Valorization of bagasse alkali lignin to water-soluble derivatives through chemical modification

Black liquor is the by-product of the pulping process where the lignin, hemicellulose, and extractive materials are separated from wood to produce paper pulp. As one of the primary lignin sources, black liquor is considered an important energy source from biomass to produce biofuels and value-added chemicals. However, soda alkaline lignin has limited industrial applications due to its insolubility in water and lack of reactivity. Therefore, chemical modification is essential to enhance its industrial applications. In this study, alkali lignin from bagasse was modified through sulfonation, sulfomethylation, and amination processes using different reaction conditions. The structural analysis of obtained products was investigated by FTIR and (HNMR)-H-1. The molecular weight distribution and thermal stability of the water-soluble products were analyzed using gel permeation chromatography (GPC) and thermogravimetric analysis (TGA), respectively. The elemental analysis was used to measure the elements (CHNSO) of the obtained water-soluble derivatives. The chemical structure analysis of the samples with FTIR and (HNMR)-H-1 confirmed the modification processes. The results indicate that modification led to increased water solubility and a decrease in the precipitation pH of lignin samples, due to the introduction of sulfonate and amin functunal groups on lignin. In addition, the molecular weight and thermal stability of modified lignins were increased due to the presence of sulfonate and amine groups compared to unmodified lignin.