Salt-free dyeing of cotton fabric and adsorption of reactive dyes in non-aqueous dyeing system: equilibrium, kinetics, and thermodynamics

In traditional water-based dyeing system, a large amount of salts and water are consumed and it is hard to treat inorganic salts in dyeing wastewater. From sustainable chemistry and engineering perspectives, a salt-free reactive dyeing system was established and the adsorption kinetic, adsorption isotherm, and the affinity between the dye and the cotton fiber were investigated. Furthermore, the influence of inorganic salts on reactive dye pilot dyeing was also evaluated. The results showed that the concentration of sodium sulfate had little influence on the color depth of dyed fabrics and the fixation of dyes. The adsorption rate of reactive dye would be increased with the increase of sodium sulfate concentration. When the amount of salt was 5.2% (o.w.f), salt had little effect on the K/S value and the level dyeing property of the dyed fabric. However, the maximum of S gamma(lambda) value of fabric was increased to + 0.06, which could result in a poor levelness and uneven dyeing when the concentration of salt was 7.8% (o.w.f). The pseudo-second-order kinetic model could best describe the adsorption kinetic of reactive dye in non-aqueous medium dyeing bath. Equilibrium adsorption data was corrected reasonably well by the Freundlich isotherm model. The affinity between cotton fiber and reactive dye was increased if salts were employed during dyeing. These successful investigations of the adsorption of reactive dye explain that salt-free reactive dyeing of cotton fabrics is feasible in non-aqueous medium dyeing bath, which greatly reduces the difficulty of waste water treatment.

Automated summary

In traditional water-based dyeing systems, a large amount of salts and water are consumed, making it difficult to treat inorganic salts in dyeing wastewater. From a sustainable chemistry and engineering perspective, a salt-free reactive dyeing system was established and the adsorption kinetics, adsorption isotherm, and affinity between dye and cotton fiber were studied. The influence of inorganic salts on reactive dye pilot dyeing was also evaluated. The results showed that the concentration of sodium sulfate had little effect on the color depth of dyed fabrics and the fixation of dyes. The adsorption rate of reactive dye increased with an increase in sodium sulfate concentration.