EP2191045A2

EP2191045A2 - Continuous method for obtaining composite fibres containing colloidal particles

Info

Publication number: EP2191045A2
Application number: EP08838292A
Authority: EP
Inventors: Alain DERRÉ; Antoine Lucas; Philippe Poulin
Original assignee: Centre National de la Recherche Scientifique CNRS; Arkema France SA
Current assignee: Centre National de la Recherche Scientifique CNRS; Arkema France SA
Priority date: 2007-09-18
Filing date: 2008-09-18
Publication date: 2010-06-02
Also published as: FR2921075A1; JP2010539342A; WO2009047456A3; WO2009047456A2; FR2921075B1; US20100196250A1; KR20100059874A; CN101802276A

Abstract

The invention relates to a method for obtaining composite fibres, that comprises dispersing colloidal particles in a solvent, injecting the dispersion into a co-flow of a polymer coagulation solution for forming a pre-fibre, circulating the pre-fibre in a duct, extracting, optionally washing and drying the pre-fibre in order to obtain a fibre, and winding the fibre thus obtained, characterised in that the minimum retention time of the fibre within the duct is adjusted so that it has a mechanical strength sufficient to be extracted from the duct, and in that its extraction is vertical and continuous. The invention also relates to composite fibres that can be made according to said method.

Description

Continuous process for obtaining composite fibers based on colloidal particles

The present invention relates to a continuous process for obtaining composite fibers based on colloidal particles, and in particular carbon nanotubes.

The invention also relates to the composite fibers obtainable by this process.

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 coiled graphite sheets. One thus distinguishes single wall Nanotubes nanotubes (SWNT) and nanotubes muitiparois (Muiti Wall Nanotubes or MWNT).

CNTs are commercially available or can be prepared by known methods. There are several methods of synthesis of CNTs, including electrical discharge, laser ablation and chemical vapor deposition or CVD (Chemical Vapor Deposition) which ensures the production of large quantities of carbon nanotubes and therefore obtaining them. 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 can include methane, ethane, 1 / ethylene, acetylene, ethanol, methanol or even a mixture of carbon monoxide and hydrogen (HIPCO process).

Thus the application WO 86 / 03455A1 of Hyperion Cataiysis International Inc. describes in particular the synthesis of CNTs. More particularly, the process comprises contacting a metal-based particle, such as in particular iron, cobalt or nickel, with a carbon-based gaseous compound 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.

CNTs have many powerful properties namely electronic, thermal, chemical and mechanical. Among their applications, there may be mentioned, in particular, composite materials intended in particular for the automotive and aerospace industry, electromechanical actuators, cables, resistant wires, chemical detectors, storage and energy conversion, electron emission, electronic components, and functional textiles.

Generally, when they are synthesized, the CNTs are in the form of a disorganized powder, which makes them difficult to implement in order to exploit their properties. In particular, for the manufacture of composite systems, it is necessary that the CNTs be present in large quantities and oriented in a preferred direction. Thus, the concentration and orientation of NIC are important parameters to take into consideration to exploit their properties on a macroscopic scale.

One of the solutions to overcome this problem is to develop composite fibers. For this, the nanotubes may be incorporated in a matrix such as an organic polymer. We can then proceed to spinning, according to traditional technologies, which allows by stretching and / or shearing to orient the CNT along the axis of the fiber. However, this technique does not make it possible to obtain high NTC fractions in the fibers and the presence of aggregates, due to the large amount of NTCs dispersed in the matrix, weakens the fibers which can then break.

Another solution, proposed in patent applications WO 01/63028 and WO 2007/101936, consists in dispersing colloidal particles, in particular CNTs, in an aqueous or organic solvent, possibly using a surfactant, and injecting this dispersion in another liquid, called coagulation solution, which flows in a pipe around the dispersion to obtain a pre-fiber. The pre-fiber thus obtained is dried to form a fiber. This process makes it possible to obtain fibers whose mass fraction of nanotubes can vary between 10% and 100%.

