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Elastomeric materials based on hydrogenated nitrile rubber for seals in carbon dioxide (R 744) high pressure service
von Dr. Hans Magg, Achim Welle
HNBR vulcanisates for automotive air conditioning systems running with carbon
dioxide (R 744) are presented.
The following properties are found relevant:
Polymers with high acrylonitrile-content plus high amounts of a special mineral filler (diatomaceous earth) enable very good barrier properties against gaseous CO2.
The vulcanisates (85 Shore A) show good resistance against thermo-oxidative ageing, sufficient low temperature flexibility up to -15 °C and – in total – a satisfying set of further properties.
Immersion tests in liquid, critical and supercritical CO2 at 7,5 MPa were carried out. Swelling can be estimated to 6 – 10 %, referring to swelling in service of probably ~ 10 – 20 %.
Trials in autoclaves enable to evaluate the resistance against explosive decompression. A low level of swelling is the most important prerequisite to avoid cracks and bubbles. In the comparison for this purpose the type of filler and the level of physical properties play a minor role.