Preparation of lignosulfonates from biorefinery lignins by sulfomethylation and their application as a water reducer for concrete

Abstract

Lignosulfonate (LG), a water-soluble polymer from sulfite pulping process of lignocellulosic biomass, has been commercially applied as admixture for concrete. In this work, lignosulfonates were produced from alkaline lignin (AL) and enzymatic hydrolysis residue (EHR) by sulfomethylation and these lignosulfonates as water reducers for concrete were then evaluated. Results showed that 94.9% and 68.9% of lignins in AL and EHR could be sulfonated under optimum sulfomethylation conditions, respectively. The sulfonic groups in lignosulfonates from AL (AL-LG) and EHR (EHR-LG) were 1.6 mmol/g and 1.0 mmol/g, respectively. Surface tension and zeta potential analysis indicated that both AL-LG and EHR-LG can be potentially used to as dispersant for improving the fluidity of the cement paste, similarly to commercial lignosulfonate (CM-LG). Adding 0.2 wt % of AL-LG, EHR-LG, and CM-LG in the concrete, the compressive strength (28 days) of concretes increased from 38.4 Mpa to 41.6, 42.6, and 40.9 Mpa, respectively. These findings suggest that the lignosulfonate from biorefinery lignin by sulfomethylation can meet the industrial standards as water reducers for cement admixtures.