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Journal of Cleaner Production 183 (2018) 810e817

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Journal of Cleaner Production

journal homepage: www.elsevier .com/locate/ jc lepro

Recycling keratin polypeptides for anti-felting treatment of woolbased on L-cysteine pretreatment

Zhuang Du a, Bolin Ji a, b, Kelu Yan a, b, *

a College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, PR Chinab National Engineering Research Center for Dyeing and Finishing of Textiles, Donghua University, Shanghai 201620, PR China

a r t i c l e i n f o

Article history:Received 7 July 2017Received in revised form27 December 2017Accepted 19 February 2018Available online 20 February 2018

Keywords:Keratin polypeptidesRecycleAnti-felting treatmentWoolL-cysteine

* Corresponding author. National Engineering ResFinishing of Textiles, College of Chemistry, Chemicnology, Donghua University, Shanghai 201620, PR Ch

E-mail address: klyan@dhu.edu.cn (K. Yan).

https://doi.org/10.1016/j.jclepro.2018.02.1960959-6526/© 2018 Elsevier Ltd. All rights reserved.

a b s t r a c t

An anti-felting finishing process based on recycling waste wool material was proposed. Wool fabric waspretreated with L-cysteine and then treated with the keratin polypeptides, extracted by protease fromthe waste wool. And then, wool fabric was treated with glycerol diglycidyl ether as cross-linking agentfor a durable anti-felting effect. The padded-out keratin polypeptides solution was collected, replenishedwith a small amount of fresh keratin polypeptides and recycled for 10 times. An excellent anti-feltingperformance was still achieved when wool fabric was treated with the 10th-recycled keratin poly-peptides. The protein concentration of 10th-recycled keratin polypeptides was almost unchanged, butthe weight-average molecular weight decreased. There was no significant difference on the modifiedsurfaces between the wool fabrics treated with recycled keratin polypeptides and those with the freshones. Compared with the control, there was an improvement in whiteness, softness, dyeability, hydro-philicity and an acceptable loss in weight (about 1%) and in strength (about 6.1% in warp direction) afterfixation of the extracted keratin polypeptides onto the fabrics. The modification mechanism wasconfirmed by scanning electron microscopy, Raman spectra and X-ray photoelectron spectroscopyanalysis of treated wool fabric that L-cysteine can erode the fiber surface, generating more reactivegroups, and then keratin polypeptides can easily cross-linked onto the fiber surface by glycerol diglycidylether or covered the fiber surface.

© 2018 Elsevier Ltd. All rights reserved.

1. Introduction

The cuticle of wool fiber plays a critical role in wool processing,especially in uptake of dyes and fixation of resins used for anti-felting (Kaur and Chakraborty, 2015). Anti-felting treatment al-ways involves the reduction/oxidation process to erode the scalelayer and/or coating the polymer on the surface of wool fiber (Smithand Shen, 2011). The traditional anti-felting treatment is chlori-nation/resin method (chlorinate-Hercosett process), while it wouldproduce harmful absorbable organic halogens (AOX) (Shi et al.,2014). To avoid release of AOX and reach the machine washablestandards, alternative and environmentally friendly processesshould be developed. Coating with polymer resins on the surface ofwool fabric can obtain satisfying anti-felting property (Zhao et al.,2013). However, a large amount of resins should be required to

earch Center for Dyeing andal Engineering and Biotech-ina.

meet the machine washable standards and thus cause wool fabric astiff handle. The proteolysis of protein compounds can be catalyzedby proteasewithout any chlorine release, nevertheless protease canpenetrate into the inner of wool fiber to degrade the macromo-lecular chains, resulting in severe damage of strength, which re-stricts its application (Cui et al., 2009). The diffusibility of enzymecan be decreased when it is immobilized to a specific polymer,which could restrict the proteolysis of protein compounds presenton the scale layer of fiber (Madhu and Chakraborty, 2017; Shenet al., 2007; Silva et al., 2006; Smith et al., 2010). Wool fabrictreated with the modified enzyme shows improvement of anti-felting property, but the immobilization of enzyme would be tooexpensive to achieve industrialization.

