UBC Theses and Dissertations

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UBC Theses and Dissertations

Thermal modification of Western hemlock (Tsuga heterophylla) Nourian, Sepideh


Thermal modification is a controlled degradation process of wood cell wall material at high temperatures that results in improving some of its properties. This process, albeit quite developed in Europe, is still in its infancy in Canada. So, use of such method might add value to local wood species and thus, allow the development of new products and markets. Western Hemlock (Tsuga heterophylla) is a locally abundant species used mostly in construction, so the development of other uses could bring extra revenues to the industry. This research focuses on exploring thermal treatment levels and their effect on some material properties in order to achieve the optimum combination for hemlock. In this regard, kiln-dried western hemlock boards with two cuts (flatsawn and quartersawn) were subjected to the Thermowood® process at three different maximum treatment temperatures (170, 212, and 230°C) for 2hrs. Samples were cut from both the treated and untreated boards for property evaluation tests including basic density, equilibrium moisture content, water absorption, anti-swelling efficiency, color change, Janka hardness, and dynamic modulus of elasticity. Data analysis revealed that there was no significant difference between the two cuts and temperature was the only factor that affected the wood properties. Basic density, equilibrium moisture content, and water absorption were lower at higher treatment temperatures, while dimensional stability considerably increased. The impact of higher treatment temperatures on hardness and stiffness of samples was hardly noticeable, but it visually influenced the color of samples and made them darker. Within the scope and limitations of this study, the optimum treatment temperature, namely, the one that enables improved dimensional stability and provided a darker color without significantly affecting the wood strength suggested establishing at 212°C. Further research is required to fully determine the performance of thermally modified wood for interior and exterior applications.

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