GB2606202A

GB2606202A - Face mask

Info

Publication number: GB2606202A
Application number: GB2106148.6A
Authority: GB
Inventors: Promnimit Arunwat
Original assignee: Haydale Graphene Industries PLC; Haydale Technologies Thailand Co Ltd
Current assignee: Haydale Graphene Industries PLC; Haydale Technologies Thailand Co Ltd
Priority date: 2021-04-29
Filing date: 2021-04-29
Publication date: 2022-11-02
Also published as: GB202106148D0; WO2022229266A2; WO2022229266A3

Abstract

The present invention relates to a face mask comprising a layer 11 comprising surface functionalised graphene particles. Preferably the surface-functionalised graphene particles have low levels of sulphur/sulfur, manganese or NOx impurities. Also claimed is a method of producing such a mask that is low in such impurities by using plasma to functionalise the graphene. Preferably the graphene is functionalized with oxygen, for example phenolic, carboxylate or hydroxyl groups. Preferably the graphene is in the form of nanoplatelets dispersed in a PVC polymer matrix, and the layer 11b is screen printed onto an outer polyester fabric layer 11a. The mask may then further comprise a non-woven spun-bound filter 12 and a water-resistant muslin cotton inner layer 13. The mask may be used as PPE to prevent the spread of bacterial or viral infection as the graphene particles have an anti-microbial function.

Description

FACE MASK

FIELD OF THE INVENTION

The present invention relates to face masks, in particular antibacterial face masks which are suitable for use as personal protective equipment.

BACKGROUND OF THE INVENTION

Pathogens, such as viruses and bacteria, are often shed in liquid droplets and aerosols from a person's mouth and nose. To limit the risk of infection from these sources, it is common for people to wear face masks covering their mouth and (typically) nose to filter out particles and droplets.

Face masks have the dual function of protecting the wearer from droplets and fine particles in the air and protecting others from droplets produced by the wearer when they breathe out.

Face masks are regularly used in hospitals, dental practices and laboratory environments where it is desirable to filter our microbial contaminants from the wearer's breath. As a result of the Coronavirus (Covid-19) pandemic there has been an increased demand for face masks from members of the general public due to a desire to reduce the spread of the virus through droplets and also due to legislation mandating the wearing of face masks in particular settings.

Surgical masks are the most commonly used face masks. These masks comprise fabric layers that trap particles and droplets from the air. These particles and droplets may comprise microbes. However, these masks are only able to act as a barrier to such particles or droplets, trapping them in the fabric layers of the mask. Surgical face masks are also intended for single use only and are not made of biodegradable materials. Therefore, the usage of large numbers of surgical masks presents a problem from an environmental perspective.

Ideally, face masks should not only act as a barrier to particles and droplets (which may be carrying microorganisms) but should also be able to actively kill the microbes contained therein. This can lead to higher levels of protection against microbes. Furthermore, from an environmental perspective it is desirable that face masks should be washable and re-usable avoiding the production of large amounts of waste. Face masks should also be comfortable to wear and cheap to produce, without leading to skin irritation when worn for extended periods of time.

There remains a need in the art to develop face masks that demonstrate improved antimicrobial properties, use less components which makes them cheaper and easier to manufacture and are washable without losing their antimicrobial properties. There is also a need to develop face masks which are comfortable to wear and which are able to prevent contaminants from sticking to the surface of the mask, meaning that the mask surface is kept clean and sanitized for extended periods of time. Furthermore, it is desirable to develop a face mask, which can be tailored to be effective against specific types of microbes.

SUMMARY OF THE INVENTION

In view of the above problems in a first aspect the present invention provides a face mask comprising * a layer comprising surface-functionalised graphene particles, wherein the surface-functionalised graphene particles preferably have one or more of the following features (henceforth referred to as "layer (A)"): i. a sulphur impurity level of less than 0.2 wt.% based on the total weight of surface-functionalised graphene particles; ii. a manganese level of less than 10 ppm; iii. a NO level of less than 10 ppm; and * optionally, wherein the face mask comprises one or more additional fabric layers.

Preferably, the face mask is a multilayer face mask comprising (A) a layer comprising surface-functionalised graphene particles; (B) a layer of non-woven fabric and (C) a layer of water-resistant fabric. Generally, layers (A), (B) and (C) are stacked on top of each other to form the mask body.

The face mask according to the present invention has a number of advantageous features.

Firstly, the surface-functionalised graphene particles lead to high levels of protection against a broad spectrum of microbes/infectious agents including having excellent anti-bacterial and anti-viral properties. In particular, the present inventors have found that the surface funcfionalised graphene particles are able to inhibit bacterial and viral replication processes leading to improved antimicrobial properties compared to the use of non-functionalised graphene. The face masks according to the present invention are preferably in compliance with the safety standard EN 14683:2019 meaning that they are suitable for use in medical settings.

The term "antimicrobial" as used in the context of the present invention relates to the ability to kill at least some types of microorganisms, or to inhibit the growth or reproduction of at least some types of microorganisms. Preferably, one or more "microorganisms" are killed by the "antimicrobial" agent. The terms "microorganism" and "microbe", which are used interchangeably in the context of the present invention, are defined to comprise any organism too small to be seen by the unaided eye, such as, especially, single-celled organisms. In particular, the terms "microorganism" and "microbe" cover prokaryotes including bacteria and archaea, eukaryotes including protists, animals like dust mites or spider mites, fungi, and plants like green algae, as well as viruses.

Secondly, graphene particles have a cooling effect due to their high thermal conductivity, meaning that the face mask is more comfortable to wear for long periods of time in warm conditions compared to conventional face masks or surgical masks. The mask also has high breathability.

