EP2294253B1 - Method of manufacturing composite conducting fibres, fibres obtained by the method, and use of such fibres - Google Patents

Abstract

The invention relates to a method of manufacturing fibres made of a composite based on a thermoplastic polymer and conducting or semiconducting particles, which includes a heat treatment, said heat treatment consisting in heating the composite, by progressively raising the temperature, having the effect of improving the conducting properties of the fibres obtained or of making the initially insulating fibres conducting. The invention also relates to the conducting fibres thus obtained and in particular to polyamide fibres and carbon nanotubes.

Description

The invention relates to a process for producing conductive composite fibers such as conductive fibers based on thermoplastic polymer and conductive or semiconductive particles, the particles possibly being carbon nanotubes (CNTs).

The invention also relates to composite conductive fibers obtained from said process and the uses of such fibers.

Carbon nanotubes are known and used for their excellent properties of electrical and thermal conductivity as well as their mechanical properties. They are thus increasingly used as additives to bring to materials including those of macromolecular type these electrical, thermal and / or mechanical properties.

It is known that the charge rate necessary for the electrical conduction of composite materials decreases sharply with the increase in the aspect ratio of the conductive particles, which is why it is preferred to use carbon nanotubes with respect to carbon black or carbon black. another form of carbon material. We can refer to the state of the art consisting of the following documents. WO 03/079375 ; D. Zhu, Y. Bin, M. Matsuo, "Electrical Conductive Behaviors in Polymer Conposites with Carbonaceous Fillers", J. of Polymer Science Part B, 45, 1037, 2007 ; Y. Bin, M. Mine, A. Koganemaru, X. Jiang, M. Matsuo, "Morphology and Mechanical and Electrical Properties of PVA-VGCF-Oriented and PVA-MWNT Composites", Polymer, 47, 1308, 2006 ).

However, the percolation threshold increases with the orientation of the carbon nanotubes as appears in the following document: F. Du, JE Fischer, KI Winey, "Effect of nanotube alignment on percolation conductivity in carbon nanotube / composite polymer", Physical Review B, 72, 121404, 2005 . Indeed, the method used for the manufacture of composite fibers which consists in extruding the mixture through a die, can induce an alignment of the carbon nanotubes parallel to the axis of the fiber.

In all cases, fiber processing processes such as extrusion and / or stretching can induce orientation of the conductive particles in the fiber axis.

Thus, the concentration of NTC required to reach the percolation threshold of a composite in fiber form can be up to an order of magnitude higher than in the form of films or non-oriented fibers.

The consequence of this orientation phenomenon is that it is necessary to increase the level of CNT to render the conductive composites, especially when these composites are used in the form of fibers. These results are detailed in the publication of: R. Andrews, D. Jacques, M. Minot, T. Rantell, entitled "Fabrication of Carbon Multiwall Nanotube / Polymer Composite by Shear Mixing", Macromolecular Materials and Engineering, 287, 395, 2002 .

Among the processes for manufacturing composite fibers, reference may be made to the patent EP 1 181 331 . This patent describes a method for manufacturing a thermoplastic polymer-based composite material whose mechanical properties are reinforced by the presence of nanotubes. In this process, a mixture of thermoplastic polymer and CNT is produced, then stretching the mixture at the melting temperature of the polymer and then a new drawing in the solid state (cold). Fibers can thus be obtained from this reinforced polymer material.

Reference may also be made to the process for manufacturing composite fibers described in the international application W0200163028 . According to this method, a dispersion of CNTs in a solvent is produced which is injected via a nozzle into a coagulation agent consisting of a polymer, then a drawing and an annealing are carried out.

Unfortunately in this case, initially conductive fibers become less conductive after extensive stretching as evidenced by: R. Haggenmueller, HH Gommans, AG Rinzler, JE Fischer, KI Winey, in the article entitled "Aligned single-wall carbon nanotubes in composites by melt processing methods", published in Chemical Physics Letters, 330, 219, 2000 .

Indeed, the stretching step performed after formation of a fiber, when it is 50% or more, degrades the conductivity properties, of course in the case where the composite material or the fibers made of composite material have conductive properties.

The object of the present invention is to overcome the disadvantages of the various processes mentioned in order to improve the electrical properties of the conductive composite fibers or to make initially insulating fibers conductive.

This object is achieved by the method of manufacturing fibers made of composite material in which the heat treatment step is performed with a temperature undergoing a gradual rise.

To this end, the invention more particularly relates to a fiber manufacturing process consisting of a composite material based on thermoplastic polymer and conductive or semiconductive particles, comprising a heat treatment, said heat treatment consisting of in a heating of the composite material made with a gradual rise in temperature.

