Dielectric Properties of Wood-Polymer Composites: Effects of Frequency, Fiber Nature, Proportion, and Chemical Composition

Chedly Bradai,Ahmed Elloumi,Imen Elloumi,Ahmed Koubaa,Wassim Kharrat

doi:10.3390/jcs5060141

Abstract

The characterization of the dielectric properties of wood–polymer composites (WPCs) is essential to understand their interaction with electromagnetic fields and evaluate their potential use for new applications. Thus, dielectric spectroscopy monitored the evolution of the dielectric properties of WPCs over a wide frequency range of 1 MHz to 1 GHz. WPCs were prepared using mixtures of different proportions (40%, 50%, and 60%) of wood and bark fibers from various species, high-density polyethylene, and maleated polyethylene (3%) by a two-step process, extrusion and compression molding. Results indicated that wood fibers modify the resistivity of polyethylene at low frequencies but have no effect at microwave frequencies. Increasing the fiber content increases the composites’ dielectric properties. The fibers’ cellulose content explains the variation in the dielectric properties of composites reinforced with fibers from different wood species. Indeed, composites with high cellulose content show higher dielectric constants.

Highlights

IntroductionDielectricspectroscopy spectroscopymeasurement measurementconsists consistsofofplacing placingaa dielectric dielectric between between two two electrodes, applying aa sinusoidal frequency to to thethe terminals of the two electrodes, sinusoidalvoltage voltageofoffixed fixed frequency terminals of the electrodes, and measuring the resulting impedance and phase shift of the induced current
The results showed that the dielectric constant and resistivity are significantly affected by the interaction between fiber type and frequency
This study investigated the dielectric properties of High-density polyethylene (HDPE) composites reinforced with wood and bark fibers

Summary

Introduction

Dielectricspectroscopy spectroscopymeasurement measurementconsists consistsofofplacing placingaa dielectric dielectric between between two two electrodes, applying aa sinusoidal frequency to to thethe terminals of the two electrodes, sinusoidalvoltage voltageofoffixed fixed frequency terminals of the electrodes, and measuring the resulting impedance and phase shift of the induced current. Two electrodes, and measuring the resulting impedance and phase shift of the induced. The electrical voltage u(t) applied to the dielectric material has a low amplitude U1 current. Electrical voltage u(t)(Equation applied to the dielectric material has a low amplitude U1 and a pulsation equal to 2πf (Equation (1)). (t) = Re (U*(iωt)), (1) where U* = U1 This voltage induces a current i(t) of the same pulse ω. Since the material is not a perfect dielectric (purely capacitive), there is a phase shift φ 6= π/2 between u(t) and i(t) perfect dielectric (purely capacitive), there is a phase shift φ ≠ π/2 between u(t) and i(t)

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Results

Conclusion