How do graphite nanoplates affect the fracture toughness of polypropylene composites?

From a mechanical perspective, graphene and its derivatives, such as graphite nanoplates, graphite oxide, carbon nanofibers, or nanotubes, are envisioned as ideal nanofillers for polymer composites. Thus, tremendous research effort has been invested to determine the reinforcing mechanism of these nanofillers in the matrix: crack bridging, crystallization enhancement, or crack deflection are some possible mechanisms that have been proposed. In this work, a detailed analysis of the fracture mechanism of graphite nanoplate (GNP)/polypropylene composites was performed. Commercially available graphite nanoplates, composed of multiple graphene layers stacked together, were used to produce polypropylene nanocomposites by following a masterbatch technique. The fracture toughness was determined by applying the Spb parameter method and the fracture mechanism was identified to be void nucleation and growth. We demonstrate how GNPs affect and improve the fracture toughness of polypropylene. This improvement is caused by the debonding of the GNP agglomerates, which promotes the matrix plastic deformation during the fracture process.