Patent Description:
The present invention relates to protective masks based on partially gelled submicron fibers and nanofibers. In particular, the present invention relates to protective masks based on partially gelled submicron fibers which are interweaved with nanofibers in order to form said protective masks. The present invention also relates to a method of making the protective masks and coatings therein.

Airborne contaminants are present everywhere in the surrounding. In hospitals, contaminants include a variety of airborne respiratory infectious diseases, such as tuberculosis and measles, and emerging diseases such as severe acute respiratory syndrome (SARS) and H1N1 influenza A. In highly polluted areas, aerosol, which is suspension of solid or liquid particles in gas, becomes the major airborne contaminant.

Absorption of airborne contaminants of high concentrations into the body can be potentially very dangerous. Airborne contaminants can be absorbed into the body through skin, eyes, or the respiratory system. Absorption of airborne particles into lungs through the respiratory system is prone to both acute and chronic health hazards.

When it comes to the harmful effects of contaminants on human respiratory system, the size of the contaminants is important. In general, smaller particles are more likely to become airborne and more dangerous. Particles larger than <NUM> usually get collected in upper part of the respiratory system. Therefore, most of them cannot get into the deep part of the lungs. However, particles smaller than <NUM> are respirable, which means that they are capable of getting into the deep part of the lungs. Those particles include but not limited to bacteria, viruses, clay, silt, tobacco smoke and metal fumes. They seem to have the unexplained ability to rapidly penetrate cells throughout the body and impair many cellular functions.

The hazard of airborne contaminants can be managed through the application of basic controls like increasing ventilation, or providing workers with protective equipment such as protective masks.

Protective masks have been widely used by personnel in hospitals, researchers in laboratories, workers in construction sites, as well as the general public in highly polluted areas or during flu season.

According to the Centers for Disease Control and Prevention (CDC), flu viruses are spread mainly by droplets made when people with the flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. According to the CDC, a person might also get the flu by touching a surface or object that has the flu virus on it and then touching his/her own mouth or nose.

A protective mask is typically composed of a filtering barrier, which is a critical component that determines the protection level of the mask.

For the same filtering barrier, the filtration efficiency depends on the particle size and the rate of airflow. Generally, it is relatively ineffective for a filtering barrier used in the conventional protective mask to filter out particles having sizes at around <NUM> and it is more difficult to filter out particles when the rate of airflow is high.

Most filtering barriers of the conventional protective masks are not functionalized with biocides or virucides. Therefore, those protective masks simply serve as a physical barrier to filter out contaminants. When it comes to viruses and bacteria, those barriers cannot kill them on the spot. The ability to kill bacteria and/or viruses on the spot is a desirable function for protective masks.

Although there are many different types of protective masks on the market, surgical/medical masks and N95 respirators are two of the most popular masks. These masks have remained virtually unchanged for the last several decades. Studies of surgical/medical masks and N95 respirators in terms of their levels of protection and general comfort have been reported (<NPL>;<NPL>).

Whether the goal is to prevent the outward escape of wearer-generated contaminants or the inward transport of hazardous aerosols, there are two critical requirements to justify the protection level of a mask. Firstly, the filter of the mask must be able to prevent penetration of hazardous particles within a wide range of sizes (from a few nanometers to a few hundred micrometers) over a range of airflow (approximately <NUM> to <NUM>/min). Secondly, leakage must be avoided at the boundary of the mask and the face. Both requirements (i.e. well-functioning filter and good face seal performance) must be met in order to claim a mask highly protective.

Different types of the conventional protective masks, including (<NUM>) surgical/medical mask, (<NUM>) respirator, (<NUM>) protective mask with filtering face seal, and (<NUM>) antibacterial/antiviral mask, are described below, respectively.

In order to claim a product as a surgical/medical mask, the product must pass a series of tests according to the standard such as ASTM F2100 or EN14683.

For ASTM F2100, the performance of a surgical/medical mask is based on testing for (<NUM>) bacterial filtration efficiency (BFE), (<NUM>) differential pressure, (<NUM>) sub-micron particulate filtration efficiency (PFE), (<NUM>) resistance to penetration tested by synthetic blood, and (<NUM>) resistance to flammability.

The table below summarizes the surgical/medical mask requirements by performance level according to ASTM F2100.

For typical surgical/medical masks, and in referencing to the BFE test and the sub-micron PFE test, the filtration efficiency percentage must not be lower than <NUM>%. The average size of the aerosol particles in the BFE test is around <NUM> while the average size of the aerosol particles in the sub-micron PFE test is around <NUM>.

The aerosol particles are trapped by protective masks comprising nonwoven meshes of fibers through a combination of mechanisms including inertial impaction capture, interception capture, and Brownian diffusion capture. Inertial impaction/interception predominates in the BFE test because of the relatively large particle size while Brownian diffusion predominates in the sub-micron PFE test because of the relatively small particle size.

The most penetrating particle size (MPPS) is <NUM>. As both diffusion and impaction/interception are inefficient for particles near the MPPS, passing the aforementioned tests (i.e. BFE test and sub-micron PFE test) does not justify the high level of protection of the surgical/medical mask.

Moreover, surgical/medical masks are not designed to seal tightly to the face. Without an adequate seal to the face, inhaled breath is not forced through the filter and instead flows through the gaps around the seal area, providing minimal protection by allowing potentially hazardous contaminants to enter the workers' breathing zone through gaps between the wearer's face and the mask. Therefore, surgical/medical masks do not provide the degree of protection to be considered respiratory personal protective equipment (PPE).

When high level of protection is required, respirators are usually used instead of surgical/medical masks. There are nine types of respirator filters, as shown in the table below.

Respirator filters are rated as N, R or P for their level of protection against oil aerosols. This rating is critical in industry because some industrial oils can remove electrostatic charges from the filter media, thereby reducing the filtration efficiency. Respirators are rated "N" if they are not resistant to oil, "R" if they are somewhat resistant to oil, and "P" if they are strongly resistant to oil.

Respirator filters that capture at least <NUM>% of the challenge aerosol are given a <NUM> rating. Those that trap at least <NUM>% receive a <NUM> rating. And those that collect at least <NUM>% receive a <NUM> rating.

N95 respirator is the most popular PPE among the aforementioned respirators. In order to claim a product as an N95 respirator, the product must pass the required National Institute for Occupational Safety and Health (NIOSH) test, which is more stringent than the tests used for surgical/medical masks in terms of protection.

The table below summarizes the N95 respirator requirements by performance level according to NIOSH.

According to NIOSH, neutralized sodium chloride (NaCl) aerosol comprising particles at the MPPS is used as the challenge. Neutralized aerosol is used to prevent attraction of particles to the sample by electrostatic force. The flow rate of the NaCl aerosol is <NUM>/min, which is higher than the flow rate employed in the BFE test (i.e. <NUM>/min). Such flow rate is also higher than the air requirement for a human under most circumstances such as sitting, walking, and even jogging. The filtration efficiency must not be lower than <NUM>% in order to maintain an N95 rating. Therefore, the N95 respirator is superior to the surgical/medical mask in terms of protective power.

Case control studies during the <NUM> SARS crisis also demonstrated that N95 respirators were more protective than surgical/medical masks against the SAR coronavirus (<NPL>; <NPL>; <NPL>; <NPL>).

Despite the high level of protection of N95 respirators, many studies of N95 respirators in the US marketplace have shown them to be associated with overall discomfort, diminished visual, vocal, or auditory acuity, excessive humidity or heat, headaches, facial pressure, skin irritation or itchiness, excessive fatigue or exertion, malodorousness, anxiety or claustrophobia, and other interferences with occupational duties (<NPL>; <NPL>; <NPL>).

