Natural and eco-friendly cotton dyeing process using eutectic solvents and curcumin

The textile industry significantly contributes to global wastewater due to inefficient dyeing processes that release synthetic dyes and hazardous chemicals. This study explores the use of eutectic solvents (ES) composed of cholinium chloride (ChCl), glycerol (Gly) and Urea (U) to dye cotton fibers with curcumin, a natural pigment. The dyeing performance of three different ES (ChCl/Gly, ChCl/U, Gly/U) was evaluated by comparing the colorimetric properties of the dyed fibers. Gly/U was identified as the most cost-effective ES, and its composition was optimized to reduce water and resource needs. Gly/U 1:1 ES with 20 % of water was the most cost-efficient dye bath, achieving curcumin exhaustions of around 30 % and color differences (∆E) of near 24.0 after one dyeing cycle. The use of ES improved curcumin solubility, enhanced dye-fiber interactions and increased dyeability. In comparison, pure or aqueous mixtures of ES-forming compounds required 40–80 % curcumin exhaustion to reach ∆E values of about 24.0. Fibers dyed with ES exhibited superior colorfastness compared to controls, with ∆E reductions of 32 % in washing fastness and 10 % in light fastness, whereas controls showed reductions of 32.5–41 % and 11–16.3 %, respectively. A circular and eco-friendly dyeing strategy using the optimized ES was designed and validated experimentally, showing excellent repeatability and recyclability over five consecutive dyeing cycles, with an 80 % reduction in water usage and elimination of inorganic salts needs. This work confirms the feasibility of designing eco-friendly and cost-efficient ES-based cotton dyeing technologies using natural pigments, reducing the reliance on harmful chemicals and energy-intensive processes in conventional textile dyeing methods, and the wastewater production and environmental impact of textile processing. • Curcumin cotton dyeing performances of three eutectic solvents (ES) were compared. • Glycerol/Urea 1:1 (20 %wt. water) was the most resource and cost-efficient ES. • ES hydrogen bonding enhances curcumin solubility, improving dyeability. • Better colourfastness properties were achieved using ES compared to control dye baths. • A circular ES-based cotton dyeing process is proposed, reducing water usage by 80 %.