Chips made from recycled composite materials and manufacturing method thereof

Abstract

The present invention relates to a chip made from a composite material containing carbon fibers in a cured adhesive, the chip having a substantially constant thickness defined between two parallel, opposing faces of the chip, the surface of each face including carbon fibers that are at least partially not contained in the cured adhesive.

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 an "adhesive" or even a "resin" (the matrix is ​​generally a polymer). 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 in this application.

[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). For some applications, specialized thermoplastic polymers such as poly(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 those of similar new parts. Composites based on recycled carbon fibers obtained by mechanical recycling methods therefore generally have limited applications in specific areas where there is no very high need for mechanical properties relative to the mass. They are therefore mainly used in construction (buildings).

[0018] 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.

[0019] Several chemical decomposition methods are known, in particular conventional solvolysis, solvolysis under "mild" conditions or solvolysis under supercritical conditions. In conventional solvolysis, the parts to be recycled are immersed in solvents at high temperatures (above 200° C.) and pressures (in the range of 180 bar) so that the resin is decomposed. These may be, for example, concentrated acids (in particular nitric acid or sulfuric acid).

[0020] Mild solvolysis uses temperatures below 200° C. that are milder than conventional solvolysis. The process 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.

[0021] 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.

[0022] 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.

[0023] 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 characteristics. Otherwise they are used for packing, for example as the powders obtained in the mechanical recycling methods mentioned above.

[0024] 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 is made up of technologies that break down resin and regenerate carbon fiber (chemical or thermal recycling).

[0025] 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. Summary of the Invention [Problem to be solved by the invention]

[0026] The present invention aims to propose a recycled element that can be incorporated into a matrix for manufacturing a composite part, said recycled element being able to overcome the above mentioned drawbacks. [Means for solving the problem]

[0027] More particularly, the present invention relates to a composite chip comprising carbon fibers in a cured adhesive, the chip having a substantially constant thickness defined between two parallel, opposing faces of the chip, each face comprising carbon fibers on a surface thereof that are at least partially not contained in the cured adhesive.

[0028] The term "chip" refers to a slice of small thickness obtained from recycled composite material containing carbon fibers. The chip comprises carbon fibers at least partially contained in a cured adhesive. At least a majority of the fibers of the chip extend substantially parallel to the opposing faces of the chip.

[0029] 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 composite part such as a panel. This possible curvature is possible due to the small thickness of the chip, which gives the chip 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 an 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.

[0030] Throughout this application, the term "significantly" refers to the perception of this feature by the system conventionally used for its measurement or production. If a feature is observed with the naked eye, the term "substantially" therefore refers to the perception of the feature by the observer. Expressions containing the term "substantially" should be interpreted as technical features 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.

[0031] The chip according to the invention advantageously has a thickness (e) which is small compared to its other dimensions. The chip is therefore essentially a two-dimensional part, with a small thickness, the other dimensions of the chip typically corresponding to the largest dimension (d) which can be measured on the surface of the chip, and also to a dimension measured perpendicularly on the surface of the chip. The term "face of the chip" therefore means either of the faces of the chip, i.e. the lower or upper face of the chip. Each of these faces has a surface, which is called the face of the chip.

[0032] 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.

[0033] In this application, unless otherwise indicated, ranges are to be understood as being inclusive.

[0034] Advantageously, the thickness of the chip is comprised between 200 μm and 1 mm, preferably between 200 μm and 500 μm.

[0035] The maximum dimension (d) of the chip may advantageously be comprised between 1 cm and 1 m, preferably between 5 cm and 50 cm, for example between 5 and 20 cm, more preferably between 7.5 and 15 cm, or even more preferably between 8 and 12 cm, or alternatively between 10 cm and 20 cm.

[0036] As an example, the length of the tip is in the range of 10 cm. The term "in the range of X" intends a value of X±10%.

[0037] The tip may have a width comprised between 2 and 20 mm, preferably between 5 and 15 mm, and even more preferably between 7 and 10 mm.

[0038] As an example, the width of the chip is in the range of 9 mm.

[0039] The term "cured adhesive" refers to an adhesive that has undergone a chemical reaction called crosslinking or polymerization, which occurs prior to the formation of the chip, and which is referred to as a cured adhesive during curing prior to the formation of the chip.

