Swelling

Polyurethane elastomers will swell when exposed to certain solvents. This swelling can range from a few percents in mild cases to several hundred percents in severe cases.

Potential Cause

Exposure to Harmful Solvents
The overwhelming cause of swelling is exposure to solvents, materials which are incompatible with the polyurethane system. In addition, solvents used at elevated temperatures further accelerate the problem. The proper specification of polyurethane for the specific solvent is critical.

Solutions

Choose the Proper Elastomer
Generally, polyether-based elastomers are the proper choice for high humidity and water applications. Polyesters, on the other hand, are generally used for applications where there is the potential for exposure to oil-based solvents.

Shield the Elastomer from the Solvent
In cases where the elastomer is being splashed by the solvent, it may be possible to mechanically shield the part from the solvent.

Test the Elastomer Before Field Exposure
Testing the elastomer with the correct solvent before field application is recommended. It is a simple test—immerse a known weight of elastomer into a container filled with the desired solvent at the desired temperature for an extended period of time. At the conclusion of the test, reweigh the elastomer to determine the uptake of solvent. If plaques of the proper thickness are used, standard ASTM tensile and tear tests can also be performed.