EP2256236A1 - Method for manufacturing conducting composite fibres with high nanotube content - Google Patents

Abstract

Fabricating a conductive composite fiber, comprises: (a) forming a dispersion of nanotubes capable of ensuring a heat and/or electrical conduction, constituted of at least one chemical element comprising elements of columns IIIa, IVa and Va of the periodic table, in a solution of homo- or copolymer of vinyl alcohol, in the presence of at least one stabilizing agent (non)covalently linked to nanotubes; (b) injecting the dispersion in a coagulation solution to form a pre-fiber; (c) extracting the pre-fiber; (d) optionally washing the pre-fiber; and (e) drying the pre-fiber. Fabricating a conductive composite fiber, comprises: (a) forming a dispersion of nanotubes capable of ensuring a heat and/or electrical conduction, constituted of at least one chemical element comprising elements of columns IIIa, IVa and Va of the periodic table, in a solution of homo- or copolymer of vinyl alcohol, in the presence of at least one stabilizing agent (non)covalently linked to nanotubes; (b) injecting the dispersion in a coagulation solution to form a pre-fiber; (c) extracting the pre-fiber; (d) optionally washing the pre-fiber; and (e) drying the pre-fiber to obtain a fiber containing 5-70 wt.% of nanotubes with respect to the total weight of the fiber. Independent claims are included for: (1) conductive composite fibers comprising: 5-70 wt.% of nanotubes; a homo- or copolymer of vinyl alcohol, and at least one stabilizing agent (non)covalently linked to nanotubes comprising non-ionic surfactants having hydrophilic-lipophilic balance of 13-16; and (2) a composite material comprising conductive composite fibers linked together by weaving or by a polymer composition.

Description

The present invention relates to a process for obtaining conductive composite fibers based on homo- or copolymer of vinyl alcohol with a high content of nanotubes capable of providing thermal and / or electrical conduction, in particular of carbon nanotubes. It also relates to the conductive composite fibers obtainable by this method, as well as their uses.

Carbon nanotubes (or CNTs) are known and possess particular crystalline structures, tubular, hollow and closed, composed of atoms arranged regularly in pentagons, hexagons and / or heptagons, obtained from carbon. CNTs generally consist of one or more graphite sheets wound coaxially. One can distinguish single wall nanotubes (SWNTs) and multiwall nanotubes (Multi Wall Nanotubes or MWNTs).

CNTs have many powerful properties, namely electrical, thermal, chemical and mechanical. Among their applications, there may be mentioned, in particular, composite materials intended in particular for the automotive, nautical and aeronautical industries, electromechanical actuators, cables, resistant wires, chemical detectors, energy storage and conversion, electron emission displays, electronic components, and functional textiles. In the automotive, aerospace and electronics fields, conductive such as NTCs allow the heat and electrical dissipation of heat and electric charges arising during friction.

Generally, when synthesized, the CNTs are in the form of a disorganized powder, consisting of entangled filaments, which makes them difficult to implement in order to exploit their properties. In particular, to exploit their mechanical and / or electrical properties on a macroscopic scale, it is necessary for the CNTs to be present in large quantities and oriented in a preferred direction.

The most conventional way of incorporating CNTs into polymer fibers is to mix one or more thermoplastic polymers with nanotubes by melt. The mixture is then extruded to form a fiber or several fibers. This method is for example described in the international patent application WO 00/69958 . Unfortunately, this approach does not make it possible to produce fibers with a high content of nanotubes, since the mixture of the nanotubes in a molten polymer has high viscosities as soon as the nanotube fraction increases.

Another approach has been proposed in the French patent application FR 2 805 179 to produce fibers by coagulation of CNTs. This method involves injecting a dispersion of nanotubes into the co-flow of a coagulating polymer solution. This method makes it possible to produce composite fibers with mass fractions of carbon nanotubes greater than 10%. These fibers have good electrical properties and mechanical. Polyvinyl alcohol (PVA) is a particularly effective coagulant. It adsorbs at the interface of the nanotubes and induces the bonding of the nanotubes together to form a fiber. However, this process is slow and unsuitable on an industrial scale. A continuous process based on the same technique has been described in the French patent application FR 2 921 075 . Its major disadvantage lies in the need to use a complex apparatus.

