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Parameter Effect Comments
Equilibrium
moisture
Reduced 50% compared untreated
wood. The difference is higher, the
relative humidity is higher.
This difference remained after years of exposure. After thermo
treatment the wood is dry - moisture content is 4-6%.
Dimensional
stability
The swelling and shrinkage (both
tangential and radial) reduces 3-5 times
for softwoods and up to 15 times for
hardwoods. This parameter is strongly
depends on the relative humidity (at
100% reduces 2 times for softwoods and
3-5 times for hardwoods)
This because of the decrease in absorptive qualities, lower equi-
librium moisture content and also due to lignin depolymerization
the length of chains of cellulose decreases and this leads to the
deformations decrease.
Color Attractive golden brown appearance and
even color at all depth.
The color is affected by the treatment temperature and time. It is
possible to receive several gradations of color based on the
process.
Appearance Attractive golden brown appearance and
even color at all depth. Color becomes
more sated and homogeneous on all
section; the structure of wood effectively
comes to light.
The color is affected by the treatment temperature and time. It is
possible to receive several gradations of color based on the
process. The effect of valuable breeds of wood is reached.
Density Lower density at 5-10%. Due to the emissions during the thermo-treatment process and
lower equilibrium moister content. This feature might improve the
cost-efficiency of shipping of the treated material.
Cell structure Changes as if after ageing for 120-250
years.
The color is affected by the treatment temperature and time. It is
possible to receive several gradations of color based on the
process. The effect of valuable breeds of wood is reached while
the absorption of moisture is decreased.
Resin Is almost fully removed.
Brinell hardness Increases as the treatment temperature
increases. However, the relative change
is very small, as the density decreases.
Certain kinds of timber change their place on the hardness scale,
as some of them become harder, while others softer as a result of
the treatment temperature and specie.
Permeability The water uptake reduced up to 5 times
depending on treatment temperature.
The surface of the thermo-treated wood is not porous but solid,
also the chemical composition of the wood changes. Reduced
water absorption has to be taken into account when working with
water solvent glue or paint.
Thermal
conductivity
Decreased by 10-30%. Thanks to the lower water content and structural changes.
Fire resistance The same as non-treated wood.
Thermo--treated wood is in fire class D.
The time of ignition a little decreased, but better than the normally
dried softwoods in terms of heat and smoke release.
Resistance to
insect attack
and termites
Significantly increased resistance to the
hardwood and softwood insects, but only
a little increased resistance to the
termites (it is expected that termites will
choose normal wood over thermo-
treated).
Tests have been carried out in Europe to evaluate the resistance
to attack from the three most common wood boring insects found
in Europe. House Longhorn beetles (Hylotrupes bajulus) are found
in the sapwood of softwood, the common furniture beetle
(Anobium punctatum) preferentially attacks hardwoods and the
Powderpost beetle (Lyctus brunneus) is found in some hardwood
species. The results of the tests found that Thermo-treated wood
was resistant to all three of the above insect species. Southern
European Subterranean termites (Reticulitermes spp) found in
Europe only attack buildings from the earth below, avoid-ing direct
sunlight where possible. Termites will attack both wood and
concrete based materials in their quest for a strong food base.
Various measures have been developed to control the problem
including polythene membranes being installed in the foundations
and various bituminous paint products are available to seal
possible routes up the building.
Rot resistance Improved. However it is not suitable for conditions where it would be satu-
rated with water or in prolonged contact with damp ground.
MAJOR FEATURES OF THERMO-TREATED WOOD