The gradual rise in temperature is made according to a ramp preferably less than 50 ° C per minute, preferably less than 30 ° C per minute, preferably less than 10 ° C per minute.

Preferably, the gradual rise in temperature is made according to a ramp equal to 5 ° C per minute.

The required heating temperature is greater than or equal to the glass transition temperature of the thermoplastic polymer. The heating temperature is at or above the melting temperature of the thermoplastic polymer when the level of conductive particles in the composite is decreased.

The heat treatment may be performed on the composite material during spinning and / or after spinning, the material constituting the formed fiber being then annealed.

In the case where the treatment is carried out after spinning, a post heat treatment is carried out, the applied heating temperature is called the annealing temperature.

Whatever the choice, during or after spinning, the heat treatment carried out with a gradual rise in the heating or annealing temperature has the effect of improving the conductive properties of the fibers obtained or making the initially insulating fibers conductive without the disadvantages of the treatments. thermally proposed so far and without causing degradation of the macroscopic structure of the fibers.

The conductive particles introduced into the composition of the fibers are chosen from the particles colloidal conductive or semiconductor in the form of rods, platelets, spheres, ribbons or tubes.

• les nanotubes de carbone,
• les métaux comme l'Or, l'Argent, le Platine, le Palladium, le Cuivre, le Fer, le Zinc, le Titane, le Tungstène, le Chrome, le Carbone, le Silicium, le Cobalt, le Nickel, le Molybdène. et leurs alliages ou composés métalliques,
• les Oxydes comme : Vanadium (V2O5), ZnO, ZrO2, WO3, PbO, In2O3, MgO, Y2O3,
• Des polymères conducteurs ou semi-conducteurs sous forme colloïdale.

The conductive colloidal particles may be chosen from:

• carbon nanotubes,
• metals such as Gold, Silver, Platinum, Palladium, Copper, Iron, Zinc, Titanium, Tungsten, Chromium, Carbon, Silicon, Cobalt, Nickel, Molybdenum. and their alloys or metal compounds,
• Oxides such as: Vanadium (V 2 O 5), ZnO, ZrO 2, WO 3, PbO, In 2 O 3, MgO, Y 2 O 3,
• Conductive or semiconductor polymers in colloidal form.

In the case where the conductive particles are carbon nanotubes, and for charge rates of less than or equal to 7%, the heating temperature is at least equal to the melting point of the polymer or higher.

For carbon nanotube charge levels greater than 7%, the heating temperature is at least equal to the glass transition temperature of the polymer or higher.

The invention also relates to fibers made of composite material based on conductive or semiconductive particles and thermoplastic polymer.

• des nanotubes de carbone,
• des métaux comme l'Or, l'Argent, le Platine, le Palladium, le Cuivre, le Fer, le Zinc, le Titane, le Tungstène, le Chrome, le Carbone, le Silicium, le Cobalt, le Nickel, le Molybdène. et leurs alliages ou composés métalliques,
• des Oxydes comme : Vanadium (V2O5), ZnO, Zr02, WO3, PbO, In2O3, MgO, Y2O3,
• des polymères conducteurs ou semi-conducteurs sous forme colloïdale.

The conductive particles can be:

• carbon nanotubes,
• metals such as Gold, Silver, Platinum, Palladium, Copper, Iron, Zinc, Titanium, Tungsten, Chromium, Carbon, Silicon, Cobalt, Nickel, Molybdenum. and their alloys or metal compounds,
• Oxides such as: Vanadium (V 2 O 5), ZnO, ZrO 2, WO 3, PbO, In 2 O 3, MgO, Y 2 O 3,
• conductive or semiconductive polymers in colloidal form.

In the case where the conductive particles are carbon nanotubes (CNTs), the composite material based on thermoplastic polymer and carbon nanotubes, comprises a mass content of CNT of less than 30%, preferably less than 20%, or of preferably between 10 and 0.1%.

The heat treatment according to the invention makes it possible to obtain a composite material constituting the fibers which has a volume resistivity of less than 10 ^E 12 Ohm.cm, preferably less than 10 ^E 8 Ohm.cm, more preferably less than 10 ^E 4 ohm.cm.

The thermoplastic polymer may be chosen from the group of polyamides, polyolefins, polyacetals, polyketones, polyesters or polyfluoropolymers or mixtures thereof and copolymers thereof.

Preferably, the composite material constituting the fibers is based on a polyamide 6, a polyamide 12 or a polyester and contains a mass content of CNT of less than 30%.

The conductive fibers made of composite material thus obtained can be used in the field of textiles, electronics, mechanics, electromechanics.