Another approach for producing CNT-loaded polymer fibers is to mix the nanotubes and a polymer in the same solution before spinning. The solution thus produced is then injected into a static bath or in a flow which induces the coagulation of the polymer. The nanotubes mixed with the polymer are trapped in the structure and the final object is a composite fiber loaded with carbon nanotubes. The advantage of this principle is that it relies on the coagulation of the polymer and not directly on the coagulation of the nanotubes. Coagulation of the polymer allows consolidated fibers to be obtained more rapidly which can be easily handled and extracted from the coagulation baths to be, for example, washed, dried, drawn and wound. The spinning of polymer fibers by solvent coagulation and their treatments are well described in the literature.

This approach has been adopted by Zhang et al. (Spinning gel of PVA / SWNT composite fiber, Polymer 45 (2004) 8801-8807 ) to produce polyvinyl alcohol fibers loaded with nanotubes. This publication describes the manufacture of composite fibers by a process wherein the PVA and the CNTs are dissolved in a mixture of water and dimethylsulfoxide (DMSO). This dispersion is injected into a coagulation solution consisting of methanol cooled to -25 ° C. It is difficult to form a dispersion of nanotubes at high concentration without causing the formation of aggregates in a PVA solution, because the PVA itself induces the coagulation of the nanotubes. The presence of aggregates causes the formation of inhomogeneities in the fiber, which are detrimental to its physical properties and uniformity of texture. As a result, the fibers described by Zhang et al. contain a mass fraction of not more than 3% of carbon nanotubes.

In another publication, Xue et al. (Electrically conductive yarns based on PVA / carbon nanotubes, Composite Structures 78 (2007) 271-277 ) have made PVA / NTC composite fibers with PVA CNT ratios of up to 40% by weight. In this process, the CNTs are dispersed in an aqueous solution of PVA. However, they found that at such concentrations, the fiber obtained was not uniform, which was attributed to a non-homogeneous dispersion of the nanotubes and the formation of aggregates.

It has been envisaged by the Applicant to adapt the above method by subjecting the CNTs to an oxidizing treatment, so as to create on their surface polar groups. This solution, however, does not prevent coagulation of CNTs in the presence of PVA. The use of ionic surfactants of the sodium lauryl sulphate (SDS) type also does not make it possible to avoid this coagulation. It was also envisaged to include poly (acid) acrylic) to remedy this problem. It has been observed, however, that this inhibits the subsequent coagulation of the PVA and thus the formation of the fiber.

There remains therefore the need to provide a simple method for preparing homogeneous conductive composite fibers with high content of nanotubes, that is to say containing at least 5% by weight of nanotubes. In addition, there is also the need to manufacture fibers having a mechanical break point greater than 100 MPa.

The Applicant has discovered that these needs could be satisfied by the implementation of a process for manufacturing conductive composite fibers, in which nanotubes dispersed in a solution of homo- or copolymer of vinyl alcohol are stabilized by means of stabilizing agents.

1. a) la formation d'une dispersion de nanotubes capables d'assurer une conduction thermique et/ou électrique et d'au moins un élément chimique choisi parmi les éléments des colonnes IIIa, IVa et Va du tableau périodique, dans une solution d'homo- ou copolymère d'alcool vinylique, en présence d'au moins un agent stabilisant lié de façon covalente ou non covalente aux nanotubes,
2. b) l'injection de ladite dispersion dans une solution de coagulation pour former une pré-fibre,
3. c) l'extraction de ladite pré-fibre,
4. d) le lavage éventuel de ladite pré-fibre,
5. e) le séchage de ladite pré-fibre pour obtenir une fibre renfermant de 5 à 70% en poids de nanotubes, par rapport au poids total de la fibre.

