COMPARISON OF VARIOUS VISCOSITY MODELS FOR PS/CO_2 SOLUTIONS

摘要

This paper describes various approaches to the modeling of PS/CO_2 solution viscosities. The shear viscosity of PS/CO_2 solutions was measured at various levels of CO_2 content, temperatures, pressures, and shear rates using a wedge die mounted on a twin-screw extruder with CO_2 injection. The PS melt viscosity at low and high shear rates was also measured using a cone and plate rheometer and a capillary rheometer, respectively. In order to mathematically describe the depression of the shear viscosity due to dissolved CO_2 in the PS melt, several theoretical models were considered. Cross, Carreau, and generalized Cross-Carreau models were employed to describe the shear-thinning behavior of PS/CO_2 solutions at various shear rates. The zero-shear viscosity in these models was derived in terms of the CO_2 content, temperature, and pressure based on the free volume change due to these variables. Various models of the zero-shear viscosity, including a generalized Arrhenius equation and a WLF equation, were studied. The modeling procedure and comparison between model predictions are presented in detail.