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.
Properties
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.
Because of chemical interactions, EPDM degrades when in contact with bituminous material such as EPDM gaskets on asphalt shingles.
Uses
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. EPDM in particular exhibits outstanding resistance to heat, ozone, steam, and weather. As such, EPDM can be formulated to be resistant to temperatures as high as 150 °C, and, properly formulated, can be used outdoors for many years or decades without degradation. EPDM has good low-temperature properties, with elastic properties to temperatures as low as −40 °C depending on the grade and the formulation.
EPDM is stable towards fireproof hydraulic fluids, ketones, hot and cold water, and alkalis.
As a durable elastomer, EPDM is conformable, impermeable, and a good electrical insulator. Solid EPDM and expanded EPDM foam are often used for sealing and gasketing, as well as membranes and diaphragms. EPDM is often used when a component must prevent fluid flow while remaining flexible. It can also be used to provide cushioning or elasticity. While EPDM has decent tensile strength, its flexibility makes it inappropriate for rigid parts such as gears, shafts, and structural beams.
It is used to create weatherstripping, seals on doors for refrigerators and freezers (where it also acts as an insulator), face masks for industrial respirators, glass run channels, radiators, garden and appliance hose (where it is used as a hose material as well as for gaskets), tubing, washers, O-rings, electrical insulation, and geomembranes.
A common use is in vehicles, where EPDM is used for door seals, window seals, trunk seals, and sometimes hood seals. Other uses in vehicles include wiper blades, cooling system circuit hoses; water pumps, thermostats, EGR valves, EGR coolers, heaters, oil coolers, radiators, and degas bottles are connected with EPDM hoses. EPDM is also used as charge air tubing on turbocharged engines to connect the cold side of the charge air cooler (intercooler) to the intake manifold.
EPDM seals can be a source of squeaking noise due to the movement of the seal against the opposing surface (and its attendant friction). The noise can be alleviated using specialty coatings that are applied at the time of manufacture of the seal. Such coatings can also improve the chemical resistance of EPDM rubber. Some vehicle manufacturers also recommend a light application of silicone dielectric grease to weatherstrip to reduce noise.
This synthetic rubber membrane has also been used for flat roofs because of its durability and low maintenance costs. As a roofing membrane it does not pollute the run-off rainwater (which is of vital importance for rainwater harvesting).