WO2020077365A1

WO2020077365A1 - Graphene coated particulate

Info

Publication number: WO2020077365A1
Application number: PCT/US2019/056342
Authority: WO
Inventors: Hiroyuki Fukushima; Brian O'neill; Liya Wang
Original assignee: XG SCIENCES Inc
Current assignee: XG SCIENCES Inc
Priority date: 2018-10-12
Filing date: 2019-10-15
Publication date: 2020-04-16
Anticipated expiration: 2021-04-12

Abstract

A composite particle for use as a filler in a composite material is provided. The composite particle includes a calcium carbonate particle and a graphene coating layer formed on at least a portion of the outer surface of the calcium carbonate particle and independent of a binder. The graphene coating is formed of graphene particles, graphene nanoplatelets, or a combination thereof. A composite material formed of a thermoplastic, thermoset, or elastomer-based polymer material and such graphene coated calcium carbonate filler particles dispersed therein is also provided. The resulting composite material has improved impact and compressive strength as well as improved chemical resistance due to the mechanical strength and flexibility, barrier properties, and chemical resistance of the graphene coated calcium carbonate filler material.

Description

GRAPHENE COATED PARTICULATE

RELATED APPLICATIONS

[0001] This application claims priority benefit of the US Provisional Application Serial Number 62/744,802 filed 12 October 2018, the content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates in general to an inorganic filler for composite materials and in particular to binder free graphene coated calcium carbonate and talc filler particulate to improve properties of a polymeric composite containing the same, with such properties including at least one of mechanical, chemical, or barrier.

BACKGROUND OF THE INVENTION

[0003] A composite material is a material made from two or more constituent materials with significantly different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure, differentiating composites from mixtures and solid solutions. Composite materials may be preferred for many reasons including being stronger, lighter, or less expensive when compared to traditional materials.

[0004] Polymer composites are formed of a thermoset, thermoplastic, or elastomer-based polymer and a filler material, which together build up the structure of the composite. Polymer composites are extensively used in the manufacture of strong, rigid, lightweight, flame retardant and abrasion resistant components for the automotive, aeronautical industries, other transportation, sporting goods, electronics, construction, and household goods. The physical properties are strongly dependent on the chemical structure and ratio of the polymer and the fillers employed.

[0005] Mineral fillers are widely used in polymer composites. The typical mineral fillers used in this application are calcium carbonate, talc, mica, silica, glass beads, clay, wollastonite, calcium sulfate, and alumina. Among these, calcium carbonate and talc are by far the most widely used fillers, which occupy a majority of the market. This is mainly because of the cost effectiveness of calcium carbonate and talc. These fillers are typically cheaper than polymers, thus, adding these fillers reduces the cost of the final composites. However, these fillers usually reduce the strength and impact strength of the resulting matrix polymer.

[0006] Calcium carbonate, CaCCh, is one of the most widely used inorganic fillers for polymer composite applications. Calcium carbonate is a common substance found in rocks as the minerals calcite and aragonite and is the main component of pearls, eggshells, and the shells of marine organisms such as clams and oysters, making calcium carbonate widely available, environmentally friendly, easy to process, non-toxic, and inexpensive. Given the low cost of calcium carbonate, it can be used in high loadings in polymer composites to adjust the overall cost of the final products. It is used in thermoset, thermoplastic, and elastomer- based composites primarily because of the low cost of the filler. However, calcium carbonate is relatively brittle and tends to crack under impact or compressive forces. Also, calcium carbonate tends to dissolve in many organic and inorganic acids. Accordingly, composite materials having calcium carbonate fillers have lower impact strength, lower compressive strength, reduced elongation, and lower resistance to acids as compared to some other advanced fillers. Additionally, calcium carbonate fillers tend to increase abrasive wear on melt processing equipment used in forming composite materials, especially at high loadings.

[0007] Talc is another mineral filler widely used in polymer composite. It is a clay mineral caused by the metamorphic reaction of magnesium silicate minerals. Talc is widely available at low cost in many areas in the world such as China, Brazil, India, US, France, Finland, Italy, Russia, and Canada. Talc has layered structure in which octahedral magnesium oxide layer is sandwiched between tetrahedral silicate layers. Because of the structure, talc has plate-like morphology. Once mixed in a polymer matrix at 20 to 40 total weight percent loading, talc can improve the stiffness and the heat deflection temperature of the resulted composite. Also, the thermal conductivity could be improved to certain extent. However, the impact strength and toughness are reduced at the same talc loading levels.

