In situ exfoliation method to fabricate a graphene-reinforced polymer matrix composite
A method for forming a graphene-reinforced polymer matrix composite is disclosed. The method includes distributing graphite microparticles into a molten thermoplastic polymer phase; and applying a succession of shear strain events to the molten polymer phase so that the molten polymer phase exfoliates the graphite successively with each event until at least 50% of the graphite is exfoliated to form a distribution in the molten polymer phase of single- and multi-layer graphene nanoparticles less than 50 nanometers thick along the c-axis direction.
1. A method for forming a graphene-reinforced polymer matrix composite, comprising:
(a) distributing graphite microparticles into a molten thermoplastic polymer phase, wherein at least 50% by weight 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 molten polymer phase in situ so that the shear stress within said molten polymer phase is equal to or greater than the Interlayer Shear Strength (ISS) of said graphite microparticles and said molten polymer phase mechanically exfoliates the graphite successively with each event until said graphite is at least partially exfoliated to form a distribution in the molten polymer phase of essentially pure and uncontaminated single- and multi-layer graphene nanoparticles less than 10 nanometers thick along the c-axis direction.
2. The method of claim 1 , wherein the graphite particles are prepared by crushing and grinding a graphite-containing mineral to millimeter-sized dimensions.
3. The method of claim 2 , wherein the millimeter-sized particles are reduced to micron-sized dimensions using ball milling and attritor milling.
4. The method of claim 3 , wherein the graphite particles are extracted from the micron-sized particle mixture by a flotation method.
5. The method of claim 4 , wherein the extracted graphite particles are incorporated in a polymer matrix using a single screw extruder with axial fluted extensional mixing elements or spiral fluted extensional mixing elements.
6. The method of claim 5 , wherein the graphite-containing polymer matrix is subjected to repeated extrusion to induce exfoliation of the graphitic material, thus forming a uniform dispersion of graphene nanoparticles in the polymer matrix.
7. The method of claim 6 , wherein the polymer is selected from the group consisting of polyether-etherketones, polyetherketones, polyphenylene sulfides, poly-ethylene sulfides, polyetherimides, polyvinylidene fluorides, polysulfones, polycarbonates, poly-phenylene ethers/oxides, nylons, aromatic thermoplastic polyesters, aromatic polysulfones, thermoplastic polyimides, liquid crystal polymers, thermoplastic elastomers, polyethylenes, polypropylenes, polystyrene, polymethylmethacrylate, polyacrylonitrile, ultra-high-molecular-weight polyethylene, polytetrafluoroethylene, acrylonitrile butadiene styrene, polyamides, poly-phenylene oxide, polyoxymethylene plastic, polyimides, polyaryletherketones, polyvinylchloride, acrylics, and mixtures of two or more thereof.
8. The method of claim 1 , wherein the succession of shear strain events is applied until at least 50% by weight of the graphite is exfoliated to form a distribution in the molten polymer phase of single- and multi-layer graphene nanoparticles less than 10 nanometers thick along the c-axis direction.
9. The method of claim 1 , wherein the succession of shear strain events is applied until at least 90% by weight of the graphite is exfoliated to form a distribution in the molten polymer phase of single- and multi-layer graphene nanoparticles less than 10 nanometers thick along the c-axis direction.
10. The method of claim 1 , wherein the succession of shear strain events is applied until at least 75% by weight of the graphite is exfoliated to form a distribution in the molten polymer phase of single- and multi-layer graphene nanoparticles less than 10 nanometers thick along the c-axis direction.
11. The method of claim 1 , wherein the graphite is doped with other elements to modify a surface chemistry of the exfoliated graphene nanoparticles.
12. The method of claim 1 , wherein the graphite is expanded graphite.
13. The method of claim 1 , wherein a surface chemistry or nanostructure of the dispersed graphite is modified to enhance bond strength with the polymer matrix to increase strength and stiffness of the graphene composite.
14. The method of claim 1 , wherein the graphene nanoparticles are directionally aligned thereby providing one-, two- or three-dimensional reinforcement of the polymer matrix phase.
15. The method of claim 1 , wherein said graphene-reinforced polymer matrix composite contains residual graphite microparticles.
16. A graphene-reinforced polymer matrix composite prepared by the method of claim 1 , wherein the composite comprises contamination-free graphene-polymer interfaces and wherein the polymer adheres to or is covalently bonded to the graphene-polymer interfaces.
17. The graphene-reinforced polymer matrix composite of claim 16 , wherein said composite contains between about 0.1% and about 30% by weight of graphene.
18. The graphene-reinforced polymer matrix composite of claim 16 , wherein said composite contains between about 1% and about 10% by weight of graphene.
19. The graphene-reinforced polymer matrix composite of claim 16 , wherein said composite contains between about 5% and about 50% by weight of graphene.
20. The graphene-reinforced polymer matrix composite of claim 16 , wherein said composite contains between about 10% and about 30% by weight of graphene.
21. The graphene-reinforced polymer matrix composite of claim 16 , wherein the polymer is selected from the group consisting of polyether-etherketones, polyetherketones, poly-phenylene sulfides, polyethylene sulfides, polyetherimides, polyvinylidene fluorides, polysulfones, polycarbonates, polyphenylene ethers/oxides, nylons, aromatic thermoplastic polyesters, aromatic polysulfones, thermoplastic polyimides, liquid crystal polymers, thermoplastic elastomers, poly-ethylenes, polypropylenes, polystyrene, polymethylmethacrylate, polyacrylonitrile, ultra-high-molecular-weight polyethylene, polytetrafluoroethylene, acrylonitrile butadiene styrene, poly-amides, polyphenylene oxide, polyoxymethylene plastic, polyimides, polyaryletherketones, polyvinylchloride, acrylics, and mixtures thereof.
22. The graphene-reinforced polymer matrix composite of claim 16 comprising residual graphite microparticles.
23. The graphene-reinforced polymer matrix composite of claim 16 , wherein the graphite is expanded graphite.
24. The graphene-reinforced polymer matrix composite of claim 16 , wherein a surface chemistry or nano structure of the dispersed graphite is modified to enhance bond strength with the polymer matrix to increase strength and stiffness of the graphene composite.