Combining Wet Oxidation and Continuous <scp>pH</scp> Adjustment Fractionation to Enhance Ultraviolet Shielding and Antioxidant Properties of Lignin/Starch Composite Films

ABSTRACT The integration of lignin with thermoplastic starch is a pioneering, sustainable approach for biodegradable plastic production. Yet, composite miscibility remains a persistent hurdle. In this study, a novel lignin (OAL2) was successfully extracted by alkaline wet oxidation black liquor treatment combined with continuous pH acid precipitation technology. It is rich in carboxyl and phenolic hydroxyl groups and has a lower molecular weight and a more uniform structure. The low molecular weight of OAL2 effectively reduces the steric hindrance, and the abundant functional groups provide a large number of sites for the formation of strong intermolecular interactions between lignin and starch, effectively improving the compatibility of the two in the melt mixing process. As a result, the cross‐section of the composite film is uniform and smooth, and the tensile strength is significantly increased by 64.62%. Meanwhile, it has excellent ultraviolet shielding ability, outstanding antioxidant ability (88.78%), and good water vapor permeability (888.61 ± 16.81 g/(m 2 ·24 h)). Moreover, this study reveals that lignin can effectively facilitate the degradation of starch films. These properties suggest the lignin/starch composite film has significant potential in active food packaging, offering a feasible solution to replace nondegradable plastics and reduce environmental impact.