EP4168615A1

EP4168615A1 - Electrostatically charged porous nonwoven web, membrane and mask derived therefrom and methods for manufacturing and cleaning

Info

Publication number: EP4168615A1
Application number: EP21740124.9A
Authority: EP
Inventors: Fabrice Domingues Dos Santos; Anthony Bonnet
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2020-06-19
Filing date: 2021-06-17
Publication date: 2023-04-26
Also published as: US20230226501A1; CN115885067A; WO2021255391A1; WO2021255390A1; JP2023530163A

Abstract

The invention relates to a nonwoven web obtained by electrospinning, suitable for filtering nanoscale and/or submicrometer scale aerosols, comprising a multiplicity of fibers having composition C1, the composition C1 containing at least 50% by weight of at least one polymer P1 based on the repeating unit derived from vinylidene fluoride (VDF), said fibres having composition C1 having a degree of crystallinity in the polar phase(s), preferably only in the beta phase, of at least 65% by weight relative to the total weight thereof. The invention also relates to a method for producing the web, to a membrane comprising the web and to a method for washing/sterilizing the web or membrane.

Description

Title: Nonwoven, porous, and electrostatically charged veil, membrane and mask by derivative, and manufacturing and cleaning processes.

Technical area

The invention relates to the field of porous webs of fibers based on fluorinated polymer (s) and membranes derived therefrom.

In particular, the invention relates to such webs for the filtration of nano and / or submicron aerosols comprising a set of fibers based on fluoropolymer.

The invention also relates to the use of such sails, or membranes derived therefrom, in air filtration devices, in particular in filtering respiratory protection devices.

The invention also relates to a method for implementing these webs and / or these membranes.

Finally, the invention relates to a method for cleaning these sails and / or these membranes.

Prior art

In the context of the health crisis linked to the Coronavirus Covid-19, it has proved to be particularly important to develop and produce air filtration devices, in particular filtering devices for respiratory protection (masks for medical use, FFP-type masks , cartridge masks with assisted ventilation or not) or other devices intended for the filtration of the air, more efficient, efficient, durable, and guarantee the good safety and the good health of the users. Regarding filtering respiratory protection devices, it was also important that they are sufficiently comfortable for their user ("good breathability") and reusable.

A key component of air filtration devices, including respiratory protection filter devices, is the presence of one or more porous membranes made from non-woven fibers. These membranes ensure the blocking of potentially harmful aerosols comprising small particles, such as bacteria or viruses.

Several methods are known for making such membranes where nonwoven fibers are or are not deposited on a porous substrate. It is in particular known processes from polymer films (for example: carding or film grinding), from polymers melted by blow molding (for example: meltblown), or from polymers in solution (for example: electrospinning solution, also known by its English term: electrospinning solution) (see: Irwin M. Hutten, in Handbook of Nonwoven Filter Media (Second Edition)).

These processes can be associated with processes making it possible to electrostatically charge the nonwovens, by plasma treatment, and in particular by direct current corona treatment, by friction (triboelectric effect), by wet steam or even by dry steam.

A membrane having fibers whose surface is electrostatically charged will have an ability to block polluting or infectious elements by electrostatic effect, and will thus have an improved filtration efficiency compared to an uncharged membrane.

The membranes are generally composed from fibers, or combinations of synthetic fibers, obtained from thermoplastic polymers such as, without being exhaustive: polyolefins, polyamides, polyvinyls, polyimides, polyacrylates, poly-methacrylates , polyurethanes or else fluoropolymers, and in particular polyvinylidene fluoride. The most widely used polymers to date are polyolefins, and in particular polypropylene.

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 fibers.

The second effect, "diffusion", is linked to the fact that the diffusing particles have a Brownian component in their displacement and are thus susceptible to make contact and adhere to the fibers. This mechanism makes it possible to prevent the passage of particles smaller than the size 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 to 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 size of the pores. The smaller the diameter of the fibers, it is more pronounced.

In addition, to assess the performance of a membrane, several criteria are commonly used, including: efficiency, pressure drop as well as the quality factor.

Efficiency, h (ΐ), is the membrane's ability to block harmful aerosols. It is evaluated by the difference in the concentration of the pollutant upstream and downstream of the filter element according to the following formula:

[Math 1] where Cm and Cost are the pollutant concentrations specifically identified as having to be filtered upstream or downstream of the filter element.

The characteristics of the pollutants specifically studied are generally defined by higher ranges of particle sizes that are sought to be eliminated.

We will generally seek to have maximum efficiency which deteriorates as little as possible as a function of time, temperature, humidity, in more or less aggressive environments, or during stages of treatment, decontamination and / or regeneration. of the membrane.

The efficiency h (ί) can be expressed as two components using the following formula:

[Math 2] h {ί rj. {M (t) + e (t ». in which m (t) is the component related to mechanical effects and e (t) is the component related to electrostatic effects.

It is easy to understand that as the characteristic pore size decreases, the mechanical component of efficiency increases and hence the efficiency of the filter element as well.

The pressure drop, DR, is the pressure difference between the upstream and downstream side of the filter element through which a gas flow may or may not include the pollutants. It thus characterizes the ability of a gas like air to pass through the filter element. In general, the aim will be to have the lowest possible pressure drop, in particular for filter elements entering into filtering respiratory protection devices, without assisted ventilation, because too great a pressure drop causes difficulty in being able to breathe without assistance. through the mask.

It is therefore generally not desirable to reduce the characteristic pore dimensions and / or the porosity too much so as not to increase the pressure drop of the filter element too much.

The quality factor, Qf (t), is defined by the formula:

[Math 3] in which h (ί) and DR are the efficiency and the pressure drop, respectively, as defined above.

The quality factor makes it possible to globally evaluate the performances and the possibilities of use of a filter, by balancing its efficiency in filtering particles of given dimensions, and its pressure drop, therefore its ability to allow a gas flow to circulate, and in particular the air sucked in or the carbon dioxide exhaled.

It is understood that the quality factor depends on an optimization, the characteristic size of the pores, the porosity (volume of the filter element not filled by the fibers) and the electrostatic efficiency. We will seek to increase the efficiency by having pores small enough to block polluting or infectious particles but large enough to allow a low loss of charged. We will also seek to maximize the electrostatic effect which makes it possible to increase the size of the pores while allowing high efficiency, and we will seek to minimize the diameter of the fibers to allow the formation of small pores while maintaining high porosity. . This compromise is all the more difficult to achieve as the particles which one seeks to filter are of small sizes. This is in particular the case for the filtration of viruses which have a characteristic size of the order of 100 nm or a few hundred nanometers.

A method particularly suited to the production of porous nonwoven membranes for protection against viruses is the electrospinning process of polymers in solution. In this process a solution containing the polymer formulation and additives in a suitable solvent formulation is pushed through a narrow, needle-shaped die or nozzle. This pathway is brought to a high electric potential (positive or negative), generally of the order of several kilovolts, or tens of kilovolts. When the solution is sufficiently polar and / or conductive, the electrostatic charges generated in the solution by the field will compensate for surface tension forces forcing the fluid drops to stretch. As the solvent evaporates almost all, if not all, of the solid fibers will form and be deposited on a collector connected to an electrical ground. The set of fibers can thus form a porous nonwoven membrane. This process makes it possible to produce fibers of variable dimensions, and in particular fibers whose diameter has the order of magnitude of ten or a hundred nanometers, which processes such as conventional fusion processes cannot do.

