WO2023113679A1

WO2023113679A1 - Functionalized graphene structure and nanocomposite comprising such functionalized graphene structure

Info

Publication number: WO2023113679A1
Application number: PCT/SE2022/051168
Authority: WO
Inventors: Govindan Induchoodan
Original assignee: Glenntex Ab
Priority date: 2021-12-14
Filing date: 2022-12-12
Publication date: 2023-06-22

Abstract

A functionalized graphene structure, comprising a graphene substrate (1) having a first surface and a second surface, a first polymer layer (2) comprising polymers having a linear or branched chain architecture, the polymers of the first polymer layer being bound to the first surface of the graphene substrate with a first end thereof, and a first additional polymer layer (3) comprising polymers having a linear or branched chain architecture, the polymers of the first additional polymer layer being covalently connected to the first polymer layer with a first end thereof and provided with a reactive terminal group (10) at a second end thereof, wherein the polymers of the first polymer layer (2) and the first additional polymer layer (3) are different. A nanocomposite comprising the functionalized graphene structure dispersed in a polymer matrix (M1, M2).

Description

FUNCTIONALIZED GRAPHENE STRUCTURE AND NANOCOMPOSITE COMPRISING SUCH FUNCTIONALIZED GRAPHENE STRUCTURE

TECHNICAL FIELD

[001] The present invention relates to a functionalized graphene structure, a nanocomposite comprising such functionalized graphene structure, and methods of producing such functionalized graphene structure and nanocomposites.

BACKGROUND

[002] A composite is by definition a physical blend of two or more materials. This blend could comprise metals, ceramics, or polymers. Nanocomposites is a class of multiphase materials that is a combination of polymers and nanomaterials. Different families of nanomaterials have been used in nanocomposites, such as graphitic nanoparticles, nanoclays, graphene and nanocellulose. In general, the nanomaterial has two roles: to reinforce a parent material (e.g., strength and Young's modulus), and to augment the material properties of the parent material (e.g., thermal conductivity, electrical conductivity, and permeability). While nanomaterials help augment a material property, there is, however, overwhelming evidence that this augmentation comes at the cost of another material property, e.g., a decrease in toughness resulting from augmenting the material strength.

[003] Overcoming the above-mentioned 'trade-off' of different material properties is crucial and necessary in material development. Attempts have been made to address material property trade-offs during tailoring (enhancing) material properties.

[004] In CN102826539A is disclosed a hyperbranched polyaramide functionalized graphene with good dispersibility in a polymer matrix, such as thermoplastic polyurethane matrix. The functionalized graphene improves the mechanical and dielectric properties of the polymer matrix.

[005] US2020247974A1 shows a graphene composite material, including a graphene/ polyethylene terephthalate (PET) nanocomposite material and a graphene/polyester composite material. The graphene/PET composite material has improved mechanical properties and electrical conductivity, and may be used in the production of functionalized polyester fibers. The graphene/polyester composite material can be used as flame-retardant and UV-resistant polyester fibers.

[006] The specific design of the polymer nanocomposite material may be chosen based on the desired features of the composite material. There is a need of more tailored materials that are improved without the mentioned material property trade-off.

SUMMARY OF THE INVENTION

[007] It is an object of the present disclosure to provide a functionalized graphene structure, a nanocomposite comprising such functionalized graphene structure, and methods of producing such functionalized graphene structure and nanocomposite. Use of the functionalized graphene structure enables tailoring of nanocomposite materials that have improved properties without or at least with a reduced 'trade-off' of different material properties.

[008] The invention is defined by the appended independent claims. Non-limiting embodiments emerge from the dependent claims, the appended drawings and the following description.

[009] According to a first aspect there is provided a functionalized graphene structure, comprising: a graphene substrate having a first surface and a second surface; a first polymer layer comprising polymers having a linear or branched chain architecture, the polymers of the first polymer layer being bound to the first surface of the graphene substrate with a first end thereof, and a first additional polymer layer comprising polymers having a linear or branched chain architecture, the polymers of the first additional polymer layer being covalently connected to the first polymer layer with a first end thereof and provided with a reactive terminal group at a second end thereof, wherein the polymers of the first polymer layer and the first additional polymer layer are different.

[0010] Graphene is a carbonaceous material with a two-dimensional honeycomb lattice structure that is closely packed with a single layer of carbon atoms.

[0011] Graphite may be exfoliated to smaller thickness (higher aspect ratio) into graphene nanoplatelets (GnP) or graphene (using e.g. liquid exfoliation).

[0012] As graphene in its sp2 state is inert in nature it must be modified to provide reactive groups on its surface for binding with the polymers of the first polymer layer. [0013] Graphene may be modified by oxidizing graphene into graphene oxide (GO) using well- known techniques such as "modified Hummer's method". The polymers of the first polymer layer may then be bound to the graphene surface by a covalent bound. Alternatively, molecular wedging can be used to transform graphene to a reactive substrate. In molecular wedging, the polymers are attached to graphene through pi-bonding (such as n-(l-pyrenyl) maleimide, 1-aminopyrene, 1-pyrenesulfonicacid hydrate, 1-pyrene butanol, 1-pyrene methylamine hydrochloride, 1,3,6,8-pyrene tetra sulfonic acid tetra sodium, and like).

Choosing molecular wedging over modified Hummer's method is based on whether the application requires a retained sp2 structure or not (electrical and thermal characteristics). The molecular wedging approach has a compromise on the bond strength and the consecutive mechanical properties of the nanocomposite in which the functionalized graphene structure may be incorporated, as the molecules are attached with pi-bond.

[0014] The graphene substrate having a first surface and a second surface may be any graphitic substrate and includes graphene nanoplatelets, graphite nanoplatelets, graphene, graphene oxide, bi-layer graphene, graphene quantum dots, graphene nanorods, and graphene nano tape.

[0015] To further improve binding of a polymer to the graphene substrate surface an additional molecule can be added to the surface of graphene oxide that would allow better growth/attachment. This can be molecules such as a triethoxysilane (aminopropyltriethoxysilane, glycidyloxypropyl trimethoxysilane, azidoeethyl propyltriethoxysilane) or azide terminals such as O-(2-Aminoethyl)-O'-(2- azidoethyl)pentaethylene glycol, which non-covalently binds the polymer to the surface.

[0016] The polymers may then be directly bound to the graphene surface or be bound via a reactive group.

[0017] The graphene substrate has a first and a second surface. Depending on the graphene substrate, such first and second surfaces may e.g. be substantially opposite surfaces of the substrate or be adjacent non-overlapping surfaces.

[0018] The polymers may be mono-polymers or co-polymers. The polymer can be linear or branched. The branched polymer may even be hyper-branched. The hyper-branched structure would be restricted by the condensation of the branch, the solubility in the solvent and the mechanical degradation of the material properties due to the branching. The hyper-branching molecular unit is too short the molecular chains are unable to rotate, elongate and may cause a negative impact on the desired property.

[0019] Highly branched polymers with a multitude of end groups are less prone than linear polymers to form entanglements and undergo crystallization. Hyperbranched polymers are phenomenologically different from linear polymers; for example, the lack of entanglements results in lower viscosity than in linear polymers of the same molecular weight.

