Effect of Heat Treatment on Some Properties of Douglas-Fir
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1969-10
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In a study of the effect of prolonged heating on dielectric and other properties of Douglas-fir, specimens were subjected to heat treatment at 170°C. for intervals that ranged from 10 to 100 hours. Weight, dimensions, and dielectric properties were measured before and after the heat treatment at two moisture levels of 8 percent and ovendry. Surface reflectance of treated specimens was also measured. Reduction in weight and density of the wood that resulted from mild thermal decomposition did not follow a first order kinetic reaction during the first 30 hours of treatment. After that, the change in both weight and density followed a first-order reaction. Equilibrium moisture content (during absorption) of the wood at 70°F. (21°C.) and 65 percent relative humidity was reduced with increasing duration of treatment. After 100 hours of treatment, the equilibrium moisture content was reduced by 1.5 percent, based on the ovendry weight. Dielectric properties also were modified by the treatment. Dielectric properties of the wood were more sensitive to the heat treatment at low frequencies (100 Hz and 1 kHz) than at 100 kHz. There was a tendency for the dielectric loss spectrum to shift toward lower frequency with increasing duration of treatment. The logarithm of surface reflectance of treated wood showed a straight-line relation with the duration of treatment, which suggests that thermal decomposition initiates at the surface, and then penetrates gradually into the wood.
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Wood Science Vol. 2, No. 2