Preparation and properties of KH550-Al₂O₃/PI-EP nanocomposite material

First, 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 epoxy resin (E-51), through thermal imide process. Then, the nanometer alumina (Al₂O₃) modified by the coupling agent, (3-aminopropyl)triethoxysilane (KH550), was doped into the PI-EP polymer matrix, using an in situ sol-gel method to prepare a series of KH550-Al₂O₃/PI-EP nanocomposite materials based on different KH550-Al₂O₃ contents. Fourier transform infrared spectroscopy (FTIR) indicated that in the presence of chemical reaction between poly(amic acid) and epoxy resin, an imide ring was formed, the thermal imidization reaction of the materials was completed and the KH550-Al₂O₃ had doped into the PI-EP polymer matrix. The heat-resistance, dielectric specification and mechanical properties of KH550-Al₂O₃/PI-EP nanocomposite materials were evaluated. The results showed that the decomposition temperatures were ranged between 438 and 450 C, dielectric constant and dielectric loss were in the range of 3.32-3.71 and 1.5 × 10^-3-2.5 × 10^-2, respectively, and they all increased with the increase of KH550-Al ₂O₃ content (0-10 wt%), but the shear strength first increased and then decreased, attained its maximum value of 10.64 MPa at 8 wt%, which was about 119 % higher than that of undoped material. The adhesive forces of nanocomposite materials were all at higher level (one or two levels). Thus, the overall performance of KH550-Al₂O₃/PI-EP nanocomposites was the best when the doping amount of KH550-Al₂O ₃ was 8 wt%. The properties such as high heat-resistance, dielectric properties and ready attachment of impregnating varnish to steel plate with very high strength fully met the necessary requirement.