CN110139896B

CN110139896B - Multipurpose graphene-based composite material

Info

Publication number: CN110139896B
Application number: CN201780068881.2A
Authority: CN
Inventors: 杜桑·洛西克; M·J·尼内; D·N·H·德兰
Original assignee: University of Adelaide
Current assignee: University of Adelaide
Priority date: 2016-09-12
Filing date: 2017-09-12
Publication date: 2021-12-31
Anticipated expiration: 2037-09-12
Also published as: CA3039985A1; KR102412811B1; SG11201903072PA; AU2017325118A1; EP3510089A1; EP3510089A4; AU2017325118C1; WO2018045436A1; AU2017325118B2; CN110139896A; KR20190085915A

Abstract

The present invention relates to graphene-based composite materials comprising hydrated sodium metaborate intercalated graphene-based materials.

Description

Multipurpose graphene-based composite material

Technical Field

The present invention relates generally to graphene-based materials. In particular, the present invention relates to graphene-based composite materials, substrates comprising the composite materials, methods of making the composite materials, and uses of the composite materials.

Background

Protecting objects such as buildings and industrial substrates against everyday use and environmental conditions presents significant challenges in today's society. For example, many objects can be adversely affected by factors such as corrosion, abrasion from abrasion, bacterial contamination, and fire damage, to name a few.

In response to this challenge, a great deal of research has been conducted to develop means for protecting objects. A common approach to providing such protection is to coat or treat the object with a protective material. For example, objects are often coated with various coating products that can protect the object from corrosion, abrasive wear, or bacterial contamination. The object may also be treated with a flame retardant to improve its flame retardancy.

While the prior art for protecting objects has proven effective, many of the protection systems employed now demonstrate their own environmental issues. For example, tin-based anti-bacterial fouling coatings and halogenated flame retardant compounds, while effective in application, their use now poses significant environmental problems.

Further, conventional protection systems are typically application specific in the sense that they lack versatility for use in a variety of different applications.

The various properties of graphene (Gr) are only now just achieved. Graphene is an allotrope of carbon with typical sp densely packed into a D-crystal ladder in a honeycomb shape²One atom thick planar sheet structure of bonded carbon atoms. The covalently bonded carbon atoms typically form a repeating unit comprising a 6-membered ring, but may also form a 5-and/or 7-membered ring. Such a layer of covalently bonded carbon atoms is commonly referred to as graphene "sheet". Graphene can be conveniently prepared synthetically or by exfoliation of graphite.

The unique properties of graphene are now being applied in protective systems, promoting, for example, improved gas impermeability, chemical resistance, flame and antibacterial effects (anti-microbial effects), and super lubricity.

However, despite the promise of graphene in protection systems, many graphene-based protection systems developed to date do not meet the quality requirements of traditional protection systems. Many graphene-based protection systems have therefore not been successfully converted into commercially viable products.

Thus, there remains an opportunity to develop new graphene-based materials that have a variety of utilities, for example, in protective applications.

Disclosure of Invention

The present invention therefore provides a graphene-based composite material comprising a hydrated sodium metaborate intercalated graphene-based material.

The present invention also provides a method of preparing a graphene-based composite material, the method comprising (i) providing a liquid composition comprising a graphene-based material and hydrated sodium metaborate, and (ii) removing liquid from the composition, thereby retaining the graphene-based material and the hydrated sodium metaborate in the composition, wherein the process of removing liquid in step (ii) facilitates intercalation of the hydrated sodium metaborate in the graphene-based material to provide the graphene-based composite material.

The present invention further provides a substrate comprising a graphene-based composite material comprising a hydrated sodium metaborate intercalated graphene-based material.

It has surprisingly been found that the graphene-based composite material according to the present invention exhibits properties that enable a variety of improved properties to be imparted to a substrate. The composite material exhibits a unique ability to protect a variety of substrates against a range of different environmental/use conditions. Such improved properties imparted to the substrate are surprisingly superior to the properties imparted to the substrate by each of the constituent components of the composite when used alone.

For example, substrates comprising graphene-based composites may advantageously exhibit improved flame retardancy, improved abrasion resistance, and/or improved antimicrobial properties.

The present invention therefore further provides a substrate having improved flame retardancy, the substrate comprising a graphene-based composite material, wherein the graphene-based composite material comprises a hydrated sodium metaborate intercalated graphene-based material.

The present invention also provides a substrate having improved wear resistance comprising a graphene-based composite material, wherein the graphene-based composite material comprises a hydrated sodium metaborate intercalated graphene-based material.

The present invention further provides a substrate having improved antimicrobial properties, the substrate comprising a graphene-based composite material, wherein the graphene-based composite material comprises a hydrated sodium metaborate intercalated graphene-based material.

While the present invention will be described with emphasis on the use of graphene-based composites to provide improved flame retardancy, improved abrasion resistance and/or improved antimicrobial properties, it is to be understood that the invention is not limited to these applications.

Accordingly, the present invention further provides a substrate having one or more improved properties, the substrate comprising a graphene-based composite material, wherein the graphene-based composite material comprises a hydrated sodium metaborate intercalated graphene-based material.

The present invention also provides a method of improving one or more properties of a substrate, the method comprising providing a substrate having a graphene-based composite material, wherein the graphene-based composite material comprises a hydrated sodium metaborate intercalated graphene-based material.

The substrate may comprise or be provided with a graphene-based composite material by any suitable means. For example, the substrate may be coated, impregnated, blended and/or compounded with a graphene-based composite material.

While the various improved properties imparted to the substrate by the graphene-based composite material may function by different mechanisms without wishing to be bound by theory, it is believed that a common feature of most, if not all, of such improved properties stems from the composite material not only being able to form a good bond with the substrate, but also the composite material itself having a strong internal bonding structure. Again without wishing to be bound by theory, it is believed that hydrated sodium metaborate plays an important role in promoting such binding characteristics.

The graphene-based composite material may include a graphene-based material selected from the group consisting of graphene, graphene oxide, reduced graphene oxide, partially reduced graphene oxide, and combinations thereof.

Substrates suitable for use according to the present invention include: including cellulosic materials, polymers, metals, ceramics, glass, and combinations thereof.

Further aspects and embodiments of the invention are described in detail below.

Drawings

The invention will be described herein with reference to the following non-limiting figures, in which:

fig. 1 shows a schematic view of a graphene-based composite material for use according to the present invention;

fig. 2 shows (a) a substrate provided with a graphene-based composite material according to the present invention and (b) the flame retardant properties provided by the graphene-based composite material used according to the present invention;

FIG. 3 shows flammability tests of (a) paper, (b) paper treated with reduced graphene oxide, and (c) paper treated with a reduced graphene oxide/sodium metaborate hydrate composite according to the present invention;

fig. 4 shows a pine lath subjected to a burn test (12 seconds of exposure to a butane flame at a distance of 20 mm) wherein (a) a pine lath is employed and (b) a pine lath coated with a reduced graphene oxide/sodium metaborate hydrate composite according to the present invention is employed; and

fig. 5 shows pellets formed from sawdust subjected to a vertical burning test (UL-94), wherein (a) pellets formed from sawdust and (b) pellets formed from sawdust provided with a reduced graphene oxide/sodium metaborate hydrate composite according to the present invention are used;

FIG. 6 shows the coating of uncoated material (glass control), graphene oxide coated (GO control), reduced graphene oxide (rGO with N₂H₂) (also control) and 0 and 24 hour bacterial colonies present on the culture dishes of graphene-based composite material according to the invention (rGO/SMB); and

fig. 7 shows a comparative characterization of the adhesion and abrasion characteristics of graphene-based composites according to the invention (rGO/SMB) versus graphene oxide (GO control) and reduced graphene oxide (rGO control) on Cu and glass substrates.

Fig. 8 shows a sample of polymer (water soluble-PVA) subjected to a burning test (UL-94), wherein (top) an untreated sample is used, and (bottom) a polymer sample impregnated with a reduced graphene oxide/sodium metaborate hydrate composite according to the present invention is used.