The subject of the present invention is therefore a method for manufacturing a conductive composite fiber, comprising the successive steps consisting of:

1. a) forming a dispersion of nanotubes capable of providing thermal and / or electrical conduction and of at least one chemical element chosen from the elements of columns IIIa, IVa and Va of the periodic table, in a solution of homo or a vinyl alcohol copolymer, in the presence of at least one stabilizing agent covalently or non-covalently bound to the nanotubes,
2. b) injecting said dispersion into a coagulation solution to form a pre-fiber,
3. c) extracting said pre-fiber,
4. d) the possible washing of said pre-fiber,
5. e) drying said pre-fiber to obtain a fiber containing from 5 to 70% by weight of nanotubes, relative to the total weight of the 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 conductive composite fiber. .

In the preamble, it is specified that, throughout this description, the expression "included (e) between" must be interpreted as including the boundaries cited.

By "fiber" is meant, within the meaning of the present invention, a strand whose diameter is between 100 nm (nanometers) and 300 microns (micrometers), preferably between 1 and 100 microns (micrometers), better, between 2 and 50 μm (micrometers). This structure may also be porous or non-porous. In terms of its uses, a fiber is intended to ensure the holding of a mechanical part and does not constitute a tube or pipe for the transport of a fluid.

According to the invention, the nanotubes consist of at least one chemical element chosen from the elements of columns IIIa, IVa and Va of the periodic table. The nanotubes must be capable of providing thermal and / or electrical conduction; they can thus be based on boron, carbon, nitrogen, phosphorus or silicon. For example, they may be constituted or contain carbon, carbon nitride, nitride of boron, boron carbide, boron phosphide, phosphorus nitride or carbon boronitride, or silicon.

Preferably, carbon nanotubes (or "CNTs") are used. These are graphitic carbon fibrils, hollow, each having one or more graphitic tubular walls oriented along the axis of the fibril. The nanotubes usually have a mean diameter ranging from 0.1 to 100 nm (nanometers), more preferably from 0.4 to 50 nm (nanometers) and better still from 1 to 30 nm (nanometers) and advantageously a length of 0, 1 to 10 μm (micrometers). Their length / diameter ratio is preferably greater than 10 and most often greater than 100 or even greater than 1000. Their specific surface area is, for example, between 100 and 500 m ² / g (including limits), generally between 100 and 300 m ^2. / g for multiwall nanotubes, and it can even go up to 1300 m ² / g in the case of single-walled nanotubes. Their apparent density may especially be between 0.05 and 0.5 g / cm ³ (inclusive) and more preferably between 0.1 and 0.2 g / cm ³ (inclusive). 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 treated or not.

Carbon nanotubes are commercially available or can be prepared by known methods. An example of crude carbon nanotubes is especially commercially available from the company Arkema France under the trade name Graphistrength® ^® C100.

There are several processes for synthesizing carbon nanotubes, including electrical discharge, laser ablation and CVD (Chemical Vapor Deposition), which allows the production of large quantities of carbon nanotubes and therefore their obtaining at a cost price compatible with their massive use. This process consists precisely in injecting a source of carbon at relatively high temperature over a catalyst which may itself consist of a metal such as iron, cobalt, nickel or molybdenum, supported on an inorganic solid such as alumina, silica or magnesia. Carbon sources may include methane, ethane, ethylene, acetylene, ethanol, bioethanol, methanol or even a mixture of carbon monoxide and hydrogen (HIPCO process).

So the demand WO 86/03345 A1 In particular, Hyperion Catalysis International Inc. describes the synthesis of carbon nanotubes. More particularly, the process comprises contacting a metal-based particle such as, in particular, iron, cobalt or nickel, with a gaseous compound based on carbon, at a temperature of between 850 ° C. and 1200 ° C. C, the dry weight proportion of the carbon-based compound relative to the metal-based particle being at least about 100: 1.

These nanotubes may be, optionally and optionally in combination, purified, 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 the known techniques used in devices such as ball mills, hammers, grinders, knives, jet gas 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, or in a ball mill.

