HARDNESS OF THERMALLY MODIFIED BEECH WOOD AND HORNBEAM WOOD

There is increasing number of products made of termally modified wood (mainly floor coverings) in wood market. Thermal modification at temperatures above 160 degrees C in oxygen free environment is known to alter the physical and mechanical properties of wood, among others. In this work, change in Brinell hardness of beech wood and hornbeam wood subjected to 200 degrees C in oxygen free environment for 48 hours was investigated in relation with unmodified wood of the same species. Beech and hornbeam were selected because of the impacts of climate change as well as future predictions on the distribution of beech and hornbeam in South East Europe. Wood hardness was investigated on cross, radial and tangential sections. The dependence of wood hardness on wood density was also shown. All measurements were performed at 12% EMC (equilibrium moisture content) of wood. The average values of Brinell hardness of termally modified beech wood arid hornbeam wood were significantly different and smaller than the average values of unmodified beech wood and hornbeam wood. As expected, thermal modification caused weight reduction and consequently, decrease in the density of beech wood and hornbeam wood. Applied thermal modification reduced Brinell hardness of beech wood cross section for 3%, radial section for 15%, and tangential section for 25%. Applied thermal modification reduced Brinell hardness of hornbeam wood cross section for 6%, radial section for 18%, and tangential section for 13%. Applied thermal modification negatively influenced Brinell hardness on all three sections of investigated beech wood and hornbeam wood. The recorded decrease in hardness still does not hinder the use of such modified wood in non-load-bearing wood structures and wood flooring.