MULTILAYER FILTER WITH ANTIMICROBIAL PROPERTIES AND USE THEREOF IN INDUSTRIAL FILTRATION APPLICATIONS AND PROTECTIVE MASKS

Abstract

The present invention falls within the area of polymeric materials applied to the sector of manufacturing materials for use in filters for filtration equipment such as ventilators and for protective masks. In particular, the invention relates to multilayer filters for ventilators and protective masks which can be biodegradable and which comprise filtration materials based on ultrafine fibers obtained by electrohydrodynamic and aerohydrodynamic processing and which exercise passive FFP1, FFP2, N95 and FFP3 protection and which can also be washable and have active antimicrobial properties.

Claims

1. A multilayer filter characterized in that it comprises at least: i) An inner layer composed of polymeric filter materials and has a surface density of at least 0.01 g/m.sup.2; ii) An intermediate layer composed of polymeric fibers, optionally containing antimicrobial substances, and has a surface density of at least 0.01 g/m.sup.2; iii) An outer layer composed of polymeric filter materials and has a surface density of at least 0.01 g/m.sup.2.

2. The multilayer filter according to claim 1, wherein the inner layer and the outer layer are made of woven or non-woven polymeric filter materials, with or without functional additives.

3. The multilayer filter according to claim 1, wherein the polymeric material that makes up the inner layer and the outer layer are independently selected from polypropylene, polyamide, polyester, natural fibers, cotton and cellulose, or any of the combinations thereof.

4. The multilayer filter according to claim 1, wherein the fibers forming the intermediate layer are made of polyvinylidene fluoride, polylactic acid or polyhydroxyalkanoates.

5. (canceled)

6. The multilayer filter according to claim 1, wherein the intermediate layer contains an antimicrobial substance selected from zinc oxide, zinc oxide nanoparticles or CTAB.

7. (canceled)

8. The multilayer filter according to claim 1, wherein the intermediate layer comprises an additional layer composed of the same polymeric fibers as those of the first intermediate layer on which it is deposited.

9. The multilayer filter according to claim 1, wherein the intermediate layer comprises an additional layer composed of polymeric fibers different from those of the first intermediate layer (b) on which it is deposited.

10.-11. (canceled)

12. The multilayer filter according to claim 9, wherein the surface density of the intermediate layer and the additional layer is is the same.

13. (canceled)

14. The multilayer filter according to claim 1, wherein the dispersion of the surface density of the intermediate layer is less than 10%.

15. The multilayer filter according to claim 1, wherein the polymers that make up the filter layers are compostable and/or biodegradable in the environment.

16. The multilayer filter according to claim 1, wherein said multilayer filter is stacked in any possible configuration on themselves or on other commercial multilayer or monolayer filters.

17. (canceled)

18. A method for obtaining a multilayer filter according to claim 1 comprising the following steps: i) Depositing the intermediate layer on the inner layer; ii) Depositing an additional intermediate layer on the inner face of the outer layer; iii) Laminating the previous layers so that intermediate and additional intermediate layers and are in contact.

19. (canceled)

20. The method according to claim 18, wherein the layers are partially or totally laminated along the surface thereof, adding protective layers below the inner layer and/or above the outer layer or not, by methods that are selected from calendering with pressure, calendering without pressure, applying adhesives, with melting points by ultrasound, stitching and heat-sealing.

21. The multilayer filter according to claim 1 for use in the manufacture of ventilators, domestic appliances, generic industrial air or liquid filtration equipment, and washable or non-washable protective masks.

22. (canceled)

23. The multilayer filter according to claim 1, for use against microorganisms.

24. (canceled)

25. A translucent face mask comprising: (i) an inner layer which is in contact with the skin, composed of a polymeric mesh fabric having a yarn diameter of 1 to 90 μm, a mesh opening between 100 and 400 μm or a number of holes per linear inch (Mesh) of 40 to 150, and a surface density of between 5 and 50 g/m.sup.2; (ii) at least one intermediate layer composed of polymeric fibers, optionally containing antimicrobial substances, having a fiber morphology of between 20-500 nm diameter and a surface density of between 0.01 and 1 g/m.sup.2; and (iii) an outer layer composed of: a polymeric mesh fabric having a yarn diameter of 1 to 90 μm, and a mesh opening between 100 and 400 μm or a number of holes per linear inch (Mesh) of 40 to 150, and a surface density of between 5 and 50 g/m.sup.2; or a micro-perforated transparent polymeric film with a thickness between 10 and 50 μm, with a perforation diameter between 0.1 and 5 mm, a distance between perforations between 0.5 and 6 mm, and a surface density between 5 and 50 g/m.sup.2.