The purification of the crude or milled nanotubes can be carried out by washing with a sulfuric acid solution, so as to rid them of any residual mineral and metallic impurities originating from their preparation process. The weight ratio of the nanotubes to the sulfuric acid may especially be between 1: 2 and 1: 3 (limits included). 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 purification may also consist of a heat treatment at high temperature, 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.

In order to eliminate the catalyst metal residues, it is also possible to subject the nanotubes to a heat treatment of at least 1000 ° C., for example 1200 ° C.

The first step of the process according to the invention consists in forming a dispersion of nanotubes in a solution of homo- or copolymer of vinyl alcohol, in the presence of at least one stabilizing agent covalently or non-covalently bonded to the nanotubes. Advantageously, the homo- or copolymer of vinyl alcohol is the polyvinyl alcohol itself.

Depending on the nature of the solution produced and the nature of the polymer, its molecular weight may be between 5,000 and 300,000 g / mol. Its degree of hydrolysis may be greater than 96%, or even greater than 99%.

For the purposes of the present invention, the term "stabilizing agent" is intended to mean a compound that allows homogeneous dispersion of the nanotubes in the solution, which protects the nanotubes from coagulation in the presence of the homo- or copolymer of vinyl alcohol, but which does not interfere with the coagulation of the homo- or copolymer of vinyl alcohol in a coagulation solution.

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

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

For the purposes of the present invention, the term "essentially nonionic surfactant" is intended to mean a nonionic amphiphilic compound, cited for example in McCutcheon's 2008 "Emulsifiers and Detergents", and preferably having an 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.

1. (i) les esters de polyols, en particulier :
   • les esters d'acide gras et de sorbitane, éventuellement polyéthoxylés, par exemple des tensioactifs de la famille des Tween^®,
   • les esters d'acides gras et de glycérol,
   • les esters d'acides gras et de sucrose,
   • les esters d'acides gras et de polyéthylèneglycol,
2. (ii) les polysiloxanes modifiés polyéthers,
3. (iii) les éthers d'alcools gras et de polyéthylèneglycol, par exemple des tensioactifs de la famille des Brij^®,
4. (iv) les alkylpolyglycosides,
5. (v) les copolymères blocs polyéthylène-polyéthylèneglycol.

For example, in the context of the present invention, the stabilizing agent (s) linked to the nanotubes non-covalently can be chosen from:

1. (i) the polyol esters, in particular:
   • fatty acid esters of sorbitan, possibly polyethoxylated, for example, surfactants of the family of Tween ^®,
   • esters of fatty acids and glycerol,
   • esters of fatty acids and sucrose,
   • esters of fatty acids and of polyethylene glycol,
2. (ii) polyether modified polysiloxanes,
3. (iii) ethers of fatty alcohols and polyethylene glycol, for example, surfactants of the family of Brij ^®,
4. (iv) alkylpolyglycosides,
5. (v) polyethylene-polyethylene glycol block copolymers.

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

The grafting of reactive units such as polyethylene glycol groups on the surface of the nanotubes can be carried out according to any method known to those skilled in the art. For example, the person skilled in the art may relate to the publication of B. Zhao et al. (Synthesis and Characterization of Water 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 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 dispersion thus produced during the first step of the process according to the invention may comprise from 2% to 30% by weight of homo- or copolymers of vinyl alcohol, from 0.1% to 5% of nanotubes, from 0.1% to 5% of stabilizing agent, relative to the total mass of the dispersion, including the solvent.

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

For the purpose of the present invention, the term "coagulation solution" means a solution which causes the homo- or copolymer of vinyl alcohol 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" (for example, refer to patents). US 3,850,901 , US 3,852,402 and US 4,612,157 ) and dry-jet wet spinning of PVA, or "dry-jet wet spinning" (refer, for example, to patents). US 4,603,083 , US 4,698,194 , US 4,971,861 , US 5,208,104 and 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 even more preferably a solvent selected from water, methanol, ethanol, a glycol acetone and their mixtures.

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 homo- or copolymer of vinyl alcohol, chosen from alkaline salts or desiccant salts such as ammonium sulphate, sulphate of potassium, sodium sulfate, 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 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 pre-fiber by solidification of the homo- or copolymer of vinyl alcohol. The nanotubes are trapped in the polymer that solidifies.

