Comparative study of silica-, nanoclay- and carbon black-filled ethylene propylene diene monomer (EPDM) rubbers treated by ultrasound

The ultrasonic treatment of unfilled EPDM and silica-, nanoclay- and CB-filled EPDM mixtures was carried out using a coaxial ultrasonic extruder at various ultrasonic amplitudes. Rheological properties, morphology, cure characteristics and mechanical properties were measured. The storage and loss moduli and complex dynamic viscosity of untreated and ultrasonically treated silica-filled EPDM mixtures were significantly higher than those of the nanoclay- and CB-filled EPDM mixtures in the frequency measurement range with the Tan Delta being significantly lower than that of the nanoclay-filled EPDM mixtures. The increase of the tensile strength and elongation at break of silica-, nanoclay- and CB-filled EPDM vulcanizates was observed with increasing ultrasonic amplitude and filler loading with the values being 26.5 MPa and 1070% in treated 30 phr silica-filled vulcanizates. The hardness of all samples was slightly decreased with increasing ultrasonic amplitude with the silica-filled EPDM showing the highest values. The minimum torque of filled EPDM mixtures gradually decreased with increasing ultrasonic amplitude. Depending of filler type and loading the maximum torque showed an increase or a decrease with ultrasonic amplitude. The scorch time of silica- and CB-filled EPDM mixtures slightly increased with increasing ultrasonic amplitude. The optimum cure time of the silica- and nanoclay-filled EPDM mixtures gradually increased and the CB-filled mixtures slightly decreased with filler loading. Ultrasonic treatment of the silica-filled EPDM leads to the formation of a transition layer on the surface of agglomerates into which macromolecular chains penetrate.