A hydration-regulated reusable hydrophobic natural deep eutectic solvent for sustainable PLA coloration

Developing sustainable coloration routes for poly(lactic acid) (PLA) fabrics requires the simultaneous achievement of efficient dye transfer, reduced thermal demand, and recyclable processing media. Herein, a water-tuned reusable hydrophobic natural deep eutectic solvent (HNaDES) medium was constructed from thymol and menthol for carrier-free coloration of PLA fabrics with Disperse Blue 60 (B60). The HNaDES/water system functioned as a tunable dye-carrying medium rather than a conventional dyeing auxiliary, in which water regulated dye solvation, dye release, solvent–fiber interaction, and dye–PLA affinity. By optimizing the water content, HNaDES-40W achieved a K/S value of 10.17 with 87.7% color retention after reduction clearing at 110 °C. More importantly, efficient coloration was realized at 90 °C, giving a K/S value of 8.53, higher than that of conventional aqueous dyeing even at 110 °C. Density functional theory and molecular dynamics simulations revealed that moderate water addition loosened the HNaDES hydrogen-bonding network, moderated excessive solvent–fiber interaction, and established a favorable balance between B60 mobility and dye–PLA affinity. The dyed fabrics retained stable morphology, chemical structure, thermal behavior, crystalline features, and practical usability. Moreover, the HNaDES-rich phase was recovered through water-induced phase separation and maintained 95.4% of the first-cycle K/S value after five reuse cycles. This work demonstrates a reusable HNaDES medium for sustainable PLA coloration and provides a solvent-regulation strategy for more resource-efficient textile wet processing.