WO2012160288A1

WO2012160288A1 - Conductive composite fibres comprising carbon-based conductive fillers and a conductive polymer

Info

Publication number: WO2012160288A1
Application number: PCT/FR2012/051062
Authority: WO
Inventors: Valérie DENIS-LUTARD; Joseph BARISCI; Maryse Maugey; Alain Derre; Cécile ZAKRI; Patrice Gaillard; Philippe Poulin
Original assignee: Arkema France; C N R S
Priority date: 2011-05-23
Filing date: 2012-05-14
Publication date: 2012-11-29
Also published as: FR2975708A1; FR2975708B1

Abstract

The present invention relates to conductive composite fibres containing carbon-based conductive fillers and at least one conductive polymer that are dispersed in a polymer matrix comprising a binder polymer such as a vinyl alcohol homopolymer or copolymer. It also relates to a process for preparing these fibres by coagulation as well as to the uses thereof.

Description

Conductive composite fibers comprising carbon conductive fillers and a conductive polymer

The present invention relates to conductive composite fibers containing conductive carbon fillers and at least one conductive polymer dispersed in a polymer matrix comprising a binder polymer such as polyvinyl alcohol. It also relates to a process for preparing these fibers by coagulation, as well as their uses.

Electrically conductive fibers are known for various applications, especially for the manufacture of heating textiles, such as clothing, blankets, car seats or cold protective linings (for example to protect fuel tanks), in which their Conductive properties are used to generate, by the Joule effect, heat. Conductive fibers are also of interest in other applications, for their antistatic properties, in particular in the manufacture of aeronautical or automotive parts or for the electromagnetic shielding of electronic equipment, for example to dissipate electrical charges resulting 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: metal wires, which have the disadvantage of being heavy, liable to oxidize and difficult to implement,

carbon fibers which, despite very good electrical conductivity, are not very flexible, which limits their textile applications,

the intrinsically conductive polymer fibers (US-7, 628, 944, US-7,264,762, US-5,783,111, US 2009/0128168, SJ POMFRET et al., Polymer, Vol 41, pp. 2265-2269, 2000), which offer satisfactory conductivity but have insufficient mechanical strength.

To overcome these drawbacks, it has been proposed hybrid conductive fibers, obtained by coating an insulating polymer fiber, usually a thermoplastic polymer, using conductive particles, in particular silver, or conductive polymer (US 2006/148351; WO 99/15725). Unfortunately, the coating of these fibers is likely to deteriorate under the effect of friction, wear and washes, which limits their use in the field of clothing and technical textiles.

Polymer fibers loaded with conductive metal particles within them have also been proposed. These fibers are more resistant to wear than fibers obtained by common coating or coextrusion technologies. However, the metals used, such as copper, are heavy and can oxidize easily, leading to degradation of fiber properties. Their mechanical properties are further affected by their high particle content metallic, necessary to obtain percolated conductive networks.

US 6,083,562 discloses thermally stable and abrasion resistant conductive fibers useful for the manufacture of antistatic textiles. The fibers contain an interpenetrating network of conductive polymer, carbon black particles and a non-conductive polymer, preferably based on acrylonitrile and optionally vinyl acetate. In this document, a pre-fiber made of carbon black and the non-conductive polymer is impregnated with conducting monomers which are then polymerized on the surface of the fiber. However, such a method does not make it possible to obtain a homogeneous dispersion of the polymer within the fiber in order to improve its conductivity.

In this respect, conductive particles having a high aspect ratio (e.g. a length / diameter ratio greater than 100), such as carbon nanotubes (hereinafter CNTs), are more advantageous than metal particles having a high aspect ratio (eg lower aspect ratio (eg a length / diameter ratio of less than 10) or even carbon black particles. They allow access to percolated networks at lower concentrations, while being chemically stable. In addition, CNTs have many interesting properties, namely electrical, thermal, chemical and mechanical, which make them good candidates for use as conductive fillers in conductive composite fibers. It has been proposed fibers Conductors obtained by coagulation from NTC and a homo- or copolymer of vinyl alcohol (EP 2,256,236).

