| In recent years, with the rapid development of electronics technology,variable frequency motors with extreme energy-saving appeared, so theinsulating materials with excellent corona resistance had been paid moreattention by research scholars from various countries. With the rapiddevelopment of nanotechnology, polymer/nanocomposites have been receivedmore attention gradually, thus providing a new direction for the preparation ofnew insulation materials. Currently, researchers mostly used TiO2, Al2O3, SiO2and other inorganic materials to improve corona resistance properties of organicmaterials, the other properties of the insulating materials are damaged.In this paper,4,4’-diaminodiphenyl ether (ODA) and pyromelliticdianhydride (PMDA) are used as raw materials, PI/Al2O3composite films with16wt%of inorganic content were prepared by in situ polymerization method.The Al2O3filler is dispersed by three different methods including mechanicaldispersion, sanding mechanical dispersion and ultrasonic dispersion respectively.Then under sanding mechanical dispersion conditions, PI/Al2O3/SiO2compositefilms with16wt%content of Al2O3and the different content of SiO2wereprepared by in situ polymerization, using hydrophilic SiO2and hydrophobic SiO2.The microstructures of PI films are characterized by scanning electronicmicroscope(SEM). The analysis results showed that dispersion of inorganicpowders of PI/Al2O3composite films by sanding mechanical dispersion is themost uniform. For PI/Al2O3/SiO2composite films, the dispersion of the inorganicparticles in the PI/Al2O3/SiO2(hydrophilic) films is better than that ofPI/Al2O3/SiO2(hydrophobic) films, when the content of hydrophilic SiO2particles is0.5wt%, the dispersion of the inorganic particles in the films is theoptimal. And the regions of breakdown aging and corona resistance aging of the films are characterized by scanning electron microscope(SEM). SEM analysisshows that the perforation position of the breakdown aging and corona resistanceaging is external and internal of the electrode, respectively. The region of thebreakdown aging is a separate hole, but the region of the corona resistance agingarea is annular, the perforation hole of the corona resistance aging is within thering and the near regions of the hole are not destroyed by corona resistance aging,so the corona resistance aging is due to the accumulation of the space charge andis not caused by electric breakdown.PI/Al2O3composite films are characterized by Fourier Transform InfraredSpectroscopy (FTIR) and X-ray diffraction(XRD), and the mechanical properties,the breakdown field strength and corona resistant time of PI/Al2O3compositefilms also have been measured and analyzed. Results show that the Al2O3powders have no effect on the amination degree of PI films, and the differentdispersion methods do not destroy the crystal of Al2O3powders. The order degreeof PI matrix in PI/Al2O3composite films by sanding mechanical dispersion ishighest. Mechanical properties and corona resistant properties of that are optimal,the tensile strength, elongation at break and corona resistant time of the films is115.4MPa,12.72%,332min respectively. The electrical breakdown fieldstrength of PI/Al2O3composite films by sanding mechanical dispersion is poorand only189.84kV/mm.The hydrophilic and hydrophobic SiO2particles are characterized bytransmission electron microscope(TEM), FTIR and XRD, and the results showthat the particle size of two kinds of powders are similar, the groups on thesurface of that are same, and which are amorphous inorganic material. Themechanical properties, the breakdown field strength and corona resistant time ofPI/Al2O3/SiO2composite films have also be measured and analyzed. Resultsshow that the comprehensive performance of PI/Al2O3/SiO2(hydrophilic) filmswith the0.5wt%content of hydrophilic SiO2is are optimal. The tensile strength,the elongation at break, the breakdown field strength and the corona resistanttime of the films are132.44Mpa,12.64%,211.15kV/mm and378min,respectively. Under the same content of inorganic particles, the mechanicalproperties and corona resistant performance of PI/Al2O3/SiO2(hydrophilic) filmsare superior to that of PI/Al2O3/SiO2(hydrophobic) films, the breakdown field strength of PI/Al2O3/SiO2(hydrophilic) composite films is inferior to that ofPI/Al2O3/SiO2(hydrophobic) films. |
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