In general, the N95 respirator is inferior to the surgical/medical mask in terms of its breathability. It is relatively comfortable to wear surgical/medical masks when compared with N95 respirators, which provide high level of protection at the expense of breathability. Medical personnel and patients are facing dilemma of choosing a comfortable but unreliable protective mask (i.e. surgical/medical mask) or choosing a highly protective but uncomfortable mask (i.e. N95 respirator). It is desirable to manufacture protective masks that combine the advantage of surgical/medical masks (i.e. low air resistance) and the advantage of N95 respirators (i.e. high protective power).

Unlike the traditional N95 respirator that seals to the face and keep air out, the surgical/medical mask does not provide an airtight seal. As such, air can still enter the breathing zone through the top, bottom and sides of the surgical/medical mask without passing through its filter. The absence of the airtight seal gives the wearer the comfort and breathability at the expense of the level of protection. In <CIT>, Messier incorporated the surgical/medical mask with an additional filtering face seal that is designed to filter air before it enters the breathing zone through the top, bottom and sides of the mask. It is believed that the modified mask is more protective than the traditional surgical/medical mask.

Typical protective masks, including surgical/medical masks and N95 respirators, are usually unable to kill airborne pathogens. These masks provide protection based on a passive, mechanical filtration design. Therefore, microorganisms attached to these masks can survive for several hours. That greatly increases the risk of cross-infection. Functional protective masks capable of not only trapping but also killing microorganisms on the spot are certainly better than most typical masks in terms of protective power.

One of the models of the Gammex® mask (A400) developed by Ansell Healthcare is able to kill microorganisms (e.g. bacteria, viruses, bacterial spores, fungi and protozoa) on the spot. To make the antimicrobial layer, iodine is fused with a polymer under heat and pressure. Incorporation of iodine controls the delivery and dosage of molecular iodine directly to microorganisms, thus providing built-in antimicrobial and antifungal activities.

On the other hand, Filligent Limited developed a functional three-layered protective mask (BioMask™) in <NUM>. The functional mask is composed of a non-active inner layer made of polypropylene as a supporting layer, a non-active middle layer comprising nonwoven fibers to filter out particulates, and a hydrophilic layer that rapidly inactivates pathogens. Virus-laden droplets are rapidly absorbed and captured within a low pH environment, wherein structural components and proteins are disrupted, and viruses inactivated. The mechanism of action is that the low pH causes non-specific denaturation of viral proteins.

Filligent Limited also developed a functional four-layered protective mask, which is composed of an antimicrobial outer layer, an antimicrobial middle layer, a non-active middle layer and a non-active inner layer. Briefly, viruses are rapidly inactivated in the outer layer by exposure to the low pH environment which causes structural rearrangement of lipids and other structures, resulting in spontaneous denaturation. Positively charged divalent copper/zinc metal ions attach to influenza viruses by binding negatively-charged groups (e.g. carboxyl/sulfhydryl) present on all viruses. This effect is known as ionic mimicry. Influenza viruses are rapidly inactivated because (i) structures, such as lipid envelopes and nucleic acids, are damaged, and (ii) biomolecules, such as proteins, lipids and enzymes, are denatured. The toxic effect of metal ions on pathogens is known as the oligodynamic effect.

Agkilbact™ is an antibacterial mask consisting of <NUM> layers: (i) the outer polypropylene nonwoven fibrous mesh; (ii) the inner nonwoven mesh comprising silver nanoparticles; (iii) the inner filtering cloth. The antibacterial mask can prevent the growth of various microbes such as extended-spectrum beta-lactamase (ESBL), methicillin-resistant staphylococcus aureus (MRSA), and vancomycin-resistant enterococcus (VRE). By coating the fibers in the masks with nano functional emulsions, the fibers become hydrophobic, thus preventing absorption and penetration of bacterium-carrying and virus-carrying liquid. <CIT> discloses methods and materials for decontamination of surfaces and fabrics, such as non-woven fabrics, that are contaminated with infestations of microorganisms such as bacteria. Biocidal oligomers having conjugated oligo-(aryl/heteroaryl ethynyl) structures and comprising at least one cationic group can be used to decontaminate infested surfaces in the presence of oxygen and, optionally, illumination. Fibers incorporating biocidal oligomers having conjugated oligo-(aryl/heteroaryl ethynyl) structures and comprising at least one cationic group, wherein the oligomer is physically associated with or covalently bonded to, or both, the fiber-forming polymer can be used to form non-woven mats. Biocidal non-woven mats prepared by methods of <CIT>, incorporating the biocidal oligomers, can be used to suppress bacterial growth in wound and surgical dressings and personal hygiene products. <CIT> discloses an antimicrobial composition comprising (a) at least two antimicrobial agents having different antimicrobial mechanisms of action and being present in amounts that together provide a synergistic antimicrobial effect or (b) an antimicrobial agent and a surface modifying agent, an antimicrobial masterbatch comprising antimicrobial composition (a) or (b) and a polymer carrier, an antimicrobial fibre composition comprising the antimicrobial masterbatch and a fibre substrate, an antimicrobial fibre comprising a fibre body or a fibre surface having the antimicrobial fibre composition, and a process for producing antimicrobial fibres. <CIT> relates to a face mask for removal of biological and mechanical impurities from breathed and/or exhaled air, comprising an inner textile layer and an outer textile layer, between which there is arranged a filtering layer of polymer nanofibres and/or active layer of polymer nanofibres, which in its structure contains a biocidal substance/s. The outer as well as the inner textile layer are formed of microfibres, while at least the outer textile layer and with it neighbouring filtering or active layer of polymer nanofibres are hydrophobic, and all layers are interconnected by a net of joints, that prevent their mutual motion and reduce permeability of the face mask only minimally. The inner textile layer is on periphery of the face mask provided with a layer of an adhesive for fastening to the face of the user. This method of fixing the face mask to the face secures perfect adhesion of the face mask to the skin along its entire periphery, thus preventing breathing of an unfiltered air. <CIT> further relates to a method for production of such face mask. <CIT> discloses a filtration medium that includes a fine filter layer having a plurality of nanofibers and a coarse filter layer having a plurality of microfibers attached to the fine filter layer. The coarse filter layer is positioned proximal to a direction of fluid flow, and the fine filter layer is positioned distal to the direction of fluid flow.

To sum up, wearing a surgical/medical mask does not cause significant discomfort generally. However, the protective power of a surgical/medical mask is low because of two reasons. Firstly, the filtration tests for surgical/medical masks do not involve the use of particles at MPPS as the challenge. So its ability to filter out contaminants at a certain range of sizes is not justified. Secondly, contaminants can bypass the filtering material of a surgical/medical mask because air can get into the gap between the surgical/medical mask and the face. On the other hand, respirators such as N95 respirators are highly protective because of their airtight design and the use of particles at MPPS as the challenge during the filtration tests. However, the breathability of N95 respirators is low, leading to low user compliance. And most N95 respirators do not possess antibacterial function. There exists a need for a highly breathable N95 mask capable of trapping viruses and killing bacteria on the spot.

