WO2013011250A1

WO2013011250A1 - Graphene-based conductive composite fibres

Info

Publication number: WO2013011250A1
Application number: PCT/FR2012/051748
Authority: WO
Inventors: Patrice Gaillard; Alexander Korzhenko; Patrick Delprat; Serge Bordere
Original assignee: Arkema France
Priority date: 2011-07-21
Filing date: 2012-07-23
Publication date: 2013-01-24
Also published as: FR2978170A1; FR2978170B1

Abstract

Graphene-based conductive composite fibres. The present invention relates to conductive composite fibre containing a polymer matrix in which nanometer-scale graphene is dispersed. It also relates to processes for preparing these fibres, and also to the uses thereof.

Description

Graphene-based conductive composite fibers

The present invention relates to conductive composite fibers comprising a polymeric matrix in which nano-sized graphene is dispersed. It also relates to processes for preparing these fibers, as well as their uses.

The electrically conductive fibers are known for different applications, making particular use of their antistatic properties, in particular for the manufacture of aeronautical or automotive parts or for the electromagnetic shielding of electronic equipment, for example to dissipate electrical charges arising from friction, induced in particular during the circulation of a fluid in a thermoplastic pipe. They can also be used in the manufacture of deformation or stress sensors.

The conductive fibers known in the prior art include:

metallic wires, which have the disadvantage of being heavy and liable to oxidize,

the intrinsically conductive polymer fibers, which are poorly resistant to washing and are not very stable, insofar as they are sensitive to oxidation and also to heat released by the Joule effect which can chemically degrade (for example crosslink) the polymer and / or alter its mechanical properties beyond a certain temperature,

the polymer fibers made conductive by deposition of conductive particles on their surface, such as silver fibers, whose coating is likely to degrade by friction and wear.

There remains therefore the need to have new conductive fibers having a satisfactory electrical conductivity without generating too much heat, which would be likely to degrade the matrix of these fibers. It would also be desirable for these fibers to have other advantageous properties, in particular that they are light and / or chemically stable and / or that they have good mechanical strength.

In this context, it appeared to the inventors that it was possible to meet these needs by proposing a graphene-based fiber dispersed in a polymeric matrix.

Composite fibers containing graphene are already known from WO 2010/107762 and US 2010/092723. These fibers are made from graphene obtained by graphite exfoliation and thus having a variable thickness depending on whether the exfoliation is more or less complete, and micrometric side dimensions. Commercially available exfoliation graphene grades have a length and width of more than 1 μm, typically 5, 15 or 25 μm and up to 50 μm. In addition, the fibers described in these documents are obtained by molten route. However, this technique does not always make it possible to obtain fibers having a good electrical conductivity, insofar as it leads to an orientation of the charges such as graphene in the direction of the fiber, which is generally pred udiciables to the electrical properties. In addition, the molten process does not achieve high levels of graphene, given the high viscosity that they generate.

Now, the inventors have discovered that the use of nanoscale graphene made it possible to prepare fibers having a high electrical conductivity and good mechanical properties. It is also possible to manufacture these fibers by a simple coagulation process to implement, under conditions of high productivity.

The subject of the present invention is thus conductive composite fibers containing graphene dispersed in a polymer matrix, characterized in that the graphene is in the form of particles having a thickness of less than 100 nm, preferably less than 50 nm. , more preferably less than 15 nm, between 0.1 and 10 nm, and lateral dimensions of about 1 μm, more preferably from 50 to 800 nm, more particularly from 100 to 600 nm, or even from 100 to 500 nm .

By "fiber" is meant, in the sense of the present invention, a strand whose diameter is between 100 nm (nanometers) and 300 μιη (micrometers), preferably between 1 and 100 μιη (micrometers), better, between 2 and 50 μιη (micrometers). This structure may also be porous or non-porous. 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). The winding of one or more sheets of graphene coaxially gives rise to the carbon nanotubes (respectively, single-wall and multi-wall), while the turbostratic stack of these sheets is a carbon nanofiber. In this description, the term "graphene" is therefore used to designate a sheet of graphite plane, 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 FLGs (Few Layer Graphene or Graphene NanoRegons), Nanosized Graphene Plates (NGPs), CNS (Carbon NanoSheets or nano-graphene sheets), and Graphene NanoRibbons (Graphene NanoRibbons). nano-ribbons of graphene). On the other hand, it excludes carbon nanotubes and nanofibers. As indicated above, the graphene used according to the invention is in the form of particles having a thickness of less than 100 nm, preferably less than 50 nm, more preferably less than 15 nm, and lateral dimensions of approximately 1 μm, preferably from 50 to 800, more preferably still from 100 to 600 nm, or even from 100 to 500 nm. Each of these particles generally contains from 1 to 50 sheets which are likely to be detached from one of the others in the form of independent leaflets, for example during an ultrasound treatment.

