Structure and breakdown property relationship of polyethylene nanocomposites containing laboratory-synthesized alumina, magnesia and magnesium aluminate nanofillers

The emergence of polymer nanocomposites has led to a new field of study in advanced dielectrics. Commonly, a few weight percent of single-metal oxide nanofillers has been added to polymers, and promising dielectric property changes have been found. Nevertheless, contradictory results have also been reported, where the use of single-metal oxide nanofillers has also resulted in degraded breakdown performances. Recently, experimental studies on ceramics showed that multi-element oxide ceramics could have a compact structure with entirely different chemical, mechanical and electrical properties from single-metal oxide ceramics. This approach is, however, less pursued from the perspective of dielectrics. In the current work, the structure and breakdown properties of polyethylene nanocomposites containing laboratory-synthesized single-metal oxide nanofillers, i.e., alumina (Al₂O₃) and magnesia (MgO), and multi-element oxide nanofiller, i.e., magnesium aluminate (MgAl₂O₄) nanofiller were compared. The results showed that the use of MgO resulted in higher breakdown strength of the nanocomposites than the use of Al₂O₃. Significantly, the use of MgAl₂O₄ resulted in much higher breakdown strength of the nanocomposites than MgO and Al₂O₃, and that the breakdown values could be comparable or even higher than the unfilled polyethylene under DC and AC applied fields. Possible mechanisms governing these property changes are discussed.