EPDM properties
Ethylene-propylene-diene rubber (EPDM) is a synthetic elastomer of the M class, characterized by its fully saturated polymethylene backbone. This structure gives it exceptional resistance to heat, oxidation, ozone, and weathering, properties that make it one of the fastest-growing and most versatile synthetic rubbers, with applications ranging from specialty to general-purpose. Its polymerization parameters allow the design of tailor-made grades for demanding processing and performance requirements, from automotive seals to waterproofing membranes in construction.
Chemical composition
Section titled “Chemical composition”EPDM is a terpolymer of ethylene, propylene, and a non-conjugated diene that provides unsaturation in the side chains to allow sulfur vulcanization. The most common dienes are ethylidene norbornene (ENB), dicyclopentadiene (DCPD), and vinyl norbornene (VNB). The ethylene content determines crystallinity and mechanical properties, while the diene controls crosslink density and cure rate. Its diene-free counterpart, ethylene-propylene rubber (EPM), lacks side unsaturations and can only be crosslinked using peroxides or high-energy radiation.
| Component | Typical range (wt%) | Main function |
|---|---|---|
| Ethylene | 45 – 80 % | Provides crystallinity, mechanical strength, and reinforcement load capacity |
| Propylene | 20 – 55 % | Imparts amorphous character and low-temperature flexibility |
| Diene (ENB, DCPD, VNB) | 0 – 15 % * | Introduces side unsaturation for sulfur vulcanization |
| Pure polymer density | 0.855 – 0.88 g/cm³ (depending on composition) | — |
- Commercial EPDM grades typically contain between 2 % and 12 % diene; the EPM variant contains 0 % diene.
Mechanical properties
Section titled “Mechanical properties”The mechanical properties of EPDM depend critically on the cure system used and the compound formulation (type and amount of fillers, plasticizers, and protective agents). Conventional sulfur accelerator systems yield heat aging resistance up to 130 °C / 266 °F, while peroxide-cured compounds achieve stability up to 160 °C / 320 °F and significantly lower compression set values at high temperature. Incorporating reinforcements such as carbon black enables high tensile strength, tear strength, and abrasion resistance.
| Property | Typical value (vulcanized) | Units |
|---|---|---|
| Shore A hardness | 30 – 95 | Shore A |
| Tensile strength | 7 – 21 MPa / 1015 – 3045 psi | MPa / psi |
| Elongation at break | 100 – 600 % | % |
| Compression set (22 h / 70 °C) | 20 – 60 % | % |
| Tear resistance | Fair to Good | Qualitative |
| Abrasion resistance | Good to Excellent | Qualitative |
| Resilience | Fair to Good (stable over wide temperature range) | Qualitative |
The full range of properties cannot be obtained in a single compound; a trade-off balance between stiffness, elasticity, tear resistance, and compression set is required.
Physical properties
Section titled “Physical properties”Amorphous or low-crystallinity grades exhibit excellent low-temperature flexibility, with elastic behavior down to −40 °C / −40 °F or lower depending on the formulation. Being non-polar elastomers, they have good electrical resistivity and low water absorption, although density increases significantly with the addition of mineral fillers or carbon black. The appearance of the vulcanized compound is typically black and non-transparent when carbon black is present, but non-black pigmented formulations also show good color stability outdoors.
| Property | Typical value | Units |
|---|---|---|
| Compound density | 0.90 to > 2.0 (depending on filler) | g/cm³ |
| Water absorption (24 h / 23 °C) | Very low (< 0.5 %) | % |
| Gas permeability | Medium-low | Qualitative |
| Color | Black (with carbon black) or customizable | — |
Thermal properties
Section titled “Thermal properties”The saturation of the main chain gives EPDM superior thermal resistance compared to unsaturated rubbers such as natural rubber (NR) or styrene-butadiene rubber (SBR). It can operate continuously in hot air within a range that spans from sub-zero temperatures to environments near 150 °C / 302 °F, and can withstand brief peaks up to 160 °C / 320 °F with appropriate formulations. The glass transition temperature is around −54 °C / −65 °F, ensuring elasticity even in cold climates.
| Property | Typical value | Units |
|---|---|---|
| Minimum service temperature | −50 to −40 (depending on grade) | °C / °F |
| Maximum service temperature (continuous) | 130 – 150 (up to 160 with peroxide) | °C / °F |
| Glass transition temperature (Tg) | −54 | °C / °F |
| Coefficient of linear thermal expansion | 160 | μm/(m·K) / μin/(in·°F) |
Electrical properties
Section titled “Electrical properties”Thanks to its non-polar nature and the ability to formulate it with high-resistivity fillers, EPDM behaves as an excellent electrical insulator. It is widely used in cable sheathing and insulation for low and medium voltage, both in indoor and outdoor applications, where its resistance to moisture and treeing gives it an advantage over other dielectrics.
| Property | Value / Classification |
|---|---|
| Dielectric strength | High |
| Volume resistivity | Excellent |
| Surface resistivity | Excellent |
| Behavior in humid environments | Good (low water absorption) |
Chemical resistance
Section titled “Chemical resistance”The saturated hydrocarbon backbone and the absence of double bonds in the main chain give EPDM outstanding resistance to polar media and atmospheric agents. It withstands hot and cold water, steam, dilute acids, alkalis, ketones, alcohols, phosphate esters, and HFC-type fire-resistant hydraulic fluids. However, as a non-polar hydrocarbon, it swells significantly in contact with mineral oils, fuels, aliphatic and aromatic solvents, and asphalt bitumens, limiting its use in applications requiring hydrocarbon resistance.
