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
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DOI: 10.1177/0040517513487790
trj.sagepub.com
Yunjie Yin1,2, Donggang Yao1, Chaoxia Wang2 and
Youjiang 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 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
400–800%. 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: youjiang.wang@mse.gatech.edu
Yin et al.
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.12–14 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.
Figure 1. Schematic of test apparatus for heat treatment.
17
Experimental details
Materials
NSBF (223.8 g/m2, 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 200–250 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
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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 180–
230 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 (T1) and atmospheric pressure
(P1), the internal pressure P2, measured by gage pressure, should increase with the internal temperature T2
as follows:
P2 ¼ P1 ðT2 =T1 1Þ
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.
ð1Þ
Figure 2. Internal pressure of the sealed reaction chamber versus time, WFR ¼ 0 (Closed).
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,
4 h)
Sample
Weight loss
Observation
Nylon
Spandex
NSBF
0.22%
100%
23.86%
No change in appearance
Spandex was completely dissolved
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).
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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.
Yin et al.
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 1.3–1.8% 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.
21
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 180–
230 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
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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.
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.
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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 cm1
(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
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.
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 cm1 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 (BK2009672), the Graduate Students Innovation
Project of Jiangsu Province in China (CX08S_016Z), and
the Excellent Doctoral Cultivation Project of Jiangnan
University.
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