Abstract:

Abstract:

Abstract:In order to enhance the comprehensive properties of glycidyl azide polymer （GAP）， the fluorine-containing GAP copolymer-based thermoplastic elastomers were developed using fluorine-containing GAP copolymer as prepolymer， butylene glycol （BDO） as chain extender and the toluene diisocyanate （TDI） as the curing agent. The molecular structure， relative molecular mass， glass transition temperature， thermally stability and mechanical properties of thermoplastic elastomers were explored via FT-IR， NMR， GPC， DSC， TG/DTG， tensile test and SEM characterizations， respectively. The number-average molecular weight of the thermoplastic elastomers was determined to be 33520 g·mol^-1. The glass transition temperature （T_g） and decomposition temperature （T_d） were found to be -33.3 ℃ and 220 ℃， respectively. The tensile strength at break was 5.94 MPa， and the corresponding elongation was 886%. Therefore， the thermoplastic elastomers exhibited good thermal stability and mechanical properties. Cook-off test was employed to investigate the thermal decomposition characteristics of the fluorine-containing GAP copolymer-based elastomers/Al composite， the response temperature peak of the composite was 301 ℃，suggesting an enhanced exothermal process.

Abstract:Starting from the multi-amine， hydroxy polybutadienes （AEHTPB）， multi-cyano， amine polybutadiene （AEHTPB-CN） was synthesized through appropriate synthesis strategies. The structure of the product was characterized via FT-IR and ¹H NMR， and its physicochemical properties such as viscosity， glass-transition temperature， hydroxyl value， and amine value were also determined. The effect of AEHTPB-CN on the mechanical properties of binder system was investigated via tensile tests， and the performance of the resultant propellant with AEHTPB-CN/HTPB mixture as a binder was explored. The results showed that the cyano groups in the AEHTPB-CN molecule could form hydrogen bonds with the urethane groups， which increased the physical crosslinking density of the elastomer and effectively improved the tensile strength. The propellant level study indicated that the AEHTPB-CN had a good bonding and burning rate inhibition effect on HTPB propellant. At room temperature， compared to HTPB-based propellant， the propellant containing AEHTPB-CN （5-8wt.%） were 35.4%-43.3% larger in tensile strength， 62.0%-91.3% higher in elongation， and the burning rate was reduced by 10.5%-11.4%.

Abstract:A mixture of 3，3-bis（chloromethyl）oxetane （BCMO） and 3-ethyl-3-oxetane methanol （EHO） were used to synthesis the azide hyperbranched copolymers （r-POB-m） via cationic ring-opening polymerization and azidation reaction with different monomer molar ratio （BCMO/EHO=m）. The chemical structures were characterized with Infrared spectroscopy （FT-IR）， nuclear magnetic resonance （NMR）， gel permeation chromatography （GPC） and elemental analysis. The results showed that the copolymer has high molecular weight （>4400 g·mol^-1）， high nitrogen content （up to 43%） and controllable branching structure. X-ray diffractometer （XRD）， Hacker rheometer and differential scanning calorimeter （DSC） were utilized to characterize crystallinity， viscosity and chemical compatibility respectively. When m=4， r-POB-4 is amorphous， possesses the lowest process viscosity and has good compatibility with the main components of the propellant， indicating that it is a potential candidate for plasticizer. In addition， compared with the GAPA plasticizer， the energetic thermoplastic elastomer （ETPE）-based propellant with r-POB-4 plasticizer exhibits higher elongation at break， lower consistency coefficient and lower viscous flow activation energy， suggesting that the azide hyperbranched copolymer could be applied as the plasticizer to effectively improve the mechanical properties and processing properties of the propellant.