[0008] Thus, there is a need for a low-cost inorganic filler that has improved mechanical (especially the impact strength), barrier and chemical resistance properties. There is a further need to reduce the wear on composite material processing equipment such as extruders, molding, and other melt processing equipment. There also exists a need for composite materials having improved impact and compressive strength as well as improved chemical resistance.

SUMMARY OF THE INVENTION

[0009] The present invention provides a composite particle for use as a filler in a composite material. The composite particle includes a solid filler particle such as calcium carbonate, talc, mica, silica, glass beads, clay, wollastonite, calcium sulfate, and alumina and similar particles and a graphene coating layer formed on at least a portion of the outer surface of the solid filler particle applied by a dry process and independent of the presence of a binder. The graphene coating is formed of graphene particles, graphene nanoplatelets, graphene sheet, few-layer graphene, single-layer graphene, double-layer graphene, graphene oxide, reduced graphene or a combination thereof. The present invention further provides a composite material formed of a thermoplastic, thermoset, or elastomer-based polymer material and a plurality of graphene coated solid filler particles compounded in the polymer material. The resulting composite material has improved impact and compressive strength as well as improved chemical resistance due to the mechanical strength and flexibility, barrier properties, and chemical resistance of the graphene coated mineral solid filler material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention is further detailed with respect to the following drawing that is intended to show certain aspects of the present invention, but should not be construed as a limit on the practice of the present invention.

[0011] FIG. 1 is a cross sectional view of an inventive composite particle with a solid particle core and a graphene coating layer.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention relates to a graphene coated solid particle filler and has utility as a low-cost inorganic filler having improved mechanical strength and flexibility and improved barrier and chemical resistance properties for use in composite materials having improved impact and compressive strength as well as improved chemical resistance. The present invention also has utility as a low-cost solid filler with reduced wear on composite material processing equipment. [0013] It is to be understood that in instances where a range of values are provided herein, that the range is intended to encompass not only the end point values of the range, but also intermediate values of the range as explicitly being included within the range and varying by the last significant figure of the range. By way of example, a recited range of from 1 to 4 is intended to include 1-2, 1-3, 2-4, 3-4, and 1-4.

[0014] A composite particle for use as a filler in a composite material is described herein. The composite particle includes a solid filler particle such as calcium carbonate, talc, mica, silica, glass beads, clay, wollastonite, calcium sulfate, and alumina and a graphene coating layer formed on at least a portion of the outer surface of the solid particle applied by a dry process and independent of the presence of a binder. According to embodiments, the solid particle is directly coated with the graphene coating layer. By directly coated, it is meant that the graphene forms a direct contact with the solid particle. The contact is sufficiently direct to allow the formation of a strong, robust interaction between the graphene coating layer and the solid particle surface. Similarly, there is no intermediary material disposed between the graphene coating layer and the solid particle.

[0015] In contrast to the prior art, in which graphene and solid particle have been used together or have been mixed together, the present disclosure provides graphene coated solid particle to improve the mechanical, chemical, and barrier properties of polymer composite materials loaded with hybrid solid particle fillers.

[0016] According to embodiments, the composite particle is spherical, cylindrical, ovoidal, polyhedronal, flake-like, plate-like, or irregular non-poly hedronal. The composite particle has the mean domain size between 0.1 and 100 microns. According to embodiments, at least 50 percent of the surface area of the solid filler particle is coated by the graphene coating layer. In further embodiments, the outer surface of the solid particle is entirely coated by the graphene coating layer. The surface area coverage is measured by electron microscopy imaging.

[0017] The starting solid filler particles can be any product produced by a known method. The present invention allows for the use of both natural and synthetic solid filler particles. For example, both the natural calcium carbonate particulate (heavy calcium bicarbonate particles) and synthetic calcium carbonate particles (light calcium carbonate particles and colloidal calcium carbonate particles) can be used.

[0018] Natural solid filler particles can be processed by mechanically crushing and grading natural ore to obtain particles adjusted to the desired size.

[0019] Synthetic solid filler particles can be formulated in various process conditions. For example, synthetic calcium carbonate particles are manufactured by first preparing a calcium oxide (quick lime) by subjecting limestone to calcination by burning a fuel, such as coke, a petroleum fuel (such as heavy or light oil), natural gas, petroleum gas (LPG) or the like, and then reacting the calcium oxide with water to produce a calcium hydroxide slurry (milk of lime), and reacting the calcium hydroxide slurry with the carbon dioxide discharged from a calcination furnace for obtaining the calcium oxide from limestone to obtain the desired particle size and shape.

