- Email: [email protected]
Recycling keratin polypeptides for anti-felting treatment of wool based on L-cysteine pretreatment
Journal of Cleaner Production 183 (2018) 810e817
Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Recycling keratin polypeptides for anti-felting treatment of wool based on L-cysteine pretreatment Zhuang Du a, Bolin Ji a, b, Kelu Yan a, b, * a b
College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, PR China 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
a b s t r a c t
Article history: Received 7 July 2017 Received in revised form 27 December 2017 Accepted 19 February 2018 Available online 20 February 2018
An anti-felting finishing process based on recycling waste wool material was proposed. Wool fabric was pretreated with L-cysteine and then treated with the keratin polypeptides, extracted by protease from the waste wool. And then, wool fabric was treated with glycerol diglycidyl ether as cross-linking agent for a durable anti-felting effect. The padded-out keratin polypeptides solution was collected, replenished with a small amount of fresh keratin polypeptides and recycled for 10 times. An excellent anti-felting performance was still achieved when wool fabric was treated with the 10th-recycled keratin polypeptides. The protein concentration of 10th-recycled keratin polypeptides was almost unchanged, but the weight-average molecular weight decreased. There was no significant difference on the modified surfaces between the wool fabrics treated with recycled keratin polypeptides and those with the fresh ones. Compared with the control, 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) after fixation of the extracted keratin polypeptides onto the fabrics. The modification mechanism was confirmed by scanning electron microscopy, Raman spectra and X-ray photoelectron spectroscopy analysis of treated wool fabric that L-cysteine can erode the fiber surface, generating more reactive groups, and then keratin polypeptides can easily cross-linked onto the fiber surface by glycerol diglycidyl ether or covered the fiber surface. © 2018 Elsevier Ltd. All rights reserved.
Keywords: Keratin polypeptides Recycle Anti-felting treatment Wool L-cysteine
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 antifelting (Kaur and Chakraborty, 2015). Anti-felting treatment always involves the reduction/oxidation process to erode the scale layer and/or coating the polymer on the surface of wool fiber (Smith and Shen, 2011). The traditional anti-felting treatment is chlorination/resin method (chlorinate-Hercosett process), while it would produce harmful absorbable organic halogens (AOX) (Shi et al., 2014). To avoid release of AOX and reach the machine washable standards, alternative and environmentally friendly processes should be developed. Coating with polymer resins on the surface of wool fabric can obtain satisfying anti-felting property (Zhao et al., 2013). However, a large amount of resins should be required to
* Corresponding author. National Engineering Research Center for Dyeing and Finishing of Textiles, College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, PR China. E-mail address: [email protected] (K. Yan). https://doi.org/10.1016/j.jclepro.2018.02.196 0959-6526/© 2018 Elsevier Ltd. All rights reserved.
meet the machine washable standards and thus cause wool fabric a stiff handle. The proteolysis of protein compounds can be catalyzed by protease without any chlorine release, nevertheless protease can penetrate into the inner of wool fiber to degrade the macromolecular chains, resulting in severe damage of strength, which restricts its application (Cui et al., 2009). The diffusibility of enzyme can be decreased when it is immobilized to a specific polymer, which could restrict the proteolysis of protein compounds present on the scale layer of fiber (Madhu and Chakraborty, 2017; Shen et al., 2007; Silva et al., 2006; Smith et al., 2010). Wool fabric treated with the modified enzyme shows improvement of antifelting property, but the immobilization of enzyme would be too expensive to achieve industrialization. It should be meaningful if anti-felting property of wool fabrics can be realized with more effective and green way. Currently, various attempts have been made to the utilization of biomass, and many kinds of biopolymers worked as resins are applied on the wool fabric to achieve anti-felting, such as silk sericin, collagen and casein, which could obtain softer handle than the synthetic poly recki and Go recki, 2010; Xu et al., mers (Cortez et al., 2007; Go
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817
2013). Keratin polypeptides (KPs) as one kind of the most abundant biomass can be extracted from keratin-containing wastes, such as waste wool, hair, feathers and so on (Reddy et al., 2014; Xie et al., 2005). It is advisable to extract and dissolve KPs from keratin wastes for development of novel biopolymers (Holkar et al., 2016). Compared with the traditional chemical extraction process, enzymatic hydrolysis is usually applied in a mild condition or enhancing the hydrolysis simply by exerting pressure without much chemical reagents, which can be a green method to extract the KPs (Brandelli et al., 2010; Marousek et al., 2013). To fix KPs onto the wool fabric, a pretreatment is generally required to improve surface affinity between wool fabric and KPs. The sodium sulfite and sodium bisulfite are frequently used as reducing agents to pretreat wool fabric, but severe fiber damage and water pollution could be generated during the treatment process. For the popular thiol-type reducing agent, Lcysteine can break the inert -S-S- group that lied in the cuticle or cortex of wool effectively and cause less damage on wool fiber than thioglycolic acid as well as less toxicity than 2-mercaptoethanol (Wang et al., 2016). It can not only cleave the -S-S- of keratin, but also connect with keratin and form new disulfide bond R-S-SCH(NH2)COO. This characteristic could play an important role in anti-felting treatment and surface modification. Most reports take L-cysteine as a green reducing agent to extract keratin from wool or feather materials (Xu and Yang, 2014). However, there is no report on L-cysteine as a pretreatment agent for wool anti-felting finish. The cleavage of -S-S- group of cuticle treated by L-cysteine can decrease the directional friction effect (DFE) of wool fabric, new disulfide bond can be generated between L-cysteine and wool fiber, and provided more reactive sites to promote the reaction between fiber and KPs. Furthermore, difunctional epoxide glycerol diglycidyl ether (GDE) works as an effective cross-linking agent to fix protein onto wool fabric by reacting with the eNH2 or eOH of wool fiber and KPs (Hesse et al., 1995; Smith and Shen, 2011). In this paper, the KPs were extracted from the waste wool fibers with protease and were fixed on the wool fabric that pretreated by L-cysteine for an anti-felting purpose. Recycle using of KPs was investigated and area shrinkage, softness, weight loss and tensile strength of the treated wool fabric were also studied. The modified surface of wool fabric was assessed by scanning electron microscopy (SEM), and the anti-felting mechanism was confirmed by Xray photoelectron spectroscopy (XPS), Raman spectra, contact angle and dyeability. 2. Experimental section 2.1. Materials Undyed waste wool fibers used in the extraction process were byproducts of wool weaving process supplied by Shandong Ruyi Wool Co. (Jining, Shandong Province, China). Scoured and undyed wool fabric (144 g/m2, wool 100%, woven), and non-ionic surfactant MP-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 Chemical Reagent Co., Ltd. (Shanghai, China) and used as received. The crosslinking agent glycerol diglycidyl ether (GDE) was purchased from Sigma-Aldrich. The reactive dye, Lanasol Red CE used to test the dyeability of treated wool fabric was supplied by Huntsman Co. (USA). The enzyme used was a serine type protease, Esperase 8.0L extracted from Bacillus subtilis was supplied by Novozymes (Beijing, China), and the enzyme activity based on casein substrate is 2.29 u/mg. Enhanced bicinchoninic acid (BCA) Protein Assay Kit to detect the protein concentration was purchased from Beyotime Biotechnology Co., Ltd. (Shanghai, China).
811
2.2. Preparation of keratin polypeptides (KPs) Waste wool fibers were firstly treated with 15 g/L Na2CO3 solution at 95 C for 15 min, and then washed by distilled water to be neutral pH condition. The washed product was dried at 80 C and subsequently milled into powders. Next, the wool powders were placed into a 0.02 M phosphate buffer (pH 8.0) containing 5 g/L Na2SO3 with a liquor to goods ratio of 20:1 and treated at 60 C for 30 min by using a Roaches Pyrotec 2000 dyeing machine at a 40 rpm shaking rate. The protease was added into the previous shaking bath to reach a concentration of 2.0 mg/mL, and then the mixed solution was agitated at 40 rpm for 2 h at 65 C. The enzyme in the mixture was deactivated by raising the temperature to 90 C for 10 min and with the agitation at 40 rpm. Then, cooled the suspension to the room temperature and separated by centrifugation at 6000 rpm using a Thermofisher Heraeus Multifuge X3 centrifuge. The supernatant liquid was collected and applied in the later wool fabric treatment (Smith and Shen, 2011). The protein concentration of extracted KPs was determined by the BCA assay kit. A gradient concentration (g/L) of bovine serum albumin (BSA) standard solution was designed and the absorbance was recorded at 562 nm (A562). A standard curve was automatically generated using the regression equation:
y ¼ ax þ b R2 0:99
(1)
where R2 represented the linear regression coefficient. The absorbance values of the samples were recorded and substituted in the regression equation to calculate the protein concentration of the KPs. The molecular weight of KPs was determined by Gel Permeation 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 a liquor 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 fabric tension caused by machine drafting process and the treated fabric was set as control sample. Different amount of L-cysteine was added into the relaxation process solution to pretreat wool fabric. And then the pretreated fabric was washed with distilled water until the washing water achieved neutral pH and then dried in air. The pretreated fabric was treated in the extracted KPs solutions with a liquor to goods ratio of 10: 1 at 60 C for 30 min by using a Roaches Pyrotec 2000 dyeing machine at a 20 rpm shaking rate, and the fabric was taken out from the KPs solution and passed through a laboratory padder (Rapid Co., Ltd.) to pad the extra KPs (pick-up 80% owf.). After the padding, we collected the remaining KPs solutions. And then, fabric was transferred into a new bath set pH at 7.3 using 0.02 M phosphate buffer containing different amounts of GDE with a liquor to goods ratio of 10:1 for 30 min at 60 C with 20 rpm. After the wet treatment steps, fabric was treated with a pad process that padded with a pick-up 80% owf. and cured at 140 C for 3 min. The fresh extracted KPs solution was added to the previous collected solutions and refilled to the initial volume (for example, 100 mL KPs would need 16 mL of fresh KPs to refill to the initial volume after treatment). And repeat previous treatment process to recycle using KPs (Scheme 1). 2.4. Fabric testing Softness and smoothness of the fabric was measured according to the AATCC 202-2012 relative hand value of textiles instrument
812
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817
Scheme 1. Schematic diagram of the anti-felting treatment of wool fabric and recycle using of extracted keratin polypeptides.