Graphene is advantageously prepared according to a chemical vapor deposition or "CVD" method. Such a process generally comprises the decomposition of a gaseous source of carbon, in particular a hydrocarbon, such as ethylene, methane or acetylene, at a temperature of 800 to 1000 ° C., over a supported catalyst. in powder form, in particular on cobalt optionally mixed with iron and supported on magnesia.

A preferred 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, such as a mixed oxide of formula AFe ₂ O ₄ where A is an element mixed valence metal having at least two valences of which one is +2, in particular selected from cobalt, copper or nickel, the catalyst being advantageously of spinel structure, b) heating said catalyst in the reactor, at a temperature 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 fluidized bed, and its 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, of preferably ethylene, which can be mixed with a flow of hydrogen as reducing agent 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 0.5% to 50%, preferably from 1% to 30%, more preferably from 3.5% to 15% by weight, relative to the total weight composite fiber.

The present invention also relates to processes for producing these conductive composite fibers by coagulation. The coagulation process may include:

either coagulation in the form of a fiber, or around a pre-formed fiber, a mixture of graphene and a polymeric binder, generally polyvinyl alcohol, by passing it through a coagulation solution,

or injection of graphene dispersed in a solvent in a co-flow of a coagulation solution containing a polymeric binder such as polyvinyl alcohol.

Thus, according to a first embodiment, the composite fibers according to the invention can be produced by a process comprising the successive steps of:

a) forming a graphene dispersion in a polymer binder solution, in the presence of at least one stabilizing agent covalently or non-covalently bound to graphene,

b) injecting said dispersion into a coagulation solution,

c) extracting the obtained fiber,

d) the possible washing of said fiber,

e) drying said fiber.

Such a method has been described in detail in application FR 2 946 177 to which reference may be made for more details.

The first step of the process according to the invention consists in forming a graphene dispersion in a binder polymer, in the presence of at least one stabilizing agent covalently or non-covalently bonded to graphene.

The binder polymer may be chosen from a homo- or copolymer of vinyl alcohol, cellulose, viscose, an alginate, poly (lactic acid), poly (lactic acid-co-glycolic acid), and mixtures thereof, particularly polyvinyl alcohol.

For the purpose of the present invention, the term "stabilizing agent" is intended to mean a compound which allows a homogeneous dispersion of graphene in the solution, which protects graphene from coagulation in the presence of the polymeric binder, but which does not interfere with the coagulation of the polymeric binder in a coagulation solution.

The stabilizing agent (s) according to the invention are bonded to graphene either covalently or non-covalently.

In the case where the stabilizing agent is non-covalently bonded to graphene, it may be chosen from essentially nonionic surfactants.

By "substantially nonionic surfactant" is meant, in the sense of the present invention, a nonionic amphiphilic compound, cited for example in the book McCUTCHEON'S 2008 "Emulsifiers and Detergents", and preferably having a HLB (hydrophilic-lipophilic balance) from 13 to 16, as well as block copolymers containing hydrophilic blocks and lipophilic blocks and having a low ionicity, for example 0% to 10% by weight of ionic monomer and 90% to 100% of nonionic monomer.

In the second case where the stabilizing agent is covalently bonded to graphene, it is preferably a hydrophilic group, preferably a polyethylene glycol group grafted on graphene.

The grafting of reactive units such as polyethylene glycol groups on the surface of graphene can be carried out according to any method known to those skilled in the art. For example, one skilled in the art may disperse graphene in dimethylformamide (DMF) before contacting it with oxalyl chloride. In one second time, the resulting dispersion will be contacted with polyethylene glycol (PEG).

