Influence of the wood quality and treatment temperature on the physical and mechanical properties of thermally modified radiata pine

In this study, the effects of the wood quality used for thermal modification on the physical and mechanical properties obtained at two treatment temperatures commonly used at the industrial level were evaluated in order to validate experimentally the pilot scale process for its future industrial scaling. The quality of the input radiata pine refers to the presence of natural defects of wood, as well as the amount of juvenile wood. Selected thermally modified samples were used to measure some quality markers (physical, mechanical, optical) and to find their correlations due to quality or treatment, so as to obtain the best characteristics of the heat-treated products. The results indicated that the quality of the input wood was only relevant to the mild treatment (190 °C), finding an acceptable correlation between the weight loss and the quality used (first quality). After both treatments, the order of anisotropy was kept and the dimensional changes were significantly reduced; thus, the weight loss during treatment did not dramatically affect its anatomical structure. Clustering the data by statistical procedures was possible to observe that samples of lower quality were ordered according to the treatment temperature, indicating a strong influence of the treatment on the properties obtained. The mechanical properties revealed that up to 190 °C the chemical changes that occur on wood affected positively the values (MOE increased by about 15–32% and MOR slightly decreased < 5%). The thermal profile of the treated samples was comparable, suggesting that the dehydration reactions were more significant for the obtained properties than the chemical changes. Moreover, the browning effect was more stable in the samples treated at 210 °C after artificial weathering cycles, being a positive outcome that could extend the service life of the thermally modified products.