temperature of dye bath was increased to 95 C at a rate of 1 C/min and kept for 60 min. After dyeing, fabric was successively washed by room temperature water, 60 C water and 95 C soaping solution containing 2 g/L Ultravon PL (Huntsman Co., USA) non-ionic surfactant to remove unfixed dyes. The dyed fabric was dried at 40 C and the K/S value of dyed fabric was measured by Datacolor 650 reflectance spectrophotometer to characterize dye uptake. Dye fixation efficiency (Fixation %) is measured according to the reference (Smith and Shen, 2011). It is the percentage of the dye originally applied to the fabric which becomes bound covalently. The dyebath solutions were collected before and after the dyeing process and the solution after soaping were diluted to the same fixed volume and the absorbance were measured at 503 nm, the wavelength of maximum absorption (lmax) specific to Lanasol Red CE, using a Hitachi U-2910 UV/visible spectrophotometer. Dye fixation efficiency (Fixation %) was calculated using Eq. (6).
Fixationð%Þ ¼ method by the PhabrOmeter 3. The relaxation treated wool fabric was set as the control, and the higher the value was, the softer handle or the smoothness surface of the fabric would be. The measurement of area shrinkage due to washing of the treated woven wool fabric was tested according to IWS TM NO.31 by using a washing machine (Washcator FOM71 CLS, Electrolux) for 1 7 A and 3 5 A programs. The area shrinkage was calculated by the following equations:
WSð%Þ ¼
L0 L1 100 L0
(2)
L0 L1 100 L0
(3)
Area Shrinkageð%Þ ¼ WS þ LS
(4)
LSð%Þ ¼
where L0 was the marked length before fabric was washed, and L1 was the length of the marked positions after standard washing, WS was the average value of three WS tests of size changing in weft direction (%) and LS was the average value of three LS tests of size changing in warp direction (%). The weight loss (WL) of the wool fabric after anti-felting treatment was calculated following Eq. (5):
WL ð%Þ ¼
W0 W1 100 W0
(5)
where W0 was the weight of conditioned wool fabric prior to extracted KPs treatment and W1 was the weight of conditioned wool fabric after extracted KPs treatment. The tensile strength of fabric at break was measured in the warp-wise and weft-wise directions using universal testing machine (H5KS, Tinius Olsen, USA) in accordance with the testing standard, ASTM D5035-1995. The fabric samples were cut into rectangular shape (100 25 mm2), and every sample took an average value of five replicates. A Datacolor 650 reflectance spectrophotometer (Datacolor, USA) was used to determine the whiteness of the treated wool fabric in terms of the CIE whiteness index. Each sample was folded into four layers and measured four times. All values were measured and calculated using ColorTools QC software with illuminant and observer conditions of D65. The treated wool fabric was dyed with the reactive dye Lanasol Red CE (2% owf.), pH was adjusted to 4.0 with acetic acid and the temperature was set at 40 C at the beginning, and then the
Abs0 Abs1 Abs2 100 Abs0
(6)
where Abs0 is the absorbance of the original dye-bath solution at lmax, Abs1 is the absorbance of the exhausted dye-bath solution at lmax and Abs2 is the absorbance of the solution after soaping at lmax. Hydrophilicity change of the treated fabric was determined by measuring the contact angle between the surface of fabric and deionized water droplet at 27 C using drop shape analyzer (DSA-25, KRUSS GmbH, Hamburg). The 4 mL drop of de-ionized water was located on the surface and the images were captured when they contacted 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, JEOL Ltd. Japan). The samples were sputter coated with gold under vacuum 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 using a Physical Electronics Industries PHI Model 5300 surface analysis system. This system employs a double-pass cylindrical mass analyzer (20-270AR) with a perpendicularly mounted dual (Mg/ Mg) X-ray source. A single MgKa X-ray source was operated at 250 W and 14 kV. Survey spectra were obtained over the range 0e1100 eV using a pass energy of 100 eV with an acquisition time of 2 min. 2.7. Raman spectra Raman spectra of the fabric samples were collected by a XploRA (HORIBA Jobin Yvon, France) Raman spectrometer. The laser excitation was provided with an argon ion laser operating at 50 mW of 514.5 nm output. The sample was focused to around 1 mm using a 100 objective. A spectra resolution of 5 cm1 with 1 scan (1000 s) was used over the scanning range of 200e2000 cm1. 2.8. Statistical analysis All of the data reported are mean ± standard deviation (SD). The statistical 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
3. Results and discussion 3.1. Pretreatment of wool fabric with L-cysteine Reducing agent L-cysteine can break disulfide bond (-S-S-) and improve the anti-felting property of wool fabric. The effect of Lcysteine concentration on properties of treated fabric was investigated, as shown in Fig. 1. The lower the area shrinkage of wool fabric is, the better the anti-felting property will be. Fig. 1(a) indicated that area shrinkage decreased from 14.3% to 8.2% by adding 0.1 M L-cysteine. However, higher concentration of L-cysteine did not effectively improve the anti-felting property, and even decrease it based on the higher area shrinkage. It should be attributed to the thiol group (-SH) of L-cysteine, which can break the disulfide (-S-S-) of the cuticle and form the Wool-S-S-CH2CH(NH2)COOH crosslinkage or crosslinked with the other part that derived from the broken wool disulfide. (Wang et al., 2016). When the concentration was lower than 0.1 M, L-cysteine demonstrated high reducibility due to generating many -S- reactive sites, and with the concentration increasing, L-cysteine could generate less -S-, indicating lower reactivity of L-cysteine, because the eCOOH in L-cysteine molecule would suppress the generation of -S- at a high L-cysteine concentration. Whiteness, weight loss and tensile strength were all affected for this reason, and the results are shown in Fig. 1(bec). Lcysteine can destroy cuticles and lipids, which increased whiteness effectively. When the concentration of L-cysteine exceeded 0.1 M, although less reactivity of L-cysteine would be, the whiteness and area shrinkage increased simultaneously. This phenomenon can be explained that positive charged eNHþ 3 of L-cysteine was adsorbed
813
onto the negative charged surface of wool fiber, which can also be confirmed by the weight gain (Kuzuhara and Hori, 2004). The tensile strength in Fig. 1(c) presented the same tendency as area shrinkage, which also confirmed the effect of concentration of Lcysteine on reactivity between L-cysteine and wool fiber. 3.2. Effects of cross-linked KPs on properties of pretreated wool fabric The cross-linking agent glycerol diglycidyl ether (GDE) was introduced to fix more extracted KPs onto the surface of wool fiber for improving the anti-felting property further, and results were shown in Table 1. The application of GDE could decrease the area shrinkage of the fabric due to more KPs were fixed on the surface of wool fibers, while area shrinkage of the control fabric without or with 0.1 M L-cysteine pretreatment and experienced 5 g/L GDE cross-linking process was decreased to 10.4% and 5.6%, respectively. This implied that the L-cysteine pretreatment could improve the amount of active groups and promote cross-linking efficiency between the fiber surface and KPs through GDE. However, it still could not meet the IWS TM NO.31 machine washable standard. KPs were necessary to be introduced and fixed on the surface of wool fabric. When the KPs were fixed on the fabric after pretreatment, the area shrinkage of treated fabric was affected by the concentration of cross-linking agent significantly. Area shrinkage decreased remarkably with the increasing amount of cross-linking agent, and a GDE concentration at 10 g/L could be a good choice for the treatment because the anti-felting performance was not further improved when the concentration of GDE was over 10 g/L. Curing process during the anti-felting treatment can result in oxidation of the peptide of wool fiber, and the fixation of KPs with the crosslinking agent, which led to the yellowing and weight loss. When more KPs were fixed on wool fibers by a higher concentration of GDE, whiteness and weight loss decreased simultaneously. The tensile strength of fabric treated with L-cysteine, and further followed with KPs and GDE cross-linking experienced a first increase and then decrease with GDE concentration increasing, which can be interpreted as that more KPs fixed onto fiber could seal the gaps of cuticle effectively and it would be helpful for improving fiber strength, while over cross-linking can restrain the slipping of fibers during stretching process, damaging the fiber strength. The 10 g/L GDE was optimized and the warp tensile strength of treated wool fabric decreased by 6.1% compared with control sample. 3.3. Recycle using of KPs
Fig. 1. The effect of L-cysteine concentration on wool fabric in terms of area shrinkage, whiteness, weight loss and tensile strength.