[0020] The provided functionalized graphene structure may be mixed with a polymer matrix such that the reactive terminal groups of the additional polymer layer react with the polymers of the polymer matrix. The terminal group could for example be a molecule that would bind with oxygen.

[0021] The polymers of the first and first additional polymer layers are different. This means that they for example may differ in polymer chain architecture. By choosing the polymers of the first and first additional polymer layers with care, the functionalised graphene can be used in a polymer matrix to simultaneously improve strength, while retaining the elasticity and yield-to-fracture. This means that one polymer layer improves the elasticity and yield-to- fracture of the polymer matrix, while the other polymer layer increase the strength of the polymer matrix. Additionally this causes a decrease in stress relaxation.

[0022] The polymers may be uniformly bound to the substrate surface, covering all surface that is reactive and available for the reaction/growth.

[0023] The size, structure, type etc. of the polymer or co-polymer of the first/additional polymer layer is dependent on the intended application of the functionalized graphene structure and the nanocomposite polymer in which it is intended to be used.

[0024] The size of the polymers used in the polymer layers may range from 90 MW to 100000 MW. The size of polymers may range from 90-75 000 MW, 90-50 000 MW, 90-25 000 MW, 90- 10000 MW, 90-5000 MW, 90-2500 MW, 90-1000 MW, 90-500 MW, 500-100000 MW, 1000- 100 000 MW, 5000-100 000 MW, 10000-100 000 MW, 25 000-100 000 MW, 50000-100 000 MW, 75 000-100 000 MW, 1000-10 000 MW, 500-2500 MW, or 5000-20 000 MW. The size of polymers of one polymer layer may be about the same size as the polymer size of that of another polymer layer. Alternatively, the polymers of different polymer layers may differ in size.

[0025] The choice of the polymer of the first additional polymer layer is dependent on the mechanical properties the first polymer layer provides. For instance, polyethylene terephthalate (PET) is stiff. To improve a PET matrix a functionalized graphene structure with a first polymer layer could be incorporated/mixed in the PET to increase the strength of the PET. This would also make it brittle and more stiff, which is not desirable. By adding a first additional polymer layer to the functionalized graphene structure comprising polymers that provide flexibility or increased strain-to-fracture to the PET matrix, the resulting PET material can be improved. The first stage would be to provide the flexibility (linear polymers) while the second stage, would be to provide strength (hyperbranched polymers).

[0026] Hyperbranching causes a notable change of the polymer's properties (broadening the molecular weight distribution, low to no chain entanglement, lowers the melt viscosity, decreases the mechanical strength, lowers the melting point, decreases the crystallinity, greater separation between chains, and enhanced free volume).

[0027] Hyperbranched functional groups have a large number of end groups. This structure significantly affects the potential interaction between the end groups and the neighboring molecules, helping create crosslinks at even moderate molecular weight. Crosslinking leads to covalent bonds that are considerably stronger (compared to the intermolecular forces that attract other polymer chains), resulting in a stronger nanocomposite.

[0028] Hyperbranching impacts flexibility and strength. The presence of branched aromatic rings in the molecular chain may lead to an intrinsic brittleness of the functional group. Aliphatic, semi-aromatic, and aromatic branches affect the applicability and mechanical properties of the hyperbranched functional group.

[0029] At a second end of the polymers of the first polymer layer is a terminal molecule that would covalently bind a first end of the polymers of the additional polymer layer. For example, if the polymers of the second polymer layer is a polyamide then the terminal group of the polymers of the first polymer layer may be epoxide, chloride, anhydride, cyclic anhydride or acid.

[0030] Thus, in general, when incorporated in a polymer matrix, the first polymer layer of the functionalized graphene structure provides compensation of lost material property of the polymer matrix and the first additional polymer layer provides the desired material property. This is accomplished by comprising different polymers in the first and first additional polymer layers.

[0031] The second surface of the graphene substrate may be provided with reactive terminal groups. [0032] These reactive terminal groups bind to the polymers of the polymer matrix in which the functionalized graphene structure is incorporated.

[0033] These reactive terminal groups may be the same or different from the reactive terminal groups provided at a second end of a polymer of a polymer layer.

[0034] The functionalized graphene may comprise a second polymer layer comprising polymers having a linear or branched chain architecture, the polymers being bound to the second surface of the graphene substrate with a first end thereof, and being provided with a reactive terminal group at a second end thereof.

[0035] The functionalized graphene structure may comprise a second polymer layer comprising polymers having a linear or branched chain architecture, the polymers being bound to the second surface of the graphene substrate with a first end thereof, and further a second additional polymer layer comprising a polymer having a linear or branched chain architecture, the polymers of the second additional polymer layer being covalently connected to the second polymer layer with a first end thereof and provided with a reactive terminal group at a second end thereof, wherein the polymers of the second polymer layer and the second additional polymer layer are different.

[0036] The polymer of a polymer layer may be selected from thermoplastics, thermosets and elastomers.

[0037] Thermoplastics include polythene, polycarbonate, polyvinyl chloride, teflon, polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyesters such as polyethylene terephthalate (PET), polymethyl methacrylate, polyether keton (PEEK), polyurethane, polyeterimide, polysulfone and polyaramide.

[0038] Thermosets include epoxies, vinyl esters, silicons, phenolics, polyesters, polyurethanes, thermosetting polyimides,

[0039] Elastomers include natural rubbers, styrene-butadiene block copolymers, polyisoprene, polybutadiene, ethylene propylene rubber, ethylene propylene diene rubber, silicone elastomers, fluoroelastomers, polyurethane elastomers, and nitrile rubbers.

[0040] The different polymer layers discussed above may have the same chemical molecules but different chain architecture, i.e., linear branched, or hyperbranched.

[0041] The polymers of a polymer layer may be an ester, ether, amide, carbonate, urethane, styrene or methyl acrylate. [0042] When polymer layers are discussed above, such polymer layers are the first polymer layer, the first additional polymer layer, the second polymer layer, and/or the second additional polymer layer, depending on if the particular functionalized graphene structure comprises such a polymer layer or layers. When discussing polymers, these polymers are the polymers of any one or more of the mentioned polymer layers.

[0043] The reactive terminal group may be selected from one or more of hydroxyl, carboxyl, thiol, epoxy, amine, amide, methyl, vinyl, benzophenone, and azo.

[0044] The terminal groups of a polymer of a polymer layer may be of one kind or the polymers of a polymer layer may have two or more different reactive terminal groups.

[0045] The second polymer layer may comprise polymers that are different from the first polymer layer and/or the second additional polymer layer may comprise polymers that are different from the first additional polymer layer.

[0046] The graphene substrate may be in the shape of spheres, sheets, rods and/or dots.

[0047] According to a second aspect there is provided a nanocomposite comprising the functionalized graphene structure described above dispersed in a polymer matrix comprising matrix polymers selected from one or more of thermoplastics, thermosets and elastomers. [0048] Thermoplastics include polythene, polycarbonate, polyvinyl chloride, teflon, polypropylene (PR), polystyrene (PS), polyvinyl chloride (PVC), polyesters such as polyethylene terephthalate (PET), polymethyl methacrylate, polyether keton (PEEK), polyurethane, polyeterimide, polysulfone and polyaramide.

