Study on the spontaneous ignition mechanism of nitric esters (I)

The spontaneous ignition mechanism of cellulose nitrate (NC) was analyzed in terms of the pressure change and the thermal behavior during isothermal storage at 393 K. During storage of the NC, atmospheric O2 was consumed during an exothermic reaction. The heat release behavior as well as the O2 decreasing behavior could be fitted to a first-order reaction. The rate constant (K) and the induction period (tindc) for the heat release behavior almost coincided with those for the O2 decreasing behavior (O2 decreasing behavior: K = 7.7 × 10−5 s−1, tindc = 10 h; heat release behavior: K = 8.1 × 10−5 s−1, tindc = 9.2 h). The reaction heat did not increase even if the initial amount of NC increased under a limited O2 condition. These results would suggest that NC released reaction heat due to autoxidation which was propagation involving O2 and radical species generated from NC. Even in a 4.7 vol.% NO2/air atmosphere, the amount of reaction heat did not significantly change from those in dry air. The reaction order was also not affected by the partial pressure of NO2. On the one hand, the K was slightly higher, and the tindc was shorter in the 4.7 vol.% NO2/air (K = 1.8 × 10−4 s−1; tindc = 3.4 h) than those in dry air. These results would indicate that NC accumulated reaction heat due to autoxidation by atmospheric O2, and NO2 contributed to the initiation process before the autoxidation occurred.