Study of the degradation behavior of heat-treated jack pine (Pinus banksiana) under artificial sunlight irradiation

Heat-treated wood, a relatively new product treated at high temperatures of 180-260 °C, possesses new versatile and attractive properties, which makes it popular for outdoor applications. It is of considerable importance to investigate the influence of sunlight on the weathering degradation processes. In order to understand the degradation processes, kiln-dried (untreated) and heat-treated (210 °C) jack pine woods (Pinus banksiana) were exposed to artificial sunlight irradiation for different periods. Before and after exposure, their color and wettability by water were determined. Structural changes and chemical modifications at exposed surfaces were also investigated using SEM, FTIR spectroscopy, and XPS. Degradation of middle lamellae, checking of cell wall and destruction of bordered pits were observed on heat-treated wood surfaces due to sunlight irradiation by SEM analyses. FTIR spectroscopy and XPS studies provided information about the behavior of functional groups of lignin during irradiation. The oxygen to carbon ratios revealed that the photo-degradation of lignin and presence of extractives played important roles in discoloration and wetting behavior of heat-treated wood surfaces during irradiation. The structural changes during irradiation also influenced wettabilty of the irradiated samples.