PS/超临界CO2挤出过程中泡孔结构演变的群体平衡模拟

Population Balance Simulation for Evolution of Cell Structure during Extrusion Foaming of PS/Supercritical CO2

为准确预测聚合物的泡孔结构并指导工业中发泡产品的性能调控和工艺优化,通过引入群体平衡方程(PBE),并耦合聚苯乙烯(PS)熔体流动方程及熔体相与气泡相中CO2传质机理,建立了挤出口模中PS/超临界CO2体系发泡过程数值模型,用于描述气泡群体的成核和生长行为。基于此模型计算,揭示了挤出口模中气泡的成核和生长行为,探明了挤出口模中泡孔结构的演变规律,并发现泡孔形成与流动特征及CO2饱和溶解度密切相关。根据气泡生长规律,可将口模内泡孔密度的演变分为四个阶段,工业上应控制气泡处于相应的生长阶段以得到期望的泡孔结构。

To accurately predict the cell structure of polymer materials and guide the foaming product performance control and process optimization in industry,by introducing the population balance equation(PBE),coupled with the flow equation of polystyrene(PS)melt and the mass transfer mechanism of CO2 between melt phase and bubble phase,the numerical model for the foaming process of PS/supercritical CO2 system in an extrusion die was established to simulate the nucleation and growth of bubble population.Based on the simulation,the nucleation and growth behaviors of bubbles in the extrusion die were clarified,and the evolution laws of the cell structure in the extrusion die were revealed.It is found that the formation of bubbles is closely related to the flow characteristics and CO2 saturation solubility.According to the law of bubble growth,the evolution of cell density in the die can be divided into four stages.In industry,the bubble should be controlled corresponding to the growth stage so that the desired cell structure can be obtained.