Dyeing of Cochineal Natural Dye on Cotton Fabrics Treated with Oxidant and Chitosan

Cotton fabrics were modified through an oxidation of the fabric with hydrogen peroxide followed by chitosan to improve their dyeability toward cochineal natural dye. Comprehensive studies were conducted on these fabrics to select chitosan modification process and assess their dyeability to cochineal in the ethanol-water system. The scanning electron micrograph showed the chitosan was deposited on the surface of cotton fiber. The infrared spectrum revealed the interaction between chitosan and cellulose further. Thermal gravity analysis showed the treatment produced little effect on the thermal stability of the cotton fabric. Treating cotton with 15 g/L chitosan and baking at 130 degrees C offered higher cochineal adsorption. Dyeing with increased time and at elevated temperatures resulted in higher dye uptake. The ratio of ethanol and water had obvious effects on solution polarity and when the proportion of ethanol and water was 9:1, cochineal adsorption reached maximum value. pH value had complex effects on K/S value and pH 7 yielded the highest color strength. Dyeing kinetics curves indicated that with the increase of the dyeing temperature, dye diffusion coefficient increased and half dyeing time decreased. The washing and rubbing fastness of the treated cotton fabrics were all improved and rated above grade 3.