Molecularly engineered alkyl-anthraquinone dyes for sustainable textile dyeing in supercritical carbon dioxide

Alkyl-chain anthraquinone dyes have promising performance but face application constraints due to hydrophobicity and pollution in conventional water-based dyeing. This study developed an eco-friendly synthesis and dyeing approach. Six dyes (AQ-5 to AQ-7, CAQ-5 to CAQ-7) were synthesized in supercritical carbon dioxide (scCO₂) via reactions of 1-chloroanthraquinone/1,5-dichloroanthraquinone with n -alkylamines. They showed good light absorption and thermal stability (5% weight loss at 245–298°C, suitable for scCO₂ dyeing). Meanwhile, scCO₂ dyeing regularity was revealed through the synergistic regulation of multiple parameters. Optimal scCO₂ dyeing conditions for polyester were determined: 16   MPa, 130°C, 90   min for AQ-5–AQ-7; the optimal dyeing conditions for CAQ-5–CAQ-7 were determined and these were included in the range of 120-135 °C, 16   MPa, 70-100   min. Dyed fabrics had uniform fixation with excellent washing, dry, and wet rubbing over than grade 4, and good light fastness. This work establishes a green scCO₂ system, overcoming traditional limitations, and provides a theoretical basis for eco-friendly dyes/technologies.