Enzymatic Modification Of Wool Surface And Its Mechanism

As a conventional shrink-proofing process, chlorine-resin treatment endows wool fabric with satisfactory anti-felting ability. However, it has the disadvantage of environmental pollution caused by the toxic adsorbable organic halogen compounds (AOX). In this study, a cutinase from the recombinant Thermobifida fusca was applied to treat wool in the reversed micelles (RS) and aqueous solutions. The differences of shrink-proofing efficacy between Savinase and papain treatments were evaluated. A keratinase from Bacillus subtilis and two lipases of L3126 and Lipex 100L were applied in the wool processing, respectively. The effects of keratinase and lipase pretreatments on the succeeding protease treatment were investigated. Furthermore, the efficacy and mechanism of the combined enzymatic process, based on mild oxidation, cutinase and protease treatments were also concerned. The main conclusions were listed as follows.1. The effects of surfactant, cutinase concentration and the mol ratio of H2O to Tween-80 in RS on the efficacy of succeeding protease treatment were investigated. The results indicated that the protease-treated wool presented improved wettability when pretreated with 2 %(o.w.f) cutinase in RS as follows: the V (cyclohexane):V (alcohol):V (Tween-80) of 5:1:1, mol ratio of 25. The characteristic of Allw?rden reaction for the treated wool became weak. Cutinase pretreatment in RS facilitated the succeeding protease treatment. The combined process endowed wool fabric with a bit higher weight loss without more noticeable increase of alkaline solubility as compared to that of the individual protease treatment. Furthermore, the wettability for the wool treated with cutinase in RS was inferior to that incubated with potassium hydroxide and methanol, the achieved contact angle was still large, which indicated that the removal of the outmost lipids from the wool surface was not completely. The whole efficacy of cutinase treatment in RS was related to the composition of organic solvent and surfactant, the mol ratio of H2O to Tween-80, the concentration of cutinase as well as the accessibility of enzyme to the fatty acids in wool surface. The efficacy of cutinase treatment in RS was to be further improved.2. The effects of cutinase pretreatment in aqueous solution on the shrink-proofing efficacy of protease treatment were discussed. The actions of two proteases during enzymatic wool processing were compared. The results indicated that wettability of the wool treated with cutinase in aqueous solution was better that treated in RS. More acceptable wool wettability was obtained after the combined use of cutinase and protease treatments. The protease of Savinase (a serine protease) showed higher ability to degrade wool protein during enzymatic processing when compared to papain (a cysteine protease), resulting in more weight loss when the concentrations of the two proteases were similar. Cutinase pretreatment efficiently promoted the Savinase treatment, the obtained anti-felting ability of wool was better than that of the sample based on cutinase-papain treatment although the tensile strengths were at the same level. Individual Savinase treatment led to less improvement of anti-felting ability, which was due to the inefficient enzymatic degradation of wool scales during enzymatic processing.3. The effects of the combined use of lipase, keratinase and cutinase pretreatments on the succeeding protease treatment were investigated. (1) Individual lipase treatment did less impact to the wettability of wool as well as to the efficacy of succeeding protease treatment. No obvious changes of weight loss and shrinkage percentage were observed with and without lipase treatment. (2) Keratinase treatment alone seeming did not affect the wool scales; no noticeable improvements of wettability and anti-felting ability were detected after the enzymatic processing. Cutinase-keratinase pretreatment promoted the succeeding protease treatment; it led to more weight loss and less area shrinkage when compared to that of the individual protease treatment. However, the obtained properties of wool did not exceed that based on cutinase-protease treatment. (3) The combination use of cutinase, keratinase and protease treatments endowed wool fabric with better wettability; the obtained area shrinkage after washing cycles was also lower than that with cutinase-protease and keratinase-protease processes. The data from the amino acid analysis of the residual protease-incubated solution indicated that the relative mass concentration of cysteine in cutinase-keratinase-protease treated bath was a bit higher than that of the cutinase-protease treated, which was probably due to the more reduction of disulphide cross-links in cuticle scales by keratinase.4. The effects of the peroxide pretreatment on the succeeding protease treatment were investigated. Individual oxidation did less impact on the outmost lipids in wool surface, no obvious changes of wettability and weight loss were observed after wool processing. The anti-felting ability of wool decreased after individual peroxide treatment when compared to the untreated one. Higher concentrations of peroxide led to more weight loss as well as some strength loss after succeeding protease treatment. However, the anti-felting ability of wool did not further improved, which can be due to the mechanism of the peroxide-protease treatment, i.e. the proteolytic reactions proceeded deeply in the fiber interior instead of evenly in wool surface. When the wool fabric sample was pretreated with high concentration of peroxide, the enzymatic degradation with protease occurred efficiently in the fiber interior, resulting in more degradation of cell memberane complex and cortex protein. For the wool based on peroxide-protease combined treatment, there was no definite correlation between weight loss and anti-felting ability of wool, thus the shrink-proofing property of wool was unsatisfactory.5. The effects of the combined use of mild oxidation and cutinase pretreatments on the succeeding protease treatment were investigated. After the wool fabric sample was combinedly treated with mild oxidation, cutinase and protease treatments, wettability and weight loss of wool increased, low area shrinkage percentage and very weak Allw?rden's effect were obtained. When the wool fabric was respectively treated with 2 g/L of peroxide (30%), 4% (o.w.f) cutinase and 2% (o.w.f) Savinase protease, the area shrinkage decreased to approximately 3~5 % after three washing cycles, the residual strength percentage was nearly 84%, which was much acceptable as compared to the wool treated with protease alone. The dyeability as well as the fabric styles (including elastic resilience, softness etc), for the combined treated wool, were also better than that based on individual protease treatment. Mild oxidation with low concentration of peroxide promoted the succeeding cutinase treatment and led to more removal of the lipids from the wool epicuticle, making the enzymatic degradation proceed efficiently from the cuticle cells. The obtained fiber damages of wool were lower than that treated with peroxide-protease. For the wool fabric combinedly treated with mild oxidation, cutinase and protease treatments, direct correlation between wettability and anti-felting ability was detected, i.e., better wettabiltiy of wool could lead to lower area shrinkage. Furthermore, the correlation between weight loss and anti-felting ability of wool was also more noticeable than that based on peroxide-protease treatment.7. The effects of cutinase, keratinase, oxidation pretreatments as well as the protease treatment on the structure and composition of wool fibers were analyzed. The FT IR spectra of wool based on cutinase pretreatments did not obviously change when compared to the untreated one. For the wool treated with cutinase, the characteristic peaks of the ester- bond (C=O) became weak, the relative mass concentration of carbon as well as the atomic ratio of carbon to nitrogen decreased, indicating that the lipids content in wool surface might decrease during cutinase pretreatment. For the wool treated with peroxide, the concentration of Cys-SO3H and the atomic ratio oxygen to carbon both increased after peroxide treatment. For the wool treated with 2 g/L of peroxide (30%), cutinase and protease, respectively, the relative mass concentration of carbon decreased, while the atomic ratio of oxygen to carbon increased, revealing that the lipids content in wool epicuticle might decrease and more polar groups exposed on the wool surface. The data from amino acid analysis of wool indicated that the relative mass concentration of cysteine for the cutinase-keratinase-protease treated wool was very low. SEM images verified that the combined use of mild oxidation and cutinase8. pretreatments could evenly increase the extent of scale removal during protease treatment.