A study of dielectric relaxations in filled ethylene propylene copolymers

Date of Completion

January 1993


Chemistry, Polymer|Physics, Condensed Matter




The addition of fillers has long been used to improve both the mechanical and electrical properties of polymers. While mechanical properties have been well investigated, only recently has more attention been paid to the effect of fillers on electrical properties. The main objective of this work is to study charge relaxation in filled ethylene propylene copolymer. Ethylene propylene rubber (EPR) copolymer is a polymer which is widely used as insulation in medium and high voltage cable. This EPR insulation is highly filled and can have as many as 20 additives. Although the major effect of these additives on mechanical performance is known the effect on the dielectric behavior is not well understood. Thermally Stimulated Discharge Current (TSDC) measurements and Time Domain Dielectric Spectroscopy (TDDS) are employed to characterize the dielectric behavior of clay (kaolin) filled ethylene propylene rubber (EPR) copolymer. The TSDC results show two peaks at $-30\sp\circ$C and $50\sp\circ$C.^ The low temperature peak is affected by the type of base polymer and is attributed to the motion of polymer chain segments. The high temperature peak is caused by the addition of the clay filler and shows dipole behavior. This peak is thought to be due to a distribution of dipole relaxations caused by the polarization at the clay/polymer interface. This peak can be described using Maxwell-Wagner interfacial effects where the polarization is dependent on the particle shape. The TDDS results show a loss peak in the low frequency region (0.001 Hz) which is also attributed to the interfacial polarization introduced by the clay. Although bulk interfacial effects are thought to be the main mechanism which causes the polarization, the results have also indicated that surface ions on the clay filler will affect the polarization. The effect of silane treated clay, ion exchange of the clay and the effect of adding red lead (an ion scavenger) strongly suggests that ion motion and type of ion will affect this mechanism. ^