Method for extracting an element made of composite from a part, recycling method and repair method

Abstract

The disclosure relates to an extraction method for extracting, from a part, an element made of composite comprising electrically conductive reinforcements included in a first matrix, the method comprising the steps of: • - providing the part (E1), the part comprising the element made of composite, the element made of composite being included in a second matrix; • - applying (E3) an atmospheric plasma to the element by sweeping a surface of the part in one or more passes so as to remove the second matrix from around the element; and • - extracting (E4) and recovering the element from the part. The disclosure also relates to a method for recycling a part and to a method for repairing a part which implement such an extraction method.

Description

[0001] Extraction process from a part of a composite material element, recycling process and repair process

[0002] TECHNICAL FIELD OF THE INVENTION

[0003]

[0001] The present invention relates to the field of composite materials. It relates in particular to the field of recycling and repair processes for certain parts made of composite material, in particular made of composite material comprising carbon fibers or other reinforcements.

[0004]

[0002] It is explained below with reference to composite materials comprising carbon fibers, which constitute a preferred application of the invention.

[0005] STATE OF THE ART

[0006]

[0003] Carbon fiber-based composite materials are used in many technical fields for their mechanical properties, particularly their strength and lightness. They are commonly used in the aeronautical, automotive, and nautical industries, as well as in construction, energy, and other sectors.

[0007]

[0004] Carbon fiber-based composite materials generally comprise carbon fibers forming reinforcements. These carbon fibers are embedded in a matrix.

[0008]

[0005] Carbon fibers can be included in the matrix in various configurations, for example in a unidirectional manner, or in the form of woven fiber sheets.

[0009]

[0006] Regarding the matrix, it is generally made of a polymer or essentially comprises a polymer. Adhesives of a similar nature can be used in the same way within the framework of the present invention.

[0010]

[0007] Thus, unless otherwise specified, glues and adhesives used as a matrix in a composite material will also be called "resin".

[0011]

[0008] The present invention can be used with composite materials whose matrix comprises a thermosetting or thermoplastic polymer. Thermosetting polymers undergo a chemical reaction called crosslinking during the shaping of the composite material. This reaction generates chemical bonds and is irreversible.

[0009] It is generally accepted that the most effective thermosetting polymers for forming a carbon fiber-based composite material are polyepoxides (known as "epoxies").

[0010] It is also common to use a polyurethane resin (or PU resin) as the matrix of a composite material. Chemically speaking, a polyurethane (PU) resin is a polymer formed by the polyaddition reaction of a diisocyanate or polyisocyanate with a polyol (a multifunctional alcohol).

[0012]

[0011] Thermoplastic polymers are polymers which, above a certain temperature, called the "phase transition temperature," which is lower than their thermal degradation temperature, become viscous and can thus be shaped. When the temperature drops below this phase transition temperature, the polymer hardens and regains its initial stiffness. This hardening is reversible by reheating the polymer.

[0013]

[0012] The most common thermoplastic polymers are polyethylene (PE), poly(ethylene terephthalate) (PET) or polycaprolactam (PA-6). For certain applications, special thermoplastic polymers may be used, such as poly(phenylene ether-ether-ketone) (PEEK), poly(phenylene sulfide) (PPS), or polyetherimide (PEI).

[0014]

[0013] Since the applications of composite materials are numerous and increasingly widespread, the question of recycling these materials arises.

[0015]

[0014] Recycling may concern end-of-life or damaged composite material elements, manufactured elements that do not meet or no longer meet certain standards required for their intended use (particularly in the aeronautical or space sector), or, more rarely, elements not used by a certain date.

[0016]

[0015] To recycle composite materials reinforced with carbon fibers, three main categories of methods have been developed: so-called mechanical recycling, so-called chemical recycling and so-called thermal recycling.

[0017]

[0016] Mechanical recycling, in principle, consists of grinding existing composite material parts to at least partially separate the fibers from the resin, so as to obtain fibers of varying lengths that can be reused in new resin.

[0017] The ground pieces of composite material are used as fillers or as reinforcement in molded parts, but are not actually intended to replace virgin carbon fibers such as those used in conventional manufacturing processes for composite parts (based on non-recycled materials).

[0018]

[0018] Indeed, such a process greatly reduces the length of the recovered fibers, so that a material using the result of grinding as reinforcement has very low mechanical properties compared to a material using virgin carbon fibers.

[0019] Overall, it is estimated that the mechanical properties (flexural strength or flexural stiffness) of a part obtained by a prior art mechanical recycling process are at least divided by four compared to a similar new part.

[0020] Composite materials made from recycled carbon fibers obtained through mechanical recycling processes are therefore generally limited to certain fields where mechanical properties, relative to mass, do not need to be very high. They are thus mainly used in construction (buildings).

