Method for manufacturing a composite based on a reinforcing element and a cross-linked functionalized resin composition

Abstract

Title: Method for manufacturing a composite based on a reinforcing element and a cross-linked functionalized resin composition. The present invention relates to a method for manufacturing a composite based on a reinforcing element and a cross-linked functionalized resin composition. The present invention also relates to a composite based on at least one reinforcing element and said cross-linked resin composition.

Description

Title of the invention: Method for manufacturing a composite based on a reinforcing element and a cross-linked functionalized resin composition technical field

[0001] The present invention relates to the field of resin compositions and composites, such as filament-resin composite laminates. In particular, the present invention relates to the field of manufacturing processes for composites using a functionalized resin composition.

[0002] Composite reinforcements made of filament-resin composite are known to those skilled in the art. An example of such a reinforcement, described for example in patent EP 1,167,080 (or US 7,032,637), is that of glass-resin composite monostrands (“GRC” for short) which exhibit high mechanical properties. The monostrands comprise continuous, unidirectional glass fibers impregnated in a crosslinked vinyl ester resin.

[0003] Document FR 3 031 757 describes a multi-composite reinforcement based on CVR monostrands exhibiting improved mechanical properties. This document describes the use of an epoxy vinyl ester resin composition, also comprising a phosphine-type photoinitiator and a crosslinking agent, tris(2-hydroxyethyl)isocyanate triacrylate.

[0004] These composites find applications in particular in connection with the reinforcement of semi-finished products or finished articles made of rubber such as tires for vehicles, of the pneumatic or non-pneumatic type.

[0005] Furthermore, one of the main challenges at present is combating climate change and seeking to reduce carbon dioxide emissions. One way to achieve this is through the development of sustainable resources, for example, through the use of renewable resources and recycled and / or reused materials.

[0006] In the composites mentioned above, glass fibers are used. Studies have therefore aimed to replace these glass fibers with natural fibers.

[0007] However, these studies encountered a major drawback. Indeed, natural fibers are hydrophilic, while polymer resins are primarily hydrophobic, which reduces their compatibility. Poor compatibility generally leads to a weak interface and lower performance.

[0008] Thus, other studies have been conducted, notably by modifying the surface of natural fibers immersed in aqueous solutions or treated with plasma. However, the results obtained are not satisfactory since a degradation of the fibers is observed.

[0009] It would therefore be desirable to find an alternative to the use of glass fibers implemented in composites, which would allow for the production of composites with improved mechanical properties. Description of the invention

[0010] Continuing its research, the Applicant unexpectedly discovered that a manufacturing process for a composite based on at least one reinforcing element and at least one cross-linked functionalized resin composition made it possible to improve the mechanical properties of said composites, with in particular improved adhesion between the reinforcing element and the cross-linked functionalized resin composition.

[0011] The present invention therefore relates to a method for manufacturing at least one composite based on at least one reinforcing element and at least one crosslinked resin composition comprising the following steps:

[0012] a) mixing at least one crosslinkable resin with at least one coupling agent comprising at least one methacrylate group and at least one functional group capable of reacting with a hydroxyl group, other than a methacrylate group,

[0013] in the presence of:

[0014] - of at least one crosslinking initiator; and

[0015] - of at least one crosslinking agent other than the crosslinking initiator and that the coupling agent, to obtain a functionalized resin composition;

[0016] b) bring at least one reinforcing element into contact with the functionalized resin composition; and

[0017] c) expose the functionalized resin composition and the reinforcing element to a temperature within a range of 90°C to 120°C.

[0018] The invention also relates to a composite based on at least one reinforcing element and said cross-linked functionalized resin composition, such as a laminate or a single strand of filament-resin composite comprising filaments embedded in said resin composition.

[0019] In this application, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0020] The expression "composition based on" means a composition comprising the mixture and / or the in situ reaction product of the various constituents used, some of these constituents being able to react and / or intended to react with each other, at least partially, during the various manufacturing phases of the composition; the composition can thus be in a totally or partially crosslinked state or in a non-crosslinked state.

