This application claims the benefit of European Patent Application 22382644.7 filed on July 5, 2022.

The present invention relates to the field of thermoset resin compositions. In particular, to thermoset epoxy resin compositions which are fully recyclable; as well as prepregs, composites and articles comprising it. The present invention also refers to a recycling process of the thermoset epoxy resin composition as well as the reinforcement phase from the composite or the article containing the recyclable thermoset epoxy resin composition.

Background Art

Today, the benefits of components and products designed and produced in composite materials - instead of metals, such as aluminium and steel - are well recognized by many industries. Their excellent mechanical properties at very low material densities, as well as their corrosion resistance, among other properties, have created a huge market demand in buildings, infrastructures automotive, industrial, aerospace, wind energy and other sectors.

Composite materials usually consist of a reinforcement phase, generally comprising continuous or discontinuous fibres, and a matrix phase, generally containing a thermoset or thermoplastic polymer. The matrix material surrounds and supports the reinforcement material by maintaining their relative positions, meanwhile the reinforcement material imparts their special mechanical and physical properties to enhance the matrix properties.

Thermosets are typically preferred over thermoplastics in high demanding applications where mechanical and thermal stability are important. The crosslinked molecular structure of thermosets is responsible for their enhanced performance, but it goes at the expenses of becoming non-meltable, insoluble and unsuitable for reprocessing and/or recycling.

In the case of thermoset composites, the resin matrix cures or hardens into a given shape through an irreversible chemical reaction. Which means that once a thermoset composite is formed, it cannot be remoulded or reshaped (that is, it is not reprocesable). Because of this, the recycling of thermoset composites is extremely difficult. Usually, the resin is removed by pyrolysis to recover the reinforcement phase. This process is time and energy-consuming and not environmentally friendly. Furthermore, the properties of the reinforcement phase can be affected.

Attempts have been made in the state of the art to reuse thermoset crosslinked epoxy resins and composites/articles containing it. For example, an attempt to provide reprocesable epoxy thermoset composites was performed by Leibler et al. in the US2013/0300020. Such composites comprise a reinforcement material and a matrix phase containing a thermosetting resin, an anhydride based hardener, and a catalyst which remains in the composite after its manufacturing. However, the recycling process of an article containing the thermoset crosslinked epoxy resin composite involves first a pulverization (grinding) step or a deformation step by the application of mechanical forces. After that, it is mixed with virgin epoxy-resin for the preparation of thermoset epoxy resin article with less demanding properties. Therefore, again the recycling process impairs and/or significantly alter the properties of the thermoset epoxy resin composition and the article obtained using it.

Other attempts of recycling thermoset crosslinked composites have been disclosed in the state of the art, which implies a chemical agent that disrupt the covalent crosslinks of the thermoset resin obtaining a soluble thermoplastic polymer. Unfortunately, this method does not permit the recovery of the initial properties of the thermoset resin composition and also involves the use of strong chemical agents such as trialkyl and triaryl phosphine, and alkali metal aluminium hydride to disrupt the covalent bonds.

Most of the attempts use catalysts that remain in the final thermoset resin. However, it has been disclosed that the use of catalyst in the field of thermoset polymers have some disadvantages. It is known that the chemical, thermal, and mechanical stability of a catalyst determines its lifetime in industrial reactors. Catalyst stability is influenced by numerous factors, including decomposition, coking, and poisoning. In this sense, it has been found that owing to competing reactions during the preparation and recovery process of thermoset resins, the catalysts suffer chemical changes, which provoke that its activity becomes compromised (catalyst deactivation) and thus its total lifetime will be reduced.

CN11015544 discloses a thermoset crosslinked epoxide resin composition prepared mixing an epoxy resin, a dicarboxylic acid monomer, epoxy resin curing agent, a catalyst, and a self-healing accelerator.

Mat. Horiz. 2016, 3(3), 241-247 relates to epoxy vitrimers obtainable by mixing diglycidyl ether of bisphenol A (DGEBA) as the epoxy monomer, and 4-aminophenyl disulfide (4-AFD) (in the absence of any catalyst).

US2003064228 discloses epoxy resin compositions for a fiber-reinforced composite material containing an alicyclic epoxy resin, a polyamine and a latent acid catalyst which can dissolve in the alicyclic epoxy resin or in the polyamine.

J. Polymer 2022, 239, 124457 it is reported a methodology to manipulate the dynamic properties of aromatic disulfide containing vitrimers by changing the hardener structure, stoichiometry or catalyst quantity.

EP2949679 relates to epoxy composites comprising a reinforcement phase comprising fibers, and a matrix phase comprising a cured epoxy resin obtainable by mixing an epoxide-functionalized resin with a functionality equal to or higher than 2 with a cross-linking agent and curing the reaction mixture, this step being performed in the absence of a catalyst. J Polymer 2022, 248, 124801 discloses self-healed vitrimers from a bisphenol A type epoxy resin, suberic acid, 4,4'-diaminodiphenyl disulfide, and tetrabutylammonium bromide resulting in a carboxylic acid-extended epoxy resin containing beta-hydroxyl esters and disulfide bonds.

Therefore, from what is known in the state of the art, in spite of the efforts made, there is still the need of providing a recyclable thermoset crosslinked epoxy resin composition that can be recycled without compromising its physical and chemical properties and neither the properties of the reinforcement material containing fibres.

Summary of Invention

Inventors have provided a recyclable thermoset crosslinked epoxy resin composition. Particularly, the inventors have found a recyclable thermoset crosslinked epoxy resin composition obtainable by a method that comprises mixing an epoxide-functionalised resin with a cross-linking agent and a catalyst; and curing the mixture thus obtained, with the proviso that the cross-linking agent comprises an aromatic disulphide bond. In particular, the inventors have demonstrated that a thermoset crosslinked epoxy resin composition obtainable by a process that comprises mixing an epoxide-functionalised resin with a functionality equal to or higher than 2, with a cross-linking agent of formula (I) containing an aromatic disulphide bond, and a catalyst as defined herein; and followed by a curing step, has recyclable properties without compromising its physical and chemical properties.

As it is demonstrating in the experimental section, a reinforcement phase comprising fibres forming part of composites and articles comprising the thermoset resin composition of the present invention are also recovered without alteration of its physical and chemical properties under mild conditions and without the use of mechanical forces or grinding methods. In fact, the recycling process of a composite and/or article comprising the thermoset crosslinked epoxy resin composition of the invention is performed by separating the thermoset crosslinked epoxy resin composition from the reinforcement phase in the presence of a solvent under mild conditions without the need of using strong reducing and/or oxidizing agents, only by the use such solvents. It is advantageous because both the thermoset crosslinked epoxy resin composition as well as the reinforcement phase thus recovered can be directly re-sold or alternative re-used and/or repurposed without hindering the quality/properties of the finally obtained composites/articles containing it.

Furthermore, the thermoset crosslinked epoxy resin composition of the present invention are also reprocesable, and reparable. In fact, the thermoset crosslinked epoxy resin composition of the present invention allows preparing re-shapable and reprocesable composites and/or articles containing them, if desired, by applying suitable temperature and/or pressure conditions, without compromising the physical, chemical, and mechanical properties of the product. The thermoset composites comprising the thermoset crosslinked epoxy resin composition of the present invention are also repairable by applying suitable temperature/pressure conditions on the damaged area. And the thermoset crosslinked epoxy resin composition of the present invention comprising bis(4-aminophenyl)disulphide of formula (III) further has a transient mechano-chromic behaviour. It happens when the composite containing it receives an impact, then a color change in the visible region of the EM spectrum is observed on the damaged area. This additional property confers to the composite of the invention a great value because it permits detecting damage by simple visual inspection.

Finally, the thermoset crosslinked epoxy resin composition of the present invention allows preparing intermediate prepregs for the preparation of composites that are partially or completely cured with improved handling properties. Specially, the prepregs pre-impregnated with thermoset crosslinked epoxy resin composition completely cured of the present invention (named enduring prepreg) are particularly advantageous because allows increasing the time between the manufacturing date of the prepreg and its processing date without altering the re-shapable, reprocesable and repairable properties of the thermoset resin of the present invention. In fact, there is no time limitation, and at any time the enduring prepreg can be processed for the preparation of composites and subsequently articles containing it.

Therefore, in view of the above, the thermoset crosslinked epoxy resin composition of the present invention and the prepregs, composites and articles containing it represent a great advance in the field of thermoset materials.

Thus, the first aspect of the invention relates to a thermoset crosslinked epoxide resin composition obtainable by a method comprising:

(I) mixing an epoxide-functionalised resin with a functionality equal to or higher than 2, with:

- a cross-linking agent of formula (I)

Ar-S-S-Ar (I) at a molar ratio between the epoxide groups of the epoxy-functionalised resin and the epoxide-reactive functional moieties of the cross-linking agent of formula (I) from the stoichiometric to a two-fold excess of epoxide reactive functional group; and

- at least one Lewis acid catalyst, and

(ii) curing the mixture obtained in step (I) at a temperature from 10°C to 200°C for a period of time such that the thermoset crosslinked epoxide resin reaches a glass transition temperature value which is equal to or higher than 10°C but equal to or lower than the maximum glass transition temperature; wherein:

Ar means a ring system from 5 to 14 carbon atoms, the system comprising 1-3 rings, where:

The rings are saturated, partially unsaturated, or aromatic;

The rings are isolated, partially, or totally fused, at least one of the carbon atoms forming the aryl moiety is substituted by an epoxide-reactive functional moiety selected from the group consisting of: -NHRw, -NH-NHRw, -CO-NH-NHRw, -COOH, -SH, -OH, -00- NHRw, -NCN-NH-NHRw, wherein the asterisk denotes the carbon atom through which the epoxide-reactive moiety binds to the ring system, and the remaining carbon atoms are optionally substituted by one or more moieties independently selected from the group consisting of (C1-C20) alkyl, (Cs-Cujaryl, -OR2, -(C0)R3, -0(C0)R4, -(SO)Rs, -NH-CO- Re, -COOR7, -NRsRg, -NO2, and halogen;

R2 to Rio are the same or different, and are selected from the group consisting of: -H, (Ci-C2o)alkyl, and phenyl; provided that:

Ar comprises at least one aromatic ring, and

Ar is bonded to the -S- atom through the aromatic ring.

