Syntheses and dyeing properties of novel water-soluble reactive sulphur black dyes

The practical application of a sulphur black dye relies on its ability to dye cotton fibres with pure black colour and maintain the colour with high light fastness. Here, we report a synthesis method to prepare a novel water-soluble reactive sulphur black dye. The approach involves the reduction of CI Sulphur Black 1 to its leuco form and subsequent reaction with a water-soluble intermediate containing reactive groups synthesised from amino acid and cyanuric chloride. The optimal carboxyl and reactive group content of the water-soluble reactive sulphur black dye is 141 mmol/100 g, and the water solubility can reach 92 g/L. The fixation of the reactive sulphur black dye on cotton reaches 89% in a pad dyeing process without using sodium sulphate. The reactive sulphur black dye can achieve a light fastness of grade 6-7, a dry rub fastness of grade 4 and a wet rub fastness of grade 2, comparable or higher than the conventional CI Sulphur Black 1. The dyeing results showed that the novel water-soluble reactive sulphur black dye has excellent performance and good application prospects.