The dyeing of silk: Part 3 the application and wash-off of modified vinyl sulfone dyes

Silk was dyed using three modified vinyl sulfone reactive dyes designed for use on nylon fibres. The extents of exhaustion and fixation of the dyes were markedly dependent on pH and temperature; low application pH (pH 3 and 4) favoured dye exhaustion but disfavoured dye fixation whilst the use of pH 9 resulted in low fixation and exhaustion. Optimum dye fixation was obtained at pH 7–8, as a corollary of the presence of nucleophilic –NH 2 groups in the substrate and conversion of the masked dyes to the corresponding reactive vinyl sulfone variant. The marked temperature-dependence of dye exhaustion and fixation observed at pH 5–9 was considered to be indicative of a rate-determined, kinetic effect that was fixation-related rather than exhaustion-driven. Of the four wash-off methods examined, none removed sufficient dye from the dyeings and, although two commercial detergent formulations were most effective for the first few wash tests, this advantage decreased with increasing number of wash tests.