The residual KPs were collected, replenished with fresh KPs for recycling after wool fabric was treated with KPs. The protein concentration and the molecular weight of recycled KPs were shown in
Table 1 The effects of GDE concentration on wool fabric in terms of area shrinkage, tensile strength, weight loss and whiteness. Sample
Controla Pretreatedb KPs@GDEc KPs@GDE KPs@GDE KPs@GDE KPs@GDE KPs@GDE a b c
GDE concentration (g/L)
5 5 0 5 10 15 20 25
Area shrinkage (%)
10.4 ± 1.1 5.6 ± 0.9 7.6 ± 0.3 2.1 ± 0.2 0.3 ± 0.1 0.1 ± 0.1 0.1 ± 0.0 0.1 ± 0.0
Tensile strength at break (N) Warp
Weft
157.9 ± 0.7 143.9 ± 1.2 146.0 ± 0.8 149.1 ± 0.4 151.9 ± 0.4 148.9 ± 1.9 148.4 ± 2.0 144.7 ± 2.2
149.0 ± 0.5 138.2 ± 0.8 138.5 ± 0.3 138.2 ± 0.2 144.5 ± 0.3 141.5 ± 1.2 140.4 ± 1.0 140.6 ± 2.3
Weight loss (%)
Whiteness Index
1.4 ± 0.3 2.7 ± 0.4 2.5 ± 0.2 2.0 ± 0.1 1.2 ± 0.2 1.2 ± 0.3 1.1 ± 0.1 0.5 ± 0.1
2.1 ± 0.3 16.2 ± 1.2 17.4 ± 0.1 15.6 ± 0.7 10.1 ± 0.5 8.6 ± 0.9 6.5 ± 0.2 6.5 ± 0.6
Treated condition: 2 g/L MP-2, 8% (owf.) Na2CO3, 1 h Treated condition: 2 g/L MP-2, 8% (owf.) Na2CO3, 0.1 M L-cysteine, 1 h Treated condition: pretreated with 2 g/L MP-2, 8% (owf.) Na2CO3, 0.1 M L-cysteine for 1 h and followed by fixation of KPs with GDE cross-linking.
814
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817
Fig. 2. The protein concentration of recycled KPs was almost unchanged with 10 recycles. However, weight-average molecular weight (Mw) decreased significantly that the KPs decreased from 5271 to 3964 and 3715 after 5 and 10 recycles, respectively. This should be attributed to the weak alkalinity of the bath, which leads to the cleavage of eCONH2e bond of the extracted KPs and wool fiber 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 recycle using times.
extracted KPs were adsorbed on the fiber surface, at the same time molecular chains of wool cortex and the extracted KPs can be hydrolyzed in the alkaline bath. Consequently, the produced smaller molecular chains can be released to the KPs bath, causing almost unchanged protein concentration and decreased molecular weight. The effects of recycle times of the extracted KPs on properties of treated fabric were shown in Fig. 3. Overall, the area shrinkage was slightly increased with recycle times increasing from 1 to 10, while it was still kept at about 1.0% and reached the IWS TM NO.31 standard. Whiteness, weight loss and tensile strength were not affected with the recycled KPs. The softness of anti-felting treated wool fabric was improved effectively compared with the untreated one. This can be explained that the cuticle and cortex of fibers was eroded by L-cysteine, decreasing the stiffness of fiber (Gouveia et al., 2012). In addition, KPs fixation process was also accompanied by chemical corrosion on the surface of fibers, but the handle (softness and smoothness) of treated fabric was not affected by the KPs recycling. Generally, recycle using of the extracted KPs for 10 times did not affect the properties of treated wool fabric compared with non-recycled ones. 3.4. Morphology and hydrophilicity of treated wool fabrics
Fig. 3. Effects of recycle times of the extracted KPs on (a) area shrinkage, (b) whiteness and weight loss, (c) tensile strength and (d) softness and smoothness of treated fabric.
The SEM pictures of treated fabrics were shown in Fig. 4. The scale morphology of surface of the untreated wool fiber could be observed clearly in Fig. 4(a), and apparent corrosion of cuticle of wool fiber pretreated with L-cysteine was observed in Fig. 4(b), which indicated that the reduction took place between L-cysteine and cuticle layer. The gaps of cuticle were sealed with KPs completely and rough surface of the fiber can be seen in Fig. 4(c), which could decrease the area shrinkage of fabrics. The surface morphology of the fibers treated with the 2nd and 6th-recycled KPs (Fig. 4(d-e)) showed similar to that shown in Fig. 4(c). Cuticle layers were not sealed completely after KPs were recycled 10 times compared with the previous samples, but cross-linking between fibers could still be observed. That was why the area shrinkage slightly increased after KPs recycle used after 10 times and all of the treated fabrics can keep satisfying shrinkage resistance. The pictures of de-ionized water contacted with fabric for 60 s were shown in Fig. 4. The untreated fabric demonstrated great
Fig. 4. The SEM pictures and water contact angle of (a) control fabric, (b) pretreated with L-cysteine only, (c) pretreated and further fixed with fresh extracted KPs, (d) recycle using KPs 2 times, (e) recycle using KPs 6 times, (f) recycle using KPs 10 times.
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817
hydrophobicity over the testing time due to the hydrophobic of cuticle (Meade et al., 2008). Fabric pretreated with L-cysteine can damage the cuticle and more hydrophilic groups such as eOH and eNH2 appeared on the surface of wool fiber, the contact angle decreased significantly when the contact time reached 60s. KPs treated fabrics showed lower contact angle compared with the Lcysteine treated ones, which should be ascribed to the cross-linking of KPs on the surface of fiber and gaps of cuticle, and recycled KPs did not affect the contact angle. These results can be confirmed by the SEM and XPS analysis. 3.5. Raman spectra of treated fabrics The Raman spectrometer was applied to investigate the influence of L-cysteine and KPs treatments on wool fibers and the result was shown in Fig. 5. The vibration bands were mainly lying in the wavenumber range of 500e1800 cm1, where could be assigned to CeS and SeS bonds of cystine, amino acids (tryptophan, tyrosine, and phenylalanine), the amide I, II, III vibrations, and the CeC skeletal stretching vibration of the a-helix (Kuzuhara, 2007). The absorbance peaks of investigated samples showed almost the same absorption position in Fig. 5. As shown, absorbance at 1658, 1558, 1243 cm1 represented the Amide I, II, and III band, respectively (Kuzuhara and Hori, 2013; Tuma, 2005). The intensities of SeS bond in the pretreated sample slightly increased and CeS band in the three curves were almost unchanged, while the SeO band at about 1040 cm1 in the L-cysteine or KPs treated samples, ascribed to cysteic acid, slightly increased. The results suggested that the cleavage of SeS groups existing in the cuticle region was due to the reduction process and was reconnected after oxidation process
815
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 element content was shown in Table 2, respectively. Pretreated sample possessed slightly lower carbon content and higher nitrogen and sulfur content. The damaging of lipids, especially the removal of hydrophobic alkanes, made the nitrogen rich protein matrix of fiber exposed to the outer space (Dai et al., 2001). Moreover, modification of native disulfide on fiber surface by L-cysteine might result in the increasing of sulfur composition, which can be also identified by Raman spectra. The fabric fixed with KPs showed significant reducing carbon content and increasing both oxygen and nitrogen contents compared with the untreated fabric. The KPs react with cross-linking agent (GDE) can form a thin film on the surface of fiber. KPs film with a relative lower carbon content and GDE with a higher composition of -C-O-C- can improve hydrophilicity of fiber effectively, which might explain the increasing of oxygen element. The fabrics treated with the 10 times recycled KPs almost possess the same element composition with an expected slightly increasing of carbon component, which might be due to that the KPs with lower Mw would not cover the surface effectively compared with the 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 fiber was eroded, bringing better hydrophilicity, and more reactive groups such as eOH or eNH2 were generated on the fibers after Lcysteine or KPs treatment. The hydrophilicity of the treated fabric can enhance the absorption of dyes. In addition, the active groups (eC(Br)]CH2 and eCH]CH2) of reactive dyes can react with eOH or eNH2 of the fibers. Consequently, the treated fabrics should exhibit better dyeability and react with more reactive dyes. To examine this, wool fabric fixed with extracted KPs was dyed with the reactive dye Lanasol Red CE at 95 C following standard dyeing protocols (Smith and Shen, 2011). The K/S value and dye fixation efficiency (Fixation %) of dyed fabric were shown in Fig. 6, in which fabric pretreated with L-cysteine showed better dyeability, effectively reflected by higher K/S value and Fixation %. Moreover, the wool fabrics fixed with KPs possessed a little higher Fixation % than
Fig. 5. Raman spectra of treated wool fabrics.
