Modification Of Cellulase And Its Action On Cellulose Fiber

Cellulases are the most successfully used enzymes in textile wet processing, such asbiopolishing, and denim washing. Cellulase treatments have many advantages, such as mildreaction conditions, clean environment-friendly processing, and improved flexibility of fabric.However, the use of cellulases used in textile processes often results in a certain loss ofcellulosic fabric strength. Cellulases can easily penetrate cellulosic fibers, leading tosignificant losses of weight and tensile strength. Tensile strength loss can be minimized bycellulase modification. Enlarging the molecule of enzyme will limit the enzyme’s action morerelatively to the surface of the cellulosic fiber and fabric, and the diffusion of an enlargedenzyme molecule is significantly inhibited particularly in the interior of cellulosic fibers.In this study, cellulases were modified with Eudragit, using carbodiimide (EDC)covalently coupling and non-covalent methods. Cellulase, laccase and Eudragit wereco-modified with covalently coupling method. The modified enzymes were applied tobio-polishing of cellulosic fabrics or denim washing, respectively. Preparation of modifiedenzymes, structure and nature of modified enzymes, action mode of modified cellulase oncellulosic fabrics, effects of treatments of modified enzymes on cellulosic fabrics, had beenstudied in detail. The research contents and conclusions were as follows:1. Preparation of modified enzymes was studied.The results of gel filtration analysis revealed that the earliest detected times of covalentmodified enzymes were earlier than those of free enzymes. This result indicated that covalentmodified enzymes had a higher molecular weight than free enzymes. The typical absorptionof protein was detected in FTIR spectra of modified cellulases with non-covalent method. Theresults showed that enzymes were successfully modified with Eudragit.The modification rates of free amino of covalent-Eudragit S-100-cellulase andcovalent-Eudragit L-100-cellulase reached50.72%and51.98%, respectively. The relativecellulase activities of covalent-Eudragit S-100-cellulase and covalent-EudragitL-100-cellulase were80.04%and76.88%, respectively. The relative cellulase activities ofnon-covalent-Eudragit S-100-cellulase and non-covalent-Eudragit L-100-cellulase were82.20%and78.20%, respectively. The modification rates of free amino of EudragitS-100-cellulase-laccase and Eudragit L-100-cellulase-laccase reached38.06%and42.24%,respectively. The relative cellulase activities of Eudragit S-100-cellulase-laccase and EudragitL-100-cellulase-laccase were78.46%and75.62%, respectively. The relative laccaseactivities of Eudragit S-100-cellulase-laccase and Eudragit L-100-cellulase-laccase were88.28%and86.76%, respectively.2. The second structure of protein, temperature and pH stability, and reusability ofmodified enzymes were studied.The results of Circular dichroism and Fluorescence emission spectra indicated that thesecond structure of enzyme protein could be changed afier the modification. The proportionof helix reduced, and the proportions of strand and turns increased. Moreover, the morechange of second structure of protein caused by Eudragit L-100than Eudragit S-100. This study showed that the modification of cellulase via covalent binding onto Eudragitgained better stability, especially at pH6.0~9.0and temperature60~80℃. The cellulasemodification with non-covalent method changed its temperature profile, and the maximumactivities of the free and modified cellulases were observed at50℃and60℃, respectively.The optimum temperature and the optimum pH of Eudragit-cellulase-laccase were50℃andpH5.0, respectively.Covalent-Eudragit-cellulase retained about50%of its original activity after five cyclesof repeated uses, showing high reusability. Non-covalent-Eudragit-cellulase retained about30%of its original activity after five cycles of repeated uses. Eudragit-cellulase-laccase retainedabout40%of its original cellulase and laccase activities.3. The effects of covalent-Eudragit S-100-cellulase treatment on cotton fiber structureand the hydrolysis of different cellulosic fabrics or different forms of substrates withcovalent-Eudragit S-100-cellulase were studied.The results of XRD, ATR-FTIR and fibre accessibility indicated that the hydrolysisoccurring in the interior of the cotton fibers was limited during covalent-EudragitS-100-cellulase treatment.The results of hydrolysis of different forms of substrates (cotton fabric, cotton yarn,cotton fiber) indicated that the reducing sugars released from cotton fiber were39.90%morethan that from cotton yarn at free cellulase treatment; the reducing sugars released from cottonfiber were71.95%more than that from cotton yarn at covalent-Eudragit S-100-cellulasetreatment; the reducing sugars released from cotton yarn and fabric were close at freecellulase treatment; the reducing sugars released from cotton fabric were less than that fromcotton yarn at covalent-Eudragit S-100-cellulase treatment.The results of hydrolysis viscose fabrics, mercerizing fabrics, cotton fabrics and ramiefabrics by free cellulase or covalent-Eudragit S-100-cellulase treatments showed the moreinfluence on hydrolysis by free cellulase with the increase of fiber accessibility of the fabrics.4. The enzymatic treatments on bio-polishing of cotton and ramie fabrics using freecellulase or covalent-Eudragit S-100-cellulase were investigated.The results revealed that weight losses of cotton fabrics with free cellulase orcovalent-Eudragit S-100-cellulase treatments (cellulase activity5.64U/mL) were7.26%and5.34%, respectively; weight losses of ramie fabrics with free cellulase or covalent-EudragitS-100-cellulase treatments were2.79%and2.62%, respectively; fiber copper values ofcotton fabrics with free cellulase or covalent-Eudragit S-100-cellulase treatments were0.04861and0.02790, respectively; fiber copper values of ramie fabrics with free cellulase orcovalent-Eudragit S-100-cellulase treatments were0.02427and0.02286, respectively. Theresults showed that the cotton and ramie fibers treated with free cellulase were morehydrolyzed and more destruction than those treated with covalent-Eudragit S-100-cellulase.The results revealed that tensile strengths of cotton fabrics with free cellulase orcovalent-Eudragit S-100-cellulase treatments (cellulase activity1.88U/mL) were15.09%and5.61%, respectively; tensile strengths of ramie fabrics with free cellulase orcovalent-Eudragit S-100-cellulase treatments were24.60%and10.65%, respectively. As seen from TM-AFM and SEM images, the covalent-Eudragit S-100-cellulasetreatment could produce smooth cotton fibre surfaces without causing serious damages to thefibre surface structures.5. The enzymatic treatments of the denim fabrics using free cellulase and modifiedenzymes were investigated.At a cellulase activity of5.64U/mL, CIE L values of the denim fabrics treated with thefree and covalent Eudragit-cellulase were close to25. This result revealed that the enzymatictreatments with the free and covalent Eudragit-cellulase produced similar decolorationefficiency for the denim fabrics. The tensile strength losses of denim fabrics treated with freecellulase or covalent Eudragit-cellulase reached46.21%and30.9%, respectively.At a cellulase activity of1.88U/mL, CIE L values of the denim fabric treated with freecellulase, covalent Eudragit-cellulase and Eudragit-cellulase-laccase were22.91,22.68and25.76, respectively. The tensile strength losses of the denim fabric treated with free cellulase,covalent Eudragit-cellulase and Eudragit-cellulase-laccase were30.13%,13.41%and12.67%, respectively. The enzymatic treatments with Eudragit-cellulase-laccase produced betterdecoloration efficiency and higher tensile strength for the denim fabrics.