Space charge distributions in EPDM compounds

The formation of space charge in EPDM (ethylene-propylene-diene terpolymer) filled with ATH (alumina trihydrate) or clay has been investigated by measuring charge distributions. It is found that the type and amount of space charge developed in crosslinked EPDM or its compounds is governed by the type of diene in EPDM and the composition of the semicon electrodes. The amount of charge in the EPDM compounds containing 1,4-hexadiene decreases with an increase of ATH content and increases with an increase of clay content. The heat treatment of EPDM compounds in a vacuum oven increases the amount of space charge in them. These features were explained by the effects of low molecular weight molecules present at the surface of fillers. It is found that the homocharge increases as the clay content increases, while EVA decreases the homocharge in the EPDM compounds. Possible reasons for these results are discussed.