Synthesis, recovery, and application of environmentally friendly disperse dyes with high light fastness

Dye wastewater has attracted great attention due to high pollution and toxicity which can cause harm to the living environment. It is common for azo-disperse dyes to be used to dye hydrophobic fibers. A reduction clearing method is used to eliminate the dye particles on the fabric after dyeing. However, when azo disperse dyes on the fiber surface are eliminated by the reduction clearing process, this can give rise to an effluent discharge due to the presence of sodium hydrosulfite. The introduction of carboxylic ester groups into dye molecules can effectively avoid this issue. Six novel environmentally friendly alkali-clearable disperse dyes, containing cyano and carboxylic ester groups, were readily synthesized by a diazo coupling reaction with various diazo components. Their dyeing properties on polyethylene terephthalate fabrics were respectively measured and compared with those of commercial reference dyes. It was indicated that some fastness properties of the synthesized dyes on polyethylene terephthalate fabrics after the alkali clearing were improved compared with those of the reference dyes due to the existence of the carboxylic ester group. Moreover, the chromaticity of dye wastewater can be further reduced by recovering hydrolyzed dyes.