Thirdly, the face mask is easy to manufacture as the use of functionalised graphene means that the graphene particles disperse well in matrix materials used during manufacture without the need for additional surfactants or other hazardous additives. This can also improve the flexibility of the face mask as the properties of layer (A) comprising the graphene particles is dominated by the matrix material and not by the graphene.

Fourthly, the face mask is washable. This means that the face mask can be used multiple times followed by washing and still maintain its anti-microbial properties. Indeed, the face mask according to the present invention demonstrates compliance with EN 14683:2019 even after 10 washes. The use of washable masks avoids the production of large amounts of waste which results from the wearing of surgical masks, and at the end of the product's life the components of the masks may be recyclable.

Fifthly, the face mask is antistatic. It is thought that this is a property of layer (A) comprising electrically conductive graphene particles. This may mean that certain contaminants are prevented from sticking to layer (A) through the effects of static charge.

Sixthly, the antibacterial properties of the graphene particles in the face mask also make the mask more skin friendly than other face masks. Without wanting to be bound by any theory it is believed that the anti-bacterial/anti-microbial properties of the face mask protect the user from infections of the skin, which might result from the user's breath being trapped inside the face mask.

Surface functionalised araphene particles Graphene demonstrates broad range anti-pathogenic activity toward microbes such as bacteria, fungi, and viruses. Surface-functionalised graphene exceeds the anti-pathogenic effect of bare unfunctionalised graphene resulting in a material that is a highly effective antimicrobial agent that destroys cellular structure of various pathogens including common cold and influenza viruses.

Layer (A) comprises surface-functionalised graphene particles.

Surface-functionalised graphene particles provide an antistatic coating on the surface of the face mask that prevents contamination sticking to the surface through static charge. Oxygen and nitrogen groups for example can be used to tune or enhance the conductive properties of the graphene.

Surface-functionalised graphene particles (which can alternatively be referred to as "surface functionalised graphene-material"), may take the form of particles of monolayer graphene (i.e. a single layer of carbon) or multilayer graphene 0.e. particles consisting of multiple stacked graphene layers). Multilayer graphene particles may have, for example, an average (mean) of 2 to 100 graphene layers per particle. When the graphene particles have 2 to 5 graphene layers per particle, they can be referred to as "few-layer graphene" particles.

The surface-functionalised graphene particles may take the form of plates/flakes/sheets/ribbons of multilayer graphene material, referred to herein as "graphene nanoplatelets" (the "nano" prefix indicating thinness, instead of the lateral dimensions).

The graphene particles may take the form of platelets having a thickness less than 100 nm and a major dimension (length or width) perpendicular to the thickness. The platelet thickness is preferably less than 70 nm, preferably less than 50 nm, preferably less than 30 nm, preferably less than 20 nm, preferably less than 10 nm, preferably less than 5 nm (this is based on >90% of the particles having these properties, measured using light scattering by a Zetasizer Ultra). The major dimension is preferably at least 10 times, more preferably at least 100 times, more preferably at least 1,000 times, more preferably at least 10,000 times the thickness. The length may be at least 1 times, at least 2 times, at least 3 times, at least 5 times or at least 10 times the width.

The surface-functionalised graphene particles are preferably at least 90 wt.% carbon based on the bulk (determined by elemental analysis), more preferably at least 92 wt.% carbon, most preferably at least 95 wt.% carbon.

The surface-functionalised graphene particles are graphene particles which have had functional groups introduced to their surfaces (including faces or edges) in order to achieve improved antimicrobial properties and to aid dispersibility (e.g. in a polymer matrix).

Bespoke functionalisation can be used to adjust the hydrophobicity and hydrophilicity of the graphene to repel or attract where needed organic materials. This can allow either the desired contamination to be repelled from or absorbed into the layer comprising surface-functionalised graphene particles.

Preferably, the graphene particles are oxygen-functionalised, hydroxy-functionalised, carboxyfunctionalised, carbonyl-functionalised, amine-functionalised, amide-functionalised, halogenfuncfionalised or a hybrid of one or more of these types of functionalisafion. More preferably the graphene particles are oxygen-functionalised, hydroxy-funcfionalised, carboxy-funcfionalised, carbonyl-funcfionalised, amine-functionalised, amide-functionalised or a hybrid of one or more of these types of funcfionalisation.

Surface functional groups present on the graphene particles can also help in this case by inhibiting bacterial/viral replication process. This is due to hydrogen and oxygen containing functional groups on the surface of graphene which interact with bacterial/viral DNA or RNA. Phenolic and hydroxyl groups have been proven to be the most effective functional groups in this case.

Alternatively, hydrophobic surface activation of functionalized graphene could prevent waterborne pathogens On droplets) from interacting with the surface keeping it clean and sanitized for an extended period of time.

Preferably the graphene particles are oxygen functionalised, which the present inventors have found to be particularly effective from the point of view of antiviral/antibacterial activity. Most preferably the functional groups present on the surface of the graphene are phenolic, hydroxyl groups and/or carboxylate groups.

The combination of high surface bactericide activity of the oxygen functional groups and the natural permeability of graphene combine well as a barrier. The oxygen groups bind to bacteria/viral cell walls and disrupt them and neutralise them. Graphene works equally well with gases or liquids as it is permeable to both, meaning that the face masks according to the present invention display a high degree of breathability.

These types of functionalities are obtainable by plasma treatment of a carbon filler in oxygen (02) gas as outlined below. Importantly, these functional groups are present at the surface of the graphene (e.g. at the surface of the graphene particles) and are generally not present in the bulk of the material. Without wanting to be bound by any theory it is believed that functionalisation is restricted to the top 1 or 2 layers of the surface functionalised graphene particles.

Any suitable type of functionalisation process can be used to achieve the desired functionalisation. However, preferably, the surface-functionalised graphene particles are plasma-functionalised graphene particles (i.e. graphene which has been functionalised using a plasma-based process). Advantageously, plasma-functionalised graphene particles can display high levels of functionalisation, and uniform functionalisation, whilst limiting or avoiding the introduction of unwanted impurities.

