Parts and manufacturing methods made from recycled composite materials

Abstract

The present invention relates to a composite material part, - chips (1), each chip (1) having a substantially constant thickness defined between two parallel opposing faces (4) of the chip, each chip comprising carbon fibres (3) at least partially contained in a hardened adhesive during a first cure prior to forming of the part, at least the majority of the fibres of the chip extending substantially parallel to the opposing faces (4) of the chip; - a matrix (2) in which each chip (1) is at least partially contained, said matrix (2) being formed from the adhesive that has hardened during a second cure; The present invention relates to a composite part, comprising: a bonding interface formed between a matrix (2) of the part and each chip.

Description

[Technical field]

[0001] The present invention relates to the field of recycling composite materials, in particular composite materials containing carbon fibres. [Background technology]

[0002] Composite materials based on carbon fibers are used in many technical fields due to their mechanical properties, in particular their strength and lightness: they are particularly common in the aviation sector, the automotive industry, boats, but also in the construction, energy, etc. sectors.

[0003] Carbon fiber based composites generally comprise carbon fibers contained within a matrix.

[0004] Several methods can be used to manufacture carbon fibers, the principle of which is the deposition of carbon at very high temperatures, either from paper or viscose ("ex-cellulose" fibers), or from polyacrylonitrile ("ex-PAN" fibers), or from petroleum or coal residues ("ex-pitch" fibers).

[0005] The carbon fibers are included in the matrix in a given orientation, for example unidirectionally, or in the form of a woven fiber web.

[0006] As regards the matrix, it generally consists of or essentially comprises a polymer. The matrix can also be called "adhesive" or even "resin" (the matrix is ​​generally polymeric). As is known, the matrix can be of thermoplastic or thermosetting nature. Glues of similar nature can be used equally well within the scope of the present invention.

[0007] Thus, unless otherwise specified, the terms "matrix," "glue," "adhesive," and "resin" are considered synonymous herein.

[0008] Thermosetting polymers undergo a chemical reaction called cross-linking when forming composites. This reaction creates chemical bonds and is irreversible. It is generally accepted that the most efficient thermosetting polymers for forming carbon fiber-based composites are polyepoxides (known as "epoxies").

[0009] Thermoplastic polymers are polymers that become viscous and therefore shapeable above a certain temperature, called the "phase transition temperature," which is lower than their thermal decomposition temperature. When the temperature drops below this phase transition temperature, the polymer hardens and returns to its initial rigidity. This hardening is reversible by heating the polymer again.

[0010] The most common thermoplastic polymers are polyethylene (PE), polyethylene terephthalate (PET), or polycaprolactam (PA-6). Specialized thermoplastic polymers such as (phenylene ether ether ketone) (PEEK), poly(phenylene sulfide) (PPS), or polyetherimide (PEI) can be used.

[0011] The numerous and ever-widening applications of composite materials based on carbon fibers give rise to the problem of recycling these materials. In addition to the fact that an increasing amount of material can be recycled, these composite materials are high-value materials (mainly due to their carbon fiber content) and their valorization will prove to be economically important.

[0012] Recycling may concern elements made from composite materials that are at the end of their life or that have become damaged, elements that have been manufactured but do not or no longer meet certain criteria required for their intended use (especially in the aeronautical or space sectors), or, more rarely, elements that have not been used on a particular date.

[0013] Three main categories of methods have been developed for recycling carbon fibre reinforced composite materials: the so-called mechanical recycling, the so-called chemical recycling and the so-called thermal recycling.

[0014] Mechanical recycling consists in principle in splitting and grinding existing composite parts to at least partially dissociate the fibers from the resin, obtaining fibers of various lengths that can be reused as reinforcement in new resin. The slightly fibrous particles obtained from grinding are in powder form and can be mixed with the resin during the formation of new composite elements.

[0015] The composite shredder is used as a filler element or as reinforcement in molded parts, but is not really intended to replace virgin carbon fibers as used in conventional methods for manufacturing composite elements (based on non-recycled materials).

[0016] In this method, the powder obtained by grinding the composite material to be recycled can be sieved and separated into several categories of particle size, which do not significantly affect the mechanical properties of the elements subsequently formed by the inclusion of these particles.

[0017] It is generally estimated that the mechanical properties (flexural strength or flexural stiffness) of parts obtained by state-of-the-art mechanical recycling methods are at least four times lower than that of a similar new part.

[0018] Composite materials based on recycled carbon fibers obtained by mechanical recycling methods therefore generally have limited applications in specific sectors where there is no very high need for mechanical properties relative to the mass, and therefore they are mainly used in construction (buildings).

[0019] Chemical recycling consists of chemically breaking down the cured resin of a composite material to recover the carbon fibers present in the composite material. The recovered fibers are then typically aligned and / or spun to create yarns from thousands of recovered fibers. The mechanical properties of parts formed from composite materials containing these recycled fibers are much lower than the mechanical properties of composite materials containing new, non-recycled carbon fibers.

[0020] Several chemical decomposition methods are known, in particular conventional solvolysis, solvolysis under "mild conditions", or solvolysis under supercritical conditions.

[0021] In conventional solvolysis processes, the parts to be recycled are immersed in a solvent at high temperature (above 200° C.) and pressure (in the range of 180 bar) so that the resin is decomposed. These may be, for example, concentrated acids (in particular nitric or sulfuric acids).

[0022] The mild solvolysis method uses milder temperatures than conventional solvolysis, below 200° C. The method is carried out at atmospheric pressure, uses milder solvents such as acetone or N,N-dimethylformamide, and optionally uses catalysts such as hydrogen peroxide or peroxyacetic acid. Pretreatment with acetic acid may also be used. However, mild solvolysis has a fairly low production efficiency.

[0023] In the supercritical solvolysis method, a solvent is used under supercritical conditions to have better diffusivity and increased solvation capacity. It is a complicated and expensive method.

[0024] Finally, thermal recycling consists, in principle, of pyrolyzing the resin of the composite material in order to recover the carbon fibers therefrom: the heat can be provided by a pyrolysis process, generally consisting of burning the resin in an oven, by a fluidized bed process using the combined action of solvents and high temperature, and finally by microwaves.

[0025] Although these methods are optimized, the recovered fibers have significantly deteriorated mechanical properties compared to new fibers. The recovered fibers are generally short and must be aligned and spun in order to be reused in applications that require the correct mechanical properties. Otherwise they are used for packing, for example as the powders obtained in the mechanical recycling methods mentioned above.

[0026] In summary, the various techniques known in the field of recycling carbon fiber based composites are: - Grinding composite materials and using the crushed material as reinforcement (mechanical recycling), - Or it consists of technologies to decompose resin and regenerate carbon fiber (chemical or thermal recycling). Summary of the Invention [Problem to be solved by the invention]

[0027] However, these two solutions each have significant drawbacks: they provide materials with poor mechanical performance and / or they are expensive and / or complex to implement. Recycling techniques that decompose the resin to recover the carbon fibers also have significant environmental costs. In fact, they release the decomposed resin in liquid or gas form. These emissions must be treated. [Means for solving the problem]

[0028] The present invention aims to propose a composite material part obtained by a recycling method which overcomes all or part of the above mentioned problems, in particular to obtain composite material parts with high mechanical properties at controlled economic and environmental costs.

[0029] The invention thus relates to a composite part comprising chips at least partially contained in a matrix. Each chip has a substantially constant thickness defined between two parallel opposing faces of the chip, each chip comprising carbon fibres at least partially contained in an adhesive that has been cured during a first cure prior to forming the part. At least the majority of the fibres of the chip run substantially parallel to the opposing faces of the chip. The matrix in which each chip is at least partially contained is formed from the adhesive that has been cured during a second cure. Thus, a bond interface is formed between the matrix and each chip of the part.

