Natural deep eutectic solvent: A novel and green mordant for the natural dye

Applying natural dye is a green and available approach for the dyeing and simultaneous functionalizing of textiles. However, the commonly used mordant of metal ions to improve the dyeing effect results in massive toxic wastewater production, which decreases the environmentally friendly characteristics. In this work, the mordant and water substitute ability of choline chloride-ethylene glycol natural deep eutectic solvent (NADES), defined as the mixture of two or more primary metabolites at a particular composition becoming liquids via H-bond forces, was investigated during the dyeing process because it has been used as a green extraction and stability agent for the natural dye. To this end, the NADES and metal ion were used in three mordant dyeing wool and cotton processes of Platycodon Grandiflorus root dye, and the color and functionalization effect were compared to verify the method advance. The result indicated that natural deep eutectic solvent had a better effect as a mordant than the metal ion by enhancing the dye solubility, the dye uptake rate of fiber, and the dye polymerization trend via rich H-bonds among fiber, dye, and NADES. The dyed textile had an excellent functional performance, including UV resistance, antibacterial, antioxidation, and burning difficulty, with the preferable fastness. This method also showed good universality for other natural dyes and NADESs. Compared to the existing mordant dyeing technologies, the proposed technology had lower chemical reagent usage, cost, and energy consumption, whose residual solvent had good reusability for at least 10 times and better degradability. Overall, this paper supplied a potential and green approach using NADESs as alternatives to metal ions for the mordant dyeing textile using natural dye.