WO2014060685A1

WO2014060685A1 - Method for producing a graphene-based thermosetting composite material

Info

Publication number: WO2014060685A1
Application number: PCT/FR2013/052420
Authority: WO
Inventors: Julien Beausoleil; Serge Bordere; Patrick Delprat; Patrice Gaillard; Alexander Korzhenko
Original assignee: Arkema France
Priority date: 2012-10-19
Filing date: 2013-10-10
Publication date: 2014-04-24
Also published as: FR2997088B1; FR2997088A1

Abstract

The invention relates to a method for producing composite materials based on: graphene obtained by means of vapour-phase chemical deposition, and a thermosetting resin which is a non-elastomer or elastomer resin base. The invention also relates to the resulting composite materials, and to the use thereof for the production of composite products.

Description

Process for the preparation of a thermosetting composite material based on graphene

The present invention relates to a process for the preparation of composite materials based on graphene obtained by chemical vapor deposition and a thermosetting resin, which is an elastomeric or non-elastomeric resin base. It also relates to the composite materials thus obtained, as well as their use for the manufacture of composite products.

Graphene is a material discovered in 2004 and has since been manufactured on an industrial scale. It is a two-dimensional crystal made up of carbon atoms arranged in a honeycomb, the stack of which constitutes graphite (where 1 mm of graphite contains several million graphene sheets). Various methods for the preparation of graphene have been proposed in the literature, including so - called mechanical exfoliation and chemical exfoliation methods, consisting in tearing graphite sheets in successive layers, respectively by means of an adhesive tape (Geim AK, Science, 306: 666, 2004) or with the aid of reagents, such as sulfuric acid combined with nitric acid, interposed between the graphite layers and the oxidants, so as to form oxide graphite that can be easily exfoliated in water in the presence of ultrasound. Another exfoliation technique involves subjecting graphite in solution with ultrasound in the presence of a surfactant (US Pat. No. 7,824,651). It is also possible to obtain graphene particles by cutting carbon nanotubes along the longitudinal axis ("Micro-Wave Synthesis of Large Few-Layer Graphene Sheets in Aqueous Solution of Ammonia", Janowska, I. et al, NanoResearch, 2009 or Narrow Graphene Nanoribbons from Carbon Nanotubes ", Jiao L. et al, Nature, 458: 877-880, 2009). Still another method of preparing graphene is to decompose at high temperature, under vacuum, silicon carbide.

Finally, several authors have described a process for the synthesis of graphene by chemical vapor deposition (or CVD), possibly associated with a radio frequency generator (RF-CVD) (Dervishi et al., J. Mater Sci., 47). : 1910-1919, 2012; DERVISHI et al., Chem., 4061-4063, 2009; PRABHAS et al., Energy Environ. Sci., 4: 778-783, 2011).

The method of CVD graphene synthesis involves the decomposition of hydrocarbons at temperatures generally ranging from 800 ° C to 1000 ° C, mainly on metal films (Co, Cu, Ni) deposited on flat substrates (S. Bhaviripudi et al., Nano Lett., 2010, 10, 4128, HJ Park et al., Carbon, 2010, 48, 1088, A. Varykhalov et al., Phys Rev. B, 2009, 80, 35437).

The production of graphene by CVD using catalysts in powder form has been described elsewhere by WANG et al. (Chem Vap Deposition, 15: 53-56, 2009) from the decomposition of methane at 1000 ° C on MgO supported cobalt, or by DERVISHI et al., Chem. Mater., 21: 5491-5498, 2009 by decomposition of acetylene at 1000 ° C on a Fe-Co / MgO system.

Research has been conducted for some years to exploit the properties of graphene, particularly in the manufacture of composite materials based on polymer matrices. Graphene has indeed good electrical conductivity, optical transparency, a high Young's modulus and good thermal and chemical stability, at an acceptable cost. It is therefore an alternative of choice to carbon nanotubes. However, the realization such composite materials runs up against the poor dispersibility of graphene in these matrices. However, it is directly correlated with its ability to improve the electrical, mechanical and thermal properties of the matrix.

