Abstract
Chemical and physical tests were conducted to determine the effects of long-term exposure to nitrogen tetroxide on Kalrez 1045, a perfluorinated copolymer. The weight and Shore A hardness of samples from two different lots were determined after exposure at two different pressures, 7320 kPa (72.5 atm) and 101 kPa (1 atm), for times ranging between 1 and 80 days and for periods up to 21 days following their exposure. The largest changes occurred in the first 8 to 10 days of exposure. The weight increased between 15 and 30% and the Shore A hardness declined from 83 to 60. Both weight and hardness partially recovered to their original values after removal from liquid N 2O 4. However, samples exposed for more than 1 day never fully recovered. The chemical stability of the Kalrez as a function of time exposed to N 2O 4 was monitored with solid probe-mass spectrometry. The results indicated that there was no main chain scission for the first 30 days of exposure. Loss of the pendant groups from the main chain was observed within 16 h. Loss of the pendant group from the crosslink site monomer, and loss of the crosslink itself occurred after 150 h of exposure to N 2O 4. The overall results indicated that Kalrez 1045 exhibited exceptional stability to N 2O 4, and seals manufactured from this material should be superior to the butyl rubber currently employed in oxidizer vessels of launch systems.
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