Mobile technology of thermal modification of wood

Abstract

Wood as a structural material has a number of disadvantages, including a short service life, relatively low dimensional stability, significant volumetric deformations under the influence of moisture, pronounced anisotropy and water absorption. Thermomodification slightly improves physical and mechanical properties, but the problem of changing surface characteristics, in particular adhesion, arises. In order to determine the technological characteristics of thermally modified wood and to develop possible measures to improve the technology of applying protective coatings, the surface energy and compressive strength limit along the fibers were determined. A comprehensive approach is applied to analyze the state of the thermally modified wood surface through the study of surface energy characteristics based on the Fowkes method, which takes into account dispersion, hydrogen and dipole-dipole interactions at the solid-liquid interface. According to the marginal angle of wetting, it was found that the process of thermal modification wood helps to increase the resistance of its surface to wetting due to a decrease in polarity by 1.68 times with an increase in the duration of modification to 30 min. At the same time, the surface free energy for samples modified at 300 °C for 5 min. is 64.5 mJ/m2, during 30 min. – 24.1 mJ/m2. Regarding compressive strength, thermal modification reduces the strength limit by 1.46 times. At a temperature of 300 ºС and a time of 5 min. and 15 min. the indicator remains at the level of ordinary wood – 42 MPa. Treatment for 30 min. reduces the strength limit to 29 MPa, wood loses plasticity. The obtained results make it possible to effectively choose stable coatings for such wood for high-quality surface treatment with paint and varnish materials. Knowing the moment of time from which the reduction of the strength limit begins, conducting the process of thermal modification becomes more controlled and makes it possible to predict the characteristics of the future material