Influence of Density on Properties of Compressed Weeping Willow (Salix babylonica) Wood Panels

Compressed wood panels (CWP) is a biomaterial that can potentially address common issues with fast-growing wood, including low density, high perishability, and low mechanical strength. As wood density is known to significantly affect material properties, this study examines the cellular structure, wettability, physicomechanical performance, water absorption (WA), and dimensional stability of compressed weeping willow wood panels (CWWWP) at various densities. The cellular structure was investigated by a scanning electron microscope, and major physicomechanical properties were also measured, i.e., modulus of rupture, modulus of elasticity, and horizontal shear strength. Contact angle measurements and surface free energy (SFE) calculations were used to elucidate CWWWP wettability. The experimental results showed that the cellular deformation, composite strength, and volume-swelling efficiency all tended to increase with increasing density. However, both the SFE and WA were negatively correlated with the CWWWP density. This study concludes that higher-density CWWWP, with better mechanical performance and lower WA, is suitable for structural wood products and engineering materials, whereas lower-density CWWWP is suited for use as decorative material because of its lower density and higher SFE, which increases the ease of coating and painting.