For example, the use of conductive fibers based on thermoplastic polymer and carbon nanotubes for reinforcing organic and inorganic matrices, protective clothing. (gloves, helmets, ...), military applications including ballistic protection, antistatic coatings, conductive textiles, antistatic fibers and textiles, electrochemical sensors, electromechanical actuators, electromagnetic shielding applications, packaging, bags etc.

The conductive fibers according to the present invention may in particular be used for the production of deformation sensors.

• La figure 1 représente l'évolution de la résistivité relative d'une fibre composite PA6/NTC en fonction de la température,
• La figure 2 représente l'évolution de la résistivité d'une fibre PA6 contenant 20 % de NTC au cours d'un cycle de chauffage allant de la température ambiante jusqu'à 120°C à une vitesse de 5°C/min, suivi d'un palier à cette température pendant une heure,
• La figure 3 présente les évolutions de la contrainte et de la résistivité de fibres comportant 3 % de NTC, traitées thermiquement à 250°C à une vitesse de 5°C/min, en fonction de l'allongement,
• La figure 4 présente les évolutions de la contrainte et de la résistivité de fibres comportant 10 % de NTC, traitées thermiquement à 250°C à une vitesse de 5°C/min, en fonction de l'allongement.

Other features and advantages of the invention will become clear from reading the description which is given below and which is given by way of illustrative and nonlimiting example and with reference to the figures in which:

• The figure 1 represents the evolution of the relative resistivity of a PA6 / NTC composite fiber as a function of the temperature,
• The figure 2 represents the evolution of the resistivity of a PA6 fiber containing 20% of CNT during a heating cycle ranging from room temperature to 120 ° C at a rate of 5 ° C / min, followed by a stand at this temperature for one hour,
• The figure 3 presents the evolutions of the stress and the resistivity of fibers comprising 3% of CNT, heat-treated at 250 ° C. at a speed of 5 ° C./min, as a function of elongation,
• The figure 4 presents the evolutions of the stress and the resistivity of fibers comprising 10% of CNT, heat-treated at 250 ° C. at a rate of 5 ° C./min, as a function of elongation.

The process described below allows the manufacture of fibers made of composite material comprising conductive or semiconducting particles and a polymer thermoplastic but other techniques can be used as well.

In addition, a material is considered in the present invention as conductive when its volume resistivity is less than 10 ^E 12 ohm.cm and insulating when its volume resistivity is greater than 10 ^E 12 ohm.cm. In many applications such as the dissipation of electrostatic charges values below 10 ^E 8 Ohm.cm are desired.

Conductive or semiconducting particles that can be used :

• des particules colloïdales conductrices ou semi-conductrices en forme de bâtonnets, de plaquettes, de sphères, de rubans ou de tubes comme :
• Des métaux :

Among the conductive or semiconducting particles, one can choose by way of nonlimiting example:

• conductive or semi-conductive colloidal particles in the form of rods, platelets, spheres, ribbons or tubes such as:
• Metals:

• Des Oxydes :

Gold, Silver, Platinum, Palladium, Copper, Iron, Zinc, Titanium, Tungsten, Chromium, Carbon, Silicon, Cobalt, Nickel, Molybdenum and their alloys or metal compounds.

• Oxides:

• Des polymères conducteurs ou semi-conducteurs sous forme colloïdale.
• Des nanotubes de carbone :

Vanadium (V 2 O 5), ZnO, ZrO 2, WO 3, PbO, In 2 O 3, MgO, Y 2 O 3.

• Conductive or semiconductor polymers in colloidal form.
• Carbon nanotubes:

The carbon nanotubes that can be used in the present invention are well known and are as described for example in Plastic World Nov 1993 page 10 or in WO 86/03455 . They include, but are not limited to, those having a relatively high aspect ratio, and preferably a size ratio of 10 to about 1000. In addition, the carbon nanotubes usable in the present invention preferably have a purity of 90% or higher.

Thermoplastic polymers that can be used:

The thermoplastic polymers that may be used in the present invention are especially those prepared from polyamide, polyacetals, polyacrylic polyketones, polyolefins, polycarbonates, polystyrenes, polyesters, polyethers, polysulfones, polyfluoropolymers, polyurethanes, polyamideimides, polyarylates, polyarylsulfones, polyethersulfones, polyarylene sulfides, polyvinyl chlorides, polyetherimides, polytetrafluoroethylenes, polyetherketones, fluoropolymers and their copolymers or mixtures thereof.

