| Summary: | 碩士 === 國立宜蘭大學 === 森林暨自然資源學系碩士班 === 100 === Three wood species include Japanese cedar (Cryptomeria japonica), southern yellow pine (Pinus spp.), and Douglas fir (Pseudotsuga menziesii) with larger cross section of 14 × 14 cm and 50 cm in the length were used in this study. Heat treatments were carried out at temperature levels of 170℃, 190℃, 210℃, and 230℃ for holding time spans of 1h, 2h, and 4h in a heating unit. The objective of this study was to investigate the effects of core drilling process on the visual grades, physical, and mechanics properties of heat-treated wood specimens. The results showed that the hygroscopicity and dimensional stability of wood could be significantly improved after heat treatment. There could be over 60% increase in the MEE(Moisture Excluding Efficiency) and ASE(Anti Shrinkage Efficiency) compared to the control specimens. The values of MEE and ASE of Japanese cedar treated at temperature levels of 170℃ and 190℃ were significantly higher than those of Douglas fir and southern yellow pine. Some degree of loss in the mass, volume, and over-dry density of test specimens were found after heat treatment. Maximums reduction values for mass and volume were respectively around 18% and 10% of test samples treated at 230℃ for 4 h. The over-dry density of wood specimens were less affected by heat treatment at temperatures of 170℃ and 190℃, moreover, some of them were increased. A darkening of three wood species occurred, with the color change being related to the temperature and time of treatment. The color difference between sapwood and heartwood of Japanese cedar was obviously reduced after thermal modification process. The defects occurred in the core-drilled specimens after heat treatment were significantly lower than those of control samples. These was a slight increase in MOE when three wood species were thermally treated. However, the rate of increase in MOE was subsequent decreased with higher heating temperatures. The values of MOE for Japanese cedar and southern yellow pine treated at temperature of 230℃ were lower than those of untreated samples, while for specimens of Douglas fir were still higher than controls. The bending properties of Douglas fir were less affected by heat treatment compared to the other species in this study. The values of compression strength parallel to grain increased for test species after heat treatment. The rate of increase in compression strength parallel to grain was subsequent decrease with higher heating temperatures and time of periods. The surface roughness of heat-treated specimens were lower than those of untreated samples. The abrasion resistance of wood surface decreased with an increasing in treated temperature.
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