[0049] Thermosets include epoxies, vinyl esters, silicons, phenolics, polyesters, polyurethanes, thermosetting polyimides,

[0050] Elastomers include natural rubbers, styrene-butadiene block copolymers, polyisoprene, polybutadiene, ethylene propylene rubber, ethylene propylene diene rubber, silicone elastomers, fluoroelastomers, polyurethane elastomers, and nitrile rubbers.

[0051] The polymer matrix may comprise virgin bio-based and petroleum-based polymers. The polymer matrix may comprise 0-50% postconsumer/recycled/reused bio-based and petroleum-based polymers. These polymers are used greatly in today's market and have complicated, and emergency need for recycling, prolonged life and improved product quality. By introducing adapted functionalized graphene structures in such polymer matrices, the quality of products based on such postconsumer/recycled/reused polymers can be improved. [0052] The choice of the polymers of the polymer layers is directly related to the polymer matrix of choice. For instance, polyethylene terephthalate (PET) is processed at 260°C -280°C. If PET is used as the polymer matrix, polymers of the polymer layers have to be selected that are thermally stable and also provides the expected function, such as the one attained from implementing a linear, branched, or hyper-branched structure.

[0053] The polymer matrix may comprise matrix polymers selected from esters, ethers, amides, carbonates, urethanes, styrenes and/or methyl acrylates.

[0054] The choice of the polymers of the first and first additional polymer layers and optionally the second and second additional polymer layer is dependent on the polymer matrix in which the functionalized graphene structure is to be incorporated. A nanocomposite can be designed using a single polymer or bi-polymer matrix. In the case that the nanocomposite contains two different matrices/matrix materials, the functionalized graphene structure can be used to interact with both matrices at the interface between the two matrix materials.

[0055] The chemical structure of the polymer layers of the functionalized graphene structure, may be selected based on the matrix used (chemical nature of the polymer), processing conditions (solvent processing, melt extrusion, compression molding and like), post-processing treatments (annealing, tempering, and like), area of application (clothing, shoes, tennis racquets strings and like), and requirements on synthesis method/conditions (toxicity, environmental impact, availability of chemical and like).

[0056] The second matrix can be a microphase. In a microphase, the second matrix would be of a very low volume fraction and physically comparable to the functionalized graphene structure.

[0057] In a bi-polymer matrix, the two polymers may: a) Differ in polymer class (e.g., acrylamides, amides, carbonates, ethers, epoxides, esters, hydroxy(meth)acrylates, and like). b) Differ in general structures, in the same polymer class (e.g., polyethylene terephthalate), poly(butylene succinate), poly(hexylene sebacate), poly(trimethylene terephthalate), and like). c) Be the same polymer, i.e., general structure and polymer class, that has different polymer histories (e.g., postconsumer polyethylene terephthalate), thermally degraded polyethylene terephthalate), UV degraded polyethylene terephthalate), recycled polyethylene terephthalate), and like).

[0058] The functionalized graphene structure and the polymer matrix may comprise the same polymer.

[0059] The polymer matrix may comprise a polymer different from the polymers of the functionalized graphene structure.

[0060] The polymers of the polymer layers in the functionalized graphene structure are arranged to compensate for properties the polymer matrix may need to improve, why the polymers of the functionalized graphene structure need not be the same as the polymer matrix they reside in.

[0061] The amount of functionalized graphene structure in the nanocomposite may be 0.001 to 10 wt.% of the total weight of the nanocomposite.

[0062] The ratio may be 0.001 to 10 wt.%, 0.01 to 10 wt.%, 0.1 to 10 wt.%, 1 to 10 wt.%, 0.001 to 8 wt.%, 0.001 to 6 wt.%, 0.001 to 4 wt.%, 0.001 to 2 wt.%, 0.001 to 1 wt.%, 0.001 to 0.1 wt.%, 0.001 to 0.01 wt.%, 0.01 to 0.1 wt.%, 0.1 to 1 wt.%, 0.1 to 2 wt.%, 1 to 4 wt.%, or 4 to 6 wt.%.

[0063] At the higher amounts of functionalized graphene structure in the nanocomposite, i.e. around 7.5 wt.% and above the functionalised graphene may start to show agglomerates and form large local lumps of agglomerated matter in the nanocomposite. The higher the concentration, the higher the number of agglomerates in the nanocomposite. Agglomerates of functionalised graphene may form entangled structures with poor binding to the polymer of the polymer matrix. The agglomerates may have a negative structural impact on the nanocomposite. Agglomerated functionalised graphene may produce local voids in the nanocomposite due to poor wetting/binding with the polymer of the polymer matrix, which may act as a nucleation site for failure of the nanocomposite. Similarly, dilution of a nanocomposite with agglomerated functionalised graphene structure (master batch to indented volume fraction) would lead to the transfer of the agglomerated functionalised graphene with poor interface, voids due to poor wetting, and excess breakage and damage of the graphene particles.

[0064] According to a third aspect there is provided a method of producing a functionalized graphene structure, comprising: providing a graphene substrate having a first and a second surface; activating the first and optionally the second surface of the substrate; arranging a first polymer layer on the first surface of the substrate, the first polymer layer comprising polymers having a linear or branched chain architecture, the polymers of the first polymer layer being bound to the first surface of the graphene substrate with a first end thereof, and arranging a first additional polymer layer on the first polymer layer, the first additional polymer layer comprising polymers having a linear or branched chain architecture, wherein the polymers of the first additional polymer layer are different from the polymers of the first polymer layer, the polymers of the first additional polymer layer being covalently connected to the first polymer layer with a first end thereof and provided with a reactive terminal group at a second end thereof. The method may optionally comprise to provide the second surface of the graphene substrate with reactive terminal groups, or to arrange a second polymer layer on the second surface of the substrate, the second polymer layer comprising polymers having a linear or branched chain architecture, the polymers of the second polymer layer being bound to the second surface of the graphene substrate with a first end thereof, and being provided with a reactive terminal group at a second end thereof, or to arrange a second polymer layer on the second surface of the substrate, the second polymer layer comprising polymers having a linear or branched chain architecture, the polymers of the second polymer layer being bound to the second surface of the graphene substrate with a first end thereof, and arranging a second additional polymer layer on the second polymer layer, the second additional polymer layer comprising polymers having a linear or branched chain architecture, wherein the polymers of the second additional polymer layer are different from the polymers of the second polymer layer, the polymers of the second additional polymer layer being covalently connected to the second polymer layer with a first end thereof and provided with a reactive terminal group at a second end thereof.

[0065] The polymer layers may be grown/polymerises on the surface (grown-on, chaingrowth, step-grown, multi-step grown).

[0066] Alternatively, the polymer layers may be formed and then bound to the substrate surface. This can be accomplished using for example click chemistry using for example the azide-alkyne chemistry.