In addition, the dispersion produced in the first step of the process according to the invention comprises a solvent which is preferably chosen from water, dimethylsulfoxide (DMSO), glycerol, ethylene glycol, diethylene glycol and triethylene glycol. , diethylene triamine, ethylene diamine, phenol, dimethylformamide (DMF), dimethylacetamide, N-methylpyrrolidone and mixtures thereof. Preferably, the solvent is chosen from water, DMSO and mixtures thereof in all proportions.

If it is an aqueous dispersion, the pH of the aqueous dispersion can be maintained preferably between 3 and 5 by addition of one or more acids, which can be chosen from inorganic acids, such as sulfuric acid, nitric acid and hydrochloric acid, organic acids such as acetic acid, tartaric acid and oxalic acid and mixtures of organic acid and organic acid salt such as acid citric acid and sodium citrate, acetic acid and sodium acetate, tartaric acid and potassium tartrate, tartaric acid and sodium citrate.

On the other hand, the dispersion may comprise boric acid, borate salts, or mixtures thereof.

In addition, the dispersion may also comprise a salt selected from zinc chloride, sodium thiocyanate, calcium chloride, aluminum chloride, lithium chloride, rhodanates and mixtures thereof. They make it possible to optimize the rheological properties of the dispersion and to promote the formation of the fiber.

According to an advantageous form of the present invention, the dispersion is carried out by means of ultrasound or a rotor-stator system or a ball mill. It can be carried out at room temperature, or by heating, for example, between 40 and 120 ° C.

The second step of the process involves injecting said dispersion obtained in the first step into a coagulation solution to form a fiber, in the form of monofilament or multi-filaments.

For the purposes of the present invention, the term "coagulation solution" is intended to mean a solution which causes the polymer binder to solidify. Such solutions are known to those skilled in the art, and the production of vinyl alcohol homo- or copolymer-based fibers is the subject of a rich literature. In general, the most common techniques are the wet spinning of PVA, or "wet spinning", refer for example to US Patents 3,850,901, US 3,852,402 and US 4,612,157). dry-jet wet spinning of PVA, or "dry-jet wet spinning" (refer, for example, to US Patents 4,603,083, US 4,698,194, US 4,971,861, US 5,208,104 and US Pat.

US 7,026,049). According to an advantageous embodiment of the present invention, the coagulation solution comprises a solvent chosen from water, an alcohol, a polyol, a ketone and their mixtures, more preferably a solvent chosen from water, methanol, ethanol, butanol, propanol, isopropanol, glycol, acetone, methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene and mixtures thereof, and still more more preferred a solvent selected from water, methanol, ethanol, a glycol, acetone and mixtures thereof.

If the solvent of the coagulation solution is essentially water, the coagulation solution advantageously has a temperature of between 10 and 80 ° C. If the solvent of the coagulation solution is essentially organic, such as methanol, the coagulation solution advantageously has a temperature between -30 and 10 ° C.

In addition, the coagulation solution may comprise one or more salts intended to promote the coagulation of the polymeric binder, chosen from alkaline salts or desiccant salts such as ammonium sulphate, potassium sulphate, sodium sulphate, sodium carbonate, sodium hydroxide, potassium hydroxide and mixtures thereof.

On the other hand, the coagulation solution may comprise one or more additional compounds which are intended to improve the mechanical properties, the water resistance of the fiber and / or facilitate the spinning of the fiber. The coagulation solution can therefore comprise at least one compound selected from boric acid, borate salts and mixtures thereof.

Preferably, the coagulation solution is saturated with salts.

Advantageously, the dispersion is injected during the second step of the process according to the invention through one or a set of needles and / or one or a set of nonporous cylindrical or conical nozzles into the coagulation solution, which can be static (static bath) or in motion (flow). The average injection speed of the dispersion may be between 0.1 m / min and 50 m / min, preferably between 0.5 m / min and 20 m / min.

The coagulant solution induces coagulation in the form of a fiber by solidification of the polymeric binder. Graphene gets trapped in the polymer that solidifies.

The next step of the process according to the invention consists in extracting, continuously or not, the fiber from the coagulation solution.

After extraction of the fiber, it may be washed once or several times. The wash tank preferably includes water. The washing step may make it possible to eliminate a portion of the peripheral polymer from the fiber and thus enrich the composition of the fiber with graphene. In addition, the washing bath may include agents that alter the composition of the fiber or interact with each other. chemically with this one. In particular, chemical or physical crosslinking agents, in particular borate salts or dialdehydes, may be added to the bath in order to reinforce the fiber. The washing step may also make it possible to eliminate the agents, in particular the surfactants, potentially pre-limpable to the mechanical or electrical properties of the fiber.