Polystyrene (PS) can also be mentioned more particularly; polyolefins and more particularly polyethylene (PE), polypropylene (PP); polyamides, polyamides for example PA-6, PA-6,6, polyamide 6 (PA-6) polyamide 6,6 (PA-6,6), polyamide 11 PA-11, polyamide 12 (PA-12); polymethyl methacrylate (PMMA); polyether terephthalate (PET); polyethersulfones (PES); polyphenylene ether (PPE); fluorinated polymers such as polyvinylidene fluoride (PVDF) or copolymers of VDF and HFE; acrylonitrile polystyrene (SAN); polyethylether ketones (PEEK); polyvinyl chloride (PVC); polyurethanes, consisting of flexible polyether blocks which are residues of polyetherdiols and rigid blocks (polyurethanes) which result from the reaction of at least one diisocyanate with at least one short diol; the short chain extending diol which may be chosen from the glycols mentioned above in the description; the blocks polyurethanes and the polyether blocks being linked by bonds resulting from the reaction of the isocyanate functions with the OH functions of the polyetherdiol; polyesterurethanes, for example those comprising diisocyanate units, units derived from amorphous polyester diols and units derived from a chain-extending short diol chosen for example from the glycols listed above; copolyamides such as polyamide block copolymers and polyether blocks (PEBA) resulting from the copolycondensation of polyamide sequences with reactive ends with polyether sequences with reactive ends, such as, inter alia 1) polyamide sequences with diamine chain ends with polyoxyalkylene sequences at the ends of dicarboxylic chains, 2) polyamide sequences with dicarboxylic chain ends with polyoxyalkylene sequences with diamine chain ends obtained by cyanoethylation and hydrogenation of aliphatic alpha-omega dihydroxylated polyoxyalkylene aliphatic polyether diols, 3) polyamide sequences with dicarboxylic chain ends with polyetherdiols, the products obtained being, in this particular case, polyetheresteramides; polyetheresters.

Mention may also be made of acrylonitrile-butadiene-styrene (ABS), acrylonitrile-ethylene / propylene-styrene (AES), methyl methacrylate-butadiene-styrene (MBS), acrylonitrile-butadiene-methyl methacrylate-styrene (ABMS), acrylonitrile-n- butylacrylate-styrene (AAS); modified polystyrene gums; polyethylenes, polypropylenes, polystyrenes; cellulose acetate; polyphenyleneoxide, polyketone, silicone polymers, polyimides, polybenzimidazoles, polyolefin-type elastomers such as polyethylene, methylcarboxylate-polyethylene, ethylene-vinylacetate and ethylene-ethylacrylate copolymers, chlorinated polyethylenes; styrene type such as styrene-butadiene-styrene block copolymers (SBS) or styrene-isoprene-styrene block copolymers (SIS), styrene-ethylene-butadiene-styrene (SEBS), styrene-butadiene or their hydrogenated form; elastomers of PVC, polyester, polyamide or polybutadiene type such as 1,2-polybutadiene or trans-1,4-polybutadiene; fluorinated elastomers.

It is also necessary to understand the copolymers produced by controlled radical polymerization, such as for example copolymers of SABuS (polystyrene-co-poly-butyl-co-polystyrene), MABuM (polymethyl methacrylate-co-poly-butyl-co-polymethylmethacrylate) and all their functionalized derivatives.

By usable thermoplastic polymer is also meant any random, gradual or block copolymers made from the homopolymers corresponding to the above description.

In the following description, the examples are given for fibers comprising carbon nanotubes (CNTs) and the process for manufacturing the fibers corresponds to a spinning process known to a person skilled in the art, such as an extrusion spinning process. a composite material based on thermoplastic polymer and carbon nanotubes.

According to the invention, the fibers can be made either from bare NTC (crude or washed or treated), or from NTC mixed with a polymer powder or NTC coated / mixed with a polymer or other additives.

The level of CNT in the composite material constituting the fibers is, according to the invention, less than 30%, less than 20% or more preferably between 0.1 and 10%.

The invention therefore proposes a process which makes it possible to increase the conductivity of thermoplastic composite materials containing CNTs, especially when the composition contains CNT levels of less than 10%.

This effect is obtained surprisingly by modifying the heat treatment step of heating the composite material, this modification consisting of a gradual rise in temperature.

The invention proposes a process which makes it possible not to deteriorate or even to improve the conductivity of thermoplastic composite fibers containing CNTs and possibly stretched, or even to make initially insulating fibers conductive.

In practice, the spinning process comprises a first thermoplastic polymer extrusion step containing less than 30% of CNT, possibly followed by a stretching step.

The invention consists in carrying out the heat treatment during spinning and / or after spinning. Heat treatment consists of a gradual increase in temperature. Thus the conductivity of thermoplastic composite fibers containing CNTs is improved. From the various examples, it is also shown that initially insulating composite fibers can be made conductive by this method.