The second aspect of the invention relates to a thermoset composite comprising: (a) a reinforcement phase comprising fibres, and (b) a matrix phase comprising the thermoset crosslinked epoxide resin composition as defined in the first aspect of the invention.

The third aspect of the invention relates to a prepreg comprising: (a') a reinforcement phase comprising fibres, and (b’) a matrix phase comprising the thermoset crosslinked epoxide resin composition as defined in the first aspect of the invention.

The fourth aspect of the invention relates to an article comprising the thermoset crosslinked epoxy resin. Particularly, the article comprises one or more composites of the second aspect of the invention; or one or more prepregs of the third aspect of the invention.

The fifth aspect of the invention relates to a process for recycling the thermoset crosslinked epoxy resin composition of the first aspect of the invention and the reinforcement phase comprising fibres from the composite of the second aspect of the invention, or the prepreg of the third aspect of the invention, or from the article of the fourth aspect of the invention, wherein the process comprises immersing the composite or the article in a solvent or mixture of solvents having a boiling temperature above the glass transition temperature of the composite and a Hansen solubility parameter (Ra) equal to or lower than 7.5 measured by equation (1):

Ra ² = 4(5DI-5D ₂ ) ² + (6P1-6P2) ² + (6H1-6H2) ² (eq. 1)

Being:

5D1 the solubility parameter of the thermoset crosslinked epoxy resin composition for dispersion expressed in MPa ^1/2 ,

5D2 the solubility parameter of the solvent or mixture of solvents for dispersion expressed in MPa ^1/2 , 5P1 the solubility parameter of the thermoset crosslinked epoxy resin composition for polars expressed in MPa ^1/2 ,

5P2 the solubility parameter of the solvent or mixture of solvents for polars expressed in MPa ^1/2 ,

5H1 the solubility parameter of the thermoset crosslinked epoxy resin composition for hydrogen-bonding expressed in MPa ^1/2 , and

5H2 the solubility parameter of the solvent or mixture of solvents for hydrogen-bonding expressed in MPa ^1/2 .

It is also part of the invention the processes for the preparation of the thermoset crosslinked epoxy resin composition of the first aspect of the invention, the thermoset composite of the second aspect of the invention, the prepreg of the third aspect of the invention, and the article of the fourth aspect of the invention.

Detailed description of the invention

All terms as used herein in this application, unless otherwise stated, shall be understood in their ordinary meaning as known in the art. Other more specific definitions terms as used in the present application are as set forth below and are intended to apply uniformly throughout the specification and claims unless an otherwise expressly set out definition provides a broader definition.

For the purposes of the present invention, any ranges given include both the lower and the upper endpoints of the range. Ranges given, such as temperatures, times, weights, and the like, should be considered approximate, unless specifically stated. The term "about" or "around” as used herein refers to a range of values ± 10% of a specified value. For example, the expression "about 0.5" or "around 0.5” includes ± 10% of 0.5, i.e. from 0.45 to 0.55.

The terms "percentage (%) by weight” or "% w/w” have the same meaning and are used interchangeable. The term "percentage by weight” refers to the percentage of an ingredient/component/compound in relation to the total weight of the final mixture/product/resin/composite. For instance, when referred to the thermoset crosslinked epoxy resin composition comprised in the matrix phase, is estimated determining the amount of the thermoset crosslinked epoxy resin composition with respect to the total weight of the matrix phase and the resulting value is multiplied by 100.

As it has been stated above, the present invention provides a recyclable, thermoset crosslinked epoxy resin composition, prepregs, composites and articles comprising it.

For the purpose of the present invention, the term "recyclable” is to be understood as that the thermoset crosslinked epoxy resin composition of the present invention is separated and recovered from the reinforcement material of the composites/prepreg/articles containing it without altering its chemical and physical properties and being appropriate for its re-use. Furthermore, the thermoset crosslinked epoxy resin composition of the present invention is also reprocesable and reparable.

For the purpose of the present invention, the term "reprocesable” is to be understood as that the thermoset crosslinked epoxy resin composition and composites/articles containing it are capable of changing its form, applying pressure and heat. The selection of specific pressure and heat conditions will depend on the specific nature of the material and shape of final part. Forms part of the routine tasks of the skilled person in the art the selection of appropriate pressure and heat conditions.

For the purpose of the present invention, the term "reparable” is to be understood as that the thermoset crosslinked epoxy resin composition and composites/articles containing it are capable of restoring the initial shape/form after suffering a damage, applying pressure and heat. The selection of specific pressure and heat conditions will depend on the extension and severity of the caused damage, as well as the specific nature of the material and shape of final part. Forms part of the routine tasks of the skilled person in the art the selection of appropriate pressure and heat conditions.

In the present invention, the term "resin” means any polymer, oligomer or monomer comprising two or more epoxide groups. In the present invention, the term "polymer” means a molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass. In the present invention, the term "oligomer” means a molecule of intermediate relative molecular mass, the structure of which essentially comprises a small plurality of units derived, actually or conceptually, from molecules of lower relative molecular mass. And, in the present invention, the term "monomer” means a molecule which can undergo polymerization, thereby contributing constitutional units to the essential structure of a macromolecule.

The terms "cross-linked” or "cross-linking” refer in the synthetic polymer science field, the use of cross-links to promote a difference in the physical properties of the polymers. The term "cross-links” refers to bonds that link one polymer chain to another or different parts of the same polymer and these bonds can be covalent or ionic bonds. The terms "cross-linker” or "cross-linking agent” refers to compound having the ability to cross-link the polymer chains.

As it has been stated above, the thermoset crosslinked epoxy resin composition is obtainable by the method as disclosed herein below and above. For the purposes of the invention, the expressions "obtainable", "obtained" and equivalent expressions are used interchangeably, and in any case, the expression "obtainable" encompasses the expression "obtained".

In an embodiment, the thermoset crosslinked epoxy resin composition is obtainable by:

(I) mixing an epoxide-functionalised resin with a functionality equal to or higher than 2, with: - a cross-linking agent of formula (I)

Ar-S-S-Ar (I) at a molar ratio between the epoxide groups of the epoxy-functionalised resin and the epoxide-reactive functional moieties of the cross-linking agent of formula (I) from the stoichiometric to a two-fold excess of epoxide reactive functional group; and

- at least one Lewis acid catalyst, and

(ii) curing the mixture obtained in step (I) at a temperature from 10°C to 200°C for a period of time such that the thermoset crosslinked epoxide resin reaches a glass transition temperature value which is equal to or higher than 10°C but lower or equal than the maximum glass transition temperature; wherein:

Ar means a ring system from 5 to 14 carbon atoms, the system comprising 1-3 rings, where:

The rings are saturated, partially unsaturated, or aromatic;

The rings are isolated, partially, or totally fused, at least one of the carbon atoms forming the aryl moiety is substituted by an epoxide-reactive functional moiety selected from the group consisting of: -NHRw, -NH-NHRw, -CO-NH-NHRw, -COOH, -SH, -OH, -CO- NHRw, -NCN-NH-NHRw, wherein the asterisk denotes the carbon atom through which the epoxide-reactive moiety binds to the ring system, and the remaining carbon atoms are optionally substituted by one or more moieties independently selected from the group consisting of (C1-C20) alkyl, (Cs-C jaryl, -OR2, -(C0)R3, -0(C0)R4, -(SO)Rs, -NH-CO- Re, -COOR7, -NRsRg, -NO2, and halogen;

R2to Rioare the same or different, and are selected from the group consisting of: -H, (Ci-C2o)alkyl, and phenyl; provided that:

Ar comprises at least one aromatic ring, and

Ar is bonded to the -S- atom through the aromatic ring.

The term "alkyl” refers to a saturated straight, or branched hydrocarbon chain which contains the number of carbon atoms specified in the description or claims. Examples include, among others, the group methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and tert-butyl.

And the term "halogen” refers to fluorine, chlorine, and bromine. In the present invention, the term "functionality equal to or higher than 2” when referred to the epoxide- functionalised resin, means that each resin molecule comprises at least two epoxide groups.

The term "molar ratio” refers to the relation of moles of epoxide groups of the epoxide-functionalised resin vs. the moles of epoxide reactive functional moieties of the cross-linking agent (such as for example the compound of formula (I)) as defined in the present invention.

In the present invention, the term "stoichiometric ratio" refers to such ratio that all the reagents are completely consumed during the process. Then, there is neither deficiency nor excess of reagents.

In the present invention, the sentence "two-fold excess of epoxide reactive group” is determined starting from the stoichiometric ratio and multiplying the number of moles related to the epoxide reactive groups by 2. For instance, when the epoxide reactive group is a -NH2 group, the stoichiometric ratio between the epoxide groups of the resin and -NH2 is 2: 1 . From this, and considering how it is estimated, the "two-fold excess” ratio for the case that the epoxide reactive group is -NH2 will be 1 :1.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (i) the epoxide-functionalised resin with a functionality equal to or higher than 2 consists of a single epoxide-functionalised type resin.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (i) the epoxide-functionalised resin with a functionality equal to or higher than 2 consists of a single epoxide-functionalised type resin selected from the group consisting of difunctional (thus having two epoxide groups), trifunctional (thus having three epoxide groups), tetrafunctional epoxide-functionalised resins (thus having four epoxide groups). In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (i) the epoxide-functionalised resin with a functionality equal to or higher than 2 consists of a single epoxide-functionalised type resin selected from the group consisting of a difunctional epoxy resin and tetrafunctional epoxy resin.

