Effects of cutinase on the enzymatic shrink-resist finishing of wool fabrics
Introduction
The treatment of wool fabrics with protease, an environmentally friendly technique, has been intensively explored as an alternative of the commercial chlorine-Hercosett process to provide shrink-resist property to wool fabrics [1]. The cuticle membrane in the wool surface is mainly composed of naturally occurring lipids connecting cysteine residues via thioester or ester bonds and covalently crosslinked isopeptide via amide bonds, which makes the wool surface highly hydrophobic and the enzymatic degradation to the cuticle cells restrictedly. Some native proteases can penetrate through the intercellular cement and cause unacceptable fiber damages [2], [3], [4]. Chemical or physical treatments, such as alkali, oxidation, chlorination, or plasma treatments, can dislodge some fatty acids bonds in the wool surface, break some disulphide crosslinks and provide polar functional groups. These pretreatments might help the accessibility of the enzyme to wool substrate during the following protease treatment [5], [6]. However, some chemical pretreatments have the disadvantages of causing excessive fiber damages and uneven treatments of wool surface.
Enzymes, such as lipases and the chemically modified proteases, have the great potential application in wool processing without causing significant damage to wool fibers. The enzymatic process based on the chemically modified proteases has been investigated by several groups [7], [8], [9]; a satisfactory anti-felting effect was achieved without any significant weight loss. Lipases are expected to remove the hydrophobic complexes and long chain fatty acids in the wool surface, which might promote the succeeding proteolytic reactions. Several papers have addressed the treatment of wool fibers with lipase since 1991. El-Sayed et al. [10] reported that the lipase pretreatment in the shrink-resist process of wool fabric could help to improve the wettability of the fibers and enhance shrink-resistance about 2–3%. Hutchinson et al. [11] studied the activities of thioesterase and several lipases with the thioester substrate mimic. Although the conversion of the substrate reached 90% under the optimal condition, there was no observable change in the wettability of the wool fabric. Monlleó et al. [12] also published a paper about the lipases treatment of wool fibers, and they found that none of the commercial lipases changes the surface of wool significantly by using microscopic examination and wettability test. Thus, the efficacy of lipases in wool processing is still argumentative.
Cutinases display hydrolytic activity towards a broad variety of aliphatic esters [13], [14], [15]. Eberl et al. [16] reported that the treatment of poly(trimethylene terephthalate) (PTT) fabrics with cutinase improved the dyeability with a significant increase in K/S value. More recently, Agrawal et al. [17] demonstrated that cutinase treatment enhanced the degradation of cotton waxes and increased the hydrolytic rate of pectinase during cotton scouring. Since the outmost bound lipids in the wool surface are a complex mixture of aliphatic lipids, cutinase might have the potential application in the pretreatment of wool fibers. The major objective of this study is to investigate the application of cutinase in the wool bioanti-felting finishing to improve the wettability and shrink-resistance of wool fabrics.
Section snippets
Materials
Cutinase was produced from a mutant Thermobifida fusca WSH04 according to the method described previously by Du et al. [18]. The activity of cutinase was determined by a continuous spectrophotometric assay utilizing p-nitrophenylbutyrate (pNPB) as the substrate. The standard assay was measured in a final volume of 1 ml containing pNPB (1 mM), enzyme, and the assay buffer (pH 8.0) at 20 °C. The reaction was initiated by the addition of pNPB. The hydrolysis of pNPB was spectrophotometrically
Effects of cutinase pretreatment on wettability of protease-treated wool fabrics
Enzymatic or chemical treatments can partially destroy or remove the covalently bound fatty layer in the surface of wool fibers that causes wool fiber hydrophobic. Table 1 shows the effects of cutinase and peroxide pretreatments on the wettability of wool fabrics in terms of wetting time and contact angle. The cutinase pretreatment had a dramatic effect on the wettability of wool fibers by hydrolysis of the hydrophobic outer layer, the wetting time and contact angle reduced to 7.9 min and 92.04°
Conclusion
The wettability of wool fabric was improved after cutinase treatment compared with that of the sample pretreated with hydrogen peroxide. The weight loss of the sample treated with cutinase was similar to that of the fabric treated with hydrogen peroxide. The encouraging shrink-resistance and weakened fiber damage were also achieved after the combination of cutinase and protease treatments. The partial dislodgement of the lipid-rich outer layer and the increase of the wettability caused by the
Acknowledgments
This work was financially supported by the National High Technology Research and Development Program of China (2008AA02Z203), Jiangsu Provincial Graduate Innovation Project (CX08B_126Z) and Qing Lan Project.
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