Fig. 9 shows a sample of polymer (oil soluble-polystyrene) subjected to a burning test (UL-94), wherein (top) an untreated sample is used, and (bottom) a polymer sample impregnated with a reduced graphene oxide/sodium metaborate hydrate composite according to the present invention is used.

Detailed Description

The present invention provides unique graphene-based composites. The graphene-based composite material comprises a hydrated sodium metaborate intercalated graphene-based material.

In the context of the present invention, the expression "graphene-based" composite material is intended to mean that the composite material has a composition comprising graphene, graphene oxide, partially reduced graphene oxide, reduced graphene oxide or a combination of two or more thereof. The expression "graphene-based" material may thus be used herein as a convenient description for graphene (material or sheet), graphene oxide (material or sheet), partially reduced graphene oxide (material or sheet), or a combination of two or more thereof.

A brief discussion of the properties of graphene is provided above.

Graphene oxide is an oxidized form of graphene, typically prepared by exfoliation of graphite oxide. Graphene oxide is considered to have a graphene-based structure substituted with oxygen-containing groups (oxidized groups) such as hydroxyl groups and epoxy groups (epoxides). Graphene oxide can be prepared using a number of techniques such as the so-called Brodie, Staudenmaier or Hummers method.

The graphene oxide may be reduced, thereby forming a reduced form of the graphene oxide. Reduced graphene oxide is chemically and physically different from graphene oxide due to the loss of its oxygen-containing groups. The degree of reduction of graphene oxide may vary, which is reflected in the residual amount of oxygen-containing groups. In the case where graphene oxide is not fully reduced, it is often referred to in the art as partially reduced graphene oxide. Reduced graphene oxide and partially reduced graphene oxide are less hydrophilic than graphene oxide. Reduced graphene oxide is sometimes referred to in the art as simply graphene as an indication that substantially all of the oxygen-containing groups have been removed. Techniques for reducing or partially reducing graphene oxide are known in the art. For example, graphene oxide may be reduced or partially reduced by chemical or thermal reduction.

Graphene oxide, partially reduced graphene oxide and reduced graphene oxide have a covalently bonded carbon atom sheet structure similar to graphene.

The graphene-based composite material comprises a hydrated sodium metaborate intercalated graphene-based material. The composite material itself will therefore comprise a plurality of sheets of graphene-based material with hydrated sodium metaborate intercalated therebetween. Graphite (II)A schematic of the graphene-based composite material is shown in fig. 1, fig. 1 emphasizing the layered (layered) sheet structure of the graphene-based material and the sodium metaborate hydrate (NaBO) intercalated within the layered sheet structure₂.xH₂O)。

The graphene-based material "intercalated" by hydrated sodium metaborate means that hydrated sodium metaborate remains as a solid between and on the layers of the graphene-based material sheet structure. In other words, the graphene-based material is intercalated with solid hydrated sodium metaborate.

Needless to say, the graphene-based composite material itself exists as a solid.

The layered sheet structure of the graphene-based material may include graphene, graphene oxide, partially reduced graphene oxide, or a combination of two or more thereof.

In one embodiment, the graphene-based composite material includes one or both of hydrated sodium metaborate intercalated graphene and reduced graphene oxide.

The sodium metaborate used in accordance with the present invention is "hydrated". By hydrating sodium metaborate it is meant that sodium metaborate contains water, such as crystal water, which is physically and/or chemically absorbed and/or bound. Hydrated Compounds are typically labeled₂And O is used as the index.

There is no particular limitation on the physical form that hydrated sodium metaborate may take, provided that it can be intercalated within the graphene-based material.

In one embodiment, the graphene-based material is intercalated with hydrated sodium metaborate in the form of microparticles, nanoparticles, films, sheets, or a combination thereof.

As used herein, reference to "nanoparticles" is a particle having a largest dimension of no greater than 100 nm.

As used herein, reference to "microparticles" is a particle having a largest dimension of no greater than 1000 nm.

When in particulate form, the maximum size of the hydrated sodium metaborate will generally be in the range of about 50-500 nm.

Typically, the graphene-based composite material will include about 20% to about 80% by weight graphene-based material and about 20% to about 80% by weight intercalated hydrated sodium metaborate.

The graphene-based composite material may include one or more other components. In this case, the weight% of the graphene-based material and/or the intercalated inorganic metal hydrate will be adjusted accordingly.

The graphene-based materials and hydrated sodium metaborate used in accordance with the present invention may be commercially available or prepared by techniques known in the art.

The graphene-based composite material may conveniently be prepared by a method comprising (i) providing a liquid composition comprising graphene-based material and hydrated sodium metaborate, and (ii) removing liquid from the composition, thereby retaining the graphene-based material and the hydrated sodium metaborate in the composition, wherein the process of removing liquid in step (ii) facilitates intercalation of the hydrated sodium metaborate in the graphene-based material to provide the graphene-based composite material.

By providing a liquid composition comprising a graphene-based material and hydrated sodium metaborate, the composition will of course also comprise a liquid. The liquid may be organic (solvent), aqueous, or a combination thereof.

It will be appreciated by those skilled in the art that graphene-based materials are substantially insoluble in most liquids, but can be readily dispersed in liquids.

The hydrated sodium metaborate may be soluble or insoluble in the liquid composition.

In one embodiment, the method of making the composite material comprises: (i) providing an aqueous liquid composition comprising a graphene-based material and hydrated sodium metaborate, and (ii) removing water from the composition.

Including hydrated sodium metaborate in a liquid dispersion of graphene-based materials and removing the liquid from the resulting composition (thereby retaining the graphene-based materials and hydrated sodium metaborate in the composition) causes the hydrated sodium metaborate to become intercalated in the layered structure of the graphene-based materials.

The liquid may be removed from the composition by any suitable means provided that the graphene-based material and hydrated sodium metaborate remain in the composition.

In one embodiment, the liquid is removed from the composition by evaporation. Heat may be applied to the composition to facilitate such evaporation, as desired.

In the case where hydrated sodium metaborate is soluble in the liquid used in the composition, removal of the liquid from the composition will promote the formation of hydrated sodium metaborate particles or crystals that are intercalated within the layered structure of the graphene-based material.

In the case where the hydrated sodium metaborate is insoluble in the liquid used in the composition, removal of the liquid from the composition will only facilitate intercalation of pre-existing hydrated sodium metaborate particles within the layered structure of the graphene-based material. In this case, the sodium metaborate particles used will, of course, be of the appropriate size to allow such intercalation to occur.

The hydrated sodium metaborate used to form the graphene-based composite material may itself be preformed and incorporated into the liquid composition provided for preparing the graphene-based composite material. Alternatively, the hydrated sodium metaborate may be prepared in situ as part of the method of preparing the graphene-based composite material.

Thus, a liquid composition comprising a graphene-based material and hydrated sodium metaborate may be provided by an aqueous liquid composition comprising graphene oxide and sodium borohydride, wherein the graphene oxide is reduced by the sodium borohydride to provide reduced graphene oxide and hydrated sodium metaborate.

In one embodiment, the graphene-based composite material is produced by: (i) providing an aqueous liquid composition comprising graphene oxide and sodium borohydride, wherein the sodium borohydride reduces the graphene oxide to provide reduced graphene oxide and sodium metaborate hydrate; and (ii) removing water from the formed composition, thereby retaining the graphene-based material and the hydrated sodium metaborate in the composition, wherein the process of removing water in step (ii) facilitates intercalation of the hydrated sodium metaborate in the graphene-based material to provide the graphene-based composite material.

The present invention provides a substrate having one or more improved properties, the substrate comprising a graphene-based composite, wherein the graphene-based composite comprises a hydrated sodium metaborate intercalated graphene-based material.

One or more improved properties include, but are not limited to, improved flame retardancy, improved abrasion resistance, improved antimicrobial properties.