Some solutions have been proposed to facilitate the dispersion of graphene in a polymer matrix. Among these, mention may be made of the grafting of isocyanate groups on oxidized graphite, which makes it possible to create amide and carbamate bonds, respectively with the carboxylic acid and hydroxyl functions of the oxidized graphite, and thus to make it less hydrophilic and more easily dispersible in a polymer matrix (STANKOVICH et al., Nature, 442: 282-286, 2006). However, this process is complex and expensive because it requires not only the treatment of the graphite with a view to oxidizing it, followed by its chemical functionalization, but also a subsequent step of reducing the oxidized graphene obtained after exfoliation of the functionalized graphite in the polymer matrix. to obtain graphene dispersed in this matrix.

In addition, US 2010/092723 discloses a method for dispersing graphene in a polymer matrix in a preferred orientation, which is believed to be important in imparting certain mechanical properties to the matrix. This process comprises the extrusion in the form of fibers of a mixture comprising graphene and a fluid matrix, consisting for example of a polymer in the molten state or in solution, which may in particular be a thermosetting resin. The fibers are then subjected to a textile operation to obtain a preform which is heated and compressed to give it its shape before being cooled. This complex process does not make it possible to obtain a conductive composite material which requires an orientation favoring the contact between the particles of graphene within the matrix.

In this context, the Applicant has developed a simple and inexpensive method for homogeneously dispersing graphene in a thermosetting resin, so as to confer electrical conduction properties. This method consists in kneading, in a compounding device, graphene obtained by CVD, which is the most promising technique for synthesizing graphene mono-slip or having a low number of layers, on a large scale and at a lower cost, so that reproducible and controlled.

The present invention thus relates to a process for preparing a composite material based on graphene, comprising:

(a) introducing, in a graphene compound obtained by chemical vapor deposition and a polymeric composition, preferably in the liquid state, containing at least one thermosetting resin, which is an elastomeric resin base; or non-elastomeric, and possibly a rheology modifier,

(b) mixing the liquid polymeric composition and graphene within said device to form a composite material,

(c) recovering the composite material, optionally after conversion into an agglomerated solid physical form such as granules. In this description, the term "graphene" is used to designate a plane graph sheet, isolated and individualized, but also, by extension, an assembly comprising between one and a few tens of sheets and having a flat structure or more or less wavy. This definition includes FLG (Few Layer Graphene or Graphene NanoRegons or Graphene NanoRibbons), NGP (Nanosized Graphene Plates), CNS (Carbon NanoSheets or nano-graphene sheets), and Graphene NanoRibbons. nano-ribbons of graphene). On the other hand, it excludes carbon nanotubes and nanofibers, which consist respectively of the winding of one or more sheets of graphene in a coaxial manner and of the turbostratic stacking of these sheets. It is furthermore preferred that the graphene used according to the invention is not subjected to an additional step of chemical oxidation or functionalization.

As indicated above, the graphene used according to the invention is obtained by chemical vapor deposition or CVD. It is typically in the form of particles having a thickness of less than 50 nm, preferably less than 15 nm, and more preferably less than 5 nm, and less than one micron side dimensions, preferably from 10 nm to less than 1000 nm, preferably from 50 to 600 nm, and more preferably from 100 to 400 nm. Each of these particles generally contains from 1 to 50 sheets, preferably from 1 to 20 sheets, more preferably from 1 to 10 sheets, or even from 1 to 5 sheets, which are capable of being disconnected from each other in the form of independent leaflets, for example during an ultrasound treatment. The process for the manufacture of graphene by CVD generally comprises the decomposition of a gaseous source of carbon, in particular a hydrocarbon, such as ethylene, methane or acetylene, under a flow of inert gas such as argon or nitrogen, the dilution ratio of the hydrocarbon in the inert gas being for example about 1: 5. This decomposition is carried out at a temperature of 900 to 1000 ° C., preferably from 960 to 1000 ° C., generally at atmospheric pressure, over a catalyst in the form of a powder. The catalyst may especially be a metal catalyst supported or not on an inert substrate. It may be for example cobalt optionally mixed with iron and supported on magnesia, in a molar ratio of cobalt to magnesia generally less than 10%. The catalyst is usually prepared by impregnating the support with alcoholic or glycol solutions of cobalt salts and optionally iron, followed by evaporation of the solvent and a calcination step.

