Determining the pressure dependency of the viscosity using PVT data: A practical alternative for thermoplastics

The relation between Pressure-Volume-Temperature (PVT) and rheological behaviour of several polymers including polypropylene, poly(methyl methacrylate), polyamide, polycarbonate, polystyrene and polystyrene/polycarbonate blends was studied. Pressure-viscosity coefficient b=(∂lnη0/∂P) was calculated by means of a revisited version of the Miller equation that accounts for pressure and temperature effect on Newtonian viscosity through the activation energy of flow and PVT parameters. Pressure-temperature dependent viscosities experimentally determined using pressure chamber capillary rheometry allow us to check the approach of the Miller equation. Incorporating the pressure effect in the Carreau-Yasuda model for η(γ˙) allows establishing the viscosity curves of thermoplastics over a wide range of shear rates and pressures.