Viscoelastic properties of solutions of polystyrene melts and carbon dioxide: Analysis of a transient shear rheology approach

Abstract

In this work, the viscoelastic, thermal, and diffusion properties of solutions of polystyrene melts and carbon dioxide (CO2) were analyzed using plate–plate rheometry in the transient mode. The objective of this study was to evaluate a transient shear rheology approach for high viscosity polymer melts, to verify superposition principles for polystyrene/CO2 solutions, and to measure the glass transition temperature as a function of pressure and CO2 concentration. Two different procedures of saturating polystyrene with carbon dioxide were applied, i.e., loading with the blowing agent below the glass transition temperature of polystyrene and at the measurement temperature. Stress-growth experiments in shear were performed in order to measure the transient viscosity of polystyrene/CO2 solutions in the linear regime. A shift of the transient viscosity data to a mastercurve was applied in order to determine the shift factor of the viscosity and the average relaxation time. Our data indicate that the steady-state viscosity and the average relaxation time are proportional to the temperature–pressure–concentration shift factor aT,p,c within experimental scatter, and consequently a time–temperature–pressure–concentration superposition principle holds for polystyrene/CO2 solutions. Whereas the viscosity of polystyrene strongly depends on the applied temperature and pressure, the elastic equilibrium compliance depicts only a weak dependence on temperature and pressure.