Preparation and properties of PI-EP/SiO2-Al2O3 composite material

In this study, polyimide (PI)-epoxy resin (EP) polymer matrix was prepared from 3,3'-diethyl-4,4'-diamino diphenyl methane (DEDADPM), benzophenone tetracarboxylic acid dianhydride (BTDA) and EP (E-51), through thermal imide process, and then the nano-SiO₂ and Al₂O₃ were doped into the PI-EP polymer matrix with Sol-gel method, prepared a series of different contents of inorganic components nano-composite materials. Morphology characterization and properties of the composite were discussed, including structure, uniformity and dispersion of inorganic phase as well as shear strength and breakdown strength of composite. And influencing factors were composed of the contents and mass ratio of inorganic components. It indicated that imidization of composite was complete in FT-IR spectra, and Si-O-Si and Al-O-Al bonds existed in PI-EP/SiO₂-Al₂O₃ composite material. There were linkages between polyimide matrix and nano-particles. And, the result of X-ray diffraction (XRD) has been seen that crystallinity existed in PI-EP/SiO₂-Al₂O₃ film. Results of diversified test indicated that inorganic contents and mass proportion of inorganic components could influence shear strength and breakdown strength of composite. When the mass ratio of SiO₂/Al₂O₃ was 3:1 and total content of inorganic components reached 5wt% its breakdown strength was the most outstanding and attained 208MV/mm and increased 20% than that of polymer matrix. When the mass ratio of SiO₂/Al₂O₃ was 0:1 and total content of inorganic components reached 5wt% the shear strength of PI-EP/SiO₂-Al₂O₃ was the highest among the samples and reached 11.9 MPa, which was 70% higher than that of PI-EP (7 MPa).