Simulation of the Melt Conveying Zone of a Single Screw Extruder using the Rheological Properties of Polymer Mixtures in the Scope of Mechanical Recycling

When designing an energetically and economically optimized extrusion process the rheological properties of the polymers used are imperative. However, the measuring of shear viscosity is time consuming, even more so when using mixtures of polymers, as is likely in the scope of a recycling process. The aim of this work is to simulate the melt conveying zone of a single screw extruder, when using contaminated polymers instead of commonly used pure materials, to optimize a mechanical recycling process and reduce the number of measurements needed for rheological input data.
For this purpose, a polypropylene (PP) grade is blended with either polyamide 12 (PA 12) or a second PP grade, which serve as impurities in this experiment. To consider the change in shear viscosity of these blends, their rheological data is both measured using a high-pressure capillary rheometer and approximated using mixing models. Moreover, a method for simulating the pressure distribution along the metering zone considering mixed polymers is presented. The calculated values for the pressure in the melt conveying zone are then experimentally confirmed using a lab scale smooth bore single screw extruder with pressure sensors along the screw channel. Results show that the application of the shear viscosity through mixing models yields pressure values similar to those measured in the experiments.