Graphene Oxide-Modified Aramid Fibers for Reinforcing Epoxy Resin Matrixes

Carboxylated and aminated graphene oxide (CGO and AGO) were first prepared by using carboxyl-terminated aromatic hyperbranched polyester (HBPC) and amino-terminated aromatic hyperbranched polyester (HBPA) noncovalent functionalized GO, respectively. Subsequently, multiscale reinforcing fibers (CGO-PDA-AF and AGO-PDA-AF) were prepared by exploiting the super adhesion of the polydopamine layer (PDA) and its physical adsorption and chemical grafting with the CGO and the AGO. This study examined the tensile strength of the modified aramid fiber (AF) monofilament and the interfacial shear strength (IFSS) between the modified AF monofilament and the EP matrix, and an investigation was conducted on the interfacial enhancement mechanism. As indicated from the results, the AGO exerted a more effective modifying effect than the CGO. The single filament tensile strength and IFSS of the AGO-PDA-AF were the maximum (4.66 GPa and 96.2 MPa), nearly 8.6 and 7.9% higher than those of the CGO-PDA-AF, respectively. The enhancement of the interface performance between the AGO-PDA-AF and the EP was attributed to the introduction of considerable amino active groups in the AGO, thereby forming a stable covalent bond with the epoxy matrix, which significantly improved the interface bonding strength. Moreover, the flexible coating layer formed by the AGO could reduce the stress concentration of the interface through deformation, so the AF could be carried more uniformly. Furthermore, the AGO increased the surface affinities of the AF and improved the mechanical interlocking with the EP matrix.