Method for recycling filtering face-piece respirators

Abstract

The present invention relates to a method for recycling a filtering face-piece respirator comprising a plurality of layers made of a single thermoplastic polymer selected from the group consisting of polypropylene, polyethylene terephthalate, polylactic acid, polyamide 6 (PA6 homopolymers and copolymers and long chain polyamides such as PA11 or PA12 and comprising a polyvinylidene fluoride filter layer.

Description

Technical Field

[0001] The invention relates to a method for recycling respiratory protection masks comprising a plurality of layers made of a single thermoplastic polymer selected from homopolymers and copolymers of polypropylene, polyethylene terephthalate, polylactic acid, polyamide 6 (PA6) and long-chain polyamides such as PA11 or PA12 and comprising a filter layer made of polyvinylidene fluoride. Background Art

[0002] Particle masks are respiratory protection devices capable of filtering particles and fine dust. These masks include personal protective equipment such as FFP masks (for "filtering facepiece particles"). Their range of protection is determined by the European standard EN 149, which specifies the minimum characteristics required for filtering half masks used as respiratory protection devices against particles, excluding those used for escape purposes. This standard defines three classes of devices, FFP1, FFP2 and FFP3, based on three criteria: maximum penetration of the filter material by aerosols with a mass mean diameter of 0.6 μm, breathing resistance and inward leakage rate.

[0003] FFP1 dust masks have an aerosol filtration rate of at least 80% and an inward leakage rate of no more than 22%.

[0004] FFP2 masks have an aerosol filtration rate of at least 94% and an inward leakage rate of no more than 8%. Such masks protect against powdered chemicals and can also be used to protect against aerosols carrying viral particles and / or bacteria.

[0005] The FFP3 mask has an aerosol filtration rate of not less than 99% and an inward leakage rate of not more than 2%. It protects against very fine particles of asbestos (asbestosis) or silicon dioxide (silicosis).

[0006] There are also masks for medical use (surgical masks) developed according to standard EN 14683, which are intended to avoid the projection of droplets emitted by the person wearing the mask into the surrounding environment. These masks also protect the wearer from the projection of droplets emitted by the person facing them. On the other hand, they do not protect against the inhalation of very small particles that are suspended in the air and may carry viruses, depending on the situation.

[0007] Respiratory protection masks usually consist of fibers, or a combination of synthetic fibers, obtained from thermoplastic polymers such as polyolefins, polyamides, polyvinyl compounds, polyimides, polyacrylates, polymethacrylates, polyurethanes or fluoropolymers, and in particular polyvinylidene fluoride (PVDF).

[0008] Among the many types of masks known, some comprise at least one nanofibrous layer particularly suitable for ensuring the barrier properties required for at least FFP2 type respiratory protection. Solution electrospinning of polymers makes it possible to obtain fibers with sufficiently small diameters under certain conditions to obtain good air permeability of membranes for air filtration and good mechanical and possibly electrostatic filtration efficiency.

[0009] Document EP 2517607 describes the advantages of masks comprising at least one nanofibrous layer, and their manufacture by electrospinning. Such masks have a sandwich-type structure, since they comprise several superimposed layers, for example three layers of the type: nonwoven layer - nanofibrous layer - nonwoven layer.

[0010] Document US2019 / 0314746 describes a nonwoven porous PVDF membrane suitable for air filtration obtained by an electrospinning method. The nanofibers are electrospun on the surface of a drum covered with a nonwoven polypropylene substrate.

[0011] The increasing use of respiratory masks, whether they are single-use (disposable) or reusable, has led to a major environmental issue in terms of managing this waste and reusing the polymer materials used to make these masks. Used masks may be laden with particles and / or contaminated with pathogenic microorganisms (bacteria and / or viruses). There are several methods for cleaning reusable masks: washing with detergents at 60 or 95°C, sterilization at 121°C for 50 minutes, irradiation with gamma or beta radiation, exposure to ethylene oxide, heating at 70°C in dry heat or water, use of hydrogen peroxide vapor.

[0012] However, even when cleaning is effective and makes it possible to remove dust particles and / or microorganisms deposited on the mask, the mask can only undergo a limited number of cleaning cycles, after which there is the problem of disposal of the used masks and the desired recovery of all or some of the raw materials used to manufacture them.

[0013] Therefore, it is necessary to develop a method for recycling used masks that can prevent their accumulation and possible pollution of the environment and recover the raw materials used to manufacture them.

