FR3067364A1 - MULTILAYER FIBER OF FLUORINATED POLYMERS - Google Patents

Abstract

The invention relates to composite piezoelectric fibers. More particularly, the invention relates to multi-component piezoelectric effect fibers made solely of polymeric materials. The invention also relates to the process for manufacturing these fibers, as well as their applications in various sectors of technical textiles, filtration, and electronics.

Description

MULTILAYER FIBER OF FLUORINATED POLYMERS

TECHNICAL AREA

The present invention relates to the field of composite piezoelectric fibers. More particularly, the invention relates to multi-component piezoelectric effect fibers made entirely of polymeric materials. The invention also relates to the process for manufacturing these fibers, as well as to their applications in various sectors of technical textiles, filtration, and electronics.

TECHNICAL BACKGROUND

The ferroelectric and ferroelectric relaxant materials which generate mechanical actuation induced by an external electric field have attracted a lot of attention and have been recognized for applications in various transducers, actuators and sensors.

Among the piezoelectric materials, ceramics are the most commonly used because of their good actuation properties and their very wide bandwidth. However, they have a fragility which prevents them from being applied to curved or complex surfaces.

Other electrically conductive devices use polymer films sandwiched between two electrodes. Among the polymers which can be used, fluoropolymers based in particular on vinylidene fluoride (VDF) represent a class of compounds having remarkable properties for a large number of applications. Polyvinylidene fluoride (PVDF) and copolymers comprising VDF and trifluoroethylene (TrFE) are particularly interesting because of their piezoelectric properties.

These flexible piezoelectric structures are only commercially available in the form of films. However, certain applications require the availability of piezoelectric polymer fibers, which can be implanted directly within certain materials, to form “smart materials”.

Such fibers have been manufactured in the laboratory as a single-component or multi-component.

The article by B. Glauss et al. in Materials 2013, 6, 2642-61 describes two-component fibers obtained by hot spinning, consisting of a conductive polypropylene core (supplemented with multi-wall carbon nanotubes and sodium stearate), and a homopolymer PVDF sheath . These fibers have been characterized by various analytical methods (wide angle X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, rheometry) but their mechanical and electrical properties have not been reported.

The work of R. Martins et al. in J. Text. Eng. 2014, 60 (2), 27-34 relate to the manufacture of bi-component piezoelectric filaments of similar constitution (an inner layer of conductive polypropylene and a layer of homopolymer PVDF). These fibers have been subjected to tensile tests, which show that the two layers break apart at 30% stretch rates (see Fig. 10). This indicates a weak adhesion between the layers.

The same drawback is observed for tri-component fibers described in the publication by R. Martins et al. in J. Appl. Polym. Sci. 2014, DOI: 10.1002 / APP.40710. These fibers have a conductive polypropylene core and sheath, and a central layer of homopolymer PVDF. Microscopy images of a cross section of these fibers show decohesive interfaces between the layers (see Fig. 7). Figure 9 of this document also demonstrates weak interfacial adhesion between the layers of polyvinylidene fluoride and polypropylene. Indeed, the tensile curves reveal the systematic presence of a sudden drop in stress during the tensile test before the complete break of the fiber. This sudden drop in stress comes from the rupture of the outer polypropylene layer and from the decohesion at the polypropylene / polyvinylidene fluoride interface. This interfacial decohesion means that after the rupture of the polypropylene layer, the latter slides over the polyvinylidene fluoride layer during traction, and the stress is only supported by the latter. Another disadvantage concerns the conditions of stretching of the fiber during the spinning process. In this same document, the stretching was carried out at 210 ° C. (see table 1), which is above the melting point of PVDF and polypropylene.

There is therefore a need to develop multi-component fibers which have both good mechanical properties, in particular increased adhesion between the layer of electroactive polymer and that (s) of polymer (s) serving as electrode ( s), allowing it to maintain its integrity during mechanical stresses such as stretching, and simultaneously the properties of relaxant materials with significant electrostrictive effects.

