Abstract
This work examines the effect of thermal modification temperatures in the production of thermally modified wood on the cutting and fracture parameters when cutting heat-treated spruce wood by a circular sawblade machine. The samples were thermally modified at 160, 180, 200, and 220 °C. One sample was unmodified and was used as a reference sample. On the basis of the performed experiments, the fracture parameters (fracture toughness and shear yield strength) were calculated for the axial–perpendicular direction of cutting. In comparison with the theoretical assumptions, the influence of temperature on the cutting and fracture parameters was confirmed. Thermally treated wood is characterized by increased fragility and susceptibility to crack formation, as well as reduced density, bending strength, and shear strength. These properties significantly affect the size of the cutting force and feed force, as well as the fracture parameters. As the temperature increases, the values of these parameters decrease. The mentioned material characteristics could be useful for the optimization of the cutting process, as well as for the issue of energy consumption during the machining of heat-treated wood.
Highlights
Wood has always been a material that humans use daily, and since it is an available renewable building material, there is a good chance that this will still be true in the future [1]
The most important change is the gradual breakdown of hemicelluloses and, partly, cellulose at the locations of its amorphous structure
The results show that the cutting force is the highest when the unmodified sample (REF) is machined
Summary
Wood has always been a material that humans use daily, and since it is an available renewable building material, there is a good chance that this will still be true in the future [1]. Over the last twenty years, it has been used for facades and terrace floors; its organic composition affects these uses rather negatively [3] This is mainly due to the fact that untreated wood is subject to biological and weathering degradation, to which it is exposed when it is used as an unprotected exterior [4]. Since the beginning of the development of thermal modification, heat-treated timber has been a frequent subject of research investigations This is one of many possible wood hydrothermal processing techniques, it is the most frequently used method after kiln drying [6]. The most important change is the gradual breakdown of hemicelluloses and, partly, cellulose at the locations of its amorphous structure This mainly results in a significant reduction in bending strength, with the modulus of elasticity in bending being disproportionately less reduced [9]. The reduction of density [11] and the esterification of cellulose mean that thermally treated wood has fewer free hydroxyl groups [12], leading to a rapid decrease in the equilibrium moisture content of the wood [13], which is, less susceptible to biodegradation [14]
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