Polybutylene succinate/lignin composites with tunable optical, mechanical, and thermal properties based on fractionation treatment.

The inherent heterogeneity, poor compatibility with polymers, and dark color of lignin limit its application in composites. In this study, original lignin (OL) was fractionated sequentially using four green organic solvents to obtain lignin fractions with different chemical structures. These well-defined lignin fractions were then blended with polybutylene succinate (PBS) to fabricate biocomposites. These composites prepared from fractionated lignin displayed improved properties. In particular, controlled tuning and selective enhancement of the composite properties were achieved by changing the lignin fraction. Benefiting from its rich phenolic acidic structure, the low molecular-weight lignin exhibited near perfect compatibility with PBS. Meanwhile, this composite had both great UV shielding properties and high visible light transmission. At a lignin content of 30 %, the elongation at break of PBS/low molecular-weight lignin remained at 315 %, while the visible light transmission reached 55.5 %. The high syringyl to guaiacyl ratio (S/G) and abundant conjugated structures of high molecular-weight lignin imparted superior rigidity and thermal stability to the composites. These findings highlight the potential of lignin fractionation as a sustainable and green strategy for the controlled preparation of lignin-based composites, offering new opportunities for UV shielding materials with high visible light transmittance.