ELECTROSPUN NANOFIBROUS POLYMER MEMBRANE FOR USE IN AIR FILTRATION APPLICATIONS

Abstract

An electrospun polymer nanofibrous membrane that provides high filtering efficiency and excellent porosity is disclosed herein. The membrane may be treated with one or more antimicrobial or antiviral agents. The treatment may preferably be a coating of one or more antiviral agents on the surface of the membrane. Alternatively, one or more antiviral agents may be impregnated into the membrane. The membrane may additionally or alternatively be impregnated with one or more metal-organic frameworks (MOFs). The membrane has a high filtering efficiency and sufficient porosity to provide breathability characteristics. In some embodiments, the membrane is suitable for use in making facemasks and respirators that are highly resistant to infectious pathogens and/or other small particulates. In some embodiments, the membrane is suitable for use in HVAC applications. In some embodiments, the membrane is suitable for use in removal of VOCs and CO.sub.2 in conjunction with a carbon nanofiber membrane.

Claims

1. An electrospun polymer nanofibrous membrane having a high filtration efficiency comprising polyvinylidene fluoride, one or more Tecophilic™ thermoplastic polyurethanes, or a blend of polyvinylidene fluoride and one or more Tecophilic™ thermoplastic polyurethanes, wherein the membrane is treated with one or more anti-pathogenic agents.

2. The membrane of claim 1, wherein the one or more anti-pathogenic agents comprise an antiviral agent.

3. The membrane of claim 2, wherein the antiviral agent is selected from the group consisting of graphene, nanoparticles, nanocomposites, multivalent metallic ions, and extracts from natural products.

4. The membrane of claim 3, wherein the antiviral agent comprises a silver-doped titanium dioxide nanomaterial.

5. The membrane of claim 3, wherein the antiviral agent comprises multivalent Cu.sup.2+ or Zn.sup.2+ cations.

6. The membrane of claim 3, wherein the antiviral agent comprises a licorice extract.

7. The membrane of claim 1, wherein the membrane is electrospun from a polymer solution that includes a surfactant selected from the group consisting of cetrimonium bromide (CTAB), lauramidopropyl betaine (LAPB), and alpha olefin sulfonate (AOS).

8. The membrane of claim 2, wherein the membrane comprises multiple integrated layers with distinguishable microstructure characteristics.

9. The membrane of claim 8, wherein the membrane is composed of three layers including a first and third layer having equal pore size separated by a second layer having a different pore size.

10. The membrane of claim 8, wherein the membrane is composed of three layers with three different pore sizes.

11. The membrane of claim 9, wherein the first and third layers have a larger pore size and the second layer has a smaller pore size, and wherein the mechanical integrity and binding forces between layers of the membrane is enhanced by electrospraying short fibers prior to electrospinning a subsequent layer of the membrane or by electrospinning wet fibers by decreasing the screen distance to generate a “tacky surface” prior to electrospinning a subsequent layer of the membrane.

12. The membrane of claim 8, wherein the membrane is formed by winding a textile material roll comprising a textile material from a first side to a second side and then performing the following steps in order: a. electrospinning one or more first nanofiber layers on the first side of the textile material at a first winding speed; b. flipping the textile material roll; and c. electrospinning one or more second nanofiber layers on the second side of the textile material at a second winding speed; wherein the first winding speed is different from the second winding speed.

13. The membrane of claim 8, wherein the membrane is formed by winding a textile material roll comprising a textile material from a first side to a second side and then performing the following steps in order: a. electrospinning one or more first nanofiber layers on the first side of the textile material at a first winding speed; and b. electrospinning one or more second nanofiber layers on the first side of the textile material at a second winding speed; wherein the first winding speed is different from the second winding speed.

14. The membrane of claim 8, wherein the membrane is formed by winding a textile material roll comprising a textile material from a first side to a second side and then performing the following steps in order: a. electrospinning one or more first nanofiber layers on the first side of the textile material at a first winding speed; b. electrospinning one or more second nanofiber layers on the first side of the textile material at a second winding speed; c. flipping the textile material roll; and d. electrospinning one or more third nanofiber layers on the second side of the textile material at a third winding speed; wherein the first winding speed is different from the second winding speed.

15. The membrane of claim 1, wherein the membrane is triboelectrically charged using a triboelectric nanogenerator (TENG).

16. The membrane of claim 15, wherein the membrane comprises three layers, including a tribo-positive layer of polyamide (PA66) nanofibers, a tribo-negative layer of poly (vinylidene fluoride) (PVDF) nanofibers, and a conductive electrode layer with polypyrrole, silver nanowires, or a conductive fabric.