Illustrative non-limitative examples of epoxide-functionalised resin with a functionality equal to or higher than 2 are: Bisphenol A diglycidyl ether, Bisphenol F diglycidyl ether, tetrabromobisphenol A diglycidyl ether, propylene glycol diglycidyl ether, butylene glycol diglycidyl ether, ethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1 ,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A polyethylene glycol diglycidyl ether, bisphenol A polypropylene glycol diglycidyl ether, and mixtures thereof. Illustrative non-limitative examples of tri-functional epoxy resins with a functionality equal to or higher than 2 are: triglycidyl ether of para-aminophenol, and triglycidyl meta-aminophenol. Illustrative non-limitative examples of tetra-functional epoxy resins are N,N,N',N'-tetraglycidyl methylene dianiline, N,N, N', N'-tetraglycidyl-m-xylene diamine, and pentaerythritol tetraglycidyl ether.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is a mixture of two or more epoxide-functionalised resins, said resins being independently selected from the group consisting of difunctional, trifunctional, and tetrafunctional epoxide-functionalised resins. The functionality of the resulting mixture is calculated as the weighted average from the functionalities of the epoxide-functionalised resins forming the mixture. For instance, if the mixture is made of two difunctional epoxide resins, then its functionality is 2; and if the mixture is made of resins with different functionalities, the functionality is calculated multiplying the percentage proportion of the resins with a particular functionality by such functionality value and summing the values. For instance, if the mixture is made of 60% (molar percentage) of difunctional resins and 40% (molar percentage) of tetrafunctional resins, the functionality of the mixture is calculated as: 2 x 0.6 + 4 x 0.4= 2.8. No special technique is required for mixing the different resins. There are available commercial resins which are mixture of resins (such as Araldite).

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is a difunctional epoxy resin or a mixture comprising one or more difunctional epoxy resins. In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is a bisphenol epoxy resin. In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide- functionalised resin with a functionality equal to or higher than 2 is a mixture of epoxy resins comprising a bisphenol epoxy resin. In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is the difunctional epoxy-resin bisphenol A diglycidyl ether or bisphenol F diglycidyl ether. In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide- functionalised resin with a functionality equal to or higher than 2 is a mixture comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is a mixture of difunctional epoxy resins. In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin a mixture of difunctional epoxy resins with a functionality equal to or higher than 2 comprising a bisphenol epoxy resin. In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide- functionalised resin with a functionality equal to or higher than 2 is a mixture of two difunctional epoxy resins comprising a bisphenol epoxy resin. In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is a mixture of two difunctional epoxy resins comprising a bisphenol epoxy resin from 60% to 99% by weight.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is a mixture of two difunctional epoxy resins comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether. In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is a mixture of two difunctional epoxy resins comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether % w/w from 60% to 99%. In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is a mixture of two difunctional epoxy resins comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether % w/w from 70% to 90%.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is a mixture comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether and 1 ,4-butanediol diglycidyl ether.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is a mixture comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether and neopentyl glycol diglycidyl ether.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin is obtainable by the process comprising: (a) mixing a difunctional epoxy resin or a mixture of difunctional epoxy resins with a cross-linking agent of formula (I) as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein in step (I) the epoxide-reactive functional group of the epoxy-functionalised resin with a functionality equal to or higher than 2 is -NHRw, or -NH-NHRw, wherein Rw is as defined above. In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein in step (I) the epoxide-reactive functional group of the epoxyfunctionalised resin with a functionality equal to or higher than 2 is -NH2.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein in step (I) the epoxide-reactive functional group of the epoxy-functionalised resin with a functionality equal to or higher than 2 — NH2, the molar ratio between the epoxide groups of the epoxide-functionalised resin and the epoxidereactive functional moieties of the cross-linking agent is comprised from 2:1 to 1 :1.

According to the present invention, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the crosslinking agent is a compound of formula (I) Ar-S-S-Ar wherein: Ar means a ring system from 5 to 14 carbon atoms, the system comprising 1-3 rings, where: the rings are saturated, partially unsaturated, or aromatic; the rings are isolated, partially, or totally fused, at least one of the carbon atoms forming the aryl moiety is substituted by an epoxide-reactive functional moiety selected from the group consisting of: -NHR10, -NH-NHR10, -CO-NH-NHRw, -COOH, -SH, -OH, -CO-NHRw, -NCN-NH-NHR10, wherein the asterisk denotes the carbon atom through which the epoxide-reactive moiety binds to the ring system, and the remaining carbon atoms are optionally substituted by one or more moieties independently selected from the group consisting of (Ci-C2o)alkyl _J (Cs-Cujaryl, -OR2, -(C0)R3, -0(C0)R4, -(SO)Rs, -NH-CO- Re, -COOR7, -NRsRg, -NO2, and halogen; R2 to Rw are the same or different, and are selected from the group consisting of: -H, (Ci-C2o)alkyl, and phenyl; provided that: Ar comprises at least one aromatic ring, and Ar is bonded to the -S- atom through the aromatic ring.

For the purpose of the invention, the term "Ar” and "aryl” and "aryl moiety” have the same meaning and are used interchangeable. They refer to a ring system from 5 to 14 carbon atoms, the system comprising 1-3 rings, as defined herein above and below. Further, the term "isolated” rings means that the ring system is formed by two or three rings and said rings are bound via a bond from the atom of one ring to the atom of the other ring. The term "isolated” also embraces the embodiment in which the ring system has only one aromatic ring, such as a phenyl. For the purpose of the invention, the term "totally fused” means that the ring system is formed by two or three rings in which two or more atoms are common to two adjoining rings. Illustrative non- limitative examples are 1 ,2,3,4-tetrahydronaphthyl, 1-naphthyl, 2-naphthyl, anthryl, or phenanthryl. For the purpose of the invention, the term "partially fused” means that the ring system is formed by three rings, being at least two of said rings totally fused (i.e. two or more atoms being common to the two adjoining rings) and the remaining ring(s) being bound via a bond from the atom of one ring to the atom of one of the fused rings.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I), the compound of formula (I) is one wherein Ar is a phenyl moiety.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the compound of formula (I) is one of formula (II) wherein: R1 and R/ are independently selected from the group consisting of: -H, (Ci-C2o)alkyl, (C5-

Cujaryl, -OR2, -(COjRs, -0(C0)R4, -(SO)Rs, -NH-CO-Re, -COOR7, -NRsRg, -NO2, and halogen; R2 to Rg are the same or different and are selected from the group consisting of: -H, (Ci-C2o)alkyl, and (Cs-Cujaryl; and m is 4.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (i) the compound of formula (I) is one of formula (II) wherein Ri and R/ are the same.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (i) the compound of formula (I) is one of formula (II) wherein the -NH2 moieties are in para-position. The term "para-position” refers to a compound with substituents at the positions 1 and 4 on an aromatic ring. It means that the substituents are directly opposite. The symbol for para- is p- or 1,4-,

In one embodiment, the thermoset epoxy resin composition is obtainable by a method wherein in step (i) the compound of formula (I) is one of formula (II) wherein the -NH2 moieties are in ortho-position. The term "ortho-position” refers to a compound with substituents at the positions 1 and 2 on an aromatic ring. The symbol for ortho- is 0- or 1,2-.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (i) the compound of formula (I) is one of formula (II) wherein R1 and R/ are hydrogen.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (i) the compound of formula (I) is a compound of formula (III), which is the bis(4-aminophenyl)disulphide:

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (i) the compound of formula (I) is a compound of formula (IV), which is the bis(2-aminophenyl)disulphide:

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (i) the compound of formula (I) is a mixture of a compound of formula (III), which is the bis(4- aminophenyl)disulphide; and the compound of formula (IV), which is the bis(2-aminophenyl)disulphide.

