Investigation of the dielectric breakdown strength of polymer nanocomposites

Abstract: The aim of this thesis is to investigate the possibility of enhancing the dielectric breakdown strength (DBS) of low density polyethylene (LDPE) with addition of voltage stabilizing additives. In the first part of the thesis, the influence of various process parameters on the alternating current DBS of pure LDPE and LDPE containing either 3 or 30 wt% magnesium oxide nanoparticles was investigated. It was found that the influence of moisture, crystalline structure and process stabilizing additives did not affect the DBS. In the second part of the thesis the effect of five different voltage stabilizing additives was investigated to enhance the DBS. No significant improvement in DBS could be seen for additives mixed with neat LDPE or LDPE nanocomposites by extrusion (typical DBS values ranged between 109-116 kV/mm for neat LDPE). However, the compounding by extrusion resulted in better stability of the breakdown data. A method to swell voltage stabilizing additives into the polymer matrix with solvents have been developed and evaluated. No significant improvements in breakdown strength could be seen for neat LDPE, but the DBS was increased by 15-20 % at low probability of failure for the LDPE nanocomposites. Further work is required to investigate if this increase is significant. It is believed that it is critical to dissolve a higher amount of the voltage stabilizing additives into the polymer matrix. The actual concentrations of the additives need to be quantified with chromatographic methods or infrared spectroscopy.