17. The membrane of claim 1, wherein the membrane is suitable for use in a facemask or respirator.

18. The membrane of claim 1, wherein the membrane is suitable for use in an air filter configured for use in an HVAC system or for use in an air filter configured for use in the removal of VOCs and CO.sub.2 in conjunction with a carbon nanofiber membrane.

19. An electrospun polymer nanofibrous membrane having a high filtration efficiency comprising polyvinylidene fluoride, one or more Tecophilic™ thermoplastic polyurethanes, or a blend of polyvinylidene fluoride and one or more Tecophilic™ thermoplastic polyurethanes, wherein one or more anti-pathogenic agents is impregnated into the membrane, wherein the membrane comprises multiple integrated layers with distinguishable microstructure characteristics.

20. The membrane of claim 19, wherein the membrane is composed of three layers including a first and third layer having equal pore size separated by a second layer having a different pore size, wherein the first and third layers have a larger pore size and the second layer has a smaller pore size, and wherein the mechanical integrity and binding forces between layers of the membrane is enhanced by electrospraying short fibers prior to electrospinning a subsequent layer of the membrane or by electrospinning wet fibers by decreasing the screen distance to generate a “tacky surface” prior to electrospinning a subsequent layer of the membrane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 shows representative scanning electron microscopy (SEM) images of embodiments of the disclosed nanofibrous polymer membranes.

[0043] FIG. 2 shows fiber diameter measurements and distribution for representative samples of an embodiment of the disclosed nanofibrous polymer membrane.

[0044] FIG. 3 shows pore size distribution for representative samples of an embodiment of the disclosed nanofibrous polymer membrane as determined by mercury porosimeter analysis.

[0045] FIG. 4 shows average porosity and the distribution of mean porosity for representative samples of an embodiment of the disclosed nanofibrous polymer membrane.

[0046] FIG. 5 shows mechanical tensile strength test results for representative samples of an embodiment of the disclosed nanofibrous polymer membrane.

[0047] FIG. 6 shows filtration efficiency test results for representative samples of an embodiment of the disclosed nanofibrous polymer membrane.

[0048] FIG. 7 shows latex filtration test results for representative samples of an embodiment of the disclosed nanofibrous polymer membrane.

[0049] FIG. 8 shows viral filtration efficiency test results for representative samples of an embodiment of the disclosed nanofibrous polymer membrane.

[0050] FIG. 9 shows bacteria filtration efficiency test results for representative samples of an embodiment of the disclosed nanofibrous polymer membrane.

[0051] FIG. 10 shows flammability test results for a representative sample of an embodiment of the disclosed nanofibrous polymer membrane.

[0052] FIG. 11 shows antiviral properties test results for representative samples of an embodiment of the disclosed nanofibrous polymer membrane.

[0053] FIG. 12 shows antibacterial properties test results for representative samples of an embodiment of the disclosed nanofibrous polymer membrane.

[0054] FIG. 13 shows how filtration efficiency is affected by the flow rate of aerosols through the membrane.

[0055] FIG. 14 shows how the pressure drop across the membrane is affected by the flow rate of aerosols through the membrane.

[0056] FIG. 15 shows an embodiment of a system for removing volatile organic compounds and carbon dioxide.

[0057] FIG. 16 shows the basic repeat units of rectangular, hexagonal, and trihexagonal opening patterns for mesh substrates.

[0058] FIG. 17 shows a schematic representation of a flexible, breathable, and antimicrobial facemask based on an all-nanofiber TENG (NF-TENG) platform.

DETAILED DESCRIPTION

[0059] An electrospun polymer nanofibrous membrane that provides high filtering efficiency and excellent porosity is disclosed herein.

[0060] The membrane may be treated with one or more antimicrobial or antiviral agents. In some embodiments, the membrane may be treated with an antiviral agent selected from the group consisting of graphene, nanoparticles, nanocomposites, multivalent metallic ions, and medicinal or other extracts from natural products. The treatment may preferably be a coating of one or more antiviral agents on the surface of the membrane. Alternatively, one or more antiviral agents may be impregnated into the nanofibrous membrane.

[0061] The membrane may additionally or alternatively be impregnated with one or more metal-organic frameworks (MOFs). The one or more MOFs may, for example, be one or more zirconium MOFs. The MOFs may provide filtration of chemical warfare agents (CWAs) and other toxic chemical agents and, in some embodiments, may also provide additional or alternate filtration of small particulates and pathogens.

[0062] The membrane may additionally or alternatively incorporate one or more photocatalytic agents for the removal of volatile organic compounds (VOCs).

[0063] The disclosed membrane may preferably have a high filtering efficiency.

[0064] In some embodiments, the porosity of the disclosed membrane may be sufficient to provide breathability characteristics suitable for use as a facemask or respirator. The disclosed membrane is suitable for use in making facemasks and respirators that are highly resistant to infectious pathogens and/or other small particulates.

