Mechanical properties of surface-compressed wood resulting from the compression ratio and density distribution

Abstract

Surface-compressed wood, with controllable mechanical properties according to the production process, could be utilized in timber products as a substitute for energy-intensive adhesives, concrete, and metals. The surface compression of wood was carried out in an open hot-pressing system at 180 °C with a compressed thickness of 2 to 18 mm. The surface-compressed wood was treated by atmospheric heat treatment or 0.30 MPa pressurized superheated-steam heat treatment at 180 °C for 2 h. This study investigated the mechanical properties of surface-compressed wood, namely, its bending, compression, and hardness properties. The results showed that the maximum density and average density of the compressed layer surpassed 1.10 g/cm3 and 0.80 g/cm3 when the compression ratio was 33%. Moreover, the surface-compressed wood with a sandwich density structure had properties that were comparable to, or even surpassed, raw wood, traditional compressed wood, and some engineered timber products. The specific strength (179 to 203 × 103 m2/s2) of surface-compressed wood was slightly higher than other wood-based materials (65 to 197 × 103 m2/s2). And the contribution of sandwich structure to MOR and MOE increase was positively correlated with wood surface density. The results obtained from this study could help engineers utilize more fast-growing wood and develop new products and wood connectors. This work may contribute toward the substantial use of surface-compressed wood in the building and construction industries with great benefits to the environment.