Flame-resistant material

Abstract

The present invention relates to a resin composition comprising (a) from 0.08 to 8 weight percent graphene, (b) from 8.5 to 15 weight percent phosphorus-containing flame retardant, and (c) from 77 to 91 weight percent polymer resin. The present invention also relates to a method of making a resin composition, comprising mixing components (a), (b) and (c), and to a method of producing a shaped resin article, comprising making a resin composition by said method and then shaping the composition to the desired shape to form the shaped resin article.

Description

[0001] FLAME-RESISTANT MA TERIAL

[0002] Field of the Invention

[0003] The present invention relates to flame-resistant materials, and particularly those containing graphene. Such materials may be useful, for example, in the construction of buildings or other objects which must meet a regulatory standard of heat and flame-resistance.

[0004] Background

[0005] It is well-known that plastic production and use has resulted in the release of environmentally damaging anthropogenic pollutants such as CO2. Despite the environmental damage, over 300 million tonnes of plastic waste is produced annually and less than 10% of all plastic waste ever produced has been recycled, resulting in an ever-growing stock of waste plastic. To deplete this stockpile, further efforts must be made to repurpose and recycle it.

[0006] Recycled plastics such as polyethylene have been utilised in the construction industry to replace, in part, highly polluting materials such as concrete. To be suitable for use in construction, plastic-derived materials must often meet high standards of flame- and he at- resista nee. Polyethylene is not inherently resistant to combustion but may meet the regulatory flame-resistance standards for use in construction with the addition of flame-retardant additives. Because of the potential for contaminants in recycled plastic to compromise this behaviour, virgin plastics tend to be used in resin-based flame-resistant materials.

[0007] Halogenated flame retardants are a class of additives which may be incorporated into plastic-based construction materials to improve their ‘flame resistance’ properties (also known as flame retardancy), such as the ability of a material to self-extinguish or to slow the rate of flame propagation through, across or over the material. While halogenated flame retardants are often effective at low loadings, they are also persistent, bioaccumulative toxins.

[0008] Conversely, hydrated metallic flame retardants such as aluminium trihydrate and nano-clays such as montmorillonite are considered non-toxic, but are less effective and may thus require higher loadings to compete with halogenated flame retardants in terms of efficacy; this often makes halogenated flame retardants a more financially attractive choice.

[0009] Phosphorus-containing flame retardants (e.g., phosphates) offer reduced toxicity compared to halogenated flame retardants and can be highly effective at low loadings, striking a balance in efficacy, toxicity, and loading requirement.

[0010] Combinations of diphosphoric acid and piperazine (piperazine pyrophosphate) in particular are known to be effective when incorporated into flame retardant composites. Unlike many hydrated metallic flame retardants and nano-clays, phosphorus-containing flame retardants have low toxicity, but it is desirable to reduce their usage and develop equally effective flame-resistant resins comprising flame retardants at yet lower loadings. Graphene-related materials have also been mentioned as possible additives in flame-resistant materials. For such graphene-related materials to exhibit strong flame resistance properties, however, it has been considered to require chemical modification (e.g., oxidation). This need to modify graphene leads to it being less favoured than other flame retardants such as phosphorus-containing flame retardants.

[0011] Thus, there remains a need for improved flame-resistant materials.

[0012] The present invention has been devised in the light of the above considerations.

[0013] Summary of the Invention

[0014] At its broadest, the present invention relates to flame-resistant materials, in particular materials that comprise a resin, graphene, and a flame retardant.

[0015] The present inventors have found that certain such compositions can solve the aforementioned problem. That is, they have developed advantageous flame-resistant compositions (which may be manufactured into various articles, as described herein). These may be less toxic while remaining effective; may exhibit flame resistance at significantly lower flame retardant loadings; or may exhibit improved flame resistance at given known flame retardant loadings. These advantages enable the use of polymer resins derived from recycled plastics rather than virgin plastic as previously known.

[0016] In a first aspect the invention provides a flame-resistant material which is a resin composition comprising, generally:

[0017] (a) from 0.05 to 8 weight percent graphene; and

[0018] (b) from 8.5 to 15 weight percent phosphorus-containing flame retardant; and

[0019] (c) from 77 to 91 weight percent of polymer resin.

[0020] Weight percent (wt%) refers to the amount of a component present by weight in terms of the total weight of the flame-resistant material. That is, the sum of the weight percentages of the components of the flame-resistant material is 100 wt%.

[0021] As used herein, ‘flame retardant’ refers to a specific additive (e.g., a phosphorus-containing flame retardant) which has and / or imparts flame resistance properties.

[0022] The term "phosphorus-containing flame retardant” refers to a flame retardant in which (atomic) phosphorus (P) is present, generally as part of the chemical structure of the relevant compound. The term is used in the art synonymously with “phosphorus-based”. There is no requirement for phosphorus atoms to be present in any particular level, as long as 1 or more are included.

[0023] The term “flame retardant” alone thus also refers to additives which do not contain phosphorus.

[0024] Herein, the term ‘flame-resistant material’ is used to refer to a composite product, especially a material comprising components (a)-(c). ‘Flame resistance’ and ‘flame-resistant’ refer to the properties of a flame-resistant material and / or flame retardant additive against fire, flame and related phenomena, for example self-extinguishing properties and flame propagation properties. The properties, of course, exist to differing magnitude; to be flame resistant a material done not need to have 100% resistance to flame and so on.

[0025] Surprisingly, the inventors have found that present materials have acceptable and even improved performance at low flame retardant loadings. For clarity, “low flame retardant loading” means below 25- 35 wt% flame retardant, which is the minimum previously recommended loading for achieving UL-94 flammability standards with phosphorus-containing flame retardants when the retardant is used in a composition comprising polyethylene or polypropylene.

[0026] In the present invention graphene is present in an amount of about 0.05 to about 8 wt%, preferably from about 0.005 to about 0.1 wt% or from about 4.0 to about 5.0 wt%.

[0027] In some embodiments, the graphene may have a flake diameter of about 1 to about 50 pm.

[0028] The graphene may preferably have an aspect ratio of about 400 to about 4000.

[0029] In some embodiments, the graphene provided in the resin composition is unfunctionalized graphene.

[0030] In some embodiments, polymer resin component (c) comprises more than one type of polymer resin. In other embodiments, only a single type of polymer resin is present in the flame-resistant material.

