Estimation of quality of thermally modified beech wood with red heartwood by FT-NIR spectroscopy

The research examines the possibility of predicting the mechanical [modulus of rupture (MOR) and modulus of elasticity (MOE)] and physical (oven-dry and air-dry densities) properties of thermally modified beech wood (Fagus moesica C.) with red heartwood by using FT-NIR spectroscopy and partial least squares regression. Samples of sapwood and red heartwood were treated for 4 h at temperatures of 170, 190, and 210 °C. FT-NIR spectra (100 scans and 4 cm−1) were collected on the radial surface at eight points before and after the thermal modification. Oven-dry and air-dry densities as well as MOR and MOE determined by three-point bending tests were evaluated. Generally, according to the residual prediction deviation (RPD), the majority of the models obtained can be used for preliminary screening (1.5 < RPD < 2.5). The results of the spectra taken from sapwood were, in most models, better than the spectra of the red heartwood. Statistically, the values of density were mostly better than the values shown in assessment of bending properties. Results show that it is possible to accurately predict the quality of wood after being subjected to high temperatures, based on the spectra collected before the thermal modification. This fact could contribute to a more rational use of wood (especially from red heartwood) in the process of thermal modification.