[0040] The hardened adhesive of the chip may advantageously be a thermosetting resin such as an epoxy resin, a cyanate ester, or a phenolic resin. 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.

[0041] Also included are modified blends of the aforementioned thermosetting polymers.

[0042] "Modified blend" refers to polymers that have been modified, typically by the addition of a rubber or thermoplastic resin.

[0043] The hardened adhesive of the chip may be a thermoplastic. Among 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.

[0044] Thermoplastic resins, depending on their nature, can be rigid in amorphous or crystalline form.

[0045] Among the amorphous thermoplastics commonly used in composites are polyetherimide (PEI), polyethersulfone (PES), and polysulfone (PSU).

[0046] 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).

[0047] A carbon fiber is considered to be contained in the cured adhesive if its entire surface is in contact with the adhesive, i.e., if all surfaces of the fiber are coated with the adhesive. Throughout this application, the terms "contained in" and "coated with" are considered equivalent.

[0048] In a tip according to the invention, the portion of the carbon fiber that is not included in the cured adhesive constitutes an uncoated fiber.

[0049] The presence of uncoated fibers on the surface of the chips is due to the chip cutting method according to the present invention.

[0050] Preferably, the chip according to the invention has an uncoated fiber area percentage of 22% or more, said percentage being relative to the total surface area of ​​the face of the chip being analyzed.

[0051] The uncovered fiber area fraction represents the surface area occupied by carbon fibers not included in the cured adhesive relative to the total surface area of ​​the face of the chip being analyzed.

[0052] The chips may have an uncoated fiber area percentage greater than or equal to 22%, preferably comprised between 24% and 60%, such as an uncoated fiber area percentage comprised between 26% and 50%.

[0053] The uncoated fiber area ratio is a) arranging the sample or chip horizontally on the stage of a digital microscope to acquire images in which the fiber orientation is vertical, the microscope being oriented at an angle of 20-40°, preferably 30°, to a line perpendicular to the plane of the sample or chip, and applying a partial annular LED type light such that the light beam reaches the surface of the fiber in a direction perpendicular to the fiber orientation axis; b) selecting pixels having a gray level threshold greater than or equal to 50; c) counting the selected pixels and obtaining a percentage of the surface area occupied by the selected pixels relative to the total surface area of ​​the image, this percentage corresponding to a value of the uncoated fiber area fraction; The carbon fiber according to the present invention is determined for a sample or chip comprising the carbon fiber by a measurement method comprising the steps of:

[0054] Annular light is light that forms a circle around the microscope objective lens.

[0055] The plane of the sample or chip is realized by one face of the sample or chip.

[0056] The circle of light can be divided into four quadrants, which are referred to as "partial annular light" when only one of the quadrants is used to illuminate the sample, thus defining a left annular light, a right annular light, a high annular light, or a low annular light, depending on the location of the quadrant relative to the microscope objective.

[0057] Annular light is to be distinguished from coaxial light, which illuminates the sample from the center of the microscope objective.

[0058] The partial annular light applied in step a) may be a right partial light, a left partial light, a high partial light or a low partial light. Preferably, the partial annular light applied in step a) is a left partial annular light or a right partial annular light, and even more preferably, the partial annular light is a right partial annular light.

[0059] For right partial annular light, the microscope is oriented at an angle of 20-40°, preferably 30°, to the right with respect to a line perpendicular to the plane of the chip.

[0060] Preferably, the uncoated fiber area percentage is determined by the method described in Example 2, item 1.

[0061] Preferably, in a tip according to the invention, one face has a roughness measured by mass loss that is equal to or greater than 0.008%, said mass loss being measured by an abrasion test carried out on a linear abrasion tester using H18 abrasive rubber for 100 cycles.

[0062] The term "roughness" of a tip refers to the condition of the surface of the tip, which has projections and recesses. Preferably, each surface of the tip has a roughness.

[0063] This roughness is determined by a measurement method which includes the following steps: a) initially weighing the chips to determine their initial mass; b) fixing the tip on a support of a linear abrasion tester; c) applying H18 abrasive rubber for 100 abrasion cycles at a cycle length of 10 cm and a cycle speed of 25 cycles / min; d) final weighing of the chips to determine the final mass of the chips; e) determining the roughness by calculating the difference between the initial mass of the tip (obtained in step a)) and the final mass of the tip (obtained in step d)).