[0020] Graphene is a 1 to 10 atom-thick layer of sp² hybridized carbon atoms in a honeycomb-like hexagonal, 2-dimensional sheet. Graphene is known to have excellent mechanical strength and flexibility, thermal and electric conductivities, and good chemical resistance and barrier properties compared to calcium carbonate. Also, graphene nanoplatelets and graphene sheets having a thickness of 3 to 100 nm, and a lateral size of 200 nm to 100 microns are operative in the present invention. An inventive graphene coating on the surface of solid filler particulate helps deflect impacting force applied thereto and as a result protect the solid filler particle due to the excellent mechanical strength of graphene. Additionally, the graphene coating protects the solid filler particles from being in contact with the environment, thereby improving the overall chemical resistance of the particles. Furthermore, the graphene coating on the solid filler particles also help reduce the wear of the composite processing equipment such as extruders and moldings. According to the present invention, the graphene coating is applied without resort to an intermediate binder thereby improving the manufacture and properties of the resulting graphene coated solid filler particulate.

[0021] The graphene coating is formed of graphene particles, graphene nanoplatelets, graphene sheet, few-layer graphene, single-layer graphene, double-layer graphene, graphene oxide, reduced graphene or a combination thereof. In some embodiments, the graphene has a size between 200 nanometers and 100 microns and a Brunauer-Emmett-Teller (BET) measured surface area of greater than about 100 m²/g. In addition, the graphene has an aspect ratio between about 25 and 100,000 which is the ratio of the maximum linear extent and the minimum linear extent, synonymously referred to herein as thickness. In further inventive embodiments, the graphene coating layer is formed of multiple graphene particles that have a maximal lateral dimension of greater than 200 nm. According to embodiments, the graphene coating layer is formed of multiple graphene nanoplatelets having a thickness of 3 nm to 100 nm. In some embodiments, the graphene nanoplatelets having a maximal lateral dimension of less than 5 microns, and some inventive embodiments the graphene nanoplatelets having a maximal lateral dimension in the range from 500 nm to 10 microns. In further embodiments, the graphene layer includes multiple layers of graphene particles of graphene nanoplatelets. In one or more inventive embodiments, the graphene particles or graphene nanoplatelets stack or overlap in the coating and form multi-layer coatings that are discontinuous in regions or everywhere, continuous in regions or everywhere, or a combination thereof. [0022] In some inventive embodiments, the graphene coating layer forms a coating from 0.1 to 20 total weight percent of an inventive coated calcium carbonate particulate.

[0023] Typical composite particles of the present invention have a mean domain size that ranges from 0.2 microns to 100 microns. In specific inventive embodiments, the mean domain size ranges from 0.5 microns to 30 microns, while in still other inventive embodiments, the mean domain size ranges from 0.8 microns to 10 microns. The composite particles are typically spherical owing to the formation process, but other shapes such as cylindrical, ovoidal, polyhedronal, flake-like, plate-like, or irregular non-polyhedronal are operative herein. When non-spherical shapes are used, the domain size refers to the longest linear extent of the particle.

[0024] The grinding techniques have been used to process ores for a long time. However, it was found that grinding under dry conditions often did not give good results in the end in terms particles size reduction as well as the particle size distribution. Thus, liquids and/or grinding agents are added to improve the efficiency of the grinding efficiency. These techniques are exemplified in US4126277A, US4136830A, and US4793985A. The grinding techniques have also been used to functionalize solids particles or fabricate composite materials based on solid particles, however, liquids and/or binder materials have also been added to those processes (e.g. US5116561A, etc.) Graphite or graphene coated solid particles have also been proposed, however, addition of binders was proposed to make such materials. These techniques are exemplified in US7402338B2.

[0025] The present invention provides graphene coated solid filler particles which are made by dry milling techniques without any binders and/or solvents and that can be mass- produced at low cost and easy to handle by conventional powder filler handling equipment yet showed significant improvement on impact strength in polymer composites. Overall, the present invention can provide a cost-effective solution to improve the impact strength of polymer composite materials based on cost-effective graphene coated solid filler materials which can be handled easily by widely available process equipment to produce polymer composite materials based on those graphene-coated solid fillers.

