Wood properties and performance can be enhanced through high temperature conditioning (typically 180 to 220°C) in the absence of oxygen for several hours. The resulting chemical changes to the wood result in a darkening of wood colour, improved dimensional stability, reduced water absorption and improved decay resistance. However, there is some loss in bending strength and other mechanical properties. There are several commercial processes for thermal modification of wood, based on drying and heating in steam or nitrogen environments, or submersion using hot vegetable oils as the heat transfer and oxygen excluding medium.
High temperature treated or thermally modified wood is a potential alternative to preservative treated wood, naturally durable wood, or wood-plastic composite lumber in exterior above-ground applications such as fences, deck boards and cladding. However, there are questions concerning the suitability of these processes for Canadian lumber species, optimal processing conditions and quality control for these processes.
The objectives of the projects described here were to evaluate the effects of different thermal modification processes on Canadian lumber species and to establish appropriate quality control procedures for these products. An additional objective was to investigate the feasibility of adding value to the process through incorporating additives such as waxes and pigments with a hot oil treatment.