Influence of process conditions and particle dispersion on the ac breakdown strength of polyethylene-aluminium oxide nanocomposites

The voltage level in power transmission systems is increasing in order to transmit energy more efficiently and this requires efficient insulating materials. The dielectric breakdown strength of polymers used as electrical insulation can be increased by the addition of inorganic nanoparticles. A uniform particle dispersion is however important; large agglomerates may have a negative effect on the breakdown strength. The effects of temperature, screw rotation velocity and processing time in a microextruder on the dispersion of neat aluminium oxide nanoparticles in LDPE were studied, and it was possible to obtain an essentially agglomerate-free particle dispersion at optimum extrusion conditions. Smaller particle agglomerates (<; 3 μm) had no significantly negative impact on the AC dielectric breakdown strength. Composites with higher filler fractions (≥ 3 wt.%) containing larger particle agglomerates (>15 μm in diameter) showed a significant reduction in the breakdown strength compared to the neat polymer.