Cellulase On Indigo-dyed Cotton Fabric And Anti-staining Mechanism

In the commercial use, the objects of cellulase treatment are the textiles dyed by dyes or pigments. By far, little systematic research on the cellulase action on indigo-dyed fabrics has been made. The effects of acid cellulase on the indigo-dyed fabrics and the backstaining of indigo were researched in this paper. It is shown that the adsorption equilibrium constant and rate constant to the indigo-dyed fabrics are 2.47ml/mg and 0.260mm^-1 respectively, comparing with 1.65ml/mg and 0.172 min^-1 to the undyed ones. The "indigo binding domain" in the cellulase amino acid subsequence is one of the reasons for the higher substantivity. In addition, the indigo in the fabrics can change the Zeta potential of the fabric, which would also facilitate the adsorption of cellulase.The indigo in the fabrics would inhibit the hydrolysis effect on the fabrics. The V_m and V_max/K_e to the indigo-dyed fabrics are 1.46mg/ml h and 3.24 respectively, comparing with 1.95mg/ml h and 3.82 to the undyed ones respectively. The optimal temperature and pH value of cellulase treatment were determined by the research. At last, it is found that the ionic surfactants have adverse effect on the hydrolysis, but the nonionic ones have favored effect on the hydrolysis in some conditions.The influences of temperature, time, pH value and cellulase concentrations on the "stone washing effect" and "indigo backstaining" were discussed. The mechanism of indigo backstaining could be explained as follows: With the hydrolysis by cellulase, the cellulose molecular chains are cut off, and some indigo in the fabrics would go into the water. With the indigo binding domain, the cellulase protein adsorbed on the fabrics would attract the free indigo and make the backstaining occur. In the other hand, some free protein are adsorbed onto the surface indigo in the solution, which makes the indigo stable dispersed in the water with small particle size and brings more backstaining.Some protease, laccase or surfactants were added into the solutions to reduce the backstaining, and the mechanism of backstaining removal was tentatively discussed.