Accordingly, according to its first embodiment, as defined in claim <NUM> as herewith attached, the present invention provides a protective mask comprising an ultrafine fibrous coating on a first microfibrous substrate, said ultrafine fibrous coating comprising electrospun partially gelled submicron fibers having an average diameter of <NUM> - <NUM>, interweaved with electrospun nanofibers having an average diameter of <NUM> - <NUM>; and a biocide which is encapsulated into, surface-attached onto, blended with, physically trapped, and/or chemically linked to said submicron fibers and nanofibers. According to a second embodiment, as defined in claim <NUM> as herewith attached, the instant invention provides a method of producing the protective mask according to the first embodiment, comprising providing a formulation for forming said coating on said first microfibrous substrate; which formulation is a polymer solution; introducing a biocide to said polymer solution; free-surface electrospinning said formulation into said coating consisting of interweaving said partially gelled submicron fibers with said nanofibers on said first microfibrous substrate in order to form an outer layer of said protective mask. Further preferred embodiments of the instant invention are defined in the dependent claims as herewith attached. Said ultrafine fibrous coating can be formed on an antistatic nonwoven substrate comprising a plurality of spunbond microfibers. Non-antistatic nonwoven can also be used but is not preferred in the present invention because it reduces the productivity due to substantial amount of residual charges on the non-antistatic nonwoven. Said coating can also be formed on a nonwoven substrate comprising a plurality of meltblown microfibers. The coating is attached to the nonwoven substrate by mechanical interlocking and / or intermolecular attraction.

The protective mask of the present invention can be foldable or non-foldable. The protective mask can also be butterfly-shaped, cup-shaped or duckbill-shaped.

In one embodiment, the protective mask of the present invention includes a main body, two elastic straps, and preferably a spongy strip attached to the inner part of the main body. The main body includes three to four nonwoven layers, which are attached to each other by ultrasonic welding. A first layer of said three to four nonwoven layers distal to the face of a wearer and a fourth layer proximal to the face of the wearer are nonwoven layers comprising spunbond polypropylene microfibers. One of the first and fourth layers is a nonwoven layer comprising antistatic spunbond polypropylene microfibers with an ultrafine fibrous coating, said coating comprising electrospun partially gelled submicron fibers having an average diameter of <NUM> - <NUM>, interweaved with electrospun nanofibers having an average diameter of <NUM> - <NUM>; and a biocide which is encapsulated into, surface-attached onto, blended with, physically trapped, and/or chemically linked to said submicron fibers and nanofibers. The coating is applied to one side of any of the first and fourth layers such that the coating is not exposed to the environment outside the protective mask. Between the first layer and the fourth layer are two middle layers (second and third layers). The second or third layer is a nonwoven layer comprising meltblown polypropylene microfibers. In other embodiment, one of the second and third layers can be omitted. A stiffening member such as a metal strip or a plastic strip is attached to the upper edge of the main body to conform the face when wearing the protective mask. Preferably, a spongy strip is attached to the inner part of the main body to further improve the face seal when the wearer is wearing the protective mask.

The elastic straps can be attached to the left hand side of the main body and the right hand side of the main body respectively such that the protective mask can be fixed onto the face with the support from the wearer's ears. The elastic straps can also be attached to the upper side of the main body and the lower side of the main body respectively such that the protective mask can be fixed onto the face with the support from the wearer's head.

The biocide-loaded polymer solution for free-surface electrospinning can include a selected biocide and a selected polymer. The electrospun fibers formed from said biocide-loaded polymer can bear electrostatic charges. The biocide in said biocide-loaded polymer solution and biocide-loaded polymer fibers can include but not limited to silver, copper, copper oxide (CuO), titanium oxide (TiO), zinc oxide (ZnO), iodine, triclosan and chlorhexidine. The biocide can be encapsulated into the electrospun fibers. The biocide can also be surface-attached onto the electrospun fibers. The biocide can be encapsulated into and surface-attached onto the electrospun fibers. The biocide can be physically trapped by the electrospun fibers. The biocide can also be chemically crosslinked to the electrospun fibers. The biocide can also be blended with the electrospun fibers.

The polymer used to form different types of polymer microfibers, submicron fibers and nanofibers of the present invention can include synthetic polymers such as cellulose acetate (CA), polyamide <NUM> (PA <NUM>), polystyrene (PS), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA), polybutylene terephthalate (PBT) and polyurethane (PU). The polymer can also include natural polymers such as gelatin, chitosan and polyhydroxybutyrate-co-hydroxyvalerate (PHBV).

The singular forms "a," "an" and "the" can include plural referents unless the context clearly dictates otherwise.

The term "protective mask" as used herein refers to facemask, face mask, mask, respirator, face shield, surgical mask, medical mask, filter mask, mouth mask, or gas mask.

The term "bacteria" refers to gram-positive bacteria or gram-negative bacteria. Examples of gram-positive bacteria include but not limited to Staphylococcus aureus, Streptococcus pneumonia, or Vancomycin-resistant enterococci (VRE). Examples of gram-negative bacteria include but not limited to Pseudomonas aeruginosa, Acinetobacter baumannii, or Escherichia coli.

The term "pore" as used herein refers to a depression, slit, or hole of any size or shape in a solid object. A pore can run all the way through an object or partially through the object. A pore can intersect other pores.

The present invention is defined by the attached claims.

The present disclosure describes a protective mask (<NUM>) comprising butterfly-shaped main body (<NUM>), two elastic straps (<NUM>) and preferably a spongy (not shown in <FIG>) attached to the inner surface of the main body. The main body includes three to four nonwoven layers (<FIG>), which are attached to each other by ultrasonic welding.

The present disclosure provides, as a comparative example, a protective mask comprising, from distal to the face to proximal to the face, an antistatic spunbond microfibrous nonwoven layer with an electrospun microfibrous coating, a meltblown microfibrous nonwoven layer, and a spunbond microfibrous nonwoven layer.

As a further comparative example, the present disclosure provides a protective mask comprising, from distal to the face to proximal to the face, an antistatic spunbond microfibrous nonwoven layer with an electrospun submicron fibrous coating, a meltblown microfibrous nonwoven layer, and a spunbond microfibrous nonwoven layer.

As a still further comparative example, the present disclosure provides a protective mask comprising, from distal to the face to proximal to the face, an antistatic spunbond microfibrous nonwoven layer with an electrospun charge-bearing submicron fibrous coating, a meltblown microfibrous nonwoven layer, and a spunbond microfibrous nonwoven layer.

In one of its embodiments, the present invention provides a protective mask comprising, from distal to the face to proximal to the face, an antistatic spunbond microfibrous nonwoven layer with an ultrafine fibrous coating consisting of electrospun partially gelled submicron fibers having an average diameter of <NUM> - <NUM>, interweaved with electrospun nanofibers having an average diameter of <NUM> - <NUM> ; and a biocide which is encapsulated into, surface-attached onto, blended with, physically trapped, and/or chemically linked to said submicron fibers and nanofibers, a meltblown microfibrous nonwoven layer, and a spunbond microfibrous nonwoven layer.

In another of its embodiments, the present invention provides a protective mask comprising, from distal to the face to proximal to the face, an antistatic spunbond microfibrous nonwoven layer with an ultrafine fibrous coating consisting of charge-bearing electrospun partially gelled submicron fibers having an average diameter of <NUM> - <NUM>, interweaved with charge-bearing electrospun nanofibers having an average diameter of <NUM> - <NUM>; and a biocide which is encapsulated into, surface-attached onto, blended with, physically trapped, and/or chemically linked to said submicron fibers and nanofibers, a meltblown microfibrous nonwoven layer, and a spunbond microfibrous nonwoven layer.

