FR3111646A1 - Process for manufacturing a set of fibers comprising a fluorinated copolymer based on VDF - Google Patents

Abstract

The invention relates to a method for manufacturing a nonwoven web of fibers comprising: a) providing a solution, respectively a homogeneous dispersion, comprising at least one fluorinated polymer in a liquid vehicle, said fluorinated polymer being based on the repeating unit derived from vinylidene fluoride (VDF); and, b) electrospinning the solution, respectively the homogeneous dispersion, to form said web; said solution, respectively said homogeneous dispersion, being characterized in that the liquid vehicle comprises at least 50% by weight of a (first) liquid having a Hansen solubility parameter δp greater than or equal to 7 MPa1/2 and has a temperature boiling above 100°C; the liquid vehicle not comprising dimethyl sulfoxide (DMSO), and not being considered, by virtue of its constituents, as carcinogenic, mutagenic or toxic for reproduction. Figure for the abstract: Figure 1

Description

Process for manufacturing a set of fibers comprising a fluorinated copolymer based on VDF

The invention relates to the field of methods for manufacturing a web of fibers comprising fibers of a polymer based on the repeating unit derived from vinylidene fluoride (VDF), in particular a web of PVDF fibers, by electrospinning of a homogeneous solution or dispersion.

The invention also relates to the field of webs of fibers likely to be obtained by these processes.

The invention finally relates to formulations of solutions or homogeneous dispersions of a polymer based on the repeating unit derived from vinylidene fluoride (VDF), in particular from a PVDF, the latter being particularly suitable for use in a process for electrospinning.

Prior art

Electrospinning, also known by its English translation: electrospinning, or electrostatic spinning, is a well-known electrohydrodynamic process, making it possible to manufacture small-size polymer fibers, in particular fibers with a diameter ranging from a few tens of nanometers to several hundred nanometers.

When a sufficiently high electrical voltage is applied to a polymer droplet in a solvent, the droplet becomes charged; the electrostatic repulsion force then opposes the surface tension forcing the droplet to stretch, until it forms a cone, called a "Taylor cone". An electrically charged jet is ejected from the top of the Taylor cone and then accelerated by the electric field. The jet expands in the direction of the electric field and thins as it travels towards a collecting electrode. The extension of the jet and its thinning are accompanied by a substantial, even almost total, evaporation of the solvent, which allows the solidification of polymer fibers. The fibers from the jet are collected on the collection electrode or on a full-fledged substrate at the end of their journey.

Electrospinning makes it possible to obtain fibers of diameters small enough to obtain veils of fibers and/or membranes comprising them which can be used for the filtration of fluids, in particular for the filtration of aerosols, ensuring both good filtration efficiency and good permeability.

There are usually three main physical mechanisms by which a filter element makes it possible to limit the passage of aerosols carried by a gas flow. Two are related to mechanical effects, the third to electrostatic effects. The first effect, “impact”, is that observed when particles have dimensions close to that of the size of the pores, and are thus blocked by impact with the fibres.

The second effect, "diffusion", is linked to the fact that the scattering particles have a Brownian component in their movement and are thus likely to come into contact with and adhere to the fibres. This mechanism makes it possible to prevent the passage of particles of sizes smaller than the dimension of the pores.

The third effect, "induction", is associated with electrostatic phenomena. If the particles to be filtered are charged or polarizable, they are likely to be attracted by fibers which themselves have charges or dipoles. This third effect makes it possible to limit the passage of particles whose dimensions are significantly smaller than the pore size. It is all the more marked as the fibers have a small diameter.

Poly(vinylidene fluoride), more commonly known as PVDF, makes it possible to obtain hydrophobic and chemically resistant membranes. PVDF is a semi-crystalline thermoplastic polymer, which presents a polymorphism, namely that it can crystallize under different crystalline phases: α, β, γ and δ. The sequence of conformations, trans (T) or left (G), along the chains as well as the arrangement of the chains between them in the crystal (symmetry) define the phase as well as its polar or non-polar character.

The alpha phase can be described by TGTḠ (Trans Left + Trans Left -) conformation sequences. This is the only apolar phase.

The beta phase can be described by sequences of only "trans" (T) conformations along the chains, themselves ordered in a non-centrosymmetric orthorhombic cell. The beta phase is the most polar phase.

There are intermediates between the alpha phase and the beta phase, notably the gamma phase, which can be described by T3GT3Ḡ conformation sequences. It is polar but much less than the beta phase. The delta phase is also polar but has been little studied.

Polar phases, especially the most polar beta phase, exhibit important ferroelectric properties. This means that the application to the material of an electric field at a value greater than a characteristic field called the coercive field (Ec), allows the orientation of the dipoles formed by the C-F bonds in the same direction. This orientation of the dipoles, sufficiently stable over time due to the ferroelectric properties, gives the material a remanent polarization at zero electric field. Thus, the presence of beta phase in the PVDF fibers is particularly interesting for aerosol filtration applications because this makes it possible to generate charges linked to the material and therefore to increase the electrostatic efficiency (higher electrostatic efficiency compared to fibers of non-ferroelectric dielectric materials).

It is known from Andrew & al. (see: Effect of electrospinning on the ferroelectric phase content of polyvinylidene difluoride fibers. Langmuir, 2008, vol. 24, no 3, p. 670-672), the electrospinning of PVDF solutions in dimethylformamide (DMF). By varying certain process parameters, in this case the PVDF concentration in the solution and the voltage applied during electrospinning, the authors manage to obtain a web of PVDF fibers with a crystallinity of 49% to 58%, the percentage of beta phase in the crystalline phase being at most 75%. Thus, the fibers obtained have a beta phase content of 37% to 47% by weight relative to the weight of fibers.

It is known from Baqueri & al. (see: Influence of processing conditions on polymorphic behavior, crystallinity, and morphology of electrospun poly (Vinylidene fluoride) nanofibers. Journal of Applied Polymer Science, 2015, vol. 132, no 30) electrospinning of PVDF solutions at a concentration of 20% by weight in DMF. The authors manage to obtain, with an electrospinning flow rate of 0.5 mL/h and a voltage applied during the electrospinning of 13 kV, a veil of PVDF fibers having a crystallinity of 53%, the percentage of beta phase in the crystalline phase being at most 83%. Thus, the fibers obtained have a beta phase content of 44% by weight relative to the weight of fibers. Moreover, their median diameter is 55 nm.