SUMMARY OF THE INVENTION

According to a first aspect, the invention relates to a piezoelectric polymer fiber consisting of three layers: a layer B consisting of at least one fluoropolymer, a layer A comprising at least one polyolefin and a layer C of polyamide, said layer B being contact over its entire surface on the one hand, with said layer C, and, on the other hand, with said layer A, said layer C being located inside the fiber.

According to a second aspect, the invention relates to a piezoelectric polymer fiber consisting of two layers having the following structures:

- a layer B consisting of at least one fluoropolymer,

- in contact with a layer A consisting of at least one polyolefin which has a chemical affinity with said fluoropolymer.

Typically for bi-component fiber:

the fluoropolymer is a functionalized fluoropolymer or a mixture of a fluoropolymer with a functionalized fluoropolymer, and

- Said layer A comprises a mixture of a polyolefin with a functionalized polyolefin carrying a reactive function with respect to the function carried by said functionalized fluoropolymer.

In the polymer fiber according to the invention, at least one of the layers A and C is charged with conductive particles such as carbon nanotubes, carbon blacks, graphene, graphite, carbon nanofibers, nanowires or metallic nanoparticles ( silver nanowires for example). This favors the polarization and the piezoelectric behavior of the fiber.

According to another aspect, the invention relates to a process for manufacturing the three-component fiber described above by coextrusion of the polymers constituting the layers A, B and C in the molten state, followed by a drawing step. According to one embodiment, the stretching step is carried out at a temperature between the glass transition temperature, Tg, and the melting temperature, Tf of the polymers constituting the layers A, B and C, that is that is to say at a temperature between the highest Tg and the lowest Tf of the various constituents, which amounts to a range between 40 ° C and 130 ° C.

More particularly for a layer B of PVDF, this stretching takes place between 80 and 120 ° C.

The invention also relates to a piezoelectric device made from the described two-component fiber.

The invention also relates to textile materials which include the two-component fibers described.

The present invention makes it possible to overcome the drawbacks of the prior art. In particular, the invention makes it possible to obtain fully polymeric piezoelectric fibers, having increased flexibility compared to ceramic-based fibers, allowing them to be used in "intelligent" materials, in particular textile materials. In addition, the fibers according to the invention have improved adhesion properties between the different layers, which guarantees their stretching capacities. Indeed, such a fiber to obtain its mechanical characteristics must be drawn in the spinning process, without impact on the cohesion of its various constituents. In addition, in particular for use in clothing textiles, this fiber will be highly stressed mechanically and to maintain its integrity, strong adhesion in the different layers is to be preferred. Finally, in the case of the use of PVDF in layer B, the stretching of the fiber makes it possible to generate the beta crystalline phase necessary for the piezoelectric effect.

Another advantage of the fibers according to the invention, exhibiting good adhesion between the layers of filaments, resides in the fact that the drawing temperatures of the multi-component fiber remain within conventional ranges of drawing temperatures, namely below the melting temperature of the component with the lowest melting point, typically less than 150 ° C.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows a bi-component fiber A / B (the filament of Example 1) unstretched, seen in cross section with a scanning electron microscope. Material A is a mixture of 70% by weight of a high density polyethylene HDPE and 30% by weight of a functionalized polyethylene PEf. Material B is a compound made of 80% by weight PVDF and 20% by weight PVDFf.

FIG. 2 represents the image of a fracture facies, obtained by scanning electron microscopy, of the two-component fiber of example 1, highly stretched (at the end of the elongation stress curve).

Figure 3 is a diagram showing the results of tensile tests corresponding to Comparative Examples 1 and 1.

DESCRIPTION OF EMBODIMENTS

The invention will now be described in more detail without limitation in the following description.

A first objective of the invention is to provide a three-component piezoelectric polymer fiber, that is to say consisting of three layers of different polymers: a layer B consisting of at least one fluoropolymer, a layer A comprising at least one polyolefin and a layer C of polyamide, said layer B being in contact over its entire surface on the one hand, with said layer C, and, on the other hand, with said layer A. Layer C is located inside the fiber. Such a structure gives rise to different geometries, such as coaxial geometry or the islands-in-sea structure.

