Effects of thermo-hydro-mechanical treatment on the structure and properties of wood

A process has been developed for densifying wood by thermo-hydro-mechanical (THM) means. The resulting product is then called THM densified wood. Small specimens of different wood species, with or without knots, were densified in their radial, tangential and transversal directions. Tests on THM densified wood show significant improvement in mechanical properties. THM densified wood is less hygroscopic and more stable, with almost no shape memory. We have shown that the shear strength of wood in its grain direction increases more than tenfold by THM treatment. This article gives testing results and micrographs of THM densified wood, and discusses the physical nature of different mechanisms intervening at the wood cell wall level during the thermo-hydro-mechanical process.