It should be meaningful if anti-felting property of wool fabricscan be realized with more effective and green way. Currently,various attempts have been made to the utilization of biomass, andmany kinds of biopolymers worked as resins are applied on thewool fabric to achieve anti-felting, such as silk sericin, collagen andcasein, which could obtain softer handle than the synthetic poly-mers (Cortez et al., 2007; G�orecki and G�orecki, 2010; Xu et al.,

Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817 811

2013). Keratin polypeptides (KPs) as one kind of the most abundantbiomass can be extracted from keratin-containing wastes, such aswaste wool, hair, feathers and so on (Reddy et al., 2014; Xie et al.,2005). It is advisable to extract and dissolve KPs from keratinwastes for development of novel biopolymers (Holkar et al., 2016).Compared with the traditional chemical extraction process, enzy-matic hydrolysis is usually applied in a mild condition or enhancingthe hydrolysis simply by exerting pressure without much chemicalreagents, which can be a greenmethod to extract the KPs (Brandelliet al., 2010; Marou�sek et al., 2013). To fix KPs onto the wool fabric, apretreatment is generally required to improve surface affinity be-tween wool fabric and KPs. The sodium sulfite and sodium bisulfiteare frequently used as reducing agents to pretreat wool fabric, butsevere fiber damage and water pollution could be generated duringthe treatment process. For the popular thiol-type reducing agent, L-cysteine can break the inert -S-S- group that lied in the cuticle orcortex of wool effectively and cause less damage onwool fiber thanthioglycolic acid as well as less toxicity than 2-mercaptoethanol(Wang et al., 2016). It can not only cleave the -S-S- of keratin, butalso connect with keratin and form new disulfide bond R-S-S-CH(NH2)COO�. This characteristic could play an important role inanti-felting treatment and surface modification. Most reports takeL-cysteine as a green reducing agent to extract keratin fromwool orfeather materials (Xu and Yang, 2014). However, there is no reporton L-cysteine as a pretreatment agent for wool anti-felting finish.The cleavage of -S-S- group of cuticle treated by L-cysteine candecrease the directional friction effect (DFE) of wool fabric, newdisulfide bond can be generated between L-cysteine and wool fiber,and provided more reactive sites to promote the reaction betweenfiber and KPs. Furthermore, difunctional epoxide glycerol diglycidylether (GDE) works as an effective cross-linking agent to fix proteinonto wool fabric by reacting with the eNH2 or eOH of wool fiberand KPs (Hesse et al., 1995; Smith and Shen, 2011).

In this paper, the KPs were extracted from the waste wool fiberswith protease and were fixed on the wool fabric that pretreated byL-cysteine for an anti-felting purpose. Recycle using of KPs wasinvestigated and area shrinkage, softness, weight loss and tensilestrength of the treated wool fabric were also studied. The modifiedsurface of wool fabric was assessed by scanning electron micro-scopy (SEM), and the anti-felting mechanism was confirmed by X-ray photoelectron spectroscopy (XPS), Raman spectra, contactangle and dyeability.

2. Experimental section

2.1. Materials

Undyed waste wool fibers used in the extraction process werebyproducts of wool weaving process supplied by Shandong RuyiWool Co. (Jining, Shandong Province, China). Scoured and undyedwool fabric (144 g/m2, wool 100%, woven), and non-ionic surfactantMP-2 were supplied by Youngor Woolen Textile Co., Ltd. (Ningbo,China). L-cysteine (HO2CCH(NH2)CH2SH), sodium carbonate(Na2CO3), sodium bicarbonate (NaHCO3), sodium sulfite (Na2SO3)are all analytical reagent (AR) purchased from Sinopharm ChemicalReagent Co., Ltd. (Shanghai, China) and used as received. The cross-linking agent glycerol diglycidyl ether (GDE) was purchased fromSigma-Aldrich. The reactive dye, Lanasol Red CE used to test thedyeability of treated wool fabric was supplied by Huntsman Co.(USA). The enzyme used was a serine type protease, Esperase 8.0Lextracted from Bacillus subtilis was supplied by Novozymes (Bei-jing, China), and the enzyme activity based on casein substrate is2.29 u/mg. Enhanced bicinchoninic acid (BCA) Protein Assay Kit todetect the protein concentration was purchased from BeyotimeBiotechnology Co., Ltd. (Shanghai, China).