Several types of conductive polymer / NTC two-component fibers have been described in the literature (see MOTTAGHITALAB et al., Synthetic Metals, Vol.152, No. 1, pp. 77-80, 2005; WO 2007/096479). ). NTCs allow an improvement in electrical conductivity, but the fact of keeping a conductive polymer as a matrix does not make it possible to overcome the limitations imposed by the latter, in terms of the mechanical properties and the chemical stability of the fibers. In addition, the level of conductive polymer used (≥ 60% by weight) induces a high cost of the fibers.

More recently, an approach has been proposed to produce three-component fibers

NTC / polyaniline / polypropylene melt (A. SOROUDI et al., Synthetic Metals, Vol 160, No. 11, pp. 1143-1147, 2010), in order to combine the good mechanical properties of polypropylene with good electrical properties of polyaniline (PANI) and CNTs. However, the high fiber diameter is not suitable for high mechanical performance or good textile properties. In addition, the technology used to produce these fibers, namely the molten route, does not allow obtaining high levels of CNT. The conductivity of these fibers is therefore insufficient. The solution proposed in document FR 2 940 659 has the same drawback. It consists in preparing conductive fibers by dispersion of CNTs in a thermoplastic polymer matrix containing a polyetherketone. ketone (PEKK), and then melt spinning the composition thus obtained.

There remains therefore the need for new conductive fibers having both a satisfactory electrical conductivity (greater than 10 ^{~ 5} S / cm and preferably greater than 10 ^{~ 2} S / cm) and a good compromise of mechanical properties for use in the manufacture of technical textiles or clothing. In particular, the conductive fibers must be light, deformable, chemically stable and have good mechanical and frictional strength, as well as a reduced diameter (less than 500 μm). More particularly, they must have a Young's modulus greater than 1 GPa and a tensile strength greater than 100 MPa.

However, the inventors have developed new conductive composite fibers meeting the above requirements, as well as a simple and inexpensive method for manufacturing these fibers from dispersions of conductive carbonaceous fillers, such as CNTs, and conductive polymer. In particular, it has been observed that these fibers, comprising a combination of conductive carbonaceous fillers and conductive polymer, produced a synergistic increase in conductivity, compared to similar fibers containing only these fillers or these polymers, while retaining the mechanical properties of the fibers.

Specifically, the subject of the present invention is conductive composite fibers containing conductive carbonaceous fillers and at least one conductive polymer. dispersed in a polymer matrix comprising a binder polymer selected from a homo- or copolymer of vinyl alcohol.

By "carbon-containing conductive fillers" is meant, according to the invention, one or more fillers chosen from carbon nanotubes, carbon nanofibers, and mixtures thereof.

The present invention also relates to a process for manufacturing these conductive composite fibers, comprising the successive steps consisting of:

a) producing a mixture comprising the conductive carbonaceous fillers, a solvent, at least one stabilizing agent covalently or non-covalently bonded to said fillers, the conductive polymer and the binder polymer,

b) injecting said mixture into a coagulation solution to form a fiber,

c) the extraction, the eventual washing and drying of said fiber.

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

In the preamble, it is specified that, throughout this description, the expression "included (e) between" must be interpreted as including each of the aforementioned terminals. Carbon nanofibers are, like carbon nanotubes, nanofilaments generally produced by chemical vapor deposition (or CVD) from a carbon source which is decomposed on a catalyst comprising 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, 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 according to the invention can be of the single-walled, double-walled or multi-walled type. The double-walled nanotubes can in particular be prepared as described by FLAHAUT et al in Chem. Com. (2003), 1442. The multi-walled nanotubes may themselves be prepared as described in WO 03/02456. It is preferred to use multi-walled nanotubes, obtained in particular by the chemical vapor deposition process. The nanotubes usually have an average diameter ranging from 0.1 to 100 nm, preferably from 0.4 to 50 nm and better still from 1 to 30 nm, indeed from 10 to 15 nm, and advantageously a length of 0.1. at 10 μm, more preferably from 0.2 to 10 μm. Their length / diameter ratio is preferably greater than 10 and most often greater than 100. Their specific surface area is, for example, between 100 and 500 m ² / g, advantageously between 200 and 300 m ² / g, and their apparent density may in particular be between 0.05 and 0.5 g / cm ³ and more preferably between 0.1 and 0.2 g / cm ^3. The multiwall nanotubes may for example comprise from 5 to 15 sheets (or walls) and more preferably from 7 to 10 sheets.

