Exploratory thermal modification of some West Coast Canadian wood species

Wood has been a cornerstone of construction for centuries because of its excellent strength-to-weight ratio, sustainability, and versatility. However, its natural tendency to absorb moisture, change dimensions with varying humidity, and deteriorate biologically can limit its use in high-performance applications. Thermal modification offers a green solution by subjecting wood to high temperatures in a controlled, low-oxygen environment, thereby enhancing its stability and overall performance compared with untreated lumber. This study examines wood from coastal British Columbia, including softwoods such as western hemlock, Douglas-fir, western red cedar, and hardwoods like red alder and paper birch. Kiln-dried boards from these species were thermally treated at two distinct temperatures, 190°C and 212°C, each for a fixed period, to assess the impacts on their properties. The evaluation focused on several physical characteristics such as density, water absorption, anti-swelling efficiency, permeability, color change, mechanical properties like Janka hardness, and dynamic modulus of elasticity. Durability was also evaluated by testing termite resistance and weathering performance. The results indicate that the wood's lightness decreases moderately when treated at 190°C and more noticeably at 212°C, resulting in a darker appearance. Furthermore, wood treated at 212°C exhibited significant improvements in moisture resistance and dimensional stability during a two-hour immersion test, whereas the lower temperature treatment had a smaller impact. Although changes in permeability varied across species, water adsorption and desorption generally decreased. Notably, the wood's density remained nearly constant, and most mechanical properties were preserved. These findings suggest that with careful optimization of processing conditions, thermal modification can considerably enhance the moisture performance and aesthetic qualities of wood from coastal British Columbia without substantially compromising its structural integrity.