A Green Cement Plasticizer from Softwood Kraft Lignin

A green cement plasticizer was produced in a one-step aerobic oxidation of kraft lignin (KL) in the presence of KOH. In this study, optimizing the reaction conditions led to the maximum carboxylic acid group and charge density of 2.6 mmol/g and 1.9 mequiv/g for oxidized lignin, respectively. The NMR, FTIR, and XPS analyses quantified the alterations in the structure of KL after the oxidation reaction. The molecular weight analysis revealed that lignin depolymerization would depend on the temperature, lignin amount, and KOH concentrations. The oxidized lignin with a higher carboxylic acid group adsorbed on the cement particles more readily than a commercial plasticizer, which increased the flowability of the pastes. The compressive strength of cement was improved much more by using oxidized lignin instead of a commercial plasticizer and lignosulfonate. The current study suggested that the one-pot KOH-mediated oxidation of kraft lignin is a promising approach to producing a green plasticizer for cement application.