[0019]

[0021] Chemical recycling involves chemically breaking down the hardened resin of a composite material to recover the carbon fibers it contains. These recovered fibers are then typically aligned and / or spun to create a yarn from thousands of individual fibers. The mechanical properties of parts made from composite materials containing these recycled fibers are significantly lower than those of composite materials made from virgin, non-recycled carbon fibers.

[0020]

[0022] Several chemical degradation processes are known, including classical solvolysis, solvolysis "under mild conditions", or solvolysis under supercritical conditions.

[0023] However, the various solvolysis processes have certain drawbacks.

[0021]

[0024] They use significant amounts of solvents which also require further processing, are potentially energy-intensive or have low yields, or are complex and expensive.

[0022]

[0025] Finally, thermal recycling essentially involves thermally degrading the resin of a composite material to recover the carbon fibers. The heat can be supplied by a pyrolysis process, which essentially involves burning the resin in a furnace, by a fluidized bed process that uses the combined action of a solvent and high temperature, or by microwaves.

[0023]

[0026] Although these processes are being optimized, the recovered fibers have significantly degraded mechanical properties compared to new fibers.

[0024]

[0027] In this context, the Applicant proposes in document FR3130819, in order to recycle parts made of composite material, to cut them into thin chips having a particular organization of fibers in each chip, and then to include these chips in a new matrix to form a new part made of composite material.

[0025]

[0028] Parts formed from recycled composite material in this way can have much better mechanical characteristics than parts obtained by previously known recycling processes.

[0026]

[0029] In addition, a part made of composite material can be formed as described in FR3130819, or, more generally, some parts may include elements themselves made of composite material.

[0030] There is a need to be able to recycle the parts thus formed, for example by recovering the various elements (chips or other components) to create new parts. Furthermore, in the event of localized damage to a composite part containing several elements (chips or other components), it would be advantageous to be able to recover the damaged element(s) in order to repair the part by replacing the damaged element(s) with new one(s).

[0027] STATEMENT OF THE INVENTION

[0028]

[0031] The present invention aims to remedy all or part of the drawbacks of the prior art mentioned above.

[0029]

[0032] To this end, the invention aims at a method of extracting from a part an element made of composite material comprising electrically conductive reinforcements included in a first matrix.

[0030]

[0033] This process includes the steps of: supplying the part, the part comprising said composite material element, said composite material element being included in a second matrix; applying an atmospheric plasma to said element by scanning a surface of the part, in one or more passes, so as to eliminate said second matrix around said element; and extracting and recovering the element from said part.

[0031]

[0034] Atmospheric plasma is defined as plasma that is created and used under atmospheric pressure conditions, as opposed to low-pressure plasma, which requires equipment capable of creating a low pressure in which the plasma is generated.

[0032]

[0035] Atmospheric plasma is also called "cold plasma" because it is implemented at lower temperatures than those required for other processes, making it possible to process heat-sensitive materials and reduce energy consumption.

[0033]

[0036] In general, plasma consists of a collection of charged particles, including free electrons and ions, and can be formed by adding energy to a gas (for example, air), which leads to the ionization of the gas's molecules or atoms. Atmospheric plasma can therefore be defined as a cloud of ionized gas generated and maintained under atmospheric pressure conditions.

[0034]

[0037] It is known in the prior art to use atmospheric plasma treatment to treat the surface of a composite material part, for example, to enable the bonding of two parts together. It is also known to use plasma to modify the surface characteristics of polymer materials (in particular) to improve the adhesion of paints or adhesives.

[0038] In particular, US9352355 proposes a method for smoothing and treating the surface of a substrate by simultaneously projecting CO2 particles and a source of ionizing heating radiation, such as a plasma, onto the treated surface. The treatment proposed in this document aims to replace chemical surface treatments of polymers designed to enhance their adhesion properties.

[0035]

[0039] Similarly, document US2021370615 relates to the preparation of a composite material surface which includes removing part of the matrix surface by plasma ablation, so as to reveal and activate a surface having exposed fibers on it, without creating a heat-affected zone.

[0036]

[0040] Nevertheless, the Plaintiff discovered that atmospheric plasma could be used to separate an element embedded in a part made of composite material.

[0037]

[0041] Indeed, without necessarily limiting the explanation of the present invention to this theory, the success of the process that is the subject of the present invention can be explained as follows. Carbon fiber, or certain other reinforcements, have a protective effect on the surrounding resin, which can be linked to the electrical conductivity of the reinforcement, which is related to its thermal conductivity (according to the Wiedemann-Franz law). This theory is confirmed by tests presented below, carried out on materials with insulating reinforcements.

