Experimental Evaluation of the Pressure Sensitivity of Molten Polymer Viscosity with a Triple-stage Capillary Rheometer

A triple pressure-stage capillary rheometer was individually developed for providing an insight of pressure effect on polymeric melts viscosity during steady and continuous flow. Three capillary dies with identical/varied diameters and aspect ratio were assembled in series along the flow direction, relying on which the flow was divided into three zones with varied pressures under the same flow rate. Several polymeric melts, such as low density polyethylene (LDPE), polystyrene (PS), polypropylene (PP) as well as its nanocomposites of PP/CaCO3, PP/Mg(OH)2, and PP/halloysite nanotubes (PP/HNTs) were taken as the experimental samples. The principles for calculating the pressure sensitivity of shear viscosity in capillary flow were discussed, including methods based on constant shear rate (CSR), constant shear stress (CSS), and curve superposition (CSP). For the several polymer melts adopted in this work, a sequence of pressure dependence of viscosity was revealed as PS > PP > LDPE, which is typically acknowledged