Measurements and modeling of PS/supercritical CO₂ solution viscosities

Abstract

Abstract This paper presents a technology to determine the melt viscosity of a PS/super‐critical CO 2 solution using a linear capillary tube die mounted on a foaming extruder. CO 2 was injected into the extrusion barrel and the content of CO 2 was varied in the range of O to 4 wt% using a positive displacement pump. Single‐phase PS/CO 2 solutions were formed using a microcellular extrusion system and phase separation was prevented by maintaining a high pressure in the capillary tube die. By measuring the pressure drop through the die, the viscosity of PS/CO 2 solutions was determined. The experimental results indicate that the PS/CO 2 solution viscosity is a senstive function of shear rate, temperature, pressure, and CO 2 content. A theoretical model based on the generalized Cross‐Carreau model was proposed to describe the shear‐thinning behavior of PS/CO 2 solutions at various shear rates. The zero‐shear viscosity was modeled using a generalized Arrhenius equation to accommo‐date the effects of temperature, pressure, and CO 2 content. Finally, the solubility of CO 2 has been estimated by monitoring the pressure drop and the absolute pressure in the capillary die.