Study on the Application of Environmentally Suitable Reduction and Solubilisation Process for Vat Dyeing of Cotton Fabric

Abstract

Cotton is one of the widely used textile fiber substrates in theworld, particularly in India, due to its comfort, aesthetic value, strength,affinity towards various chemicals and dyestuffs, and customer - friendly end-use products.Cotton is dyed by various dyestuffs including natural dyes, theprominent among which are direct dye, reactive dye, sulphur dye, pigmentdye and vat dye. From these dyes, vat dyes give exceptional properties oncotton material and hence they are welcome by textile industries. However,vat dye has some applicational problems. Vat dye is insoluble in water; hence,powerful reducing agent like sodium hydrosulphite (hydrose) in the presenceof strong alkali is required for its solubilisation (vatting). This process createseffluent and environmental problems that reduce the utility of vat dyes in thetextile market.Therefore, the aim of this research work is to reduce the problem ofvat dyeing due to the commercial reducing agent (hydrose) and to revive theuse of vat dyes for cotton dyeing within the effluent parameters set forindustries. With respect to solving this problem, the methodology was fixedafter many literature surveys and dyeing trials in the laboratory and in anindustry using various techniques and reducing agents. ivEventhough many research have been carried out on vat dyeing ofcotton materials, they are not being practiced in industries anywhere. Afteradapting these techniques and methods in the industrial trial, it was decided toimplement a simple technique commercially for industries.Against this background, a vat dye (Jade green XBN) was selectedin this research work, for dyeing on cotton fabric. For the reduction of vatdye, reducing agents such as hydrose, zinc and ferrous sulphate and theircombinations in different proportions were selected. The sequence of study isas follows: Different reducing agents for vat dyeing on cotton fabric wereapplied. Then effect of reducing agents on vat dyeing of cotton fabric wasstudied. Using different reducing agents Vat dyed cotton fabric was analysedfor fabric strength, fastness properties, colour strength, SEM study and FTIRstudy. Vat dye bath during and after dyeing was analysed for reductionpotential and effluent parameters respectively. Optimum combination ofreducing agents for vat dyeing on cotton fabric was then selected. Reducingagents of vat dyeing for industries with respect to cotton fabric properties andeffluent parameters can be preferred.The selected reducing agents were Hydrose 2.0% owm, Zinc 2.0%owm, FeSO4 2.0% owm and their combination asZinc 0.5% owm + Hydrose1.5% owm, Zinc 1.0% owm + Hydrose 1.0% owm, Zinc 1.5% owm +Hydrose 0.5% owm, FeSO40.5% owm + Hydrose 1.5% owm, FeSO41.0%owm + Hydrose 1.0% owm, FeSO41.5% owm + Hydrose 0.5% owm,FeSO41.5% owm + zinc 0.5% owm, FeSO41.0% owm + zinc 1.0% owm, andFeSO40.5% owm + zinc 1.5% owm. vThe results of vat dyeing on cotton fabric using different reducingagents are summarized below;The reduction potential of the reducing agent combination FeSO4and hydrose combination is good. There is a uniform change in the reductionpotential for this combination. This is particularly very good for FeSO41.0%owm + Hydrose 1.0% owm reducing combination compared with othercombinations.There is a good colour strength based on k/s value for the vat dyedcotton fabric using reducing agent combination of FeSO41.0% owm +Hydrose 1.0% owm. Compared to the other reducing agents, FeSO4 +Hydrose combination gives good colour strength to vat dyed cotton fabric.Using various reducing agents the vat dyed cotton fabric revealsgood dyeing effect which was confirmed by scanning electron microscopephotograph. The dyeing effect is very good on vat dyed cotton fabric usingFeSO4 and hydrose combinations, especially for FeSO41.0% owm + Hydrose1.0% owm, as reducing agent. This dyeing effect on vat dyed cotton fabricwas also confirmed by FTIR analysis, as given for original vat dye and for thevat dyed cotton fabric using different reducing agents especially FeSO41.0%owm + Hydrose 1.0% owm.After vat dyeing on cotton fabrics using various reducing agents theeffluent parameters are of different levels. The effluent parameters are less forvat dyed cotton fabric using the combination of FeSO4 + Hydrose as reducingagents, and they are within the limit prescribed for waste water of textile vichemical processing industries for FeSO41.0% owm + Hydrose 1.0% owmcombination.In general the results are convincing for the textile material, asthere is no considerable change in the tensile strength of the cotton fabric aftervat dyeing using various reducing agents, and the fastness properties(washing, light and rubbing) are also very good relevant to the textilematerials.