Reactive modified curcumin for high-fastness nonaqueous SC-CO₂ dyeing of cotton fabric

Modified curcumin, which has the advantages of low toxicity, high solubility, and little color change after modification, is very suitable for nonaqueous supercritical carbon dioxide cotton dyeing. However, the existing curcumin modification technology focuses on improving its solubility. Modified curcumin is directly adsorbed onto cotton fabrics, and the main interaction forces are van der Waals forces, which causes the poor fastness of modified curcumin to dyed cotton fabrics. In this study, reactive groups (hydroxyalkyls) were introduced into curcumin to enhance its fastness to cotton fabrics. The results showed that, similar to alkyl groups, hydroxyalkyl groups can enhance the color depth of dyed cotton fabrics by elevating the solubility of modified curcumin in supercritical carbon dioxide. The higher the solubility of modified curcumin in supercritical carbon dioxide was, the higher the K/S value of the dyed cotton fabric. Furthermore, the hydroxyl groups on the modified curcumin could form ether bonds with the hydroxyl groups on cotton fabrics. Therefore, the washing and rubbing fastness of hydroxyalkyl-curcumin-dyed cotton fabric was better than that of alkyl-curcumin-dyed cotton fabric.