Abstract:The thermal stabilities and mechanical properties of explosives are important factors affecting the safety of weapons. In order to improve the thermal stability of hexanitrohexaazaisowurtzitane（CL-20） and1，1-diamino-2，2-dinitroethylene（FOX-7） explosives and the mechanical properties of the CL-20 and FOX-7 based PBXs， modified CL-20 and FOX-7 crystals were prepared based on the oxidative self-polymerization reaction of dopamine （DA）. Scanning electron microscope （SEM）， thermal analysis （TG）， dynamic mechanical analysis （DMA）， static contact angle， laser particle size analyzer， high performance liquid chromatography （HPLC）， BMA impact sensitivity， infrared absorption spectrometer and universal material testing machine were used to test the morphology and structure of modified particles， and also the particle size， coating content， sensitivity， thermal decomposition and the mechanical performance of prepared PBX. Results show that DA forms a good polydopamine（PDA） coating layer on the surface of energetic crystals， and different surface coating morphologies can be obtained by adjusting the polymerization time. At the same time， PDA can also improve the interface properties of explosives crystals， which is beneficial to the uniformity of the binder’s distribution. PDA coating inhibits the crystal transformation and increases the activation energy of CL-20， resulting in improved thermal stabilities. The mechanical properties tests showed that the Brazilian strength and compression strength of CL-20 based PBX had been improved by 34.27% and 10.21%， respectively， and the Brazilian strength and compression strength of FOX-7 based PBX had also been improved by 40.44% and 11.92%， respectively. After coating with PDA， the strain of the samples had all increased. In addition， the creep strains of the two explosives were obviously suppressed， leading to enhance creep resistance.

Abstract:In order to investigate the effects of graphene oxide （GO） on the thermal expansion coefficient of GAP modified spherical propellant composites， GAP modified spherical propellant composites containing GO with 0%， 0.5%， 1%， 1.5% were prepared， respectively. Fourier transform infrared spectroscopy （FTIR）， scanning electron microscopy （SEM） and differential scanning calorimetry （DSC） were used to investigate the structure， morphology and thermal properties of the composites， respectively. The effect of GO content on thermal expansion coefficient and glass transition temperature was investigated using a static thermomechanical tester （TMA）. The results showed that the addition of GO had little significant effect on the structure and thermal properties of the cured system and no chemical reaction occurred. The addition of GO resulted in a reduction to the expansion coefficient of the composites. When the content of GO is 1%， the expansion coefficient presents the greatest reduction， decreasing from 3.236×10^-4 K^-1 to 2.692×10^-4 K^-1. The glass transition temperature increased from 20.8 ℃ to 25.1 ℃ with the addition of GO content relative to the pure GAP modified spherical propellant composite.

Abstract:In order to improve the combustion efficiency of Al powder， Al/modified-fluororubber composite fuel（FKM-GW@Al） was prepared with the silane modified-fluororubber（FKM-GW） by sol-gel method. The stability of FKM-GW@Al in solvent was studied， and the results show that with functional groups， the FKM-GW@Al is stabile in ethyl acetate. The application of FKM-GW@Al in NEPE high-energy and low burning-rate solid propellant was studied. Results show that compared with Al powder， FKM-GW@Al with fluorine mass fraction 2.58%， make the explosion heat of the propellant increase from 6348.8 J·g^-1 to 6831.6 J·g^-1， the content of activated aluminum in residues decreased from 1.02% to 0.06%， and both the static and dynamic burning rates of the propellant containing FKM-GW@Al decrease. The thermal decomposition properties of FKM-GW@Al and the propellant containing FKM-GW@Al were studied by DSC-TG， and the influence mechanism of FKM-GW@Al on combustion characteristics of the propellant was analyzed.

Abstract:In order to improve the adaptability of bonding agent to various energy-containing fillers and modify the interfacial bonds of solid propellants， a kind of multifunction telechelic bonding agent was designed and prepared. The bonding effectiveness was studied by molecular dynamics simulations and experimental evaluations. The results show that this bonding agent can show decent interactions with various energy-containing fillers. By altering the molecule backbone of this bonding agent， it can adapt to different adhesive systems. As compared to the three-claw bonding agent， the two-claw one has fewer branches， better diffusivity in adhesive， higher transferability toward interface， and better bonding effectiveness.

Abstract:In order to study the aging migration process and influencing factors of deterred DB propellants， a theoretical model on the deterrent distribution and the change of combustion performance caused by aging migration was established based on the normal distribution characteristics of deterrent and the inference of Fickian second diffusion law. Six kinds of propellants with different contents of nitroglycerin（NG） and dibutyl phthalate（DBP） were treated by accelerated aging experiments at different temperatures and times， and the combustion performances of propellants were tested by closed bomb vessel. The kinetic process and thermodynamic influence of aging migration for propellants were analyzed. Theoretical analysis shows that the integral value growth rate of the dynamic vivacity for deterred spherical propellants presents a good linear growth relationship with aging time. The results of the closed bomb vessel show that the percentage increase of the maximum dynamic activity for the six propellants after accelerated aging also gives a good linear relationship with aging time， which is consistent with the theoretical research results. The established thermodynamic equation of aging migration for deterred propellants is basically consistent with the experimental results， and the logarithm of migration driving factor and the reciprocal of temperature present an obvious linear negative correlation. When the total content of NG and DBP in propellants is greater than 15%， the migration driving factor is more susceptible to the influence of temperature， leading to migration invalidation. When the total content of NG and DBP is less than 15%， the invalidation rate caused by deterrent migration is relatively slow， which is more conducive to the use and shooting safety after the storage of propellants.

