Constructing of Dyes Suitable for Eco-friendly Dyeing Wool Fibers in Supercritical Carbon Dioxide

Compared with traditional water dyeing, supercritical carbon dioxide (scCO(2)) dyeing is more environmentally benign. scCO(2) is widely used as a green solvent in dyeing synthetic fibers. However, studies involving dyeing natural fibers in scCO(2) are scarce. The commonly used methods result in corrosion of the dyeing equipment. Thus, the development of new special dyes suitable for scCO(2) dyeing is necessary; in addition, insight into the dyeing mechanism is important in promoting the design and synthesis of dyes for wool fibers in scCO(2). On the basis of our previous work, a possible dyeing mechanism in which the dyes exhibit hydrophobic interaction with keratins is proposed. The N=N bond twisting in azo dyes promotes the dyes embedding into the spaces of the alpha helices in proteins. According to the proposed mechanism, two new azo disperse dyes (azo thiazole-N(CH3)(2) and azo thiazole-OCH3) were synthesized; these dyes enable the dyeing of wool fibers in scCO(2). Meanwhile, the introduction of a succinimidyl ester group results in the fixation rate of the new reactive disperse dyes azo thiazole-NHS and azo-NHS reaching 100%. The byproduct of azo thiazole-NHS and azo-NHS reacting with the amino group of wool keratin is not corrosive to the dyeing equipment, thus enabling an eco-friendly dyeing process for wool fibers. Our strategy of introducing a succinimidyl ester reactive group will promote the development of new functional disperse dyes suitable for dyeing wool fibers in scCO(2).