26. The mask according to claim 25, that comprises two intermediate layers: a first intermediate layer and an additional layer, which have a surface density of less than or equal to 0.5 g/m.sup.2.

27. (canceled)

28. The mask according to claim 25, wherein the inner layer fiber material is selected from polyvinylidene fluoride, polylactic acid, and polyhydroxyalkanoates, or any combination thereof.

29. The translucent face mask according to claim 25, wherein the inner layer fiber materials contain additives to reduce fiber diameter and/or impart antimicrobial properties.

30.-31. (canceled)

32. The translucent face mask according to claim 25, characterized in that it has an aerosol filtration efficiency over 75%.

33.-34. (canceled)

Description

BRIEF DESCRIPTION OF THE FIGURES

[0098] FIG. 1 shows a diagram of the tri-layer structure with smooth ultrafine PVDF fibers.

[0099] FIG. 2 shows a diagram of the tri-layer structure with beaded ultrafine PVDF fibers.

[0100] FIG. 3 shows a diagram of the tri-layer structure with smooth ultrafine PHBV fibers.

[0101] FIG. 4 shows a diagram of the multilayer structure of sequentially electrospun PVDF and as a symmetrical sandwich.

[0102] FIG. 5 shows a diagram of the co-deposition of electrospun ultrafine PVDF and PAN fibers in situ.

[0103] FIG. 6 shows a diagram of the tri-layer structure with smooth PHBV microfibers.

[0104] FIG. 7 shows a diagram of a three-layer sandwich model mask, with the outer (1) and inner (1′) layer comprising the same material, and an intermediate layer of nanofibers (2).

[0105] FIG. 8 shows a diagram of a three-layer sandwich model mask, with the outer (3) and inner (1) layers comprising two different type of materials, and an intermediate layer of nanofibers (2).

[0106] FIG. 9 shows a diagram of a four-layer sandwich model mask with the outer (1) and inner (1′) layer comprising the same material, and two intermediate layers of nanofibers (2) and (2′).

EXAMPLES

[0107] Next, the invention will be illustrated by some examples carried out by the inventors for each type of filter developed (e.g., passive FFP3 filter, with antimicrobial capacity and biodegradable design) which demonstrates the effectiveness of the product of the invention.

Example 1: FPP3 Trilayer Structure System with Electrospun PVDF with Smooth Ultrafine Fiber Structure

[0108] The central layer of electrospun ultrafine fibers was made of polyvinylidene fluoride with a molecular weight of 300 kDalton. To do this, a solution of PVDF at 15% by weight (wt. %) in a DMF/Acetone mixture (50:50 wt.) was used. Once dissolved, the fiber sheet was then manufactured using the electrospinning technique. To do this, an emitter voltage of 18 kV and a linear multi-emitter injector voltage were used. These ultrafine fibers were deposited on a rotating collector at a speed of 200 revolutions per minute (rpm) on a 30 g/m.sup.2 polypropylene (PP) substrate and at a distance of 20 cm. Said manufacture was carried out at a temperature of 30° C. and a relative humidity of 30%. This layer has a surface density of 1 g/m.sup.2. After production, a 30 g/m.sup.2 PP layer was placed on the PVDF deposition and calendered at 80° C. so that the final material ends up like the multilayer filter described in FIG. 1.

TABLE-US-00001 Grammage Material (g/m.sup.2) Outer Layer Non-woven PP spunbond 30 Intermediate Electrospun PVDF with 1 Layer smooth fibers Inner Layer Non-woven PP spunbond 30

[0109] The PVDF layer generated by the electrospinning technique was observed with a scanning electron microscope (SEM), resulting in a fiber microstructure with a constant diameter of between 220 and 280 nm, as can be seen in FIG. 1. When this material is subsequently subjected to a washing cycle with stirring in hot water at 60° C. and detergent and then dried, the consistency and morphology of the intermediate layer measured by SEM is not affected.

[0110] Assays of resistance to penetration with paraffin aerosol according to standard 149:2001+A1:2009 (point 8.11) gave a value of 0.9%; therefore, this filter would be classified as FFP3 type (out of every 100 aerosol particles, 1 or less than 1 passes).