In the various examples described below, the resistivity of a thermoplastic composite fiber containing CNTs decreases during the rise in temperature and the level reached is maintained during the cooling step.

The improvement of the conductivity by this method is almost instantaneous. Holding for one hour at the required heating temperature does not significantly improve the level of conductivity then attained.

The examples described below show that a fixed temperature heat treatment is not very or not at all effective, while a heat treatment consisting of a gradual rise in the heating temperature systematically improves the conductivity of thermoplastic composite fibers. containing CNTs, in a range from 3% to 20% of CNTs. As can be seen, under certain conditions of heating temperature and charge rate in CNT, initially insulating fibers become even conductive.

The method makes it possible to manufacture conductive composite fibers based on thermoplastic polymer and carbon nanotubes (CNTs) comprising a CNT content of less than 30%, preferably between 0.1% and 10%. The fibers obtained have a resistivity which is less than 10 ^E 12 Ohm.cm, preferably less than 10 ^E 8 Ohm.cm, more preferably less than 10 ^E 4 Ohm.cm.

The composite fibers are obtained by melt spinning a composite material based on conductive particles and thermoplastic polymer, as mentioned above. The diameter of the fibers obtained is between 1 and 1000 μm.

In order to obtain finer fibers, a technique other than melt spinning, for example electro-spinning, spinning by centrifugation, etc., will be used.

Examples.

In the examples below, it is polyamide fibers with different levels of CNT. The fibers comprising 3% and 7% of CNT are based on PA12 AMNO TLD, those whose CNT level is 10% and 20% are based on of PA6 Donamid® 27. The resistances are measured using a Keithley 2000 multimeter.

Example 1: Process conditions for improving the conductivity of composite fibers based on thermoplastic polymer and CNT, or for rendering electrically insulating fibers of this type.

• Soit traitées thermiquement à température fixe : dans ce cas les fibres sont recouvertes à leurs extrémités de laque d'argent, positionnées à plat sur un porte-échantillon en aluminium et placées dans une étuve à la température de recuit choisie pendant 30 minutes. Elles sont ensuite refroidies et leur résistance est mesurée à température ambiante.
• Soit traitées thermiquement avec une montée progressive de la température : dans ce cas le multimètre est connecté à des tiges d'invar sur lesquelles les fibres sont accrochées, le contact est assuré par de la laque d'argent et l'ensemble est placé dans une enceinte thermique asservie à un contrôleur de température. Le traitement thermique consiste à chauffer progressivement la fibre de la température ambiante jusqu'à 250°C à une vitesse de 5°C/min. La fibre est ensuite sortie de l'étuve et refroidie. Au cours de ce traitement, la résistance est directement enregistrée en continue en fonction de la température. On constate qu'il n'y a pas de différence notable entre la résistance enregistrée à 250°C et celle enregistrée après refroidissement de la fibre.

In this example, fibers containing different levels of CNTs are considered. They are subjected to two different heat treatments in order to highlight the effects of the heat treatment according to the invention in improving the conductivity of the fibers. So the fibers are:

• Either thermally treated at a fixed temperature: in this case the fibers are covered at their ends with silver lacquer, positioned flat on an aluminum sample holder and placed in an oven at the annealing temperature chosen for 30 minutes. They are then cooled and their resistance is measured at room temperature.
• Either heat treated with a progressive rise in temperature: in this case the multimeter is connected to invar rods on which the fibers are hooked, the contact is provided by silver lacquer and the assembly is placed in a thermal enclosure controlled by a temperature controller. The heat treatment consists of gradually heating the fiber from room temperature to 250 ° C at a rate of 5 ° C / min. The fiber is then removed from the oven and cooled. During this treatment, the resistance is directly recorded continuously according to the temperature. It is noted that there is no noticeable difference between the resistance recorded at 250 ° C and that recorded after cooling the fiber.

In these two cases, two annealing temperatures are considered to be 120 ° C., which is higher than glass transition temperature of the polyamide, and 250 ° C, temperature above the melting temperature of the polyamide.

Table 1 below summarizes all these results. % NTC Diameter (μm) ρ ₁ (Ω.cm) Fixed temperature heat treatment Heat treatment at a rise speed of 5 ° C / min ρ _{120 ° C} (Ω.cm) P _{250 ° C} (Ω.cm) ρ _{120 ° C} (Ω.cm) P _{250 ° C} (Ω.cm) 3% 388 - - - - 3.90 x 10 ³ 7% 293 - - - - 1.00 x 10 ² 10% 495 - - - 2.42 x 10 ⁵ 2.18 x 10 ³ 20% 565 4.30 x 10 ⁴ 7.77 x 10 ³ 9.01 x 10 ³ 1.41 x 10 ⁴ 4.84 x 10 ²

• ρi : résistivité initiale avant traitement thermique ;
• - : la résistance est supérieure à la limite de détection.