As it has been stated above, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein step (i) comprises at least one Lewis acid catalyst. For the purpose of the invention the term "catalyst” refers to a compound which can reduce the activation energy of a reaction without being used up itself, without itself being consumed during the reaction. In the present invention, the catalyst remains in the thermoset epoxy resin composition modifying the final recyclability of the thermoset crosslinked epoxy resin.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein in step (i) the catalyst is one or more Lewis acids. For the purpose of the invention, the term "Lewis acids” refers to an atom, ion, or molecule with an incomplete octet of electrons capable of accepting a pair of electrons of a Lewis base.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein in step (i) the catalyst is one or more Lewis acids selected from the group consisting of metal halide, metalloid halide, metal complex with carboxylate ligand, trihalide metalloid adduct, and organometallic-Lewis acid complex and the halide is selected from the group consisting of fluoride, chloride, bromide, and iodide; the metal is selected from the group consisting of an alkali metal, an alkaline earth metal, a transition metal, a lanthanoid metal, and an actinoid metal; and the metalloid is selected from the group consisting of boron, silicon, arsenic, germanium, and lead.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein in step (i) the catalyst is selected from the group consisting of alkali metal halide, metalloid halide, metal complex with carboxylate ligand, trihalide metalloid adduct and a mixture thereof. In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein in step (i) the catalyst is selected from the group consisting of boron trifluoride ethylamine, chromium (III) 2-ethylhexanoate, zinc chloride and zinc (II) 2-ethylhexanoate and mixture thereof.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein in step (i) the amount of the catalyst is from 0.2% to 3% weight ratio.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (i) is performed by mixing a mixture of difunctional epoxy resins, the mixture comprising a bisphenol epoxy resin, with a crosslinking agent of formula (I) as defined above, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (i) is performed by mixing a mixture of two difunctional epoxy resins, the mixture comprising a bisphenol epoxy resin, with a cross-linking agent of formula (I) as defined above, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (i) is performed by mixing a mixture comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether with a cross-linking agent of formula (I) as defined above, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and 1 ,4-butanediol diglycidyl ether, with a cross-linking agent of formula (I) as defined above, and a catalyst as defined above. In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and neopentyl glycol diglycidyl ether, with a cross-linking agent of formula (I) as defined above, and a catalyst as defined above. In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a difunctional epoxy resin or mixture of difunctional epoxy resins with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of difunctional epoxy resins with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of difunctional epoxy resins, the mixture comprising a bisphenol epoxy resin, with a crosslinking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of two difunctional epoxy resins, the mixture comprising a bisphenol epoxy resin, with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and 1 ,4-butanediol diglycidyl ether, with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and neopentyl glycol diglycidyl ether, with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a difunctional epoxy resin or mixture of difunctional epoxy resins with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety where uniquely one carbon atom of the ring is substituted, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of difunctional epoxy resins with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, where uniquely one carbon atom of the ring is substituted, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of difunctional epoxy resins, the mixture comprising a bisphenol epoxy resin, with a crosslinking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, where uniquely one carbon atom of the ring is substituted, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of two difunctional epoxy resins, the mixture comprising a bisphenol epoxy resin, with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, where uniquely one carbon atom of the ring is substituted, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of bisphenol A diglycidyl ether, or bisphenol F diglycidyl ether; and 1 ,4-butanediol diglycidyl ether, with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, where uniquely one carbon atom of the ring is substituted, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of bisphenol A diglycidyl ether, or bisphenol F diglycidyl ether; and neopentyl glycol diglycidyl ether, with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, where uniquely one carbon atom of the ring is substituted, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a difunctional epoxy resin or mixture of difunctional epoxy resins with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety where uniquely one carbon atom of the ring is substituted with an -NH2 moiety, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of difunctional epoxy resins with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, where uniquely one carbon atom of the ring is substituted with an -NH2 moiety, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of difunctional epoxy resins, the mixture comprising a bisphenol epoxy resin, with a cross- linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, where uniquely one carbon atom of the ring is substituted with an -NH2 moiety, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of two difunctional epoxy resins, the mixture comprising a bisphenol epoxy resin, with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, where uniquely one carbon atom of the ring is substituted with an -NH2 moiety, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of bisphenol A diglycidyl ether, or bisphenol F diglycidyl ether; and 1 ,4-butanediol diglycidyl ether, with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, where uniquely one carbon atom of the ring is substituted with an -NH2 moiety, and a catalyst as defined above.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein step (I) is performed by mixing a mixture of bisphenol A diglycidyl ether, or bisphenol F diglycidyl ether; and neopentyl glycol diglycidyl ether, with a cross-linking agent of formula (I) as defined above, wherein Ar is a phenyl moiety, where uniquely one carbon atom of the ring is substituted with an -NH2 moiety, and a catalyst as defined above.

As it has been stated above, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein the curing step (ii) comprises curing the mixture obtained in step (I) at a temperature from 10°C to 200°C for a period of time such that the thermoset crosslinked epoxide resin reaches a glass transition temperature value which is equal to or higher than 10°C but equal to or lower than the maximum glass transition temperature.

The selection of specific curing time will depend on the specific nature of the epoxy resin and its Tg, as well as of the curing temperature, and the nature of the catalyst and the thermoset crosslinked epoxy resin composition to be obtained. Forms part of the routine tasks of the skilled person in the art the selection of appropriate curing time.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein the curing step (ii) is performed at a temperature from 10°C to 200 °C for a period of time such that the resin reaches at least 25% of the maximum Tg value to obtain a thermoset crosslinked epoxy resin composition partially cured. Commonly, the time required for reaching the at least 25% of maximum Tg value to obtain a thermoset crosslinked epoxy resin composition partially cured.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method wherein the curing step (ii) is performed at a temperature from 10°C to 200 °C for a period of time such that the resin reaches at maximum Tg value to obtain a thermoset crosslinked epoxy resin composition completely cured.

In the present invention, the term "curing” refers to the hardening of a mixture of epoxide-functionalised compounds and hardener by chemical cross-linking, brought about by chemical additives, ultraviolet radiation, electron beam, microwave, infrared radiation, or heat. In the curing process, the resin viscosity drops initially upon the application of heat, passes through a region of maximum flow, and begins to increase as the chemical reactions increase the average length and the degree of cross-linking between the constituent resins. This process continues until a continuous 3-dimensional network of polymer chains is created - this stage is termed gelation. In terms of processability of the resin this marks an important watershed: before gelation, the system is relatively mobile, after it the mobility is very limited, the micro-structure of the resin and the composite material is fixed and severe diffusion limitations to further cure are created. Thus, in order to achieve vitrification in the resin, it is usually necessary to increase the process temperature after gelation. For the purpose of the invention, the term "vitrification” is the development of the glassy state of a compound or composition (such as the thermoset crosslinked resin composition) as the curing reaction increases and the glass transition temperature (Tg) reaches the curing temperature (Tcure). It means that the vitrification occurs when the Tg and the Tcure are equal.

For the purpose of the present invention, the glass transition temperature (Tg) value has to be understood as the temperature at which the mechanical properties of the resin radically changed due to the internal movement of the polymer chains that form the resin. In order to determine the Tg value, Differential Scanning Calorimetry (DSC) method can be performed according to ISO 11357-2 standard.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of difunctional epoxy resins with a cross-linking agent of formula (II) as defined above, in a molar ratio comprised from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of difunctional epoxy resins comprising a bisphenol epoxide polymer, with a cross-linking agent of formula (II) as defined above, in a molar ratio comprised from 2.1 to 1.1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins with a cross-linking agent of formula (II) as defined above, in a molar ratio 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising: (a) mixing a mixture of two difunctional epoxy resins comprising a bisphenol epoxy resin, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature comprised from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins comprising a bisphenol epoxy resin from 60% to 99% by weight, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature comprised from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins comprising a bisphenol A diglycidyl ether or bisphenol F diglycidyl ether from 60% to 99% by weight, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature comprised from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins comprising a bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and 1 ,4-butanediol diglycidyl ether, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins comprising a bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and neopentyl glycol diglycidyl ether, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and 1 ,4-butanediol diglycidyl ether, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature comprised from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and neopentyl glycol diglycidyl ether, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature comprised from 10 °C to 200 °C. In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of difunctional epoxy resins with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio comprised from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of difunctional epoxy resins comprising a bisphenol epoxy resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins comprising a bisphenol epoxy resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins comprising a bisphenol epoxy resin at from 60% to 99% by weight, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins comprising a bisphenol A diglycidyl ether or bisphenol F diglycidyl ether at from 60% to 99% by weight, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10°C to 200°C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins comprising a bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and 1 ,4-butanediol diglycidyl ether, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio comprised from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins comprising a bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and neopentyl glycol diglycidyl ether, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio comprised from 2: 1 to 1 : 1 , and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and 1 ,4-butanediol diglycidyl ether, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; and neopentyl glycol diglycidyl ether, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is a mixture of epoxide- functionalised resins comprising one or more tetrafunctional resins.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method wherein in step (I) the epoxide-functionalised resin with a functionality equal to or higher than 2 is the tetrafunctional epoxy resin tetraglycidyl methylene dianiline.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins and a tetrafunctional epoxy resin, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising: (a) mixing a mixture of two difunctional epoxy resins, one of them being a bisphenol epoxy resin, and a tetrafunctional epoxy resin, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins, one of them being a bisphenol epoxy resin, and a tetrafunctional epoxy resin from 20% to 80% by weight, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins, one of them being a bisphenol A diglycidyl ether or bisphenol F diglycidyl ether from 20% to 80% by weight, and a tetrafunctional epoxy resin, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture of epoxy functionalised resins comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; 1 ,4-butanediol diglycidyl ether; and a tetrafunctional epoxy resin, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture of epoxy functionalised resins comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; neopentyl glycol diglycidyl ether; and a tetrafunctional epoxy resin, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; 1 ,4-butanediol diglycidyl ether; and a tetrafunctional epoxy resin, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1:1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; neopentyl glycol diglycidyl ether; and a tetrafunctional epoxy resin, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C. In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising difunctional and tetrafunctional epoxy resins with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above;