DMF is labeled "H360D - May damage the unborn child" and "H332 - Harmful by inhalation". It is therefore considered to be a CMR solvent (Carcinogenic, or Mutagenic, or Toxic for reproduction). The LC50 index (median lethal concentration by inhalation) is the concentration of a substance, statistically deduced, which should cause during an exposure or, after this one, during a defined period, the death of 50% of the animals exhibited for a specified period. Studies have shown that the CL50 of DMF in rats was: 9400 ppm/2h – 15,000 mg/m3. Thus, the use of DMF to manufacture fiber assemblies by solution electrospinning therefore presents several risks/disadvantages. A first risk is for the operator who has to handle the DMF for the solution electrospinning process. Further, as explained, the solvent is caused to be evaporated almost entirely, ideally entirely. Thus large quantities of solvents end up in the atmosphere surrounding the electrospinning process and must be treated with extreme care. Finally, if the set of fibers is intended to be in contact with humans through its use, for example if the set of fibers is intended to be used as the membrane of an air filtration mask or In a respirator, even minute amounts of solvent in the fibers, caused in particular by incomplete evaporation during the electrospinning process, are undesirable.

There is therefore a need to provide electrospinning processes using a liquid vehicle which is not considered, by virtue of its constituents, to be carcinogenic, mutagenic or toxic for reproduction.

There is also a need to provide electrospinning processes that make it possible to obtain webs of fibers having a greater proportion of beta phase relative to the weight of fibers in order to improve the ferroelectric properties of the web.

Finally, because of the risks of toxicity of nano-objects for humans, there is also a need to provide electrospinning processes making it possible to obtain veils of fibers not containing or containing only very few fibers of diameter less than or equal to 0.1 µm.

GEE & al. (see: Optimizing electrospinning parameters for piezoelectric PVDF

compared the electrospinning of a PVDF solution in a 60:40 (v:v) DMF:acetone mixture and a 60:40 (v:v) DMSO:acetone mixture. DMSO has the advantage of not presenting any harmful character like DMF. Nevertheless, Gee & al. concluded their study by the fact that the membranes electrospun using the DMSO:acetone mixture were not as satisfactory as those obtained by the DMF:acetone mixture. In particular, they noticed a significant increase in the median diameter of the fibers, the presence of gamma phase with beta phase and an increase in fiber density.

In addition, DMSO can have an odor considered unpleasant, often described as garlic. It is therefore particularly undesirable to use it as a solvent for the electrospinning of membranes intended for use in filtering respiratory protection devices because the latter could be felt by the user, even in the form of a trace.

Goals

An object of the invention is to propose a method which makes it possible to manufacture a nonwoven web of fibers of fluorinated polymer(s) using a liquid vehicle which is not considered by its constituents as carcinogenic, neither mutagenic nor toxic for reproduction and does not include DMSO.

Another objective is to propose, at least according to certain embodiments, a process making it possible to obtain a veil and/or a membrane suitable for air filtration, in particular for the filtration of nano and/or sub-micron aerosols .

Another object is to provide, at least according to certain embodiments,

a process which makes it possible to manufacture a non-woven veil of fibers of fluorinated polymer(s), the fibers of which have improved ferroelectric properties.

Another object of the invention is to propose, at least according to certain embodiments, a method making it possible to obtain a web and/or a membrane suitable for the filtration of air intended to be breathed, and therefore presenting no toxicological hazard to human health and does not present an odor deemed to be unpleasant.

Another objective of the invention is, at least according to certain embodiments, to propose a method making it possible to obtain a veil and/or a membrane intended to be used as the filtering part of a filtering device for respiratory protection.

The invention relates to a method for manufacturing a non-woven web of fibers. The process includes:

a) the supply of a solution, respectively of a homogeneous dispersion, comprising at least one fluorinated polymer in a liquid vehicle,

said fluorinated polymer being based on the repeating unit derived from vinylidene fluoride (VDF); And,

b) the electrospinning of the solution, respectively of the homogeneous dispersion, to form said web.

The solution, respectively the homogeneous dispersion, is characterized in that the liquid vehicle comprises at least 50% by weight of a (first) liquid having a Hansen solubility parameter δ _p greater than or equal to 7 MPa ^1/2 and a a boiling point above 100°C. In addition, the liquid vehicle does not include dimethyl sulfoxide (DMSO), and is not considered, by virtue of its constituents, to be carcinogenic, nor mutagenic, nor toxic for reproduction.

According to certain embodiments, the (first) liquid has a Hansen solubility parameter δ _p of 8 MPa ^1/2 to 20 MPa ^1/2 , and preferably of 10 MPa ^1/2 to 19 MPa ^1/2 .

According to certain embodiments, the (first) liquid is chosen from the list consisting of: cyclopentanone, dimethyl phthalate, ethyl acetoacetate, triethyl phosphate, ethyl lactate, gamma-butyrolactone, propylene carbonate, and mixtures thereof.

According to some embodiments, the fluoropolymer is a VDF homopolymer; a copolymer having a repeating unit derived from VDF and at least one repeating unit derived from a monomer other than VDF, the other monomer being chosen from the list consisting of: vinyl fluoride (VF), tetrafluoroethylene ( TFE), trifluoroethylene (TrFE), chlorofluoroethylene (CFE), chlorodifluoroethylene, chlorotrifluoroethylene (CTFE), dichlorodifluoroethylene, trichlorofluoroethylene, hexafluoropropylene (HFP), trifluoropropene, tetrafluoropropene, chloro-trifluoropropene, hexafluoroisobutylene, perfluorobutylethylene, a pentafluoropropene, a perfluoroether, in particular a perfluoroalkylvinylether, ethylene, an acrylic monomer, a methacrylic monomer and their mixture; or a mixture of homopolymer(s) and copolymer(s).

According to certain variants, the (first) liquid has a Hansen solubility parameter δ _p of 15 MPa ^1/2 to 20 MPa ^1/2 , preferably of 15 MPa ^1/2 to 18 MPa ^1/2 . The first liquid may in particular consist of gamma-butyrolactone, propylene carbonate, or a mixture thereof. This variant is particularly suitable when the fluorinated polymer comprises a PVDF or consists of a PVDF.

According to other variants, the (first) liquid has a Hansen solubility parameter δ _p of 8 MPa ^1/2 to 15 MPa ^1/2 , preferably of 10 MPa ^1/2 to 15 MPa ^1/2 . The first liquid may in particular consist of cyclopentanone, dimethyl phthalate, ethyl acetoacetate, triethyl phosphate, ethyl lactate, and their mixture.

According to certain embodiments, the fluoropolymer comprises or consists of: a P(VDF-TrFE), a P(VDF-HFP), a P(VDF-TFE), a P(VDF-TrFE-CFE), a P(VDF-TrFE-CTFE), a P(VDF-TFE-CFE), a P(VDF-TFE-CTFE), and mixtures thereof.

According to certain embodiments, the (first) liquid consists of cyclopentanone.

According to certain embodiments, the liquid vehicle comprises at least a second liquid, the second liquid having a boiling point less than or equal to 100°C. The second liquid can in particular be chosen from the list consisting of: acetone, ethyl acetate, 2-butanone, water and their mixture. Advantageously, the second liquid consists of ethyl acetate or a mixture of ethyl acetate and water.

According to certain embodiments, the liquid vehicle comprises water, the water constituting up to 5% by weight, preferably up to 3% by weight of the liquid vehicle.

According to some embodiments, the liquid carrier is made up of said at least one first liquid and said at least one second liquid.

