EPDM Rubber
The only common rubber with a fully saturated backbone. The cure sites hang off the side of the chain instead, which is why an EPDM roof is still there after thirty years and an EPDM seal survives under a bonnet.
Molecular Structure
What is EPDM Rubber?
EPDM is a terpolymer of ethylene, propylene and a small proportion of a diene. Ethylene and propylene alone would give a saturated rubber that no ordinary sulphur system could cure, so a diene is added to supply crosslinking sites — but the diene is chosen so that only one of its double bonds enters the chain. The other remains pendant, hanging off the backbone.
That architecture is the reason EPDM exists. The backbone contains no carbon-carbon double bonds at all, so there is nothing for ozone, oxygen or ultraviolet light to attack along the main chain. Sulphur curing still works, because the pendant unsaturation provides the sites. The result is a general purpose rubber with weather, ozone and heat resistance that unsaturated rubbers cannot approach.
Three variables set the grade. Ethylene content governs crystallinity, green strength and extrusion behaviour. Diene content and type govern cure rate and crosslink density. Molecular weight, quoted as Mooney viscosity, governs processing and ultimate properties, and is often brought into a workable range by extending with oil at the plant.
EPDM is a hydrocarbon rubber, and it swells badly in hydrocarbons. It is outstanding against water, steam, glycol brake fluid, ozone, acids and bases, and unusable against mineral oil, petrol or diesel. Specifying it for a seal that will meet engine oil is one of the most common material selection errors in sealing.
Quick Reference
Key Physical & Chemical Properties
Structure & Bonding
An ethylene-propylene backbone with no double bonds in it at all, and a diene-derived unsaturation hanging off the side. The pendant double bond is the cure site; keeping it off the main chain is what gives EPDM its weather resistance.
Chain segment — saturated backbone with pendant diene unsaturation
Structural Identity
- PolymerEthylene propylene diene rubber
- Composition(C₂H₄·C₃H₆·diene)ₙ
- BackboneFully saturated
- Cure sitePendant, from the diene termonomer
- Common dieneENB — ethylidene norbornene
- Ethylene controlsCrystallinity and green strength
- Diene controlsCure rate and crosslink density
- ResistsOzone, weather, steam, glycol, acids
- Swells inMineral oil, fuels, hydrocarbons
- CAS Number25038-36-2
- Specified byMooney, ethylene, diene, oil
Product Specifications
Chelora supplies EPDM Rubber in standard and custom grades. Contact us for specification sheets tailored to your process.
| Polymer | Ethylene propylene diene rubber |
|---|---|
| CAS Number | 25038-36-2 |
| Composition | (C₂H₄·C₃H₆·diene)ₙ |
| Ethylene content | 45 – 75 wt%, declared per grade |
| Diene content | 0.5 – 12 wt%, declared per grade |
| Diene type | ENB, DCPD or VNB — specify |
| Mooney viscosity ML(1+4) 125 °C | 20 – 90, grade dependent |
| Oil content — extended grades | 50 – 100 phr, declared |
| Volatile matter (max) | ≤ 0.75 wt% |
| Ash (max) | ≤ 0.30 wt% |
| Glass transition | −45 to −60 °C depending on composition |
| Raw polymer density | 0.86 g/cm³ |
| Cure system | Sulphur / accelerator, or peroxide for VNB and high heat |
| Service temperature | −50 to +150 °C, compound dependent |
| Ozone resistance | Excellent — no in-chain unsaturation |
| Oil resistance | Poor — swells in mineral oil and fuels |
| Supply form | Bales, pellets or crumb depending on grade |
| Packaging | 25 or 35 kg bales, palletised or crated |
| Transport classification | Not regulated as dangerous goods |
Downstream Applications & Derivatives
Key derivative chains and industrial uses of EPDM Rubber.
Automotive Weatherstrip
The largest outlet. Door, window and boot seals extruded and cured continuously, where thirty years of ozone and UV exposure with no cracking is the requirement.
Roofing Membrane
Single-ply EPDM membrane for flat and low-slope commercial roofing, with service lives measured in decades and no plasticiser to migrate out.
