The effects of the partial replacement of silica or calcium carbonate (CaCO3) by bentonite
(Bt) on the curing behaviour, tensile and dynamic mechanical properties and morpho-logical characteristics of ethylene propylene diene monomer (EPDM) composites were
studied. EPDM/silica/Bt and EPDM/CaCO3/Bt composites containing five different EPDM/
filler/Bt loadings (i.e., 100/30/0, 100/25/5, 100/15/15, 100/5/25 and 100/0/30 parts per
hundred rubber (phr)) were prepared using a laboratory scale two-roll mill. Results show
that the optimum cure (t90) and scorch (tS2) time decreased, while the cure rate index (CRI)
increased for both composites with increasing Bt loading. The tensile properties of EPDM/
CaCO3/Bt composites increased with the replacement of CaCO3by Bt from 0 to 30 phr of Bt.
For EPDM/silica/Bt composites, the maximum tensile strength and Ebwere obtained at a Bt
loading of 15 phr, with enhanced tensile modulus on further increase of Bt loading. The
dynamic mechanical studies revealed a strong rubber-filler interaction with increasing Bt
loading in both composites, which is manifested by the lowering of tan dat the glass
transition temperature (Tg) for EPDM/CaCO3/Bt composites and tan dat 40
C for EPDM/
silica/Bt composites. Scanning electron microscopy (SEM) micrographs proved that
incorporation of 15 phr Bt improves the dispersion of silica and enhances the interaction
between silica and the EPDM matrix.