According to certain embodiments, the mass proportion of first liquid relative to the second liquid is from 20:80 to 80:20, and preferably from 50:50 to 75:25.

According to certain embodiments, the solution, respectively the homogeneous dispersion, has a BROOKFIELD viscosity at 25° C. of 50 to 300 cP, preferentially of 75 to 265 cP, and still preferentially of 80 to 150 cP.

According to certain embodiments, the fluoropolymer has a melt index at 230° C. under a load of 10 kg, of 0.15 g/10 minutes to 15 g/10 minutes, preferably of 1 g/10 minutes to 10 g/ 10 minutes, and more preferably from 3 g/10 minutes to 8 g/10 minutes, as measured according to standard ASTM D1238-13.

According to certain embodiments, the fluoropolymer represents from 3% to 20% by weight, preferably from 6% to 15% by weight, relative to the total weight of solution, respectively of homogeneous dispersion.

The invention also relates to a veil capable of being obtained by the process described above.

The invention finally relates to a solution, or homogeneous dispersion, of at least one fluorinated polymer in a liquid vehicle. The fluoropolymer is based on the repeating unit derived from vinylidene fluoride (VDF). The liquid vehicle comprises at least 50% by weight of a first liquid having a Hansen solubility parameter δ _p greater than or equal to 7 MPa ^1/2 and a boiling point greater than 100°C, and at least a second liquid, the second liquid having a boiling point less than or equal to 100°C. In addition, the liquid vehicle does not include dimethyl sulfoxide (DMSO), and is not considered, by virtue of its constituents, to be carcinogenic, nor mutagenic, nor toxic for reproduction. This solution is claimed as such for any use other than electrospinning.

tricks

schematically represents a first device for electrospinning (“with needle”).

schematically represents a second device for electrospinning (“needleless”).

schematically represents a membrane according to a first embodiment.

schematically represents a membrane according to a second embodiment.

schematically represents a membrane according to a third embodiment.

schematically represents a filtering half-mask comprising a membrane according to the invention.

schematically represents a possible architecture of the filter used in the half-mask according to Figure 6.

Detailed description of the invention

In the present application, the singular forms "un", respectively "le", mean by default "at least one", and respectively "said at least one" (the latter formulations are not always used so as to lighten certain turns of phrase). sentence), unless otherwise indicated.

In all the ranges set out in this application, the terminals are included unless otherwise stated.

Fluoropolymer used in the process

The fluorinated polymer used in the process according to the invention is based on the repeating unit derived from vinylidene fluoride (VDF). The proportion of the repeating unit derived from the VDF represents at least 50% molar relative to the total number of moles of the repeating units of the fluorinated polymer.

According to certain embodiments, the fluoropolymer comprises at least 60%, or at least 70%, or at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 95% , or at least 99% by mole of units derived from VDF. The fluorinated polymer can in particular be a copolymer. The term “copolymer” is understood to mean, in the broad sense, designating a polymer resulting from the copolymerization of at least two types of chemically different monomers, called co-monomers. A copolymer, in the broad sense, has at least two types of repeating units, the (at least two) types being determined by different chemical formulas. It can for example be formed of two, three or four types of repeating patterns. A copolymer, in the strict sense, is formed from exactly two types of repeat units, such as P(VDF-TrFE).

The fluorinated polymer can be a VDF homopolymer or a copolymer having a repeating unit derived from VDF and at least one repeating unit derived from a monomer other than VDF, the monomer being chosen from the list consisting of: fluoride of vinyl (VF), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorofluoroethylene (CFE), chlorodifluoroethylene, chlorotrifluoroethylene (CTFE), dichlorodifluoroethylene, trichlorofluoroethylene, hexafluoropropylene (HFP), trifluoropropene, tetrafluoropropene , a chloro-trifluoropropene, hexafluoroisobutylene, perfluorobutylethylene, a pentafluoropropene, a perfluoroether, in particular a perfluoroalkylvinylether, ethylene, an acrylic monomer, a methacrylic monomer, and their mixture; and a mixture of the aforementioned homopolymer(s) and copolymer(s).

It is understood that all the geometric isomers of the aforementioned fluorinated compounds are included in the terminologies above, such as: 1,1-chlorofluoroethylene (1,1-CFE), 1,2-chlorofluoroethylene (1,2- CFE), 1,2-dichloro-1,2-difluoroethylene, 1,1-dichloro-1,1-difluoroethylene and 1,1,2-trichloro-2-fluoroethylene, 3,3,3-trifluoropropene, 2 -chloro-3,3,3-trifluoropropene (1233xf), 1-chloro-3,3,3-trifluoropropene (1233zd), 1,3,3,3-tetrafluoropropene, 2,3,3,3- tetrafluoropropene (or 1234yf), 3-chloro-2,3,3-trifluoropropene (or 1233yf), 3-chloro-3,3,3-trifluoropropene, 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene.

Among the perfluoroalkylvinylethers, mention may be made of those of general formula: R _f -O-CF-CF ₂ , R _f being an alkyl group, preferably C1 to C4 and for example methyl vinyl ether (MVE) or isopropyl vinyl ether (PVE ).

Among the monomers of acrylic or methacrylic type, mention may be made of: acrylic acid, methacrylic acid, (2-trifluoromethyl)acrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypopyl methacrylate, hydroxyethylhexyl acrylate, hydroxyethyl hexyl methacrylate, and mixtures thereof.

According to certain embodiments, the fluoropolymer or the mixture of fluoropolymers comprises a PVDF or consists of a PVDF. This includes variants in which said at least one fluorinated polymer is a mixture of PVDFs of different molecular weights. PVDF is generally more difficult to dissolve, respectively to disperse homogeneously, in the liquid vehicle than its copolymers. This is the reason why advantageous embodiments have been proposed specifically for PVDFs with in particular a Hansen solubility parameter δ _p of 15 MPa ^1/2 to 20 MPa ^1/2 , preferentially of 15 MPa ^1/2 to 18 MPa ^1/2 .

According to certain variants, said at least one fluoropolymer is a mixture consisting of:

- a PVDF,

- a copolymer chosen from the list of copolymers given above;

the proportion by weight of PVDF relative to that of the copolymer ranging from 1:99 to 99:1, preferably from 10:90 to 90:10, and extremely preferably from 25:75 to 75:25.

According to certain embodiments, the fluoropolymer used in the process comprises, or consists of, a copolymer chosen from the list consisting of: a P(VDF-TrFE), a P(VDF-HFP), a P(VDF- TFE), a P(VDF-TrFE-CFE), a P(VDF-TrFE-CTFE), a P(VDF-TFE-CFE), and a P(VDF-TFE-CTFE).

According to certain variants, said at least one fluoropolymer is a mixture consisting of:

- a PVDF,

- a copolymer chosen from: a P(VDF-TrFE), a P(VDF-HFP), a P(VDF-TFE), a P(VDF-TrFE-CFE), a P(VDF-TrFE-CTFE), a P(VDF-TFE-CFE), and a P(VDF-TFE-CTFE);

the mass proportion of PVDF relative to that of the copolymer ranging from 10:90 to 90:10, preferably from 25:75 to 75:25.

