Butyl — isobutene-isoprene (IIR)
Butyl elastomer has similar chemical
resistance to ethylene-propylene. Very
low gas permeability makes butyl popular
for vacuum and high-pressure gas
applications. It must not be used with
mineral oils.
Epichlorhydrin (ECO)
Compounds based on this elastomer have
good resistance to mineral oils, fuels and
ozone. Corrosive properties and poor
compression set resistance limit the use of
these materials for sealing applications.
Chlorosulphonyl polyethylene (CSM)
These elastomers show excellent
resistance to weathering and give good
service in many media. They are not
recommended for dynamic seals as
compression set resistance is limited.
Polyurethane (AU, EU)
Stress relaxation at above 50°C often
precludes these elastomers from ‘O’
ring sealing applications. However many
polyurethane ‘O’ rings are used in drive
transmissions where their tensile strength,
elongation characteristics and wear
resistance prove invaluable.
These materials also have excellent
resistance to weathering and oxygen, and
good resistance to hydrocarbon fuels and
mineral oils. Resistance to acids is low,
and some grades