[0021] By "embedded", it is meant that the reinforcing element is directly in contact with the resin composition over its entire surface, with the possible exception of the cutting areas of the composite.

[0022] By "resin composition", we mean here the resin as such or any composition based on this resin and comprising at least one additive (i.e. one or more additives) before crosslinking.

[0023] By "crosslinked" resin or "crosslinked" resin composition, it is understood that the resin is hardened (thermosetting), in other words in the form of a network of three-dimensional bonds, in a state characteristic of so-called thermosetting polymers (as opposed to so-called thermoplastic polymers).

[0024] In this application, the term "fibre" is equivalent to the term "monofrain". Thus, the two terms may be used interchangeably.

[0025] On the other hand, any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​from greater than a to less than b (i.e., excluding the bounds a and b), while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​from a to b (i.e., including the strict bounds a and b). In the present case, when an interval of values ​​is designated by the expression "from a to b", the interval represented by the expression "between a and b" is also and preferably designated. Brief description of the figures

[0026] [Fig-1] Fig. 1 represents a diagram of the single-strand synthesis process according to the invention.

[0027] [Fig. 2] Fig. 2, not drawn to scale for ease of understanding, is a drawing representing a cross-section of the single strand according to the invention. Description of the invention

[0028] As previously stated, the manufacturing process according to the invention includes, in particular, step a):

[0029] a) mixing at least one crosslinkable resin with at least one coupling agent comprising at least one methacrylate group and at least one functional group capable of reacting with a hydroxyl group, other than a methacrylate group,

[0030] in the presence of:

[0031] - of at least one crosslinking initiator; and

[0032] - of at least one crosslinking agent other than the crosslinking initiator and that the coupling agent.

[0033] At the end of step a), a functionalized resin composition is obtained.

[0034] The crosslinkable resin is advantageously chosen from the group consisting of vinyl ester resins and their mixtures.

[0035] "Vinylester" resins are well known in the field of composite materials.

[0036] Without this definition being limiting, the vinyl ester resin is preferably of the epoxy vinyl ester type. A vinyl ester resin, in particular of the epoxy type, is more preferably used, which at least in part is based on (i.e. grafted onto a structure of the type) novolac (also called phenoplast) and / or bisphenolic, or preferably a vinyl ester resin based on novolac, bisphenolic, or novolac and bisphenolic.

[0037] A novolac-based epoxyvinylester resin (part in brackets in formula I below) corresponds, for example, in a known manner, to the following formula (I):

[0038] A bisphenol A-based epoxyvinylester resin (part in brackets of formula (II) below) corresponds, for example, to the formula (the "A" indicating that the

[0039] A novolac and bisphenolic type epoxyvinylester resin has shown excellent results. As an example of such a resin, the vinyl ester resins "ATLAC 590" and "ATLAC E-Nova FW 2045" from the company AOC (diluted with about 40% styrene) described in applications EP-A-1 074 369 and EP-A-1 174 250 may be cited in particular.

[0040] The proportion of crosslinkable resin in the functionalized resin composition may be in the range of 65% to 93% by weight, preferably in the range of 70% to 90% by weight, and more preferably in the range of 75% to 85% by weight relative to the total weight of the functionalized resin composition. When the crosslinkable resin includes a diluent, the aforementioned proportions of crosslinkable resin include said diluent.

[0041] As previously stated, the coupling agent comprises at least one methacrylate group and at least one function capable of reacting with a hydroxyl group, other than a methacrylate group.

[0042] Thus, the coupling agent reacts with the crosslinkable resin via the methacrylate group.

[0043] The coupling agent is directly introduced into the formulation of the resin composition, thus constituting an interesting advantage related to ease of implementation and therefore to industrial cost.

[0044] Advantageously, at least one function capable of reacting with a hydroxyl group of said coupling agent is chosen from the group consisting of an epoxy group, an isocyanate group, a maleic anhydride group, a carbonylamino group and a halogen group, preferably chosen from the group consisting of an epoxy group.

