A constitutive equation for low density polyethylenes.

Polymer melts with long side branches, such as low density polyethylene, have high viscosities in uniaxial extensional deformations and modest viscosities in shear and biaxial extension. It is important to be able to model the rheological behavior of polymer melts in these three types of deformation, since they all occur, in various combinations, in polymer processing applications such as extrusion, cable jacketing, and mold filling. We present here a constitutive equation (stress-strain relationship) that accurately describes the stresses in each of these three types of deformation for a low density polyethylene. The constitutive equation is an empirical equation of the Kaye-BKZ form.