Changes in hygroscopic, mechanical and surface properties of Scottish-grown Sitka Spruce (Picea sitchensis) wood subjected to dry heat treatment
L Awoyemi, M C Jarvis, A Hapca
Heat-treatment is a wood modification method which has been used to some extent in improving timber quality. However, the main limitation in the use of this technique despite its numerous advantages is the adverse effects on the various properties associated with the use of wood as an engineering material. Dry heat treatment of Scottish-grown Sitka spruce (Picea sitchensis) wood was carried out at 160°C and 200°C for 2 hours. The hygroscopic behaviour, total surface energy, pH-buffering capacities and mechanical properties were determined by water soaking, sessile drop-contact angle method, cold water extraction and bending tests respectively. Heat treatment resulted in significant reductions in wood hygroscopy, total surface energy, pH, acid-buffering capacity, alkaline buffering capacity and modulus of rupture. However, it is important to note that the significance of the changes in the modulus of rupture is limited to 200°C treatment. The reduction in hygroscopic behaviour indicates potential for stability in wood-water relationships especially when the material will be used in a continuously-changing ambient environment. While the reductions in surface energy can constitute a menace through reduction in the interfacial attractions between the wood (substrate) and adhesive, the reductions in pH can be a benefit through reduction in gel time.