Study On Performance Of SiO₂/NA-PI Composite Material

Thermosetting polyimide has been widely used in the airspace, aerospace, nuclear power and electric industries for excellent chemistry stability, toughness, wear resistant, inflaming retarding, electric insulation property and other mechanical performance. The research on modified nanometer is seldom reported at insulation adhesive and impregnating varnish. The uses of thermosetting resin have problems of low toughness, short corona resistant time, lower breakdown strength filed on adhesive and impregnating varnish aspect. This restricted its use on high voltage electromotor and frequency conversion system. Then, it is urgent to improve the toughness, to extend anti-corona time and improve the breakdown strength field of thermosetting resin.Composite material (SiO₂/NA-PI) was synthesized with technology of two-phase polymerization, inorganic precursor were methyl triethoxysilane and TEOS respectively, in system of DEDADPM, PMDA and DMAc, and thermal imide method. The system of methyl triethoxysilane and TEOS were A, B respectively.Aggregation structures of composite material were tested with SEM method. Thermal properties, mechanics performance and adhesion were tested with TGA, electronic tensile testing machine and adhesion tester. Electric properties of composites were tested with anti-corona resistant equipment, anti-voltage tester and dielectric spectrometer. The results showed that SiO₂ particles were dispersed in PI resins, diameter was less than 100 nm. Thermal stability of two systems A and B were also increased, thermal decomposition temperation of 8wt%SiO₂/NA-PI was 495.92℃, was 5.72℃higher than pure thermosetting PI. Mechanical properties of two system declined with the increasing of inorganic doping amount, but adhesion of composite materials were at a higher level of hierarchy, in which was first as the doping content of 1% 3%. The corona resistant property of SiO₂/NA-PI composite materials was increased with the increasing of SiO₂ content, corona resistance time reached 41.7h, which (A) 6wt% -SiO₂/NA-PI , breaddown strength of A system was better than that of B system, and were 277% than the standard of silicone impregnating varnish (JB/T3078-1999) and imine epoxy impregnating varnish (JB/T7095-1993). Dielectric constants of two kinds of composite were improved with increasing of SiO₂ content. Dielectric loss was increased with increasing of frequency, dielectric constant and dielectric loss of B system composite slightly higher than that of A system, under the same amount of inorganic doping conditions.