Reference to "improving", "improved" or "to improve" the performance in the context of the present invention is intended to mean an improvement of the performance of the substrate relative to a substrate not comprising the graphene-based composite material according to the present invention.

Graphene-based composites can advantageously impart improved properties to various substrates.

Substrates suitably used according to the present invention include: including cellulosic materials, polymers, metals, ceramics, glass, and combinations thereof.

Examples of cellulosic materials include, without limitation, wood, paper, sawdust, and natural fibers.

Examples of polymers include, without limitation, thermoset polymers and thermoplastic polymers.

Specific examples of polymers include, without limitation, polyolefins, polyamides, polyesters, polyvinyl alcohols, polystyrenes, polyacrylates, polyurethanes, polycarbonates, epoxies.

Examples of metals include, without limitation, steel, copper, and aluminum.

There is no particular limitation on the physical form that the substrate may take. For example, the substrate may be in the shape of a sheet, film, plate, bundle (beam), granule, powder, slab (tank), or any shaped product.

By "including" the graphene-based composite or "providing" a substrate with the composite, it is meant that the composite is suitably physically associated with the substrate, thereby imparting improved performance. In other words, the substrate comprises or is provided with a graphene-based composite material such that the composite material is in physical communication with the substrate.

The graphene-based composite material may be located on a surface of the substrate and/or within the substrate matrix. The substrate may comprise or be provided with the composite material by coating, absorbing or impregnating the composite material in, and/or compounding with, the substrate material.

For example, the composite material may be present as a coating film on the surface of the substrate, and/or the composite material may be distributed throughout the substrate matrix material.

The substrate may be provided with the graphene-based composite material by any suitable means.

When providing a substrate with a graphene-based composite material, the graphene-based composite material may be used in a preformed state (i.e., in the form of the composite material itself). For example, the graphene-based composite material may form part of a liquid composition that is coated on or impregnated into a substrate using coating techniques known to those skilled in the art. In this case, the liquid composition may include the graphene-based composite material in the form of a dispersion in a liquid (organic-based (solvent), aqueous-based, or a combination thereof).

As a preformed material, the graphene-based composite material may also be used in the form of a solid (e.g., a powder) and combined with a substrate material, wherein the resulting blend of substrate material and graphene-based composite material is optionally processed to provide a product made from the substrate material comprising the graphene-based composite material. For example, the substrate may be in the form of a thermoplastic polymer, whereby the thermoplastic polymer is melt processed with the graphene-based material to provide a thermoplastic polymer product comprising the graphene-based composite material distributed throughout a thermoplastic polymer matrix.

As a preformed material, the graphene-based composite material may also be blended with a cellulosic material, such as sawdust, and the resulting blend compressed to form a so-called reconstituted wood product comprising the graphene-based composite material distributed throughout the product.

Alternatively, the graphene-based composite material may be prepared in situ using the precursor components as part of the process of disposing it to the substrate. For example, the graphene-based material may be dispersed in a liquid that also includes hydrated sodium metaborate. The resulting liquid composition can then be used to coat or impregnate the substrate. Removal of liquid from the coated or impregnated liquid composition, while retaining the graphene-based material and hydrated sodium metaborate in the composition, may facilitate in situ formation of the composite material.

In one embodiment, the substrate is provided with a graphene-based composite using a precursor component of the graphene-based composite.

Reference herein to a "precursor component" of a graphene-based composite material is intended to include graphene-based materials and hydrated sodium metaborate. As a "precursor component," the hydrated sodium metaborate is not intercalated with the graphene-based material, but rather intercalation occurs as part of the process of providing a substrate with the graphene-based composite material.

The graphene-based composite material or precursor components thereof may be provided in the form of a coating composition that is applied to the substrate using conventional techniques such as spraying, dipping, doctor blading and/or brushing.

The coating composition may be in the form of a coating composition.

Where the substrate is suitably an absorbent, a liquid composition comprising the graphene-based composite material or a precursor component thereof may be used to impregnate the substrate.

Alternatively, the graphene-based composite material itself may be blended with the substrate material, wherein the resulting blend is optionally further processed, e.g. compressed or extruded.

In one embodiment, a substrate is provided with a graphene-based composite by coating the substrate with a composition comprising the graphene-based composite or a precursor component thereof. Coating a substrate with the composition can be carried out by techniques such as spraying, dipping, doctor blading and/or brushing.

In another embodiment, the substrate is provided with the graphene-based composite by impregnating the substrate with a composition comprising the graphene-based composite or a precursor component thereof. The impregnation of the substrate with the composition may be carried out by soaking the substrate in the composition.

The composition including the graphene-based composite material for coating or impregnating the substrate may be a liquid composition. The liquid component of the composition can be organic (solvent), aqueous, or a combination thereof. The composition may include other components such as polymers.

In a further embodiment, the substrate is a thermoplastic polymer and the substrate is provided with the graphene-based composite by melt processing the polymer with the graphene-based composite.

In yet a further embodiment, the substrate is a thermoset polymer and the substrate is provided with the graphene-based composite by blending the graphene-based composite with a precursor material for making the thermoset polymer. Precursor materials used to make thermoset polymers include monomers and prepolymers that polymerize and crosslink to form a thermoset polymer matrix.

In one embodiment, the substrate is provided with the graphene-based composite by coating or impregnating the substrate with a liquid composition comprising the graphene-based composite.

In another embodiment, a substrate is provided with a graphene-based composite by: (i) coating or impregnating a substrate with a liquid composition comprising a graphene-based material and hydrated sodium metaborate, and (ii) removing liquid from the coated or impregnated liquid composition while retaining the graphene-based material and hydrated sodium metaborate in the composition, thereby forming and providing a graphene-based composite material.

In a further embodiment, the substrate is provided with the graphene-based composite material by: (i) coating or impregnating a substrate with an aqueous composition comprising a graphene-based material and hydrated sodium metaborate, and (ii) removing water from the coated or impregnated liquid composition, thereby forming and providing a graphene-based composite.

As described herein, the hydrated sodium metaborate used to form the graphene-based composite material may be preformed and incorporated into the liquid composition provided for preparing the graphene-based composite material. Alternatively, the hydrated sodium metaborate may be prepared in situ as part of the process of preparing or forming the graphene-based composite material.

Thus, the "precursor component" of the graphene-based composite material may also include a precursor compound for preparing hydrated sodium metaborate. Precursor compounds for hydrated sodium metaborate may include oxidized sodium borohydride, sodium carbonate in combination with borax, and sodium tetraborate in combination with sodium hydroxide.

In one embodiment, a substrate is provided with a graphene-based composite material by: (i) providing an aqueous liquid composition comprising graphene oxide and sodium borohydride, wherein the graphene oxide is reduced by sodium borohydride to provide reduced graphene oxide and sodium metaborate hydrate, (ii) coating or impregnating a substrate with the aqueous liquid composition provided in step (i), and (iii) removing water from the coated or impregnated aqueous liquid composition to form and provide a graphene-based composite.

The present invention may further include providing a substrate with hydrated sodium metaborate that does not form part of the graphene-based composite material itself. In this case, the substrate will comprise the graphene-based composite material and also comprise hydrated sodium metaborate which does not form part of the graphene-based composite material.

For example, in one embodiment, the substrate used is impregnated with hydrated sodium metaborate. In this case, the substrate is impregnated with hydrated sodium metaborate and may then also be impregnated and/or coated with the graphene-based composite material.

Providing a substrate having hydrated sodium metaborate that does not form part of the graphene-based composite material itself can further improve the flame retardancy of the substrate.

As a coating on a substrate, the graphene composite may be provided in the form of a film of an average thickness according to the intended use. For example, the graphene composite film may have a thickness of 500 micrometers or less.

Improved flame retardancy of substrates

The graphene-based composite material according to the present invention can impart improved flame retardancy to a substrate.

The substrate may comprise or be provided with a graphene-based composite material as described herein.