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising difunctional and tetrafunctional epoxy resins comprising a bisphenol epoxy resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio comprised from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising two difunctional epoxy resins and a tetrafunctional resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising two difunctional epoxy resins, one of them being a bisphenol epoxy resin, and a tetrafunctional epoxy resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising two difunctional epoxy resins, one of them being a bisphenol epoxy resin from 20% to 80% by weight, and a tetrafunctional epoxy resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising two difunctional epoxy resins, one of them being a bisphenol A diglycidyl ether or bisphenol F diglycidyl ether from 20% to 80% by weight, and a tetrafunctional epoxy resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising: (a) mixing a mixture comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; 1 ,4-butanediol diglycidyl ether; and a tetrafunctional epoxy resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; neopentyl glycol diglycidyl ether; and a tetrafunctional epoxy resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; 1 ,4-butanediol diglycidyl ether; and a tetrafunctional epoxy resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; neopentyl glycol diglycidyl ether; and a tetrafunctional epoxy resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (II) as defined above, in a molar ratio epoxide: -NH2 from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins, one of them being a bisphenol epoxy resin, and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising: (a) mixing a mixture of two difunctional epoxy resins, one of them being a bisphenol epoxy resin at from 20% to 80% by weight, and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and (b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture of two difunctional epoxy resins, one of them being a bisphenol A diglycidyl ether or bisphenol F diglycidyl ether at from 20% to 80% by weight, and tetraglycidyl methylene dianiline, with a crosslinking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture of epoxy functionalised resins comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; 1 ,4-butanediol diglycidyl ether; and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture of epoxy functionalised resins comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; neopentyl glycol diglycidyl ether; and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; 1 ,4-butanediol diglycidyl ether; and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; neopentyl glycol diglycidyl ether; and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (II) as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising difunctional and tetraglycidyl methylene dianiline with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C. In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising difunctional and tetraglycidyl methylene dianiline comprising a bisphenol epoxy resin, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising two difunctional epoxy resins and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising two difunctional epoxy resins, one of them being a bisphenol epoxy resin, and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising two difunctional epoxy resins, one of them being a bisphenol epoxy resin from 20% to 80% by weight, and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising two difunctional epoxy resins, one of them being a bisphenol A diglycidyl ether or bisphenol F diglycidyl ether from 20% to 80% by weight, and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; 1 ,4-butanediol diglycidyl ether; and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising: (a) mixing a mixture comprising bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; neopentyl glycol diglycidyl ether; and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; 1 ,4-butanediol diglycidyl ether; and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

In one embodiment, the thermoset crosslinked epoxy resin composition is obtainable by a method comprising:

(a) mixing a mixture consisting of bisphenol A diglycidyl ether or bisphenol F diglycidyl ether; neopentyl glycol diglycidyl ether; and tetraglycidyl methylene dianiline, with a cross-linking agent of formula (III) or formula (IV) or a mixture thereof as defined above, in a molar ratio from 2:1 to 1 :1, and a catalyst as defined above; and

(b) curing the reaction mixture at a temperature from 10 °C to 200 °C.

It is also part of the present invention, the method for the preparation of the thermoset crosslinked epoxy resin composition of the first aspect of the present invention, which comprises:

(I) mixing an epoxide-functionalised resin with a functionality equal to or higher than 2, with:

- a cross-linking agent of formula (I)

Ar-S-S-Ar (I) at a molar ratio between the epoxide groups of the epoxy-functionalised resin and the epoxide-reactive functional moieties of the cross-linking agent of formula (I) from the stoichiometric to a two-fold excess of epoxide reactive functional group; and

- at least one Lewis acid catalyst, and

(II) curing the mixture obtained in step (I) at a temperature from 10°C to 200°C for a period of time such that the thermoset crosslinked epoxide resin reaches a glass transition temperature value which is equal to or higher than 10°C but equal to or lower than the maximum glass transition temperature.

All the embodiments disclosed above in relation to steps (I) and (II) and particularly to the epoxide- functionalised resin, the cross-linking agent and the catalyst for the thermoset crosslinked epoxy resin composition characterized by its preparation process of the first aspect of the present invention, also apply herein to the preparation process of the thermoset crosslinked epoxy resin.

As it has been stated above, the second aspect of the invention refers to a thermoset composite comprising:

(a) a reinforcement phase comprising fibres, and

(b) a matrix phase comprising the thermoset crosslinked epoxide resin composition of the present invention. In the present invention, the term "composite” refers to a material made from two or more constituent materials with significantly different physical or chemical properties, that when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure. Composite materials are generally used for buildings, bridges, wind blades, aircraft and automotive structural components, boat hulls, storage tanks, among others.

In an embodiment, the thermoset composite of the present invention comprises:

(a) from 25 to 75 volume % with respect to the total volume of the composite of the reinforcement phase comprising fibres, and

(b) from 30 to 75 volume % with respect to the total volume of the composite of the matrix phase comprising the thermoset crosslinked epoxide resin composition as defined in the first aspect of the invention, being the sum of being the sum of volumes of (a) and (b) equal to 100%.

In an embodiment, the thermoset composite of the present invention comprises:

(a) a reinforcement phase comprising fibres, and

(b) a matrix phase comprising from 50-100% by weight with respect to the total weight of the matrix phase of the thermoset crosslinked epoxide resin composition of the present invention.

The term "volume percentage (%)” when referred to the reinforcement and matrix phases, is estimated dividing the volume of the phase with respect to the total volume of the composite and the resulting value is multiplied by 100. Depending on the nature of the fibre, the fibre volume of a composite material may be determined by chemical matrix digestion (ASTM D3171) or resin burn-off (ASTM D2584), in which the matrix is eliminated and the fibres weighed and calculated from substituent weights and densities. Alternatively, a photomicrographic technique may be used in which the number of fibres in a given area of a polished cross section is counted and the volume fraction determined as the area fraction of each constituent.

In one embodiment, the thermoset composite of the present invention is a multilayer composite. In one embodiment, the thermoset composite of the present invention is a multi-layered composite comprising two or more layers comprising each one of the layers: a) a reinforcement phase comprising fibres, and (b) a matrix phase comprising the thermoset crosslinked epoxide resin as defined in the present invention. In one embodiment, the thermoset composite of the present invention is a multi-layered composite comprising two or more layers as defined above, wherein each layer is a prepreg as defined in the present invention.

In the present invention, the term "reinforcement phase comprising fibres” is a material that comprise one or more fibre layers in a discontinuous or continuous way. The term "fibres” encompasses woven, non-crimped, non-woven, unidirectional UD, and multi-axial textile structure form. Illustrative examples of woven fibre forms include plain, satin or twill weave style. Illustrative examples of non-crimped and multi-axial fibre forms include a number of plies and fibre orientations. Such styles and forms are well known in the composite reinforcement field and are commercially available from a number of companies.

In one embodiment, the composite is one wherein the (a) reinforcement phase comprises fibres selected from the group consisting of organic fibres and inorganic fibres. In one embodiment, the composite is one wherein the (a) reinforcement phase comprises fibres selected from the group consisting of glass, carbon, aramide (made of aromatic polyamides), flax, and combination thereof. In one embodiment, the composite is one wherein the (a) reinforcement phase comprises glass fibre. In one embodiment, the composite is one wherein the (a) reinforcement phase consists of glass fibre. In one embodiment, the composite is one wherein the (a) reinforcement phase comprises carbon fibre. In one embodiment, the composite is one wherein the (a) reinforcement phase consists of carbon fibre.

The composite of the second aspect of the invention, and particularly the matrix phase of the composite, further comprises one or more additional excipients or carriers. Non-limitative examples of additional excipients or carriers include, among others, polymers different from the thermoset crosslinked epoxy resin composition of the first aspect of the invention, pigments, dyes, fillers, plasticizers, flame retardants, antioxidants, lubricants, metals, and mixtures thereof. Illustrative non-limitative examples of polymers include, among others, elastomers, thermoplastics, thermoplastic elastomers, impact additives, and combinations thereof.

The term "pigments" means coloured particles that are insoluble in the thermoset crosslinked epoxy resin composition of the first aspect of the invention. As pigments that may be used in the invention, mention may be made of titanium oxide, carbon black, carbon nanotubes, metal particles, silica, metal oxides, metal sulphides or any other mineral pigment; mention may also be made of phthalocyanines, anthraquinones, quinacridones, dioxazines, azo pigments or any other organic pigment, natural pigments (madder, indigo, crimson, cochineal, etc.) and mixtures of pigments. The pigments may represent from 0.05% to 15% by weight relative to the weight of the material.

The term "dyes" means molecules that are soluble in the thermoset crosslinked epoxy resin composition of the first aspect of the invention and that have the capacity of absorbing part of the visible radiation.

Among the fillers that may be used in the thermoset crosslinked epoxy resin composition of the invention, mention may be made of: trihydrate alumina, silica, clays, calcium carbonate, carbon black, kaolin, and whiskers.

In an embodiment, the composite of the present invention has a recycling rate of the thermoset crosslinked epoxy resin composition of the first aspect of the invention equal to or higher than 70% w/w. In an embodiment, the composite of the present invention has a recycling rate of the thermoset crosslinked epoxy resin composition of the first aspect of the invention equal to or higher than 75% w/w. In an embodiment, the composite of the present invention has a recycling rate of the thermoset crosslinked epoxy resin composition of the first aspect of the invention equal to or higher than 80% w/w. In an embodiment, the composite of the present invention has a recycling rate of the thermoset crosslinked epoxy resin composition of the first aspect of the invention equal to or higher than 85% w/w. In an embodiment, the composite of the present invention has a recycling rate of the thermoset crosslinked epoxy resin composition of the first aspect of the invention equal to or higher than 90% w/w. In an embodiment, the composite of the present invention has a recycling rate of the thermoset crosslinked epoxy resin composition of the first aspect of the invention equal to or higher than 95% w/w.

In an embodiment, the composite of the present invention has a recycling rate of the reinforcement phase comprising fibres equal to or higher than 95% w/w. In an embodiment, the composite of the present invention has a recycling rate of the reinforcement phase comprising fibres equal to or higher than 96% w/w. In an embodiment, the composite of the present invention has a recycling rate of reinforcement phase comprising fibres equal to or higher than 97% w/w. In an embodiment, the composite of the present invention has a recycling rate of the reinforcement phase comprising fibres equal to or higher than 98% w/w. In an embodiment, the composite of the present invention has a recycling rate of the reinforcement phase comprising fibres equal to or higher than 99% w/w. In an embodiment, the composite of the present invention has a recycling rate of the reinforcement phase comprising fibres of about 100% w/w.