[0030] The concept of substantially constant thickness is interpreted as follows: the thickness corresponds to the smallest dimension of the chip, which is small compared to the other dimensions (for example compared to the length and width of a rectangular chip). The thickness of the chip is substantially constant since the chip has two opposing (main) faces that are substantially parallel at all points. The chip is flat when unconstrained, but may be curved when included in a component that is the subject of the present invention. This possible curvature is possible due to the small thickness of the chip, which gives it a certain degree of flexibility. The thickness of the chip measured perpendicularly to the main faces of the chip is constant at all points on the chip, or at least is perceived as constant by the observer. It is in this sense that the thickness is indicated as "substantially" constant, i.e. perceived as naturally constant. Alternatively, the thickness is considered to be substantially constant if the minimum thickness is equal to or greater than half of the maximum thickness measured on the chip, preferably if the difference between the maximum and minimum thicknesses measured on the chip does not exceed 25%. Alternatively, the thickness is considered to be substantially constant if the difference between the minimum and maximum thicknesses measured at the tip does not exceed 0.5 mm.

[0031] The bond interface may essentially comprise a mechanical adhesive bond.

[0032] The term "mechanical adhesive bonds" refers to mechanical bonds such as mechanical fixation (physical fixation of the adhesive in the irregularities of the solid surface of the chip) and possibly diffusion bonds (diffusion of the adhesive in the chip) and / or thermodynamic type bonds, in particular "van der Waals" type bonds. Mechanical adhesive bonds are essentially distinct from ionic-covalent bonds.

[0033] The expression "essentially mechanical adhesive bond" refers to the fact that, although the first cure is considered to be complete, it cannot be excluded that a few rare sites remain on the chip that can form ionic-covalent bonds with the matrix of the part. In other words, the chip adhesive cures during the first cure, i.e. polymerizes into a thermosetting or thermoplastic adhesive, as a result of which the chip adhesive no longer contains (or contains few) sites that can form chemical bonds with the adhesive in which the chip is contained for the second cure. Thus, during the second cure, ionic-covalent bonds between the chip and the cured adhesive are rare or even non-existent, as a result of which the bond interface between the chip and the adhesive is visible to the naked eye, as highlighted in Figures 2 and 3 described below.

[0034] Throughout this specification, the term "substantially" conventionally refers to the perception of this feature by the system used for its measurement or production. If a feature is observed with the naked eye, the term "substantially" therefore refers to the observer's perception of the feature. Expressions containing the term "substantially" should be interpreted as technical features that are produced within the tolerances of their manufacturing method. In particular, the feature "substantially parallel" between two elements can be understood to be up to an angle of within 10°. If the considered fibers are included in a woven fabric (typically taffeta, twill or satin), the direction of fiber extension is considered by ignoring the fiber undulations associated with weaving.

[0035] The term "chips at least partially contained within the matrix" refers to the fact that each chip is embedded in the matrix, with the possible exception of certain chips that may appear on the surface of the part. Similarly, the term "carbon fibers at least partially contained in the adhesive cured during the first cure" refers to the fact that the carbon fibers are embedded in the adhesive of the chip, with the possible exception of certain carbon fibers that may appear on the surface area of ​​the chip.

[0036] The curing process (or crosslinking, these terms are used synonymously unless otherwise noted) transforms the resin through a crosslinking process. Energy and / or catalysts are added to cause molecular chains to react at chemically active sites and bond into a rigid 3D structure. The crosslinking process causes molecules to form with higher molecular weights, resulting in a material with a higher melting point. During the reaction, the molecular weight increases until the melting point is higher than the ambient temperature and the material transforms into a solid material.

[0037] Suitable adhesives for composites can be selected from the group consisting of thermosetting resins such as epoxy resins, cyanate esters and phenolic resins. Suitable epoxy resins include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, novolac epoxy resins and N-glycidyl ethers, glycidyl esters, aliphatic and cycloaliphatic glycidyl ethers, aminophenol glycidyl ethers, glycidyl ethers of any substituted phenols and mixtures thereof.

[0038] Also included are modified blends of the aforementioned thermosetting polymers.

[0039] "Modified blend" typically refers to a polymer that has been modified by the addition of a rubber or thermoplastic resin.

[0040] Any suitable catalyst (or "curing agent") can be used. The catalyst is selected to be compatible with the resin being used.

[0041] The catalyst can be accelerated.

[0042] For example, when dicyandiamide catalyst is used, substituted ureas can be used as accelerators.

[0043] The curing agent for the epoxy resin may also be selected from dapsone (DDS), diaminodiphenylmethane (DDM), BF3-amine complexes, substituted imidazoles, accelerated anhydrides, metaphenylenediamines, diaminodiphenyl ethers, aromatic polyether amines, aliphatic amine adducts, aliphatic amine salts, aromatic amine adducts, and aromatic amine salts.

[0044] Suitable accelerators include diuron, monuron, fenuron, chlortoluron, toluene diisocyanate bis-urea and other substituted homologs.

[0045] Adhesives suitable for composites can also be selected from the group consisting of thermoplastics. Among the thermoplastics, a distinction can be made between high-performance plastics, engineering plastics and standard plastics. Most thermoplastics used in composites are high-performance or engineering plastics. These plastics are distinguished from standard plastics in particular by their greater abrasion and chemical resistance.

[0046] Thermoplastic resins, depending on their nature, can be rigid in amorphous or crystalline form.

[0047] Among the amorphous thermoplastics commonly used in composites are polyetherimide (PEI), polyethersulfone (PES), and polysulfone (PSU).

[0048] Among the crystalline thermoplastics commonly used in composites are polyamide (PA), poly(ethylene terephthalate), polyphthalamide (PPA), poly(phenylene sulfide) (PPS), and polyether ether ketone (PEEK).

[0049] Each chip is formed such that the orientation of the majority of the fibers it contains is parallel to the plane of the chip. Thus, the fibers can have significant length and controlled orientation in the chip. Ultimately, the length and orientation of the fibers in the chip, and the arrangement of the chips in the part, impart high mechanical properties to the part.

[0050] The chips are in particular obtained by cutting out recycled carbon fibre based composite elements, as will be explained in more detail below. The formation of parts according to the invention therefore allows the recycling of such elements by low-pollution mechanical methods, whilst providing good mechanical performances to the parts formed.

[0051] The face of each chip must be at least 1 cm2, called the surface area of ​​the chip. 2 may have a surface area of

[0052] These values ​​given as an example should be understood as minimum values. Depending on the component under consideration, the chip may be, for example, 3 cm 2 , 5cm 2 , 10cm 2 Or 20cm 2 , 100cm 2 In the range of 0.1 to 100 nm, the surface area can be much larger.

[0053] Thus, the chips formed and used within the scope of the present invention have a significant surface area capable of encapsulating very long carbon fibers because the carbon fibers extend substantially parallel to the opposing faces of the chip.

[0054] The bonding interface between each chip and the matrix may not have an inflection point across the entire surface area of ​​the chip.

[0055] In particular, the interface may be substantially flat over a majority of the surface area of ​​the chip.

[0056] This is due to the relative stiffness of each chip, which contains the carbon fiber in a cured adhesive prior to being encapsulated in a matrix to form the composite part.

[0057] Each chip advantageously has a thickness (e) that is small compared to its other dimensions, so that the chip is essentially a two-dimensional piece, with a small thickness, the other dimensions of the chip typically corresponding to the largest dimension (d) that can be measured over the surface area of ​​the chip, and also a dimension measured perpendicularly over the surface area of ​​the chip.

[0058] Advantageously, the ratio (e) / (d) is comprised between 0.05 and 0.0005, preferably between 0.01 and 0.001, and even more preferably between 0.005 and 0.001.