[0031] In some embodiments, component (a) is incorporated into the materials as a ‘graphene dispersion’. In such embodiments, graphene is mixed with (i.e. dispersed in) a polymer resin (carrier resin) to form a graphene dispersion. The graphene dispersion can then be mixed with component (b) and optionally additional polymer resin (either of the same type as the carrier resin or a different type) so as to form a composition according to the present invention. In such embodiments, it is noted that in the total of the content of carrier resin and any additional resin makes up polymer resin component (c); that is, the weight percentage content for component (c) is the sum of that for the carrier resin and any additional resin(s).

[0032] In some embodiments, component (b) is incorporated into the materials as a ‘flame retardant dispersion’. In such embodiments, flame retardant is mixed with (i.e. dispersed in) a polymer resin (carrier resin) to form a flame retardant dispersion. The flame retardant dispersion can then be mixed with component (a) and optionally additional polymer resin (either of the same type as the carrier resin or a different type) so as to form a composition according to the present invention. In such embodiments, it is noted that in the total of the content of carrier resin and any additional resin makes up polymer resin component (c); that is, the weight percentage content for component (c) is the sum of that for the carrier resin and any additional resin(s).

[0033] In some embodiments, each of component (a) and component (b) is provided as a dispersion. In such embodiments, each of component (a) and component (b) comprises carrier resin. The carrier resin of component (a) is not limited to being the same polymer or polymers as the carrier resin of component (b). For example, a carrier resin of the flame retardant may comprise LDPE while a carrier resin of a graphene dispersion may comprise HDPE, and equally any additional polymer resin added to make up the totality of component (c) may comprise the same or different polymer or polymers as all carrier resins. The polymer resin component (c) may thus comprise the sum of all carrier resins and any additional polymer resin. In embodiments which contain carrier resin, the carrier resin weight percent is included in the weight percent of component (c).

[0034] In some embodiments, component (c) may comprise polymer or polymers of non-uniform structure, for example HDPE comprising linear chains and branched chains, and / or LDPE comprising linear chains and branched chains.

[0035] In some embodiments, the graphene component (a) is provided as graphene powder without carrier resin.

[0036] In some embodiments, flame retardant component (b) is provided without carrier resin.

[0037] In some embodiments, the graphene is uniformly dispersed throughout the resin composition.

[0038] In some embodiments, flame retardant is contained in an amount from about 8.5 wt% to about 15 wt%, preferably from about 11 .0 to about 13.0 wt%.

[0039] In some embodiments, the phosphorus-containing flame retardant comprises diphosphoric acid and piperazine (hereafter referred to as piperazine pyrophosphate).

[0040] In some embodiments, polymer resin component (c) is exclusively HDPE. The term HDPE is well understood in the art; it is not limited to meaning high-density polyethylene of a uniform chemical structure (for example, exclusively linear polyethylene chains). [The same applies for all polymers mentioned herein; LDPE, for example, is not limited to meaning low-density polyethylene of uniform chemical structure].

[0041] In some embodiments, polymer resin component (c) does not comprise HDPE.

[0042] In some embodiments, polymer resin component (c) is substantially recycled polymer material. For example, polymer resin component (c) may comprise at least 50 wt% recycled polymer, preferably at least 75 wt% recycled polymer, and more preferably at least 99 wt% recycled polymer. It is noted that these wt% are a function of the content of polymer resin (c): that is, of the polymer resin (c) at least 50 wt% is preferably recycled polymer; that means that in the resin composition as a whole preferably at least 38.5 wt% is recycled polymer.

[0043] In some embodiments, the flame-resistant material may comprise further components, such as dye additives, additional flame retardants, additional polymer resin, anti-tack agents, adhesive agents, rheology modifiers, plasticisers, anti-oxidants, UV stabilisers, blowing agents, and odour agents.

[0044] The compositions discussed herein have found use as flame-resistant materials. For example, the inventors have found that materials according to the present invention exhibit excellent flame resistance properties when ignited.

[0045] While the exact mechanism of flame resistance is not known, it is postulated that two processes may occur to resist flame propagation and extinguish flames: at least one mechanism arising from the incorporated phosphorus-containing flame retardant (b) and at least one other mechanism arising from the graphene (a). Both flame retardant and graphene are required to achieve the present flame resistance, so it is believed that there may be an association or synergy between the processes of each component.

[0046] When an ignited material according to the present invention is at temperatures below around 200 °C, it is thought that the mechanism involving of graphene is dominant, with aligned graphene sheets acting as a barrier to reduce heat transfer deeper into the material and limit the formation of flammable gases resulting from pyrolysis of the material. As the temperature of the material elevates to around 200-350 °C it is thought that a catalytic process involving the phosphorus-containing flame retardant may dominate; a protective char layer is believed to form, which acts as a condensed phase heat- and fire-barrier, disrupting the combustion process.

[0047] In a second aspect the present invention relates to a method of manufacturing the resin composition according to the present invention.

[0048] In some embodiments the method of manufacturing comprises mixing the graphene, flame retardant, and polymer resin according to a predetermined composition.

[0049] In some embodiments, the mixed components are extruded according to an extrusion step at a predetermined temperature and extruder speed. In some embodiments, the predetermined temperature is above the melting point of the polymer resin.

[0050] In some embodiments, the method of manufacturing the resin composition comprises an extrusion step or extrusion steps. An extrusion step may comprise extrusion with a single-screw extruder and / or a twin- screw extruder.

[0051] In a third aspect, the present invention relates to a method of manufacturing articles using materials of the present invention.

[0052] In such a method, a material according to the present invention is subjected to a shaping steps of, for example, extruding, stamping, and / or moulding such that the material adopts a predetermined shape.

[0053] In a fourth aspect the present invention relates to use of the present materials and / or articles as flameresistant materials. Use of the resin compositions may include, for example, application as a flameretardant composite material in a construction. For example, the present materials many be used as part of a building materials; the invention thus provides a building material comprising the present flameresistant material.

[0054] The invention includes the combination of the aspects and features described except where such a combination is clearly impermissible or expressly avoided.

[0055] Embodiments of the invention may also include any one or more of the following features. Features mentioned in relation to the first or any other aspect of the invention may apply equally to the other aspects. Detailed Description of the Invention

[0056] Aspects and embodiments of the present invention will now be discussed. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0057] Herein, the term “flame-resistant material” is used to refer to a composite material which has flame resistance properties. The ‘active ingredient’ of such a flame-resistant material, which provides the flame resistance properties, is termed a flame retardant.

[0058] Initially, it is worth discussing the definitions of various terms that are used herein.

[0059] “Graphene”, for example, is used to refer not only to monolayer graphene but also to few-layer graphene; as described below, in fact, the graphene used in many embodiments is not a single layer but have multiple layers.

