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Ethylene-propylene elastomers (EP elastomers) are the third-largest synthetic rubber consumed worldwide, after styrene-butadiene rubber and polybutadiene rubber. EP elastomers are characterized by their outstanding resistance to oxygen, ozone and heat, making them particularly useful in many applications such as automotive, roofing and power cables. Two basic types of EP elastomer are produced: ethylene-propylene copolymer (EPM), which requires vulcanization by means of free radical generators, and ethylene-propylene terpolymer (EPDM), made by copolymerizing ethylene and propylene with a small amount of a nonconjugated diolefin that is vulcanized in the conventional manner with sulfur or with peroxides. EPDM is estimated to account for 80–85% of total world production of ethylene-propylene elastomers. The following pie chart shows world consumption of EP elastomers in 2004:
Supply was very tight in 2004 and some end users were put on allocation as consumption outstripped production slightly. It is believed that off-grade materials and changes in stocks accounted for the production deficit. Supply is expected to remain tight at least for the next two years because 2005 capacity includes 140 thousand metric tons of metallocene-based plants built by Dow and ExxonMobil, which are primarily for making ethylene/alpha-olefin copolymers. Although they can act as swing capacity for making metallocene-based EPDM, it is difficult or undesirable in practice. Thus, the effective operating rate for making EPDM is estimated at 91% in 2004–2005. Mitsui has announced plans to build a new metallocene-based plant with 75 thousand metric tons of capacity totally dedicated to production of EPDM, but the plant will not come on stream until 2007.
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