High-pressure rheology of polystyrene melts plasticized with CO2: Experimental measurement and predictive scaling relationships
✍ Scribed by Joseph R. Royer; Yvon J. Gay; Joseph M. Desimone; Saad A. Khan
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 255 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0887-6266
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✦ Synopsis
A high-pressure extrusion slit die rheometer was constructed to measure the viscosity of polymer melts plasticized by liquid and supercritical CO 2 . A novel gas injection system was devised to accurately meter the follow of CO 2 into the extruder barrel. Measurements of pressure drop, within the die, confirm the presence of a one-phase mixture and a fully developed flow during viscosity measurements. Experimental measurements of viscosity as a function of shear rate, pressure, temperature, and CO 2 concentration were conducted for three commercial polystyrene melts. The CO 2 was shown to be an effective plasticizer for polystyrene, lowering the viscosity of the polymer melt by as much as 80%, depending of the process conditions and CO 2 concentration. Existing theories for viscoelastic scaling of polymer melts and the prediction of T g depression by a diluent were used to develop a free volume model for predicting the effects of CO 2 concentration and pressure on polymer melt rheology. The free volume model, dependent only on material parameters of the polymer melt and pure CO 2 , was shown to accurately collapse the experimental data onto a single master curve independent of pressure and CO 2 concentration for each of the three polystyrene samples. This model constitutes a simple predictive set of equations to quantify the effects of gas-induced plasticization on molten polymer systems.