Summary
The concentration of individual resin acids and the equilibrium moisture content at a relative humidity
of 100% were studied in brown-rot resistant and susceptible Scots pine (Pinus sylvestris L.)
heartwood. About 90% of the resin acids in the heartwood were of the abietane type, abietic acid
being the most abundant. The concentration of resin acids was higher in the decay-resistant heartwood
than in the decay-susceptible heartwood. Resin acids are presumably in part responsible for
the decay resistance of Scots pine heartwood. However, no clear relationship was found between
the concentration of resin acids and the equilibrium moisture content. The role of resin acids may
also be ascribed to mechanisms other than their hydrophobic properties alone. The reasons for the
slight differences in moisture content between the decay classes require further study.
A prototype of the electrical impedance spectroscopy (EIS) device for the measurement of internal moisture gradients in wood was developed. The EIS device consists of a hand-held probe connected to a control unit interfaced with a portable personal computer and a power unit. In the measurement, parallel flat electrodes of the measuring probe are laid against the wood specimen and the sine wave excitation is applied in the frequency range 1–100 kHz. The measured amplitude and phase spectral data were analyzed using the model based on constant phase elements. A spectral analysis software package was designed for measurement of subsurface transverse moisture gradients. The EIS device was tested with many types of uniform, desorption, and absorption gradients in lumber, pulpwood, and log specimens from spruce, pine, and birch. The EIS device can be easily transferred in a small case allowing field measurements.
This study examined the effects of physical (moisture content, water content and wood density) and chemical properties (concentration of phenolics and resin acids) on the electrical properties of Scots pine (Pinus sylvesteris L.) wood specimens. Complex impedance was measured from heartwood and sapwood specimens using frequencies between 5 kHz and 1 MHz. Significant correlation between density and electrical properties was found at high frequencies with sapwood specimens in which the extractive content was low. Moisture content had an effect on electrical properties over the whole frequency range. Electrical properties of heartwood samples with high extractive content were differently affected by the chemical and physical properties. Electrical properties were sufficient to distinguish between the samples from the brown-rot resistant and susceptible Scots pine trees.
An electrical impedance frequency spectrum (20 Hz to 1MHz) was measured in wood specimens with uniform, absorption and desorption transverse moisture content (MC) gradient. Parallel plate single sided capacitive and conductive electrodes were used. Capacitance, conductance and impedance locus analyses were included in the study, the desorption and absorption moisture gradients (MG) were estimated using frequency based analysis. This study suggests that the transverse MG can be estimated using impedance spectroscopy analysis. Both used electrode types and all the studied methods gave similar results which shows that frequency based analysis can be used. It was not possible to achieve very good accuracy when estimating MG using pure conductive or capacitance measurement method. The electrical distributed network circuit modelling was found to be the most promising method in estimation of transverse MG. Holzforschung 53 (1999) 68-76 Holzforschung / Vol. 53 / 1999 / No. 1
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