[0065] In some embodiments, the disclosed membrane may be suitable for use in making air filters for use in indoor air filtration applications, such as use in air filters for HVAC systems.

[0066] In some embodiments, the disclosed membrane may be used in conjunction with a separate membrane that facilitates removal of carbon dioxide, such as a carbon nanofiber membrane.

[0067] The disclosed membrane may preferably have a filtering efficiency of at least 95%, more preferably at least 98%, even more preferably at least 99%, and most preferably at least 99.5%.

[0068] In some embodiments, the disclosed membrane may be substantially transparent. The transparency may preferably be at least 80%.

[0069] The disclosed membrane may preferably be capable of intercepting and exterminating infectious pathogens on its surfaces.

[0070] In some preferred embodiments, the disclosed membrane is non-flammable.

[0071] The disclosed membrane may be suitable for the production of non-flammable high-performance textiles.

[0072] In some preferred embodiments, the disclosed membrane is ultrathin and lightweight.

[0073] In some preferred embodiments, the disclosed membrane does not degrade upon exposure to water or selected organic solvents such as ethanol or acetone. Thus, products made using the membrane may be washed and reused.

[0074] In some embodiments, the nanofibrous polymer membrane may be made from polyvinylidene fluoride (PVDF). In some alternate embodiments, the nanofibrous polymer membrane may be made from one or more Tecophilic™ thermoplastic polyurethanes (TPUs). In other alternate embodiments, the nanofibrous polymer membrane may be made from one or more polycaprolactams. In some additional alternate embodiments, the nanofibrous polymer membrane may be made from polyvinylpyrrolidone (PVP). In some additional alternate embodiments, the nanofibrous polymer membrane may be made from poly(vinylidene fluoride-co-hexafluoro propylene) (PVDF-HFP). In some additional alternate embodiments, the nanofibrous polymer membrane may be made from polylactic acid (PLA). In some other alternate embodiments, the nanofibrous polymer membrane may be made from a blend of two or more of polyvinylidene fluoride, one or more Tecophilic™ thermoplastic polyurethanes, one or more polycaprolactams, polyvinylpyrrolidone, poly(vinylidene fluoride-co-hexafluoro propylene), and polylactic acid.

[0075] The nanofibrous polymer membrane may be made using electrospinning techniques. A polymer is dissolved in a solvent prior to electrospinning. In some embodiments, the solvent may preferably be selected from the group consisting of dimethylformamide (DMF), dimethylacetamide (DMA), ethanol, hexafluoroisopropanol (HFIP), acetone, ethyl acetate, dichloromethane (DCM), formic acid, water, or a combination thereof. In some preferred embodiments, the solvent may be hexafluoroisopropanol (HFIP).

[0076] In some embodiments, a surfactant may be added to the polymer solution. Adding a surfactant to the polymer solution may promote a smaller fiber diameter and thus yield a membrane which has a smaller pore size and thus higher filtration efficiency. In some preferred embodiments, the surfactant may be one or more surfactants selected from the group consisting of cetrimonium bromide (CTAB), lauramidopropyl betaine (LAPB), and alpha olefin sulfonate (AOS).

[0077] In some embodiments, a salt or salt solution may be added to the polymer solution. Adding a salt or salt solution to the polymer solution may promote formation of thinner and more uniform fibers, may reduce bead formation, and/or may increase branching within the fibers. By increasing charge density and conductivity, the presence of salts in the polymer solution promotes elongation of the spinning jet, which leads to the generation of thinner fibers. In some preferred embodiments, the salt or salt solution may be one or more salts or salt solutions selected from the group consisting of alkali metal halides, substituted or unsubstituted ammonium halides, and phosphate-buffered saline (PBS). In some more preferred embodiments, the salt or salt solution may be one or more salts selected from the group consisting of sodium chloride (NaCl), lithium chloride (LiCl), and potassium chloride (KCl).

[0078] The nanofibrous polymer membrane may be a single layer membrane or may alternatively be an integrated multi-layer membrane. In some embodiments, the membrane may be composed of multiple integrated layers with distinguishable microstructure characteristics. A membrane that is composed of multiple integrated layers may provide enhanced filtration efficiency and low airflow resistance. Low airflow resistance corresponds to high breathability in applications where this is relevant. The enhanced filtration efficiency of an integrated multi-layer membrane may result from superior barrier protection against small pathogen particles and small diameter particulate matter.

[0079] In some embodiments, the integrated multi-layer membrane is composed of two layers with different pore sizes. In some alternate embodiments, the integrated multi-layer membrane is composed of three layers with two layers of equal pore size separated by a layer with a different pore size. The pore size may preferably be between 1 and 20 .Math.m for the layer(s) with smaller pore size and between 20 and 200 .Math.m for the layer(s) with larger pore size.

