Effect of hydrophobically-modified sulfonated lignin on thermal stability of disperse dye paste

This study aims to develop a lignin-based dispersant with excellent high-temperature dispersion properties by introducing cyclohexyl and phenyl hydrophobic groups into sulfomethylated lignin (SAL) molecules through a grafting modification strategy, thereby addressing the limitations of traditional disperse dye pastes in terms of grinding efficiency and thermal stability. The results show that graft-modified lignin dispersants outperform both SAL and the commercial dispersant Reax-85A. They not only improve the grinding efficiency of disperse dye pastes but also markedly enhance their thermal stability. The particle size of disperse dye paste significantly decreased from greater than 5 μm to 1 μm. The lignin dispersant containing cyclohexyl and phenyl groups significantly enhanced the hydrophobic van der Waals adsorption forces toward disperse dyes. Under high-temperature conditions, the prepared disperse dye pastes maintained excellent diffusion performance and thermal stability. QCM-D studies revealed that the adsorption capacity |ΔF| of hydrophobically-modified SAL on disperse dyes was significantly enhanced compared to that of SAL and Reax-85A, and it exhibited strong adsorption stability with minimal desorption, demonstrating robust adhesion to disperse dyes. Furthermore, the adsorption quantity of phenyl-modified SAL on disperse dyes was greater than that of cyclohexyl-modified SAL.