These nanotubes can be purified and / or treated (for example oxidized) and / or milled before being used in the process according to the invention.

The grinding of the nanotubes may in particular be carried out cold or hot and be carried out according to known techniques used in devices such as ball mills, hammers, grinders, knives, gas jet or any other system. grinding capable of reducing the size of the entangled network of nanotubes. It is preferred that this grinding step is performed according to a gas jet grinding technique and in particular in an air jet mill.

The purification of the raw or milled nanotubes can be carried out by washing with a sulfuric acid solution, so as to rid them of any residual mineral and metal impurities, such as by iron, from their process of preparation. The weight ratio of the nanotubes to the sulfuric acid may especially be between 1: 2 and 1: 3. The purification operation may also be carried out at a temperature ranging from 90 to 120 ° C, for example for a period of 5 to 10 hours. This operation may advantageously be followed by rinsing steps with water and drying the purified nanotubes. The nanotubes may alternatively be purified by high temperature heat treatment, typically greater than 1000 ° C.

The oxidation of the nanotubes is advantageously carried out by putting them in contact with a solution of sodium hypochlorite containing from 0.5 to 15% by weight of NaOCl and preferably from 1 to 10% by weight of NaOCl, for example in a weight ratio of nanotubes to sodium hypochlorite ranging from 1: 0.1 to 1: 1. The oxidation is advantageously carried out at a temperature below 60 ° C. and preferably at room temperature, for a duration ranging from a few minutes to 24 hours. This oxidation operation may advantageously be followed by filtration and / or centrifugation, washing and drying steps of the oxidized nanotubes.

Purified nanotubes, obtained for example by sulfuric acid treatment of crude carbon nanotubes such as those commercially available from the company ARKEMA under the trademark Graphistrength C100, are preferably used in the present invention. Alternatively, however, it is possible to use raw carbon nanotubes, that is to say that have not been purified or oxidized.

Furthermore, in the case of using carbon nanofibers as carbon conductive fillers, it is preferred to use the carbon nanofibers having a diameter of 100 to 200 nm, e.g., about 150 nm (VGCF ^® from SHOWA DENKO), and advantageously a length of 100 to 200 μm.

These conductive carbonaceous fillers are associated, in the fiber according to the invention, with 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 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. According to the invention, it is preferred to use emeraldine, which corresponds to the oxidation state. intermediate of polyaniline, presenting 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 polystyrene sulfonic acid which is the doping agent preferentially 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 may be obtained chemically or electrochemically, according to techniques known to those skilled in the art. Some are also available commercially, especially from PANIPOL.

The conductive composite fibers according to the invention may be manufactured by a so-called "coagulation" process, which will now be described in more detail, and which is also the subject of this invention.

The first step of this process consists in producing a mixture comprising the carbon-containing conductive fillers, at least one stabilizing agent covalently bonded or non-covalent to said fillers, the conductive polymer, the binder polymer and at least one solvent.

This mixing can be done in one step. It is preferred, however, that step a) of the method according to the invention comprises the following sub-steps a1) to a3):

al) forming a first dispersion containing the conductive carbonaceous fillers, a solvent and at least one stabilizing agent covalently or non-covalently bonded to said fillers,

a2) forming a second dispersion containing the conductive polymer dispersed in a solution of the binder polymer in a solvent,

a3) mixing the first and second dispersions.

For the purposes of the present invention, the term "stabilizing agent" is intended to mean a compound which allows homogeneous dispersion of the carbonaceous feedstocks in the solvent, and which does not hinder the subsequent coagulation of the binder polymer with the carbonaceous feedstocks and the conductive polymer in a coagulation solution.