Relevant flame retardancy is those known in the art and includes the flammability and burn rate of the substrate, the release of toxic/flammable volatiles from the substrate upon exposure of the substrate to an ignition source such as fire or extreme heat, self-extinguishing and intumescent properties, char formation/yield and oxygen barrier properties.

For example, it has been found that a substrate provided with a graphene-based composite material according to the present invention exhibits one or more of reduced flammability, lower burning rate, significant swelling effect, and reduced release of toxic/flammable volatiles upon exposure to a source of ignition relative to the same substrate not provided with a graphene-based composite material according to the present invention.

The flame retardancy of the substrate can be determined using techniques known in the art. Such techniques include TGA, STA, UL-94, calorimeter, Limiting Oxygen Index (LOI) measurements.

The substrate exhibiting improved flame retardancy according to the present invention will of course be a substrate which is itself flammable. In other words, the present invention can provide a combustible substrate having improved flame retardancy.

Examples of such flammable substrates include: those comprising cellulosic materials, polymers, and combinations thereof.

Examples of cellulosic materials include those described herein.

Examples of polymers include those described herein.

In one embodiment, the combustible substrate comprises a cellulosic material, a polymeric material, or a combination thereof.

It is considered that the excellent flame retardancy imparted to the substrate by the graphene-based composite material acts by a wide variety of mechanisms.

Without wishing to be bound by theory, it is believed that hydrated sodium metaborate functions as a heat sink as it undergoes endothermic dehydration which releases water into the surrounding environment. This is believed to in turn promote a unique swelling effect.

It is believed that graphene-based materials act synergistically to promote fire resistance by providing at least four combined functions including: (i) preventing oxygen from entering the combustible substrate, (ii) providing self-extinguishing, (iii) preventing the escape of toxic and combustible volatiles from the substrate, and (iv) exhibiting carbon formation and expansion effects.

It is believed that the graphene-based material also acts as a carbon donor to establish a physical barrier between the unburnt substrate and the flame, thereby protecting the substrate.

Still further, it is believed that the hydrated sodium metaborate promotes a high degree of bonding between the layers of graphene-based material and between the substrate and the composite graphene-based composite material, thereby providing a strong flame retardant system. This is particularly useful where the composite material is provided as a coating on a substrate.

The unique flame retardancy imparted by graphene-based composites can be further illustrated with reference to fig. 2.

Fig. 2(a) shows a substrate coated with a graphene-based composite material according to the present invention. The graphene-based composite coating may be viewed as including a hydrated sodium metaborate intercalated graphene-based material.

Fig. 2(b) shows the graphene-based composite coated substrate of fig. 2(a) exposed to a fire. The graphene-based composite material used according to the present invention is believed to provide several mechanisms by which improved flame retardancy is imparted to the substrate. First, and again without wishing to be bound by theory, it is believed that intercalated hydrated sodium metaborate not only promotes good adhesion (adhesion) between the layers of the graphene-based material structure, but also promotes adhesion of the graphene-based composite to the substrate. Such adhesive properties provide a strong flame retardant system. The strongly bonded layered structure of the graphene-based composite material is thought to block the transfer of oxygen to the substrate, thereby reducing the possibility of the substrate catching fire. Similarly, it is believed that the strongly bonded layered structure of the graphene-based composite hinders volatile components (e.g., CH) from the substrate that may be toxic and also contribute to combustion₄) Is/are as followsAnd (4) releasing. Further, upon exposure to fire, hydrated sodium metaborate may undergo endothermic dehydration, thereby functioning as a heat sink, also releasing water into the surrounding environment. This is believed to in turn promote a unique swelling effect. Such a combination of features of graphene-based composites has been found to function as an efficient, effective, and robust flame retardant system.

The excellent flame retardancy imparted by the graphene-based composite material is clearly shown in fig. 3, which fig. 3 shows the results of a series of flame tests. In the flame test, a paper sample is exposed to an open flame and its flammability is evaluated as a function of time. Fig. 3(a) tests a base paper sample, fig. 3(b) tests a base paper sample coated with only reduced graphene oxide, and fig. 3(c) tests a base paper sample coated with a graphene-based composite according to the present invention comprising hydrated sodium metaborate intercalated reduced graphene oxide. As can be clearly seen from fig. 3, the base paper sample and the reduced graphene oxide coated paper were easily ignited and completely burned after about 10 seconds. However, paper samples coated with the graphene-based composite material according to the present invention failed to ignite when exposed to an open flame for at least 120 seconds.

Similarly, fig. 4 shows a pine lath subjected to a burn test (12 seconds of exposure to a butane flame at a distance of 20 mm) wherein (a) a pine lath is employed and (b) a pine lath coated with a reduced graphene oxide/sodium metaborate hydrate composite according to the present invention is employed. It can be seen that the untreated pine laths burn almost completely after 30 seconds, whereas the pine laths coated with the composite material according to the invention can be seen to be affected by the flame only at their contact points, the fire does not spread and the rest of the laths is largely undamaged.

In addition, fig. 5 shows pellets formed of sawdust subjected to a vertical burning test (UL-94), in which (a) pellets formed of sawdust were used and (b) pellets formed of sawdust provided with a reduced graphene oxide/sodium metaborate hydrate composite according to the present invention were used. The coated pellets (b) show excellent flame retardancy without flame propagation behavior. For the composite treated samples, no flaming or glowing combustion was observed, and therefore those samples were rated V-0. The combustion of the composite treated samples stopped immediately without vertical rise of flame, while the untreated sawdust pellets showed a higher degree of flammability: at approximately linear burn rate 0.5mm/s continued until the end (reaching the holding fixture).

Figures 8 and 9 show how combustible polymers (PVA and polystyrene-top) are rendered flame retardant (bottom) by compounding with reduced graphene oxide/sodium metaborate hydrate composites according to the present invention.

Improved antimicrobial properties of substrates

The graphene-based composite material according to the present invention may impart improved antimicrobial properties, such as antibacterial and/or antifungal properties, to the substrate.

The substrate may be provided with a graphene-based composite as described herein.

Relevant antimicrobial properties are those known in the art and include preventing or reducing colonization of microorganisms such as bacteria or fungi on the substrate (colonisation).

For example, it has been found that a substrate comprising a graphene-based composite material according to the present invention prevents or reduces colonization by microorganisms, such as bacteria or fungi, relative to the same substrate not comprising a graphene-based composite material according to the present invention. In other words, it has been found that a substrate comprising the graphene-based composite material according to the present invention exhibits microbiocidal or microbe-inhibiting properties, such as bacteriostatic, bactericidal, fungistatic and/or fungicidal properties.

The antimicrobial properties of the substrate can be determined by techniques known in the art.

Substrates exhibiting improved antimicrobial properties according to the present invention will of course be substrates which are themselves susceptible to microbial colonization. In other words, the present invention may provide substrates susceptible to microbial colonization with improved bacterial resistance.

Examples of substrates susceptible to microbial colonization include: including cellulosic materials, polymers, glass, metals, ceramics, and combinations thereof.

Examples of cellulosic materials include those described herein.

Examples of polymers include those described herein.

Examples of glass include those described herein.

Examples of metals include those described herein.

Examples of ceramics include those described herein.

In one embodiment, the antimicrobial property of the substrate comprising the graphene-based composite material according to the present invention is antibacterial and/or antifungal.

The term "microorganism" or related terms such as "microbial" and "microbial organism" as referred to herein is intended to mean any organism present as microscopic cells, including in the field of archaea or eukaryotes. Thus, the term is intended to encompass prokaryotic or eukaryotic cells or organisms having microscopic dimensions and including all species of bacteria, archaea and eubacteria as well as eukaryotic microorganisms such as yeasts and fungi.

Related microorganisms also include gram positive and gram negative bacteria.