[0045] Preferably, the coupling agent is chosen from the group consisting of 2-isocyanatoethyl methacrylate, 2-[(3,5-dimethylpyrazolyl) carboxyamino]ethyl methacrylate, 2-(O-[l'-methylpropylideneamino] carboxyamino)ethyl methacrylate, methacryloyl chloride, methacrylic anhydride and glycidyl methacrylate, preferably the coupling agent is glycidyl methacrylate.

[0046] Advantageously, the rate of said coupling agent comprising at least one methacrylate group and at least one function capable of reacting with a hydroxyl group is in the range of 1% to 10% by weight, preferably in the range of 2% to 8% by weight, more preferably in the range of 3% to 7% by weight relative to the total weight of the functionalized resin composition.

[0047] The crosslinking initiator can be any initiator known to a person skilled in the art.

[0048] The crosslinking initiator can be chosen from the group consisting of azobisisobutyronitrile and peroxides, preferably from the group consisting of peroxides.

[0049] Cumene peroxide can be cited as an example of a crosslinking initiator that can be used in the context of the present invention.

[0050] The rate of said crosslinking initiator is advantageously within a range of 0.5% to 2% by weight, preferably within a range of 0.5% to 1.5% by weight relative to the total weight of the functionalized resin composition.

[0051] As an example of a crosslinking agent other than the crosslinking initiator and the coupling agent, we can cite the multifunctional acrylate or methacrylate derivatives well known to those skilled in the art.

[0052] The crosslinking agent, other than the crosslinking initiator and the coupling agent, may be chosen from the group consisting of multifunctional (meth)acrylates, and their mixtures, preferably in the group consisting of tri(meth)acrylates and their mixtures.

[0053] In a particularly preferred manner, the crosslinking agent is chosen from the group consisting of the family of triacrylates.

[0054] Advantageously, the rate of said crosslinking agent other than the crosslinking initiator and the coupling agent is in the range of 5% to 15% by weight, preferably in the range of 10% to 15% by weight relative to the total weight of the functionalized resin composition.

[0055] The composite manufactured by the process according to the invention is based on at least one reinforcing element.

[0056] By "reinforcing element" is meant an element enabling the mechanical reinforcement of a matrix in which this reinforcing element is intended to be embedded. The reinforcing element may be a wire element.

[0057] The wire element can be metallic or textile. By "wire element", we mean an element having a length at least 10 times greater than the largest dimension of its cross-section, regardless of the shape of the latter: circular, elliptical, oblong, polygonal, in particular rectangular, square or oval.

[0058] Advantageously, the reinforcing element is a reinforcing fiber chosen from the group consisting of natural fibers, preferably from the group consisting of flax fibers.

[0059] The use of flax fibers in the context of the invention is of great interest because of their low cost and availability and because they are a renewable resource.

[0060] As is well known to those skilled in the art, natural fibers comprise at least cellulose, that is to say a polymer made up of monomeric units comprising several hydroxyl functions, and also lignin and hemicellulose.

[0061] Thus, the coupling agent reacts with the hydroxyl groups of the natural fibers via the function capable of reacting with a hydroxyl group, different from a methacrylate group.

[0062] As previously stated, the invention also relates to a composite based on at least one reinforcing element and at least one crosslinked resin composition as defined above.

[0063] The reinforcing element is as indicated above.

[0064] The composite comprising a reinforcing element is preferably a filament-resin composite laminate or monofilament (abbreviated "FRC") comprising filaments embedded in said resin composition, said resin composition being crosslinked (i.e., a resin hardened after crosslinking). In other words, the composite including a reinforcing element is preferably a laminate or a single strand in CFR comprising filaments embedded in a crosslinked resin from the resin composition as defined above.

[0065] The filaments can be chosen from the group consisting of natural fibers, preferably from the group consisting of flax fibers.