Plasma functionalisation of the graphene particles may be achieved as follows: the starting graphene material is subjected to a particle treatment method for disaggregating, de-agglomerating, exfoliating, cleaning or functionalising particles, in which the particles for treatment are subject to plasma treatment and agitation in a treatment chamber. Preferably, the treatment chamber is a rotating container or drum. Preferably the treatment chamber contains or comprises multiple electrically-conductive solid contact bodies or contact formations, the particles being agitated with said contact bodies or contact formations and in contact with plasma in the treatment chamber.

Preferably, the contact bodies are moveable in the treatment chamber. The treatment chamber may be a drum, preferably a rotatable drum, in which a plurality of the contact bodies are tumbled or agitated with the particles to be treated. The wall of the treatment vessel can be conductive and form a counter-electrode to an electrode that extends into an interior space of the treatment chamber.

The plasma treatment may be glow discharge plasma treatment. In instances involving the use of contact bodies or contact formations, glow discharge plasma preferably forms on the surfaces of the contact bodies or contact formations.

The pressure in the treatment vessel is usually less than 500 Pa. Desirably, during the treatment, gas is fed to the treatment chamber and gas is removed from the treatment chamber through a filter. That is to say, it is fed through to maintain a chemical composition if necessary and/or to avoid build-up of contamination.

The treated graphene material, that is, the particles or disaggregated, deagglomerated or exfoliated components thereof resulting from the treatment, may be chemically functionalised by components of the plasma-forming gas, forming e.g. carboxy, carbonyl, hydroxyl, amine, amide or halogen functionalities on their surfaces. Plasma-forming gas in the treatment chamber may be or may comprise e.g. any of oxygen, water, hydrogen peroxide, alcohol, nitrogen, ammonia, amino-bearing organic compound, halogen such as fluorine, halohydrocarbon such as CF4, and noble gas (e.g. argon). Preferably the gas used is oxygen, giving graphene particles which are oxygen functionalised.

Any other treatment conditions disclosed in W02010/142953 and W02012/076853 may be used, additionally or alternatively. Or, other means of functionalising and/or disaggregafing graphene particles/graphene materials may be used for the present processes and materials.

Plasma functionalisafion may be used to precisely tune the degree of functionality present on the surface of the graphene, whilst avoiding large amounts of other impurities being present in the surface-functionalised graphene particles. This includes impurities such as sulphur, NO (various forms of nitrogen oxides, including NO, NO2, N20) and manganese.

When wet chemical methods, such as the Hummers method are used to funcfionalise graphene, this can result in contamination of the graphene with impurities, in particular sulphuric acid residues. It is difficult to remove acid residues present on surface-functionalised graphene particles and even where these residues can be removed the removal is time consuming and requires high volumes of water producing large amounts of acidic waste.

Preferably, the surface-functionalised graphene particles in the face mask according to the present invention comprises less than 0.2 wt.%, preferably less than 0.15 wt.% sulphur based on the total weight of surface-functionalised graphene particles present in the face mask (determined by XPS). Preferably, the total amount of sulphur impurities in layer (A) is less than 1 wt.%, preferably less that 0.5 wt.%, more preferably less than 0.2 wt.% based on the total weight of layer (A) (determined by XPS). In contrast, levels of sulphur of up to 5 wt.% can be present in graphene oxide obtained through wet chemical processes for graphene functionalisation such as the Hummers method.

Sulphuric acid is known to be harmful to organic matter and can cause irritation to the skin if present, in the worst case resulting in chemical burns. Therefore, it is essential that impurities resulting from sulphuric acid are minimised in a face mask, which is designed to be applied to the sensitive skin of the face for extended periods of time. Additionally, if sulphuric acid residues are present in the functionalised graphene particles used in layer (A) this may result in a wearer breathing in toxic acid residues. The presence of sulphuric acid impurities can also complicate disposal of the face mask, which may contaminate landfill sites.

Plasma functionalisation also avoids nitrogen impurities in the form of nitric acid and NO (various forms of nitrogen oxides, including NO, NO2, N20), which may result from nitric acid used in wet chemical methods of functionalisation.

Preferably, the amount of nitric acid present in the surface-functionalised graphene particles is less than 10 ppm based on the total amount of surface-functionalised graphene particles, preferably less than 5 ppm, most preferably less than 1 ppm. Preferably, the amount of NO present in the surface-functionalised graphene particles is less than 10 ppm, preferably less than 5 ppm, most preferably less than 1 ppm. The amount of nitric acid and NO is determined by XPS. Impurities such as sulphur, nitric acid and NO are left over from wet chemistry processes and not found in surface-functionalised graphene particles obtained by plasma treatment.

Impurities such as sulphate and NO can interfere with the intended use of the surface functionalised graphene particles. For example, NO may prevent effective cross linking in the polymer matrix material.

Plasma functionalisation also results in materials with lower (or no) levels of manganese contaminants than materials functionalised through the Hummers method. Preferably, the amount of manganese present in the surface-functionalised graphene particles in the face mask according to the present invention is less than 10 ppm based on the total amount of surface functionalised graphene particles, preferably less than 5 ppm, most preferably less than 1 ppm (determined by XPS). Preferably, the total amount of manganese impurities in layer (A) is less than 0.1 wt.%, preferably less that 10 ppm, more preferably less than 5 ppm, most preferably less than 1 ppm based on the total weight of layer (A) (determined by XPS). The presence of manganese compounds may cause skin irritation or burns due to their strong oxidising nature.

