Studies On Dyeing Of Black Dye Containing Polycarboxylic Acid Groups On Cotton Fibers

In this paper, a black dye containing polycarboxylic acid groups (polycarboxylic acid dye is used for short) was applied to dyeing of cotton fibers by esterification reaction to form crosslinking fixation through ester linkage, which provide the dyed fibers certain anti-wrinkle performance and good fastness properties. The existence of multiple carboxyl groups and the stability of them enhanced the dye fixation and made the recycle of the dye solution possible, which could reduce dyeing pollution and realize green dyeing process.The solubility and the adsorption and reflectance spectra of the polycarboxylic acid dye were studied in the paper. The aqueous solution and aggregation state of the dye on cotton were investigated by XRD small-angle scattering analysis. The dyeing dynamics and thermodynamics were also examined. It presented that the adsorption isotherm of the dye on cotton followed Nernst-type partition mechanism.The dyeing behaviors of the polycarboxylic acid dye on cotton fibers were systematically investigated. Based on thermal analysis results, it was proposed that by addition of dehydrating agents, baking temperature could be decreased. Exhaust dyeing, dip-pad dyeing and exhaust-pad-bake dyeing methods were designed for the dye and the dyeing process was finally set up. It showed that dye fixation could reach 98% under optimal dyeing conditions. The application of the black dye provided the dyed cotton with not only saturated color, high color fastness, but also anti-wrinkle and easy-care properties. The dyeing properties of the black dye was investigated and its colorfastness on cotton was measured, it presented that the light fastness could reach 6 grade, water and wash fastness was 4-5 grade, dry rub fastness was 4 grade and wet rub fastness was 2-3 grade. The anti-wrinkle finishing performance of the dyed fibers was studied and it displayed that the dye not only had satisfactory dyeing properties, and it also provided anti-wrinkle finishing performance on cotton.This paper studied the recycle utilization of the dye liquor. The recycle dyeing method by addition of the polycarboxylic acid dye in dye liquor was established and dyeing results were much stable. Recycle application of the dye liquor enhanced dye utilization ratio, reduced dyeing cost and decreased dye effluent discharging, which was quite essential to solve the environmental problem in dyeing industry.Thermo-gravimetric Analysis and FT-IR spectroscopy were used to investigate the dyeing mechanism of ester linkage between the polycarboxylic acid dye and the cotton fibers, and methods of color stripping, fiber dissolving in cuprammonia and fiber oxidation were employed to indirectly testify the existence of ester bonds crosslinking. Accordingly, the conclusion was drawn that ester linkage formed between the polycarboxylic acid dye and the cotton fibers in dyeing process. The hydrolysis stability of the ester bonds between the polycarboxylic acid dye and cotton fibers were analyzed and it concluded that under weak acidic, neutral and weak basic conditions the bonds were stable.