| Medium | Behavior |
|---|---|
| Water / steam | Excellent resistance |
| Dilute acids and alkalis | Excellent resistance |
| Ketones and alcohols | Good resistance |
| Phosphate esters | Good resistance |
| Brake fluids (DOT 3, DOT 4) | Compatible (typical application) |
| Mineral oils and fuels | Not resistant (high swelling) |
| Aromatic and aliphatic solvents | Not resistant |
| Bituminous materials | Degradation by chemical interaction |
Applications by industry
Section titled “Applications by industry”The versatility of polymer design and its exceptional weather resistance have extended the use of EPDM to virtually all industrial sectors requiring a durable elastomer for outdoor applications or in contact with water and steam. The automotive and construction industries together account for more than 60% of global demand, followed by electrical, appliance, and consumer goods applications.
| Industry | Representative applications |
|---|---|
| Automotive | Weatherstrips and seals for doors, windows, and trunks; glass run channels; radiator, heater, and turbocharger hoses; gaskets and seals in cooling systems; extruded profiles |
| Construction | Waterproofing membranes for roofs (EPDM roofs); expansion joints; weathertight profiles for facades and windows; geotextile sheets |
| Electrical / Electronics | Insulation and sheathing for low and medium voltage cables; watertight connectors and bushings; terminal encapsulations |
| Appliances | Hoses for washing machines and dishwashers; appliance gaskets; parts in contact with hot water and steam |
| General industrial | Garden and agricultural hoses; transmission belts; diaphragms and membranes; molded technical parts; impact modification of plastics (PP/EPDM) |
| Additives | Viscosity index improver in engine oils (predominantly EPM) |
Comparison with similar materials
Section titled “Comparison with similar materials”Compared to other general-purpose synthetic elastomers, EPDM stands out in weather resistance, ozone resistance, and hot water resistance, as well as excellent dielectric behavior. The following table compares its key attributes with those of other rubbers used in similar applications (NBR, CR, SBR, and VMQ). The main trade-off is its poor resistance to oils and fuels, for which NBR or FKM are preferred.
| Property | EPDM | NBR | CR (Neoprene) | SBR | VMQ (Silicone) |
|---|---|---|---|---|---|
| Service temperature (°C) | −50 to +150 | −30 to +100 | −35 to +90 | −40 to +110 | −50 to +200 |
| Ozone / weather resistance | Excellent | Poor | Good | Poor | Excellent |
| Dry heat resistance (air) | Very good (up to 150 °C) | Fair (up to 100 °C) | Good (up to 90 °C) | Fair | Excellent |
| Mineral oil resistance | Poor | Excellent | Fair-Good | Poor | Poor (except FVMQ) |
| Low-temperature flexibility | Excellent (−50 °C) | Good (−30 °C) | Good (−35 °C) | Good (−40 °C) | Excellent (−50 °C and lower) |
| Electrical properties | Excellent | Good | Good | Good | Excellent |
| Abrasion resistance | Good–Excellent | Good–Excellent | Good | Excellent | Poor–Fair |
| Relative cost | Medium | Medium | Medium–High | Low | High |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the difference between EPDM and EPM?
Section titled “What is the difference between EPDM and EPM?”EPDM incorporates a small percentage of a diene (typically between 2% and 12%) that introduces side unsaturations and allows sulfur vulcanization. EPM lacks diene and can only be crosslinked by peroxides or radiation, which limits curing options but provides even greater thermal and electrical stability.
Does EPDM contain natural latex and can it cause allergies?
Section titled “Does EPDM contain natural latex and can it cause allergies?”No, EPDM is a completely synthetic rubber derived from petroleum. It contains no natural latex proteins, so it is considered safe for people with latex allergies and is frequently used in devices and environments free of this allergen.
What is the maximum temperature that EPDM can withstand?
Section titled “What is the maximum temperature that EPDM can withstand?”In continuous service, well-stabilized formulations withstand 150 °C / 302 °F. Peroxide-cured compounds with suitable antioxidants can tolerate peaks up to 160 °C / 320 °F for limited periods while maintaining acceptable tensile and compression set properties.
Is EPDM suitable for contact with food or drinking water?
Section titled “Is EPDM suitable for contact with food or drinking water?”Yes, there are specific grades formulated with non-toxic fillers and plasticizers that meet requirements of regulations such as FDA, NSF/ANSI 61, or European standards for contact with drinking water and food. These grades are free of migratory substances under intended use conditions, although the specific certification of the compound must be verified.
Why is EPDM not recommended in contact with oils or fuels?
Section titled “Why is EPDM not recommended in contact with oils or fuels?”EPDM is a non-polar polymer with a saturated backbone. Its chemical affinity with liquid hydrocarbons causes intense swelling and loss of mechanical properties when in contact with mineral oils, gasoline, diesel, or organic solvents. For these applications, NBR, HNBR, or FKM, which are specifically designed to resist hydrocarbons, are recommended.
Can EPDM be bonded or repaired?
Section titled “Can EPDM be bonded or repaired?”Yes, although its low surface energy makes adhesion difficult. For robust bonds, contact adhesives based on polyurethane, flexible epoxy, or cyanoacrylates specific for low-polarity elastomers are used. Surface preparation by cleaning with appropriate solvents and light abrasion or primer treatment significantly improves bond strength.