Example 2: FFP1 Tri-Layer Structure System with Electrospun PVDF with Beaded Ultrafine Fiber Structure

[0111] The central layer was made of polyvinylidene fluoride with a molecular weight of 500 kDalton. To do this, a solution of PVDF at 10% by weight (wt. %) in a DMF/Acetone mixture (50:50 wt.) was used. Once dissolved, the fiber sheet was then manufactured using the electrospinning technique. To do this, an emitter voltage of 19 kV and a collector voltage of −7 kV were used. A flow rate of 10 ml/h through a linear multi-emitter injector was also used. The fibers were deposited on a rotating collector at 200 rpm covered by a 30 g/m.sup.2 non-woven PP substrate and at a distance of 20 cm. Said manufacture was carried out at a temperature of 30° C. and a relative humidity of 30%. This layer has a surface density of 3 g/m.sup.2. After production, a 30 g/m.sup.2 PP layer was placed on the PVDF deposition and calendered at 80° C. so that the final material ends up like the multilayer filter illustrated in FIG. 2.

TABLE-US-00002 Material Grammage (g/m.sup.2) Outer Layer Non-woven PP spunbond 30 Intermediate Electrospun PVDF with 3 Layer beaded fibers Inner Layer Non-woven PP spunbond 30

[0112] The PVDF layer generated by electrospinning was observed with a scanning electron microscope (SEM), resulting in a fiber structure of around 200 nanometres with micrometre-sized beaded structures, which correspond to areas of the fibers where their size increases considerably forming a type of particle, thus being called beaded fibers. This beaded morphology provides advantages in the breathability of the fabric since the beads help to optimize the packing density of the fiber and the presence thereof increases the distance between the fibers to reduce the pressure drop on the filters.

[0113] Assays of resistance to penetration with paraffin oil according to standard 149:2001+A1:2009 (point 8.11) gave a value of 17.8%; therefore, this filter would be classified as FFP1 type (out of every 100 aerosol particles, 20 or less than 20 pass).

Example 3: FFP2 Tri-Layer Structure System with Smooth Ultrafine Electrospun PAN and Zinc Oxide Fibers

[0114] The central layer was made of polyacrylonitrile (PAN). To do this, a solution of PAN at 11% by weight (wt. %) with dimethylformamide (DMF) and zinc oxide (ZnO) nanoparticles in a percentage of 2 by weight (wt. %) was used to generate antimicrobial properties. Once dissolved, the fiber sheet was then manufactured using the electrospinning technique. To do this, an emitter voltage of 30 kV and a collector voltage of −10 kV were used, and a flow rate of 5 ml/h through a linear multi-emitter injector was also used. The fibers were deposited on a rotating collector at a speed of 200 rpm covered by a 30 g/m.sup.2 non-woven PP substrate and at a distance of 20 cm. Said manufacture was carried out at a temperature of 30° C. and a relative humidity of 30%. This layer has a surface density of 0.5 g/m.sup.2. After production, a 30 g/m.sup.2 non-woven PP layer was placed on the PAN deposition and calendered at 80° C. so that the final material ends up similar to the multilayer filter described in FIG. 1.

TABLE-US-00003 Material Grammage (g/m.sup.2) Outer Layer Non-woven PP spunbond 30 Intermediate Electrospun PAN with 0.5 Layer smooth fibers Inner Layer Non-woven PP spunbond 30

[0115] Likewise, the antimicrobial properties of this structure were evaluated using a modification of the Japanese Industrial Standard JIS Z 2801 (ISO 22196:2007) against the strains of Staphylococcus aureus (S. aureus) CECT240 (ATCC 6538p) and Escherichia coli (E. coli) CECT434 (ATCC 25922). The filters were analysed in terms of the capacity to inhibit the growth of these populations in the material and it was observed, as illustrated in Table 1, that the filters showed strong growth inhibition of both strains (R≥3) with a reduction of 3 recorded units with respect to the control (filters without ZnO) on the first day of measuring it. These results indicate that these filters efficiently inhibit this type of strain, since an R<0.5 would indicate that the inhibition of the material towards bacteria is not significant, while an R≥1 and <3 would indicate that it is slightly significant. An R≥3 would indicate that it is clearly significant, which means that the inhibition of the growth of microorganisms is effective and constant over time.