Table 2 Element analysis by X-ray photoelectron spectroscopy. Recycle times of KPs
Element composition (%) C
O
N
S
Control Pretreated 0 2 4 6 10
75.65 74.13 70.23 70.30 71.57 72.16 72.66
15.16 15.18 18.92 18.73 16.63 17.94 16.86
6.98 8.23 8.62 8.77 9.47 7.92 8.23
2.22 2.45 2.24 2.20 2.33 1.97 2.25
Fig. 6. The K/S value and dye fixation of wool fabrics that dyed with 2% (owf.) Lanasol Red CE. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
816
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817
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 referred to the web version of this article.)
the only pretreated ones and the recycled KPs did not affect the dye fixation of treated wool fabric after dyeing with 2% Lanasol Red CE. This might be ascribed to the higher reactivity and better affinity to dyes when KPs were fixed onto fabric surface (Kantouch et al., 2011). The photos of dyed fabrics were shown in Fig. 7. Compared with untreated fabric, L-cysteine pretreated and KPs fixed fabrics demonstrated relative deeper color and better planeness especially the edges of fabrics. This could confirm the modification of fabric surface and the improvement of anti-felting property.
4. Conclusions In this work, a green anti-felting finishing process based on Lcysteine pretreatment followed by KPs cross-linking fixation was investigated. The padded-out KPs solution was collected and replenished with a small amount of fresh KPs for recycle using. Area shrinkage about 1.3% still could be achieved after 7 A and 3 times 5 A washes according to IWS TM NO.31 when the KPs were recycled for 10 times. The protein concentration of waste KPs solution was almost unchanged after recycle using, despite the weight-average molecular weight decreased significantly. Compared with untreated 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) after fixation of the extracted KPs. The SEM photos demonstrated the corrosion of cuticle of wool fiber when fabric was pretreated with L-cysteine, and the gaps of cuticle were sealed completely with KPs besides rough surface of the fiber can also be observed. Raman spectra revealed that the cleavage and reconnection of -S-S- groups when fabric treated by L-cysteine pretreatment or KPs fixation process. The fabric treated with the extracted KPs showed significant reducing carbon content, and increasing both oxygen and nitrogen contents compared with the untreated fabric by XPS analysis. There was no significant difference of fabric properties between the wool fabrics treated with the recycled KPs and those with the fresh one. These improvements in various properties indicated that durable fixation of KPs onto surface of wool fiber and recycle using of KPs have great potential to be applied in environmental friendly shrink-resistant process.
Conflicts of interest None.
Acknowledgements The authors thank the National Engineering Research Center for Dyeing and Finishing of Textiles for financial support and the State Key Laboratory for Modification of Chemical Fibers and Polymer Materials for spectroscopic measurements and SEM examination. References Brandelli, A., Daroit, D.J., Riffel, A., 2010. Biochemical features of microbial keratinases and their production and applications. Appl. Microb. Biotechnol. 85 (6), 1735e1750. Cortez, J., Anghieri, A., Bonner, P.L.R., Griffin, M., Freddi, G., 2007. Transglutaminase mediated grafting of silk proteins onto wool fabrics leading to improved physical and mechanical properties. Enzyme Microb. Technol. 40 (7), 1698e1704. Cui, L., Wang, Q., Wang, P., Huan, Q., Fan, X., 2009. Transglutaminase-mediated crosslinking of gelatin onto wool surfaces to improve the fabric properties. J. Appl. Polym. Sci. 113 (4), 2598e2604. Da Silva, C.M.L., Spinelli, E., Rodrigues, S.V., 2015. Fast and sensitive collagen quantification by alkaline hydrolysis/hydroxyproline assay. Food Chem. 173, 619e623. Dai, X.J., Elms, F.M., George, G.A., 2001. Mechanism for the plasma oxidation of wool fiber surfaces from XPS studies of self-assembled monolayers. J. Appl. Polym. Sci. 80 (9), 1461e1469. Du, Z., Hu, C., Xie, Z., Yan, K., 2017. A bio-antifelting agent based on waterborne polyurethane and keratin polypeptides extracted by protease from waste wool. Fibers Polym. 18 (4), 641e648. recki, R.S., Go recki, M.T., 2010. Utilization of waste wool as substrate amendment Go in pot cultivation of tomato, sweet pepper, and eggplant. Pol. J. Environ. Stud. 19 (5), 1083e1087. , D., Henriques, M., 2012. Functionalization of wool with L-cysteine: Gouveia, I.C., Sa process characterization and assessment of antimicrobial activity and cytotoxicity. J. Appl. Polym. Sci. 124 (2), 1352e1358. €cker, H., 1995. Zero-AOX shrinkproofing treatment for Hesse, A., Thomas, H., Ho wool top and fabric part II: collagen resin application. Text. Res. J. 65 (7), 371e378. Holkar, C.R., Jadhav, A.J., Bhavsar, P.S., Kannan, S., Pinjari, D.V., Pandit, A.B., 2016. Acoustic cavitation assisted akaline hydrolysis of wol bsed keratins to produce organic amendment fertilizers. ACS Sustain. Chem. Eng. 4 (5), 2789e2796. Kantouch, A., Allam, O., El-Gabry, L., El-Sayed, H., 2011. Effect of pretreatment of wool fabric with keratin on its dyeability with acid and reactive dyes. Indian J. Fiber Text. Res. 37, 157e161. Kaur, A., Chakraborty, J.N., 2015. Controlled eco-friendly shrink-resist finishing of wool using bromelain. J. Clean. Prod. 108, 503e513. Kuzuhara, A., 2007. Analysis of structural changes in permanent waved human hair using Raman spectroscopy. Biopolymers 85 (3), 274e283. Kuzuhara, A., Hori, T., 2004. Diffusion behavior of reducing agents into keratin fibers using microspectrophotometry. J. Appl. Polym. Sci. 94 (3), 1131e1138. Kuzuhara, A., Hori, T., 2013. Analysis of heterogeneous reaction between reducing agents and keratin fibers using Raman spectroscopy and microspectrophotometry. J. Mol. Struct. 1037, 85e92. Madhu, A., Chakraborty, J.N., 2017. Developments in application of enzymes for textile processing. J. Clean. Prod. 145, 114e133. Marousek, J., Itoh, S., Higa, O., Kondo, Y., Ueno, M., Suwa, R., Tominaga, J.,
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817 Kawamitsu, Y., 2013. Enzymatic hydrolysis enhanced by pressure shockwaves opening new possibilities in Jatropha CurcasL. processing. J. Chem. Technol. Biotechnol. 88 (9), 1650e1653. Meade, S.J., Caldwell, J.P., Hancock, A.J., Coyle, K., Dyer, J.M., Bryson, W.G., 2008. Covalent modification of the wool fiber surface: the attachment and durability of model surface treatments. Text. Res. J. 78 (12), 1087e1097. Reddy, N., Chen, L., Zhang, Y., Yang, Y., 2014. Reducing environmental pollution of the textile industry using keratin as alternative sizing agent to poly(vinyl alcohol). J. Clean. Prod. 65, 561e567. Shen, J., Rushforth, M., Cavaco-Paulo, A., Guebitz, G., Lenting, H., 2007. Development and industrialisation of enzymatic shrink-resist process based on modified proteases for wool machine washability. Enzyme Microb. Technol. 40 (7), 1656e1661. Shi, J., Han, X., Kelu, Y., 2014. A novel bio-functional finishing agent for wool based on waterborne polyurethane mixed with chitosan. Text. Res. J. 84 (11), 1174e1182. Silva, C.J.S.M., Zhang, Q., Shen, J., Cavaco-Paulo, A., 2006. Immobilization of proteases with a water solubleeinsoluble reversible polymer for treatment of wool. Enzyme Microb. Technol. 39 (4), 634e640. Smith, E., Schroeder, M., Guebitz, G., Shen, J., 2010. Covalent bonding of protease to
817
different sized enteric polymers and their potential use in wool processing. Enzyme Microb. Technol. 47 (3), 105e111. Smith, E., Shen, J., 2011. Surface modification of wool with protease extracted polypeptides. J. Biotechnol. 156 (2), 134e140. Tuma, R., 2005. Raman spectroscopy of proteins: from peptides to large assemblies. J. Raman Spectrosc. 36 (4), 307e319. Wang, K., Li, R., Ma, J.H., Jian, Y.K., Che, J.N., 2016. Extracting keratin from wool by using l-cysteine. Green Chem. 18 (2), 476e481. Xie, H., Li, S., Zhang, S., 2005. Ionic liquids as novel solvents for the dissolution and blending of wool keratin fibers. Green Chem. 7 (8), 606e608. Xu, H., Yang, Y., 2014. Controlled de-cross-linking and disentanglement of feather keratin for fiber preparation via a novel process. ACS Sustain. Chem. Eng. 2 (6), 1404e1410. Xu, L., Wang, Z., Mao, P., Liu, J., Zhang, H., Liu, Q., Jiao, Q.C., 2013. Enzymatic synthesis of S-phenyl-L-cysteine from keratin hydrolysis industries wastewater with tryptophan synthase. Bioresour. Technol. 133, 635e637. Zhao, Q., Sun, G., Yan, K., Zhou, A., Chen, Y., 2013. Novel bio-antifelting agent based on waterborne polyurethane and cellulose nanocrystals. Carbohyd. Polym. 91 (1), 169e174.
Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Recycling keratin polypeptides for anti-felting treatment of wool based on L-cysteine pretreatment Zhuang Du a, Bolin Ji a, b, Kelu Yan a, b, * a b
College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, PR China 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
a b s t r a c t
Article history: Received 7 July 2017 Received in revised form 27 December 2017 Accepted 19 February 2018 Available online 20 February 2018
An anti-felting finishing process based on recycling waste wool material was proposed. Wool fabric was pretreated with L-cysteine and then treated with the keratin polypeptides, extracted by protease from the waste wool. And then, wool fabric was treated with glycerol diglycidyl ether as cross-linking agent for a durable anti-felting effect. The padded-out keratin polypeptides solution was collected, replenished with a small amount of fresh keratin polypeptides and recycled for 10 times. An excellent anti-felting performance was still achieved when wool fabric was treated with the 10th-recycled keratin polypeptides. The protein concentration of 10th-recycled keratin polypeptides was almost unchanged, but the weight-average molecular weight decreased. There was no significant difference on the modified surfaces between the wool fabrics treated with recycled keratin polypeptides and those with the fresh ones. Compared with the control, 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) after fixation of the extracted keratin polypeptides onto the fabrics. The modification mechanism was confirmed by scanning electron microscopy, Raman spectra and X-ray photoelectron spectroscopy analysis of treated wool fabric that L-cysteine can erode the fiber surface, generating more reactive groups, and then keratin polypeptides can easily cross-linked onto the fiber surface by glycerol diglycidyl ether or covered the fiber surface. © 2018 Elsevier Ltd. All rights reserved.
Keywords: Keratin polypeptides Recycle Anti-felting treatment Wool L-cysteine
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 antifelting (Kaur and Chakraborty, 2015). Anti-felting treatment always involves the reduction/oxidation process to erode the scale layer and/or coating the polymer on the surface of wool fiber (Smith and Shen, 2011). The traditional anti-felting treatment is chlorination/resin method (chlorinate-Hercosett process), while it would produce harmful absorbable organic halogens (AOX) (Shi et al., 2014). To avoid release of AOX and reach the machine washable standards, alternative and environmentally friendly processes should be developed. Coating with polymer resins on the surface of wool fabric can obtain satisfying anti-felting property (Zhao et al., 2013). However, a large amount of resins should be required to
* Corresponding author. National Engineering Research Center for Dyeing and Finishing of Textiles, College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, PR China. E-mail address: [email protected] (K. Yan). https://doi.org/10.1016/j.jclepro.2018.02.196 0959-6526/© 2018 Elsevier Ltd. All rights reserved.
meet the machine washable standards and thus cause wool fabric a stiff handle. The proteolysis of protein compounds can be catalyzed by protease without any chlorine release, nevertheless protease can penetrate into the inner of wool fiber to degrade the macromolecular chains, resulting in severe damage of strength, which restricts its application (Cui et al., 2009). The diffusibility of enzyme can be decreased when it is immobilized to a specific polymer, which could restrict the proteolysis of protein compounds present on the scale layer of fiber (Madhu and Chakraborty, 2017; Shen et al., 2007; Silva et al., 2006; Smith et al., 2010). Wool fabric treated with the modified enzyme shows improvement of antifelting property, but the immobilization of enzyme would be too expensive to achieve industrialization. It should be meaningful if anti-felting property of wool fabrics can be realized with more effective and green way. Currently, various attempts have been made to the utilization of biomass, and many kinds of biopolymers worked as resins are applied on the wool fabric to achieve anti-felting, such as silk sericin, collagen and casein, which could obtain softer handle than the synthetic poly recki and Go recki, 2010; Xu et al., mers (Cortez et al., 2007; Go
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817
2013). Keratin polypeptides (KPs) as one kind of the most abundant biomass can be extracted from keratin-containing wastes, such as waste wool, hair, feathers and so on (Reddy et al., 2014; Xie et al., 2005). It is advisable to extract and dissolve KPs from keratin wastes for development of novel biopolymers (Holkar et al., 2016). Compared with the traditional chemical extraction process, enzymatic hydrolysis is usually applied in a mild condition or enhancing the hydrolysis simply by exerting pressure without much chemical reagents, which can be a green method to extract the KPs (Brandelli et al., 2010; Marousek et al., 2013). To fix KPs onto the wool fabric, a pretreatment is generally required to improve surface affinity between wool fabric and KPs. The sodium sulfite and sodium bisulfite are frequently used as reducing agents to pretreat wool fabric, but severe fiber damage and water pollution could be generated during the treatment process. For the popular thiol-type reducing agent, Lcysteine can break the inert -S-S- group that lied in the cuticle or cortex of wool effectively and cause less damage on wool fiber than thioglycolic acid as well as less toxicity than 2-mercaptoethanol (Wang et al., 2016). It can not only cleave the -S-S- of keratin, but also connect with keratin and form new disulfide bond R-S-SCH(NH2)COO. This characteristic could play an important role in anti-felting treatment and surface modification. Most reports take L-cysteine as a green reducing agent to extract keratin from wool or feather materials (Xu and Yang, 2014). However, there is no report on L-cysteine as a pretreatment agent for wool anti-felting finish. The cleavage of -S-S- group of cuticle treated by L-cysteine can decrease the directional friction effect (DFE) of wool fabric, new disulfide bond can be generated between L-cysteine and wool fiber, and provided more reactive sites to promote the reaction between fiber and KPs. Furthermore, difunctional epoxide glycerol diglycidyl ether (GDE) works as an effective cross-linking agent to fix protein onto wool fabric by reacting with the eNH2 or eOH of wool fiber and KPs (Hesse et al., 1995; Smith and Shen, 2011). In this paper, the KPs were extracted from the waste wool fibers with protease and were fixed on the wool fabric that pretreated by L-cysteine for an anti-felting purpose. Recycle using of KPs was investigated and area shrinkage, softness, weight loss and tensile strength of the treated wool fabric were also studied. The modified surface of wool fabric was assessed by scanning electron microscopy (SEM), and the anti-felting mechanism was confirmed by Xray photoelectron spectroscopy (XPS), Raman spectra, contact angle and dyeability. 2. Experimental section 2.1. Materials Undyed waste wool fibers used in the extraction process were byproducts of wool weaving process supplied by Shandong Ruyi Wool Co. (Jining, Shandong Province, China). Scoured and undyed wool fabric (144 g/m2, wool 100%, woven), and non-ionic surfactant MP-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 Chemical Reagent Co., Ltd. (Shanghai, China) and used as received. The crosslinking agent glycerol diglycidyl ether (GDE) was purchased from Sigma-Aldrich. The reactive dye, Lanasol Red CE used to test the dyeability of treated wool fabric was supplied by Huntsman Co. (USA). The enzyme used was a serine type protease, Esperase 8.0L extracted from Bacillus subtilis was supplied by Novozymes (Beijing, China), and the enzyme activity based on casein substrate is 2.29 u/mg. Enhanced bicinchoninic acid (BCA) Protein Assay Kit to detect the protein concentration was purchased from Beyotime Biotechnology Co., Ltd. (Shanghai, China).
811
2.2. Preparation of keratin polypeptides (KPs) Waste wool fibers were firstly treated with 15 g/L Na2CO3 solution at 95 C for 15 min, and then washed by distilled water to be neutral pH condition. The washed product was dried at 80 C and subsequently milled into powders. Next, the wool powders were placed into a 0.02 M phosphate buffer (pH 8.0) containing 5 g/L Na2SO3 with a liquor to goods ratio of 20:1 and treated at 60 C for 30 min by using a Roaches Pyrotec 2000 dyeing machine at a 40 rpm shaking rate. The protease was added into the previous shaking bath to reach a concentration of 2.0 mg/mL, and then the mixed solution was agitated at 40 rpm for 2 h at 65 C. The enzyme in the mixture was deactivated by raising the temperature to 90 C for 10 min and with the agitation at 40 rpm. Then, cooled the suspension to the room temperature and separated by centrifugation at 6000 rpm using a Thermofisher Heraeus Multifuge X3 centrifuge. The supernatant liquid was collected and applied in the later wool fabric treatment (Smith and Shen, 2011). The protein concentration of extracted KPs was determined by the BCA assay kit. A gradient concentration (g/L) of bovine serum albumin (BSA) standard solution was designed and the absorbance was recorded at 562 nm (A562). A standard curve was automatically generated using the regression equation:
y ¼ ax þ b R2 0:99
(1)
where R2 represented the linear regression coefficient. The absorbance values of the samples were recorded and substituted in the regression equation to calculate the protein concentration of the KPs. The molecular weight of KPs was determined by Gel Permeation 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 a liquor 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 fabric tension caused by machine drafting process and the treated fabric was set as control sample. Different amount of L-cysteine was added into the relaxation process solution to pretreat wool fabric. And then the pretreated fabric was washed with distilled water until the washing water achieved neutral pH and then dried in air. The pretreated fabric was treated in the extracted KPs solutions with a liquor to goods ratio of 10: 1 at 60 C for 30 min by using a Roaches Pyrotec 2000 dyeing machine at a 20 rpm shaking rate, and the fabric was taken out from the KPs solution and passed through a laboratory padder (Rapid Co., Ltd.) to pad the extra KPs (pick-up 80% owf.). After the padding, we collected the remaining KPs solutions. And then, fabric was transferred into a new bath set pH at 7.3 using 0.02 M phosphate buffer containing different amounts of GDE with a liquor to goods ratio of 10:1 for 30 min at 60 C with 20 rpm. After the wet treatment steps, fabric was treated with a pad process that padded with a pick-up 80% owf. and cured at 140 C for 3 min. The fresh extracted KPs solution was added to the previous collected solutions and refilled to the initial volume (for example, 100 mL KPs would need 16 mL of fresh KPs to refill to the initial volume after treatment). And repeat previous treatment process to recycle using KPs (Scheme 1). 2.4. Fabric testing Softness and smoothness of the fabric was measured according to the AATCC 202-2012 relative hand value of textiles instrument
812
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817
Scheme 1. Schematic diagram of the anti-felting treatment of wool fabric and recycle using of extracted keratin polypeptides.
