Study On Polystyrene Foaming Extrusion By Using Supercritical CO₂

Polystyrene has been applied in the industrial production of extrusion foaming for a long time, because of its good foamability. However, the foaming agent used for the production is mostly the chemical foaming agent and the phisical agent, such as freon, bunate. As a new type of foaming agent, the supercritical CO₂ has been paid more attention. Many people researched on the applications of the supercritical CO₂ in the PS foam both abroad and home, and acquired great achievements.In this research, the rheological behavior of polystyrene/CO₂ is studied by using an on-line slit rheometer. The equations of zero-shear viscosity and non-Newtonian index are deduced. At the same time, the degassing pressure of PS/CO₂ is determined through ultrasonic detecting system. On the basis of the rheological experiment, Physical and finite element models of foaming die are brought forward and built. The distribution of pressure, viscosity and shear rate in the foaming die were simulated and analyzed by using POLYFLOW software. Pressure, viscosity and shear rate distribution of fluid field are obtained. The influence of die geometry and operating condition parameters on pressure profile, viscosity profile and shear rate profile and pressure drop rate are also analyzed and discussed. On the other hand, the the effects of the temperature, pressure and gas concentration on the foam density of the sample are studied based on the extrusion experiment using the twin screw-single screw extruder system.