Methods for preparing a graphene dispersion and for functionalizing graphene, graphene dispersions, and uses of graphene dispersions

Abstract

The invention relates to a method for preparing a graphene dispersion comprising a step of contact between graphene and a dispersing agent in a container, wherein the container is subjected to translation and rotation movement.

Description

[0001] Methods for preparing a graphene dispersion and for graphene functionalization, graphene dispersions and uses of graphene dispersions.

[0002] Technical Field

[0003]

[0001] The invention relates to a method for preparing a graphene dispersion, a method for functionalizing graphene, graphene dispersions obtained by the processes described herein, and applications of graphene dispersions.

[0004] State of the Art

[0005]

[0002] Graphene is a general term referring to a two-dimensional carbon material, which is presented in the form of sheets or flakes of graphite with at least one nanometric dimension. Graphene can be represented simply as one or more layers of individual carbon atom sheets stacked together, with the limit by definition being 10 layers.

[0006]

[0003] A few-layered graphene generally refers to a crystalline material that has one to ten layers of carbon atoms. A multilayer graphene containing five to ten layers is generally called graphene nanoplatelets, and above ten layers is called graphite nanoplatelets. All are generically called graphene. The different layers of carbon nanoplatelets are linked by weak intermolecular forces known as TT-TT stacking, and the set of these interconnected layers forms a three-dimensional structure. Graphene has a thickness on the nanometer scale or smaller, and the other two dimensions are on the micrometer scale. Graphene is formed by carbon atoms with sp hybridization. 2 Graphene is a structure in which each carbon atom is bonded to three other carbon atoms in a hexagonal pattern. In practice, graphene consists of aggregates and clusters of graphene sheets.

[0007]

[0004] Due to its mechanical, thermal, and electrical properties, and high specific surface area, graphene finds application in diverse areas such as paints, polymers, semiconductors, cementitious materials, ceramics, lubricants, and capacitors.

[0008]

[0005] To obtain a better graphene mixture, that is, the best dispersion of the material in a final composition such as an ink, in polymeric materials (e.g., composites, concentrated compounds such as masterbatches), cementitious materials, or a lubricating oil, graphene is typically premixed with other chemical compounds, such as dispersing and / or wetting agents, thus forming a graphene dispersion. Graphene can also be mixed with functionalizing compounds to enable its wet chemical functionalization.

[0009]

[0006] The hydrophobic nature of graphene makes preparing a stable additive with high concentrations challenging, due to the presence of van der Waals forces between the graphene plates. This promotes plate agglomeration, which negatively influences the properties of the resulting additive.

[0010]

[0007] In order to combat the problems associated with the tendency of graphene to clump together, as well as its weak interaction with certain matrices, various dispersion and functionalization methods are used. The most commonly used dispersion techniques are ultrasonication, high shear, ball milling, mechanical and magnetic agitation, among others. Their main function is to fragment the agglomerates of graphene nanoparticles, resulting in their dispersion. On the other hand, known functionalization methods are based on the surface modification of graphene nanoparticles, with the aim of maintaining stable dispersion and, in some cases, promoting a more suitable interaction between the nanoparticles and the matrix of interest. There are chemical and physical functionalization methods, depending on how the process interacts with the carbon atoms on the surface of the graphene nanoparticles.

[0011]

[0008] Document CN105733750, for example, describes a lubricant additive containing nanometric graphene, prepared from graphene, oleic acid, boric acid ester and an oily solvent. A low concentration dispersion of graphene, from 0.1 to 0.8% by weight, is carried out using magnetic stirring with temperature and ultrasound.

[0012]

[0009] Document CN111363609 presents a method for preparing a graphene lubricant oil additive using chemical reflux synthesis.

[0010] Document CN106883904 describes a process for preparing a concentrated graphene suspension using mechanical agitation at a controlled temperature and high pressure. The process comprises emulsification and dispersion steps in a multi-level emulsification device at controlled temperature, and homogenization and circulation of the emulsified and dispersed paste using a high-pressure homogenization device.

[0013]

[0011] Document CN 107325858 refers to a method for preparing a liquid-type graphene additive. The method uses several steps together, such as mechanical milling, ultrasonic shearing, ultrasonic dispersion, centrifugal treatment, and the like.

[0014]

[0012] Document CN112920878 refers to obtaining an anti-friction lubricating oil containing modified graphene. The base oil further comprises 5 to 8% by weight of ferric oxide and is placed in an electromagnetic field environment for magnetization during the preparation process for better dispersion.

[0015]

[0013] Known graphene dispersion processes in the art have some disadvantages. Firstly, the time required for graphene dispersion can be excessively long, for example from 2 to 20 hours. Furthermore, these processes are limited by the increasing viscosity of the additive, which limits the final graphene concentration. In processes using ultrasound, for example, scaling up production to larger volumes is challenging due to the size of the probe, and achieving and maintaining the stability of additives with high graphene concentrations is difficult.

[0016]

[0014] It is also noteworthy from the state of the art that graphene dispersions are generally difficult to manufacture and, in order to make production feasible, low graphene contents are used in the final dispersion, particularly below 20% by weight of graphene. The production of graphene dispersions with higher concentrations is desirable as it allows the addition of a smaller amount of graphene to the final composition of graphene composites. This facilitates the storage and transport of the dispersion by requiring smaller total volumes, in addition to reducing any influence that the other chemical compounds that make up the dispersion may have on the final composition. Furthermore, it is desirable to develop graphene production methods that are short-duration and scalable to larger volumes.

[0017]

[0015] Therefore, there is a need to develop methods for preparing graphene dispersions and graphene functionalization that are short-lived and easier to scale up. There is also a need for methods for preparing graphene dispersions that allow the incorporation of larger quantities of this compound, preferably greater than 20% by weight of graphene, that maintain the stability of the dispersion over time and are applicable as additives in a wide variety of industries of interest.