Abstract:To explore the aging mechanism and performance of antioxidants N-（1，3-dimethyl）butyl-N"-phenyl-p-phenylenediamine（4020）， N-isopropyl-N"-phenyl-p-phenylenediamine （4010NA）， N-phenyl-2-naphthylamine （D） in hydroxyl-terminated polybutadiene polyurethane （HTPB-TDI） system， quantum mechanics （QM） simulation， molecular dynamics （MD） simulation， monte carlo （MC） simulation were used to calculate the dissociation free energy， diffusion coefficient， solubility parameter and permeability coefficient of the HTPB-TDI system and each component. Results show that the order of the bond dissociation free energy of the three antioxidants is ΔG_D>ΔG_4010NA>ΔG₄₀₂₀， and they are all less than the minimum free energy of dissociation of HTPB-TDI （345.63 kJ·mol^-1）， indicating that the three antioxidants can preferentially react with the active free radicals in HTPB-TDI and slow down the progress of the free radical chain reaction in HTPB-TDI. The difference of diffusion coefficient and solubility parameter between antioxidant 4020 and HTPB-TDI is the smallest， which shows that antioxidant 4020 has poor diffusion ability and good compatibility with HTPB-TDI， so it can exist in HTPB-TDI stably and uniformly； The order of the permeability coefficient of oxygen in the three kinds of hydroxyl-terminated polybutadiene polyurethane antioxidant systems is P_HTPB-TDI/D＞P_{HTPB-TDI/4010NA}＞P_{HTPB-TDI/4020}， which manifests that D has the worst oxygen barrier ability. According to the chemical reaction difficulty， mobility， compatibility and oxygen permeability of the three kinds of antioxidants， the order of antiaging properties of the three kinds of antioxidants is 4020>4010NA>D.

Abstract:It is reported herein that the interfacial adhesion between binder and filler has distinct effect on mechanical properties of propellant. The tensile fracture progress of propellant （nitrate ester plasticized glycidyl azide polymer （GAP） / hexanitrohexaazaisowurtzitane （ε-CL-20） polyether propellant and polyethylene glycol （PEG） / octogen （β-HMX） polyether propellant） was monitored by in-situ tensile scanning electron microscope. In addition， the interaction strength between binder matrices and solid fillers was characterized by adhesion work and binding energy. The adhesion work was studied by inverse gas chromatography （IGC） and contact angle method， and the binding energy was calculated via molecular dynamics （MD）. Results shows that the dehumidification and fracture expanding progress of GAP/ε-CL-20 propellant are more serious than these of PEG/β-HMX propellant during stretching progress. GAP/ε-CL-20 propellant breaks when the elongation is more than 60% while PEG/β-HMX propellant breaks when the elongation is more than 80%. Besides， the adhesion work 70.69 mJ·m^-2 and binding energy 259.90 kJ·mol^-1 between GAP matrix and ε-CL-20 are both lower than the adhesion work 98.61 mJ·m^-2 and binding energy 335.65 kJ·mol^-1 for PEG/β-HMX system， suggesting that the poor interfacial adhesion between GAP binder matrix and ε-CL-20 is one of main reasons for inferior mechanical properties of GAP/ε-CL-20 propellant.

