Theoretical and experimental study on the effect of nitrogen content on the thermal characteristics of nitrocellulose under low heating rates

The thermal behavior of nitrocellulose (NC) with different nitrogen contents has been widely investigated in previous works. However, most of the experiments were carried out under high heating rates, a situation in which it is difficult to capture minor changes during the thermal decomposition process. In the present study, the thermal characteristics of NC with different nitrogen contents were theoretically and experimentally investigated using a CALVET heat flux calorimeter C80 at heating rates from 0.2 to 0.8 °C/min. Before thermal analysis, the results of high-precision scanning electron microscopy showed that more cracks and coarser surfaces were detected on NC fibers with higher nitrogen contents. It was found that a “turning point” was detected on the heat flow curves of NC with higher nitrogen contents. Furthermore, the heat flow curves of NC transformed from “bell shape” to “right triangles” with increases in the nitrogen content, which suggested that NC with high nitrogen contents exhibited autocatalysis characteristics under low heating rates. This characteristic was also confirmed by the isothermal experiment results that showed the autocatalytic properties became increasingly obvious by increasing the isothermal temperature. Moreover, the relevant chemical kinetic and thermodynamic parameters were obtained. The heat of the reaction (ΔH) increased and the activation energy values in the initial stages of NC decomposition decreased as the nitrogen content was increased. Furthermore, the critical explosion temperature (T_b), which is as an important parameter to evaluate the thermal hazard of NC, decreased by elevating the nitrogen content.