Modeling fiber dispersion and damage of recycled organic sheets in the injection molding process

• Applicant: Professor Dr.-Ing. Elmar Moritzer
• Subject Area: Polymeric and Biogenic Materials and Derived Composites
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 534022466

Fiber-reinforced plastics are increasingly used in high-tech applications in the automotive or aerospace industry for example for lightweight construction in order to reduce resource consumption, especially due to their very good weight-specific, mechanical properties. To realize high mechanical properties in the components, so-called organic sheets are used, in which the continuous fibers are arranged as different fabric structures or unidirectional scrims in a thermoplastic matrix. Through the process of mechanical recycling, there is the possibility of high-quality reuse of end-of-life organic sheets into new long-fiber-reinforced components. In the mechanical recycling process, the fiber-matrix composite is reduced in size via granulators or shredders, and the regrind can then be directly reprocessed into new products in the injection molding process. Compared to short- or long-fiber-reinforced plastics, fabric-reinforced regrind faces the challenge of fabric disintegration and homogeneous fiber dispersion in the injection molding unit. Therefore, this project aims to develop a mathematical model that describes the resulting fiber length after plasticizing in the injection molding process when recycling organic sheets. Furthermore, the dispersion behavior of the fibers is to be considered in the model. The conflicting goals of minimizing the fiber length reduction and simultaneously maximizing the dispersion and homogenization of the fibers in the injection molding unit will be addressed. Within the scope of the project, regrind is initially produced from organic sheets with different fabric structures in defined particle sizes, so that different initial fiber lengths are available in the regrind for the injection molding process. For the specific investigation of the dispersion behavior of the fabric structures, a test rig will be set up that allows the recording of temporally staggered dissolution of the fabric structures in the plastic melt at different shear rates and pressures. The dissolution of the fabric structures is then analyzed using computer tomography and the determined correlations are integrated into the model. The feed behavior of the regrind into the injection molding unit is studied through dead-stop investigations. Screw drawing investigations allow sampling for the analysis of fiber dispersion as well as fiber shortening along the screw. The obtained results are used for mathematical modeling of fiber dispersion and damage of recycled organic sheets in the injection molding process. In addition, the results along the screw channel are used to validate the model-based results. For industrial companies, the mathematical model will be highly relevant to use recycled organic sheets in components in the future, as it allows accurate prediction of fiber length and fiber dispersion in the injection molding unit which is necessary to estimate the mechanical properties of the resulting component.

• DFG Programme: Research Grants