Influence of dispersion methods of inorganic powders on performance of PI/Al2O3 composite films

PI/Al₂O₃ films have been extensively studied due to its´ excellent corona resistance. In this paper, a series of PI/Al₂O₃ films with inorganic content of 16% are prepared via in-situ polymerization method. The Al₂O₃ filler is dispersed by three different methods include mechanical dispersion, sanding mechanical dispersion and ultrasonic dispersion respectively. The films are characterized by scanning electron microscope (SEM). Results show that the Al₂O₃ powders of PI/Al₂O₃ films prepared by sanding mechanical dispersion dispersed most uniform, then the films prepared by ultrasonic dispersion and the films prepared by mechanical dispersion. In addition, the mechanical properties, the breakdown field strength and resistance to corona time of PI/Al₂O₃ films are tested and the regions of breakdown aging and corona resistance aging of the films are characterized by scanning electron microscope (SEM). Test results show that the mechanical properties and corona resistance performance of PI/Al₂O₃ films prepared by sanding mechanical dispersion are optimal, the tensile strength, elongation at break and corona resistance times of PI/Al₂O₃ are 115.4MPa, 12.72% and 332min respectively, the breakdown field strength of the composite films is only 189.84kV/mm and not as good as that of the films(217.5kV/mm) prepared by ultrasonic dispersion. SEM analysis shows that the perforation position of the breakdown aging and corona resistance aging are external and internal of the electrode, respectively. The region of the corona resistance aging area is annular, the perforation of corona aging is within the ring, which indicate that the corona resistance aging is caused by the accumulation of the space charge.