Characterization of dimethyl sulfoxide-treated wool and enhancement of reactive wool dyeing in non-aqueous medium

Abstract

Wool pretreated with dimethyl sulfoxide (DMSO) was characterized and its dyeing behavior in non-aqueous green solvents was investigated. Reactive dyeing of wool in deep shades is challenging because the mandatory alkaline aftertreatment to match the fastness of mordant dyes inevitably causes damage to wool keratin. The current study showed that the colorfastness-integrity dilemma could be solved by replacing water with organic solvents as the dyeing medium. Covalent fixation is predominantly favored in solvent dyeing so that excellent colorfastness is achievable at any given shade without alkali aftertreatment. Compared with aqueous dyeing, solvent dyeing was found to give 30% higher covalent fixation on average, which translated to better colorfastness (0.5–1 grade) at higher color depth (Δ K/ S = 1.3–4.9). In addition, scanning electron microscopy, X-ray diffraction and attenuated total reflection-infrared spectroscopy results indicated that DMSO pretreatment induced morphological and structural changes of wool in favor of dyeability. The findings are crucial to the phasing-out of metal-containing dyes for eco-friendly wool dyeing.