Establishment of moisture diffusion regularities through the polymer shell of thermally modified wood
DOI:
https://doi.org/10.31548/forest2021.01.005Abstract
An analysis of the process of thermal modification of wood, which was obtained by a controlled heating process, was done. The unique technological properties (durability, low hygroscopicity and dimensional stability) of thermomodified wood make it possible to use it in various scope. Due to the influence of temperature there are some chemical changes in the structures of the wood cell wall components (lignin, cellulose and hemicellulose). This leads to an increase in density, hardness, improved hydrophobicity (water repellency), thereby reducing their ability to absorb moisture and swell. The products absorb moisture gradually, are less prone to swelling and shrinkage, but still need the elastic coatings application. It is proved that heat-treated wood turns gray over time under the influence of sunlight, and therefore requires additional surface treatment with a coating. Additional protective substances application on the thermo-modified wood products surface promotes dimensional stability and protects against rapid weathering of the surface in open air conditions. The use of transparent coatings and oils does not protect the surface from discoloration during weathering. They are recommended for products are manufactured from thermomodified wood, which are operated away from direct sunlight and rain. The parameters of moisture penetration into wood are mathematically modeled on the basis of the moisture diffusion quasi-stationary equation through the polymer coating on the flat sample surface. The dynamics of moisture content changes in thermally modified wood by different schedules parameters has been experimentally studied. The obtained mathematical relations based on the experimental studies results make it possible to calculate the moisture diffusion coefficient in thermally modified wood in the presence of a polymer shell. It is established that the wax coating application on the surface of the product reduces the moisture diffusion process more than 10 times for surfaces treated at a temperature of 160 °C for 1 hour. That is, such products can be used on objects with high humidity.
Keywords: wood, efficiency of thermal modification, moisture absorption, water diffusion, decomposition, wood stability.
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