It is of great importance for polymer processing whether and how viscosity influences the wettability of tool surfaces. We demonstrate the existence of a distinct relationship between the contact angle of molten polymers and zero shear viscosity in this paper. The contact angle of molten polypropylene and polymethylmethacrylate on polished steel was studied in a high temperature chamber using the sessile drop method. A high pressure capillary rheometer with a slit die was employed to determine the shear viscosity curves in a low shear rate range. A linear relation between the contact angle and zero shear viscosity was obtained. Furthermore, the contact angle and the zero shear viscosity values of the different polymers were combined to one function. It is revealed that, for the wetting of tool surfaces by molten polymers, a lower viscosity is advantageous. Furthermore, a model based on the temperature shift concept is proposed which allows the calculation of the contact angle of molten polymers on steel for different temperatures directly from shear viscosity data.

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%.

Processing of thermoplastic composites is increasingly gaining importance due to their excellent mechanical properties combined with their recycling‐feasibility. However, distinguishing anisotropic thermal properties of these materials make process simulation challenging. This work deals with an alternative way of analytical modeling of the anisotropic thermal conductivity of fabrics embedded in a thermoplastic matrix, as in the case of sheets for thermoforming applications, in which heating times are often process limiting. By creation of a unit cell and applying heat flux balances, the thermal conductivity in the fiber direction and in the transversal direction can be calculated. The transversal direction is the most important factor for the addressed thermoforming applications. The proposed model is then successfully validated through Hot Disk measurements of glass fiber reinforced polyamide sheets. Furthermore, authentication is reached by the comparison to measured thermal conductivity values from another study. Hence, it can be shown that the model proves to be more accurate than existing analytical models.

Modeling how thermoplastic composites are processed using thermoforming is a challenging task, and not only due to the heterogenic nature of the material. During the thermoforming processes, the polymeric matrix has to be heated above the softening temperature, enabling the composite to be formed into three‐dimensional parts. As the system mobility increases, thermal deconsolidation takes place, and voids are created or expand within the composite sheet. These voids alter the sheet's material properties and aesthetic characteristics. The formation of gas‐filled voids in the material hinders the heat transport, resulting in longer heating times and inefficient processes. Moreover, such voids invalidate models widely used for processing thermoplastic composites. This study resulted in a novel analytical model that can be applied to calculate the anisotropic thermal conductivity of thermoplastic composites depending on the deconsolidation temperature and the fiber orientation. The model was validated by running hot disk tests on polypropylene reinforced with glass fibers (PP/GF) and applying X‐ray computed tomography to the composite samples. The samples are first consolidated in a hot‐plate press and consecutively deconsolidated in a pressure‐free process. The study findings show that the model is highly accurate within the temperature range relevant to composite processing and will be a useful asset in process modeling.