Use of a polymer shell of thermally modified wood to establish moisture diffusion patterns

This study analyses the process of thermal modification of wood, obtained by a controlled heating process. The unique technological properties (durability, low hygroscopicity, and dimensional stability) of thermally modified wood allow using it in various fields. Due to the effect of temperature, some chemical changes occur in the structures of the cell wall components (lignin, cellulose, and hemicellulose) of wood. This leads to an increase in density, hardness, hydrophobicity (water repulsion), thereby reducing the ability of wood to absorb moisture and swell. Products absorb moisture gradually, are less prone to swelling and drying out, but still need elastic coatings. It was proved that heat-treated wood eventually turns grey when exposed to sunlight, and therefore added surface treatment with a coating is necessary. Added application of protective substances on the surface of products made of thermally modified wood contributes to dimensional stability and protects against rapid weathering of the surface in open air conditions. Clear coatings and oils do not protect surfaces from discolouration during weathering. They are recommended for products made of thermally modified wood, which are used away from direct sunlight and rain. The parameters of moisture penetration into wood are mathematically modelled based on the quasi-stationary equation of moisture diffusion through a polymer film on the surface of a flat sample. The dynamics of changes in the moisture content in thermally modified wood were experimentally investigated under different regime parameters. Mathematical relations obtained from experimental studies allow calculating the moisture diffusion coefficient in thermally modified wood in the presence of a polymer shell. It was established that the application of a wax coating on the surface of the product reduces the moisture diffusion by more than 10 times for surfaces already treated at 160°C for one hour, which allows using it on objects with increased humidity