temperature of dye bath was increased to 95 C at a rate of 1 C/min and kept for 60 min. After dyeing, fabric was successively washed by room temperature water, 60 C water and 95 C soaping solution containing 2 g/L Ultravon PL (Huntsman Co., USA) non-ionic surfactant to remove unfixed dyes. The dyed fabric was dried at 40 C and the K/S value of dyed fabric was measured by Datacolor 650 reflectance spectrophotometer to characterize dye uptake. Dye fixation efficiency (Fixation %) is measured according to the reference (Smith and Shen, 2011). It is the percentage of the dye originally applied to the fabric which becomes bound covalently. The dyebath solutions were collected before and after the dyeing process and the solution after soaping were diluted to the same fixed volume and the absorbance were measured at 503 nm, the wavelength of maximum absorption (lmax) specific to Lanasol Red CE, using a Hitachi U-2910 UV/visible spectrophotometer. Dye fixation efficiency (Fixation %) was calculated using Eq. (6).
Fixationð%Þ ¼ method by the PhabrOmeter 3. The relaxation treated wool fabric was set as the control, and the higher the value was, the softer handle or the smoothness surface of the fabric would be. The measurement of area shrinkage due to washing of the treated woven wool fabric was tested according to IWS TM NO.31 by using a washing machine (Washcator FOM71 CLS, Electrolux) for 1 7 A and 3 5 A programs. The area shrinkage was calculated by the following equations:
WSð%Þ ¼
L0 L1 100 L0
(2)
L0 L1 100 L0
(3)
Area Shrinkageð%Þ ¼ WS þ LS
(4)
LSð%Þ ¼
where L0 was the marked length before fabric was washed, and L1 was the length of the marked positions after standard washing, WS was the average value of three WS tests of size changing in weft direction (%) and LS was the average value of three LS tests of size changing in warp direction (%). The weight loss (WL) of the wool fabric after anti-felting treatment was calculated following Eq. (5):
WL ð%Þ ¼
W0 W1 100 W0
(5)
where W0 was the weight of conditioned wool fabric prior to extracted KPs treatment and W1 was the weight of conditioned wool fabric after extracted KPs treatment. The tensile strength of fabric at break was measured in the warp-wise and weft-wise directions using universal testing machine (H5KS, Tinius Olsen, USA) in accordance with the testing standard, ASTM D5035-1995. The fabric samples were cut into rectangular shape (100 25 mm2), and every sample took an average value of five replicates. A Datacolor 650 reflectance spectrophotometer (Datacolor, USA) was used to determine the whiteness of the treated wool fabric in terms of the CIE whiteness index. Each sample was folded into four layers and measured four times. All values were measured and calculated using ColorTools QC software with illuminant and observer conditions of D65. The treated wool fabric was dyed with the reactive dye Lanasol Red CE (2% owf.), pH was adjusted to 4.0 with acetic acid and the temperature was set at 40 C at the beginning, and then the
Abs0 Abs1 Abs2 100 Abs0
(6)
where Abs0 is the absorbance of the original dye-bath solution at lmax, Abs1 is the absorbance of the exhausted dye-bath solution at lmax and Abs2 is the absorbance of the solution after soaping at lmax. Hydrophilicity change of the treated fabric was determined by measuring the contact angle between the surface of fabric and deionized water droplet at 27 C using drop shape analyzer (DSA-25, KRUSS GmbH, Hamburg). The 4 mL drop of de-ionized water was located on the surface and the images were captured when they contacted 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, JEOL Ltd. Japan). The samples were sputter coated with gold under vacuum 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 using a Physical Electronics Industries PHI Model 5300 surface analysis system. This system employs a double-pass cylindrical mass analyzer (20-270AR) with a perpendicularly mounted dual (Mg/ Mg) X-ray source. A single MgKa X-ray source was operated at 250 W and 14 kV. Survey spectra were obtained over the range 0e1100 eV using a pass energy of 100 eV with an acquisition time of 2 min. 2.7. Raman spectra Raman spectra of the fabric samples were collected by a XploRA (HORIBA Jobin Yvon, France) Raman spectrometer. The laser excitation was provided with an argon ion laser operating at 50 mW of 514.5 nm output. The sample was focused to around 1 mm using a 100 objective. A spectra resolution of 5 cm1 with 1 scan (1000 s) was used over the scanning range of 200e2000 cm1. 2.8. Statistical analysis All of the data reported are mean ± standard deviation (SD). The statistical 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
3. Results and discussion 3.1. Pretreatment of wool fabric with L-cysteine Reducing agent L-cysteine can break disulfide bond (-S-S-) and improve the anti-felting property of wool fabric. The effect of Lcysteine concentration on properties of treated fabric was investigated, as shown in Fig. 1. The lower the area shrinkage of wool fabric is, the better the anti-felting property will be. Fig. 1(a) indicated that area shrinkage decreased from 14.3% to 8.2% by adding 0.1 M L-cysteine. However, higher concentration of L-cysteine did not effectively improve the anti-felting property, and even decrease it based on the higher area shrinkage. It should be attributed to the thiol group (-SH) of L-cysteine, which can break the disulfide (-S-S-) of the cuticle and form the Wool-S-S-CH2CH(NH2)COOH crosslinkage or crosslinked with the other part that derived from the broken wool disulfide. (Wang et al., 2016). When the concentration was lower than 0.1 M, L-cysteine demonstrated high reducibility due to generating many -S- reactive sites, and with the concentration increasing, L-cysteine could generate less -S-, indicating lower reactivity of L-cysteine, because the eCOOH in L-cysteine molecule would suppress the generation of -S- at a high L-cysteine concentration. Whiteness, weight loss and tensile strength were all affected for this reason, and the results are shown in Fig. 1(bec). Lcysteine can destroy cuticles and lipids, which increased whiteness effectively. When the concentration of L-cysteine exceeded 0.1 M, although less reactivity of L-cysteine would be, the whiteness and area shrinkage increased simultaneously. This phenomenon can be explained that positive charged eNHþ 3 of L-cysteine was adsorbed
813
onto the negative charged surface of wool fiber, which can also be confirmed by the weight gain (Kuzuhara and Hori, 2004). The tensile strength in Fig. 1(c) presented the same tendency as area shrinkage, which also confirmed the effect of concentration of Lcysteine on reactivity between L-cysteine and wool fiber. 3.2. Effects of cross-linked KPs on properties of pretreated wool fabric The cross-linking agent glycerol diglycidyl ether (GDE) was introduced to fix more extracted KPs onto the surface of wool fiber for improving the anti-felting property further, and results were shown in Table 1. The application of GDE could decrease the area shrinkage of the fabric due to more KPs were fixed on the surface of wool fibers, while area shrinkage of the control fabric without or with 0.1 M L-cysteine pretreatment and experienced 5 g/L GDE cross-linking process was decreased to 10.4% and 5.6%, respectively. This implied that the L-cysteine pretreatment could improve the amount of active groups and promote cross-linking efficiency between the fiber surface and KPs through GDE. However, it still could not meet the IWS TM NO.31 machine washable standard. KPs were necessary to be introduced and fixed on the surface of wool fabric. When the KPs were fixed on the fabric after pretreatment, the area shrinkage of treated fabric was affected by the concentration of cross-linking agent significantly. Area shrinkage decreased remarkably with the increasing amount of cross-linking agent, and a GDE concentration at 10 g/L could be a good choice for the treatment because the anti-felting performance was not further improved when the concentration of GDE was over 10 g/L. Curing process during the anti-felting treatment can result in oxidation of the peptide of wool fiber, and the fixation of KPs with the crosslinking agent, which led to the yellowing and weight loss. When more KPs were fixed on wool fibers by a higher concentration of GDE, whiteness and weight loss decreased simultaneously. The tensile strength of fabric treated with L-cysteine, and further followed with KPs and GDE cross-linking experienced a first increase and then decrease with GDE concentration increasing, which can be interpreted as that more KPs fixed onto fiber could seal the gaps of cuticle effectively and it would be helpful for improving fiber strength, while over cross-linking can restrain the slipping of fibers during stretching process, damaging the fiber strength. The 10 g/L GDE was optimized and the warp tensile strength of treated wool fabric decreased by 6.1% compared with control sample. 3.3. Recycle using of KPs
Fig. 1. The effect of L-cysteine concentration on wool fabric in terms of area shrinkage, whiteness, weight loss and tensile strength.
