Treeing phenomenon of thermoplastic polyethylene blends for recyclable cable insulation materials

Lunzhi Li,Guanghui Chen,Mingli Fu,Lisheng Zhong,Kai Zhang,Jinghui Gao,Man Xu

doi:10.1063/1.4977718

Abstract

Owing to its good recyclability and low processing energy consumption, non-crosslinked polyethylene blends (e.g. LLDPE-HDPE blends) are considered as one of potential environmental-friendly substitutions for crosslinked polyethylene (XLPE) as cable insulation material. Although extensive work has been performed for measuring the basic dielectric properties, there is a lack of the investigations on the aging properties for such a material system, which hinders the evaluation of reliability and lifetime of the material for cable insulation. In this paper, we study the electric aging phenomenon of 0.7LLDPE-0.3HDPE blending material by investigating the treeing behavior, and its comparison with XLPE and LLDPE. Treeing tests show that the 0.7LLDPE-0.3HDPE blends have lower probability for treeing as well as smaller treeing dimensions. Further thermal analysis and microstructure study results suggest that the blends exhibit larger proportion of thick lamellae and higher crystallinity with homogeneously-distributed amorphous region, which is responsible for good anti-treeing performance. Our finding provides the evidence that the 0.7LLDPE-0.3HDPE blends exhibits better electric-aging-retardance properties than XLPE, which may result in a potential application for cable insulation.

Highlights

INTRODUCTIONXLPE (crosslinked polyethylene) has been used as conventional extruded cable insulation material for its favorable performance of electrical and mechanical properties
XLPE has been used as conventional extruded cable insulation material for its favorable performance of electrical and mechanical properties
We investigate the electric aging phenomenon of non-crosslinked 0.7LLDPE0.3HDPE blends by studying its treeing behavior, which is compared with commercialized XLPE as well as LLDPE insulation material

Summary

INTRODUCTION

XLPE (crosslinked polyethylene) has been used as conventional extruded cable insulation material for its favorable performance of electrical and mechanical properties. In order to obtain the fraction for lamellae with different thickness, we used a differential scanning calorimeter (DSC, TA instruments) to do the successive self-nucleation and annealing (SSA) analysis, which has important applications for the characterization of polymers that crystallize over a broad temperature range and produces better fractionation of qualitatively characterize chain branching distribution than SC (Step-Crystallization).[24] In order to remove the temperature history, the samples were firstly heated to 170◦C for 3min, and cooled to 25◦C They were heated again at the first temperature step T s1 which is selected to be slightly higher than melting point that would be enough to melt all the crystalline regions. By using such a special etching method, the chains with high degree of branching can be dissolved, leaving the portion with high linearity which usually form thicker lamellae

AND DISCUSSION

Findings

CONCLUSIONS