Use of graphene to increase the glass transition temperature of a thermosetting resin

Abstract

The subject of the invention is the use of graphene sheets for increasing the glass transition temperature of a material comprising at least one thermosetting resin, as well as a method for increasing the glass transition temperature of a material comprising at least one thermosetting resin.

Description

Title of the invention: Use of graphene to increase the glass transition temperature of a thermosetting resin Technical field

[0001] The present invention relates to the technical field of graphene and its various applications. The invention relates in particular to the use of a particular graphene for increasing the glass transition temperature of a thermosetting resin. The invention also relates to a method for increasing the glass transition temperature of a thermosetting resin using said graphene. State of the art

[0002] Thermosetting resins are polymers which, once hardened by heat treatment, cannot change state, unlike thermoplastic resins, which can be softened and reformed repeatedly by heat treatment.

[0003] These resins are of considerable interest in many fields due to their properties, including their heat resistance, rigidity, chemical resistance and stability.

[0004] Thermosetting resins find applications in many industries such as automotive, aerospace, electronics, and construction. In particular, they are very useful in high-temperature environments where other materials might degrade or lose their properties.

[0005] A key parameter for these high-temperature applications is the glass transition temperature (Tg) of the resin. The Tg is the temperature at which a polymer changes from a rigid glassy state to a more flexible rubbery state. The higher the Tg, the more the resin can withstand high temperatures without losing its mechanical properties.

[0006] Thus, for certain applications, such as the manufacture of composites for aerospace or for certain printed circuits for electronics, it is desirable to have a high Tg to ensure the stability and performance of the material at high temperatures.

[0007] Increasing the Tg of thermosetting resins is an area of ​​active research and development and promises to open up new possibilities for these materials.

[0008] To meet this need, certain prior art documents describe the use of functionalized graphene, such as graphene functionalized by a amine (US20210363328) or carboxylated graphene (CN110885419) to increase the glass transition temperature of thermosetting resins.

[0009] Graphene is a crystalline two-dimensional material composed of carbon atoms arranged in a hexagonal pattern, forming a sheet. Functionalized graphene is a modified form of graphene. Functionalization involves the addition of functional groups to the structure of graphene to modify its properties. These functional groups can be added by various chemical methods, allowing graphene to bind to other substances or change its properties. For example, graphene can be functionalized to improve its solubility in water or to give it specific properties such as thermal or electrical conductivity.

[0010] However, there are several drawbacks to using these types of functionalized graphene. The production of functionalized graphene can be expensive, thus increasing the overall cost of the thermosetting resin.

[0011] Furthermore, the increase in Tg remains dependent on the amount of functionalized graphene added to the resin. Thus, the effectiveness of the increase in Tg can vary depending on the amount of functionalized graphene used, thus making it difficult to control and reproduce this parameter. On the other hand, the amount of functionalized graphene required to generate a satisfactory increase in Tg remains too high, thus considerably increasing the cost price of thermosetting resins comprising functionalized graphene.

[0012] Document CN113337082 describes the use of non-functionalized graphene, resolving some of the drawbacks associated with the use of functionalized graphene. However, the increase in Tg following the use of graphene from document CN113337082 still remains dependent on the quantity added to the resin.

[0013] Furthermore, the solutions of the prior art, although effective in increasing the Tg, do not resolve the problems linked to the use of thermoset sand resin.

[0014] For example, graphene as described in the prior art documents has poor dispersibility. Indeed, graphene has a hydrophobic nature and tends to form aggregates due to the strong interactions between the graphene sheets. Poor dispersion can lead to uneven distribution of the graphene in the resin, which can affect the final properties of the resin and therefore the Tg.

[0015] Furthermore, the addition of additives generally causes a change in the viscosity of the thermosetting resin, making the use of said resin difficult.

[0016] There is therefore a need to develop alternative solutions making it possible to increase the glass transition temperature of thermosetting resins while resolving the drawbacks of the prior art. Summary of the invention

[0017] To meet this need, the invention proposes to increase the glass transition temperature of a thermosetting resin by using at least one graphene sheet having: - an average thickness of less than 3nm; and - an average lateral size of between 0.1 and 6pm.

[0018] The inventors have surprisingly discovered that the use of graphene comprising at least one sheet having an average thickness of less than 3 nm and an average lateral size of between 0.1 and 6 pm makes it possible to significantly increase the Tg of a material comprising a thermosetting resin while overcoming all the drawbacks of the prior art. Indeed, the specific characteristics of the graphene sheets (thickness and lateral size) used make it possible to guarantee in particular that the graphene has satisfactory dispersibility in thermosetting resins in comparison with existing solutions, while making it possible to increase the mechanical properties of the resin, such as in particular hardness, tensile strength, elongation.

[0019] According to a preferred embodiment, the graphene has a concentration of less than 0.1% by weight of the weight of the material, i.e. of the total weight of the material consisting of the thermosetting resin(s), the graphene and any other elements constituting it. In other words, the graphene used to increase the Tg of a thermosetting resin is present at a mass concentration of less than 0.1% by weight of the total weight of the material.

[0020] Advantageously, the increase in the glass transition temperature of the material comprising at least one thermosetting resin is not dependent on the quantity of graphene used in the context of the invention. On the other hand, the variation in the graphene concentration in the resin can have an impact on other properties of the resin such as its mechanical properties or electrical conductivity or thermal conductivity properties. Consequently, the use of at least one graphene sheet having an average thickness of less than 3 nm and an average lateral size of between 0.1 and 6 pm has numerous advantages, namely: * limit the impact of graphene on the viscosity of the material and therefore facilitate its use; * offer greater flexibility in the formulation of the thermosetting resin. Indeed, the presence of a low proportion of graphene leaves the possibility of adding other additives that could potentially improve other properties of the resin; *reduce the manufacturing cost of thermosetting resin with improved Tg.