According to one embodiment, the polymers present in each of the layers A, B and C have crystallization temperatures Te respecting the condition: Te A <Te B <Te C in order to ensure the best possible cohesion within the sorting fiber -component. Indeed, the fiber is produced by simultaneous coextrusion of the three materials. By respecting this temperature order, the solidification of the core is guaranteed first, followed by that of the fluorinated material and finally of the outer layer. This procedure makes it possible to avoid decohesion phenomena at the interfaces due to shrinkage during crystallization, and leads to the production of a denser and more tenacious fiber.

According to a second aspect, the invention relates to a piezoelectric polymer fiber consisting of two layers having the following structures:

- A layer B consisting of at least one fluoropolymer, in contact with a layer A consisting of at least one polyolefin which has a chemical affinity with said fluoropolymer.

Typically for said two-component fiber:

the fluoropolymer is a functionalized fluoropolymer or a mixture of a fluoropolymer with a functionalized fluoropolymer, and

- Said layer A comprises a mixture of a polyolefin with a functionalized polyolefin carrying a reactive function with respect to the function carried by said functionalized fluoropolymer.

According to one embodiment of the tri-component fiber, the fluoropolymer of layer B is a functionalized fluoropolymer or a mixture of a fluoropolymer with a functionalized fluoropolymer, and said layer A comprises a mixture of a polyolefin with a functionalized polyolefin carrying a reactive function with respect to the function carried by said functionalized fluoropolymer.

This particular structure guarantees a cohesive interface between layer B and layer A of the two- or three-component fiber, and does not lead to delamination during mechanical stress.

Layer B

The fluoropolymer of layer B is any polymer having in its chain at least one monomer chosen from compounds containing a vinyl group capable of opening to polymerize and which contains, directly attached to this vinyl group, at least one atom. fluorine, fluoroalkyl group or fluoroalkoxy group.

By way of example of a monomer, mention may be made of vinyl fluoride; vinylidene fluoride (VDF); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro (alkyl vinyl) ethers such as perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE) and perfluoro (propyl vinyl) ether (PPVE); perfluoro (1,3-dioxole); perfluoro (2,2-dimethyl1,3 -dioxole) (PDD); the product of formula CF2 = CFOCF2CF (CF3) OCF2CF2X in which X is SO2F, CO2H, CH2OH, CH2OCN or CH20PO3H; the product of formula CF2 = CFOCF2CF2SO2F; the product of formula F (CF2) nCH20CF = CF2 in which n is 1, 2, 3, 4 or 5; the product of formula R1CH2OCF = CF2 in which RI is hydrogen or F (CF2) z and z is 1, 2, 3 or 4; the product of formula R3OCF = CH2 in which R3 is F (CF2) zet z is 1, 2, 3 or 4; perfluorobutyl ethylene (PFBE); 3,3,3-trifluoropropene and 2trifluoromethyl-3, 3, 3 -trifluoro- 1 -propene.

The fluoropolymer can be a homopolymer or a copolymer, it can also comprise non-fluorinated monomers such as ethylene.

According to one embodiment, said fluoropolymer is a homopolymer polyvinylidene fluoride (PVDF) or a VDF copolymer, containing, by weight, at least 50% of VDF, more preferably at least 75% and better still at least 85%, with at least one comonomer chosen from trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), CFE or 1,1-chlorofluoroethylene, CDFE or 2-chloro-1,1, -trifluoroethylene, hexafluoropropene (HFP), tetrafluoroethylene (TFE).

According to one embodiment, said fluoropolymer is a terpolymer such as P (VDF-TrFECFE) or P (VDF-TrFE-CTFE).

According to one embodiment, the layer B entering a tri-composite fiber according to the invention is a functionalized fluoropolymer or a mixture of a fluoropolymer described above with a functionalized fluoropolymer.

According to one embodiment, the functionalized fluoropolymer carries an established grafted monomer, as described in the above-mentioned EP 1484346. The grafted unsaturated monomer is chosen from unsaturated carboxylic acids and their derivatives.

