Dyeability of Acid Dyes on Wool Fabrics Treated with an Oxidizing Agent and an Enzyme

To clarify the dyeability of shrink-proofed wool fabrics treated with permonosulfate (PMS) and a keratinase, the sorption behaviors of four kinds of leveling acid dyes containing mono-, di-, and tri-sulfonate groups were investigated. The dyeing rate and sorption isotherms were determined to elucidate the effects of the dye structure and the treatment of wool fibers. The dyeing rate was discussed using apparent diffusion coefficients. The sorption isotherms were analyzed using dual sorption mechanism to calculate the sorption parameters, the number of binding sites S , the intrinsic binding constant KL, and the partition coefficient KP. As a result, the dyeing rate and the equilibrium dye uptake for the fibers treated with PMS alone were much smaller than those of the untreated ones. The dyeing rate and the equilibrium dye uptake were restored by the subsequent treatment with the enzyme. The S and KL values were also decreased by the oxidation with PMS. On the other hand, the ESCA and FT-IR spectra showed the presence of cystine monoxide (-SO-S-), cystine dioxide (-SO2-S-), and cysteic acid (-SO3 -) after the treatment with PMS. The observations obtained for the dyeing behaviors can be explained in the presence of cysteic acid generated in the fibers after the PMS treatment. It is likely that the decrease of dye uptake and S is due to the neutralization between the cysteic acid introduced by the oxidation and the protonated amino groups in the fibers that work as the binding sites for the dye anions. This tendency appeared strongly for the tri-sulfonate dye compared to the mono-sulfonate dye.