Molecular Dynamics Simulation For Mechanical Properties Of Polymer Blended Energetic Materials

The novel dihydroxylamm onium 5,5'-bistetrazole-1,1'-diol salt?TKX-50?is a high-energy ion explosive with high energy storage,high detonation velocity,low sensitivity and low toxicity.It thus has great development prospects in military and civilian fields.The mechanical properties and security are improved with adding polymer binder into energetic materials as polymer bonded explosives?PBXs?.In this work,TKX-50 was chosen as energetic material,the effects of the concentration and structure of the polymer binder on the mechanical properties of PBXs were investigated by statistical mechanics of elasticity and no-equilibrium molecular dynamic?NEMD?simulation.The mechanical properties of PBXs were analyzed from the configuration changes of polymers and energetic materials.First four short-chain polymers were added to TKX-50 to construct new energetic materials PBXs.They are polyaddition glycidyl ether?GAP?,polyglycidyl ether nitrate?PGN?,polytetrahydrofuran?poly-THF?and polyethylene glycol?PEG?,with a mass fraction of 1%,5% and 11%,respectively.The results show that the elastic moduli of PBXs are reduced as the concentration of polymer increasing,indicating the flexibility is reinforced and rigidity is reduced.The structures of the polymers have different effects on the mechanical properties of TKX-50,and the increasing order of elastic moduli is poly-THF<PEG?PGN<GAP.It is proved that the effect of polymers without side chains on the flexibility of TKX-50 are better than that of polymers with side chains.And the backbone-[O?CH₂?₄]-?poly-THF?has better improvement than-[O?CH₂?₂]-?PEG?for the flexibility of TKX-50,the side chain-CH₂ONO₂ is more effective than-CH₂N₃ in the same backbone on improving the flexibility of TKX-50.Moreover,the plasticity of PBXs is best when the polymers are inserted into TKX-50 along the z axis of the?100?surface.Some of the systems were subjected to tensile deformation using NEMD simulations.It is found that the maximum stress and Young's moduli of PBXs are reduced.The order of the Young's moduli of four polymers is in good agreement with the results calculated by statistical mechanics of elasticity.The microstructure changes of tension show that the GAP and PGN self-crimp on the surface of TKX-50,while PEG and poly-THF are extended on the surface of TKX-50.In addition,two long-chain binders were additionally added to TKX-50.The mass fraction of polymer is adjusted by the length of the polymer chain.Among them,the mass fraction of poly-?azidomethyl?oxetane?poly-BAMO?is 3.83% and 8.07%,the mass fraction of poly-?fluoromethyl?oxetane?poly-BFMO?is 2.65% and 8.60%.Elastic mechanics calculation of the four PBXs show that the blending of polymer binder with TKX-50 can reduce E and G and improve the plasticity and plasticity of the explosive.Moreover,when the concentration of the binder increases,the system becomes softer and more insensitive.Poly-BFMO has a better effect on the elasticity and plasticity of TKX-50 due to its different structure,indicating that the side chain-CH₂F has a better flexibility-improving effect on TKX-50 than-CH₂N₃.The non-equilibrium dynamics was used to simulate the tensile deformation.The results show that the blending of polymer binder with TKX-50 can reduce E and reinforce the elasticity of the explosive.As the concentration of the binder increases,the maximum stress and Young's modulus of the system decrease.The microscopic behavior of tensile deformation shows that the bulk of the explosive tends to occur fracture at the end of the polymer chain.When the fracture occurs in the middle of the polymer chain,the polymer at the fracture still provides tensile stress.The interaction between polymer and TKX-50 in tensile deformation is related to the elastic moduli of the system.When the system exhibits better elasticity,the polymer acts as a binder to maintain the internal structure of the TKX-50 crystal,which enhances the elasticity of the polymer blended materials.