2.2. Preparation of keratin polypeptides (KPs)

Waste wool fibers were firstly treated with 15 g/L Na2CO3 so-lution at 95 �C for 15min, and then washed by distilled water to beneutral pH condition. The washed product was dried at 80 �C andsubsequently milled into powders. Next, the wool powders wereplaced into a 0.02M phosphate buffer (pH 8.0) containing 5 g/LNa2SO3 with a liquor to goods ratio of 20:1 and treated at 60 �C for30min by using a Roaches Pyrotec 2000 dyeing machine at a40 rpm shaking rate. The protease was added into the previousshaking bath to reach a concentration of 2.0mg/mL, and then themixed solution was agitated at 40 rpm for 2 h at 65 �C. The enzymein the mixture was deactivated by raising the temperature to 90 �Cfor 10min and with the agitation at 40 rpm. Then, cooled the sus-pension to the room temperature and separated by centrifugationat 6000 rpm using a Thermofisher HeraeusMultifuge X3 centrifuge.The supernatant liquid was collected and applied in the later woolfabric treatment (Smith and Shen, 2011). The protein concentrationof extracted KPs was determined by the BCA assay kit. A gradientconcentration (g/L) of bovine serum albumin (BSA) standard solu-tion was designed and the absorbance was recorded at 562 nm(A562). A standard curve was automatically generated using theregression equation:

y ¼ axþ b�R2 � 0:99

�(1)

where R2 represented the linear regression coefficient. The absor-bance values of the samples were recorded and substituted in theregression equation to calculate the protein concentration of theKPs. The molecular weight of KPs was determined by Gel Perme-ation Chromatography according to our previous report (Du et al.,2017).

2.3. Anti-felting treatment of wool fabric and recycle using of KPs

Wool fabric was firstly pretreated by immersing in a bath with aliquor to goods ratio of 20: 1 that contained 2 g/L MP-2 and 8% owf.(on weight of fabric) Na2CO3 treated for 1 h to relax the fabrictension caused by machine drafting process and the treated fabricwas set as control sample. Different amount of L-cysteine wasadded into the relaxation process solution to pretreat wool fabric.And then the pretreated fabric was washed with distilled wateruntil the washing water achieved neutral pH and then dried in air.The pretreated fabric was treated in the extracted KPs solutionswith a liquor to goods ratio of 10: 1 at 60 �C for 30min by using aRoaches Pyrotec 2000 dyeing machine at a 20 rpm shaking rate,and the fabric was taken out from the KPs solution and passedthrough a laboratory padder (Rapid Co., Ltd.) to pad the extra KPs(pick-up 80% owf.). After the padding, we collected the remainingKPs solutions. And then, fabric was transferred into a new bath setpH at 7.3 using 0.02M phosphate buffer containing differentamounts of GDE with a liquor to goods ratio of 10:1 for 30min at60 �Cwith 20 rpm. After thewet treatment steps, fabric was treatedwith a pad process that padded with a pick-up 80% owf. and curedat 140 �C for 3min. The fresh extracted KPs solution was added tothe previous collected solutions and refilled to the initial volume(for example, 100mL KPs would need 16mL of fresh KPs to refill tothe initial volume after treatment). And repeat previous treatmentprocess to recycle using KPs (Scheme 1).

2.4. Fabric testing

Softness and smoothness of the fabric was measured accordingto the AATCC 202-2012 relative hand value of textiles instrument

Scheme 1. Schematic diagram of the anti-felting treatment of wool fabric and recycleusing of extracted keratin polypeptides.

Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817812

method by the PhabrOmeter 3. The relaxation treated wool fabricwas set as the control, and the higher the value was, the softerhandle or the smoothness surface of the fabric would be.

The measurement of area shrinkage due to washing of thetreated woven wool fabric was tested according to IWS TM NO.31by using awashingmachine (Washcator FOM71 CLS, Electrolux) for1� 7 A and 3� 5 A programs. The area shrinkage was calculated bythe following equations:

WSð%Þ ¼ L0 � L1L0

� 100 (2)

LSð%Þ ¼ L0 � L1L0

� 100 (3)

Area Shrinkageð%Þ ¼ WSþ LS (4)

where L0 was the marked length before fabric was washed, and L1was the length of the marked positions after standard washing,WSwas the average value of three WS tests of size changing in weftdirection (%) and LS was the average value of three LS tests of sizechanging in warp direction (%).

