Mechanical properties of polymer melt-impregnated fiber tape sandwiches using injection molding technology

In this study, the direct melt impregnation of unidirectional glass fiber tapes in an injection molding process is investigated. The simple textile structures were used for a load-adapted reinforcement of injection-molded parts, determining the impregnation quality by mechanical tests. A sandwich layer construction was made with an outer unidirectional fiber layers and an inner injection-molded layer with pure or additionally short fiber-reinforced polypropylene (PP). The glass fiber tapes were produced in a continuously working fiber–foil process where the aligned fiber bundles have been fixed with one side on a PP foil under temporarily acting pressure and temperature. A special bundle spreading device reduced the number of individual fiber layers, which ensured the direct melt impregnation in the injection molding process. The mechanical properties of the sandwich structures were determined using a three-point bending flexural test as well as Charpy and puncture impact tests to investigate the energy absorption. The results were compared to unreinforced and globally short fiber-reinforced test samples. The local reinforcement, designed for bending stiffness and energy absorption, led to a considerable reinforcement effect with minimal mass increase in comparison with the short fiber-reinforced samples. The fiber masses required to achieve commensurable properties were significantly reduced. Thus, when using the fiber tapes, only one-third of the fiber mass necessary for reinforcement with short glass fibers was required.