Water-Saving and Less-Salt Cotton Dyeing Process Using Deep Eutectic Solvents

Traditional cotton textile dyeing processes are extensively dependent on electrolytes and auxiliaries, generating wastewater laden with hydrolyzed dyes and salts that present substantial environmental risks. This work developed a water-saving and less-salt dyeing method for cotton textiles by integrating deep eutectic solvent (DES) swelling pretreatment. This innovative approach alters the intra- and intermolecular hydrogen bonding of cellulose, inducing structural modifications, such as increased fiber diameter, enhanced amorphous cellulose content, and expanded porous architecture. These changes significantly improve dye accessibility and the uptake efficiency. Among the DES systems evaluated, K2CO3-glyceryl DES exhibited the highest Sw% in cotton fibers (59.5%). DES swelling method offers significant advantages over conventional processes, such as reduced environmental impact (e.g., lower water/energy consumption, fewer harsh chemicals), enhanced dye uptake efficiency, or improved fiber integrity. Furthermore, the DES retained its swelling efficacy after multiple recycling cycles, underscoring its reusability. This advancement not only aligns with eco-friendly textile manufacturing goals but also demonstrates economic viability.