Structural-Phenomenological Rheological Model for Engineering Calculations of Polymeric Media Flows

Abstract

Studying the behavior of flows of solutions and polymer melts in the field of nonlinear viscoelasticity allows describing the rheological properties in more details and more accurately assess the adequacy of rheological models. A new structural-phenomenological model is proposed to describe the rheological behavior of melts of branched polymers. This model can be recommended for engineering calculations of flows of polymeric media. The model is obtained from the modified Vinogradov-Pokrovsky model which is based on the microstructur-al approach and describes the dynamics of a polymer fluid. Stationary viscometric functions for simple shear and uniaxial tension, as well as stationary shear viscosity, the first-difference coefficient of normal stresses, stationary viscosity at uniaxial tension, are calculated using the obtained model. Also, the influence of model parameters on the form of the functions has been studied. It is shown that the model describes with good accuracy the nonlinear viscoelastic behavior of flowing polymer systems: an anomaly in viscosity, a drop in the coefficient of the first difference of normal stresses, and a nonmonotonic nature of the dependence of the steady-state elongation viscosity on the tensile rate. The viscometric functions data are compared with the experimental data for an industrial polyethylene melt sample.