Ethylene-Propylene Rubbers & Elastomers
Properties and Applications Ethylene-propylene rubbers & elastomers (also called EPDM and EPM) continue to be one of the most widely used and fastest growing synthetic rubbers having both specialty and general-purpose applications. Sales have grown to 870 metric tons (or 1.9 billion pounds) in 2000 since commercial introduction in the early 1960’s.Polymerization and catalyst technologies in use today provide the ability to design polymers to meet specific and demanding application and processing needs. Versatility in polymer design and performance has resulted in broad usage in automotive weather-stripping and seals, glass-run channel, radiator, garden and appliance hose, tubing, belts, electrical insulation, roofing membrane, rubber mechanicalgoods, plastic impact modification, thermoplastic vulcanizates and motor oil additive applications.
Fig. 1 – Cross section of EPDM automotive weather-stripping seal showing sponge and dense phase sections
Ethylene-propylene rubbers are valuable for their excellent resistance to heat, oxidation, ozone and weather aging due to their stable, saturated polymer backbone structure. Properlypigmented black and non-black compounds are color stable. As non-polar elastomers, they have good electrical resistivity, as well as resistance to polar solvents, such as water, acids, alkalies, phosphate esters and many ketones and alcohols. Amorphous or low crystalline grades have excellent low temperature flexibility with glass transition points of about minus 60°C. Heat aging resistance up to 130°Ccan be obtained with properly selected sulfur acceleration systems and heat resistance at 160°C can be obtained with peroxide cured compounds. Compression set resistance is good, particularly at high temperatures, if sulfur donor or peroxide cure systems are used. These polymers respond well to high filler and plasticizer loading, providing economical compounds. They can develop high tensile andtear properties, excellent abrasion resistance, as well as improved oil swell resistance and flame retardance. A general summary of properties is shown in Table I below.
Table 1. - Properties of Ethylene-Propylene Elastomers ____________________________________________________________
______________________________ Polymer Properties Mooney Viscosity, ML 1+4 @ 125°C 5-200+ Ethylene Content, wt. %45 to 80 wt. % Diene Content, wt. % 0 to 15 wt. % Specific Gravity, gm/ml 0.855-0.88 (depending on polymer composition)
Vulcanizate Properties* Hardness, Shore A Durometer Tensile Strength, MPa Elongation, % Compression Set B, % Useful Temperature Range, °C Tear Resistance Abrasion Resistance Resilience Electrical Properties
30A to 95A 7 to 21 100 to 600 20 to 60 -50° to +160° Fair to GoodGood to Excellent Fair to Good (stable over wide temp. ranges) Excellent
* Range can be extended by proper compounding. Not all of these properties can be obtained in one compound.
. Producers 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. Wide ranges of grades are available worldwide to provide solutions to many product requirements. Chemistry and Manufacturing Processes Ethylene-propylene rubbers use the same chemical building blocks or monomers as polyethylene (PE) and polypropylene (PP) thermoplastic polymers. These ethylene (C2) and propylene (C3) monomers are combined in a random mannerto produce rubbery and stable polymers. A wide family of ethylene-propylene elastomers can be produced ranging from amorphous, non-crystalline to semi-crystalline structures depending on polymer composition and how the monomers are combined. These polymers are also produced in an exceptionally wide range of Mooney viscosities (or molecular weights). The ethylene and propylene monomers combine to...
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