[0066] Thus, preferably, the laminate or monofilament is made of flax-resin composite (abbreviated “CLR”).

[0067] As examples of fibers that can be used in the context of the present invention, Ecotechnilin's "FlaxDry UDI80" and Safilin's "Flax Low Twist Roving" flax fibers may be cited. The latter (Safilin's) can be washed in an alkaline bath to remove grease from the fibers.

[0068] If necessary, a person skilled in the art knows very well how to adapt the sizing to the surface of the filaments to improve the compatibility of the filaments with the resin used in the mineral-resin composite, in particular with the help of a silane-type compatibilizing agent.

[0069] The filaments advantageously represent 60% to 80% by weight, preferably 65% ​​to 75% by weight of the laminate or monostrand in filament-resin composite and the resin composition represents 20% to 40% by weight, preferably 25% to 35% by weight of the laminate or monostrand in filament-resin composite.

[0070] The weight percentage of the filaments is calculated by dividing the initial fiber count by the count of the final laminate (single strand). The count (or linear density) is determined on at least three samples, each corresponding to a length of 50 m, by weighing this length; the count is given in tex (weight in grams of 1000 m of product – as a reminder, 0.111 tex is equivalent to 1 denier). The percentage by weight of crosslinked resin can be obtained by calculating the difference between the count of the final laminate (single strand) and the count of the initial fiber.

[0071] Typically, the filaments are present in the form of a single multifilament fiber or several multifilament fibers linked together. In the latter case, the multifilament fibers are preferably essentially unidirectional. Each of the multifilament fibers may comprise several dozen, or even hundreds, of individual filaments.

[0072] Advantageously, the filaments each have an average diameter ranging from 20 to 100 pm, more preferably from 40 to 80 pm.

[0073] When the composite is a monostrand, the monostrand advantageously has a diameter ranging from 0.2 to 1.3 mm, preferably from 0.25 to 1.25 mm, more preferably from 0.3 to 1.2 mm.

[0074] The average diameter covers both monostrands of essentially cylindrical shape (with a circular cross-section) and monostrands of different shapes, by Examples include oblong monostrands (of a more or less flattened shape) or rectangular cross-sections. In the case of a non-circular cross-section, and unless otherwise specified, the average diameter is conventionally the so-called overall diameter, that is, the diameter of the imaginary cylinder of revolution enveloping the monostrand, in other words, the diameter of the circumscribed circle surrounding its cross-section.

[0075] The glass transition temperature (Tg) of the crosslinked resin is preferably greater than 175°C, preferably greater than 180°C, in particular greater than 185°C. It is measured in a known manner by DSC (Differential Scanning Calorimetry), on the second pass, for example and unless otherwise specified in this application, according to ASTM D3418 of 1999 (Mettler Toledo "822-2" DSC apparatus; nitrogen atmosphere; samples previously heated from room temperature (23°C) to 250°C (10°C / min), then rapidly cooled to 23°C, before final recording of the DSC curve from 23°C to 250°C, according to a ramp of 10°C / min).

[0076] A method for manufacturing at least one single strand of filament-resin composite comprising filaments embedded in a crosslinked resin may include the following steps:

[0077] i) to create a straight arrangement of filaments and to drive this arrangement in a direction of advancement;

[0078] ii) bringing said arrangement of filaments into contact with a functionalized resin composition to obtain an impregnated material containing the filaments and the functionalized resin composition,

[0079] said functionalized resin composition being obtained after mixing at least one crosslinkable resin with at least one coupling agent comprising at least one methacrylate group and at least one function capable of reacting with a hydroxyl group, other than a methacrylate group,

[0080] in the presence,

[0081] - of at least one crosslinking initiator; and

[0082] - of at least one crosslinking agent other than the crosslinking initiator and that the coupling agent,

[0083] iii) passing said impregnated material through a calibration die having a predefined surface area and shape section, to impose on it a single-strand shape;

[0084] iv) downstream of the die, in a crosslinking chamber, polymerize the functionalized resin composition under the action of a heat treatment at a temperature in the range of 90°C to 120°C, the crosslinking chamber comprising a tube, called crosslinking tube, through which the single strand being formed flows.