It is known in the prior art, for example in US2019 / 0314746, to obtain a porous nonwoven PVDF web by an electrospinning process, suitable for air filtration. More specifically, US2019 / 0314746 describes the electrospinning process of a PVDF solution, the PVDF used having a molecular weight of 530,000, at 20% w / v (weight for volume) in a mixture of DMF / acetone solvents in proportions 8/2 (v / v), at a voltage of 20 kV. The nanofibers are electrospun on the surface of a drum covered with a non-woven polypropylene (PP) substrate. Once the electrospinning of the nanofibers is completed, the membrane formed by the PVDF veil on its PP substrate is dried at 40 ° C in a vacuum oven to best remove the residual solvent. The dried membrane is then polarized by Corona to fully charge the electrets. The set of PVDF fibers in the membrane has a diameter distribution with a median diameter of 450 nm.

The electrospinning in solution makes it possible to obtain, under certain conditions, fibers of sufficiently small diameters for good breathability and good mechanical filtration efficiency of the membrane for air filtration. Poly (vinylidene fluoride), more commonly known as PVDF, provides hydrophobic and chemically resistant membranes. PVDF is a semi-crystalline thermoplastic polymer, which exhibits polymorphism, that is, it can crystallize in different crystalline phases: a, b, y and d. 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 nonpolar character.

The alpha phase can be described by sequences of TGTG conformation (Left Trans + Left Trans -). This is the only non-polar phase.

The beta phase can be described by sequences of uniquely “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, in particular the gamma phase, which can be described by chains of T3GT3G conformation. It is polar but much less than the beta phase. The delta phase is also polar, but has been little studied.

The polar phases, especially the more 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 (E _c ), allows the orientation of the dipoles formed by the CF bonds in the same direction. This orientation of the dipoles, sufficiently stable over time due to ferroelectric properties, gives the material a remanent polarization with zero electric field. Thus, the presence of beta phase in PVDF fibers is particularly advantageous for air 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), electrospinning of solutions of PVDF in dimethylformamide (DMF). By varying certain parameters of the process, in this case the concentration of PVDF in the solution and the voltage applied during the electrospinning, the authors manage to obtain a veil of PVDF fibers having 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 level of 37% to 47% by weight relative to the weight of fibers.

It is known from Baqueri & al. (see: Influence of Processing conditions on polymorphie 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 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 level of 44% by weight relative to the weight of fibers. In addition, their median diameter is 55 nm.

There is a need to provide webs of fibers having a proportion of beta phase to the greater weight of fibers in order to improve the ferroelectric properties of the web.

Moreover, due to the limited solubility of PVDF in a small number of generally quite toxic solvents, such as DMF, the implementation of an electrospinning process of PVDF fibers in solution can be rather tedious due to the handling of large quantities of these solvents. It should also not be overlooked, in certain cases at least and to a certain extent, that these solvents can remain impregnated in the PVDF fibers. This poses potential health and safety concerns for users, in particular, if the membranes are used to manufacture products. filtering respiratory protection devices. There is therefore a need to do away with the use of toxic solvents, or at the very least to use less toxic solvents, to manufacture a fluoropolymer veil and / or a membrane derived therefrom.

In addition, it is preferable, because of the risks of toxicity of nano-objects for humans, that the veil and / or the membrane derived from it does not contain or only contains very few fibers with a diameter less than or equal to 0.1 pm. It is therefore necessary to develop veils and / or membranes by derivative whose electrostatic efficiency component is improved so as to possibly compensate for a loss of mechanical efficiency, due to the use of fibers having a diameter greater than 0.1 μm.

Goals

The objective of the invention is to provide a web and / or a membrane for the filtration of nanometric and / or submicron aerosols meeting at least one of the aforementioned needs.

An objective of the invention is to provide, at least according to certain embodiments, a web and / or a membrane suitable for filtering air, the fibers of which have improved ferroelectric properties.

Another objective of the invention is to provide, at least according to certain embodiments, a veil and / or a membrane suitable for filtering air intended to be breathed in, and therefore not presenting any toxicological danger to human health. .

Another objective of the invention is, at least according to certain embodiments, to provide a veil and / or a membrane intended to be used as a filtering part of a filtering respiratory protection device.

Another object of the invention is to provide, at least according to certain embodiments, a web and / or a membrane for filtering air which, for a given pressure drop, has improved efficiency.

Another objective of the invention is to provide, at least according to certain embodiments, a web and / or a membrane for filtering the air which, for a given efficiency, has a lower pressure drop. Another objective of the invention is to provide, at least according to certain embodiments, a web and / or a membrane for filtering air, the electrostatic efficiency of which is stable over time, in particular under various operating conditions. humidity and temperature.

Another object of the invention is to provide, at least according to certain embodiments, a veil and / or a membrane "durable", that is to say having a low impact on the environment. In particular, one objective is to provide a web and / or a membrane for filtering air which can be reused after cleaning and / or sterilization.

Other objectives arising directly from the aforementioned objectives are in particular to:

- proposing a process for manufacturing the veil and / or the membrane;

- Provide a filter comprising the web and / or the membrane as well as any assembly on which the filter can be mounted removably or not;

- provide a method for washing and / or sterilizing the veil and / or the membrane, a derivative filter, or even an assembly on which the filter is mounted removably or not.

Summary of the invention

The invention relates to a nonwoven, porous and electrostatically charged web, suitable for the filtration of nano and / or submicron aerosols. It comprises a multiplicity of fibers of composition C1. Composition C1 comprises at least 50% by weight of at least one polymer P1 based on the repeating unit derived from vinylidene fluoride (VDF). The fibers of composition C1 have a degree of crystallinity in polar phase (s), preferably in beta phase only, of at least 65% by weight, relative to their total weight.

Thus the web according to the invention, due in particular to better ferroelectric properties, has improved electrostatic efficiency.

According to certain embodiments, the fibers of composition C1 have a degree of crystallinity in polar phase (s), preferably in only beta phase, of at least 75%, or of at least 80%, or of at least 85%, or at least 90%, or at least 95%, or at least 96%, or at least 97%, or at least 98%, or at least 99% by weight, based on their total weight. According to some embodiments, the polymer P1 is selected from the group consisting of: a VDF homopolymer; a copolymer having a repeat unit derived from VDF and at least one repeat 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), a chlorofluoroethylene (CFE), a chlorodifluoroethylene, chlorotrifluoroethylene (CTFE), dichlorodifluoroethylene, a trichlorofluoroethylene, hexafluoropropylene (FIFP), a trifluoropropropene, trifluoropropene, a tetoropropene hexafluoroisobutylene, perfluorobutylethylene, a pentafluoropropene, a perfluoroether, in particular a perfluoroalkylvinylether, ethylene, an acrylic monomer, a methacrylic monomer and their mixture; and a mixture of homopolymer (s) and copolymer (s).

According to some embodiments, the polymer P1 is a PVDF, a P (VDF-HFP), a P (VDF-TFE), a P (VDF-TrFE), or a mixture thereof.