However, this process is slow since it consists of two distinct steps (formation of the ρre-fiber then recovery in an intermediate tray, and extraction of the pre-fiber for final drying and winding) and limits the production of the fibers, which makes it unsuitable for the industrial scale. Indeed, once the recovery tank filled, the process must be stopped and it is then also necessary to extract the pre-fibers formed and stored in the intermediate tray recovery.

Another disadvantage is the lack of control of the residence time of the pre-fibers in the coagulation solution. Indeed, the pre-fiber parts formed in the first instants remain an extended time in the presence of the coagulation solution as long as they remain in the recovery tank, unlike the pre-fiber portions formed at the end of operation which stayed there less However, the residence time is likely to affect the structure and properties of the fibers. This method therefore does not make it possible to continuously prepare homogeneous fibers.

Finally, the method described in the application WO 2007/101936 does not lead to composite fibers in which the colloidal particles are aligned in the polymer, insofar as the polymer is premixed with the colloidal particles and their solvent before introduction into the polymer. coagulant agent which consists of a non-solvent of the polymer.

There is therefore still a need to provide a simple, fast, economical and suitable process on an industrial scale, making it possible to prepare, from colloidal particles, composite fibers in which the colloidal particles are homogeneously arranged and possibly aligned. The Applicant has discovered that this need could be satisfied by the implementation of a continuous process using a polymer as a coagulating agent and making it possible to control the residence time of a pre-fiber in the flow of a coagulation solution. by adjusting the length of the pipe and using an extraction system in vertical configuration of said prefibre.

The subject of the present invention is therefore a continuous process for obtaining composite fibers, said process comprising: the dispersion of colloidal particles in a solvent possibly using a surfactant, the injection of the dispersion of colloidal particles into co-plating a coagulation solution comprising a polymer as a coagulating agent, to form a pre-fiber, - circulating said pre-fiber in a pipe, extracting said pre-fiber, - optionally washing said pre-fiber, drying said pre-fiber to obtain a fiber, and - winding the fiber thus obtained, characterized in that the minimum residence time of the pre-fiber within said pipe is adjusted so the pre-fiber has sufficient mechanical strength to be extracted from said pipe, and in that the extraction of said pre-fiber is a continuous vertical extraction. The process according to the invention can be applied to colloidal particles in general, and more particularly to aπisotropic particles such as nanotubes, for example carbon nanotubes, tungsten sulphide, molybdenum sulphide, boron nitride, vanadium oxide, cellulose whiskers, silicon carbide whiskers, and clay chips. It is preferred to use carbon nanotubes.

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 nanctubes can in particular be prepared as described by FLAHAUT et ai in Chem. Com. (2003), 1442. The multi-walled nanotubes may themselves be prepared as described in WO 03/02456.

The nanotubes used according to the invention usually have a mean diameter ranging from 0.1 to 200 nm, preferably from 0.1 to 100 nm, more preferably from

0.4 to 50 nm and better still from 1 to 30 nm and advantageously a length of more than 0.1 μm and advantageously from 0.1 to 20 μm, for example about 6 μm. Their length / diameter ratio is advantageously greater than 10 and most often greater than 100. These nanotubes therefore include nanotubes called "VGCF" nanotubes.

(carbon fibers obtained by chemical vapor deposition, or Vapor Grown Carbon Fibers). Their specific surface area is for example between 100 and 300 m ² / g and their apparent density may especially be between 0.05 and 0.5 g / cm ³ and more preferably between

0.1 and 0.2 g / cm ^J. Multi-walled carbon nanotubes can for example comprise from 5 to 15 sheets and more preferably from 7 to 10 sheets.

An example of crude carbon nanotubes is especially commercially available from Arkema under the trade name Graphistrength® ^® ClOO.

The nanotubes may be purified and / or treated (in particular oxidized) and / or milled before being used in the process according to the invention. They can also be functionalized by solution chemistry methods such as amination or reaction with coupling agents.