[0018] Summary of the Invention

[0019]

[0016] In a first aspect, the present invention relates to a method of preparing a graphene dispersion comprising a step of contacting graphene with a dispersing agent in a container, wherein the container is subjected to translational and rotational motion.

[0020]

[0017] In a second aspect, the present invention relates to a method for functionalizing graphene comprising a step of contacting the graphene dispersion with a dispersing agent in a container, wherein the container is subjected to a translational and rotational motion.

[0021]

[0018] In a third aspect, the present invention relates to a graphene dispersion comprising an amount of graphene greater than 20% by weight, based on the total weight of the dispersion, and a dispersing agent.

[0022]

[0019] In a fourth aspect, the present invention relates to a graphene dispersion obtained by the method of preparing a graphene dispersion described herein.

[0023]

[0020] In a fifth aspect, the present invention relates to a functionalized graphene dispersion obtained by the graphene functionalization method described herein.

[0024]

[0021] In a sixth aspect, the present invention relates to the use of the graphene dispersion described herein as a chemical additive or water-based dispersions.

[0022] In a seventh aspect, the present invention relates to the use of the functionalized graphene dispersion described herein as a chemical additive or water-based dispersions.

[0025] Brief Description of the Figures

[0026]

[0023] Figure 1 presents the results of graphene dispersions obtained by a milling method described in the prior art. Figure 1A shows a 20 wt% graphene dispersion and Figure 1B an attempt at a 38 wt% graphene dispersion.

[0027]

[0024] Figure 2 shows the Raman spectra of functionalized graphene dispersions obtained by the method described in the present invention.

[0028]

[0025] Figure 3 presents the thermogravimetric analysis (TGA) results for graphene samples designated as A0, A8, and A20.

[0029]

[0026] Figure 4 presents the thermogravimetric analysis (TGA) results for graphene dispersions produced by the method described here from graphenes designated as A0, A8 and A20.

[0030]

[0027] Figures 5 and 6 are illustrative representations of a container under translational, rotational, and simultaneous rotational and translational motion.

[0031]

[0028] Figure 7 presents the stability results of graphene dispersions, with Figure 7A being a graphene dispersion according to the present invention and Figure 7B a graphene dispersion according to the prior art.

[0032]

[0029] Figure 8 shows the results of graphene dispersions produced by the method of preparing a graphene dispersion according to the present invention for graphene concentrations of 20% to 60% by weight.

[0033] Detailed Description

[0034] Graphene Dispersion Preparation

[0035]

[0030] In a first aspect, the present invention relates to a method of preparing a graphene dispersion comprising a step of contacting graphene with a dispersing agent in a container, wherein the container is subjected to translational and rotational motion.

[0036]

[0031] The method for preparing a graphene dispersion according to the present invention is capable of producing graphene dispersions with varying amounts of graphene, which is not particularly limited, and may be, for example, greater than or equal to 0.001% by weight of graphene, based on the total weight of the graphene dispersion, for example from 0.001% to 99.9% by weight of graphene, from 0.001% to 90% by weight of graphene, from 0.001% to 80% by weight of graphene, from 0.001% to 70% by weight of graphene, from 0.001% to 60% by weight of graphene, for example from 0.001% to 50% by weight of graphene. In one or more embodiments, the method for preparing a graphene dispersion according to the present invention produces graphene dispersions with a graphene content greater than 20% by weight of graphene, based on the total weight of the graphene dispersion. In one or more embodiments, the graphene dispersion produced by the method described herein contains up to 99.9% by weight graphene, up to 90% by weight graphene, up to 80% by weight graphene, up to 70% by weight graphene, up to 60% by weight graphene, up to 50% by weight graphene, particularly 25% to 99.9% by weight graphene, 25% to 90% by weight graphene, 25% to 80% by weight graphene, 25% to 70% by weight graphene, 25% to 60% by weight graphene, 25% to 50% by weight graphene, more particularly 30% to 99.9% by weight graphene, 30% to 90% by weight graphene, 30% to 80% by weight graphene, 30% to 70% by weight graphene, 30% to 80% Graphene percentages range from 30 to 70% graphene by weight, from 30 to 60% graphene by weight, and from 30 to 50% graphene by weight, based on the total weight of the graphene dispersion. Contact of graphene with a dispersing agent in a container under translational and rotational motion is capable of promoting not only graphene dispersion but also its exfoliation and, depending on the composition of the dispersing agent, its wetting and / or functionalization.Furthermore, the method for preparing a graphene dispersion according to the present invention is short in duration and can be scaled up to larger volumes.

[0037]

[0032] The term “graphene” as used in the present invention is not limited solely to pure graphene, but also includes other forms of graphene known in the art such as graphene oxide, reduced graphene oxide and functionalized graphene.

[0038]

[0033] The term “dispersing agent” in the context of the present invention refers to a preferably homogeneous fluid composition that acts as a continuous phase in a dispersion, in which graphene is distributed during the contact step. In one or more embodiments, the dispersing agent is a liquid dispersing agent under ambient temperature and pressure conditions (25°C and 1 atm, respectively). The contact step of graphene with the dispersant according to the present invention may be referred to as the contact step, dispersion step, or deagglomeration step.

[0039]

[0034] The dispersing agent comprises at least one component, which will act as a functionalizer and / or wetting agent. When the dispersing agent acts as a wetting agent, the contact step may be called a dispersion and wetting step, or a deagglomeration and wetting step. When the dispersing agent acts as a functionalizer, the contact step may be called a dispersion and functionalization step, or a deagglomeration and functionalization step. When the dispersing agent acts as both a wetting agent and a functionalizer, the contact step may be called a dispersion, wetting and functionalization step, or a deagglomeration, wetting and functionalization step. In all these steps, graphene exfoliation is considered to occur.

