Enzyme washing of indigo and sulphur dyed denim

Introduction Denim as a fabric, has received the widest acceptance among all textile products. It has had an incredible influence on consumers both socially and culturally (Paul 2015). This twill cotton fabric usually has warp threads indigo dyed while weft remains plain white. The warp faced fabric therefore looks blue on one side and white on reverse. The warp being ring dyed, creates denim’s fading characteristics, which is unique compared to every other textile material. With changing times, many new variants of denim came into existence. Denim washing is one of the key areas in getting the faded look. Earlier stone washing used to be done to achieve soft feel and the desired appearance. During washing, the pumice stone, scraps off the dye particles from the yarn surface in the denim fabric. Due to the ring dyeing of denim fabric and heavy abrasion during stone washing process, the faded effect is achieved. Oxidative bleaching agent with or without the addition of stones have also been used to get fading effect. Difficulty in removing residual pumice from fabric, damage to equipment and clogging of machine drainage passage due to particulate material proved to be major drawbacks with the technique (Heikinheimo et al. 2000). Later on use of enzymes became a sustainable option to get the worn out look in denim. The enzymes used are cellulase enzymes, specifically acting on the cellulose part, mainly on the surface of the fabric. This gives the desired look Abstract A wide ranging finish effects have been given to denim fabrics in industrial scale to make it more fashionable and functional. Among the numerous wet and dry treatments given, worn out looks of various kinds have received the maximum attention. In this context, herein, two denim fabrics, one dyed with vat indigo and the other with sulphur black were enzyme washed. The enzymes used were acid cellulase and neutral cellulase and the treatments were done at varying concentrations, time and mechanical agitation. The trials so taken were based on design of experiments, and the effect was analysed in terms of decrease in colour depth and weight loss. Back staining of fabric during the wash was also checked and acid enzyme despite higher colour removal, caused significant staining in sulphur dyed quality. Attempt was made to contain this back staining by suitable treatment. The application conditions of cellulases on the denim qualities were also optimized for fading effect.