The grinding of the nanotubes may in particular be performed 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 grinding system likely to reduce 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 or ball mill.

The purification of the nanotubes may be carried out by washing with a sulfuric acid solution, or another acid, so as to rid them of any residual mineral and metal impurities from their preparation process. The weight ratio of nanctubes to sulfuric acid may especially be between 1: 2 and 1: 3. The operation of purification 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 oxidation of the nanotubes is advantageously made métrant thereof into contact with a solution of ^f sodium hypochlorite containing from 0.5 to 15% by weight NaOCl and preferably 1 to 10% by weight of NaOCl, e.g. 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 of less than 60 ^° C. and preferably at ambient 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.

The first step of the process according to the invention may especially be as described in application WO 01/63028. It thus consists in dispersing colloidal particles (of hydrophobic nature) in an aqueous or organic solvent such as water or an alcohol such as ethanol, optionally with the aid of a surfactant conventionally used to disperse hydrophobic particles in such a solvent. In the case where the solvent used is water, such a dispersion can be obtained with different molecular or polymeric, aπioπic, cationic or neutral surfactants. in particular sodium dodecyl sulphate (SDS), alkylaryl esters or bromide tétradécyltriraéthylammoniuiïi. Depending on the characteristics of the agents used, their concentration varies from a few thousandths of a% to a few%.

Regarding the amount of colloidal particles in the dispersion, it is preferable to use the most concentrated suspensions possible while trying to qarder the homogeneous suspensions. For example, when the solvent is water, it is advantageous to use a mass concentration of nanotubes of between 0.1% and 2% and a mass concentration of SDS of between 0.5% and 2%.

The second step of the process according to the invention consists in injecting the dispersion obtained after the first step through at least one opening opening into the co-flow, advantageously laminar, of a coagulation solution whose viscosity must preferably be greater than that of said dispersion, the viscosities being measured under the same conditions of temperature and pressure, in order to cause the shearing forces to cause the alignment of the colloidal particles in the direction initially imposed by the flow of said coagulation solution .

The coagulation solution is also called flocculation solution or even coagulating solution. A polymer such as a polyol or a polyalcohol (polyvinyl alcohol (PVA), which also has a viscosifying role, alginate or cellulose) is used as coagulant, as described in application WO 01/63028. As solvents, mention may in particular be made of water or DMSO (dimethyl sulfoxide). Preferably, the solution is a polyvinyl alcohol solution. It is possible to use, in particular, solutions of polyvinyl alcohol in water or DMSO (dimethyl sulfoxide) at mass concentrations of between 1% by weight and 10% by weight relative to the total weight of the coagulation solution, with various molecular weights.

The flow rate of the coagulation solution measured at the center of the pipe is from 1 m / min to 100 m / min, preferably from 2 m / min to 50 m / min, and still more preferably from 5 m / min. at 25 m / min.

The viscosity measured at 20 ^° C. in a Couette cell of the coagulation solution is between 1 mPa. and 1000 mPa.s, preferably between 30 mPa.s and 300 mPa. s.

Advantageously, the dispersion of colloidal particles is injected through a needle and / or a non-porous cylindrical or conical nozzle into the co-flow of the coagulation solution. The average injection speed of the dispersion is between 0.1 m / min and 50 m / min, preferably between 0.5 m / min and 20 m / min, and even more preferably between 1 m / min. and 6 m / min. The coagulant solution induces coagulation in the form of a pre-fiber by destabilization of the dispersion of colloidal particles. For the particles to orient, it is preferable that the injection speed of the dispersion is lower than the flow rate of the coagulation solution. This difference in speed results in needle or nozzle output shear which causes the preferential orientation of the particles in the axis of the pre-fiber that is formed. The viscosity of the injected dispersion is at 20 ^° C. of between 1 mPa. s and 100 mPa.s, preferably between 1 mPa.s and 10 mPa. s.