[0014] It has now been found that used masks comprising layers made of a given main thermoplastic polymer, chosen from polypropylene, polyethylene terephthalate, polylactic acid and certain polyamides, and PVDF in the form of nanofibers, can provide a recycling method leading to a masterbatch capable of being used as a polymer processing aid (PPA), i.e. an additive that makes it possible, among other things:

[0015] - reducing or eliminating surface defects that occur when extruding said thermoplastic resin,

[0016] - reducing the pressure at the head of the extrusion die, thus making it possible to increase the flow rate of the extrusion line,

[0017] -limit the frequency of cleaning the extrusion die,

[0018] -Limiting the formation of surface defects on extruded films. Summary of the invention

[0019] The object of the present invention is to provide a method for recycling respiratory protection masks containing 98.5% to 99.5% by weight of a main thermoplastic polymer selected from homopolymers and copolymers of polypropylene, polyethylene terephthalate, polylactic acid, polyamide 6 (PA6) and long-chain polyamides such as PA11 or PA12; and 0.05% to 1.5% of poly(vinylidene fluoride) or PVDF in the form of nanofibers, the method comprising the following steps:

[0020] a) grinding the mask so as to obtain flakes,

[0021] b) Pelletizing (extrusion) the flakes, resulting in a masterbatch in the form of pellets.

[0022] Advantageously, said masterbatch obtained by the recycling process according to the invention can be used as a polymer processing aid in the melt processing of primarily thermoplastic materials for the manufacture of all types of articles, in particular in the form of films, fibers, cables or molded parts.

[0023] According to one embodiment, the mask subjected to the recycling method according to the invention comprises a layer of PVDF nanofibers obtained by an electrospinning process, said layer being deposited on a main thermoplastic polymer substrate.

[0024] The present invention relates to a method for regenerating used respiratory protection masks, allowing the recovery of the polymer raw materials used in their composition. More particularly, the method according to the invention is applied to masks comprising a plurality of layers made of a main thermoplastic polymer chosen from homopolymers and copolymers of polypropylene, polyethylene terephthalate, polylactic acid, polyamide 6 (PA6) and long-chain polyamides such as PA11 or PA12, and comprising a filter layer made of polyvinylidene fluoride; and leading to the production of a masterbatch that can be used directly as a polymer processing aid for the extrusion of the main thermoplastic polymer.

[0025] The use of the masterbatch in a line for processing a primary thermoplastic polymer results in an increase in the productivity of the line of up to 10% and a reduction in the extrusion pressure of 10% to 20% compared to the extrusion of the same thermoplastic polymer in the absence of the polymer processing aid. Furthermore, it has been observed that the persistence of the electret on the surface of the thermoplastic polymer obtained using the polymer processing aid produced according to the method of the invention is increased compared to the same unmodified polymer. DETAILED DESCRIPTION

[0026] The invention will now be described in more detail in a non-limiting manner in the following description.

[0027] The present invention is based on the discovery of the ability of respiratory protection masks comprising a main thermoplastic polymer chosen from homopolymers and copolymers of polypropylene, polyethylene terephthalate, polylactic acid, polyamide 6 (PA6) and long-chain polyamides such as PA11 or PA12 and a filter layer made of polyvinylidene fluoride nanofibers, in particular masks of the FFP1 to FFP3 type and surgical masks, to be subjected to a recycling process to provide a masterbatch capable of acting as a polymer processing aid in the molten state during the processing of the main thermoplastic polymer, resulting in a reduction in the pressure at the head in the extruder, allowing an increase in the flow rate during extrusion and reducing the material deposited at the head of the die, which can generate defects on the extruded fibers, rods or films. This makes it possible to reduce the frequency of cleaning the equipment and thus the frequency of machine stops.

[0028] According to a first aspect, the present invention provides a method for recycling respiratory protection masks containing 98.5% to 99.5% by weight of a main thermoplastic polymer chosen from homopolymers and copolymers of polypropylene, polyethylene terephthalate, polylactic acid, polyamide 6 (PA6) and long-chain polyamides such as PA11 or PA12; and 0.05% to 1.5% of poly(vinylidene fluoride) or PVDF (in particular in nanofibrous form), the method comprising a step of grinding the masks, thereby resulting in obtaining flakes, and a step of pelletizing (extruding) the flakes, thereby obtaining a masterbatch in the form of pellets.

[0029] According to various embodiments, the method comprises the following features in combination where appropriate.