Abstract:The effects of four typical stabilizers （DPA， C2， AKⅡ， MNA） on the thermal decomposition behavior of nitrocellulose， the thermal decomposition parameters of nitrocellulose samples under different conditions are obtained by DTA， DSC and ARC. The results of non-isothermal calorimetry show that the critical temperature of thermal explosion of nitrocellulose increases by 0.06， 0.82， 1.00 and 1.56 K， respectively， after adding four typical stabilizers. The adiabatic thermal test show that the stabilizers have limited effect on the initial temperature rise rate and pressure of nitrocellulose at the initial stage， but reduces the maximum temperature rise rate of nitrocellulose by 0.39， 0.64， 0.70 and 0.65 K·min^-1. The effects of thermal history on the thermal decomposition of nitrocellulose samples are investigated by DSC interruption and re-scanning method. The results show that four typical stabilizers have good thermal stability. Although the initial thermal decomposition of nitrocellulose is less affected by stabilizers， but with the progress of thermal decomposition reaction， the severe autocatalytic decomposition caused by nitrocellulose thermal decomposition products could be alleviated by rapid reaction with stabilizers， and the influence of thermal history on the thermal decomposition of nitrocellulose could be reduced. N-methyl-4-nitroaniline has the most obvious inhibition effect on the autocatalytic decomposition of nitrocellulose.

Abstract:Improving the reaction performance of traditional binary thermites is one of the research hotspots in the field of energetic materials in recent years. The introduction of additives to form composite thermite is an effective method. According to the application fields and the different effects of additives， the composite thermites were divided into fuel-enhanced type， gas-producing type and modified additive type. The research status of composite thermite and its related engineering applications were reviewed， and then the new research directions and ideas for composite thermite were proposed， including the use and preparation of new alloy fuels and alloy hydrides， the combined use of non-azide gas generating agents and thermite， the influence of the types and amounts of inert additives， and the coating technology of the binder on the surface of the thermite， etc.

Abstract:In order to analyze the factors affecting the ignition delay time in the gas phase reaction process between hydrazine fuel and NO₂， the reaction process was simulated by using density functional theory. The reaction activities， active sites， potential energy surfaces and reaction rate constants in hydrogen extraction reaction process of hydrazine （N₂H₄）， methyl hydrazine （MMH） and unsymmetrical dimethyl hydrazine （UDMH） were calculated. The results showed that the energy difference between the highest occupied orbital and the lowest vacant orbital of UDMH was the smallest among the three hydrazine fuels， which was 0.20522 eV， indicating that UDMH had the highest activity， so it has the fastest reaction rate with NO₂， which in line with the characteristic of the shortest ignition delay time. The active sites of three hydrazine fuels were identified， N（1） or N（4） for N₂H₄， N（1） for MMH and N（1） for UDMH. The active sites of hydrogen extraction reaction of three hydrazine fuels were calculated， it was found that the reaction barrier of UDMH is the smallest， which is 3.589 kJ ·mol^-1， and the reaction rate constant is the largest， which is 9.81×10⁵ L·s^-1·mol^-1， which is consistent with the shortest ignition delay time， it is concluded that in hydrazine fuel， the smaller the hydrogen extraction reaction barrier with NO₂， the larger the reaction rate constant， and the shorter the ignition delay time.

Abstract:The attachment energy （AE） model and molecular dynamics （MD） methods were used to predict the crystal morphology of 1，1-diamino-2，2-dinitroethylene （FOX-7） under vacuum condition and in eight solvent systems including dimethylsulfoxide （DMSO）， acetone， methanol， N-methylpyrrolidone （NMP）， N，N-Dimethylacetamide （DMAC）， ethylacetate （EA）， water （H₂O）， and DMSO/H₂O （V/V=2/1）. By calculating the interaction energies between the solvent and crystal plane， and the attachment energies under the influence of the solvent， the simulated crystal habit and its aspect ratio were obtained. The results show that FOX-7 crystal has six important growth planes under vacuum： （1 0 ）， （1 0 1）， （0 1 1）， （0 0 2）， （1 1 0）， （1 1 ）. Among them， the area of （0 1 1） plane accounts for the largest proportion， which is the most important crystal plane affecting the crystal morphology of FOX-7. The influence degree of solvent on the aspect ratio of crystal is in the following order： DMSO2O2O. By recrystallization experiments， FOX-7 crystals have a bulk-like shape in DMSO， methanol， and DMSO/H₂O； a rod-like shape in acetone and NMP； a needle-like shape in DMAC and H₂O； a flake-like shape in EA. The theoretical prediction results are in good agreement with the experimental results， which proves that the simulation of the crystal habit of FOX-7 based on the AE model can provide better guidance for the crystallization experiment. Results in thermal properties show that the crystal surface morphology and internal defects affect the phase transition temperature and thermal decomposition temperature of FOX-7. The fewer the crystal defects， the higher the α→β transformation temperature. The larger the crystal aspect ratio， the smaller the particle size， and the lower the first decomposition temperature.