[0060] Few-layer graphene refers to graphene having up to 15 layers, which corresponds to a flake thickness of up to about 4.5 nm.

[0061] The term “graphene” is also used to refer not only to unfunctionalized graphene but also to functionalized graphene such as graphene oxide. Unfunctionalized graphene is graphene that is substantially free from chemical functionalization, comprising close to 100 percent carbon by composition.

[0062] The graphene used herein preferably has an oxygen content of about 40 wt% or less, for example 30 wt% or less, for example 25 wt% or less, for example 20 wt% or less, for example 15 wt% or less, for example 10 wt% or less, for example 8 wt% or less, for example 7 wt% or less, for example 6 wt% or less, for example 5 wt% or less, for example 3 wt% or less, for example 1 wt% or less (here, wt% being the mass of oxygen in the graphene material relative to the total mass of the graphene material).

[0063] Methods of measuring oxygen content and functionalisation are well known in the art and may include X- ray photoelectron spectroscopy (XPS).

[0064] Preferably the graphene used herein has an oxygen content of about 5 wt% or less.

[0065] In some embodiments, where the graphene is functionalized, that is suitably present on the edges (perimeter) of the graphene flakes. This may be termed “edge functionalisation”.

[0066] For example, it may be that >50%, >70%, >90%, >95% or even >99% of functionalization is at the edge of the graphene flakes rather than on the basal plate surfaces.

[0067] Where the graphene has an oxygen content of about 5 wt% or less, >50%, >70%, >90%, >95% or even >99% of that oxygen may preferably be in functionalizations on the edges of the graphene flakes.

[0068] In some other embodiments, graphene oxide (GO) is used as the graphene.

[0069] In some embodiments, reduced graphene oxide (rGO) is used as the graphene. The “flake diameter” of a graphene sample refers to the average lateral flake dimension of the graphene flakes in the sample. Defining a graphene sample by its flake diameter does not exclude the possibility of agglomeration of graphene flakes within a graphene sample or within the resin composite. Techniques for measuring the flake diameter of graphene are well known and include, for example, scanning electron microscopy. The lateral flake dimension of graphene is generally measured at the longest dimension of the flake. The “average” lateral flake dimension (i.e., flake diameter as used herein) refers to the dso median average.

[0070] The aspect ratio of a graphene sample refers to the value calculated by dividing the flake diameter of the graphene sample by the flake thickness of the graphene sample.

[0071] Graphene, provided either as a raw material (e.g., powdered graphene) or as a dispersion, is routinely supplied by manufacturers with information about the flake diameter(s) contained in the supply.

[0072] In some embodiments, the graphene has a flake diameter from about 5 pm to about 50 pm, preferably from about 10 pm to about 30 pm. That is, the dso may suitably be about 5 pm or greater, or about 10 pm or greater. The dso may suitably be about 50 pm or lower, or about 30 pm or lower.

[0073] In some embodiments, the graphene has a flake thickness from about 0.3 nm to about 4.5 nm, for example from about 0.6 to about 4.5 nm, for example from about 0.9 to about 4.5 nm, for example from about 1 .2 to about 4.5 nm, for example, from about 1 .5 to about 4.5 nm, for example from about 1 .8 to about 4.5 nm, for example from about 2.1 to about 4.5 nm, for example from about 2.4 to about 4.5 nm, for example from about 2.4 to about 4.2 nm, for example from about 2.4 to about 3.9 nm, for example from about 2.4 to about 3.6 nm, for example from about 2.4 to about 3.3 nm, for example from about 2.7 to about 3.3 nm. This corresponds to a number of graphene layers from about 1 to about 15 layers. Preferred graphenes may have a number of layers from 1 to 10 layers, for example from 5 to 10 layers, for example from 7 to 10 layers.

[0074] The graphene may preferably have an aspect ratio of at least around 400 to at most around 4000, for example from at least around 400 to at most around 3000, for example from at least around 400 to at most around 2000, for example from at least around 400 to at most around 1000, for example from at least around 400 to at most around 800, for example from at least around 400 to at most around 600.

[0075] Alternatively, in some embodiments, the graphene may preferably have an aspect ratio of at least around 500 to 4000, for example from at least around 1000 to at most around 4000, for example from at least around 2000 to at most around 4000, for example from at least around 2500 to at most around 4000, for example from at least around 2500 to at most around 3500, for example from at least around 2500 to at most around 3000.

[0076] In some embodiments, the graphene is provided as a graphene dispersion. Graphene products meeting these criteria are commercially available, and various methods of making graphene are well known.

[0077] In some embodiments the graphene is graphene which has been formed by (electro)chemical exfoliation. Suitable exfoliants for graphene may include, for example, sulphuric acid, nitric acid, phosphoric acid, perchloric acid, peroxyacetic acid, and mixtures thereof. In these embodiments, graphene may comprise residual exfoliant. The inventors believe that such residual exfoliants may affect the flame-resistance properties of the overall composition. For example, it is postulated that acidic exfoliants may remain residually trapped between graphene layers; on heating the layers expand, releasing the acid to give an intumescent effect. It is also postulated that additional oxygenated edges of the graphene flakes in such embodiments may interact to catalyse the action of the phosphorus-containing flame retardant.

[0078] In some embodiments the graphene is graphene which has been formed by mechanical exfoliation, such as by ball milling exfoliation.

[0079] In the present invention, graphene is present in the flame-resistant material in an amount, based on the total weight of the material, of 0.05 to 8 wt%.

[0080] In some embodiments, the content is towards the lower end of this range, for example from 0.05 to 3.0 wt%, for example from 0.05 to 2.5 wt%, for example from 0.05 to 2.0 wt%, for example from 0.05 to 1 .5 wt%, for example from 0.08 to 1 .5 wt%, for example from 0.08 to 1 .05 wt%, or for example from 1 .05 to 1 .5 wt%.

[0081] Alternatively, graphene may be present in an amount towards the upper end of this range, for example 1 .05 to 8.0 wt%, for example from 1 .5 to 8.0 wt%, for example from 2.0 to 8.0 wt%, for example from 2.5 to 8.0 wt%, for example from 3.0 to 8.0 wt%, for example from 3.0 to 7.5 wt%, for example from 3.0 to 7.0 wt%, for example from 3.0 to 6.5 wt%, for example from 3.0 to 6.0 wt%, for example from 3.0 to 5.5 wt%, for example from 3.5 to 5.5 wt%, for example from 4.0 to 5.5 wt%, for example from 4.0 to 5.0 wt%, or for example from 4.0 to 4.5 wt%.

