EFFECT OF TEMPERATURE AND TIME OF DIMENSIONAL STABILIZING PROCESS ON PROPERTIES OF SHAPE TRANSFORMED COMPRESSED WOOD

Abstract

In the compressed wood production technology, the heat treatment for dimensional stability of compressed wood plays an important role as it reduces tension in the wood after shape transformed compressing. This study has mentioned the effects of temperature (160.170, 180, 190, 200, 210^oC) and duration (0.5, 2.5, 4.5, 6.5, 8.5h) of  treatment of Styrax tonkinensis woodin a vacuum condition of 650mmHg. The results indicated that: i) When the heat treatment time increased, the recovery of set of compressed wood decreased and anti-swelling efficiency increased, which means the dimensional stability increased with the treatment time. That changes were reflected most clearly in the period from 0.5 - 4.5h. However, when the time exceeded 7.0h, the weight loss of compressed wood tended to halt. For temperature, when increasing it gradually in the treatment, the wood dimensional stability also rose up. When the temperature reached 200^oC, the dimensional stability redirected and halted. ii)In the process of dimensional stability treatment with high temperature, the compressed wood density slightly decreased and some of the mechanical properties of compressed wood also decreased, but those were still higher than untreated wood (uncompressed). In particular: Parallel compressed strength reduced with maximum speed at the beginning of the process (from 0.5 - 2.5h), then the effects of the temperature did not affect significantly and this stress was almost constant, especially since 6.5 to 8.5 hours; When extending the heat treatment time to stabilize the dimension of wood from 0.5 to 8.5h in vacuum condition with temperature of 210^oC, the tangential section’s hardnesss (actually the outer surface) of 4-side compressed wood reduced inversely with treatment time.