Research On Polymer Matrix PTC Composites And Its Magnetic Field Technology

Because of the functions of automatic adjustment, temperature controling, temperature compensation, demagnetization and the protective function against over-heat, over-current and over-voltage, PTC(Positive Temperature Coefficient)composites have been widely used in the fields of electrization, electron, aviation, national defence, correspondence, petrochemical industry et al. polymer matrix PTC matrials with low temperature resistivity, high PTC intensity, easily controlled PTC transition temperature are payed more attention by reaserchers at home and abroad for a long time. A large number of reaserches show that the orientation and the distribution of the filler in the polymer matrix composites can be changed under external field treatment such as stress field, electric field and magnetic field, and the property of the composites is improved greatly. Therfore, the development and preparation of polymer matrix PTC composites with excellent properties under external field have broad prospects.The effct of the type of polyethylene and carbon black, carbon black content and small amount of carbon nanotubes and iron filled in the composites under magnetic field on the room temperature resistivity and PTC characteristics of composites are researched in this paper. The results show that the PTC intensity of conductive carbon black(DCB)/PE composites is lower, and the PTC intensity of ACET/PE composites is higher; the PTC characteristics of ACET/LDPE and ACET/HDPE are better than those of ACET/LLDPE apparently. The room temperature resistivity can be reduced by adding a small amount of DCB in composites, so the PTC intensity can be increased under the condition that the carbonblack content is reduced. The orientation of carbonnanotubes and Fe in the CNTs/ACET/PE composites and Fe/ACET/PE composites will be parallel to the direction of magnetic field when imposed magnetic during the process of hot pressing, and leading to the reduction of the room temperature of the composites. The composites with excellent PTC characteristics through magnetic treatment can be prepared when the ACET content is reduced.