The Mechanism Of Indigo Backstaining Durning Cellulase Washing

Due to the environment problems and other disadvantanges, stone washing would be replaced by cellulase washing. However, during the cellulase washing, the removed indigo was found to backstain on the reverse side of fabric,which reduced the desired contrast between the white and the indigo dyed fibres. Therefore, it affected the appearance of denim fabrics and reduced the additional value. We studied the mechanism of indigo backstaining during the cellulase washing in this paper. The mechanism was important to solve the problem of indigo backstaining and improve the additional value of denim fabrics.The cellulase activity was affected by many factors. Therefore, we studied these factors and made out the best hydrolysis technics. The best pH value was 5.0, temperature was forty degree centigrade, and time was thirty minutes. The acetate buffer was used in the treatment process. The non-ionic surfactants could increase the enzyme activity, however, the ionic surfactants and indigo dyes inhibited the enzyme activity.During the cellulase washing, the cellulase enzyme must be adsorbed on the cellulose fibers and then hydrolysis the fibers. So, we studied the factors which would affect the adsorption ability of cellulase and fabrics. We learned from the results that there was a best adsorption when the pH value was the suitable value of cellulase. The cellulase enzyme was quickly adsorbed on the fabric, and it could be reach the maximum adsorption in twenty minutes. The adsorption isotherm of cellulase in forty degree centigrade indicated that the adsorption of cellulase on the fabric was multi-molecule layer. The indigo dyes could promote the adsorption ability of cellulase and fabric.The problem of indigo backstaining during cellulase washing was studied by imitating indigo's direct backstaining to the undyed cotton fabrics. And the backstaining levels were influenced by different conditions. There was a higher backstaining when the fabric was adsorbed by the cellulase. The backstaining level became higher with the increase of cellulase concentration. The backstaining levels and the combine states of cellulase, indigo dyes and cellulose fibers were influenced when the pH value was changed. We studied the Zeta potentials of cellulase, indigo dyes and fabrics, and discussed the combine state of them. The results claimed that the affnity of cellulase with indigo was higher than that of cellulase with fabric. Indigo dyes particles were also influenced by the cellulase. There were two kinds of power between cellulase and indigo dyes. On the one hand, the cellulase could make the indigo dyes assemble, on the other hand, there was a affinity between them. The backstaining levels were influenced by the two power. However, there was only the affinity when the cellulase was adsorbed on the fabric. Thus, the intense affinity between cellulase and indigo dyes was the main reason of indigo backstaining.Besides, the surfactants and laccase were also studied in this paper. The non-ionic surfactants TX-10 and AEO-9 could reduce the indigo backstaining, so they could be used as anti-backstaining agents. The laccase could also reduce the backstaining when we put them in the washing solution durning the cellulase washing. The laccase had the best anti-backstaining when the laccase concentration was 0.9g/L.