Page 54 - FDMAsia Jan/Feb 2026

52 MATERIALS JAN/FEB 2026 FDM ASIA | www.fdmasia.com

tested at higher RH. High RH increases the equilibrium water than those at 20 deg C. The tan δ values showed only marginal
content, which leads to an increase in dielectric properties. differences with respect to measurement temperature.
Water molecules have a higher dielectric constant (~80 at These differences were much more pronounced in samples
20 deg C) than wood. At higher RH, free water accumulates with higher moisture content. Similar results were obtained in
in the cell cavities and enhances the dipolar and interfacial previous studies, which showed that the ε′ and tan δ increase
polarisation mechanisms. up to 100 deg C when measuring wood samples with the

This dual contribution results in a pronounced increase in same properties.
ε′ with moisture content and increased dielectric losses due This increase is relatively small. The reason for the increase
to additional relaxation and conduction paths. in dielectric values is that interfacial and dipolar mechanisms
Steamed lamellas exhibited slightly higher ε′ and tan δ are thermally activated (in the first case, the migration of
values compared to non-steamed samples of similar density charge carriers through structural domains, and in the second,
and moisture content. It is known that steam treatment causes the general mobility of molecules).
changes in the cell wall of wood (degradation of hemicellulose Due to this behaviour during heating and exposure to
and changes in the structure of lignin). heat, the test temperature affects the dielectric properties
These changes affect the hydroxyl groups, which leads to of wood. Increasing temperature improves the orientation of

a change in the hygroscopicity of wood. These changes then polar molecules within the wood (primarily water, but also
affect the mobility of water molecules within wood, which are cellulose) towards the electric field, leading to an increase in
one of the carriers of the dielectric properties of the material dielectric values.
which could explain these slightly higher values. The significant increase in ε′ observed with increasing
The effect of measurement temperature was also statistically lamella sample density is consistent with previous findings.
significant. At 90 deg C, the ε′ values were on average higher This dependence of ε′ on density is due to the lower porosity

pixnio.co