Plasma functionalisation also has the advantage that levels of functionalisation are highly tuneable. For example, it is possible to obtain levels of functionalisation of up to 28% oxygen (where 100% equates to full monolayer coverage), which is similar to levels achieved using wet chemistry methods. The surface coverage of oxygen containing groups in the surfacefunctionalised graphene particles may be at least 1 %, at least 1.5 %, at least 2 %, at least 10 %, at least 15 % or at least 20 % (wherein monolayer coverage is considered 100% coverage). This is determined by determining the atomic weight % of the added functionality using XPS compared to the unfunctionalised material. The total surface area of the graphene particles is calculated using the BET isotherm method (gas adsorption). However, generally for the present application levels of oxygen functionalisation of from 1 to 20%, preferably from 1.5 to 15 %, more preferably from 2 to 10 °A, are used based on the total weight of surface-functionalised graphene particles present in the face mask (determined by XPS).

Without wanting to be bound by any theory it is preferable to use lower levels of functionalisation as this avoids having to treat the graphene for extended periods of time.

Therefore, levels of functionalisation of less than 20 %, preferably less than 15 %, preferably less than 101% are preferred (wherein monolayer coverage is considered 100% coverage).

When other types of functionalisation such as oxygen-functionalised, hydroxy-functionalised, carboxy-functionalised, carbonyl-functionalised, amine-functionalised, amide-functionalised, halogen-functionalised or a hybrid of one or more of these types of functionalisation are instead present, then the surface coverage of these functional groups is also preferably from 1 to 20 %, more preferably from 1.5 to 15%, most preferably from 2 to 10% (wherein monolayer coverage is considered 100% coverage). This is determined by determining the atomic weight % of the added functionality using XPS compared to the unfunctionalised material. The total surface area of the graphene particles is calculated using the BET isotherm method (gas adsorption).

Plasma functionalisation also means that the specific type of functionalisation can also be tailored for different applications, for example, high levels of oxygen can lead to a reduction in conductivity, but an increased surface area with sp3 hybridisation, can also lead to improved dispersion in polar solvents.

Polymer matrix material Preferably the surface-functionalised graphene particles in layer (A) are dispersed in a polymer matrix material.

Preferably, the polymer matrix material is an elastic material. The particular choice of elastic material is not particularly limited, provided that it is sufficiently elastically deformable at normal room and outdoor temperatures (such as from 0 °C to 25 °C), and holds the graphene particles in position (so that the distribution of graphene does not change over time).

Suitable materials include, for example, vinyl polymers (including polymers or copolymers of vinyl chloride, vinyl acetate and vinyl alcohol), polyester polymers, phenoxy polymers, epoxy polymers, acrylic polymers, polyamide polymers, polypropylenes, polyethylenes, silicones, elastomers such as natural and synthetic rubbers including styrene-butadiene copolymer, polychloroprene (neoprene), nitrile rubber, butyl rubber, polysulfide rubber, cis-1,4-polyisoprene, ethylene-propylene terpolymers (EPDM rubber), and polyurethane (polyurethane rubber). The polymer matrix material may be, for example, a copolymer of vinyl chloride, vinyl acetate and/or vinyl alcohol.

The polymer matrix material may be a thermoplastic material. Alternatively, the polymer matrix material may be a thermosetting material.

The polymer matrix material may comprise or be polyurethane, for example a thermoplastic polyurethane elastomer. Advantageously, the present inventors have found that using polyurethane (especially thermoplastic polyurethane elastomer) as the polymer matrix material produces layers with good mechanical properties, in particular a good level of flexibility. This helps the face mask to conform to the face of the wearer, leading to increased comfort.

Alternatively, the polymer matrix material may comprise a biodegradable polymer, such as e.g. polyvinyl acetate (PVA) or polylactic acid (PLA) resin. Without being bound by any theory it is believed that this will lead to a face mask with improved biodegradability/green credentials.

Moreover, the additives and surface functionalised graphene particles used in the face mask according to the present invention are all non-toxic, meaning that they will not lead to contamination of landfill or composing sites, when the face masks are eventually disposed of.

The types of treatment used to produce the functionalised graphene particles can be adjusted depending on the different matrix types.

Alternatively, the polymer matrix may comprise or be polyvinyl chloride (PVC), which also displays high levels of flexibility again helping the face mask to confirm to a wearer's face.

Surface functionalisation of the graphene material has been found to reduce the amount of graphene required to achieve a desired level of anti-microbial activity compared to use of nonfunctionalised graphene. This can lead to cost savings and allow the properties (in particular, the mechanical properties) of the polymer matrix material to dominate. Moreover, the surface functionalisation helps the graphene to stay dispersed during the manufacturing process meaning than the graphene is evenly distributed throughout the layer, when it is formed into a face mask.

More generally, surface functionalisation may improve ease of manufacture.

The loading of surface-functionalised graphene particles in the polymer matrix material may be, for example, 0.25 wt.% or more, 0.5 wt.% or more, 1 wt.% or more, 2 wt.% or more, 5 wt.% or more, 10 wt.% or more, 15 wt.% or more, 20 wt.% or more, 30 wt.% or more, 40 wt.% or more, 50 wt.% or more or 60 wt.% or more of the total weight of layer (A) (e.g. the weight of graphene particles, polymer matrix and fabric). The upper limit for the loading of surface-functionalised graphene particles in the polymer matrix material may be, for example, 1 wt.%, 2 wt.%, 5 wt.%, 10 wt.%, 15 wt.%, 20 wt.%, 30 wt.%, 40 wt.%, 50 wt.%, or 60 wt.% or 70 wt.%. If the loading of surface-functionalised graphene particles is too low, then the required antimicrobial properties may not be achieved. If the loading is too high, then this can adversely affect the mechanical properties of the face mask On particular, flexibility and stretchability). For these reasons, it is preferable for the loadings of the graphene particles to be in the range of, for example, 5 to 50 wt.%, 10 to 40 wt.%, or 20 to 40 wt.%.