Another CVD method for obtaining graphene according to this invention comprises the following steps:

a) the introduction into a synthesis reactor, and optionally the fluidized bed in said reactor, of an active catalyst for the synthesis of graphene, comprising a mixed oxide of formula AFe ₂ O ₄ where A is at least one element mixed valence metal having at least two valencies, one of which is equal to +2, in particular chosen from cobalt, copper or nickel, the catalyst being of spinel structure, b) heating said catalyst in the reactor, a temperature of between 500 and 1500 ° C., preferably between 500 and 800 ° C., or even between 610 and 800 ° C.,

c) contacting a gaseous carbon source with the catalyst of step b), optionally in a bed fluidized, and catalytic decomposition at a temperature of 500 to 800 ° C, preferably from 610 to 800 ° C, the gas source being selected from alcohols C ₁ -C ₁ 2 and hydrocarbons C ₁ -C ₁ 2 such as alkanes or alkenes, preferably ethylene, which can be mixed with a stream of a reducing agent such as hydrogen and optionally with an inert gas,

d) the recovery of graphene produced in c) at the outlet of the reactor.

The amount of graphene used according to the invention represents from 0.005 to 40% by weight, preferably from 0.1% to 30% by weight, and more preferably from 1 to 15% by weight, relative to the weight. total of the composite material.

In the process according to the invention, graphene is kneaded with a thermosetting resin in a compounding device.

By "compounding device" is meant, in the present description, an apparatus conventionally used in the plastics industry for the melt blending of thermoplastic polymers and additives to produce composites. In this apparatus, the polymeric composition and the additives are mixed using a high-shear device, for example a co-rotating twin-screw extruder or, a co-kneader comprising a rotor provided with fins adapted to cooperate. with teeth mounted on a stator. The melt generally comes out of the apparatus either in agglomerated solid physical form such as granules or in the form of rods, tape or film. Examples of co-kneaders that can be used according to the invention are the BUSS MDK 46 co-kneaders and those of the BUSS MKS or MX series sold by the company BUSS AG, all of which consist of a screw shaft provided with fins. , disposed in a heating sleeve optionally consisting of several parts and whose inner wall is provided with kneading teeth adapted to cooperate with the fins to produce shear of the kneaded material. The shaft is rotated and provided with oscillation movement in the axial direction by a motor. These co-kneaders may be equipped with a granule manufacturing system, adapted for example to their outlet orifice, which may consist of an extrusion screw or a pump.

The co-kneaders that can be used according to the invention preferably have an L / D screw ratio ranging from 7 to 22, for example from 10 to 20, while the co-rotating extruders advantageously have an L / D ratio ranging from 15 to 56, for example from 20 to 50.

It has been found by the Applicant that this process makes it possible to obtain composite materials, in particular masterbatches comprising up to 30% by weight of graphene, and which are easily handled, in the case where they are in a form agglomerated solid, especially in the form of granules, in that they can be transported in bags from the production center to the processing center. These composite materials may also be shaped according to the methods conventionally used for shaping thermoplastic materials, such as extrusion, injection or compression. By "thermosetting resin" is meant, in the present description, a material which is capable of being cured, under the effect of heat, of a catalyst, or a combination of both, to obtain a thermoset resin. which may or may not be elastomeric. This consists of a material containing polymeric chains of variable length interconnected by covalent bonds, so as to form a three-dimensional network. In terms of its properties, this thermoset resin is infusible and insoluble. It can be softened by heating it above its glass transition temperature (Tg) but, once a shape has been imparted to it, it can not be reshaped later by heating.

Thermosetting resins constituting non-elastomeric resin bases include: unsaturated polyesters, epoxy resins, vinyl esters, phenolic resins, polyurethanes, cyanoacrylates and polyimides, such as bis-maleimide resins, aminoplasts (resulting from the reaction of an amine such as melamine with an aldehyde such as glyoxal or formaldehyde) and mixtures thereof, without this list being limiting.