[0030] The masks employed in this recycling method are used masks that exclusively contain a single thermoplastic polymer, called "primary", selected from homopolymers and copolymers of polypropylene, polyethylene terephthalate, polylactic acid, polyamide 6 (PA6) and long-chain polyamides such as PA11 or PA12, and PVDF. More particularly, these masks contain 98.5% to 99.5% by weight of the primary thermoplastic polymer, and 0.05% to 1.5% of poly(vinylidene fluoride) or PVDF in nanofiber form, in particular in nanofiber form.

[0031] According to one embodiment, the recycling method uses surgical masks that comply with standard EN 14683.

[0032] According to one embodiment, the recycling method uses FFP type masks complying with standard EN 149.

[0033] According to one embodiment, the recycling method employs a mixture of surgical masks and FFP-type masks, provided that they have the composition indicated above.

[0034] The term "used masks" as used herein includes masks that have served their purpose (worn out), as well as unused masks that have expired because they have exceeded the warranty period provided by the manufacturer, and even scrap materials (particularly thermoplastic polymers) recycled during mask manufacturing (which can account for 15% to 16% of the total materials used).

[0035] According to one embodiment, the mask used in the recycling method is a respiratory mask, which consists of a body and a fixing belt, the body consisting of at least two layers and preferably three layers including a PVDF filter material layer, the body including a nose pad (nose bridge), and the fixing belt is preferably fixed to the body of the mask by welding without adding materials. In this mask, except for the PVDF fibers, all layers of the material constituting the body and the fixing belt are composed of non-woven fabrics of the same main thermoplastic polymer material. The main thermoplastic polymer is selected from homopolymers and copolymers of polypropylene, polyethylene terephthalate, polylactic acid, polyamide 6 (PA6) and long-chain polyamides such as PA11 or PA12.

[0036] Long-chain polyamides are aliphatic polyamides having an average number of carbon atoms per nitrogen atom of more than 8.5, preferably more than 9 and in particular more than 10.

[0037] PVDF as used in the context of the present invention is also a thermoplastic polymer.The fluoropolymer used in the present invention and represented by the abbreviation PVDF is a polymer based on vinylidene fluoride.

[0038] The term "thermoplastic" as used herein refers to non-elastomeric polymers. Elastomeric polymers are defined as polymers that can be stretched to twice their original length at ambient temperature and, upon release of the stress, rapidly recover their original length to within about 10% as specified in ASTM Special Technical Publication, No. 184.

[0039] According to one embodiment, the mask to be recycled contains a nonwoven thermoplastic polymer inner layer having a density of between 20 and 100 g / m 2 and has a grammage between 500 and 1500 l / m 2 / s, measured at 100 Pa. The thermoplastic polymer has a melt flow rate (MFR) of 34 g / 10 min at 230° C. under 2.16 kg.

[0040] According to one embodiment, the mask to be recycled comprises a core layer comprising a 2 and has a grammage between 500 and 2500 l / m 2 / s, measured at 100 Pa.

[0041] According to one embodiment, the substrate is manufactured by spunbonding from a thermoplastic polymer having a melt flow rate of 34 g / 10 min at 230° C. and 2.16 kg.

[0042] According to another embodiment, the support layer (substrate) is produced by blow molding from a thermoplastic polymer having a melt flow rate of 34 g / 10 min at 230° C. and 2.16 kg.

[0043] According to one embodiment, deposited on the substrate via an electrospinning process is a PVDF nanofiber layer. According to one embodiment, the PVDF comprises and preferably consists of:

[0044] i. PVDF homopolymer;

[0045] ii. a mixture of two PVDF homopolymers having different viscosities or different molar masses or different structures such as different degrees of branching;

[0046] iii. a copolymer comprising units of vinylidene fluoride (VDF) and units of one or more types of comonomers compatible with vinylidene fluoride (hereinafter referred to as "VDF copolymer");

[0047] iv. a mixture of PVDF homopolymer and VDF copolymer;

[0048] v. A mixture of two VDF copolymers.

[0049] Comonomers compatible with vinylidene fluoride may be halogenated (fluorinated, chlorinated or brominated) or unhalogenated. The term "compatible comonomer" is understood here to mean the ability of said comonomer to copolymerize with VDF and thus form a copolymer.