The surface-functionalised graphene particles are preferably uniformly dispersed throughout the polymer matrix material. It is not straightforward to achieve a suitably uniform dispersion of graphene particles since such particles have a powerful tendency to agglomerate; however, functionalisation of the graphene leads to better dispersions.

When the surface-functionalised graphene particles are present in the polymer matrix material, they are not configured to have a voltage applied across them or to carry a charge across the face mask. The anfimicriobial properties of the face mask result from the passive properties of the surface functionalised graphene particles themselves and are not the result of a voltage being applied to the face mask.

Combination with copper, silver and zinc.

Layer (A) may further comprise metal powders of copper, silver and/or zinc in combination with the surface-funcfionalised graphene particles. These metals may help to enhance the antibacterial properties of the surface-functionalised graphene particles. Preferably, the metal powder is copper or silver. Most preferably the metal powder is copper.

The metal powders may be present at from 0.5 wt.% -20 wt.% based on the total weight of layer (A), more preferably they are present at 1 wt.% -10 wt.%, most preferably at 2 wt.% -25 5wt.%.

Layer (A) may comprise 0.5 wt.% -20 wt.% copper, or 0.5 wt.% -20 wt.% silver; or 0.5 wt.% -20 wt.% zinc, or mixtures of these fillers, wherein the total amount of metal powder in all cases is in the range of 0.5 wt.% -20 wt.%. Preferably, layer (A) may comprise 1 wt.% -10 wt.% copper, 1 wt.% -10 wt.% silver; or 1 wt.% -10 wt.% zinc, or mixtures of these fillers, wherein the total amount of metal powder in all cases is in the range of 1 wt.% -10 wt.%. More preferably, layer (A) may comprise 2 wt.% -5wt.% copper, or 2 wt.% -5wt.% wt.% silver; or 2 wt.% -5wt.% zinc, or mixtures of these fillers, wherein the total amount of metal powder in all cases is in the range of 2 wt.% -5wt.%.

Layer (A) Layer (A) comprises surface-functionalised graphene particles.

Layer (A) may comprise or consist of the surface functionalised graphene particles in a matrix material. Preferably, layer (A) comprises or consists of surface functionalised graphene particles in a polymer matrix material.

Usually for layer (A) the surface functionalised graphene particles are deposited on a fabric layer.

In a specific embodiment layer (A) comprises a fabric with graphene particles bound to the fabric. In certain such embodiments, layer (A) may consist of a fabric and a polymer with surface-functionalised graphene particles distributed within it. In certain such embodiments the surface-functionalised graphene particles may have partially penetrated into the fabric structure.

The fabric is not particularly limited apart from being a breathable (gas permeable) fabric Preferably the fabric is a polyester fabric The graphene layer may be obtainable by screen printing the surface-functionalised graphene particles onto a fabric layer. Preferably the surface-functionalised graphene particles are added as an ink and dispersed into an ink coating. Preferably, the inks used in the graphene layer can be dissolved in organic solvents. This means that when the face masks according to the present invention come to the end of their working lives the functionalised graphene particles may be recycled and used again.

The position of layer (A) in the face mask is not particularly limited. In some embodiments the graphene may be present on the surface of the face mask.

Preferably, layer (A) is relatively thin to allow a user to easily breath through the face mask.

Preferably layer (A) has a thickness of from 100 pm to 1 mm, more preferably from 200 pm to 500 pm, most preferably from 300 pm to 400 pm.

Multi-layer face mask The face mask according to the present invention may comprise one, two or three or more layers.

Preferably the face mask according to the present invention is a multilayer face mask further comprising one or more additional fabric layers.

Preferably the face mask is a multilayer face mask comprising 3 or more layers of fabric.

Preferably, the multilayer face mask comprises: (A) said layer comprising surface-functionalised graphene particles; (B) a layer of non-woven fabric and/or (C) a layer of water-resistant fabric.

The multilayer face mask may also comprise additional intermediate fabric layers. These intermediate layers are not particularly limited. The intermediate layers may be intermediate layers of woven or non-woven fabric.

Preferably, the multilayer face mask comprises the following layers: (A) said layer comprising surface-functionalised graphene particles (B) a layer of non-woven fabric; and (C) a layer of water-resistant fabric.

Preferably, the multilayer face mask consists of (A) a layer comprising surface-functionalised graphene particles (B) a layer of non-woven fabric; and (C) a layer of water-resistant fabric.

These specific additional fabric layers (B) and (C) are discussed in more detail below.

Layer (B) Layer (B) is a layer of non-woven fabric. This layer acts as an additional filter layer trapping microbes, droplets and dust particles.

The term "non-woven fabric" refers to a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from various processes such as, for example, meltblowing processes, spunbonding processes, and bonded carded web processes.

Generally, layer (B) is designed to act as a filter layer and to protect the wearer from particles with a size of greater than 10 pm (PM 10 filter), preferably to protect the wearer from particles with a size of greater than 5 pm (PM 5 filter), more preferably to protect the wearer from particles with a size of greater than 2.5 pm (PM 2.5 filter).

The type of non-woven fabric is not particularly limited.

Preferably, layer (B) is a non-woven spunbond filter. Spunbonded filters are a specific type of non-woven farbic made from spunbonded fibers that are formed by extruding molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries of a spinneret with the diameter of the extruded filaments then being rapidly reduced to fibers as disclosed in for example, in U.S. Pat. No. 4,340,563 U.S. Pat. No. 3,692,618 and U.S. Pat. No. 3,802,817. Spunbond fibers can be continuous and have diameters generally greater than about 7 pm, more particularly, between about 10 and about 20 pm.

The materials used to produce the non-woven fabric are not particularly limited and can be selected from natural fibers (e.g. cotton, wool, flax, silk), synthetic fibers (polyester fibres, polyester-polyurethane copolymers such as Lycra®, acrylic fibres, and polyamide fibres such as nylon), special fibers (glass, carbon, nanofiber, bi-component, superabsorbent fibers).

