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56 MATERIALS MAY/JUN 2024 FDM ASIA | www.fdmasia.com

Jonathan Taylor created due to changes in the chemical structure of wood.
The degradation of hemicelluloses, which are extremely
vulnerable to thermal destruction, is responsible for the majority
of the ML. A higher ML after TM often correlates with better

biological durability and dimensional stability of wood. However,
it has a disadvantage in terms of mechanical strength. The
ML after TM for birch wood ranged from 5.9 to 12 percent.
These results are related to the initial birch wood densities
of 627 ± 14 kg × m−3. The maximum average ML (10.1%–
12.0%) was obtained for birch wood after TM at 160 deg C
for 120 min and 170 deg C.
The lowest average ML was obtained after TM at 160 deg
C for 60–90 min. When all other process parameters were

held constant, a rise in initial pressure resulted in a higher
ML after TM. It should be emphasised, however, that the ML
values produced using TM had large error margins.
The birch wood board dimensions were substantially
reduced after TM in both the radial and tangential axes.
The tangential direction of TM birch wood showed a greater
reduction (4.4–6.4%) than the radial (2.9–4.7%).

The most significant changes in both the tangential and
20 × 20 mm3) at relative humidity (RH) of 65, 75, and 98% radial directions of birch wood were observed after TM at 170
at 20 ± 2 deg C. After being completely dried, the wood deg C and a time at Tmax of 120 min, while the least change
specimens were placed in a conditioning room with an RH occurred after TM at 160 deg C and shorter treatment times.
of 65%. This could be explained by the fact that the wood structure
Wood conditioning at higher RH conditions was performed varies in different directions, which affects the swelling capability
in desiccators by placing specimens over a saturated NaCl of the wood cell wall. After TM, radial and tangential direction
salt solution (RH of 75%) and CuSO4 × 5H2O salt solution reduction resulted in total birch board volumetric changes
(RH of 98%). ranging from 7.1 to 10.2 percent.

Specimens were stored at successively increasing RHs The ML after TM for pine wood was 2.6–9 percent. These
of 65, 75, and 98%. When the mass of the wood samples results are related to the initial pine wood densities of 581 ± 10
remained constant across three weightings at 48-hour intervals kg × m−3. After TM, pine wood had a lower ML (2.6%–9.0%)
(up to 30 days), the equilibrium moisture content (EMC) and than birch wood (5.9%–12.0%). The maximum ML of pine
dimensional changes were determined. wood (7.6%–9.0%) was obtained at 180 deg C and 170 deg
C with a duration at Tmax of 120 min. For all exposition times
Mass Loss & Physical Changes at Tmax, the lowest ML was obtained at 160 deg C.

ML is used as a criterion to characterise the TM process’s An increase in the initial pressure from four to six bar
intensity and the degree of wood degradation. ML is typically at 170 deg C had no noticeable effect on ML after TM. In