Graphene oxide-mediated thermo-reversible bonds and in situ grown nano-rods trigger ‘self-healable’ interfaces in carbon fiber laminates

Abstract

Carbon fiber reinforced epoxy (CFRE) laminate structures have emerged as futuristic materials having surpassed metals in strength and durability. The interfacial chemistry determines the mechanical performance of such laminates. In this study, a unique approach was adopted wherein the alternate layers of the carbon fiber (CF) mat were grown in situ with ZnO nano-rods and modified with bis-maleimide (BMI), and epoxy resin containing 0.2 or 0.5 wt% graphene oxide (GO) was infused using conventional VARTM technology to enhance the mechanical interlocking of epoxy with the fiber as well as to impart self-healing properties to the laminate. While ZnO rods offer surface roughness thereby facilitating better wetting of epoxy, the Diels–Alder thermo-reversible bonds between BMI and GO facilitate self-healing properties besides improving the interfacial adhesion between epoxy and CF. The rationale behind this work is to synergistically improve the interface-dominated mechanical properties like interlaminar shear strength (ILSS) while maintaining or even improving fiber-dominated properties like flexural strength (FS) as well as imparting considerable recovery in strength post the self-healing cycle. The laminates after this treatment (having 0.5 wt% GO) indeed exhibited 46% improvement in FS and 33% improvement in ILSS properties as well as an ILSS recovery of 70%. The surface analysis suggests that ZnO nano-rods offer surface roughness that helps in the wettability of the matrix on the fibers. In addition, the 2D and 3D representative volume analysis (RVE) model was established to identify the load transfer behaviour in the ZnO-CF-epoxy interface in the microscale reference region. The fractographic analysis confirmed that rigid ZnO nano-rods allowed better matrix adhesion resulting in improved mechanical performance.