Structure and interfacial shear strength of polypropylene-glass fiber/carbon fiber hybrid composites fabricated by direct fiber feeding injection molding

The structure and interfacial shear strength (IFSS) of polypropylene-glass fiber/carbon fiber hybrid composites fabricated by a new method called direct fiber feeding injection molding (DFFIM) process were investigated based on the skin-core-skin structure and modified Kelly-Tyson equation, respectively. The fiber dispersion state was evaluated qualitatively by scanning electron microscopy (SEM) and quantitatively by the fiber distribution index (FDI). Carbon fiber agglomeration is more likely to occur in hybrid composites and was present in the core layer of DFFIM composites in this study. However, glass fiber has shown relatively uniform dispersion in hybrid composites with a greater tendency to be distributed in the skin layers. This is attributed to the difference in feeding method, where glass fibers were fed through the hopper while carbon fibers were inserted from the vent hole. The IFSS between fibers and polypropylene of different composites in different layers is discussed by considering fiber length and orientation distributions in the core and skin layers, respectively.