The P(VDF-HFP) advantageously has a molar proportion of repeating units derived from HFP of 1% to 20%.

P(VDF-TFE) advantageously has a molar proportion of repeating units derived from TFE of 8% to 30%, preferentially from 15% to 28%, more preferentially from 18% to 25%, and extremely preferably from 20 % to 22%, relative to the total number of moles of units derived from VDF and TFE.

The P(VDF-TrFE) advantageously has a molar proportion of repeat unit derived from TrFE of 15 to 50%, preferentially from 16% to 35%, preferentially still from 17% to 32%, and extremely preferably from 18% at 28%, relative to the total number of moles of units derived from VDF and TrFE.

According to certain embodiments, the fluoropolymer may have a melt flow index (MFI or else Melt Flow Index) at 230° C. under a load of 10 kg, from 0.10 g/10 minutes to 15 g/10 minutes, such than measured according to ASTM D1238-13. Equipment such as the "Dynisco D4059 B Flowmeter" can be used by determining the cumulative weight that passes through the measuring die after 10 minutes when the device is operated at 230°C and 10 kg load on the polymer molten. The fluorinated polymer preferably has a melt index of 1 g/10min to 10 g/10min, and even more preferably of 3 g/10min to 8 g/10min.

Homogeneous solution or dispersion

By “liquid vehicle”, is meant any mixture of miscible liquids serving as a support for the polymer(s) (and for any other additives). In general, the liquid vehicle may be capable of dissolving said polymer to form a true solution (that is to say single-phase or homogeneous at the molecular level), or on the contrary not be capable of completely dissolving said polymer. The term "homogeneous dispersion" means a dispersion of polymer particles, more or less swollen with vehicle, in a continuous phase of vehicle. The homogeneity of the dispersion is thus a macroscopic homogeneity (that is to say that by observing it with the naked eye the dispersion has a homogeneous appearance), characterized in that the dispersion does not present any granular or macro-separated appearance. The term “homogeneous dispersion” is thus used as opposed to a “heterogeneous dispersion”, that is to say a dispersion with a partially granular macroscopic appearance or presenting a macroscopically visible or gelled phase separation.

According to preferred embodiments, the liquid vehicle used makes it possible to dissolve the fluoropolymer in such a way as to form a true solution. Indeed, the inventors consider that, in this way, it is easier to obtain a nonwoven web of fibers with a higher proportion of beta phase, in particular for the embodiments where the fluorinated polymer comprises, or consists of , PVDF.

According to certain variants, the liquid vehicle used may not make it possible to dissolve the fluoropolymer in such a way as to form a true solution but make it possible to obtain, at the very least, a homogeneous dispersion. Preferably, the homogeneous dispersion is a colloidal suspension, that is to say made up of particles with a size ranging from a few nanometers to a micrometer.

The solution, respectively the colloidal dispersion, can be obtained by adding the fluorinated polymer or the mixture of fluorinated polymers and the constituents of the liquid vehicle in any order and stirring under suitable temperature and hydrodynamic conditions. The temperature during stirring is generally 15°C to 100°C, preferably 20°C to 80°C and extremely preferably 40°C to 65°C. The hydrodynamic conditions depend on the type of agitator used. Agitators promoting axial flow are particularly preferred. The stirring time is usually 30 minutes to 24 hours. The stirring time is preferably less than or equal to 12 hours, more preferably less than or equal to 6 hours, and extremely preferably less than or equal to 4 hours.

The term "Hansen's solubility parameters" means the following three parameters:

δ _d : dispersive component (relating to the energy linked to the forces of dispersion between the molecules of the composition);

δ _p : polar component (relating to the energy linked to the intermolecular dipolar forces between the molecules of the composition); And

δ _h : hydrogen bond component (relating to the energy linked to the hydrogen bonds between the molecules of the composition).

The Hansen solubility parameter δ _p is generally expressed in MPa ^1/2 at a temperature of 25°C and atmospheric pressure (1013 hPa). The book: “Hansen, CM (2007). Hansen solubility parameters: a user's handbook. CRC press” gives the δ _p value for more than 1200 chemical compounds. For a chemical compound not appearing in this work, the Hansen solubility parameter δ _p can be evaluated by Formula I below, known as the Hansen & Beerbower formula:

where: μ is the dipole moment of the chemical compound, expressed in Debye; and V is the molar volume, expressed in cm ³ .mol ^-1 .

The liquid vehicle used in the process according to the invention forms a homogeneous phase of mutually miscible liquids, at least in the proportions used to form the liquid vehicle.

The liquid vehicle comprises at least 50% by weight of a (first) liquid having a Hansen solubility parameter δ _p greater than or equal to 7 MPa ^1/2 and has a boiling point greater than 100°C.

The liquid vehicle does not include dimethyl sulfoxide (DMSO), and is not considered, by its constituents, to be carcinogenic, mutagenic or toxic for reproduction.

“Carcinogenic” means that a substance can, by inhalation, ingestion or skin penetration, cause cancer or increase its frequency.

“Mutagenic” means that a substance can, by inhalation, ingestion or skin penetration, produce hereditary genetic defects or increase their frequency.

“Reproductive toxicant” means that a substance may, by inhalation, ingestion or skin penetration, produce or increase the frequency of non-hereditary harmful effects in the offspring or impair reproductive functions or capacities.

There are several classifications of chemical agents with regard to their CMR properties. For example, the European classification provided for by the so-called “CLP” regulation (Classification, Labeling and Packaging) can be cited.

Other organizations, such as the International Agency for Research on Cancer (IARC), American organizations (for example: US-EPA, OSHA, NIOSH, ACGIH) or European national organizations (for example: German MAK commission).

According to certain embodiments, the liquid vehicle is not considered as CMR, European classification provided for by the regulation called “CLP. Preferably, the liquid vehicle is not considered to be CMR by any of the aforementioned bodies.

Said (first) liquid generally has a Hansen solubility parameter δ _p of 7 MPa ^1/2 to 20 MPa ^1/2 . The (first) liquid can in particular be chosen from the list consisting of: cyclopentanone, dimethyl phthalate, ethyl acetoacetate, triethyl phosphate, ethyl lactate, gamma-butyrolactone, propylene carbonate, and their blend. Said (first) liquid advantageously has a surface tension value less than or equal to 40 mN.m ^-1 , at 25° C. and at 1015 hPa, as measured by methods well known to those skilled in the art (capillary depression, hanging drop, …). The (first) liquid can in particular be chosen from the list consisting of: acetoacetate, cyclopentanone, triethyl phosphate, ethyl lactate, and their mixture.

According to certain advantageous embodiments, said (first) liquid has a Hansen solubility parameter δ _p of 8 MPa ^1/2 to 20 MPa ^1/2 , and preferably of 10 MPa ^1/2 to 19 MPa ^1/2 .

