Chemical, hygroscopic, and mechanical properties of various wood species heat treated via the ThermoWood® method

Abstract

Fourier-transform infrared spectroscopy (FTIR), energy dissipation spectrometry, dimensional stability, and compressive strength tests were conducted parallel to the fibers on various heat-treated trees, i.e., narrow-leaved ash (Fraxinus angustifolia Vahl), aspen (Populus tremula L.), Oriental spruce (Picea orientalis (L.) Link.), and Uludağ fir (Abies bornmüelleriana Mattf.), which grow naturally in forests in Turkey. Panels made from these trees were first heat treated via the ThermoWood® method, producing ThermoWood® panels. Then, FTIR, as well as energy dissipation spectrometry analysis, dimensional stability, and compressive strength tests were performed on test samples prepared from the panels. The FTIR data showed that the hemicelluloses were degraded in the ThermoWood® test samples and the proportion of cellulose increased. The energy dissipation spectrometry results showed that the amount of carbon increased, the amount of oxygen decreased, while the amount of hydrogen remained approximately the same in the ThermoWood® panels compared to the control samples. It was determined that the proportion of silicon increased in the narrow-leaved ash panels. In addition, among the physical properties, the amount of shrinkage and swelling decreased in all the tested ThermoWood® panels compared to the control samples, whereas the compressive strength values, which are considered a mechanical property, increased.