Preferably the non-woven fabric is made from polypropylene or polyester.

Layer (C) Layer (C) is composed of a layer of water resistant fabric. The type of water resistant fabric is not particularly limited. Without being bound by any theory, it is believed that having a water resistant layer protects wearers from spreading their own particles to the outside (i.e. spreading their own particles to others).

"Water resistance" within the meaning of this invention is defined as a fabric which is able to resist the penetration of water into the fabric. This definition also includes fabrics that are waterproof and do not allow the penetration of any water into the fabric. The water resistant fabric may be naturally water resistant or may have been made water resistant due to the application of a coating material, such as wax. Water resistance may be determined in accordance with the rain test method (ISO 22958-2005 test standard drench). Fabrics are considered water resistant if after 5 minutes at rain water pressure (1830 mm pressure) water does not penetrate the fabric.

Preferably, layer (C) is a woven fabric. Preferably, layer (C) is a water resistant cotton fabric. More preferably layer (C) is a water resistant muslin cotton fabric, which may have been treated with a coating material to make the muslin material water resistant.

Face mask assembly Preferably, the face mask is designed in an ergonomic manner and has a thickness of from 50 pm to 3 mm, more preferably from 100 pm to 2 mm, more preferably from 500 pm to 1.5 mm to allow good breathability.

The face mask may be constructed as a flat sheet. In this case, when the face mask is a mulfilayer face mask all of the layers of the face mask may be attached together at the edges. Alternatively, the face mask may be configured (shaped) to conform to a wearers face, for example in the form of a cup shape whose concave portion accommodates the wearer's nose and mouth.

The face mask may comprise a mechanism for fixing the face mask to a user's face. Preferably, this may include using loops to attach the face mask to a wearer's ears. The loops may be made from elastic, string or cloth strips.

The face mask may also comprise a nose wire, which helps to increase the comfort of the face mask when worn by a user. Preferably the nose wire is made from wire with a polymer/elastomer cladding. More preferably, from galvanized wire with a polyethylene cladding.

The face mask may further comprise stoppers or elastic cord locks, which can be used to adjust the size of the loops meaning that the face mask can be fitted more easily to different face shapes and sizes, such as, for example, so that the face mask can also be fitted to children. Preferably the stoppers are made from soft silicone, rubber or plastic.

Without being bound by any theory, it is believed that the specific construction and materials used in the construction of the face mask leads to an extended shelf life.

Preferably, the face mask is flexible (i.e. capable of bending and returning to its original shape without breaking). Optionally, the face mask is stretchable (i.e. capable of being made longer or wider without tearing or breaking). Face masks formed from flexible and/or stretchable materials are able to conform to a user's face as they move.

When the face mask is a multilayer face mask, generally the layers of the face mask are stacked on top of each other to form the face mask. The layers may be attached together just at the edges or with additional areas of attachment over the surface of the face mask.

The ordering of layers in the multilayer face mask is not particularly limited. Generally, the multilayer face mask has an outside layer which is designed to be on the outside of the face mask when worn and an inside layer designed to be the layer which is in contact with a wearer's face when the face mask is worn. The face mask may also comprise interior layer(s) which are sandwiched between the outside and inside layers.

Any method of attachment may be used to attach the layers together such as e.g. glueing, stapling and sewing/stitching. Preferably the layers are sewn together.

When the face mask is a multilayer face mask comprising layers (A), (B) and (C), layer (A) may be present as the outside layer. In which case, the graphene particles may be on the outside of the face mask.

Preferably, layer (B) is placed between layer (A) and layer (C), wherein layer (A) is designed to be the outside layer and layer (C) is the inside layer.

Alternatively, layer (A) may be the inside layer and layer (C) may be the outside layer, with layer (B) placed between layers (A) and (C).

In some embodiments, the multilayer face mask may also include an additional outer fabric layer to protect layer (A) such as for example an additional water-resistant outer fabric layer.

Antimicrobial properties A key advantage of the graphene face mask according to the present application is that it has excellent antibacterial and antiviral properties. Preferably the face mask is 99 % antibacterial, more preferably 99.5% antibacterial, determined in accordance with ISO 20743:2013.

Preferably the face mask is in compliance with EN 14683:2019. Use

In a further embodiment, the present invention relates to the use of a face mask according to the present invention to prevent the spread of a bacterial or viral infection.

The face masks may be used as personal protective equipment (PPE). In particular, the use of PPE to prevent the spread of a bacterial or viral infection. This includes infections such as influenza, SARS viruses (e.g. SARS-00V-2/Covid-19) and cold viruses.

Optionally, the face mask is used in a clinical setting or for medical applications. A clinical setting within the meaning of this invention refers to a hospital, dentists, research facilities, vaccination centre, medical centre, surgery, clinic, veterinarians or other facility in which medical professionals operate.

The use of the face mask may simply involve members of staff or patients/subjects in the clinical setting wearing the face masks in order to prevent the spread of a bacterial or viral infection.

Method of preparation In a further embodiment, the present invention relates to a method of manufacture of a face mask of the invention, the method comprising the following steps: Step 1: plasma functionalising a graphene material to form surface functionalised graphene particles; Step 2: forming layer (A) from the surface functionalised graphene particles produced in step 1.

Preferably the surface functionalised graphene particles produced in step 1 have one or more of the following features: i. a sulphur impurity level of less than 0.2 wt.% based on the total weight of surface-functionalised graphene particles; ii. a manganese level of less than 10 ppm; iii. a NO level of less than 10 ppm.