The unsaturated polyesters result from the condensation polymerization of dicarboxylic acids containing an unsaturated compound (such as maleic anhydride or fumaric acid) and glycols such as propylene glycol. They are generally hardened by dilution in a reactive monomer, such as styrene, and then reaction of the latter with the unsaturations present on these polyesters, generally with the aid of peroxides or a catalyst, in the presence of heavy metal salts or of an amine, or with the help of a photoinitiator, ionizing radiation, or a combination of these different techniques.

The vinyl esters include the products of the reaction of epoxides with (meth) acrylic acid. They can be cured after dissolution in styrene (similar to polyester resins) or with the aid of organic peroxides.

The epoxy resins consist of materials containing one or more oxirane groups, for example from 2 to 4 oxirane functions per molecule. In the case where they are polyfunctional, these resins may consist of linear polymers bearing epoxy end groups, or whose backbone comprises epoxy groups, or whose skeleton carries pendant epoxy groups. They generally require as the hardening agent an acid anhydride or an amine.

These epoxy resins may result from the reaction of epichlorohydrin with a bisphenol such as bisphenol A. It may alternatively be alkyl- and / or alkenylglycidyl ethers or esters; polyglycidyl ethers of optionally substituted mono- and polyphenols, especially polyglycidyl ethers of bisphenol A; polyglycidyl polyol ethers; polyglycidyl ethers of aliphatic or aromatic polycarboxylic acids; polyglycidyl esters of polycarboxylic acids; of polyglycidyl ethers of novolac. In another variant, it may be products of the reaction of epichlorohydrin with aromatic amines or glycidyl derivatives of mono- or aromatic diamines. Cycloaliphatic epoxides can also be used in this invention. It is preferred according to the invention to use diglycidyl ethers bisphenol A (or DGEBA), F or A / F. DGEBA resins are particularly preferred.

Thermosetting resins constituting elastomeric resin bases are organic or silicone polymers which, after vulcanization, form an elastomer capable of withstanding large deformations in a quasi-reversible manner, that is to say capable of being subjected to deformation uniaxially, advantageously at least twice its original length at room temperature (23 ° C), for five minutes, then recover, once the stress is released, its initial dimension, with a remanent deformation less than 10% of its initial dimension.

From the structural point of view, elastomers (or elastomeric resins) generally consist of polymer chains interconnected with covalent bonds, which constitute points of chemical crosslinking, to form a three-dimensional network. These crosslinking points are formed by vulcanization processes employing a vulcanizing agent which may for example be chosen, according to the nature of the elastomer, from sulfur-based vulcanization agents, in the presence of metal salts of dithiocarbamates. ; zinc oxides combined with stearic acid; bifunctional phenol-formaldehyde resins optionally halogenated in the presence of tin chloride or zinc oxide; peroxides; amines; hydrosilanes in the presence of platinum; etc.

The elastomeric resin base may optionally be used according to the invention in a mixture with at least one non-reactive elastomer, that is to say non-vulcanizable (such as hydrogenated rubbers). Thermosetting resins suitable as bases for elastomeric resins may be chosen from: fluorocarbon or fluorosilicone polymers; nitrile resins; homo- and copolymers of butadiene, optionally functionalized with unsaturated monomers such as maleic anhydride, (meth) acrylic acid, and / or styrene (SBR); neoprene (or polychloroprene); polyisoprene; copolymers of isoprene with styrene, butadiene, acrylonitrile and / or methyl methacrylate; copolymers based on propylene and / or ethylene and in particular terpolymers based on ethylene, propylene and dienes (EPDM), as well as copolymers of these olefins with an alkyl (meth) acrylate or vinyl acetate; halogenated butyl rubbers; silicone resins; polyurethanes; polyesters; acrylic polymers such as poly (butyl acrylate) bearing carboxylic acid or epoxy functions; as well as their modified or functionalized derivatives and their mixtures, without this list being limiting.

It is preferred according to the invention to use at least one polymer chosen from: nitrile resins, in particular copolymers of acrylonitrile and butadiene (NBR); silicone resins; fluorocarbon polymers, in particular copolymers of hexafluoropropylene (HFP) and of vinylidene difluoride (VF2); and their mixtures.

