Epichlorohydrin rubber (ECO)

Epichlorohydrin rubber – abbreviated to ECO – is a specialised synthetic material based on polyether, which combines a set of properties that hardly any other material in elastomer technology can match: excellent resistance to mineral oils, excellent compression set and, at the same time, outstanding resistance to ozone and weathering.

The reason this combination is rare is that resistance to oil and weathering are structurally conflicting requirements: materials with good oil resistance typically have polar polymer chains, which makes weathering and ozone resistance difficult to achieve. ECO resolves this conflict of objectives through its specific molecular structure.

The main polyether chain is free of double bonds – meaning it is not susceptible to attack by either ozone or oxygen. The chloromethylated side groups give the material its polarity and thus its resistance to mineral oils and non-polar media.

Properties of ECO

ECO elastomers are typically characterised by:

• very good resistance to mineral oils, fuels and lubricants
• very good ozone and weather resistance – ECO can be used outdoors without the addition of protective additives
• very good resistance to compression set – a key criterion for permanently compressed seals
• good resistance to diluted acids and alkalis
• good tear propagation resistance
• extremely low gas permeability – comparable to butyl rubber or IIR, making ECO one of the first choices for fuel systems and diaphragms where diffusion through the wall is critical; satisfactory resistance to hot water up to 100 °C
• satisfactory abrasion resistance

ECO is flammable and not flame-retardant. The typical operating temperature range is between –40 °C and +120 °C, depending on the compound, with short-term exposure up to +130 °C. Its cold flexibility down to –40 °C makes ECO a suitable candidate for applications where NBR reaches its low-temperature limit – whilst also meeting the required weather resistance that NBR does not offer.

The hardness range of typical ECO compounds is between 40 and 90 Shore A, with a tensile strength of between 6 and 15 N/mm² and an elongation at break of 150–500 per cent.

Processing and special features

ECO compounds require significantly longer vulcanisation times compared with other synthetic rubbers. This increases production costs and must be taken into account during process design. In addition, post-vulcanisation tempering of the components is usually required to drive out residual cross-linking agents and achieve the final mechanical properties – similar to FKM compounds.

Design note: As ECO contains chlorine in the polymer, appropriate compound stabilisation should be ensured in the event of direct contact with corrosion-sensitive metals to prevent the possible release of hydrogen chloride under extreme conditions.

These processing requirements are the main reason why ECO, despite its attractive property profile, has remained a specialised material and is not considered one of the standard materials in sealing technology.

How ECO and NBR differ

ECO is often described as an extension of the NBR range – and that is a fair assessment. Both materials offer very good resistance to mineral oils and low compression set. The key difference lies in their weather and ozone resistance: NBR, with its double bonds in the polymer backbone, is sensitive to ozone and unsuitable for outdoor applications without the addition of protective additives. ECO overcomes precisely this weakness.

Whereas EPDM is weather-resistant but offers no oil resistance, and NBR is oil-resistant but sensitive to ozone, ECO bridges the gap for applications that require both properties simultaneously.

Typical applications for ECO

Its specific performance profile makes ECO the material of choice for applications requiring both oil and weather resistance:

• Seals in fuel and lubrication systems exposed to the external environment
• Fuel hoses – the low gas permeability reduces fuel diffusion through the hose wall
• Diaphragms in fuel pumps and control valves
• Roller covers in the printing industry and mechanical engineering
• Engine mounts and vibration dampers in automotive engineering subject to combined oil and weathering stresses.

ECO at a glance: Key data and resistance properties

Epichlorohydrin rubber (ECO) combines the favourable properties of NBR rubber with regard to

• mineral oil resistance and
• low compression set

with good weathering and ozone resistance.

Disadvantage: ECO compounds require relatively long vulcanisation times. Furthermore, post-vulcanisation tempering of the vulcanised parts is usually necessary.

Temperature range: -40 to +120°C

Applications: ECO is primarily used for seals, diaphragms, hoses and roller covers where good resistance to mineral oils is required alongside good weather and ozone resistance.

Disposal

According to the “Regulation on the European Waste Catalogue (AVV)”, the waste product from ECO can be classified according to Chapter 7 “Wastes from organic chemical processes” and the waste code 07 02 99. This waste code stands for waste classified as non-hazardous.

They can therefore be disposed of in normal household quantities with normal household waste. Please use the container provided by your public waste disposal authority for residual waste as the appropriate disposal container.

Synonyms: Epichlorhydrin-rubber