[0059] In this application, ranges are understood to be inclusive unless otherwise indicated.

[0060] In a composite material part, the carbon fibres advantageously extend mainly in parallel planes.

[0061] For example, the chips may have a unidirectional arrangement of carbon fibers. For example, the chips may be oriented such that the carbon fibers of the component are oriented in substantially the same direction. Alternatively, the chips may be oriented such that the carbon fibers of the component are oriented substantially in only two different directions, such as a first direction and a second direction that form a 90° angle between them.

[0062] The chips are advantageously arranged in the component in a repeating pattern.

[0063] The pattern corresponds to a particular relative arrangement of several chips. The pattern particularly corresponds to a non-random arrangement and is generally repeatable in the part being formed.

[0064] According to one embodiment, the carbon fibers present in each chip are arranged in webs, each having a carbon fiber weave.

[0065] Thus, a controlled orientation of the fibers in the chip, and therefore in the component, makes it possible to obtain the desired mechanical properties.

[0066] In a composite part, the chips may all have substantially the same shape and dimensions, for example, each chip is substantially rectangular in shape (i.e., the face of each chip is substantially rectangular).

[0067] The two-dimensional shape of the chip is therefore a parameter that can be optimized to improve the mechanical properties of the part and / or to match the shape of the element to be recycled.

[0068] The thickness of the chip may be comprised, for example, between 200 μm and 1 mm.

[0069] The invention also relates to a composite part comprising a fibrous region formed by the chips and accounting for 20% to 85% by volume of the part, and a non-fibrous region consisting of an adhesive that is added and cured during a second cure and forms the remainder of the part.

[0070] The present invention relates to - a plurality of regions comprising carbon fibers and a first adhesive, the carbon fibers having a non-random orientation within the same region, the carbon fiber-containing region having a substantially constant thickness defined between two parallel opposing faces, and all carbon fibers in the carbon fiber-containing region being oriented along substantially parallel planes; - at least one region comprising a second adhesive and not comprising carbon fibres; Including, The present invention also relates to a composite part, wherein the plurality of regions comprising carbon fibres and the first adhesive are at least partially contained within at least one region comprising the second adhesive and not comprising carbon fibres.

[0071] The term "all of the carbon fibers in the region are oriented along substantially parallel planes" means that the carbon fibers present in the region are oriented along substantially parallel planes, and this is done on a region-by-region basis.

[0072] The term "a plurality of regions comprising carbon fibers and a first adhesive at least partially contained within at least one region comprising a second adhesive and no carbon fibers" means that the second adhesive of the at least one region not comprising carbon fibers encompasses at least 75%, preferably at least 80%, and even more preferably at least 85%, e.g., 90%, of the surface area of ​​the plurality of regions comprising carbon fibers and a first adhesive.

[0073] As will be described in more detail below with reference to FIG. 5, a cross-sectional view of a composite part according to the invention makes it possible to visualize multiple regions containing carbon fibers (light grey stripes shown in FIG. 5, the stripes being carbon fibers) and at least one region not containing carbon fibers (dark grey).

[0074] The carbon fiber containing regions may also be distributed in a pattern throughout the composite part.

[0075] Advantageously, the area containing carbon fibres occupies between 20% and 85% by volume of the part.

[0076] The regions containing carbon fibers, also called fiber regions, are actually chips contained in the composite part.

[0077] According to a first embodiment, the first adhesive is the same as the second adhesive, and the first adhesive is cured before the second adhesive.

[0078] According to a second embodiment, the first and second adhesives are different.

[0079] In such parts, the carbon fibers may be oriented substantially parallel, orthogonal, and / or at 45° within the same region.

[0080] The composite part may be, for example, a flat or curved panel.

[0081] The present invention further relates to a method for producing a composite material part, comprising the steps of: - providing a composite material including carbon fibers in an adhesive that is cured during a first cure; - cutting the composite material into chips, each chip having a substantially constant thickness defined between two parallel opposing faces of the chip, each chip comprising carbon fibers at least partially contained in the adhesive that has hardened during a first cure, at least a majority of the fibers of the chip extending substantially parallel to the opposing faces of the chip; - coating the chip with an adhesive; - arranging the chips so as to form an intertwining of the chips (i.e. a superposition forming a nesting and / or intermixing of the chips); - The process of hardening the liquid adhesive, called the second cure.

[0082] Finally, the invention relates to a composite material part which may be obtained by such a manufacturing method.

[0083] Other features and advantages of the present invention will become apparent from the following description. [Brief description of the drawings]

[0084] The accompanying drawings are illustrated by way of non-limiting example. [Figure 1] FIG. 1 illustrates, in a block diagram, a method according to one embodiment of the present invention. [Diagram 2] FIG. 2 shows in a photograph a so-called random chip arrangement which can be realised within the scope of the present invention. [Diagram 3]FIG. 3 shows in a photograph a so-called unidirectional chip arrangement which can be realised within the scope of the present invention. [Figure 4] FIG. 4 shows diagrammatically a so-called bidirectional chip arrangement which can be realised within the scope of the present invention. [Diagram 5] FIG. 5 shows in photographic form a cross-section of a composite material part according to one embodiment of the present invention at 50x magnification. [Figure 6] FIG. 6 illustrates in graph form the flexural modulus of a panel according to one embodiment of the present invention in which the chips are unidirectionally organized, and a panel containing new directionally oriented carbon fibers. [Figure 7a] FIG. 7a illustrates an embodiment of a panel manufactured according to one embodiment of the present invention, in which the chips are arranged in a non-random pattern. [Figure 7b] FIG. 7b illustrates an embodiment of a panel manufactured according to one embodiment of the present invention, in which the chips are arranged in a non-random pattern. [Figure 7c] FIG. 7c illustrates an embodiment of a panel manufactured according to one embodiment of the present invention, in which the chips are arranged in a non-random pattern. [Figure 8a] FIG. 8a illustrates another panel embodiment manufactured according to an embodiment of the present invention, in which the chips are arranged in a non-random pattern. [Figure 8b] FIG. 8b illustrates another panel embodiment manufactured according to an embodiment of the present invention, in which the chips are arranged in a non-random pattern. [Figure 9a] FIG. 9a illustrates yet another panel embodiment manufactured according to an embodiment of the present invention, in which the chips are arranged in a non-random pattern. [Figure 9b] FIG. 9b illustrates yet another panel embodiment manufactured according to an embodiment of the present invention, in which the chips are arranged in a non-random pattern. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0085] FIG. 1 shows, generally by means of a block diagram, a method according to an embodiment of the invention, which allows to obtain a composite material part according to an embodiment of the invention.

[0086] The method implements the steps described below.

[0087] Cutting the chip (Step S1)

[0088] The realization of the invention requires the formation of chips from carbon fiber based composite elements that are to be recycled.

[0089] For this purpose, the element is mechanically cut to obtain chips.

[0090] The cutting of the chips can be carried out using a cutting machine, such as a blade device, which may be a planar system, that is, a cutting machine equipped with a blade that makes it possible to separate thin slices of regular thickness from the surface of the element that passes through it.

[0091] When an element is cut to form a chip, the blade of the blade device is conventionally arranged with its edges extending in a plane parallel to the cutting direction.

[0092] The material to be cut is placed in the cutter according to the carbon fibre texture it contains.

[0093] If the fibers in the material to be cut are unidirectional, that is to say contained in a matrix substantially parallel in only one direction, the fibers will be oriented parallel to the direction of advancement of the blade device.

[0094] When the fibres are included in the form of a woven web, the parts are preferably laid so that the weft or warp threads are substantially parallel to the advance direction of the blade device.

[0095] The fibers can also be arranged in successive layers, each layer containing unidirectional fibers, but with different fiber orientations. This is the case, for example, of what is called a "four-way" material, whose layers can have successive relative orientations of 0° (reference layer), 90°, 45°, and -45°.

