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The purpose of this study was to modify the dimensional
stability, color changes and the improved effects of mechanical
properties of wood by heat treatments at different temperatures
and different times by sand-heat methods. The species applied
for this experiment were Chinese cedar, Japanese cedar,
paulownia, acacia, teak and red oak. The main results obtained
by this study are summarized as the follows:
1. The percentage of reduction in specific gravity had
evidently increased with the increasing of temperature and time
of the treatments, but it was inversely correlated with the
specific gravity of wood.
2. The values of △E* of treated specimen had increased with
the temperature and time of the treatment, it indicated that
the color turned more severely than the untreatment. It could
improve the color of wood surfaces by heat treatments.
3. The values of antishrink efficiency (ASE) in radial
direction were increased with the increasing in the temperature
and time of treatment, these were higher than that of
tangential direction. The values of ASE under the conditions of
40℃、90﹪R.H. were higher than that of 20℃、65﹪R.H. The wood
with lower specific gravity appeared to have the higher
improved effect than that of the higher specific gravity.
4. The values of moisture excluding efficiency (MEE) appeared
to be increased with increasing in the temperature and time of
treatment. The values of MEE under the conditions of 40℃、90﹪
R.H. were higher than that of 20℃、65﹪R.H. . There was a
tendency to show that the higher MEE effect was found to be
occurred in the wood with lower specific gravity.
5. The values of ASE and MEE of sapwood increased with
increasing in the temperature and time of treatment, they had a
tendency to have the higher values than heartwood. The specimen
with lower moisture content had higher effect on the
dimensional stability of wood.
6. The compressive strength parallel to grain of wood was not
severely affected after the treatment at 220℃,240℃,260℃,
while the strength of paulownia was significantly reduced when
treated at 240℃,260℃.
7. The static bending strength (MOE) of heartwood such as
paulownia, acacia, and teak had severely reduced after the heat
treatment at 220℃, whereas Chinese cedar and Japanese cedar of
softwoods had not been affected. The MOR of softwoods began to
reduce its strength after the treatment for 90 minutes at 240℃.
8. The percentage of reduction in MOE by heat treatments was
significantly increased with the increasing in temperature and
time. There was a tendency to show that the wood with higher
specific gravity was evidently affected after the heat
treatment at 260℃.
9. The abrasive resistance of specimen after the heat treatment
at 220℃, 240℃, 260℃ and different time showed that it would
be reduced as the temperature and time increased especially the
wood with lower specific gravity.
10. From the viewpoint of the improvement of hardness, there
was no effect for Chinese cedar, Japanese cedar and paulownia,
while the wood with higher specific gravity, such as acacia,
teak and red oak, the surface hardness was evidently enhanced.
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