In an embodiment, the composite of the present invention has a recycling rate of the thermoset crosslinked epoxy resin composition of the first aspect of the invention equal to or higher than 70% w/w; particularly equal to or higher than 75% w/w; particularly equal to or higher than 80% w/w; particularly equal to or higher than 85% w/w; particularly equal to or higher than 90% w/w; particularly about 95% w/w; and a recycling rate of the reinforcement phase comprising fibres equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98% w/w; particularly equal to or higher than 99% w/w; particularly about 100% w/w. In an embodiment, the composite of the present invention has a recycling rate of the thermoset crosslinked epoxy resin composition of the first aspect of the invention is about 95% w/w; and a recycling rate of the reinforcement phase comprising fibres of about 100% w/w.

In an embodiment, the composite of the present invention is one that when submitted to the recycling process of the present invention then the recycled thermoset crosslinked epoxy resin composition of the first aspect of the invention has a chemical purity equal to or higher than 95% w/w; particularly equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98% w/w; particularly equal to or higher than 99% w/w; particularly about 100% w/w.

In an embodiment, the composite of the present invention is one that when submitted to the recycling process of the present invention then the recycled reinforcement phase comprising fibres has a chemical purity equal to or higher than 95% w/w; particularly equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98% w/w; particularly equal to or higher than 99% w/w; particularly about 100% w/w. In an embodiment, the composite of the present invention is one that when submitted to the recycling process of the present invention then the recycled thermoset crosslinked epoxy resin composition of the first aspect of the invention has a chemical purity equal to or higher than 95% w/w; particularly equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98% w/w; particularly equal to or higher than 99% w/w; particularly about 100% w/w; and the recycled reinforcement phase comprising fibres has a chemical purity equal to or higher than 95% w/w; particularly equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98% w/w; particularly equal to or higher than 99% w/w; particularly about 100% w/w. In an embodiment, the composite of the present invention is one that when submitted to the recycling process of the present invention then the recycled thermoset crosslinked epoxy resin composition of the first aspect of the invention has a chemical purity equal to or higher than 95% w/w; and the recycled reinforcement phase comprising fibres has a chemical purity equal to or higher than 95% w/w.

In an embodiment, the composite of the present invention is one that when submitted to the recycling process of the present invention then the recycled thermoset crosslinked epoxy resin composition of the first aspect of the invention has a chemical purity equal to or higher than 95% w/w; particularly equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98% w/w; particularly equal to or higher than 99% w/w; particularly about 100% w/w; and the composite of the present invention has a recycling rate of the reinforcement phase comprising fibres equal to or higher than 95% w/w; particularly equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98% w/w; particularly equal to or higher than 99% w/w; and particularly about 100% w/w.

In an embodiment, the composite of the present invention is one that when submitted to the recycling process of the present invention then the recycled reinforcement phase comprising fibres has a chemical purity equal to or higher than 95%; particularly equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98% w/w; particularly equal to or higher than 99% w/w; particularly about 100% w/w; and a recycling rate of the reinforcement phase comprising fibres equal to or higher than 96% w/w; particularly equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98% w/w; particularly equal to or higher than 99% w/w; particularly about 100% w/w. In an embodiment, the composite of the present invention is one that when submitted to the recycling process of the present invention then the recycled reinforcement phase comprising fibres has a chemical purity is about 100% w/w; and a recycling rate of the reinforcement phase comprising fibres of about 100% w/w.

In an embodiment, the composite of the present invention is one that when submitted to the recycling process of the present invention then the recycled thermoset crosslinked epoxy resin composition of the first aspect of the invention has a chemical purity equal to or higher than 95% w/w; particularly equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98% w/w; particularly equal to or higher than 99% w/w; particularly about 100% w/w; and the composite of the present invention has a recycling rate of the recycled thermoset crosslinked epoxy resin composition equal to or higher than 70% w/w; particularly equal to or higher than 75% w/w; particularly equal to or higher than 80% w/w; particularly equal to or higher than 85% w/w; particularly equal to or higher than 90% w/w; and particularly about 95% w/w; and when submitted to the recycling process of the present invention then the recycled reinforcement phase comprising fibres has a chemical purity equal to or higher than 95% w/w; particularly equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98% w/w; particularly equal to or higher than 99% w/w; particularly about 100% w/w; and a recycling rate of the reinforcement phase comprising fibres equal to or higher than 96% w/w; particularly equal to or higher than 96% w/w; particularly equal to or higher than 97% w/w; particularly equal to or higher than 98%; particularly equal to or higher than 99% w/w; particularly about 100% w/w.

For the purpose of the present invention, the "recycling rate" refers to the dry weight of the recycled component (i.e. the recycled thermoset crosslinked epoxy resin composition or the recycled reinforcement phase comprising fibres) with respect to the dry weight of the component used as starting material ((i.e. the thermoset crosslinked epoxy resin composition or the reinforcement phase comprising fibres) for the preparation of the composite, and the resulting value is multiplied by 100.

For the purpose of the present invention the "chemical purity” refers to the measurement of the amount of impurities found in a chemical sample. For example, the chemical purity of the recycled thermoset crosslinked epoxy resin composition is measured as the weight of thermoset crosslinked epoxy resin with respect to the total weight of the recycled thermoset crosslinked epoxy resin (which may contain variable amounts of reinforcement phase comprising fibres) and the resulting value is multiplied by 100. In the case of the reinforcement phase comprising fibres, the chemical purity of the recycled reinforcement phase comprising fibres is measured as the weight of reinforcement phase comprising fibres with respect to the total weight of recycled reinforcement phase comprising fibres (which may contain a variable amount of crosslinked epoxy resin composition) and the resulting value is multiplied by 100. For the purpose of the invention, the chemical purity can be measured by any appropriate method known in the state of the art. In the present invention, the chemical purity is measured by thermogravimetric analysis (TGA) or by Fourier transform infrared spectroscopy (FTIR).

It is also a part of the present invention a process for the preparation of the composite of the second aspect of the invention. Several methodologies for the preparation of composites are known in the state of the art. All of them can be applied to the present invention. The skilled person, making use of its general knowledge, is able of selecting and optimizing the parameters for performing any of the processes disclosed above according to the type of composite to be prepared.

Illustrative non-limitative examples of processes for the preparation of the composition of the present invention are disclose herein below: Method 1 (Wet lay-up/hand lay-up). This method involves that the reinforcements are impregnated by hand with resin; this is accomplished by rollers or brushes for forcing resin into the fabrics. Laminates are left to cure using several methods. In the simplest procedure, curing takes place at room temperature. Curing can be accelerated by applying heat, typically in an oven, and pressure, by means of vacuum. For the latter, a vacuum bag with breather assemblies is placed over the lay-up and attached to the tool; then, before curing, air is evacuated using a vacuum pump.

Method 2 (Filament winding). This process is primarily used for hollow, generally circular, or oval sectioned components, such as pipes and tanks. Fibre tows are passed through a resin bath before being wound onto a mandrel in a variety of orientations, controlled by the fibre feeding mechanism, and rate of rotation of the mandrel. Finally, the resin is cured at room temperature or in an oven, applying heat.

Method 3 (Pultrusion). Fibres are pulled from a creel through a resin bath and then on through a heated die. The die completes the impregnation of the fibre, controls the resin content, and cures the material into its final shape as it passes through the heated die. This cured profile is then automatically cut to length. Fabrics may also be introduced into the die to provide fibre direction other than at 0°C.

Method 4 (RTM: Resin Transfer Moulding). Fabrics are laid up as a dry stack of materials. These fabrics can pre-pressed to the mould shape and held together by a binder. These ‘preforms' are then laid into the mould tool more easily. A second mould tool is then clamped over the first, and resin is injected into the cavity under low to moderate pressure. Vacuum can also be applied to the mould cavity to assist resin in being drawn into the fabrics. This is known as Vacuum Assisted Resin Injection (VARI) or Vacuum Assisted RTM (when additional pressure is not applied, just vacuum). Once all the fabric is wet out, the resin inlets are closed, and the laminate is allowed to cure. Both injection and cure can take place at either ambient or elevated temperature.

Method 5 (Infusion). Fabrics are laid up as a dry stack of materials as in RTM. The fibre stack is then covered with peel ply and a knitted type of non-structural fabric. The whole dry stack is then vacuum bagged, and once bag leaks have been eliminated, resin is allowed to flow into the laminate under vacuum. The resin distribution over the whole laminate is aided by resin flowing easily through the non-structural fabric and wetting the fabric out from above.

Method 6 (RFI: Resin Film Infusion). Dry fabrics are laid up interleaved with layers of semi-solid resin film supplied on a release paper. The lay-up is vacuum bagged to remove air through the dry fabrics, and then heated to allow the resin to first melt and flow into the air-free fabrics, and then after a certain time, to cure.

Method 7 (SMC: Sheet Moulding Compound). Sheet Moulding Compound is an integrated ready-to-mould composition of fibres, resin, and filler. SMC is made by metering a resin paste onto a thin plastic carrier film. The compound is made by chopping continuous fibres onto the resin paste as it is conveyed on the film. This fibre/resin mix is further covered by another layer of resin on a second carrier film. Compaction rollers knead the fibres into the resin for uniform fibre distribution and wetting. The compound sandwiched between the carrier films is gathered into rolls and stored until it matures. Upon maturation, SMC is tack free and has a leather-like consistency. The carrier film is removed and the sheet is prepared into a charge of predetermined weight and shape. The charge is placed on the bottom of two mould halves in a compression press and it cures under specific heat and pressure conditions.

