Molecular Dynamics Simulation On The Performance Of Azido Energetic Plasticizers/Nitrocellulose

With the development of military technology,the usage of the nitrocellulose（NC）binder as the main component of explosives is increasing.Plasticizers are usually added in binders to reduce their viscosity during the processing.Therefore,it is important to study the correlation between plasticizers and binders.In this paper,the molecular models of the azido plasticizers,including 1-azido acetoxy-2,2-azido methyl-3-azido propane（TAMPAA）,1-ethyl acetoxy-2,2-azido methyl-3-azido propane（TAPAC）and 1,5-diazido-3-oxapentane（AZDEGDN）and three types of NC chains with different nitrogen contents（9.11%,11.08%and 12.73%）were established.The compatibility of plasticizer/NC was investigated.The pyrolysis products of these blended system at different temperatures were analyzed.The effect of plasticizers on the mechanical properties of NC was obtained by the stress-strain curve.The main research contents and conclusions of this paper are as follows.（1）The molecular dynamics（MD）method was used to acquire the properties of the plasticizer/NC blended system in terms of solubility parameters,diffusion coefficient,radial distribution function,radius of gyration and free volume.The addition of the plasticizer reduced the interaction between the main atoms of the NC molecular chain and increased the free volume of the blended system,with the enhancing on the movement of NC molecular chains.The azido group of the plasticizer AZDEGDN had a stronger hydrogen bonding with the NC molecular chain,which made the AZDEGDN/NC blend have the highest binding energy and diffusion coefficient,and spread more easily in blend system.（2）Reactive molecular dynamics（Reax FF）method was used to study the pyrolysis reactions of the plasticizers/NC blends at different temperatures.The cleavage of NC started with the breakage of the C-O bond to form small molecular ring fragments,and then the carbon backbone of the ring and oxygen bridge bonds were opened to generate small molecular fragments.The pyrolysis rate of blends increased with the temperature rising.At higher temperatures,the pyrolysis reaction was more complete.The higher temperature was beneficial to the cleavage reaction of the C₁-C₄ products to yield C₅₊fragments,especially the formation reaction of char.The activation energy of the NC molecular chain was reduced by addition of the plasticizer,which accelerated the pyrolysis reaction of NC.The main gaseous products of plasticizer/NC were NO₂,N₂,CO₂,NH₃,H₂O,and H₂.The pyrolysis products of AZDEGDN/NC blend contained less carbon and more gas,making the pyrolysis more complete.（3）The stress-strain curves of NC and plasticizer/NC blends at different tensile rates were investigated using the deform method.The stress-strain curves of the pure NC had no yielding,while the yield strength and maximum tensile strain of NC decreased with the addition of plasticizers.The tensile strength and tensile modulus increased with increasing tensile rate.There was not enough time to relax to accommodate the high tensile rates for NC molecular chains at faster tensile rates.Their molecular models developed sparse regions,with the decreasing of the degree of atomic relaxation.Thus,it was difficult for NC to undergo deformation,and the tensile strength was enhanced.The mass density distribution analysis also confirmed this results.