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

After extraction of the pre-fiber, it may be washed once or several times. The wash tank preferably includes water. The washing step can eliminate a portion of the peripheral polymer of the pre-fiber and thus enrich (up to 70% by weight) the composition of the pre-fiber into nanotubes. In addition, the washing bath may comprise agents which make it possible to modify the composition of the pre-fiber or which chemically interact with it. In particular, chemical or physical crosslinking agents, in particular borate salts or dialdehydes, may be added to the bath to reinforce the pre-fiber. The washing step can also make it possible to eliminate the agents, in particular the surfactants, potentially detrimental 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 pre-fiber directly after the extraction. The drying is preferably carried out in an oven that will dry the pre-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 stretching in solvents at different times.

This stretching step may be carried out at a temperature above the glass transition temperature (Tg) of the homo- or copolymer of vinyl alcohol and preferably below its melting point (if it exists). Such a step, described in the patent US 6,331,265 enables the nanotubes and the polymer to be oriented 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 rupture threshold. The draw ratio, defined as the ratio of the length of the fiber after drawing to its length before drawing, may be between 1 and 20, preferably between 1 and 10, included. 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.

Another subject of the present invention is the conductive composite fibers that can be obtained according to the method of the invention.

Said conductive composite fibers obtained are characterized in that they contain from 5 to 70% by weight of nanotubes, preferably from 5 to 50%, more preferably from 5 to 30%, and more preferably from 5 to 25%, by in relation to the total weight of the fibers. It is therefore possible to obtain composite fibers with a high content of nanotubes.

• un seuil de rupture mécanique (ou ténacité) de préférence supérieur à 100 MPa, plus préférentiellement supérieur à 300 MPa, et mieux encore supérieur à 500 MPa ;
• un allongement à la rupture de préférence compris entre 0,1 et 500% d'étirement, plus préférentiellement entre 1 et 400% d'étirement, et mieux encore entre 3 et 400% d'étirement ; et
• un module d'Young (ou module de traction) compris de préférence entre 1 et 100 GPa, de préférence entre 2 et 60 GPa.

The fiber obtained is homogeneous, which gives it good mechanical properties. The fiber can be mechanically characterized by a tensile test and has:

• a mechanical rupture threshold (or toughness) preferably greater than 100 MPa, more preferably greater than 300 MPa, and more preferably greater than 500 MPa;
• an elongation at break preferably between 0.1 and 500% stretching, more preferably between 1 and 400% stretching, and more preferably between 3 and 400% stretching; and
• a Young's modulus (or traction modulus) preferably comprised between 1 and 100 GPa, preferably between 2 and 60 GPa.

In addition, the conductive composite fibers obtained according to this process have a resistivity which can be between 10 ^-3 and 10 ⁵ ohm.cm at room temperature. This electrical conductivity can be further improved by heat treatments.

• de 5 à 70% en poids, par rapport au poids total des fibres, de nanotubes capables d'assurer une conduction thermique et/ou électrique et constitués d'au moins un élément chimique choisi parmi les éléments des colonnes IIIa, IVa et Va du tableau périodique,
• un homo- ou copolymère d'alcool vinylique, et
• au moins un agent stabilisant, lié de façon non covalente aux nanotubes, choisi parmi les tensioactifs essentiellement non ioniques ayant une HLB de 13 à 16.

The present invention also relates to conductive composite fibers comprising:

• from 5 to 70% by weight, relative to the total weight of the fibers, of nanotubes capable of providing thermal and / or electrical conduction and consisting of at least one chemical element chosen from the elements of columns IIIa, IVa and Va of periodic table,
• a homo- or copolymer of vinyl alcohol, and
• at least one stabilizing agent, non-covalently bonded to the nanotubes, selected from substantially nonionic surfactants having a HLB of 13 to 16.

