Dielectric Performance of Silica-Filled Nanocomposites Based on Miscible (PP/PP-HI) and Immiscible (PP/EOC) Polymer Blends

Xiaozhen He,Mika Paajanen,Christelle Mazel,Anke Blume,Rafal Anyszka,Hadi Naderiallaf,Kari Lahti,Gabriele Perego,Amirhossein Mahtabani,Eetta Saarimaki,Paolo Seri,Wilma Dierkes,Ilkka Rytoluoto,Minna Niittymaki

doi:10.1109/access.2021.3052517

Abstract

This study compares different polymer-nanofiller blends concerning their suitability for application as insulating thermoplastic composites for High Voltage Direct Current (HVDC) cable application. Two polymer blends, PP/EOC (polypropylene/ethylene-octene copolymer) and PP/PP-HI (polypropylene/ propylene - ethylene copolymer) and their nanocomposites filled with 2 wt.% of fumed silica modified with 3-aminopropyltriethoxysilane were studied. Morphology, thermal stability, crystallization behavior dynamic relaxation, conductivity, charge trap distribution and space charge behavior were studied respectively. The results showed that the comprehensive performance of the PP/PP-HI composite is better than the one of the PP/EOC composite due to better polymer miscibility and flexibility, as well as lower charging current density and space charge accumulation. Nanosilica addition improves the thermal stability and dielectric properties of both polymer blends. The filler acts as nucleating agent increasing the crystallization temperature, but decreasing the degree of crystallinity. Dynamic mechanical analysis results revealed three polymer relaxation transitions: PP glass transition ( $\beta$ ), weak crystal reorientation ( $\alpha 1$ ) and melting ( $\alpha 2$ ). The nanosilica introduced deep traps in the polymer blends and suppressed space charge accumulation, but slightly increased the conductivity. A hypothesis for the correlation of charge trap distribution and polymer chain transition peaks is developed: In unfilled PP/EOC and PP/PP-HI matrices, charges are mostly located at the crystalline-amorphous interface, whereas in the filled PP/EOC/silica and PP/PP-HI /silica composites, charges are mostly located at the nanosilica-polymer interface. Overall, the PP/PP-HI (55/45) nanocomposite with 2 wt.% modified silica and 0.3 wt.% of antioxidants making it $a$ promising material for PP based HVDC cable insulation application with $a$ reduced space charge accumulation and good mechanical properties.

Highlights

IntroductionHigh Voltage Direct Current (HVDC) technology shows advantages of lower dielectric losses and lower costs of long
The nanosilica was selectively located in the PP phase in the PP/EOC/Silica composite, but evenly dispersed in the whole matrix of the PP/PP-HI/Silica
THERMOGRAVIMETRIC ANALYSIS (TGA) results showed that the thermal weight loss of PP/PP-HI is lower at a certain temperature than of the loss of the PP/EOC blend

Summary

Introduction

High Voltage Direct Current (HVDC) technology shows advantages of lower dielectric losses and lower costs of long. He et al.: Dielectric Performance of Silica-Filled Nanocomposites distance power transmission in comparison to High Voltage Alternating Current (HVAC). The insulation material for cables plays an important role in the efficiency of power transmission in HVDC. Polypropylene (PP) as one of the possible insulation materials exhibits a relatively high melting temperature, recyclability and good dielectric properties. PP exhibits low temperature brittleness, limiting its application for HVDC cables. To overcome this shortcoming, most studies for PP as insulation material nowadays are focused on PP-copolymers [4], [5] and PP/polyolefin blends [2], [6]

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Conclusion