Experimental and numerical studies of stress fields of a branched polybutadiene in a flat die

There is a growing body of laboratory and industrial evidence that the viscoelastic characteristics of molten polymers contribute to improving the efficiency of polymer extrusion molding. Understanding the behavior of molten polymers in manufacturing processes requires the qualitative and quantitative determination of flow kinematics and stress distribution. The optimization of forming processes and final properties of transformed products requires the mastery of high-performance simulation models. So, it is necessary to be able to correctly describe the non-linear rheological behavior of the molten polymers by appropriate constitutive equations and a relatively easy implementation in computer codes. In this work, experimental and numerical studies are performed to investigate the rheological behavior of branched polybutadiene into a two-dimensional channel of a capillary rheometer. The stress field in the flow was analyzed with a birefringence device to identify areas of stress concentration and to show its progress in different areas of the extrusion die. Also, we obtain the stress field with numerical simulations using ANSYS Fluent 16.0 as a solver and Gambit as a mesh generator. The power law model, or Ostwald-de Waele, adopted in this numerical study is a rheophysical approach used to simulate the rheological behavior of branched polybutadiene during extrusion molding. Furthermore, this numerical approach can be adopted for large flow rates where experimental study becomes very difficult.