[0050] Examples of suitable fluorinated comonomers are: vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, trifluoropropylene, and in particular 3,3,3-trifluoropropylene, tetrafluoropropylene, and in particular 2,3,3,3-tetrafluoropropylene or 1,3,3,3-tetrafluoropropylene, hexafluoroisobutylene, perfluorobutylethylene, pentafluoropropylene, and in particular 1,1,3,3,3-pentafluoropropylene or 1,2,3,3,3-pentafluoropropylene, perfluoroalkyl vinyl ethers, and in particular those with the general formula Rf-O-CF-CF2, Rf being an alkyl group, preferably C1 to C4 alkyl groups (preferred examples are perfluoropropyl vinyl ether and perfluoromethyl vinyl ether). The fluorinated monomer may contain chlorine or bromine atoms. It may in particular be selected from bromotrifluoroethylene, chlorofluoroethylene, chlorotrifluoroethylene and chlorotrifluoropropylene. Chlorofluoroethylene may represent 1-chloro-1-fluoroethylene or 1-chloro-2-fluoroethylene. 1-chloro-1-fluoroethylene isomers are preferred. The chlorotrifluoropropene is preferably 1-chloro-3,3,3-trifluoropropene or 2-chloro-3,3,3-trifluoropropene.

[0051] The VDF copolymers may also contain non-halogenated monomers, such as ethylene and / or acrylic acid or methacrylic acid comonomers.

[0052] When the nanofiber layer is composed of a mixture of two components among those mentioned above (ii., iv. and v.), the mass ratio between the components ranges from 1:99 to 99:1.

[0053] According to one embodiment, the PVDF nanofibers have an average fiber diameter Dv50 between 30 and 500 nm, preferably between 30 and 300 nm. Dv50 is the volume median diameter, which corresponds to the value of the particle size that divides the examined particle population exactly in half. Dv50 is measured according to standard ISO 9276 - parts 1 to 6.

[0054] According to one embodiment, the electrospun PVDF layer has a 2 Up to 3g / m 2 The weight between.

[0055] The average thickness of the PVDF nanofiber layer is 0.1 μm to 100 μm. The diameter of the fibers, their thickness and their distribution can be estimated by scanning electron microscopy (SEM).

[0056] The solvent used to dissolve PVDF in electrospinning is selected from cyclopentanone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, acetone, ethyl methyl ketone, tetrahydrofuran, γ-butyrolactone, hexafluoroisopropanol, or mixtures thereof in all proportions.

[0057] The PVDF layer deposited by electrospinning can be charged by corona treatment to improve its filtration properties and obtain an aerosol filtration rate of at least 80%, preferably greater than 94%, or even greater than 98%, and a pressure drop of much less than 70 Pa.s for an air inhalation flow rate of 95 l / min.

[0058] According to one embodiment, the used mask to be recycled comprises an outer layer of a thermoplastic polymer having a melt flow rate (MFR) of 34 g / 10 min at 230° C. at 2.16 kg; the nonwoven layer having a melt flow rate (MFR) of 20 to 100 g / m 2 and has a grammage between 500 and 1500 l / m 2 / s measured at 100 Pa.

[0059] According to one embodiment, the fixing strap of the mask made of thermoplastic polymer to be recycled is an adjustable ring produced by injection molding or 3D printing, or a plastic having a weight of 10 to 100 g / m 2 An elastic tape (nonwoven or wound filament) made from the thermoplastic polymer having a grammage between 500 Å and 250 Å and a melt flow rate of 34 g / 10 min at 230° C. and 2.16 kg.

[0060] According to one embodiment, the nose pad is made of a mixture of 50% by weight of a PVDF homopolymer having a melt flow rate of 32 g / 10 min at 230°C and 2.16 kg and 50% by mass of a main thermoplastic polymer, wherein the main thermoplastic polymer is selected from homopolymers and copolymers of polypropylene, polyethylene terephthalate, polylactic acid, polyamide 6 (PA6) and long-chain polyamides such as PA11 or PA12 and has a melt flow rate of 34 g / 10 min at 230°C and 2.16 kg.

[0061] The recycling method according to the invention comprises a first step of grinding the masks resulting in obtaining flakes.

[0062] According to one embodiment, the used masks are passed through a shredder to process them into fibers of a few millimeters, for example 1 to 10 nm, preferably 1 to 5 nm. The screen allows the fiber pulp to be calibrated according to the desired length.

[0063] In the case of semicrystalline thermoplastic polymers, milling is carried out at a temperature at least 30° C. below the melting temperature Tm of the material to be processed and in the case of amorphous thermoplastic polymers at least 30° C. below the glass transition temperature Tg.

[0064] According to one embodiment, the mask is milled in an extruder (which may be of the single-screw or twin-screw type) or in a BUSS co-kneader.