[0067] According to a fourth aspect there is provided a method of producing a nanocomposite, comprising providing a polymer matrix, producing a functionalized graphene structure according to the method described above, and mixing the polymer matrix and the functionalized graphene structure, forming the nanocomposite. [0068] The polymer matrix and the functionalized graphene structure may be mixed e.g. through melt blending in an extruder or through solution mixing. The functionalised graphene is dispersed in the polymer matrix. The polymer matrix may be as discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figs la-lc show different functionalized graphene structures.

[0070] Fig. 2 shows a more detailed view of the functionalized graphene structure of Fig. la. The functionalized graphene structure comprises a graphene substrate having a first surface and a second surface. A first polymer layer comprises polymers having a linear architecture, which polymers are bound to the first surface of the graphene substrate with a first end thereof. It further comprises a first additional polymer layer comprising polymers having a hyperbranched chain architecture, wherein the polymers of the first additional polymer layer are covalently connected to the first polymer layer with a first end thereof and provided with a reactive terminal group at a second end thereof. The second surface of the graphene substrate is provided with reactive terminal groups.

[0071] Fig. 3 shows a nanocomposite comprising a matrix of a single polymer in which is dispersed the functionalized graphene structure illustrated in Fig. 2.

[0072] Fig. 4 shows a nanocomposite comprising a bi-polymer matrix in which is dispersed the functionalized graphene structure illustrated in Fig. 2.

[0073] Fig. 5 shows tensile test data from measurements of virgin polyethylene terephthalate (PET) compared with PET with functionalized graphene structure incorporated in the matrix thereof.

[0074] Fig. 6 shows a SEM image of a fracture surface of a PET string with functionalized graphene structure incorporated in the matrix thereof.

DETAILED DESCRIPTION

[0075] In nanocomposites the nanomaterial has two roles: to reinforce a parent material (e.g., strength and Young's modulus), and to augment the material properties of the parent material (e.g., thermal conductivity, electrical conductivity, and permeability). While nanomaterials help augment a material property, there is, however, overwhelming evidence that this augmentation comes at the cost of another material property, e.g., a decrease in toughness resulting from augmenting the material strength. Overcoming this 'trade-off' of different material properties is crucial and necessary in material development. Below is described a functionalized graphene structure and nanocomposites comprising such functionalized graphene structures. Use of the functionalized graphene structure enables tailoring of nanocomposite materials that have improved properties without or at least with a reduced 'trade-off' of different material properties.

[0076] The general functionalized graphene structure is illustrated in Figs la-lc. The functionalized graphene structure shown in Fig. la comprises a graphene substrate 1 having a first surface and a second surface. On the first surface of the graphene substrate is arranged a first polymer layer 2 comprising polymers having a linear or branched chain architecture. The polymers of the first polymer layer being bound to the first surface of the graphene substrate with a first end thereof. A first additional polymer layer 3 comprising polymers having a linear or branched chain architecture is arranged on the first polymer layer 2. The polymers of the first additional polymer layer 3 are covalently connected to the first polymer layer with a first end thereof and provided with a reactive terminal group 10, such as of hydroxyl, carboxyl, thiol, epoxy, amine, amide, methyl, vinyl, benzophenone, and azo, at a second end thereof. The polymers of the first polymer layer and the first additional polymer layer are different, and may for example differ in chain architecture.

[0077] The second surface of the graphene substrate 1 may be provided with reactive terminal groups 11 (Fig. 2).

[0078] In Fig. 2 is shown a more detailed example of a functionalized graphene structure of Fig. la. The functionalized graphene structure comprises a graphene substrate 1 having a first surface and a second surface. A first polymer layer 2 comprises polymers having a linear architecture, wherein the polymers of the first polymer layer are bound to the first surface of the graphene substrate 1 with a first end thereof. It further comprises a first additional polymer layer 3 comprising polymers having a hyperbranched chain architecture, wherein the polymers of the first additional polymer layer 3 are covalently connected to the first polymer layer 2 with a first end thereof and provided with a reactive terminal group 10 at a second end thereof. The second surface of the graphene substrate is provided with reactive terminal groups 11.

[0079] In Fig. lb is illustrated an alternative functionalized graphene structure, which in addition to a first polymer layer 2 and a first additional polymer layer 3 on the first surface of the substrate 1 comprises a second polymer layer 4 comprising polymers having a linear or branched chain architecture arranged on the second surface of the graphene substrate 1. The polymers are bound to the second surface of the graphene substrate with a first end thereof, and are provided with a reactive terminal group at a second end thereof.

[0080] In yet an alternative, see Fig. lc, the functionalized graphene structure comprises a second polymer layer 4 arranged on the second surface of the graphene substrate 1 comprising polymers having a linear or branched chain architecture. The polymers being bound to the second surface of the graphene substrate with a first end thereof. A second additional polymer layer 5 comprising a polymer having a linear or branched chain architecture, the polymers of the second additional polymer layer 5 being covalently connected to the second polymer layer 4 with a first end thereof and provided with a reactive terminal group at a second end thereof, wherein the polymers of the second polymer layer and the second additional polymer layer are different.

[0081] The functionalized graphene structure of any of Figs la, lb and lc may be incorporated in a polymer matrix Ml, M2, thereby forming a nanocomposite architecture. The functionalized graphene structure acts as a flexible substrate on top of which 'functional groups' are attached. The attached functional groups, along with the graphene, contribute to the augmentation of the thermo-mechanical properties of the nanocomposite while retaining the desired properties (usefulness). This form of enhanced material is called a 'multifunctional' nanocomposite.

[0082] The polymer matrix may comprise polymers selected from esters, ethers, amides, carbonates, urethanes, styrenes and/or methyl acrylates. The functionalized graphene structure and the polymer matrix may comprise the same polymer or different polymers. [0083] The choice of the polymers of the first and first additional polymer layers 2, 3 and optionally the second and second additional polymer layers 4, 5 is dependent on the polymer matrix Ml, M2 in which the functionalized graphene structure is to be incorporated. A nanocomposite can contain up to two different polymer matrices. The two matrices Ml, M2 can be distinct or similar polymers. In the case that the nanocomposite contains two matrices the functionalized graphene structure can be used to interact with both matrices at the interface thereof. Such a functionalized graphene structure based nanocomposite architecture may be called 'nanoglue' and the corresponding nanocomposite a 'multifunctional bi-polymer nanocomposite'. [0084] The chemical structure of the polymer layers, are selected based on the matrix (chemical nature of the polymer), processing conditions (solvent processing, melt extrusion, compression molding and like), post-processing treatments (aneling, tempering, and like), area of application (clothing, shoes, tennis racquets strings and like), and requirements on synthesis method/conditions (toxicity, environmental impact, availability of chemical and like). [0085] A nanocomposite can be designed using a single polymer Ml has illustrated in Fig. 3 in which a functionalized graphene structure shown in Fig. 2 has been incorporated.

