A novel approach to investigating the relation between color strength and relative dye concentration and to controllably modifying the color strength of dyed polyester fabrics through supercritical fluid treatment

Widely utilized polyester fibers generally have excellent color fastness, making it quite challenging to controllably modify their color strength (K/S value), especially in regulated decolorization. In this study, the relation between the color strength and the relative dye concentration of dyed polyester fabrics was investigated based on the principle that dyes may migrate and reach redistribution equilibrium through supercritical carbon dioxide fluid treatment. The results demonstrated that the relation agreed well with an exponential decay fitting, allowing for the controllable modification of the color strength of dyed polyester fabrics using the derived regression formulas. Furthermore, the correlation between the residual dye in the supercritical fluid treatment vessel and the color strength of the previously treated fabric was clarified. To verify the universality of the above strategies, three dyes with representative anthraquinone, heterocyclic, and azo structures were employed in this study. Furthermore, it was observed that the dyes were evenly diffused throughout the polyester fibers following the supercritical fluid treatment, promising the fibers’ good color fastness. These findings might be significant for exploring the dyeing behavior of fibers in supercritical fluids, stimulating the reutilization of colored polyester and carbon neutrality of textiles, and expanding the potential applications of supercritical fluid technology.