[0064] Preferably, the roughness is measured by the method described in Example 2.2.

[0065] Preferably, the chips have a roughness measured by mass loss comprised between 0.014% and 0.20%, more preferably the mass loss is comprised between 0.014% and 0.15%.

[0066] Advantageously, the chips according to the invention have an uncoated fibre area fraction greater than or equal to 22% and a roughness measured by mass loss greater than or equal to 0.008%. Preferably, the chips have an uncoated fibre area fraction comprised between 24% and 60% and a mass loss comprised between 0.014% and 0.20%. Even more preferably, the chips may have an uncoated fibre area fraction comprised between 26% and 50% and a mass loss comprised between 0.014% and 0.15%.

[0067] Advantageously, in a tip according to the invention, the carbon fibres extend substantially parallel to the opposing faces of the tip.

[0068] More specifically, the carbon fibers contained within the cured adhesive extend substantially parallel to the opposing faces of the chip.

[0069] The carbon fibers not included in the cured adhesive may extend substantially parallel to the opposing faces of the chip.

[0070] Advantageously, in the chip according to the invention, the carbon fibres are oriented in the same direction.

[0071] Carbon fibers oriented in the same direction are also called unidirectional.

[0072] More specifically, the carbon fibers contained in the cured adhesive are oriented in the same direction.

[0073] The carbon fibers not included in the cured adhesive may be oriented in the same direction.

[0074] Advantageously, the chip has a rectangular shape.

[0075] Preferably, each face of a chip according to the invention is at least 1 cm 2 has a surface area of

[0076] Each face has a surface area referred to as the surface area of ​​the chip.

[0077] The surface area of ​​the chip must be at least 3 cm 2 , 5cm 2 , 10cm 2 Or 20cm 2 , 100cm 2 It could be.

[0078] Therefore, the surface area of ​​the chip is between 1 and 100 cm 2 , 2~25cm 2 Or 5~15cm 2 may be included in

[0079] The present invention also relates to a method for producing a chip according to the invention, comprising the following steps: - providing a composite material comprising substantially parallel oriented carbon fibers in a cured adhesive; - mechanically cutting the composite material using a blade device, the cutting being performed by positioning the carbon fibres parallel to the direction of travel of the blade of the blade device.

[0080] By way of example, the blade device may be a planar system, that is, a cutter 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.

[0081] The method for manufacturing the chip is described in more detail in Example 1.

[0082] The invention also relates to the use of a chip as defined above in a composite material part.

[0083] The chip according to the invention has the advantage that it has improved adhesion with the matrix.

[0084] In particular, the inventors have discovered that chips having an uncoated fiber area fraction equal to or greater than 22% and / or a roughness measured by mass loss equal to or greater than 0.008%, as defined above, have improved adhesion with the matrix. Improving the adhesion between the matrix and the carbon fibers leads to better cohesion of the chips, thus limiting the degradation of the chips and, consequently, of the composite parts comprising the chips according to the invention.

[0085] Other characteristics and advantages of the invention will become apparent from the drawings and the following examples, given by way of example. [Brief description of the drawings]

[0086] [Figure 1] FIG. 1 represents in graph form the flexural modulus of a panel containing unidirectionally organized chips according to the invention, the chips being obtained from recycled composite material, and the flexural modulus of a virgin panel containing unidirectionally oriented carbon fibers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0087] Example 1: Obtaining a chip according to the invention The chips are formed from elements made from composite materials based on recycled carbon fibers.

[0088] For this purpose, the element is mechanically cut to obtain chips.

[0089] The cutting of the chips can be carried out using a cutting machine, such as a blade device, which can 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.

[0090] When an element is cut to form a chip, the blade of the blade device is conventionally arranged so that the edge of the blade moves in a plane parallel to the direction of advance of the blade of the blade device, which is a straight line.

[0091] The "edge of the blade", also called the "sharp edge", corresponds to the edge of the blade which first penetrates the material being cut.

