EPDM Gasket Compatibility
EPDM gaskets play a vital role in glazing installations. However, the importance of specifying the correct type of gasket is often overlooked. Materials known as plasticizers are frequently used in the formulation of EPDM gaskets to achieve specific physical and processing properties. These materials can be incompatible with acrylic and polycarbonate glazing, leading to cracking, crazing, or discoloration. The majority of plasticizers that are specified (if no guidelines are given) will not remain in the rubber matrix and will migrate out of the EPDM rubber. This migration allows the plasticizer to be in contact with the glazing material and subsequently attack and dissolve the glazing material. The following guidelines for specifying EPDM gaskets must be followed to obtain a quality gasket that will not damage acrylic and polycarbonate sheet:
- The gasket compounder must only use non-migratory plasticizers, which allow the EPDM gasket to comply with the "Styrene Mar" test. (Described below)
- The gasket should have fair to good compressive set (fair to good elastic memory). The gasket should have the ability to return to its original dimensions (after compression) without any appreciable permanent deformation.
- The gasket should have a minimum tensile strength of 1500 psi.
- The gasket should have a durometer measurement of approximately 75 to 85 shore A.
The "Styrene Mar" test described here is not a compatibility test for the gasket. This test will simply show whether or not the gasket has migratory plasticizers in it. If the gasket does have migratory plasticizers, then it should not be used in contact with acrylic.
- Obtain and cut a one-inch diameter circle from a sample of the EPDM material to be tested. The sample thickness range should be 0.060 to 0.125 inches.
- Place the EPDM sample on a square (2"x 2") of polystyrene sheet (clear, colorless) and place a 300-gram weight on top of the sample to ensure proper contact between the sample and the polystyrene sheet.
- Place the EPDM sample, polystyrene sheet, and 300-gram weight (as described above) in an oven set at 140°F for 24 hours.
- Remove the assembly from the oven and evaluate the polystyrene sheet. If no evidence of surface mar is present, the plasticizer is considered to be non-migratory. If the surface of the sheet is distorted, crazed, or hazed, the EPDM formulation is considered incompatible.
Compounders can typically perform this test as a service to their customers. COMPATIBILITY OF EPDM RUBBER GASKETS MUST BE TESTED!