Coolant & Brake Systems
Radiator and heater hose, and glycol brake system seals — EPDM is the standard choice for anything carrying water, steam or glycol rather than oil.
Cable Insulation
Medium and high voltage cable insulation and jacketing, and accessories, where electrical properties, weather resistance and heat life all matter together.
TPV & Compounds
The elastomer phase in thermoplastic vulcanisates, dynamically cured within a polypropylene matrix to give a rubber that injection moulds like a plastic.
Lubricant & Plastics Additive
Amorphous grades as viscosity index improvers in engine oil, and as impact modifiers toughening polypropylene compounds.
Why source EPDM Rubber through Chelora Petrochem?
Verified Origin
Full origin certification and asset-backed supply chain documentation — no grey-market supply.
Grade Flexibility
ENB, DCPD and VNB grades supplied across the ethylene and Mooney range, including oil-extended. We match on ethylene content, diene type and loading, and oil level, because those three decide how the compound cures and extrudes.
Full Documentation
CoA covering Mooney with test conditions, ethylene and diene content, oil loading, volatiles and ash; SDS; REACH compliance; and potable water or cable specification documentation where the grade supports it.
Logistics Support
Experienced in bale and pellet elastomer logistics — palletised and crated bales with film wrapping, containerised delivery with attention to stack height and temperature, for Indian and international delivery.
Storage & Handling Guidelines
Always refer to the full SDS before handling. The following is a summary of key requirements.
- Store cool, dry and out of direct sunlight, and limit stack height. Oil-extended and low-Mooney grades in particular cold flow and knit together under sustained load.
- Keep grades strictly segregated. Ethylene content, diene type and oil loading are invisible in a bale, and a substitution will change cure rate and extrusion behaviour before anyone notices.
- Confirm the diene type before setting up a cure. ENB cures fastest with sulphur, DCPD is slower, and VNB is intended for peroxide systems — a recipe developed for one will not work with another.
- Match the cure system to the application. Sulphur cures are cheaper and faster; peroxide cures give better heat ageing and compression set, which matters for seals held under load at temperature.
- Never specify EPDM where mineral oil, petrol or diesel contact is possible. It swells badly, and the failure is progressive rather than immediate, so it often escapes prototype testing.
- Expect high ethylene grades to be stiff at ambient. They mill and extrude well warm but are difficult to handle cold, and bale storage below about 10 °C makes them noticeably harder to break down.
- Provide extraction at mixing and curing. Peroxide cures in particular release decomposition products that should not be breathed.
- Keep bales off concrete floors and away from external walls to avoid moisture pickup, which causes porosity in the cured article.
- Manage the compounding ingredients under their own controls — the exposure risk in an EPDM shop is from oils, peroxides and accelerators rather than from the polymer.
Hazard Summary
Classification: EPDM as supplied is not classified as hazardous under CLP. The polymer is inert and is used in potable water and food-adjacent applications. Occupational risk arises from the compounding ingredients and process fume.
Oil and fuel incompatibility: EPDM is a hydrocarbon elastomer with no polar groups, so hydrocarbons dissolve into it freely. Contact with mineral oil, petrol, diesel or hydrocarbon solvents causes substantial swelling and loss of sealing force. This is the single most common EPDM specification error, and because the swelling is progressive it frequently passes short-term testing and fails in service.
Peroxide cure hazards: organic peroxide curing agents are oxidisers with their own significant handling requirements, including temperature-controlled storage, segregation from accelerators and reducing agents, and specific fire precautions. The peroxide, not the rubber, is the hazardous material in a peroxide-cured shop.
Vulcanisation fume: mixing and curing release oil volatiles and cure system decomposition products. Rubber process fume is a recognised occupational exposure with regulatory attention in several jurisdictions, and local extraction at mixers, mills and presses is expected.
Cold flow of extended grades: highly oil-extended and low-viscosity grades deform under sustained load and knit together in the stack. Limit stack height and rotate stock.
Fire: EPDM burns readily once ignited, with dense black smoke, high heat release and carbon monoxide. Bale stores warrant specific fire design and separation, and roofing membrane fire performance is a property of the assembly rather than the membrane alone.
