One of the most persistent problems with mechanically densified wood is
its inherent dimensional instability. The effects of heat post-treatment
on the changes in spring-back (SB), compression ratio recovery (CRR),
thickness swelling (TS), and water absorption (WA) of newly-tested
Uludag fir (Abies bornmuelleriana Mattf.) and black poplar (Populus
nigra L.) wood samples that had been thermo-mechanically densified were
investigated. Samples were densified with compression ratios of 25\% and
50\% with temperatures of 100 and 140 degrees C, respectively. Then, the
heat post-treatment was applied to the samples at 185 and 212 degrees C
for 2 h. For the two newly-tested wood types, results of the preliminary
study show that SB and TS were higher at a 50\% compression ratio
compared with 25\%. Regarding densification temperature, TS was lower in
samples densified at 140 degrees C, while SB was higher. WA values were
lower in compressed samples (50\%) at high rates. The effect of the
densification temperature on WA was insignificant. Heat post-treatment
had a considerable effect on the dimensional stability and
hygroscopicity of the densified Uludag fir and black poplar samples.
With an increase in heat treatment temperature, the dimensional
stability increased, while the hygroscopicity of densified samples
decreased. As a result of heat post-treatment applied at 212 degrees C,
SB, CRR, TS, and WA decreased by 88\%, 85\%, 79\%, and 53\%,
respectively