The residual KPs were collected, replenished with fresh KPs for recycling after wool fabric was treated with KPs. The protein concentration and the molecular weight of recycled KPs were shown in
Table 1 The effects of GDE concentration on wool fabric in terms of area shrinkage, tensile strength, weight loss and whiteness. Sample
Controla Pretreatedb KPs@GDEc KPs@GDE KPs@GDE KPs@GDE KPs@GDE KPs@GDE a b c
GDE concentration (g/L)
5 5 0 5 10 15 20 25
Area shrinkage (%)
10.4 ± 1.1 5.6 ± 0.9 7.6 ± 0.3 2.1 ± 0.2 0.3 ± 0.1 0.1 ± 0.1 0.1 ± 0.0 0.1 ± 0.0
Tensile strength at break (N) Warp
Weft
157.9 ± 0.7 143.9 ± 1.2 146.0 ± 0.8 149.1 ± 0.4 151.9 ± 0.4 148.9 ± 1.9 148.4 ± 2.0 144.7 ± 2.2
149.0 ± 0.5 138.2 ± 0.8 138.5 ± 0.3 138.2 ± 0.2 144.5 ± 0.3 141.5 ± 1.2 140.4 ± 1.0 140.6 ± 2.3
Weight loss (%)
Whiteness Index
1.4 ± 0.3 2.7 ± 0.4 2.5 ± 0.2 2.0 ± 0.1 1.2 ± 0.2 1.2 ± 0.3 1.1 ± 0.1 0.5 ± 0.1
2.1 ± 0.3 16.2 ± 1.2 17.4 ± 0.1 15.6 ± 0.7 10.1 ± 0.5 8.6 ± 0.9 6.5 ± 0.2 6.5 ± 0.6
Treated condition: 2 g/L MP-2, 8% (owf.) Na2CO3, 1 h Treated condition: 2 g/L MP-2, 8% (owf.) Na2CO3, 0.1 M L-cysteine, 1 h Treated condition: pretreated with 2 g/L MP-2, 8% (owf.) Na2CO3, 0.1 M L-cysteine for 1 h and followed by fixation of KPs with GDE cross-linking.
814
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817
Fig. 2. The protein concentration of recycled KPs was almost unchanged with 10 recycles. However, weight-average molecular weight (Mw) decreased significantly that the KPs decreased from 5271 to 3964 and 3715 after 5 and 10 recycles, respectively. This should be attributed to the weak alkalinity of the bath, which leads to the cleavage of eCONH2e bond of the extracted KPs and wool fiber 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 recycle using times.
extracted KPs were adsorbed on the fiber surface, at the same time molecular chains of wool cortex and the extracted KPs can be hydrolyzed in the alkaline bath. Consequently, the produced smaller molecular chains can be released to the KPs bath, causing almost unchanged protein concentration and decreased molecular weight. The effects of recycle times of the extracted KPs on properties of treated fabric were shown in Fig. 3. Overall, the area shrinkage was slightly increased with recycle times increasing from 1 to 10, while it was still kept at about 1.0% and reached the IWS TM NO.31 standard. Whiteness, weight loss and tensile strength were not affected with the recycled KPs. The softness of anti-felting treated wool fabric was improved effectively compared with the untreated one. This can be explained that the cuticle and cortex of fibers was eroded by L-cysteine, decreasing the stiffness of fiber (Gouveia et al., 2012). In addition, KPs fixation process was also accompanied by chemical corrosion on the surface of fibers, but the handle (softness and smoothness) of treated fabric was not affected by the KPs recycling. Generally, recycle using of the extracted KPs for 10 times did not affect the properties of treated wool fabric compared with non-recycled ones. 3.4. Morphology and hydrophilicity of treated wool fabrics
Fig. 3. Effects of recycle times of the extracted KPs on (a) area shrinkage, (b) whiteness and weight loss, (c) tensile strength and (d) softness and smoothness of treated fabric.
The SEM pictures of treated fabrics were shown in Fig. 4. The scale morphology of surface of the untreated wool fiber could be observed clearly in Fig. 4(a), and apparent corrosion of cuticle of wool fiber pretreated with L-cysteine was observed in Fig. 4(b), which indicated that the reduction took place between L-cysteine and cuticle layer. The gaps of cuticle were sealed with KPs completely and rough surface of the fiber can be seen in Fig. 4(c), which could decrease the area shrinkage of fabrics. The surface morphology of the fibers treated with the 2nd and 6th-recycled KPs (Fig. 4(d-e)) showed similar to that shown in Fig. 4(c). Cuticle layers were not sealed completely after KPs were recycled 10 times compared with the previous samples, but cross-linking between fibers could still be observed. That was why the area shrinkage slightly increased after KPs recycle used after 10 times and all of the treated fabrics can keep satisfying shrinkage resistance. The pictures of de-ionized water contacted with fabric for 60 s were shown in Fig. 4. The untreated fabric demonstrated great
Fig. 4. The SEM pictures and water contact angle of (a) control fabric, (b) pretreated with L-cysteine only, (c) pretreated and further fixed with fresh extracted KPs, (d) recycle using KPs 2 times, (e) recycle using KPs 6 times, (f) recycle using KPs 10 times.
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817
hydrophobicity over the testing time due to the hydrophobic of cuticle (Meade et al., 2008). Fabric pretreated with L-cysteine can damage the cuticle and more hydrophilic groups such as eOH and eNH2 appeared on the surface of wool fiber, the contact angle decreased significantly when the contact time reached 60s. KPs treated fabrics showed lower contact angle compared with the Lcysteine treated ones, which should be ascribed to the cross-linking of KPs on the surface of fiber and gaps of cuticle, and recycled KPs did not affect the contact angle. These results can be confirmed by the SEM and XPS analysis. 3.5. Raman spectra of treated fabrics The Raman spectrometer was applied to investigate the influence of L-cysteine and KPs treatments on wool fibers and the result was shown in Fig. 5. The vibration bands were mainly lying in the wavenumber range of 500e1800 cm1, where could be assigned to CeS and SeS bonds of cystine, amino acids (tryptophan, tyrosine, and phenylalanine), the amide I, II, III vibrations, and the CeC skeletal stretching vibration of the a-helix (Kuzuhara, 2007). The absorbance peaks of investigated samples showed almost the same absorption position in Fig. 5. As shown, absorbance at 1658, 1558, 1243 cm1 represented the Amide I, II, and III band, respectively (Kuzuhara and Hori, 2013; Tuma, 2005). The intensities of SeS bond in the pretreated sample slightly increased and CeS band in the three curves were almost unchanged, while the SeO band at about 1040 cm1 in the L-cysteine or KPs treated samples, ascribed to cysteic acid, slightly increased. The results suggested that the cleavage of SeS groups existing in the cuticle region was due to the reduction process and was reconnected after oxidation process
815
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 element content was shown in Table 2, respectively. Pretreated sample possessed slightly lower carbon content and higher nitrogen and sulfur content. The damaging of lipids, especially the removal of hydrophobic alkanes, made the nitrogen rich protein matrix of fiber exposed to the outer space (Dai et al., 2001). Moreover, modification of native disulfide on fiber surface by L-cysteine might result in the increasing of sulfur composition, which can be also identified by Raman spectra. The fabric fixed with KPs showed significant reducing carbon content and increasing both oxygen and nitrogen contents compared with the untreated fabric. The KPs react with cross-linking agent (GDE) can form a thin film on the surface of fiber. KPs film with a relative lower carbon content and GDE with a higher composition of -C-O-C- can improve hydrophilicity of fiber effectively, which might explain the increasing of oxygen element. The fabrics treated with the 10 times recycled KPs almost possess the same element composition with an expected slightly increasing of carbon component, which might be due to that the KPs with lower Mw would not cover the surface effectively compared with the 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 fiber was eroded, bringing better hydrophilicity, and more reactive groups such as eOH or eNH2 were generated on the fibers after Lcysteine or KPs treatment. The hydrophilicity of the treated fabric can enhance the absorption of dyes. In addition, the active groups (eC(Br)]CH2 and eCH]CH2) of reactive dyes can react with eOH or eNH2 of the fibers. Consequently, the treated fabrics should exhibit better dyeability and react with more reactive dyes. To examine this, wool fabric fixed with extracted KPs was dyed with the reactive dye Lanasol Red CE at 95 C following standard dyeing protocols (Smith and Shen, 2011). The K/S value and dye fixation efficiency (Fixation %) of dyed fabric were shown in Fig. 6, in which fabric pretreated with L-cysteine showed better dyeability, effectively reflected by higher K/S value and Fixation %. Moreover, the wool fabrics fixed with KPs possessed a little higher Fixation % than
Fig. 5. Raman spectra of treated wool fabrics.