[0082] The inventors have found that further improvements in flame resistance are present across sub-ranges of graphene loading described above. For example, particularly advantageous improvements in flameresistance may be found when graphene is present in an amount, based on the total weight of the flameresistant material, of 0.05 to 1 wt%, such as from 0.05 to 0.8 wt%, from 0.05 to 0.7 wt%, from 0.05 to 0.6 wt%, from 0.05 to 0.5 wt%, from 0.05 to 0.4 wt%, from 0.05 to 0.3 wt%, from 0.05 to 0.2 wt%, or from 0.05 to 0.1 wt%.

[0083] Alternatively, particularly advantageous improvements in flame resistance may be found for example when graphene is present in an amount, based on the total weight of the flame-resistant material, of 2.0 to 5.0 wt%, 2.5 to 5.0 wt%, 3.0 to 5.0 wt%, 3.5 to 5.0 wt%, or from 4.0 to 5.0 wt%, or from 4.0 to 4.5 wt%.

[0084] As such, graphene may be present in an amount, based on the total weight of the flame-resistant material, of at least 0.05 wt%, for example at least 0.08 wt%, for example at least 0.1 wt%, for example at least 0.2 wt%, for example at least 0.3 wt%, for example at least 0.4 wt%, for example at least 0.5 wt%, for example at least 0.6 wt%, for example at least 0.7 wt%, for example at least 0.8 wt%, for example at least 0.9 wt%, for example at least 1 .0 wt%, for example at least 1 .05 wt%, for example at least 1 .5 wt%, for example at least 2.0 wt%, for example at least 2.5 wt%, for example at least 3.0 wt%, for example at least 3.5 wt%, for example at least 4.0 wt%, for example at least 4.5 wt%, for example at least 5.0 wt%, for example at least 5.5 wt%, for example at least 6.0 wt%, for example at least 6.5 wt%, for example at least 7.0 wt%, or for example at least 7.5 wt%.

[0085] As such, graphene may be present in an amount, based on the total weight of the flame-resistant material, of at most 8.0 wt%, for example at most 7.5 wt%, for example at most 7.0 wt%, for example at most 6.5 wt%, for example at most 6.0 wt%, for example at most 5.5 wt%, for example at most 5.0 wt%, for example at most 4.5 wt%, for example at most 4.0 wt%, for example at most 3.5 wt%, for example at most 3.0 wt%, for example at most 2.5 wt%, for example at most 2.0 wt%, for example at most 1 .5 wt%, for example at most 1 .05 wt%, for example at most 1 .0 wt%, for example at most 0.9 wt%, for example at most 0.8 wt%, for example at most 0.7 wt%, for example at most 0.6 wt%, for example at most 0.5 wt%, for example at most 0.4 wt%, for example at most 0.3 wt%for example at most 0.2 wt%, for example at most 0.1 wt%, or for example at most 0.08 wt%.

[0086] In an embodiment of the present invention, the graphene is supplied or obtained as a graphene powder, which is then mixed with a carrier resin to form a graphene dispersion. This graphene dispersion can be mixed with component (b) and, optionally, additional polymer resin so as to form a material according to the present invention.

[0087] The inventors have identified an advantage in providing component (a) in a graphene dispersion form. Graphene in the form of a dispersion, when mixed with additional components so as to form a material according to the present invention, is homogeneously distributed throughout the composition with less mixing than if the graphene is incorporated in the form of a graphene powder.

[0088] The carrier resin is not particularly limited as long as it contains a polymer or polymers, HDPE and / or LDPE for example.

[0089] In some embodiments, for example, the graphene dispersion comprises more than one polymer as the carrier resin, such as HDPE and LDPE, each optionally being of non-uniform structure.

[0090] Flame retardant

[0091] “Flame retardant” refers to a chemical composition which imparts flame resistance properties on composites or mixtures which include it. Flame retardants used in the present invention comprise at least one phosphorus compound (e.g., diphosphoric acid) - that is, they are phosphorus-containing.

[0092] Examples of phosphorus-containing flame retardants may include but are not limited to 9,10-dihydro-9- oxa-10-phosphorus-10-oxide (DOPO), N,N-bis-(2-hydroxylethyl) aminomethane phosphoric acid diethyl ester, poly(m-phenylene methylphosphonate), phosphonate oligomers, poly[phosphonate-co-carbonate], phosphoric acid, alkyl phosphates, aryl phosphates, phosphoric acid mixed esters with [1 , 1 '-bisphenyl- 4,4'-diol] and phenol, oligomeric phosphonate polyol, oligomeric ethyl ethylene phosphate, melamine phosphate, melamine pyrophosphate, piperazine phosphate, ammonium polyphosphate, red phosphorus, phosphinic acid aluminium salt, ethylenediamine-o-phosphate, diethylphsophinate aluminium salt, Fyrol™ HF-5, and 6H-dibenz[c,e][1 ,2]oxa-phosphotin-6-propanoic acid.

[0093] Examples of aryl phosphates may include but are not limited to triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, phosphoric acid bis(methylphenyl) phenyl ester, bisphenol A bis(diphenyl phosphate), isopropyl phenyl phosphate, tris(p-t-butylphenyl) phosphate

[0094] In some embodiments, the flame retardant comprises piperazine phosphate.

[0095] In those embodiments, the molar ratio of piperazine and phosphoric acid may satisfy formula (I):

[0096] (I) 0.8 < piperazine I diphosphoric acid < 1 .2

[0097] In some embodiments, the molar ratio of piperazine and phosphoric acid according to formula (I) may preferably have a lower limit of 0.85, for example 0.9, for example 0.95, for example 1 .0.

[0098] In some embodiments, the molar ratio of piperazine and phosphoric acid according to formula (I) may preferably have an upper limit of 1 .15, for example 1 .1 , for example 1 .05, for example 1 .0.

[0099] In some embodiments, the flame retardant also comprises zinc oxide. The inventors believe that zinc oxide may further improve the flame resistance afforded by the flame retardant.

[0100] Flame retardant may be present in an amount, based on the total weight of the flame-resistant material, of 8.5 to 15.0 wt%, for example from 8.75 to 15.0 wt%, for example from 9.0 to 15.0 wt%, for example from 9.5 to 15.0 wt%, for example from 10.0 to 15.0 wt%, 10.5 to 15.0 wt%, for example from 11 .0 to 15.0 wt%, for example from 11 .5 to 15.0 wt%, for example from 12.0 to 15.0 wt%, for example from 12.25 to 15.0 wt%, for example from 12.5 to 15.0 wt%, for example from 13.5 to 15.0 wt%, or for example from 14.0 to 15.0 wt%.

