In situ exfoliation method to fabricate a graphene-reinforced polymer matrix composite

A method for forming a graphene-reinforced polymer matrix composite, comprising:

• (a) distributing graphite microparticles into a molten thermoplastic polymer phase comprising one or more molten thermoplastic polymers to form a graphite-molten thermoplastic polymer phase, wherein at least 50% of the graphite in the graphite microparticles consists of multilayer graphite crystals between 1.0 and 1000 microns thick along a c-axis direction;
• and
• (b) applying a succession of shear strain events to the graphite-molten thermoplastic polymer phase so that shear stress within said molten polymer phase exceeds the Interlayer Shear Strength (ISS) of said graphite micro articles and said molten polymer phase exfoliates the graphite microparticles successively with each event until said graphite microparticles are at least partially exfoliated to form a distribution in the molten polymer phase of single- or multilayer graphene nanoparticles, or both, less than 10 nm thick in a c-axis direction, and further continuing the shear strain events until graphene fractures of said exfoliated single- or multilayer graphene sheets are formed across the basal plane defined by a-axis and b-axis, wherein the edges of the graphene fractures further comprise reactive free radical graphenic carbon bonding sites directly covalently bonded to and inter-molecularly cross-linking thermoplastic polymer chains.