According to certain embodiments, said at least one polymer P1 is a mixture consisting of:

- a PVDF,

- a copolymer chosen from: P (VDF-HFP), P (VDF-TFE) and P (VDF-TrFE); the mass proportion 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 polymer P1 represents at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 97.5%, or at least 99, 0%, by weight of composition C1.

According to certain embodiments, composition C1 further comprises at least one RG polymer chosen from the list consisting of: a poly (methyl methacrylate) (PMMA), a poly (ethyl methacrylate) (PEMA), a poly ( methyl acrylate) (PMA), poly (ethyl acrylate) (PEA), poly (vinyl acetate) (PVAc), poly (vinyl methyl ketone) (PVMK), thermoplastic polyurethane (TPU), thermoplastic starch, copolymers derived therefrom, and mixtures thereof. According to certain embodiments, the polymer P1 consists of a PVDF and the polymer P1 ′ consists of a PMMA, the proportion by mass of P1 ′ relative to the sum of the masses of the polymers P1 and P1 ′ being 15% at 40%, preferably from 16% to 30%, and extremely preferably from 17% to 23%.

According to certain embodiments, the veil according to the invention consists of fibers of composition C1.

According to certain embodiments, the web has a basis weight of 0.01 g / m ² to 3 g / m ² , preferably from 0.02 g / m ² to 1 g / m ² , and extremely preferably from 0.03 g / m ² to 0.5 g / m ² .

According to certain embodiments, the web comprises less than 1%, preferably less than 0.5%, and more preferably less than 0.1%, by number of fibers having a diameter strictly less than 100 nm.

The invention also relates to a method of manufacturing a nonwoven, porous and electrostatically charged web, suitable for the filtration of nano and / or submicron aerosols, the web being according to the embodiments described above. The process includes:

- the provision of at least one composition C1, said composition C1 comprising at least 50% by weight of at least one polymer P1 based on a repeating unit obtained from VDF;

a step of forming the veil by electrospinning of composition C1.

The invention further relates to a membrane suitable for the filtration of nano and / or submicron aerosols comprising:

- at least one veil according to the embodiments described above; and,

- a support layer supporting said web.

According to certain embodiments, the web within the membrane has a basis weight of 0.01 g / m ² to 3 g / m ² , preferably from 0.02 g / m ² to 1 g / m ² , and extremely preferably from 0.03 g / m ² to 0.5 g / m ² .

According to certain embodiments, the support layer is a nonwoven set of fibers chosen from: polyolefins, such as polyethylene (PE) or polypropylene (PP), polyesters, such as 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, a polyacrylonitrile (PAN), fluoropolymers, such as a polyvinylidene fluoride (PVDF), a fluorinated ethylene propylene (FEP) or a polytetrafluoroethylene (PTFE), and their mixture.

Finally, the invention relates to a method for washing / sterilizing a veil according to the embodiments described above or of a membrane according to the embodiments described above comprising a heat treatment step implemented. at a temperature of 40 ° C to 90 ° C, preferably from 55 ° C to 85 ° C, and extremely preferably at a temperature of 65 ° C to 80 ° C.

Figures

[Fig. 1] schematically represents a first device for electrospinning (“with needle”).

[Fig. 2] schematically shows a second device for electrospinning (“without needle”).

[Fig. 3] schematically shows a membrane according to a first embodiment.

[Fig. 4] schematically shows a membrane according to a second embodiment.

[Fig. 5] schematically shows a membrane according to a third embodiment.

[Fig. 6] schematically shows a filtering half-mask comprising a membrane according to the invention.

[Fig. 7] schematically represents a possible architecture of the filter used in the half-mask according to Figure 6.

Detailed description of the invention

Sail The invention relates to a nonwoven, porous and electrostatically charged web, suitable for the filtration of nano and / or submicron aerosols, comprising a multiplicity of fibers of composition C1. Composition C1 comprises at least 50% by weight of at least one polymer P1 based on a repeating unit obtained from VDF. The fibers of composition C1 have a degree of crystallinity in polar phase (s) of at least 65% by weight relative to the total weight of fibers. Advantageously, the beta phase is the majority polar phase, that is to say it represents more than 50% by weight of the polar phases. Preferably, the beta phase represents more than 80%, or even more than 95% of the polar phases. In many cases, the gamma and / or delta phases are not detected, and the fibers are then considered to consist only of the beta phase as the polar crystalline phase.

The beta phase can be described by chains of all-trans (T) conformations along the polymer chains P1. It is the most polar phase among the different possible phases that the polymer P1 can adopt. Due to the presence of crystals in the form of beta phase, the polymer P1 is ferroelectric. It can be characterized by a cycle of hysteresis of the electric displacement-applied electric field curve. Its coercive field at 25 ° C is typically greater than or equal to 40 V / pm. Its remanent polarization at 25 ° C is quite high, and can typically reach a value greater than 40 mC / m ² .

Thus, the fibers of the web according to the invention, in particular the fibers of composition C1, are polarizable at a relatively weak coercive electric field and exhibit a relatively high remanent polarization. Polarized fibers form permanent dipoles which are stable over time and against humidity (hydrophobicity). Polarized fibers are also temperature stable. This makes it possible to consider methods of washing / sterilizing the veil and / or a membrane by deriving it and reusing the latter without significant loss of filtration efficiency.

The term “porous” is understood to mean that the web has a set of empty spaces called pores. The pores are advantageously mainly open pores, i.e. they can be connected between them to form very fine channels. This makes it possible to make the veil and therefore any membrane by drifting permeable to air.

By "electrostatically charged" is meant that the web has dipole charges and, where appropriate, space charges.

The term "aerosol" is understood to denote a suspension in a gas, in particular air, of solid and / or liquid particles having a negligible fall speed. In air at 25 ° C and 1015 hPa, this generally corresponds to particles smaller than about 100 µm. Aerosol particles with their three external dimensions less than 1 micrometer (also called PM1) are referred to as submicron. Aerosol particles having their three external dimensions of less than 100 nanometers are referred to as nanometric.

Sub-micron or nanometric aerosols include dust, mists and mists, as well as bioaerosols.

Dust, mists and fog can be emitted by automobile traffic (incomplete combustion) or certain industrial activities (particles of chemical and / or thermal origin, or secondary particles, formed during a change of state of the material , during a chemical reaction or during gas condensation or liquid solidification steps.

Bioaerosols are aerosols containing living microorganisms (viruses, bacteria, molds and protozoa) or substances or products from these organisms (eg: toxins, dead microorganisms or fragments of microorganisms). Bioaerosols are ubiquitous in the environment and in the workplace. They can come from people, animals, plants and manipulated material, or be generated by a process, for example. In the case of the Covid 19 virus, the virus can be present in the air as droplets propelled by sneezing, coughing, spitting, or emitted by simple exhalations.

There are various measurement methods, indirect (for example by sampling, measurement of concentration and microscopic observation) or direct (for example by electrical methods), well known to those skilled in the art, in order to evaluate the concentration of particles and their particle size distribution in an aerosol. Aerosols comprising NaCl particles with sizes ranging from 50 nm to 500 nm can advantageously be used to test the effectiveness of the veil, or of the membrane drifting, against loads of the bioaerosol type.

