Structure and dielectric properties of polypropylene containing multi-element oxide nanofillers

Abstract

Polymer nanocomposites have attracted significant research attention especially in the field of high voltage insulation. The enhancement in the dielectric properties of polymer nanocomposites is led by the unique interphase interactions between nanoparticles and base polymers. However, common single metal oxide nanofillers, which are supposed to improve the dielectric properties of nanocomposites, often led to reduced electrical breakdown strength. Recently, multielement oxide nanofillers have been shown to possess favorable properties compared to single metal oxide nanofillers. Nevertheless, very few systematic studies have been carried out to determine the structure-dielectric property relationship of multi-element oxide nanofillers, especially when added to polypropylene (PP). In the current work, different types of multi-element oxide nanofillers, namely, untreated magnesium aluminate (MgAl2O4), untreated calcium carbonate (CaCO3), and surface-modified calcium carbonate (t-CaCO3), were added to PP to determine their effects on thermal, chemical, structural, and dielectric properties of PP, before and after aging. As such, thermogravimetric analysis, differential scanning calorimetry, Fourier transforms infrared, scanning electron microscopy, dielectric response, AC breakdown, and DC breakdown measurements were performed. The results demonstrated that PP nanocomposites containing MgAhO4 possessed up to 58% lowered breakdown strength than unfilled PP. Adding CaCO3 to PP resulted in up to 43% higher breakdown strength of the nanocomposites compared to PP/MgAhO4 nanocomposites. Notably, PP/t-CaCO3 nanocomposites possessed the highest breakdown strength (up to 45%) among the nanocomposite systems considered. While unfilled PP showed much reduced breakdown strength (up to 27%) after aging, all the nanocomposites demonstrated less detrimental effects on their breakdown strength (up to only 21%) compared to unfilled PP, and that the breakdown strength of PP nanocomposites was generally more predictable after aging. The structure-property relationship governing these dielectric changes is subsequently discussed. This paves the way for the development of future power cable insulation systems based on nanostructured PP technology.