Simulation of the Melt Conveying Zone of a Single-Screw Extruder for Mixed Polymer Materials Using an Isothermal Analytical Flat Plate Model

An optimized extrusion process is desired for both an environmentally friendly and economically sustainable recycling process. The aim of this study 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 to reduce the number of measurements needed for rheological input data by using mixing rules. Polypropylene (PP) is blended with a polyamide 12 (PA 12) grade and another PP grade to introduce polymer impurities into the material. The blends are subjected to extrusion experiments in a lab-scale single-screw extruder with pressure and temperature sensors along the barrel. An isothermal analytical simulation model is proposed using representative shear rate values and rheological mixing rules to calculate the pressure distribution along the screw channel throughout the melt conveying zone. The rheological input data for the simulation is taken from high-pressure capillary rheometric measurements, but also substituted with values derived from mixing rules. The results show that the application of the shear viscosity through mixing models yields simulated pressure values similar to those measured in the experiments. With the introduction of representative viscosity into the model, relative deviations of around 5% at certain screw speeds can be achieved.