The Mitigation Effect of Synthetic Polymers on Initiation Reactivity of CL-20: Physical Models and Chemical Pathways of Thermolysis

Abstract

In this paper, the thermal decomposition physical models of different CL-20 polymorph crystals and their polymer bonded explosives (PBXs) bonded by polymeric matrices using polyisobutylene (PIB), acrylonitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), Viton A, and Fluorel binders are obtained and used to predict the temperature profiles of constant rate decomposition. The physical models are further supported by the detailed decomposition pathways simulated by a reactive molecular dynamics (ReaxFF-lg) code. It has been shown that both ε-CL-20 and α-CL-20 decompose in the form of γ-CL-20, resulting in close activation energy (169 kJ mol −1 ) and physical model (first-order autoaccelerated model, AC1). Fluoropolymers could change the decomposition mechanism of ε-CL-20 from the "first-order autocatalytic" model to a "three-dimensional nucleation and growth" model (A3), while the polymer matrices of Formex P1, Semtex, and C4 could change ε-CL-20 decomposition from a single-step process to a multistep one with different activation energies and physical models. Compared to fluoropolymers, PIB, SBR and NBR may make ε-CL-20 undergo more complete N−NO 2 scission before collapse of the cage structure. This is likely the main reason why those polymer bases could greatly mitigate the decomposition process of ε-CL-20 from a single step to a multistep, resulting in lower impact sensitivity, whereas fluoropolymers have only a little effect on that. For ε-CL-20 and its PBXs, the impact sensitivity depends not only on the heat built-up period of their decomposition, but also on the probability of hotspot generation (defects in solid crystals and interfaces) especially when it decomposes in a solid state.

The mechanisms for desensitization effect of synthetic polymers on BCHMX: Physical models and decomposition pathways

“…In this case, it is better to compare the decomposition physical models and chemical pathways due to interaction between polymer chains and BCHMX molecules. As proved recently by our work group, the kinetic parameters and thermolysis pathways of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20) could be greatly changed by polymer matrices, and such changes are responsible for the improvement of its impact sensitivity [29]. However, the decomposition physical models for most of the BCHMX based PBXs are not known from the literature, and hence first this paper is principally concerned with the determination and interpretation of the physical models.…”

Preparation and Sensitivity Measurements of Graphene Oxide-RDX Composite

“…1.st step putting 90 mL H 2 SO 4 and 60 mL H 3 PO 4 in beaker 250 ml, adding 3.0 g Graphite in this beaker with stirring in ice bath for 30 min, till the temp. Reach 0 °C, adding slowly 20 g KMnO 4 , and stirring for 1 h. The second step was removing the beaker from ice bath and putting it hotplate at 60 °C for 24 hr. then adding a 500 ml of cold deionized water to the forms avoid temperature increase ˃ 50 °C, adding 30 ml H 2 O 2 the color turn from brown to yellow, adding 500 ml DW for 24 hr.…”

“…The researchers are seeking to obtain modern explosives with high performance and high safety during handling and transportations [4][5][6]. The sensitivities of the explosives could be enhanced by controlling the crystal shapes and sizes [7,8].…”

Application of BCHMX in Shaped Charges against RHA Targets Compared to Different Nitramine Explosives

“…Plastic bonded explosives (PBXs) containing ε-HNIW (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, ε-CL-20) have been intensively investigated, since it has an excellent explosive performance [15,16], high energy density, and good thermal stability [13]. PBX compositions based on octahydro-l,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and ε-HNIW tend to be significantly more expensive than conventional ones based on hexahydro-l,3,5-trinitro-1,3,5-triazine (RDX).…”