<FIG> illustrates the basic structure of a protective mask. The layer distal to the face (<NUM>) and the layer proximal to the face (<NUM>) are nonwoven layers comprising spunbond polypropylene microfibers. One of these layers (<NUM>, <NUM>) is a nonwoven layer comprising antistatic spunbond polypropylene microfibers with an ultrafine fibrous coating comprising electrospun fibers. The ultrafine fibrous coating can be composed of microfibers or submicron fibers or of combinations thereof (as illustrated by comparative examples), or - according to the invention - the ultrafine fibrous coating can be composed of electrospun partially gelled submicron fibers having an average diameter of <NUM> - <NUM>, interweaved with electrospun nanofibers having an average diameter of <NUM> - <NUM>; and a biocide which is encapsulated into, surface-attached onto, blended with, physically trapped, and/or chemically linked to said submicron fibers and nanofibers. The ultrafine fibrous coating can bear electrostatic charges. The coating is applied to one side of the nonwoven layer (<NUM>, <NUM>) such that the coating is not exposed to the environment outside the protective mask. The electrospun fibers (including eletrospun microfibers and eletrospun nanofibers) of said coating can be polymer fibers or biocide-loaded polymer fibers. Between the layer <NUM> and layer <NUM> are two middle layers (<NUM> and <NUM>). The second or third layer (<NUM>, <NUM>) is a nonwoven layer comprising meltblown polypropylene microfibers. In an other embodiment, one of the second and third layers can be omitted. A stiffening member such as a metal strip or a plastic strip is attached to the upper edge of the main body to conform the face when wearing the protective mask. Preferably, a spongy strip is attached to the inner part of the main body to further improve the face seal when the wearer is wearing the protective mask.

The biocide can include but is not limited to silver, copper, CuO, TiO, ZnO, iodine, triclosan and chlorhexidine. The biocide can be encapsulated into the electrospun fibers. The biocide can also be surface-attached onto the electrospun fibers. The biocide can be encapsulated into and surface-attached onto the electrospun fibers. The biocide can be physically trapped by the electrospun fibers. The biocide can also be chemically crosslinked to the electrospun fibers. The biocide can also be blended with the electrospun fibers. The biocide-loaded polymer fibers can contain <NUM>% - <NUM>% weight/weight (w/w) biocides, such as <NUM>% - <NUM>% (w/w) biocides, with respect to the polymer.

In an example, the present invention provides electrospun fibers, and an electrospun ultrafine fibrous coating made from electrospun partially gelled submicron fibers having an average diameter of <NUM> - <NUM>, interweaved with electrospun nanofibers having an average diameter of <NUM> - <NUM>; and a biocide which is encapsulated into, surface-attached onto, blended with, physically trapped, and/or chemically linked to said submicron fibers and nanofibers which are polymer fibers. The polymer used to form different types of polymer microfibers, submicron fibers and nanofibers as recited in claim <NUM> can include synthetic polymers such as cellulose acetate (CA), polyamide <NUM> (PA <NUM>), polystyrene (PS), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA), polybutylene terephthalate (PBT) and polyurethane (PU). The polymer can also include natural polymers such as gelatin, chitosan and polyhydroxybutyrate-co-hydroxyvalerate (PHBV). The ultrafine fibrous coating can be composed of electrospun microfibers (<NUM>) (<FIG>, COMPARATIVE), electrospun submicron fibers (<NUM>) (<FIG>, COMPARATIVE), electrospun partially gelled submicron fibers (<NUM>) interweaved with electrospun nanofibers (<NUM>) as recited in claim <NUM> (<FIG> INVENTION), or any combination thereof.

When the ultrafine fibrous coating comprising electrospun microfibers is used in a protective mask (thus resulting in a COMPARATIVE configuration, not encompassed by the invention as claimed), the coating has to be very thick in order to achieve N95 level of protection because the inter-fiber pores between microfibers are very large and the surface area-to-volume ratio of the coating is very low when compared with submicron fibers or nanofibers. The thick microfibrous coating improves the filtration efficiency at the expense of breathability.

When the ultrafine fibrous coating comprising electrospun submicron fibers is used in a protective mask (thus resulting in a COMPARATIVE configuration, not encompassed by the invention as claimed), the required surface density of the coating for achieving N95 level of protection is reduced when compared with the fibrous coating comprising electrospun microfibers because of the smaller inter-fiber pore size and the higher surface area-to-volume ratio. However, the submicron fibers collapse when stacking on each other, thus undermining the breathability.

When the ultrafine fibrous coating comprising charge-bearing electrospun submicron fibers is used in a protective mask (thus resulting in a COMPARATIVE configuration, not encompassed by the invention as claimed), the required surface density of the coating for achieving N95 level of protection is further reduced when compared with the fibrous coating comprising electrospun submicron fibers without retained charges because particles can be trapped by the charge-bearing fibers due to electrostatic attraction.

Conversely, when the ultrafine fibrous coating comprising electrospun partially gelled submicron fibers interweaved with electrospun nanofibers as recited in claim <NUM> is used in a protective mask, the partially gelled submicron fibers serve as a scaffolding support to prevent the nanofibers from collapsing, thus reducing the inter-fiber pore size and increasing the surface area-to-volume ratio of the coating without increasing the fiber density significantly. This structure can achieve N95 level of protection at a higher breathability, when compared with the coating comprising microfibers or submicron fibers.

When the ultrafine fibrous coating comprising charge-bearing electrospun partially gelled submicron fibers interweaved with charge-bearing electrospun nanofibers as recited in claim <NUM> is used in a protective mask, the protective mask can achieve N95 level of protection at a higher breathability, when compared with the protective mask having the same structure without retained charges. A possible reason is that charge-bearing fibers can trap particles by electrostatic attraction, which is an additional particle-trapping mechanism that is not available for the fibers without retained charges. Due to this additional mechanism, the thickness, and hence the air resistance, of the charge-bearing coating can be reduced while maintaining the same level of protection.

The ultrafine fibrous coating described above can be formed using free-surface electrospinning, in particular according to the method according to claim <NUM>.

<FIG> illustrates the welding parts of the main body of the protective mask. The melting point of the material to be welded is <NUM> or below. The peripheral part of the main body (<NUM>) is welded such that different layers are attached together into one single piece. Four straight lines at the centre of the main body (<NUM>) are also welded such that the layer proximal to the face would not be sucked to the face during inhalation.

The sheet resistance of the spunbond polypropylene microfibers without antistatic treatment in layer <NUM> or layer <NUM> is <NUM><NUM>- <NUM><NUM> Ω/sq, such as <NUM><NUM> Ω/sq. The sheet resistance of the antistatic spunbond polypropylene microfibers in layer <NUM> or layer <NUM> is <NUM><NUM> - <NUM><NUM> Ω/sq, such as <NUM><NUM> Ω/sq.

The surface potential of the spunbond polypropylene microfibers without antistatic treatment in layer <NUM> or layer <NUM> is <NUM> - <NUM> V, such as <NUM> - <NUM> V. The surface potential of the antistatic spunbond polypropylene microfibers in layer <NUM> or layer <NUM> is <NUM> - <NUM> V, such as <NUM>-<NUM> V.

The average diameter of the spunbond polypropylene microfibers without antistatic treatment in layer <NUM> or layer <NUM> is <NUM> - <NUM>, such as <NUM>. The average diameter of the antistatic spunbond polypropylene microfibers in layer <NUM> or layer <NUM> is <NUM> - <NUM>, such as <NUM>.

The surface density of the layer comprising the spunbond polypropylene microfibers without antistatic treatment in layer <NUM> or layer <NUM> is <NUM> - <NUM>/m<NUM>, such as <NUM>/m<NUM>. The surface density of the layer comprising the antistatic spunbond polypropylene microfibers in layer <NUM> or layer <NUM> is <NUM> - <NUM>/m<NUM>, such as <NUM>/m<NUM>.

