Study of dielectric strength in EPDM by nondestructive dynamic mechanical analysis in high electrical field

Abstract

In the present work the value of the degree of the area swept by the polymer chain due to an electrical force for a given mesostructure was related to the corresponding value of the dielectric strength. This value was deduced from the electric inclusion formalism applied to dynamic mechanical analysis (DMA) studies conducted under high electric field, which were performed in commercial ethylene-propylene-diene M-class rubber (EPDM); used for the housing of polymeric electrical insulators. EPDM samples with different arrangements of the polymer chains and crystalline degree, promoted by controlled neutron irradiation were studied. Several characterization techniques, as infrared absorption spectroscopy (IR), differential scanning calorimetry (DSC), positron annihilation lifetime spectroscopy (PALS) and dielectric strength (DS) were also used. The relationship between the DS and the degree of movement of polymer chains promoted by electrical forces coming from the electric field applied in a non destructive test as the DMA was successfully established. In fact, a larger empty space in the sample leads to larger areas swept by the polymer chains during bending under the application of the field strength in the dynamic mechanical analysis tests. Therefore, an increase in the capability of movement of charges occurs, corresponding to smaller dielectric strength values. Crystallinity improves the dielectric strength due to the increase in the internal stresses which decreases the capability of movement of the polymer chains and electric carriers by electric forces.