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

In the case where the stabilizing agent is bonded to the carbonaceous feeds in a non-covalent manner, 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 8 to 20, for example 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 context of the present invention, the at least one stabilizing agent (s) bound to the non-covalently carbonaceous feedstocks may thus be chosen from:

(i) the polyol esters, in particular:

esters of fatty and sorbitan acids, optionally polyethoxylated, for example surfactants of the Tween® family,

esters of fatty acids and of glycerol,

esters of fatty acids and of sucrose,

esters of fatty acids and of polyethylene glycol,

(ii) polyether modified polysiloxanes,

(iii) ethers of fatty alcohols and of polyethylene glycol, for example surfactants of the Brij® family,

(iv) alkylpolyglycosides,

(v) polyethylene-polyethylene glycol block copolymers.

In the second case where the stabilizing agent is covalently bonded to the carbonaceous fillers, it is preferably a hydrophilic group, advantageously a polyalkylene oxide group, in particular a polyethylene glycol group, grafted on these carbonaceous fillers.

The grafting of reactive units such as polyethylene glycol groups on the surface of the carbonaceous feeds, in particular carbon nanotubes, may be carried out according to any method known to those skilled in the art. For example, those skilled in the art will be able to refer to the publication of B. Zhao et al. (Synthesis and Characterization of Soluble Single Walled Carbon Nanotube Graft Copolymers, J. Am Chem Soc (2005) Vol 127 No 22). According to this publication, the nanotubes are dispersed in dimethylformamide (DMF) and are contacted with oxalyl chloride. In a second step, the dispersion obtained is brought into contact with polyethylene glycol (PEG). The nanotubes thus grafted are purified.

In addition, the mixture produced in the first step of the process according to the invention comprises a solvent. The solvent used is generally a compound for solubilizing the binder polymer, preferably chosen from water; monoalcohols (especially ethanol or methanol); dimethylsulfoxide (DMSO); glycerine; glycols such as ethylene glycol, diethylene glycol and triethylene glycol; diethylene triamine; ethylene diamine; phenol; dimethylformamide (DMF); dimethylacetamide; N-methylpyrrolidone; and their mixtures. Preferably, the solvent is chosen from water, DMSO and mixtures thereof in all proportions. According to an advantageous form of the present invention, the dispersion of the conductive carbonaceous fillers in the solvent 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.

As indicated above, the conductive polymer and the binder polymer may be dispersed with the conductive carbonaceous fillers or they may be separately dispersed in a solvent identical to or different from that used to disperse the conductive fillers and chosen from the list given above.

It is preferred to use as the binder polymer the polyvinyl alcohol itself. Its molecular weight can be between 5,000 and 300,000 g / mol. Its degree of hydrolysis may be greater than 96%, or even greater than 99%.

Alternatively, the binder polymer may be selected from: cellulose, viscose, alginate, poly (lactic acid), poly (lactic acid-co-glycolic acid), and mixtures thereof, and mixtures thereof with a homo - or vinyl alcohol copolymer as described above.

It is further preferred that the conductive polymer is polymerized directly in the binder polymer in solution, from a monomer mixture, a doping agent, a polymerization initiator and optionally at least one oxidizing agent chosen from for example ammonium, sodium or potassium persulfates. In the case where a first dispersion of conductive carbonaceous fillers and a second conductive polymer dispersion and of the binder polymer are formed separately, these first and second dispersions may be mixed by any means, for example with magnetic stirring.

The next step of the inventive method consists in injecting the resulting mixture into a coagulation solution to form a fiber in the form of mono ^¬ filament or multi-filaments.

For the purposes of the present invention, the term "coagulation solution" is intended to mean a solution which causes the binder polymer to solidify with the carbonaceous fillers and the conductive polymer.

Such solutions are known to those skilled in the art, and the production of fibers based on a binder polymer such as a homo- or copolymer of vinyl alcohol is the subject of a rich literature. In general, the most common techniques are wet spinning, refer for example to US Pat. Nos. 3,850,901, 3,852,402 and 4,612,157. Dry-jet wet or "dry-jet wet spinning" (see for example US Pat. Nos. 4,603,083, 4,698,194, 4,971,861, 5,208,104 and 7,226,049).