TABLE-US-00004 TABLE 1 Reduction of S. aureus and E. coli on filters with antimicrobial capacity after 24 hours. Control PAN + 2% (PAN filter) ZnO filter Log Log Microorganism Days (CFU/ml) (CFU/ml) R S. Aureus 1 6.91 ± 0.06 3.00 ± 0.05 3.91 E. coli 1 6.91 ± 0.06 3.78 ± 0.08 3.13

[0116] Assays of resistance to penetration with paraffin oil according to standard 149:2001+A1:2009 (point 8.11) gave a value of 5%; therefore, this filter would be classified as FFP2 type (of every 100 aerosol particles, 6 or less than 6 pass).

Example 4: Bactericidal Properties as a Function of the Contact Time of an Intermediate Layer of Smooth Ultrafine Electrospun PAN and Zinc Oxide Fibers

[0117] The central nanofiber layer was made of polyacrylonitrile (PAN). To do this, a solution of PAN at 11% by weight (wt. %) with dimethylformamide (DMF) and zinc oxide (ZnO) nanoparticles with a percentage of 3 by weight (wt. %) was used to generate antimicrobial properties. Once dissolved, the fiber sheet was then manufactured using the electrospinning technique. To do this, an emitter voltage of 30 kV and a collector voltage of −10 kV were used, and a flow rate of 5 ml/h through a linear multi-emitter injector was also used. The fibers were deposited on a rotating collector at a speed of 200 rpm covered by a black conductive non-porous polyethylene substrate. The nanofiber layer had a surface density of 0.4 g/m.sup.2.

[0118] The antimicrobial properties of this structure were evaluated using a modification of the Japanese Industrial Standard JIS Z 2801 (ISO 22196:2007) against the strains of Staphylococcus aureus (S. aureus) CECT240 (ATCC 6538p) and Escherichia coli (E. coli) CECT434 (ATCC 25922) over a period of up to 8 hours. The filters were analyzed in terms of the capacity to inhibit the growth of these populations in the material and it was observed, as illustrated in Table 2, that the filters showed strong growth inhibition of both strains (R≥3) with a reduction of 3 recorded units with respect to the control (filters without ZnO) at 3 hours of contact. These results indicate that these filters efficiently inhibit this type of strain, since an R<0.5 would indicate that the inhibition of the material towards bacteria is not significant, while an R≥1 and <3 would indicate that it is slightly significant. An R≥3 would indicate that it is clearly significant, which means that the inhibition of the growth of microorganisms is effective and constant over time.

TABLE-US-00005 TABLE 2 Reduction of S. aureus and E. coli on filters with antimicrobial capacity after 1, 3, 6 and 8 hours of contact. Control Nanofibers Time (h) Log (CFU/ml) Log (CFU/ml) R S. aureus 1 6.01 ± 0.11 3.76 ± 0.21 2.25 (99%) 3 6.86 ± 0.17 3.68 ± 0.15 3.18 (99.9%) 6 7.18 ± 0.19 3.10 ± 0.18 4.08 (99.99%) 8 7.86 ± 0.13 2.99 ± 0.17 4.87 (99.999%) E. coil 1 5.98 ± 0.09 3.96 ± 0.11 2.02 (99%) 3 6.36 ± 0.10 3.29 ± 0.13 3.07 (99.9%) 6 7.01 ± 0.14 3.32 ± 0.10 3.69 (99.99%) 8 7.88 ± 0.11 3.28 ± 0.15 4.60 (99.999%)

Example 5: Bactericidal Properties as a Function of the Time of a Surgical Mask with Smooth Ultrafine Electrospun PVDF and Zinc Oxide Fibers

[0119] The central layer was made of polyvinylidene fluoride. To do this, a solution of PVDF at 13% by weight (wt. %) in a DMF/Acetone mixture (50:50 wt.) and with 3 percent by weight of ZnO (wt. %) with respect to the polymer was used. This solution was sonicated for 3 minutes before being electrospun, and then the fiber sheet was manufactured. To do this, an emitter voltage of 30 kV and a collector voltage of −10 kV were used, and a flow rate of 5 ml/h through a linear multi-emitter injector was also used. These ultrafine fibers were deposited on a roll-to-roll system in LE-500-Fluidnatek equipment from Bioinicia SL on a 17 g/m.sup.2 polypropylene (PP) spunbond substrate and at a distance of 20 cm. Said manufacture was carried out at a temperature of 30° C. and a relative humidity of 30%. This layer had a surface density of 0.3 g/m.sup.2. It was then laminated to another 17 g/m.sup.2 PP spunbond layer in a laminator and sealed on the edges with ultrasound. This roll was used to make a surgical mask sealed by stitching and adding two more 30 g/m.sup.2 PP spunbond layers to each side.

