Experimental study on space charge and electrical strength of MgO nano-particles/polypropylene composite

The electrical and thermal characteristics of isotactic polypropylene (i-PP) are revealed to be superior to polyethylene (PE), and i-PP is suitable for recycle use as the recent environmental requirement. The electrical characteristics of nano-filler/PP composite are investigated and studied in this paper. Nano-particles of MgO were added to i-PP to prepare nanocomposites for testing of AC/DC breakdown strength (BDs), permittivity, differential scanning calorimetry (DSC) and distribution of space charge. It is found that MgO nano-particals improve AC BDs (breakdown strength) of PP, while DC BDs decreases with loading of nano-MgO. The value of DC BDs is higher than that of AC BDs. The distribution of space charge was investigated by PEA devices, and few volume of space charge appeared in PP under low electrical field (10 kV/mm and 30 kV/mm). A lot of Heter-opolar space charges appeared in PP under electrical field of 50 kV/mm. The volume of space charge decreases with increase of particles' concentration. It is revealed that nano-MgO is considered to have an effect of suppression of charge injection in PP composite. The differential scanning calorimetry (DSC) measurement was carried out to investigate the melting and crystallizing temperature of PP composites. The crystallization temperatures of the PP show a large increase of 4 K as loaded by MgO nano fillers, which indicates that the nanoparticles act as nucleating agents during the crystallization of PP. The electrical capacitance bridge was used to detect the permittivity of composites. The permittivity of sample was measured under frequency of 50 Hz and temperatures of 293, 303, 313, 333, 363 and 383 K. The results show that the permittivity of PP increases slightly with loading of nano-MgO, and it increases first and then decreases with temperature.