According to an advantageous embodiment of the present invention, the coagulation solution comprises a solvent chosen from water, an alcohol, a polyol, a ketone, aromatic hydrocarbons and mixtures thereof, more preferably a solvent selected from water, methanol, ethanol, propanol, isopropanol, butanol, a glycol, acetone, methyl-ethyl- ketone, methyl isobutyl ketone, benzene, toluene and mixtures thereof, and even more preferably 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 binder polymer, chosen from alkaline salts or desiccant salts such as ammonium sulfate, 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 may 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 mixture is injected during this step of the process according to the invention through one or a set of needles and / or one or a set of non-porous cylindrical or conical nozzles in the coagulation solution, which may 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 binder polymer. The carbonaceous fillers and the conductive polymer are then trapped in the binder polymer which 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 washing tank preferably comprises a solvent of the binder polymer mentioned above, such as water. The washing step may make it possible to eliminate a portion of the peripheral polymer from the fiber and thus enrich (up to 50% by weight) the composition of the fiber with carbonaceous fillers. The washing step may also make it possible to eliminate the agents, in particular the surfactants, potentially detrimental to the mechanical or electrical properties of the fiber.

In addition, the washing bath may comprise agents that make it possible to modify the composition of the fiber or which interact chemically with it. 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. Finally, the washing bath may contain salts in low concentration, such as alkaline salts or desiccant salts, including ammonium sulfate, potassium sulfate, sodium sulfate, sodium carbonate, sodium hydroxide and the like. sodium, potassium hydroxide and mixtures thereof.

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 that will dry the fiber through a gas flowing in an interior duct of the oven. The drying can also be carried out by infrared radiation.

The method according to the invention may also comprise a winding step, and optionally a hot stretching step performed between the drying step and the winding step. It may also include stretches in solvents at different times, as well as hot stretching in the air. The hot stretching in the air may be carried out at a temperature above the glass transition temperature (Tg) of the binder polymer and preferably below its melting point (if it exists). Such a step, described in US Pat. No. 6,331,265, makes it possible to orient the carbonaceous fillers and the polymers substantially in the same direction, along the axis of the fiber, and thus to improve the mechanical properties of the latter, in particular its Young's modulus and its threshold of stress at break. The draw ratio, defined as the ratio of the length of the fiber after drawing to its length before drawing, may be from 1 to 20, preferably from 1 to 10, inclusive. Stretching can be done in one go, or several times, allowing the fiber to relax slightly between each stretch. This stretching step is preferably conducted by passing the fibers through a series of rolls having different rotational speeds, those which unroll the fiber rotating at a lower speed than those receiving it. To achieve the desired draw temperature, the fibers may be passed through ovens arranged between the rolls, or heated rollers may be used, or these two techniques may be combined. This stretching step makes it possible to consolidate the fiber and to achieve high breaking point stresses.

The conductive composite fibers obtained at the end of this process are characterized by the fact that they contain the conductive carbonaceous fillers, the conductive polymer and the binder polymer distributed homogeneously within them. It is thought that the presence of Conductive polymer between the carbonaceous charges makes it possible to reduce the contact resistances between these charges. These fibers usually contain from 5 to 50% by weight, preferably from 5 to 30% by weight, more preferably from 5 to 20% by weight, of conductive carbonaceous fillers relative to the total weight of the fibers. It is therefore possible to obtain composite fibers with a high content of these fillers. They also generally contain from 1 to 50% by weight, preferably from 3 to 30% by weight, of conductive polymer.

The fiber obtained has good mechanical properties and good chemical stability. Specifically, this fiber can be mechanically characterized by a tensile test and has:

a threshold of stress at break (or toughness) greater than 100 MPa, more preferably greater than 150 MPa, or even greater than 200 MPa;

an elongation at break preferably between 0.1 and 500% of stretching, more preferably between 1 and 400% of stretching, and more preferably between 5 and 200% of stretching; and or

a Young's modulus (or traction modulus) of between 1 and 100 GPa, preferably between 2 and 50 GPa, as measured according to standard NF EN ISO 5079 / 1996-02.