TABLE-US-00006 Material Grammage (g/m.sup.2) Double Outer Layer Non-woven PP spunbond 30 and 17 Intermediate Layer Electrospun PVDF with 0.3 smooth fibers Double Inner Layer Non-woven PP spunbond 17 and 30

[0120] The bactericidal performance of this mask configuration was determined according to the guidelines of the macrodilution protocol, which is described in Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically; Approved Standard-Tenth. Edition (M07-A10) by the Clinical and Laboratory Standards Institute (CLSI)). The antibacterial properties of this structure were evaluated against strains of Staphylococcus aureus (S. aureus) CECT240 (ATCC 6538p) and Escherichia coli (E. coli) CECT434 (ATCC 25922) over 8 hours and the results are shown in Table 3.

[0121] In this case, it was observed that the mask showed strong growth inhibition of both strains with a reduction of 3 recorded units with respect to the control (same mask, but without ZnO) after 8 hours of contact, showing that the antimicrobial activity after 1 hour already indicated that there was a slightly significant inhibition of the mask against both strains. An R<0.5 would indicate that the inhibition of the material towards bacteria is not significant, while an R≥1 and <3 would indicate that it is slightly significant. An R≥3 would indicate that it is clearly significant, which means that the inhibition of the growth of microorganisms is effective and constant over time (See Table 3).

TABLE-US-00007 TABLE 3 Reduction of S. aureus and E. coli in a surgical mask with bactericidal capacity after 1, 3, 6 and 8 hours of contact. Control Mask Time (h) Log (CFU/ml) Log (CFU/ml) R S. aureus 1 6.06 ± 0.21 4.53 ± 0.25 1.53 (95%) 3 6.91 ± 0.20 4.33 ± 0.18 2.58 (99.6%) 6 7.23 ± 0.16 4.22 ± 0.17 3.01 (99.9%) 8 7.91 ± 0.19 4.10 ± 0.20 3.81 (99.99%) E. coil 1 6.03 ± 0.18 4.61 ± 0.15 1.42 (95%) 3 6.42 ± 0.21 4.19 ± 0.20 2.23 (99%) 6 7.11 ± 0.17 4.15 ± 0.19 2.96 (99.9%) 8 7.89 ± 0.15 4.12 ± 0.13 3.77 (99.99%)

Example 6: FFP2 Tri-Layer Structure System with Electrospun PHBV with Smooth Ultrafine Fiber Structure

[0122] The central layer was made of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) supplied by Ocenic Resins SL, Valencia. To do this, a solution of PHBV at 2% by weight (wt. %) in trifluoroethanol (TFE) was used. Once dissolved, it was manufactured with and without the addition of LiBr (0.2 wt %) and the fiber sheet was then manufactured using the electrospinning technique. To do this, an emitter voltage of 18 kV and a collector voltage of −8 kV were used, and a flow rate of 20 ml/h through a linear multi-emitter injector was also used. The fibers were deposited on a rotating collector at a speed of 200 rpm covered by a 30 g/m.sup.2 biodegradable non-woven cellulose spunlace substrate and at a distance of 20 cm. Said manufacture was carried out at a temperature of 30° C. and a relative humidity of 30%. This layer has a surface density of 1 g/m.sup.2. After production, a 30 g/m.sup.2 biodegradable non-woven cellulose spunlace layer was placed on the PHBV deposition and calendered at 80° C. so that the final material ends up like the multilayer filter described in FIG. 3.

TABLE-US-00008 Material Grammage (g/m.sup.2) Top Layer Cellulose spunlace 30 Intermediate Layer Electrospun PHBV 1 Lower Layer Cellulose spunlace 30

[0123] The PHBV layer generated by electrospinning was observed with a scanning electron microscope, resulting in a fiber microstructure with a constant diameter of between approximately 200 and 300 nm, as can be seen in FIG. 4.

[0124] Biodisintegration assays were carried out according to ISO 20200 “Plastics—Determination of the degree of disintegration of plastic materials under simulated composting conditions in a laboratory-scale test”. The PHBV filter could be considered fully compostable according to ISO 20200 since the disintegration process of the PHBV nanofiber layer reached total disintegration after 20 days of assays. This short degradation time is probably related to the low thickness of the nanofiber layer of the filter, necessary for good breathing. The multilayer system reached complete disintegration in 80 days.

[0125] Assays of resistance to penetration with paraffin oil according to standard 149:2001+A1:2009 (point 8.11) gave a value of 5.5%; therefore, this filter would be classified as FFP2 type (of every 100 aerosol particles, 6 or less than 6 pass).