[0085] The various preferred embodiments described above in the context of the manufacturing process of the composite according to the invention and of the composite according to the invention are applicable for the manufacturing process of said monostrand.

[0086] The composite based on at least one reinforcing element can be manufactured by any method known to a person skilled in the art, depending on the object to be produced.

[0087] The attached [Fig.1] schematically illustrates very simply an example of a device 10 enabling the production of single strands in CVR.

[0088] A reel 1 is shown containing, in the illustrated example, flax fibers 11b (in the form of multifilaments). The reel is continuously unwound by drive, so as to create a straight arrangement 12 of these fibers 11b. Generally, reinforcing fibers are supplied as "rovings," that is, already in groups of fibers wound in parallel on a reel; for example, fibers marketed by Safilin under the designation "Flax Low Twist Roving" are used. It is, for example, the traction exerted by the rotating receiver 26 that will allow the parallel fibers and the single strand in CLR to advance along the entire length of the installation 1.

[0089] This arrangement 12 then passes through a vacuum chamber 13 (connected to a vacuum pump not shown), disposed between an inlet tube 13a and an outlet tube 13b opening into an impregnation chamber 14, the two tubes preferably having rigid walls having for example a minimum cross-section greater (typically twice as much) than the total cross-section of fibers and a length much greater (typically 50 times more) than said minimum cross-section.

[0090] As already demonstrated by PPE application 174250A1, the use of rigid-walled tubing, both for the inlet orifice in the vacuum chamber and for the outlet orifice of the vacuum chamber and for the transfer from the vacuum chamber to the impregnation chamber, proves compatible with high fiber flow rates through the orifices without breaking the fibers, while also ensuring sufficient sealing. If necessary, experimentally, it is sufficient to determine the largest possible cross-sectional area, given the total cross-section of the fibers to be treated, that still provides sufficient sealing, considering the fiber feed rate and the length of the tubing. Typically, the vacuum inside chamber 13 is, for example, on the order of 0.1 bar, and the length of the vacuum chamber is approximately 1 meter.

[0091] Upon exiting the vacuum chamber 13 and the outlet tube 13b, the arrangement 12 of fibers 11b passes through an impregnation chamber 14 comprising a feed reservoir 15 (connected to a metering pump not shown) and a sealed impregnation reservoir 16 completely filled with an impregnation composition 17 based on a vinyl ester-type curable resin (for example, "ATLAC E-Nova FW 2045" from AOC). By way of example, the composition 17 further comprises (at a weight rate of 0.5% to 1.5%) a suitable crosslinking initiator for polymerization, for example cumene peroxide. Of course, the impregnation composition 17 is in liquid form.

[0092] Preferably, the length of the impregnation chamber is several meters, for example between 2 and 10 m, in particular between 3 and 5 m.

[0093] Thus, from the impregnation chamber 14, in a sealed outlet tube 18 (still under primary vacuum), an impregnated material comprising, for example (% by weight) 65% to 75% of solid fibers 11b, the remainder (25% to 35%) being made up of the liquid impregnation matrix 17.

[0094] The impregnated material then passes through calibration means 19 comprising at least one calibration die 20 whose channel (not shown here), for example circular, rectangular, or conical in shape, is adapted to the specific manufacturing conditions. The calibration die, by means of a cross-section of determined dimensions, generally and preferably circular or rectangular, allows the proportion of resin relative to the fibers to be adjusted, while imposing on the impregnated material the shape and thickness targeted for the monofilament. By way of example, this channel has a minimum circular cross-section whose downstream orifice has a diameter slightly larger than that of the targeted monofilament. The die has a length that is typically at least 100 times greater than the minimum dimension of the cross-section.Its function is to ensure high dimensional accuracy of the finished product; it can also play a role in dosing the fiber content relative to the resin. According to one possible embodiment, the die 20 can be directly integrated into the impregnation chamber 14, which avoids, for example, the use of the outlet tube 18.

