Analysis of Enzyme Washing of Denim using Experimental Design

Denim fabric with its wide acceptance has been subjected to various kinds of finish effects by processors, the worn out look being the most prominent. The process of imparting this fading effect has also evolved with time, particularly with use of enzymes as an option. In this context, herein three denim fabrics are treated with a modified neutral cellulase to study the wash down effect. Two of the fabrics are indigo vat dyed, one in light blue shade and the other dark blue shade, while the third one is of sulphur black. The enzyme wash was done by varying the concentration of enzyme, time of treatment and mechanical agitation. To reduce the number of trials, Box Behnken design of experiment was used and the process in the design region was optimized by ridge analysis. Other than studying the effect of process parameters, back staining during the enzyme action was also evaluated. The extent of colour fading was checked by finding the colour strength in terms of K/S (Absorption/ Scattering) values, while surface fibre removal due to cellulase action was determined by weight loss method. The trends and optimized conditions were observed to be dye and shade specific with reasonable coherence. Although back staining was not found much in the vat dyed fabrics but it was of prominence in sulphur black, possibly due to redeposition of the dye.