[0101] Alternatively, flame retardant may be present in an amount, based on the total weight of the flameresistant material, of 10.0 to 14.5 wt%, for example from 10.0 to 14.0 wt%, for example from 10.0 to 13.5 wt%, for example from 10.5 to 13.5 wt%, for example from 11 .0 to 13.5 wt%, for example from 11 .0 to 13.0 wt%, for example from 11 .5 to 13.0 wt%, for example from 11 .5 to 12.5 wt%, for example from 12.0 to 12.5 wt%, or for example from 12.0 to 12.25 wt%.

[0102] As such, the flame retardant may be present in an amount of at least 8.5 wt%, for example at least 8.75 wt%, for example at least 9.0 wt%, for example at least 9.5 wt%, for example at least 10.0 wt%, for example at least 10.5 wt%, for example at least 11 .0 wt%, for example at least 11 .5 wt%, for example at least 12.0 wt%, for example at least 12.25 wt%, for example at least 12.5 wt%, for example at least 13.0 wt%, for example at least 13.5 wt%, for example at least 14.0 wt%, or for example at least 14.5 wt%.

[0103] As such, the flame retardant may be present in an amount of at most 15.0 wt%, for example at most 14.5 wt%, for example at most 14.5 wt%, for example at most 14.0 wt%, for example at most 13.5 wt%, for example at most 13.0 wt%, for example at most 12.5 wt%, for example at most 12.25 wt%, for example at most 12.0 wt%, for example at most 11 .5 wt%, for example at most 11 .0 wt%, or for example at most 10.5 wt%, for example at most 10.0 wt%, for example at most 9.5 wt%, for example at most 9.0 wt%, for example at most 8.75 wt%.

[0104] In some embodiments, the flame retardant may be provided or obtained as a flame retardant dispersion. In such embodiments, flame retardant can be mixed with a carrier resin to form a flame retardant dispersion. This flame retardant dispersion can be mixed with component (a) and, optionally, additional polymer resin so as to form a material according to the present invention.

[0105] The carrier resin is not particularly limited as long as it contains polymer or polymers, HDPE and / or LDPE for example.

[0106] The inventors have identified an advantage in providing component (b) as a flame retardant dispersion form. Flame retardant in the form of a dispersion, when mixed with additional components so as to form a material according to the present invention, is homogeneously distributed throughout the composition with less mixing than if the flame retardant is incorporated in its raw form.

[0107] Polymer resin

[0108] As mentioned above, the content of polymer resin (c) includes any carrier resin present when graphene and / or flame retardant is / are incorporated as dispersions. That is, (c) includes all polymer resin present in the flame-resistant material.

[0109] Accordingly, the polymer resin may be of a single type or may be a mixture of several different types of polymer resin.

[0110] The polymer resin(s) that may be used is not particularly limited. The polymer resin may comprise at least one of hydrocarbon polymer such as polyethylene, polypropylene, polybutylene, or polyisobutylene.

[0111] For example, the polyethylene may comprise at least one of ultra-high-molecular-weight polyethylene (HMWPE), high-molecular-weight polyethylene (HMWPE), high-density polyethylene (HDPE), high- density cross-linked or cross-linkable polyethylene (HDXLPE), medium-density polyethylene (MDPE), linear medium-density polyethylene (LMDPE), cross-linked or cross-linkable polyethylene (PEX or XLPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), very-low-density polyethylene (VLDPE), or ultra-low-molecular-weight polyethylene (PE-WAX).

[0112] In some embodiments, polymer resin comprises at least one polyethylene and / or at least one polypropylene. Suitable polyethylenes include high density polyethylene (HDPE, density >930 kgnr3) and low density polyethylene (LDPE, density <930 kgrrr3).

[0113] In some embodiments the polymer resin comprises HDPE. In some embodiments the polymer resin comprises LDPE. In some embodiments the polymer resin comprises both HDPE and LDPE.

[0114] The terms HDPE and LDPE throughout are not limited to meaning HDPE or LDPE of uniform chemical structure (for example, HDPE with exclusively linear chains). In some embodiments, the polymer resin of component (c) may comprise recycled polymer resin.

[0115] Recycled polymer resin describes non-virgin material.

[0116] Optional additives

[0117] The flame-resistant materials of the present invention are not limited to including only components (a)-(c) and may, for example, comprise at least one additional additive. Such additives may include dyes, additional flame retardants, additional polymer resin, anti-tack agents, adhesive agents, rheology modifiers, plasticisers, anti-oxidants, UV stabilisers, blowing agents, and odour agents.

[0118] Examples of dye additives may include but are not limited to phthalocyanine dyes, vat dyes, and azo dyes.

[0119] Examples of additional flame retardants may include but are not limited to tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and aluminium trihydroxide.

[0120] Examples of anti-tack agents may include but are not limited to zinc stearate, silicone oils, and stearic acid.

[0121] Examples of adhesive agents may include but are not limited to epoxy resins, polyurethane adhesives, and hot melt adhesives.

[0122] Examples of rheology modifiers may include but are not limited to hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), and bentonite clay.

[0123] Examples of plasticisers may include but are not limited to diisononyl phthalate (DINP), dibutyl phthalate (DBP), and bis(2-ethylhexyl) phthalate (DEHP).

[0124] Examples of anti-oxidants may include but are not limited to butylated hydroxytoluene (BHT), vitamin E (tocopherols), and phosphite antioxidants.

[0125] Examples of UV stabilisers may include but are not limited to benzophenones, hindered amine light stabilizers (HALS), and benzotriazoles.

[0126] Examples of blowing agents may include but are not limited to azodicarbonamide, sodium bicarbonate, carbon dioxide, nitrogen, and hydrochlorofluorocarbons (HCFCs).

[0127] Examples of odour agents may include but are not limited to esters, aldehydes, and terpenes.

[0128] Optional additives may be present in a combined amount, based on the total weight of the flame-resistant material, of up to 14.42 wt%, for example up to about 14 wt%, for example up to about 12 wt%, for example up to about 10 wt%, for example up to about 8 wt%, for example up to about 6 wt%, for example up to about 5 wt%, for example up to about 4 wt%, for example up to about 3 wt%, for example up to about 2 wt%, for example up to about 1 wt%, for example up to about 0.75 wt%, for example up to about 0.5 wt%, for example up to about 0.3 wt%, for example up to about 0.1 wt%. Production of flame-resistant material

[0129] The present flame-resistant materials can be produced by a general method according to the steps below:

[0130] (i) Graphene is mixed with the flame retardant and polymer resin (for example in the form of pellets) in relative amounts according to a predetermined composition.