[0086] A nanocomposite can be designed using a bi-polymer matrix, Ml and M2 as illustrated in Fig. 4 in which a functionalized graphene structure shown in Fig. 2 has been incorporated. [0087] By incorporating such functionalized graphene structures into a polymer material, tailored material properties can be provided to the parent polymer. The functionalized graphene structure allows for multifunctional enhancement of the parent material, specifically the arrangement of the various units on the functionalized graphene and the modular design that allows for swapping polymer chains and functional groups in the units.

[0088] A general method of producing a functionalized graphene structure, comprises to provide a graphene substrate 1 having a first and a second surface and to activate the first and optionally the second surface of the substrate. A first polymer layer 2 is arranged on the first surface of the substrate, the first polymer layer comprising polymers having a linear or branched chain architecture, the polymers of the first polymer layer being bound to the first surface of the graphene substrate with a first end thereof. A first additional polymer layer 3 is arranged on the first polymer layer 2, the first additional polymer layer comprising polymers having a linear or branched chain architecture, wherein the polymers of the first additional polymer layer are different from the polymers of the first polymer layer, the polymers of the first additional polymer layer being covalently connected to the first polymer layer with a first end thereof and provided with a reactive terminal group at a second end thereof. Optionally, the method comprises to provide the second surface of the graphene substrate 1 with reactive terminal groups, or to arrange a second polymer layer 4 on the second surface of the substrate, the second polymer layer comprising polymers having a linear or branched chain architecture, the polymers of the second polymer layer 4 being bound to the second surface of the graphene substrate with a first end thereof, and being provided with a reactive terminal group at a second end thereof, or to arrange a second polymer layer 4 on the second surface of the substrate, the second polymer layer 4 comprising polymers having a linear or branched chain architecture, the polymers of the second polymer layer being bound to the second surface of the graphene substrate with a first end thereof, and arranging a second additional polymer layer 5 on the second polymer layer, the second additional polymer layer comprising polymers having a linear or branched chain architecture, wherein the polymers of the second additional polymer layer are different from the polymers of the second polymer layer, the polymers of the second additional polymer layer being covalently connected to the second polymer layer with a first end thereof and provided with a reactive terminal group at a second end thereof.

[0089] The polymer layers may be grown/polymerised on the surface (grown-on, chaingrowth, step-grown, multi-step grown). Alternatively, the polymer layers may be formed and then bound to the substrate surface. This can be accomplished using for example click chemistry such as azide-alkyne.

[0090] In scheme 1 below is described a specific example of a method of producing a functionalized graphene structure having a first polymer layer 2 consisting of a linear oligomer of 3 repeat units synthesized from 4,4'-Bis(4-aminophenoxy)biphenyl and terephthalic chloride and a first additional polymer layer 3 consisting of a 3rd generation hyperbranched oligomer, synthesized from TGIC (triglycidyl isocyanurate and bisphenol. On the second surface of the substrate is a second polymer layer 2 consisting of a linear oligomer of three repeat units synthesized from 4,4'-Bis(4-aminophenoxy)biphenyl and terephthalic chloride and a first additional polymer layer 3 consisting of a 3rd generation hyperbranched oligomer, synthesized from TGIC and bisphenol A. PMDA (Pyromellitic dianhydride) is attached as the terminal molecule. The functionalised structure obtained in the method is of the structure of Fig.lc. The end goal of the design is to produce first and second polymer layers, and first and second additional polymer layers on the graphene substrate that mimic other polymers such as polyamides, polycarbonates, and polyamides; in linear and branched form to obtain the properties of that family of polymers in a nanoscale and through this, contribute to the overall function and structure of the nanocomposite, family of polymers in a nanoscale and through this, contribute to the overall function and structure of the nanocomposite.

[0091] Scheme 1.

[0092] In step 1 the graphene substrate is changed into a graphene oxide (GO) substrate. In step 2 reactive groups, epoxy groups, are added to the graphite oxide surface. In step 2 the ratio of NaOHrHzO may be selected to have a pH of 9. The ratio of ECH (Epichlorohydrin) to GO may be selected based on the expected surface functionalisation. The weight fraction of GO in NaOHrHzO may be a ratio of 1.5 mg/ml. The ratio of the molecules in step 3-6 should be stoichiometrically selected and balanced based on the expected number of reaction sites expected in step 2. In step 3 i) the ratio would be 1:1 and in step 3 ii) the ratio would be 1:1. In step 4 TGIC (Triglycidyl isocyanurate) : NH-GO should be 1:1 and Bisphenol A : TGIC should be 2:1. In step 5, Bisphenol A to TGIC should be 2:1.

[0093] The steps can be repeated depending on the number of desired hyperbranched generations. The synthesis in step 4 and 5 can be performed together or separate in step-by- step synthesis, one-pot synthesis or pseudo-one-pot synthesis. The ratio of PMDA (Pyromellitic dianhydride) : OH-Go (Step 6) should be 1:1. After synthesis, the GO substrate can be reduced.

[0094] The first polymer layer and first additional polymer layer can also be synthesized by repeating monomers of di-heteroatomic groups with a linear or aromatic back bone such as a diisocyanate monomer (2,4-tolylene diisocyanate, 4,40-diphenylmethane diisocyanate) or a diamines monomer (4,4'-Thiodia niline, p-phenylenediamine, 4'4'-Diamino-3,3'- dimethyldiphenylmethane, 4,4'-methylenebis(2-ethyl-6-methylaniline), 4,4'-methylenebis (2,6-diethylaniline), 4,4'-(Hexafluoroisopropylidene)bis(p-phenyleneoxy)dianiline, ), and a corresponding diatomic binding molecule with an aromatic or linear backbone such as diphthalic anhydride (4,4'-Oxydiphthalic anhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride), diacid (Terephthalic acid), di-acyl chloride (Sebacoyl chloride, Terephthaloyl chloride), diglycidul (diglycidylterephthalate).

[0095] The first polymer layer and first additional polymer layer can also be synthesised using an AB-type difunctional monomer that can undergo a chain growth where terminal-A of a monomer can react with terminal-B of another monomer of the same family, such as an azide-alkyne difunctional monomer (3-azidopropyl pent-4-ynoate), or amine-carboxylic difunctional monomer (Amine PEG carboxylic acid hydrochloride).

[0096] The first polymer layer and first additional polymer layer can also be synthesized by AB2 type monomers such as triglycidyl monomer (triglycidyl isocyanurate, rimethylolpropane triglycidyl ether, tris(4-hydroxyphenyl)methane triglycidyl ether, trimethylolethane triglycidyl ether), trioctyl monomer (trioctyl trimellitate), triamine monomer (Melamine), isophthalic acid monomer (5-Amino Isophthalic Acid, 5-(3-amino-4-chloro-phenylsulfamoyl)-isophthalic acid), isophthalate (dimethyl 5-aminoisophthalate) and a corresponding di-atomic monomer binding molecule with a linear or aromatic back bone such as diisocyanate monomer (2,4-tolylene diisocyanate, 4,4-diphenylmethane diisocyanate), diamines monomer (4,4'-Thiodia niline, p- phenylenediamine, 4'4'-Diamino-3,3'-dimethyldiphenylmethane, 4,4'-methylenebis(2-ethyl-6- methylaniline), 4,4'-methylenebis (2,6-diethylaniline), 4,4'-(Hexafluoroisopropylidene)bis(p- phenyleneoxy)dianiline, ethylenediamine), diphthalic anhydride (4,4'-Oxydiphthalic anhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, 4,4'- (Hexafluoroisopropylidene)diphthalic anhydride), diacid (Terephthalic acid), di-acyl chloride (Sebacoyl chloride, Terephthaloyl chloride). [0097] The first polymer layer and first additional polymer layer can also be synthesised using an AB2-type difunctional monomer that can undergo a chain growth where terminal-A of monomer 2 and terminal-A of monomer 3 can react with the 2 terminals-B and B' of monomer 1 of the same family, forming a hyperbranched or highly branched structure, such as an AB2- type blocked isocyanate monomers (5-Amino Isophthalic Acid).

