Physicomechanical properties of hydrothermally treated Japanese cedar timber and their relationships with chemical compositions

Traditional wood preservatives such as creosote, pentachlorophenol, and copper chromate arsenate have a negative impact on the environment. Therefore, it is imperative to develop environmentally friendly wood modification methods to extend the service life of wood, especially in outdoor applications. Of those modification methods, hydrothermal treatment is an attractive approach. Accordingly, the objective of the present study was to investigate the physicomechanical properties and chemical composition of hydrothermally treated Japanese cedar timber. The results revealed that the dimensional stability increased with increasing treatment temperature and duration. However, the flexural properties were decreased, which may limit the use of wood in structural applications. To understand how Japanese cedar timber responds to hydrothermal treatment, Spearman's correlation test between physicomechanical properties and second derivative attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra was conducted. The results demonstrated that almost all physicomechanical properties were more correlated with hemicellulose and cellulose than lignin, suggesting the importance of polysaccharide degradation during hydrothermal treatment. The volume shrinkage and water absorption were more correlated with lignin than with hemicellulose and cellulose. Additionally, among all hydrothermally treated timbers, the timber processed at 200 °C for 8 h not only increases the dimensional stability and hydrophobicity of timber but also retains ≥80% of its flexural strength.