Investigation on Electrical Properties of Solid Polymer Sheets (HDPE AND LDPE) at Audio Frequency Range

doi:10.26565/2312-4334-2021-2-10

Abstract

Two different groups of solid polymer sheets: low density polyethylene (LDPE) sample of thickness 0.006 cm and 0.007 cm along with high density polyethylene (HDPE) sample of the thickness of 0.009 cm, 0.010 cm were taken in this work. The measurement of electrical properties such as dielectric constant, ε' and dielectric loss, ε'' for LDPE and HDPE polymer sheets have been measured using a dielectric cell. The dielectric cell has been fabricated which consists of two circular parallel plates of pure stainless steel each of 5 cm diameter and 2 mm thickness. An impedance bridge (GRA 650A) was used for measurement of capacitance, C, and dissipation factor, D in the audio frequency (AF) range, 100 Hz to 10 kHz. Different samples were loaded in between the two plates of the cell and the capacitance as well as the dissipation factor were estimated from the dial readings of the bridge. Effect of frequency variation on ε', ε'', relaxation time, τ , dissipation factor, tanδ and ac conductivity, σ were also discussed at audio frequency range. The complex permittivity, ε*, related to free dipole oscillating in an alternating field and loss tangent, tanδ were calculated. The frequency-dependent conductivity, dielectric behavior, and electrical modulus, both real (M') and imaginary (M") parts of LDPE and HDPE have been studied in this work. The values of the real part of the electrical modulus (M') did not equal to zero at low frequencies and it is expected that the electrode polarization may develop in both sheets. These findings reveal an increased coupling among the local dipolar motions in a short-range order localized motion. The analysis of real (ε') and imaginary (ε'') parts of dielectric permittivity and that electrical modulus real (M') and imaginary (M") parts signify poly dispersive nature of relaxation time as observed in Cole-Cole plots.

Highlights

Where is the dielectric constant of the material a dimensionless property of the material between the two plates and 0 is the permittivity of free space
If a loss-free dielectric is considered in an alternating electric field, there would be no dissipation of energy, and charging voltage and current in a capacitor would be 90° out of phase
When subjected to an alternating field, the polar molecules of a system rotate towards an equilibrium distribution in molecular orientation with corresponding dielectric polarization

Summary

Introduction

Where is the dielectric constant of the material a dimensionless property of the material between the two plates and 0 is the permittivity of free space. The dielectric constant is conveniently expressed as the ratio of the capacitance of the capacitor with the material in place to its capacitance with vacuum (or air, for which =1.0005 at 20°C) between the plates. If a loss-free dielectric is considered in an alternating electric field, there would be no dissipation of energy, and charging voltage and current in a capacitor would be 90° out of phase. Due to either very large size of the polar molecule or high frequency of the alternating field, the rotating motion of the molecule may not be sufficiently rapid for attaining equilibrium, and the polarization acquires a component out of phase with the electric field [15,16]. The problem reduces to the measurement of capacitance of a capacitor with and without the dielectric medium for which is calculated. With measured values of and at a number of frequencies above the glass transition temperature, the ColeCole plot ( ~ ) can be drawn

Methods

Results

Conclusion