In the embodiments where the fluoropolymer comprises a PVDF, said (first) liquid advantageously has a Hansen solubility parameter δ _p of 15 MPa ^1/2 to 20 MPa ^1/2 , and preferentially of 15 MPa ^1/2 to 18 MPa ^1/2 . The (first) liquid can in particular be chosen from the list consisting of: gamma-butyrolactone, propylene carbonate, or a mixture thereof.

In the embodiments where the fluorinated polymer comprises a VDF copolymer, said (first) liquid advantageously has a Hansen solubility parameter δ _p of 8 MPa ^1/2 to 15 MPa ^1/2 . The (first) liquid can in particular be chosen from the list consisting of: cyclopentanone, dimethyl phthalate, ethyl acetoacetate, triethyl phosphate, ethyl lactate, and mixtures thereof. Preferably, said (first) liquid has a Hansen solubility parameter δ _p of 10 MPa ^1/2 to 15 MPa ^1/2 .

In certain embodiments, in particular in those where the fluoropolymer comprises or consists of: a P(VDF-TrFE), a P(VDF-HFP), a P(VDF-TFE), a P(VDF-TrFE- CFE), a P(VDF-TrFE-CTFE), a P(VDF-TFE-CFE), a P(VDF-TFE-CTFE), and their mixture, the (first) liquid can consist of cyclopentanone. Cyclopentanone a Cyclopentanone has a low surface tension of: 33.31 mN/m and a Hansen solubility parameter _δp of 11.1.

According to certain embodiments, the liquid vehicle comprises at least a second liquid, the second liquid having a boiling point less than or equal to 100°C. The presence of the second liquid has the particular advantage of reducing the boiling temperature of the liquid vehicle and of promoting its evaporation during electrospinning.

According to certain embodiments, the second liquid is chosen from the list consisting of: acetone, ethyl acetate, 2-butanone, water and their mixture. In the embodiments where the second liquid comprises water, the water generally represents at most 5%, and preferably at most 3% by weight of the total weight of the liquid vehicle. Water is generally a non-solvent for the fluoropolymer and therefore can only be introduced in limited amounts. Nevertheless, water has the advantage of increasing the conductivity of the solution, respectively of the homogeneous dispersion.

According to some embodiments, the second liquid consists of ethyl acetate or a mixture of ethyl acetate and water. Ethyl acetate does not present any particular toxicity and has a characteristic fruity odor.

According to some embodiments, the liquid carrier is made up of said at least one first liquid and said at least one second liquid. Advantageously, the mass proportion of first liquid relative to the second liquid is from 20:80 to 80:20, and preferably from 50:50 to 75:25.

According to certain embodiments, the solution, respectively the homogeneous dispersion, has a BROOKFIELD viscosity at 25° C. of 50 to 300 cP, preferentially of 75 to 265 cP, and still preferentially of 80 to 150 cP.

According to certain embodiments, the fluoropolymer represents from 3% to 20% by weight, preferably from 6% to 15% by weight, relative to the total weight of solution, respectively of homogeneous dispersion.

The solution, respectively the homogeneous dispersion, may optionally comprise in addition to the fluoropolymer and the liquid vehicle:

• at least one other polymer different from said at least one fluorinated polymer; and or
• at least one additive.

The other polymer, different from the fluorinated polymer, can only be added insofar as it can be dissolved, or at the very least dispersed homogeneously in the liquid vehicle. According to certain embodiments, the other polymer can be introduced into the liquid vehicle in a mass proportion with said at least one fluorinated polymer of 40:60 to 0:100, preferably of 25:75 to 0.1:99.9 and extremely preferably from 10:90 to 1:99.

The other polymer may in particular be: a poly(methyl methacrylate) (PMMA), a poly(ethyl methacrylate) (PEMA), a poly(methyl acrylate) (PMA), a poly(ethyl acrylate) (PEA), a poly(vinyl acetate) (PVAc), a poly(vinyl methyl ketone) (PVMK), a thermoplastic polyurethane (TPU), a thermoplastic starch, copolymers derived therefrom, such as for example with regard to PMMA : poly(methylmethacrylate-co-ethylacrylate), and mixtures thereof.

The additive may in particular be an additive making it possible to modulate certain electrohydrodynamic properties of the solution, respectively of the homogeneous dispersion, during electrospinning. The additive may in particular be a salt. Examples include NaCl and LiCl or ammonium salts such as: TBAC (tetrabutyl ammonium chloride), TEAC (tetraethylammonium chloride) or TEAB (tetraethylammonium bromide). These salts are advantageously removed by washing with water after formation of the fibers by electrospinning.

According to alternative embodiments, the solution, respectively homogeneous dispersion, consists of the fluoropolymer or mixture of fluoropolymers and of the liquid vehicle. In other words, in these embodiments the solution, respectively the homogeneous dispersion, does not comprise any additive, nor any polymer other than the fluorinated polymer.

Electrospinning process

The invention relates to a method for manufacturing a non-woven web of fibers.

The process includes:

a) the supply of a solution, respectively of a homogeneous dispersion, as presented above; And,

b) the electrospinning of the solution, respectively of the homogeneous dispersion, to form said web.

The term “fiber” is understood to denote a filamentous element, which can generally be described by a diameter and a length.

The term "non-woven veil of fibers" denotes a set of fibers obtained in particular by assembling fibers, without weaving or knitting. A complementary definition has been proposed by the EDANA ( European Disposal and Nonwoven Association ), following the EN ISO 9092 standard, as meaning made of a sheet of individual fibres, oriented directly or randomly, linked by friction, cohesion or adhesion.

Electrospinning is a well-known electrohydrodynamic process, making it possible to manufacture small-sized polymer fibers, in particular fibers with a diameter ranging from a few tens of nanometers to several hundreds of nanometers. When a sufficiently high electrical voltage is applied to a polymer droplet in the molten state or in solution, the droplet becomes charged. An electrostatic repulsion force then opposes the surface tension of the droplet, forcing it to stretch until it forms a cone, called a "Taylor cone". An electrically charged jet is ejected from the top of the Taylor cone and then accelerated by an electric field. The jet expands in the direction of the electric field and thins as it travels toward a grounded collecting electrode. The extension of the jet and its thinning are accompanied by a solidification of polymer fibers. The fibers from the jet are collected directly on the collection electrode, or advantageously on a substrate placed in front of the collection electrode, at the end of their journey.

Electrospinning can notably be “with needle” or “without needle”, as explained schematically by figures 1 and 2 below. In order to facilitate the explanations, we will consider thereafter, purely educational and in no way limiting, the electrospinning of a real solution of fluorinated polymer.

