Quality evaluation of heat-treated sessile oak (Quercus petraeaL.) wood by colour and FT-NIR spectroscopy

The prediction of physical (wood density, mass loss) and mechanical (bending properties, compressive strength parallel to grain, and Brinell hardness) properties of heat-treated sessile oak (Quercus petraea L.) by FT-NIR spectroscopy, colour change, and partial least squares regression (PLS) was studied. Samples of oak sapwood and heartwood were treated for 4 h at temperatures at 170, 190, and 210°C. FT-NIR spectra (100 scans and 4 cm−1) and colour parameters (CIE L*a*b* system) were collected on the radial surface before and after heat treatment. The applied heat treatment changed wood properties, darkened the colour and reduced the colour difference between heartwood and sapwood. According to the residual prediction deviation (RPD), most models obtained could be used for preliminary wood quality screening (1.5 < RPD < 2.0) and the properties of heartwood were better predicted than those of sapwood. Mass loss prediction by colour change can be used for quality control while for the other properties FT-NIR provided a more clear picture of the heat-treated oak wood and can serve as a quality indicator.