Sulfonation of Alkali Lignin and Its Potential Use in Dispersant for Cement

Abstract

Sulfonation modification of alkali lignin from wheat straw pulping spent liquid, carried out under normal pressure and medium temperature, was investigated, and the properties of the resulting sulfonated lignin were characterized. It was found that condensed lignin was degraded into lignin fragments with lower molecular weight by oxidation reaction, producing more active sites to react with formaldehyde, consequently forming more active hydroxymethyl groups for sulfonation. Therefore, it is feasible to carry out the sulfonation of alkali lignin under conditions of normal pressure and medium temperature. As higher contents of sulfonic group were introduced, sulfonated lignin with 1.49 mmol/g of sulfonation degree exhibits 96.9% of solubility at neutral aqueous solution and good surface activity. Compared to commercial lignosulfonate, sulfonated lignin produced by the present work contributes higher adsorption amount and zeta potential to cement particles, and hence shows better dispersion effect to the cement matrix.

Keywords:

• Alkali lignin
• dispersant
• lignosulfonate
• pulping spent liquid
• sulfonation

Acknowledgments

This work was financially supported by the National Natural Science Fund of China (Grant 20876064) and the Guangdong Provincial Natural Science Fund (Grant 05103536).

Notes

Conditions: 1 hour of oxidation followed by 2 hours of hydroxymethylation and 2.5 hours of sulfonation.

*Mn: number-average molecular weight.