Method 8 (Prepreg based technologies). The fibrous reinforcement is typically impregnated, fully or partially, by the uncured epoxy matrix composition in accordance with any of the known prepreg manufacturing techniques, such as hot melt processing to produce unidirectional UD and fabric prepregs or solvent dip processing to produce fabric prepregs Once the reinforcement is impregnated, the epoxy matrix is partially cured (referred to as B-staged) and tacky, and in this form is supplied to the composite manufacturer, who can use it to lay-up the part (by hand lay-up, or automatic tape laying ATL or automatic fibre placement AFP) on the mould and by vacuum bag moulding, autoclave moulding, or press moulding. The vacuum bag technique involves the placing and sealing of a flexible bag over a composite lay-up and evacuating all the air from under the bag. The removal of air forces the bag down onto the lay-up with a consolidation pressure of up to 1 atmosphere (1 bar). The completed assembly, with vacuum still applied, is placed inside an oven or on a heated mould with good air circulation, and the composite is produced after a relatively short cure cycle. The autoclave technique requires a similar vacuum bag but the oven is replaced by an autoclave. The autoclave is a pressure vessel which provides the curing conditions for the composite where the application of vacuum, pressure, heat up rate and cure temperature are controlled. Compression moulding describes the process whereby a stack of prepregs is compressed between a set matched dies using a powerful press, and then cured while under compression. The moulds may be heated or the prepregs may be preheated and formed in relatively cool moulds. Also a diaphragm forming autoclave technique can be used. Diaphragm forming is an autoclave technique used solely for thermoplastic matrix composites. The laminate is laid up flat between two diaphragms (superplastic aluminium sheets or high temperature polymeric films), the diaphragms are clamped in a frame (the laminate is not clamped), then the laminate is formed using heat, vacuum, and pressure in the autoclave.

Then, "prepregs” are appropriate intermediate materials for the manufacturing of composites. For the purpose of the invention the term "prepreg” means an intermediate ready-to mould material comprising a reinforcement material layer totally or partially pre-impregnated with the thermoset crosslinked epoxy resin composition of the first aspect of the invention. A prepreg refers to a moulding intermediate material the handleability of which is made good by impregnating a matrix resin comprising the thermoset crosslinked epoxide resin of the invention into the fiber reinforcing material and removing flowability and adhesiveness. In the present invention, the form of a fiber reinforcing material that forms a prepreg is not particularly limited.

Thus, it is also a part of the invention a "prepreg”. The third aspect of the invention relates to "prepreg” comprising:

(a') a reinforcement phase comprising fibres, and

(b’) a matrix phase comprising the thermoset crosslinked epoxide resin of the present invention.

All embodiments mentioned above for the reinforcement phase comprising fibres (a) and matrix phase comprising the thermoset crosslinked epoxide resin (b) (particularly to the epoxide-functionalised resin, the cross-linking agent, the catalyst, and the reaction conditions of the preparation process); also apply herein for the reinforcement phase comprising fibres (a'), and the matrix phase comprising the thermoset crosslinked epoxide resin of the present invention (b’).

In one embodiment, the prepreg is a "partially (pre)-impregnated” prepreg. The term "partially (pre)- impregnated” means a prepreg wherein the reinforcement material layer is (pre)-impregnated with the thermoset crosslinked epoxide resin of the invention from one side.

In one embodiment, the prepreg is a "totally (pre)-impregnated” prepreg. The term "totally (pre)-impregnated” means that both sides of the reinforcement material layer are (pre)-impregnated with the thermoset crosslinked epoxide resin of the invention.

In one embodiment, the prepreg is one which comprises a thermoset crosslinked epoxide resin composition partially cured of the invention, partially or totally (pre)-impregnated. As it is mentioned above, the term "thermoset crosslinked epoxide resin composition partially cured” is one obtainable by a method as defined herein above and below, wherein the curing step (ii) is performed at a temperature from 10°C to 200 °C for a period of time such that the resin reaches at least 25% of the maximum Tg value.

In one embodiment, the prepreg is one which comprises a thermoset crosslinked epoxide resin composition completely cured of the invention, partially or totally (pre)-impregnated. As it is mentioned above, the term "thermoset crosslinked epoxide resin composition completely cured” is one obtainable by a method as defined herein above and below, wherein the curing step (ii) is performed at a temperature from 10°C to 200 °C for a period of time such that the resin reaches at maximum Tg value. For the purpose of the present invention, the term "prepreg comprising a thermoset crosslinked epoxide resin completely cured of the invention” and "enduring prepreg” have the same meaning and are used interchangeable. The term "enduring prepreg” means that the prepreg has no time limitation between the manufacturing date and the processing date of the prepreg.

It is also a part of the invention the use of the "prepreg” of the present invention, and particularly the "enduring prepregs” of the present invention for the manufacture of the composites of the second aspect of the invention. The manufacturing of the final composition from the prepreg can be performed under different conditions depending on the nature of the prepreg and the type of composite intended to be obtained. There are well-known standard technologies in the state of the art for the manufacture of composites from prepregs as disclosed herein above (see method 8).

In one embodiment, the manufacturing of the composites of the present invention starting from one or more partially cured prepregs of the present invention comprises curing an moulding the prepreg simultaneously into the desired shape of the composite. In one embodiment, the manufacturing of the composites of the present invention starting from one or more enduring prepregs of the present invention comprises applying the appropriate temperature and pressure to allow the moulding into the desired shape.

It is also a part of the present invention a process for the preparation of the prepregs as disclosed herein above. Several methodologies for the preparation of prepregs are known in the state of the art. All of them can be applied to the present invention. The skilled person, making use of its general knowledge, is able of selecting and optimizing the parameters for performing any of the processes disclosed above according to the type of prepreg to be prepared. In particular, there are two main methods of producing prepreg; hot melt and solvent dip. The hot melt method can be used to produce unidirectional (UD) and fabric prepregs. This requires two processing stages. In the first stage, the epoxide-functionalised resin with a functionality equal to or higher than 2, the cross-linking agent of formula (I) and the at least one Lewis acid catalyst, is coated onto a paper substrate in a thin film. Then, the reinforcement (unidirectional fibres or fabric) and the thin film obtained in the first stage are then brought together on the prepreg machine. Impregnation of the thin film obtained in the first stage into the fibre is achieved using heat and pressure from nip rollers. The final prepreg is then wound onto a core. The solvent dip method can only be used to produce fabric prepregs. In this technique, the mixture of the first stage is dissolved in a bath of solvent and reinforcing fabric is dipped into. The solvent is evaporated from the prepreg in a drying oven. This can be horizontal or vertical.

The fourth aspect of the present invention relates to an article comprising the thermoset crosslinked epoxy resin. In an embodiment, the article comprises one or more thermoset composite of the present invention comprising the thermoset crosslinked epoxy resin. In an embodiment, the article comprises one or more prepregs of the present invention comprising the thermoset crosslinked epoxy resin.

All embodiments and combinations thereof mentioned above for the thermoset crosslinked epoxide resin (particularly to the epoxide-functionalised resin, the cross-linking agent, the catalyst, and the reaction conditions of the preparation process); the composite (particularly the reinforcement phase comprising fibres, and the matrix phase), and the prepreg, also apply herein for the article of the fourth aspect of the invention. The articles of the present invention are useful in a wide range of technical fields, such as for example the automotive, the aerospace, the railway, the sports and goods, and the renewable energy sectors, among others.

The fifth aspect of the invention is a process for recycling the thermoset crosslinked epoxy resin composition of the present invention as well as the reinforcement phase comprising fibres from a composite, or from a prepreg, or from an article comprising the thermoset crosslinked epoxy resin composition of the present invention. As it is demonstrated in the experimental section, a composite, or prepreg, or article comprising the thermoset crosslinked epoxy resin composition of the present invention is easily recyclable under mild conditions without alteration of the physical and chemical properties of both the thermoset crosslinked epoxy resin composition and the reinforcement phase. Fact that allows its re-used and/or repurposed without hindering the quality/properties of the composites/articles containing the recycled thermoset crosslinked epoxy resin composition. The recycling process comprises immersing the composite, or the prepreg, or the article comprising the thermoset crosslinked epoxy resin composition of the present invention in a solvent or mixture of solvents having a boiling temperature above the glass transition temperature of the thermoset crosslinked epoxy resin composition and a Hansen solubility parameter (Ra) equal to or lower than 7.5.

The Hansen solubility parameter (Ra) is commonly measured by equation (1):

Ra ² = 4(5DI-5D ₂ ) ² + (5PI-5P ₂ ) ² + (5HI-5H ₂ ) ² (eq. 1)

Being:

5D1 the solubility parameter of the thermoset crosslinked epoxy resin composition for dispersion expressed in MPa ^1/2 ,

5D2 the solubility parameter of the solvent or mixture of solvents for dispersion expressed in MPa ^1/2 ,

5P1 the solubility parameter of the thermoset crosslinked epoxy resin composition for polars expressed in MPa ^1/2 ,

5P2 the solubility parameter of the solvent or mixture of solvents for polars expressed in MPa ^1/2 ,

5H1 the solubility parameter of the thermoset crosslinked epoxy resin composition for hydrogen-bonding expressed in MPa ^1/2 , and

5H2 the solubility parameter of the solvent or mixture of solvents for hydrogen-bonding expressed in MPa ^1/2 . Nevertheless, the Hansen solubility parameter of a solvent is available in the state of the art; or alternatively, the Hansen solubility parameter of a mixture of solvents can be measured (cf. Hansen Solubility Parameters: A User's Handbook, Second Edition published in 2007 by CRC Press available in https://www.hansen- solubility.com/HSP-science/solvent-blends.php on May 19th, 2022).