[0080] In embodiments with three layers having two layers of equal pore size separated by a layer with a different pore size, the layers of equal size may preferably have a larger pore size and the layer in between these two layers may preferably have a smaller pore size. This configuration decreases the likelihood of delamination and also decreases the pressure drop that is generated as a gas passes through the multi-layer membrane, which corresponds to increased breathability, without appreciably reducing the filtration efficiency of the membrane.

[0081] In some other alternate embodiments, the integrated multi-layer membrane is composed of three layers with three different pore sizes.

[0082] The pore size of the layers in integrated multi-layer membranes may be adjusted by adjusting the viscosity of the polymer solution and the electrospinning process conditions. Electrospinning process conditions may be adjusted to further stabilize the spinning jet used in the electrospinning setup. Solutions with lower viscosity will typically generate smaller pore size layers, and solutions with higher viscosity will typically generate larger pore size layers.

[0083] In some embodiments, the mechanical integrity and binding forces between layers of the membrane may be enhanced by electrospraying short fibers prior to electrospinning the subsequent layer. In some other embodiments, the mechanical integrity and binding forces between layers of the membrane may be enhanced by electrospinning wet fibers by decreasing the screen distance to generate a “tacky surface” prior to electrospinning the subsequent layer.

[0084] In some embodiments, the disclosed nanofibrous polymer membrane may be laminated onto a textile material. Alternatively, the nanofibers may be directly electrospun on nonwoven fabrics such as polyethylene terephthalate (PET), polypropylene (PP), polyamides such as PA6, PET copolymers, and spunbond Bico materials. Transparent nonwoven fabrics may be used for applications where transparency of the electrospun nanofibrous polymer membranes is desirable. The use of PET copolymers or spunbond Bico materials results in enhanced adhesion between the nanofibers and textile, which thereby reduces peeling.

[0085] In some embodiments, the disclosed nanofibrous polymer membrane is directly electrospun onto a mesh substrate. The mesh substrate may have an opening pattern specifically designed to be suitable for electrospinning nanofibers thereon. The opening pattern of the mesh substrate may, for example, be a rectangular, hexagonal, or trihexagonal opening pattern, as shown in FIG. 16. Electrospinning onto a mesh substrate may allow the production of a transparent or substantially transparent nanofibrous polymer membrane.

[0086] In some embodiments, the disclosed nanofibrous polymer membrane is triboelectrically charged using a triboelectric nanogenerator (TENG). This yields a membrane that is self-charging. In some embodiments, the nanofibrous tribo-negative layer may be composed of polyvinylidene fluoride (PVDF). In some embodiments, the nanofibrous tribo-positive layer may be composed of polyamide (PA66) nanofibers.

[0087] In some embodiments, the conductive electrode layer may be composed of a polypyrrole-coated nanofibrous membrane. In some alternate embodiments, the conductive electrode layer may be composed of silver nanofibers. In some other alternate embodiments, the conductive electrode layer may be composed of conductive fabrics

[0088] In some embodiments, a cellulose-based adhesive is applied to an electrospinning substrate prior to electrospinning to enhance the mechanical integrity of the nanofibrous membrane layers under high air flow conditions.

[0089] In some embodiments, a polyvinylacetate (PVAc) layer is electrospun onto an electrospinning substrate at the same time as electrospinning of the target polymer.

[0090] The disclosed nanofibrous polymer membrane may be treated with an anti-pathogenic agent such as an antiviral agent selected from the group consisting of graphene, nanoparticles, nanocomposites, multivalent metallic ions, and medicinal or other extracts from natural products. The graphene may be functionalized or non-functionalized. The nanoparticles may preferably be metal nanoparticles such as silver nanoparticles or zinc nanoparticles. The nanocomposites may preferably be silver-doped titanium dioxide nanomaterials. The multivalent metallic ions may preferably be metal ions such as Cu.sup.2+ or Zn.sup.2+ cations. The extracts from natural products may preferably be licorice extracts.

[0091] The anti-pathogenic agent(s) may be physically coated on the surface of the membrane. The coating may be applied using chemical or electrochemical methods such as atomic layer deposition, vapor deposition methods such as physical vapor deposition (PVD) or chemical vapor deposition (CVD), spray coating methods such as plasma spraying or spray painting, or physical coating methods such dip-coating or spin-coating.

[0092] The anti-pathogenic agent(s) may alternatively be incorporated into the membrane by blending the anti-pathogenic agent(s) into the polymer solution prior to electrospinning, thereby generating a membrane impregnated with the anti-pathogenic agent(s).