Manual handling: bales are heavy and awkward, and oil-extended bales are slippery. Mechanical handling should be the default.
PPE minimum: gloves and safety footwear for bale handling; eye protection, gloves and respiratory protection appropriate to the compound at the mixer and press, with additional controls where peroxides are used.
Consult the full SDS for the polymer and for every compounding ingredient, particularly the cure system, before mixing.
Frequently Asked Questions
Technical and commercial questions about EPDM Rubber sourcing and specifications.
What is EPDM used for?
Automotive weatherstrip and sealing is the largest outlet — door, window and boot seals that have to survive decades of sun and ozone without cracking. Single-ply roofing membrane is the next largest. Beyond those, EPDM covers radiator and heater hose, glycol brake system seals, medium and high voltage cable insulation, and the elastomer phase in thermoplastic vulcanisates. Amorphous grades also serve as viscosity index improvers in engine oil and as impact modifiers in polypropylene.
Why is EPDM so much more weather resistant than other rubbers?
Because there are no double bonds in its backbone. Ozone attacks carbon-carbon double bonds, and in natural rubber, SBR, polybutadiene or nitrile those bonds sit in the main chain — so ozone attack cuts the chain and the rubber cracks under strain. EPDM's backbone is built from ethylene and propylene and is completely saturated. The diene termonomer supplies the double bonds needed for sulphur curing, but it is chosen so that only one of its double bonds polymerises into the chain and the other remains pendant on the side. Ozone attacking a pendant group removes a crosslink site; it does not sever the backbone. That structural distinction is the whole basis of EPDM's position in sealing and roofing.
What do ethylene content and diene content actually control?
Ethylene content controls crystallinity and therefore the physical character of the raw polymer. High ethylene grades above about 65% are semi-crystalline, with high green strength and excellent extrusion behaviour and shape retention before cure — good for complex weatherstrip profiles — but they are stiff and harder to process cold, and their low-temperature flexibility is poorer. Low ethylene grades are amorphous, softer and more flexible in the cold. Diene content controls the cure: more diene means more crosslink sites, faster cure and higher crosslink density, at the cost of heat ageing performance, since each remaining pendant double bond is an oxidation site. Most grades sit between 4 and 9% diene.
Why does EPDM fail in contact with oil?
Because like dissolves like. EPDM is a pure hydrocarbon elastomer with no polar groups anywhere in the structure, and mineral oil, petrol and diesel are also hydrocarbons. They dissolve into the polymer network freely, swelling it substantially, softening it and destroying the sealing force of a compressed seal. The rubbers that resist oil — nitrile, hydrogenated nitrile, fluoroelastomers — all contain polar groups that make them thermodynamically incompatible with hydrocarbons. The corollary is that EPDM is outstanding against the fluids that defeat nitrile: water, steam, glycol brake fluid, phosphate esters, acids, bases and many polar solvents.
What is the difference between ENB, DCPD and VNB dienes?
They differ mainly in cure speed and cure system compatibility. Ethylidene norbornene is by far the most common because its pendant double bond is highly reactive towards sulphur cure systems, giving the fastest cure rates and the best balance of properties — it is the default unless there is a reason otherwise. Dicyclopentadiene cures more slowly and is generally cheaper, and its slower cure can be an advantage where long processing time before cure is needed. Vinyl norbornene has a pendant vinyl group that is particularly efficient in peroxide cure systems, so it is chosen for high heat resistance and low compression set applications where peroxide curing is required. A compound recipe is diene-specific and does not transfer between them.
What documentation does Chelora provide?
Every shipment includes a Certificate of Analysis covering Mooney viscosity with test conditions stated, ethylene content, diene content and type, oil loading for extended grades, volatile matter and ash; a Safety Data Sheet to GHS and REACH format; REACH polymer compliance confirmation; potable water, cable or roofing specification documentation where the grade supports it; an origin certificate; and destination-market certificates where required.
Request a quote or specification sheet
Talk to Chelora's sourcing team about EPDM Rubber grade, volume, logistics, documentation, and lead times. We respond within one business day.
