Butyl
ASTM D1418, ISO 1629 Designation: IIR
ASTM D2000, SAE J200 Type/Class: AA, BA
Standard Color: Black
Trade Names:
- Exxon Butyl® (Exxon Chemicals)
- Polysar® (Bayer Corp.)
Relative Cost: Moderate
General Temperature Range: -50° to +250° F
An unsaturated copolymer of isobutylene and isoprene (thus the designation IIR), butyl has two defining traits: (1) it is composed entirely of petroleum, limiting its usefulness around hydrocarbons (since "likes dissolve likes"); and (2) it offers low gas permeability, making it ideal for vacuum seals.
Though ethylene propylene is now used rather than butyl for a number of applications, butyl is still widely used in hydraulic systems. Butyl offers stronger resistance to sunlight and ozone than isoprene alone; presence of the saturated isobutylene in the polymer chain makes this possible. Butyl also resists heat, chemicals, and abrasion.
IIR performs well in:
- MEK
- Phosphate ester type hydraulic fluids (e.g. Skydrol®, Fyrquel®, Pydraul®)
- Silicone fluids and greases
IIR does not perform well in:
- Di-ester based lubricants
- Hydrocarbon solvents and oils
