Preparation And Properties Of Al₂O₃Nanometer By Hydrothermal Method Of Modified Polyimide Films

Nano-Al₂O₃has the advantages of high temperature resistance, goodinsulation, good chemical stability, large specific surface area and high thermalconductivity, which is doped into the polyimide film can obviously improve thematerial corona resistance. Polyimide with high thermal stability and high glasstransition temperature can contribute to the stability of nanometer size dispersedparticles with no reunit, and it is very favorable to the synthesis of compositematerial. Nanometer Al₂O₃sol modified polyimide can improve thecomprehensive properties of polyimide.In this paper, firstly the prepared Al₂O₃sol with nanometer scale wassynthesized by the hydrothermal method. Then the nano-Al₂O₃sol/polyamideacid composite glue was prepared by the in-situ method. After the thermalimidization process, the Al₂O₃/polyimide nanometer composite films wereprepared. The microstructure and performances of the Al₂O₃/PI nanometercomposite films were investigated. Scanning Electrical Microscopy （SEM）results indicated that after the curing process, all the boehmite sol totally changedto the Al₂O₃nanoparticles and they were homogenously dispersed in the PImatrix without any agglomeration. Results of the mechanical properties ofAl₂O₃/PI composite films showed that, if the inorganic particle doping content islow, the mechanical properties of the composite film were rather high. However,with the doping content increased, the tensile strength and breaking elongationrate of the composite films were to same degree, lower than that of the pure film.Electrical performance testing results showed that, with the increase of theamount of inorganic particles, the surface resistance and volume resistivity of composite films decreased and all of it were lower than that of the pure film. Thedielectric constant and loss tangent values were higher than the undopedpolyimide film, and with the doped amount increase showed a trend of increase.With the increase of the amount of inorganic particles, composite film breakdownfield strength increased first and then decreased.The thermal stability test of thecomposite films showed that the composite film doped by inorganic particle hadheat stability better than pure membrane. With the doped volume of thecomposite thin films increasing, the thermal stability increased. Moreover, theresults of corona resistance tests indicated that the addition of Al₂O₃nanoparticles greatly improved the corona resistance of PI composite films.When the Al₂O₃content was12wt.%, the corona resistance time reached136hours, which has only0.5hour, nearly300times compared with the pure film.