Predictability of Gaseous Impact Ignition Sensitivity from Autoignition Temperature Data

An analysis of cumulative binomial probabilities for a quantal test like ASTM G 74 indicates that for a probability of reaction in a single trial of 0.05, the probability of obtaining zero reactions in 20 trials is approximately 36 percent. Since the lack of precision of the ASTM G 74 test logic could be potentially misleading, an investigation was conducted to determine if pneumatic impact sensitivity could be predicted more reliably from other, more precise test methods. Pneumatic impact sensitivity testing was conducted following ASTM G 74 but using a rigorous test logic; autoignition temperature (AIT) testing was conducted per ASTM G 72. Polyethylene, polyoxymethylene, polytetrafluoroethylene (PTFE), polyamide, hexafluoropropylene/vinylidene fluoride copolymer, and silicone were the polymers used. After a fixed number of pneumatic impact tests was performed at set pressures, a plot of reaction frequency over a 3.4 to 24.1 MPa impact pressure range indicated that PTFE, hexafluoropropylene/vinylidene fluoride copolymer, and silicone would outperform the other polymers tested. The 50 percent pneumatic impact reactivity level was determined with the Bruceton test method. The data obtained resulted in a strong correlation between the 50 percent reactivity level and the AIT of polymers, indicating similar ignition mechanisms.