Examples of unsaturated carboxylic acids are those having 2 to 20 carbon atoms such as acrylic, methacrylic, maleic, fumaric and itaconic acids. The functional derivatives of these acids include, for example, anhydrides, ester derivatives, amide derivatives, imide derivatives and metal salts (such as alkali metal salts) of unsaturated carboxylic acids. Mention may also be made of undecylenic acid.

Unsaturated dicarboxylic acids having 4 to 10 carbon atoms and their functional derivatives, particularly their anhydrides, are particularly preferred grafting monomers.

These grafting monomers include, for example, maleic, fumaric, itaconic, citraconic, allylsuccinic, cyclohex-4-ene-1,2,2-dicarboxylic, 4-methylcyclohex-4-ene-1,2,2-dicarboxylic, bicyclo acids , l) hept-5-ene-2,3-dicarboxylic, x— methylbicyclo (2,2, l-hept-5-en-2,3-dicarboxylic, maleic anhydrides, itaconic, citraconic, allylsuccinic, cyclohex-4 -ene-1,2-dicarboxylic, 4-methylenecyclohex-4ene-1,2-dicarboxylic, bicyclo (2,2, l) hept-5-ene-2,3-dicarboxylic, and x— methylbicyclo (2,2, l) hept-5-ene-2,2-dicarboxylic acid.

Layer A

The polyolefin (PO) which can be used in layer A of the fiber according to the invention is a polymer comprising, as monomer, an alpha-olefin, that is to say the homopolymers of an olefin or the copolymers of at least one alpha. olefin and at least one other copolymerizable monomer, the alpha-olefin advantageously having from 2 to 30 carbon atoms.

Examples of alpha-olefins that may be mentioned include ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3 -methyl-1-pentene, 1-octene, 1-decene, 1dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene, 1-dococene, 1-tetracocene, 1-hexacocene, 1-octacocene, and 1-triacontene. These alpha-olefins can be used alone or as a mixture of two or more than two.

As examples, we can cite:

homopolymers and copolymers of ethylene, in particular low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), polyethylene obtained by catalysis metallocene, homopolymers and copolymers of propylene, essentially amorphous or attactic polyalphaolefins (APAO), ethylene / alpha-olefin copolymers such as ethylene / propylene, EPR (ethylene-propylene-rubber) elastomers, and EPDM (ethylene-propylene) -diene), and blends of polyethylene with an EPR or EPDM, the styrene / ethylene-butene / styrene block copolymers (SEBS), styrene / butadiene / styrene (SBS), styrene / isoprene / styrene (SIS), and styrene / ethylene-propylene / styrene (SEPS), copolymers of ethylene with at least one product chosen from salts or esters of unsaturated carboxylic acids such as for example (met h) alkyl acrylates, the alkyl possibly having up to 24 carbon atoms, vinyl esters of saturated carboxylic acids such as for example vinyl acetate or propionate, and dienes such as for example 1 , 4-hexadiene or polybutadiene.

The functionalized polyolefin can be a polymer of alpha olefins having reactive units (functionalities); such reactive units are the acid, anhydride or epoxy functions. By way of example, mention may be made of the preceding polyolefins grafted or co- or ter polymerized by unsaturated epoxides such as glycidyl (meth) acrylate, or by carboxylic acids or the corresponding salts or esters such as acid ( meth) acrylic (which can be totally or partially neutralized by metals such as Zn, etc.) or also by anhydrides of carboxylic acids such as maleic anhydride. A functionalized polyolefin is for example a PE / EPR mixture, the weight ratio of which can vary within wide limits, for example between 40/60 and 90/10, said mixture being co-grafted with an anhydride, in particular maleic anhydride, according to a grafting rate for example of 0.01 to 5% by weight.

The functionalized polyolefin can be chosen from the (co) polymers mentioned above, grafted with maleic anhydride or glycidyl methacrylate, in which the grafting rate is for example from 0.01 to 5% by weight.

