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MATERIALS 53
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of wood with higher density and greater cell wall thickness. pixnio.co
In this context, density should be regarded as a macroscopic
descriptor reflecting underlying anatomical characteristics of
wood, such as porosity, cell wall thickness, and the relative
proportions of earlywood and latewood, rather than as an
independently controlled variable.

The statistical significance of moisture content observed in
the present analysis suggests that variations in bound water,
even below the fibre saturation point, have a measurable
influence on the dielectric properties of oak lamellae. on dielectric properties, although the moisture contents of the
While ionic conduction and polarisation of free water are samples were below the fibre saturation point.
not expected under these conditions, the increased contribution The results also showed that relative air humidity, a
of bound water to dipolar relaxation can explain the observed conditioning parameter, closely aligned with moisture content’s
effects, in agreement with previous reports. effect on dielectric properties, which was expected, as higher
Compared to beech wood, which is most commonly used relative air humidity leads to higher moisture in wood samples.

for the bending process, oak wood showed similar dielectric A wider range of moisture contents should be examined
properties with increasing frequency. in future studies, especially above the fibre saturation point.
Beech wood has on average a slightly higher dielectric Throughout the entire frequency range of the electric
constant than oak wood at the same frequency. Their loss field used in this work, a decrease in the dielectric constant
tangent is on average similar. The same parameters that had with increasing frequency is observed, which is especially
a statistically significant effect on the dielectric constant during pronounced up to one MHz.
heating before plasticisation of beech were also significant In contrast, the highest values of the loss tangent were

for oak. recorded at higher frequencies, except for the sample with the
Compared to other commercial hardwood species, oak highest moisture content and at the highest relative humidity
wood has on average higher dielectric constant and loss (100%), in which the highest values of the loss tangent were
tangent values under the same test conditions. These results recorded at frequencies below one MHz.
mostly correlate with rise of average density of each species. From an industrial perspective, the results of this work
highlight the importance of controlling environmental factors and
Conclusions the physical properties of oak wood after the drying process
The results of this study confirmed that the dielectric properties and before exposure to the electric field.
of oak wood lamellae (Quercus robur L.) depend on both Improved control of these factors and properties enables

structural properties (density, moisture content) and environmental a better understanding of how they affect dielectric properties
factors (relative air humidity, temperature). and could contribute to more efficient dielectric heating.
Although density showed a strong statistical association with Future studies should investigate how the dielectric
both dielectric constant and loss tangent, this dominance should characteristics identified in this work can be incorporated into
be interpreted as reflecting structural heterogeneity inherent the design and control of heating processes for oak wood
to the material rather than a direct effect of density alone. prior to bending. FDM
Moisture content did have a statistically significant effect ENQUIRY NO. 1401