[0098] The second polymer layer and second additional polymer layer can also be synthesized by repeating monomers of di-heteroatomic groups with a linear or aromatic back bone such as a diisocyanate monomer (2,4-tolylene diisocyanate, 4,4-diphenylmethane diisocyanate) or a diamines monomer (4,4'-Thiodia niline, p-phenylenediamine, 4'4'-Diamino-3,3'- dimethyldiphenylmethane, 4,4'-methylenebis(2-ethyl-6-methylaniline), 4,4'-methylenebis (2,6-diethylaniline), 4,4'-(Hexafluoroisopropylidene)bis(p-phenyleneoxy)dianiline, ), and a corresponding diatomic binding molecule with an aromatic or linear backbone such as diphthalic anhydride (4,4'-Oxydiphthalic anhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride), diacid (Terephthalic acid), di-acyl chloride (Sebacoyl chloride, Terephthaloyl chloride), diglycidul (diglycidylterephthalate).

[0099] The second polymer layer and second additional polymer layer can also be synthesised using an AB-type difunctional monomer that can undergo a chain growth where terminal-A of a monomer can react with terminal-B of another monomer of the same family, such as an azide-alkyne difunctional monomer (3-azidopropyl pent-4-ynoate), or amine-carboxylic difunctional monomer (Amine PEG carboxylic acid hydrochloride).

[00100] The second polymer layer and second additional polymer layer can also be synthesized by AB2 type monomers such as triglycidyl monomer (triglycidyl isocyanurate, rimethylolpropane triglycidyl ether, tris(4-hydroxyphenyl)methane triglycidyl ether, trimethylolethane triglycidyl ether), trioctyl monomer (trioctyl trimellitate), triamine monomer (Melamine), isophthalic acid monomer (5-Amino Isophthalic Acid, 5-(3-amino-4- chloro-phenylsulfamoyl)-isophthalic acid), isophthalate (dimethyl 5-aminoisophthalate) and a corresponding di-atomic monomer binding molecule with a linear or aromatic back bone such as diisocyanate monomer (2,4-tolylene diisocyanate, 4,4-diphenylmethane diisocyanate), diamines monomer (4,4'-Thiodia niline, p-phenylenediamine, 4'4'-Diamino-3,3'- dimethyldiphenylmethane, 4,4'-methylenebis(2-ethyl-6-methylaniline), 4,4'-methylenebis (2,6-diethylaniline), 4,4'-(Hexafluoroisopropylidene)bis(p-phenyleneoxy)dianiline, ethylenediamine), diphthalic anhydride (4,4'-Oxydiphthalic anhydride, 3,3', 4,4'- benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, 4,4'- (Hexafluoroisopropylidene)diphthalic anhydride), diacid (Terephthalic acid), di-acyl chloride (Sebacoyl chloride, Terephthaloyl chloride).

[00101] The first polymer layer and first additional polymer layer can also be synthesised using an AB2-type difunctional monomer that can undergo a chain growth where terminal-A of monomer 2 and terminal-A of monomer 3 can react with the 2 terminals-B and B' of monomer 1 of the same family, forming a hyperbranched or highly branched structure, such as an AB2-type blocked isocyanate monomers (5-Amino Isophthalic Acid).

[00102] To obtain a functionalised graphene structure of Fig. la the second surface of graphene may be inactivated before the first surface of the graphene is functionalized. Such inactivation may take place by dispersing graphene in a two-phase Pickering emulsion, such as water and paraffin wax. Once graphene is stabilized on the interface between the phases, graphene stabled phase of the Pickering emulsion is extracted, such as wax coated with graphene. The phases of the Pickering emulsion are chosen based on the synthesis conditions such as temperature, pressure, and reactivity of the phases towards the solvents in the synthesis of first functional surface. After the synthesis, the second phase of the Pickering emulsion, on which graphene is dispersed is dissolved in the appropriate solvent. Later, the terminal group is attached onto the functionalised graphene.

[00103] To obtain a functionalised graphene structure of Fig. lb the second surface of graphene is inactivated, after the synthesis of first and second polymer layers, by dispersing graphene in a two-phase Pickering emulsion. Once graphene is stabilized on the interface between the phases, graphene stabled phase of the Pickering emulsion is extracted, such as wax coated with graphene. The phases of the Pickering emulsion are chosen based on the synthesis conditions such as temperature, pressure, and reactivity of the phases towards the solvents in the synthesis of first functional surface. After the synthesis, the second phase of the Pickering emulsion, on which graphene is dispersed is dissolved in the appropriate solvent. Later, the terminal group is attached onto the functionalised graphene.

[00104] To obtain a functionalised graphene structure of Fig.lc with dissimilar polymer layers on the first and second surface, the second surface of graphene is inactivated after step 3 by dispersed graphene in a two-phase Pickering emulsion. Once graphene is stabilized on the interface between the phases, graphene stabled phase of the Pickering emulsion is extracted, such as wax coated with graphene. The phases of the Pickering emulsion are chosen based on the synthesis conditions such as temperature, pressure, and reactivity of the phases towards the solvents in the synthesis of first functional surface. After the synthesis, the second phase of the Pickering emulsion, on which graphene is dispersed is dissolved in the appropriate solvent. Later, the desired second functional layer and second additional functional layer is attached onto the second functional surface, e.g., by method such as click reaction.

[00105] In this work wax was heated at 60 °C. Graphene is dispersed in deionized water of pH.5. After graphene was dispersed in water, wax is added to the acidic water and a shear mixer at an RPM of 5000 for 10 minutes to produce a Pickering emulsion. The Pickering emulsion can be used for performing reaction at room temperature.

[00106] In scheme 2 below is a specific example of a method of producing a functionalized graphene structure having a first polymer layer 2 consisting of hyperbranched polyethylene oxide and a first additional polymer layer 3 consisting of polyamide. On the second surface of the substrate is second polymer layer 2 consisting of hyperbranched polyethylene oxide and a second additional polymer layer 3 consisting of polyamide. Epoxide molecule is used as a terminal molecule.