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

The term “nonwoven web of fibers” is understood to denote a set of fibers obtained in particular by assembling fibers, without weaving or knitting. An additional definition has been proposed by the EDANA (European Disposai and Nonwoven Association), according to the EN ISO 9092 standard, as meaning made of a sheet of individual fibers, oriented directly or at random, linked by friction, cohesion or adhesion.

The expression "degree of crystallinity in the polar phase" is understood to mean the proportion by mass of crystals being in a polar phase relative to the total weight of fiber. It can be obtained by making the product of the rate of crystallinity of the fiber by the relative rate of polar crystalline phase (s) within the crystalline phases.

The "degree of crystallinity" can be measured by wide angle x-ray scattering (WAXS). This gives a spectrum of the intensity diffused as a function of the diffraction angle. This spectrum identifies the presence of crystals, when peaks are visible on the spectrum in addition to the amorphous halo. In the spectrum, we can measure the area of the crystal peaks (denoted AC) and the area of the amorphous halo (denoted AH). The mass proportion of crystalline phase in the fiber is then calculated by the ratio: (AC) / (AC + AH).

Alternatively, one method of quickly estimating the rate of crystallinity is to measure the enthalpy of fusion of fibers (DH) by Differential Scanning Calorimetry (DSC) on first heat at a temperature ramp of 10 ° C / min. The mass proportion of crystalline phase in the fiber is then estimated by the ratio: (AHm + AHc) / DH100%, in which DHiti is the enthalpy of fusion, DHo is the enthalpy associated with the Curie transition and DH100% is l theoretical enthalpy of a 100% crystalline sample.

The relative rate of polar crystalline phase (s) in the crystalline phases corresponds in particular to the mass proportion of beta, gamma and delta phases in the crystalline phases. It can be determined by different techniques such as Differential Scanning Calorimetry (DSC), X-ray spectroscopy or Fourier transform infrared spectroscopy (FTIR). The beta phase being the most polar phase and / or the gamma and delta phases being able to be minority or nonexistent, the relative rate of polar crystalline phase (s) in the crystalline phases can generally be simplified, to a greater or lesser extent. approximate, as the beta phase rate only in the crystalline phases.

In addition, the state of the art shows that the crystal phases of fibers obtained by electrospinning PVDF are almost exclusively alpha and beta. In order to estimate the relative proportion, F (P), of beta phase to crystal phases in a sample from its infrared spectrum, we use the relative intensities and characteristic band absorption coefficients of the two phases. F () is given by the relation:

[Math 4] in which: x _a and C _b are the relative fractions of alpha and beta phase in the crystal phases,

A _a is the absorbance of a characteristic band of the alpha phase, for example at 766cm ¹ ,

A _b is the absorbance of a band characteristic of the beta phase, for example at 840cm ¹ ,

K _a is the absorption coefficient corresponding to the characteristic wavelength of the alpha phase (for 766 cm ¹ , K _a is estimated at 6, 1.10 ⁴ ).

K _b is the absorption coefficient corresponding to the characteristic wavelength of the beta phase (for 840 cm ¹ , K _b is estimated at 7.7.10 ⁴ ).

The term “copolymer” is understood in the broad sense to denote a polymer resulting from the copolymerization of at least two types of chemically different monomers, called comonomers. A copolymer, in the broad sense, is therefore formed of at least two repeat patterns. It can for example be formed of two, three or four repeating patterns. A copolymer, in the strict sense, is formed of exactly two repeating units, such as, for example, P (VDF-TrFE).

The term “mixture of polymers” is understood to denote a macroscopically homogeneous polymer composition. The term encompasses mixtures of compatible polymers, that is to say miscible, the mixture exhibiting a glass transition temperature intermediate to those of these polymers considered individually. The term also encompasses such compositions composed of phases which are immiscible with one another and dispersed on a micrometric scale.

The term “melting temperature” is understood to denote the temperature at which an at least partially crystallized polymer changes to a viscous liquid state. The melting temperature can be measured by differential scanning calorimetry (DSC) according to standard NF EN ISO 11357-3: 2018, in second heating, using a heating rate of 10 ° C / min.

In the present application, the singular forms “one”, respectively “the”, mean by default “at least one”, and respectively “said at least one” (these latter formulations are not always used so as to alleviate certain turns of phrase. sentence), unless otherwise noted.

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

According to certain embodiments, the fibers of composition C1 have a degree of crystallinity in polar phase (s) of at least 65%, and preferably of at least 75%, or of at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 96%, or at least 97%, or at least 98%, or at least 99% by weight relative to their total weight.

Preferably, the fibers of composition C1 have a degree of crystallinity in the beta phase of at least 65%, and preferentially of at least 75%, or of at least 80%, or of at least 85%, or of at least 90%, or at least 95%, or at least 96%, or at least 97%, or at least 98%, or at least 99% by weight relative to their total weight. Advantageously, the fibers of composition C1 have a degree of crystallinity of at least 60%, or of at least 65%, or of at least 70%, or of at least 75%, or of at least 80%. , or at least 85%, or at least 90%, or at least 95%, or at least 99%.

Advantageously, the fibers of composition C1 have a relative rate of polar crystalline phase (s), in particular of beta phase, of at least 85%, or of at least 90%, or of at least 95 %, or at least 99%.

The level of crystallinity and / or the relative level of polar crystalline phase (s) can be increased in various ways, as shown in embodiments below.

According to some embodiments, the polymer P1 is selected from the group consisting of: a VDF homopolymer; a copolymer having a repeat unit derived from VDF and at least one repeat 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), a chlorofluoroethylene (CFE), a chlorodifluoroethylene, chlorotrifluoroethylene (CTFE), dichlorodifluoroethylene, a trichlorofluoroethylene, hexafluoropropylene (HFP), a trifluoropropropene, trifluoropropene, a tetoropropene 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 above terminologies, 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: Rf-O-CF-CF2, Rf being an alkyl group, preferably C1 to C4, and for example methyl vinyl ether (MVE) or isopropyl vinyl ether (PVE).

Among the acrylic or methacrylic type monomers, 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 a mixture thereof.

In the embodiments where P1 comprises a copolymer, the latter is advantageously a random copolymer.

In preferred embodiments, the polymer P1 is a PVDF, a P (VDF-HFP), a P (VDF-TFE), a P (VDF-TrFE), or a mixture thereof.

According to certain embodiments, said at least one polymer P1 consists of PVDF. This includes mixtures of PVDFs, in particular PVDFs having different molecular weight molecular masses.

According to some embodiments, said at least one polymer P1 consists of a P (VDF-HFP), or of a P (VDF-TFE), or of a P (VDF-TrFE). This includes mixtures of copolymers, for example P (VDF-TrFE), having different monomer ratios and / or different molecular weight molecular weights.

- a PVDF,

- a copolymer chosen from: P (VDF-HFP), P (VDF-TFE) and P (VDF-TrFE); the mass proportion of PVDF relative to that of the copolymer ranging from 1: 99 to 99: 1.

Preferably, the proportion by mass of PVDF relative to that of the copolymer is from 10:90 to 90:10. More preferably, the proportion by weight of PVDF relative to that of the copolymer is from 25:75 to 75:25.

