Carmine natural dyeing of chitosan-treated cotton: statistical analysis to enhance energy saving and environmental impact

Low molecular weight chitosan was employed for surface modification of cotton fabrics suitable for dyeing with carmine natural dye, without the addition of any coadjuvants into the liquor bath. The dyeing performance was evaluated through the color strength K/S calculated on the dyed fabrics. A full-factorial design of experiments was employed, followed by ANOVA statistical analysis. Two sets of experiments were designed. In the first set the focus was on assessing the influence of chitosan and dye concentration on the color strength (K/S) of the dyed fabrics. The second set of experiments was designed to investigate if shorter dissolution and impregnation times at room temperature would result in acceptable values of color strength K/S, aiming at higher throughput for eventual future industrialization of the process. The results evidenced that it is possible to obtain positive dyeing results with 2% chitosan concentration and 4% owf (on weight of fibers) dye concentration, drastically reducing the chitosan dissolution time and the fabric impregnation time. In addition, the antibacterial activity of selected fabrics was evaluated. The data obtained demonstrated that neither the dyeing process nor the washing severely impacted the antibacterial activity conferred to the fabrics by chitosan.