The thickness of the layer comprising the spunbond polypropylene microfibers without antistatic treatment in layer <NUM> or layer <NUM> is <NUM> - <NUM>, such as <NUM> - <NUM>. The thickness of the layer comprising the spunbond polypropylene microfibers without antistatic treatment in layer <NUM> or layer <NUM> is <NUM> - <NUM>, such as <NUM> - <NUM>.

The sheet resistance of the ultrafine fibrous coating comprising electrospun microfibers is <NUM><NUM> - <NUM><NUM> Ω/sq, such as <NUM><NUM> Ω/sq. The sheet resistance of the ultrafine fibrous coating comprising electrospun submicron fibers is <NUM><NUM> - <NUM><NUM> Ω/sq, such as <NUM><NUM> Ω/sq. The sheet resistance of the ultrafine fibrous coating comprising partially gelled electrospun submicron fibers interweaved with electrospun nanofibers as recited in claim <NUM> is <NUM><NUM> - <NUM><NUM> Ω/sq, such as <NUM><NUM> Ω/sq.

The surface potential of the ultrafine fibrous coating comprising charge-bearing electrospun fibers is <NUM> - <NUM> V, such as <NUM> - <NUM> V. Charge-bearing electrospun fibers can be made from hydrophobic polymers such as PHBV, PBT, PLA and PLGA. The surface potential of the ultrafine fibrous coating comprising electrospun fibers without retained electrostatic charges is <NUM> - <NUM> V, such as <NUM> - <NUM> V. Electrospun fibers without retained charges can be made from polar polymers such as polyamide <NUM>, gelatin, chitosan and PU.

The average diameter of the electrospun microfibers is <NUM> - <NUM>, such as <NUM>. The average diameter of the electrospun submicron fibers is <NUM> - <NUM>, such as <NUM> - <NUM>. The average diameter of the charge-bearing electrospun submicron fibers is <NUM> - <NUM>, such as <NUM> - <NUM>. The average diameter of the partially gelled electrospun submicron fibers is <NUM> - <NUM>, such as <NUM> - <NUM>. The average diameter of the electrospun nanofibers interweaved with the partially gelled electrospun submicron fibers is <NUM> - <NUM>, such as <NUM> - <NUM>. The average diameter of the partially gelled charge-bearing electrospun submicron fibers is <NUM> - <NUM>, such as <NUM> - <NUM>. The average diameter of the charge-bearing electrospun nanofibers interweaved with the partially gelled charge-bearing electrospun submicron fibers is <NUM> - <NUM>, such as <NUM> - <NUM>.

The surface density of the ultrafine fibrous coating comprising electrospun microfibers is <NUM> - <NUM>/m<NUM>, such as <NUM> - <NUM>/m<NUM>. The surface density of the ultrafine fibrous coating comprising electrospun submicron fibers is <NUM> - <NUM>/m<NUM>, such as <NUM> - <NUM>/m<NUM>. The surface density of the ultrafine fibrous coating comprising charge-bearing electrospun submicron fibers is <NUM> - <NUM>/m<NUM>, such as <NUM> - <NUM>/m<NUM>. The surface density of the ultrafine fibrous coating comprising partially gelled electrospun submicron fibers interweaved with electrospun nanofibers as recited in claim <NUM> is <NUM> - <NUM>/m<NUM>, such as <NUM> - <NUM>/m<NUM>. The surface density of the ultrafine fibrous coating comprising partially gelled charge-bearing electrospun submicron fibers interweaved with charge-bearing electrospun nanofibers as recited in claim <NUM> is <NUM> - <NUM>/m<NUM>, such as <NUM> - <NUM>/m<NUM>.

The thickness of the ultrafine fibrous coating comprising electrospun microfibers is <NUM> - <NUM>, such as <NUM> - <NUM>. The thickness of the ultrafine fibrous coating comprising electrospun submicron fibers is <NUM> - <NUM>, such as <NUM> - <NUM>. The thickness of the ultrafine fibrous coating comprising charge-bearing electrospun submicron fibers is <NUM> - <NUM>, such as <NUM> - <NUM>. The thickness of the ultrafine fibrous coating comprising partially gelled electrospun submicron fibers interweaved with electrospun nanofibers as recited in claim <NUM> is <NUM> - <NUM>, such as <NUM> - <NUM>. The thickness of the coating comprising partially gelled charge-bearing electrospun submicron fibers interweaved with charge-bearing electrospun nanofibers as recited in claim <NUM> is <NUM> - <NUM>, such as <NUM> - <NUM>.

When the ultrafine fibrous coating comprising electrospun microfibers is used in a (COMPARATIVE) protective mask, the coating has to be very thick (<NUM> - <NUM>) and the surface density of the coating has to be very high (<NUM> - <NUM>/m<NUM>) in order to filter out more than <NUM>% of particles at the MPPS (i.e. N95 level of protection) because the inter-fiber pores between microfibers are very large and the surface area-to-volume ratio of the coating is very low when compared with submicron fibers or nanofibers. The thick microfibrous coating improves the filtration efficiency at the expense of breathability.

When the ultrafine fibrous coating comprising electrospun submicron fibers is used in a (COMPARATIVE) protective mask, the required surface density of the coating for achieving N95 level of protection is reduced (<NUM> - <NUM>/m<NUM>) when compared with the fibrous coating comprising electrospun microfibers because of the smaller inter-fiber pore size and the higher surface area-to-volume ratio. However, the submicron fibers collapse when stacking on each other, thus still undermining the breathability.

When the ultrafine fibrous coating comprising electrospun charge-bearing submicron fibers is used in a (COMPARATIVE) protective mask, the required surface density of the coating for achieving N95 level of protection is further reduced (<NUM> - <NUM>/m<NUM>) when compared with the fibrous coating comprising electrospun submicron fibers without retained charges because particles can be readily trapped by the charge-bearing fibers by electrostatic attraction.

When the ultrafine fibrous coating comprising electrospun partially gelled submicron fibers interweaved with electrospun nanofibers as recited in claim <NUM> is used in a protective mask according to the instant invention, the partially gelled submicron fibers serve as a scaffolding support to prevent the submicron fibers and nanofibers from collapsing, thus achieving N95 level of protection without significantly reducing the breathability.

When the ultrafine fibrous coating comprising charge-bearing electrospun partially gelled submicron fibers interweaved with charge-bearing electrospun nanofibers as recited in claim <NUM> is used in a protective mask according to the instant invention, the required surface density of the coating for achieving N95 level of protection is further reduced (<NUM> - <NUM>/m<NUM>) when compared with the ultrafine fibrous coating comprising the same fiber structure without retained charges because particles can be readily trapped by the charge-bearing fibers by electrostatic attraction.

Between the layer distal to the face (layer <NUM>) and the layer proximal to the face (layer <NUM>) are two middle layers (layer <NUM> and layer <NUM>). The middle layer (layer <NUM> or layer <NUM>) is a nonwoven layer comprising meltblown polypropylene microfibers. One of the middle layers (layer <NUM> or layer <NUM>) can be omitted in some cases.

The sheet resistance of the meltblown polypropylene microfibers is <NUM><NUM>- <NUM><NUM> Ω/sq, such as <NUM><NUM> Ω/sq.

The surface potential of the coating comprising meltblown polypropylene microfibers is <NUM> - <NUM> V, such as <NUM> V.

The average diameter of the meltblown polypropylene microfibers is <NUM> - <NUM>, such as <NUM> - <NUM>.

The surface density of the layer comprising the meltblown polypropylene microfibers is <NUM> - <NUM>/m<NUM>, such <NUM>/m<NUM>.