The weight loss (WL) of the wool fabric after anti-felting treat-ment was calculated following Eq. (5):

WLð%Þ ¼W0 �W1

W0� 100 (5)

where W0 was the weight of conditioned wool fabric prior toextracted KPs treatment and W1 was the weight of conditionedwool fabric after extracted KPs treatment.

The tensile strength of fabric at break was measured in thewarp-wise and weft-wise directions using universal testing ma-chine (H5KS, Tinius Olsen, USA) in accordance with the testingstandard, ASTM D5035-1995. The fabric samples were cut intorectangular shape (100� 25mm2), and every sample took anaverage value of five replicates.

A Datacolor 650 reflectance spectrophotometer (Datacolor, USA)was used to determine the whiteness of the treated wool fabric interms of the CIE whiteness index. Each sample was folded into fourlayers and measured four times. All values were measured andcalculated using ColorTools QC software with illuminant andobserver conditions of D65.

The treated wool fabric was dyed with the reactive dye LanasolRed CE (2% owf.), pH was adjusted to 4.0 with acetic acid and thetemperature was set at 40 �C at the beginning, and then the

temperature of dye bath was increased to 95 �C at a rate of 1 �C/minand kept for 60min. After dyeing, fabric was successively washedby room temperaturewater, 60 �C water and 95 �C soaping solutioncontaining 2 g/L Ultravon PL (Huntsman Co., USA) non-ionic sur-factant to remove unfixed dyes. The dyed fabric was dried at 40 �Cand the K/S value of dyed fabric was measured by Datacolor 650reflectance spectrophotometer to characterize dye uptake. Dyefixation efficiency (Fixation %) is measured according to the refer-ence (Smith and Shen, 2011). It is the percentage of the dye origi-nally applied to the fabric which becomes bound covalently. Thedyebath solutions were collected before and after the dyeing pro-cess and the solution after soaping were diluted to the same fixedvolume and the absorbance were measured at 503 nm, the wave-length of maximum absorption (lmax) specific to Lanasol Red CE,using a Hitachi U-2910 UV/visible spectrophotometer. Dye fixationefficiency (Fixation %) was calculated using Eq. (6).

Fixationð%Þ ¼ Abs0 � Abs1 � Abs2Abs0

� 100 (6)

where Abs0 is the absorbance of the original dye-bath solution atlmax, Abs1 is the absorbance of the exhausted dye-bath solution atlmax and Abs2 is the absorbance of the solution after soaping atlmax.

Hydrophilicity change of the treated fabric was determined bymeasuring the contact angle between the surface of fabric and de-ionized water droplet at 27 �C using drop shape analyzer (DSA-25,KRUSS GmbH, Hamburg). The 4 mL drop of de-ionized water waslocated on the surface and the images were captured when theycontacted at 60 s.

2.5. Scanning electronic microscopy (SEM)

To determine any changes of the external surface of the fiber,micrographs were taken by a JSM-5600LV instrument (SEM, JEOLLtd. Japan). The samples were sputter coated with gold undervacuum for 50 s using an Edwards ES150 sputter coater.

2.6. X-ray photoelectron spectroscopy (XPS) experiments

XPS experiments were carried out in an ultra high vacuum usinga Physical Electronics Industries PHI Model 5300 surface analysissystem. This system employs a double-pass cylindrical massanalyzer (20-270AR) with a perpendicularly mounted dual (Mg/Mg) X-ray source. A single MgKa X-ray source was operated at250W and 14 kV. Survey spectra were obtained over the range0e1100 eV using a pass energy of 100 eVwith an acquisition time of2min.

2.7. Raman spectra

Raman spectra of the fabric samples were collected by a XploRA(HORIBA Jobin Yvon, France) Raman spectrometer. The laser exci-tation was provided with an argon ion laser operating at 50mW of514.5 nm output. The sample was focused to around 1 mm using a100�objective. A spectra resolution of 5 cm�1 with 1 scan (1000 s)was used over the scanning range of 200e2000 cm�1.

