Utilization of lignin upon successive fractionation and esterification in polylactic acid (PLA)/lignin biocomposite

The study presents the preparation of novel biocomposites based on different lignin fractions and polylactic acid (PLA). Based on the improvement of PLA mechanical properties, we proposed a process to assemble a series of lignin samples and PLA matrix using melt blending to investigate the effects on PLA properties from the perspective of the structure and molecular weight for lignin. The lignin was extracted from pine residue using deep eutectic solvent (DES) and was subjected to fractionation with ethanol and acetone as well as esterification modification with succinic anhydride (SAn). The treated lignin samples were used as additives, which not only improved the mechanical properties of PLA on the basis of retaining its thermal stability, but also granted excellent antimicrobial and biocompatibility properties. The results showed that the molecular weight of lignin was negatively correlated with the phenolic hydroxyl content, and the mechanical properties of the composites were also significantly affected by different molecular weights of lignin, indicating that the inhomogeneity of lignin affects its value-added utilization. The enhanced mechanical properties, antibacterial effect, and steady biocompatibility provide potential possibilities for lignin-based composites in biomedical applications.