• pour la fabrication de nez, d'ailes ou de carlingues de fusées ou d'avions ;
• pour la fabrication d'armures de flexible off-shore ;
• pour la fabrication d'éléments de carrosserie automobile, de châssis moteur ou de pièces support pour l'automobile ;
• pour la fabrication de revêtements de sièges automobiles ;
• pour la fabrication d'éléments de charpentes dans le domaine du bâtiment ou des ponts et chaussées ;
• pour la fabrication d'emballages et de textiles antistatiques, notamment de rideaux antistatiques, de vêtements antistatiques (par exemple, de sécurité ou pour salle blanche) ou de matériaux pour la protection de silos ou le conditionnement et/ou le transport de poudres ou de matériaux granulaires ;
• pour la fabrication d'éléments d'ameublement, notamment de mobilier pour salle blanche ;
• pour la fabrication de filtres ;
• pour la fabrication de dispositifs de blindage électromagnétique, notamment pour la protection de composants électroniques ;
• pour la fabrication de textiles chauffants ;
• pour la fabrication de câbles conducteurs ;
• pour la fabrication de capteurs, notamment de capteurs de déformation ou de contraintes mécaniques ;
• pour la fabrication d'électrodes ;
• pour la fabrication de dispositifs de stockage d'hydrogène ; ou de dispositifs biomédicaux tels que des fils de suture, des prothèses ou des cathéters.

Finally, the subject of the present invention is the use of the conductive composite fibers according to the invention for the following applications:

• for the manufacture of nose, wings or cabins of rockets or airplanes;
• for the manufacture of off-shore flexible armor;
• for the manufacture of automobile bodywork components, engine chassis or automobile support parts;
• for the manufacture of car seat coverings;
• for the manufacture of structural elements in the field of buildings or bridges and roadways;
• for the manufacture of antistatic packaging and 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;
• for the manufacture of furniture items, including clean room furniture;
• for the manufacture of filters;
• for the manufacture of electromagnetic shielding devices, in particular for the protection of electronic components;
• for the manufacture of heating textiles;
• for the manufacture of conductive cables;
• for the manufacture of sensors, in particular deformation sensors or mechanical stresses;
• for the manufacture of electrodes;
• for the manufacture of hydrogen storage devices; or biomedical devices such as sutures, prostheses or catheters.

The manufacture of these composite parts can be carried out according to various processes, generally involving a step of impregnating the composite fibers. conductive according to the invention by a polymeric composition containing at least one thermoplastic material, elastomeric or thermosetting. 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 thus 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.

In another 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 the impregnation of the fibers and the manufacture of the composite part.

• les fibres de polymère étiré, à base notamment : de polyamide tel que le polyamide 6 (PA-6), le polyamide 11 (PA-11), le polyamide 12 (PA-12), le polyamide 6.6 (PA-6.6), le polyamide 4.6 (PA-4.6), le polyamide 6.10 (PA-6.10) ou le polyamide 6.12 (PA-6.12), de copolymère bloc polyamide/polyéther (Pebax^®), de polyéthylène haute densité, de polypropylène ou de polyester tel que les polyhydroxyalcanoates et les polyesters commercialisés par DU PONT sous la dénomination commerciale Hytrel^® ;
• les fibres de carbone ;
• les fibres de verre, notamment de type E, R ou S2 ;
• les fibres d'aramide (Kevlar^®) ;
• les fibres de bore ;
• les fibres de silice ;
• les fibres naturelles telles que le lin, le chanvre, le sisal le coton ou la laine ; et
• leurs mélanges, tels que les mélanges de fibres de verre, carbone et aramide.

In these processes, the conductive composite fibers according to the invention may be woven or knitted, alone or with other fibers, or used, alone or in combination with other fibers, for the manufacture of felts or non-woven materials. woven. 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), 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
• mixtures thereof, 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 characteristics and advantages of the invention will appear on reading the nonlimiting and purely illustrative examples which follow.

EXAMPLES Example 1

0.5% by weight of single-walled carbon nanotubes and 1% of Brij®78 were dispersed in water. This dispersion was then homogenized by an ultrasonic probe set at the power of 20 W.