[0096] The blade device can advantageously be adjusted so that the blade cuts into the element between two layers of fabric, whether these be two layers of unidirectional fabric or two textile webs.

[0097] The cut surfaces are advantageously maintained between the layers of fibers in order to maintain as much of the integrity of the layers of fibers as possible.

[0098] In this way, slices of composite material are obtained, which may in particular have a thickness comprised between 200 μm and 1 mm, preferably between 200 μm and 500 μm.

[0099] The elements to be cut are brought to the desired length for the chips before being cut into slices by the cutter, so that chips having the desired length are obtained directly at the outlet of the cutter.

[0100] Alternatively, the slices are subsequently recut to obtain chips. Typically, they are cut transversely by any suitable cutting means, for example by sawing, to form fine rectangular chips of regular length. Of course, chips of other shapes may also be cut from the resulting slices.

[0101] For example, in the manufacture of flat panels, chips of lengths 10 cm to 20 cm have been obtained with very good results in terms of mechanical performance, as exemplified below. Longer lengths, such as in the range of 50 cm or even 1 m, can also be achieved.

[0102] Obviously, the above mentioned cutting methods can be adapted depending on the application considered and the quantities to be produced.

[0103] If the material to be recycled is a pre-coated but uncured carbon fiber fabric, this material is first cured (polymerized in the case of materials coated with thermosetting resin) and then cut into the desired shape of the chips. Such fabrics generally have a thickness comprised between 200 μm and 500 μm, the chips thus obtained having a thickness perfectly adapted to be realized by the present invention for the formation of composite materials, in particular molded parts.

[0104] Thus, when the chips are formed, they take the form of microelements comprising carbon fibres at least partially contained in the hardened resin. They are therefore in the form of substantially two-dimensional parts (their thickness is very small compared to the other dimensions). The surface of the chips advantageously has a dimension of at least 1 cm. 2 and preferably 3 cm 2 Exceeds 10cm 2 or even larger, for example up to about 100 cm 2 It is.

[0105] The hardening of the chip matrix occurs prior to forming the final part by molding and is referred to as the first cure (to distinguish it from the hardening of the part matrix intended to bond the chip, which is carried out during molding of the part).

[0106] The carbon fibers are oriented in the cured resin of the chip. Preferably, they are substantially parallel, perpendicular to each other, and / or oriented at 45° to each other.

[0107] The fibers of the chip, which has a substantially constant thickness, include two opposing faces between which the thickness is defined. The cutting of the chip is performed in such a way as to keep the carbon fibers as intact as possible. To do this, the chip is cut so that the fibers (the majority of them, or even almost all or all) extend parallel to the opposing faces of the chip. The fibers therefore extend in a plane parallel to the general plane in which the chip extends, and can have a large length despite the small thickness of the chip.

[0108] The term "majority" means more than 50% in number; The term "almost all" means greater than 90% in number.

[0109] Coating (Step S2)

[0110] The chips are then mixed with a liquid adhesive to coat the chips for molding purposes.

[0111] This step can be carried out before, during or even after placing the chip in a mold intended to form the desired part. In the following, obtaining a part according to one embodiment of the present invention is described on a pilot or prototype scale. In this example, the chip is mixed with the adhesive before being placed in the mold.

[0112] At prototype scale, mixing can be performed manually in a suitable container, for example made of aluminium.

[0113] The chips are first weighed into a container (step S3), then the adhesive (e.g., a resin / hardener system, see below) is prepared (step S4) and added. When each chip is evenly covered with adhesive, the coating is complete.

[0114] The addition of the adhesive and the mixing of the chips with the adhesive can be done automatically. An automatic mixer can be used to agitate the chips and adhesive.

[0115] The amount of adhesive added to the chip is determined by the characteristics of the part (eg, panel) that is intended to be manufactured.

[0116] The amount of adhesive added depends, for example, on the desired volume or weight percentage of chips in the final material to obtain desired mechanical properties, and on the adhesive used, particularly its density.

[0117] The mass applied is also determined by the thickness of the panel that is to be obtained.

[0118] In many applications requiring significant mechanical performance, it is appropriate to maximize the percentage of chips in the material. Applicants have produced parts containing up to 80% by weight of chips and estimate that parts containing up to 85% by weight of chips, or slightly more, can be produced without difficulty.

[0119] A variety of adhesives can be used without problems: in general, all adhesives known to be used as matrices in composites containing carbon fibers can be used, with the possible exception of adhesives that are incompatible with the cured adhesive present in the chip.

[0120] The term "incompatible" means that the adhesive used will either cause an undesirable chemical reaction with the cured adhesive present in the chip or is not well suited to forming a mechanical bond with the chip.

[0121] As examples, two two-component epoxy-based type adhesives are described below.

[0122] A two-component epoxy system includes an epoxy resin and a hardener.

[0123] When the resin and hardener come into contact, polymerization begins. Polymerization times vary depending on the nature of the system used.

[0124] A first two-component epoxy system that may be mentioned by way of example is the system sold by the company SIKA under the name ADEKIT H9011 (ADEKIT is a registered trademark).

[0125] This system is a generic system and can be used in many metal, ceramic, glass, rubber, rigid plastic adhesive applications, or general material bonding applications according to the manufacturer's recommendations. It is suitable for most industrial and technical applications.

[0126] The resin is light amber in colour, has a density of 1.16 at 25 °C and a viscosity of 25-50 Pa·s at 25 °C. The hardener is amber in colour, has a density of 0.96 at 25 °C and a viscosity of 20-40 Pa·s at 25 °C. The mixture of the two is light amber in colour, has a density of 1.07 at 23 °C after polymerization and a viscosity of 25-50 Pa·s at 25 °C. The mixed mass ratio of the resin / hardener mixture is 100 / 80 and the volume ratio at 25 °C is 100 / 100. The period during which the mixture can be used after contact of the two components at 25 °C for 110 g (commonly referred to by the expression "pot life" and given for a given mass and temperature) is 100 minutes.

[0127] The adhesive, once cured, is transparent, making it possible to see the chips in the final part.

[0128] A second two-component epoxy system that may be mentioned by way of example is the system sold under the name "SR 1700 EPOXY RESIN+SD 2803 STANDARD CURING AGENT" by the company SICOMIN.

[0129] This system is a generic system and can be used for lamination applications in various fields such as boats, car bodies and model building, following the recommendations of the manufacturer.

[0130] The mixture has a viscosity of 0.6-0.7 Pa·s at 20 °C. The mass mix ratio of the resin / hardener mixture is 100 / 39, the volume ratio is 100 / 45. The period during which the mixture can be used after contact of the two components at 20 °C for 500 g (commonly referred to by the expression "pot life" and given for a given mass and temperature) is 120 min.

[0131] As mentioned above, numerous adhesives can be used to form parts according to various embodiments of the present invention, particularly systems intended for composite manufacturing applications (infusion resins, injected resins, laminating resins), as well as systems provided for structural applications as adhesives.

[0132] The systems may in particular have a density comprised between 1.03 and 1.38 at 25° C. Their dynamic viscosity may in particular be comprised between 0.4 and 80 Pa·s. They may in particular have an elastic modulus (after curing) comprised between 2 GPa and 4 GPa.

[0133] Polymerization of these adhesives can be carried out at ambient temperature or at higher temperatures in the range of 70°C.

[0134] Polymerization times vary substantially depending on the thermosetting adhesive system, and the selection of the system may also be influenced by this polymerization time, depending on the mechanical properties and desired cycle time.

[0135] Alternatively, the adhesive may be a thermoplastic resin.

[0136] Finally, regardless of the color additives that may be added to the adhesive (as described below), each adhesive has a specific color and a specific transparency (or opacity) that can be exploited to obtain the desired appearance of the final part.

