Polyethylene/nanoclay specimens containing from 0 to 5% nanoclays were prepared from a commercially available premixed PE/nanoclay masterbatch containing 50% wt of nanoclay. The masterbatch was diluted to the desired concentration by adding PE along with various amounts of compatibilizer in order to achieve the best possible dispersion of the nanoclay platelets. The dielectric response of the compounded samples was investigated using a combination of time and frequency-domain spectroscopy in order to cover a wide frequency window. Both techniques were in good agreement when the time-domain data was transformed into frequency-domain data. Despite their low concentration, the addition of the dispersed nanoclays led to a significant alteration of the material dielectric response in the form of the appearance of various interfacial relaxation processes and an increase of charge carrier transport within the insulation material. Moreover, an onset of nonlinear charge transport process was observed at moderate fields for specimens containing a relatively low level of nanoclays. The high-field breakdown strength was shown to have been improved by the incorporation of the nanoparticles, particularly when the exfoliation was enhanced by the use of a maleic anhydride grafted polyethylene compatibilizer.

This paper evaluates dielectric breakdown measurements according to the ASTM D149-09 standard for various specimen thicknesses and surrounding media. This study was performed on LLDPE/nanoclay with three different surrounding media. Pre-breakdown partial discharge activity was monitored and the electrical field in the breakdown area was computed by FEM modeling.It was observed that the variations of the dielectric breakdown values from the neat polymer to the nanostructured polymers strongly depends on the surrounding medium, a situation which could lead to non-valid conclusions if appropriate care is not taken to select the optimal experimental procedure. Also, the results underscore the influence of the pre-breakdown partial discharge gas generation on the electrical field distribution and the influence of the surrounding medium degradation.To conclude, the ASTM D149 Standard shows a lack of normalization in terms of the surrounding medium parameters and the sample thickness, even though a certain amount of normalization is needed in order to compare breakdown results from one experiment to the other and to improve the understanding of the solid dielectric breakdown phenomena.

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