Rubber - The Basic Elastomers
Natural Rubber (NR)
The original gum rubber possesses several excellent mechanical properties. It has good tear and abrasion resistance, high resilience and good low temperature flexibility. Its use is limited in gaskets by very low chemical resistance (especially to solvents and oil which greatly reduce its strength), poor resistance to sunlight and ozone (which causes cracking) and the restricted temperature range.
Neoprene (CR) - Neoprene is the registered trade name of Du Pont.
The oldest of the bulk produced synthetics. More correctly referred to as polychloroprene. It is superior to NR and SBR in resistance to ozone, sunlight and weather. It also has a degree of resistance to attack by petrol, mineral oil and other light hydrocarbons and can be made flame resistant. It only has moderate low temperature flexibility and tends to suffer from poor compression set especially when hot.
Hypalon (CSM) - Hypalon is the registered trade name of Du Point.
Chlorosulphonated polyethylene. Possesses excellent resistance to ozone and good resistance to flame, mineral oil, heat, weather and acid, making it ideal for use outdoors or near sparking electrical equipment.
Styrene Butadiene (SBR)
A synthetic equivalent to natural rubber. The two are usually compounded together to produce an elastomer with similar mechanical properties to NR but with better high temperature performance, flexibility and a slightly greater resistance to attack from animal and vegetable oils.
A copolymer of butadiene and acrylonitrile. Especially resistant to mineral oils and aromatic and aliphatic hydrocarbons and alcohols - depending on the actual nitrile content of the elastomer. High and low temperature performance can be good. Oil resistance can be increased by compounding, at the expense of low temperature flexibility. Ozone, sunlight and weather resistance is poor.
Ethylene Propylene (EP)
Often supplied in a diene modified form (EPDM). It has good mechanical properties and is resistant to ageing, weathering, ozone, oxygen, steam and water. It is especially resistant to phosphate ester based hydraulic fluids but is not recommended for use with petroleum oils or fluids. Good resistance to mineral acids.
A copolymer of isoprene and isobutylene. Similar to EP in its ability to cope with phosphate ester based hydraulic fluids and mineral oils. It is highly impermeable to gas and moisture and has good general chemical resistance including mineral acids. Resistance to petroleum oils and fluids is low.
Viton (FPM) - Viton is the registered trade name of Du Pont.
A copolymer of vinylidene fluoride and hexafluoropropylene. It will cope well with petrol, oils, chlorinated solvents, concentrated alkalis and fuming acids. Ozone and weather resistance are excellent and high temperature performance is good. It has poor low temperature flexibility and should not be used with some esters or ketones.