The scope of this work is the development of a method to estimate the temperature and shear rate-dependent viscosity of mixtures composed of two polymers. The viscosity curve of polymer mixtures is crucial for the modeling and optimization of extrusion-based recycling, which is the most efficient way to recycle polymeric materials. The modeling and simulation of screw extruders requires detailed knowledge of the properties of the processed material, such as the thermodynamic properties, the density, and the rheological behavior. These properties are widely known for pure materials; however, the incorporation of impurities, like other polymers in recycled materials, alters the properties. In this work, miscible, immiscible, and compatibilized immiscible polymer mixtures are considered. A new method based on shear stress is proposed and compared to the shear rate-based method. Several mixing rules are evaluated for their accuracy in predicting mixture viscosity. The developed methods allow the prediction of the viscosity of a compatibilized immiscible mixture with deviations below 5% and that of miscible polymer mixtures with deviations below 3.5%.

Melting models for flood fed single screw extruders, like the Tadmor model, describe the melting of pure thermoplastic polymers. However, the melting behavior of heterogenous polymer systems is of great interest for recycling issues, for example. In this work, the melting of polymer mixtures and that of pure bulk polymers by the drag induced melt removal principle is examined both theoretically and experimentally. The applied model experiments represent the melting of the solid bed at the barrel in single screw extruders. As polymer pellet mixtures, polypropylene-homopolymer mixed with polypropylene-block-copolymer, high density polyethylene, polyamide 6, and polymethylmethacrylate were studied using different mixing ratios. The melting rate and the shear stress in the melt film were evaluated dependent on the mixing ratio. The results show that when processing unfavorable material combinations, both shear stress and melting rate can be far below that of pure materials, which was also confirmed by screw extrusion and screw pull-out experiments. Furthermore, approaches predicting the achievable melting rate and the achievable shear stress of polymer mixtures based on the corresponding values of the pure materials are presented.

This work deals with the melting of polymeric bulk materials and the melt penetration into the solid bed utilizing a model experiment that simulates the melting process in single screw plasticating units. The polymer granules are pressed onto a heated rotating shaft. The thickness distribution of the resulting melt film is measured according to the principle of optical triangulation (light intersection). This new method and the measurement of the bulk density using a piston position measurement were presented earlier by the authors. The combination of these different principles allows the determination of the melt penetration into the solid bulk as it takes place in the delay zone of single screw plasticating units. The melting behavior of spheroidal and cylindrical shaped polypropylene-homopolymer (PP-H) bulk solids is analyzed at different applied pressure. Spheroidal bulk solids show significant advantages compared to cylindrical shaped granules which melt much slower, particularly at higher pressures. The melt clearly penetrates deeper into the spheroidal bulk compared to cylindrical bulk.

The bulk density of polymers is a crucial factor for the throughput and the pressure build-up of single screw plasticating units. It depends not only on the density of the polymeric materi...