In a particular embodiment, the coagulation is ensured by the adsorption of the polymer chains of the coagulant on the colloidal particles.

The pre-fiber thus formed and the coagulation solution then flow into an advantageously cylindrical pipe having a length L defined by the following equation L = T _{: rιin} * V in which V is the speed of circulation of the pre-fiber in the pipe, this velocity being measured at the center of the flow of the coagulation solution, that is to say in the center of the pipe, and T _πln is the minimum residence time.

In the equation above, the term "minimum residence time TV _11n " of the pre-fiber in the coagulation solution in the context of the present invention, the minimum residence time of the pre-fiber in the pipe , which is necessary to give the pre-fiber sufficient strength to extract it out of the pipe. This time corresponds to the time during which the pre-fiber will interact with the coagulation solution. This parameter governs the strength of said pre-fiber.

Indeed, at the macroscopic scale, if the residence time is too short, the pre-fiber will be too fragile to be extracted from the coagulation solution and may break at any time. On the other hand, starting from a certain value of the residence time named minimum residence time, the pre-fiber will have a good behavior and can be extracted from the coagulation solution without breaking.

Those skilled in the art will be able to determine by simple routine operations the minimum residence time. As an indication, it can be from a few seconds to a few tens of seconds.

It is understood from the foregoing that the residence time and, therefore, the length of the pipe, is an important parameter for the continuous obtaining of homogeneous fibers since the residence time is likely to affect the structure and property of the fibers.

It is understood that it is industrially advantageous to use a conduit of minimum length to reduce clutter. The speed of circulation of the pre-fiber in the pipe must then be reduced to the maximum if one wants to respect the minimum residence time.

In the process according to the invention, it is therefore possible to adjust the length of the pipe by a series of tubes depending on the flow rate of the coagulation solution to reach a given residence time before the extraction of the coagulation solution. the preflora.

The minimum residence time depends on the diffusion kinetics of the polymers in the polymer. fiber. In order to reduce this minimum residence time, it is therefore possible to use solutions of polymers of lower molecular weights, or mixtures of different molecular masses, which will then diffuse more rapidly within the pre-fiber.

Another solution to reduce the minimum residence time is to use the chemical route by adding to the coagulant solution agents that promote coagulation.

The next step of the process according to the invention consists in continuously extracting the pre-fiber from the coagulation solution.

This extraction can be carried out independently of the configuration initially chosen for the device for implementing the method, provided that it is performed vertically.

In vertical configuration, in fact, the continuous extraction is performed by overflow of the coagulation solution in a chamber placed around the pipe where the pre-fiber and the coagulation solution flow. The pre-fiber is then continuously driven by means of a roller placed above the pipe, at a linear speed of between 1 m / min and 100 m / min, preferably between 2 m / min and 50 m / min. min, and even more preferably between 5 m / min and 25 m / min. This configuration has certain major advantages for obtaining fibers on an industrial scale.

Indeed, the first advantage is that it is possible to redirect the coagulation solution to a tank or outer enclosure to then maintain it in recirculation. In a particular embodiment where a surfactant has been incorporated in the dispersion of colloidal particles, this reservoir can allow an easy change of the polymer solution to prevent its possible aging of the surfactant used or possible chemical degradation.

Another advantage of the vertical configuration is that it allows a precise adjustment of the residence time. Indeed, the pre-fiber is not stored in an intermediate bath, its residence time in the coagulation solution is accurate and identical at the beginning or end of the experiment. This gives a homogeneous pre-fiber.

However, the extraction of the pre-fiber during the overflow of the coagulation solution in the outer enclosure can be made difficult when the flow rate V of the coagulation solution in the tube is large. Indeed, the coagulation solution then tends to cause the pre-fiber in the outer enclosure. It is then possible to adapt geometries at the outlet of the pipe, such as a conical piece or a piece with successive flares, to cause a slowing down of the pre-fiber and to facilitate its manipulation and its extraction. Yet another advantage of the vertical configuration is the freedom from the effects of gravity during the flow of the pre-fiber into the pipe.

