Patent Publication Number: US-2018030277-A1

Title: Uniform Dispersing of Graphene Nanoparticles in a Host

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of International Application No. PCT/US2016/022229, filed on Mar. 12, 2016 claiming the priority to U.S. Provisional Application No. 62/132,699 filed on Mar. 13, 2015, the contents of each of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates in general to the field of graphite, and more particularly, to compositions and methods of graphite oxide entrainment in cement and asphalt composites. 
     BACKGROUND OF THE INVENTION 
     Without limiting the scope of the invention, its background is described in connection with composite materials. 
     Graphene is an allotrope of carbon. Graphene&#39;s purest form is a one-atom-thick planar sheet of sp 2 -bonded carbon atoms that are densely packed in a honeycomb or hexagonal crystal lattice. In the last few years scientists have identified multi-layer graphene oxide or a few layer of graphite oxide to be of sufficient strength and electrical conductivity to be useful as an additive in a host to provide superior mechanical, chemical, thermal, gas barrier, electrical, flame retardant and other properties compared to the native host. Improvement in the physicochemical properties of the host depends on: 1) a uniform distribution and entrainment of the graphene flake, 2) optimizing the interfacial bonding between the graphene flake and host&#39;s matrix, 3) removal of gasses entrained in the host during processing, 4) optimizing the additive&#39;s innate properties, e.g. flatness, and 5) optimizing the thickness to surface-area ratio of the graphene flake and/or the chemical functionalization or decoration on the flake/particle. 
     Graphene is one of the strongest materials ever tested. Various research institutes have loaded hosts with carbon allotropes such as carbon nanotubes (CNT), graphene flakes (GF), graphene oxide (GO), and graphite oxide and have seen up to a 200% increase in tensile strength in the loaded host, but with inconsistent results. Measurements have shown that graphene has a breaking strength 200 times greater than steel, with a tensile modulus (stiffness) of 1 TPa (150,000,000 psi). An atomic Force Microscope (AFM) has been used to measure the mechanical properties of a suspended graphene sheet. 
     Graphene sheets held together by van der Waals forces were suspended over SiO 2  cavities where an AFM tip was probed to test its mechanical properties. Its spring constant was in the range 1-5 N/m and the Young&#39;s modulus was 0.5 TPa (500 GPa) thereby demonstrating that graphene can be mechanically very strong and rigid. 
     Depending on whether they are single walled CNTs (SWCNTs) or multi-walled CNTs (MWCNTs), generally, SWCNTs have the diameter of 1-3 nm and MWCNTs have the diameters 5-50 nm. The length of CNTs can be up to centimeters, which gives an aspect ratio exceeding 1000. CNTs also exhibit extraordinary strength with moduli of elasticity on the order of TPa and tensile strength in the range of GPa. With the concurrent benefits of high aspect ratio to surface area, CNTs and MWCNTs have been found to improve the electrical, mechanical and thermal properties of the host material. However, incorporation of CNTs in composites has proven to be complex, yielding inconsistent results. Researchers have found that the addition of CNTs results in little change in strength or even deterioration of the composite. Owing to strong attractive forces between particles, CNTs tend to form agglomerates, self-attraction or self-assembly similar to that seen in carbon black creating defect sites in the composites. Non-uniform distribution/dispersion of CNT bundles is responsible for the deterioration of the host&#39;s properties. 
     Graphitic nanomaterials such as graphene, graphene oxide, and carbon nanotubes are currently being investigated as multifunctional polymer fillers. Because of the incredible strength, chemical stability, electrical and thermal conductivity of these materials, their incorporation into a polymer matrix increases material strength and makes otherwise electrically and thermally insulating polymers have more metal-like properties. The greatest difficulty in efficient and effective dispersion of graphene stems from its attraction to itself, leading researchers to go to great lengths to find compatible polymers. This is typically done through chemical functionalization of the graphitic surface, sacrificing the graphene&#39;s properties for compatibility. 
     Most recent methods of dispersing graphene and graphite oxide into host such as a polymers, metal, or ceramic center around solvent-assisted methods or melt-compounding. In a solvent-assisted dispersion of graphene, the graphene is first dispersed into a solvent, which is soluble or dissolves the target host. The solvent, that is often flammable, must then be removed. Eliminating the solvent from the process makes the process less expensive and safer. 
