Impact of Dye and Auxiliary Structures on Vapor Decolorization and Closed‐Loop Recycling of Waste PET Textiles

Residual dyes and auxiliaries constitute a critical bottleneck restricting the high‐value recycling of waste polyethylene terephthalate (PET) textiles. Although the decolorization of dyed PET fabrics by ethylene glycol (EG) vapor during glycolysis has been widely recognized, the influence of dye/auxiliary structures on decolorization behavior and the subsequent recycling of dyes remains insufficiently understood. In this work, model PET waste textiles were dyed with various chromophores (anthraquinone or azo) and dispersants (MF and NNO), and subsequently extracted with EG vapor. The dye dissolution behavior and the compositional evolution of the decolorization liquor were investigated to evaluate the feasibility of dye reuse. The results demonstrated that EG vapor exhibits excellent decolorization performance for fabrics dyed with different dye/auxiliary formulations. Specifically, the decolorization ratio of disperse red 60 reached 98.83% within 30 min, and compared with dispersant NNO, residual dispersant MF facilitated EG vapor permeation and dye detachment. Among the four dyes tested, anthraquinone dyes retained intact structure enabling re‐dyeing, whereas azo dyes underwent azo bond cleavage; the chromophore type appears key, but substituent effects may also contribute. Anthraquinone dyes retained their intact structure after treatment, enabling re‐dyeing of PET. In contrast, azo dyes underwent glycolysis induced cleavage of the azo bond in the presence of EG and could not be directly reused. This study provides a theoretical basis and a technical route for the classified treatment and green recycling of waste PET textiles in accordance with dye structures.