[0137] Additives can also be added to the adhesive, eg, the glue / hardener mixture, before coating the chip.

[0138] The additive(s) may include dyes, pigments, pigment pastes (pigments already mixed with resin).

[0139] Significant coloring of the transparent resin could be obtained by mixing only 0.94% of the paste, relative to the mass of the resin / hardener mixture. This proportion was sufficient to give the mixture a very opaque color. The color can be seen on the resulting parts, e.g. panels, after molding.

[0140] The chips on the surface of the part remained visible and gave the part a valuable engineered appearance.

[0141] With the various commercially available color additives (pigments, pigment pastes, etc.) that have been tested, good coloration is obtained with at most 5% by weight of pigment and / or at most 5% by weight of dye.

[0142] The additive(s) may also include fillers. Fillers refer to all particulate elements that can be added to the adhesive to change its properties and / or reduce its cost per equivalent volume. Fillers that come into consideration include, in particular, inorganic or organic particles that may improve certain properties of the final part, in particular its resistance to scratches or abrasion.

[0143] These fillers are most often inorganic in the form of particles with particle sizes in the nanometer or micrometer size range (aluminum, calcium fillers, etc.).

[0144] The adhesive may include glass microbeads.

[0145] The used filler may, for example, include carbon dust from the operations of preparation and cutting of the elements to be recycled, and therefore in this case it is an organic filler.

[0146] Molding (Step S5)

[0147] The chip and adhesive mixture is then molded.

[0148] As explained above, an adhesive is optionally used to create a topping of the mold (step S6), which makes it possible to create a layer of resin on the surface, giving the manufactured part a beautiful surface finish, for example a smooth surface finish, or a surface finish that perfectly matches the surface finish provided by the mold.

[0149] As an alternative to topping, overmolding can be performed. To do this, at the end of polymerization (see below), resin is injected into the mold to cover the molded part, obtaining an effect similar to that of topping. The high injection pressure during overmolding can make it possible to add functional elements to the surface of the molded part (grooves, notches, rails, etc.) or to create a desired surface appearance.

[0150] Instead of or in addition to a topping or overmold, a gelcoat (also referred to as gel coat) can be applied to the mold, and as an alternative to the gelcoat, a topcoat (also referred to as finish coat) can be applied to the molded part.

[0151] In the following, the case of manufacturing a flat panel will be considered.

[0152] The mold used has a recess called a female imprint and a portion that forms a corresponding male imprint.

[0153] The coating is made on the surface of the female imprint and on the surface of the male imprint. For flat panels, the surface area of ​​the female imprint is equal to the surface area of ​​the male imprint, and the following rules can be used:

[0154] For each side, apply 10% of the amount of adhesive used plus half the amount of excess adhesive (ie, the amount of adhesive intentionally provided in excess and expelled during molding).

[0155] For toppings made on the side of the male imprint, adhesive can be deposited on the surface of the male imprint or on the chips placed in the female imprint, as described below.

[0156] For example, if the amount of glue used is 68g and there is 5g of excess glue, then the amount of glue for topping will be 9.3g for each side, or 18.6g in total.

[0157] To create the topping, the glue may be applied using a flexible applicator or may be dumped onto the wall to be coated. Depending on the production scale, this step can be performed by an operator or automatically.

[0158] Prior to placement of the topping and / or chips, a release agent may be applied to the interior surfaces of the mold to facilitate removal of the molded part.

[0159] Once the chip is mixed with the adhesive, the chip should be placed into the female imprint of the mold and then finished in a press mold.

[0160] Depending on the production scale considered, chip placement can be done manually using templates or visual cues (eg, guides formed by a laser) or automatically.

[0161] The adhesive-covered chip is placed in the female imprint of the mould on the extraction plate. The extraction plate allows the panel to be extracted from the mould after the pressing operation. It can also be used to adapt the thickness of the panel to be formed (several thicknesses can be made with the same mould by varying the thickness of the extraction plate). When an extraction plate is used, it forms the inner surface of the mould and is therefore the extraction plate that is topped with adhesive if necessary and also with a release agent beforehand if necessary.

[0162] The step of arranging the chips in the mould (step S7) may be important for the mechanical properties of the panel (or more generally the part) that is formed.

[0163] Starting from the hypothesis that the chips have unidirectional carbon fibres, the chips can be arranged in the mould according to three main types of distribution.

[0164] The first arrangement is called a random arrangement. The term "random" means that the chips are arranged in various orientations and overlap each other irregularly. The so-called random arrangement is illustrated in FIG. 2, which more specifically represents the surface of a planar panel according to an embodiment of the present invention, in which the chips have a so-called random arrangement. The chips used here are rectangular. A panel with a random chip arrangement 1 is generally substantially isotropic in the plane in which it extends, as far as its mechanical properties are concerned.

[0165] When random arrangement of chips 1 is performed in the mold, the applicant has nevertheless realized that, particularly in panels of small thickness (typically 2 mm or less), it is necessary to minimize vacant volume by overlapping the chips.

[0166] The second arrangement is called unidirectional arrangement. An example of a so-called unidirectional arrangement is shown in FIG. 3. According to this arrangement, the chips are all arranged in the same direction (A), i.e. the carbon fibers contained in the different chips are all oriented in substantially the same direction. An angular tolerance in the range of plus or minus 10° is acceptable. This tolerance is measured by the angle α formed between the theoretical direction (A) of the chip 10 and the general extension direction of each chip (typically along the length of the chip for rectangular chips). Furthermore, it is acceptable that up to 10% of the chips do not meet the desired orientation and angular tolerance. Nevertheless, the tolerance of the angle and / or the proportion of the incorrectly oriented chips can be made smaller, which contributes to obtaining the desired mechanical properties. Thus, the chips 1 are oriented in the same way, but without a strict organization relative to each other according to a structure that could cause a weakening of the panel. It is therefore preferable to arrange the chips randomly in the longitudinal and transverse directions, while ensuring their longitudinal alignment. This arrangement allows to obtain an anisotropic panel with respect to its mechanical properties. These properties, especially bending strength and breaking strength, are highly favorable in the direction of tip and fiber alignment (A) and unfavorable in the direction perpendicular to the fibers (B).

[0167] A third arrangement is called a multi-directional arrangement, for example a bidirectional arrangement. An example of a so-called bidirectional arrangement is shown in FIG. 4. It consists of making several plies (each containing one or more layers of chips) with different chip orientations between adjacent plies. For example, for rectangular chips, it is possible to alternate the plies with the chips of one ply oriented at 90° to the chips of the adjacent ply. A bidirectional arrangement can therefore be defined as a stack of unidirectional layers as described above. Two plies are partially shown in FIG. 4 (i.e., only certain chips of each ply are represented to illustrate the overlapping of the chips), namely an upper ply in which the chips are oriented in a first direction (x) and a lower fold in which the chips are oriented in a direction (y) perpendicular to the direction (x). The chips of the planar panel given as an example here are arranged parallel to the (x,y) plane.

[0168] According to the above principles, any multi-directional arrangement can be considered.

[0169] The arrangements presented above concern thin planar panels. To form parts with significant thickness (e.g., cubes) or parts with complex three-dimensional shapes, it is also possible to arrange the chips for molding perpendicular to the plane of extension of the chips forming random, unidirectional, or bidirectional configurations as described above. These chips extending through the thickness of the part increase the mechanical properties of the part in their direction of extension. Considering a Cartesian coordinate system (x,y,z), as shown in FIG. 4, the majority of the chips are oriented in a plane parallel to the plane (x,y), and chips arranged perpendicular to the z-direction (e.g., parallel to the (x,z) plane or the (y,z) plane) therefore mechanically reinforce the part in the z-direction.