[0093] In some embodiments, the disclosed nanofibrous polymer membrane may be impregnated with one or more metal-organic frameworks (MOFs), such as zirconium MOFs. The MOFs may be incorporated into the membrane by blending the MOFs into the polymer solution prior to electrospinning, thereby generating a membrane impregnated with the MOFs.

[0094] In some embodiments, MOF-impregnation into the membrane may be in addition to coating with or impregnation of anti-pathogenic agent(s). In other embodiments, MOF-impregnation into the membrane may be an alternative to coating with or impregnation of anti-pathogenic agent(s). Membranes impregnated with MOFs may provide filtration of chemical warfare agents (CWAs) and other toxic chemical agents. In some embodiments, membranes impregnated with MOFs may also exhibit antiviral, antibacterial, or other anti-pathogenic properties.

[0095] Thus, it is not intended that the MOFs described herein are necessarily distinct from the anti-pathogenic agents, such as antiviral or antibacterial agents, described herein. Rather, the anti-pathogenic agent may be a MOF or may alternatively be one of the other anti-pathogenic agents described herein. It is also not intended that the MOFs described herein will necessarily exhibit antiviral, antibacterial, or other anti-pathogenic properties. MOFs that are impregnated in the disclosed membranes may provide filtration of chemical warfare agents (CWAs) and other toxic chemical agents but, in some embodiments, may not exhibit antiviral, antibacterial, or other anti-pathogenic properties or provide filtration of small particulates.

[0096] In some embodiments, the disclosed nanofibrous polymer membrane may be impregnated with one or more photocatalysts, such as TiO.sub.2, N-doped TiO.sub.2, Ag-doped TiO.sub.2, or Al.sub.2O.sub.3-TiO.sub.2. The photocatalyst may be incorporated into the membrane by blending the photocatalyst into the polymer solution prior to electrospinning, thereby generating a membrane impregnated with the photocatalyst.

[0097] In some embodiments, photocatalyst-impregnation into the membrane may be in addition to coating with or impregnation of anti-pathogenic agent(s). In other embodiments, photocatalyst-impregnation into the membrane may be an alternative to coating with or impregnation of anti-pathogenic agent(s). Membranes impregnated with photocatalysts may facilitate degradation of VOCs. In some embodiments, membranes impregnated with photocatalysts may also exhibit antiviral, antibacterial, or other anti-pathogenic properties.

[0098] Thus, it is not intended that the photocatalysts described herein are necessarily distinct from the anti-pathogenic agents, such as antiviral or antibacterial agents, described herein. Rather, the anti-pathogenic agent may be a photocatalyst or may alternatively be one of the other anti-pathogenic agents described herein. It is also not intended that the photocatalysts described herein will necessarily exhibit antiviral, antibacterial, or other anti-pathogenic properties. Photocatalysts that are impregnated in the disclosed membranes may facilitate degradation of VOCs but, in some embodiments, may not exhibit antiviral, antibacterial, or other anti-pathogenic properties.

[0099] In some embodiments, the photocatalyst-impregnated nanofibrous polymer membrane may be used in conjunction with a carbon nanofiber (CNF) membrane for removal of CO.sub.2. In some alternate embodiments, the membrane may have one or more photocatalyst-impregnated layers and one or more CNF layers.

[0100] The photocatalyst-impregnated membrane preferably exhibits high filtration efficiency, thermal insulation, and photodegradation capability, and allows for efficient VOC degradation and small particle filtration. The use of an additional CNF membrane in the system allows effective in situ CO.sub.2 capture during photocatalytic degradation. The rate of VOC degradation is preferably greater than 95%, and the CO.sub.2 adsorption rate is preferably greater than 20 mmol/m.sup.2s.

[0101] In some embodiments, a yttria-stabilized zirconia (YSZ) / silica nanofibrous membrane may be additionally or alternatively be used in the applications described herein, particularly in applications that include photocatalytic removal of VOCs.

[0102] To increase the breathability of textile materials coated with the disclosed nanofibrous polymer membranes, multiple nanofiber layers of differing thicknesses may be electrospun on the same or opposite sides of textile materials. A textile material that is in the form of a textile material roll may be coated with one or more nanofiber layers by electrospinning. In some embodiments, one or more first nanofiber layers are electrospun on a first side of a textile material at a first winding speed, the textile material roll is flipped, and one or more second nanofiber layers are electrospun on a second side of the textile material at a second winding speed, where the first winding speed is different from the second winding speed. In other embodiments, one or more first nanofiber layers are electrospun on a first side of a textile material at a first winding speed, and one or more second nanofiber layers are then electrospun on the first side of the textile material at a second winding speed, where the first winding speed is different from the second winding speed. In yet other embodiments, one or more first nanofiber layers are electrospun on a first side of a textile material at a first winding speed, one or more second nanofiber layers are then electrospun on the first side of the textile material at a second winding speed, the textile material roll is then flipped, and one or more third nanofiber layers are electrospun on a second side of the textile material at a third winding speed, where the first winding speed is different from the second winding speed. In yet other embodiments, additional electrospinning steps may be added to include additional nanofiber layers of different thicknesses on one or both sides of the textile material.

