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 (CO 2) 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/CO 2 solutions and to measure the glass transition temperature as a function of pressure and CO 2 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/CO 2 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 a T,p,c within experimental scatter, and consequently a time-temperature-pressureconcentration superposition principle holds for polystyrene/CO 2 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.

An exact analytical solution for viscoelastic fluids with pressure-dependent viscosity

“…Typical values for b à are 10-50 GPa À1 for polymer melts [1,5,6,[30][31][32], 10-70 GPa À1 for lubricants [18,33] and 10-20 GPa À1 for mineral oils [34]. These values for b à are usually reported for the exponential law; however, they are also valid for small or medium pressure differences p à À p à ref .…”

“…However, the dependence of k à on p à is not clear and, surprisingly, experimental data for k à versus p à do not exist in the literature (at least as far as the author this work is aware). Handge and Altstadt [32] have suggested that if the time-temperature-pressure superposition principle is fulfilled, which appears to be the case for the polystyrene melts that they report on, then all relaxation times must scale with the same factor as the viscosity. In the present paper however k à is assumed to be constant; as shown in Ref.…”

Analysis of compaction and life‐time prediction of porous polymer membranes: influence of morphology, diffusion and creep behaviour

“…Consequently, the regimes of glass transition and viscous flow appear at earlier times than for the pristine polymer phase. For amorphous polymers, this effect can be described by the time–temperature–pressure shift factor a T,p , i.e. in Eqns (1) and (2) the time t has to be replaced by t / a T,p for a sample which has been fully plasticised at time t = 0.…”

“…In principle, the local variation of concentration can be treated by a numerical analysis. In a pore–channel geometry, the solution for diffusion in a cylindrical hollow fibre can be applied in order to calculate the time of saturation, with and the initial porosity ϵ 0 of the membrane. Since the time for a complete saturation is infinity, the experimental saturation time is estimated by the time t 95 which corresponds to a saturation of 95% of the equilibrium value.…”

Thermal properties, rheology and foams of polystyrene-block-poly(4-vinylpyridine) diblock copolymers

“…[43], the reduction of the transient shear viscosity and the plasticisation effect, respectively, in polystyrene melts caused by carbon dioxide was investigated. In general, homopolymers and blends of homopolymers have been studied more in depth compared to block copolymers.…”