Preparation of polyvinyl alcohol / carboxylated lignin composite and its application in paper coating

The PVA film usually absorbs moisture from the environment due to its good water solubility, which results in a decrease in mechanical strength, thereby limiting the application of PVA films in plastics. In this study, modified PVA with vanillin was combined with carboxylated lignin to prepare polyvinyl alcohol/carboxylated lignin composites (VPVAL@Ca) by a crosslink reaction with calcium ions. The composite film demonstrated good hydrophobicity with a water contact angle of 95°. The mechanical strength was improved with a tensile strength of 90.1 MPa and fracture strain of 16 %. Additionally, the material demonstrated excellent UV resistance, effectively blocking UVB and UVC rays while shielding most of the UVA. When VPVAL@Ca was used as a coating material for paper, the coated paper exhibited superior barrier properties with a water contact angle of 92°, oil resistance of KIT 12, a Cobb120 value of 5.4 g/m², and an oxygen permeability of only 0.7 cm³/(m²·24h·0.1 MPa). Furthermore, the VPVAL@Ca paper composite material displayed good biodegradability in soil, with nearly complete degradation after 36 days. This study presents a novel approach for developing high-performance biodegradable materials and enhancing the value of PVA and lignin.