It is believed that the excellent antimicrobial properties imparted to the substrate by the graphene-based composite material are achieved through a wide variety of mechanisms. Without wishing to be bound by theory, it is believed that antimicrobial properties relate to: destructive lipid extraction by sharp-edged graphene-based materials, which destroys the integrity of the microbial membrane and the interwoven microbial pores, creating perturbation of the cell membrane, and charge transfer between the graphene-based material sheet and the microbial cells leading to DNA damage. Further, it is also believed that the presence of hydrated sodium metaborate in the composite material itself imparts an antimicrobial effect. In the case of a substrate in contact with an aqueous environment, the hydrated sodium metaborate may advantageously leach slowly from the composite to impart such antimicrobial effects. Thus, it is believed that the composite as a whole imparts effective antimicrobial properties to the substrate.

The unique antimicrobial properties imparted by the graphene-based composite material may be further illustrated with reference to fig. 6.

FIG. 6 shows the coating of uncoated material (glass control), coated with graphene oxide (GO control), coated with reduced graphene oxide (rGO with N₂H₂) And 0 and 24 hours of bacterial colonies present on the petri dishes coated with graphene-based composite material (rGO/SMB) according to the invention. Only the rGO/SMB samples showed a significant reduction in bacterial colonization after 24 hours.

Improved abrasion resistance of substrates

The graphene-based composite material according to the present invention can impart improved abrasion resistance to a substrate.

Relevant wear characteristics are those known in the art and include measuring the amount of wear when subjected to abrasive force (abrasive force).

For example, it has been found that a substrate comprising a graphene-based composite material according to the present invention exhibits improved wear properties relative to the same substrate not comprising a graphene-based composite material according to the present invention.

The abrasion resistance of the substrate can be determined by techniques known in the art. Such techniques include ASTM D4060.

The substrate exhibiting improved wear resistance according to the present invention will of course be a substrate which is itself susceptible to wear. In other words, the present invention can provide a substrate susceptible to abrasion having improved abrasion resistance.

Examples of substrates susceptible to abrasion resistance include: including cellulosic materials, polymers, glass, metals, ceramics, and combinations thereof.

Examples of cellulosic materials include those described herein.

Examples of polymers include those described herein.

Examples of glass include those described herein.

Examples of metals include those described herein.

Examples of ceramics include those described herein.

It is considered that the excellent wear resistance imparted to the substrate by the graphene-based composite material is achieved by a wide variety of mechanisms. Without wishing to be bound by theory, it is believed that the wear resistance works by a combination of the lubricity provided by the graphene-based material, the strong internal bonding of the composite structure provided by the hydrated sodium metaborate, and the strong bonding of the graphene-based composite to the substrate also provided by the hydrated sodium metaborate. Thus, it is believed that the composite as a whole imparts a strong abrasion resistant system to the substrate.

The unique wear resistance imparted by the graphene-based composite material may be further illustrated with reference to fig. 7.

Fig. 7 shows a comparative characterization of adhesion and abrasion characteristics of graphene-based composites according to the invention (rGO/SMB) versus graphene oxide (GO control) and reduced graphene oxide (rGO control) on Cu and glass substrates. Sections (a-D) show cross-cut scratch tape adhesion tests (ASTM D3359-09e2) for coatings deposited on Cu and glass substrates, where (a and D) are GO (control), (b and e) are rGO (control), and (c and f) are rGO/SMB. Parts (a-d) show various adhesion between the graphene-based composite material and the substrate, wherein parts (c and f) show the best results with little damage to the graphene-based composite material after adhesion testing. Part (g) shows the wear type after wear testing combining micro-pits and parallel grooves identified on the coated surface, and part (h) shows the weight loss behavior for different wear lengths of the coated surface.

The invention will be described later herein with reference to the following non-limiting examples.

Examples

Synthesis of Graphene Oxide (GO)

Mixing graphite flakes (flakes) ((II))<45 μm) were chemically stripped according to a modified Hummers method. Using a 9:1 ratio of H₂SO₄/H₃PO₄(360:40ml) with 18g of KMnO₄The complete reaction was carried out to oxidize 3g of graphite flakes. While stirring at the same timeThe stripping was carried out at 50 ℃ for 12 h. The solution was then cooled to room temperature and poured to 30% H with 3ml₂O₂On ice cubes (300 ml). Finally, the mixture was centrifuged repeatedly at 4000rpm for 2h, in order to wash with distilled water (twice), 32% HCl (twice) and ethanol (twice), respectively, to obtain GO, which was oven dried at 40 ℃ for 12 h.

Composite Material formulation-1

Reduction of Graphene Oxide (GO) and formation of hydrated Sodium Metaborate (SMB): reduced go (rgo) is prepared by: 50ml of an aqueous GO dispersion (3.5mg/ml) was treated with a quantity of NaBH as reducing agent₄Reduction to form 0.1mol L^-1NaBH₄Then refluxed and stirred at 60 ℃ for 8 hr. The reaction simultaneously produces NaBH from solution₄Sodium metaborate hydrate (shown in formula 1).

The final solution contains rGO and hydrated SMB, which form graphene-based composites when water is removed by curing with heat.

Composite Material formulation-2

Graphene Oxide (GO) hydrazine (N) was used in an aqueous solution of GO (3mg of GO in 1 μ l) according to the method provided in the literature (N)₂H₄) To be chemically reduced. Next, hydrated sodium metaborate was mixed from an external source to produce an aqueous solution of reduced GO and dissolved hydrated SMB, varying in composition percentage from 40 to 80 wt%.

Preparation of graphene composite material coating

The prepared rGO/SMB solution was deposited on the substrate (from edge to edge) by a drop-on or spray-on method on a copper flat plate (3cm × 3cm × 0.2cm) and a glass slide (2.5cm × 3.5cm) covering the whole area, and then dried in an oven at 60 ℃ for 3 h. The same conditions were used to prepare comparative coatings with control solutions of GO, rGO. For abrasion testing, the coated graphene-based surface was placed under a Taber abrasion tester (ASTM D4060).

Characterization of

Scanning electron microscopy (SEM-FEI QUANTA450, Japan) was used to analyze GO and rGO surface morphology, and to measure the coating thickness of vertically aligned samples at an acceleration voltage of 5 KV. An energy dispersive X-ray (EDX) unit was used to capture the elemental peaks of rGO coatings containing sodium metaborate crystals at 5.0 KV. High resolution Philips CM200, Transmission Electron Microscope (TEM), japan, was used to image exfoliated GO sheets at 200 KV. TEM samples were prepared by dispersing the synthesized GO in ethanol to form a homogeneous dispersion. Nikon optical polarization microscope (LV100 POL, USA) was used to analyze the scribed surface to mark adhesion levels. The mode of vibro-striction of the different oxygen functional groups in GO and rGO was studied by fourier transform infrared spectroscopy (FTIR) (Nicolet 6700Thermo Fisher, USA). TGA (thermogravimetric analysis) and DTG (derivative thermogravimetric analysis) of treated and untreated sawdust were analyzed by TA instruments (Q-500, Tokyo, japan) in an air atmosphere. When burning in an air environment, the temperature rises from ambient temperature to 600 ℃ at a rate of 5 ℃/min. Thermogravimetric analysis (TGA-FTIR) combined with fourier transform infrared for real-time analysis of various gas phase compounds released from combustion samples was done by a PerkinElmer TG-IR EGA system (TG-IR EGA, PerkinElmer Ltd, UK) connected to TL 8000. This operation was carried out in an air atmosphere at a rate of 6 ℃/min to achieve a sample mass of about 16 mg.

Crosshatch adhesion test

Adhesion of the rGO/SMB coatings to metal (Cu) and glass (microscope slide) substrates was measured according to the standard tape test ASTM D3359-09e 2. Cross-hatch adhesion test kit (QFH-HG600) was purchased from Bioughed Laboratory Instruments (Guangzhou, China). The cutting tool insert comprised eleven teeth spaced 1.0mm apart. Prior to using the cutting tool, the coated substrate was placed on a laboratory bench supported by a rail. After applying the cross-hatch pattern (about 90 °), any peeled-off pieces of the coating were removed with the brush of the kit and a scotch tape (scotch tape) was placed on the cross-hatch with gentle pressure. The cut samples were examined with a high power Microscope (Nikon-Petrographic Microscope) and rated according to the ASTM rating scheme.