[0103] A facemask or respirator made from the disclosed nanofibrous polymer membrane is also disclosed herein. The facemask or respirator may preferably have a high filtration capacity and suitable breathability characteristics for comfortable use by a wearer. The disclosed facemask or respirator may preferably have a filtering efficiency of at least 95%, more preferably at least 98%, even more preferably at least 99%, and most preferably at least 99.9%.

[0104] In some embodiments, a facemask made from the disclosed nanofibrous polymer membrane is a flexible, breathable, and antimicrobial facemask based on an all-nanofiber TENG (NF-TENG) platform. In some embodiments, the facemask comprises multiple layers. In some embodiments, the multilayer facemask includes a tribo-positive layer of polyamide (PA66) nanofibers, a tribo-negative layer of poly (vinylidene fluoride) (PVDF) nanofibers, and a conductive electrode layer with polypyrrole, silver nanowires, or a conductive fabric.

[0105] A method of making a facemask or respirator from the disclosed nanofibrous polymer membrane is also disclosed herein. The method may preferably allow the anti-pathogenic, physical, chemical, and mechanical properties to be fine-tuned according to the requirements of the specific application.

[0106] A method of making an air filter for use in an HVAC system from the disclosed nanofibrous polymer membrane is also disclosed herein.

[0107] A method of making an air filter for use in the removal of VOCs and CO.sub.2 from the disclosed nanofibrous polymer membrane and a carbon nanofiber membrane is also disclosed herein.

Sample Preparation

[0108] The following sample preparation materials and methods are exemplary. Other suitable materials and methods may be used within the scope of the invention.

[0109] Materials. Multiple Tecophilic™ thermoplastic polyurethanes (TPU) were purchased from Lubrizol. Knyar 2801 polyvinylidene fluoride (PVDF) was purchased from Arkema. Zytel 7301 polycaprolactam was provided by DuPont. Hexafluoroisopropanol (HFIP) was purchased from Oakwood Products Inc. Dimethylacetamide (DMAc), acetone, formic acid, cetrimonium bromide (CTAB), lithium chloride (LiCl), and tetrabutylammonium chloride (TBAC) were purchased from Fisher Scientific. Silver nanopartcies (15 nm) were purchased from Skyspring Nanomaterials. ZnO and CuO (Zn—Cu) were purchased from Sigma Aldrich. Ag-doped TiO.sub.2 (Ag—TiO.sub.2) nanoparticles were provided by JM Material Technology Inc. Licorice extracts were provided by XSL USA Inc.

[0110] Solution Preparation. TPU polymers were added to HFIP to create 7 and 15 w/v solutions. 16.5% wt PVDF was dissolved in 3:1 DMAc/acetone containing 0.85% CTAB and 0.04% LiCl, NaCl, or TBAC. All of the solutions were mixed on a stirring plate until the polymer pellets/powder completely dissolved.

[0111] Antiviral Treatment. Two antiviral treatment methods were used: (1) the membranes were submerged in an aqueous dispersion containing antiviral particles, or (2) the antiviral agents were added to the polymer solutions to directly fabricate antiviral nanofibrous membranes. The antiviral agents used were 2% citric acid and silver, Ag—TiO.sub.2 and Zn-Cu nanoparticles, and licorice extracts.

[0112] Membrane Fabrication. The membrane fabrication process was a roll-to-roll system, where a textile material was wound from one side to the other side and the nanofiber layer was laminated on the textile during the winding process. The thickness of the nanofiber layers was controlled by controlling the winding speed.

[0113] The electrospinning process was performed in a single step or alternatively in at least three separate steps.

[0114] In the one-step process, one syringe was filled with a polyvinylacetate (PVAc) solution and one or more additional syringes were filled with the target polymer solution. The PVAc and target polymer solutions were electrospun simultaneously. The layer contacting the substrate was formed of PVAc and thereby provided increased adhesion between the substrate and the nanofibrous membrane layers.

[0115] In the three-step process, the substrate was first coated with a cellulose-based adhesive using a sponge coating process. Then electrospun nanofibers were coated onto the substrate. Finally, the coated substrates were dried by heating.