[0021] The graphene used according to the invention is constituted by at least one sheet having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm, but it may be constituted by at least several sheets having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm. Preferably, the graphene is constituted by between 1 and 200 graphene sheets having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm, even more preferably between 1 and 100, between 1 and 30, between 1 and 20, between 1 and 15, between 1 and 11, between 1 and 10 sheets having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm.

[0022] According to another variant, the graphene used according to the invention comprises several graphene sheets, at least one of which has an average thickness of less than 3 nm and an average lateral size of between 0.1 and 6 pm.

[0023] According to the invention, the material in which the graphene is added comprises a thermosetting resin or consists exclusively of a thermosetting resin.

[0024] According to a preferred object, the material in which the graphene according to the invention is added comprises at least one thermosetting resin which is an epoxy resin. Preferably the material comprises at least one epoxy resin comprising diglycidyl ether of bisphenol A.

[0025] Advantageously, the use of graphene sheets having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm is particularly suitable in epoxy resins.

[0026] According to another aspect, the invention relates to a method for increasing the Tg of a material comprising a thermosetting resin, having a transition temperature TgO, comprising the implementation of the following steps: - (1) preparation or recovery of graphene comprising at least one sheet having: -an average thickness less than 3nm; - an average lateral size between 0.1 and 6pm. - (2) mixing the graphene of step (1) with at least one thermosetting resin, - (3) mixing the step (2) with a hardener and / or an accelerator and / or additives as described in the present application to obtain a thermosetting resin material with a Tgl greater than TgO.

[0027] Preferably, step (1) consists of preparing a liquid dispersion of graphene, and comprises the implementation of the following steps: a) Solubilization of graphite in a solvent, preferably an aprotic polar solvent, carried out under an inert atmosphere so as to obtain a graphene solution; b) Oxidation of the graphene solution obtained in step a) to obtain an organic dispersion of graphene; c) Transfer of the organic graphene dispersion into a matrix forming a liquid graphene dispersion; and d) Evaporation and / or distillation of the solvent.

[0028] Other characteristics and advantages will emerge from the detailed description of the invention, the examples and the figures which follow. Brief description of the drawings

[0029] [Fig.l] [Fig.l] is a graphical representation of the glass transition temperature results of an Epikote 827 resin with an Aradur HY5052 hardener, in which a graphene according to the invention was used according to a DSC1 (1st cycle of temperature increase from -50°C to 150°C or 180°C or 250°C at 10°C / min under 50mL / min N2), as a function of the mass concentration of graphene (concentration by weight relative to the total weight of the material).

[0030] [Fig.2] [Fig.2] is a representation of the glass transition temperature results of an Epikote 827 resin with an Epikure 340 hardener, in which a graphene according to the invention was used according to a DSC1 (1st cycle of temperature increase from -50°C to 150°C or 180°C or 250°C at 10°C / min under 50mL / min N2), as a function of the mass concentration of graphene (concentration by weight relative to the total weight of the material).

[0031] [Fig.3] [Fig.3] is a representation of the glass transition temperature results of an Epikote 834 resin with an Epikure 340 hardener, in which a graphene according to the invention was used according to a DSC1 (1st cycle of temperature increase from -50°C to 150°C or 180°C or 250°C at 10°C / min under 50mL / min N2), as a function of the mass concentration of graphene (concentration by weight relative to the total weight of the material).

[0032] [Fig.4] [Fig.4] is a representation of the glass transition temperature results of a LY564 resin with an Aradur HY2954 hardener, in which a graphene according to the invention was used according to a DSC1 (1st cycle of temperature increase from -50°C to 150°C or 180°C or 250°C at 10°C / min under 50mL / min N2), as a function of the mass concentration of graphene (concentration by weight relative to the total weight of the material).

[0033] [Fig.5] [Fig.5] is a representation of the glass transition temperature results of an Epikote 827 resin with an Aradur HY5052 hardener, in which a graphene according to the invention was used according to DSC2 (2nd cycle of temperature increase from -50°C to 150°C or 180°C or 250°C at 10°C / min under 50mL / min N2, the sample having already undergone the 1st temperature increase and cooling from 150°C or 180°C or 250°C to -50°C at 20°C / min under 50mL / min N2.), depending on the mass concentration of graphene (concentration by weight relative to the total weight of the material).

[0034] [Fig.6] [Fig.6] is a representation of the transition temperature results vitreous of an Epikote 827 resin with an Epikure 340 hardener, in which a graphene according to the invention was used according to DSC2 (2nd cycle of temperature increase from -50°C to 150°C or 180°C or 250°C at 10°C / min under 50mL / min N2, the sample having already undergone the 1st temperature increase and cooling from 150°C or 180°C or 250°C to -50°C at 20°C / min under 50mL / min N2.), depending on the mass concentration of graphene (concentration by weight relative to the total weight of the material).

[0035] [Fig.7] [Fig.7] is a representation of the transition temperature results vitreous of an Epikote 834 resin with an Epikure 340 hardener, in which a graphene according to the invention was used according to DSC2 (2nd cycle of temperature increase from -50°C to 150°C or 180°C or 250°C at 10°C / min under 50mL / min N2, the sample having already undergone the 1st temperature increase and cooling from 150°C or 180°C or 250°C to -50°C at 20°C / min under 50mL / min N2.), depending on the mass concentration of graphene (concentration by weight relative to the total weight of the material). Detailed description of the invention

[0036] Definitions:

[0037] By "aggregate" within the meaning of the invention, we mean an agglomerated structure formed of several graphene sheets in the 3 directions of space, the size of which is large compared to the dimensions of the graphene sheet.

