Polyethylene nanodielectrics: The effect of nanosilica and its surface treatment on electrical breakdown strength

The topic of polymer nanocomposites remains an active area of research in terms of potential applications for dielectric materials. Although more than a decade has passed since these systems were first considered as dielectric materials, the precise effects of incorporating nanofillers into different polymers are yet to be confirmed. This paper reports on an investigation into the AC and DC breakdown behaviours of nanofilled polyethylene. A blend of low density and high density polyethylene was selected as the matrix while the chosen nanofiller was nanosilica; different nanofiller loading levels (2 wt%, 5 wt% and 10 wt%) and surface chemistries (untreated and silane treated) are discussed. The surface chemistry of the treated materials was characterised by Fourier transform infrared spectroscopy while the lamellar morphology and dispersion state of the final nanocomposites was determined by scanning electron microscopy (SEM). Breakdown results show that the introduction of 2 wt% or 5 wt% of nanosilica does not have a significant effect on the AC breakdown response and that this applies to both the untreated and treated nanosilica. In both cases, the AC breakdown strength was commensurate with that of the unfilled polyethylene. However, where severe clustering occurred, as evinced from SEM micrographs, the AC breakdown strength was found to be reduced significantly. Meanwhile, in DC breakdown testing, increasing the amount of untreated nanosilica was found to reduce the DC breakdown strength of the polyethylene. In contrast, surface treatment of nanosilica increased the DC breakdown strength compared with samples containing equivalent amount of untreated nanosilica.