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Matrices based on polyisobutylene (PIB), polymethyl‐methacrylate (PA), Viton A 200, Dyneon FT 2481 (Fluorel), and polydimethyl‐siloxane binders were studied as desensitizers. A series of plastic explosives (PBXs) were prepared, based on four different nitramines, namely RDX (1,3,5‐trinitro‐1,3,5‐triazinane), β‐HMX (β‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane), BCHMX (cis‐1,3,4,6‐tetranitro‐octahydroimidazo‐[4,5‐d]imidazole) and ε‐HNIW (ε‐2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane, ε‐CL‐20), bonded by the matrices mentioned. For comparison, pentaerythritol tetranitrate and certain commercial explosives based on it, Semtex 1A, Semtex 10 and Sprängdeg m/46, were used. Detonation velocities, sensitivities to impact and friction, and peak temperatures of thermal decomposition by differential thermal analysis technique (DTA) for all the explosives studied were determined. Heat of detonation was calculated by means of a thermodynamic calculation program (EXPLO 5 code). Fluoroelastomers have a neutral to positive effect on the thermal stability of nitramines and they have a significant effect on decreasing the friction sensitivity. However, their anti‐impact efficiency is the lowest in this study although they have a positive effect on performance of the corresponding PBXs. PA and PIB matrices markedly decrease thermal stability of nitramines, the anti‐impact influences of PIB‐binders are better than those of PA‐binders, while PA‐binders have a higher anti‐friction effect and slightly less negative influence on the performance of the PBXs in comparison with PIB mixtures. The polydimethyl‐siloxane matrix has a neutral effect on thermal stability of the nitramines studied, it has an influence on the volume thermochemistry of detonation comparable with that of fluoroelastomers although it does not provide comparable performance, and its corresponding PBXs have optimum sensitivity parameters.

Abstract:In this paper, the thermal behavior and decomposition kinetics of trinitrohexahydrotriazine (RDX) and its polymer bonded explosive (PBX) containing a hydroxyl-terminated polybutadiene (HTPB) based polyurethane binder in the ratio 80% RDX/ 20% HTPB were investigated using various experimental techniques and analytical methods. The HTPB polyurethane matrix contains other additives and was cured using hexamethylene diisocyanate (HMDI). Thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), Vacuum Stability Test (VST) and Ignition Delay Techniques were applied both isothermally and non-isothermally. The kinetic parameters were determined using both the isoconversional (model free) and the model-fitting methods. For comparison, Advanced Kinetics and Technology Solution (AKTS) software was also used. It was found that the addition of an HTPB-based polyurethane matrix to pure RDX decreased its decomposition temperature. It was also found that RDX/ HTPB has a lower activation energy than pure RDX. The polyurethane matrix had a significant effect on the decomposition mechanism of RDX resulting in different reaction models. It was concluded that the activation energies obtained using the Ozawa, Flynn, and Wall (OFW) and Kissinger-Akahira-Sunose (KAS) methods were very close to the results obtained via the AKTS software lying in the range 218.3-220.2 kJ·mol −1. The VST technique yielded kinetic parameters close to those obtained using TG/DTG. On the other hand, the Ignition Delay Technique yielded different and inconsistent kinetic parameters.

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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.

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At present, cis‐1,3,4,6‐tetranitro‐octahydroimidazo‐[4,5‐d]imidazole (bicyclo‐HMX, BCHMX) and ε‐2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (ε‐HNIW, CL‐20) are a topic of interest from the attractive and the potentially attainable nitramines. They were chosen to be studied in comparison with 1,3,5‐trinitro‐1,3,5‐triazinane (RDX) and β‐1,3,5,7‐tetranitro‐1,3,5‐tetrazocane (β‐HMX). Marginal attention is devoted also to 4,8,10,12‐tetranitro‐2,6‐dioxa‐tetraazawurtzitane (Aurora 5). BCHMX, ε‐HNIW, RDX, and HMX were studied as plastic bonded explosives (PBXs) with elastic properties based on Composition C4 and Semtex 10 matrices. Also they were studied as a highly pressed PBXs based on the Viton A binder. The detonation parameters and sensitivity aspects of these nitramines and their corresponding PBXs were determined. Relative explosive strengths (RS) of these compositions are mentioned with mutual relationships between the measured RS values and some detonation parameters. These relationships indicate a possibility of changes in detonation chemistry of these mixtures filled mainly by HNIW. A sensitivity of RS‐CL20 (HNIW with reduced sensitivity) is reported and the new findings in the friction sensitivity are discussed.