[0038] For the purposes of the invention, the term "inert atmosphere" means a gas or a mixture of gases which does not promote the re-oxidation of the reduced graphene planes into neutral graphene planes. The method according to the invention can thus be carried out under an argon or nitrogen atmosphere.

[0039] For the purposes of the invention, the term “graphite intercalation compound” means a compound comprising at least two individual negatively or positively charged graphene planes intercalated by positive or negative counterions. Graphite alkali salts are a particular case of graphite intercalation compounds where the graphene planes are negatively charged and the counterions are alkali ions. They can be formed by intercalation of at least one alkali metal into graphite.

[0040] For the purposes of the invention, the term "atomic layer" means a layer composed in one direction of space of a single atom. A graphene sheet is constituted by at least one atomic layer.

[0041] By "without aprotic polar solvent" within the meaning of the invention, it is meant that the aqueous dispersion of graphene contains less than 0.1% of aprotic polar solvent.

[0042] For the purposes of the invention, the term “graphene solution” means a solution comprising negatively charged graphene sheets.

[0043] By "RAMAN spectrophotometry" within the meaning of the invention, we mean a non-destructive vibrational spectroscopy method which makes it possible to determine the molecular composition and the external structure of a material.

[0044] By "stable" in the sense of the invention, it is meant that the liquid dispersion of graphene does not contain any aggregate. Thus, destabilization phenomena such as creaming or sedimentation do not occur over time, in particular for at least 3 months.

[0045] By "dispersibility" of X in Y within the meaning of the invention is meant the capacity of X to be able to be dispersed in Y. Good dispersibility of X in Y corresponds to a uniform distribution of X in Y. According to the invention, the particular graphene selected for the use according to the invention has satisfactory dispersibility in thermosetting resins, that is to say that the particular graphene selected according to the invention is distributed uniformly in the thermosetting resins, unlike the graphenes proposed in the prior art. The dispersibility can be evaluated by any means known to those skilled in the art, in particular visually.

[0046] By "without impacting the viscosity" of a formulation, within the meaning of the invention, is meant a variation in the dynamic viscosity of less than 10% for the same temperature and the same shear between a formulation with and without graphene according to the invention.

[0047] For the purposes of the invention, the term “hardener” means a substance used to initiate and / or control the setting of a synthetic resin.

[0048] For the purposes of the invention, the term "accelerator" means a substance that allows a synthetic resin to set more quickly.

[0049] Uses

[0050] The present invention therefore relates to the use of at least one graphene sheet having: - an average thickness of less than 3nm; and - an average lateral size of between 0.1 and 6pm, in a material comprising at least one thermosetting resin, to increase the glass transition temperature of said thermosetting resin.

[0051] According to a preferred embodiment, the invention aims at the use of at least one sheet having an average thickness of less than 3nm, and an average lateral size of between 0.1 and 6pm, to increase the Tg of a thermosetting resin by at least 10°C, preferably at least 20°C. Preferably, the invention aims at the use of at least one sheet having an average thickness of less than 3nm, and an average lateral size of between 0.1 and 6pm, to increase the Tg of a thermosetting resin between 10°C and 50°C, preferably between 10°C and 40°C, between 20°C and 50°, between 20°C and 40°C, between 20 and 30°C.

[0052] The graphene used according to the invention to increase the glass transition temperature in a thermosetting resin is constituted by at least one sheet having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm.

[0053] The graphene used to increase the glass transition temperature in a thermosetting resin according to the invention may comprise or be constituted by one or more graphene sheets, one or more of which have an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm.

[0054] According to a variant, all the sheets constituting the graphene used to increase the glass transition temperature of a thermosetting resin according to the invention have an average thickness of less than 3 nm and an average lateral size of between 0.1 and 6 pm.

[0055] According to another variant, a portion of the sheets constituting the graphene used to increase the glass transition temperature of a thermosetting resin according to the invention have an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm.

[0056] Preferably, the graphene used according to the invention to increase the glass transition temperature of a thermosetting resin is constituted by between 1 and 200 graphene sheets, even more preferably between 1 and 100, between 1 and 30, between 1 and 20, between 1 and 15, between 1 and 11, between 1 and 10 graphene sheets, at least one of which has an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm.

[0057] Preferably, the graphene used according to the invention to increase the glass transition temperature of a thermosetting resin is made up of between 1 and 200 graphene sheets having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm, even more preferably between 1 and 100 having an average thickness of less than 3nm. and an average lateral size of between 0.1 and 6pm, between 1 and 30 having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm, between 1 and 20 having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm, between 1 and 15 having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm, between 1 and 11 having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm, between 1 and 10 sheets having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm.

[0058] The thickness and the average lateral size of the graphene sheets are parameters whose measurement methods are well known to those skilled in the art. In the context of the invention, the thickness of each graphene sheet can be measured, for example, using an atomic force microscope. The lateral size of the graphene sheets can be measured, for example, using a transmission electron microscope.

[0059] Advantageously, the particular characteristics of the graphene sheets used in the context of the invention make said sheets particularly suitable for increasing the Tg of a thermosetting resin.

[0060] Preferably, the graphene used in the context of the invention comprises at least one sheet having a thickness of less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers, less than 2 atomic layers.

[0061] According to a variant, all the sheets constituting the graphene used to increase the glass transition temperature of a thermosetting resin according to the invention have an average thickness of less than 3 nm and an average lateral size of between 0.1 and 6 pm.

[0062] According to another variant, a portion of the sheets constituting the graphene used to increase the glass transition temperature in a thermosetting resin according to the invention have an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm.

[0063] The graphene used to increase the glass transition temperature in a thermosetting resin according to the invention may comprise or be constituted by one or more graphene sheets, one or more of which have a thickness of less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers, less than 2 atomic layers.

