Silica Surface-Modification for Tailoring the Charge Trapping Properties of PP/POE Based Dielectric Nanocomposites for HVDC Cable Application

Xiaozhen He,Wilma Dierkes,Rafal Anyszka,Ilkka Rytoluoto,Kari Lahti,Mika Paajanen,Eetta Saarimaki,Amirhossein Mahtabani,Anke Blume

doi:10.1109/access.2020.2992859

Abstract

This paper focuses on novel insulation polypropylene/poly(ethylene-co-octene) (PP/POE) nanocomposites for High Voltage Direct Current (HVDC) cable application. The composites contain silica modified by a solvent-free method using silanes differing in polarity and functional moieties. Thermogravimetric Analysis and Fourier Transform Infrared Spectroscopy showed that the solvent-free method is an effective way to modify silica by silanes. Silica/PP/POE nanocomposites were prepared in a mini twin-screw compounder, and the effect of silica on crystallization, dispersibility and dielectric properties of the samples was investigated. Differential Scanning Calorimetry results showed that the unmodified and modified silicas acted as nucleation agents and increased the onset of the crystallization temperature of the polymeric matrix. Scanning Electron Microscopy images showed that the silica is mostly located in the PP phase matrix. For the PP/POE nanocomposites filled with unpolar silica, a higher trap density (measured by Thermally Stimulated Depolarization Current, TSDC) was found; this might be caused by the larger interfacial area due to a better dispersion of the unpolar silica in the polymeric matrix. Polar silicas introduce deeper traps than the unpolar ones, which is most likely due to the hetero-atom introduction. Nitrogen atoms were found to have the strongest effect on the charge trapping properties. According to these results, amine-modified silica is a promising candidate for PP/POE nanocomposites for HVDC cable applications.

Highlights

Thermoplastic dielectric composites containing nanofillers have attracted a lot of interest in the field of high voltage insulation field [1]–[3]
A catalyst successfully accelerates the silica surface modification. The efficiency of this method was supported by TGA, Fourier Transform Infrared Spectrometry (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) elemental mapping measurements
Based on the TGA results, the modification of the silica surface assisted by an acid catalyst is more stable than the one achieved by a base catalyst

Summary

Introduction

Thermoplastic dielectric composites containing nanofillers have attracted a lot of interest in the field of high voltage insulation field [1]–[3]. It is widely accepted that the large interface formed between a nanofiller and a polymer matrix plays a critical role in the high voltage dielectric properties of nanocomposites [4]–[6]. One of the general problems in the preparation of nanocomposite preparation is to achieve good dispersion of the nanofillers in the polymer matrix. The associate editor coordinating the review of this manuscript and approving it for publication was Boxue Du. reported that the dc conductivity of LDPE increases remarkably with higher nanofiller loading (>3 phr) than the one filled with a lower amount of nanofiller (1 to 3 phr) duo to extensive nanofiller agglomerate formation [7].

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Conclusion