The functionalized polyolefin can also be a co- or ter polymer of at least the following units: (1) ethylene, (2) alkyl (meth) acrylate or vinyl ester of saturated carboxylic acid and (3) anhydride such as maleic anhydride or (meth) acrylic or epoxy acid such as glycidyl (meth) acrylate.

By way of example of functionalized polyolefins of the latter type, mention may be made of the following copolymers, where the ethylene preferably represents at least 60% by weight and where the ter monomer (the function) represents for example from 0.1 to 10% by weight of the copolymer:

- ethylene / alkyl (meth) acrylate / (meth) acrylic acid or maleic anhydride or glycidyl methacrylate copolymers;

- ethylene / vinyl acetate / maleic anhydride or glycidyl methacrylate copolymers;

ethylene / vinyl acetate or (meth) acrylate / alkyl (meth) acrylic acid copolymers or As examples of such polymers, mention may be made of the ter polymers of ethylene, of alkyl acrylate and maleic anhydride or glycidyl methacrylate such as the Lotaders® from the Applicant or polyolefins grafted with maleic anhydride such as the Orevac® from the Applicants as well as ter polymers of ethylene, alkyl acrylate and (meth) acrylic acid, maleic anhydride or glycidyl methacrylate.

Layer C

The nomenclature used to define polyamides is described in ISO standard 1874-1: 2011 Plastics - Polyamide materials (PA) for molding and extrusion - Part 1: Designation, in particular on page 3 (tables 1 and 2) and is well known by the skilled person.

Layer C is made of polyamide. The polyamide is chosen so that its crystallization temperature is higher than that of layers A and B. According to one embodiment, the polyamide of layer C is polyamide 12 (PA 12), which is an aliphatic polyamide manufactured by opening of the lauryllactam cycle (therefore a polylauroamide). Its inherent viscosity can be between 1 and 2 and advantageously between 1.2 and 1.8. The inherent viscosity is measured at 20 ° C for a concentration of 0.5% in meta-cresol.

Polyamides 11.6, 6.10, 6.12, 10.10, 10.12 and 6.6 are also suitable for layer C. The polyamide in layer C can contain from 0 to 30% by weight of at least one product chosen from plasticizers and modifiers shock for respectively 100 to 70% of polyamide.

Examples of plasticizers that may be mentioned are benzene sulfonamide derivatives, such as nbutyl benzene sulfonamide (BBSA), ethyl toluene sulfonamide or N-cyclohexyl toluene sulfonamide; esters of hydroxy benzoic acids, such as ethyl 2 hexyl parahydroxybenzoate and 2-decyl hexyl parahydroxybenzoate; esters or ethers of tetrahydrofurfuryl alcohol, such as oligoethyleneoxytetrahydrofurfuryl alcohol; esters of citric acid or hydroxy malonic acid, such as oligoethyleneoxy malonate. Mention may also be made of decyl hexyl parahydroxybenzoate and ethyl hexyl parahydroxybenzoate. A particularly preferred plasticizer is n-butyl benzene sulfonamide (BBSA).

By way of example of impact modifier, mention may be made of polyolefins, crosslinked polyolefins, elastomers EPR, EPDM, SB S and SEBS, these elastomers which can be grafted to facilitate their compatibilization with the polyamide, the copolymers with polyamide blocks and polyether blocks. These polyamide block and polyether block copolymers are known in themselves, they are also designated by the name PEBA (polyether block amide). Mention may also be made of acrylic elastomers, for example those of the NB R, HNBR, X-NBR type.

This polyamide may contain additives such as anti UV, stabilizers, antioxidants, or flame retardants.

When the inner polyamide layer is loaded with conductive particles, it provides the conductivity and mechanical properties to the fiber according to the invention.

According to one embodiment, at least one of the layers A and C is charged with conductive particles such as carbon nanotubes, carbon blacks, graphene, graphite, carbon nanofibers, metallic nanowires or nanoparticles (nanowires 'money for example). The polymers thus charged become electrical conductors and are capable of playing the role of electrodes. The optimal charge rate is thus between 2 and 30% by mass relative to the weight of each layer A and C, depending on the conductive charge considered to obtain an electrical conductivity sufficient for the use of the polymer as an electrode.