A drying step is also included in the process according to the invention. This step can take place either directly after extraction or after washing. In particular, if it is desired to obtain a polymer-enriched fiber, it is desirable to dry the fiber directly after the extraction. The drying is preferably carried out in an oven which will dry the fiber by means of a gas circulating in an interior duct of the oven. The drying can also be carried out by infrared radiation. According to a second embodiment, the composite fibers according to the invention may be produced according to a process comprising the successive steps consisting of:

the dispersion of graphene in a solvent possibly using a surfactant,

injecting the graphene dispersion into a co-flow of a coagulation solution containing a polymeric binder,

extraction of the obtained fiber,

the eventual washing of said fiber, and

drying said fiber. The solvents, surfactants, coagulation solutions and polymeric binders may be chosen from those mentioned above. For a more precise description of this process, reference may be made to application FR 2 921 075.

According to a third embodiment, the composite fibers according to the invention can be produced according to a process comprising the successive steps consisting of:

a) dispersing graphene in a solvent, in the presence of a stabilizing agent covalently or non-covalently bound to graphene and a polymeric binder, to form a coating composition,

b) coating a natural or synthetic fiber with said coating composition,

c) passing the composite fiber obtained in a coagulation solution, comprising at least one coagulation agent,

d) extraction, possible washing and drying of the coagulated composite fiber.

A multilayer fiber is thus obtained containing: a core formed of a natural or synthetic fiber,

a bark containing a polymeric binder and graphene. The solvents, stabilizing agents, polymeric binders and coagulation solutions used in this process may be chosen from those mentioned above. An example of such a process has been described in the application FR 2 946 178, to which reference may be made for further details.

It is understood that the methods described above may optionally comprise other preliminary stages, intermediate and / or subsequent to those mentioned above, provided that these do not adversely affect the formation of the desired composite fibers.

Thus, they may include a winding step, and possibly a hot stretching step performed between the drying step and the winding step. They may also include stretches in solvents at different times.

In addition, although the composite fibers obtained by this method are intrinsically conductive, their electrical conductivity can be further improved by heat treatments.

Whatever the embodiment used to prepare them, the composite fibers according to the invention may comprise other conductive carbonaceous fillers in addition to graphene, in particular one or more fillers chosen from carbon nanotubes, nanofibres of carbon, and mixtures thereof. Carbon nanofibers are, like carbon nanotubes, nanofilaments generally produced by chemical vapor deposition (or CVD) from a carbon source that is decomposed on a catalyst having a transition metal (Fe, Ni, Co, Cu) in the presence of hydrogen at temperatures of 500 to 1200 ° C. However, these two carbonaceous charges are differentiated by their structure (I. MARTIN-GULLON et al., Carbon, Vol 44, 1572-1580, 2006). Indeed, the carbon nanotubes consist of one or more sheets of graphene wound concentrically to form a cylinder having a diameter of 1 to 100 nm. On the contrary, carbon nanofibers are composed of more or less organized graphitic zones (or turbostratic stacks) whose planes are inclined at variable angles with respect to the axis of the fiber. These stacks can take the form of platelets, fish bones or stacked cups to form structures generally ranging in diameter from 100 nm to 500 nm or more.

The carbon nanotubes that can be used in the present invention are advantageously of multi-wall type, containing from 5 to 15 walls, and are preferably obtained by a chemical vapor deposition (CVD) process. They advantageously have a mean diameter ranging from 0.1 to 100 nm and a length of 0.1 to 20 μm. Examples of crude carbon nanotubes are those commercially available from ARKEMA under the trademark Graphistrength C100.

Examples of carbon nanofibers are those available under the trade name VGCF from SHOWA DENKO. More particularly, the fibers according to the invention may comprise an assembly of carbon and graphene nanotubes capable of being obtained by decomposition at a temperature of 500 to 1500 ° C. of a source of carbon in the gaseous state, implemented contact with an active catalyst A for the synthesis of carbon nanotubes and an active catalyst B for the synthesis of graphene. This assembly can thus be obtained by adapting the graphene synthesis process described above to add catalyst A. The latter may in particular comprise a metal such as iron, cobalt, nickel, molybdenum, titanium and mixtures thereof. supported on a solid inert support, for example alumina. Such a catalyst may especially be prepared by impregnating a dry substrate with an aqueous or alcoholic impregnation solution comprising metal salts.

