Dielectric, Ultrasonic and Viscoelastic Properties of Rubber Wood
Dielectric, ultrasonic and viscoelastic properties of rubber wood were studied with various physical parameters, such as moisture contents (MC), grain directions and temperatures. Three anisotropic directions, namely longitudinal, radial and tangential to the growth ring were considered for the m...
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| Format: | Thesis |
| Language: | English English |
| Published: |
1998
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/9437/1/FSAS_1998_28_A.pdf |
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| Summary: | Dielectric, ultrasonic and viscoelastic properties of rubber wood were
studied with various physical parameters, such as moisture contents (MC), grain
directions and temperatures. Three anisotropic directions, namely longitudinal,
radial and tangential to the growth ring were considered for the measurement
of these properties. Dielectric properties were measured at low frequencies
from 10⁻² to 10⁻⁵ Hz and at microwave frequencies from 1 to 18 GHz. Ultrasonic
properties were determined with a commercial ultrasonic tester at 45 kHz.
Viscoelastic properties were carried out with the Dynamic Mechanical Thermal
Analyzer at frequency ranging ,from 0.01 to 1 00 Hz.
At low frequencies, five types of dielectric mechanism were observed for
different MC such as 1) less than 5%, 2) 5-10%, 3) 11 - 17%, 4) 18-25% and 5)
more than 25%. Dielectric constant increased with temperature for these
frequencies while dielectric loss factor showed minimum value in oven-dry
condition. Dielectric constant and dielectric loss factor varied in the order of
longitudinal> radial 2:. tangential directions. Dielectric data at low frequency are in well agreement with those calculated from equivalent circuit using the
concept of universal capacitor. Three equivalent circuits fitted well for data at
very low MC or for oven-dried wood, MC below fiber saturation point and MC
above fiber saturation point. Activation energies were 0.27eV, 0.34eV and
0.41eV for longitudinal, radial and tangential directions respectively.
At microwave frequencies, dielectric constant and dielectric loss factor
were found to increase with MC ranging from oven-dry up to saturation point.
Dielectric constant also decreased with temperature and dielectric loss factor
exhibited peaks at 10 GHz. Dielectric constants are predicted well by Winner,
Lichteneker and generalized equations with lower value of the exponents.
Above 3 G Hz, dielectric loss factor fitted well with the predicted values using
Winner, Kraszewski, Looyenga or with generalized equations with lower values
of the exponents. Below 3 GHz, dielectric loss factor are unpredictable by these
mixture equations. |
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