In the first step of the process according to the invention, the polymeric composition containing the thermosetting resin is preferably introduced into the compounding device in the liquid state. By "liquid" is meant that the composition is capable of being pumped into the device compounding, that is to say it advantageously has a dynamic viscosity ranging from 0.1 to 30 Pa.s, preferably from 0.1 to 15 Pa.s. The composition may have this viscosity at room temperature (23 ° C.) or, failing that, be heated so as to give it the aforementioned viscosity before injection into the compounding apparatus. It is preferred in this case that the melting point of the thermosetting resin does not exceed 100 ° C. Alternatively, the viscosity of the polymeric composition can be adjusted by adding one or more rheology modifiers, particularly when this composition contains an elastomeric resin base in gum form.

In any case, the polymeric composition is in the liquid state, that is to say that it has the aforementioned viscosity, before coming into contact with graphene within the compounding device.

The dynamic viscosity measurement is based on a general method for determining the viscoelastic properties of polymers in the liquid state, in the molten state or in the solid state. The samples are subjected to deformation (or stress), most often sinusoidal in tension, compression, flexion or torsion for solids and in shear for liquids. The response of the samples to this stress is evaluated either by the force or the resulting torque, or by the deformation when working at imposed stress. The viscoelastic properties are thus determined either in terms of modulus or viscosity, or in terms of creep or relaxation function. In flow, the samples are subjected to a sweep of stresses and / or deformations in order to predict their behavior as a function of the shear gradient. For this determination, a viscoelasticimeter consisting of the following elements is used:

• An enclosure or a thermal regulation system (optionally, the atmosphere during the test can be either nitrogen gas and / or liquid, or air)

• A central control unit

• A system for regulating the flow and drying of air and nitrogen

• A measuring head

• A computer system for controlling the device and processing data

• Crews "sample holder"

As usable equipment, there may be mentioned for example the RDA2, RSA2, DSR200, ARES or RME apparatus from the manufacturer Rheometrics, or MCR301 from Anton Paar.

The dimensions of the sample are defined according to its viscosity and the geometric limits of the chosen "sample holder" system.

For carrying out a test and determining the dynamic viscosity of a thermosetting resin, the steps described in the user manual of the viscoelastic meter used will be methodologically followed. In particular, it will be ensured that the relationship between deformation and stress is linear (linear viscoelasticity).

An example of a rheology modifier adapted to impart the aforementioned viscosity to the polymer composition containing the thermosetting resin is an acrylic block copolymer such as the triblock copolymer pol (methyl methacrylate) / poly (butyl acrylate) / poly (methyl methacrylate) ) available from the ARKEMA company under the trade name Nanostrength® M52N. Such a copolymer is particularly well suited for use in an epoxy resin, in which it can be introduced in powder form and solubilized with stirring in order to increase its viscosity. This copolymer also makes it possible to improve the dispersion of graphene by facilitating the transfer of mechanical energy during shearing in the compounding tool, and also to facilitate the formation of granules from the thermosetting resin. Alternatively, it is possible to use a polystyrene / 1,4-polybutadiene / poly (methyl methacrylate) copolymer also marketed by Arkema, under the reference Nanostrength.

Another example of a rheology modifying agent is a branched fatty acid glycidyl ester such as the highly branched carboxylic acid glycidyl ester of CIO marketed by HEXON under the trade name Cardura® E10P. In addition to its viscosity reducing effect, this compound is also able to react with the hardener of the epoxy resins. Added at the end of compounding, it also reduces the risks of crosslinking epoxy resins by cooling the medium.

In addition to the rheology modifying agents, it is possible to add, in the first step of the process according to the invention, carbon nanotubes (hereafter NTC), advantageously of the multi-wall type, obtained for example by CVD. . These usually have a mean diameter ranging from 0.1 to 200 nm, preferably from 0.1 to 100 nm, more preferably from 0.4 to 50 nm and better still from 1 to 30 nm, for example from 3 to at 30 nm, and advantageously a length of more than 0.1 μm and advantageously from 0.1 to 20 μm, for example about 6 ym. Their length / diameter ratio is advantageously greater than 10 and most often greater than 100. Their specific surface area is for example between 100 and 300 m ² / g and their apparent density may especially be between 0.01 and 0.5 g. / cm ³ and more preferably between 0.07 and 0.2 g / cm ³ . They may comprise from 5 to 15 sheets and more preferably from 7 to 10 sheets.

