Adaptation of the Direct Reaction Injection Molding Process for Production and Processing of Long FiberReinforced Thermosets (LFD-Injection Molding Process) to the use of carbon fibers instead of glass fibers

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Fiber reinforced phenolic molding resins are among the oldest engineering polymers and are very versatile due to their advantageous properties. In addition to good thermo-mechanical properties, they have excellent media resistance and high dimensional stability. They are typically processed by injection molding. In contrast to thermoplastics, components made from phenolic molding compounds exhibit a low elongation at break and a low impact strength. These disadvantageous material properties restrict the use of fiber-reinforced phenolic resins in numerous applications. The project "LFD injection molding process" investigated the extent to which these disadvantages can be mitigated by increasing the fiber length in the molded part. The scope of the current project is to find out how the property profile of long fiber reinforced phenolic molding compounds can further be improved by using long carbon fibers (LCF) instead of long glass fibers (LGF). This will be realized by a variable feeding of the LCF into the injection molding process. To achieve this, the differences between LGF and LCF in terms of cutting, feeding and homogenization of the fibers are to be determined. In parallel, analysis methods already established for glass fibers will be adapted to carbon fiber-reinforced phenolic resins.Within the scope of the project, suitable carbon fibers and phenolic resins will be selected for the LFD process and compounded to short fiber molding compounds by twin screw extrusion. The moldability of the compounds will be ensured with the aid of calorimetric (DSC), rheological (oscillatory rheology) and typical at-line quality assurance methods (Orifice Flow Test OFT). To reliably evaluate the effects of different material and process parameters on the fiber length distribution, a valid and reproducible measurement method is required. For this reason, a measurement method that was developed for glass fibers will be adapted and validated for carbon fibers as well. The method is based on the pyrolytic removal of the matrix, followed by automated image evaluation of an aqueous fiber suspension. The existing LFD process technology will be adapted to the use of carbon fibers with as little changes as possible , so that the process designs for glass and carbon fibers will be comparable. The incorporation quality of the carbon fibers into the phenolic resin will be characterized by evaluating the opposing effects of (undesired) fiber shortening and (required) fiber dispersion. Fiber length measurements and computer tomographic evaluations will be used for this purpose. Finally, the aim of the project is to draw together the results of the previous work and to derive the process-structure-property relationship for the molding compounds and components produced.