The layers adhere to each other without a coextrusion binder.

The adhesion of the different polymers within a multi-component fiber of the core-bark 10 bark or three-component iles-en-mer type is a determining criterion for obtaining the desired properties:

- possibility of stretching the multi-component fiber without delamination of the layers and obtaining the fluoropolymer under majority beta phase

- mechanical strength of the fiber after stretching for textile application

- cohesive interface between the various constituents of the fiber allows polarization of the fluoropolymer avoiding the problems of electrical breakdown under high voltage at the interface (presence of air avoided)

- better recovery of piezoelectric charges generated by deformation of the piezoelectric fluoropolymer.

Another objective of the invention is to provide a process for the preparation of the two-component fiber described above by coextrusion of the polymers constituting the layers A and B in the molten state, followed by a step of hot drawing.

More specifically, the process for manufacturing the three-component fiber comprises the following steps:

- supply the polymers making up each of layers A and B in the molten state.

coextruding said polymers in the molten state in the form of filaments. The processing temperatures of polymers A and B must be as close as possible and define that of the two-component sector. In the case of a fiber made of PA12, PVDF, HDPE this die temperature is ideally between 21 CEC and 240 ° C.

stretch the fiber thus extruded. Melt stretching has no influence on the adhesion of layers A and B and has little impact on the rate of final beta phase in the fluorinated phase. In accordance with the practices of a person skilled in the art, it is the post-stretching step, once the filament has cooled and solidified, which will give the wire its high mechanical properties as well as obtaining PVDF in its majority beta form. This post-stretching step is carried out in the solid state and preferably at a temperature between 80 and 120 ° C. The stretching factor R designating the speed ratio between the stretching rollers is preferably between 3 and 6, this ratio leading to the mechanical and beta phase properties mentioned.

- winding together said extruded filaments to form a fiber.

The production of a polymer piezoelectric fiber is preferably carried out when the electrodes are directly manufactured during the spinning step. A simple way is to use multi-component spinning (or coextrusion) in which the piezoactive material (PVDF, copolymers or terpolymers of VDF) is surrounded by electrically conductive polymers which act as electrodes.

It is also possible that the polymer material used is an electrostrictive and electroactive material, for example a polymer (P (VDF-TrFE-CFE) or P (VDF-TrFE-CTFE). In these materials, the application of a field electric at the terminals of the material causes its size to be reduced in the direction of application of the field as well as its elongation in the direction perpendicular to the field applied. A fiber according to the invention composed of such a polymer, and having a conductive core, constituting a first electrode, and an external conductive coating constituting a second electrode can thus constitute an actuator. The application of an electric field between these electrodes makes it possible to modify the mechanical characteristics of the fiber. If this fiber is integrated into a textile structure , the application of this electric field makes it possible to modify the mechanical characteristics of this textile structure.

The spinning of multi-component fibers makes it possible to obtain new properties by the combination of different materials within the same filament. These multi-component fibers can find applications in various sectors of technical textiles, filtration, but also in electronics.

The invention also relates to a piezoelectric device made from the described two-component fiber.

The invention also relates to textile materials which include two-component fibers described.

EXAMPLES

The following examples illustrate the invention without limiting it.

products

Layer A polymer materials

- High density polyethylene (noted HDPE): polyethylene characterized by a melt index of 23 g / 10 '(190 ° C under 2.16 kg), a melting temperature of 128 ° C and a crystallization temperature of 117 ° C measured by thermal analysis.

- Functionalized polyethylene (denoted PEf): terpolymer of ethylene, butyl acrylate and glycidyl methacrylate characterized by a melt flow index of 12 g / 10 '(190 ° C under 2.16 kg), a melting temperature of 74 ° C and a crystallization temperature of 54 ° C.

Layer B polymer materials

- Polyvinylidene fluoride (denoted PVDF): vinylidene fluoride homopolymer characterized by a melt index of 33 g / 10 '(230 ° C under 2.16 kg), a melting temperature of 172 ° C and a crystallization temperature of 138 ° C measured by thermal analysis.

