Prepration And Performance Study Of Novel Thermostable Dielectric Composite Membranes Based On Polybenzimidazole

With the development of modem industry, the demand for miniaturization and large capacity of energy storage materials has become more and more urgent. High dielectric-property polymer composites are of great importance for their good dielectric properties, light quality, easy processing and other excellent performance at the same time. However, common polymer composites can’t be long-term used at high temperature because the matrixes of them usually suffer from poor heat resistance. Polybenzimidazole with high glass transition temperature was chosen as polymer matrix for high dielectric-property polymer composites. Three series high dielectric property composite membranes of PBI/TiO2 composite membranes, PBI/Gn-TiO2 composite membranes and PBI/Ag@TiO2 composite membranes were prepared and corresponding microstructure, crystallization properties, thermal stability and dielectric properties were studied as well. The specific research contents are as follows.(1) PBI/TiO2 composite membranes from blending PBI and TiO2 nanoparticles or modified TiO2 (kTiO2) in different ratios were prepared by the solution casting method and the corresponding properties were studied. PBI was synthesized by a solution polycondensation method under microwave irradiation. Rutile TiO2 nanoparticles were prepared by modified sol-gel method and were modified using 3-triethoxysilylpropylamine. The results show that the nanoparticles are dispersed uniformly in the polymer matrix and all the membranes exhibit excellent thermostability with little weight loss under 450℃. With the increase of TiO2 content, the permittivity of the PBI/TiO2 composite membranes first decrease and then increase, and the dielectric constant of the PBI/TiO2 composites was about 20.5 with the TiO2 content of 20wt% at 1000 Hz. With the addition of kTiO2 nanoparticles, the dielectric permittivity decrease, while the frequency dependence is reduced notably. The loss tangent of the composite membranes remains at a low level.(2) PBI/Gn-TiO2 composite membranes from blending PBI and Gn-TiO2 nanoparticles in different ratios were prepared by the solution casting method and the corresponding properties were studied. PBI was synthesized by a solution polycondensation method under microwave irradiation. Graphite oxide (GO) was prepared by improved Hummer method. Gn-TiO2 was prepared by one pot solvent-thermal method. The results show that Gn-TiO2 is dispersed uniformly in the polymer matrix and all the membranes exhibit excellent thermostability with little weight loss under 500℃. The dielectric permittivity and the loss tangent of the composite membranes show obvious increase at the Gn-TiO2 content of 3wt%, indicating it reach the percolation threshold at this concentration.(3) PBI/Ag@TiO2 composite membranes from blending PBI and Ag@TiO2 nanoparticles in different ratios were prepared by the solution casting method and the corresponding properties were studied. PBI was synthesized by a solution polycondensation method under microwave irradiation. Ag@TiO2 was prepared by one-pot reduction and hydrolysis method. The results show that Ag@TiO2 are dispersed uniformly in the polymer matrix and form net structure. All the membranes exhibit excellent thermostability with little weight loss under 500℃. With the increase of Ag@TiO2 content, the permittivity of the PBI/Ag@TiO2 composite membranes first decrease and then increase at room temperature. The dielectric content and dielectric loss increase slightly under 60℃ and when the temperature is above 60℃ the dielectric constant and dielectric loss of the composite membranes increase significantly with the increasing temperature.