[0064] According to a variant, all the sheets constituting the graphene used to increase the glass transition temperature of a thermosetting resin according to the invention have a thickness of less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers, less than 2 atomic layers.

[0065] According to another variant, a portion of the sheets constituting the graphene used to increase the glass transition temperature of a thermosetting resin according to the invention have a thickness of less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers, less than 2 atomic layers.

[0066] Preferably, the graphene used according to the invention to increase the glass transition temperature of a thermosetting resin is constituted by between 1 and 200 graphene sheets, even more preferably between 1 and 100, between 1 and 30, between 1 and 20, between 1 and 15, between 1 and 11, between 1 and 10 graphene sheets, at least one of which has a thickness of less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers, less than 2 atomic layers.

[0067] Preferably, the graphene used according to the invention to increase the glass transition temperature of a thermosetting resin is constituted by between 1 and 200 graphene sheets having a thickness of less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers, less than 2 atomic layers, even more preferably between 1 and 100 having a thickness of less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers, less than 2 atomic layers, between 1 and 30 having a thickness of less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers, less than 2 atomic layers,between 1 and 20 having a thickness less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers, less than 2 atomic layers, between 1 and 15 having a thickness less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers, less than 2 atomic layers, between 1 and 11 having a thickness less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers, less than 2 atomic layers, between 1 and 10 sheets having a thickness less than 10 atomic layers, even more preferably less than 5 atomic layers, less than 4 atomic layers, less than three atomic layers,less than 2 atomic layers. ,

[0068] Advantageously, the fewer atomic layers the sheets comprise, the greater the performance of the graphene in the material, in particular the performance in increasing the Tg.

[0069] According to the invention, graphene is used in a material comprising a thermosetting resin. In addition to the thermosetting resin, the material may comprise other constituents, in particular at least one hardener and / or at least one accelerator and / or one or more other additives. Preferably, the material comprises at least one thermosetting resin and at least one hardener.

[0070] Thus the material comprising at least one thermosetting resin in which graphene is added for the use according to the invention, comprises: - one or more thermosetting resin(s), - one or more graphene sheets, - optionally one or more hardener(s) such as for example polyamines (IPDA, TETA, ...), diamides, phenol and acid, - optionally one or more accelerator(s); such as for example the following molecules: Imidazoles (2 Ethyl 4 Methyl Imidazole, 4 Methyl 2 phenylimidazole, 1 cyanoethyl 2 Ethyl 4 Methylimidazole, imidazole, 2 Methyl Imidazole). - possibly one or more other additive(s), such as for example one or more additives chosen from carbon black, thermoplastics (polybutadiene for example), metal particles), foaming agents, anti-foaming agents.

[0071] The thermosetting resins of the materials according to the invention can be any thermosetting resins, in particular epoxy resins, polyurethane resins, polyesters, vinylesters.

[0072] According to one embodiment, the thermosetting resin is an epoxy resin, preferably an epoxy resin comprising bisphenol A diglycidyl ether.

[0073] The dispersion of graphene in the material can be visualized in particular by infrared mapping. The dispersion in the material of the graphene specifically used according to the invention is homogeneous.

[0074] Advantageously, the graphene used in the context of the invention makes it possible to generate a significant increase in the Tg of a thermosetting resin, even when used at a very low concentration, thus limiting the production costs of such a resin. Advantageously, the increase in the Tg is not dependent on the quantity or concentration of the particular graphene according to the invention used. A concentration of graphene sheets having an average thickness of less than 3 nm and an average lateral size of between 0.1 and 6 pm of 0.001% by weight of the total weight of the thermosetting resin is sufficient to increase the Tg significantly. However, it may be advantageous in certain cases to increase the concentration of graphene used in the thermosetting resin. to modify other characteristics of the resin such as mechanical properties such as tensile strength, hardness, elongation or contraction for example, or to give the resin other properties such as electrical conductivity or thermal conductivity properties.

[0075] According to one embodiment, the particular graphene used in the context of the invention is used at a concentration less than or equal to 10% by weight of the weight of the thermosetting resin, preferably less than or equal to 5%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, less than or equal to 0.1%.

[0076] According to one embodiment, the particular graphene used in the context of the invention represents a concentration less than or equal to 0.1% by weight of the total weight of the final material comprising the thermosetting resin, the total weight of the final material corresponding to the weight of the thermosetting resin(s), graphene sheets and any other constituents of the material such as for example a hardener and / or an accelerator and / or one or more other additives.Preferably, the particular graphene used according to the invention is used to be present at a concentration of between 0.001 and 0.1%, more preferably between 0.001 and 0.01% by weight of the total weight of the final material comprising the thermosetting resin, the total weight of the final material corresponding to the weight of the thermosetting resin(s), graphene sheets and any other constituents of the material such as for example a hardener and / or an accelerator and / or one or more other additives.

[0077] Advantageously, the concentrations of graphene used according to the invention do not modify the viscosity of the thermosetting resin and / or of the material comprising the thermosetting resin.

[0078] According to another advantage, the increase in Tg by graphene in the context of the invention is reproducible and does not depend on other uncontrolled parameters. Thus, the use of at least one graphene sheet having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm makes it possible to guarantee a significant and reproducible increase in the Tg of a thermoset resin.

[0079] Once the resin has hardened, in the final material comprising the thermosetting resin, the specific graphene used according to the invention is dispersed homogeneously in the material. Also, the subject of the invention is a material comprising at least one thermosetting resin and at least one graphene sheet having: - an average thickness of less than 3nm; and - an average lateral size of between 0.1 and 6pm.

