Theoretical investigation of the safety of nitroguanidine-based PBXs containing the nonpolar desensitizing agent polytetrafluoroethylene.

In order to elucidate why the inclusion of a nonpolar desensitizing agent in polymer-bonded explosives (PBXs) affects their sensitivity and safety, the intermolecular interactions between nitroguanidine (NQ: a high-energy-density compound used as a propellant and in explosive charges) and F2C=CF2 were investigated theoretically at the B3LYP/6-311++G(2df,2p) and M06-2X/6-311++G(2df,2p) levels of theory, focusing especially on the influence of intermolecular interactions on the strength of the trigger bond in NQ. The binding energies and mechanical properties of various β-NQ/polytetrafluoroethylene PBXs were also studied via molecular dynamics simulation. The results indicated that the weak intermolecular interactions between NQ and F2C=CF2 have almost no effect on the strength of the trigger bond or the energy barrier to the intramolecular hydrogen-transfer isomerization of NQ, as also confirmed by an AIM (atoms in molecules) analysis. However, the mechanical properties of the β-NQ/polytetrafluoroethylene PBXs were found to be significantly different from those of pure β-NQ: the PBXs showed reduced rigidity and brittleness, greater elasticity and plasticity, and-in particular-better ductility. Thus, β-NQ-based PBXs with polytetrafluoroethylene are predicted to be less sensitive to external mechanical stimuli, leading to reduced explosive sensitivity and increased safety. Only mechanical properties influence the safety of nitroguanidine-based PBXs.