2.8. Statistical analysis

All of the data reported are mean± standard deviation (SD). Thestatistical analysis was carried out by Origin 8.5Pro (Origin lab,USA) and statistical significance was considered at P <0:05.

Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817 813

3. Results and discussion

3.1. Pretreatment of wool fabric with L-cysteine

Reducing agent L-cysteine can break disulfide bond (-S-S-) andimprove the anti-felting property of wool fabric. The effect of L-cysteine concentration on properties of treated fabric was investi-gated, as shown in Fig. 1. The lower the area shrinkage of woolfabric is, the better the anti-felting property will be. Fig. 1(a) indi-cated that area shrinkage decreased from 14.3% to 8.2% by adding0.1M L-cysteine. However, higher concentration of L-cysteine didnot effectively improve the anti-felting property, and even decreaseit based on the higher area shrinkage. It should be attributed to thethiol group (-SH) of L-cysteine, which can break the disulfide (-S-S-)of the cuticle and form the Wool-S-S-CH2CH(NH2)COOH cross-linkage or crosslinked with the other part that derived from thebrokenwool disulfide. (Wang et al., 2016). When the concentrationwas lower than 0.1M, L-cysteine demonstrated high reducibilitydue to generating many -S- reactive sites, and with the concen-tration increasing, L-cysteine could generate less -S-, indicatinglower reactivity of L-cysteine, because the eCOOH in L-cysteinemolecule would suppress the generation of -S- at a high L-cysteineconcentration. Whiteness, weight loss and tensile strength were allaffected for this reason, and the results are shown in Fig. 1(bec). L-cysteine can destroy cuticles and lipids, which increased whitenesseffectively. When the concentration of L-cysteine exceeded 0.1M,although less reactivity of L-cysteine would be, the whiteness andarea shrinkage increased simultaneously. This phenomenon can beexplained that positive charged eNH3

þ of L-cysteine was adsorbed

Fig. 1. The effect of L-cysteine concentration on wool fabric in terms of area shrinkage,whiteness, weight loss and tensile strength.

Table 1The effects of GDE concentration on wool fabric in terms of area shrinkage, tensile stren

Sample GDE concentration (g/L) Area shrinkage (%) Te

W

Controla 5 10.4± 1.1 15Pretreatedb 5 5.6± 0.9 14KPs@GDEc 0 7.6± 0.3 14KPs@GDE 5 2.1± 0.2 14KPs@GDE 10 0.3± 0.1 15KPs@GDE 15 0.1± 0.1 14KPs@GDE 20 0.1± 0.0 14KPs@GDE 25 0.1± 0.0 14

a Treated condition: 2 g/L MP-2, 8% (owf.) Na2CO3, 1 hb Treated condition: 2 g/L MP-2, 8% (owf.) Na2CO3, 0.1M L-cysteine, 1 hc Treated condition: pretreated with 2 g/L MP-2, 8% (owf.) Na2CO3, 0.1M L-cysteine fo

onto the negative charged surface of wool fiber, which can also beconfirmed by the weight gain (Kuzuhara and Hori, 2004). Thetensile strength in Fig. 1(c) presented the same tendency as areashrinkage, which also confirmed the effect of concentration of L-cysteine on reactivity between L-cysteine and wool fiber.