[0080] The invention also relates to a material comprising at least one thermosetting resin and graphene in the form of one or more graphene sheets having: - an average thickness of less than 3nm; and - an average lateral size of between 0.1 and 6pm, characterized in that the graphene is present in the material at a concentration of between 0.001 and 0.1%, preferably between 0.001 and 0.01% by weight of the total weight of the material.

[0081] According to one embodiment, the graphene sheets used in the context of the invention are not functionalized. In other words, the graphene sheets used have not undergone any chemical transformation aimed at adding a functional group to improve their properties. According to one variant, if several graphene sheets are used, at least one graphene sheet is not functionalized. According to another variant, if several graphene sheets are used, none of the graphene sheets used according to the invention is a functionalized graphene sheet.

[0082] The graphene sheets useful according to the invention, having an average thickness of less than 3 nm and an average lateral size of between 0.1 and 6 pm, can be obtained by any method known from the state of the art making it possible to obtain sheets with such characteristics. They can in particular be obtained by the Hummer method, by mechanical exfoliation or chemical exfoliation. Preferably, they are obtained by implementing a method comprising the following steps carried out under an inert atmosphere: (a) Intercalation of at least one alkali metal into graphite, resulting in a graphite intercalation compound; and b) Chemical exfoliation combined with mechanical exfoliation of the graphite intercalation compound, characterized in that the graphite intercalation compound is mixed with a solvent in a turbulent regime having: - a Reynolds number greater than 1000; - a Froude number less than 1; and - a shear rate less than 400s1, -so as to obtain a graphene solution.

[0083] According to one embodiment, the graphene sheets useful according to the invention, having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm, are obtained according to, for example, in a non-limiting manner, a method described in application FR2302670 or a method described in patent FR0705803.

[0084] The graphene useful according to the invention, namely at least one sheet having an average thickness of less than 3nm and an average lateral size of between 0.1 and 6pm, may be in any form suitable for use in a thermosetting resin, for example in the form of a liquid graphene dispersion, a graphene paste or a graphene powder.

[0085] Preferably, the graphene used in the context of the invention is in the form of a liquid dispersion of graphene, the liquid in which the graphene is dispersed being able to be water or any other matrix in which the graphene can be dispersed. It is preferably a stable dispersion, preferably for a period of at least 3 months from its obtaining, that is to say that the aqueous dispersion of graphene does not have any aggregates, in particular no aggregates resulting from the reaggregation of the graphene sheets, for at least 3 months from its obtaining.

[0086] According to one embodiment, the graphene used according to the invention is in the form of an aqueous dispersion of graphene having an absorption spectrum comprising a peak at 269 nm. The absorbance can be measured using a UV spectrophotometer. UV spectroscopy is one of the techniques used according to the invention to guarantee the absence of aggregates. Advantageously, the presence of a peak at 269 nm is a parameter describing the presence of graphene. It is thus an indicator of the quality of the dispersion demonstrating that the solution contains graphene and not graphite or oxidized graphene. Thus the presence of a peak at 269 nm is an indirect indicator of the stability of the aqueous dispersion of graphene.

[0087] Preferably, the invention relates to the use of an aqueous dispersion of graphene having an absorption spectrum not comprising a peak at 230nm. Indeed, the presence in the absorption spectrum of a peak at 230nm is significant of the presence of graphene oxide.

[0088] The aqueous dispersion of graphene useful according to the invention can be characterized using 3 vibrational bands observed by RAMAN spectrophotometry, namely: - 1350 cm-1 (peak D); - 1580 cm-1 (peak G); and - between 2680 and 2700 cm-1 (2D peak).

[0089] These three peaks are characteristic of a graphitic signature.

[0090] Thus, according to a particularly preferred embodiment, the aqueous dispersion of graphene useful according to the invention comprises 3 vibrational bands observed by RAMAN spectrophotometry: - 1350 cm-1 (peak D); - 1580 cm-1 (peak G); and - between 2680 and 2700 cm-1 (2D peak).

[0091] The presence of peak D is representative of a disorder or defect (sp3) in the graphene dispersion. The presence of peak G is representative of the presence of graphene (sp2 vibration in the plane). Finally, the presence of the 2D peak is representative of the number of layers. When the 2D peak is thin, symmetrical and intense, it is a single-sheet. When the 2D peak is broad, with a shoulder and of low intensity, it is graphite.

[0092] Thus, the intensity of the vibrational bands of the aqueous graphene dispersion can be used to define the stability of said dispersion.

[0093] According to one embodiment, the aqueous dispersion of graphene comprises: - a peak intensity ratio D / peak intensity G less than 1.5; and - a 2D peak intensity / G intensity ratio greater than 1.

[0094] According to another embodiment, the invention aims at the use for increasing the Tg of a thermosetting resin, of an aqueous dispersion of graphene comprising: - a peak D with a width at half-height of less than 33 cm-1; and / or - a 2D peak with a width at mid-height less than 55cm-1, preferably less than 50cm-1.

[0095] Advantageously, the intensity and the width at half-height of the vibrational bands make it possible to demonstrate the quality of the graphene present in the dispersion.

[0096] Preferably, the invention aims at the use for increasing the Tg of a thermosetting resin of an aqueous dispersion of graphene having a conductivity of less than 5000 pS / cm, preferably less than 2500 pS / cm, in particular less than 1000 pS / cm, even more preferably less than 200 pS / cm.

[0097] The pH of the aqueous dispersion of graphene according to the invention is preferably between 7.5 and 9.

[0098] UV spectroscopy, RAMAN spectrophotometry, conductivity and pH are parameters that can be measured over time to show the stability and / or quality of the aqueous graphene dispersion according to the invention.