A separate aspect within the present invention relates to a method of manufacture of a face mask of the invention, the method comprising the following steps: Step 1: providing surface functionalised graphene particles, wherein the surface functionalised graphene particles have one or more of the following features: i. a sulphur impurity level of less than 0.2 wt.% based on the total weight of surface-functionalised graphene particles; ii. a manganese level of less than 10 ppm; iii. a NO level of less than 10 ppm Step 2: forming layer (A) from the surface functionalised graphene particles in step 1.

Preferably, the surface functionalised graphene particles have all of the following features: i. a sulphur impurity level of less than 0.2 wt.% based on the total weight of surface-functionalised graphene particles; ii. a manganese level of less than 10 ppm; iii. a NO level of less than 10 ppm Preferably, step 2 comprises depositing one or more layers of the surface-functionalised graphene particles onto a fabric to form layer (A).

Preferably, step 2 involves dispersing the surface-functionalised graphene particles in a polymer matrix material to form an "ink" before depositing them onto the fabric.

The step of depositing one or more layers of surface-functionalised graphene particles onto the fabric to form (A) a layer comprising surface-functionalised graphene particles preferably involves depositing (coating) an ink comprising surface-functionalised graphene particles on to the fabric. Suitable deposition techniques include, for example, bar coating, screen printing (including rotary screen printing), flexography, rotogravure, inkjet, pad printing, and offset lithography, whereby the conductive ink comprises the surface-functionalised graphene particles dispersed in a solvent and polymer material. Preferably, the deposition technique used is screen printing.

When multiple layers comprising surface-functionalised graphene particles are printed, each layer is preferably dried before a subsequent layer is added. The device may be heated after the application of each layer comprising surface-functionalised graphene particles to speed up the drying of the ink.

When using a conductive ink, the method preferably involves a step of preparing the ink for printing. This preparation step may involve mixing or homogenising the ink to evenly distribute the surface-functionalised graphene particles in the ink's polymer binder. Preferably, the preparation step involves homogenising the ink, since the inventors have found that this ensures a uniform distribution of carbon nanoparticles and can help to break up agglomerates of nanoparticles in the ink. Suitable homogenisation can be achieved using, for example, a three roll-mill or rotor-stator homogeniser.

Preferably the methods of manufacture further comprise the following steps: Step 3: providing layer (B) a layer of non-woven fabric and layer (C) a layer of water-resistant fabric and optionally additional intermediate layers; Step 4: stacking the layers from step 3 on top of each other to form a mask body; Step 5: attaching the layers together to form a multilayer face mask.

In certain embodiments, the layers may be attached together by stitching or sewing the layers together in order to form a face mask. Preferably, the layers are attached together by stitching.

Preferred embodiments Particularly preferred embodiments include: A face mask comprising layer (A) a layer comprising surface-functionalised graphene particles, wherein the surface-functionalised graphene particles have one or more of the following features: i. a sulphur impurity level of less than 0.2 wt.% based on the total weight of surface-functionalised graphene particles; ii. a manganese level of less than 10 ppm; iii. a NO level of less than 10 ppm.

Preferably, the surface-functionalised graphene particles have: i. a sulphur impurity level of less than 0.2 wt.% based on the total weight of surface-functionalised graphene particles; ii. a manganese level of less than 10 ppm; and iii. a NO level of less than 10 ppm.

Preferably, the face mask is a multilayer face mask further comprising one or more additional fabric layers.

Preferably, the functional groups present on the surface of the graphene particles are phenolic, carboxylate and hydroxyl groups.

Preferably, layer (A) comprises surface-funcfionalised graphene particles in a polymer matrix coated onto a polyester fabric layer.

In a particularly preferred implementation, the multilayer face mask according to the present invention consists of: A) a layer comprising surface-functionalised graphene particles in a polymer matrix coated onto a polyester fabric layer; B) a layer of spunbond non-woven fabric; and C) a layer of water-resistant muslin cotton fabric.

Preferably, the polymer matrix is polyurethane or silicone.

Preferably, the spunbond non-woven fabric is a non-woven spunbond filter, wherein the nonwoven spunbond filter is a PM 2.5 filter.

Preferably, the amount of sulphur present in the surface functionsed-graphene is less that 0.2 wt.% based on the bulk (as determined by elemental analysis).

Preferably, layer (B) is placed between layer (A) and layer (C), wherein layer (A) is designed to be the layer on the outside of a face mask when worn by a user and layer (C) is the inside layer.

BRIEF DESCRIPTION OF THE FIGURES

The present proposals are now explained further with reference to the accompanying figures in which: Fig. 1 (a) is a perspective view schematically showing the arrangement of each layer of the multilayer face mask.

Fig. 1 (b) is a cross-sectional schematic showing the layers of the multilayer face mask. Fig. 2 is a cross-sectional schematic showing the layers of the multilayer face mask according to an embodiment of the present invention, comprising surface functionalised particles coated onto a fabric layer.

Fig. 3 is a diagram showing a face mask according to the present invention

DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains.

Although, any methods and materials similar or equivalent to those described herein can be used in practice for testing of the present invention, the preferred materials and methods are described herein. In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. Unless clearly indicated otherwise, use of the terms "a," "an," and the like refers to one or more.

Figures 1, 2 and 3 show multilayer face masks according to one aspect of the present invention. The perspective view in figure 1(a) shows the layers of the face mask which make up the mask body (1), this comprises an outer layer (11), an interior layer (12) and an inner layer (13). Figure 1(b) shows a cross-section of the face mask body (1). Preferably, the outer layer comprises surface-functionalised graphene particles, the interior layer is a non-woven fabric and the inner layer is a layer of water resistant fabric. Although, the layers are shown as being pressed against each other, they are not necessarily attached along their faces and can be attached along their edges only.

Figure 2 shows a cross-section of the face mask body, in a specific embodiment of the present invention, the outer layer (11) comprises a fabric (11a) and a coating comprising surface-functionalised graphene particles (11b). The surface-functionalised graphene particles may be suspended in a polymer matrix.

