How thermal treatment affects the chemical composition and the physical, mechanical and swelling properties of Scots pine juvenile and mature wood

High variations in juvenile wood properties in the radial direction and its worse performance than mature wood make it less suitable for some applications and often
treated as waste material. This study aimed to assess how thermal modifcation afects the chemical composition and the physical, mechanical and swelling properties of Scots pine juvenile and mature wood. An additional goal was to evaluate if the modifcation can equalise the diferences in selected properties of juvenile wood
to those of mature wood so that from waste material, juvenile wood can become a fully-fedged raw material for various industrial applications. Thermal treatment
at 220 °C infuenced wood chemical composition, degrading mainly hemicelluloses but also afecting cellulose and lignin, which resulted in a reduction of hydroxyls
and carbonyl/carboxyl groups. These changes were more pronounced for mature than juvenile wood. It reduced mass loss and swelling rate, and increased swelling pressure in the tangential and radial directions to a higher degree for juvenile than mature wood. Changes in mechanical properties in compression were statistically signifcant only for mature wood, while wood hardness remained unafected. Although the applied heat treatment improved the performance of juvenile wood by reducing its swelling rate, it did not equalise the examined properties between juvenile and mature wood. Since higher juvenile wood proportion is expected in the wood supply from the future intensively managed forests, there is still a need to
fnd suitable modifcation methods or better processing techniques so that instead of being thrown away as waste, it could be used broadly in various industrial applications.