[0099] According to one embodiment, the graphene used in the context of the invention to increase the Tg of a thermosetting resin is in the form of a liquid dispersion of graphene obtained by a method comprising the implementation of the following steps: 1) Solubilization of graphite in a solvent, such as an aprotic polar solvent, carried out under an inert atmosphere so as to obtain a graphene solution; 2) Oxidation of the graphene solution obtained in step b) to obtain an organic dispersion of graphene; 3) Transfer of the organic graphene dispersion into a viscous matrix forming a liquid graphene dispersion; and 4) Evaporation and / or distillation of the solvent, so that the graphene dispersion is without polar aprotic solvent.

[0100] Method for increasing the glass transition temperature of a thermoset sand resin

[0101] The invention also relates to a method for increasing the Tg of a thermoset sand resin.

[0102] In particular, the invention relates to a method for increasing the glass transition temperature of a material comprising at least one thermosetting resin, comprising the implementation of the following steps: - (1) preparation or recovery of graphene comprising at least one sheet having: -an average thickness less than 3nm; - an average lateral size between 0.1 and 6pm. - (2) mixing the graphene from step (1) with at least one thermosetting resin having a TgO (TgO is the reference Tg of the material comprising the resin without graphene), - (3) mixing step (2) with a hardener and / or an accelerator and / or additives as described in the present application to obtain a thermosetting resin material with a Tgl greater than TgO.

[0103] Preferably, the graphene prepared or recovered in step (1) is a liquid dispersion of graphene comprising at least one sheet having: -an average thickness less than 3nm; - an average lateral size between 0.1 and 6pm.

[0104] Step (2) is preferably carried out under the following conditions: - Duration between 30 minutes and 15 hours, and / or - Temperature between 30°C and 70°C, at a constant temperature or with temperatures that can vary over the duration of the mixing, and / or - With stirring, preferably with mechanical stirring, preferably between 75 and 250 revolutions per minute, and / or - Graphene being added to the resin at a concentration less than or equal to 10% by weight of the weight of the thermosetting resin, preferably less than or equal to 5%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, less than or equal to 0.1%.

[0105] All the characteristics described for the products and processes in the part relating to the uses of the present application can also be applied to the process for increasing the Tg of a thermosetting resin.

[0106] According to a variant, step (1) of the method according to the invention comprises the implementation of the following steps: a) Solubilization of graphite in a solvent, such as an apolar aprotic solvent under an inert atmosphere so as to obtain a graphene solution b) Oxidation of the graphene solution obtained in step b) to obtain an organic dispersion of graphene; c) Transfer of the organic dispersion of graphene into a matrix forming a liquid dispersion of graphene; the matrix may in particular be water or a viscous matrix, preferably a matrix having a minimum viscosity of 0.01 Pa.s at 25°C and a maximum of 300 Pas.s at 25°C; and d) Evaporation and / or distillation of the solvent. Examples

[0107] Example 1:

[0108] A particular example of graphene useful according to the invention is presented below.

[0109] It is obtained by implementing the following method.

[0110] The graphene dispersions described in this example are obtained by implementing a method according to the invention comprising the following steps under an inert atmosphere: - Mixture of 1.77 g of graphite with 0.73 g of potassium at 150°C for 5 hours; - The obtained KC8 salt is placed in a glass reactor with 500mL of THF and stirred at a shear rate of 50s-1 for 140h; - The unexfoliated salt is removed by sedimentation then centrifugation. - The obtained graphene solution free of aggregate is oxidized in synthetic air at a flow rate of 0.1L / min and then immediately mixed with the corresponding matrix in a ratio of 1:1 by mechanical stirring with a magnetic bar at 75 rpm at 50°C; - THF is removed by distillation to obtain a dispersion of graphene in the matrix.

[0111] The graphene dispersion has the following characteristics:

[0112] Raman spectroscopy:

[0113] Raman spectroscopy confirms the presence of quality graphene with: - a peak intensity ratio D / peak intensity G less than 1.5; and - a 2D peak intensity / G intensity ratio greater than 1. - a peak D with a width at mid-height less than 33 cm-1 - a 2D peak with a width at half-height less than 55 cm-1, preferably less than 50 cm-1.

[0114] Atomic force microscope:

[0115] Average thickness of graphene sheets: 3 nm

[0116] Transmission electron microscope:

[0117] Average width of graphene sheets: 0.4 pm

[0118] Average length of graphene sheets: 0.8 pm

[0119] Example 2:

[0120] A particular example of graphene useful according to the invention is presented below.

[0121] It is obtained by implementing the following method.

[0122] The graphene dispersions described in this example are obtained by implementing a method according to the invention comprising the following steps under an inert atmosphere: - Mixture of 3.54 g of graphite with 1.46 g of potassium at 150°C for 5 hours; - The obtained KC8 salt is placed in a glass reactor with 500mL of THF and stirred at a shear rate of 50s-1 for 140h; - The unexfoliated salt is removed by sedimentation then centrifugation. - The obtained graphene solution free of aggregate is oxidized in synthetic air at a flow rate of 0.1L / min and then immediately mixed with the corresponding matrix in a ratio of 1:1 by mechanical stirring with a paddle stirrer at 75 rpm at 40°C; - THF is removed by distillation to obtain a dispersion of graphene in the matrix

[0123] The graphene dispersion has the following characteristics:

[0124] Raman spectroscopy:

[0125] Raman spectroscopy confirms the presence of quality graphene with: - a peak intensity ratio D / peak intensity G less than 1.5; and - a 2D peak intensity / G intensity ratio greater than 1. - a peak D with a width at mid-height less than 33 cm-1 - a 2D peak with a width at half-height less than 55 cm-1, preferably less than 50 cm-1.