Table 2 Element analysis by X-ray photoelectron spectroscopy. Recycle times of KPs
Element composition (%) C
O
N
S
Control Pretreated 0 2 4 6 10
75.65 74.13 70.23 70.30 71.57 72.16 72.66
15.16 15.18 18.92 18.73 16.63 17.94 16.86
6.98 8.23 8.62 8.77 9.47 7.92 8.23
2.22 2.45 2.24 2.20 2.33 1.97 2.25
Fig. 6. The K/S value and dye fixation of wool fabrics that dyed with 2% (owf.) Lanasol Red CE. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
816
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817
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 referred to the web version of this article.)
the only pretreated ones and the recycled KPs did not affect the dye fixation of treated wool fabric after dyeing with 2% Lanasol Red CE. This might be ascribed to the higher reactivity and better affinity to dyes when KPs were fixed onto fabric surface (Kantouch et al., 2011). The photos of dyed fabrics were shown in Fig. 7. Compared with untreated fabric, L-cysteine pretreated and KPs fixed fabrics demonstrated relative deeper color and better planeness especially the edges of fabrics. This could confirm the modification of fabric surface and the improvement of anti-felting property.
4. Conclusions In this work, a green anti-felting finishing process based on Lcysteine pretreatment followed by KPs cross-linking fixation was investigated. The padded-out KPs solution was collected and replenished with a small amount of fresh KPs for recycle using. Area shrinkage about 1.3% still could be achieved after 7 A and 3 times 5 A washes according to IWS TM NO.31 when the KPs were recycled for 10 times. The protein concentration of waste KPs solution was almost unchanged after recycle using, despite the weight-average molecular weight decreased significantly. Compared with untreated 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) after fixation of the extracted KPs. The SEM photos demonstrated the corrosion of cuticle of wool fiber when fabric was pretreated with L-cysteine, and the gaps of cuticle were sealed completely with KPs besides rough surface of the fiber can also be observed. Raman spectra revealed that the cleavage and reconnection of -S-S- groups when fabric treated by L-cysteine pretreatment or KPs fixation process. The fabric treated with the extracted KPs showed significant reducing carbon content, and increasing both oxygen and nitrogen contents compared with the untreated fabric by XPS analysis. There was no significant difference of fabric properties between the wool fabrics treated with the recycled KPs and those with the fresh one. These improvements in various properties indicated that durable fixation of KPs onto surface of wool fiber and recycle using of KPs have great potential to be applied in environmental friendly shrink-resistant process.
Conflicts of interest None.
Acknowledgements The authors thank the National Engineering Research Center for Dyeing and Finishing of Textiles for financial support and the State Key Laboratory for Modification of Chemical Fibers and Polymer Materials for spectroscopic measurements and SEM examination. References Brandelli, A., Daroit, D.J., Riffel, A., 2010. Biochemical features of microbial keratinases and their production and applications. Appl. Microb. Biotechnol. 85 (6), 1735e1750. Cortez, J., Anghieri, A., Bonner, P.L.R., Griffin, M., Freddi, G., 2007. Transglutaminase mediated grafting of silk proteins onto wool fabrics leading to improved physical and mechanical properties. Enzyme Microb. Technol. 40 (7), 1698e1704. Cui, L., Wang, Q., Wang, P., Huan, Q., Fan, X., 2009. Transglutaminase-mediated crosslinking of gelatin onto wool surfaces to improve the fabric properties. J. Appl. Polym. Sci. 113 (4), 2598e2604. Da Silva, C.M.L., Spinelli, E., Rodrigues, S.V., 2015. Fast and sensitive collagen quantification by alkaline hydrolysis/hydroxyproline assay. Food Chem. 173, 619e623. Dai, X.J., Elms, F.M., George, G.A., 2001. Mechanism for the plasma oxidation of wool fiber surfaces from XPS studies of self-assembled monolayers. J. Appl. Polym. Sci. 80 (9), 1461e1469. Du, Z., Hu, C., Xie, Z., Yan, K., 2017. A bio-antifelting agent based on waterborne polyurethane and keratin polypeptides extracted by protease from waste wool. Fibers Polym. 18 (4), 641e648. recki, R.S., Go recki, M.T., 2010. Utilization of waste wool as substrate amendment Go in pot cultivation of tomato, sweet pepper, and eggplant. Pol. J. Environ. Stud. 19 (5), 1083e1087. , D., Henriques, M., 2012. Functionalization of wool with L-cysteine: Gouveia, I.C., Sa process characterization and assessment of antimicrobial activity and cytotoxicity. J. Appl. Polym. Sci. 124 (2), 1352e1358. €cker, H., 1995. Zero-AOX shrinkproofing treatment for Hesse, A., Thomas, H., Ho wool top and fabric part II: collagen resin application. Text. Res. J. 65 (7), 371e378. Holkar, C.R., Jadhav, A.J., Bhavsar, P.S., Kannan, S., Pinjari, D.V., Pandit, A.B., 2016. Acoustic cavitation assisted akaline hydrolysis of wol bsed keratins to produce organic amendment fertilizers. ACS Sustain. Chem. Eng. 4 (5), 2789e2796. Kantouch, A., Allam, O., El-Gabry, L., El-Sayed, H., 2011. Effect of pretreatment of wool fabric with keratin on its dyeability with acid and reactive dyes. Indian J. Fiber Text. Res. 37, 157e161. Kaur, A., Chakraborty, J.N., 2015. Controlled eco-friendly shrink-resist finishing of wool using bromelain. J. Clean. Prod. 108, 503e513. Kuzuhara, A., 2007. Analysis of structural changes in permanent waved human hair using Raman spectroscopy. Biopolymers 85 (3), 274e283. Kuzuhara, A., Hori, T., 2004. Diffusion behavior of reducing agents into keratin fibers using microspectrophotometry. J. Appl. Polym. Sci. 94 (3), 1131e1138. Kuzuhara, A., Hori, T., 2013. Analysis of heterogeneous reaction between reducing agents and keratin fibers using Raman spectroscopy and microspectrophotometry. J. Mol. Struct. 1037, 85e92. Madhu, A., Chakraborty, J.N., 2017. Developments in application of enzymes for textile processing. J. Clean. Prod. 145, 114e133. Marousek, J., Itoh, S., Higa, O., Kondo, Y., Ueno, M., Suwa, R., Tominaga, J.,
Z. Du et al. / Journal of Cleaner Production 183 (2018) 810e817 Kawamitsu, Y., 2013. Enzymatic hydrolysis enhanced by pressure shockwaves opening new possibilities in Jatropha CurcasL. processing. J. Chem. Technol. Biotechnol. 88 (9), 1650e1653. Meade, S.J., Caldwell, J.P., Hancock, A.J., Coyle, K., Dyer, J.M., Bryson, W.G., 2008. Covalent modification of the wool fiber surface: the attachment and durability of model surface treatments. Text. Res. J. 78 (12), 1087e1097. Reddy, N., Chen, L., Zhang, Y., Yang, Y., 2014. Reducing environmental pollution of the textile industry using keratin as alternative sizing agent to poly(vinyl alcohol). J. Clean. Prod. 65, 561e567. Shen, J., Rushforth, M., Cavaco-Paulo, A., Guebitz, G., Lenting, H., 2007. Development and industrialisation of enzymatic shrink-resist process based on modified proteases for wool machine washability. Enzyme Microb. Technol. 40 (7), 1656e1661. Shi, J., Han, X., Kelu, Y., 2014. A novel bio-functional finishing agent for wool based on waterborne polyurethane mixed with chitosan. Text. Res. J. 84 (11), 1174e1182. Silva, C.J.S.M., Zhang, Q., Shen, J., Cavaco-Paulo, A., 2006. Immobilization of proteases with a water solubleeinsoluble reversible polymer for treatment of wool. Enzyme Microb. Technol. 39 (4), 634e640. Smith, E., Schroeder, M., Guebitz, G., Shen, J., 2010. Covalent bonding of protease to
817
different sized enteric polymers and their potential use in wool processing. Enzyme Microb. Technol. 47 (3), 105e111. Smith, E., Shen, J., 2011. Surface modification of wool with protease extracted polypeptides. J. Biotechnol. 156 (2), 134e140. Tuma, R., 2005. Raman spectroscopy of proteins: from peptides to large assemblies. J. Raman Spectrosc. 36 (4), 307e319. Wang, K., Li, R., Ma, J.H., Jian, Y.K., Che, J.N., 2016. Extracting keratin from wool by using l-cysteine. Green Chem. 18 (2), 476e481. Xie, H., Li, S., Zhang, S., 2005. Ionic liquids as novel solvents for the dissolution and blending of wool keratin fibers. Green Chem. 7 (8), 606e608. Xu, H., Yang, Y., 2014. Controlled de-cross-linking and disentanglement of feather keratin for fiber preparation via a novel process. ACS Sustain. Chem. Eng. 2 (6), 1404e1410. Xu, L., Wang, Z., Mao, P., Liu, J., Zhang, H., Liu, Q., Jiao, Q.C., 2013. Enzymatic synthesis of S-phenyl-L-cysteine from keratin hydrolysis industries wastewater with tryptophan synthase. Bioresour. Technol. 133, 635e637. Zhao, Q., Sun, G., Yan, K., Zhou, A., Chen, Y., 2013. Novel bio-antifelting agent based on waterborne polyurethane and cellulose nanocrystals. Carbohyd. Polym. 91 (1), 169e174.