The P (VDF-FIFP) advantageously has a molar proportion of repeating unit derived from the FIFP of 15% to 35%. The P (VDF-TFE) advantageously has a molar proportion of repeating unit derived from TFE of 8% to 30%, preferably from 15% to 28%, more preferably 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 repeating unit derived from TrFE of 15 to 50%, preferably from 16% to 35%, more preferably from 17% to 32%, and extremely preferably from 18%. at 28%, relative to the total number of moles of the units derived from VDF and TrFE.

According to certain embodiments, the polymer P1 has a melt index at 230 ° C under a load of 12.5 kg, from 0.1 to 15 g / 10 minutes, preferably from 1 to 10 g / 10 minutes, and again preferably from 3 to 8 g / 10 minutes, as measured according to the standard ASTM D1238-13.

Composition C1 comprises at least 50% by weight of polymer P1 relative to the total weight of C1. Sufficiently high proportions of polymer P1 in C1 make it possible to guarantee good crystallization of C1 in predominantly ferroelectric form. According to certain embodiments, composition C1 comprises at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 97.5%, or at least 99.0% of the polymer P1.

According to certain embodiments, composition C1 can also comprise at least one PT polymer other than the polymer P1. The PT polymer can in particular be chosen from the list consisting of: a poly (methyl methacrylate) (PMMA), a poly (ethyl methacrylate) (PEMA), a poly (methyl acrylate) (PMA), a poly ( ethyl acrylate) (PEA), poly (vinyl acetate) (PVAc), poly (vinyl methyl ketone) (PVMK), thermoplastic polyurethane (TPU), thermoplastic starch, copolymers derived therefrom, and mixtures thereof .

According to certain embodiments, composition C1 comprises a polymer P1 and a PT polymer, P1 consisting of a PVDF and PT consisting of a PMMA. Advantageously, the mass proportion of PMMA relative to the sum of the masses of PMMA and PVDF is advantageously from 15% to 40%, preferably from 16% to 30%, and even more preferably from 17% to 23%. The addition of PMMA to PVDF in these proportions makes it possible to significantly increase the level of crystallinity in the beta phase and only affects the level of crystallinity to a lesser extent.

According to some embodiments, composition C1 can further include a number of additives. An example of an additive is, for example, an additive with a bactericidal or fungicidal effect. Composition C1 preferably comprises less than 5% by weight, or less than 4% by weight, or less than 3% by weight, or less than 2% by weight, or less than 1% by weight of additive.

Advantageously, composition C1 does not include an electrically and / or thermally conductive additive, such as carbon nanotubes, graphene or even an organosilicate. Indeed, such conductive additives can have a negative effect on the stability of the space charges that can participate in the induction efficiency (electrostatic efficiency) of the membrane. In particular, they are likely to cause premature discharge of fibers over time or premature in specific environments (eg washing and / or sterilization).

Likewise, and advantageously, composition C1 does not include any inorganic ferroelectric particle, such as ferrite particles, or BaTiO3 particles.

Likewise, and advantageously, composition C1 does not include a nanofiller, that is to say a filler having at least one dimension less than or equal to 100 nm. Indeed, such loads would be likely to present risks by inhalation for human health.

Alternatively to these embodiments, composition C1 can consist solely of polymer P1.

The web generally comprises at least 50% by weight of fibers of composition C1 relative to the total weight of the web. According to some embodiments, the haze comprises at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 97.5%, or at least 99 , 0% fibers of composition C1.

According to certain embodiments, the veil can also comprise at least one composition C1 ′ different from composition C1. This other composition can be a composition consisting of at least 50% by weight of at least one polymer other than P1. This other composition can in particular be a composition consisting of at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95% by weight of 'another polymer than P1. The polymer other than P1 can be one of the aforementioned polymers P1 ′. The polymer other than P1 can also be a polymer chosen from the list consisting of: a polyolefin, such as a polyethylene or a polypropylene, a polyamide (PA 11; PA 12; PA 6; PA 6.6; PA 6.10) , a poly (ethylene terephthalate) (PET), a polyaryletherketone, a polyether sulfone, a polymethacrylic ester, a polyacrylic ester, a polyethylene oxide (PEO), a polyethylene glycol (PEG), a polystyrene (PS), an acid polylactic acid (PLA), a polyacrylic acid (PA), a polyvinyl alcohol (PVA), a polysulfone, a polyacrylonitrile, a polyurethane, a polycaprolactone, a polyimide, a fluoropolymer, such as a PVDF, a P (VDF-HFP), one P (VDF-TFE), one P (VDF-CFE), one P (VDF-TrFE-CFE), one P (VDF-T rFE-CTFE), polyvinyl fluoride (PVF), polychlorotrifluoroethylene (PCTFE) , polytetrafluoroethylene (PTFE), poly (ethylene-co-tetrafluoroporpene (ETFE), poly (tetrafluoroethylene-co-perfluoropropyl ether) (PFA), poly (ethylene-co-chlorotrifluoroethylene) (E-CTFE), u n poly (tetrafluoroethylene co-perfluoropropene) (E-CTFE), a polymethyl methacrylate (PMMA), a copolymer of PMMA, such as a poly (methylmethacylate-co-ethylacrylate) or a PMMA-PS block copolymer, a poly (methacrylate of ethyl) (PEMA), poly (methyl acrylate) (PMA), poly (ethyl acrylate) (PEA), poly (vinyl acetate) (PVAc), poly (vinyl methyl ketone) (PVMK) , thermoplastic polyurethane (TPU), thermoplatic starch, copolymers derived therefrom, and mixtures thereof.

As an alternative to these embodiments, the web can consist solely of fibers of composition C1.

The fibers of the web advantageously have a median diameter strictly greater than 100 nm. The diameter of the fibers and their distribution can be estimated by scanning electron microscopy (SEM), counting and analysis by dedicated software. According to certain embodiments, the median diameter of the fibers of the web is greater than or equal to 150 nm, or greater than or equal to 200 nm, or greater than or equal to 250 nm.

According to some embodiments, the median diameter of the fibers of the web is less than or equal to 1600 nm, or less than or equal to 1400 nm, or less than or equal to 1200 nm, or less than or equal to 1000 nm, or less than or equal to 800 nm, or less than or equal to 600 nm, or less than or equal to 550 nm, or less than or equal to 500 nm, or less than or equal to 450 nm.

These embodiments are particularly advantageous when the veil is intended for use in a filtering device for respiratory protection because of the potential risks generated by the breathing of nanometric objects, that is to say having at least one size dimension. less than 100 nm.

According to certain embodiments, the median diameter of the fibers of the web can in particular be from 150 nm to 600 nm, preferably from 200 nm to 500 nm, and even more preferably from 250 nm to 450 nm.

According to some embodiments, the web has a basis weight (basis weight) of 0.01 g / m ² to 3 g / m ² . The basis weight can be estimated by simply weighing a given area, for example 200 mm x 250 mm, preferably after baking to ensure the absence of residual solvent. The web preferably has a basis weight of 0.02 g / m ² to 1 g / m ² and, more preferably, a basis weight of 0.03 g / m ² to 0.5 g / m ² .