The thickness of the layer comprising the meltblown polypropylene microfibers is <NUM> - <NUM>, such as <NUM> - <NUM>.

A stiffening member such as a metal strip or a plastic strip is attached to the upper edge of the main body to conform the face when wearing the protective mask. The thickness of the metal strip or the plastic strip is <NUM> - <NUM>, such as <NUM>.

Preferably, a spongy strip is attached to the inner part of the main body to further improve the face seal when wearing the protective mask. The distance between the upper edge of the spongy strip and the edge of the main body is <NUM> - <NUM>, such as <NUM>.

The present disclosure also describes formulations and scalable methods for providing the protective mask described above. More specifically, the present disclosure describes formulations and scalable methods for forming the electrospun fibrous coating on the antistatic nonwoven substrate comprising a plurality of spunbond polypropylene microfibers.

A polymer, such as CA, PA <NUM>, PS, PAN, PVP, PVA, PLA, PLGA, PBT, PU, gelatin, chitosan or PHBV, is dissolved in an appropriate solvent, such as dimethylformamide (DMF), acetic acid (AA), formic acid (FA), dichloromethane (DCM), chloroform, acetone, <NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>-hexafluoro-<NUM>-propanol (HF2P), trifluoroacetic acid (TFA), <NUM>,<NUM>,<NUM>-trifluoroethanol (TFE), cyclohexanone, water, or the combination thereof. A biocide, such as silver, copper, CuO, TiO, ZnO, iodine, triclosan and chlorhexidine, is mixed with the polymer solution through gentle stirring and heating using a hotplate magnetic stirrer. The stirring speed is <NUM> - <NUM> rpm, such as <NUM> - <NUM> rpm. The heating temperature is <NUM> - <NUM>, such as <NUM> - <NUM>. The stirring and heating duration is <NUM> - <NUM> hours, such as <NUM> - <NUM> hours. The viscosity of the polymer solution is <NUM> - <NUM> cP, such as <NUM> - <NUM> cP. The conductivity of the polymer solution is <NUM> - <NUM>/cm, such as <NUM> - <NUM>/cm.

Fibrous coating is formed by free-surface electrospinning of the polymer solution using the Nanospider (NS1WS500U, Elmarco, Czech Republic) together with a tailor-made external winding and unwinding system. The diameter of the stainless steel collecting electrode (CE) is <NUM> - <NUM>, such as <NUM>. The diameter of the stainless steel spinning electrode (SE) is <NUM> - <NUM>, such as <NUM>. The sheet resistance of the antistatic spunbond substrate is <NUM><NUM> - <NUM><NUM> Ω/sq, such as <NUM><NUM> Ω/sq. The distance between the CE and the substrate is <NUM> - <NUM>, such as <NUM>. The distance between the SE and the substrate is <NUM> - <NUM>, such as <NUM>. The applied voltage is <NUM> - <NUM> kV, such as <NUM> kV. The current is <NUM> - <NUM> mA, such as <NUM> - <NUM> mA. The temperature is <NUM> - <NUM>, such as <NUM> - <NUM>. The relative humidity is <NUM> - <NUM>%, such as <NUM> - <NUM>%. The substrate speed is <NUM> - <NUM>/min, such as <NUM>/min.

The embodiments of the present invention can be better understood by reference to the following examples and comparative examples, which are offered by way of illustration. The present invention is not limited to the examples given herein.

Polyurethane (PU) was dissolved in a mixture of cyclohexanone and water (cyclohexanone : water = <NUM> : <NUM> by volume) at a concentration of <NUM>% (w/w) to form a PU solution. CuO was mixed with the PU solution at a concentration of <NUM>% (w/w). The mixture was stirred at <NUM> rpm for <NUM> hours at room temperature to form the PU/CuO solution. The viscosity of the polymer solution was <NUM> cP. The conductivity of the polymer solution was <NUM>/cm.

Fibrous coating was formed on an antistatic spunbond substrate by free-surface electrospinning of the PU/CuO solution using the Nanospider (NS1WS500U, Elmarco, Czech Republic) together with a tailor-made external winding and unwinding system. The diameter of the stainless steel collecting electrode (CE) was <NUM>. The diameter of the stainless steel spinning electrode (SE) was <NUM>. The sheet resistance of the antistatic spunbond substrate was <NUM><NUM> Ω/sq. The distance between the CE and the substrate was <NUM>. The distance between the SE and the substrate was <NUM>. The applied voltage was <NUM> kV. The current was <NUM> mA. The temperature was <NUM>. The relative humidity was <NUM>%. The substrate speed was <NUM>/min.

<FIG> shows the SEM image of the electrospun PU/CuO microfibers formed by the free-surface electrospinning of the PU/CuO solution in this example. The sheet resistance of the coating comprising electrospun PU/CuO microfibers is <NUM><NUM> Ω/sq. The surface potential of the coating comprising PU/CuO microfibers is <NUM> V. The average diameter of the electrospun PU/CuO microfibers is <NUM>. The surface density of the coating comprising the electrospun PU/CuO microfibers is <NUM>/m<NUM>. The thickness of the coating comprising the electrospun PU/CuO microfibers is <NUM>.

The antistatic spunbond substrate with the coating comprising the electrospun PU/CuO microfibers (i.e. Layer <NUM>) was assembled with Layer <NUM>, Layer <NUM>, Layer <NUM> and elastic straps into a protective mask, where layer <NUM> or <NUM> is a nonwoven layer comprising meltblown polypropylene microfibers. The performance of this type of protective mask was assessed through two tests, namely, (<NUM>) sodium chloride (NaCl) aerosol test and (<NUM>) inhalation and exhalation resistance tests.

The NaCl aerosol test was performed to evaluate particulate filter penetration as specified in <NUM> CFR Part <NUM> and TEB-APR-STP-<NUM> for requirements on an N95 respirator. Prior to testing, the protective masks were placed in an environment of <NUM> ± <NUM>% relative humidity (RH) and <NUM> ± <NUM> for <NUM> ± <NUM> hours. The filter tester used in this test was a TSI® CERTITEST® Model <NUM> Automated Filter Tester capable of measuring filtration efficiency up to <NUM>%. It produces a particle size distribution with a count median diameter of <NUM> ± <NUM>. The mass median diameter is approximately <NUM>, which is generally regarded as the MPPS. The reservoir was filled with a <NUM>% NaCl solution and the instrument allowed a minimum warm-up time of <NUM>. The main regulator pressure was set to (<NUM> ± <NUM> pounds per square inch (psi)) <NUM> ± <NUM> MPa. The filter holder regulator pressure was set to approximately (<NUM> psi) <NUM>,<NUM> MPa. The NaCl aerosol generator pressure was set to approximately (<NUM> psi) <NUM> MPa and the make-up airflow rate was set to approximately <NUM> liters per minute (L/min). The neutralized NaCl test aerosol was verified to be at <NUM> ± <NUM> and <NUM> ± <NUM>% RH. The NaCl concentration of the test aerosol was determined in mg/m<NUM> by a gravimetric method prior to the load test assessment. The entire protective mask was mounted on a test fixture, placed into the test article holder, and the NaCl aerosol passed through the outside surface of the test article at a continuous airflow rate of <NUM> ± <NUM>/min.

The NIOSH N95 filter efficiency as stated in <NUM> CFR Part <NUM> is a minimum efficiency for each filter of ≥ <NUM>%. The average filtration efficiency of the protective masks with the coating comprising electrospun PU/CuO microfibers was <NUM>% and none of them possessed filtration efficiency less than <NUM>%, meaning that the protective masks conform to the NIOSH N95 criteria for filter efficiency.

