Preparation of lignin-based dye dispersant with favorable heat stability and slight fiber staining

Abstract

The performances of lignin-based dye dispersant largely rely on the molecular weight and phenolic hydroxyl content of lignin. In order to evaluate their impacts, dye dispersants with different molecular weight and different phenolic hydroxyl content were prepared by fractionation, sulfonation, and etherification. Experimental results indicated that relatively high molecular weight benefits the dispersion performance. The staining grade of the dispersant to the fiber raised from 3 to 4.5 with the decrement of phenolic hydroxyl content, Noteworthily, the dispersant with M_w of 13,556 Da contains 0.91 mmol g⁻¹ of phenolic hydroxyl and 1.55 mmol g⁻¹ of sulfonic group, exhibiting superior heat stability at 130 °C and slight fiber staining (grade 4.5). Furthermore, the dye uptake of the dispersant with M_w of 13,556 Da reached the highest value of 84.8% in all those samples. Etherification is a promising method to raise the molecular weight of lignin and to reduce the content of phenolic hydroxyl groups, which improves the performances of lignin-based dye dispersants.

Graphical Abstract

Keywords:

• Dye dispersant
• sulfonated lignin
• molecular weight
• heat stability
• fiber staining effect

Acknowledgments

The authors would like to thank State Key Laboratory of Pulping and Paper Engineering, South China University of Technology.