Relationship between dielectric loss and interphase structure of filled-type polymer composites

Abstract

Polymeric materials or systems in practical use are generally heterogeneous, in which macroscopic or microscopic interfaces exist. Microscopic interfaces formed by filler particles introduced for property modifying purpose should be analysed due to their large volume or surface area. Changes of electrical and mechanical properties of composites are always remarkable when compatibility between fillers and polymer matrix is not good, while the internal process are very complicated. How does the dielectric loss of filled polymers increase when they are applied as insulators? Generally the dielectric responses of a composite system rely on characteristics of each phase and their make-up on circuits. Moreover, there is interfacial polarisation between two different dielectrics under a field, from which results an additional dielectric loss. Changes on dielectric loss tangent of the composite system are difficult to determine because the physical and chemical composition of a transitional region called interphase is still not clear. In the samples of EPR filled with organic and inorganic fillers, remarkable loss increments are observed and are analyzed; and mechanical property measurements are conducted to make clear the interphase condition. By controlling various parameters of each dielectric phase and the mixing, moulding processes for polymer composites with satisfactory dielectric and mechanical properties can be obtained. To evaluate the dielectric loss of filled-type composite system mixed circuits effects and interfacial polarisation effect should be both considered. Interfacial polarisation has very complicated processes, and the relaxation time has a wide-range distribution according to dispersed condition of fillers. Interphase layer between polymers is vague where there is no remarkable interfacial polarisation, newly-emerged polar groups in transitional region contribute to dielectric loss of the composite. However interphase introduced by inorganic filler particle is clear, with filler conductivity more than 10/sup -/9 S/m. Interfacial relaxation occurs under field around 50Hz and causes increased tan /spl delta/; this unwished-for effect is weakened through silane treatment of filler.