The tests were performed to evaluate the differential pressure of protective masks in accordance with <NUM> CFR Part <NUM>. The air exchange differential or breathability of protective masks was measured for inhalation resistance using NIOSH procedure TEB-APR-STP-<NUM> and exhalation resistance with NIOSH procedure TEB-APR-STP-<NUM>. The differential pressure technique is a simple application of a basic physical principle employing a water manometer differential upstream and downstream of the test material, at a constant flow rate. A complete protective mask was mounted to a test fixture comprised of a metal plate with an approximate <NUM> inch diameter hole in the center to allow airflow to reach the mask. The sample holder was assembled by placing a Plexiglas collar around the test fixture and topping with another metal disc with a <NUM> inch opening in the center. The sample holder is held tightly together with clamps and connected to an air source. The manometer is attached to the sample holder by a connection port on the Plexiglas collar. Before testing, the manometer was zeroed and the back pressure in the sample holder checked and verified to be negligible. Resistance measurements were taken with a manometer capable of measuring at least <NUM> inches of water. For inhalation testing, a negative airflow (vacuum) was applied. For exhalation testing, a positive airflow (compressed air) was used. Airflow was passed through the sample holder at approximately <NUM> ± <NUM>/min.

The inhalation resistance criteria as stated in <NUM> CFR Part <NUM> is an initial inhalation not exceeding35 mm water column height pressure (mm H<NUM>O). The exhalation resistance criteria as stated in <NUM> CFR Part <NUM> is an initial exhalation not exceeding <NUM> H<NUM>O. The average inhalation resistance of the protective masks with the coating comprising electrospun PU/CuO microfibers was <NUM> H<NUM>O and none of them exceeded <NUM> H<NUM>O while the average exhalation resistance of the protective masks with the coating comprising electrospun PU/CuO microfibers was <NUM> H<NUM>O and none of them exceeded <NUM> H<NUM>O, meaning that the protective masks conform to this NIOSH criterion for airflow resistance.

PU was dissolved in a mixture of cyclohexanone and water (cyclohexanone : water = <NUM> : <NUM> by volume) at a concentration of <NUM>% (w/w) to form a PU solution. CuO was mixed with the PU solution at a concentration of <NUM>% (w/w). The mixture was stirred at <NUM> rpm for <NUM> hours at room temperature to form the PU/CuO solution. The viscosity of the polymer solution was <NUM> cP. The conductivity of the polymer solution was <NUM>/cm.

<FIG> shows the SEM image of the electrospun PU/CuO submicron fibers. The sheet resistance of the coating comprising electrospun PU/CuO submicron fibers is <NUM><NUM> Ω/sq. The surface potential of the coating comprising PU/CuO submicron fibers is <NUM> V. The average diameter of the electrospun PU/CuO submicron fibers is <NUM>. The surface density of the coating comprising the electrospun PU/CuO submicron fibers is <NUM>/m<NUM>. The thickness of the coating comprising the electrospun PU/CuO submicron fibers is <NUM>.

The substrate with the coating comprising electrospun PU/CuO submicron fibers (i.e. Layer <NUM>) was assembled with Layer <NUM>, Layer <NUM>, Layer <NUM> and elastic straps into a protective mask, where layer <NUM> or <NUM> is a nonwoven layer comprising meltblown polypropylene microfibers. The performance of this type of protective mask was assessed through two tests, namely, (<NUM>) sodium chloride (NaCl) aerosol test and (<NUM>) inhalation and exhalation resistance tests.

The NaCl aerosol test was conducted as described in Example <NUM>.

The average filtration efficiency of the protective masks with the coating comprising electrospun PU/CuO submicron fibers was <NUM>% and none of them possessed filtration efficiency less than <NUM>%, meaning that the protective masks conform to the NIOSH N95 criteria for filter efficiency.

The inhalation and exhalation resistance tests were conducted as described in Example <NUM>.

The average inhalation resistance of the protective masks with the coating comprising electrospun PU/CuO submicron fibers was <NUM> H<NUM>O and none of them exceeded <NUM> H<NUM>O while the average exhalation resistance of the protective masks with the coating comprising electrospun PU/CuO submicron fibers was <NUM> H<NUM>O and none of them exceeded <NUM> H<NUM>O, meaning that the protective masks conform to this NIOSH criterion for airflow resistance.

PHBV was dissolved in <NUM>,<NUM>,<NUM>-trifluoroethanol at a concentration of <NUM>% (w/w). CuO was mixed with the PHBV solution at a concentration of <NUM>% (w/w). The mixture was stirred at <NUM> rpm for <NUM> hours at <NUM> to form the PHBV/CuO solution. The viscosity of the polymer solution was <NUM> cP. The conductivity of the polymer solution was <NUM>/cm.

Fibrous coating was formed on an antistatic spunbond substrate by free-surface electrospinning of the PHBV/CuO solution using the Nanospider (NS1WS500U, Elmarco, Czech Republic) together with a tailor-made external winding and unwinding system. The diameter of the stainless steel collecting electrode (CE) was <NUM>. The diameter of the stainless steel spinning electrode (SE) was <NUM>. The sheet resistance of the antistatic spunbond substrate was <NUM><NUM> Ω/sq. The distance between the CE and the substrate was <NUM>. The distance between the SE and the substrate was <NUM>. The applied voltage was <NUM> kV. The current was <NUM> mA. The temperature was <NUM>. The relative humidity is <NUM>%. The substrate speed was <NUM>/min.

<FIG> shows the SEM image of the electrospun PHBV/CuO submicron fibers. The sheet resistance of the coating comprising electrospun PHBV/CuO submicron fibers is <NUM><NUM> Ω/sq. The surface potential of the coating comprising PU/CuO submicron fibers is <NUM> V. The average diameter of the electrospun PHBV/CuO submicron fibers is <NUM>. The surface density of the coating comprising the electrospun PHBV/CuO submicron fibers is <NUM>/m<NUM>. The thickness of the coating comprising the electrospun PHBV/CuO submicron fibers is <NUM>.

The substrate with the coating comprising electrospun PHBV/CuO submicron fibers (i.e. Layer <NUM>) was assembled with Layer <NUM>, Layer <NUM>, Layer <NUM> and elastic straps into a protective mask. The performance of this type of protective mask was assessed through two tests, namely, (<NUM>) sodium chloride (NaCl) aerosol test and (<NUM>) inhalation and exhalation resistance tests.

The average filtration efficiency of the protective masks with the coating comprising electrospun PHBV/CuO submicron fibers was <NUM>% and none of them possessed filtration efficiency less than <NUM>%, meaning that the protective masks conform to the NIOSH N95 criteria for filter efficiency.

The average inhalation resistance of the protective masks with the coating comprising electrospun PHBV/CuO submicron fibers was <NUM> H<NUM>O and none of them exceeded <NUM> H<NUM>O while the average exhalation resistance of the protective masks with the coating comprising electrospun PHBV/CuO submicron fibers was <NUM> H<NUM>O and none of them exceeded <NUM> H<NUM>O, meaning that the protective masks conform to this NIOSH criterion for airflow resistance.

PU/CuO solution was prepared as described in Example <NUM>.

Fibrous coating was formed on an antistatic spunbond substrate by free-surface electrospinning as described in Example <NUM> except that the relative humidity was <NUM>% and the substrate speed was <NUM>/min. The purpose of increasing the relative humidity was to reduce the evaporation rate of the solvent during electrospinning such that part of the electrospun jet was not completely solidified before reaching the substrate, thus leaving the partially jelled fibrous structures among the submicron fibers. The portions between the partially jelled portions became nanofibers due to stretching of the polymer solution to the partially jelled portions. Since increasing the substrate speed can reduce the thickness of the coating, it is not necessary to form a very thick coating to achieve N95 level of protection due to the presence of the nanofibers interweaved with the partially gelled submicron fibers.