3.2. Effects of cross-linked KPs on properties of pretreated woolfabric

The cross-linking agent glycerol diglycidyl ether (GDE) wasintroduced to fix more extracted KPs onto the surface of wool fiberfor improving the anti-felting property further, and results wereshown in Table 1. The application of GDE could decrease the areashrinkage of the fabric due to more KPs were fixed on the surface ofwool fibers, while area shrinkage of the control fabric without orwith 0.1M L-cysteine pretreatment and experienced 5 g/L GDEcross-linking process was decreased to 10.4% and 5.6%, respectively.This implied that the L-cysteine pretreatment could improve theamount of active groups and promote cross-linking efficiency be-tween the fiber surface and KPs through GDE. However, it still couldnot meet the IWS TM NO.31 machine washable standard. KPs werenecessary to be introduced and fixed on the surface of wool fabric.When the KPs were fixed on the fabric after pretreatment, the areashrinkage of treated fabric was affected by the concentration ofcross-linking agent significantly. Area shrinkage decreasedremarkably with the increasing amount of cross-linking agent, anda GDE concentration at 10 g/L could be a good choice for thetreatment because the anti-felting performance was not furtherimproved when the concentration of GDE was over 10 g/L. Curingprocess during the anti-felting treatment can result in oxidation ofthe peptide of wool fiber, and the fixation of KPs with the cross-linking agent, which led to the yellowing and weight loss. Whenmore KPs were fixed on wool fibers by a higher concentration ofGDE, whiteness and weight loss decreased simultaneously. Thetensile strength of fabric treated with L-cysteine, and further fol-lowed with KPs and GDE cross-linking experienced a first increaseand then decrease with GDE concentration increasing, which canbe interpreted as that more KPs fixed onto fiber could seal the gapsof cuticle effectively and it would be helpful for improving fiberstrength, while over cross-linking can restrain the slipping of fibersduring stretching process, damaging the fiber strength. The 10 g/LGDE was optimized and the warp tensile strength of treated woolfabric decreased by 6.1% compared with control sample.

3.3. Recycle using of KPs

The residual KPs were collected, replenished with fresh KPs forrecycling after wool fabric was treated with KPs. The protein con-centration and the molecular weight of recycled KPs were shown in

gth, weight loss and whiteness.

nsile strength at break (N) Weight loss (%) Whiteness Index

arp Weft

7.9± 0.7 149.0± 0.5 1.4± 0.3 2.1± 0.33.9± 1.2 138.2± 0.8 2.7± 0.4 16.2± 1.26.0± 0.8 138.5± 0.3 2.5± 0.2 17.4± 0.19.1± 0.4 138.2± 0.2 2.0± 0.1 15.6± 0.71.9± 0.4 144.5± 0.3 1.2± 0.2 10.1± 0.58.9± 1.9 141.5± 1.2 1.2± 0.3 8.6± 0.98.4± 2.0 140.4± 1.0 1.1± 0.1 6.5± 0.24.7± 2.2 140.6± 2.3 0.5± 0.1 6.5± 0.6

r 1 h and followed by fixation of KPs with GDE cross-linking.

Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817814

Fig. 2. The protein concentration of recycled KPs was almost un-changed with 10 recycles. However, weight-average molecularweight (Mw) decreased significantly that the KPs decreased from5271 to 3964 and 3715 after 5 and 10 recycles, respectively. Thisshould be attributed to the weak alkalinity of the bath, which leadsto the cleavage of eCONH2e bond of the extracted KPs and woolfiber cortex at 60 �C (Da Silva et al., 2015). Although a lot of the

Fig. 2. The (a) protein concentration and (b) molecular weight with different recycleusing times.

Fig. 3. Effects of recycle times of the extracted KPs on (a) area shrinkage, (b) whitenessand weight loss, (c) tensile strength and (d) softness and smoothness of treated fabric.

Fig. 4. The SEM pictures and water contact angle of (a) control fabric, (b) pretreated with L-cKPs 2 times, (e) recycle using KPs 6 times, (f) recycle using KPs 10 times.

extracted KPs were adsorbed on the fiber surface, at the same timemolecular chains of wool cortex and the extracted KPs can be hy-drolyzed in the alkaline bath. Consequently, the produced smallermolecular chains can be released to the KPs bath, causing almostunchanged protein concentration and decreased molecular weight.

The effects of recycle times of the extracted KPs on properties oftreated fabric were shown in Fig. 3. Overall, the area shrinkage wasslightly increased with recycle times increasing from 1 to 10, whileit was still kept at about 1.0% and reached the IWS TM NO.31standard. Whiteness, weight loss and tensile strength were notaffected with the recycled KPs. The softness of anti-felting treatedwool fabric was improved effectively compared with the untreatedone. This can be explained that the cuticle and cortex of fibers waseroded by L-cysteine, decreasing the stiffness of fiber (Gouveiaet al., 2012). In addition, KPs fixation process was also accompa-nied by chemical corrosion on the surface of fibers, but the handle(softness and smoothness) of treated fabric was not affected by theKPs recycling. Generally, recycle using of the extracted KPs for 10times did not affect the properties of treated wool fabric comparedwith non-recycled ones.

