Compatibility and Thermal Decomposition Kinetics of Hexahydro-1,3,5- trinitro-1,3,5-triazine with Different Polyester-based Polyurethanes

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Backround: The compatibility study is an important aspect before pre-formulation of the energetic composites. Any sort of the incompatibility between the ingredients of the energetic composites greatly affects the safety and functionality of the energetic composites. Therefore, to develope safer energetic composites, the compatibility between the different ingredients of the energetic formulations and their thermal decomposition kinetics is important study as it is directly linked with the safety and functionality of the energetic composites. Methods: The compatibility of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) with different polyester-based polyurethanes (PUs) were studied by using vacuum stability tester (VST) and differential scanning calorimetry (DSC) methods as outlined by North Atlantic Treaty Organisation Standardisation Agreement (STANAG 4147). The mixture of RDX with polyester-based PUs was cured with MDI (4,4’-methylene diphenyl diisocyanate), IPDI (isophorone diisocyanate) and TMDI (2,2,4- trimethylhexamethylene diisocyanate) as curatives to get polyester-based PUs. The VST measurements were carried out at isothermal temperature of 100℃ for 40 h. For kinetic study, all the samples were subjected to heat from 25-600℃ at different heating rates under flow rate of nitrogen gas of 40 mL/min Results: The VST results revealed that energetic RDX was compatible with all polyester-based PUs and was chemically stable. The thermal decomposition behaviour was studied by employing thermogravimetric analysis (TGA) and DSC. The DSC results indicated that peak temperature difference (∆Tp) between pure RDX and binary mixture of RDX and polyester-based PUs i.e., RDX/PE/MDI, RDX/PE/IPDI and RDX/PE/TMDI were found to be greater than 4℃, indicating that RDX was not compatible with all types polyester-based PUs. The thermal stability in terms of Tmax values of RDX/PE/MDI, RDX/PE/IPDI and RDX/PE/TMDI was found to be significantly reduced as compared to pure RDX. The activation energy obtained by the Kissinger method for RDX/PE/MDI, RDX/PE/IPDI and RDX/PE/TMDI samples was found to be 220.2, 271.5 and 210.4 kJ/mol, respectively. The experimental results showed that the values are comparable and in good agreement with the values obtained by Ozawa method. Conclusion: This study provides useful information for selecting polyester -based PUs as polymeric binder for the preparation of RDX-based energetic composites.