High‐pressure rheology and viscoelastic scaling predictions of polymer melts containing liquid and supercritical carbon dioxide

Abstract

Abstract High‐pressure rheological behavior of polymer melts containing dissolved carbon dioxide (CO 2 ) at concentrations up to 6 wt % were investigated using a high‐pressure extrusion slit die rheometer. In particular, the steady shear viscosity of poly(methyl methacrylate), polypropylene, low‐density polyethylene, and poly(vinylidene fluoride) with dissolved CO 2 were measured for shear rates ranging from 1 to 500 s −1 and under pressure conditions up to 30 MPa. The viscosity of all samples revealed a reduction in the presence of CO 2 with its extent dependent on CO 2 concentration, pressure, and the polymer used. Two types of viscoelastic scaling models were developed to predict the effects of both CO 2 concentration and pressure on the viscosity of the polymer melts. The first approach utilized a set of equations analogous to the Williams–Landel–Ferry equation for melts between the glass‐transition temperature ( T g ) and T g + 100 °C, whereas the second approach used equations of the Arrhenius form for melts more than 100 °C above T g . The combination of these traditional viscoelastic scaling models with predictions for T g depression by a diluent (Chow model) were used to estimate the observed effects of dissolved CO 2 on polymer melt rheology. In this approach, the only parameters involved are physical properties of the pure polymer melt that are either available in the existing literature or can be measured under atmospheric conditions in the absence of CO 2 . The ability of the proposed scaling models to accurately predict the viscosity of polymer melts with dissolved high‐pressure CO 2 were examined for each of the polymer systems. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3055–3066, 2001