The effects of Al2O3 contents on the morphology and electrical properties of polyimide/nano-Al2O3 composite films

Polymer-inorganic composite materials, which offer enormous scientific and technological promise in areas ranging from microelectronics to nanobiotechnology, is an exciting area of research. In this paper, a boehmite sol, which used as the precursor of nano-alunima particles, was firstly synthesized by the hydrothermal process using aluminum isopropoxide as the precursor of aluminu and toluene as solvent. Then this obtained hoehmite sol was in situ added into the polyimide (PI) matrix to fabricate the polyimide/Al₂O₃ (PI/Al₂O₃) nano-composite films. The effects of different hoehmite contents on the morphology, mechanical, thermal stability and electrical properties of PI composite films were investigated. Scanning Electrical Microscopy (SEM) results indicated that after the curing process, all the boehmite sol totally changed to the Al₂O₃ nanoparticles and they were homogenously dispersed in the PI matrix without any agglomeration. Thermal Gravimetric Analysis (TGA) showed that the initial decomposition temperature of PI/Al₂O₃ nanocomposite films was slightly increased with the increased of hoehmite sol contents, which meaned that the thermal stability of PI/Al₂O₃ composite films was improved. Moreover, the results of corona resistance tests indicated that the addition of Al₂O₃ nanoparticles greatly improved the corona resistance of PI composite films. When the Al₂O₃ content was 12wt.%, the corona resistance time reached 136 hours, while the pure PI film was only 0.5 hour. This improvement in corona resistance of PI/Al₂O₃ composite films should be attributed to the preventing charge accumulation effect of Al₂O₃ nanoparticles.