Moreover, the composite fibers according to the invention may contain at least one conductive polymer. By "conducting polymer" is meant a homo- or copolymer whose main chain contains conjugated double bonds - for example in the form of one or more (hetero) aromatic rings - and which forms, after possible oxidation and doping with the using at least one doping agent, a salt or complex having electrical conduction properties. Examples of usable conductive polymers include homo- and copolymers comprising one or more monomers selected from aniline, pyrrole, optionally substituted thiophene, acetylene, phenylene vinylene, phenylene sulfide and mixtures thereof. An example of a substituted thiophene polymer is the poly (3,4-ethylenedioxythiophene) or PEDOT. PEDOT and polyaniline (PANI) are preferred for use in the present invention. Polyaniline exists under different oxidation states, related to the proportions of imine and amine functions contained in the molecule. It is preferred according to the invention to use emeraldine, which corresponds to the intermediate oxidation state of polyaniline, having the best electrical properties.

Examples of doping agents include strong protonic acids having a pKa of less than 3, such as hydrochloric acid, sulfuric acid and its salts such as sodium dodecyl sulphate, phosphonic acids and sulphonic compounds, especially 2-acrylamido-2-methylpropanesulphonic acid (AMPS), dodecylbenzenesulfonic acid, camphorsulfonic acid, toluenesulphonic acid, methanesulphonic acid and sulphonic function (s) polymers, such as that the poly (styrene sulfonic acid) which is the doping agent preferably used in combination with the PEDOT to form a colloidal solution PEDOT: PSS. Other doping agents include polyacrylamide and polyacrylic acid. The salts or complexes of conductive polymers and doping agents can be obtained chemically or electrochemically, according to techniques known to those skilled in the art. Some are also available commercially, especially from PANIPOL.

These conductive polymers can be incorporated in the composite fibers according to the invention in one of or the other of the variants described above, by mixing them with the polymeric binder before the coagulation step.

The present invention also relates to the use of the above-mentioned conductive composite fibers for the manufacture of nose, wings or cockles of rockets or airplanes; off-shore flexible armor; automotive bodywork components, engine chassis or automobile support parts; automotive seat coverings; structural elements in the field of buildings or bridges and roadways; packaging and antistatic textiles, in particular antistatic curtains, antistatic clothing (for example, safety or clean room) or materials for the protection of silos or the packaging and / or transport of powders or granular materials; furnishing items, including clean room furniture; filters; electromagnetic shielding devices, in particular for the protection of electronic components; conductive cables; sensors, in particular deformation sensors or mechanical stresses; electrodes; hydrogen storage devices; biomedical devices such as sutures, prostheses or catheters; displays, keyboards or connectors incorporated into clothing; or receivers and emitters of electromagnetic waves.

The manufacture of these composite parts can be carried out according to various processes, generally involving a step of impregnating the conductive composite fibers according to the invention with a composition polymeric material comprising at least one thermoplastic, elastomeric or thermosetting material. This impregnation step may itself be carried out according to various techniques, depending in particular on the physical form of the polymeric composition used.

(pulverulent or more or less liquid). The impregnation of the conductive composite fibers is preferably carried out according to a fluidized bed impregnation process, in which the polymeric composition is in the form of powder. Pre-impregnated fibers are thus obtained.

Semi-finished products are obtained which are then used in the manufacture of the desired composite part. Different preimpregnated fiber fabrics, of identical or different composition, can be stacked to form a plate or a laminated material, or alternatively subjected to a thermoforming process. As a variant, the pre-impregnated fibers may be combined to form ribbons which may be used in a filament winding process which makes it possible to obtain hollow pieces of almost unlimited shape, by winding the ribbons on a mandrel having the shape of the part to be made. In all cases, the manufacture of the finished part comprises a step of consolidating the polymeric composition, which is for example melted locally to create zones for fixing the fibers pre-impregnated with each other and / or to secure the fiber ribbons pre-impregnated with each other. impregnated in the filament winding process. alternatively, it is possible to prepare one from the polymeric composition impregnation, in particular by means of an extrusion or calendering process, said film having for example a thickness of about 100 μm, and then of placing it between two mats of conductive composite fibers according to the invention, the whole being then pressed hot to allow the impregnation of the fibers and the manufacture of the composite part.