In addition, the conductive composite fibers obtained according to this method have much higher electrical conductivity values than could be expected, namely a resistivity which can be between 10 ^{~ 4} and 10 ⁵ ohm. cm, preferably between 0.01 and 10 ³ ohm. cm and more preferably between 0.1 and 100 ohm.com at room temperature. The resistivity of the fibers according to the invention can be measured using a Keithley 2000 multimeter, according to the method described in the article F. Grillard et al., Polymer 53 (2012) 183-187. The electrical conductivity of the fibers can be further improved by heat, chemical or physical treatments. It is therefore preferred that the process according to the invention comprises such an additional step, in particular a step of thermal annealing of the fibers obtained. These fibers are also piezoresistive, that is to say that their electrical resistivity varies according to their elongation at room temperature, as shown in Figure 2.

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; heated textiles; 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 polymeric composition containing 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. Alternatively, the pre-impregnated fibers may be combined to form ribbons which are capable of being used in a filament winding process for obtaining hollow pieces of almost unlimited form, by winding ribbons on a mandrel having the shape of the workpiece. 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.

As a further variant, it is possible to prepare a film from the polymeric impregnating composition, in particular by means of an extrusion or calendering process, said film having for example a thickness of about 100 μm, then of placing it between two conductive composite fiber mats according to the invention, the assembly then being hot-pressed to allow impregnation of the fibers and 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 that 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 present invention thus has for another object composite materials comprising conductive composite fibers according to the invention, bonded together by weaving or by a polymeric composition.

Other features and advantages of the invention will become apparent on reading the nonlimiting and purely illustrative examples which follow.

EXAMPLES

Example 1 Preparation of a NTC / PANI / APV Fiber

An aqueous dispersion is prepared comprising 0.9% by weight of purified multi-walled carbon nanotubes (or CNTs) and 1.2% by weight of solubilizer (Brij® 78). The dispersion is homogenized by an ultrasonic probe of power 20 W for 2 hours for a volume of 50 ml. In parallel, aniline is polymerized to polyaniline (or PANI) in an aqueous solution of polyvinyl alcohol (or PVA) at 8% by weight and with a molecular weight of 195 kg / mol. The APV solution is acidified with 1 mol / l hydrochloric acid in order to render the polymer conductive. The aniline is oxidized with ammonium persulfate of concentration 0.5 mol / l. This mixture is homogenized by magnetic stirring.

The NTC dispersion and the APV / PANI solution are mixed by magnetic stirring in a weight ratio of 50:50.

The mixture obtained is then injected into a static bath of a sodium sulfate solution of concentration 320 g / l at 40 ° C. The fiber is extracted from the coagulation bath after a residence time of about 30 seconds. It is then directed into a rinsing bath consisting of 50 g / l sodium sulfate. It is then dried by infrared heating. The fiber is directed back into a wash bath containing water. After a residence time of 20 seconds in the bath, the fiber is again dried by infrared and wound.

The fiber obtained contains 15% by weight of CNT, 5% ΠΠ weight of PANI and 80% by weight of APV.

It has an electrical resistivity of 20 Ω.cm, a breaking stress of 240 MPa, an elongation at break of 40% and a Young's modulus of 9 GPa. This fiber is annealed at 180 ° C. for 1 hour. It then has an electrical resistivity of only 5 Q.cm.

Example 2 Preparation of a NTC / PEDOT / APV Fiber

A solution of PEDOT: PSS is prepared which is mixed with a solution of APV (195 kg / mol) at 12% by weight and with the multi-wall CNT dispersion described in Example 1. Following the procedure described in Example 1, a fiber filled with 15% by weight of CNT is obtained, having an electrical resistivity of 55 Ω · cm, a breaking stress of 180 MPa, an elongation at break of 120% and a modulus of 'Young of 5 GPa. This fiber is illustrated in Figure 1, which shows a cross-sectional view through a scanning electron microscope.

These fibers are then stretched by 50% at 100 ° C. A decrease in their electrical resistivity which reaches 20 Ω.cm is observed. Their breaking stress is 185 MPa, their elongation 18% and their Young's modulus of 8 GPa.

Example 3 Preparation of an NTC / PC / APV Fiber

A dispersion containing 0.5% by weight of mono-wall CNT and 1% by weight of stabilizer (Brij® 78) is prepared. The dispersion may be mixed with a solution of conductive polymer (PC) chosen from polyaniline, polypyrolle or polythiophene, as specified in Examples 1 and 2. Following the same process as that described in Example 1, got a fiber NTC / PANI / APV charged with 8% by weight of NTC, having an electrical resistivity of 1000 Q.cm.

