Sustainable ultrasonic dyeing of unscoured and unbleached cotton sliver using low liquor ratio

The conventional dyeing process for cotton usually requires a high liquor ratio to achieve adequate dye migration and penetration to obtain uniform dyeing. However, a high liquor ratio increases water and chemical con-sumption, placing a heavy burden on dyeing effluent treatment. In this study, ultrasonic energy was used during the dyeing process to reduce the liquor ratio and improve the dye migration and exhaustion performance. The dyeing parameters, including liquor ratio, dyeing time, ultrasonic power, salt, and alkali concentration, were systematically studied. The dye uptake percentage, color strength, and CIE colorimetric values of the samples were examined, in addition to the scanning electron microscopic and optical images of the samples. The results show that the ultrasonic energy could facilitate the dyeing process by enhancing the diffusion and penetration of dye molecules, thereby ensuring uniform and thorough dyeing performance. The dye uptake percentage and color strength were improved by 120.0% and 25.6% when compared to the results of conventional dyeing process. The liquor ratio was significantly reduced to 6:1, and the high-energy consuming scouring and bleaching pretreatment processes normally required for conventional dyeing were avoided. Additionally, the dyeing time and consumption of alkali were also significantly decreased through the dye-promoting effect of ultrasonic en-ergy, by more than 60.0% and 50.0%, respectively.