New insight on improving electrical strength and toughness of polyethylene blends: Turning point of supramolecular structure

Lunzhi Li,Man Xu,Lisheng Zhong,Yu Wang,Kai Zhang,Jinghui Gao

doi:10.1063/1.5053416

Abstract

We report an effective approach on improving the electrical strength and mechanical impact toughness in polyethylene blends by locating the composition on a submicroscopic supramolecular structure turning point. The designed linear low density polyethylene (LLDPE)-high density polyethylene (HDPE) blends exhibit the enhanced electrical breakdown strength and toughness with the optimal value of E0=95.48kV/mm and G=54.67 kJ·m-2 respectively, which is around 6% and 18% higher than pure LLDPE. The scanning electron microscopic (SEM) investigation and X-ray diffraction (XRD) study show no obvious variation in mesoscopic and microscopic structure with the change of HDPE content. Further differential scanning calorimetric (DSC) study using successive self-nucleation/annealing (SSA) method reveals that the turning point with optimal performance corresponds with a peculiar supramolecular structure with a high density of tie molecules, which enhances the toughness and the electromechanical breakdown strength. Our work provides a new insight on improving electrical strength and toughness for dielectric polymers, and may aid to enhance the electric insulation performance for dielectric materials in power equipment.

Highlights

Dielectric material, which refers to an electrical insulator that can be polarized by an applied electric field, has been found wide applications in energy storage devices and power equipment.[1–6] One of the advantages for such a material is that it exhibits large dielectric strength enabling a high voltage level for equipment
We propose a new insight on improving the electrical strength and toughness of polyethylene blends by manipulating the supramolecular structure
It can be concluded that spherulite structure as well as crystal structure do not vary with the composition, which implies that the structure difference for turning point may exist in their intermediate scale

Summary

INTRODUCTION

Dielectric material, which refers to an electrical insulator that can be polarized by an applied electric field, has been found wide applications in energy storage devices and power equipment.[1–6] One of the advantages for such a material is that it exhibits large dielectric strength enabling a high voltage level for equipment. One of the advantages for such a material is that it exhibits large dielectric strength enabling a high voltage level for equipment. Of interfacial structure: With the addition of nanoparticle fillers, the polymers (known as nanocomposite polymers) form a large amount of interfacial regions,[7,8] which produces traps that scatters the electron or restrict the electron motion, enabling an enhanced dielectric strength.[9,10]. The dielectric strength of different specimens of 400μm was measured by AC breakdown tests at 50Hz with a ramp of 1.5kV/s, and the mechanical toughness was detected by Izod impact tests with a 22J hammer. The following self-nucleation process consists of six circles, each of which was performed by heating the specimens to the corresponding temperature step (132◦C, 127◦C, 122◦C, 117◦C, 112◦C and 107◦C) and kept for 5 min, followed by cooling down to ambient temperature. SSA fractionation curves were obtained by heating the samples to 170◦C with a rate of 10◦C/min

AND DISCUSSION

Findings

CONCLUSIONS