[0095] Preferably, the length of the calibration zone is several centimeters, for example between 5 and 50 cm, in particular between 5 and 20 cm.

[0096] Thanks to the calibration means (19, 20) a "liquid" composite monostrand 21 is obtained at this stage (liquid in the sense that its impregnation resin is always liquid) whose cross-section shape is preferably essentially circular.

[0097] At the outlet of the calibration means (19, 20), the liquid composite monostrand 21 thus obtained is then polymerized by passing through a crosslinking chamber 22 comprising a sealed glass tube 23 through which the composite monostrand flows; said tube, the diameter of which is typically a few cm (for example 2 to 3 cm), is subjected to the action of a heat treatment at a temperature for example within a range of 90 to 120°C.

[0098] The polymerization or crosslinking chamber then has the function of polymerizing the resin under the action of the heat treatment.

[0099] The crosslinking chamber may include infrared lamps capable of providing heat, in particular at a temperature within a range of 90 to 120°C.

[0100] The diameter of the tube (preferably made of glass) is preferably between 10 and 80 mm, more preferably between 20 and 60 mm.

[0101] Preferably, the length of the crosslinking chamber is several meters, for example between 2 and 15 m, in particular between 3 and 10 m.

[0102] In this example, tube 23 is traversed by a nitrogen current.

[0103] The crosslinking conditions are preferably adjusted so that, at the outlet of the impregnation chamber, the temperature of the CLR monostrand, measured on the surface of the latter (for example using a thermocouple), is greater than the Tg of the crosslinked resin (in other words greater than 175°C), and more preferably less than 200°C.

[0104] Once the resin has polymerized (hardened), the CLR 25 monostrand, now in solid state, carried in the direction of arrow F, then arrives on its final receiving reel 26.

[0105] Between the calibration die and the final receiving support, it is preferable to maintain the tensions experienced by the mineral fibers at a moderate level, preferably between 0.2 and 2.0 cN / tex, more preferably between 0.3 and 1.5 cN / tex; to control this, it will be possible, for example, to measure these tensions directly at the outlet of the crosslinking chamber, using appropriate tensiometers well known to those skilled in the art.

[0106] A finished composite block is finally obtained as schematically shown very simply in [Fig.2], in the form of a continuous CLR monostrand 25, of very long length, whose unitary flax filaments 251 are distributed homogeneously throughout the entire volume of hardened resin 252. Its diameter is for example equal to about 1 mm.

[0107] The continuous CLR monostrand 25 can then be cut to a predetermined length (not shown in [Fig. 1]), as required, by any means known to those skilled in the art, for example, using a hydraulic guillotine, such as the "SH-5214" from Baileigh. This step can be carried out directly at the exit of the curing chamber 23. It can also be carried out after being conditioned onto a final receiving reel 26. In this case, it is preferable to unwind the monostrand from the reel from the outermost axial end of the monostrand, in order to avoid helical deformation of the monostrand. Indeed, if the monostrand is unwound from the innermost axial end of the reel, this helical deformation of the monostrand can be detrimental to the breaking strength. Examples Measurement methods

[0108] Mechanical properties

[0109] The mechanical properties in extension of the rolled (Young's modulus, maximum flexural strength and shear strength) were measured using an "INSTRON" 68TM50 tensile testing machine (BLUEHILL® UNIVERSAL software supplied with the tensile testing machine), according to ASTM D4848-98 (2012) (for Young's modulus), D7264 / D7264M (2021) (for maximum flexural strength) and D2344 / D2344M - 00e 1 (for shear strength).

[0110] The measurements were carried out on laminates with or without glycidyl methacrylate.

[0111] Before measurement, these laminates were kept protected from moisture.