Indeed, in horizontal configuration, the pre-fiber does not always remain in the center of the flow in the pipe, its density being different from that of the coagulation solution. It may then be necessary to integrate a 90 ° elbow at the end of the pipe to allow extraction by vertical overflow.

When the pipe carrying the pre-fiber is in horizontal configuration, it is possible to make one or more turns at 180 ° to chain more tubes. If the experiment takes place in a small space, the length of the pipe can be adjusted to reach a given residence time. The pre-fiber is not damaged by these turns if a low radius of curvature is chosen. If the radius of curvature is large, the pre-fiber travels a great distance and spends a long time in these bends. It may then gradually move away from the axis of the tube under the action of centrifugal force, until rubbing on the walls of the tube, get tangled and / or break.

However, it is likely that beyond a certain radius of curvature, it must again be possible to make a half turn to the pre-fiber without damaging it. Indeed, the centrifugal force increases when the difference in density between the pre-fiber and the coagulation solution increases. It also grows when the radius of curvature decreases or when the flow rate of coagulation solution and pre-fiber increases. Likewise, the passage time in the turn is decreased when the radius of curvature is reduced or when the flow velocity of the coagulant solution and the pre-fiber increases. The success of this turn requires a compromise between the intensity of the centrifugal force applied to the pre-fiber and the passage time in this turn.

After continuous extraction of the pre-fiber from the pipe, it can be driven to a wash tank comprising water. The washing step makes it possible to eliminate a portion of the peripheral polymer from the pre-fiber and thus to enrich the composition of the pre-fiber with colloidal particles. 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 may be added to the bath to reinforce the pre-fiber.

The pre-fiber is advantageously driven to the washing bath by at least one roller. The pre-fiber could also be carried by a treadmill constituted by multiple rolls driven by gears. The use of a treadmill during the washing step avoids uncontrolled elongation of the pre-fiber.

A drying step is also included in the process according to the invention. This step can have lieα either directly after extraction, or consecutively 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.

When the drying is consecutive to washing, the presence of a second roll leaving the wash bath allows its continuous drive to an oven that will dry the pre-fiber through hot air circulating in an inner conduit of the oven. It is necessary to increase the rotational speed of this second roller relative to the speed of the one at the inlet of the bath to prevent a build-up of pre-fiber in the bath.

The pre-fiber is advantageously driven to the oven by at least one roller. It could also be carried by a treadmill consisting of multiple rolls driven by gears.

The last step of the process, well known to those skilled in the art, comprises winding the fiber thus obtained via a conventional winder located at the end of the spinning line.

The method according to the invention may also comprise a heat-stretching step that would be performed between the drying step and the winding step.

The diameter of the fibers obtained is between 9.50 mm and 100 mm, and preferably between 0.02 mm and 0.04 mm. The length of the fibers is indefinite since as long as the installation works, fiber production is continuous.

The process described above is advantageously carried out in a device comprising at least one reservoir containing a coagulation solution, at least one reservoir containing a dispersion of colloidal particles, at least one means for feeding said coagulation solution, at least one means for feeding said dispersion, at least one means for injecting said dispersion into said coagulation solution, at least one means for circulating a pre-fiber in a co-flow of said coagulation solution, at least one means for extracting the pre-fiber, optionally at least one washing means, optionally at least one drying means, at least one winding means, and at least one means for driving the pre-fiber, the fiber . Said circulation means is a pipe whose length L is defined by the equation L = TV _n × V where TV _n is the minimum residence time of the pre-fiber in the coagulation solution to give it a rigidity sufficient to allow its extraction and V is the flow rate of said coagulation solution measured in the center of said pipe, and in that said extraction means is in vertical configuration.