Example 7: FFP3 Multilayer Structure System with Sequentially Electrospun PVDF Arranged as a Symmetrical Sandwich

[0126] The central layer was made of polyvinylidene fluoride (PVDF, molecular weight 300 kDalton) at 13% by weight of DMF/Acetone (50:50 wt.). Once the solution was dissolved, the fiber sheet was then manufactured using the electrospinning technique. To do this, an emitter voltage of 25 kV, as well as a collector voltage of −10 kV, was used. A flow rate of 10 ml/h through a linear multi-emitter injector was also used. The fibers were deposited on a rotating collector (200 rpm) covered by a 30 g/m.sup.2 non-woven PP substrate and at a distance of 20 cm. Said manufacture was carried out at a temperature of 30° C. and a relative humidity of 30%. This layer has a surface density of 1 g/m.sup.2.

[0127] This same layer was prepared in duplicate under the same conditions, but at 0.5 g/m.sup.2 on a 30 g/m.sup.2 non-woven PP layer and it was folded like a symmetrical sandwich, so that the structure would be as shown in FIG. 4. This structure improves filtration performance because it fixes the fibers on the substrate and the entire filter is adhered by interaction between the nanofibers.

[0128] The PVDF layers generated by electrospinning were observed with a scanning electron microscope where a constant diameter of between approximately 200 and 300 nm was obtained. When this material was subsequently subjected to a washing cycle with stirring in hot water at 60° C. and detergent and then dried, the consistency and morphology of the intermediate layer measured by SEM is not affected.

[0129] Assays of resistance to penetration with paraffin oil according to standard 149:2001+A1:2009 (point 8.11) gave a value for the 1 g/m.sup.2 monolayer fiber structure of 2.3% (FFP2 type), while the symmetric sandwich double layer structure gave 0.9%. Therefore, the latter filter would be classified as FFP3 type (of every 100 aerosol particles, 1 or less than 1 passes).

[0130] Resistance to inhalation was measured according to EN149: 2001+A1:2009 (point 8.9) over an area of approximately 53 cm.sup.2 on Sheffield test head equipment with constant breathing and a digital flow meter. Respiration results for the monolayer were 0.7 millibars for an air flow of 30 l/min; and results for the double layer structure were 0.8 millibars, within the limits of the FFP3 certification. Inhalation assays carried out at 85 l/min, as recommended by the N95 certification, gave values of 3.3 for the double-layer structure, within the limits of N95.

Example 8: FFP3 Tri-Layer Structure System with Several Layers Electrospun by Co-Deposition

[0131] The central layer was made of polyvinylidene fluoride (PVDF, molecular weight 300 kDalton) and polyacrylonitrile (PAN) to obtain a filter with different fiber diameters. To do this, a solution of PVDF at 13% by weight (wt. %) in DMF/Acetone (50:50 wt.) and a solution of PAN at 11% by weight (wt. %) in DMF were used. Once both solutions were dissolved, the fiber sheet was then manufactured using the electrospinning by co-deposition technique, wherein both types of fibers are simultaneously electrospun by two linear multi-emitter injectors. To do this, an emitter voltage of 18 kV and 25 kV was used for the solution of PVDF and PAN, respectively, as well as a collector voltage of −30 kV. A flow rate of 13.8 ml/h for PVDF and 3 ml/h for PAN through 2 linear multi-emitter injectors placed in parallel was also used. The fibers were deposited on a rotating collector (200 rpm) covered by a 30 g/m.sup.2 non-woven PP substrate and at a distance of 20 cm. Said manufacture was carried out at a temperature of 30° C. and a relative humidity of 30%. This layer has a surface density of 1.2 g/m.sup.2.

[0132] After production, a 30 g/m.sup.2 non-woven PP layer was placed on the PAN deposition and calendered at 80° C. so that the final material ends up like the multilayer filter illustrated in FIG. 5.

TABLE-US-00009 Material Grammage (g/m.sup.2) Top Layer Non-woven PP spunbond 30 Intermediate Co-electrospun PVDF 1.2 (1 PVDF + 0.2 PAN) Layer and PAN Lower Layer Non-woven PP spunbond 30

[0133] The PVDF and PAN layer generated by electrospinning was observed with a scanning electron microscope where a constant diameter of between approximately 150 and 250 nm for the PAN fibers and a diameter of between 300-500 nm for the PVDF fibers were obtained.

