Experimental And Numerical Prediction Study On Dissolution Of Supercritical CO₂ In Polymer Melt Under Different Stirring Elements

In the continuous extrusion process of microporous plastics,screw and other stirring elements are often used to accelerate the dissolution of CO2 in the polymer melt.The amount of CO2 dissolved in the polymer melt in a limited time will directly affect the final performance of the product,such as the distribution and size of the bubble.Therefore,it is necessary to know not only the solubility of CO2 in polymeric melt under certain conditions,but also the amount of dissolved in a certain period of time.The dissolution rate can be obtained from the dissolution amount,and the numerical prediction of the dissolution rate is helpful to guide the process formulation of microporous plastics extrusion and the structural design of the mixing element of the extrusion screw.Based on the dissolution process of supercritical CO2 in polymer melt during the continuous molding of microporous plastics,this paper took polystyrene(PS)as the research object,carried out the dissolution experiment of supercritical CO2 in PS melt under different temperatures,pressures and stirring elements by means of an experimental device built independently with constant temperature,constant pressure and replaceable stirring elements,and made numerical prediction.The specific research content is as follows:Experimental study on different dissolution conditions.The effects of temperature and pressure on the solubility,mass and dissolution rate of CO2 in polymer melt were studied by dissolution experiments at different temperatures and pressures.The dissolution experiments under different stirring elements were carried out,and the dissolution rates of CO2 without stirring and under different stirring elements were compared,and the influence of stirring elements on the solubility rate was studied.The dissolution experiments were carried out at different rotational speeds to study the effect of rotational speed on the solubility rate of CO2.(1)Numerical study of pin stirring element.According to the stirring mode of the pin stirring element in the process of CO2 dissolution,the dissolution mechanism of CO2 under the pin stirring was analyzed,the method of solving the solubility and diffusion coefficient was proposed,and the numerical prediction function of the dissolution was derived and verified by experiments.The verification results show that the numerical prediction function of dissolution is in good agreement with the experimental results.The numerical prediction function of CO2 dissolution rate,dissolution equilibrium time,initial dissolution rate and dissolution rate acceleration under pin stirring element were studied,and the numerical prediction function were compared between no stirring and pin stirring.(2)Numerical study of plow stirring element.By analyzing the dissolution process and mechanism of CO2 under the plow stirring element,the numerical prediction of CO2 dissolution under the plow stirring element was studied,and the dissolution function was obtained and verified by experiments.The verification results show that the solubility function is accurate.The numerical prediction of the dissolution rate,dissolution equilibrium time,initial dissolution rate and dissolution rate acceleration of CO2 under the plow stirring element were analyzed according to the dissolution function,and compared with the numerical prediction function under pin stirring element.