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Wood is a renewable material widely used in the construction industry. However, it is susceptible to fungal degradation. Several chemical products have been developed to improve its durability, but the toxicity of some of these products limits their use. One alternative to chemical treatment is thermal modification of wood. This method improves the dimensional stability of wood and reduces its susceptibility to decay. The impact of different parameters (maximum temperature, heating rate, holding time, and gas moisture content) of thermal modification on the mechanical properties of Betula papyrifera was studied in a prototype furnace. The results show a marked decrease in the modulus of rupture with increasing temperature while the modulus of elasticity does not seem to be affected. The hardness increases with maximum modification temperature, and in the absence of moisture in gas, and there is an improvement of the dimensional stability after thermal modification.

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This study was aimed at evaluating the effect of thermal modification temperature on the mechanical properties, dimensional stability, and biological durability of Picea mariana. The boards were thermally modified at different temperatures 190, 200 and 210°C. The results indicated that the thermal modification of wood caused a significant decrease in the modulus of rupture (MOR) after 190°C, while the modulus of elasticity (MOE) seemed less affected with a slight increase up to 200°C and slight decrease with further increase in temperature. The hardness of the thermally modified wood increased in the axial direction. This increase was also observed in tangential and axial directions but at a lesser extent. The final value was slightly higher in axial direction and lower in radial and tangential directions compared to those of the untreated wood. Dimensional stability improved with thermal modification in the three directions compared to the dimensional stability of unmodified wood. The fungal degradation results showed that the decay resistance of thermally modified wood against the wood-rotting fungi Trametes versicolor and Gloephyllum trabeum improved compared to that of the untreated wood. By contrast, the thermal modification of P. mariana had a limited effect on the degradation caused by the fungus Poria placenta.

The effect of heat treatment on decay resistance of white birch was evaluated for different incubation periods ranging from 2 to 12 weeks using three species of brown rot and one species of white rot fungus. The results of weight loss tests showed that the white rot fungus, Trametes versicolor, effectively degraded the untreated wood (73.5%). While the degradation of untreated wood by brown rot fungi species, Gloephyllum trabeum (11.6%) and Conifora puteana (6.2%), was considerably less compared to T. versicolor, the third brown rot fungi studied, Poria placenta, caused an appreciable degradation of the same species (52.4%). The results clearly showed that the heat treatment reduced the effect of fungi attack on white birch. Increasing the heat treatment temperature from 195 to 2158C resulted in reduction of weight loss, consequently, reduction in fungal attack. As an example, the weight loss reductions due to T. versicolor, P. placenta, G. trabeum and C. puteana attack was 62.2%, 71.3%, 89.6% and 100%, respectively, compared to the weight loss of untreated wood when it is heat treated at 2158C. Thus, these results confirmed that the heat treatment increased the biological resistance of white birch.

The resistance of thermally modified Canadian Pinus banksiana against four wood decaying fungi was evaluated. Wood samples were treated at different temperatures (190ºC, 200ºC and 210ºC) and exposed to three brown rot fungi as well as to a white rot fungus. Results showed that the untreated wood samples lost more weight when exposed to P. placenta, T. versicolor and G. trabeum compared to the weight loss observed in case of C. puteana. Thermal modification at 210°C improved the resistance of Pinus banksiana against G. trabeum and T. versicolor fungi as evident from the fact that reduction in weight loss of wood was found to be 98.3% and 96.3%, respectively.

A study was carried out to investigate the effect of thermal treatment on biological resistance of Populus tremuloides wood against four decay fungi, including T. versicolor, P. placenta, G. trabeum and C. puteana. The weight loss data showed that degradation of untreated wood by the white rot fungus T. versicolor resulted in higher weight loss (57.1%) compared to those by brown rot fungi G. trabeum (21.9%), P. placenta (36.7%) and C. puteana (7.1%). When this species was heat treated at 220°C, the weight loss was reduced to less than 10%. Increasing temperature and the holding time appeared to affect the resistance against T. versicolor, P. placenta and G. trabeum attacks, but the effect on the resistance against C. puteana was not significant. The humidity during thermal modification affected the degradation of wood against T. versicolor attack, but it did not have a significant effect the other fungi.