EPDM rubber

EPDM rubber (ethylene propylene diene monomer rubber) is a type of synthetic rubber that is used in many applications. Dienes used in the manufacture of EPDM rubbers are ethylidene norbornene (ENB), dicyclopentadiene (DCPD), and vinyl norbornene (VNB). 4-8% of these monomers are typically used. EPDM is an M-Class rubber under ASTM standard D-1418; the M class comprises elastomers with a saturated polyethylene chain (the M deriving from the more correct term polymethylene). EPDM is made from ethylene, propylene, and a diene comonomer that enables crosslinking via sulfur vulcanization. The earlier relative of EPDM is EPR, ethylene propylene rubber (useful for high-voltage electrical cables), which is not derived from any diene precursors and can only be crosslinked using radical methods such as peroxides. As with most rubbers, EPDM is always used compounded with fillers such as carbon black and calcium carbonate, with plasticisers such as paraffinic oils, and has functional rubbery properties only when crosslinked. Crosslinking mainly occurs via vulcanisation with sulfur but is also accomplished with peroxides (for better heat resistance) or phenolic resins. High-energy radiation, such as from electron beams, is sometimes used to produce foams, wire, and cable. Typical properties of EPDM vulcanizates are given below. EPDM can be compounded to meet specific properties to a limit, depending first on the EPDM polymers available, then the processing and curing method(s) employed. EPDMs are available in various molecular weights (indicated in Mooney viscosity ML(1+4) at 125 °C), varying levels of ethylene, third monomer, and oil content. Due to chemical interactions, EPDM degrades when in contact with bituminous material such as EPDM gaskets on asphalt shingles. Relative to rubbers with unsaturated backbones (natural rubber, SBR, neoprene), rubbers with saturated polymer backbones, such as EPDM, exhibit superior resistance to heat, light, and ozone exposure. For this reason they are useful in external harsh environments.