The installation for carrying out the method according to the invention can adopt either a vertical configuration or a horizontal configuration, as described above. The reservoirs that can be used in the device according to the invention are any type of reservoir known to those skilled in the art.

The supply means are any type of means known to those skilled in the art such as pipes, pipes, and tubes or tubular ducts.

The injection means is in particular an injector which can be coupled to two pumps, the first pump serving for the flow of the coagulating solution and the second serving for the injection of the dispersion of colloidal particles, such as in particular a volumetric pump such as than a gear pump. In the case of using a needle for injection and a glass tube for co-flow, the injector allows adjustment of the coaxiality of the needle in the glass tube. Indeed, it can center the needle by tightening adjusting screws located at the rear of the injector.

The means for circulating a pre-fiber may be any means known to those skilled in the art and advantageously a cylindrical pipe. This pipe may, in particular, consist of a series of cylindrical glass tubes or a single tube of suitable length. Tubes of different sections can be used such as, for example, tubes of 2 mm and 4 mm internal diameter. Advantageously, preferred small diameter tubes, namely an internal diameter of between 0.5 mm and 15 mm, and preferably 2 mm, to avoid inhomogeneities due to the presence of bubbles. air. It is understood that the smaller the inner diameter of the tube or tubes and the more the pump necessary for the flow must be powerful.

In a preferred embodiment, the extraction means in vertical configuration comprises at the outlet of the pipe, a conical piece or a piece with successive evasemenrs.

The means for driving the pre-fiber or the fiber may be at least one roller or conveyor belt constituted by multiple rollers driven by gears.

The device according to the invention may also comprise additional equipment on the spinning line, such as, in particular, hot drawing rollers located between the oven and the winder.

Another subject of the invention is a composite fiber that can be obtained according to the method of the invention.

Other characteristics and advantages of the invention will appear on reading the description which follows. Embodiments and embodiments of the invention are given by way of non-limiting example, illustrated by the accompanying drawings in which: - the single figure illustrates a general view of the installation for implementing the method according to the invention; 'invention. EXAMPLE

Example 1: Process for manufacturing a continuous composite fiber

This example is illustrated by the attached figure which represents a general view of an installation for implementing the method according to the invention in a preferred embodiment.

The figure represents a plant 1 for the continuous production of homogeneous fibers based on CNT. This installation 1 comprises two tanks 2 and 3 connected to an injector 4 by pipes 5 and 6 respectively. The injector 4 comprises at the outlet a needle 7 which passes longitudinally and centrally through a cylindrical pipe 8 made of glass. An extraction zone 9, in vertical configuration, is located at the outlet of the pipe 8 and comprises an outer enclosure 10 connected to the tank 3 by a pipe 12 and a conical part 11 overlying the pipe 8. Rollers 13, 14 and 15 allow the training of the pre-fiber 16 thus obtained to a washing unit 17, a drying unit (or oven) 18 and a winding unit (or winder) 19, respectively.

0.3% by weight of Anticarb ³ single-phase Naπotubes from Thomas Swan was dispersed by uitrascnicaticn in a solution comprising water and 1% by weight of sodium decdecyl sulphate (SDS). The dispersion is placed in the tank 2. In the tank 3, a solution containing 5% by weight of polyvinyl alcohol (PVA) Mowiol 56-98 from the company Clariant with a mass of 195 kDa is used as the coagulating solution. The NTC dispersion of the tank 2 is fed through the pipe 5 to the injector 4 while the coagulating polymer solution of the tank 3 is fed through the pipe 6 to the injector 4. The dispersion is injected into the cylindrical pipe 8 via the needle 7 with a diameter of 0.3 mm, at an average injection speed of 4.2 m / min. The average flow rate of the coagulating polymer solution in the pipe is V = 4.4 m / min, which corresponds to a center speed of the pipe of 8.8 m / min. A pre-fiber 16 is thus formed in the pipe 8.