[0040]

[0035] In the context of the present invention, the term “functionalizer” refers to components capable of interacting with graphene covalently or non-covalently, thus resulting in the functionalization of graphene. Covalent functionalization involves the formation of chemical bonds between the functionalizer and the graphene structure, promoting a break in the extended TT conjugation on the graphene surface, forming sp single bonds. 3 (sigma). Non-covalent functionalization, on the other hand, involves the adsorption of molecules onto the graphene surface and does not promote distortion of the extended TT conjugation on the graphene surface, relating to intermolecular interactions involving TT systems between the functionalizer and the graphene.

[0041]

[0036] The term “humectant” refers to liquid compounds or compositions capable of maintaining contact with the surface of graphene particles and promoting their wettability. Effective wetting of graphene particles is particularly desirable since there is an energy difference at the graphene / matrix interface, which hinders the wettability of aggregates and agglomerates of particles. The humectant acts by reducing the energy difference at the graphene / matrix interface, thus favoring the penetration of the matrix into the graphene particle agglomerates, facilitating the dispersion process.

[0042]

[0037] Dispersing agents may be selected from the group consisting of polyaromatic hydrocarbon compounds, preferably selected from pyrene or pyrene derivatives, peptides, DNA molecules, cationic compounds such as imidazolium cations and imidazolium-modified polymers. They may also be selected from surfactants, particularly cationic, anionic or non-ionic surfactants. Anionic surfactants useful for the present invention may be selected from alkyl sulfonates and aryl sulfonates. Non-ionic surfactants may be selected from polyethylene glycols (PEGs) or block copolymers of polyethylene oxide and polypropylene oxide.Dispersing agents according to the present invention may also be selected from compounds containing a carboxylic acid functional group, such as C1-C30 mono- or dicarboxylic acids with saturated or unsaturated, normal or branched, open or closed, aliphatic or aromatic chains, compounds containing an amine functional group such as C2-C20 aliphatic amines, compounds containing a hydroxyl functional group such as polyvinyl alcohol (PVOH), compounds containing an isocyanate functional group, such as C1-C10 alkyl and aryl isocyanates, C2-C10 thioesters and salts thereof, silanes and anhydrides, particularly saturated or unsaturated C4-C10 cyclic anhydrides, ionic solutions or polymers with surfactant action.Dispersing agents can also be selected from solvents such as water, organic solvents such as C3-C10 ketones, C5-C10 dicarbonyls, C2-C10 alcohols, C2-C10 di-alcohols, aromatic or non-aromatic C4-C8 heterocyclic compounds containing at least one O, N or S heteroatom, amides such as N-(C1-C10-alkyl)amides, N,N-(C1-C10-dialkyl)amides, or C3-C10 cyclic amides such as lactams and pyrrolidones, C3-C10 ethers, C4-C10 alkanes, C4-C10 haloalkanes, optionally substituted monoaromatic hydrocarbon compounds with C1-C10 alkyl and / or halogen substitutes, C2-C10 sulfoxides, cyclic esters. C4-C10, Ce-C-io aryl sulfoxides, sulfonic acids such as mono- or diaromatic sulfonic acids or salts thereof, oils such as vegetable oils and mineral oils or greases, and may also be a combination of the components listed here.

[0043]

[0038] The components of the dispersing agent can be added one by one to the container or pre-mixed and then added to the container. They can be added to the container independently of each other before or after the addition of graphene, with no limitation as to the order in which the components are added to the container.

[0044]

[0039] The term “rotation” refers to the circular motion of an object around its own axis, also called the axis of rotation, and the term “translation” refers to the motion of an object around an axis external to it, also called the axis of translation. In one or more embodiments, rotational and translational motion occur simultaneously. In the terms of the present invention, “simultaneous motion” and similar terms refer to motions that occur at the same time, but which may be initiated and / or terminated individually, particularly initiated and / or terminated at different times, or also initiated and / or terminated at the same time.

[0045]

[0040] Rotational and translational movements can be performed in the same direction or in opposite directions, preferably in opposite directions. In one or more embodiments, the rotational movement is performed clockwise and the translational movement counterclockwise. In one or more embodiments, the rotational movement is performed counterclockwise and the translational movement clockwise.

[0046]

[0041] In one or more embodiments, the rotational and translational movements in the contact step are performed in one or more cycles, in order to avoid overheating of the graphene dispersion, to favor particle collision for better functionalization efficiency and graphene exfoliation. In one or more embodiments, 1 to 10 cycles are performed, more preferably 2 to 5 cycles. The cycles have independent durations and preferably last from 10 seconds to 1 hour, preferably from 1 minute to 30 minutes, more preferably 10 minutes.

[0042] The translational and rotational speeds can also be independently selected cycle by cycle, and independently selected by type of movement.In one or more embodiments, a rotational speed of 600 to 3500 rpm is used, preferably 1000 to 3000 rpm, more preferably 1500 to 2500 rpm, and a translational speed of 100 to 1000 rpm, preferably 400 to 1000 rpm, more preferably 800 rpm.

[0047]

[0043] The rotational movement of the container is performed around an axis of rotation, and the translational movement of the container is performed around an axis of translation, wherein the axis of rotation and the axis of translation of the container form an angle 0. In one or more embodiments, the axis of rotation and the axis of translation of the container form an angle 0 between them of 30° to 60°, preferably 40 to 50°, more preferably about 45°.

[0048]

[0044] Simultaneous rotational and translational movements can be performed by double-axis rotation equipment, capable of setting a container in rotational and translational motion. Examples of useful equipment in the present invention are double-axis rotation mixers, more particularly double-axis centrifugal mixers.

[0049]

[0045] Figure 5 is an illustrative representation of a container under translational, rotational, and simultaneous rotational and translational motion.

[0050]

[0046] In one or more embodiments, the method of preparing a graphene dispersion according to the present invention comprises a subsequent contact step, in which the graphene dispersion is brought into contact with a dispersing agent in a container, and the container is subjected to translational and rotational motion. In one or more embodiments, the container is subjected to simultaneous rotational and translational motion.

