Experimental investigation of the rheological behaviors of polypropylene in a capillary flow

Abstract

The rheological characterization of polymer melts is strongly related to their material properties. In this study, we focused on the rheological behaviors of a polypropylene (PP) melt through a capillary die. With an advanced twin-bore capillary rheometer with dies measuring 1.0, 0.5, and 0.25 mm in diameter, experiments were performed over a shear-rate range of 3 3 10 2 to 5 3 10 3 s 21 at three temperatures, 210, 220, and 230 8C. The results demonstrate that the geometry dependence of the PP viscosity relied on the die diameter and the temperature of the PP melt. The viscosity values of the PP melt in the 0.25-mm diameter die were higher than were those in the 0.5-and 1.0-mm dies at 220 and 230 8C. However, the viscosity values in all of the tested dies were similar at 210 8C. The tendency for the viscosity to decrease as the temperature of the polymer melt increased weakened in the 0.25-mm diameter die. As a result, the pressure applied to the PP melt in the 0.25-mm diameter die increased; this caused a decrease in the free volume between molecules. On the basis of the Barus equation, the contribution of pressure to the changed viscosity in each die at each of the tested temperatures was calculated and was found to be as high as 32.86% in the 0.25-mm die at 230 8C. Additionally, the effect of the wall slip on the geometry dependence of the PP viscosity in the tested dies was investigated with a modified Mooney method. The values of the slip velocity revealed that wall slip occurred only in the 0.25-mm die at 210 8C.

Comparisons of the rheological behaviors of polypropylene and polymethyl methacrylate in a capillary die

“…For the investigated PP/PMMA melts, the observed differences in the temperature sensitivity and geometric dependence of the shear viscosity are also in agreement with the analysis reported in our previous study . An increasing temperature leads to a decrease of viscosity, whereas an increasing pressure is linked to an increase in the viscosity of polymer melt.…”

Development of a Rheology Die and Flow Characterization of Gas-Containing Polymer Melts

“…Bagley correction becomes unnecessary, as no inlet and outlet pressure losses occur. Meng et al [ 15 ] performed viscosity measurements of PP using various capillary diameters and showed that no wall slip occurs in a 1 mm capillary at 210–230 °C. In our experiments, we therefore assumed that the no-slip condition is valid, which also rendered a Mooney correction unnecessary.…”

Effects of Heating Temperature and Load Weight on Rheological Properties of Waste Plastic Cup

“…Increasing temperature causes a decrease in shear stress, fracture strength and fracture strain. Meng et al 13 examined the effect of die diameter and operating temperature on the viscosity of recycled PP. A decrease in die diameter and operating temperature leads to an increase in the viscosity of recycled PP.…”