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

[0093] If the fibres in the material to be cut are unidirectional, ie contained in a matrix substantially parallel in only one direction, the fibres will be arranged parallel to the direction of advance of the blades 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 direction of advancement of the blades 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 materials called "four-way" materials, whose layers can have successive relative orientations of 0° (reference layer), 90°, 45°, -45°. Thus, a "four-way" material is a laminate material containing several layers of unidirectional carbon fibers, the layers being oriented in four different directions: 0°, 90°, 45°, -45°.

[0096] The blade device can advantageously be adjusted so that the blade cuts into the element between two layers of fibers, whether these are two layers of unidirectional fibers or two woven 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] Advantageously, the blade device can be equipped with a micrometric wedge system consisting of a superposition of elements placed on either side of the material to be cut, said wedge system being placed on a reference plane and having an accuracy of less than one tenth of a millimeter. Such a wedge system makes it possible to control the cutting area of ​​the blade and therefore to make a more precise cut between the layers of fibre. This system therefore makes it possible to control the thickness of the resulting chips whilst keeping the carbon fibres intact.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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 used.

[0103] Obviously, the above mentioned cutting methods can be adapted depending on the application considered and the quantities to be produced.

[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 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.

[0106] 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.

[0107] The term "majority" means greater than 50% in number.

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

[0109] Example 2: Characterization of the chip according to the invention The applicant has carried out tests enabling the properties of the chip according to the invention to be evaluated. These tests were carried out using the materials listed in Table 1.

[0110] These materials are in the form of composite rods, composite plates or composite webs.

[0111] A composite rod is a cylinder obtained by pultrusion of the composite material.

[0112] Composite webs are distinguished from composite plates by their thickness: in fact, webs have a thickness in the range of 0.2 mm, while composite plates have a thickness of several millimeters.

[0113] Partially consolidated composite webs are webs in which the carbon fibers are embedded in a matrix or resin in which polymerization has been initiated but not completed, and thus are distinguished from composite webs which include carbon fibers in a non-polymerized matrix because polymerization has not been initiated for the latter.

[0114] Where no details are provided regarding the state of polymerization of the matrix of the materials listed in Table 1 above, this is meant to indicate that the matrix is ​​polymerized. [Table 1] * UD: Unidirectional carbon fiber alignment Table 1: List of materials used

[0115] Materials 1-12 were all sized to the same width: 9mm, and the same length: 100mm. To do this, materials 1 and 2 were sized using a miter saw, material 3 was sized using a paper trimmer, and materials 4-12 were sized via the paper trimmer or using scissors.

[0116] Next, the materials 1 to 3 were cut to obtain the chips according to the present invention. The chips according to the present invention were obtained by the method described in Example 1.

[0117] Mechanical cutting with a plane is carried out in such a way that it favours cutting along the axis of the fibres. In fact, materials 1-3 consisting mainly of unidirectional fibres, i.e. fibres oriented in a single direction, are arranged parallel to the direction of advance of the blade of the mechanical blade cutting device.

[0118] Cutting as described above makes it possible to obtain chips of regular thickness, to keep the carbon fibers as intact as possible, and to obtain chips containing longer fibers.

[0119] The chips obtained from materials 1 to 4 have a thickness comprised between 0.3 and 0.5 mm.

[0120] Materials 4 to 12 were used as comparative examples and were not cut.

[0121] 1. Surface analysis: Determination of the uncoated fiber area fraction Surface analysis was performed on all chips obtained from materials 1–12 according to the procedure detailed below.

[0122] The uncoated fiber area fraction is defined as the surface occupied by uncoated carbon fibers, i.e. carbon fibers not contained in or coated with resin, relative to the total surface analyzed.

[0123] The uncoated fiber area fraction was determined for each of materials 1-12 using a VHX-970F digital microscope commercially available by the Keyence brand. The latter is equipped with a VH-Z20T zoom objective lens capable of providing magnifications ranging from 20x to 200x. Image processing was performed using ImageJ software, version 2.1.0 / 1.53c.

[0124] The principle of the measurement is to select the brightest areas, which theoretically correspond to the carbon fibers, and by extracting them, to measure the surface area they occupy, using image processing under a microscope. The protocol is as follows: a) Sample sequence The sample or chip is placed horizontally on the microscope stage so that the orientation of the fibers on the captured image is vertical. The microscope is oriented at an angle of 30° (preferably to the right) relative to a line perpendicular to the plane of the sample or chip, and a partial annular light of the LED type (preferably to the right relative to the microscope objective) is applied so that the light beam reaches the surface of the fiber in a direction perpendicular to the axis of the fiber. This configuration makes it possible, on the one hand, to avoid considering fibers coated with a transparent resin and, on the other hand, to prevent reflections in the resin areas.

