Abstract
The effect of pressure on the viscosity of polymer melts is an often forgotten parameter due to the inherent difficulty to measure this quantity. Different experimental approaches have already been undertaken in literature in the past. A popular methodology to measure the pressure dependence of the viscosity is to use a capillary rheometer equipped with a counter pressure chamber in which the exit pressure can be controlled. In order to process the data, one of the key elements is the Bagley correction that is required to determine the correct entrance pressure at a specific shear rate. In all analysis approaches presented in literature on data at controlled exit pressure, the Bagley correction was always determined at atmospheric exit pressure, disgarding possible effects of an enhanced exit pressure. In this paper, a new analytical approach is presented that for the first time allows for a direct assessment of the entrance pressures obtained when capillary measurements are performed with controlled counter pressures. It is demonstrated, using polycarbonate, that the entrance pressure correction needed to obtain correct viscosity values under pressure is significantly different than the one needed to correct measurements performed at atmospheric exit pressure.
References
Cardinaels, R., Van Puyvelde, P. and Moldenaers, P., “Evaluation and Comparison of Routes to Obtain Pressure Coefficients from High-pressure Capillary Rheometry Data”, Rheol. Acta, 46, 495–505 (2007) 10.1007/s00397-006-0148-5Search in Google Scholar
Couch, M. A., Binding, D. M., “High Pressure Capillary Rheometry of Polymeric Fluids”, Polymer, 41, 6323–6334 (2000) 10.1016/S0032-3861(99)00865-4Search in Google Scholar
Dees, M., Mangnus, M., Hermans, N., Thaens, W., Hanot, A.-S. and Van Puyvelde, P., “On the Pressure Correction of Capillary Melt Rheology Data”, Rheol. Acta, 50, 117–124 (2011) 10.1007/s00397-011-0529-2Search in Google Scholar
Driscoll, P. D., Bogue, D. C., “Pressure Effects in Polymer Rheology”, J. Appl. Polym. Sci., 39, 1755–1768 (1990) 10.1002/app.1990.070390813Search in Google Scholar
Duvdevani, I. J., Klein, I., “Analysis of Polymer Melt Flow in Capillaries Including Pressure Effects”, Soc. Pet. Eng. J., 23, 41–45 (1967)Search in Google Scholar
Goubert, A., Vermant, J., Moldenaers, P., Göttfert, A. and Ernst, B., “Comparison of Measurement Techniques for Evaluating the Pressure Dependence of the Viscosity”, Appl. Rheol., 11, 26–37 (2001)Search in Google Scholar
Kadijk, S. E., Van Den Brule, B. H. A. A., “On the Pressure Depencency of the Viscosity of Molten Polymers”, Polym. Eng. Sci., 34, 1535–1546 (1994) 10.1002/pen.760342004Search in Google Scholar
Koran, F., Dealy, J. M., “A High Pressure Sliding Plate Rheometer for Polymer Melts”, J. Rheol., 43, 1279–1290 (1999) 10.1122/1.551046Search in Google Scholar
Laun, H. M., “Polymer Melt Rheology with a Slit Die”, Rheol. Acta, 22, 171–185 (1983) 10.1007/BF01332370Search in Google Scholar
Laun, H. M., “Capillary Rheometry For Polymer Melts Re-visited”, Rheol. Acta43, 509–528 (2004) 10.1007/s00397-004-0387-2Search in Google Scholar
Mackley, M. R., Spitteler, P. H. J., “Experimental Observations on the Pressure-dependent Polymer Melt Rheology of Linear Low Density Polyethylene Using a Multi-Passrheometer”, Rheol. Acta, 35, 202–209 (1996) 10.1007/BF00396047Search in Google Scholar
Maxwell, B., Jung, A., “Hydrostatic Pressure Effect on Polymer Melt Viscosity”, Modern Plastics, 35, 174–182 (1957)Search in Google Scholar
Moldenaers, P., Vermant, J. and Mewis, J., “Origin of Nonlinearities in the Bagley Plots of Thermotropic Copolyesters”, J. Rheol., 40, 203–219 (1996) 10.1122/1.550799Search in Google Scholar
Pantani, R., Sorrentino, A., “Pressure Effect on Viscosity for Atactic and Syndiotactic Polystyrene”, Polymer Bull., 54, 365–376 (2005) 10.1007/s00289-005-0397-ySearch in Google Scholar
Sorrentino, A., Pantani, R., “Pressure-dependent Viscosity and Free Volume of Atactic and Syndiotactic Polystyrene”, Rheol. Acta, 48, 467–478 (2009) 10.1007/s00397-009-0348-xSearch in Google Scholar
Steuten, J. M., Arnouts, J. E. F. and Van Gurp, M., “Dependence of Polymer Melt Viscosity on Hydrostatic Pressure: Results from Rheological and PVT Measurements”, Progress and Trends in Rheology IV, Proc. 4the European Rheology Conference, Seville (1994)Search in Google Scholar
Utracki, L. A., “Pressure Dependence of Newtonian Viscosity”, Polym. Eng. Sci., 23, 446–452 (1983) 10.1002/pen.760230806Search in Google Scholar
Utracki, L. A., “A Method of Computation of the Pressure Effects on Melt Viscosity”, Polym. Eng. Sci., 25, 655–668 (1985) 10.1002/pen.760251104Search in Google Scholar
Utracki, L. A., Sedlacek, T. “Free Volume Dependence of Polymer Viscosity”, Rheol. Acta, 46, 479–494 (2007) 10.1007/s00397-006-0133-zSearch in Google Scholar
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