Water-free dyeing of polypropylene fabrics in supercritical CO2 with functional dispersants for eco-friendly textile applications

Owing to rising environmental awareness, the textile dyeing and finishing industry faces increasing pressure to reduce water consumption and chemical wastewater generation of conventional aqueous dyeing processes. Supercritical carbon dioxide (scCO₂) dyeing, a water-free dyeing method, conserves water resources and prevents water pollution. Polypropylene (PP) fabrics are promising eco-friendly textile materials owing to their simple structure, low carbon emissions, and less weight. High crystallinity and lack of polar functional groups in their molecular structure makes them difficult to dye. PP fibers are commonly colored via mass pigmentation. However, limited flexibility in masterbatch formulations restricts color mixing and shade modification. In this study, a series of styrene–maleic anhydride (SMA) copolymers grafted with long-chain alkyl amines were synthesized and used as dispersing agents in scCO₂ dyeing systems to enhance the disperse dye uptake of PP fibers. When applied to a disperse yellow dye (JY) and blue dye (JB), the SMA dispersants significantly improved dyeing performance under scCO₂ conditions. For a JY with an SMA dispersant, the Kubelka–Munk function (K/S) value increased by approximately 27.7%, whereas levelness (ΔE*) decreased by 47.1%. For a JB with an SMA dispersant, the K/S value increased by 39.7%, and ΔE* decreased by 42.6%. In a mixed-dye system, the SMA dispersant addition resulted in a 39.5% increase in K/S and 20.5% reduction in ΔE*. This study demonstrates the feasibility of using SMA–alkylamine polymeric dispersants to improve the dyeing performance and surface hydrophobicity of PP fabrics under water-free scCO₂ dyeing conditions without the use of fluorinated additives.