     Melt-compounding raw compound materials are typically in the form of small beads or powder and are fed from a hopper into the barrel of an extruder or hot press. In the case of an extruder, additives and fillers, such as graphene, are in the form of mixed powders prior to placing the material in the hopper. The combined material enters near the rear of the barrel and comes into contact with the screw that moves the combined material forward through the barrel. The combined material is then moved through heated sections of the barrel, which allows the combined materials to melt gradually as they are pushed through the barrel. Additional heat is generated from the intense pressure and friction inside the barrel. However, the melt-compounding process often leads to a non-uniform dispersion particularly when the additive is less than a few percent. In the case of a hot press, the powder is placed into a vessel that exposes the host material to both high temperature and pressure simultaneously. To date, the difficulty in the traditional dispersion techniques has limited the use of graphene and graphite oxide in polymers, composites and in general are limited to laboratory-scale projection. 
     SUMMARY OF THE INVENTION 
     This invention deals with a simple, scalable method of dispersing graphene into a host. In one embodiment, the present invention includes a method of large-scale production of graphene composites with mechanical-thermal-compounding. Graphene loaded into a host can improve the mechanical properties, and is thermally conductive and electrically conductive. This invention utilizes a jar mixing method to disperse the graphene/graphite oxide powder into a host powder to form a composite powder. The composite powder is then placed into a cold press to induce mechanical exfoliation of graphene/graphite oxide flakes and mechanochemical interaction between elements of the composite powder forming a loosely bound structure. Mechanical-thermal-compounding uses a cold press to apply pressure to form a loosely bound solid structure from the mixed powders. The compaction process induces mechanical exfoliation of graphene/graphite oxide flakes and mechanochemical interaction between elements of the powder and results in a loosely bound solid structure. This is similar to compression molding. Cold compression molding or cold molding is used in the plastic, pharmaceutical and ceramics industry industries to form tablets or preformed “biscuits” to form near net shape structures prior to sintering extrusion of melt casting. The compression molded composite powder is mechanically processed back to a powder. Subsequent cold compression molding of the composite powder improves the exfoliation of graphene/graphite oxide and mechanochemical interaction between elements in the composite powders. After the last cold compression molding and mechanical processing to a powder, the powder can be used as the source material for a composite structure. The thermal treatment can be performed by traditional processes including but not limited to compression molding with heating, hot pressing, extrusion or injection molding that results in a composite with the desired physical characteristics. The resulting composite can be molded into useful shapes and sizes while keeping the advantages imparted by graphene and graphite oxide. 
     In one embodiment, the present invention includes a method of making a composite of graphene/graphite oxide powder and a host powder by a solventless process comprising: cold compressing a mixture of the graphene/graphite oxide powder and the host powder to form a biscuit; crushing, powderizing, or grounding the biscuit into a powderized biscuit; and combining the powderized biscuit with an extrudable material to form a composite. In one aspect, the method further comprises a second compression molding and a second powderizing steps. In another aspect, the method further comprises the step of dispersing the graphene/graphite oxide powder into a host powder to form a composite powder prior to cold compressing the mixture. In another aspect, the method further comprises the step of dispersing the graphene/graphite oxide powder into a host powder to form a composite powder in the presence of ball bearings to break up clumps or agglomerations. In another aspect, the method further comprises a first and a second cold compression molding step, wherein the first cold compression uses a pressure of at least lkPa, and the second cold compression molding is at a pressure equal to or greater than 10 kPa. In another aspect, the second cold compression forms a second biscuit that is also crushed, powdered, or grounded into a second powderized biscuit prior to mixing with the extrusion material to form the composite. In another aspect, the host powder is selected from ordinary Portland cement, polypropylene (PP), polyethylene (PE), Polycarbonate (PC), ceramic powders, ceramic powder is aluminum oxide, zirconium oxide, silica, silicon dioxide, or combination thereof, metal powders, metal powders of titanium, titanium hydride, tantalum, cobalt chrome, niobium, stainless steel, nickel, copper, aluminum, or combinations thereof, a polycrystalline material, polyvinylidene fluoride (PVF), or polyvinylidene difluoride (PVDF), polyurethane, poly(butyleneterephthalate), nylon 11, poly(ethyleneterephthalate), poly(ether ether ketone), poly(phenylene sulfide), polyolefin, an oxide, carbonate or silicate of an element of Groups 2a, 3a, 4a and 4b of the Periodic Table, poly(vinyl chloride) (PVC), poly(methylmethacrylate), polystyrene, polycarbonate/nylon alloy, polycarbonate/polyester alloy, ABS, ABS/nylon alloy, ABS/PVC alloy, acrylic copolymers, polysulfone, polysulfone/ABS alloy, polyetherimides, polyamide-imides, polyarylates, fluoropolymers, polyphenylene oxide/polystyrene blend, or poly(phenylene sulfide). In another aspect, the method further comprises the step of compression molding with heating, hot pressing, extrusion or injection molding the powderized biscuit with an extrudable material to form the composite. In another aspect, the graphene/graphite oxide flake is exfoliated to be less 10 nm during the cold compression molding process without changing the surface area of the graphene/graphite oxide flake. 
