Sustainable Low‐Temperature Dyeing of Polyester Enabled by Deep Eutectic Solvent Pretreatment

To mitigate energy consumption and environmental impacts of conventional high‐temperature polyester dyeing, a thymol‐coumarin deep eutectic solvent (DES, molar ratio 1:1) was adopted as a multifunctional pretreatment for polyester fabrics. We systematically explored how DES‐induced interfacial regulation alters PET structure, low‐temperature dyeing performance, and surface wettability. FTIR confirmed that DES pretreatment preserved PET's chemical skeleton. XRD and DSC verified PET structural relaxation: crystallinity declined from 56% to 39% after DES treatment at 100°C, and glass‐transition temperature ( T g ) dropped from 78.2°C to 72.5°C at 90°C. After DES pretreatment, disperse‐dyed PET at 90°C attained color depth comparable to untreated fabric dyed at 100°C. Relative to untreated samples dyed at 90°C, K/S values rose by 54% (Disperse Red), 43% (Disperse Yellow), and 20% (Disperse Blue). The dyed fabrics possessed good fastness: dry‐rubbing, washing and sublimation fastness reached grade 5, while wet‐rubbing fastness exceeded grade 4. DES treatment also increased fabric hydrophobicity with a water contact angle of 130.09°. This work proves that DES‐based pretreatment is a promising sustainable route for low‐temperature polyester dyeing and functional finishing.