Eco-friendly Dyeing of Chitosan Treated Silk Fabric using Nutgrass (Cyperus rotundus) and Bistorata (Polygonum bistorta) Root Extracts

In this study, the influence of chitosan pre-treatment on dyeing of silk fabric with roots extracted from Cyperus rotundus (Nutgrass) and Polygonum bistorta (Bistorata) was investigated. Chitosan pre-treatment was done before dyeing at four different concentrations (0.25, 0.5, 0.75 and 1%) using pad-dry-cure method. Optimum dyeing conditions such as dye extraction pH, dye extraction time, dyeing pH, dye concentration and dyeing time were determined. Colour measurements and colour fastness properties were analyzed and evaluated. Colour strength (K/S) of chitosan treated silk fabric dyed with both the natural dyes was significantly higher than the untreated fabric. For Nutgrass dye, 1% chitosan concentration sample showed 26.42% increase in KS value while an increase of 11.76% was observed in Bistorata dyed sample as compared to untreated fabric. Moreover, when compared to Bistorata dye, Nutgrass showed higher K/S value indicating a better dye uptake property when treated with chitosan. The CIE Lab for Nutgrass and Bistorata dyed silk samples showed significant decreased L* value, concentration dependent increased in a*, b* and C* value in chitosan treated fabric as compared to untreated dyed fabric. The chitosan treated silk fabrics showed excellent fastness to washing in term of colour change as well as increase in colour intensity. The colour change to rubbing fastness in wet and dry conditions for both chitosan treated and untreated samples were excellent. The perspiration fastness grades in term of colour change in both acidic and alkaline medium were observed to be excellent along with increase in colour in chitosan treated and untreated silk sample. Thus, chitosan pre-treated silk fabrics showed higher dye uptake for both the dyes whereas the fastness properties of the untreated dyed fabrics which were already very good to excellent remained same after chitosan treatment.