Precipitated silica improves the physical properties of zinc sulfonated EPDM of high ethylene content Both paraffinic oil and zinc stearate plasticize the silica filled zinc sulfonated EPDM compound. While the plasticizing ability oi zinc stearate is observable only at temperatures above its melting point (> 129 degrees C), that of paraffinic oil is evident both at ambient conditions and at elevated temperatures. The silica filled compound containing both paraffinic oil and zinc stearate show low melt viscosity. The thermoplastic elastomeric nature oi the compound is evident from the retention oi stress-strain properties and melt viscosity even after three cycles of repeated processing.