An aqueous solution of polyvinyl alcohol (PVA) at 8% by weight, molecular weight 195,000 g / mol and degrees of hydrolysis of 98% was added. The dispersion thus obtained, consisting of 0.25% by weight of single-walled nanotubes, 0.5% of Brij®78 and 4% of PVA in water, was homogenized by magnetic stirring.

The dispersion was then injected into a static bath of a saturated sodium sulfate coagulant solution (320 g / L) at 40 ° C.

The pre-fiber was extracted from the coagulation bath after a residence time of less than ten seconds. It was then dried by infra-red radiation, then redirected into a washing bath containing water. After 1 min, it was dried again by infrared radiation and then wound.

The final fiber obtained contains 8% of nanotubes in mass. This value was obtained by thermogravimetric analysis (TGA). The snapshot of scanning microscopy presented Figure 1 shows a circular fiber with a diameter of 40 μm.

The fiber is cylindrical and homogeneous and has been mechanically characterized by traction. It has a breaking energy of 475 J / g, an elongation at break of 425% stretching and a Young's modulus of 3 GPa. After hot stretching at 200 ° C of 400%, its Young's modulus increases to 29 GPa and its rupture threshold increases to 12% stretching.

Example 2

Composite fibers were made starting from aqueous dispersions of multiwall nanotubes. 0.9% by weight of nanotubes and 1.2% Brij®78 were dispersed in water. By the same method as described in Example 1, fibers loaded with 17% multiwall nanotubes were obtained.

These fibers have the advantage of combining good mechanical properties with quite interesting electrical properties, since they are electrically conductive, with a resistivity of 10 Ω.cm. They have a toughness of 340 MPa, a Young's modulus of 5.5 GPa and an elongation at break of 240%.

Example 3

0.9% by weight of multi-walled carbon nanotubes and 1.2% of Brij®78 were dispersed in water. The mixture was then homogenized by an ultrasound probe set at the power of 20 W.

To this dispersion was then added an aqueous PVA solution at 16% by weight, with a molecular weight of 61,000 g / mol and with a degree of hydrolysis of 98%. The dispersion thus obtained was homogenized by magnetic stirring. Boric acid was added to this dispersion at a level of 0.5% by weight relative to PVA, and the pH was brought to a value of less than 5 by adding dilute nitric acid. There was thus obtained a dispersion consisting of 0.45% by weight of single-walled nanotubes, 0.6% of Brij®78 and 8% of PVA in water.

The solution was then injected into a static bath of a saturated sodium sulfate coagulant solution (320 g / L) at 40 ° C to form a fiber.

The final fiber obtained contains 12% of nanotubes in mass. It has a toughness of 360 MPa, a Young's modulus of 4 GPa and an elongation at break of 325%, as well as a resistivity of 30 Ω.cm.

Example 4

The dispersion described in Example 3 was injected into a coagulant bath containing sodium hydroxide (50 g / L) and sodium sulfate (300 g / L) at 40 ° C.

The final fiber obtained contains 12% of nanotubes in mass. It has a toughness of 320 MPa, a Young's modulus of 7 GPa and an elongation at break of 200%, as well as a resistivity of 100 Ω.cm.

Example 5

0.5% by weight of single-walled carbon nanotubes and 1% Brij®78 were dispersed in a water / DMSO mixture comprising the same mass fraction of each solvent.

A solution of PVA at 16% by weight in a water / DMSO mixture, with a molecular weight of 61,000 g / mol and a degree of hydrolysis of 98%, was then added to this dispersion. The dispersion thus obtained, consisting of 0.25% by weight of single-walled nanotubes, 0.5% Brij®78 and 8% PVA, was homogenized by magnetic stirring.

The dispersion was then injected into a methanol coagulant bath at -20 ° C containing 10% DMSO to form 8% nanotube filled fibers.