In these processes, the conductive composite fibers according to the invention can be woven or knitted, alone or with other fibers, or used, alone or in combination with other fibers, for the manufacture of cables, felts or nonwoven materials. Examples of materials constituting these other fibers include, without limitation:

stretched polymer fibers, based in particular on: polyamide such as polyamide 6 (PA-6), polyamide 11 (PA-11), polyamide 12 (PA-12), polyamide 6.6 (PA-6.6) the polyamide 4.6 (PA-4,6), polyamide-6,10 (PA-6.10) or polyamide 6.12 (PA-6.12), copolymer polyamide / polyether block (Pebax ^®), high density polyethylene, polypropylene or polyester such as polyhydroxyalkanoates and polyesters marketed by Du Pont under the trade name Hytrel ^®;

- carbon fibers;

glass fibers, especially of type E, R or

S2;

- aramid fibers (Kevlar ^® );

- boron fibers;

- silica fibers;

- natural fibers such as linen, hemp, sisal cotton or wool; and - their mixtures, such as fiberglass, carbon and aramid blends.

The invention will be better understood in light of the examples below which are given for purposes of illustration only and are not intended to limit the scope of the invention.

EXAMPLES

Example 1 Manufacture of Composite Fibers According to the Invention

Step 1: Synthesis of assemblages of carbon nanotubes and graphene (NTC / GP)

1-1. Preparation of Catalyst A

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 was added.

(Co (NO 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 of iron nitrate to 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 one hour. order of 12 hours 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 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. A crystalline powder of cobalt ferrite was thus obtained.

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.

1-2. Catalyst B preparation

A catalyst was prepared from Puralox ^® SCCa-5/150 alumina with a median diameter of approximately 85 μιη and a specific surface area of 160 m ² / g. In a 1 1 reactor equipped with a double jacket heated to 120 ° C, 100 g of alumina was introduced and flushed with air. 80 ml of a 45 g / l solution of ammonium molybdate tetrahydrate were then continuously injected, followed by 560 ml of a 675 g / l solution of iron nitrate nonahydrate. The target ratio (metal mass / catalyst mass) being 32% for iron and 3% for molybdenum, the duration of addition was 25 h. The catalyst was then heated in situ at 220 ° C under dry air for 8 hours and then placed in a muffle furnace at 400 ° C for 8 hours.

1-3. Synthesis of the NTC / GP assembly

A catalytic test was carried out by putting a mass of about 1.9 g of catalyst A and about 0.6 g catalyst B in a quartz reactor of 5 cm in diameter and 1 meter effective heating height.

It was heated at 650 ° C. under 2.66 l / min of nitrogen for 30 minutes and then a reduction stage was maintained for 30 minutes under 2 l / min of nitrogen and 0.66 l / min of hydrogen. Once this plateau reached, an ethylene flow rate of 2 l / min and hydrogen of 0.66 l / min was introduced. After 60 minutes, the heating was stopped and the reactor was cooled under a stream of nitrogen of 2 l / min.

The amount of product recovered at the end of the reaction was 47 g. The theoretical NTC / GP mass ratio in this test was 90/10.

Similarly, an assembly of carbon and graphene nanotubes (CNT / GP) in a weight ratio of 80/20 was prepared.

Step 2: Production of Composite Fibers Three aqueous dispersions were carried out, respectively from the two aforementioned assemblies and from NTC without graphene. To this was charged in water 0.9% by weight of the aforementioned charges and 1.2% by weight of a surfactant (Brij ^® 78). These suspensions were then passed to the ultrasound microprobe for

60 minutes. An aqueous solution of polyvinyl alcohol was then added to each to obtain a spinning solution. This was then injected into a coagulation bath composed of sodium sulfate, concentrated to 320 g / l in water and heated to 40 ° C. The fiber was then washed in a first bath containing 0.1% sodium tetraborate in water and then passed to a second bath containing only the water. The fiber was then dried and coiled. Monofilament fiber was obtained. The fibers obtained from a NTC / GP ratio of 90/10 and 80/20 respectively had a theoretical graphene content of 1.1 and 2.3% by weight. Their average diameter was about 45 μm.