It is preferred that these CNTs be used in the raw state, possibly after grinding, that is to say without having been purified and / or treated (in particular oxidized or functionalized). An example of crude carbon nanotubes is especially commercially available from Arkema under the trade name Graphistrength® ^® C100.

The polymeric composition used according to the invention may furthermore contain various additives such as fillers, in particular silica or calcium carbonate; UV filters, especially based on titanium dioxide; flame retardants; and their mixtures. The polymeric composition may alternatively or additionally contain at least one solvent of the thermosetting resin. It may furthermore contain blowing agents, in particular preparations based on diamine of azodicarbonic acid, such as those marketed by the company LANXESS under the trade name Genitron®. These are compounds that decompose at 140-200 ° C to form, during the compounding step, cavities in the composite material that facilitate its subsequent introduction into a polymer matrix. Other additives which can be used are the hardeners or vulcanizing agents of the thermosetting resin, provided that their activation temperature is greater than the compounding temperature.

The compounding step is generally carried out at a temperature which is a function of the polymer specifically used and generally mentioned by the supplier of the polymer. By way of example, the compounding temperature can range from 20 ° C to 260 ° C, for example from 30 ° C to 260 ° C, in particular from 80 ° C to 120 ° C.

At the end of the process according to the invention, a composite material is obtained which can, after cooling, advantageously be in a solid form which can be used directly. The subject of the invention is also the composite material that can be obtained by the process described above.

This composite material can be used as it is, that is to say, shaped according to any suitable technique, in particular by injection, extrusion, compression or molding, followed by a treatment at 140-150 ° C., for example, intended activating the hardener or vulcanizing agent. The latter may either have been added to the composite material during the compounding step (in the case where its activation temperature is greater than the compounding temperature), or it may be added to the composite material immediately before it is shaped.

In this embodiment, the composite material according to the invention can thus be used to manufacture films, pre-impregnated materials, ribbons, profiles, strips or fibers. For this purpose, it is possible to provide at the output of the compounding device a forming die of the composite material.

Alternatively, the composite material according to the invention can be used as a masterbatch and thus diluted in a polymer matrix to form a composite product after shaping and heat treatment. Here again, the hardener or vulcanizing agent may be introduced during the compounding step, or during the formulation of the polymer matrix or during the shaping of the polymer matrix.

The invention also relates to the use of the composite material described above for the manufacture of a composite product and / or to confer at least one electrical, mechanical and / or thermal property to a polymer matrix.

It also relates to a method of manufacturing a composite product comprising:

the manufacture of a composite material according to the process described above, and

the introduction of the composite material into a polymer matrix.

The polymer matrix generally contains at least one polymer chosen from homoliters or copolymers with gradients, blocks, statistical or sequenced, thermosetting. At least one thermosetting resin chosen from those listed above is preferably used according to the invention.

The polymer matrix may furthermore contain at least one hardener and / or a curing catalyst or a curing agent for the thermosetting resin, as indicated above, and various adjuvants and additives such as lubricants, pigments, stabilizers, fillers or reinforcements, anti ^¬ static agents, fungicides, flame retardants, and solvents.

Advantageously, when it is in the form of granules, the masterbatch is first immersed in a part of the polymer matrix for several hours, for example overnight, and optionally heated, for example to about 80.degree. in order to soften the granules before introducing them into the rest of the polymer matrix. It is possible to use heating means such as microwaves or induction making it possible to use the resistive capacities of the CNTs and to heat the masterbatch very quickly. The mixture is then preferably subjected to high shear, in particular by means of a rotor-stator device. It is then possible to add the additives of the polymer matrix to the mixture.

In this embodiment of the invention, the compounding device, in which the composite material is manufactured, can be coupled to another device intended to be fed, on the one hand, by the composite material and, on the other hand, on the other hand, by the polymer matrix described above. This other device can in this case be provided with a die for shaping the composite product formed.

