Salt-free and environment-friendly reactive dyeing of cotton in cottonseed oil/water system

This research studies the reactive dyeing in cottonseed oil/water dual-phase solvents system (CWDS) and establishes sustainable industrial dyeing procedures using cottonseed oil. The conventional aqueous dyeing generates large quantities of wastewater containing high concentrations of salts and dyes and has very low dye-fixation. Substituted dyeing technologies not only failed to completely solve problems of aqueous dyeing but also generated new problems such as high cost for modifications of dyeing facilities and new environmental pollution. Using cottonseed oil as external dyeing phase notably increases the dye concentration in the internal solvent phase via raising the chemical potential of dyes at outer phase without the use of salts. The dye fixation based on the total dye added to the dyebath for CWDS increases by up to 30% compared to aqueous dyeing. Besides, the external phase in CWDS is recyclable and biodegradable. Furthermore, using CWDS, fabrics are dyed in current jet-dyeing facilities on a pilot scale and have the same levelness and colorfastness as those from aqueous dyeing. Dye fixation using pilot-scale jet dyeing machines in CWDS achieves 90%+. The materials and energy costs of CWDS are lower than those of aqueous dyeings.