Stability studies of double-base propellants with centralite and malonanilide stabilizers using MO calculations in comparison to thermal studies

Propellants containing nitrate esters need stabilizers to avoid early decomposition or even explosion during storage. Newly prepared malonanilides M1-M5 were tested in stabilizing double-base propellants (DBPs). Their stabilization was compared with the effect of classical stabilizer N,N′-diethyldiphenyl urea (C1) using both practical thermal stability tests (qualitative and quantitative tests) and theoretical molecular orbital calculations. This research shows that the new stabilizers (malonanilides) have good stabilizing effects. Some of malonanilides e.g. (M5) and (M2) have higher stability effects. Different mechanisms were suggested to explain the role of different stabilizers. Molecular orbital calculations using the semi-empirical program AM1 are performed on the new and classical stabilizers. Correlation was made between the volume (ml) of NOx, weight loss (wt%), other thermal analyses data, calculated thermodynamic parameters like activation energy (Ea, kJ mol−1) of the decomposed propellant samples containing different stabilizers and some of their calculated properties such as HOMO, LUMO energies, the charge distribution and the π-bond order. The stabilization effect decreases with the increase in HOMO energy. The correlation between the net charge and parameters measured for the stabilization effect shows good accordance. Comparison of the results obtained show that the high electron charge on N atom of the stabilizers and on its benzene ring is the most important factor, but not the only factor governing the stabilization effect of the stabilizers.