     Yet another embodiment of the present invention includes a method of making a graphene/graphite oxide composite from a cold compression molded powder comprising the steps of: cold compressing a mixture of the graphene/graphite oxide powder and the host powder to form a biscuit; crushing, powderizing, or grounding the biscuit into a powderized biscuit; and compression molding with heating, hot pressing, extrusion or injection molding the powderized biscuit with an extrudable material to form the composite. In one aspect, the method further comprises a second compression molding and a second powderizing steps. In another aspect, the method further comprises the step of dispersing the graphene/graphite oxide powder into a host powder to form a composite powder prior to cold compressing the mixture. In another aspect, the method further comprises the step of dispersing the graphene/graphite oxide powder into a host powder to form a composite powder in the presence of ball bearings to break up clumps or agglomerations. In another aspect, the method further comprises a first and a second cold compression molding step, wherein the first cold compression uses a pressure of at least 1 kPa, and the second cold compression molding is at a pressure equal to or greater than 10 kPa. In another aspect, the step second cold compression forms a second biscuit that is also crushed, powdered, or grounded into a second powderized biscuit prior to mixing with the extrusion material to form the composite. In another aspect, the host powder is selected from ordinary Portland cement, polypropylene (PP), polyethylene (PE), Polycarbonate (PC), ceramic powders, ceramic powder is aluminum oxide, zirconium oxide, silica, silicon dioxide, or combination thereof, metal powders, metal powders of titanium, titanium hydride, tantalum, cobalt chrome, niobium, stainless steel, nickel, copper, aluminum, or combinations thereof, a polycrystalline material, polyvinylidene fluoride (PVF), or polyvinylidene difluoride (PVDF), polyurethane, poly(butyleneterephthalate), nylon 11, poly(ethyleneterephthalate), poly(ether ether ketone), poly(phenylene sulfide), polyolefin, an oxide, carbonate or silicate of an element of Groups 2a, 3a, 4a and 4b of the Periodic Table, poly(vinyl chloride) (PVC), poly(methylmethacrylate), polystyrene, polycarbonate/nylon alloy, polycarbonate/polyester alloy, ABS, ABS/nylon alloy, ABS/PVC alloy, acrylic copolymers, polysulfone, polysulfone/ABS alloy, polyetherimides, polyamide-imides, polyarylates, fluoropolymers, polyphenylene oxide/polystyrene blend, or poly(phenylene sulfide). In another aspect, the graphene/graphite oxide flake is exfoliated to be less 10 nm during the cold compression molding process without changing the surface area of the graphene/graphite oxide flake. 
     Another embodiment of the present invention includes a method of making a composite powder of a graphene/graphite oxide powder in a host powder by a solventless process comprising: dispersing the graphene/graphite oxide powder into a host powder to form a composite powder; a first cold compression molding of the composite powder to form a biscuit; crushing, powderizing, or grounding the biscuit into a powderized biscuit; and extruding the powderized biscuit into an extrudable material to form a composite, wherein the method improves the dispersion and exfoliation of the graphene/graphite oxide flakes in the composite. In one aspect, the host powder is selected from ordinary Portland cement, polypropylene (PP), polyethylene (PE), Polycarbonate (PC), ceramic powders, ceramic powder is aluminum oxide, zirconium oxide, silica, silicon dioxide, or combination thereof, metal powders, metal powders of titanium, titanium hydride, tantalum, cobalt chrome, niobium, stainless steel, nickel, copper, aluminum, or combinations thereof, a polycrystalline material, polyvinylidene fluoride (PVF), or polyvinylidene difluoride (PVDF), polyurethane, poly(butyleneterephthalate), nylon 11, poly(ethyleneterephthalate), poly(ether ether ketone), poly(phenylene sulfide), polyolefin, an oxide, carbonate or silicate of an element of Groups 2a, 3a, 4a and 4b of the Periodic Table, poly(vinyl chloride) (PVC), poly(methylmethacrylate), polystyrene, polycarbonate/nylon alloy, polycarbonate/polyester alloy, ABS, ABS/nylon alloy, ABS/PVC alloy, acrylic copolymers, polysulfone, polysulfone/ABS alloy, polyetherimides, polyamide-imides, polyarylates, fluoropolymers, polyphenylene oxide/polystyrene blend, or poly(phenylene sulfide). In another aspect, the graphene/graphite oxide flake is exfoliated to be less 10 nm during the cold compression molding process without changing the surface area of the graphene/graphite oxide flake. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which: 
         FIG. 1  shows the electrical performance of the invention in two different plastics PVDF and polyurethane. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention. 
     To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a”, “an” and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims. 