[0112] The tested laminates were subjected to tensile testing at a nominal speed of 50 m / min, under a preload of 0.5 MPa before testing (distance between the jaws: 150 mm). All results given are an average of 10 measurements. Preparation of resin compositions

[0113] Two resin compositions were prepared (Cl and C2).

[0114] For each of the compositions, vinyl ester resin (“ATLAC E-NOVA FW2045” from AOC), cumene peroxide from Sigma Aldrich, as a crosslinking initiator, and a crosslinking agent (triacrylate hardener (“SR 368” from Sartomer)) were used. The crosslinking initiator content was 1% by weight relative to the total weight of the resin composition, and the crosslinking agent content was 15% by weight relative to the total weight of the resin composition.

[0115] When a coupling agent was present (glycidyl methacrylate from Sigma Aldrich), the level was 5% by weight relative to the total weight of the composition.

[0116] The compositions Cl and C2 are summarized in Table 1 below:

[0117] [Tables] Composition Cl C2 Vinylester resin (% by weight) 84 79 Crosslinking initiator (% by weight) 1 1 Triacrylate hardener (% by weight) 15 15 Glycidyl methacrylate (% by weight) - 5 Preparing the laminates

[0118] Laminates were manufactured according to the process below.

[0119] Layers of fabric comprising flax fibers were first placed in an oven for 2 hours at 80°C in order to evaporate the moisture absorbed by the flax.

[0120] Then, approximately 10 to 15 g of the Cl (or C2) resin composition was spread onto an aluminum plate the size of the final laminate (25 mm by 25 mm with a thickness of 3 mm). A first layer of fabric was then laid on the plate, and approximately 10 to 15 g of resin was poured onto the first layer. A second layer of fabric was then laid. This layering of alternating fabric-resin layers was repeated until resin-impregnated layers were obtained. A brush can be used to help spread the resin along the edges of the fabric layers, if necessary.

[0121] To ensure thorough impregnation of the fibers, the pre-impregnated laminate was placed in a plastic bag equipped with a valve to create a vacuum. The bag was sealed, and a vacuum was applied to remove any remaining air from the fibers. The resin composition then occupies the space left by the extracted air bubbles. Once the infusion process was complete, the laminate was removed and placed in a mold with a spacer of appropriate thickness. An excess of resin composition was then poured onto the laminate, and a second aluminum plate was placed on top.

[0122] The mold was then closed and placed under pressure at 120°C with a pressure of 4 bar for 1h. Excess resin composition can be evacuated through an outlet, which also allows any remaining air bubbles to be expelled.

[0123] The mold was then removed from the press, and the laminate was then cold-demolded.

[0124] The laminates L1 and L2 comprise respectively the resin compositions Cl and C2.

[0125] The flax fibres of the laminates L1 and L2 were "FlaxDry UD180" fabrics (UD for unidirectional; 180 for 180 gsm = 180g / m2).

[0126] The mechanical properties of the L1 and L2 laminates are presented in Table 2 below.

[0127] [Tables2] L1 (comparative) L2 (invention) laminates Young's modulus (GPa) 23.0 29.1 Maximum bending strength (MPa) 264 284 Shear strength (MPa) 21.1 23.6

[0128] The results presented above show that the presence of a coupling agent as defined above makes it possible to obtain significantly improved mechanical properties.

[0129] Indeed, the Young's modulus, maximum flexural strength, and shear strength of the L2 laminate according to the invention have values ​​higher than those of the comparative L1 laminate.

[0130] In particular, the improved shear strength of the L2 laminate according to the invention implies a stronger resin-fiber interface than that of the comparative L1 laminate. Thanks to the presence of the coupling agent as defined above, the adhesion between the natural fibers and the cross-linked functionalized resin composition is thus improved. Here, the methacrylate group of the coupling agent reacts with the acrylate group of the resin, and the epoxy group of the coupling agent reacts with the hydroxyl groups present in the cellulose, which is itself present in the natural fibers. Thus, the coupling agent used in the context of the invention makes the resin and the natural fibers more compatible, thereby constituting a highly advantageous feature.