[0051]

[0047] Dispersing agents may be selected from the group consisting of polyaromatic hydrocarbon compounds, preferably selected from pyrene or pyrene derivatives, peptides, DNA molecules, cationic compounds such as imidazolium cations and imidazolium-modified polymers. They may also be selected from surfactants, particularly cationic, anionic or non-ionic surfactants. Anionic surfactants useful for the present invention may be selected from alkyl sulfonates and aryl sulfonates. Non-ionic surfactants may be selected from polyethylene glycols (PEGs) or block copolymers of polyethylene oxide and polypropylene oxide.Dispersing agents according to the present invention may also be selected from compounds containing a carboxylic acid functional group, such as C1-C30 mono- or dicarboxylic acids with saturated or unsaturated, normal or branched, open or closed, aliphatic or aromatic chains, compounds containing an amine functional group such as C2-C20 aliphatic amines, compounds containing a hydroxyl functional group such as polyvinyl alcohol (PVOH), compounds containing an isocyanate functional group, such as C1-C10 alkyl and aryl isocyanates, C2-C10 thioesters and salts thereof, silanes and anhydrides, particularly saturated or unsaturated C4-C10 cyclic anhydrides, ionic solutions or polymers with surfactant action.Dispersing agents can also be selected from solvents such as water, organic solvents such as C3-C10 ketones, C5-C10 dicarbonyls, C2-C10 alcohols, C2-C10 di-alcohols, aromatic or non-aromatic C4-C8 heterocyclic compounds containing at least one O, N or S heteroatom, amides such as N-(C1-C10-alkyl)amides, N,N-(C1-C10-dialkyl)amides, or C3-C10 cyclic amides such as lactams and pyrrolidones, C3-C10 ethers, C4-C10 alkanes, C4-C10 haloalkanes, optionally substituted monoaromatic hydrocarbon compounds with C1-C10 alkyl and / or halogen substitutes, C2-C10 sulfoxides, cyclic esters. C4-C10, Ce-C-io aryl sulfoxides, sulfonic acids such as mono- or diaromatic sulfonic acids or salts thereof, oils such as vegetable oils and mineral oils or greases, and may also be a combination of the components listed here.

[0052]

[0048] The components of the dispersing agent can be added one by one to the container or pre-mixed and then added to the container. They can be added to the container independently of each other before or after the addition of graphene, with no limitation as to the order in which the components are added to the container.

[0053]

[0049] In one or more embodiments, the aftercontact step is performed at a pressure equal to or below atmospheric pressure of 1 atm. Operating conditions below atmospheric pressure may also be referred to as “vacuum” in the context of the present invention. The aftercontact step may be performed at a pressure between 0 and 1 atm (including 1 atm), for example from 0.5 to 1 atm. In the aftercontact step, as illustrated in Figure 6, the rotational and translational movements of a container result in a centrifugal force which, together with the applied vacuum, promotes the formation of air bubbles that expand and reach the surface of the container's contents. Upon reaching the surface, the bubbles are broken down due to the applied rotational movement.Thus, performing a post-contact step, for example a vacuum post-contact step, is related to removing or reducing air bubbles in the continuous phase of the graphene dispersion to increase the intercalation of the continuous phase with the graphene particles.

[0054]

[0050] In one or more embodiments, the method for preparing a graphene dispersion according to the present invention comprises an additional exfoliation step, in which the graphene dispersion is subjected to shear. Although graphene and the graphene dispersion are respectively subjected to shear, and consequently exfoliation, in the contact step and optionally in the subsequent contact step, an additional exfoliation step may be proposed for sample homogenization purposes and improved dispersion and exfoliation of graphene in the continuous phase. The degree of exfoliation of the graphene dispersion obtained by the method described herein may vary depending on the intended final application. The shearing in the additional exfoliation step may be performed by means of mixing, grinding, ultrasonic motion or centrifugal motion.In one or more embodiments, equipment such as sonicators, ultrasonicators, centrifuges, mixers, centrifugal mixers, high-energy mixers, shears, and mills of various types such as three-roll mills, horizontal mills, ball mills, and ball mills may be used.

[0055]

[0051] In one or more embodiments, the additional exfoliation step is carried out in a high-shear mixer, in one or more cycles, in order to avoid overheating of the graphene dispersion. In one or more embodiments, 1 to 10 cycles are performed, more preferably 1 to 5 cycles, most preferably 3 cycles. The cycles have independent durations and preferably last from 10 seconds to 1 hour, preferably 1 minute to 30 minutes, most preferably 10 minutes. In one or more embodiments, the one or more cycles are performed at speeds of 1000 to 20000 rpm, preferably 5000 to 15000 rpm, most preferably 10000 rpm.

[0056]

[0052] In one or more embodiments, the additional exfoliation step is carried out in a mill, in one or more cycles, in order to avoid overheating of the graphene dispersion. In one or more embodiments, 1 to 50 cycles are performed, more preferably 10 to 40 cycles, most preferably 25 cycles. The cycles have independent durations and preferably last from 10 seconds to 1 hour, preferably 1 minute to 30 minutes, most preferably 15 minutes. In one or more embodiments, the one or more cycles are performed at speeds of 100 to 1000 rpm, preferably 300 to 800 rpm, most preferably 550 rpm.

[0057]

[0053] In one or more embodiments, the applied speeds can also be selected independently cycle by cycle. In one or more embodiments, a speed of 100 to 1000 rpm is used, preferably 400 to 800 rpm, more preferably 600 rpm.

[0058]

[0054] In one or more embodiments, the additional exfoliation is performed in equipment distinct from the contact step equipment and the additional contact step, when present.

[0059]

[0055] The process for producing a graphene dispersion described here is capable of producing a graphene dispersion useful for use as a graphene additive, particularly useful for use as a chemical additive or water-based dispersions.

