The dyeing of silk: Part 4 heterobifunctional dyes

The exhaustion and fixation of three, commercial aminochlorotriazine/masked vinylsulfone dyes were both pH- and temperature-dependent. Optimum dye fixation was obtained at pH 8, as a corollary of a high number of nucleophilic –NH2 groups in the fibre, high conversion of the masked form of the dye to the reactive VS variant as well as reaction with OH-containing amino acid residues. The marked, temperature-dependence of dye fixation achieved in the pH range 3 to 9 demonstrated the importance of kinetic factors in dye–fibre reaction. The wash-off method used was very effective in removing unfixed/hydrolysed dye from the silk fabric and, as a result, the dyeings displayed very good fastness to washing at 40 °C.