Rheological characterization of complex materials and modeling of shear-free flows.

Abstract

The behaviour of complex materials, the main study of rheology, is investigated in this work. In an effort to better understand these materials, a two-step process was undertaken. First, the nonlinear behaviour of such materials was determined in a laboratory. Second, experimental measurements were extracted from the literature with respect to shear-free flows of complex materials and simulations were performed for the shear-five flows in question. These flows involve uniaxial extension in the case of fiber spinning and film casting, and biaxial extension in the caw of film blowing. Rheological experiments were conducted on polymer solutions, namely poly(ethylene oxide) and polyacrylamide, at room temperature and on a polypropylene (PP) polymer melt at high temperature, with a Weissenberg rheogoniometer in a laboratory. The shear viscosity and first normal stress difference were measured at varying shear rates. An integral constitutive equation of the K-BKZ type was used to predict the nonlinear behaviour of these materials. Transient regression was performed to find the parameters of the K-BKZ model for the U-Stamylan low-density polyethylene (LDPE), and predictions for steady-state materials functions were given. Fiber-spinning simulations were undertaken for a series of complex materials at a wide range of operating conditions. Film-casting simulations were also undertaken for a series of complex materials. (Abstract shortened by UMI.)