Abrasion resistance test

A standard (ASTM D4060) Taber abrader (Dongguan bridge construction test equipment, Inc., model JQ-802A) test was conducted to evaluate the progressive wear of the bonded rGO/SMB coating under a 250g load on a 52mm diameter pair of grinding wheels. For testing, copper and glass coated coupons (10cm x 10cm) were placed on a table and collected on the table to rotate 3000 cycles at a constant speed of 60 rpm. Abrasion loss was measured by weighing the sample every ≈ 300 cycles after a smooth brush to remove loose particles on the abraded surface. The wear samples were photographed under SEM and raman imaging systems to observe the wear pattern and the percentage of molecular area occupied after wear.

Antibacterial testing

Quantitative assessments of antibacterial efficiency of GO, rGO and rGO/SMB coated glass samples were performed on gram negative bacteria escherichia coli (e.coli) (ATCC 25922) according to AATCC test method 100-. Bare and GO coated slides were performed as primary and secondary controls. For the coated samples, slides (2.5 cm. times.2.0 cm) were drop-coated with 0.8ml of a solution of the original concentration of the graphene derivative of 3 mg/ml. The coated and uncoated samples were placed in sterile microplates (6 wells), respectively, and 0.35mL of overnight-cultured bacterial suspension (10mL)⁷CFU/mL). After inoculation, each sample was placed in 50mL of saline solution (0.85% (w/v)) and shaken vigorously for 1 minute. To measure the number of bacteria at time zero, the samples were placed in saline immediately after inoculation. Total bacteria counts were determined by serial dilution and pour plate method using Luria-Bertani agar medium plates (10g peptone, 5g yeast extract, 10g NaCl and distilled water to 1L; pH-7) incubated at 37 ℃ for 48 hours. The antibacterial efficiency of all samples was calculated using equation (2).

Wherein R is the percent reduction in bacteria, C₀And C₂₄Bacterial counts immediately after inoculation and 24 hours after inoculation, respectively.

Borate impregnation and composite coating

The prepared rGO/SMB aqueous solution produced a homogeneous mixture in which SMB was in solution. For impregnation, 2.6g of purified pine sawdust (500 μm to 1mm) was treated with 50ml of rGO/SMB into a beaker and kept stirring at 70 ℃ for 5 hours. A sample of dried sawdust was impregnated with SMB and found to be well coated with rGO/SMB composite.

Volatile suppression and flame retardancy test

The smoke and volatiles suppression test was carried out in a glass cylinder with an internal diameter of 4cm closed at one end so that the smoke and volatiles could be visually observed. Two small beakers (10ml) containing 300mg of preheated (at 80 ℃) sawdust (treated and untreated) were placed on a hot surface (300 ℃). The hotplate was allowed to thermally stabilize at 300 ℃ for 10 minutes before the sample was placed. The beaker with the sample was covered by two similar glass cylinders for observation. The immediate response of the sample placed on the hotplate was recorded for 30 minutes by a high definition video camera (Sony HDR-PJ 260).

For the pyrophoricity test, both untreated and treated sawdust (80mg) were placed on a screen well positioned above the bunsen burner (3cm from the burner tip) to contact the flame. The flame height and the gas flow of the bunsen burner are set by a gas hole kept half open, which is constant for both samples and placed in the middle of the flame. The burning phenomena (spontaneous combustion, flame propagation) were recorded for further analysis by a high definition camera (Sony HDR-PJ 260).

Pellets of size 120mm x 13mm x 3.5mm were made from untreated and treated sawdust at a hydraulic pressure of 5 tons. The flame retardant behaviour of these pellets was evaluated by the vertical burning test of the UL-94 standard. Five coupons of each sample were measured to ensure reproducibility of the data and to grade their flammability. The time until the flame self-extinguishes and the distance of combustion propagation have been measured and then the linear combustion rate in mm/min is derived.

To test the flammability of the rag paper (rag-paper) with the rGO/SMB material applied as a coating, a fiber based paper (fibre based paper) was dip coated and cured several times at 50 ℃ and the material loading was increased to 15 wt%. Samples with and without coating were subjected to flame retardant testing (see figure 3).

Results

Exfoliation of GO sheets from graphite was determined by Transmission Electron Microscopy (TEM). By NaBH₄The hydrolysis of (a) simultaneously reduces GO and forms SMB to form an aqueous rGO/SMB solution. The presence of hydrated SMB between (intercalated) and on rGO sheets was confirmed by TEM. EDX (energy dispersive X-ray) of the formed graphene-based composite material showed elemental peaks of boron (B), carbon (C), oxygen (O), and sodium (Na) at 0.185, 0.277, 0.523, and 1.040KeV, and existence of SMB on the surface of rGO was confirmed, respectively.

Samples of the rGO/SMB composite were taken under FTIR spectroscopy to investigate the characteristic peaks of synergy. In the use of NaBH₄The oxygen functionality of GO was almost completely removed during the reduction process of (a), indicating successful reduction of GO. At 692cm^-1And 783cm^-1The appearance of a new peak observed in the sample indicates an asymmetric bending of the O-B-O ring. The asymmetric stretching vibration of the ring B-O strongly appears at 932cm^-1、1083cm^-1、1248cm^-1And 1432cm^-1To (3). Further, 3353cm^-1The peaks indicate hydrogen bonding between the hydroxyl groups of the metaborate anion and water.

Thermogravimetric analysis of GO and rGO/SMB composites (N)₂Atmosphere, heating at 5 ℃/min) showed significant differences in mass loss curves. The GO sample shows a first stage mass loss (14.45%) from ambient temperature to 100 ℃ due to evaporation of water molecules in the GO structure, which is slightly higher than rGO/SMB at this stage. In the second stage between 100 ℃ and 250 ℃, the GO sample had a substantial mass loss (54.68%), mainly due to the removal of oxygen functional groups, while rGO/SMB showed a contribution from the release of additional water molecules from the hydrated SMBResulting in a 25.72% loss. Anhydrous sodium metaborate and rGO are present when the temperature exceeds 350 ℃.

Flame retardancy

Modification and coating of pine sawdust was achieved by solution treatment of aqueous rGO with dissolved SMB. Loading was performed by soaking sawdust into rGO/SMB solution. The dry mass increase of the treated sample ≈ 14.67% does not make large the difference in total heat released (≈ 460 Cal/g) between samples determined by high pressure (3000KPa) oxidative combustion of both untreated and treated sawdust in a bomb calorimeter (bomb calorimeter).

The evolution of gaseous products and the suppression of volatiles were analyzed by FTIR. FTIR spectra (4000-^-1) Showing evolution of the gaseous product with temperature. The presence of water above 250 ℃ is caused by the cleavage of aliphatic hydroxyl groups, which is caused by 4000-^-1The presence of bands at (a). At 3000-^-1The characteristic peak at (A) indicates that the compound is due to methoxy (OCH)₃-) and methyl (CH₃-) presence of methane evolving between 250 ℃ and 300 ℃. Methylene (-CH) at elevated temperature₂-) also produces methane (CH₄). With the temperature rising to 350 ℃, at 2400-^-1Carbon dioxide (CO) of₂) The intensity peak of (a) is strengthened. Large amount of CO₂The release is caused by the cracking of cellulose and lignin and the burning of carbonized char at that temperature. Incomplete combustion of pine sawdust also occurs at temperatures between 300 ℃ and 350 ℃ as described in 2260-1990cm^-1Identified carbon monoxide (CO). 1900 and 1660cm^-1And 1500cm^-1The absorption bands at (a) relate to the C ═ O stretching of aldehyde or ketone compounds, the C — O — C bending stretching of phenolic groups, respectively. 900cm^-1And 650cm^-1The absorption at (b) is assigned to the C-H stretch of the aromatic hydrocarbon. At elevated temperatures (350 ℃), organic volatile compounds (aldehydes or ketones, phenols, alkanes, alkenes and aromatics) start to be released vigorously.