[0060]

[0056] In one or more embodiments, the graphene dispersion produced by the method described herein can be used as a chemical additive for paints and coatings, polymers, semiconductor and conductive materials, lubricating oils, cementitious and ceramic materials, electrode paste for batteries, capacitors and solar cells.

[0061] Graphene Functionalization

[0057] In a further aspect, the present invention relates to a method for functionalizing graphene. The graphene to be functionalized is in the form of a graphene dispersion, and the graphene content in the graphene dispersion to be functionalized by the functionalization method described herein is not particularly limited, and may be, for example, greater than or equal to 0.001% by weight of graphene, based on the total weight of the graphene dispersion, for example from 0.001% to 99.9% by weight of graphene, from 0.001% to 90% by weight of graphene, from 0.001% to 80% by weight of graphene, from 0.001% to 70% by weight of graphene, from 0.001% to 60% by weight of graphene, for example from 0.001% to 50% by weight of graphene.

[0062]

[0058] Dispersing agents may be selected from the group consisting of polyaromatic hydrocarbon compounds, preferably selected from pyrene or pyrene derivatives, peptides, DNA molecules, cationic compounds such as imidazolium cations and imidazolium-modified polymers. They may also be selected from surfactants, particularly cationic, anionic or non-ionic surfactants. Anionic surfactants useful for the present invention may be selected from alkyl sulfonates and aryl sulfonates. Non-ionic surfactants may be selected from polyethylene glycols (PEGs) or block copolymers of polyethylene oxide and polypropylene oxide.Dispersing agents according to the present invention may also be selected from compounds containing a carboxylic acid functional group, such as C1-C30 mono- or dicarboxylic acids with saturated or unsaturated, normal or branched, open or closed, aliphatic or aromatic chains, compounds containing an amine functional group such as C2-C20 aliphatic amines, compounds containing a hydroxyl functional group such as polyvinyl alcohol (PVOH), compounds containing an isocyanate functional group, such as C1-C10 alkyl and aryl isocyanates, C2-C10 thioesters and salts thereof, silanes and anhydrides, particularly saturated or unsaturated C4-C10 cyclic anhydrides, ionic solutions or polymers with surfactant action.Dispersing agents may also be selected from solvents such as water, organic solvents such as C3-C10 ketones, C5-C10 dicarbonyls, C2-C10 alcohols, C2-C10 di-alcohols, aromatic or non-aromatic C4-C8 heterocyclic compounds containing at least one O, N or S heteroatom, amides such as N-(C1-C10-alkyl)amides, N,N-(C1-C10-dialkyl)amides, or C3-C10 cyclic amides such as lactams and pyrrolidones, C3-C10 ethers, C4-C10 alkanes, C4-C10 haloalkanes, optionally substituted monoaromatic hydrocarbon compounds with C1-C10 alkyl and / or halogen substitutes, C2-C10 sulfoxides, cyclic esters C4-C10, Ce-C-io aryl sulfoxides, sulfonic acids such as mono- or diaromatic sulfonic acids or salts thereof, oils such as vegetable oils and mineral oils or greases, and may also be a combination of the components listed here.

[0063]

[0059] The components of the dispersing agent can be added one by one to the container or pre-mixed and then added to the container. They can be added to the container independently of each other before or after the addition of graphene, with no limitation as to the order in which the components are added to the container.

[0064]

[0060] In one or more embodiments, rotational and translational motion occur simultaneously.

[0065]

[0061] The rotational and translational movements can be performed in the same direction or in opposite directions, preferably in opposite directions. In one or more embodiments, the rotational movement is performed clockwise and the translational movement counterclockwise. In one or more embodiments, the rotational movement is performed counterclockwise and the translational movement clockwise.

[0066]

[0062] In one or more embodiments, the rotational and translational movements in the contact step are performed in one or more cycles, in order to avoid overheating of the graphene dispersion, favor the collision between particles for better functionalization efficiency and graphene exfoliation. In one or more embodiments, 1 to 10 cycles are performed, more preferably 1 to 5 cycles. The cycles have independent durations and preferably last from 10 seconds to 1 hour, preferably from 1 minute to 30 minutes, more preferably 10 minutes.

[0067]

[0063] The translational and rotational speeds can also be selected independently cycle by cycle, and selected independently by type of motion. In one or more embodiments, a rotational speed of 600 to 3500 rpm is used, preferably 1000 to 3000 rpm, more preferably 1500 to 2500 rpm, and a translational speed of 100 to 1000 rpm, preferably 400 to 1000 rpm, more preferably 800 rpm.

[0068]

[0064] In one or more embodiments, the rotational motion of the container is performed around an axis of rotation, and the translational motion of the container is performed around an axis of translation, wherein the axis of rotation and the axis of translation of the container form an angle 6. In one or more embodiments, the axis of rotation and the axis of translation of the container form an angle 6 between them of 30° to 60°, preferably 40 to 50°, more preferably about 45°.

[0069]

[0065] Simultaneous rotational and translational movements can be performed by double-axis rotation equipment, capable of setting a container in rotational and translational motion. Examples of useful equipment in the present invention are double-axis rotation mixers, more particularly double-axis centrifugal mixers.

[0070]

[0066] The graphene functionalization process described here is capable of producing a functionalized graphene dispersion useful for use as a graphene additive, particularly useful for use as a chemical additive or even water-based dispersions.

[0071]

[0067] In one or more embodiments, the functionalized graphene dispersion produced by the functionalization method described herein can be used as a chemical additive for paints, polymers, semiconductor materials, lubricating oils, and also as water-based additives or dispersions for cementitious and ceramic materials, as well as a paste for electrodes in batteries, capacitors and solar cells.

[0072] Graphene Dispersion

[0073]

[0068] In another aspect, the present invention relates to a graphene dispersion comprising an amount of graphene greater than 20% by weight, based on the total weight of the dispersion, and a dispersing agent.