According to some embodiments, the web has an average thickness of 0.1 µm to 100 µm. The average thickness can, for example, be estimated using a mechanical micrometer, an optical or laser sensor, or by optical microscopy or by scanning electron microscopy (SEM). The web preferably has an average thickness of 0.2 μm to 10 μm and, more preferably, from 0.3 μm to 0.8 μm.

According to some embodiments, the web has a pressure drop less than or equal to 500 Pa for a nominal air flow rate of 95 L / min and / or a pressure drop less than or equal to 100 Pa for a nominal air flow of 95 L / min. 30 L / min air (see standard EN149 + A1: 2009). The web preferably has a pressure drop of less than or equal to 350 Pa, preferably less than or equal to 250 Pa, preferably less than or equal to 100 Pa, and extremely preferably less than or equal to 50 Pa for an air flow rate of 95 L / min. The web preferably has a pressure drop of less than or equal to 75 Pa, preferably less than or equal to 50 Pa and extremely preferably less than or equal to 25 Pa for an air flow rate of 30 L / min.

According to some embodiments, the membrane has an efficiency of at least 75% for aerosols of a nebulized NaCl solution (particle size ranging from 50 nm to 500 nm). The membrane can in particular have an efficiency of at least 80%, or of at least 85%, or of at least 90%, or of at least 94%, or of at least 95%, or of at least at least 96%, or at least 99%, or at least 99.90%, or at least 99.95%.

According to certain embodiments, the units derived from VDF in the polymer P1 are derived, at least in part, from a bio-based VDF. The term “biobased” means “derived from biomass”. This improves the ecological footprint of the membrane. Bio-based VDF can be characterized by a renewable carbon content, i.e. carbon of natural origin and originating from a biomaterial or biomass, of at least 1 atomic% as determined by the carbon content. 14C according to standard NF EN 16640. The term “renewable carbon” indicates that the carbon is of natural origin and comes from a biomaterial (or biomass), as indicated below. According to some embodiments, the bio-carbon content may be greater than 5%, preferably greater than 10%, preferably greater than 25%, preferably greater than or equal to 33%, preferably greater than 50%, of preferably greater than or equal to 66%, preferably greater than 75%, preferably greater than 90%, preferably greater than 95%, preferably greater than 98%, preferably greater than 99%, advantageously equal to 100%.

Process

A method for manufacturing a web according to the invention comprises a step of forming the web by electrospinning (electrospinning) of at least one composition C1. Electrospinning 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 droplet of polymer in the molten state or in solution, the droplet becomes charged. An electrostatic repulsion force then opposes the surface tension of the droplet forcing the latter 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 extends in the direction of the electric field and thins as it travels toward a grounded collection electrode. The extension of the jet and its thinning are accompanied by a solidification of polymer fibers. The fibers resulting from the jet are recovered directly on the collection electrode, or advantageously on a substrate placed in front of the collection electrode, at the end of their journey. The electrospinning can in particular be “with needle” or “without needle”, as explained schematically by Figures 1 and 2 below. In order to facilitate the explanations, we will consider hereafter, purely for educational purposes and in no way limiting, that the veil consists of a single composition C1, itself made up of the polymer P1.

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 polymer P1. The syringe is generally fitted with a pump (not shown) allowing the flow of solution to be controlled as it exits. 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.

FIG. 2 shows the diagram of a “needleless” electrospinning installation, generally advantageous in order to allow greater productivity (quantity deposited for a given time), over a larger surface. The installation 20 comprises a bath 21, open, comprising the polymer P1 in a fluid state (in solution, in the molten state, etc.) and a rotating electrode 22 immersed in the bath 21. The speed of rotation of the electrode makes it possible to adapt the flow of composition C1 being ejected from the bath. Facing the bath 21 and the rotating electrode 22 is a collecting electrode 24 connected to earth. A high voltage generator 23 between the bath 21 / rotating electrode 22 and the collecting 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 an unwinding strip.

Several process parameters can be adjusted so as to obtain a web with advantageous properties, in particular having good filtration efficiency and / or low pressure drop and / or can have fibers of size 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 polymer P1 can be dissolved in different solvents or mixtures of solvents (“liquid vehicle”).

According to a first embodiment, the liquid vehicle does not include dimethylsulfoxide (DMSO) and comprises, consists essentially of, or consists of: at least 50% by weight of a (first) liquid having a solubility parameter of Hansen dr from 7 MPa ^1/2 to 20 MPa ^1/2 and has a boiling point above 100 ° C.

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

According to other variants, the (first) liquid has a Hansen solubility parameter dr of 8 MPa ^1/2 to 15 MPa ^1/2 , preferably from 10 MPa ^1/2 to 15 MPa ^1/2 . The first liquid can in particular consist of cyclopentanone, dimethyl phthalate, ethyl acetoacetate, triethyl phosphate, ethyl lactate, and their mixture. According to the first embodiment, 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. Preferably, the (first) liquid can be chosen from the list consisting of: cyclopentanone, dimethyl phthalate, ethyl acetoacetate, triethyl phosphate, ethyl lactate, and their mixture.

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

The liquid vehicle of this first embodiment can comprise at least a second liquid, the second liquid having a boiling point of 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 a mixture thereof. Advantageously, the second liquid consists of ethyl acetate or a mixture of ethyl acetate and water.

In some embodiments, the liquid vehicle comprises water, with water constituting up to 5% by weight, preferably up to 3% by weight of the liquid vehicle.

According to some embodiments, the liquid vehicle consists of said at least one first liquid and said at least one second liquid.

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

According to a second embodiment, the vehicle comprises: at least 15% by weight of dimethylsulfoxide (DMSO), relative to the total weight of liquid vehicle, and at least one second liquid, the second liquid having a Hansen solubility parameter dr from 7 MPa ^1/2 to 15 MPa ^1/2 and a boiling point strictly above 100 ° C.

According to certain embodiments, the DMSO represents at least 20%, preferably at least 25%, and more preferably at least 30% by weight of the total weight of the liquid vehicle.

According to some embodiments, the second liquid represents at least 10% by weight of the total weight of the liquid vehicle. According to certain embodiments, the second liquid has a Hansen solubility parameter dr greater than or equal to 8 MPa ^1/2 , preferably greater than or equal to 9 MPa ^1/2 and extremely preferably greater than or equal to 10 MPa ^{1 / 2} .

According to some embodiments, the second liquid is selected from the list consisting of: cyclopentanone, dimethyl phthalate, ethyl acetoacetate, triethyl phosphate, ethyl lactate, and a mixture thereof.

According to some embodiments, the second liquid consists of cyclopentanone.

According to certain embodiments, the mass ratio of DMSO relative to the second liquid is then advantageously from 40:60 to 60:40.

According to some embodiments, the liquid vehicle consists of DMSO and said at least one second liquid. The mass ratio of DMSO relative to the second liquid is then advantageously from 40:60 to 60:40.

According to some embodiments, the liquid vehicle comprises at least a third liquid, the third liquid having a boiling point of less than or equal to 100 ° C. The third liquid advantageously represents from 5% to 60% by weight relative to the total weight of the liquid vehicle.

According to some embodiments, the third liquid is selected from the list consisting of: acetone, ethyl acetate, 2-butanone, water, and a mixture thereof. In some embodiments, the third liquid is ethyl acetate or a mixture of water and ethyl acetate.