[0126] Atomic force microscope:

[0127] Average thickness of graphene sheets: 3 nm

[0128] Transmission electron microscope:

[0129] Average width of graphene sheets: 0.4 pm

[0130] Average length of graphene sheets: 0.8 pm

[0131] Results

[0132] Several tests were carried out. In these tests, the method implemented for this test consists of mixing graphene according to the invention with a thermosetting resin having a TgO (corresponds to the value of the Tg measured without graphene), then mixing the graphene / resin mixture with a hardener under different operating conditions.

[0133] Impact of the concentration of graphene selected according to the invention on the Glass Transition Temperature of a thermosetting resin.

[0134] The objective of this test is to observe the impact of the graphene concentration according to the invention on the glass transition temperature of a thermosetting resin.

[0135] DGEBA 1 resin is an Epoxy Epikote 827 resin

[0136] Hardener 1 is Aradur HY5052.

[0137] The graphene used is that of example 2.

[0138] Five different concentrations of graphene according to the invention were tested in order to measure the impact of the graphene concentration on the Tg: from 0.01 to 0.08%m.

[0139] Tg is measured as the inflection point in the heat flow versus temperature curve.

[0140] The sample undergoes two identical heating cycles (10°C / min) the Tgl is recorded during the first heating cycle and the Tg2 during the 2nd heating cycle.

[0141] The results obtained are presented in Table 1 below.

[0142] [Tables 1] Resin Hardener DS C Method Curing method Graphene concentration according to T in vention (%m) Tgl (°C) Tg2 (°C) DGEBA 1 Hardener 1 -50°C to 250 °C at 10°C / m in 4h@100°C 0 109* 118* DGEBA 1 Hardener 1 -50°C to 180 °C at 10°C / m in 4h@100°C 0.01 120 150 DGEBA 1 Hardener 1 -50°C to 180 °C at 10°C / m in 4h@100°C 0.02 120 140 DGEBA 1 Hardener 1 -50°C to 180 °C at 10°C / m in 4h@100°C 0.04 121 146 DGEBA 1 Hardener 1 -50°C to 180°C at 10°C / m in 4h@100°C 0.06 123 140 DGEBA 1 Hardener 1 -50°C to 180°C at 10°C / m in 4h@100°C 0.08 122 144 DGEBA 1 Hardener 1 -50°C to 180°C at 10°C / m in 4h@100°C 0.39 122 150 DGEBA 1 Hardener 1 -50°C to 180°C at 10°C / m in 4h@100°C 0.79 119 146 DGEBA 1 Hardener 1 -50°C to 180°C at 10°C / m in 4h@100°C 1.57 120 144 DGEBA 1 Hardener 1 -50°C to 180°C at 10°C / m in 4h@100°C 2.34 120 145

[0143] It is noted that no significant difference is measured between the different concentrations for Tgl and Tg2. There is therefore no effect of the concentration on the increase in Tg between 0.01%m and 0.08%m. Similarly, by increasing the concentration, no variation in the increase in Tg is measured up to 2.34%m. An increase of 12 ± 2°C on Tgl and 26 ± 4°C on Tg2 is noted compared to the reference.

[0144] Impact of the variability of production of graphene according to the invention

[0145] The objective of this test is to observe whether the production of graphene is repeatable.

[0146] DGEBA 1 resin is an Epoxy Epikote 827 resin

[0147] Hardener 1 is Aradur HY5052.

[0148] The graphene used is that of example 2.

[0149] Two batches of graphene were used to enrich Epikote 827 at 0.04%m and 0.08%m in order to measure the impact of the variability of the production batches on the Tg of the final resin: Batch 1 and Batch 2.

[0150] Tg is measured as the inflection point in the heat flow versus temperature curve.

[0151] The sample undergoes two identical heating cycles (10°C / min) the Tgl is recorded during the first heating cycle and the Tg2 during the 2nd heating cycle.

[0152] The results obtained are presented in Table 2 below.

[0153] [Tables2] Resin Hardener Method D SC Curing method Concentration in Gr aph'Up (% m) Tgl (°C) Tg2 (°C) Batch of graphene DGEBA 1 Hardener 1 -50°C to 25 0°C to 10°C / min 4h@100°C 0 109* 118* / DGEBA 1 Curing agent 1 -50°C to 180°C to 10°C / min 4h@100°C 0.04 121 146 Batch 1 DGEBA 1 Curing agent 1 -50°C to 180°C to 10°C / min 4h@100°C 0.08 122 144 Batch 1 DGEBA 1 Curing agent 1 -50°C to 180°C to 10°C / min 4h@100°C 0.04 120 141 Batch 2 DGEBA 1 Curing agent 1 -50°C to 180°C to 10°C / min 4h@100°C 0.08 117 142 Batch 2

[0154] No difference is measured between the two batches for the two concentrations. In each case, there is an increase of 12 ± 2°C on the Tgl and 26 ± 4°C on the Tg2 compared to the reference. There is therefore no impact on the quality of graphene production.

[0155] Impact of the formulation

[0156] The objective of this test is to observe that the invention does not depend on the DGEBA resin used, nor on the hardener used.

[0157] DGEBA 1 resin is Epikote 827.

[0158] DGEBA 2 resin is LY564.

[0159] DGBEA 3 Epikote 834 resin.

[0160] Hardener 1 is Aradur HY5052.

[0161] Hardener 2 is Epikure 340

[0162] Hardener 3 is Aradur HY2954.

[0163] The graphene used is that of example 2.

[0164] The results obtained are presented in Table 3 below and in Figures 1 to 7.