[0116] Functionalization. The membrane was functionalized either by adding the desired functionalizing agents to the electrospinning solution or by suspending the electrospun membrane in a dispersion of the desired functionalizing agent in a solvent, such as 2% zirconium MOF, 2% citric acid and silver, Ag—TiO.sub.2, ZnO or CuO nanoparticles, or licorice extract.

[0117] Photocatalyst-Impregnated Membrane Preparation. A photocatalyst precursor is prepared with 2.5 mL of a 1-100 mg/mL solution of a photocatalytic material or photocatalytic material precursor selected from the group consisting of titanium tetraisopropoxide, Al(acac).sub.3, and AgNO.sub.3, 0.3 g of a surfactant selected from the group consisting of polyvinylpyrrolidone (PVP), lauramidopropyl betaine (LAPB), alpha olefin sulfonate (AOS), and cetrimonium bromide (CTAB), 4.5 mL of ethanol, and 3.0 mL of acetic acid. The solution is subsequently stirred on a stirring plate for over 12 h.

[0118] Nanofibers carriers for the photocatalyst are fabricated using an electrospinning apparatus. The process parameters used for electrospinning are a flow rate of 0.5 mL/h, a vertical distance from the needle to grounded aluminum foil of 10-15 cm, and an applied voltage of 15-20 kV. The electrospun nanofibers are calcined at 600° C. for 2 h in air, with a ramping rate of 1-3° C./min.

[0119] The nanofiber carriers are submerged in the prepared photocatalyst precursor for 5 min under vacuum and then rinsed thrice with 2-propanol. The photocatalyst-impregnated nanofibers are dried overnight under ambient conditions, and are then calcined at 500° C. for 1 h in air, with a ramping rate of 5° C./min.

[0120] Carbon Nanofiber Membrane Preparation. A carbon nanofiber membrane is prepared by treating an eletrospun nanofiber mat. The prepared eletrospun nanofiber mat is chemically dehydrofluorinated at 70° C. for 1 h in a 4 M aqueous NaOH solution containing 12.5 mM of tetrabutylammonium bromide (TBAB). After chemical dehydrofluorination is complete, the mat is washed with water and ethanol several times, and is then dried under reduced pressure at 60° C. Finally, the mat is treated by a carbonization process: the mat is heated at a rate of 3° C. /min up to 1000° C. under an argon atmosphere and maintained at this temperature for 1 h.

Characterization of Representative Samples

[0121] To investigate the feasibility of using the disclosed nanofibrous polymer membranes in facemasks and respirators or in HVAC or other air filtration applications, the morphology, fiber diameter, filtering efficiency, porosity, wettability, mechanical strength, and optionally antiviral activity and particulate-retention capacity of representative samples of embodiments of the disclosed nanofibrous polymer membrane were characterized.

[0122] Nanofibrous polymer membranes were characterized using scanning electron microscopy (SEM) imaging. FIG. 1 shows representative SEM images of an embodiment of the disclosed nanofibrous polymer membrane. The larger images show 2000X magnification, while each inset shows the respective 5000X magnification image. As shown in FIG. 1, the internal and external surfaces of each nanofiber membrane display consistent morphology between samples. In addition, the nanofibrous membranes show good orientation and are free of breading, splitting, and other undesirable morphological features.

[0123] FIG. 2 shows fiber diameter measurements and distribution for representative samples of an embodiment of the disclosed nanofibrous polymer membrane. The average fiber diameter of representative samples was 0.224 .Math.m, with a median fiber diameter of 0.210 .Math.m and a standard deviation of 0.106. The average orientation was 79 °, and the area coverage was 16%.

[0124] FIG. 3 shows pore size distribution for representative samples of an embodiment of the disclosed nanofibrous polymer membrane as determined by mercury porosimeter analysis. The mean pore diameter was found to be 0.0025 .Math.m.

[0125] FIG. 4 shows average porosity and the distribution of mean porosity for representative samples of an embodiment of the disclosed nanofibrous polymer membrane. The average porosity as determined by gravimetric measurements was shown to be distributed around a center point of 78.5%. As shown in FIG. 4, all samples showed consistent porosity in the range of 75% to 83%. High porosity of the membrane is a critical requirement to increase the breathability of a facemask or filter made from the membrane.

[0126] FIG. 5 shows mechanical tensile strength test results for representative samples of an embodiment of the disclosed nanofibrous polymer membrane.

[0127] A representative sample of an embodiment of the disclosed nanofibrous polymer membrane was also tested for filtration efficiency. The observed efficiency was 99.61% for 30 L/min, with a pressure loss of 1.265 mbar, and 99.85% for 95 L/min, with a pressure loss of 4.3 mbar.

[0128] Table 1 shows a summary of test results for representative samples of an embodiment of the membrane.

