Visualization for measuring the PVT property of viscoelastic polystyrene/CO2 mixtures at elevated temperatures and pressures

Abstract

Pressure-volume–temperature (PVT) data for polymer/gas solutions are fundamental to the design and control of such polymer processes as injection molding, foaming, blending and extraction reaction. Previous studies have offered methodologies based on the observation of an axisymmetric polymer pendent/sessile drop, which is used to measure the polymer's PVT behavior at elevated temperatures and pressures. Because polymer generally has high viscosity and elasticity, it is not easy to form an axisymmetric shape out of some types of polymer drops. Our study uses a novel rotational device in a high-pressure and high-temperature cell with a visualization window. This makes it possible to measure the PVT behavior of polymer/gas solutions in those cases where it is not easy to obtain an axisymmetrically-shaped polymer drop. The degree of asymmetry is mathematically defined, and an algorithm is developed to integrate the asymmetric profile for determining the PVT (that is, the volume swelling) of the polymer/gas solution. We have presented a case study on the pressure-volume-temperature (PVT) property of a polystyrene (PS)/CO2 solution at temperatures elevated in the range of 423 K–523 K and at pressures from 6.895 MPa to 27.579 MPa. We found that the volume of the asymmetric sessile drops of PS/CO2 in the PS melt determined the extent of the melt's swelling with the dissolved CO2.