Modeling of rheological properties of polyethylene melts during uniaxial stretching

The paper considers the use of the modified Vinogradov and Pokrovskii rheological model to describe the occurrence of stresses in a polymer melt during uniaxial stretching. One of the changes introduced in the model concerns the anisotropic law of internal friction, which makes it possible to take into account the nonmonotonic dependence of the stationary elongational viscosity on the extension rate. Another change is associated with the multimode nature of the relaxation processes accompanied the deformation of the polymer melt. The above changes made it possible to evaluate an increase in the longational viscosity of the melt, which was found to be three times higher than its shear viscosity in the linear deformation mode. A comparison between the results of calculation and the experimental data available in the literature was performed for five industrial samples of polyethylene with a branched structure of macromolecules. The calculations according to the mathematical model were carried out by the Runge-Kutta method...