[0131] (ii) The mixed components are fed into a pre-heated twin-screw extruder which is heated to a predetermined temperature and which extrudes at a predetermined speed.

[0132] (iii) The mixture is passed through the twin-screw extruder which imparts high shear to disperse the graphene and flame retardant throughout the polymer resin, before being extruded, for example through a die as pellets of the flame-resistant material.

[0133] (iv) The resultant material is cooled and dried if necessary.

[0134] Production of resin articles

[0135] A shaped article may be produced from flame-resistant material, for example in the form of pellets, according to the general method below:

[0136] (i) The flame-resistant material is fed into a single-screw extruder which has been heated to a predetermined temperature above the melting point of the polymer resin component of the flame-resistant material.

[0137] (ii) The molten flame-resistant material is passed through the single-screw extruder and extruded through a die to the desired extruded shape.

[0138] (iii) The extruded article may be further shaped, stamped or moulded etc. into a desired shape.

[0139] Resin articles

[0140] Articles according to the invention may be formed from the present flame-resistant materials. They may be formed by any known shaping process - processing of pelletised material into desired shapes, for example, is well known. The articles have, by nature of the use of the present flame-resistant material, enhanced flame resistance. Suitable shapes into which the materials may be formed include bars, plates, slabs, bricks, dumbbell shapes and so on.

[0141] Such articles may themselves be included in larger items, for example building materials such as panels.

[0142] Extrusion temperature

[0143] In the above method of producing a flame-resistant material, components (a)-(c), and optional additives if present, are fed through a twin-screw extruder. The temperature of the twin-screw extruder is not particularly limited and may be suitably selected to allow mixing of the components. In some embodiments the extrusion temperature is above the melting point of polymer resin (c). If polymer resin (c) comprises polymers of more than one melting point, the extrusion temperature may be above at least one of those melting points.

[0144] The temperature of the twin-screw extruder may be set to at least 100 °C, for example at least 110 °C, for example at least 120 °C, for example at least 130 °C, for example at least 140 °C, for example at least 150 °C, for example at least 160 °C, for example at least 170 °C, for example at least 180 °C, for example at least 190 °C, for example at least 200 °C, for example at least 210 °C, for example at least 220 °C, for example at least 230 °C, for example at least 240 °C, or for example at least 250 °C.

[0145] In the above method of producing a resin article, a single-screw extruder is used. The temperature of the single extruder may be set to at least 100 °C, for example at least 110 °C, for example at least 120 °C, for example at least 130 °C, for example at least 140 °C, for example at least 150 °C, for example at least 160 °C, for example at least 170 °C, for example at least 180 °C, for example at least 190 °C, for example at least 200 °C, for example at least 210 °C, for example at least 220 °C, for example at least 230 °C, for example at least 240 °C, or for example at least 250 °C.

[0146] Extruder speed

[0147] Where an extruder is used in the above methods (single-screw or twin-screw) it may be set to a predetermined extruder speed. An extruder speed may be suitably selected from a range of 100 revolutions per minute (rpm) to 300 rpm, for example about 100 rpm, or about 125 rpm, or about 150 rpm, or about 175 rpm, or about 200 rpm, or about 225 rpm, or about 250 rpm, or about 275 rpm, or about 300 rpm.

[0148] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0149] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0150] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0151] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described. Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” 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.

[0152] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

[0153] Examples

[0154] Materials and methods

[0155] Ingredients for preparing sample compositions were obtained as follows.

[0156] Polymer resins:

[0157] Viridor = rHDPE-NATURAL-PELLET-DEODORISED product; a recycled HDPE-based polymer resin with a melt flow index (5 kg, measured at 190 °C) of 2.7 g / (10 min), a density (at 20 °C) of 0.93-0.97 g / cm3, and a colour of green.

[0158] Biffa Jazz = “Biffa HDPE JAZZ FLAKE” product; a HDPE-based polymer resin with a melt flow index (5 kg, measured at 190 °C) of 3.4 g / (10 min), a density (at 20 °C) of 0.92-0.98 g / cm3, and a colour of “jazz” Monoworld Jazz = “HDPE Jazz Flake” product; a HDPE-based polymer resin with a melt flow index (2.16 kg, measured at 190 °C) of 2.8 g / (10 min), a density (at 20 °C) of 0.93-0.96 g / cm3, and a colour of “jazz”.

[0159] Flame Retardants:

[0160] Tosaf = “Tosaf FR2655PE EU” purchased from Tosaf UK; a phosphorus-based flame retardant.

[0161] ATH Apyral 60CD = “Apyral® 60 CD” purchased from Wilfrid Smith; an aluminium trihydroxide-based flame retardant.

[0162] Graphenes:

[0163] FG = “PureGRAPH® 10” purchased from First Graphene. The product is produced through a process having an electrochemical exfoliation step. “FG” has around 3-4% oxygen functionalisation.

[0164] FG (low oxidation) = Experimental graphene product purchased from First Graphene. The product is produced through the same process as “PureGRAPH® 10” but using a different electrolyte in the electrochemical exfoliation step. “FG (low oxidation)” has around 1-2% oxygen functionalisation.

[0165] NX = “M3X-HDP18.0” purchased from Nanoxplore. The product is produced through a process having a ball milling step. “NX” has around less than 1% oxygen content. Tensile

[0166] The tensile strength of a composite material sample is measured in line with ASTM D638 using a Labortech Labtest 6.20 instrument. Dumbbell-shaped samples meeting the Type IV sample dimension specifications were used.

[0167] The tensile modulus of composite material sample is measured in line with ASTM D638, using a Labortech Labtest 6.20 instrument. Dumbbell-shaped samples meeting the Type IV sample dimension specifications were used.

[0168] In order to measure or quantify the flame resistance properties of the present materials, the inventors have assessed the Self-Extinguishing Rate, Time Taken, Flame Travel Distance, and Flame Propagation Rate as an average over five samples (n = 5).

[0169] Self-Extinguishing Rate describes the percentage of the samples of a given material (n = 5) to selfextinguish when ignited according to the protocol described below.

[0170] Time Taken is the time elapsed before a sample self-extinguished after the flame had reached the startpoint according to the protocol described below. If the flame did not self-extinguish then the Time Taken is the time for the flame to reach the end-point.