[0170] Generally, the arrangement of the chips, unless it is purely random, will be such that the chips form a particular pattern that is repeated to form a panel (or, more generally, a component).

[0171] The pattern corresponds to a specific arrangement of some chips among the chips in three dimensions. Thus, apart from purely random arrangements, other considered arrangements (unidirectional, bidirectional, multidirectional, where appropriate three-dimensional arrangements of chips, etc.) can be considered as repeating patterns of chips.

[0172] Examples of patterns illustrating the advantages that can be obtained with non-random arrangement of chips are given below (Example III and Example IV).

[0173] The arrangement, geometry, size and ply thickness of the used tips can be adapted depending on the intended application.

[0174] To a certain extent, the longer the chips, the better the mechanical properties. However, in practice, the length of the chips that can be formed and used depends on the elements to be recycled and on the newly formed parts, and in particular on their geometric complexity (it is quite clear that it is easier to incorporate chips of large length in large flat panels than in curved parts with complex geometric shapes and / or with a large number of geometric details). As a rule, it is advantageous to realize chips whose maximum dimension, such as length, is comprised between 3 and 20 cm.

[0175] Preferably, the plies forming the outer faces of the part (e.g. the two opposing faces of a panel) have their tips 11 oriented longitudinally, i.e. in the main extension direction of the part, or, if this direction cannot be determined, in an arbitrary fixed direction, and the inner ply, or one of every two inner plies, has its tips 12 oriented transversely (i.e. at right angles to the longitudinally oriented tips). It is also possible to vary the performance of the panel in these two directions by varying the thickness of each ply.

[0176] In all of the above arrangements, each ply can have one or more tip layers.

[0177] Once the chip is placed in the female imprint of the mold, the mold is closed by placing the male imprint (mold closing step S8).

[0178] The mould is placed in a press which is activated to put the contents of the mould under pressure (press moulding step S9). Panel prototypes were produced by applying a force of 20 tonnes (about 1600 daN). Nevertheless, substantially lower pressures may also be sufficient. If a thermosetting resin is used, the polymerization can be carried out at ambient temperature. Advantageously, the mould can be heated to accelerate the polymerization. To obtain an efficient and uniform heating (temperatures in the range of 70°C may be desirable), two heating plates can be used on either side of the mould. To regulate the heating and take into account the exothermic nature of the polymerization of the adhesive, a closed loop control, for example of the PID type (proportional, integral, derivative) can be used.

[0179] When the adhesive has cured sufficiently to produce a part that can be handled without deformation, the part is demolded (demolding step S10). However, polymerization is not necessarily fully completed at the time of demolding, which allows the press to be released for another molding.

[0180] To complete the curing of the part (step S11), the part can be placed in an oven, typically at 70°C.

[0181] For the ADEKIT H9011 system, the polymerization time is 16 hours at 70° C. For comparison, complete polymerization of this adhesive takes about one week at ambient temperature.

[0182] By means of the above method it is therefore possible to obtain moulded parts made of composite material formed from composite material elements based on carbon fibres which it is desirable to recycle.

[0183] The above method achieves the formation of the part, or other shaping techniques can be used, for example pultrusion or calendaring.

[0184] In the pultrusion method making it possible to obtain parts according to the invention, the chips are coated and oriented in a nozzle, from which they leave in the desired arrangement in a resin that undergoes a (second) hardening. Pultrusion can be used in particular to obtain very long parts (beams, panels, etc.).

[0185] In the calendaring process which makes it possible to obtain a part according to the invention, a mass of adhesive which is in the process of polymerization and which contains precisely aligned chips, passes through a nip of rollers to form a thin part, for example a thin panel.

[0186] Unlike known recycling methods, which generally aim to extract carbon fibers for their reuse, the present invention proposes forming chips in which the fibers remain, at least in part, included in the hardened matrix of the recycled element.

[0187] Many part geometries are possible.

[0188] Figure 5 shows in photographic form at a magnification of 50x a cross section of a composite part according to an embodiment of the invention. In this case, it shows a cross section of a planar panel comprising chips 1 arranged parallel to one another and contained in a matrix 2. The chips 1 in Figure 5 are rectangular chips and aligned unidirectionally in the longitudinal direction. The cross section that is made is a longitudinal cross section of the panel, perpendicular to the plane in which the panel extends.

[0189] In this cross-sectional photograph, the chip 1 can be seen as light grey stripes, which correspond to the carbon fibers 3, and the areas inside the chip located between the carbon fibers 3 correspond to the adhesive that has hardened during the first cure.

[0190] The matrix 2 formed from the hardened adhesive during the second cure and containing the chips 1 corresponds to the areas without carbon fibres which appear dark grey in FIG.

[0191] The chips 1 remain separate from the matrix 2, and the bonding interface between each chip 1 and the matrix 2 is perceptible. Figure 5 thus visualizes that each chip is an essentially two-dimensional element of small thickness e, measured between two parallel faces 4 of the chip 1 (thickness is conventionally the smallest distance between the faces 4, i.e. measured perpendicular to these faces 4). EXAMPLES

[0192] Example I: Characterization of panels obtained according to the invention The Applicant has carried out characterization tests on the mechanical properties of the materials obtained according to the invention, which are described in the following examples.

[0193] The tests for which the results are presented below were carried out on a prototype plate measuring 23 cm x 23 cm and having a thickness comprised between 3.5 mm and 3.6 mm.

[0194] The chips used in the tests presented in this example are from composite material elements that contain unidirectional carbon fibers in an epoxy resin type adhesive. The elements used are from the aeronautical industry. The composite material has the same or similar properties as the "UD carbon plate" material, which are shown in Table 1 below.

[0195] The chip used is rectangular, has a length a of 100 mm, a width b of 9 mm and a thickness comprised between 0.3 mm and 0.5 mm.

[0196] The plate is manufactured according to the method described above with reference to FIG.

[0197] The mold is coated with release agent and topped under the conditions described above.

[0198] The adhesive used was the ADEKIT H9011 system used according to the manufacturer's recommendations recalled above.

[0199] The chips are manually placed into the mold.

[0200] The chip to adhesive ratio is 65 / 35 by weight in the finished plate unless otherwise stated.

[0201] The molding is carried out under a press by applying a force of 20 tons and controlling the temperature at about 70°C.

[0202] After removal from the mould, the plates are kept at ambient temperature (20° C.) for one week before being used for measurements.

[0203] The tests made it possible to obtain the results shown in the table below.

[0204] The properties of plates according to the embodiments are presented in the table in comparison with a reference material.

[0205] [Table 1] "UD carbon plate" refers to a plate made of a new unidirectional carbon fiber based composite material.

[0206] "Bidirectional carbon plate" corresponds to a plate of a composite material based on new carbon fibers organized in two directions, i.e. with an equal number of alternating layers with longitudinal and transverse fibers.

[0207] "Plate UD1" and "Plate UD2" correspond to composite plates according to an embodiment of the invention obtained as described above, whose chips, and therefore the fibres, are arranged according to a unidirectional array.

[0208] The "BD1 plate" corresponds to a material with a bidirectional arrangement of chips and fibers, i.e. the plate tested has two outer plies (forming the outer surface of the part) in which the chips and therefore the fibers are arranged in a longitudinal unidirectional arrangement, and an inner ply in which the chips and therefore the fibers are arranged in a transverse unidirectional arrangement. The inner ply has a thickness twice that of each of the outer plies.

[0209] The "BD2 plate" corresponds to a material with a bidirectional arrangement of chips and fibers, i.e. the plate tested comprises two outer plies in which the chips and therefore the fibers are arranged in a longitudinal unidirectional arrangement, and an inner ply in which the chips and therefore the fibers are arranged in a transverse unidirectional arrangement, the inner ply having a thickness approximately six times that of each of the outer plies (providing an isotropic behavior in these directions, longitudinal and transverse, for plate BD2 of the panel under reference).

