An Experimental Study of Rheological Properties of Polymer Melts in Laminar Shear Flow and of Interface Deformation and Its Mechanisms in Two-Phase Stratified Flow

Abstract

The stress state of four rheologically characterized polymer melts—low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), and poly(methyl methacrylate) (PMMA)—in laminar shearing flow was completely determined by measuring the non-Newtonian viscosity μ and the first and second normal stress differences N1 and N2. The mean N2 function was negative and about 0.1–0.3 the value of N1. The measurements were made in a Weissenberg rheogoniometer using cone- and parallel-plate geometries. Additional viscosity measurements were made in a capillary rheometer. An experimental study of interface distortion in the stratified two-phase flow has been carried out using these melts. It was found in the stratified flow experiments that the lower viscosity melts exhibited concave interfaces and encapsulated the higher viscosity melts irrespective of the relative values of N1 and N2. The rate of interface distortion and encapsulation increases with increasing viscosity differences. The pressure losses for stratified flow tended to be close to the values for the lower viscosity phase, especially for long dies. The problem of instabilities at the interface between the two melts is briefly discussed.