[0074]

[0069] In one or more embodiments, the graphene dispersion contains up to 99.9% by weight of graphene, up to 90% by weight of graphene, up to 80% by weight of graphene, up to 70% by weight of graphene, up to 60% by weight of graphene, up to 50% by weight of graphene, particularly 25% to 99.9% by weight of graphene, 25% to 90% by weight of graphene, 25% to 80% by weight of graphene, 25% to 70% by weight of graphene, 25% to 60% by weight of graphene, 25% to 50% by weight of graphene, more particularly 30% to 99.9% by weight of graphene, 30% to 90% by weight of graphene, 30% to 80% by weight of graphene, 30 to 70% by weight of graphene, 30 to 80% by weight of graphene, 30 to 70% by weight of graphene, 30 to 60% by weight of graphene, 30 to 50% by weight of graphene, based on the total weight of the graphene dispersion. In one or more embodiments, the graphene dispersion comprises an amount of graphene of 25 to 50% by weight, preferably 30 to 50% by weight, based on the total weight of the graphene dispersion.

[0075]

[0070] Embodiments of the dispersing agent contained in the graphene dispersion are in accordance with the embodiments described for the dispersing agent of the method for preparing a graphene dispersion of the present invention. In one or more embodiments, the graphene dispersion comprises up to 80% by weight of a dispersing agent, particularly from 0.1% to 75% by weight, from 10% to 75% by weight of a dispersing agent, from 20% to 75% by weight of a dispersing agent, from 30% to 75% by weight of a dispersing agent, from 40% to 75% by weight of a dispersing agent, from 50% to 75% by weight of a dispersing agent, more particularly from 0.1% to 70% by weight of a dispersing agent, from 10% to 70% by weight of a dispersing agent, from 20% to 70% by weight of a dispersing agent, from 30% to 70% by weight of a dispersing agent, from 40% to 70% by weight of a dispersing agent, from 50% to 70% by weight of a dispersing agent, based on the total weight of the graphene dispersion.

[0076]

[0071] In one or more embodiments, the graphene dispersion is obtained from the method of preparing a graphene dispersion according to the present invention.

[0077]

[0072] The graphene dispersion described herein is useful for use as a graphene additive, particularly useful for use as a chemical additive. In one or more embodiments, the graphene dispersion of the present invention may be used as a chemical additive for paints, polymers, semiconductor materials, lubricating oils, and also as water-based additives or dispersions for cementitious and ceramic materials, or even in pastes for electrodes of batteries, capacitors and solar cells.

[0078] EXAMPLES

[0079]

[0073] The present invention will be better understood by means of the following examples, which are not limiting to the invention described herein.

[0080] Example 1 - Dispersion of graphene in a conventional mill at 20% by weight of graphene.

[0081]

[0074] To represent a conventional state-of-the-art process, a LabStar Zeta horizontal mill supplied by NETZSCH was used. Grinding was performed using high-density, high-hardness cerium-stabilized zirconium oxide grinding beads with particle sizes ranging from 2.8 to 3.3 mm (CeraBeads 3.0). One kg of graphene nanoplatelets with more than 10 layers and a dispersing agent containing 0.05 kg of an organic compound with a carboxylic acid functional group and 3.95 kg of mineral oil were added to the grinding chamber, resulting in a solids content of 20% and a total density of 2.2 kg / L. Grinding was performed for 30 minutes at a temperature of approximately 100 °C. The resulting dispersion had a viscous appearance and is shown in Figure 1A.

[0082] Example 2 - Dispersion of graphene in a conventional mill at 38% by weight of graphene.

[0083]

[0075] The horizontal mill described in Example 1 was used to manufacture a 38 wt% graphene dispersion. Milling was performed using high-density, high-hardness cerium-stabilized zirconium oxide grinding beads with particle sizes ranging from 2.8 to 3.3 mm (CeraBeads 3.0). 1.9 kg of graphene nanoplatelets with more than 10 layers and a dispersing agent containing 0.095 kg of an organic compound with a carboxylic acid functional group and 3.005 kg of mineral oil were added to the milling chamber, resulting in a solids content of 38 wt% graphene. Milling was performed for 30 minutes at a temperature of approximately 100 °C. The proposed process was not viable due to the high viscosity of the dispersion, resulting in the equipment becoming inoperable. The resulting product is shown in Figure 1B, where it is possible to see high viscosity and poor dispersion of the graphene particles, making it unsuitable for use as an additive.

[0084] Example 3 - Non-covalent functionalization of graphene

[0085]

[0076] For the study of non-covalent functionalization of graphene, dispersions were produced with three different types of graphene, named: AO, A8 and A20. The dispersions were prepared with 30% by weight of graphene dispersed in 70% by weight of dispersing agent containing a mixture of 0.9% organic compound containing a carboxylic acid functional group and 69.1% mineral oil, based on the total weight of the graphene dispersion.

[0086]

[0077] The main characteristics of the three types of graphene used are shown in Table 1.

[0087] Table 1

[0088]

[0078] The graphene dispersion production process was carried out in a single step, in which graphene together with the dispersing agent were placed in a container and processed in a double-shaft centrifugal mixer (translation and rotation). The processing was carried out for a period of 5 min at a rotation speed of 2500 rpm and a translation speed of 800 rpm. The resulting material had the consistency of a paste with high viscosity.

[0089]

[0079] Graphene differs in the number of layers, as observed in Raman spectroscopy analyses shown in Figure 2. The spectra of A0 and A8 show low intensities in the D band (1200 to 1400 cm⁻¹). -1 ) and smaller width in the G band (1500 to 1600 cm' 1 The quantification of the material characteristics (Table 2) shows that no significant defects occurred and that these 2 samples exhibit similar behavior.