[0026] Further embodiments of the present invention provide a composite material formed of a polymer material and a plurality of the above described graphene coated solid filler particles compounded in a matrix of the polymer material or a precursor monomer or prepolymer therefor, the precursors or prepolymers then being cured to form the polymer matrix. This is accomplished for example, using extrusion, injection molding, protrusion, thermoforming, rotational molding, Bunbury mixing, continuous mixing, double planetary mixing, Cowles blade mixing, rotor stator mixing, high pressure homogenization, high shear mixing, etc. The polymer material can be a thermoset polymer illustratively including epoxy, vinyl ester, unsaturated polyester, phenolic resin, polyurethane, polyurea, silicone resin, polysiloxane, alkyds, and polyimide where polymer curing involves coupling or crosslinking reactions. The polymer material can alternatively be a thermoplastic polymer illustratively including polyolefins, polyamides, polyesters, polyethers, polyurethanes, phenol- formaldehydes, urea-formaldehydes, melamine-formaldehydes, polysulfides, polyacetals, polyethylene oxides, polycaprolactams, polycaprolactones, polylactides, polyimides, thermoplastic elastomers, copolymer thereof, and a mixture thereof. Specifically included are polyolefins, polyamides, thermoplastic elastomers, and polycarbonates. The resulting composite material has a high impact strength and a high compressive strength compared to like materials containing normalized amounts of like-dimensioned conventional calcium carbonate particulate. The inventive composite material also has a high resistance to acids that would otherwise degrade solid filler particles. [0027] The amount of inventive graphene coated solid filler particle in the polymer matrix material may be varied depending on the desired characteristics of the resulting composite material and the presence (or absence) of other fillers. The amount of inventive graphene coated calcium carbonate particulate filler varies from a low level (e.g., less than 5 percent by weight) if other fillers are present and heavily relied upon, to high level (e.g., 20 percent by weight and more). According to certain inventive embodiments, the graphene coated solid filler particles are present in an amount of at least 1 total weight percent of the composite material.

[0028] Referring now to the figures, FIG. 1 shows an inventive composite particle generally at 10. The composite particle 10 includes a solid filler particle 12 and a graphene coating layer 14. The solid filler particle has a domain size and a surface defined by radius r; although it is appreciated that oblong pellets are also envisioned with the scope of the present invention. The coating 14 has a thickness, t and shown in partial cutaway. In certain embodiments, the linear ratio r:t is between 1:0.001-0.2

[0029] The present invention is further detailed with respect to the following non- limiting examples.

Example 1

[0030] Composite particles having the form depicted in FIG. 1 are formed by coating mean diameter 5 um spherical calcium carbonate (CaCCri) particles with xGnP™ graphene nanoplatelets. The calcium carbonate particle has a typical surface area of 1.2 m²/g while the graphene nanoplatelets have a typical surface area of 200 m²/g. The xGnP™ graphene nanoplatelets used in this example has the average particle diameters in between 0.5 to 5 pm. The coating coverage being 100 percent of the surface area with an average thickness of about

0.1 pm. Example 2

[0031] Composite particles having the form depicted in FIG. 1 are formed by coating mean diameter 39 um spherical alumina particles with xGnP™ graphene nanoplatelets. The alumina particle has a typical surface area of 0.2 m²/g while the graphene nanoplatelets have a typical surface area of 200 m²/g. The xGnP™ graphene nanoplatelets used in this example has the average particle diameters in between 0.5 to 5 microns. The coating coverage being 100 percent of the surface area with an average thickness of about 0.1 microns.

[0032] A composite material is formed using the composite particles of Example 1. The xGnP™ coated calcium carbonate particles are compounded in polypropylene (PP) with an extruder and injection molding machine The composite material includes 2.5 weight percent xGnP-coated CaCCb in the PP. The resulting composite material shows 67 percent improved Notched Izod Impact Strength over a control PP sample, while 2.5 weight percent conventional CaCCb (no coating) in PP showed 5 percent worse Notched Izod Impact Strength compared to the control PP sample.

[0033] A composite material is formed using the composite particles of Example 2. The xGnP™ coated alumina particles are compounded in polypropylene (PP) with an extruder and injection molder. The composite material includes 2.5 weight percent xGnP-coated Alumina in the PP. The resulting composite material shows 2lpercent improved Notched Izod Impact Strength over a control PP sample, while 2.5 weight percent conventional Alumina (no coating) in PP showed only 7 percent improved Notched Izod Impact Strength over the control PP sample.

