) spectro-photometer (Thermo Electron Co., MA,USA) equipped with an OMNI-Sampler was usedto study the chemical structure of the fiber andfabric samples.

Figure 2. Internal pressure of the sealed reaction chamber versus time, WFR 0 (Closed).

18 Textile Research Journal 84(1)

Results and discussion

Spandex removal by solvent extraction

Spandex was removed by solvent extraction in DMF todetermine the content of spandex in NSBF, and theresults are given in Table 1.

After treatment in DMF, there was no noticeableweight loss or change in appearance for the nylonfibers. In contrast, the spandex fibers disappeared andwere completely dissolved in DMF. The weight loss forthe NSBF sample was 23.86%, which corresponded toloss of the spandex component in the fabric. In add-ition, the elasticity of the treated fabric decreased sig-nificantly when stretched by hand. From thedissolubility of nylon and spandex in DMF, the contentof spandex in NSBF was estimated at 23.86%. When

the DMF solvent containing dissolved spandex wasallowed to evaporate, a spandex film was recoveredwhose weight matched that of the weight loss of theoriginal sample. Besides being an effective method todetermine the spandex content in NSBF, solventextraction with DMF and other chemicals could alsobe used to obtain high-purity nylon from the blendedfabrics.

Effect of heat treatment on fabric structure

After NSBF samples were heat treated under the fourconditions at 220C for 2 h, their appearances wereexamined under a microscope (Figure 3). FromFigure 3(a) and (b), it can be observed that the fiber/fabric structure of the fabric samples was destroyedwhen liquid water was added to the test chamber forthe heat treatment. In contrast, the NSBF samples trea-ted without added liquid water remained in fabric form(Figure 3(c) and (d)), and they exhibited reducedelasticity.

The weight losses of fabric samples before andafter heat treatments are shown in Figure 4. Theweight losses corresponding to the four conditions(WFR 4, 1, 0 (Closed), and 0 (Open)) were 5.82%,4.88%, 1.34%, and 1.83%, respectively. There werenegligible weight losses (

(about 56%) was observed for treatments when liquidwater was added, and this loss was mainly due to thedisintegration of the fabric structure causing somesmall particles to be lost when water was removedafter heat treatment.

Effect of washing after heat treatment

The spandex macromolecule was degraded into someshort-chain residue after heat treatment at 220C for2 h. The residue was not an integral part of the

fabric structure, but adsorbed or adhered to the sur-face of nylon fibers. Three solvents (water, ethanol,and acetone) were used to remove the spandex resi-due by a washing process, and the amount of weightreduction after washing is reported in Figure 5.Water appeared to be an ineffective solvent toremove the spandex residual, and the weight losseswere lower than 8% for samples treated under allthe four conditions. This was likely because most ofthe spandex residue was insoluble in water after theheat treatment.

Figure 5. Weight losses after washing in solvents.

Figure 4. Weight losses of fabrics after heat treatment under the four conditions.


When ethanol and acetone were used for washing,the weight loss for samples heat treated with liquidwater (WFR 1 and 4) was lower than that for samplestreated without liquid water (WFR 0; Closed orOpen). There were two main reasons for the lowermass loss after washing for the liquid water treatedsamples. Firstly, some of the degraded spandex residuewas already removed by the liquid, which was reflectedby the 56% weight loss after the heat treatment.Secondly, due to the disintegration of the fabric struc-ture, the fabric became clumps, causing some degradedspandex residue to be trapped inside the clump, makingit difficult to wash away. It was therefore concludedthat heat treatment conditions with liquid water(WFR 1 and 4) were not as effective as those withoutliquid water.

Comparing the weight losses after washing in acet-one and ethanol (Figure 5), the two solvents showednearly identical results for samples treated withoutliquid water, all about 22%. Based on the contentof spandex in the NSBF (about 23.86%; Table 1)and a weight loss of 1.31.8% after the heat treat-ment (Figure 4), these results show that the spandexcomponent was essentially fully removed by heattreatment without liquid water followed by washingwith ethanol or acetone. For economical and envir-onmental reasons, ethanol was clearly the preferredchoice. For effectiveness, simplicity, and lower oper-ating cost, heat treatment at atmospheric pressure(Open condition) was found to be a desirable pro-cessing method. Therefore, further studies were onlycarried out at atmospheric pressure and using ethanolas the washing solvent.

