Exposure to chemicals can cause material ageing and can cause the material properties of a rubber to deteriorate. In material selection, it is very important to consider the chemicals which will be in contact with the rubber. Depending on the chemical structure of the rubber polymer, the rubber will react differently to various substances.
For example, in outdoor water-based environments, EPDM is usually a good choice of material as it has excellent UV resistance as well as providing good resistance to nitrogen, potassium and sodium.
Contact with oil can cause rubber to swell. This happens as the hydrocarbons from the oil are absorbed into the hydrocarbon polymer network.
The following rubbers offer some degree of oil resistance:
- CR - Polycholorprene
- NBR - Nitrile
- PU - Polyurethane
- FKM - Fluorocarbon
- Q - Silicone
Nitrile (NBR) is the standard rubber used in applications which require oil resistance such as automative and machine environments. High grades of Nitrile can be fully submerged in oil.
Oxidation and Ozone Attack
Exposure to oxygen can often cause rubber to harden, reducing its flexibility and causing cracking. Oxidation and ozone attack occur when oxygen atoms react with the polymer chains within a rubber. Rubbers with double bonds in the polymer chain are particularly susceptible to degradation by oxygen. Additives can be added to the formulation of the compound to increase the material resistance to these effects. Neoprene, Butyl and Viton will seal against oxygen.
Contact with chemicals can lead to rapid degradation of rubbers. It is important to ensure that a rubber is compatible with all chemicals in its intended environment. A list of common chemicals and appropriate material choices for applications in these environments are shown below. A comprehensive Rubber Chemical Resistance Chart can be found here.
- Ammonia - EPDM, Neoprene.
- Anti-freeze - Glycol based Nitrile, EPDM, Neoprene.
- Chlorine - Viton® with PTFE envelope.
- Ethanol - EPDM, Neoprene, Butyl.
- Helium - All polymers will seal against helium.
- Hydrogen Gas - Nitrile, EPDM, Neoprene.
- Methanol - Viton®, Nitrile (grade A), Silicone rubber and Fluor silicone.
- Nitrogen Gas - Most rubbers will seal against nitrogen gas (Nitrile, Natural rubber or EPDM are normally used).
- Sulphuric Acid Above 96% - PTFE and expanded PTFE, Viton® FKM, AFLAS, and EPDM with a PTFE envelope.
Table 1: Chemical compatibility of common rubbers and chemicals.
|Nitrile (NBR)||Ethylene Propylene Diene Methylene (EPDM)||Neoprene (CR)||Styrene Butadiene Rubber (SBR)||Silicone (VMQ)||Butyl (IIR)||Viton (FKM)||Polyurethane (AU, EU)|
|Sulphuric Acid||Insufficient Data||Doubtful||Insufficient Data||Insufficient Data||Insufficient Data||Insufficient Data||Satisfactory||Doubtful|