- The extraordinary mechanical properties of graphene prompt its incorporation into a wide range ofpolymeric nanocomposite materials (NCMs). However, similar to other nanomaterials (NMs), the rein-forcement efficiency of graphene and its derivatives is hindered by their agglomeration and poorcompatibility with the polymer matrix. In this paper, edge-functionalized graphene nanoribbons (EF-GNR) are incorporated in brittle epoxy polymer matrix. The functionalization process by polyvinylamine(PVAM) chains occurs only at the edges, preserving the in-plane sp2of the graphene; thereby the PVAMEF-GNRs are both compatible and strong. The produced NCMs exhibit a wide range of enhanced me-chanical properties including fracture toughness,flexural strength and shear strength at low EF-GNRloading (0.15 wt%). The effect of the edge functionalization is indeed critical, demonstrating superiormechanical properties by the EF-GNR loaded NCMs compared to pristine-GNR loaded composites.Finally, a comparative overview of various carbon NM-loaded NCMs indicates that EF-GNR possess highreinforcement efficiency (enhancement % per NM loading %) making it an attractivefiller for polymersystems. Graphene Nanoribbon - Polymer Composites: The Critical Role of Edge Functionalization. Available from: https://www.researchgate.net/publication/287508105_Graphene_Nanoribbon_-_Polymer_Composites_The_Critical_Role_of_Edge_Functionalization [accessed Jan 10, 2016].