[0090] Table 2

[0091]

[0080] The peak intensity ratio D to G (ID / IG), the distance between point defects (LD), and the surface density of point defects (no) show the same value, ~0.10, 40 nm and 2 (1010 cm⁻¹). 2 ), respectively, indicating high crystalline quality of the samples. Despite the number of coupled layers, <n>2D, for A0 and A8, appearing above 10 layers, according to Silva, Diego L, et al. "Raman spectroscopy analysis of number of layers in mass-produced graphene flakes." Carbon 161 (2020): 181-189, which describes a protocol to determine the number of coupled layers in graphene through the 2D band profile, it is possible to observe in Figures 2A and 2B that the 2D band profile for A8 is different compared to A0. These results suggest that A8 is more exfoliated than A0. The A20 sample represented in Figure 2C presents a distinct Raman spectrum, with an increase in the intensity of the D peak and the appearance of the D' peak, which are related to defects present in the graphene structure. Furthermore, for A20, a smaller number of uncoupled layers is observed in relation to the others, below 10 layers.

[0081] For analysis of graphene functionalization, thermogravimetric analyses were performed, which are represented in Figure 3.TGA analyses were initially performed in an oxidizing atmosphere to verify the impact on the oxidation temperature of graphene. Analyzing Figure 3, it is possible to verify that the oxidation temperatures of graphene for AO, A8, and A20 are 756, 777, and 742 °C, respectively. After the production of the dispersions, Figure 4, it is observed that all oxidation temperatures increased to 860, 828, and 805 °C for the graphene dispersions containing graphene named AO, A8, and A20, respectively. Furthermore, it is also observed that the temperature of oleic acid also increased after the functionalization process for all samples, being more significant for sample A8. These results show that the functionalization process increases the thermal stability of the components, suggesting an interaction process between them.

[0092] Example 4 - Production of graphene dispersion at 38% by weight

[0093]

[0082] A graphene dispersion containing 38% by weight of graphene dispersed in a mixture of 1.9% maleic anhydride and 60.1% mineral oil was prepared using the method of the present invention.

[0094]

[0083] In a first deagglomeration and functionalization step, 100 g of graphene and 5 g of maleic anhydride were placed in a container and processed in a twin-shaft centrifugal mixer (translation and rotation). In this first step, 5 cycles of 1 minute and 45 seconds each were performed, at a rotation speed between 800 and 1500 rpm and a translation speed of 800 rpm.

[0095]

[0084] In a second stage, 158.16 g of mineral oil were added to the graphene / maleic anhydride mixture and the materials were processed again in the twin-shaft centrifugal mixer. In the second stage, 5 cycles of 7 min each were performed, at a rotational speed of 800 to 2500 rpm and a translational speed of 800 rpm and a pressure of 1 atm.

[0096]

[0085] The resulting material is a paste, which underwent a third exfoliation stage of the graphene. For exfoliation, the paste was mixed in a three-roll mill using openings of 10, 7, 4, and 1 µm. The paste was processed in the mill with 2 to 5 passes for each opening between the rolls. The resulting product was a very homogeneous paste with high viscosity.

[0097] Example 5 - Production of graphene dispersion at 26% by weight

[0098]

[0086] A dispersion containing 26% by weight of graphene dispersed in a mixture of 5% by weight of sodium naphthalene sulfonate (NSS) and 69% polyethylene glycol (PEG) was prepared using the method of the present invention.

[0099]

[0087] The process was carried out in a single step, in which 26 g of AO graphene, together with 5 g of NSS and 69 g of PEG, were placed in a container and processed in a twin-shaft centrifugal mixer (translation and rotation). The processing was carried out for 5 min at a rotation speed of 2500 rpm and a translation speed of 800 rpm. The resulting material had the consistency of a paste with high viscosity.

[0100] Example 6 - Stability test of graphene dispersions

[0101]

[0088] For the purpose of evaluating the stability of graphene dispersions obtained by the method of the present invention (Figure 7A) and the prior art (Figure 7B), two different graphene dispersions were prepared.

[0102]

[0089] The dispersion according to the present invention was prepared with 20% by weight of graphene dispersed in 80% by weight of a dispersing agent containing a mixture of 1.0% organic compound containing a carboxylic acid functional group and 79% mineral oil, based on the total weight of the graphene dispersion. The graphene dispersion production process was carried out in a single step, in which graphene together with the dispersing agent were placed in a container and processed in a double-shaft centrifugal mixer (translation and rotation). The processing was carried out for a period of 5 min at a rotation speed of 2500 rpm and a translation speed of 800 rpm. The resulting material had the consistency of a paste with high viscosity.

[0103]

[0090] The dispersion according to the state of the art was prepared at 20% by weight of graphene dispersed in 80% by weight of dispersing agent containing a mixture of 1.0% organic compound containing a carboxylic acid functional group and 79% mineral oil, based on the total weight of the graphene dispersion. The graphene dispersion production process was carried out in a horizontal mill. Milling was performed using high-density, high-hardness cerium-stabilized zirconium oxide milling beads with particle sizes ranging from 2.8 to 3.3 mm (CeraBeads 3.0). Graphene nanoplatelets with more than 10 layers and dispersing agent were added to the milling chamber, resulting in a solids content of 20%. Milling was performed for 30 minutes at a temperature around 100 °C.

[0104] For stability evaluation, both dispersions produced were placed in a hermetically sealed plastic container and left to stand for 1 day at a temperature of 24 °C. After the specified time, it was observed that the prior art dispersion had sedimented, forming an oily supernatant as illustrated in Figure 7B. In contrast, the dispersion according to the present invention maintained the graphene dispersed in the oily matrix, without the formation of sediments or supernatant, confirming its stability.

