Extrusion Of Energetic Polymer Substitute Assisted By The Supercritical Fluid

In order to improve the rheological properties of the nitrocellulose in single screw extrusion processing,the extrusion device of energetic polymer assisted by the supercritical fluid was designed in this work,the supercritical fluid was injected into the CDA of nitrocellulose substitute in extrusion processing by using the device,the rheological behaviors were characterized by the slit rheometer,the in-line rheological properties of CDA solution at different processing conditions were investigated,on this basis the rheological properties of CDA solution assisted by supercritical CO₂ in extrusion processing were studied.And the flow behavior of CDA solution in the die was studied by the professional simulation software POLYFLOW.The experimental results provide experimental fundamentals and important reference value for the continuous and safe extrusion of gun propellant and further investigation.The experimental results show that the CDA solution and the CDA/CO₂ solution system are non-Newtonian pseudoplastic fluids.The presence of supercritical CO₂ reduces the shear viscosity,the viscosity coefficient,the extrusion temperature,the dependence of the shear viscosity on temperature and the concentration of solvent of CDA solution,improving non-Newtonian index,and the extrusion flow.After the injection of supercritical CO₂,the viscosity reduction of CDA solution at different extrusion temperatures changes greatly between 6rpm and lOrpm,which can reach 46.75%.At the same condition of content of solvent,the supercritical CO₂ has a great influence on the viscosity reduction of CDA solution at 6rpm and the reduction of viscosity can reach 48.10%.With the increasing of the screw speed,the solvent content or the extrusion temperature,the shear viscosity of CDA solution with and without CO₂ decreases.With the increasing of gas flow,the shear viscosity of CDA/CO₂ solution decreases.With the increasing of the shear rate,viscous flow activation energy of CDA solution and CDA/CO₂ solution system decreases.With the increasing of the extrusion temperature,the viscosity of CDA/CO₂ solution system decreases greatly when the screw speeds are 6rpm and 8rpm.According to the simulation results,the presence of supercritical CO₂ reduces the die entrance pressure,and increases average velocity of CDA solution through cross section of die.The shear viscosity of CDA solution and CDA/CO₂ solution system is lower in the center of the slit wall,and is larger in the boundary region of slit wall.With the increasing of the extrusion temperature or solvent content,the die entrance pressure of CDA solution and CDA/CO₂ solution gradually reduces,the average velocity of materials through cross section of die increases.With the increasing of the gas flow,the die entrance pressure of CDA/CO₂ solution system decreases,the average velocity of CDA/CO₂ solution system through cross section of die increases.With the increasing of thickness of the slit die,the die entrance pressure of the CDA/CO₂ solution system decreases and the shear viscosity of CDA/CO₂ solution system increases on the slit wall.