Regulating the hydroxyl groups reactivity of cellulose by grafting the quaternary ammonium group to achieve a salt-free and low alkali dyeing process for reactive dye.

In this work, a salt-free and low alkali dyeing process was developed through cationic modification of cotton fabric with a series of quaternary ammonium salts (QAS). The dyeing performance indicated that the cationic cotton fabric treated with 3-chloro-2-hydroxypropyldimethyloctane ammonium chloride (CT-8) achieved better K/S value (8.87) and dye fixation (90.47 %) compared to the conventional dyeing process. Notably, the CT-8 treated fabric performed exceptionally under salt-free conditions and with a NaCO concentration of 5 g/L. The rationale behind the adoption of a salt-free and low-alkali dyeing process was attributed to the positive charge of quaternary ammonium groups, which had an augmenting impact on the hydroxyl reaction activity of cotton fabrics. The condensed Fukui function, atomic charge, and HOMO orbital calculations showed that the QAS structure could regulate the hydroxyl reactivity of cationic cotton fabric. Our salt-free and low alkali dyeing process not only achieved the aim of reducing chemical consumption and emissions, but also contributed to better understand the effect of hydroxyl reactivity of cationic cotton on the fixation reaction with reactive dye, and provided a new direction to achieve the require of sustainable development and clean production for a variety of industrial crops and products.