Characterization of Polypropylene Modified by Blending Elastomer and Nano-Silica.

Wenfeng Liu,Xiaohong Zhang,Shengtao Li,Xiaohong Chi,Lu Cheng

doi:10.3390/ma11081321

Abstract

Polypropylene (PP) contains promising application prospects in thermoplastic cables for high voltage direct current (HVDC) power transmission because of its outstanding thermal and dielectric properties. However, the problem of poor toughness and space charge has restricted the application of pure PP in HVDC cables. In this paper, polyolefin elastomer (POE) and nano-silica were blended thoroughly and added into a PP mixture by a melting method. Scanning electron microscopy (SEM) was employed to observe the dispersion of POE and nanoparticles. Thermal properties were characterized by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Mechanical properties were evaluated by tensile tests. The elastomeric properties of composites were improved as the dispersed POE could transfer and homogenize external mechanical forces. DC breakdown results showed that the fail strength of composite with 10 phr POE and 1 phr nano-silica was obviously enhanced. The pulsed electro-acoustic (PEA) results showed that the injection and accumulation of space charge was increased by the introduction of POE, while it was restrained by the collective effect caused by nano-silica filling. X-ray diffraction (XRD) spectrograms showed that secondary ordered structures existed in the composites of PP, POE, and nano-silica, and that the ordered structure around the nanoparticles contributed to the enhancement of breakdown strength. The mechanical and dielectric properties were modified synergistically, which made the modified PP a propitious insulation material for HVDC cables.

Highlights

The high-voltage direct current (HVDC) system, which requires smaller cables and less loops, has obvious advantages over alter current (AC) systems in long-distance transmission
The PP-based composites with various polyolefin elastomer (POE) and nano-SiO2 content were fabricated by a melting blend method, and samples were evaluated by DC breakdown strength to select the optimum composition
In composites compounded with PP and POE, a micro-scale continuous phases formed when the POE content was more than 10 phr

Summary

Introduction

The high-voltage direct current (HVDC) system, which requires smaller cables and less loops, has obvious advantages over alter current (AC) systems in long-distance transmission. The HVDC system has become an important part of the electrical grid. More reliable and environment-friendly DC cables are required. Cross-linked polyethylene (XLPE) is the currently used insulation material for HVDC cables. XLPE is difficult to recycle due to its thermosetting structure. The problem of space charge caused by HVDC fields makes XLPE less dependable and greatly shortens its service life [1,2,3]. Unlike XLPE, polypropylene (PP) is easy to process and recycle because of its thermoplastic structure. Modified PP, which has excellent dielectric and thermo-mechanical properties, is a relatively ideal substitute for XLPE [4]

Results

Discussion

Conclusion