Correlation between morphology and electrical breakdown strength of the polypropylene/maleic anhydride grafted polypropylene/nano-ZrO₂ ternary system

A ternary system composed of isotactic polypropylene (PP), maleic anhydride grafted polypropylene (PP-g-MAH), and nano-ZrO₂ was designed. To investigate the influence of each composition, we systematically designed orthogonal tests with 25 samples with various PP-g-MAH (0–70 wt %) and nano-ZrO₂ concentrations (0–5 wt %). Microscopic observation showed that the introduction of PP-g-MAH could distinctively benefit the dispersion of nanoparticles. This can be understood by chemical bonds between PP-g-MAH and the nano-ZrO₂ surface, which was evidenced by infrared spectroscopy. Meanwhile, both the crystalline properties and aggregation structures were improved within this ternary system. Macroscopically, a great enhancement of DC breakdown strength (BDS) as high as 43.3% was achieved when the PP-g-MAH concentration was 50 wt % and the nano-ZrO₂ concentration was 0.5 wt %. Moreover, the effects of PP-g-MAH and nano-ZrO₂ were revealed respectively. The increase of nano-ZrO₂ content could cause the first increase and then decrease of BDS. The influence of PP-g-MAH on breakdown strength was obviously shown by the analysis of variance, and the rising PP-g-MAH concentration could lead to the nano-ZrO₂ content with the highest BDS shifted to higher loading, indicating that the modified dispersion of nanoparticles played the dominant role in the breakdown performance improvement.