Mechanical properties of beech wood treated with malic acid-based polyester

Abstract While chemical modification enhances wood’s resistance to deterioration and dimensional stability, it often results in alterations to the mechanical properties, limiting its engineering applications. This study focuses on the in situ esterification of beech wood using malic acid/polyol mixtures and evaluates its impact on mechanical properties. The results of the compression tests yielded limited information, characterized by a notable degree of variability as indicated by the high standard deviation. The four-point bending tests conducted here revealed an increase in the modulus of elasticity (MOE). However, this improvement in MOE was accompanied by a decrease in the modulus of rupture (MOR), indicating a trade-off between stiffness and strength. To better understand the mechanisms affecting the treated wood’s mechanical properties, we compared the experimental and theoretical glass transition (Tg) of the polymers with material stiffness. X-ray computed tomography revealed that treatment increases specimen density and creates a gradient, with higher density near the surface, potentially contributing to increased stiffness. These findings suggest a nuanced impact of the in situ esterification process using malic acid/polyol mixtures on the mechanical properties of beech wood.