Extrusion Foaming Process Of Supercritical Carbon Dioxide Assisted Energetic Materials

In order to study the extrusion foaming process of microporous energetic materials,The microporous energetic material is prepared in a single screw extruder.Among them,supercritical carbon dioxide(SC-CO₂)as the physical blowing agent,and cellulose acetate(CA)as the nitrocellulose(NC)substitute.The effect of process conditions on the microporous structure is investigated through a large number of experiments.Then the flow properties of the energetic material under foaming conditions were studied by a slit rheometer.The cell growth process and pressure distribution of energetic materials in the extrusion die are simulated by POLYFLOW.The research results in this paper have certain guiding effect on the continuous processing of microporous energetic materials,especially high burning rate propellants and microporous propellants.The scanning electron micrographs illustrates that as the SC-CO₂ gas injection volume increases,the density of the foamed sample decreases by 0.15 g·cm^-3,the cell density increases from 1.48×10¹⁴ cells/cm³ to 8.7×10¹⁵ cells/cm³,and the cell diameter decreases by 18.6?m.As the amount of alcohol and ketone solvent increases,the porosity first increased by 3.84%,and then decreased to 29.10%.The cell diameter increased by 66.3?m,and the cell density decreased.With the increasing of the screw speed,the cell density increased from5.6×10¹³ cells/cm³ to 7.9×10¹⁵ cells/cm³,and the cell diameter decreased by 55.6?m.As the mold temperature increased,the cell diameter increased by 12.1?m,the cell density decreased by 46%,and the porosity increased by 9.47%.When the temperature increased to30?,the porosity decreased.The rheological performance test results show that with the increase of the volume of CO₂ injection,the viscosity of C A decreases and the flow performance improves.The pressure drop rate between the two sensors in the slit rheometer increases from 1.12×10⁵ Pa·s^-1 to 1.35×10⁵ Pa·s^-1.Increasing extrusion temperature and solvent ratio will decrease the shear viscosity of CA.The increase of the screw speed reduced the viscosity of SC-CO₂/CA and increased the pressure drop rate from 1.27×10⁵ Pa·s^-1 to4.457×10⁵ Pa·s^-1.The simulation results of the cell growth process showed that with the increasing of the volume of CO₂ injection,the cell radius at the die exit decreased from 32?m to 7?m,and the fluid density at the die exit also decreased.After the die temperature increased from 40? to 60?,the cell radius at the die exit increased from 12.5?m to 43?m.The simulation results are in good agreement with the experimental conclusions.As the entrance angle increases,the maximum pressure at the die inlet slightly increased.The length of the capillary section was doubled,a nd the maximum pressure at the die inlet increased from 4.8×10⁶ Pa to 9.6×10⁶ Pa,but the pressure drop rate was basically unchanged.As the diameter of the capillary section increases from 1 mm to 4 mm,the maximum pressure at the die inlet decreased from 1.5×10⁹ Pa to 6.1×10⁵ Pa,and the pressure drop rate decreased significantly.