[0171] Flame Travel Distance describes the mean distance that the flame travelled along the length of the sample from the start-point to the end-point before self-extinguishing, according to the protocol described below. If the flame did not self-extinguish, the Flame Travel Distance is the distance between the startpoint and end-point.

[0172] Flame Propagation Rate is calculated by dividing the Flame Travel Distance by the Time Taken.

[0173] For testing, composite material samples of 127 mm in length, 13 mm in width, and 1 mm in height were used. The following method was used for flame resistance testing:

[0174] (i) Each composite sample (resin bar) is marked with two lines perpendicular to the longitudinal axis (length) of the sample. The first line (start-point) is marked at 25 mm from the end of the resin bar to be ignited and the second line (endpoint) is marked at 100 mm from the end of the resin bar to be ignited. (ii) The resin bar is clamped horizontally over a wire gauze. The unclamped end of the resin bar is the end to be ignited.

[0175] (iii) A flame is applied with a burner to the unclamped end of the resin bar at a depth of 6 mm below the sample, with the burner central axis at a 45-degree angle from the longitudinal axis of the bar.

[0176] (iv) The burner is applied for 30 seconds or until the flame reaches the start-point line. The burner is removed after 30 seconds if the flame does not reach the start-point line within the 30-second time period.

[0177] (v) A timer is started if the flame reaches the start-point and the timer is stopped when the flame self-extinguishes or when the flame reaches the endpoint. The time elapsed between the timer starting and stopping is the Time Taken. If the flame does not reach the start-point, a flame distance of 0 mm is recorded, and both time taken and burn rate are not recorded.

[0178] (vi) The Flame Travel Distance is measured.

[0179] (vii) The Flame Propagation Rate is measured.

[0180] (viii) The Self-Extinguishing measurement is taken for the sample. Samples for which the flame does not reach the start-point are included for self-extinguishing measurement.

[0181] Production of test samples

[0182] Table 1 lists the compositional make-up of each of the composite samples evaluated herein. The weight percentages provided in Table 1 are based on the total weight of the composition.

[0183] The compositions described in Table 1 were produced according to the following steps:

[0184] (i) Graphene (a) is mixed into a hopper with the flame retardant (b) and polymer resin pellets (c) in relative amounts according to a predetermined composition (per Table 1).

[0185] (ii) The mixed components are drawn from the hopper into a pre-heated twin extruder of which is heated to a predetermined temperature and which extrudes at a predetermined speed (per Table 1).

[0186] (iii) The mixture is passed through a twin-screw extruder which imparts high shear to disperse the components (a) and (b) throughout polymer resin (c), before being extruded through a 3 mm circular die as pellets of the resin composition.

[0187] (iv) The resin composition pellets are cooled and dried if necessary.

[0188] (v) The resin composition pellets are drawn from a second hopper into a single-screw extruder which has been pre-heated to a predetermined temperature and which extrudes at a predetermined speed (per Table 1). (vi) The molten resin composition is passed through the single-screw extruder and extruded through a die of 100 mm width and 1 mm thickness.

[0189] (vii) The extruded sheet is die stamped to form either a cuboid-shaped resin article of length 127 mm, width 13 mm, and thickness 1 mm (for samples to be used for measuring flame- resistance properties), or a dumbbell-shaped resin article meeting the Type IV sample dimension specifications of ASTM D638 (for samples to be used for measuring tensile strength and tensile modulus properties).

[0190] able 1

[0191] esults or each example, certain test values were measured according to the protocols set out above. The results are presented in Table 2. A blank cell indicates that no easurement of that property was taken. able 2 self-extinguished before reaching start-line; “Tailed to extrude reliably.

[0192] Discussion

[0193] Example 1

[0194] Five test samples were prepared using materials and method parameters as described in Table 1 . That is, samples according to Example 1 comprise Viridor resin (87.65 wt%), Tosaf phosphorous-containing flame retardant (12.25 wt%), and FG graphene (0.1 wt%) provided as a dispersion in HDPE, and extrusion occurs using a twin extruder temperature of 180 °C, a twin extrusion speed of 250 rpm, a single extruder temperature of 200 °C, and a single extruder temperature of 250 rpm.

[0195] An excellent self-extinguish rate of 100% was observed for samples according to this composition. Flame distance was low at only 8 mm. High tensile modulus and tensile strength were observed.

[0196] From this Example, it is evident that articles according to the present composition have excellent flame resistance properties and preferentially high strength properties. Articles according to the composition are therefore desirable for construction purposes and have reduced flame retardant loadings compared to known flame-resistant materials.

[0197] Examples 2 and 3

[0198] Example 2 was as Example 1 , except that both the twin extruder and single extruder temperatures and extruder speeds were modified.

[0199] Example 3 was as Example 1 , except that only the single extruder temperature and speed were modified, each having the same value as in Example 2, and flame retardant loading was reduced to 8.75 wt%.

[0200] Samples according to the compositions of both Examples 2 and 3 exhibited self-extinguish rates of 100%, demonstrating that such results are possible for a range of extruder temperatures and speeds, even when the flame retardant content is reduced.

[0201] Example 3 also had a reduced burn rate compared to Example 1 .

[0202] Examples 4 and 5

[0203] Examples 4 and 5 were as Example 1 , except that the polymer resin was changed compared to Example 1 . These examples demonstrate that different types of polymer resins, obtained from different manufacturers, can be used effectively within the present invention.

[0204] Example 6

[0205] Example 6 was as Example 1 , except that graphene was provided as a powder instead of a dispersion.

[0206] Samples according to the composition exhibited excellent self-extinguish but had increased burn rate and flame distance compared to Example 1 . Samples according to the composition exhibited increased tensile strength and reduced tensile modulus compared to Example 1 . Both properties were more than adequate.

[0207] The inventors postulate that the dispersion of graphene throughout compositions according to Example 6 may differ from the dispersion of graphene throughout compositions according to Example 1 , which in turn may affect the flame-resistance properties and strength properties of articles according to the composition. Hence provision of graphene as a dispersion, for example in HDPE, is preferred.

[0208] Example 7 was as Example 6, except that graphene loading was increased to 5 wt% and it was of lower oxidation (“FG (low oxidation)” rather than “FG” was used).

[0209] The present example demonstrates that excellent self-extinguish properties of 80% are achieved at increased graphene loadings, and at varying levels of oxygen content.

[0210] Example 8

[0211] Example 8 was as Example 6, except that flame retardant loading was reduced to 8.75%.

[0212] Samples according to the composition exhibited excellent flame resistance properties despite reduced flame retardant loading, having a self-extinguish rate of 80% and unchanged burn rate compared to Example 6.