In an embodiment, the recycling process of the invention is performed in the absence of a base or an acid. Non-limiting examples of appropriate solvents or mixtures of solvents include, but not limited to, dimethylformamide, dimethyl sulfoxide, N-Methyl-2-pyrrolidone, gamma-Valero lactone, benzyl alcohol, methoxybenzene, cyclopentanone, cyclohexanone, N-buty l-pyrrolone, a mixture of dimethyl sulfoxide: acetone (40:60), a mixture of Dimethylformamide and methyl ethyl ketone (63:37).

In an embodiment, the recycling process of the invention further comprises a separation step of the thermoset crosslinked epoxy resin of the invention and the reinforcement phase comprising fibres after the immersing step consisting of removing the reinforcement phase comprising fibres from the solvent media.

In an embodiment, the recycling process of the invention further comprises a recovery step after the separation step.

In an embodiment, the recycling process of the invention further comprises a recovery step of the thermoset crosslinked epoxy resin composition after the separation step comprising removing the solvent by any of the suitable techniques known to a person skilled and known in the art (such as evaporation, centrifugation, among others).

In an embodiment, the recycling process of the invention further comprises a recovery step of the reinforcement after the separation step comprising drying the reinforcement. This step is commonly performed in an oven under vacuum conditions.

It is also part of the invention a prepreg and article comprising the recyclable thermoset crosslinked epoxide resin of the present invention, which when submitted to the recycling process conditions of the process of the present invention; then, the recycling rate of the thermoset crosslinked epoxide resin, and reinforcement; as well as the chemical purity of recycled thermoset crosslinked epoxide resin, and reinforcement are those mentioned herein above for the composite of the present invention.

Throughout the description and claims the word "comprise" and variations of the word, are not intended to exclude other technical features, additives, components, or steps. Furthermore, the word "comprise” encompasses the case of "consisting of”. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples are provided by way of illustration, and they are not intended to be limiting of the present invention. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments described herein.

Examples

1. Materials and methods

Epoxy resin D.E.R 332 was purchased from Sigma-Aldrich, hardeners Diethyltoluenediamine (DETDA) and 4- bis(amino phenyl) disulphide (4-AFD) were purchased from Biosynth Carbosynth and glass fibre reinforcement (HexForce 1103 PLAIN, basis weight 290 g/m2) was purchased from Hexcel. Boron trifluoride ethylamine, Chromium (III) 2-ethylhexanoate, Zinc chloride, Zinc (II) 2-ethylhexanoate, Dimethylethanolamine (DMAE), Dimethyl sulfoxide (DMSO), Dimethylformamide (DMF), g-Valero lactone, Cyclopentanone, Toluene and Glycerol were purchased from Sigma-Aldrich. All these materials were used as received.

Thermal analysis was performed on a differential scanning calorimetry (DSC) instrument from Perkin Elmer (Pyris Diamond DSC) over a temperature range from 30 °C to 250 °C under nitrogen. The DSC was calibrated for temperature from the melting point of indium (156.6 °C). Measurement of glass transition temperature (Tg) was carried out by DSC, wherein Tg was obtained as the inflection point of the heat flow step recorded at a scan rate of 20 °C min-1.

2. Recyclable thermoset crosslinked epoxy resin compositions 2.1. recyclable, thermoset crosslinked epoxy resin compositions of the present invention having Tg = 130°C (Examples 1-4)

General preparation process

D.E.R 332 (10 g), AFD (4.6 g) and the catalyst (150 mg) were fed into a 50 mL flask. The mixture was heated at 80 °C until the AFD was completely dissolved in the resin, while degassing by magnetic stirring under vacuum. Then, the mixture was poured onto a 2 mm thick mould and was allowed to cure at 130 °C for 60 minutes.

Following the general preparation process, the recyclable thermoset crosslinked epoxy resin compositions of the invention Examples 1-4 were prepared. In all cases, the resulting recyclable thermoset crosslinked epoxy resin compositions were obtained as transparent yellowish solid materials with the same Tg = 130 °C (determined by DSC). The catalyst used in each Example is disclosed herein below:

2.2. Comparative thermoset crosslinked epoxy resin compositions

Comparative Example 1 was obtained following the process for the preparation of Example 1 (cf. section 2.1 .) BUT changing the hardener AFD by the hardener DETDA (3.6 g) falling outside the scope of the present invention.

Comparative Example 2 was obtained following the process for the preparation of Example 1 (cf. section 2.1 .) BUT changing the boron trifluoride ethylamine catalyst by the Dimethylethanolamine (DMAE) catalyst (150 mg) falling outside the scope of the present invention.

Comparative Example 3 was obtained following the process for the preparation of Example 1 (cf. section 2.1 .) BUT in the absence of a catalyst, falling outside the scope of the present invention.

3. Multilayer epoxy composites

3.1. Multilayer epoxy composites of the present invention having Tg = 130°C (Examples 5-8)

A general process for the preparation of multilayer epoxy composites having Tg = 130°C by manual impregnation is disclosed herein below:

A sealant tape was placed on a 400 x 400 mm square glass mould. Then, a releasing agent (Frekote 770-NC) was sprayed evenly onto the surface of the mould. A 250 x 250 mm sheet of glass fibre HexForce 1103 PLAIN (basis weight 290 g/m ² ) was placed on the mould. This was then manually impregnated with a mixture of a thermoset crosslinked epoxy resin composition of the present invention obtained in section 2.1 . (9.65 g) using a brush. Then, another 250 x 250 mm layer of glass fibre was placed, and the same operation was repeated until a total of 9 impregnated layers were completed. After, a release film was placed onto the part and then a layer of breather cloth was placed to soak up excess resin and ensure an adequate path for the vacuum pressure. Finally, the part was sealed with a vacuum bagging film and a hose connected to a vacuum pump was attached to the sealed part. Vacuum was then applied to the enclosed part which was compacted by the vacuum. Once air was evacuated, curing was carried out in an oven at 130 °C for 60 minutes.

3.2. Comparative multilayer epoxy composites (Comparative Examples 3-4)

Comparative multilayer composites (comparative Examples 4, 5and 6) were obtained following the general preparation process for composites disclosed in section 3.1 BUT changing the thermoset crosslinked epoxy resin composition of the present invention by the comparative thermoset crosslinked epoxy resin compositions 1, 2 or 3, respectively.

4. Chemical resistance Test

Chemical resistance of the multilayer epoxy composites of Examples 5-8 of the present invention and the comparative multilayer epoxy composites of Examples 4-6 was tested towards different solvents and chemical agents.

The tested composites were immersed in sodium hydroxide 1N, hydrochloric acid 1 N, tetrahydrofuran (THF), toluene and acetone separately at room temperature. After 72 hours at that temperature all samples remained unaltered.

5. Recovery of the thermoset crosslinked epoxy resin composition and the fibre reinforcement

The separation of the thermoset crosslinked epoxy resin compositions and the fibre reinforcement from the multilayer epoxy composites of the present invention (Examples 5-8) and comparative multilayer epoxy composites (comparative Examples 4-6) were performed in different solvents.

Further, the Tg of the thermoset crosslinked epoxy resins and the cleanliness level of the fibres thus separated were determined.

The general separation process is disclosed herein below:

20x20x2 mm ³ of a multilayer epoxy composite of the present invention (Examples 5-8) or a comparative multilayer epoxy composite (Comparative Examples 4-6) were immersed in different solvents as shown in Table 1 . The resulting mixtures were magnetically stirred at 130 °C for 24 hours, and afterwards the thermoset crosslinked epoxy resin composition separation from the glass fibre reinforcement and the cleanliness level of the fibres were visually evaluated. Moreover, the Tg of the recovered thermoset crosslinked epoxy resin composition (powder) was measured. The glass fibre reinforcement thus separated was recovered by drying in an oven at 100 °C with vacuum for 24 hours.

The results of these tests are summarized in Table 1 herein below:

Table 1

(a) Tg represents the Tg value of the thermoset crosslinked epoxy resin composition in powder form obtained after submitting the multilayer epoxy composite to the general separation (recovery) process

As it is shown in the results of Table 1, only the multilayer epoxy composites comprising a thermoset crosslinked epoxy resin composition of the present invention obtainable by a method that comprises mixing an epoxide-functionalised resin with a cross-linking agent and a catalyst; and curing the mixture thus obtained, with the proviso that the cross-linking agent comprises a disulphide bond are recyclable in the presence of solvents under mild conditions without the use of additional chemical agents (such as acid or bases). In particular, the recycling step is only performed by the use of a solvent or a mixture of solvents having a boiling temperature above the Tg of the composite to be recycled and a Hansen solubility parameter (abbreviated as HSP but commonly called Ra) below 7.5. On the contrary, the comparative composites which have been prepared with another catalyst or hardener different from that used in the present invention are maintain unaltered requiring extreme conditions.

Therefore, it is concluded that only the multilayer epoxy composites prepared from the thermoset crosslinked epoxy resin composition of the present invention show the ability of being recyclable under mild conditions. In fact, both the thermoset crosslinked epoxy resin composition and the fibrous reinforcement can be separated at the end of its life and recovered maintaining its original properties, allowing its directly re-sold, re-used, or repurposed without hindering the quality/properties of the recycled composites/articles containing it.

Furthermore, the thermoset epoxy resin composition of the present invention also has a mechanochromic behaviour, which mean that when the thermoset crosslinked epoxy resin composition or a composite containing it receives an impact, a color change in the visible region of the EM spectrum is observed on the damaged area. Such mechanochromic behaviour is reversible and disappears in a few hours. This property confers to the composite of the invention a great value because it permits detecting damage by simple visual inspection.

Citation List

1. ASTM D3171 (chemical matrix digestion)

2. ASTM D2584 (resin burn-off)