[0065] If the milled mask includes metal parts, such as nose pads, these can be removed with a magnet.

[0066] The recycling method according to the invention then comprises a step of pelletizing (extrusion) said flakes leading to obtaining a masterbatch in the form of pellets.

[0067] According to one embodiment, granulation is carried out in the molten state by extrusion through a die with circular holes, followed by chopping of the cooled strands and drying to produce pellets of 1 to 5 mm diameter.

[0068] According to another embodiment, the melt granulation is carried out in a BUSS-type co-kneader, wherein shredding takes place underwater and lens-shaped granules are produced.

[0069] According to a second aspect, the invention relates to the use of said masterbatch as a polymer processing aid in the extrusion of the same main thermoplastic polymer constituting the recycled mask, except for PVDF.

[0070] The polymer processing aid obtained by the recycling method according to the present invention is used to reduce or eliminate surface defects that occur during extrusion of the main thermoplastic resin. It significantly reduces the time to obtain stable and defect-free extrusion within the extrusion parameter range that usually exhibits significant extrusion instability.

[0071] The polymer processing aid and the thermoplastic resin are contacted in the solid state before extrusion. They can be premixed in the solid state or simply introduced into the extruder hopper. The polymer processing aid can also be introduced in the molten state at any point in the extruder used to extrude the thermoplastic resin, such as using a side extruder.

[0072] According to one embodiment, the weight proportion of the polymer processing aid is 1% to 30%, preferably 1% to 10%, preferably 1.5% to 10%, even more preferably 2% to 10%, for 70% to 99%, preferably 90% to 99%, preferably 90% to 98.5%, even more preferably 90% to 98%, respectively, of the thermoplastic resin to be extruded.

[0073] Masterbatches are particularly useful for extruding thermoplastic polymers in the form of films or in the form of tubes, profiles or hollow bodies. In addition to the advantages already mentioned, it helps to obtain a smooth and defect-free surface, which is particularly important in the case of films for obtaining good optical properties. Polymer processing aids also make it possible to reduce the pressure and gel level at the die gap. This also makes it possible to reduce deposits at the die outlet to a certain extent.

[0074] Example

[0075] The following examples illustrate the invention without limiting it.

[0076] Example 1: At 18 g / m 2 Electrospun fibers produced on spunbond polypropylene (spunbond PP)

[0077] According to the composition shown in Table 1, VF2 homopolymer was stirred at 55°C for 2 hours. and copolymers The mixture was dissolved.

[0078]

[0079]

[0080] Table 1

[0081] Then at 18g / m 2 The solution was fed to an electrospinning process on a PP spunbond support. For example, Mogul sells such a nonwoven. Thus, using the conditions indicated in Table 2, a filtration membrane based on electrospun fibers with a width of 480 mm was produced.

[0082]

[0083] Table 2

[0084] Example 2: At 28 g / m 2 Electrospun Fibers Produced on Spunbond Polyester (Spunbond PET)

[0085] In 28g / m 2 The electrospinning solution prepared as described in Example 1 was supplied to the electrospinning process on a PET spunbond support. For example, Mogul sells such a nonwoven under the name Buffalo. Thus, using the conditions indicated in Table 3, a filtration membrane based on electrospun fibers with a width of 480 mm was produced.

[0086]

[0087]

[0088] Table 3

[0089] Example 3: Nose pad production

[0090] The nose support pad is formed from a rod of 1.5 mm diameter and 10 cm length obtained by mixing / extruding at 230°C in a single screw extruder a 50 / 50 (by mass) mixture of a PVDF homopolymer having a melt flow rate of 32 g / 10 min at 230°C at 2.16 kg and a polypropylene having a melt flow rate of 35 g / 10 min at 230°C at 2.16 kg.

[0091] Example 4: Assembling a mask from the elements produced in Examples 1 to 3

[0092] The elements obtained in the previous examples were used to produce a mask having the following structure: Spunbond PP 1 - Espun PP film 1 - Spunbond PP 2. "Spunbond PP 1" nonwoven (40 g / m 2 ) forms the outer layer and improves the mechanical strength of the mask body. The "EspunPP1" middle layer provides aerosol filtration. Finally, the "Spunbond 2" nonwoven (18 g / m 2 ) is intended to come into contact with the user's face and it protects the filter layer from possible degradation. The elastic band is a polypropylene round stock, such as is sold by Liasa.

[0093] Assembly follows the steps described below:

[0094] - Cohesion between nonwoven layers is achieved by lamination.

