Mechanical properties, dimensional stability, and mold resistance of heat-treated jack pine and aspen

Quebec wood species, jack pine (Pinus banksiana Lamb.) and aspen (Populus tremuloides Michx.), were thermally treated in an industrial furnace using 'Bois Perdure' technology. The species were heated from room temperature up to their respective maximum heat-treatment temperatures. The mechanical properties, dimensional stability, and mold resistance of these species were determined and compared with those of untreated wood. This information is essential for the users of these new products. Results indicate that modulus of rupture (MOR) of heat-treated jack pine and aspen decreased, whereas modulus of elasticity (MOE) of the same heat-treated species increased, respectively. The increased MOE indicates that jack pine and aspen became stiffer after the heat treatment. Compared to the untreated species, hardness of treated jack pine in radial, tangential, and longitudinal directions increased whereas the hardness of heat-treated aspen decreased in radial and tangential directions, and increased in longitudinal direction. Screw withdrawal strength of heat-treated jack pine decreased, but this decrease was not significantly different from the untreated controls. Screw withdrawal strength of heat-treated aspen was found to be relatively higher than that of untreated aspen. Dimensional stability was evaluated using both the percentage thickness swelling (TS) tests and water soaking tests for both species before and after heat treatment. All the tests were carried out with a different set of specimens. First, all the specimens were conditioned at 65 percent relative humidity (RH) and 22 °C. Three different tests were carried out using these specimens. TS measurements were carried out for a group of specimens right after the conditioning. The second group of specimens were soaked in water for 24 hours, and their weight change and TS were measured. The third group of specimens were reconditioned at 95 percent RH and 22 °C. Afterwards, their TS was measured. Results show that the dimensional stability of heat-treated jack pine and aspen was improved considerably after heat treatment. Mold resistance of heat-treated jack pine was improved compared to the untreated sample; mold resistance was improved for heat-treated aspen; however, it was not significantly different from the untreated aspen.