[0213] Tensile modulus and Tensile strength are reduced compared to Example 6. Both properties were still more than adequate.

[0214] Examples 9-11

[0215] Examples 9, 10 and 11 were as Example 1 , except that graphene loading was increased to 0.5 wt%, 1 .0 wt% and 4.0 wt% respectively.

[0216] These Examples, in addition to Example 1 , highlighted a bimodal distribution in flame resistance properties. That is, the inventors found that peak self-extinguish properties were achieved at graphene loadings from about 0.005 to about 0.1 wt% and from about 4.0 to 5.0 wt%, with relatively reduced self- extinguish at around 1 .0% wt% graphene. The self-extinguish was still superior to embodiments where no additives were included in the resin (see Example 17).

[0217] The inventors postulate that the dominant mechanism for resisting and extinguishing flames may change as the graphene loading is increased or decreased, in turn resulting in the bimodal distribution of improved flame resistance properties.

[0218] Examples 12-15

[0219] Examples 12, 13, 14, and 15 all contained a different graphene as compared to the graphene in Example 1. That is, Examples 12-15 contained NX graphene instead of FG graphene. Example 12 was as Example 1 , apart from the difference in type of graphene. Excellent flame resistance properties were observed, with 100% self-extinguish and reduced flame distance compared to Example 1.

[0220] Example 13 was as Example 12, except that graphene loading was increased to 2.0 wt%, twin extruder speed was increased to 450 rpm.

[0221] Example 14 was as Example 12, except that graphene loading was increased to 2.0 wt%, twin extruder temperature was increased to 200 °C and single extruder speed was reduced to 150 rpm.

[0222] Example 15 was as Example 12, except that graphene loading was increased to 1 .05 wt%, flame retardant loading was reduced to 8.75%, twin extruder speed and temperature were increased, and single extruder speed and temperature were decreased.

[0223] All of Examples 12-15 demonstrated that samples containing different types of graphene retained improved flame resistance properties. For example, graphenes having a range of aspect ratios are well- tolerated, in addition to graphenes having different numbers of layers, graphenes generated by different processes (e.g., mechanical versus electrochemical exfoliation), and graphenes having different oxygen contents.

[0224] Examples 12 to 15 also indicate that a bimodal distribution of self-extinguish properties occurs for different graphenes.

[0225] Examples 16 was as Example 15, except that FG graphene was used instead of NX graphene. As with Example 15, reduced self-extinguish was observed in comparison to Example 1 , but self-extinguish still occurs at a rate of 20%.

[0226] Example 17 was as Example 1 , except that flame retardant and graphene were removed. The composition thus contained only polymer resin. Self-extinguish did not occur when flame retardant and graphene were absent (i.e., a self-extinguish rate of 0% was observed), and both tensile modulus and tensile strength were significantly reduced compared to Example 1 .

[0227] Examples 18 (reference) and 19 (reference)

[0228] Example 18 contained a different type of flame retardant compared to Example 1 ; the flame-retardant ATH Apyral 60CD was used at a loading of 35 wt%. Graphene loading was also increased to 2.0 wt% and both single screw temperature and speed were reduced.

[0229] A self-extinguish rate of 40% was observed. However, the flame retardant loading was much higher. Example 19 also contained ATH Apyral 60CD instead of Tosaf flame retardant, but at reduced loading compared to Example 18. Graphene loading was also reduced compared to Example 18, and both twin extruder speed and single extruder speed differ to Example 18.

[0230] Flame extinguish occurred at a rate of 0% for Example 19, demonstrating that a combination of Tosaf (phosphorus-based) flame retardant and graphene had greater flame resistance properties at lower loadings than a combination of ATH Apyral 60CD flame retardant and graphene.

[0231] Example 20 was as Example 1 , except that graphene loading was increased to 2.0 wt% and flameretardant loading was reduced to 5.25 wt%.

[0232] Example 21 was as Example 1 , except that flame retardant loading was reduced to 5.25 wt% and NX graphene was used instead of FG graphene.

[0233] Examples 20 and 21 demonstrate that self-extinguish did not occur when flame retardant content was below around 8.5 wt%, even when graphene loading was in a preferred range (around 0.1 wt%).

[0234] Example 22 was as Example 1 , except that flame retardant loading was increased to 17.75 wt%.

[0235] Samples according to the composition could not be reliably extruded, meaning that flame resistance properties and strength properties could not be measured.

[0236] Conclusions

[0237] The examples show that improved flame resistance properties are observed when the composition and / or production method are varied within the bounds of the present invention.

[0238] For example, improved flame resistance properties are observed for (i) different types of graphene; (ii) different graphene loadings, wherein a bimodal distribution of peak performance is observed; (iii) graphene which is either supplied or provided as either a dispersion or powder; (iv) graphene having a range of functionalisation, including oxygen content; (v) different types of resin; (vi) different phosphorous- containing flame retardant loadings.

[0239] Poor flame resistance properties are observed when flame retardant loading is below around 8.5 wt%, and compositions cannot be reliably extruded when flame retardant loading is above around 15 wt%. Worse flame resistance properties are also observed when a flame retardant comprising aluminium hydroxide is used instead of a phosphorous-containing flame retardant.

Claims

Claims:1 . A resin composition comprising:(a) from 0.08 to 8 weight percent graphene; and(b) from 8.5 to 15 weight percent phosphorus-containing flame retardant; and(c) from 77 to 91 weight percent of polymer resin.

2. The resin composition according to claim 1 , wherein the composition comprises as (a) from 0.005 to 0.1 wt% or from 4.0 to 5.0 wt% graphene.

3. The resin according composition to claim 1 or claim 2, wherein the composition comprises as (b) from 11 .0 to 13.0 wt% phosphorus-containing flame retardant.

4. The resin composition according to any one of the preceding claims, wherein the graphene has a flake diameter of 1 to 50 pm.

5. The resin composition according to any one of the preceding claims, wherein the phosphorus- containing flame retardant comprises piperazine pyrophosphate.

6. The resin composition according to any one of the preceding claims, wherein polymer resin (c) comprises recycled polymer, preferably recycled HDPE.

7. The resin composition according to any one of the preceding claims, wherein polymer resin (c) comprises at least 50 wt% percent recycled HDPE.

8. A method of making a resin composition according to any one of the preceding claims, comprising mixing components (a), (b) and (c).

10. A method of producing a shaped resin article, comprising making a resin composition by a method according to claim 8 and then shaping the composition to the desired shape to form the shaped resin article.

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