<FIG> shows the SEM image of the electrospun partially gelled PU/CuO submicron fibers interweaved with PU/CuO nanofibers. The sheet resistance of the coating comprising electrospun partially gelled PU/CuO submicron fibers interweaved with PU/CuO nanofibers was <NUM><NUM> Ω/sq. The surface potential of the coating comprising electrospun partially gelled PU/CuO submicron fibers interweaved with PU/CuO nanofibers was <NUM> V. The average diameter of the electrospun partially gelled PU/CuO submicron fibers was <NUM>. The average diameter of the electrospun PU/CuO nanofibers interweaved with the partially gelled PU/CuO submicron fibers was <NUM>. The surface density of the coating comprising the electrospun partially gelled PU/CuO submicron fibers interweaved with PU/CuO nanofibers was <NUM>/m<NUM>. The thickness of the coating comprising the electrospun partially gelled PU/CuO submicron fibers interweaved with PU/CuO nanofibers was <NUM>.

The substrate with the coating comprising electrospun partially gelled PU/CuO submicron fibers interweaved with PU/CuO nanofibers (i.e. Layer <NUM>) was assembled with Layer <NUM>, Layer <NUM>, Layer <NUM> and elastic straps into a protective mask. The performance of this type of protective mask was assessed through two tests, namely, (<NUM>) sodium chloride (NaCl) aerosol test and (<NUM>) inhalation and exhalation resistance tests.

The average filtration efficiency of the protective masks with the coating comprising electrospun partially gelled PU/CuO submicron fibers interweaved with PU/CuO nanofibers was <NUM>% and none of them possessed filtration efficiency less than <NUM>%, meaning that the protective masks conform to the NIOSH N95 criteria for filter efficiency.

The average inhalation resistance of the protective masks with the coating comprising electrospun partially gelled PU/CuO submicron fibers interweaved with PU/CuO nanofibers was <NUM> H<NUM>O and none of them exceeded <NUM> H<NUM>O while the average exhalation resistance of the protective masks with the coating comprising electrospun partially gelled PU/CuO submicron fibers interweaved with PU/CuO nanofibers was <NUM> H<NUM>O and none of them exceeded <NUM> H<NUM>O, meaning that the protective masks conform to this NIOSH criterion for airflow resistance.

PHBV/CuO solution was prepared as described in Example <NUM>.

Fibrous coating was formed on an antistatic spunbond substrate by free-surface electrospinning as described in Example <NUM> except that the substrate speed was further increased to <NUM>/min. The purpose of increasing the substrate speed was to reduce the thickness of the coating because it was not necessary to form a very thick coating to achieve N95 level of protection due to the charge-bearing ability of the PHBV/CuO fibers, which enhanced particles trapping by electrostatic attraction.

<FIG> shows the SEM image of the electrospun partially gelled PHBV/CuO submicron fibers interweaved with PHBV/CuO nanofibers. The sheet resistance of the coating comprising electrospun partially gelled PHBV/CuO submicron fibers interweaved with PHBV/CuO nanofibers was <NUM><NUM> Ω/sq. The surface potential of the coating comprising electrospun partially gelled PHBV/CuO submicron fibers interweaved with PHBV/CuO nanofibers was <NUM> V. The average diameter of the electrospun partially gelled PHBV/CuO submicron fibers was <NUM>. The average diameter of the electrospun PHBV/CuO nanofibers interweaved with the partially gelled PHBV/CuO submicron fibers was <NUM>. The surface density of the coating comprising the electrospun partially gelled PHBV/CuO submicron fibers interweaved with PHBV/CuO nanofibers was <NUM>/m<NUM>. The thickness of the coating comprising the electrospun partially gelled PHBV/CuO submicron fibers interweaved with PHBV/CuO nanofibers was <NUM>.

The substrate with the coating comprising electrospun partially gelled PHBV/CuO submicron fibers interweaved with PHBV/CuO nanofibers (i.e. Layer <NUM>) was assembled with Layer <NUM>, Layer <NUM>, Layer <NUM> and elastic straps into a protective mask. The performance of this type of protective mask was assessed through three tests, namely, (<NUM>) sodium chloride (NaCl) aerosol test, (<NUM>) inhalation and exhalation resistance tests, and (<NUM>) antimicrobial tests.

The average filtration efficiency of the protective masks with the coating comprising electrospun partially gelled PHBV/CuO submicron fibers interweaved with PHBV/CuO nanofibers was <NUM>% and none of them possessed filtration efficiency less than <NUM>%, meaning that the protective masks conform to the NIOSH N95 criteria for filter efficiency.

The average inhalation resistance of the protective masks with the coating comprising electrospun partially gelled PHBV/CuO submicron fibers interweaved with PHBV/CuO nanofibers was <NUM> H<NUM>O and none of them exceeded <NUM> H<NUM>O while the average exhalation resistance of the protective masks with the coating comprising electrospun partially gelled PHBV/CuO submicron fibers interweaved with PHBV/CuO nanofibers was <NUM> H<NUM>O and none of them exceeded <NUM> H<NUM>O, meaning that the protective masks conform to this NIOSH criterion for airflow resistance.

The antimicrobial tests consisted of inoculating uniform pieces of the test material with the test organism(s), then determining the percent reduction of the test organism(s) after specified exposure periods.

Tubes of soybean casein digest broth (SCDB) media were inoculated with stock cultures of bacteria and incubated at <NUM>-<NUM> for <NUM>-<NUM> days. The cultures were vortexed to remove clumps and the concentration was adjusted to the appropriate challenge level.

The protective masks with different coatings prepared according to the examples described hereinabove were cut into <NUM> x <NUM> ± <NUM> swatches. All tests were performed in three replicates for each type of the protective masks. A <NUM> aliquot of the test culture was added to each sample and positive control. The inoculum was vortexed frequently to ensure uniform distribution of challenge. The test swatches were held at room temperature for the designated time intervals. At time <NUM>, <NUM>, and <NUM> minutes the test articles were extracted by removing the test sample from the containers and placing them into <NUM> bottles containing neutralizer broth. The bottles were shaken manually for one minute or <NUM> times in a <NUM> inch path to extract surviving organism.

The extract fluid from all test article extraction bottles was tested for viable organisms. All plating was performed in triplicate using a standard spread plate method. Bacterial test articles were plated onto SCDA and incubated at <NUM> ± <NUM> for <NUM>-<NUM> days.

A positive control was performed by testing sterile gauze in the same manner as the test article. A negative control was tested by plating aliquots from a sterile <NUM> bottle of neutralizer broth onto the appropriate media in triplicate.

Organism counts represent the number of organism per specimen article. The percent reduction for organism was calculated by the test article treatment as follows <MAT> where.

The protective mask sample from Example <NUM> exhibited <NUM>%, <NUM>%, and <NUM>% reduction of Staphylococcus aureus (ATCC #<NUM>) within <NUM> minutes, <NUM> minutes, and <NUM> minute, respectively.

Claim 1:
A protective mask comprising an ultrafine fibrous coating on a first microfibrous substrate, said ultrafine fibrous coating comprising:
electrospun partially gelled submicron fibers having an average diameter of <NUM> - <NUM>, interweaved with electrospun nanofibers having an average diameter of <NUM> - <NUM>; and
a biocide which is encapsulated into, surface-attached onto, blended with, physically trapped, and/or chemically linked to said submicron fibers and nanofibers.