In some embodiments, the third liquid comprises water, with water constituting up to 5% by weight, preferably up to 3% by weight, of the liquid vehicle.

According to certain embodiments, the mass ratio by weight of the sum of the weights of DMSO and of the second liquid relative to the weight of the third liquid is advantageously from 20:80 to 80:20, preferably from 40:60 to 60:40.

According to some embodiments, the liquid vehicle consists of DMSO, said at least one second liquid and said at least one third liquid. The mass ratio by weight of the sum of the weights of DMSO and the second liquid relative to the weight of the third liquid is advantageously from 20:80 to 80:20, preferably from 40:60 to 60:40.

Advantageously, none of the following solvents is used in the composition of the liquid vehicle to dissolve the polymer P1, because of their CMR risk (carcinogenic, mutagenic, toxic for reproduction): NN-dimethylformamide (DMF), N, N-dimethylacetamide (DMac), tetrahydrofuran (THF), tetramethylurea, trimethylphosphate and N-methyl-2-pyrrolidone.

In some embodiments, the polymer P1 is dissolved in a DMSO / cyclopentanone / ethyl acetate liquid vehicle. Acetone and ethyl acetate in particular make the mixtures more volatile and ensure good crystallization of the fibers.

The concentration of the polymer P1 in one of the abovementioned solvents or their mixture is between a minimum value and a maximum value, below or beyond which the electrospun age no longer substantially forms a filament but also beads. Generally, the amount of polymer P1 in one of the aforementioned solvents or their mixture represents from 3% to 30% by weight, preferably from 6% to 20% by weight, and extremely preferably from 9% to 12% of the total weight of solution.

The polymer P1 generally has a weight-average molecular mass chosen between a minimum value and a maximum value. In fact, too low a molecular mass results in the presence of unwanted beads during electrospinning. Too high a molecular weight tends to produce fibers of too large a diameter. The polymer P1 generally has a mass molecular weight average ranging from 100,000 g / mol to 2,000,000 g / mol. Preferably, it has a weight average molecular mass of 300,000 g / mol to 1,500,000 g / mol, and extremely preferably of 400,000 to 700,000 g / mol.

For a polymer P1 of given molecular weight, in a given solvent or mixture of solvents, the concentration of P1 is necessarily greater than the critical entanglement concentration.

The viscosity of the polymer solution P1, measured by a BROOKFIELD viscometer at 25 ° C., is generally 50 to 300 cP. Preferably, the viscosity of the solution is 75 to 265 cP, and extremely preferably 80 to 150 cP.

According to some embodiments, the solution may include an additive to improve the processability of the filament to be electrospun. The additive can in particular be an additive making it possible to modulate certain electrohydrodynamic properties of the solution. The mass proportion of the additive generally does not exceed 5% of the total weight of the solution.

The additive can in particular be water. The advantage of water is that it increases the conductivity of the solution and evaporates during the electrospinning step.

The additive can also be a salt. Examples include NaCl and LiCl or else ammonium salts such as: TBAC (tetrabutylammonium chloride), TEAC (tetraethylammonium chloride) or TEAB (tetraethylammonium bromide). These salts can advantageously be removed, at least in part, by washing, in particular by washing with water, after formation of the fibers by electrospinning.

Equipment parameters, such as for the devices used in the installations shown in Figures 1 and 2, can also be adjusted:

- the inter-electrode voltage: the latter 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 prevent at best any risk 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 polymer P1 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 polymer filament P1 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 can 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 polymer filament P1 is intended to move; preferably, this humidity is 20% to 60% at the temperature of the medium.

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

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

The web formed by electrospinning can undergo, after its formation, an annealing step at a temperature below the melting temperature of the polymer and then cooled to ambient temperature (25 ° C.). This annealing step optionally evaporates the residual solvent and optionally increases the crystallinity, and therefore the ferroelectric properties, of P1. The annealing step will usually be followed by a polarization step, by contact or by corona.

Membrane

The web according to the invention can be thick enough on its own to form a membrane suitable for the filtration of nano and / or submicron aerosols.

Conversely, a nano and / or submicron 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 web.

According to some embodiments, the web has a basis weight of 0.01 g / m ² to 3 g / m ² . The web preferably has a basis weight of 0.02 g / m ² to 1 g / m ² and, more preferably, a basis weight of 0.03 g / m ² to 0.5 g / m ² .

In some embodiments, the web has an average thickness of 0.1 µm to 100 µm. The web preferably has an average thickness of 0.2 µm to 10 µm and more preferably 0.3 µm to 0.8 µm.

The support layer makes it possible in particular to ensure the good mechanical strength of the membrane. The backing layer can be a woven or non-woven assembly of fibers.

Advantageously, the support layer has a low pressure drop.

According to certain embodiments, in particular when the web is implemented by electrospinning, the support layer can be the substrate on which the web has been electrospun.

According to certain embodiments, the support layer can be a nonwoven assembly of thermoplastic fibers. The support layer can in particular be a nonwoven set 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), fluoropolymers, such as polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP) or polytetrafluoroethylene (PTFE), and a mixture thereof.

According to certain embodiments, the support layer is capable of being obtained by a meltblown process or by a 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 / m ² to 100 g / m ² , preferably from 10 g / m ² to 50 g / m ² and extremely preferably from 15 g / m ² to 40 g / m ² .

According to particular embodiments, a membrane comprises one or more webs according to the invention, for example essentially constituted (s), or constituted (s), of PVDF fibers or of fibers consisting of a mixture of PVDF and: P (VDF-HFP) or P (VDF-TFE) or P (VDF-TrFE), or of fibers consisting of a mixture of PVDF and PMMA. The web (s) are obtained by electrospinning and have a basis weight of 0.02 g / m ² to 1 g / m ² . The substrate can in particular be a PVDF, a PP or else a PET obtained by meltblowing and having a basis weight of 10 g / m ² to 50 g / m ² .

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

Figure 4 shows a multilayer membrane 40 consisting of a support layer 41 covered on each side (“sandwich”) 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 composition and / or a different grammage and / or a thickness. For example, the web 42 may be of the same chemical composition as the 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 composition and / or a different basis weight and / or a thickness.

Nano and / or sub-micron aerosol filtration device from the air

The web and / or the membrane according to the invention can constitute a filter and / or form part of a multilayer assembly constituting a filter, constituting or forming part of a device for filtering nano and / or submicron aerosols of the air.

According to certain embodiments, the device for filtering nano and / or submicron aerosols from the air is a filtering device for respiratory protection. There are many different designs of respiratory protection devices, well known to those skilled in the art (INERIS publication, ED 6106, Respiratory protection devices, August 2019 - ISBN 978-2-7389-2503-9). The respiratory protection device can in particular be a filtering half-mask, a half-mask comprising a filter or a mask comprising a filter. The respirator may be free-ventilated or assisted-ventilated.

According to preferred embodiments of the invention, the breathing apparatus is ventilated. The respiratory protection device can 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 some embodiments, the filter comprising the web 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 web and / or the membrane is a combined filter allowing the filtration of nano and / or submicron aerosols and the anti-gas filtration.

FIG. 6 represents 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) .

With reference 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 face of a user. contact with the external environment as well as a middle layer formed by the membrane 30.

