Stability analysis of non-isothermal film blowing process for non-Newtonian fluids using variational principles

Abstract

In this study, a numerical stability analysis of the film blowing process is performed. The numerical scheme used is based on a variational principle model of the film blowing operation. This model employs non-isothermal processing conditions, non-Newtonian behavior of the polymer and physically limiting criteria (maximum tensile and/or hoop stress) to investigate the complex relationship between processing conditions (internal bubble pressure, heat transfer coefficient, mass flow rate, cooling air temperature, melt/die temperature), material parameters (rupture stress, Newtonian viscosity, flow activation energy, power law index) and film blowing stability. It has been shown that the melt/die temperature has the highest impact on the film blowing stability window size as well as on the maximum and minimum achievable film thickness. In more detail, it has been found that processing parameters together with flow activation energy have much higher effect on the film blowing stability and maximum achievable film thickness than the basic rheological characteristics of the polymer melt. On the other hand, the effect of basic rheological parameters of the polymer melt become much more important than processing parameters (except of melt/die temperature) in order to reach minimum film thickness.