[00107] In step 1 the graphene substrate is changed into graphene oxide substrate. In step 2 NaN3 : (3-Chloropropyl)triethoxysilane (CI-PTES) may be 2:1. The ratio of 3- (Azidopropyl)triethoxysilane (Az-PETS) : GO must be selected based on the desired number of click sites. An ideal ratio will be 10:1 respectively. In step 4 tBuOK (Potassium tert-butoxide) is added at 10% molar fraction of Hexane-l-ol. Similar to synthesis 1 above, the ratio of the molecules must be selected based on the number of reactive sites on the molecule.

[00108] The main difference between scheme 1 and scheme 2 is that scheme 2 is performed using click reaction. The structure is more uniformly gown before attaching onto graphene.

[00109] In step 1 of scheme 2 graphene is converted into graphene oxide. Later chloride silane is separately transformed into an azide silane. This step is important for the click reaction. The azide based silane is attached to the graphene. Hexane-l-ol, has an alkyne terminal that will react with azide to form an azide-alkyne Huisgen cycloaddition (step 5). In step 4 the glycidol reacts with the hydroxyl group on hexane-l-ol to undergo a continuous hyper branching reaction (1:2 growth). Step 4a and steep 4b can be combined but are in this example kept separate to control the growth. In step 4a, the glycidol molecules (ring opened, gen 1) are evenly distributed and then in 4b the growth for the generations (gen x, usually gen 4) are allowed. In step 5 cycloaddition is performed. In step 6, a polyamide is grown as an additional functional group (1st and 2nd).

[00110] Scheme 2 may be used for lower temp polymers where the thermal conditions of the extruder is not high. Scheme 1 may be used for high temp polymer processing.

[00111] This design would decompose at higher temperatures such as the one for PET. The polyethylene oxide (PEO is formed from hyperbranching of glycidol) would be the molecule to decompose. The PEO can be replaced by other hyperbranched molecules with a A2B structure and shorter chains to contribute to the nano void.

[00112] The synthesis of scheme 2 can be used to produce a nanocomposite with PETG (polyethylene terephthalate glycol).

[00113] Since the primary hyperbranched molecule is polyethylene oxide (PEO), the processing conditions (decomposition) are similar for PETG. Beyond those temperatures PEO will decompose.

[00114] The PEO will help produce a hyperbranched void and the PA oligomer will provide increased strength. Such a design will allow us to produce strings with voids that can be flexible and absorb energy, while the PA functional layer will help improve the strength.

[00115] This will allow us to avoid using another polymer to create a bi-filament string of PETG-PA. Thus, we shrink the PA into PETG, and create voids for energy absorption.

Scheme 2.

[00116] Since PETG is more flexible than PET, we are not trying to retain the flexibility but rather maintain an attainable strength, while creating the voids to improve energy absorption. [00117] This is a second example of a PA-PETG hybrid that is shrunk into one single microstructure.

[00118] The advantage is that we do not have to use different filaments, and so we save material, controlled distribution of polymers than using a copolymer, improved energy absorption and finally a monofilament single nanocomposite (reduce processing time, energy and machinery).

[00119] Attaching the polymers onto the graphene substrate would increase the structural accuracy of the polymer layers. When polymers are grown on the graphene substrate, the growth and average properties of the polymers would depend on the thermodynamics and growth kinetics. While this is a restriction, growing polymer layers on the graphene substrate is economical (time and money).

[00120] Nanocomposites are formed by mixing the polymer matrix and the functionalized graphene structure e.g. through melt blending in an extruder or through solution mixing. An amount of functionalized graphene structure in the nanocomposite may be 0.001 to 10 wt.% of the total weight of the nanocomposite.

[00121] In melt mixing, the functionalised graphene is distributed on the surface of the polymer matrix. It is done by wet coating on the surface. This is then introduced into an extruder and then the functional graphene binds to the polymer inside.

[00122] The functionalised graphene can be attached to polymer pellets in a solvent and then dried. For example to attach PMDA one would need a chemical such as m-cresol to open the anhydride. PET is soluble in m-cresol. Also use other solvents that are compatible with the polymer can be used.

[00123] In applications such as tennis strings, a PET string would be expected to absorb the impact of the tennis ball. Additionally, the string must be strong enough to not fracture during a game. In such a circumstance, the PET string is expected to undergo simultaneous compression (energy absorption) and improvement in material strength. To improve the properties of the PET material for the tennis string application, a functionalized graphene structure having the structure as illustrated in Fig. la, lb or lc may be incorporated in the PET matrix. At least one of the polymer layers of the structure comprises hyperbranched polymers, which provides voids that can absorb energy and undergo compression. This will also make the string stronger/more brittle, and so at least on polymer layer of the structure comprises linear polymers, which provide sufficient toughness and strength to the tennis string.

[00124] In one example of such a tennis string, the polymer matrix comprises polyethylene terephthalate and the functionalized graphene structure comprises a first polymer layer of linear oligomers of three repeat units synthesized from 4,4'-Bis(4- aminophenoxy)biphenyl and terephthalic chloride, and additional polymer layer of 3rd generation hyperbranched oligomer, synthesized from TGIC and bisphenol A. A second polymer layer of linear oligomers of 3rd repeat units were synthesized from 4,4'-Bis(4- aminophenoxy)biphenyl and terephthalic chloride and a second additional layer of a 3rd generation hyperbranched oligomer, synthesized from TGIC and bisphenol A. PMDA was attached as the terminal molecule. The synthesis was performed in the conditions presented in scheme 1 above. 0.5 g of graphene oxide was synthesized using modified Hummer's method, as shown in Step 1. Following step 1, 1 ml of ECH was introduced to 1.5 mg/ml of graphene oxide, dispersed in water of pH 9.8 in the same synthesis conditions as step 2 of synthesis 1. Following Step 2, 1:1 molar weight ratio of 4,4'-Bis(4-aminophenoxy)biphenyl to ECH and 1:1 molar weight ratio of terephthalic chloride to 4,4'-Bis(4-aminophenoxy)biphenyl, were introduced in step wise addition as shown in step 3 of synthesis 1. Step 3 of synthesis 1 was repeated 3 times. Later, 1:1 ratio of TGIC to 4,4'-Bis(4-aminophenoxy)biphenyl was introduced, as shown in step 4 of synthesis 1. Following step 4, bisphenol A was added at a molar ratio of 2:1 to TGIC, as shown in step 5 of synthesis 1. Step 4 and step 5 was repeated 3 times to produce a hyperbranched oligomer of 3 generations. Finally, PMDA was added to a ratio of 1:1 to the 3rd repetition of the molar mass of bisphenol A in step 5 of synthesis 1, as shown in Step 6 of synthesis 1. Finally, the functionalized graphene is extracted by centrifugation and dried in vacuum. After drying, 0.5 wt % functionalized graphene was deposited on the surface of 99.5 wt % PET. Functionalized graphene was dispersed in ethanol and coated on the surface of PET. The container was shaken until uniform distribution was attained. Later the container was dried at 60 °C for 12 hours to remove ethanol and potential hydration. The functionalized graphene coated PET was processed using a single screw extruder. The extruder was heated to 280 °C at the feeder and had a die exit temperature of 180 °C. The die diameter of the appropriate string thickness was used to produce the string. [00125] The aim of the tennis string design was to maintain sufficient strain for tennis strings, while improving strength and reducing stress relaxation.