[0125] b) Pixel selection The pixel selection is performed by the software by carrying out the following steps in the "Image" > "Adjust" > "Color Threshold" tab. This option allows the selection of the brightness at which the pixels are selected. For all test materials, the gray level was set to 50 ("Brightness" parameter). In this way, all areas with a gray level of 50 or higher were selected.

[0126] c) Result After selecting the pixels, count the pixels by going to the "Analyze" > "Analyze Particles" tab. Set the pixel size from 0 and the pixel circularity from 0 to 1. The software then gives as a result the percentage of the surface area occupied by the selected pixels relative to the total surface area of ​​the image, which corresponds to the value of the uncoated fiber area fraction.

[0127] For each material, three chips are analyzed, with ten measurements per chip. The percentage of uncoated fiber area per chip is obtained by averaging these ten measurements. The percentage of uncoated fiber area per material is obtained by averaging the ratios obtained by each of the three chips. The results are shown in Table 2 below. [Table 2] Table 2: Uncoated fiber area ratio for materials 1 to 12

[0128] The chips obtained from materials 1-3 (according to the invention) all have an uncoated fiber area percentage of 22% or more (taking into account the standard deviation), which is not observed in the comparative chips of materials 4-12.

[0129] This technical feature defining the chip according to the invention makes it possible to obtain a composite material with high mechanical properties, as will be demonstrated below.

[0130] 2. Abrasion test In order to characterize the roughness of the chips, wear tests were performed to determine the mass loss of the chips.

[0131] The test was carried out using a Taber® Linear Abrasion Tester (5750) equipped with H18 abrasion rubber. The test is carried out according to the procedure detailed below. The sample is fixed on a support and then subjected to the action of H18 abrasive rubber (a characteristically non-elastic material) mounted on a linear abrasion tester. The following parameters are used: - No loads are applied other than to the supports; - Number of wear cycles: 100; -Cycle length: 10cm; - Cycle speed: 25 cycles / min

[0132] The samples are weighed initially, then after 50 cycles, and finally after 100 cycles to determine the total mass loss. For each material, at least three samples were tested and the average of the obtained values ​​was calculated.

[0133] The mass loss provides information about the surface condition of the chip. In fact, the action of the abrasive rubber on a smooth surface results in less mass loss compared to its action on a rough surface containing irregularities. This is explained by the fact that the action of the abrasive rubber eliminates these surface irregularities.

[0134] Thus, the greater the mass loss, the rougher the surface is and therefore the more asperities it contains.

[0135] The results shown in Table 3 are expressed in grams and as a percentage of the initial mass. [Table 3] Table 3: Wear test results

[0136] From Table 3 it can be seen that the chips obtained from materials 1 to 3 have a roughness measured by mass loss that is greater than or equal to 0.008%, taking into account the standard deviation.

[0137] These technical features which define the chip according to the invention make it possible to obtain a composite material with high mechanical properties, as will be demonstrated below.

[0138] Example 3: Mechanical properties of composite parts The Applicant has carried out characterization tests with regard to the mechanical properties of the material obtained from the chip according to the invention.

[0139] The tests whose results are described 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.

[0140] 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 characteristics as the "UD carbon plate" material, which are shown in Table 4 below.

[0141] The chips are cut according to Example 1 from a starting composite material comprising unidirectionally aligned carbon fibres in an epoxy resin type adhesive.

[0142] The obtained chip is rectangular, with a length l of 100 mm, a width b of 9 mm and a thickness comprised between 0.3 mm and 0.5 mm.

[0143] Plates are made from these chips according to the method described below: - Coating the chips: mixing the chips with a liquid adhesive to coat them with the aim of shaping the chips; - forming the chip into a flat panel form; - Pressing the mould; - Removing the part from the mold; and - Hardening of parts.

[0144] The mold is coated with a release agent and topped to create a layer of adhesive on the surface of the mold.

[0145] The adhesive used was the ADEKIT H9011 series, used according to the manufacturer's recommendations.

