Wood retification : process and applications

Wood is one of the first materials used by man. It is renowned for its acoustic and insulating properties, its mechanical performance and its lightweight construction. It's easy to machine and requires little energy. However, wood does have its drawbacks. It is an anisotropic material, hydrophilic and dimensionally unstable with variations in humidity. Its sensitivity to biological degradation agents limits its durability, which varies greatly from one species to another. Exotic species, renowned for their stability and durability, are costly and their exploitation is contested. Species from temperate regions (softwood and hardwood) require chemical treatments to protect them from humidity and biodegradation agents, but the compounds used are hazardous to varying degrees, and wood treated in this way is difficult to manage at the end of its life.

Improving wood stability and durability via heat treatment is a more environmentally-friendly alternative. In this article, we present the "retification" of wood, a heat treatment in an oxygen-poor atmosphere, intended for species from temperate countries (softwood or hardwood). Retification is presented first from the physico-chemical angle of the transformations induced by the rise in temperature, and then from the point of view of the process. Industrial implementation is briefly discussed, as are competing processes. The evolution of the solid material as a function of heat treatment conditions is then presented: improvements in stability and durability are described, along with the concomitant deterioration in mechanical properties. The specific properties of retified wood are integrated into a usage guide and illustrated in a panorama of applications.