[0131] Furthermore, since the coupling agent is directly incorporated into the resin, the fibers are not degraded. This represents an additional advantage, particularly compared to prior art solutions where fiber degradation is observed due to the environment in which the fibers are processed.

Claims

Demands

1. A method for manufacturing at least one composite based on at least one reinforcing element and at least one crosslinked resin composition comprising the following steps: a) mixing at least one crosslinkable resin with at least one coupling agent comprising at least one methacrylate group and at least one function capable of reacting with a hydroxyl group, other than a methacrylate group, in the presence of: - at least one crosslinking initiator; and - at least one crosslinking agent other than the crosslinking initiator and the coupling agent, to obtain a functionalized resin composition; b) contacting at least one reinforcing element with the functionalized resin composition; and c) exposing the functionalized resin composition and the reinforcing element to a temperature in the range of 90°C to 120°C.

2. A method according to claim 1, characterized in that the crosslinkable resin is chosen from the group consisting of vinyl ester resins and their mixtures.

3. A process according to claim 1 or 2, characterized in that the percentage of crosslinkable resin in the functionalized resin composition is in the range of 65% to 93% by weight, preferably in the range of 70% to 90% by weight, more preferably in the range of 75% to 85% by weight relative to the total weight of the functionalized resin composition.

4. A method according to any one of the preceding claims, characterized in that at least one function capable of reacting with a hydroxyl group of said coupling agent is chosen from the group consisting of an epoxy group, an isocyanate group, a maleic anhydride group, a carbonylamino group and a halogen group, preferably chosen from the group consisting of an epoxy group.

5. A method according to any one of the preceding claims, characterized in that the coupling agent is selected from the group consisting of 2-isocyanatoethyl methacrylate, 2-[(3,5- dimethylpyrazolyl)carboxyamino]ethyl methacrylate, 2-(O-[r-methylpropylideneamino]carboxyamino)ethyl methacrylate, methacryloyl chloride, methacrylic anhydride and glycidyl methacrylate, preferably the coupling agent is glycidyl methacrylate.

6. A process according to any one of the preceding claims, characterized in that the proportion of said coupling agent comprising at least one methacrylate group and at least one function capable of reacting with a hydroxyl group is in the range of 1% to 10% by weight, preferably in the range of 2% to 8% by weight, more preferably in the range of 3% to 7% by weight relative to the total weight of the functionalized resin composition.

7. A method according to any one of the preceding claims, characterized in that the crosslinking initiator is chosen from the group consisting of azobisisobutyronitrile and peroxides, preferably from the group consisting of peroxides.

8. A method according to any one of the preceding claims, characterized in that the rate of said crosslinking initiator is in the range of 0.5% to 2% by weight, preferably in the range of 0.5% to 1.5% by weight relative to the total weight of the functionalized resin composition.

9. A method according to any one of the preceding claims, characterized in that the crosslinking agent is selected from the group consisting of the family of triacrylates.

10. A process according to any one of the preceding claims, characterized in that the rate of said crosslinking agent other than the crosslinking initiator and the coupling agent is in the range of 5% to 15% by weight, preferably in the range of 10% to 15% by weight relative to the total weight of the functionalized resin composition.

11. A method according to any one of the preceding claims, characterized in that the reinforcing element is a reinforcing fiber selected from the group consisting of natural fibers, preferably from the group consisting of flax fibers.

12. Composite based on at least one reinforcing element and at least one crosslinked resin composition as defined in any one of claims 1 to 10.

13. Composite according to claim 12, characterized in that it is a monostrand or a filament-resin composite laminate comprising filaments embedded in said crosslinked resin composition.

14. Composite according to claim 13, characterized in that the filaments represent 60% to 80% by weight, preferably 65% ​​to 75% by weight of the laminate or monostrand of filament-resin composite and the resin composition represents 20% to 40% by weight, preferably 25% to 35% by weight of the laminate or monostrand of filament-resin composite.

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