[0210] It is noteworthy that the flexural modulus and tensile strength of the plate UD2 (with 65% by mass of chips) are significantly greater than 50% of the values ​​obtained for the reference UD carbon plate, i.e. for a composite material based on comparable new unidirectional fibers (from which used chips can be extracted). In particular, the obtained flexural modulus is equal to 57% of the flexural modulus of a comparable new unidirectional material based on carbon fibers in the longitudinal direction. If these results are combined with the mass of the panel (taking into account the observed differences in density), the flexural modulus of the plate UD2 (with 65% by mass of chips) is equal to 63% of the flexural modulus of the reference UD carbon plate.

[0211] Regarding the panels obtained with bidirectional texturing, plate BD2 gives similar results: in fact, in both the longitudinal and transverse directions, the flexural modulus and tensile strength of plate BD2 significantly exceed 50% of the values ​​obtained for the bidirectional carbon plate.

[0212] Furthermore, plate BD1 offers the same flexural modulus in the longitudinal direction as the reference bidirectional carbon plate (and therefore, for an equal mass, greater performance in the longitudinal direction than the new panel) at the expense of lower performance in the transverse direction.

[0213] The results shown above show that recycled materials with high mechanical performance are obtained. These results are obtained for materials containing a percentage of chips (up to a 65 / 35 mass ratio in the examples shown) that can be further increased relative to the amount of adhesive added. However, the applicant has observed that the percentage of chips directly influences the mechanical performance obtained, since it induces the percentage of fibers in the material. In particular, the flexural modulus of plate UD2 (containing 65% by mass of chips) is almost 50% higher than that of plate UD1 (containing 50% by mass of chips). The breaking strength increases by more than 20%.

[0214] The invention therefore makes it possible to obtain, by means of a simple manufacturing process, recycled materials with a low environmental impact compared to chemical or thermal recycling processes, with a mechanical performance of almost 70%, in particular a flexural modulus of 70%, and materials equivalent to those based on new fibers (with a performance of up to 75% to 80% for the same mass).

[0215] Furthermore, even higher performance can be achieved, and the applicant has successfully produced parts containing more than 65% by weight of chips (in this case up to 78% by weight, with panels containing about 85% by weight of chips appearing to be feasible).

[0216] Example II: Characterization of panels obtained according to the invention FIG. 6 depicts the flexural modulus of a panel according to an embodiment of the invention in which the chips are unidirectionally textured, and a panel containing new directionally oriented carbon fibers.

[0217] Flexural modulus is plotted on the ordinate.

[0218] The abscissa indicates the angle at which the measurements are taken: an angle of 0° corresponds to the direction of extension of the fibre or chip, and 90° corresponds to a direction transverse to the fibre and / or chip.

[0219] The triangle corresponds to a measurement carried out on a plate of material according to an embodiment of the invention, whose chips formed from elements containing unidirectional carbon fibres are unidirectionally organised and have a flexural modulus of 47 GPa measured in the direction of extension of the chips and the fibres they contain.

[0220] The circles represent the theoretical flexural modulus calculated for an equivalent plate made from the new composite material based on new unidirectional carbon fibres, which has a flexural modulus of 47 GPa in the direction of the fibres contained in the plate.

[0221] Surprisingly, it is clear that the measurements carried out on the composite material formed according to the invention are in perfect agreement with the theoretical values ​​obtained for a material formed with new equivalent continuous fibers.The mechanical properties of the elements formed according to the invention, at least for the chips containing unidirectionally organized fibers and organization in plies, can be predicted according to the knowledge generally applicable to composite materials based on new equivalent continuous carbon fibers.

[0222] Example III: Laminated Panels Comprising Plies Made with a Tip Pattern Comprising Woven Carbon Fiber This embodiment relates to the formation of a panel using chips of two different non-random patterns, each pattern allowing for the formation of a layer of chips, the layers of chips formed according to the two patterns being arranged alternately in the panel.

[0223] For reference, the mechanical properties shown in the table below were measured on a laminate panel having dimensions of 230 mm x 230 mm x 4 mm, formed by a so-called "semi-random" chip arrangement, in which the chips are manually placed in the mould in order to obtain a good filling of the mould, but which nevertheless does not create a specific or repetitive pattern.

[0224] A chip with dimensions of 60 mm x 60 mm x 0.4 mm was used to form the reference panel.

[0225] In these examples, the chips are obtained by cutting a composite material incorporating woven carbon fibers arranged in a woven web, the cutting to form the chips being carried out between layers whenever possible.

[0226] The adhesive and conditions for obtaining the panels are similar to those described in Example I.

[0227] The flexural properties (determined by a three-point bending test according to standard ISO 14125:1998) as well as the density of the prototype panels thus formed are summarized in Table 2 below.

[0228] The means and deviations presented in Table 2 below are each obtained from six measurements.

[0229] [Table 2] The coefficient of variation, CV, is the ratio of the standard deviation to the mean, expressed as a percentage. The higher the value of the coefficient of variation, the greater the dispersion around the mean.

[0230] Therefore, the measured bending properties show significant variation between the different manufactured prototypes. In particular, it is noted that the coefficient of variation is much higher than 10% for the mechanical properties.

[0231] A laminate panel of the same dimensions (ie 230 mm x 230 mm x 4 mm) was then formed and the chips were obtained of the same material and with the same thickness as the reference panel.

[0232] To construct the patterns described with reference to Figures 7a, 7b and 7c, tips with the following dimensions were used: A: 60×60×0.4mm B: 60×48×0.4mm C: 60×30×0.4mm D: 60×18×0.4mm E: 48×48×0.4mm F: 30×30×0.4mm G: 30×18×0.4mm H: 18×18×0.4mm FIG. 7a shows the first pattern where the chips are arranged end-to-end, forming a layer of 230 mm×230 mm.

[0233] The designations of the chips used (A to H from the list above) are indicated on each represented chip.

[0234] FIG. 7b shows the second pattern where the chips are arranged end-to-end to form a layer of 230 mm×230 mm.

[0235] The designations of the chips used (A to H from the list above) are indicated on each represented chip.

[0236] To form a panel, the chips are placed into a mold, alternating layers of a first pattern with layers of a second pattern.

[0237] FIG. 7c shows the superposition of a first patterned layer (dotted lines) and a second patterned layer (solid lines).

[0238] The idea behind the formation of this panel is to ensure that the abutment area between two chips, which could constitute a mechanically weak area, is always sandwiched between the two chips.

[0239] It should be noted that control and consistency of the chip thickness is important as it is this dimension that defines the thickness of each layer (also called a ply).

[0240] However, ply thickness is an important parameter in the formation of laminates (whether recycled or not), and having a consistent chip thickness therefore allows control over the ply thickness, arrangement, thickness of the formed panel (or part), as well as its mechanical properties.

[0241] The prototype panels obtained as described above were also tested in a three-point bending test to measure their density, the values ​​obtained are summarized in Table 3 below.

[0242] [Table 3] Thus, the use of a non-random repeating pattern results in an increase in tensile strength value of approximately 30% for the example construction given herein.

[0243] This means that the weak areas of the panel are reduced.

[0244] Furthermore, the variation in mechanical properties between different panels was significantly reduced compared to the reference panel. The variation in flexural properties was halved compared to the reference panel, such that the coefficient of variation of tensile strength was limited to 10%. The variation in panel density was very small.

[0245] Thus, by controlling the repeating pattern (or patterns) and non-random arrangement of the chips, a homogenous material can be obtained, whose mechanical properties can be optimized, are controlled, predictable and have little variation.

