Indigo Backstaining During Cellulase Washing

Cellulase washing of denim garments is an environmental friendly process, which hasgiven fabric fashionable stone washed look and unique styles. However, during enzymatictreatment the removed indigo dye was found to backstain the cotton fabric. Theredeposition of indigo dye on the cotton fibers diminishes the desired contrast betweenwhite and blue yarns, and can be easily noted on the reverse side of the fabric and bagplaces. Therefore, it could affect the outward appearance of denim fabric and reduces itsadditional value.In this paper, the key factors including the concentration of cellulase and substrate, pHvalues, as well as temperature and time, which affect the adsorption characteristics of acidcellulase SHL on cotton fabric, were discussed. It is showed that bigger cellulaseconcentration and higher temperature would increase the protein adsorption. When pHvalue ranged from 4.2 to 4.8, the adsorption was higher than that in other pH. The initialrate of adsorption was rather fast, it could reach the maximum adsorption after 30mins.K₁(the half saturation adsorption constant) and a (the maximum ratio of cellulase whichcould adsorb on cellulose) were 0.4948 and 0.4835 respectively, indicated that it was veryeasy for the cotton fabric to combine with cellulase enzyme. Compared indigo-dyedfabric with undyed fabric; we found the adsorption on indigo-dyed fabric was more thanthat on undyed. Furthermore, the influence of different indigo concentration on fabric tothe enzyme adsorption amounts as well as cellulase activity was researched.The problem of indigo backstainig during cellulase washing was studied by imitatingindigo's direct backstainig to undyed cotton fabrics. Backstaining levels were influencedby different cellulase washing conditions, for example, pH values, temperature, time andwater, etc. According to the results, indigo backstaining levels didn't increase with theincreasing amount of cellulase adsorbed on fabrics. While cellulase, indigo and fabricsexisted at the same time, the adsorption probability between cellulase and indigo wasgreater than that of cellulase and fabrics.Moreover, several kinds of additives were tested and compared, with the aim ofpreventing the backstaining problem. It was observed that PVP, PVA, PEG, and 1815 hadsome antibackstaining effect to a certain extent, so they could be used as antibackstainingagents during cellulase washing. Compared with other auxiliaries, CMC and Span85could reduce backstaining levels greatly, although they might slightly affect cellulaseactivity. Since their effective antibackstaining performance, they could match with otheragents as dye antiredeposition components.Besides, the indigo particle sizes had been measured when applied additives to enzymewashing process. Results confirmed that PVP, PVA and Span85 could all increase theparticle sizes of indigo. Among these three agents, the impact of PVP to indigo particlewas maximal and PVA was the weakest.