EPM and EPDM rubber

EPM (ethylene-propylene) is a saturated rubber made by copolymerization of ethylene and propylene. Owing to the lack of double bonds, this kind of rubber cannot have cross-links with sulphur or chemicals that release sulphur, but only with organic peroxides.
As to EPDM (ethylene-propylene-diene), it was developed because the peroxidic cross-linking adopted in saturated ethylene-propylene rubber (EPM) has some drawbacks as well. EPDM has additonal double lateral bonds created by a reaction with a “diene”; this makes cross-linking with sulphur and accelerants possible.

Properties

  • The properties of vulcanized products depend above all upon the kind of rubber used, nevertheless they are on the whole quite similar.
  • As a rule cured EPDM products show good resistance to high and low temperatures, ageing and chemicals, good elasticity and good insulation properties
  • Impact strength: 40 to 60%
  • Extensibility: 150 to 500%
  • Heat resistance:
    • EPM with peroxidic cross-linking provides better heat resistance (up to about 150°C)
    • Cured peroxidic EPDM products with suitable composition can withstand water and steam up to 200°C. for a long time without being severely affected..
  • Resistance to low temperatures: up to about -50°C.
  • Gas permeability: quite high, not recommended when this is an issue.
  • Resistence to chemicals:
    • very high thanks to its polymeric chain.
    • Vulcanized EPDM rubber products can withstand::
      Water and hot steam to +130°C, also up to peaks of 200°C.
      Glycol-based brake fluids
      Leaching fluids containing sodium and potassium carbonate (detergents and many organic-inorganic bases)
      Saline solutions and oxidizing agents.
      Hydraulic fluids containing water and glycols
      Hydraulic fluids containing phosphoric acid esthers
      Silcione-based oil and grease
      Many polar solvents such as alcohols, ketones and esthers; Skydrol 500 and 7000
      Vulcanized EPM and EPDM products are not recommended for use with hydrocarbons in general.


Applications

  • The automobile industry is currently the largest consumer of EPDM, employed for instance in spongy rubber gaskets for car doors and boots, seals for windows and headlights, bumpers, hose and gaskets in general.
  • Joints, hose and gaskets for household appliances (washing machines and dishwashers): EPDM is widely used because of its resistance to detergent liquids and solutions and to high temperatures.
  • In electric cables EPDM is also frequenty used because of its good electrical properties (combined with a good resistance to weathering and limited water absorption).



   

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