[0246] Example 4: Laminated Panels Comprising Plies Made with a Tip Pattern Containing Unidirectional Carbon Fiber This embodiment also relates to the formation of a panel using chips of two different non-random patterns, each pattern allowing for the formation of a layer of chips, the layers of chips formed according to the two patterns being arranged alternately in the panel.

[0247] For reference, the mechanical properties shown in the table below were measured on a laminate panel having dimensions of 230 mm x 230 mm x 4 mm, formed by a so-called "semi-random" chip arrangement, in which the chips are manually placed in the mould in order to obtain a good filling of the mould, but which nevertheless does not create a specific or repetitive pattern.

[0248] In these examples, the chips are obtained by cutting a composite material incorporating unidirectional carbon fibers.

[0249] The chip used has dimensions of 100 mm x 10 mm x 0.4 mm.

[0250] The adhesive and conditions for obtaining the panels are similar to those described in Example I.

[0251] The flexural properties (determined by a three-point bending test according to standard ISO 14125:1998) as well as the thickness of the prototype panels thus formed are summarized in Table 4 below.

[0252] [Table 4] As described below, panels (Panel 1 and Panel 2) were formed using chips having the following dimensions: I: 100×10×0.4mm J: 70×10×0.4mm K: 65×10×0.4mm L: 55×10×0.4mm M: 25×10×0.4mm A laminate panel (Panel 1) of the same dimensions (ie 230 mm x 230 mm x 0.4 mm) was then formed, with chips made of the same materials as the reference panel.

[0253] FIG. 8a shows the first pattern in which the chips are arranged end-to-end, forming a layer of 230 mm×230 mm.

[0254] FIG. 8b shows a second pattern in which the chips are arranged end-to-end to form a layer of 230 mm×230 mm.

[0255] The panel 1 is formed by alternating layers of chips according to the pattern of FIG. 8a and the pattern of FIG. 8b.

[0256] The designations of the chips used (I to N from the list above) are indicated on each depicted chip.

[0257] A laminated panel (Panel 2) of the same dimensions (ie 230 mm x 230 mm x 4 mm) was then formed, with chips made of the same materials as the reference panel.

[0258] FIG. 9a shows the first pattern where the chips are arranged end-to-end, forming a layer of 230 mm×230 mm.

[0259] FIG. 9b shows a second pattern in which the chips are arranged end-to-end to form a layer of 230 mm×230 mm.

[0260] The designations of the chips used (I to N from the list above) are indicated on each depicted chip.

[0261] The above resulting prototype panels (Panel 1 and Panel 2) were also tested according to the three-point bending test to measure their thickness, and the obtained values ​​are summarized in Table 5 below.

[0262] [Table 5] It should be noted that the fact of using a repeating pattern and a controlled arrangement of the tips does not necessarily mean that the results, in terms of mechanical properties, are better than those obtained with a so-called semi-random arrangement (reference panel).

[0263] Arrangement 1 allows for panels with mechanical properties comparable to those of the reference panel, but with a higher variability in terms of flexural tensile strength.

[0264] In a non-random device, the variation rate of the panel thickness is very low. Therefore, the fact of using a non-random pattern (or multiple non-random patterns) to make the panel allows to limit the variation of the thickness of the manufactured panels. In fact, the above-mentioned panels all have the same number of plies, but the "semi-random" arrangement of the chips leads to an overlap of certain chips in the same ply. This results in a large panel thickness and a large variation in thickness from panel to panel.

[0265] Panel 2 performs much better in bending with similar variation compared to the semi-random arrangement, i.e., 25% more in flexural modulus and 15% more in tensile strength compared to the reference panel, but at the same time, Panel 2 is thinner for the reasons explained above.

[0266] Thus, Examples III and IV collectively demonstrate that the use of non-random repeating patterns can improve the mechanical properties of parts formed according to the present invention. It can also reduce the variability of part properties. The resulting properties are more controlled, stable, and predictable, allowing for the most accurate sizing of parts.

Claims

1. A composite material part, - chips (1), each having a substantially constant thickness defined between two parallel opposite faces (4) of said chip, each comprising carbon fibres (3) at least partially contained in an adhesive that has hardened during a first cure prior to forming said part, at least the majority of said fibres of said chips extending substantially parallel to said opposite faces (4) of said chips (1); a matrix (2) in which each chip (1) is at least partially contained, said matrix (2) being formed from the adhesive hardened during a second cure; A composite material part, comprising: a bonding interface formed between said matrix (2) of said part and each chip (1).

2. The composite part of claim 1 , wherein the bond interface comprises an essentially mechanical adhesive bond.

3. The face (4) of each chip (1) has an area of ​​at least 1 cm2, referred to as the surface area of ​​the chip. ２ 3. The composite part according to claim 1 or claim 2, having a surface area of

4. 4. The composite part of claim 3, wherein the bond interface between each chip and the matrix (2) does not have an inflection point across the chip.

5. 3. A composite part according to claim 1 or 2, wherein each chip (1) has a thickness (e) and a largest dimension (d) that can be measured over the surface area of ​​said chip, such that the ratio (e) / (d) is comprised between 0.05 and 0.0005.

6. 3. Composite part according to claim 1 or 2, wherein the carbon fibres (3) extend mainly in parallel planes.

7. 3. Composite part according to claim 1 or 2, wherein the tip has a unidirectional arrangement of the carbon fibres (3).

8. 8. A composite material part according to claim 7, wherein the chips are oriented such that the carbon fibres (3) of the part are oriented in substantially the same direction.

9. 3. A composite material part according to claim 1 or 2, wherein the chips are oriented such that the carbon fibres (3) of the part are oriented substantially in only two different directions, for example in a first direction and a second direction forming an angle of 90° between them.

10. 3. The composite part of claim 1 or 2, wherein the chips are arranged in a repeating pattern.

11. 3. Composite part according to claim 1 or 2, wherein the chips (1) have substantially the same shape and dimensions.

12. 12. Composite part according to claim 11, wherein the face (4) of each tip (1) is substantially rectangular in shape.

13. 3. Composite part according to claim 1 or 2, wherein the thickness of the chip is comprised between 200 μm and 1 mm.

14. 3. The composite part of claim 1, wherein the part comprises a fiber region formed by the chips and comprising 20% ​​to 85% by volume of the part, and a non-fiber region consisting of the adhesive added and cured during the second cure and forming the remainder of the part.

15. 1. A composite material article comprising: a plurality of regions comprising carbon fibres and a first adhesive, the carbon fibres having a non-random orientation within the same region, the region comprising carbon fibres having a substantially constant thickness defined between two parallel opposite faces, and all carbon fibres in the region comprising carbon fibres being oriented along substantially parallel planes; at least one area comprising a second adhesive and not comprising carbon fibres; Including, 1. A composite part, wherein the plurality of regions comprising carbon fiber and a first adhesive are at least partially contained within at least one region comprising a second adhesive and not comprising carbon fiber.

16. 16. Composite part according to claim 15, wherein the carbon fibres (3) are oriented substantially parallel, orthogonal and / or at 45° within the same region.

17. The composite part of claim 1 , wherein the part is a flat or curved panel.

18. A method for manufacturing a composite material part, comprising the steps of: - providing a composite material comprising carbon fibers (3) in an adhesive that has hardened during a first cure; - cutting (S1) said composite material into chips, each chip (1) having a substantially constant thickness defined between two parallel opposite faces (4) of said chip, each chip comprising carbon fibres (3) at least partially contained in the adhesive hardened during a first cure, at least the majority of said fibres of said chip extending substantially parallel to said opposite faces (4) of said chip; - coating the chip with adhesive (S2); - arranging said chips so as to form an intertwining of chips (S7); - A step (S11) of hardening the liquid adhesive, called second hardening.

19. A composite material part obtainable by the method according to claim 18.

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