[0134] Assays of resistance to penetration with paraffin oil according to standard 149:2001+A1:2009 (point 8.11) gave a value for the 1.2 g/m.sup.2 structure of 0.6%. Therefore, the latter filter would be classified as FFP3 type (of every 100 aerosol particles, 1 or less than 1 passes).

Example 9: Electrospun Tri-Layer Structure System with Micrometric Fibers

[0135] The central layer was made of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) supplied by Ocenic Resins SL, Valencia. To do this, a solution of PHBV at 6% by weight in trifluoroethanol (TFE) was used. Once dissolved, the fiber sheet was then manufactured using the electrospinning technique. To do this, an emitter voltage of 15 kV and a collector voltage of −8 kV were used, a flow rate of 20 ml/h through a multi-emitter injector was also used. The fibers were deposited on a rotating collector at a speed of 200 rpm covered by a 30 g/m.sup.2 biodegradable non-woven cellulose spunlace substrate and at a distance of 20 cm. Said manufacture was carried out at a temperature of 30° C. and a relative humidity of 30%. This layer has a surface density of 0.5 g/m.sup.2. After production, a 30 g/m.sup.2 non-woven cellulose spunlace layer was placed on the PHBV deposition.

[0136] The PHBV layer generated by electrospinning was observed with a scanning electron microscope, resulting in a fiber microstructure with a constant diameter of 900-1200 nm, as can be seen in FIG. 6.

[0137] Assays of resistance to penetration with paraffin oil according to standard 149:2001+A1:2009 (point 8.11) gave a value for the 0.5 g/m.sup.2 monolayer structure of 87%, corroborating the need to obtain ultrafine fibers for this particular application.

Example 10: Preparation of a Viricidal Intermediate Layer of Smooth Ultrafine Electrospun PVDF and Zinc Oxide Fibers

[0138] A solution of PVDF at 13% by weight (wt. %) in a DMF/Acetone mixture (50:50 wt.) and with amounts of ZnO particles of 3, 20 and 30 by weight (wt. %) with respect to the polymer. These solutions were sonicated for 3 minutes before being electrospun, and then the fibers were deposited. To do this, an emitter voltage of 30 kV and a collector voltage of −10 kV were used, and a flow rate of 5 ml/h through a linear multi-emitter injector was also used. These ultrafine fibers were deposited on a rotating collector at a speed of 200 revolutions per minute (rpm) on a black conductive non-porous polyethylene substrate. Said manufacture was carried out at a temperature of 30° C. and a relative humidity of 30%. This nanofiber layer had a surface density of 0.3 g/m.sup.2.

[0139] The viricidal properties of the nanofibers produced were studied on this system. To do this, the standard for determining antiviral activity in textiles (ISO 18184:2019) against a feline coronavirus strain (Feline Coronavirus, strain Munich) was used. These assays were performed at the certified MSL Solutions Providers facility, Bury, GB. As can be observed in Table 4, the nanofiber layer without the antimicrobial agent showed a certain antiviral nature, probably due to the nanometric topography of the material. However, the addition of the viricidal agent showed very strong inhibition of up to 97.13% for the highest content. The viricidal effect did not significantly increase with the increase in ZnO content, probably because higher contents lead to the agglomeration of antimicrobial particles.

TABLE-US-00010 TABLE 4 Percentage of growth inhibition against feline coronavirus after 2 hours of contact. Percentage of inhibition at Sample Reduction 2 hours of contact Control (PVDF fibers without ZnO) 0.58 73.90% PVDF fibers + ZnO at 3 wt. % 1.44 96.41% PVDF fibers + ZnO at 20 wt. % 1.39 95.92% PVDF fibers + ZnO at 30 wt. % 1.54 97.13%

Example 11: Three-Layer Sandwich Mask Model

[0140] Hygienic masks were assembled as a sandwich-like structure, where the interlayer was made of nanofiber of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). To do this, a 2.5 wt. % of PHBV and a 0.05 wt. % hexadecyltrimethylammonium bromide (CTAB) was dissolved in trifluoroethanol (TFE). Once dissolved, the solution was electrospun at a voltage of 48 kV at the emitter and a voltage in the collector of −25 kV. A flow rate of 340 g/h was used in a multi-injector emitter. The fibers were deposited over a Nylon 80 mesh textile with a grammage of 20 g/m.sup.2. For the electrospinning, a Fluidnatek LE-500 with a roll-to-roll system was used at a speed of 65 mm/s. The layer of PHBV was deposited at a density of 0.3 g/m.sup.2 and had a fiber diameter of 200-300 nm. After electrospinning deposition, the material was laminated without temperature and a non-coated layer of Nylon 80 mesh was applied on top of the PHBV electrospun mesh.

