Polymer Types

  1. Maximum temp. at which vulcanizates can be aged 70 hrs with changes in tensile strength no greater than ± 30%, elongation no greater than -50%, and hardness no greater than ± 15 points.
  2. % volume increase in ASTM IRM 903 Oil, 70 hrs exposure

EPDM

EPDM is a modern, chemically ‘tailored’ rubber that has a fully saturated backbone, unlike other volume and speciality rubbers. There is a small amount of unsaturation present, only in the short side chains, sufficient to allow vulcanisation. This gives the rubber outstanding resistance to the usual degrading influences and also imparts a higher electrical resistance than rubbers with higher unsaturation levels. There is also a version of the rubber with no unsaturation at all (EPM) for even better electrical properties.

There is now a wide range of EPDMs to give improved processing and physical properties. Major usage areas for EPDM compounds are in seals and gaskets for steam and boiler room applications, and also in electrical wire insulation and coating.

Heat Resistance: 150oC
Oil Resistance: n/a

Nitrile

The range of Nitrile rubbers first appeared about 1937 to satisfy the need for an oil resistant rubber. It rapidly became extensively used in engine seals and gaskets and is still widely used. The oil resistance depends very much on the level of the ingredient Acrylonitrile used in the polymer, and this normally varies from about 18 – 40%, the higher levels giving better oil resistance but also making the low temperature performance much poorer, which is important in Scandinavia, the Arctic and Antarctic regions, and even in the UK in wintertime.

Nitrile compounds are used wherever there is expected contact of the rubber with oils, and the nitrile content can be chosen for suitable oil resistance. Top usage temperatures are about 140C and the lower temperature limit can be as high as -minus 5C.

Heat Resistance: 100oc
Oil Resistance: 15%

HNBR

Hydrogenated Nitrile Rubber first appeared about 1980 in response to the automotive requirements that pushed ordinary Nitrile to its limits. Hydrogenation reduced the unsaturation in Nitrile to a controllable level sufficient only for vulcanisation and thus greatly improved the environmental resistance of the rubber to lift the maximum useful temperature limit and also give some other useful property improvements.

Due to the method of manufacture, HNBR is much more expensive than NBR and so is not generally used to replace NBR but has taken over several areas due to improved Dynamic and Chemical resistance properties as well as the better heat and oil resistance.

Heat Resistance: 150oC
Oil Resistance: 20%

FKM

Compounds of Carbon and Fluorine are strongly bonded and very heat stable. The first polymer from these was PTFE, discovered by DuPont about 1942 and several fluoro-polymers have been produced since. They can be hard and non-rubbery expensive materials that are difficult to process, but have very desirable properties such as excellent resistance to oils and solvents, heat resistance to almost 100C higher than hydrocarbon rubbers, excellent resistance to strong acids and bases (including HF), and useful electrical properties.

FKM is much used in high performance seals and gaskets for both heat and solvent resistance, chemical plant linings, oilfield and space applications.

Heat Resistance: 250oC
Oil Resistance: 10%

Silicone

Silicone is a semi-organic elastomer with outstanding resistance to extremes of temperature with corresponding resistance to compression set and retention of flexibility. Silicone elastomers also have excellent weathering, ozone and aging properties.

Silicone rubbers have poor mechanical properties and abrasion resistance and are therefore mainly used for static sealing applications and are not recommended for dynamic applications. Silicones are highly permeable to gases, and are generally not recommended for exposure to ketones, concentrated acids, or steam.

Heat Resistance: 200oC
Oil Resistance: 60%

Fluorosilicone

Fluorosilicone rubber which combines the good high and low temperature stability of Silicone with the fuel oil and solvent resistance of Fluorocarbons. It is most often used in aerospace applications for systems requiring fuel and/or diester-based lubricant resistance up to a dry heat limit of 400° F. Its features good compression set and resilience properties. It is suitable for exposure to air, ozone, chlorinated and aromatic hydrocarbons.

Fluorosilicone is designed for static sealing use. Because of its limited physical strength, poor abrasion resistance and high friction characteristics, Fluorosilicone is not recommended for dynamic sealing applications. It is also not recommended for exposure to brake fluides, hydrazine, or ketones.

Heat Resistance: 210oC
Oil Resistance: 10%

Neoprene

Neoprene is a homopolymer of chlorobutadiene and is unusual in that it is moderately resistant to both petroleum oils and weather (ozone, UV, oxygen). This qualifies neoprene uniquely for certain sealing applications where many other materials would not be satisfactory. Neoprene is classified as a general purpose elastomer which has relatively low compression set, good resilience and abrasion, and is flex cracking resistant.

Neoprene has excellent adhesion qualities to metals for rubber to metal bonding applications.
It is used extensively for sealing refrigeration fluids due to its excellence resistance to Freon and ammonia.

Heat Resistance: 100oC
Oil Resistance: 80%

Styrene Butadiene (SBR)

Styrene-Butadiene (SBR) is a copolymer of styrene and butadiene.

SBR compounds have properties similar to those of natural rubber. SBRs primary custom moulded application is the use in hydraulic brakes system seals and diaphragms, with the major of the industry usage coming from the tire Industry.
SBR features excellent resistance to brake fluids, and good water resistance.

Heat Resistance: 70oC
Oil Resistance: n/a

Polyacrylate

Polyacrylates are copolymers of ethyl and acrylates which exhibit excellent resistance to petroleum fuels and oils and can retain their properties when sealing petroleum oils at continuous high temperatures up to 347 °F. These properties make polyacrylates suitable for use in automotive automatic transmissions, steering systems, and other applications where petroleum and high temperature resistance are required.

Polyacrylates also exhibit resistance to cracking when exposed to ozone and sunlight.
Polyacrylates are not recommended for applications where the elastomer will be exposed to brake fluids, chlorinated hydrocarbons, alcohol, or glycols.

Heat Resistance: 175oC
Oil Resistance: 20%

Isobutylene Isoprene Rubber (IIR)

Butyl rubber is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for Isobutylene Isoprene Rubber. Polyisobutylene, also known as “PIB” or polyisobutene, (C4H8)n, is the homopolymer of isobutylene, or 2-methyl-1-propene, on which butyl rubber is based. Butyl rubber is produced by polymerization of about 98% of isobutylene with about 2% of isoprene. Structurally, polyisobutylene resembles polypropylene, having two methyl groups substituted on every other carbon atom. Polyisobutylene is a colourless to light yellow viscoelastic material. It is generally odourless and tasteless, though it may exhibit a slight characteristic odour.

Butyl rubber has excellent impermeability, and the long polyisobutylene segments of its polymer chains give it good flex properties.

Heat Resistance: 100oC
Oil Resistance: n/a