- Functionalized polyvinylidene fluoride (noted PVDFf): homopolymer of vinylidene fluoride grafted with 0.5% by weight of maleic anhydride characterized by a melt flow index of 16 g / 10 '(230 ° C under 3.8 kg), a temperature of 172 ° C and a crystallization temperature of 137 ° C measured by thermal analysis.

Layer C polymer materials

- Polyamide 12 (noted PA12): homopolymer of lauryllactam characterized by a melt index of 50 g / 10 '(235 ° C under 2.16 kg) and a melting temperature of 180 ° C and a crystallization temperature of 153 ° C measured by thermal analysis.

Conductive materials

- Carbon black (noted CB):

- Carbon nanotubes (noted NTC).

Preparation of functionalized and conductive compounds

HDPE mixtures with functionalized HDPE or PVDF mixtures with functionalized PVDF are called functionalized compounds. Conductive compounds are called HDPE mixtures (functionalized or not) with conductive fillers or P Al 2 with conductive fillers.

Functionalized compounds are produced by the melt using an extrusion process. For this, a twin-screw extruder is preferably used and allows the mixing of non-functional polymers with functionalized polymers at controlled rates. The granules of each material are mixed in proportions chosen in the solid state and then conveyed in the extrusion machine according to an increasing temperature profile whose values are generally between Tf + 20 and Tf + 70 ° C. After extrusion, a rod is obtained and then granulated.

The first step in producing a conductive compound consists in the manufacture of a masterbatch concentrated in conductive fillers, a mixture also called master-batch. This masterbatch is produced by molten extrusion using a mixing tool with a high shear rate such as a co-mixer or a twin-screw type extruder with shearing profile. This step is essential to optimally disperse the conductive filler in the polymer. Advantageously, a high level of fillers is used in the masterbatch, typically between 15 and 50% by weight, and makes it possible to obtain a high viscosity promoting the shearing and therefore the dispersion of the fillers. The material is conveyed in the molten channel in the extrusion machine according to an increasing temperature profile, the values of which are generally between Tf + 20 and Tf + 70 ° C. The conductive charges are supplied by a lateral metering device to the molten material in the desired quantity. A rod is obtained at the outlet of the extruder, cooled and then granulated.

These masterbatch granules are diluted in the matrix considered by the molten extrusion process, on a twin-screw type machine. Similarly, an increasing temperature profile is applied to the molten material to allow optimal dilution of the masterbatch, whose values are between Tf + 20 and Tf + 70 ° C.

Spinning of bi-component and tri-component filaments

From functionalized and conductive compounds, two-component and three-component structures were produced under the following conditions.

Example 1: Bi-component fiber A / B

Material A is a mixture of 70% by weight of a high density polyethylene HDPE and 30% by weight of a functionalized polyethylene PEf. Material B is a compound made of 80% by weight PVDF and 20% by weight PVDFf.

These compounds A and B are melted and conveyed in two single-screw extruders, which optionally fill two booster pumps used to fix the output flow. At the end of the extrusion or pumping step, the two compounds A and B are routed through a pipe and then injected into a two-component spinning pack allowing compounds A and B to be brought to the periphery respectively (sheath ) and in the center (heart) of each extruded filament. The spinning pack is produced according to the knowledge of a person skilled in the art for ensuring two-component spinning of core-shell geometry and can be made up, among other parts, of an injection cone, flow distribution plates, filters, a support plate and a die.

The elements specific to each compound: extruder, pump, pipe are brought to temperatures allowing the melting of said compound TfA and Tæ, the spinning pack is brought to a temperature at T> TfB in the case or TfB> Tfc. This temperature T must not lead to the degradation of any of the compounds A or B.

For compounds A and B cited in Example 1, this temperature T is preferably between 205 and 220 ° C and a two-component monofilament die is used. The extrusion rates are chosen so as to obtain a sheath A / core B volume ratio of 30/70.

