Effect Of Magnetic Field On Dielectric Properties And Microstructure Of Polyethylene Matrix Composites

The performance of polymer-matrix composites is closely dependent on their structural morphology, which includs the spatial network structure and arrangement style of polymer molecules, the crystallization of polymers, the distribution of functional fillers, as well as the interfacial state between matrix and functional fillers. As a soft-matter, the typical characteristics of polymer materials are easy to respond to the external field stimulation (including the temperature field, stress field, ultrasonic field, high-energy radiation field, electric field and magnetic field, etc.). meanwhile, filling phases are mostly in micron or nano-scale, so they are at non-equilibrium state in thermodynamics, also, it is sensitive to the effect of external field because of their own physical properties such as hot, electric, magnetic, etc. Therefore, it has becomed an important research direction in the field of composites science and composites preparation by using extral field to prepare and develop new, high-performance polymer matrix composites.Magnetic field is one of the most important physical fields, it can transmit energy to materials non-contactly,change thermodynamics and kinetics conditions during the processes of preparing materials,even directly impact on the migration and matching behaviors of atoms, molecules and ions in materials,thus it has deep and fundamental influence on the organization,micro-structure and properties of materials. This paper applied constant-strength magnetic field on polyethylene(LDPE and LLDPE) and polyethylene-matrix composites in the hot-press-molding process, and studied the effect of magnetic treatment on the microstructure and properties of polyethylene and polyethylene-matrix composites.The results show that the magnetic field treatment makes polyethylene crystallinity increase, which led to the electrical conductivity decreasing; treated by the magnetic field, the electrical conductivities reduce of SiC / LDPE, zinc oxide / LDPE, barium titanate/LDPE composites, and the change degree is more obvious than polyethylene sample; the effect of magnetic field treatment on the trends and the extent of the dielectric constant and loss angle tangent value is not identical, which also related to the performance of inorganic fillers in the system; magnetic field induced and formed the"induce magnetic moment"in the graphite lamellar and carbon nano-tubes, so the graphite lamellar and carbon nano-tubes orientated separately in vertical and parallel magnetic field direction, as a result, after the magnetic field treatment, the conductivity of graphite/ polyethylene reduced, but the conductivity of carbon nano-tubes/ polyethylene increased; and magnetic field treatment resulted in partial discharge quantity and frequency increased.