This table shows the comparison of the average resistivities p of PA-based composite fibers containing different levels of CNT, depending on the type of heat treatment received: either a 30-minute treatment at a fixed temperature or a treatment from room temperature. up to the annealing temperature at a rise rate of 5 ° C / min. In both cases, two annealing temperatures are considered, 120 ° C and 250 ° C, and the average is obtained from three different samples. The resistivities are measured at room temperature with the exception of that at 120 ° C in the case of treatment under a ramp at 5 ° C / min.

• ρi: initial resistivity before heat treatment;
• -: the resistance is greater than the limit of detection.

It can be seen that annealing at a fixed temperature does not make it possible to make the fibers which initially are not, that is to say containing up to 10% of NTC. In the case of a fiber containing 20% of NTC, initially conductive, the conductivity seems slightly improved by a fixed temperature annealing. But the annealing temperature does not seem to have any influence, the level of conductivity reached is not better at high temperature. It also remains an order of magnitude lower than that achieved through a gradual rise in temperature.

A heat treatment with a gradual rise rate of the temperature of 5 ° C./min is effective for all the composite fibers considered in a range of 3% to 20% of CNT. For the lowest charge rates (3% and 7%) it is necessary to reach a temperature above the melting temperature of the polymer. This heat treatment makes it possible to make fibers containing 10% of CNT conductive from 120 ° C. With a ramp of 5 ° C / min, this temperature is reached in just 20 minutes and the treatment is effective, while a treatment of 30 minutes at 250 ° C is not.

These results clearly highlight the importance of the gradual rise of the annealing temperature to be able to provide and / or improve the conductivity of the PA / NTC composite fibers. A simple annealing at high temperature, even higher than the melting temperature of the polymer, is much less effective.

Example 2: Typical Evolution of the Resistivity of a Composite Fiber Based on Thermoplastic Polymer and CNT During Heat Treatment

The following example relates to the typical evolution of the resistivity of a PA6 Donamid® 27 and CNT-based composite fiber, which is initially conductive, during a heat treatment ranging from room temperature to 250.degree. speed of 5 ° C / min. A first cycle of heating is performed, then the fiber is cooled at a rate of about 2 ° C / min to a temperature below 50 ° C. A second heating cycle identical to the first is then performed. The figure 1 presents the typical evolution of the relative resistivity of a fiber as a function of the temperature during such a heat treatment. Relative resistivity (ρ / ρ0) is the ratio between the resistivity ρ of the fiber at the temperature considered and its resistivity ρ0 at room temperature.

There is a large variation in the resistivity during the first rise in temperature. The resistivity gradually decreases initially and then drops sharply beyond 200 ° C, that is to say when approaching the melting temperature of the polymer which in this case is 221 ° C . This improvement is generally preserved during cooling, and the effect of the second temperature rise is relatively limited.

Example 3 Effect of the annealing time on the resistivity of a composite fiber based on thermoplastic polymer and CNT.

In this example, the influence of the time parameter on the resistivity has been observed by the depositor insofar as the latter has realized that it is the gradual increase of the temperature which makes it possible to improve the conductivity whereas until there, the heat treatment was carried out at a fixed temperature.

A PA6 Donamid® 27 fiber containing 20% NTC is placed in a thermal chamber where it is heated from ambient temperature to 120 ° C at a rate of 5 ° C / min and then maintained at this temperature for a period of time. one o'clock.

The evolution of the resistivity recorded over time is presented figure 2 . This is the evolution of the resistivity of a PA6 fiber containing 20% of CNT during a heating cycle from room temperature up to 120 ° C at a rate of 5 ° C / min, followed by a plateau at this temperature for one hour.

During the first step, while the temperature increases, there is a significant decrease in resistivity as expected (see Example 2). When the temperature is kept constant, however, we notice that the evolution of the resistivity is negligible. The resistivity then varies by only about 7% in one hour, whereas it varies from 56% in 20 minutes during the rise in temperature. This reveals that the effect of the heat treatment on the conductivity is not only a function of temperature, but also almost instantaneous. This is consistent with the relatively limited effect of a second rise in temperature demonstrated in Example 2.

Example 4: Use of composite fibers based on thermoplastic polymer and thermally treated NTC as deformation sensor.

