EPDM

Introduction to EPDM Rubber

EPDM, or Ethylene Propylene Diene Monomer rubber, is a terpolymer synthesized from ethylene (40-80%), propylene (20-60%), and a small amount of diene monomer (e.g., ethylidene norbornene, dicyclopentadiene, or vinyl norbornene, typically 2-10%) to enable sulfur vulcanization. It was first commercialized in the 1960s as an alternative to natural rubber for applications requiring superior environmental stability. The diene content allows cross-linking, while the ethylene-propylene backbone provides flexibility and durability. EPDM can be produced via solution or suspension polymerization and is often compounded with fillers like carbon black or silica, oils, and antioxidants. Variations include oil-extended EPDM for improved processing and high-ethylene grades for better green strength. It's available in solid, sponge, or foam forms.

 

Characteristics of EPDM Rubber

EPDM offers a unique combination of properties, particularly excelling in environmental resistance. Here are its key characteristics:

  1. Mechanical Properties: EPDM has moderate tensile strength (7-20 MPa), high elongation at break (300-600%), and good tear resistance. It exhibits excellent flexibility and resilience over a wide temperature range, with low compression set, making it suitable for sealing applications. However, it may require reinforcement for high-abrasion uses.
  2. Chemical Resistance: Outstanding resistance to water, steam, polar solvents (e.g., alcohols, ketones), dilute acids, alkalis, and oxidizing agents. It's highly resistant to ozone, UV radiation, and weathering due to its saturated backbone. However, EPDM has poor resistance to hydrocarbons, oils, and non-polar solvents, which can cause swelling.
  3. Thermal Properties: EPDM performs well in a broad temperature range of -50°C to +150°C (or up to +175°C for peroxide-cured grades). It maintains elasticity at low temperatures without crystallization and resists heat aging effectively.
  4. Durability and Aging: Superior long-term stability in outdoor environments, with minimal degradation from ozone or UV exposure. It has good electrical insulation properties and low water absorption. Flame resistance is poor unless formulated with halogenated additives.
  5. Processing and Cost: Easy to process via extrusion, calendering, injection, and compression molding. It mixes well and has good shelf life. EPDM is cost-effective compared to specialty rubbers like silicones or fluorocarbons, though more expensive than general-purpose ones like SBR.
  6. Other Properties: Low gas permeability, good adhesion to metals (with primers), and compatibility with water-based systems. It can be vulcanized with sulfur, peroxides (for better heat resistance), or radiation. Specific gravity is low (around 0.86-0.88), contributing to lightweight applications. It's odorless and can be colored easily.

In formulations, EPDM is often blended with other rubbers (e.g., NR for better tack or NBR for partial oil resistance) and filled to optimize cost and performance.

 

Applications of EPDM Rubber

EPDM's weatherproof nature makes it ideal for outdoor and sealing applications across various industries:

  1. Automotive Sector: Used in weatherstripping, window seals, door seals, radiator hoses, and brake components for its durability against heat, ozone, and fluids like coolants.
  2. Construction and Roofing: The primary material for single-ply roofing membranes, pond liners, and geomembranes due to its waterproofing and UV resistance. It's also in expansion joints and seals for buildings.
  3. Electrical Insulation: In cable jackets, grommets, and insulators for outdoor power lines and appliances, leveraging its dielectric strength and weather resistance.
  4. Hoses and Tubing: For garden hoses, washing machine hoses, and industrial tubing handling water or mild chemicals.
  5. Seals and Gaskets: In HVAC systems, appliances, and plumbing for O-rings, gaskets, and diaphragms that require long-term sealing without oil exposure.
  6. Other Uses: Vibration dampers in machinery, playground surfaces, conveyor belts, and solar panel seals. It's also in consumer products like wiper blades and sports equipment.

EPDM is environmentally friendly, recyclable, and produced in billions of pounds annually worldwide. Ongoing developments include bio-based EPDM and enhanced flame-retardant grades.