Wood modification developments

The last decades developments in the arena of wood modification have accelerated considerably. This acceleration is due to a number of circumstances of which the environmental awareness, the increasing demand for high and constant quality and the increasing prices and availability of tropical hardwood species. This has led to the up-scaling and the market introduction of a number of wood modification techniques. Modification can be done without added chemicals by heat treatment only, or with the aid of added chemicals. Examples of both principles are given. Several products of thermally modified wood are already available on the market. More recently the first chemical modification processes have reached (or are about to reach) market introduction. Chemical modification makes wood with superior qualities of tailor-made products possible. The variability in degree of modification within wood is discussed with acetylated wood as an example. Different treatabilities in different wood species also reflect in acetic anhydride impregnation. However, in contrast to waterborne systems this does not result in sharp fronts but in more gradual profiles. The gas diffusion of the chemical into the wood plays an important role in this phenomenon. In the further process developments these effects need to be taken into account.