This example shows the evolution of the resistivity of composite fibers annealed in-situ as a function of stretching.

The heat-treated fiber is glued on a paper test-tube. The multimeter is connected to the fiber by two copper wires also glued on the specimen, and the contact is provided by silver lacquer. The fibers are stretched at a rate of 1% deformation per minute and the resistance is recorded at the same time as the tensile test. We can therefore deduce the evolution of the resistivity as a function of elongation, making sure to correct the diameter of the fiber by elongation.

The Figures 3 and 4 present the evolution of the stress and the resistivity of fibers comprising respectively 3% and 10% of NTC, heat treated with 250 ° C at a rate of 5 ° C / min, depending on the elongation. These two quantities are "corrected", that is to say that the variation of the section with the elongation has been taken into account.

The resistivity of the fiber, after a slight decrease, increases with elongation until the fiber breaks. The variation of the electrical properties under mechanical stress therefore allows applications as deformation or stress sensors.

Applications and advantages of the described fibers.

• Les textiles techniques ou d'habillements dits « intelligents », c'est-à-dire capables de répondre à des sollicitations extérieures ou d'exercer des fonctions sous certaines stimulations,
• Les textiles, composites et fibres chauffantes par effet Joules,
• Les textiles, composites et fibres antistatiques (sac, emballage, ameublement, etc.)
• Les textiles, composites et fibres pour capteurs électromécaniques (capteurs de déformation ou de contrainte)
• Les textiles, composites et fibres pour blindage électromagnétique,
• Les Textiles et fibres conductrices pour la réalisation d'afficheurs, de claviers ou de connecteurs intégrés à des vêtements,
• La réalisation d'antennes de réception et d'émission d'ondes électromagnétiques,
• Leur avantage par rapport à des fibres existantes conductrices :

The conductive fibers that have just been described make it possible to use numerous applications, in particular:

• Technical textiles or so-called "intelligent" clothing, that is to say capable of responding to external demands or performing functions under certain stimuli,
• Textiles, composites and heating fibers by Joule effect,
• Textiles, composites and antistatic fibers (bag, packaging, furniture, etc.)
• Textiles, composites and fibers for electromechanical sensors (strain or strain sensors)
• Textiles, composites and fibers for electromagnetic shielding,
• Textiles and conductive fibers for the production of displays, keyboards or connectors integrated into clothing,
• The realization of antennas for receiving and emitting electromagnetic waves,
• Their advantage over existing conductive fibers:

Compared to metallic fibers (copper, iron, gold, silver, metal alloys): metal fibers are difficult to weave, they are heavy and can be degraded by corrosion. They are not very suitable for the production of technical textiles or lightweight and high performance garments, unlike the composite fibers according to the invention.

With respect to carbon fibers: these have a high electrical conductivity and a high tensile strength in the axis of the fiber. However, they lack flexibility and can be woven only by specific methods unlike composite fibers according to the invention. In addition the carbon fibers are not suitable for applications in which they would be subject to strong deformations (stretching, folding, knotting).

Compared with polymer fibers covered with conductive particles: fibers and textiles covered with silver particles are marketed for heating textiles or antistatic bags. However money deposits are expensive and have only a limited life time. These fibers and textiles have their conduction properties degraded over time and especially after washing operations.

With respect to the conductive polymer fibers: these are light and conductive. However, their poor chemical stability is an obstacle to their use in a practical way.

The composite conductive fibers according to the invention constitute a fifth category which circumvents the weaknesses of the fibers previously described, the table below illustrating the properties in the various cases. Conductive fibers Weight Chemical stability Washing and surface aggression Flexibility Deformability Metal - - + - Carbon + + + - Metal deposits on polymer fibers (example: silver particles) + - - + Conductive polymers + - - + Conductive fibers according to the invention + + + +

Claims (21)

1. A process for manufacturing fibers made of a composite based on a thermoplastic; polymer and on conductive or semiconductive particles, comprising a heat treatment, characterized in that said heat treatment consists of heating the composite produced with a gradual rise in the temperature by a ramp of less than 50°C per minute.
2. The process for manufacturing composite fibers as claimed in claim 1, characterized in that the gradual rise in temperature is achieved by a ramp preferably of less than 30°C per minute, preferably of less than 10°C per minute.
3. The process for manufacturing composite fibers as claimed in claim 2, characterised in that the gradual rise is achieved by a ramp of 5°C per minute.
4. The process for manufacturing fibers as claimed in any one of the preceding claims, characterized in that the heating temperature necessary is greater than or equal to the glass transition temperature of the thermoplastic polymer.
5. The process for manufacturing fibers as claimed in any one of the preceding claims characterized in that the heating temperature necessary may range up to a temperature greater than or equal to the melting temperature of the thermoplastic polymer.
6. The process for manufacturing fibers as claimed in any one of the preceding claims, characterized in that the conductive particles are chosen from conductive or semiconductive colloidal particles in the form of rode, small plates, spheres, strips or tubes.
7. The process for manufacturing composite fibers as claimed in claim 6, characterized in that the conductive colloidal particles are chosen from:

   carbon nanotubes;