From 100 to 350 deg.CThe heating process is started at 4000-^-1Water content was identified because the treated sawdust contained relatively more water molecules due to the presence of hydrated sodium metaborate. The bound water molecules are released in two steps; once between 83 and 155 ℃ and a second between 249 and 280 ℃. However, other gases (CH) released from the treated sample₄、CO₂CO, organic compounds) decreases significantly at the selected temperature, which may be due to the non-permeable gas barrier effect of the graphene-based composite. The barrier effect of the graphene-based composite was also confirmed by visual inspection when the treated and untreated samples were placed on a hot plate set at 300 ℃ for 30 minutes after preheating at 80 ℃ to ensure the loss of additional moisture. Untreated sawdust started to release smoke (probably CO) at 3 minutes₂) And moisture (from aliphatic hydroxyl groups) and release of other organic volatiles (yellow and brown) was also observed between 10 and 20 minutes, while the treated sawdust showed no significant release of organic volatiles as observed.

The coated and modified loose sawdust also showed excellent resistance to flame propagation when an 80mg sample was placed on a screen 3cm above the bunsen burner from the burner tip. Untreated sawdust started spreading the flame between 15 and 20 seconds, intensified in 25 seconds and finally burned out in 70 seconds. On the other hand, the treated sawdust samples did not show spontaneous combustion behavior during 100 seconds of combustion.

Furthermore, the flame retardant behaviour was further evaluated by the vertical burning test (UL-94) using samples made of uncoated and coated sawdust (120mm x 13mm x 3.5 mm). The coated wood pellets showed excellent flame retardancy as follows: there was no flame propagation behavior for wood pellets made from the treated sawdust. For each of the five treated coupons, no flaming and glowing combustion was observed; the material was therefore classified as V-0. Each combustion of the treated coupons was immediately stopped without vertical elevation of the flame, while the untreated sawdust pellets showed a higher degree of flammability: at approximately linear burn rate 0.5mm/s continued until the end (reaching the holding fixture).

Experiments were also performed to demonstrate the flame retardancy of rGO/SMB coatings in which rag paper (rag paper) was used as the model substrate. Using raw paper (prime paper) and using paper of the same type₂H₄In a comparative experiment of the prepared rGO treated paper, the impregnated rag paper sample was ignited with a natural gas (methane) flame (see fig. 3). The original rag paper was completely burned with up to 20 seconds with little evidence of the sample, while the rGO-loaded sample showed only negligible resistance and structural integrity for extended periods of time during a fire. On the other hand, the rGO/SMB samples showed no signs of flame propagation behavior during the flame test. The sample limited its structure and showed self-extinguishing properties with little white smoke emission due to the release of additional water molecules bound to the hydrated SMB. The total mass loss of the flame retarded sample after 60 seconds of introduction of the natural gas flame was ≈ 25%. TGA in the air atmosphere of uncoated and coated rag paper show different mass loss curves. The mass loss curve for the untreated rag paper showed a loss of 78.69% between 300 and 400 ℃ including the moisture content that initially evaporated during combustion, while the rGO/SMB treated rag paper lost only 43.81% of its total mass despite the loss of additional water molecules bound to the SMB. Upon completion of the 1000 ℃ combustion process, the rGO/SMB coated samples left approximately 14% more residue compared to untreated rag paper.

Post-incineration char analysis revealed some additional flame retardancy of the material. The original tight fiber rag paper turned into a fluffy ash and did not retain its structural shape. On the other hand, rGO-containing SMB shows an expansion effect, which provides expansion properties mainly due to the presence of hydrated SMB between rGO layers. The material starts to release water molecules between 90 ℃ and 250 ℃. The underlying free water molecules start to evaporate and grow volumetrically during a fire, which pushes out through the impermeable graphene layer (go out), eventually causing the coating to swell. This swelling effect has been identified on the entire surface of the rGO/SMB treated samples, which is capable of protecting the underlying fibrous paper from flames.

The rGO/SMB composite proved to exhibit a very high degree of flame retardancy when applied to combustible rag paper. Hydrated SMB with graphene shows effective expansion effect and self-extinguishing property to protect the combustible material at the bottom from fire for a long time. These excellent flame retardant properties can be demonstrated by the synergistic effect of the flame retardancy of SMB nanocrystals and the barrier properties of the graphene film that prevents oxygen from contacting the flammable fraction underneath the coating.

Preparation of composite formulation-A (solution system)

Two forms of graphene materials, namely reduced Graphene Oxide (GO) prepared by chemical reduction, thermal reduction or any other method or graphene artificially synthesized or prepared from graphite by electrochemical, thermal/mechanical or any other method, are used to make graphene flame retardant composite solutions. Graphene water solution with concentration of 2-10% was mixed with hydrated sodium metaborate to make a dissolved hydrated SMB, with composition percentages varying between 10 and 80 wt%.

Preparation of composite formulation B (powder System)

The composite formulation (powder system) was prepared by: using solution-based formulation-a, a fine powder comprising graphene sheets modified with inorganic metal hydrates such as SMB nanoparticles is formed by drying, followed by grinding the resulting product with a mill or ball mill.

Preparation of non-combustible Polymer Material (part A)

A water-soluble polymer material in the form of pellets, granules or powder, for example, polyvinyl alcohol (PVA), is mixed with formulation-a or powder-based formulation-B and stirred at 90 ℃ for 3 hours, followed by making a nonflammable polymer by a casting or extrusion method (see fig. 8).

Preparation of non-combustible Polymer Material (part B)

A solvent-soluble polymeric material (e.g., polystyrene) in pellet, granule, or powder form is dissolved in DMF and mixed with formulation-a or powder-based formulation-B at a concentration of 20 wt% to 50 wt% of the mixture. The mixture was stirred at 115 ℃ for 3 hours, followed by casting or extrusion method to make a nonflammable polymer (see fig. 9).

Mechanical bonding and abrasion resistance

The total thickness of the rGO/SMB coatings made for the cross-hatch adhesion test was ≦ 2 μm, as determined by optical profilometry and SEM. Table 1 shows the adhesion properties of coated samples with different comparative coating formulations rated according to standard ASTM ratings for both copper (Cu) and glass substrates. These results show that the rGO/SMB coating had the best adhesion to both Cu and glass surfaces, as also shown in fig. 7(b) and (e) as determined by the cross-hatch adhesion test followed by the scotch tape process. Preparation of control (N)₂H₄Reduced) rGO coating to compare with rGO/SMB coating to check the intrinsic adhesion of the material to Cu and glass substrates. From sample (rGO-N)₂H₄) The resulting coating failed to exhibit appreciable minimum adhesion (ASTM grade 0B) to either of the Cu and glass substrates.

TABLE 1 adhesion properties of the coatings determined by ASTM D-3359-02.

The deposition of rGO with and without SMB revealed that the coating without SMB did not have any adhesive properties, as determined by the cross-hatch adhesion test. GO and rGO (reducing agent N) found on both Cu and glass substrates₂H₄) While the rGO/SMB samples showed an ASTM adhesion rating of 4B for both Cu and glass substrates (demonstrating less than 5% cross-hatched area as affected). Further, rGO/SMB coatings were also applied to other metals (i.e., aluminum (Al), stainless steel) and the results confirmed that the adhesion was independent of the metal substrate. The bond strength between the metal plate and the coating may develop between the native metal oxide and borate interface.