[0165] [Tables3] Resin Hardener Method DS C Curing method Concentration in Graph' Up (%m) Tgl (°C) DSC1 Tg2 (°C) DSC2 DGEBA 1 Hardener 1 -50°C to 250°C at 10°C / m in 4h@100°C 0 109* Figure 1 118* Figure 5 DGEBA 1 Hardener 1 -50°C to 180°C at 10°C / m in 4h@100°C 0.39 122 Figure 1 150 Figure 5 DGEBA 1 Hardener 2 -50°C to 150°C at 10°C / m in min 24h @TA 0 14 Figure 2 19.98 Figure 6 DGEBA 1 Hardener 2 -50°C to 150 °C at 10°C / m in min 24h @TA 0.36 38 Figure 2 56 Figure 6 DGEBA 2 Hardener 3 -50°C to 250 °C at 10°C / m in -50°C to 250 °C at 10°C / m in 0 84.39 Figure 4 - DGEBA 2 Hardener 3 -50°C to 250 °C at 10°C / m in -50°C to 250 °C at 10°C / m in 0.05 130.41 Figure 4 - DGEBA 3 Hardener 2 -50°C to 250 °C at 10°C / m in min 24h @TA 0 72 Figure 3 72* Figure 7 DGEBA 3 Hardener 2 -50°C to 250°C at 10°C / m in min 24h @TA 0.45 62*+ Figure 3 84* Figure 7

[0166] A test was also carried out using another hardener (Hardener 2) with DGEBA 1. This formulation underwent a different curing. As for the DGEBA 1 + Hardener 1 formulation, an increase in Tgl of 24°C was obtained after crosslinking and after annealing an increase in Tg2 of 36°C.

[0167] Tests were also carried out on different systems, all the resins are DGEBA but have different chain lengths resulting in different viscosities and the use of other hardeners, and therefore different cooking methods:

[0168] - DGEBA 2 + Hardener 3: Once crosslinked, we note as for DGEBA 1, a 46°C increase in Tg.

[0169] - DGEBA 3 + Hardener 2: The formulation containing graphene is partially crosslinked unlike the reference without graphene. We cannot therefore make the comparison of the Tg only on the 2nd temperature increase. Once crosslinked, we note, as for DGEBA 1, an increase of 12°C in the Tg. An additional temperature rise cycle is required to see a greater increase in Tg.

[0170] All DGEBA + Hardener formulations show a significant increase in Tg in the presence of graphene according to the invention. The degree of increase will vary, among other things, depending on the resin, the hardener and the curing method.

Claims

Claims

1. Use of at least one graphene sheet having: - an average thickness of less than 3nm; - an average lateral size of between 0.1 and 6pm, to increase the glass transition temperature (Tg) of a material comprising at least one thermosetting resin.

2. Use according to the preceding claim, characterized in that at least one graphene sheet has a sheet thickness of less than 10 atomic layers, preferably less than 5 atomic layers.

3. Use according to one of the preceding claims, from 1 to 200 graphene sheets of which at least one graphene sheet has: - an average thickness of less than 3nm; - an average lateral size of between 0.1 and 6pm.

4. Use according to one of the preceding claims, from 1 to 200 graphene sheets of which all the graphene sheets have: - an average thickness of less than 3nm; - an average lateral size of between 0.1 and 6pm.

5. Use according to one of the preceding claims, characterized in that the graphene represents between 0.001 and 0.1% by weight of the total weight of the material, preferably between 0.001 and 0.01%.

6. Use according to one of the preceding claims, characterized in that the graphene is not functionalized.

7. Use according to one of the preceding claims, characterized in that the thermosetting resin is an epoxy resin, preferably an epoxy resin comprising diglycidyl ether of bisphenol A.

8. Use according to one of the preceding claims, characterized in that the graphene is used to increase the glass transition temperature of the material by at least 10°C, preferably by at least 20°C.

9. Use according to one of the preceding claims, characterized in that the graphene sheet(s) is(are) in the form of a liquid dispersion of graphene.

10. Use according to the preceding claim, characterized in that the liquid dispersion of graphene is a liquid dispersion of graphene

11.

12.

13. obtained by a process comprising the implementation of the following steps: a. Solubilization of graphite carried out under an inert atmosphere in order to obtain a graphene solution. b. Oxidation of the graphene solution obtained in step b) to obtain an organic dispersion of graphene; c. Transfer of the organic graphene dispersion into a viscous matrix forming a liquid graphene dispersion; and d. Evaporation and / or distillation of the aprotic polar solvent. Method for increasing the glass transition temperature of a material comprising at least one thermosetting resin, having a glass transition temperature TgO, comprising the implementation of the following steps: - (1) preparation or recovery of graphene comprising at least one sheet having: -an average thickness less than 3nm; - an average lateral size between 0.1 and 6pm. - (2) mixing the graphene from step (1) with at least one thermosetting resin, - (3) mixing step (2) with a hardener and / or an accelerator and / or additives as described in the present application to obtain a thermosetting resin material with a glass transition temperature Tgl greater than TgO. Method according to the preceding claim, characterized in that step (1) comprises the implementation of the following steps: a. Solubilization of graphite carried out under an inert atmosphere in order to obtain a graphene solution. b. Oxidation of the graphene solution obtained in step b) to obtain an organic dispersion of graphene; c. Transfer of the organic graphene dispersion into a viscous matrix forming a liquid graphene dispersion; and d. Evaporation and / or distillation of the aprotic polar solvent. Method according to one of claims 11 or 12, characterized in that the thermosetting resin is an epoxy resin, preferably an epoxy resin comprising bisphenol A diglycidyl ether.

14. Method according to one of claims 11 to 13, characterized in that the mixing step (2) is carried out under the following conditions: - Duration between 30 minutes and 15 hours, and / or - Temperature between 30°C and 70°C, at constant temperature or with temperatures which can vary over the duration of the mixing, and / or - With stirring, preferably with mechanical stirring, preferably between 75 and 250 revolutions per minute, and / or - The graphene being added to the resin at a concentration less than or equal to 10% by weight of the weight of the thermosetting resin, preferably less than or equal to 5%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, less than or equal to 0.1%.

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