Example 2: Mechanical Tests and Electrical Conductivity

Mechanical tensile tests were carried out on the three fibers obtained in Example 1. The results obtained, averaged over 5 test pieces, are collated in Table 1 below.

Table 1

It is apparent from this test that the breaking stress of graphene-containing fibers is greater than that of fibers which lack them.

The electrical conductivity of the fibers of Example 1 was also measured. The results obtained, averaged over 6 test pieces, are shown in Table 2 below. Table 2

Fibers that do not contain graphene have an electrical resistance greater than the detection threshold of the device used (Keithley ^® 2000 multimeter), due to the orientation of the NTC along the fiber, which is unfavorable to the transmission of the current. In contrast, graphene-containing fibers have satisfactory electrical conductivity, which could be further enhanced by heat treatment.

Claims

1. Conductive composite fibers containing graphene dispersed in a polymer matrix, characterized in that the graphene is in the form of particles having a thickness of less than 100 nm, preferably less than 50 nm, more preferably less than 15 nm, and of lateral dimensions of about 1 μm, preferably from 50 to 800, more preferably from 100 to 600 nm, or even 100 to

500 nm.

2. Composite fibers according to claim 1, characterized in that graphene is obtained by a chemical vapor deposition (CVD) process.

3. Composite fibers according to one of claims 1 and 2, characterized in that they further contain one or more fillers selected from carbon nanotubes, carbon nanofibers, and mixtures thereof.

4. Composite fibers according to claim 3, characterized in that they contain an assembly of carbon nanotubes and graphene obtainable by decomposition at a temperature of 500 to

1500 ° C of a source of carbon in the gaseous state, brought into contact with an active catalyst A for the synthesis of carbon nanotubes and an active catalyst B for the synthesis of graphene.

5. Composite fibers according to any one of claims 1 to 4, characterized in that they contain in addition at least one conductive polymer, such as that poly (3,4-ethylenedioxythiophene) (PEDOT) and polyaniline.

6. Composite fibers according to any one of claims 1 to 5, characterized in that they contain from 0.5 to 50% by weight, preferably from 1 to 30% by weight, more preferably from 3.5 to 15% by weight. % by weight of graphene.

7. A method of manufacturing composite fibers according to any one of claims 1 to 6, characterized in that it consists of a coagulation process comprising:

either coagulation in the form of fiber, or around a pre-formed fiber, a mixture of graphene and a polymeric binder, by passing it through a coagulation solution,

or the injection of graphene dispersed in a solvent in a co-flow of a coagulation solution containing a polymeric binder.

8. Method according to claim 7, characterized in that it comprises the successive steps consisting of: a) forming a graphene dispersion in a polymer binder solution, in the presence of at least one stabilizing agent bound in a covalent or non-covalent to graphene,

b) injecting said dispersion into a coagulation solution,

c) extracting the obtained fiber,

d) the possible washing of said fiber,

e) drying said fiber.

9. Method according to claim 7, characterized in that it comprises the successive steps consisting in: the dispersion of graphene in a solvent possibly using a surfactant,

extraction of the obtained fiber,

the eventual washing of said fiber, and

drying said fiber.

10. Process according to claim 7, characterized in that it comprises the successive stages consisting of: a) the dispersion of graphene in a solvent, in the presence of a stabilizing agent covalently or non-covalently bound to graphene and of a polymeric binder, to form a coating composition,

b) coating a natural or synthetic fiber with said coating composition,

d) extraction, possible washing and drying of the coagulated composite fiber.

11. Use of the conductive composite fibers according to any one of claims 1 to 6 for the manufacture of nose, wings or cabins of rockets or airplanes; off-shore flexible armor; automotive bodywork components, engine chassis or automobile support parts; automotive seat coverings; structural elements in the field of buildings or bridges and roadways; packaging and antistatic textiles, in particular antistatic curtains, antistatic clothing (for example, safety or clean room) or materials for the protection of silos or the packaging and / or transport of powders or granular materials; furnishing items, including clean room furniture; filters; electromagnetic shielding devices, in particular for the protection of electronic components; conductive cables; sensors, in particular deformation sensors or mechanical stresses; electrodes; hydrogen storage devices; biomedical devices such as sutures, prostheses or catheters; displays, keyboards or connectors incorporated into clothing; or receivers and emitters of electromagnetic waves.