The extruded filament is cooled in the ambient air, driven by an omega roller drawing bench allowing to fix the diameter and the stretch in the molten state. This filament is then collected and wound without further solid state stretching.

The attached Figure 1 illustrates the bi-component fiber A / B of Example 1, unstretched.

Characterization of adhesion by tensile test on fiber

The adhesion between the A / B layers was evaluated by a two-component filament tensile test.

To do this, a universal testing machine is used in tensile test mode. It is 5 provided with a fixed cross member and a mobile instrumented cross member, a force sensor and jaws and jaws suitable for testing on filaments. A device allows the recording of the force measured by the sensor as a function of the movement of the mobile crossmember. The filaments are placed between the two jaws and the tensile test is carried out until the filaments are completely broken, using a test speed of 50 or 100% / min in accordance with ISO 5079 or ISO 2062, according to Whether you are testing single or multi-filaments.

Figure 2 attached shows the fiber of Example 1, stretched to 800%. It shows that the two materials remain adhered even after a significant stretch, and break simultaneously.

The structures produced are shown in Table I below.

The curves corresponding to the tensile tests of Examples 1 and Comparative 1 are shown in FIG. 3.

Layer A Layer B Layer C Diameter of filament Ratio between the layers Example 1 Mixed HDPE / HDPEf 70/30 by weight Mixed PVDF / PVDFf 80/20 by weight 360 A / B: 30/70 Example 1 comparative HDPE PVDF 230 pm A / B: 33/66

Table I

Figure 3: The filament example 1 has a constrained curve - smooth elongation and characteristic of a single-component filament. The comparative example 1 filament, which does not consist of functionalized polymers, exhibits a different behavior. A significant drop in stress is observed from the transition from the elastic regime to the plastic deformation regime. This fall is characteristic of a rupture of one of the two components, in this case that of the HDPE sheath. This sheath is gradually removed / delaminated from the PVDF core of the filament as shown by the noisy behavior of the curve.

Claims (8)

1. Piezoelectric polymer fiber consisting of two layers: a layer B consisting of at least one functionalized fluoropolymer or a mixture of a fluoropolymer with a functionalized fluoropolymer, and a layer A comprising a mixture of a polyolefin with a polyolefin functionalized carrying a reactive function vis-à-vis the function carried by said functionalized fluoropolymer, said layer B being in contact over its entire surface with said layer A. 2. Fiber according to claim 1 in which the layer A is charged with conductive particles such as carbon nanotubes, carbon blacks, graphene, graphite, carbon nanofibers, metallic nanowires or nanoparticles. 3. Fiber according to one of claims 1 or 2, wherein said functionalized fluoropolymer carries an implanted graft monomer chosen from unsaturated carboxylic acids and their derivatives. 4. Fiber according to claim 3, in which said grafting monomer is chosen from maleic, fumaric, itaconic, citraconic, allylsuccinic, cyclohex-4ene-1,2-dicarboxylic acid, 4-methyl-cyclohex-4-ene-1 , 2-dicarboxylic, bicyclo (2,2, l) hept-5-ene-2,3-dicarboxylic, x-methylbicyclo (2,2, l-hept-5-en-2,3dicarboxylic, maleic anhydrides, itaconic , citraconic, allylsuccinic, cyclohex-4-ene-1,2-dicarboxylic, 4-methylenecyclohex-4-ene-1,2-dicarboxylic, bicyclo (2,2, l) hept-5-ene 2,3-dicarboxylic , and x-methylbicyclo (2,2,1) hept-5-en2,2-dicarboxylic. 5. Fiber according to one of claims 1 to 4 wherein said functionalized polyolefin carries epoxy groups. 6. Method for manufacturing a piezoelectric polymer fiber according to one of claims 1 to 5 comprising the following steps: providing the polymers making up each of layers A and B in the molten state, coextruding said polymers in the molten state in the form of filaments, winding together said extruded filaments to form a fiber, hot drawing the fiber thus extruded 7. Piezoelectric device made from fibers according to one of claims 1 to 5 5. 8. Textile material comprising fibers according to one of claims 1 to 5.