In Europe, the thermal modification of wood goes back to the early 1990s. Heating of wood within a range of temperatures varying from 160oC to 245oC transforms its chemical components and brings about a change in its physical and mechanical properties. The properties of thermally modified wood present several interesting aspects for the marketing of new products for exterior and interior applications. In Eastern Canada, however, the industrial production of thermally modified wood occurs on a rather small scale, but interest in this new material is growing steadily.
During the implementation of this project, work on thermally modified wood focused on meeting specific objectives focusing on the evaluation of various technologies for the thermal modification of wood, the characterization of certain Canadian species, the development of a quality-control process and the establishment of a foundation for a certification program. Work was carried out in four phases.
First, the physical and mechanical properties of thermally modified jack pine and balsam fir were evaluated. The work focused on the Finnish ThermoWood process, the French Retification process and the Quebec Perdure process initially developed in France. In general, thermally modified wood is characterized by enhanced resistance to decay and by a significant increase in dimensional stability, as well as heavy coloration of the wood. However, the treatment reduces impact and abrasion resistance and the MOR of treated material.
The Perdure process was used to treat a load of Douglas fir from Western Canada. Upon completion of the treatment, the test material was returned to Forintek’s Western Laboratory for analysis. In the lab, thermally modified and untreated Douglas fir exhibited similar levels of mass loss following exposure to the G. trabeum and P. placenta fungi, and were respectively deemed to be highly and moderately resistant to fungal degradation. The results of weathering tests on Douglas fir wood in exterior applications will be available at a later date.
Two non-destructive quality control methods were evaluated as part of a Master’s student thesis. The non-destructive nature and simplicity of colorimetry and ultrasonography set these methods apart from the others. Results are promising in terms of determining treatment temperature on the basis of the coloration of thermally modified wood and the detection of internal checks by an acousto-ultrasonic method developed during the project.
The last phase of the project focused on the study of the treatment classes established by various organizations such as the Finnish ThermoWood Association. Work on the characterization of jack pine thermally modified using the Finnish ThermoWood process at various temperature levels, including the Thermo-S and Thermo-D treatment classes. This work constitutes the first step in the definition of treatment classes as a function of wood properties such as colour, resistance to decay and dimensional stability. Finally, the fundamental elements that should be taken into consideration for the purpose of establishing a certification program were addressed.