TABLE-US-00001 Laboratory Test Standard Results ATI International Filtration Efficiency NIOSH >99% mean filtration efficiency Nelson Labs Synthetic Blood Penetration ASTM F2100 no penetration Nelson Labs Flammability Test ASTM F2101 Class 1 Nelson Labs Cytotoxicity ASTM F2102 Grade 0 Nelson Labs Particle Filtration Efficiency ASTM F2103 average 99% Nelson Labs Virus Filtration Efficiency ASTM F2104 average 99.5% Nelson Labs Bacterial Filtration Efficiency ASTM F2105 average 99.5% MicroChem MS2 Bacteriophage AATCC 100 >99% reduction MicroChem Human Coronavirus 229E AATCC 100 >99.9% reduction Matregenix E. coli ASTM E2315 >99.9% reduction Matregenix GFP Lentivirus AATCC 100 >99.9% reduction Matregenix Membrane Microstructure N/A SEM fiber diameter analysis porosity measurements contact angle measurements

[0129] Representative samples of an embodiment of the membrane did not degrade after washing with water or ethanol. By contrast, a sample of a melt-blown membrane showed a significant decrease in filtration efficiency after washing with ethanol.

[0130] A comparison between a representative sample of an embodiment of the disclosed nanofibrous polymer membrane and a typical melt-blown membrane is shown in Table 2.

TABLE-US-00002 Parameter Melt-Blown Membrane Nanofiber Membrane Thickness (gsm) 35 0.8 Fiber Diameter (.Math.m) 10 0.15 Pore Size 6 0.05 Filtration Efficiency (%) 95 99 Post-Washing Filtration Efficiency (%) 62 99 Water Vapor Transmission Rate (WVTR) 142 155 Water Contact Angle (°) 119 153 Cytocompatibility (%) 105 155

[0131] The filtration efficiency and observed pressure drop for various membrane samples for use in personal protective equipment applications is shown in Table 3.

TABLE-US-00003 Sample No. Flow Rate (L/min) Filtration Efficiency (%) Pressure Drop (mm wg ) QF-117 85 97.10 13.8 QF-104 85 99.58 20.8 QF-105 85 99.02 18.7 QF-108 85 99.49 18.9 MXF011 20 98.17 3.0 MXF011 32 98.10 4.6 MXF011 60 98.46 8.8 MXF011 80 97.16 11.8 MXF011 100 97.65 16.7 MXF012 20 98.57 2.9 MXF012 32 97.76 4.4 MXF012 60 97.65 8.9 MXF012 80 97.89 12.2 MXF012 100 98.18 16.6 MXF013 20 95.61 2.4 MXF013 32 96.22 4.0 MXF013 60 95.98 8.6 MXF013 80 97.62 11.8 MXF013 100 96.99 15.6

[0132] The filtration efficiency and observed pressure drop for various membrane samples for use in HVAC applications is shown in Table 4.

TABLE-US-00004 Sample No. Flow Rate (L/min) Substrate Filtration Efficiency (%) Pressure Drop (mm wg) Filtration Efficiency (%) Pressure Drop (mm wg) QFM-080 32.5 978/100 20 0.2 70 0.40 QFM-081 32.5 978/100 20 0.2 66 0.30 QFM-084 32.5 778/70G 20 0.2 77 0.50 QFM-085 32.5 778/70G 20 0.2 72 0.35

[0133] FIGS. 6-12 show test results for filtration efficiency, flammability, and antiviral and antimicrobial properties for representative samples of an embodiment of the disclosed nanofibrous polymer membrane intended for use in personal protective equipment applications.

[0134] FIG. 13 shows how filtration efficiency is affected by the flow rate of aerosols through the membrane.

[0135] FIG. 14 shows how the pressure drop across the membrane, which is a measure of breathability of the membrane, is affected by the flow rate of aerosols through the membrane.

[0136] FIG. 15 shows an embodiment of a system for removing volatile organic compounds and carbon dioxide that is composed of a photocatalyst-impregnated nanofibrous polymer membrane and a carbon nanofiber membrane.

[0137] FIG. 16 shows the basic repeat units of rectangular, hexagonal, and trihexagonal opening patterns for mesh substrates.

[0138] FIG. 17 shows a schematic representation of a flexible, breathable, and antimicrobial facemask based on an all-nanofiber TENG (NF-TENG) platform.

[0139] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention disclosed herein. Although the various inventive aspects are disclosed in the context of one or more illustrated embodiments, implementations, and examples, it should be understood by those skilled in the art that the invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. It should be also understood that the scope of this disclosure includes the various combinations or sub-combinations of the specific features and aspects of the embodiments disclosed herein, such that the various features, modes of implementation, and aspects of the disclosed subject matter may be combined with or substituted for one another. The generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0140] All references cited are hereby expressly incorporated herein by reference.