3.4. Morphology and hydrophilicity of treated wool fabrics

The SEM pictures of treated fabrics were shown in Fig. 4. Thescale morphology of surface of the untreated wool fiber could beobserved clearly in Fig. 4(a), and apparent corrosion of cuticle ofwool fiber pretreated with L-cysteine was observed in Fig. 4(b),which indicated that the reduction took place between L-cysteineand cuticle layer. The gaps of cuticle were sealed with KPscompletely and rough surface of the fiber can be seen in Fig. 4(c),which could decrease the area shrinkage of fabrics. The surfacemorphology of the fibers treatedwith the 2nd and 6th-recycled KPs(Fig. 4(d-e)) showed similar to that shown in Fig. 4(c). Cuticle layerswere not sealed completely after KPs were recycled 10 timescompared with the previous samples, but cross-linking betweenfibers could still be observed. That was why the area shrinkageslightly increased after KPs recycle used after 10 times and all of thetreated fabrics can keep satisfying shrinkage resistance.

The pictures of de-ionized water contacted with fabric for 60 swere shown in Fig. 4. The untreated fabric demonstrated great

ysteine only, (c) pretreated and further fixed with fresh extracted KPs, (d) recycle using

Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817 815

hydrophobicity over the testing time due to the hydrophobic ofcuticle (Meade et al., 2008). Fabric pretreated with L-cysteine candamage the cuticle and more hydrophilic groups such as eOH andeNH2 appeared on the surface of wool fiber, the contact angledecreased significantly when the contact time reached 60s. KPstreated fabrics showed lower contact angle compared with the L-cysteine treated ones, which should be ascribed to the cross-linkingof KPs on the surface of fiber and gaps of cuticle, and recycled KPsdid not affect the contact angle. These results can be confirmed bythe SEM and XPS analysis.

3.5. Raman spectra of treated fabrics

The Raman spectrometer was applied to investigate the influ-ence of L-cysteine and KPs treatments onwool fibers and the resultwas shown in Fig. 5. The vibration bands were mainly lying in thewavenumber range of 500e1800 cm�1, where could be assigned toCeS and SeS bonds of cystine, amino acids (tryptophan, tyrosine,and phenylalanine), the amide I, II, III vibrations, and the CeCskeletal stretching vibration of the a-helix (Kuzuhara, 2007). Theabsorbance peaks of investigated samples showed almost the sameabsorption position in Fig. 5. As shown, absorbance at 1658, 1558,1243 cm�1 represented the Amide I, II, and III band, respectively(Kuzuhara and Hori, 2013; Tuma, 2005). The intensities of SeS bondin the pretreated sample slightly increased and CeS band in thethree curves were almost unchanged, while the SeO band at about1040 cm�1 in the L-cysteine or KPs treated samples, ascribed tocysteic acid, slightly increased. The results suggested that thecleavage of SeS groups existing in the cuticle regionwas due to thereduction process and was reconnected after oxidation process

Fig. 5. Raman spectra of treated wool fabrics.

Table 2Element analysis by X-ray photoelectron spectroscopy.

Recycle times of KPs Element composition (%)

C O N S

Control 75.65 15.16 6.98 2.22Pretreated 74.13 15.18 8.23 2.450 70.23 18.92 8.62 2.242 70.30 18.73 8.77 2.204 71.57 16.63 9.47 2.336 72.16 17.94 7.92 1.9710 72.66 16.86 8.23 2.25

while some of eSH groups were converted to cysteic acid.

3.6. X-ray photoelectron spectroscopy (XPS)

The XPS analysis of fabric surface and the specific elementcontent was shown in Table 2, respectively. Pretreated samplepossessed slightly lower carbon content and higher nitrogen andsulfur content. The damaging of lipids, especially the removal ofhydrophobic alkanes, made the nitrogen rich proteinmatrix of fiberexposed to the outer space (Dai et al., 2001). Moreover, modifica-tion of native disulfide on fiber surface by L-cysteine might result inthe increasing of sulfur composition, which can be also identifiedby Raman spectra. The fabric fixed with KPs showed significantreducing carbon content and increasing both oxygen and nitrogencontents compared with the untreated fabric. The KPs react withcross-linking agent (GDE) can form a thin film on the surface offiber. KPs filmwith a relative lower carbon content and GDE with ahigher composition of -C-O-C- can improve hydrophilicity of fibereffectively, which might explain the increasing of oxygen element.The fabrics treated with the 10 times recycled KPs almost possessthe same element compositionwith an expected slightly increasingof carbon component, which might be due to that the KPs withlower Mw would not cover the surface effectively compared withthe ones treated with less times of recycled KPs.

