Regulating the surface charge and reactivity of cellulose through quaternized modification to achieve salt-free reactive dyeing process

Limited research exists on how the structure of quaternary ammonium salt (QAS) affects the electrostatic attraction and hydroxyl reactivity of cationic cotton, which strongly affects reactive dye adsorption, diffusion, and fixation. Thus, in our work, the effects of QAS structure on the electrostatic attraction, hydroxyl reactivity, and dyeing properties were investigated. The intensity at 402.5 eV (-N+(CH3)3) in the XPS rose from 34 % to 70 % as the QAS alkyl chain length increased from 4 to 18 carbon atoms, signifying an enhancement of the positive charge and electrostatic attraction between reactive dye and QAS modified cotton. However, molecular dynamic (MD) simulations of the QAS-modified cotton with octadecyl chains revealed that the reactive dye demonstrated slower molecular mobility compared to the untreated cotton. This is not conducive to the diffusion and fixation of reactive dyes. The QAS-modified cotton with hexyl chains not only alters the activity of hydroxyl at the 6th but also generates additional hydroxyl at the beta-position that contributes to enhancing the improvement of fixation through Gaussian simulations. Therefore, cationic cotton treated with 60 g/L of (3-chloro-2-hydroxypropyl)dimethyl-octadecylazanium chloride (CT-8) exhibits superior dye uptake levels (91.84 %), K/S values (13.10), and dye fixation percent (88.38 %).