Effect of heat treatment temperature

Figure 6 shows photographic images of fabric samplesafter heat treatment for 2 h at atmospheric pressure andat temperatures from 180C to 230C. The structure ofthe original NSBF was tight with good elasticity. Theappearance of the spandex fiber showed no obviouschange after being treated at 180C. It showed someslight change when the treatment temperature wasincreased to 190C, revealing open spaces among theyarns (Figure 6(b)). From Figure 6(c), much irregularspandex residue on the nylon fiber surface was visiblefor samples treated at 200C. In samples treated at210C or 220C, the size of the spandex residue,adhered to the knots of the yarns, was decreased.Further increasing the temperature to 230C, thenylon component in the NSBF was seen to be damaged,and the fabric became hard with a total loss of elasti-city. Comparing the effect of treatment at these tem-peratures, a heat treatment temperature of 220C wasfound to be the preferred condition.

In order to analyze the changes of the appearancesof nylon and spandex fibers in detail, these fibers weretreated at 220C for 2 h. From Figure 7(a) and (c), theappearances of nylon fibers before and after thetreatment were identical. However, the spandex fiberschanged significantly after the treatment (Figure 7(b)and (d)). The spandex had degraded into a wax-likeshort-chain spandex residue, and this made it easilyremoved from the remaining nylon structure of thefabric.

Effect of washing with ethanol

After the NSBF samples were heat treated at 180230C for 2 h at atmospheric pressure, the sampleswere washed with ethanol at 60C for 30min. Weightreduction due to washing was found to increase withthe heat treatment temperature (Figure 8). It was notedthat the washing loss was 24.65% for the sample trea-ted at 230C, higher than the spandex content. This wascaused by the disintegration of nylon fibers such thatsome brown nylon fragments were left in the ethanolsolvent after the washing process, making it difficult toseparate the nylon and spandex at the 230C treatmenttemperature. Overall, treatment at 220C was found tobe most effective, yielding a weight loss after washingclosely matching the spandex content in NSBF.

Figure 9 shows photographic images of fabric sam-ples washed with ethanol after heat treatment for 2 h atatmospheric pressure and at temperatures from 180Cto 230C. Figure 9(a) reveals no change in the fabricstructure after washing in ethanol for the untreatedNSBF. This is not unexpected, since both the nylonand the spandex would not dissolve in ethanol underthe condition for washing. When the NSBF was treatedat 180C and 190C, respectively, the fabric showedsome slight change in appearance after washing withethanol (Figure 9(b) and (c)). Although the spandexfibers were still visible in the yarns, the elasticity ofthe fabric decreased and the fabric became less dense.After being heat treated at 200C and 210C followedby washing with ethanol, most of the spandex fibersdisappeared and only some residue on the nylon fiberyarns was visible (Figure 9(d) and (e)). Heat treatmentat 220C allowed the spandex residue to be washed offcompletely while retaining the fabric structure of nylonyarns (Figure 9(f)). When the heat treatment tempera-ture was raised to 230C, the treated NSBF becamebrittle and fragmented (Figure 9(g)), with many smallpieces and fiber segments besides the main remnantpieces. This observation confirms again that heat treat-ment at 220C provides the best effect of removingspandex from NSBF.

The NSBF samples after heat treatment and washingwere further analyzed at a higher magnification with a

Yin et al. 21

focus on the appearance of the spandex residue, asshown in Figure 10 where the spandex residue appearedas brown clumps. The size of the spandex residueclumps decreased as the heat treatment increased,making it easier to be washed off with ethanol. Whenheat treated at 220C, the spandex residue was fullyremoved by washing, and no spandex residueclumps could be seen in the images of the treated

fabric (Figure 10(e)). When the treatment tempera-ture was increased to 230C, many fragmentednylon fiber ends could be seen (Figure 10(f)). The deg-radation of nylon fiber is undesirable, as it inter-feres with full removal of spandex residue, makes itdifficult to handle in recycling the nylon component,and makes the nylon unsuitable for further meltprocessing.

Figure 6. Photographs of nylon/spandex blended fabric samples heat treated for 2 h at atmospheric pressure and different tem-

peratures: (a) before treatment; (b) 180C; (c) 190C; (d) 200C; (e) 210C; (f) 220C; and (g) 230C.