Figure 3 shows a frontal view of the multilayer face mask, showing an inner layer (13), an outer layer (11) and a nose wire (21). Preferably, the inner layer (13) is a water-resistant muslin cotton fabric and the outer layer is made of functionalised graphene particles in a PVC-vinyl matrix material coated onto the polyester fabric. The nose wire may be made of polyethylene cladding with galvanized wire. Preferably, the face mask also comprises ear loops made of elastic, string or cloth strips, and stoppers made of soft silicone.

Claims

CLAIMS1 A face mask comprising * layer (A), a layer comprising surface-functionalised graphene particles, wherein the surface-functionalised graphene particles preferably have one or more of the following features: i. a sulphur impurity level of less than 0.2 wt.% based on the total weight of surface-functionalised graphene particles; ii. a manganese level of less than 10 ppm; iii. a NO level of less than 10 ppm; and * optionally, wherein the face mask further comprises one or more additional fabric layers.
2. The face mask according to claim 1, wherein the amount of sulphur present in the surface-functionalised graphene particles is less than 0.2 wt.%, preferably less than 0.15 wt.% based on the total amount of surface functionalised graphene particles.
3. The face mask according to claim 1 or 2, wherein the amount of manganese present is less than 10 ppm, preferably less than 5 ppm, most preferably less than 1 ppm based on the total amount of surface functionalised graphene particles.
4 The face mask to any one of the preceding claims, wherein the NO level present in the surface-functionalised graphene particles is less than 10 ppm, preferably less than 5 ppm, most preferably less than 1 ppm based on the total amount of surface functionalised graphene particles.
The face mask according to any one of the preceding claims, wherein the surfacefunctionalised graphene particles are oxygen-functionalised, hydroxy- functionalised, carboxy-functionalised, carbonyl-functionalised, amine-functionalised, amide-functionalised and/or halogen-functionalised.
6. The face mask according to claim 5, wherein the surface-functionalised graphene particles are oxygen-functionalised.
7. The face mask according to claim 5 or 6, wherein the functional groups present on the surface of the graphene are phenolic, carboxylate and/or hydroxyl groups.
8. The face mask according to any one of the preceding claims, wherein the surfacefunctionalised graphene particles are graphene nanoplatelets.
9. The face mask according to any one of the preceding claims, wherein layer (A) comprises surface-functionalised graphene particles dispersed in a polymer matrix material.
10. The face mask according to claim 9, wherein the polymer matrix material is an elastic material.
11. The face mask according to claim 10, wherein the polymer matrix material is PVC.
12. The face mask according to claim 10, wherein the polymer matrix material comprises polyurethane or silicone, preferably wherein the polymer matrix material is polyurethane.
13. The face mask according to any one of claims 9 to 12, wherein layer (A) comprises surface-funcfionalised graphene particles dispersed in a polymer matrix material coated onto a fabric layer, preferably a polyester fabric layer.
14. The face mask according to claim 13, wherein layer (A) is obtainable by screen printing the surface-functionalised graphene particles dispersed in a polymer matrix material onto a fabric layer.
15. The face mask according to any one of the preceding claims, wherein layer (A) has a thickness of from 100 pm to 1 mm.
16. A face mask according to any one of the preceding claims, wherein the face mask is a multilayer face mask further comprising one or more additional fabric layers.
17. The multilayer face mask according to claim 16 further comprising: B) a layer of non-woven fabric; and C) a layer of water-resistant fabric.
18. The multilayer face mask according to claim 17, wherein layer (B) is a non-woven spunbound filter, preferably wherein the non-woven spundbond filter is made of polypropylene or polyester, preferably wherein the non-woven spunbond filter is a PM 2.5 filter.
19. The multilayer face mask according to claim 17 or 18, wherein layer (C) is a water resistant cotton fabric, preferably wherein layer (C) is a water resistant muslin cotton fabric.
20. The multilayer face mask according to any one of claims 17 to 19, wherein layer (A) is the outside layer, layer (C) is the inner layer and layer (B) is placed between layer (A) and layer (C).
21. Use of the face mask according to any one of the preceding claims as personal protective equipment to prevent the spread of a bacterial or viral infection.
22. A method of manufacture of a face mask according to any one of claims 1-20, the method comprising the following steps: Step 1: plasma functionalising a graphene material to form surface functionalised graphene particles; Step 2: forming layer (A) from the surface functionalised graphene particles produced in step 1, preferably wherein the surface functionalised graphene particles in step 1 have one or more of the following features: i. a sulphur impurity level of less than 0.2 wt.% based on the total weight of surface-functionalised graphene particles; ii. a manganese level of less than 10 ppm; iii. a NO level of less than 10 ppm.
23. A method of manufacture of a face mask according to any one of claims 1-20, the method comprising the following steps: Step 1: providing surface functionalised graphene particles, wherein the surface functionalised graphene particles have one or more of the following features: i. a sulphur impurity level of less than 0.2 wt.% based on the total weight of surface-functionalised graphene particles; ii. a manganese level of less than 10 ppm; iii. a NO level of less than 10 ppm Step 2: forming layer (A) from the surface functionalised graphene particles in step
24. The method of claim 22 or 23, wherein step 2 comprises depositing one or more layers of the surface-functionalised graphene particles onto a fabric to form layer (A), optionally wherein the step 2 involves dispersing the surface-functionalised graphene particles in a polymer matrix material before depositing them onto the fabric.The method of any one of claims 22 to 24, further comprising the following steps: Step 3: providing layer (B), a layer of non-woven fabric and layer (C) a layer of water-resistant fabric and optionally additional intermediate layers; Step 4: stacking the layers from step 3 on top of each other to form a mask body; Step 5: attaching the layers together to form a mulfilayer face mask, optionally wherein the layers in step 5 are attached together by stitching.