[0146] The chips are manually placed into the mold.

[0147] The chip to adhesive ratio is 65 / 35 by weight in the finished plate unless otherwise stated.

[0148] The molding is carried out under a press by applying a force of 20 tons and controlling the temperature at about 70°C.

[0149] After removal from the mold, the plates are kept at ambient temperature (20° C.) for one week to allow for complete curing before being used for measurements.

[0150] The plate thus obtained corresponds to a plate of composite material in which the chips, and therefore the fibres, are arranged in a unidirectional array.

[0151] Table 4 below compares the mechanical characteristics of plates UD1 and UD2 with the reference plates (UD carbon plate, wood plate, aluminum plate). [Table 4] Table 4: Mechanical properties

[0152] The term "UD carbon plate" corresponds to a plate made of a new composite material based on unidirectional carbon fibres.

[0153] "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.

[0154] 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.

[0155] The results shown above demonstrate the production of recycled materials with high mechanical performance. 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 affects the mechanical performance obtained, since it results in the percentage of fibers in the material. In particular, the flexural modulus of plate UD2 (containing 65 mass % chips) is almost 50% higher than that of plate UD1 (containing 50 mass % chips). The tensile strength has increased by more than 20%.

[0156] The chips according to the invention therefore make it possible to obtain recycled materials with approximately 70% of the mechanical performance of comparable materials based on new fibres, in particular 70% of the flexural modulus, and (up to 75%-80% of the performance for the same mass), with a lower environmental impact compared to chemical or thermal recycling methods, through a simple manufacturing process.

[0157] 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).

[0158] Example 3: Mechanical properties of composite parts FIG. 1 shows the flexural modulus of a panel made from unidirectionally textured chips according to the invention (obtained from a recycled composite material) and a panel obtained from a new composite material containing unidirectionally oriented carbon fibers.

[0159] Flexural modulus is plotted on the ordinate.

[0160] 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.

[0161] The triangles correspond to measurements carried out on a plate of material comprising chips according to the invention containing unidirectional carbon fibres, the chips being unidirectionally organised, the flexural modulus of this plate being 47 GPa, measured in the direction of extension of the chips and the fibres they contain.

[0162] The circles represent the theoretical flexural modulus calculated for an equivalent plate made from the new composite material based on unidirectional carbon fibres, which has a flexural modulus of 47 GPa in the direction of the fibres contained in the plate.

[0163] Surprisingly, it is clear that the measurements carried out on the composite material containing chips according to the invention are in perfect agreement with the theoretical values ​​obtained for the new material formed from comparable continuous fibers.

[0164] The mechanical properties of components formed with chips according to the invention are therefore predictable, in accordance with the knowledge generally applicable to comparable new composite materials based on continuous carbon fibres.

Claims

1. 1. A composite chip comprising carbon fibers in a cured adhesive, the chip having a substantially constant thickness defined between two parallel, opposite faces of the chip, each face comprising carbon fibers on a surface thereof that are at least partially not contained in the cured adhesive.

2. The chip of claim 1 , wherein the portions of the carbon fibers that are not at least partially contained in the cured adhesive constitute uncoated fibers.

3. 3. The chip of claim 2 having an uncoated fiber area percentage of 22% or greater, said percentage being relative to the total surface area of ​​said face of said chip being analyzed.

4. 2. The tip of claim 1, wherein one surface of the tip has a roughness measured by mass loss that is 0.008% or greater, the mass loss being measured by an abrasion test performed on a linear abrasion tester using H18 abrasive rubber for 100 cycles.

5. The chip according to claim 1, having a thickness comprised between 200 μm and 1 mm.

6. The chip of claim 1 , wherein the carbon fibers extend substantially parallel to the opposing faces of the chip.

7. The chip of claim 1 , wherein the carbon fibers are oriented in the same direction.

8. The chip of claim 1 having a rectangular shape.

9. Each side of the chip is at least 1 cm ２ 10. The chip of claim 1 having a surface area of

10. A method for producing a chip according to any one of claims 1 to 9, comprising the steps of: - providing a composite material comprising substantially parallel oriented carbon fibers in a cured adhesive; - mechanically cutting the composite material using a blade device, said cutting being carried out by placing the carbon fibres parallel to the direction of travel of the blade of the blade device.

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