Effect of Acetylation on the Physical and Mechanical Performances of Mechanical Densified Spruce Wood

Abstract

Inherent drawbacks (e.g., loose structures, dimensional instabilities, and poor mechanical performances) restrict the applications of fast-growing wood species. In this study, a thermal compression treatment was carried out to densify acetylated spruce wood. The aim of acetylation was to improve the plasticity and water resistance of spruce wood. The water absorption, set-recovery, surface hardness, modulus of rupture, modulus of elasticity, and microstructure of the resulting wood were analyzed. The results show that acetylation can improve the plasticity of wood and reduce the interaction between wood and water, significantly reducing the set recovery of the compressed wood. When the water immersion time reaches 168 h, the water absorption rate of wood is reduced by 37% after acetylation, and the densification can further reduce the water absorption (55% for AD-40 and 70% for AD-60). The hardness of the densified wood is significantly higher than that of control wood and increases with the increase of the compression ratio. The cell wall of acetylated wood is thicker than that of control wood, which could increase the compression density of the wood. As a result, the hardness and MOR of acetylated densified wood are remarkably higher than that of unacetylated densified wood. However, a high compression ratio (60%) could lead to structural damage and, thus, reduce the mechanical properties.