[0105] Example 7 - Production of graphene dispersions at different concentrations

[0106]

[0091] Graphene dispersions at different concentrations were produced by the graphene dispersion preparation method according to the present invention, where different amounts of graphene were brought into contact with a dispersing agent containing a mixture of 5% by weight, with respect to solids content (graphene), of an organic compound containing a carboxylic acid functional group and the remainder of mineral oil. The graphene dispersion production process was carried out in a single step, in which graphene together with the dispersing agent were placed in a container and processed in a double-shaft centrifugal mixer (translation and rotation). The processing was carried out for a period of 5 min at a rotation speed of 2500 rpm and a translation speed of 800 rpm. The resulting materials had the consistency of a paste with high viscosity, and are shown in Figure 8.Dispersions of 20%, 30%, 40%, 50%, and 60% graphene by mass were produced, figures 8A, 8B, 8C, 8D, and 8E, respectively.< / n>

Claims

CLAIMS 1. A method for preparing a graphene dispersion, characterized by comprising a step of contacting graphene with a dispersing agent in a container, wherein the container is subjected to translational and rotational motion.

2. Method, according to claim 1, characterized in that the container is subjected to simultaneous translational and rotational motion.

3. A method according to any one of claims 1 to 2, characterized in that the dispersing agent is a liquid dispersing agent.

4. A method according to any one of claims 1 to 3, characterized in that the dispersing agent comprises at least one component selected from the group consisting of surfactants, polycyclic aromatic hydrocarbon compounds, peptides, DNA molecules, imidazolium cations and imidazolium-modified polymers, compounds containing an amine functional group, compounds containing a hydroxyl functional group, compounds containing an isocyanate functional group, C2-C10 thioesters and salts thereof, silanes, anhydrides, oils, greases, organic solvents, or a combination thereof.

6. A method according to any one of claims 1 to 5, characterized by comprising a subsequent contact step in which the graphene dispersion is brought into contact with a dispersing agent in a container, wherein the container is subjected to translational and rotational motion.

7. Method according to claim 6, characterized in that, in the subsequent contact step, the container is subjected to simultaneous translational and rotational motion.

8. A method, according to any one of claims 6 to 7, characterized in that the subsequent contact step is carried out at a pressure equal to or below atmospheric pressure.

9. Method, according to any one of claims 6 to 8, characterized in that the dispersing agent is selected from the group consisting of surfactants, polycyclic aromatic hydrocarbon compounds, peptides, DNA molecules, imidazolium cations and imidazolium-modified polymers, compounds containing amine functional groups, compounds containing hydroxyl functional groups, compounds containing isocyanate functional groups, C2-C10 thioesters and salts thereof, silanes, anhydrides, oils, greases, organic solvents, or a combination thereof.

10. A method, according to any of the preceding claims, characterized by comprising an additional exfoliation step in which the graphene dispersion is subjected to shear.

11. Method according to claim 10, characterized in that shearing is carried out by means of mixing, grinding, ultrasonic motion or centrifugal motion.

12. Method, according to any one of claims 10 to 11, characterized in that the exfoliation is carried out in cycles, preferably from 1 to 10 cycles.

13. Method according to claim 12, characterized in that each cycle independently has a duration of 10 seconds to 1 hour.

14. Method, according to any one of claims 12 to 13, characterized in that each cycle is performed independently at a rotational speed of 100 to 550 rpm.

15. Method, according to any of the preceding claims, characterized in that the rotational motion of the container is carried out around an axis of rotation, and the translational motion of the container is carried out around an axis of translation, wherein the axis of rotation and the axis of translation of the container form an angle (0) of 30° to 60°, preferably 40 to 50°.

16. A method, according to any of the preceding claims, characterized in that, in the contact step of the graphene with the dispersing agent, the rotational and translational movements are performed in opposite directions.

17. A method, according to any of the preceding claims, characterized in that, in the step of contact of the graphene with the dispersing agent, rotational and translational movements can be performed in one or more cycles, preferably from 1 to 10 cycles.

18. Method according to claim 17, characterized in that each cycle independently has a duration of 10 seconds to 1 hour.

19. Method, according to any one of claims 17 to 18, characterized in that each cycle is performed independently at a rotational speed of 600 to 3500 rpm, and at a translational speed of 100 to 1000 rpm.

20. A method, according to any of the preceding claims, characterized in that the graphene dispersion has a graphene content greater than 20% by weight, based on the total weight of the graphene dispersion.

21. Method for functionalizing graphene, characterized by comprising a contact step of the graphene dispersion with a dispersing agent in a container, wherein the container is subjected to translational and rotational motion.

22. Method according to claim 21, characterized in that the container is subjected to simultaneous translational and rotational motion.

23. Graphene dispersion, characterized by comprising a quantity of graphene greater than 20% by weight, based on the total weight of the dispersion, and a dispersing agent.

24. Graphene dispersion obtained by the method as defined in any one of claims 1 to 20, characterized by comprising an amount of graphene greater than 20% by weight, based on the total weight of the dispersion, and a dispersing agent.

25. Graphene dispersion, according to any one of claims 23 to 24, characterized by comprising an amount of graphene of 25 to 99.9% by weight, preferably 30 to 99.9% by weight, based on the total weight of the graphene dispersion.

26. Functionalized graphene dispersion, characterized by being obtained by the method as defined in claim 21.

27. Use of graphene dispersion as defined in any one of claims 23 to 25, characterized in that it is used as a chemical additive or water-based dispersion.

28. Use according to claim 27, characterized by being a chemical additive for paints and coatings, polymers, semiconductor and conductive materials, lubricating oils, water-based additives or dispersions for cementitious and ceramic materials, paste for battery electrodes, capacitors and solar cells.

29. Use of functionalized graphene dispersion as defined in claim 26, characterized in that it is used as a chemical additive or water-based dispersion.

30. Use according to claim 29, characterized by being a chemical additive for paints and coatings, polymers, semiconductor and conductive materials, lubricating oils, water-based additives or dispersions for cementitious and ceramic materials, paste for battery electrodes, capacitors and solar cells.

Images