Temperature and trap distribution dependence of electrical tree growth characteristics in polypropylene/elastomer blends for recyclable cable insulation

Abstract

Polypropylene (PP)/elastomer blends as a promising cable insulation material have to face the challenge of electrical treeing which possibly leads to unexpected insulation failure. In this work, two types of elastomers, i.e. polyolefin elastomer and propylene-based elastomer, have been blended into isotactic PP. Effects of the elastomer content and type on electrical treeing behaviours have been investigated under different ambient temperatures. Isothermal surface potential decay measurement has been performed to explore the influence of trap distribution on the treeing behaviour, scanning electron microscope and differential scanning calorimetry measurements were performed to characterise the structure of blends. It was found that with the increase of elastomer content, the trap energy level was reduced and the shallow trap density was increased, which resulted in the enhancement of the tree growth rate and the decrease in the breakdown time. With the temperature changing from 20 to 100°C, the growth rate tended to be increased except that an anomalous reduction in the rate occurred at 80°C. It is suggested that the compatibility between PP matrix and elastomer plays an important role in determining the morphology of blends, which in turn influences the trap distribution and the temperature dependent treeing behaviours.