3.7. Dyeability of treated wool fabrics

According to the discussion in SEM and Raman, cuticle of fiberwas eroded, bringing better hydrophilicity, and more reactivegroups such as eOH or eNH2 were generated on the fibers after L-cysteine or KPs treatment. The hydrophilicity of the treated fabriccan enhance the absorption of dyes. In addition, the active groups(eC(Br)]CH2 and eCH]CH2) of reactive dyes can react with eOHor eNH2 of the fibers. Consequently, the treated fabrics shouldexhibit better dyeability and react with more reactive dyes. Toexamine this, wool fabric fixed with extracted KPs was dyed withthe reactive dye Lanasol Red CE at 95 �C following standard dyeingprotocols (Smith and Shen, 2011). The K/S value and dye fixationefficiency (Fixation %) of dyed fabric were shown in Fig. 6, in whichfabric pretreated with L-cysteine showed better dyeability, effec-tively reflected by higher K/S value and Fixation %. Moreover, thewool fabrics fixed with KPs possessed a little higher Fixation % than

Fig. 6. The K/S value and dye fixation of wool fabrics that dyed with 2% (owf.) LanasolRed CE. (For interpretation of the references to colour in this figure legend, the readeris referred to the web version of this article.)

Fig. 7. The picture of wool fabrics dyed with Lanasol Red CE with or without recycled KPs. (For interpretation of the references to colour in this figure legend, the reader is referredto the web version of this article.)

Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817816

the only pretreated ones and the recycled KPs did not affect the dyefixation of treated wool fabric after dyeing with 2% Lanasol Red CE.This might be ascribed to the higher reactivity and better affinity todyes when KPs were fixed onto fabric surface (Kantouch et al.,2011). The photos of dyed fabrics were shown in Fig. 7. Comparedwith untreated fabric, L-cysteine pretreated and KPs fixed fabricsdemonstrated relative deeper color and better planeness especiallythe edges of fabrics. This could confirm the modification of fabricsurface and the improvement of anti-felting property.

4. Conclusions

In this work, a green anti-felting finishing process based on L-cysteine pretreatment followed by KPs cross-linking fixation wasinvestigated. The padded-out KPs solution was collected andreplenishedwith a small amount of fresh KPs for recycle using. Areashrinkage about 1.3% still could be achieved after 7 A and 3 times5 Awashes according to IWS TMNO.31 when the KPs were recycledfor 10 times. The protein concentration of waste KPs solution wasalmost unchanged after recycle using, despite the weight-averagemolecular weight decreased significantly. Compared with un-treated wool fabric, there was an improvement in whiteness,softness, dyeability, hydrophilicity and an acceptable loss in weight(about 1%) and in strength (about 6.1% in warp direction) afterfixation of the extracted KPs. The SEM photos demonstrated thecorrosion of cuticle of wool fiber when fabric was pretreated withL-cysteine, and the gaps of cuticle were sealed completely with KPsbesides rough surface of the fiber can also be observed. Ramanspectra revealed that the cleavage and reconnection of -S-S- groupswhen fabric treated by L-cysteine pretreatment or KPs fixationprocess. The fabric treated with the extracted KPs showed signifi-cant reducing carbon content, and increasing both oxygen and ni-trogen contents compared with the untreated fabric by XPSanalysis. There was no significant difference of fabric propertiesbetween the wool fabrics treated with the recycled KPs and thosewith the fresh one. These improvements in various propertiesindicated that durable fixation of KPs onto surface of wool fiber andrecycle using of KPs have great potential to be applied in environ-mental friendly shrink-resistant process.

Conflicts of interest

None.

Acknowledgements

The authors thank the National Engineering Research Center forDyeing and Finishing of Textiles for financial support and the StateKey Laboratory for Modification of Chemical Fibers and PolymerMaterials for spectroscopic measurements and SEM examination.

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