Figure 1 shows the diagram of a "needle" electrospinning installation, generally used in the laboratory. The installation 10 comprises a syringe 11 comprising a solution 12 of fluoropolymer. The syringe is generally fitted with a pump (not shown) making it possible to control the flow of solution on leaving it. Facing the syringe is a collection electrode 14 connected to ground. A high voltage generator 13 between the syringe and the collection electrode 14 generates an electric field. A filament 15, subjected to the electric field, is ejected from the syringe 11, and is preferably deposited on a substrate 16, different from the collection electrode 14.

Figure 2 presents the diagram of a “needleless” electrospinning installation, generally advantageous to allow greater productivity (quantity deposited for a given time), over a larger surface. The installation 20 comprises a bath 21, open, comprising the fluoropolymer solution and a rotating electrode 22 dipping in the bath 21. The speed of rotation of the electrode makes it possible to adapt the flow of solution ejected from the bath. Facing bath 21 and rotating electrode 22 is a collection electrode 24 connected to ground. A high voltage generator 23 between the bath 21/rotating electrode 22 and the collection electrode 24 makes it possible to generate an electric field. Filaments 25, subjected to the electric field, are ejected from the bath 21. They are preferably deposited on a substrate 26, different from the collection electrode 24. The substrate 26 can in particular be a drop-down strip.

Several parameters of the process can be adjusted so as to obtain a veil with advantageous properties, in particular having good filtration efficiency and/or low pressure drop and/or few fibers with a size of less than 100 nm. The parameters are in particular adjusted so as to obtain fibers of the desired size, with a substantially homogeneous appearance and minimizing the presence of beads.

The parameters linked to the polymer and/or to the liquid vehicle are the subject of the present invention.

Other parameters to consider are the fitting parameters. Fitting parameters for devices, such as those shown in Figures 1 and 2, include:

- the inter-electrode voltage: this can generally be adjusted to a value of 5 kV to 40 kV; preferably the inter-electrode voltage is chosen so as to be as low as possible so as to limit the energy consumption of the process and to best prevent any risk, preferably from 9 kV to 25 kV and extremely preferably from 10 kV to 20 kV;

- the distance between the polymer ejection zone and the substrate: the latter is generally adjusted from 5 cm to 30 cm, and preferably from 10 cm to 20 cm;

- the homogeneous solution/dispersion ejection rate: the latter is advantageously chosen so as to be as high as possible depending on the type of equipment (syringe 11 or rotating electrode 22 soaking in the bath 21);

- the temperature of the medium in which the fluoropolymer filament being formed is intended to move: this directly influences the evaporation temperature of the solvent from the solution; preferably, this temperature is close to ambient temperature. It may in particular be from 10°C to 80°C, preferably from 20°C to 60°C and more preferably from 25°C to 45°C.

- the relative humidity in which the forming fluoropolymer filament is intended to move; preferably, this humidity is from 20% to 60% at the temperature of the medium.

- or other specific conditions, for example forced air convection to promote solvent evaporation.

The veil formed by electrospinning does not necessarily require an additional polarization step, since due to the strong electric field exerted, the fibers are in a polarized state.

The veil formed by electrospinning can undergo, after its formation, an annealing step at a temperature below the melting point of the polymer and then cooled to ambient temperature (25° C.). This annealing step makes it possible to possibly evaporate the residual solvent and to possibly increase the crystallinity, and therefore the ferroelectric properties, of the fluoropolymer. The annealing step will usually be followed by a polarization step, by contact or by corona.

Membrane

The veil manufactured according to the invention can be sufficiently thick on its own to form a membrane suitable for the filtration of nano and/or sub-micron aerosols.

Conversely, a nano and/or sub-micron aerosol filtration membrane according to the invention may comprise:

- at least one veil according to the invention; And,

- A porous support layer supporting said at least one veil.

According to certain embodiments, the veil has a basis weight of 0.01 g/m² to 3 g/m². The web preferably has a basis weight of 0.02 g/m² to 1 g/m² and more preferably a basis weight of 0.03 g/m² to 0.5 g/m².

According to certain embodiments, the web has an average thickness of 0.1 μm to 100 μm. The veil preferably has an average thickness of 0.2 μm to 10 μm and, even more preferably, of 0.3 μm to 0.8 μm.

The support layer in particular ensures the good mechanical strength of the membrane. The support layer can be a woven or non-woven set of fibers.

Advantageously, the support layer has a low pressure drop.

According to certain embodiments, in particular when the veil is implemented by electrospinning, the support layer may be the substrate on which the veil is electrospun.

According to certain embodiments, the support layer can be a non-woven assembly of thermoplastic fibers. The support layer may in particular be a nonwoven assembly of fibers chosen from: polyolefins, such as a polyethylene (PE) or a polypropylene (PP), polyesters, such as a poly(ethylene terephthalate) (PET), a poly (butylene terephthalate) (PBT), or a poly(ethylene naphthalate) (PEN), polyamides or copolyamides, such as a PA 11, a PA 12, a PA 6, a PA 6.6, a PA 6 10, polyacrylonitrile (PAN), fluorinated polymers, such as polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP) or polytetrafluoroethylene (PTFE), and mixtures thereof.

According to certain embodiments, the support layer is capable of being obtained by a melt-blown (“ meltblown ”) process or by a spun-topping (“ spunbond ”) process. A “meltblown ” process generally makes it possible to obtain fibers having a diameter ranging from 0.5 μm to 10 μm. A “ spunbond ” process generally makes it possible to obtain fibers having a diameter ranging from 10 μm to 50 μm and is generally less expensive to implement than a “ meltblown ” process.

According to certain embodiments, the support layer has a basis weight of 5 g/m² to 100 g/m², preferentially from 10 g/m² to 50 g/m² and extremely preferably from 15 g/m² to 40 g/m².

Figure 3 shows a multilayer membrane 30 consisting of a support layer 31 and a single veil 32.

Figure 4 shows a multilayer membrane 40 consisting of a support layer 41 covered on each side (“sandwiched”) respectively with a web 42 and a web 43. The webs 42 and 43 may be identical or, on the contrary, different. , in particular have a different composition and/or weight and/or thickness. For example, web 42 may have the same chemical composition as web 43 but have a different basis weight and/or thickness.

Figure 5 shows a multilayer membrane 50 consisting of a support layer 51 successively covered with three webs 52, 53 and 54 according to the invention. The webs 52, 53 and 54 may be identical or, on the contrary, different, in particular have a different composition and/or weight and/or thickness.

Device for filtering nano and/or sub-micron aerosols from the air

The veil and/or the membrane according to the invention can constitute a filter and/or be part of a multilayer assembly constituting a filter, constituting or forming part of a device for filtering nano and/or sub-micron aerosols of the air.

According to certain embodiments, the device for filtering nano and/or sub-micron aerosols of the air is a filtering device for respiratory protection.

There are many different designs of respiratory protective devices, well known to those skilled in the art (INERIS publication, ED 6106, Respiratory protective devices, August 2019 – ISBN 978-2-7389-2503-9).

The respiratory protective device may in particular be a filtering half-mask, a half-mask comprising a filter or a mask comprising a filter. The respirator may be free-breathing or powered-breathing.

