Chemistry of EPDM vulcanisation
Martin van Duin, LANXESS Elastomers
Terpolymerisation of ethylene, propylene and a diene monomer results in EPDM polymers, which i) have a low glass transition temperature and are amorphous (or very low crystalline) at application temperatures and ii) can be crosslinked, and, thus, can be applied as an elastic rubber. Because of its low level of unsaturation in side groups, EPDM has an excellent resistance against oxygen, ozone, heat and irradiation. The apolar character of EPDM and the very high entanglement density explain the very high acceptance of plasticiser oil and, as a consequence, of carbon black. Combined with the very low density, EPDM compounds are among the most cost-effective rubber products. The apolar character also results in a poor resistance against oil and apolar solvents though. EPDM is the largest, non-tire, synthetic rubber (1100 kton/year) with main applications in outdoor and elevated temperatures, such as automotive sealing systems, window gaskets, roof sheeting, hoses, tires and tubes, mechanical goods, wire & cable and thermoplastic vulcanisates. Crosslinking of EPDM is typically performed with accelerated sulfur (~80%), sometimes with peroxide and, for special applications like thermoplastic vulcanisates, with activated resol systems. The current views on the chemistry of these 3 EPDM vulcanisation systems will be presented, supported by results from experimental studies using state-of-the-art analytical techniques. Recent developments by LANXESS, such as high-VNB-EPDM for enhanced peroxide curing efficiency and the use of zeolites to improve the cure characteristics of resol curing will be highlighted.