[0141] From this material, the mask was confectioned using an industrial process based in the following stages: Folding and flattening, sewing and cutting process, together with elastic fasteners sewing

[0142] Translucency was measured using a spectrophotometer visible-UV (DINKO UV4000), obtaining a value of 3.9 mm.sup.−1. This showed a good translucency allowing the interlocutor to see through the user's mask.

[0143] Aerosols Filtration was carried out by penetration resistance assay with paraffin oil following the standard EN149:2001+a1:2009 (point 8.11), employing an equipment PALAS PMFT1000. The obtained value of filtration was 90%, and a pressure drop of 264 Pa in 100 cm.sup.2 area using a flow rate of 160 l/min.

[0144] The material developed in this example was evaluated by the certifying company Eurofins, where the bacterial filtration efficiency (BFE) was measured following the EN 14683: 2019+AC: 2019 Annex B standard, obtaining a value of 75.6%. The exhalation of the samples was also evaluated following Annex C of the EN 14683: 2019+AC: 2019 standard, obtaining a value of 39 Pa/cm.sup.2.

[0145] The three layers disposition, where the internal and external layer are equal, is shown in FIG. 7.

Example 12: Three-Layer Sandwich Mask Model with Microperforated Film

[0146] Hygienic masks were assembled in a sandwich-like structure, where the inner and interlayer layer were produced similar to the previous example with the same materials, whilst the outer layer was made of a transparent microperforated film of CPP (cast polypropylene). This layer had a thickness of 20 μm, and also a perforation diameter of 1.5 mm with a separation between them of 3.5 mm and a surface density of 30 g/m.sup.2 (FIG. 8).

[0147] Layers were laminated without temperature, then the mask was confectioned using an industrial process based in the following stages: Folding and flattening, ultrasonic bonding and cutting process together with elastic fasteners ultrasonic bonding.

[0148] Translucency was measured using a spectrophotometer visible-UV (DINKO UV4000), obtaining a value of 3.5 mm.sup.−1. This showed a good translucency allowing the interlocutor to see through the user's mask.

[0149] Aerosols Filtration was carried out by penetration resistance assay with paraffin oil following the standard EN149:2001+a1:2009 (point 8.11), employing an equipment PALAS PMFT1000. The obtained value of filtration was 80%, and a pressure drop of 218 Pa in 100 cm.sup.2 area using a flow rate of 160 l/min.

Example 13: Four Layers Sandwich Mask Model

[0150] Hygienic masks were assembled in a sandwich-like structure of four layers, where the interlayer was prepared with nanofiber of Polyvinylidene fluoride (PVDF) with 500 kDa of molecular weight. To this end, a 13 wt. % of PVDF was dissolved in a mixture of DMF/Acetone (50:50 weight ratio). Once dissolved, the solution was electrospun at a voltage of 47 kV at the emitter and a voltage in the collector of −25 kV. A flow rate of 360 g/h was used in a multi-injector emitter. The fibers were deposited over a Nylon 80 mesh textile with a grammage of 20 g/m.sup.2. For the electrospinning, a Fluidnatek LE-500 with a roll-to-roll system was used at a speed of 65 mm/s. The layer of PHBV was deposited at a density of 0.25 g/m.sup.2 and had a fiber diameter of 200-300 nm.

[0151] After electrospinning deposition, the material was laminated without temperature and another similar layer was applied on top following the structure showed in the FIG. 9. Therefore, the second and third layers are formed by electrospun PVDF, with a surface density of 0.25 g/m.sup.2 on each one of the layers.

[0152] From this material, the mask was confectioned using an industrial process based in the following stages: Folding and flattening, sewing; and cutting process together with elastic fasteners sewing

[0153] As the same of the previous examples, translucency was measured using a spectrophotometer visible-UV (DINKO UV4000), obtaining a value of 2 mm.sup.−1. This showed a good translucency allowing the interlocutor to see through the user's mask.

[0154] Aerosol's filtration was carried out by penetration resistance assay with paraffin oil following the standard 149:2001+a1:2009 (point 8.11), employing and equipment PALAS PMFT1000. The obtained value of filtration was 90%, and a pressure drop of 184 Pa in100 cm.sup.2 using a flow rate of 160 l/min.