EPDM is a saturated polymer with a small amount of diene for cure. It is used in automotive sealing, water systems, brake systems (with the right cure), roofing and many general seals.
Identification
- IR shows strong CH₂ and CH₃ absorption and a methylene rocking band near 720 cm⁻¹ when ethylene sequences are long. No nitrile, carbonyl or halogen bands.
- DSC gives a glass transition around −50 to −55 °C.
- Density of a black compound is around 1.0 to 1.2 g/cm³ for most grades, increasing with mineral fillers.
Polymer details worth estimating
- Ethylene content (typically about 45 to 75 %): affects crystallinity, strength and low-temperature flexibility. Higher ethylene gives stronger green strength and poorer cold flexibility.
- Diene type (ENB, DCPD or VNB): affects cure rate and cure efficiency. Often it can only be said that a diene is present, with ENB the most common.
- Oil extension: some grades are supplied extended with paraffinic oil. GC-MS of the extract helps to separate polymer oil from compounder oil.
Cure
- Sulfur cure with thiazole or dithiocarbamate accelerators, common in general-purpose goods.
- Peroxide cure with coagent, preferred for low compression set, high temperature and steam.
- Sulfur content in the compound tells you which one: a very low sulfur figure points to peroxide.
Fillers
Carbon black loadings of 80 to 150 phr are common, with calcium carbonate, clay and process oil extending the compound. The extract is often large (20 to 30 %).
Matching
Match polymer type (ethylene and diene), filler and oil system, cure type and hardness. Compression set at the duty temperature and the rheometer curve of the trial mix tell you whether the cure matches.
About this article. It is original writing prepared from public sources, standards and general industry practice. It is not a copy of any book or standard and it is not engineering advice. Confirm values against the current edition of the standard and test in your own application. Only analyse material you own or are entitled to analyse.