After 3000 cycles of completion at 250g per wheel, the abrasion test gave the smallest weight loss (6.33 mg/cm)²，max^m). rGO/S before and after abrasion testingThe surface morphology of the MB samples has been shown for comparison in fig. 7(g and h), where SMB-crystals were found to be distributed evenly on both abraded and unabraded surfaces. As shown by the red arrows in fig. 7(h), the pattern of wear damage can be clearly classified into parallel grooves and a plurality of dents. The micro-dents were generated by loss of SMB crystals during the abrasion test. Raman mapping of the abraded surface was performed to analyze the percentage area of the component in the inner coating, which showed about 71% occupied by rGO and 29% of SMB crystals.

The excellent adhesion of the graphene-based composite film is class 4B as determined by standard ASTM testing, with a high degree of wear resistance. The characterization results confirmed the presence of SMB crystals at the interface and inside the graphene layer, indicating that the mechanical strength of the layered composite and the adhesion to external substrates (metal and glass) were significantly promoted. A possible mechanism for improved adhesion between graphene films and surfaces (metal plates) may be the result of strong binding interactions between natural (native) metal oxides and borates (SMB nanocrystals).

Antibacterial

Uncoated (glass slides) and coated (GO, rGO-N)₂H₄And rGO/SMB) samples were evaluated for bacterial resistance by AATCC test method 100-. Bacterial strains grew similarly well on all test samples at zero time, while growth was further enhanced only on the uncoated (control) samples after 24 hours. Other samples containing graphene derivatives showed strong antibacterial activity after 24 hours at a uniform concentration of GO (3mg/ml) as starting material (fig. 6). GO was found to be reduced by 85.34% of E.coli colonies, while rGO-N₂H₄The effect was lower compared to GO (54.47%). The antibacterial ability (99.9%) of rGO/SMB is superior to that of GO and rGO-N₂H₄And (4) coating.

SEM analysis was performed to qualitatively investigate the interaction between the coated surface and the bacteria to confirm the potential antibacterial effect. The formation of thick biofilms was identified on slides in which E.coli was susceptible to proliferation. GO coated surfaces were found to interact with bacterial cells to reduce proliferation. At higher magnification, it was observed that single bacterial cells entangled with GO sheets causing membrane perturbation, which was reported to be one of several possible mechanisms of GO's antibacterial properties. Further, for samples containing rGO/SMB, bacterial membrane damage and cytoplasmic leakage were observed, where bacterial cells were found to be randomly distributed.

And rGO-N₂H₄The presence of SMB on/in rGO sheets increases the wettability of rGO/SMB composite coatings (≈ 32 ° WCA) compared to coatings (≈ 84 ° WCA), which can enhance the interaction between graphene sheets and bacteria.

It has been demonstrated that the strong antibacterial effect of graphene-based composites shows almost 100% resistance against escherichia coli colonization, with significantly better performance compared to GO and rGO used as controls. The results indicate that surface wettability should be employed as an activity parameter that will affect the antibacterial properties of graphene-based composites. Together with the inherent antibacterial properties of SMB, it is believed that the increased hydrophilicity of the surface may bring e.coli cells into close contact with the sharp graphene sheets, thus causing the destruction of the bacterial cells towards the active membrane.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgment or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of technology to which this specification relates.

Claims

1. A graphene-based composite material comprising hydrated sodium metaborate intercalated graphene-based materials in the form of microparticles, nanoparticles, or a combination thereof, wherein the graphene-based materials are present in an amount of 20% to 80% by weight and the hydrated sodium metaborate is present in an amount of 20% to 80% by weight.

2. The graphene-based composite material according to claim 1, wherein the graphene-based material comprises one or both of reduced graphene oxide and graphene.

3. A method of preparing a graphene-based composite material, the method comprising: (i) providing a liquid composition comprising graphene-based material in an amount of 20 to 80% by weight and hydrated sodium metaborate in an amount of 20 to 80% by weight, and (ii) evaporating liquid from the composition, thereby retaining the graphene-based material and the hydrated sodium metaborate in the composition, wherein the process of evaporating liquid in step (ii) facilitates intercalation of the hydrated sodium metaborate in the graphene-based material in the form of microparticles, nanoparticles, or a combination thereof, to provide the graphene-based composite material.

4. The method of claim 3, wherein the liquid composition is an aqueous liquid composition and in step (ii), water is evaporated from the composition.

5. The method of claim 3 or 4, wherein the liquid composition comprising graphene-based material and hydrated sodium metaborate is provided by an aqueous liquid composition comprising graphene oxide and sodium borohydride, wherein the graphene oxide is reduced by the sodium borohydride to provide reduced graphene oxide and the hydrated sodium metaborate.

6. A substrate comprising a graphene-based composite material comprising a hydrated sodium metaborate intercalated graphene-based material in the form of microparticles, nanoparticles, or a combination thereof, wherein the graphene-based material is present in an amount of 20% to 80% by weight and the hydrated sodium metaborate is present in an amount of 20% to 80% by weight.

7. The substrate of claim 6, wherein the graphene-based composite is coated on a surface of the substrate, or distributed throughout a substrate matrix, or a combination thereof.

8. The substrate of claim 6 or 7, wherein the substrate comprises a cellulosic material, a polymer, a metal, a ceramic, a glass, or a combination thereof.

9. The substrate of claim 6 or 7, exhibiting improved flame retardancy, improved abrasion resistance, improved antimicrobial properties, or a combination thereof, relative to a substrate in the absence of the graphene-based composite.

10. The substrate of claim 8, exhibiting improved flame retardancy, improved abrasion resistance, improved antimicrobial properties, or a combination thereof, relative to a substrate in the absence of the graphene-based composite.

11. A method of improving a performance of one or more of a substrate for flame retardancy, abrasion resistance, and antimicrobial properties, the method comprising providing a substrate having a graphene-based composite material, wherein the graphene-based composite material comprises a hydrated sodium metaborate intercalated graphene-based material in the form of microparticles, nanoparticles, or a combination thereof, wherein the graphene-based material is present in an amount of 20 wt.% to 80 wt.%, the hydrated sodium metaborate is present in an amount of 20 wt.% to 80 wt.%, the improved performance relative to the substrate in the absence of the graphene-based composite material.

12. The method of claim 11, wherein the substrate is provided with the graphene-based composite by coating or impregnating the substrate with a liquid composition comprising the graphene-based composite.

13. The method of claim 11, wherein the substrate is provided with the graphene-based composite by: (i) coating or impregnating a substrate with a liquid composition comprising a graphene-based material and hydrated sodium metaborate, and (ii) evaporating liquid from the coated composition, thereby retaining the graphene-based material and hydrated sodium metaborate in the coated or impregnated composition and forming the graphene-based composite material.

14. The method of claim 13, wherein the liquid composition comprising graphene-based material and hydrated sodium metaborate is provided by an aqueous liquid composition comprising graphene oxide and sodium borohydride, wherein the graphene oxide is reduced by the sodium borohydride to provide reduced graphene oxide and the hydrated sodium metaborate.

15. The method of claim 11, wherein the substrate is a thermoplastic polymer and the substrate is provided with the graphene-based composite by melt processing the polymer with the graphene-based composite.

16. The method of claim 11, wherein the substrate is a thermoset polymer and the substrate is provided with the graphene-based composite by blending the graphene-based composite with a precursor material used to make the thermoset polymer.

17. The method of any one of claims 11 to 16, wherein the graphene-based material comprises one or both of reduced graphene oxide and graphene.

18. The method of any one of claims 11 to 16, wherein the substrate comprises hydrated sodium metaborate that does not form part of the graphene-based composite material.

19. Use of a graphene-based composite material for improving the performance of one or more of flame retardancy, wear resistance and antimicrobial properties of a substrate, wherein the graphene-based composite material comprises a hydrated sodium metaborate intercalated graphene-based material in the form of microparticles, nanoparticles or a combination thereof, wherein the graphene-based material is present in an amount of 20 to 80 wt.%, the hydrated sodium metaborate is present in an amount of 20 to 80 wt.%, the improved performance relative to a substrate in which the graphene-based composite material is absent.