Claims (17)

A method of manufacturing a conductive composite fiber, comprising the successive steps of: a) forming a dispersion of nanotubes capable of providing thermal and / or electrical conduction, consisting of at least one chemical element chosen from the elements of columns IIIa, IVa and Va of the periodic table, in a solution of homopolymer or copolymer of vinyl alcohol, in the presence of at least one stabilizing agent covalently or non-covalently bound to the nanotubes, b) injecting said dispersion into a coagulation solution to form a pre-fiber, c) extracting said pre-fiber, d) the possible washing of said pre-fiber, e) drying said pre-fiber to obtain a fiber containing from 5 to 70% by weight of nanotubes relative to the total weight of the fiber. A method of manufacturing a conductive composite fiber according to claim 1, characterized in that the nanotubes are carbon nanotubes. Process for manufacturing a conductive composite fiber according to one of Claims 1 and 2, characterized in that the stabilizing agents are non-covalently bound to the nanotubes and are chosen from essentially nonionic surfactants, such as (i) the polyol esters, in particular: the fatty acid and sorbitan esters, optionally polyethoxylated, 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, (iv) alkylpolyglycosides, and (v) polyethylene-polyethylene glycol block copolymers. Process for manufacturing a conductive composite fiber according to one of Claims 1 and 2, characterized in that the stabilizing agents are hydrophilic groups, advantageously polyethylene glycol groups grafted onto the nanotubes. Process for manufacturing a conductive composite fiber according to one of the preceding claims, characterized in that the homo- or copolymer of vinyl alcohol is polyvinyl alcohol. A method of manufacturing a conductive composite fiber according to any one of the preceding claims, characterized in that the dispersion comprises a solvent selected from water, dimethylsulfoxide (DMSO), glycerine, ethylene glycol, diethylene glycol triethylene glycol, diethylene triamine, ethylene diamine, phenol, dimethylformamide (DMF), dimethylacetamide, N-methylpyrrolidone and mixtures thereof, preferably a solvent selected from water, DMSO and mixtures thereof. all proportions. A method of manufacturing a conductive composite fiber according to any one of the preceding claims, characterized in that the dispersion further comprises boric acid, borate salts or mixtures thereof. A method of manufacturing a conductive composite fiber according to any one of the preceding claims, characterized in that the dispersion is carried out by means of ultrasound or a rotor-stator system or a ball mill. Process for manufacturing a conductive composite fiber according to any one of the preceding claims, characterized in that the coagulation solution comprises at least one solvent chosen from water, an alcohol, a polyol, a ketone and their mixtures, more preferably a solvent selected from water, methanol, ethanol, butanol, propanol, isopropanol, 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. Process for the production of a conductive composite fiber according to any one of the preceding claims, characterized in that the coagulation solution comprises at least one compound chosen from ammonium sulfate, potassium sulphate, sodium sulphate, sodium carbonate, sodium hydroxide, potassium hydroxide, boric acid, borate salts and mixtures thereof. Conductive composite fibers obtainable by the method according to any one of Claims 1 to 10. Conductive composite fibers according to claim 11, characterized in that said fibers contain from 5 to 50%, preferably from 5 to 30% and more preferably from 5 to 25% by weight of nanotubes, relative to the total weight of the fibers. Conductive composite fibers according to one of claims 11 and 12, characterized in that said fibers have a mechanical rupture threshold greater than 100 MPa, preferably greater than 300 MPa, and more preferably still greater than 500 MPa. Conductive composite fibers according to any one of claims 11 to 13, characterized in that said fibers have an electrical resistivity of between 10 ^-3 and 10 ¹⁰ ohm.cm. Conductive composite fibers comprising: from 5 to 70% by weight, relative to the total weight of the fiber, of nanotubes capable of providing electrical and / or thermal conduction and consisting of at least one chemical element chosen from the elements of columns IIIa, IVa and Go from the periodic table, a homo- or copolymer of vinyl alcohol, and at least one stabilizing agent, non-covalently bound to the nanotubes, chosen from essentially nonionic surfactants having a HLB of 13 to 16. Use of the conductive composite fibers according to any one of claims 11 to 15 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; or biomedical devices such as sutures, prostheses or catheters. Composite material comprising conductive composite fibers according to any one of claims 11 to 15, bonded together by weaving or by a polymeric composition.

Images