Tailoring polyester crosslinking networks for multifunctional wood composites

Wood is a natural biomaterial and plays an important role in global carbon neutralization. To optimize its application, wood modification is needed to overcome drawbacks in dimensional stability, absolute strength, and microbial resistance. The in-situ polyesterification of citric acid and sorbitol (SorCA) in wood is a green and effective method to improve its properties; however, different polyester crosslinking networks have significant and complex effects. By adjusting the monomer ratio, the polyester structure varies from linear to highly crosslinked, altering multiscale interactions with wood components. High crosslinking density polyesters form in cellulose amorphous regions, where chemical bonds and intermolecular forces induce a more ordered cellulose chain arrangement. This enhances water resistance, with mechanical performance improvements including a 138.6 % increase in modulus of elasticity, a 14.7 % increase in modulus of rupture, and a 110.7 % increase in compressive strength, expanding the potential for structural applications. In contrast, linear polyesters enable ether bonding with lignin, forming compact networks via lignin-carbohydrate complex (LCC) interactions. This suppresses wood's dimensional changes in humid conditions, offering ideal moisture stability. Moreover, the linear flexible network alleviates the toughness loss caused by rigid polyesters. The synergy between cellulose structural optimization and polyester crosslinking network reinforcement reconstructs wood's nanoscale ultrastructure, enabling performance-tailored composites. By unveiling the “structure–property” response mechanism of wood polyesterification, this study proposes new strategies for high-performance, sustainable wood composite development.