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MATERIALS 53
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period is questionable. bar pressure.
There is no mention of it in the literature. Wood Treatment The data are difficult to compare because EMC (at relative
Technology recently launched a new closed-system TM humidity (RH) 30, 65, 80, and 100%) and swelling are presented
procedure in a nitrogen atmosphere. The TM process under as percentage reductions.

pressure in nitrogen has a higher heat transfer capacity and According to the data provided, the approximate EMC
requires no energy to convert water to steam. values for TM spruce are six to eight percent (65% of RH)
The procedure is carried out at higher pressures (up to and 17–20 percent (100% of RH). The untreated control EMC
18 bar), with the elevated pressure acting as a temperature values were 12–13 percent and 30 percent, respectively.
replacement. As a result, the maximum modification temperature TM beech wood EMC was five to seven percent (65% RH)
and processing cycle time can be reduced to 8–12 hours. and 13–23 percent (100% RH), whereas untreated control EMC
In terms of manufacturing costs and productivity, the was 10 percent and 30 percent, respectively. In comparison
closed-type process in nitrogen appears to be a superior to other specimens, the EMC of TM beech wood at 185 deg
technology that necessitates more extensive scientific research. C was the lowest.

The scientific literature contains a wealth of information about TM in a nitrogen environment was generally conducted
the TM of several wood species in a nitrogen environment at in small-sized laboratory reactors for one to eight hours,
atmospheric pressure. with a total processing period of 20 to 50 hours, over a
However, insufficient information on the TM process in a wide maximum temperature range of 130 to 260 deg C in a
nitrogen environment at elevated pressure and the qualities of variety of experiments.
the TM wood is known dating back to the 1970s and 1980s. Larch (Larix gmelinii) and red oak (Quecus rubra) were
The dimensional stabilisation of wood by the Feuchte– heated in a tub furnace in a nitrogen environment, with the

Wärme–Druck process was evaluated in a 1.8 cubic metres ambient temperature of wood samples set at 200, 250, 300,
volume pilot-scale reactor at 180–200 deg C in an inert gas and 400 deg C. Wood’s water absorption (WU) dropped as
environment of 8–10 bar. Heat/pressure treatment of beech, the TM temperature increased, and it reduced drastically
birch, poplar, pine, and spruce wood, fibre, particle board, over 300 deg C.
and plywood is demonstrated. The pressure in the system during the modification phase
After treatment, there is a 50–80 percent reduction in is not mentioned in the publications; however, based on the
swelling and shrinkage, an improvement in resistance to fungi
and insects, and an improvement in the remaining physical
and mechanical wood qualities.

When the maximum temperature is held, it appears Benjamin Genz
that the pressure in the reactor remains constant. However,
the entire process time (5–15 hours) is ambiguous and not
specified in the temperature and time plan, and the heating/
cooling speed is suspect.
Weathering stability, equilibrium moisture content (EMC),
and swelling of European spruce (Picea abies) and beech

(Fagus sylvatica) wood were investigated after TM in nitrogen
at 175 deg C for 2 hours and 185 deg C for 3 hours at 10