Variations in the natural density of European oak wood affect thermal degradation during thermal modification

Abstract

One of the main difficulties in developing thermo-modified wood products at an industrial scale lies in the difficulty of obtaining consistent products with a stable quality (durability, dimensional stability, color). This may be due either to the thermal treatment process itself or to inter- or intra-specific heterogeneity of wood properties. We investigated the effect of the natural variability of oak wood, particularly in density, on the degree of thermo-degradation during thermal treatments. X-ray computed tomography was used to assess the effect of initial wood density of oak boards on their thermo-degradation. Intra-ring wood density was estimated using thermogravimetric analysis and micro-densitometry. X-ray CT did not allow establishment of a clear correlation between initial wood density and mass loss due to thermo-degradation, while thermogravimetric analysis, performed separately on earlywood and latewood samples, revealed a larger susceptibility to thermal degradation of the less dense earlywood samples compared to more dense latewood samples. Initial wood density, which is directly controlled by the earlywood/latewood ratio modulated by silvicultural practices, directly influences thermo-degradation during thermal treatment. Initial wood density therefore appears to be a potential parameter influencing industrial thermal treatment processes.