Effect of Thermal Degradation on Shrinkage and Collapse of Wood from Three Australian Species

Eucalyptus regnans (F. Muell.), E. diversicolor (F. Muell.), and E. pubescens (F. M. Bail) were subjected to temperatures ranging from 20? to 137?C for a duration from 1/4 day to 14 days. Subsequent to the heat treatment one-half of the specimens were cut into shavings, extracted with distilled water, and the pH then measured. The other half of the specimens were dried at 20?C and 63 percent RH. After 12 percent moisture content was reached the specimens were conditioned in saturated steam at 100?C, redried to 12 percent moisture content, then ovendried. Weight and dimensions of each specimen were recorded before and after each step listed. Large increases in total shrinkage (15 to 30 percent) and severely reduced recovery (100 to 0 percent) resulted from thermal degradation of green wood. Acidity of the material measured after heat treatment increased with temperature and duration up to a maximum of 2.9 to 3.7 pH after l day and decreased to 3.4 to 5.0 pH, depending on the species. The effect of thermal degradation on shrinkage and recovery is highly significant for treatments exceeding 1 to 2 days at 82?C, 6 hours at 110?C, and about 2 hours at 137?C. Shrinkage increase is roughly proportional to the increased acidity to its maximum. Species which normally do not collapse approach the behavior of collapsing species after heat treatment.

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