HetGroMelt: Melting of Heterogeneous Polymers in SSE with Grooved Melting Sections

Single screw extruders are the most important machines in polymer processing. Those devices are used to convey, compress and melt plastic bulk materials. In practice, there are numerous different concepts of single screw extruders with diverging geometries and features. The melting of the solid particles is output rate limiting in most of the designs. There are different mechanisms to describe the melting of those polymeric pellets, none of which can be used universally. This project will focus on the modeling of the melting of both pure, homogeneous polymers and mixed, heterogeneous plastics, as often found in recycling. This is achieved by refining and enhancing existing models as well as by creating new ones which take the combination of different melting mechanisms into account. Hypothesis: By creating and combining different models of melting and transport mechanisms and verifying the validness of those models in experiments, an increase in the general knowledge and understanding of melting and transport phenomena can be achieved. Methods: Experimental data is needed for the computational modeling. For this purpose, a novel melting experiment is used which features a unique optical measurement system. Further model experiments include the determination of the pressure and temperature dependent shear force that is necessary to enable a highly efficient melting mechanism as well as extrusion experiments to confirm the gathered data. The computational modeling is derived from the results of the model experiments. The analytical modeling of the transport and melting mechanisms of (heterogeneous) polymeric materials in single screw extruders with and without barrel grooves in the melting section will be combined with a numerical model based on the network theory. Innovation and novelty: The few contemporary scientific papers dealing with the above mentioned topics still leave many questions unanswered and show that the contents of his proposal are highly relevant and both wished and needed by the scientific community. Experimental investigations of the melting of heterogeneous plastics in single screw extruders have shown a behavior, indescribable by the existing models. This made the necessity of a model to compute this new mechanism obvious which would be considered a valuable contribution to science and technology. The modeling of a combination of the mechanisms resulting in a hybrid melting mechanism is highly innovative and would increase the general knowledge and understanding of this phenomenon. This is both wished and needed by the scientific community.

Single-screw extruders are one of the most important machineries in the polymer processing Industry. Based on the economic framework, the primary objective of machine manufacturers is to increase the output rate while guaranteeing excellent melt quality. To meet the ever-increasing demands on the machinery, the process requires further optimization. Thus, a deeper understanding of the transport phenomena's in the plasticating unit governing the physical processes is essential. In this research Project we focused on grooved barrel single-screw extruders (SSE) with extended barrel grooves featuring grooves in the plasticating zone. Additionally, we investigated the melting behavior of homogeneous and heterogeneous polymers. In most cases, especially for grooved barrel SSE, the melting capability is the rate-limiting factor. Hence, in the last few years machine manufactures increasingly developed SSE with barrel grooves in the plasticating zone to increase the melting capability. In order to enable a physically based screw design and optimization of such systems we systematically analyzed and modeled the transport phenomena's inside these machines for homogeneous and heterogeneous materials. We carried out comprehensive experimental investigations of single-screw extruders using various grooved-barrel designs and polymers. The characteristic processing parameters such as screw speed, throughput, pressure profile, melting profile, and energy consumption were evaluated. For modeling the melting behavior experiments were conducted on a specially developed testing device using virgin (homogeneous), as well as mixtures of materials (heterogeneous). To predict the process and melting behavior we improved existing models and developed completely new models. Especially, to predict the viscous dissipation, being mainly responsible for the melt temperature increase along the screw, we developed novel analytical models. The novelty of these models lies in the coupling of the shear-thinning flow behavior of polymer melts and the underlying three-dimensional flow field in the screw channel. Removing the need for numerical simulations, the new models predict the viscous dissipation rate for both pressure-generating and pressure-consuming screw sections. Compared to existing approaches, the prediction accuracy is improved significantly.