Evaluation of Aging in Nanofilled Polypropylene by Surface Discharges

Literature indicates conflicting results on improvement/degradation of electrical characteristics due to introduction of nanofillers into polymers. Since polypropylene has superior electrical, mechanical and thermal properties and has significant utility in electrical industry, this work investigates the effect of nanofiller content on the partial discharge resistance and breakdown strength of the polypropylene films with 0%, 2% and 6% organoclay nanofillers. Since the surface discharges are random in nature, the overall partial discharge behavior is quantified in terms of temporal behavior of the Weibull parameters of the partial discharge pulse amplitude spectra obtained during sample aging and analyzed within the framework of time series analysis. Experiments indicate that the partial discharge characteristics are affected by the percentage of nanofiller content. Microscopic examinations indicate that on exposure to aging by partial discharges, the defect volume decreased in nanofilled polymer and was found to be least in samples where nanofiller content was below the percolation threshold. Profilometric studies indicate that the partial discharge resistance increases with increase in filler content. Results indicate that in fresh unaged samples, the breakdown strength improves with nanofiller content. However, the reduction in breakdown strength due to aging in nanofilled samples is noticeably higher as compared to unfilled samples.