The invention also relates to the composite product obtainable by this process. It also deals with the use of this composite product to produce processed finished objects for use in the electronics, computer, cable, transportation or automotive industries.

The invention will be better understood in the light of the following nonlimiting and purely illustrative examples.

EXAMPLES

Example 1: Graphene synthesis by CVD

1- Preparation of a CoFe ₂ O catalyst for the synthesis of graphene

In a 250 ml beaker, 37.5 ml of an aqueous solution of citric acid at a concentration of 0.4 M was prepared, to which 1.1 g of cobalt nitrate (Co (Ν0 ₃₎ ₂ ), 6H ₂ O) and 3.1 g of iron nitrate (Fe (NO ₃ ) ₃ ), 9H ₂ O). The pH of the resulting solution was adjusted to a value of 6 by adding, dropwise and stirring, ammonia (NH ₄ OH). The molar ratio between iron nitrate and cobalt nitrate in the aqueous solution was substantially of the order of 2. This aqueous solution was placed in a Pyrex crystallizer at a temperature of 80 ° C. for a period of substantially order of 12 hours, so as to form a substantially dehydrated homogeneous gel.

The homogeneous gel thus obtained was heated to a temperature of the order of 200 ° C. so as to decompose the citric acid. The expansion of the homogeneous gel was then observed to foam which was allowed to develop for about 30 minutes until stabilization. This foam was then crushed gently to form a powder which was heated at 400 ° C for 4 hours in atmospheric air. Thus a crystalline powder of ferrite of cobalt.

This powder had a single oxide phase having a spinel type structure with a crystalline domain size of between 14 nm and 20 nm (determined by X-ray diffraction) and a specific surface area of 7 m ² / g.

2- Graphene synthesis

Graphene synthesis was performed in a horizontal quartz reactor. 20 mg of the catalyst powder obtained above was placed in an alumina crucible which was placed in the center of a horizontal quartz tubular reactor with an inside diameter of about 18 mm. The catalyst powder was heated under a gaseous flow of hydrogen (¾ 53 cm ³ / min) and argon (Ar 160 cm ³ / min) to a temperature of 650 ° C. temperature gradient of 630 ° C / h. When the temperature reached 650 ° C, ethylene (C ₂ H ₄ , 32 cm ³ / min) was introduced into the gas mixture and the gas flow and the temperature were maintained for one hour. After 1 h, the heating and gaseous flows of ethylene and hydrogen were stopped. The powder obtained was cooled to a temperature of 300 ° C. under argon. The amount of product recovered at the end of the reaction was 220 mg.

Example 2: Manufacture of ion masterbatch or composite material based on epoxy resin

In the first feed hopper of a BUSS MDK 46 (L / D = 11) co-kneader equipped with an extrusion screw and a granulation device, graphene obtained as described in FIG. EXAMPLE 1 An epoxy resin base (DGEBA or diglycidyl ether of bisphenol A) is injected in liquid form at 80 ° C into the ^1st zone of the co-kneader. The instructions of temperature within the co-kneader are as follows: Zone 1 = 120 ° C, Zone 2 = 120 ° C, Vis = 80 ° C. The flow rate was set at 15 kg / h.

At the apparatus outlet, granules of a masterbatch containing 15% by weight of graphene and 85% by weight of epoxy resin are obtained.

These granules can then be diluted in a polymer matrix in equipment allowing heating at 130-140 ° C.

Example 3: Manufacture of ion masterbatch or composite material containing a base of nitrile resin

In the first feed hopper of a BUSS MDK 46 (L / D = 11) co-kneader equipped with an extrusion screw and a granulation device, graphene obtained as described in FIG. Example 1 and an acrylic copolymer powder (Nanostrength M52N ^® ARKEMA). A butadiene-acrylonitrile copolymer (Nipol 1312V HallStar ^®) is preheated to 160 ° C and then injected in liquid form at 190 ° C in the ^first zone of the co-kneader. The temperature setpoints and the flow rate within the co-kneader are set at 200 ° C and 12 kg / h, respectively. The rotational speed of the screw is 240 rpm.

