Performance Study On Thermosetting Polyimide Modified By Inorganic Nano-alumina

Polyimide (PI) that serves as a typical kind of engineering polymer material has been used widely in the aerial, martial and electric industries, because of its outstanding characteristics, such as excellent thermal stability, relatively high tensile strength and modulus, low thermal expand coefficient, preminent insulation capability and solvent resistance. However, as high polymer it has inferior corona-resistance property, which limits its application in the fields of high voltage electromotor and variable frequency adjusting speed. The application of organic-inorganic nano composites in the aspect of modification demands high developmet of PI nano composite material too.The thermosetting polyimide material was prepared from 3,3'-diethyl-4,4'-diamino diphenyl methane (DEDADPM), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) and nadic anhydride (NA), and chemical imide process was used. Alumina was added by reverse sequence, via Sol-gel method, then A-172 was added, and nano-composite material was solidied at some temperature grades at last.The chemical structure, aggregation structure and the thermal properties of the composite material were respectively characterized by Fourier Transform Infrared Spectroscope (FT-IR), Atomic Force Microscope (AFM), Scanning Electronic Microscope (SEM), X-ray Diffraction(XRD), Thermogravimetric Analysis (TGA), and their electric properties were characterized by corona discharge measuring equipment and dielectric spectrometer. All the results indicated that Al2O3 particals spreaded uniform in the PI resin matrix, and the two phase interface became very faint, when the amount of alumna was 16wt%. The adding of A-172 make the inorganic nano particles dimensions minish, spread uniform, reunite decrease, distribution of particles diameter narrow. When the amount of alumna was 16wt%, the thermal decomposition is 16.75℃higher than that of pure PI. The thermal decomposition temperature of BTDA-PI was 482.88℃, the thermal decomposition temperature of PMDA-PI was 472.56℃, the thermal decomposition temperature of BTDA-PI was higher than that of the PMDA-PI very much. The corona-resistant lifespan of pure PI material is 11 hours, as the amount of alumina increased, the corona-resistant property of the composite material increased greatly, and that of the PI film with 16wt% amount of alumina was 165 hours, 14 times longer than that of pure material. At all test frequencies, the dielectric constant and the dielectric loss of the PI composite growed with the amout of alumina increased. The dielectric constant and dielectric loss of BTDA-PI were higher than that of the PMDA-PI.