Figure 7. Appearances of nylon and spandex fibers: (a) nylon and (b) spandex before treatment; (c) nylon and (d) spandex after

treatment at 220C for 2 h at atmospheric pressure.

Figure 8. Weight losses after washing in ethanol at 60C for 30 min for nylon/spandex blended fabric samples treated at differenttemperatures.

Yin et al. 23

Spectra analysis with FTIR-ATR

Nylon fiber and NSBF samples after heat treatment at220C for 2 h at atmospheric pressure were analyzed byFTIR-ATR spectra analysis. From Figure 11, the mainabsorption peaks of nylon fibers before and after heattreatment were nearly the same, and there were no newpeaks or fading peaks. This confirmed that the molecu-lar structure of nylon was not changed by heat treat-ment at 220C.

The FTIR-ATR spectra of the original NSBF pre-sented strong absorption peaks at 1650 and 1720 cm1

(Figure 12, curve a), corresponding to the -CON-group, which was part of the urethane and urea link-ages in spandex and the amide linkage in nylon. AfterNSBF was heat treated at 220C for 2 h, the absorptionpeaks of -CON- of the sample decreased in intensity,and this was likely caused by damages to the aminogroup in spandex molecules as they were degradedinto oligomers. The weakened absorption peaks of

Figure 9. Photographs of nylon/spandex blended fabric samples heat treated for 2 h at atmospheric pressure and different tem-

peratures and washed with ethanol: (a) before treatment; (b) 180C; (c) 190C; (d) 200C; (e) 210C; (f) 220C; and (g) 230C.


Figure 10. Photographs of nylon/spandex blended fabric fragments (magnification 50) heat treated for 2 h at atmospheric pressureand different temperatures and washed with ethanol: (a) 180C; (b) 190C; (c) 200C; (d) 210C; (e) 220C; and (f) 230C.

Figure 11. Fourier transform infraredattenuated total reflectance spectra of nylon fiber.

Yin et al. 25

-CON- were due to the amino group in the nylon and inthe spandex residue. When the spandex residue wasremoved by washing with ethanol, the absorptionpeaks at 1650 and 1720 cm1 decreased further(Figure 12, curve c).

Conclusions

Effective and environmentally friendly methods toremove the spandex component in a NSBF were stu-died to enable the recovery of nearly pure nylon forfurther processing. The study showed that spandex sep-aration via selective degradation was a promising route,which involved heat treatment of the fabric followed bya washing process. The samples were examined byweight loss analysis comparing with the spandex con-tent in the blended fabric, appearance analysis using anoptical microscope, and FTIR spectra analysis.

For the heat treatment, the effect of temperature,WFR, and pressure were studied. The presence ofliquid water in a sealed chamber for the heat treatmentat elevated temperatures disintegrated the fabric struc-ture and made removal of spandex difficult. Heat treat-ments in a sealed chamber and in an open chamberyielded similar results in spandex degradation whenno liquid water was added to the chamber in the pro-cess. Without added liquid water, heat treatment at atemperature of 220C, just below the nominal meltingtemperature of nylon 6, was found to have little effecton the nylon fiber but was effective to cause sufficientspandex degradation for the spandex residue to bereadily washed off. Removing the degraded spandexresidue after heat treatment was accomplished by a

washing process. Among water, acetone, and ethanol,ethanol was found to be the most desirable washingsolvent for its effectiveness and being environmentallybenign. A simple process using only heat and ethanolwas found to be the most effective, which involved heattreatment at 220C for 2 hours under atmospheric pres-sure followed by a washing process with ethanol. Theprocess was able to remove essentially all the spandexcomponent from the blended fabric, resulting in afabric containing nylon yarns only. As the spandex inthe blended fabric was removed, a decrease in -CON-absorption peaks was observed in the FTIR-ATRspectra of the heat-treated and washed fabrics. Thisselective degradation method provides an effectivepathway to recycle NSBF waste. Further study isunderway to investigate the melt processing character-istics and thermal and mechanical properties of therecovered nylon from NSBFs.

Funding

This work was supported by Aquafil USA, and also theBusiness Doctoral Innovation Project of Jiangsu Province in

China (BK2009672), the Graduate Students InnovationProject of Jiangsu Province in China (CX08S_016Z), andthe Excellent Doctoral Cultivation Project of JiangnanUniversity.

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spandex recycling

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