Preparation, Morphology and Properties of Nano-silica-alumina Co-doped Polyimide Three-layer Composite Films

A series of novel nano-silica-alumina co-doped polyimide (PI/nano-SiO 2 -Al 2 O 3 ) three-layer composite films were prepared via combination of sol-gel process and ultrasonic-mechanical method. The effects of different inorganic phase contents and different Si/Al weight ratio on the properties of composites were investigation. The amination process of PI composite films was analyzed by Fourier transform infrared (FT-IR), and the inorganic phases’ morphology and its distribution in composite films were observed by scanning electron microscopy (SEM). Results indicated that a homogeneous dispersion of SiO 2 -Al 2 O 3 particles was obtained when the inorganic phase content was below 6 wt.%. The thermal and mechanical properties of the three-layer composite films were measured and compared to the pure PI. It was also observed that when Si/Al weight ratio was 4:1 and the total inorganic phase weight content reached 4 wt.%, the composite film had the highest tensile strength, which was 30% higher than pure PI. Moreover, the electric breakdown strength of composite films was examined and its effective factors were analysed.