[00126] Table 1 and Fig. 5 show a comparison of tensile test data from measurements of virgin PET and a nanocomposite comprising PET matrix with incorporated functionalized graphene structure produced as discussed above. In Fig. 5 is shown a stress-strain graph for such nanocomposite, line B in the graph, vs virgin PET, line A in the graph. Compared to the virgin PET, the nanocomposite showed an improvement of 40% in Young's Modulus, 56% increase in strength, 45.5% increase in Yield strength and a retained strain of 41%. [00127] Test Conditions used were: 2 kN Load Cell, Constant Strain (0.1/min), Sample side : 25 mm, Sample Conditioning : ASTM D638-14 /527-1. (American Society for Testing and

Materials. D638 is the protocol for performing tensile test on samples.)

Table 1. Material data of virgin PET vs PET with functionalized graphene structure

[00128] The PET underwent cold drawing/super plasticity during strain. Due to this the PET samples did not fracture during the measurements. Instead the final value was extrapolated from the data sheet at 2.5 strain.

[00129] The PET nanocomposite was also tested after fracture. When zooming into the fracture surface, see Fig. 6, regions of ductile and brille fractures could be seen with regions of elongations and local necking of the nanocomposite. The functionalized graphene structure can be seen as lighter contract. A good interface was seen to have formed between functionalized graphene structure and the PET matrix. Further the structure was seen at a region of elongation of the polymer/ the fracture interface. This indicates that the fracture took place at the interface where functionalized graphene structure resisted fracture during the tensile test. The image in Fig. 6 shows that there is a ductile fracture pattern. This means that the polymer was not made brittle due to mixing with the functionalized graphene.

Claims

28 CLAIMS

1. A functionalized graphene structure, comprising:

- a graphene substrate (1) having a first surface and a second surface;

- a first polymer layer (2) comprising polymers having a linear or branched chain architecture, the polymers of the first polymer layer being bound to the first surface of the graphene substrate with a first end thereof,

- a first additional polymer layer (3) comprising polymers having a linear or branched chain architecture, the polymers of the first additional polymer layer being covalently connected to the first polymer layer with a first end thereof and provided with a reactive terminal group (10) at a second end thereof, wherein the polymers of the first polymer layer (2) and the first additional polymer layer (3) are different.

2. The functionalized graphene structure of claim 1, wherein the second surface of the graphene substrate (1) is provided with reactive terminal groups (11).

3. The functionalized graphene structure of claim 1, comprising a second polymer layer (4) comprising polymers having a linear or branched chain architecture, the polymers being bound to the second surface of the graphene substrate (1) with a first end thereof, and being provided with a reactive terminal group (10) at a second end thereof.

4. The functionalized graphene structure of claim 1, comprising a second polymer layer (4) comprising polymers having a linear or branched chain architecture, the polymers being bound to the second surface of the graphene substrate (1) with a first end thereof, a second additional polymer layer (5) comprising a polymer having a linear or branched chain architecture, the polymers of the second additional polymer layer (5) being covalently connected to the second polymer layer (4) with a first end thereof and provided with a reactive terminal group (10) at a second end thereof, wherein the polymers of the second polymer layer (4) and the second additional polymer layer (5) are different.

5. The functionalized graphene structure of any of claims 1-4, wherein the polymers of a polymer layer are selected from thermoplastics, thermosets and elastomers.

6. The functionalized graphene structure of claim 5, wherein the polymer of a polymer layer is an ester, ether, amide, carbonate, urethane, styrene or methyl acrylate.

7. The functionalized graphene structure of any of claims 1 to 6, wherein the reactive terminal group (10, 11) is selected from one or more of hydroxyl, carboxyl, thiol, epoxy, amine, amide, methyl, vinyl, benzophenone, and azo.

8. The functionalized graphene structure of any of claims 3-6, wherein the second polymer layer (4) comprises polymers that are different from the first polymer layer (2) and/or the second additional polymer layer (5) comprises polymers that are different from the first additional polymer layer (3).

9. The functionalized graphene structure of any of claims 1-8, wherein the graphene substrate (1) is in the shape of spheres, sheets, rods and/or dots.

10. A nanocomposite comprising the functionalized graphene structure of any of claims 1- 9 dispersed in a polymer matrix (Ml, M2) comprising matrix polymers selected from one or more of thermoplastics, thermosets and elastomers.

11. The nanocomposite of claim 10, wherein the polymer matrix (Ml, M2) comprises matrix polymers selected from esters, ethers, amides, carbonates, urethanes, styrenes and/or methyl acrylates.

12. The nanocomposite of claim 10 or 11, wherein the functionalized graphene structure and the polymer matrix (Ml, M2) comprises the same polymer. The nanocomposite of claim 10 or 11, wherein the polymer matrix (Ml, M2) comprises a matrix polymer different from the polymers of the functionalized graphene structure. The nanocomposite of any of claims 10-13, wherein an amount of functionalized graphene structure in the nanocomposite is 0.001 to 10 wt.% of the total weight of the nanocomposite. Method of producing a functionalized graphene structure, comprising:

- providing a graphene substrate (1) having a first and a second surface,

- activating the first and optionally the second surface of the substrate,

- arranging a first polymer layer (2) on the first surface of the substrate, the first polymer layer comprising polymers having a linear or branched chain architecture, the polymers of the first polymer layer (2) being bound to the first surface of the graphene substrate (1) with a first end thereof, and

- arranging a first additional polymer layer (3) on the first polymer layer (2), the first additional polymer layer comprising polymers having a linear or branched chain architecture, wherein the polymers of the first additional polymer layer (3) are different from the polymers of the first polymer layer (2), the polymers of the first additional polymer layer being covalently connected to the first polymer layer with a first end thereof and provided with a reactive terminal group (10) at a second end thereof, and optionally

- providing the second surface of the graphene substrate (1) with reactive terminal groups (11), or

- arranging a second polymer layer (4) on the second surface of the substrate (1), the second polymer layer comprising polymers having a linear or branched chain architecture, the polymers of the second polymer layer (4) being bound to the second surface of the graphene substrate with a first end thereof, and being provided with a reactive terminal group (10) at a second end thereof, or

- arranging a second polymer layer (4) on the second surface of the substrate (1), the second polymer layer comprising polymers having a linear or branched chain architecture, the polymers of the second polymer layer (4) being bound to the second surface of the graphene substrate with a first end thereof, and - arranging a second additional polymer layer (5) on the second polymer layer (4), the second additional polymer layer comprising polymers having a linear or branched chain architecture, wherein the polymers of the second additional polymer layer (5) are different from the polymers of the second polymer layer (4), the polymers of the second additional polymer layer (5) being covalently connected to the second polymer layer (4) with a first end thereof and provided with a reactive terminal group (10) at a second end thereof. Method of producing a nanocomposite, comprising providing a polymer matrix (Ml, M2), producing a functionalized graphene structure according to the method of claim 15, and mixing the polymer matrix (Ml, M2) and the functionalized graphene structure, forming the nanocomposite.