According to preferred embodiments of the invention, the respiratory protective device is freely ventilated. The respiratory protective device may in particular be a filtering half-mask as presented below. The breathing apparatus can in particular be a mask for medical use (see standard EN 14683) or an FFP type mask (see standard EN 149).

According to certain embodiments, the filter comprising the veil and/or the membrane only allows the filtration of nano and/or sub-micron aerosols from the air.

According to certain embodiments, the filter comprising the veil and/or the membrane is a combined filter allowing the filtration of nano and/or sub-micron aerosols and the anti-gas filtration.

Figure 6 shows a filtering half-mask 60 comprising a filter 61, means for fixing the filter to the face, and in particular a nose bar 62, an elastic flange 63, as well as an exhalation valve 64 (optional in certain configurations) .

Referring to Figure 7, the filter 61 consists of three layers: two outer layers 72 and 73, one adapted and intended to be in contact with the face of a user, the other adapted and intended to be in contact with the external environment as well as a middle layer constituted by the membrane 30.

Examples

The assembly used comprises a vertical reactor of diameter D (D=10cm), double-jacketed, made of glass, with a maximum capacity of 2 L, provided with a cover, in the center of which passes a stirring wheel, connected to a motor. . The double jacket is connected to a heating/cooling circuit using a heat transfer fluid from a thermostated bath. The stirring impeller is of the 2-stage four-blade type.

Example 1

Cyclopentanone (Sigma Aldrich) (1504 g) was introduced into the reactor at room temperature (25°C). The temperature-controlled bath setpoint was set at 50°, stirring was started at a speed of 200 rpm and the vapor condensation/reflux system was put into operation.

Fluorinated copolymer (96 g), consisting of 20 molar % TrFE and 80 molar % VDF, was introduced in powder form all at once into the reactor. The melt index, MFI, of the polymer was measured at 3.25 g/10 minutes at 230°C under a 10 kg load, according to ASTM D1238-13.

The stirring speed was increased to 400 rpm (blade tip speed of 1.05 m/s) once all the polymer was introduced.

Half an hour after all the polymer had been introduced, the temperature of the temperature controlled bath was increased to 60°C. Three hours after the end of the introduction of the powder and under continuous stirring, it was observed with the naked eye that the polymer was completely dissolved, forming a homogeneous solution with no trace of residual powder.

The polymer solution was recovered, hot, by draining the reactor through the bottom valve.

The dry extract of the solution is measured by gravimetry in a ventilated oven, to give a value close to the theoretical value of 6% wt.

Example 2

Triethyl phosphate (TEP) (Sigma Aldrich) (1440 g) was introduced into the reactor at ambient temperature (25° C.). The temperature-controlled bath setpoint was set at 50°, stirring was started at a speed of 200 rpm and the vapor condensation/reflux system was put into operation.

Fluorinated copolymer (160 g), consisting of 20 molar% of TrFE and 80 molar% of VDF, was introduced in powder form all at once into the reactor. The melt index, MFI, of the polymer was measured at 3.39 g/10 minutes at 230°C under a 10 kg load, according to ASTM D1238-13.

The stirring speed was increased to 400 rpm (blade tip speed of 1.05 m/s) once all the polymer was introduced.

Half an hour after all the polymer had been introduced, the temperature of the temperature controlled bath was increased to 60°C. Three hours after the end of the introduction of the powder and under continuous stirring, it was observed with the naked eye that the polymer was completely dissolved, forming a homogeneous solution with no trace of residual powder.

The polymer solution was recovered, hot, by draining the reactor through the bottom valve.

The dry extract of the solution is measured by gravimetry in a ventilated oven, to give a value close to the theoretical value of 10% wt.

Example 3

Gamma butyrolactone (GBL) (Sigma Aldrich) (1472 g) was introduced into the reactor at ambient temperature (25° C.). The temperature-controlled bath setpoint was set at 50°, stirring was started at a speed of 200 rpm and the vapor condensation/reflux system was put into operation.

Fluorinated copolymer (128 g), consisting of 25 molar% of TrFE and 75 molar% of VDF, was introduced in powder form all at once into the reactor. The melt index, MFI, of the polymer was measured at 5.28 g/10 minutes at 230°C under a 10 kg load, according to ASTM D1238-13.

The stirring speed was increased to 400 rpm (blade tip speed of 1.05 m/s) once all the polymer was introduced.

Half an hour after all the polymer had been introduced, the temperature of the temperature controlled bath was increased to 60°C. Three hours after the end of the introduction of the powder and under continuous stirring, it was observed with the naked eye that the polymer was completely dissolved, forming a homogeneous solution with no trace of residual powder.

The polymer solution was recovered, hot, by draining the reactor through the bottom valve.

The dry extract of the solution is measured by gravimetry in a ventilated oven, to give a value close to the theoretical value of 8% wt.

Example 4

Cyclopentanone (Sigma Aldrich) (1504 g) was introduced into the reactor at room temperature (25°C). The temperature-controlled bath setpoint was set at 50°, stirring was started at a speed of 200 rpm and the vapor condensation/reflux system was put into operation.

Fluorinated copolymer (96 g), consisting of 10% by mass of HFP and 90% by mass of VDF, was introduced in the form of granules all at once into the reactor. The melt index, MFI, of the polymer was measured at 5.0 g/10 minutes at 230°C under a 12.5 kg load, according to ASTM D1238-13.

Half an hour after all the polymer had been introduced, the temperature of the temperature controlled bath was increased to 60°C. Three hours after the end of the introduction of the powder and under continuous stirring, it was observed with the naked eye that the polymer was completely dissolved, forming a homogeneous solution with no trace of residual powder.

The polymer solution was recovered, hot, by draining the reactor through the bottom valve.

The dry extract of the solution is measured by gravimetry in a ventilated oven, as indicated in the text above to give a value close to the theoretical value of 6% wt.

Example 5

Cyclopentanone (Sigma Aldrich) (720 g) was introduced into the reactor at room temperature (25°C). The temperature-controlled bath setpoint was set at 50°, stirring was started at a speed of 200 rpm and the vapor condensation/reflux system was put into operation.

Fluorinated copolymer (80 g), consisting of 10% by mass of HFP and 90% by mass of VDF, was introduced in the form of granules all at once into the reactor. The melt index, MFI, of the polymer was measured at 5.1 g/10 minutes at 230°C under a 12.5 kg load, according to ASTM D1238-13.

Half an hour after all the polymer has been introduced, the set temperature of the thermostated bath is maintained at 50° C. and 720 g of acetone are added to the reactor. Three hours after the end of the introduction of the granules and with continuous stirring, it was observed with the naked eye that the polymer was completely dissolved, forming a homogeneous colloidal dispersion.

The polymer dispersion was recovered, hot, by draining the reactor through the bottom valve.

The dry extract of the dispersion is measured by gravimetry in a ventilated oven, as indicated in the text above to give a value close to the theoretical value of 5.3% wt.