[0095] - The nose pad produced in Example 3 was inserted into the space formed by folding the nonwoven material over a width of 5±2 mm close to the periphery of the mask. The beams were held by regularly placed welds along the length of the fold.

[0096] - Elastic bands are fixed on each side of the mask to form a loop and are fixed by ultrasonic welding without adding material.

[0097] Example 6: Grinding / Pelletizing and Extrusion of Recycled Materials

[0098] After decontamination by passing through an oven at 70°C for one hour, the mask was ground in a chopper. The flakes obtained were fed into a BUSS type twin screw extruder at 230°C to produce pellets.

[0099] The pellets obtained consisted of about 0.9 wt.% PVDF and were used as a masterbatch to achieve a concentration of 500 ppm PVDF in PP and then in a process for the manufacture of multifilaments by extrusion spinning.

[0100] The pressure reached at the extruder head during the production of PP multifilaments in the presence of 500 ppm PVDF was about 4.8 MPa, i.e., about 20% lower than the pressure conventionally obtained during the processing of PP alone. Likewise, the effect of the presence of PVDF was visually observed to be less fouling of the die after several hours of extrusion.

Claims

1. A method for recycling respiratory protection masks containing 98.5% to 99.5% by weight of a main thermoplastic polymer chosen from homopolymers and copolymers of polypropylene, polyethylene terephthalate, polylactic acid, polyamide 6 (PA6) and long-chain polyamides; and 0.05% to 1.5% of PVDF in the form of nanofibers, the method comprising a step of grinding the mask, thereby resulting in obtaining flakes, and a step of pelletizing the flakes, thereby resulting in obtaining a masterbatch in the form of pellets, The long-chain polyamide is an aliphatic polyamide having an average carbon atom number of greater than 8.5 per nitrogen atom.

2. The method for recycling respiratory protection masks as claimed in claim 1, wherein the long-chain polyamide is selected from PA11 or PA12.

3. A method for recycling respiratory protection masks as claimed in claim 1, wherein the mask used is composed of a main body and a fixing belt, wherein the main body is composed of at least two layers including a PVDF filter material layer, and the fixing belt is fixed to the main body of the mask without adding materials.

4. A method for recycling a respiratory protection mask according to any one of claims 1 to 3, wherein the mask comprises a nonwoven inner layer having a thickness of 20 to 100 g / m 2 and is made of a thermoplastic polymer having a melt flow rate of 34 g / 10 min at 230°C at 2.16 kg.

5. A method for recycling a respiratory protection mask according to any one of claims 1 to 3, wherein the mask comprises a core layer comprising a 2 and has a grammage between 500 and 2500 l / m 2 / s measured at 100 Pa for a nonwoven substrate.

6. The method for recycling a respiratory protection mask according to claim 5, wherein the substrate is produced by blow molding or spunbonding of a thermoplastic polymer having a melt flow rate of 34 g / 10 min at 230°C and 2.16 kg.

7. The method for recycling a respiratory protection mask according to claim 5, wherein the core layer comprises a PVDF nanofiber electrospun layer.

8. A method for recycling a respiratory protection mask as described in any one of claims 1 to 3, wherein the PVDF comprises: a PVDF homopolymer; a mixture of two PVDF homopolymers; a copolymer comprising units of vinylidene fluoride (VDF) units and one or more types of units of comonomers compatible with vinylidene fluoride; a mixture of a PVDF homopolymer and a VDF copolymer; or a mixture of two VDF copolymers.

9. The method for recycling a respiratory protection mask according to claim 7, wherein the PVDF nanofibers have an average fiber diameter D50 between 30 and 500 nm.

10. The method for recycling a respiratory protection mask according to claim 7, wherein the average thickness of the PVDF nanofiber layer is 0.1 μm to 100 μm.

11. A method for recycling a respiratory protection mask according to any one of claims 1 to 3, wherein the mask comprises a nonwoven outer layer having a thickness of 20 to 100 g / m 2 and is made of a thermoplastic polymer having a melt flow rate of 34 g / 10 min at 230°C at 2.16 kg.

12. The method for recycling a respiratory protection mask according to claim 3, wherein the fixing strap is an adjustable ring produced by injection molding or 3D printing or an elastic strap made of the main thermoplastic polymer.

13. Use of the masterbatch obtained by the method for recycling respiratory protection masks according to any one of claims 1 to 12 as a polymer processing aid in the extrusion of the thermoplastic polymer.

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