At the outlet of the apparatus, a rod is obtained which is cut under water jet into granules consisting of a masterbatch containing 30% by weight of graphene, 65% by weight of nitrile resin and 5 by weight of acrylic copolymer. . These granules are then dried at approximately 50 ° C. before being packaged.

These granules can then be diluted in a polymer matrix containing a vulcanizing agent, and shaped.

Alternatively, a part of the nitrile resin may be introduced into the co-kneader in solid form, granulated or milled, for example in the first feed hopper.

Claims

A process for preparing a graphene-based composite material, comprising:

(a) introducing, into a compounding device, graphene obtained by chemical vapor deposition, a polymeric composition, preferably in the liquid state, comprising at least one thermosetting resin, which is a resin base; elastomeric or non-elastomeric, and optionally a rheology modifier,

(c) recovering the composite material, optionally after conversion into an agglomerated solid physical form such as granules.

2. Method according to claim 1, characterized in that the graphene is in the form of particles having a thickness of less than 50 nm, preferably less than 15 nm, more preferably less than 5 nm, and lateral dimensions. from 10 to 1000 nm, preferably from 50 to 600 nm, and more preferably from 100 to 400 nm, and in that each of the graphene particles contains from 1 to 50 leaves, preferably from 1 to 20 leaves, more preferably from 1 to 10 leaflets, or even 1 to 5 leaflets.

3. Method according to one of claims 1 and 2, characterized in that the compounding device is a co-kneader preferably having an L / D screw ratio ranging from 7 to 22, more preferably from 10 to 20.

4. Method according to any one of claims 1 to 3, characterized in that the polymeric composition contains at least one thermosetting resin constituting a base of non-elastomeric resin which is selected from: unsaturated polyesters, epoxy resins, vinyl esters, phenolic resins, polyurethanes, cyanoacrylates, polyimides such as bis-maleimide resins, aminoplasts (resulting from the reaction of a amine such as melamine with an aldehyde such as glyoxal or formaldehyde) and mixtures thereof.

5. Method according to any one of claims 1 to

4, characterized in that the polymeric composition contains at least one thermosetting resin constituting an elastomeric resin base which is selected from: fluorocarbon or fluorosilicone polymers; nitrile resins; homo- and copolymers of butadiene, optionally functionalized with unsaturated monomers such as maleic anhydride, (meth) acrylic acid, and / or styrene (SBR); neoprene (or polychloroprene); polyisoprene; copolymers of isoprene with styrene, butadiene, acrylonitrile and / or methyl methacrylate; copolymers based on propylene and / or ethylene and in particular terpolymers based on ethylene, propylene and dienes (EPDM), as well as copolymers of these olefins with an alkyl (meth) acrylate or vinyl acetate; halogenated butyl rubbers; silicone resins; polyurethanes; polyesters; acrylic polymers such as poly (butyl acrylate) bearing carboxylic acid or epoxy functions; as well as their modified or functionalized derivatives and their mixtures.

6. Process according to any one of claims 1 to

5, characterized in that the amount of graphene represents from 0.005 to 40% by weight, preferably from 0.1% to 30% by weight, and more preferably from 1 to 15% by weight, relative to the total weight composite material.

7. Composite material obtainable by the method according to any one of claims 1 to 6.

8. Use of the composite material according to claim 7 for the manufacture of a composite product and / or for imparting at least one electrical, mechanical and / or thermal property to a polymer matrix.

9. Use of the composite material according to claim 7 for the production of films, pre-impregnated materials, ribbons, profiles, strips or fibers.

A method of manufacturing a composite product comprising:

the manufacture of a composite material according to the method according to any one of claims 1 to 6, and

the introduction of the composite material into a polymer matrix.

11. The method of claim 10, characterized in that the compounding device, in which the composite material is manufactured, is coupled to another device intended to be fed, on the one hand, by the composite material and, on the other hand, on the other hand, by the polymer matrix, and in that this other device is optionally provided with a die for shaping the composite product formed.

12. Composite product obtainable by the method according to one of claims 10 and 11.

13. Use of the composite product according to claim 12 for manufacturing transformed finished objects usable in the sectors of the electronics industry, computer, cable, transport or automobile.