Hydrolyzed Reactive Red 195 adsorption on cellulose: Experimental and theoretical investigations

In this investigation, the mechanism of dye transfer during the mixed washing of natural cellulosic fabrics was elucidated through a comprehensive study of the hydrolysis of Reactive Red 195 (RR 195) and the subsequent adsorption of its hydrolysis products onto cellulose, approached both experimentally and theoretically. Initially, Reversed-phase high-performance liquid chromatography (RP-HPLC) was employed to identify the final products of Reactive Red 195 hydrolysis, collectively referred to as the unfixed dye substance ( UDS). This data provided theoretical insight into the hydrolysis mechanism of the dye. Following this identification, an adsorption kinetic model was established to delineate the interaction of the hydrolysis products with cellulose. Adsorption exhibited its maximal rate at a temperature of 60°C, under conditions of a wash bath ratio of 120:1 and a pH value of 7. Furthering the investigation, a molecular dynamics model was constructed to detail the adsorption process of these hydrolysis products on the hydrophobic surface Iβ(1 0 0) of cellulose within an aqueous environment. This model offered precise insights into the adsorption volume, kinetics, and mechanistic interaction at a molecular scale. Conclusive evidence from both theoretical analyses and experimental results suggested that the hydrolysis products, devoid of reactive groups, were incapable of chemically interacting with the hydroxyl groups inherent to cellulose. Instead, it was discerned that these products underwent a physical adsorption process onto the cellulose surface. Such adsorptive behavior is postulated to be a predominant factor influencing the dye transfer phenomenon in mixed washing conditions.