Material · Synthetic

EPDM

The weatherproof rubber — car door seals, flat roofs and hose for anything except oil, which destroys it.

EPDM's backbone is saturated — ethylene and propylene with only a small amount of diene, and the diene is placed on a side group rather than in the chain. That matters because ozone and ultraviolet light attack double bonds, and a rubber with almost none in its backbone does not perish.

So EPDM is the outdoor elastomer. It handles sunlight, ozone, weather and steam for decades, works from about −50 °C to 150 °C, and resists water, alkalis, acids and brake fluid.

And it swells badly in hydrocarbon oils and fuels, for the same reason it resists water: it is non-polar itself. Putting EPDM where nitrile belongs is one of the more common and more expensive elastomer selection errors, and the seal does not fail immediately — it swells, softens and then leaks.

Processing

Extruded into profile — most of what a car's door and window seals are — moulded, and calendered into sheet for roofing membrane. Vulcanised with sulfur where the diene content allows, or cured with peroxide for better heat resistance and compression set at the cost of some processing convenience.

It accepts extremely high loadings of filler and oil, which is why it is cheap per unit volume despite the polymer itself not being especially so.

Uses

Vehicle weatherstripping, door and window seals, and radiator and heater hose — EPDM handles hot coolant, which is water and glycol, and is exactly wrong for a fuel line.

Single-ply roofing membrane for flat roofs, where a fifty-year exposure life is the requirement. Window glazing gaskets. Pond and reservoir liners. Washing machine door seals. Brake system seals, because brake fluid is glycol-based and attacks most other rubbers. Electrical cable insulation and high-voltage insulator sheds. And the black rubber on a garden hose.

History

Developed in the late 1950s and early 1960s, following directly from the Ziegler-Natta catalysts that made polypropylene possible — the same chemistry that could arrange propylene into a crystalline plastic could also copolymerise it with ethylene into an amorphous rubber.

It displaced natural rubber and SBR from outdoor sealing applications within about a decade, on weathering alone.

Environmental impact

Vulcanised, therefore not remeltable and not mechanically recycled; ground EPDM is used as playground and sports surfacing. Thermoplastic vulcanisates — EPDM particles dispersed in a polypropylene matrix — are a genuinely recyclable substitute and have taken a substantial share of automotive sealing for that reason among others.

Its long service life is the environmental argument that carries most weight: a roofing membrane that lasts fifty years is a smaller impact than three that last fifteen, and durability is a legitimate sustainability property that is easy to overlook when only end-of-life is counted.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is produced by

Polymerisation — process · ethylene and propylene copolymerised with a Ziegler-Natta catalyst, plus a few per cent of a diene to give vulcanisation something to work with

is an input to

Extrusion — process · the door and window seal profiles on every car, made as continuous lengths and cut to fit

is used as

Sealing and gasketing — application · water, steam, brake fluid and weather; emphatically not oil or fuel, which swell it until the seal fails

is used in

Construction — industry · single-ply flat roofing membrane and glazing gaskets, chosen for a fifty-year exposure life
Automotive manufacture — industry · every door and window seal, and the coolant hoses — and it is exactly wrong for a fuel line

is an alternative to

Natural rubber — material · EPDM displaced natural rubber from every outdoor sealing application within about a decade, on weathering alone

belongs to the group

Rubber — material · the weatherproof one — and the one destroyed by the oil that nitrile handles

Sources

Material World
Our own writing
Wikidata
Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)

Where it comes from, and what it becomes

Follow EPDM back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

EPDM → is produced by (ethylene and propylene copolymerised with a Ziegler-Natta catalyst, plus a few per cent of a diene to give vulcanisation something to work with) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as the brine the cell electrolyses, and as the source of the hydrogen that comes off the cathode) → Water → is sourced from (by desalination, where energy is cheap and coastline available — the only route that adds fresh water rather than moving it) → Seawater
EPDM → is produced by (ethylene and propylene copolymerised with a Ziegler-Natta catalyst, plus a few per cent of a diene to give vulcanisation something to work with) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is produced by (electrolysis of potassium bifluoride, which is molten and conducts — there is no chemical oxidant strong enough to displace fluorine from a compound, so electricity is the only route and always has been) → Molten salt electrolysis → takes as input (after concentration, as one of the two routes to lithium chloride) → Lepidolite
EPDM → is produced by (ethylene and propylene copolymerised with a Ziegler-Natta catalyst, plus a few per cent of a diene to give vulcanisation something to work with) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is extracted from (by electrolysis of brine, which yields chlorine and sodium hydroxide together) → Halite
EPDM → is produced by (ethylene and propylene copolymerised with a Ziegler-Natta catalyst, plus a few per cent of a diene to give vulcanisation something to work with) → Polymerisation → takes as input (as tetrafluoroethylene, which is where a substantial share of industrial fluorine chemistry ends up) → Fluorine → is extracted from (the only significant source; hydrofluoric acid is made from it and everything fluorinated follows) → Fluorite
EPDM → is produced by (ethylene and propylene copolymerised with a Ziegler-Natta catalyst, plus a few per cent of a diene to give vulcanisation something to work with) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (the largest single use of salt, and the process the whole chlorine and caustic soda industry rests on) → Salt → is produced by (in the solar route — the same process, read from the other end) → Brine evaporation
EPDM → is produced by (ethylene and propylene copolymerised with a Ziegler-Natta catalyst, plus a few per cent of a diene to give vulcanisation something to work with) → Polymerisation → takes as input (as vinyl chloride, which is why more than half of PVC's weight is salt rather than oil) → Chlorine → is produced by (at the anode) → Chlor-alkali electrolysis → takes as input (as brine; the salt is the feedstock for both products at once) → Halite

These are the most distinct paths back. EPDM can be traced through others besides.

Downstream — what it becomes

EPDM → is an input to (the door and window seal profiles on every car, made as continuous lengths and cut to fit) → Extrusion
EPDM → is used as (water, steam, brake fluid and weather; emphatically not oil or fuel, which swell it until the seal fails) → Sealing and gasketing
EPDM → is used in (single-ply flat roofing membrane and glazing gaskets, chosen for a fifty-year exposure life) → Construction
EPDM → is used in (every door and window seal, and the coolant hoses — and it is exactly wrong for a fuel line) → Automotive manufacture