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MATERIALS 55
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kg × m−3, respectively. holding temperature, and cooling, ranged from 16 to 19 hours,
TM was performed in a 340 L stainless steel pilot-scale depending on the maximum TM temperature.
chamber constructed by Wood Treatment Technology (Grinsted, The mass loss (ML) was calculated by weighing wood
Denmark). The jacket’s temperature was maintained stable boards (20 for each treatment) before and after the TM in a

with circulating hot mineral oil. nitrogen atmosphere. The ML was calculated for each treatment
The modification chamber is designed to operate at as a percentage of the original mass of the fully dry wood.
pressures ranging from 0.1 bar to 20 bar, with temperatures The anti-swelling efficiency (ASE) of 15 specimens with
reaching 190 deg C. dimensions of 20 × 20 × 20 mm3 (L × T × R) was examined
A program controls the equipment automatically, allowing under cyclic conditions. Before each cycle, specimens were
it to switch between manual and automatic modes during the conditioned in a normal climate (temperature 20 ± 2 deg C,
TM process. Prior to heating, the samples were stored in the relative humidity 65 ± 5%).
autoclave for 30 min under a 0.2 bar vacuum to remove oxygen. Five full-cell saturation and oven-drying cycles were
Nitrogen was fed into the autoclave from a nitrogen gas performed. The ASE was calculated using the volumetric

cylinder after the vacuum step to create the required initial swelling (VS) coefficients of the treated specimens (St) in
pressure (3–6 bar). At the start, a small amount of water comparison to the untreated controls (Su).
(1–1.5 L) was pumped into the autoclave to generate a small The soaking phase consisted of vacuum water impregnation
amount of steam to catalyse the hydrolysis of hemicelluloses. (0.2 bar, 120 min) followed by 24 hours of water storage at
Until the pressure-release stage, the TM system remained 22 deg C. The drying phase included a 72h step at 20 deg
sealed and static (no mixing was used). The TM parameters for C, followed by eight hours at 45 deg C, eight hours at 60
silver birch. Tmax, time at Tmax, and initial nitrogen pressure deg C, eight hours at 80 deg C, and lastly, eight hours at

were varied from 160 to 170 deg C, 30 to 120 min, and three 103 deg C.
to six bar, respectively. The ASE estimate was based on the average measurements
The TM parameters for Scots pine. Tmax, time at Tmax, of radial, tangential, and axial swelling. The ASE was determined
and initial nitrogen pressure were varied from 160 to 180 deg for each treatment.
C, 30 to 180 min, and four to six bar, respectively. Moisture uptake from the environment with constant humidity
From ambient temperature to 100 deg C, the heating was measured for 15 TM wood specimens (dimensions 20 ×
rate of the modification chamber was 0.36–0.42 deg C/min,
and from 100 deg C to Tmax, it was 0.24–0.32 deg C/min.
The temperature was maintained after heating (30–180 min).

The pressure in the autoclave grew during the TM process, Alexander Schimmeck
reaching a maximum in the Tmax stage.
The chamber was then cooled by pumping out a mixture
of nitrogen and wood thermal destruction products until
atmospheric pressure was reached. The modification chamber
door was partially opened to allow for additional cooling. The
modification chamber was cooled at a rate of 0.30–0.35deg

C/min.
The overall time for the TM process, including heating,