Compensation for hydrolysis in the reuse of reactive dyes

In conventional exhaust processes for applying reactive dyes, the alkali ac celerates dye hydrolysis, restricting subsequent reuse. Step-up and: chemic al build-up can complicate accurate color duplication with reused dyes as w ell. A two-bath method of first applying the dye from a salt and dye bath f ollowed by treatment in a separate alkali bath eliminates the possibility o f alkali-induced hydrolysis, step-up, and chemical build-up effects. In thi s study, four reactive dyes differing in reactive group and dyeing temperat ures are applied to cotton poplin fabric from original and reused dyebaths by one- and two-bath application methods, and the percent fixation of adsor bed dyes and the K/S values are determined. Dye hydrolysis and step-up and wash-off effects that occur in the one-bath method interfere with reuse. Th ese complications are eliminated when the reactive dyes are reused by the t wo-bath method.