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

Massimo Virgilio flow or whether the system is filled with nitrogen and closed
It is unclear whether the TM is operating in a nitrogen

during the modification phase. It is mentioned that the TM
chamber has forced air circulation.

We investigated the TM of silver birch (Betula pendula)
and Scots pine (Pinus sylvestris) wood in this study, with a
particular focus on enhancing the dimensional stability and
minimising the hydrophilicity.
Birch and pine wood were chosen as the most frequent
deciduous and coniferous wood species in the Republic
of Latvia, as they offer a wide range of applications in the
national economy.
The study’s goal was to examine the correlations between

TM parameters in a closed nitrogen atmosphere under pressure
and TM wood water and humidity uptake. The information
available on the process parameters is insufficient.
As a result, a thorough analysis of this TM approach is
an obvious next phase to confirm, supplement, or update
the existing knowledge.

Thermal Modification Process
maximum pressure listed in the equipment characteristics, it For each TM, silver birch (Betula pendula) and Scots pine
did not exceed two bar. (Pinus sylvestris) wood boards with dimensions of 1000 ×
The effects of TM parameters on the mechanical 100 × 25 mm (longitudinal × tangential × radial) were used
characteristics, colour, chemical composition, and dimension (20 for each treatment).
stability of black poplar (Populous nigra L.) wood in a nitrogen The boards used were of the finest grade, with no evident
environment have been widely researched in the temperature material faults (knots, grain slop, resin pocked, bark pocked,
range of 160–220 deg C. reaction wood, wanes, blue stains, decays, bug holes, shakes,
Mass loss (ML) occurs after TM in nitrogen; the chemical distortions, and so on). All boards were conditioned in a

composition changes; the density, compressive strength, standard climate (temperature 20 ± 2 deg C, relative humidity
modulus of rupture, modulus of elasticity, and EMC decrease; 65 ± 5%) prior to TM.
while dimensional stability improves. Sapwood and heartwood were not removed from the Scots
The characteristics of black poplar wood are more affected pine wood, and randomly selected boards within specified
by an increase in TM temperature. There is no indication of density limitations were utilised for TM.
pressure throughout the TM process. The wood moisture content was evaluated using ISO
However, the operating pressures of the TM chamber (0.25 13061-1:2014 and the density was determined using ISO

cubic metres) are mentioned differently in the experimental 13061-2:2014. Before TM, the average densities of silver
sections (−1 to 1 atm and −1 to 5 atm). birch and Scots pine were 627± 14 kg × m−3 and 581 ± 10