Enhanced Morphology-Dependent Tensile Property and Breakdown Strength of Impact Polypropylene Copolymer for Cable Insulation.

Kai Yang,Yun Liu,Yitao Liu,Shengtao Li,Zhenghong Jing,Jianying Li,Zhimin Yan,Ye Tian

doi:10.3390/ma13183935

Abstract

The decrease in electrical properties caused by the toughening of polypropylene (PP) is a difficult problem for the modification of PP used for cable insulation. In this research, an isotactic PP, a cross-linked polyethylene (XLPE) and two impact PP copolymers (IPCs) with an ethylene–propylene rubber phase content of 15 and 30% were prepared to assess the possibility of IPCs to be used as cable insulating material. The tensile properties and breakdown strength were evaluated, meanwhile, the rubber phase content dependence of the crystalline structure, morphology and trap distribution were also investigated. Results show that IPCs with a 15% rubber phase content (IPC15) can achieve the simultaneous improvement of elongation at break and breakdown strength compared with isotactic PP, which can be attributed to the special crystalline structure. According to the results of differential scanning calorimetry (DSC) and FTIR, it is proposed that the lamella thickness of IPC15 is maximal and some ethylene segments exist in PP crystals of IPC15 as crystalline structure defects, which is responsible for this enhanced breakdown strength. The morphology results reveal that rubber microspheres are found to coexist with spherulites, which can promote the relative sliding among lamellas under external force and further results in the increase in the elongation at break.

Highlights

Polypropylene (PP)-based thermoplastic insulation has attracted tremendous interest because of its high temperature stability and excellent recyclability in the past
2) The enhanced breakdown strength of IPCs with a 15% rubber phase content (IPC15) is attributed to the impact of lamella thickness e 1.063eV e and crystalline structure defects
The lamellae thickness of IPC15 is larger than isotactic PP (iPP) and impact PP copolymers (IPCs), which e crystalline electron deep trap leads to an elevated breakdown strength

Summary

Introduction

Polypropylene (PP)-based thermoplastic insulation has attracted tremendous interest because of its high temperature stability and excellent recyclability in the past. Compared with traditional cross-linked polyethylene (XLPE) insulation, PP possesses advantages of an increased operating temperature and facile manufacturing processing with reduced costs [1]. The production efficiency of cables insulated by thermoplastic insulation can be boosted by the absence of cross-linking and degassing [2]. Conventional PP cannot be used directly as power cable insulation duo to its high modulus, low flexibility and poor aging resistance [3,4]. Results showed that the melting point and tensile modulus of the copolymer both decreased with the increase in ethylene

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