Efficient zero wastewater and salt-free of cotton fiber dyeing via hydrophobic organic chemical/water two-phase dyeing system

For cotton fabric dyeing, a significant quantity of salt and water are typically consumed in the conventional water dyeing bath. In this study, an environmentally friendly alternative was investigated that could eliminate water waste and salt usage, as well as reducing chemical consumption. This method, which employs a hydrophobic organic chemical/water two-phase dyeing system, solely involves fiber swelling, dye dissolution, and the use of alkaline agents. By substituting the water required for heat and mass with an organic chemical, 71.43% dye reduction can be achieved in dye consumption compared to traditional water-based dyeing method. Benefiting from the natural affinity between dyes and cotton fibers, without any interaction with hydrophobic organic chemicals, reactive dye can diffuse into the fiber surface, which can achieve above 98% dye uptake and 90% fixation rate. The K/S value of the dyed cotton fabric is much higher than that of conventional water bath at the same dye concentration, and it is the highest when the water content is 120 %. Moreover, the uniform distribution of dye and the color fastness of the dyed fabric are comparable to traditional water-based dyeing. Due to the influence of intermolecular forces, the aggregation of dye is changed to varying degrees in different hydrophilic and hydrophobic cotton fiber dyeing systems, which further influences the dyeing quality. This study not only improves the utilization of dye but achieves salt-free, no wastewater emission and reduces the dyeing cost, providing an economical and sustainable dyeing method for the industrial dyeing of cotton fabric. •A 71.43% reduction of dye consumption can achieve.•Wastewater and salt free of cotton fiber dyeing.•The aggregation of dye is successfully determined in two-phase dyeing system.•The aggregation of dye on different wettability fibers in dyeing system is observed.