Explanation of the Compensation Law and the Isokinetic Point in the Electrical Conduction of Crosslinked Polyethylene

Roger Walker,Michael Lanagan,William H Hunter Woodward,Eugene Furman,Qinglin Wu

doi:10.1155/2022/7060337

Abstract

Thermally activated direct current (DC) electrical conductivity in low-density polyethylene (LDPE) is known to be subject to the compensation law. Accordingly, the preexponential factor follows a specific relation with activation energy, reducing overall changes in conductivity. This relationship is governed by the Meyer-Neldel temperature. However, there is no published evidence for a corresponding isokinetic point, a temperature where the conductivity of all LDPE samples is the same. Here, it is determined that the compensation law applies to both DC and alternating current (AC) conduction for LDPE and for crosslinked polyethylene (XLPE) without an observed isokinetic point. The potential origins of compensation in polyethylene are discussed as well as reasons for similarity between LDPE and XLPE. It is observed that prolonged water exposure removed the compensation behavior. Meanwhile, preheating samples in the oven prior to measurements modifies the compensation behavior and reduced the spread around the isokinetic point. It is thus deduced that an isokinetic point can be observed in polyethylene but is obscured by contributions from water and other impurities.

Highlights

Electrical conduction in many polymeric insulators, such as polyethylene, is a thermally activated process
This study shows that, like low-density polyethylene (LDPE), XLPE exhibits the compensation law, which addresses the variations in insulation performance
To create XLPE, 2.1-10 wt% dicumyl peroxide (DCP) was soaked into LDPE in an oven at 55°C

Summary

Introduction

Electrical conduction in many polymeric insulators, such as polyethylene, is a thermally activated process. For many materials including ionic conductors, electronic semiconductors, and polymers, it has been observed that within a family of related materials, or for the same material processed under varying conditions, EA is not constant and is instead related to σ0. This observation is the “compensation law” [1], called as such because the change in σ0 partially compensates for the change in EA, leading to similar conductivity values between samples at certain temperatures.

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Conclusion