Example 6

Gamma butyrolactone (GBL) (Sigma Aldrich) (1475 g) was introduced into the reactor at ambient temperature (25° C.). The temperature-controlled bath setpoint was set at 50°, stirring was started at a speed of 200 rpm and the vapor condensation/reflux system was put into operation.

Fluorinated homopolymer (120 g), consisting solely of VDF, was introduced in the form of a powder all at once into the reactor. The melt index, MFI, of the polymer was measured at 3.0 g/10 minutes at 230°C under a 12.5 kg load, according to ASTM D1238-13.

The stirring speed was increased to 400 rpm (blade tip speed of 1.05 m/s) once all the polymer was introduced.

Half an hour after all the polymer had been introduced, the temperature of the temperature controlled bath was increased to 60°C. Three hours after the end of the introduction of the powder and under continuous stirring, it was observed with the naked eye that the polymer was completely dissolved, or at the very least formed a colloidal suspension, with no trace of residual powder.

The polymer solution was recovered, hot, by draining the reactor through the bottom valve.

Claims (22)

Process for manufacturing a nonwoven web of fibers comprising:
a) the supply of a solution, respectively of a homogeneous dispersion, comprising at least one fluorinated polymer in a liquid vehicle,
said fluorinated polymer being based on the repeating unit derived from vinylidene fluoride (VDF); And,
b) the electrospinning of the solution, respectively of the homogeneous dispersion, to form said web;
said solution, respectively said homogeneous dispersion, being characterized in that the liquid vehicle comprises at least 50% by weight of a (first) liquid having a Hansen solubility parameter δ _p greater than or equal to 7 MPa ^1/2 and has a boiling point above 100°C;
the liquid vehicle not comprising dimethyl sulfoxide (DMSO), and not being considered, by virtue of its constituents, as carcinogenic, nor mutagenic, nor toxic for reproduction. Process according to claim 1, wherein said (first) liquid has a Hansen solubility parameter δ _p of 8 MPa ^1/2 to 20 MPa ^1/2 , and preferably of 10 MPa ^1/2 to 19 MPa ^1/2 . Process according to Claim 1, in which the (first) liquid is chosen from the list consisting of: cyclopentanone, dimethyl phthalate, ethyl acetoacetate, triethyl phosphate, ethyl lactate, gamma-butyrolactone, propylene carbonate, and their mixture. Process according to any one of claims 1 to 3, in which the fluoropolymer is a homopolymer of VDF; a copolymer having a repeating unit derived from VDF and at least one repeating unit derived from a monomer other than VDF, the other monomer being chosen from the list consisting of: vinyl fluoride (VF), tetrafluoroethylene ( TFE), trifluoroethylene (TrFE), chlorofluoroethylene (CFE), chlorodifluoroethylene, chlorotrifluoroethylene (CTFE), dichlorodifluoroethylene, trichlorofluoroethylene, hexafluoropropylene (HFP), trifluoropropene, tetrafluoropropene, chloro-trifluoropropene, hexafluoroisobutylene, perfluorobutylethylene, a pentafluoropropene, a perfluoroether, in particular a perfluoroalkylvinylether, ethylene, an acrylic monomer, a methacrylic monomer and their mixture; or a mixture of homopolymer(s) and copolymer(s). Process according to any one of Claims 1 to 4, in which the said (first) liquid has a Hansen solubility parameter δ _p of 15 MPa ^1/2 to 20 MPa ^1/2 , preferably of 15 MPa ^1/2 to 18 MPa ^1/2 . A method according to claim 5, wherein said first liquid consists of gamma-butyrolactone, propylene carbonate, or a mixture thereof. A method according to any of claims 5 and 6, wherein the fluoropolymer comprises a PVDF or consists of a PVDF. Process according to any one of Claims 1 to 4, in which the said (first) liquid has a Hansen solubility parameter δ _p of 8 MPa ^1/2 to 15 MPa ^1/2 , preferably of 10 MPa ^1/2 to 15 MPa ^1/2 . Process according to claim 8, in which the (first) liquid is selected from the list consisting of: cyclopentanone, dimethyl phthalate, ethyl acetoacetate, triethyl phosphate, ethyl lactate, and mixtures thereof. Process according to any one of claims 1 to 9, in which the fluoropolymer comprises or consists of: a P(VDF-TrFE), a P(VDF-HFP), a P(VDF-TFE), a P( VDF-TrFE-CFE), a P(VDF-TrFE-CTFE), a P(VDF-TFE-CFE), a P(VDF-TFE-CTFE), and a mixture thereof. Process according to any one of claims 1, 4 and 10, in which the (first) liquid consists of cyclopentanone. A method according to any of claims 1 to 10, wherein the liquid carrier comprises at least a second liquid, the second liquid having a boiling point of 100°C or less. Process according to Claim 12, in which the second liquid is chosen from the list consisting of: acetone, ethyl acetate, 2-butanone, water and their mixture. A method according to claim 12, wherein the second liquid consists of ethyl acetate or a mixture of ethyl acetate and water. A method according to any of claims 12 to 14, wherein the second liquid comprises water, the water constituting up to 5% by weight, preferably up to 3% by weight of the liquid carrier. A method according to any of claims 12 to 15, wherein the liquid vehicle is comprised of said at least one first liquid and said at least one second liquid. Process according to any one of Claims 12 to 16, in which the mass proportion of first liquid relative to the second liquid is from 20:80 to 80:20, and preferably from 50:50 to 75:25. Manufacturing process according to any one of Claims 1 to 17, in which the solution, respectively the homogeneous dispersion, has a BROOKFIELD viscosity at 25°C of 50 to 300 cP, preferentially of 75 to 265 cP, and still preferentially of 80 at 150 cP. Manufacturing process according to any one of claims 1 to 18, in which the fluoropolymer has a melt index at 230°C under a load of 10 kg, of 0.15 g/10 minutes to 15 g/10 minutes, preferably from 1 g/10 minutes to 10 g/10 minutes, and even more preferably from 3 g/10 minutes to 8 g/10 minutes, as measured according to standard ASTM D1238-13. Manufacturing process according to any one of claims 1 to 19, in which the fluoropolymer represents from 3% to 20% by weight, preferably from 6% to 15% by weight, relative to the total weight of solution, respectively of dispersion homogeneous. Veil obtainable by the process according to any one of Claims 1 to 20. Solution, or homogeneous dispersion, of at least one fluoropolymer in a liquid vehicle,
said fluorinated polymer being based on the repeating unit derived from vinylidene fluoride (VDF),
said liquid vehicle comprising at least 50% by weight of a first liquid having a Hansen solubility parameter δ _p greater than or equal to 7 MPa ^1/2 and a boiling point greater than 100°C, and at least a second liquid, the second liquid having a boiling point less than or equal to 100°C;
the liquid vehicle not comprising dimethyl sulfoxide (DMSO), and not being considered, by virtue of its constituents, as carcinogenic, nor mutagenic, nor toxic for reproduction.