Ethylene-Propylene Diene (EPDM) Rubber
EPDM rubber (ethylene propylene diene monomer (M-class) rubber), a type of synthetic rubber, is an elastomer which is characterized by a wide range of applications. The E refers to ethylene, P to propylene, D to diene and M refers to its classification in ASTM standard D-1418. The M class includes rubbers having a saturated chain of the polymethylene type. Dienes currently used in the manufacture of EPDM rubbers are dicyclopentadiene (DCPD), ethylidene norbornene (ENB), and vinyl norbornene (VNB).
EPDM rubber is closely related to ethylene propylene rubber (ethylene propylene rubber is a copolymer of ethylene and propylene whereas EPDM rubber is a terpolymer of ethylene, propylene and a diene-component).
EPDM is relatively low density rubber, its density is 0.87. Ethylene propylene rubber has a temperature range of -50°C to +120°/150°C (-60°F to +250°/300°F), depending on the curing system. EPDM exhibits satisfactory compatibility with fireproof hydraulic fluids, ketones, hot and cold water, and alkalis, and unsatisfactory compatibility with most oils, gasoline, kerosene, aromatic and aliphatic hydrocarbons, halogenated solvents and concentrated acids.
The main properties of EPDM are its outstanding heat, ozone and weather resistance. The resistance to polar substances and steam are also good. It has excellent electrical insulating properties.
Major producers and suppliers of EPDM and EPM are Bayer Polymers, Crompton Corp., Exxon-Mobil Chemical Co., DSM Elastomers, Dupont Dow Elastomers, Herdillia, JSR, Kumho Polychem, Mitsui Chemicals, Polimeri Europa, and Sumitomo Chemical Co.
The projected demand for EPDM in India for 2016-17 is around 46 KTA.
EPDM compounds are typically developed with sulfur or peroxide cure system. Peroxide-cured compounds are suitable for higher temperature exposure and typically have improved compression set performance.
EPDM rubber is used in seals (for example it is used in cold-room doors since it's an insulator as well as in the face seals of industrial respirators in automotive paint spray environments, where silicon must be avoided).
EPDM is also used in glass-run channels, radiators, garden and appliance hose, tubing, pond liners, washers, belts, electrical insulation, vibrators, O-rings, solar panel heat collectors, UV protection (for tubular motors in shutters) and speaker cone surrounds.
It is also used as a medium for water resistance in electrical cable-jointing, roofing membranes (since it does not pollute the run-off rainwater, which is of vital importance for rainwater harvesting), geomembranes, rubber mechanical goods, plastic impact modification, thermoplastic, vulcanizates, and many other applications.
Granulated, colored EPDM granules are mixed with polyurethane binders and trawled or sprayed onto concrete, asphalt, screenings, interlocking brick, wood etc. to create a non-slip, soft, porous safety surface for wet-deck areas such as pool decks or playgrounds.
The most common use of EPDM in vehicles is in door seals, window seals, trunk seals, and sometimes hood seals. Frequently these seals are the source of noise due to movement of the door versus the car body due to friction between the EPDM rubber and the mating surface (car painted sheet metal or glass).
This can be alleviated using specialty coatings that are applied at the time of manufacture of the weather seal; such coatings can also greatly increase the chemical resistance of EPDM rubber. Some vehicle manufacturers also recommend a light application of silicone dielectric grease to weather-stripping to reduce noise.
Other uses in vehicles include cooling system circuit hoses where water pumps, thermostats, EGR valves, EGR coolers, heaters, oil coolers, radiators and degas bottles are connected with EPDM hoses; as well as charge air tubing on turbo charged engines to connect the cold side of the charge air cooler (intercooler) to the intake manifold.
EPDM can be manufactured commercially in three major processes, solution, slurry (suspension), and gas-phase.
The Slurry process of polymerizing EPDM is a modification of bulk polymerization wherein the monomers and catalyst system are injected into a propylene filled reactor. The polymerization reaction is immediate and cubs of polymer are formed that are not soluble in the propylene. This process of slurry polymerization reduces the needs for solvents and solvent handling equipment. The low viscosity of the slurry also allows for more stable temperature controlling and easier handling of the product. The process is not limited by solution viscosity, meaning a high molecular weight polymer can still be produced through slurry polymerization without a penalty to production.
The process of solution polymerization is a widely used method which is highly versatile in making a wide range of polymers. In this process, polymerization of the ethylene, propylene and catalyst systems takes place in an excess of hydrocarbon solvent. If the compound requires stabilizers and oils, they are added directly after polymerization. Following this, the solvent and unreacted monomers are flashed of by mechanical devolatilization or by using hot water or steam leaving only the EPDM compound. The remaining polymer, which is in crumb form, is next dried using either mechanical press, drying ovens, or dewatering in screens. From here, the crumb can be formed into bales or extruded into pellets.
Gas-phase polymerization was developed for the manufacturing of ethylene-propylene rubbers. It involves a reactor that consists of a vertical fluidized bed into which the monomers, catalysts and nitrogen in gas form are fed, and solid product is removed. The intense heat of the reaction is removed through the use of circulating gas which also will serve to fluidize the polymer bed. In gas-phase polymerization, solvents are not used thus eliminating the needs for solvent stripping, washing and drying. However, when engaging in this process, continuous injection of a substantial amount of carbon black is necessary. This additive acts as a partitioning aid which prevents the polymer granules from sticking to each other and the reactor walls. To enable rapid mixing, products are made in granular form.