Effect of heating rate on the thermal behavior of nitrocellulose

In the previous study, it was observed that the stability of nitrocellulose (NC) cannot be determined by thermal analyses such as differential scanning calorimetry (DSC) at heating rates of 1-10 K/min. This was because the thermal curves of NC samples with different stabilities could not be distinguished from one another. In this study, we explain why such thermal analyses cannot be used to evaluate the thermal stability of NC and identify the conditions under which thermal analyses can be used for this purpose. We investigated the effect of heating rate on the thermal behavior of pure NC and NC stabilized with diphenylamine (DPA) or akarditeII (AKII), which is a conventional stabilizer, by using the heat flux calorimeter (C80). At high heating rates (0.2-0.3 K/min), only single exothermic peak was observed in the thermal curves of both pure NC and NC/DPA and the thermal curve of pure NC was practically similar to that of NC/DPA. At low heating rate (0.02 K/min), two exothermic peaks were observed for both pure NC and NC/DPA. The heat amount of the first peak depended on the partial pressure of O(2) in the atmosphere. The first peak in the thermal curve of NC/DPA was slightly suppressed as compared to that of pure NC. These results indicate that the stability of NC probably depends on the first exothermic peak that represents oxidation of NC by atmospheric O(2). From this, on the thermal analyses at high heating rates, thermal curves of pure NC and NC/DPA could not be distinguished from one another. This is because the decomposition of NC itself occurs in the second exothermic peak before the oxidation of NC by atmospheric O(2) in the first peak, which is attributed to the stability of NC. The results of the thermal analyses under isothermal conditions at 393 K in an O(2) atmosphere revealed that the induction period of NC/DPA and NC/AKII was longer than that of pure NC. From these results, it is speculated that the stability of NC can be evaluated by thermal analyses carried out under O(2)-rich conditions at low heating rates.