Study On Thermal Decomposition Of RDX-based PBX Explosive Promoted Or Inhibited By Different Binders

As the main energy material of the weapon system,energetic materials are an indispensable part of the national defense military force.In order to expand the scope of application and improve the safety performance,polymer boned explosive(PBX)is usually prepared by mixing energetic materials and binders.Therefore,it is necessary to find more binders that can affect the thermal decomposition reaction of energetic materials.In this paper,energetic material RDX(1,3,5-Trinitro-1,3,5-triazacyclohexane,RDX)was used as the main explosive.Five kinds of binders were coated on RDX by different coating processes,and RDX-based PBX was studied.The promotion or inhibition of each binder on the thermal decomposition of PBX was discussed.The specific contents are as follows :(1)Pure RDX is treated by four methods(grinding method,water suspension method,water precipitation method after dissolving in acetone and direct drying method after dissolving in acetone)without adding any binder.Scanning electron microscope(SEM),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),differential scanning calorimetry(DSC)and other characterization techniques were used.The original RDX and RDX samples after treatment were characterized.The results showed that the particle size of RDX decreased from 100 μm to several μm after treatment.The particle morphology changed from irregular block to spherical or flake with the experimental method,but the crystal structure and exothermic process did not change.The apparent activation energy of RDX after treatment increased,indicating that the experimental method could improve the particle defects and improve the crystal quality.(2)RDX was coated by ethylene vinyl acetate copolymer(EVA)and thermoplastic polyurethanes(TPU),respectively.PBX materials were prepared by grinding method,direct method and water suspension method.The morphology and structure of PBX samples were characterized by SEM,XRD and FTIR.The results show that the two polymers can be successfully coated on the surface of RDX.The thermal decomposition behavior of PBX was compared by DSC.It was found that the effect of two coating layers on the pyrolysis of RDX was not related to the preparation method.The decomposition peak temperature of RDX/TPU decreased,and that of RDX/EVA increased.The thermal gravimetric / infrared / mass spectrometry(TG/IR/MS)instrument was used to further analyze the PBX prepared by direct method.It was found that the coating layer did not change the type of pyrolysis products,but delayed the generation time and dissipation time of gas products.Through the calculation of thermal decomposition kinetic parameters,it is found that the two polyesters will change the pyrolysis mechanism of RDX.The impact sensitivity and laser ignition performance tests show that both polyesters can improve the ignition performance of RDX.EVA coating reduces the impact sensitivity of RDX compared with TPU coating,which effectively improves the safety of RDX.(3)Three kinds of water-soluble polymers : Water Soluble Phenol-Formaldehyde Resin(WSPR),Polyacrylamide(PAM)and Polypropylene glycol(PPG)were coated with RDX by dry grinding,wet grinding,direct method,water suspension method,homogeneous solution method and solvent-nonsolvent method,respectively.FTIR characterization confirmed that water-soluble polymers were successfully coated on RDX surface;DSC analysis showed that the dry grinding,wet grinding and solvent-nonsolvent coating of water-soluble phenolic resin could promote the pyrolysis of RDX,while the direct method and homogeneous phase dissolution method could inhibit the pyrolysis of RDX,and the water suspension method could control the peak temperature ahead or behind through the dilution of WSPR solution.No matter how the polyacrylamide was coated,it did not significantly promote or inhibit the pyrolysis of RDX.When polyether is wrapped by water suspension method and homogeneous phase solution method,the pyrolysis process of RDX is obviously promoted,and the endothermic melting peak of RDX is weakened or disappeared.