Example 4 (Comparative) Preparation of a PA I / APV Fiber

The procedure of Example 1 is repeated except that no dispersion of CNT is used. Only a solution of APV / PANI is injected into the coagulation bath. A fiber having an electrical resistivity of 10 ⁶ Ω.cm is obtained.

Example 5 (Comparative) Preparation of a PEDOT / APV Fiber

A solution of APV at 12% by weight was mixed with a solution of PEDOT: PSS in a weight ratio of 1: 1. By following the same method as that described in Example 1, a fiber having an electrical resistivity of 2000 Ω.cm was obtained.

EXAMPLE 6 Demonstration of the Synergistic Effect of the NTC / PEDOT Association

Fibers having the different compositions indicated in the table below are prepared according to the procedure described in Example 1. The properties of the fibers obtained are also presented in this table. Synergy is very well observed. The addition of NTC or PEDOT in the APV improves the electrical resistivity and the addition of both leads to a synergistic decrease in electrical resistivity. Constraint

Resistivity Module

Composition at Alongment

Young's electric fiber breakage (%)

(Ω cm) (GPa)

(MPa)

APV 1 E +14 230 50 7

APV / Pedot

7.7 E +05 275 40 7 15%

APV / NTC

3.4 E +04 160 95 5

15%

APV / NTC

15% / Pedot 55 180 120 5 15%

Claims

1. Conductive composite fibers containing carbon-based conductive fillers chosen from carbon nanotubes, carbon nanofibers and mixtures thereof, and at least one conductive polymer dispersed in a polymer matrix comprising a binder polymer chosen from a homo- or copolymer of vinyl alcohol.

2. Fibers according to claim 1, characterized in that the conductive carbonaceous fillers comprise carbon nanotubes.

3. Fibers according to one of claims 1 and 2, characterized in that the conductive polymer is a homo- or copolymer comprising one or more monomers selected from aniline, pyrrole, optionally substituted thiophene, acetylene, phenylene vinylene, phenylene sulphide and mixtures thereof, preferably polyaniline.

4. Fibers according to any one of claims 1 to 3, characterized in that they contain from 5 to 50%, preferably from 5 to 30% and more preferably from 5 to 20% by weight, of conductive carbonaceous fillers.

5. Fibers according to any one of claims 1 to 4, characterized in that they contain from 1 to 50% by weight, preferably from 3 to 30% by weight, of conductive polymer.

6. Fibers according to any one of claims 1 to 5, characterized in that the binder polymer is polyvinyl alcohol.

7. Fibers according to any one of claims 1 to 6, characterized in that they present:

a Young's modulus (or traction modulus) of between 1 and 100 GPa, preferably between 2 and 50 GPa,

as measured according to standard NF EN ISO 5079 / 1996-02.

8. conductive composite fibers according to any one of claims 1 to 7, characterized in that they have an electrical resistivity of between 10 ^{~ 4} and 10 ⁵ ohm. cm, preferably between 0.01 and 10 ³ ohm. cm, and more preferably between 0.1 and 100 ohm. cm.

9. A method of manufacturing conductive composite fibers according to any one of claims 1 to 8, comprising the successive steps consisting of: a) the realization of a mixture comprising the conductive carbonaceous fillers, a solvent, at least one stabilizing agent bound covalently or non-covalently to said fillers, the conductive polymer and the binder polymer, d) injecting said mixture into a coagulation solution to form a fiber,

e) extracting, optionally washing and then drying said fiber.

10. Process according to claim 9, characterized in that step a) comprises the following sub-steps al) to a3):

a3) mixing the first and second dispersions.

11. Method according to one of claims 9 and 10, characterized in that it further comprises a heat treatment step, chemical or physical fibers obtained to improve their conductivity, preferably a thermal annealing step.

12. Use of conductive composite fibers according to any one of claims 1 to 8 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, including antistatic curtains, antistatic clothing (eg 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; heated textiles; 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.

13. Composite material comprising conductive composite fibers according to any one of claims 1 to 8, bonded together by weaving or by a polymeric composition.