Mechanical and thermal properties of carbon fibers and graphene nanoplatelets reinforced polypropylene hybrid nanocomposites

The automotive industry increasingly demands lightweight, strong materials capable of large-scale production. Therefore, the objective of this work is to develop polypropylene (PP) composites reinforced with short carbon fibers (SCF) and graphene nanoplatelets (GnP) that can be processed by injection molding. This study evaluates the effect of incorporating this hybrid reinforcement on the performance of PP composites. The response surface methodology (RSM) was used to model the mechanical properties as a function of the composition of the composites obtained. A co-rotating twin-screw extruder was used to prepare the set of binaries (PP/SCF and PP/GnP) and hybrid (PP/GnP/SCF) composites, followed by the injection molding process. Melt flow index (MFI) tests were performed to obtain preliminary information of the flow behavior of the composites. Conventional characterization techniques were used to determine the properties of the composites, such as thermogravimetrical analysis (TGA), flexural and impact strength tests. The GnP were characterized using Raman spectroscopy, the Brunauer-Emmett-Teller (BET) method, field emission gun-scanning electron microscopy (FEG-SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results suggest that the graphene used has a sparse number of stacked layers and defects, classifying it as a better-quality material. Both the GnP and SCF contributed to increasing the thermal stability and flexural properties of the composites produced. Only the PP/SCF composites showed superior impact properties than PP. The 75/5/20 PP/GnP/SCF hybrid composites showed the best flexural properties.