Washing / sterilization process

The veil and / or the membrane according to the invention can advantageously be washed and / or sterilized so that it can be reused. They can preferably be washed / sterilized, at least 5 times, preferably at least 10 times, more preferably at least 20 times, again preferably at least 30 times and, extremely preferably at least 50 times.

Washing can be done in particular with water, preferably with hot water. Methods of sterilization include:

- chemical treatment, by a chemical substance in the liquid state or in the vapor state;

- UV-C treatment,

- heat treatment; and

- a combination of treatments.

An example of chemical treatment is treatment with hydrogen peroxide (HPV / HPVP), VHP, HPGP, iHP and aHP

UV-C treatment is treatment with radiation with a wavelength ranging from 100 to 280 nm. It allows the veil and / or the membrane to be sterilized. Advantageously, the UV-C treatment is implemented by a lamp having a radiation peak between 230 nm and 270 nm, in particular around 254 nm. The treatment is generally applied at a dose of 1 J / cm to 120 J / cm, preferably 1 J / cm to 50 J / cm.

The heat treatment can be carried out at a temperature generally greater than or equal to 40 ° C. for a sufficient period of time, preferably less than or equal to 30 minutes and more preferably less than or equal to 15 minutes. It can in particular be used at a temperature greater than or equal to 50 ° C, or greater than or equal to 60 ° C, or greater than or equal to 70 ° C, or greater than or equal to 80 ° C.

The heat can be so-called "dry" heat or so-called "wet" heat (humidity above 50%).

Devices making it possible to carry out such treatments are in particular heating cabinets, water baths, autoclaves, ovens.

The treatment is to be chosen and adapted according to various constraints: nature and resistance of the materials other than the veil to undergo the treatment, use in hospitals or for domestic purposes, etc. It is therefore recommended for the user of a washable and / or sterilizable respiratory protection device to be well informed by carefully reading the manufacturer's instruction manual as well as the recommendations of official bodies. normative and / or health, these recommendations may change over time. To our knowledge, domestic ovens and microwave ovens for domestic use are not, at the time of writing this application, of the washing / sterilization methods recommended for masks for domestic use by the main official regulatory bodies. and / or health, in particular due to the lack of existing data and the potential risk of biological / chemical contamination of the ovens. The ANSM, in its opinion of March 25, 2020, revised on April 21, 2020, recommends, for example, for fabric masks for non-sanitary use, planned in the context of the COVID epidemic, for home treatment: i) a machine wash with a detergent suitable for the fabric, the cycle of which will include at least a 30-minute tray at 60 ° C and ii) mechanical drying or conventional drying, followed in both cases by steam ironing at a temperature compatible with the composition of the mask.

Claims

1. Nonwoven web obtained by electrospinning, suitable for the filtration of nano and / or submicron aerosols, comprising a multiplicity of fibers of composition C1, composition C1 comprising at least 50% by weight of at least one polymer P1 based on the repeating unit derived from vinylidene fluoride (VDF), said fibers of composition C1 having a degree of crystallinity in polar phase (s), preferably in only beta phase, of at least 65% by weight , relative to their total weight.

2. Sail according to claim 1, wherein said fibers of composition C1 have a degree of crystallinity in polar phase (s), preferably in only beta phase, of at least 75%, or at least 80%. , or at least 85%, or at least 90%, or at least 95%, or at least 96%, or at least 97%, or at least 98%, or at least 99% by weight, relative to their total weight.

3. Sail according to any one of claims 1 and 2, wherein the polymer P1 is selected from the group consisting of: a VDF homopolymer; a copolymer having a repeat unit derived from VDF and at least one repeat 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), a chlorofluoroethylene (CFE), a chlorodifluoroethylene, chlorotrifluoroethylene (CTFE), dichlorodifluoroethylene, a trichlorofluoroethylene, hexafluoropropylene (FIFP), a trifluoropropropene, trifluoropropene, a tetoropropene hexafluoroisobutylene, perfluorobutylethylene, a pentafluoropropene, a perfluoroether, in particular a perfluoroalkylvinylether, ethylene, an acrylic monomer, a methacrylic monomer and their mixture; and a mixture of homopolymer (s) and copolymer (s).

4. Sail according to any one of claims 1 to 3, wherein the polymer P1 is a PVDF, a P (VDF-HFP), a P (VDF-TFE), a P (VDF-TrFE), or a mixture thereof. .

5. Sail according to any one of claims 1 to 4, wherein said at least one polymer P1 is a mixture consisting of:

- a PVDF,

- a copolymer chosen from: P (VDF-HFP), P (VDF-TFE) and P (VDF-TrFE); the proportion by mass 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.

6. Sail according to any one of claims 1 to 5, wherein the polymer P1 represents at least 60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 97.5%, or at least 99.0%, by weight of composition C1.

7. Sail according to any one of claims 1 to 6, wherein composition C1 further comprises at least one polymer P1 'chosen from the list consisting of: a poly (methyl methacrylate) (PMMA), a poly (methacrylate). ethyl) (PEMA), poly (methyl acrylate) (PMA), poly (ethyl acrylate) (PEA), poly (vinyl acetate) (PVAc), poly (vinyl methyl ketone) ( PVMK), thermoplastic polyurethane (TPU), thermoplastic starch, copolymers derived therefrom, and mixtures thereof.

8. Sail according to claim 7, wherein the polymer P1 consists of a PVDF and the polymer P1 ′ consists of a PMMA, the proportion by weight of P1 ′ relative to the sum of the masses of the polymers P1 and P1 ′. being from 15% to 40%, preferably from 16% to 30%, and extremely preferably from 17% to 23%.

9. Sail according to any one of claims 1 to 8, consisting of fibers of composition C1.

10. Sail according to any one of claims 1 to 9, having a basis weight of 0.01 g / m ² to 3 g / m ² , preferably from 0.02 g / m ² to 1 g / m ² , and extremely preferably from 0.03 g / m ² to 0.5 g / m ² .

11.Veil according to any one of claims 1 to 10, comprising less than 1%, preferably less than 0.5%, and more preferably less than 0.1%, by number of fibers having a diameter strictly less than 100 nm. .

12. Sail according to any one of claims 1 to 11, not comprising any of the solvents from the list consisting of: NN-dimethylformamide (DMF), N, N-dimethylacetamide (DMac), tetrahydrofuran (THF), tetramethylurea, trimethylphosphate and N-methyl-2-pyrrolidone.

13. Membrane suitable for filtration of nano and / or submicron aerosols comprising:

- at least one veil according to any one of claims 1 to 12.

- a support layer supporting said web.

14. The membrane of claim 13, wherein said support layer is a nonwoven set of fibers selected from: polyolefins, such as polyethylene (PE) or polypropylene (PP), polyesters, such as poly (terephthalate). ethylene) (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, PA 6.10, polyacrylonitrile (PAN), fluoropolymers, such as polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP) or polytetrafluoroethylene (PTFE), and their mixture.

15. A method of washing / sterilizing a veil according to any one of claims 1 to 12 or of a membrane according to any one of claims 13 and 14 comprising a heat treatment step implemented at a temperature. from 40 ° C to 90 ° C, preferably from 55 ° C to 85 ° C, and extremely preferably at a temperature from 65 ° C to 80 ° C.