   - metals such as gold, silver, platinum, palladium, copper, iron, zinc, titanium, tungsten, chromium, carbon, silicon, cobalt, nickel, molybdenum and metallic compounds or alloys thereof;

   - oxides such as: vanadium oxide (V₂O₅), ZnO, ZrO₂, WO₃, PbO, In₂O₃ MgO and Y₂O₃; and

   - conductive or semiconductive polymers in colloidal form.
8. The process for manufacturing fibers as claimed in any one of the preceding claims, characterized in that the thermoplastic polymer may be chosen from the group of polyamides, polyolefins, polyacetals, polyketones, polyesters or polyfluoropolymers or blends thereof and copolymers thereof.
9. The process for manufacturing fibers as claimed in claims 7 and 8, characterized in that in the case where the conductive particles are carbon nanotubes (CNTs), the composite based on a thermoplastic polymer and on carbon nanotubes comprises a weight content of CNTs of less than 30%, preferably of less than 20% or even preferably between 10 and 0.1% and in that the heat treatment makes it possible to obtain a composite constituting the fibers that has a volume resistivity of less than 10^E12 ohm.cm, preferably of less than 10^E8 ohm.cm, more preferably less than 10^E4 ohm.cm.
10. The process for manufacturing fibers as claimed in claim 9, characterized in that in the case where the conductive particles are carbon nanotubes, and for filler contents of less than or equal to 7%, the heating temperature is at least equal to the melting temperature of the polymer or higher.
11. The process for manufacturing fibers as claimed in claim 9, characterized in that for carbon nanotube filler contents greater than 7%, the heating temperature is at least equal to the glass transition temperature of the polymer or higher.
12. The process for manufacturing fibers as claimed in any one of the preceding claims, characterised in that it comprises a melt-spinning step, and in that the heat treatment may be carried out on the composite during the spinning and/or after spinning.
13. Conductive fibers obtained by the process as claimed in any one of the preceding claims, characterized in that they are constituted of a composite based on a thermoplastic polymer and on conductive or semiconductive particles and in that the volume resistivity of the composite constituting them is less than 10^E12 ohm.cm, preferably less than 10^E8 ohm.cm, more preferably less than 10^E4 ohm.cm.
14. The conductive fibers as claimed in claim 13, characterized in that the conductive particles are chosen from conductive or semiconductive colloidal particles in the form of rods, small plates, spheres, strips or tubes.
15. The conductive fibers as claimed in claim 14, characterized in that they comprise conductive colloidal particles chosen from:

    - carbon nanotubes;

    - metals such as gold, silver, platinum, palladium, copper, iron, zinc, titanium, tungsten, chromium, carbon, silicon, cobalt, nickel, molybdenum and metallic compounds or alloys thereof;

    - oxides such as: vanadium oxide (V₂O₅), ZnO, ZrO₂, WO₃, PbO, In₂O₃, MgO and Y₂O₃; and

    - conductive or semiconductive polymers in colloidal form.
16. The conductive fibers as claimed in claim 15, characterized in that they comprise carbon nanotubes (CNTs), the weight content of CNT filler being less than 30%, preferably less than 20%, preferably between 0.1 and 10%.
17. The conductive fibers as claimed in claim 13, characterized in that they comprise a thermoplastic polymer chosen from the group of polyamides, polyolefins, polyacetals, polyketones, polyesters or polyfluoropolymers or blends thereof and copolymers thereof.
18. The conductive fibers as claimed in claims 16 and 17, characterized in that they comprise a polyamide and carbon nanotubes.
19. The use of composite conductive fibers as claimed in any one of claims 13 to 17 in textiles, electronic components, mechanical components and electromechanical components.
20. The use of conductive fibers made of a composite based on a thermoplastic polymer and on carbon nanotubes as claimed in any one of claims 13 to 17, for reinforcing organic and inorganic matrices, protective clothing in ballistic protection devices, antistatic clothing, conductive textiles, antistatic fibers and textiles, electrochemical sensors, electromechanical actuators, electromagnetic shielding applications, packaging and bags.
21. The use of conductive fibers as claimed in claim 20, for producing strain sensors.

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