[0034] Any patents or publications mentioned in this specification are indicative of the level of those skilled in the art to which the invention pertains. These patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference.

[0035] One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The present methods, procedures, treatments, molecules, and specific compounds described herein are presently representative of preferred embodiments, are exemplary, and are not intended as limitations on the scope of the invention. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention as defined by the scope of the claims.

Claims

1. A composite particle defined by a shape and a size comprising:

a solid filler particle; and

a graphene coating layer formed on at least a portion of an outer surface of said calcium carbonate particle and independent of a binder.

2. The composite particle of claim 1 wherein the shape is cylindrical, ovoidal, polyhedronal, flake-like, plate-like, or irregular non-polyhedronal.

3. The composite particle of claim 1 wherein the mean domain size is between 0.5 and 100 microns.

4. The composite particle of claim 1 wherein the mean domain size is between 0.8 and 30 microns.

5. The composite particle of claim 1 wherein the mean domain size is between 1 and 10 microns.

6. The filler particle of claim 1 wherein said solid filler particle has a Brunauer- Emmett-Teller (BET) specific surface area of 0.1 to 100 m²/g.

7. The filler particle of claim 1 wherein said solid filler particle has a Brunauer- Emmett-Teller (BET) specific surface area of 0.5 to 50 m²/g.

8. The filler particle of claim 1 wherein said solid filler particle has a Brunauer- Emmett-Teller (BET) specific surface area of 0.8 to 20 m²/g.

9. The composite particle of claim 1 wherein said graphene coating layer is present from

0.1 to 20 total weight percent of the composite particle.

10. The composite particle of claim 1 wherein said graphene coating layer is present from 0.5 to 15 total weight percent of the composite particle.

11. The composite particle of claim 1 wherein said graphene coating layer is present from 1 to 10 total weight percent of the composite particle.

12. The composite particle of claim 1 wherein said graphene coating layer comprises a plurality of graphene particles having a maximal linear extent of greater than 1 micron.

13. The composite particle of claim 1 wherein said graphene coating layer comprises a plurality of overlapping graphene nanoplatelets.

14. The composite particle of any one of claims 1 to 13 wherein said graphene coating layer comprises a plurality of graphene nanoplatelets having a thickness of 0.35 nm to 100 nm.

15. The composite particle of any one of claims 1 to 13 wherein said graphene coating layer comprises a plurality of graphene nanoplatelets having a thickness of 1 nm to 20 nm.

16. The composite particle of any one of claims 1 to 13 wherein said graphene coating layer comprises a plurality of graphene nanoplatelets having a thickness of 2 nm to 10 nm.

17. The composite particle of any one of claims 1 to 13 wherein said graphene coating layer comprises a plurality of graphene nanoplatelets having a lateral dimension of 0.2 microns to 100 microns.

18. The composite particle of any one of claims 1 to 13 wherein said graphene coating layer comprises a plurality of graphene nanoplatelets having a lateral dimension of 0.5 microns to 30 microns.

19. The composite particle of any one of claims 1 to 13 wherein said graphene coating layer comprises a plurality of graphene nanoplatelets having a lateral dimension of 0.8 microns to 10 microns.

20. The composite particle of any one of claims 1 to 13 wherein at least 50 percent of the outer surface of the solid filler particle is coated by the graphene coating layer.

21. The composite particle of any one of claims 1 to 13 wherein the outer surface of said solid filler particle is entirely coated by the graphene coating layer.

22. The composite particle of any one of claims 1 to 13 wherein the composite particle is a filler in a polymer composite material.

23. A composite material comprising:

a polymer material; and

a plurality of composite particles of claim 1 in said polymer material.

24. The composite material of claim 23 wherein said polymer material is a thermoset, a thermoplastic, or an elastomer.

25. The composite material of claim 23 wherein said polymer material is polypropylene.

26. The composite material of claim 23 wherein said plurality of graphene coated solid filler particles are homogeneously distributed in a solid matrix of said polymer material.

27. The composite material of claim 23 wherein said plurality of graphene coated solid filler particles are present in an amount of 0.25 to 60 weight percent of said composite material.

28. The composite material of claim 23 wherein said plurality of graphene coated solid filler particles are present in an amount of 0.5 to 30 weight percent of said composite material.

29. The composite material of claim 23 wherein said plurality of graphene coated solid filler particles are present in an amount of 1 to 5 weight percent of said composite material.