The pipe 8 consists of a plurality of tubes whose diameter is 6 mm. The length of the pipe 8 is adjusted so that the residence time is minimal, according to the equation L = T _raiπ x (2 * V), where 2 * V is the flow velocity at the center of the pipe.

At the outlet of the pipe 8, the continuous extraction of the pre-fiber is carried out in an overflow vertical configuration by means of the conical part 11 situated at the top of the pipe. The coagulant polymer solution is redirected to the outer enclosure 10 and is then returned to the tank 3 by the pipe 12. Simultaneously, the pre-fiber 16 is driven continuously by the roller 13 to the washing bath 17 in order to remove a portion of the peripheral polymer and thus enrich the composition of the pre-fiber in CNT. The pre-fiber 16 is then driven by the roller 14 to the oven 18 where it is dried by hot air. Once dried, a fiber 20 thus obtained is driven by a roll 15 to a winder 19 to be wrapped around a spool and easily stored. Example 2: Evaluation of T ~, _in

The strength of the fibers, obtained as described in Example 1, was studied as well as their behavior by varying the length L of the pipe 8 in order to be able to evaluate the minimum residence time under these well-defined conditions. The results are summarized in Table 1 below.

It can be seen that using a pipe of length L: (4.5 m going + 0, 6 m turning + 4.5 m returning + 1 m vertical extraction) and L ₂ (3 m going + 0.6 m turning + 3 m return + 1 m vertical extraction), the pre-fibers obtained are robust and manipulable. They can be extracted continuously with a roller at a speed of about 11 m / min.

With the length L3 (1.5 m going + 0.6 m turn + 1.5 m return + 1 m vertical extraction), the pre-fiber has hold but is difficult to manipuiable. We manage to extract it continuously but with difficulty. With the length Lt (1.5 m going + 1 rα vertical extraction), the pre-fiber is not robust enough and can not be extracted continuously.

In view of these results and under the specified conditions, the minimum residence time at T ~ _in = 30 s is evaluated.

Claims

1. A continuous process for obtaining composite fibers, said process comprising: the dispersion of colloidal particles in a solvent possibly using a surfactant, the injection of the dispersion of co-dissolved particles into a co-flow of a coagulation solution comprising a polymer as a coagulating agent, to form a pre-fiber, the circulation of said pre-fiber in a pipe, the extraction of said pre-fiber, the possible washing of said pre-fiber; drying said pre-fiber to obtain a fiber, and winding the fiber thus obtained, characterized in that the minimum residence time of the pre-fiber within said pipe is adjusted so that the pre-fiber has a mechanical strength sufficient to be extracted from said pipe, and in that the extraction of said ρre-fiber is a continuous vertical extraction.

2. Method according to claim 1, characterized in that the colloidal particles are chosen from nanotubes such as carbon nanotubes, tungsten sulphide, molybdenum sulphide, boron nitride, vanadium oxide, whiskers. cellulose, silicon carbide whiskers, and clay wafers.

3, Process according to claim 2, characterized in that the colloidal particles are carbon nanotubes.

4. Method according to claim 3, characterized in that the nanotubes have a length of 0.1 to 20 microns.

5. Method according to claim 3 or claim

4, characterized in that the nanotubes have a diameter ranging from 0.1 to 100 nm, preferably from 0.4 to 50 nm and better still from 1 to 30 nm.

6. Process according to any one of claims 1 to

5, characterized in that the polymer is a polyhydric alcohol, especially a polyvinyl alcohol, an alginate or cellulose.

7. Process according to claim 6, characterized in that the polymer is polyvinyl alcohol.

8. Process according to any one of claims 1 to

7, characterized in that the flow rate of the coagulation solution measured at the center of the pipe is from 1 m / min to 100 m / min, preferably from 2 m / min to 50 m / min, and even more preferably from 5 m / min to 25 m / min.

9. Process according to any one of claims 1 to

8, characterized in that the extraction is a continuous overflow extraction of the coagulation solution.

10. Composite fiber obtainable by the method according to any one of claims 1 to