     The present invention uses a mixing step (e.g., mixing in a jar or jar mixing) to disperse the graphene/graphite oxide powder into a host powder to form a composite powder. The composite powder is then placed into a press for cold compression molding forming a biscuit with enhanced exfoliation of graphene/graphite oxide flakes and mechanochemical induced interaction between graphene/graphite oxide and host powder. The cold compression molding requires a pressure of at least 1 kPa to achieve exfoliation of graphene/graphite oxide flakes and mechanochemical interaction. The resulting biscuit is then crushed or ground into a more homogeneous composite powder relative to the starting powder mixture. The powderized biscuit is then placed into the cold press for a second cold compression molding at a pressure of greater than 1 kPa, preferably 10 kPa, to induce additional mechanical exfoliation of graphene/graphite oxide flakes and mechanochemical interaction forming a second biscuit structure. The cold compression molding and biscuit powderized is repeated several times. Each cold compression molding and biscuit powderized iteration improves dispersion and exfoliation of the graphene/graphite oxide flakes in the host powder. After the last cold compression molding and mechanical processing to a powder the powder can be used as the source material to for a composite structure. The composite structure has enhanced physical properties. As can be seen in  FIG. 1 , a dramatic enhancement in conductivity was obtained as a function of this invention relative to other materials and dispersion techniques. The enhanced conductivity is well over 100 times that of other materials and dispersion techniques in PVDF and polyurethane. The thermal treatment can be performed by traditional processes including but not limited to compression molding with heating, hot pressing, extrusion or injection molding resulting in a composite with the desired physical characteristics. The resulting composite is of useful shapes and sizes while keeping the advantages imparted by graphene and graphite oxide. 
     In one non-limiting example, the host powder is selected from ordinary Portland cement, polypropylene (PP), polyethylene (PE), Polycarbonate (PC), ceramic powders, ceramic powder is aluminum oxide, zirconium oxide, silica, silicon dioxide, or combination thereof, metal powders, metal powders of titanium, titanium hydride, tantalum, cobalt chrome, niobium, stainless steel, nickel, copper, aluminum, or combinations thereof, a polycrystalline material, polyvinylidene fluoride (PVF), or polyvinylidene difluoride (PVDF), polyurethane, poly(butyleneterephthalate), nylon 11, poly(ethyleneterephthalate), poly(ether ether ketone), poly(phenylene sulfide), polyolefin, an oxide, carbonate or silicate of an element of Groups 2a, 3a, 4a and 4b of the Periodic Table, poly(vinyl chloride) (PVC), poly(methylmethacrylate), polystyrene, polycarbonate/nylon alloy, polycarbonate/polyester alloy, ABS, ABS/nylon alloy, ABS/PVC alloy, acrylic copolymers, polysulfone, polysulfone/ABS alloy, polyetherimides, polyamide-imides, polyarylates, fluoropolymers, polyphenylene oxide/polystyrene blend, or poly(phenylene sulfide). The skilled artisan will recognize that these and other materials can be used in a cold compression step to capture the graphene/graphite oxide flakes and form a powder or biscuit into which the graphene/graphite oxide flakes are dispersed and from which the charge problems associated with the prior art are eliminated. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 
     It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention. 
     It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims. 
     All publications and patent applications mentioned in the specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects. 
     As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. In embodiments of any of the compositions and methods provided herein, “comprising” may be replaced with “consisting essentially of” or “consisting of”. As used herein, the phrase “consisting essentially of” requires the specified integer(s) or steps as well as those that do not materially affect the character or function of the claimed invention. As used herein, the term “consisting” is used to indicate the presence of the recited integer (e.g., a feature, an element, a characteristic, a property, a method/process step or a limitation) or group of integers (e.g., feature(s), element(s), characteristic(s), propertie(s), method/process steps or limitation(s)) only. 
     The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context. 
     As used herein, words of approximation such as, without limitation, “about”, “substantial” or “substantially” refers to a condition that when so modified is understood to not necessarily be absolute or perfect but would be considered close enough to those of ordinary skill in the art to warrant designating the condition as being present. The extent to which the description may vary will depend on how great a change can be instituted and still have one of ordinary skilled in the art recognize the modified feature as still having the required characteristics and capabilities of the unmodified feature. In general, but subject to the preceding discussion, a numerical value herein that is modified by a word of approximation such as “about” may vary from the stated value by at least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%. 
     Additionally, the section headings herein are provided for consistency with the suggestions under 37 CFR 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a “Field of Invention,” such claims should not be limited by the language under this heading to describe the so-called technical field. Further, a description of technology in the “Background of the Invention” section is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Neither is the “Summary” to be considered a characterization of the invention(s) set forth in issued claims. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of such claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein. 
     All of the compositions and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.