Decolorization of dyed polyester fabrics by synergistic effect of supercritical carbon dioxide fluid and co-solvent

Currently, the majority of waste polyester has not been properly reused, causing increasingly severe resource waste and environmental issues. Decolorization treatment is the prerequisite and key to the fiber-to-fiber recycling of waste colored polyester fabrics. Herein, a new method for decolorizing dyed polyester fabrics through the synergistic effect of supercritical carbon dioxide (scCO 2 ) fluid and co-solvent was demonstrated. The dyed polyester fibers were swollen substantially by the high-temperature scCO 2 fluid, which enhanced polymer chain segmental mobility and promoted polymer free volume. As a result, the dyes originally fixed in the amorphous region of the polyester molecular chain have a great chance of diffusing and then be continuously captured by the co-solvent, thereby achieving the purpose of decolorization. The temperature, duration, bath ratio, dosage of co-solvent, and the method of introducing the co-solvent for the appropriate decolorization treatment were discussed individually. It was found that the dyed polyester sample would likely experience a higher decolorization rate (DCR) when the co-solvent's solubility parameter (SP) value was close to that of the dye. Three polyester samples dyed with representative anthraquinone, azo, and heterocyclic dyes all reached a DCR of over 95 %, suggesting that this decolorization strategy has a wide range of applicability. • Decolorization of polyester using supercritical fluid and co-solvent synergy. • Decolorization rate correlates strongly with the co-solvent's SP value. • Three dyes with representative structures were employed for the study. • Over 95 % decolorization achieved for all three dyed polyester fabrics.