[0038]

[0042] A conductive material is defined as a material that typically has a resistivity less than approximately 10⁻¹⁰. 4Qm. This resistivity value corresponds, corollarily, to Mott's minimum metallic conductivity for semiconductors, a concept that establishes the conductivity value below which a material can be considered an insulator, and above which it is considered to behave like a metal. The conductive materials considered in the invention therefore include common metals as well as other materials such as carbon fiber.

[0039]

[0043] Thus, by applying an atmospheric plasma to the element that one wishes to extract from the part, the matrix of the part which includes the element can be efficiently eliminated, while the element retains its cohesion because the matrix of the element is at least partially preserved.

[0040]

[0044] The process thus allows for the minimally or non-destructive extraction of a component from a composite material part. The process removes the resin surrounding the component while keeping the fibers in place, preserving their order and potentially minimizing damage to the fibers themselves through the use of a lower temperature process (than known thermal processes), and allows for the recovery of the component.

[0041]

[0045] The component can then be recovered for reuse in a new part. If the component is removed for replacement, for example because it is damaged, it is recovered and can be processed through another composite materials waste recycling stream.

[0042]

[0046] The proposed process thus offers advantages compared, for example, to known fiber recovery processes based on pyrolysis, which consume a great deal of energy and damage the fibers. Furthermore, after pyrolysis, the final product consists of dry fibers, which are difficult to process and end up disordered, whereas the proposed process preserves the fibers and their arrangement.

[0043]

[0047] This allows the removal of elements containing reinforcements embedded in a resin, for various purposes.

[0044]

[0048] The elements extracted using the process can be reused to manufacture new products.

[0045]

[0049] The proposed process is environmentally friendly, in particular because the energy consumed by the cold atmospheric plasma is low due to the fact that only the electrons of the plasma are heated, and not the transport gas.

[0046]

[0050] The atmospheric plasma used can be a dielectric barrier discharge plasma, an atmospheric pressure plasma jet, a corona discharge generated plasma, a plasma needle generated plasma, or a plasma pencil generated plasma.

[0047]

[0051] These solutions are particularly well-suited to applying plasma to the surface of a part from which an element is to be extracted. However, any solution that allows the formation of a cold plasma is theoretically usable within the scope of the present invention.

[0048]

[0052] The extraction step can be carried out using a robotic gripper.

[0049]

[0053] The gripping robot may include a means of gripping by suction, for example by suction cup, or by adhesion to the element made of composite material.

[0050]

[0054] Robot extraction enables automatic, rapid, and precise retrieval of the component. When extraction is repeated on several, or even all, components of the part, automated extraction allows for rapid, industrial-scale retrieval. The process can therefore be used for large-scale recycling of parts containing (or composed of) elements with reinforcements embedded in a matrix.

[0051]

[0055] Obviously, the extraction of the element from the part for the purpose of its recovery can alternatively be carried out using a manual tool, such as pliers or a suction cup.

[0056] The recovered element may be a chip having a substantially constant thickness defined between two parallel opposite faces of the chip, the chip comprising carbon fibers at least partly included in an adhesive hardened during a first hardening prior to the formation of said part, said hardened adhesive constituting the first matrix, at least a majority of said fibers of the chip extending substantially parallel to said opposite faces of the chip.

[0057] It is possible, in particular, to recycle the pieces obtained according to document FR3130819 by recovering the shavings they contain in order to form new pieces, if necessary. The "substantially parallel" nature of two elements can be understood to within 10° of an angle. If the fiber in question is included in a fabric (typically taffeta, twill, or satin), the direction of fiber extension is considered by neglecting any undulations in the fiber caused by weaving.

[0052]

[0058] The second matrix can be a thermosetting or thermoplastic resin that has been hardened to form the part.

[0053]

[0059] The first matrix and / or the second matrix can be an epoxy resin.

[0054]

[0060] The first matrix and / or the second matrix can be a polyurethane resin.

[0055]

[0061] The first matrix and / or the second matrix can be a thermoplastic resin.

[0056]

[0062] The Applicant successfully removed elements included in matrices of this nature.

[0057]

[0063] As an example, the power generated by the plasma can be between 200 W and 900 W, preferably between 570 W and 770 W.

[0058]

[0064] As another example, the plasma application distance is between 3 mm and 20 mm, preferably between 5 mm and 7 mm.

[0059]

[0065] As another example, the scanning (during the plasma application stage) can be carried out at a speed between 4 mm / s and 50 mm / s, preferably between 5 mm / s and 7 mm / s.

[0066] The number of passes can, for example, be between 1 and 20.

[0060]

[0067] In such a process, these parameters (power generated by the plasma, distance, scanning speed, and number of passes) depend on each other to achieve the desired result, namely the removal of the element without damaging it or its environment.

[0061]

[0068] Thus, the process may also include a step of selecting the plasma application parameters before the application step, during which the power generated by the plasma, the plasma application distance, the scanning speed and the number of passes are determined.

[0062]

[0069] The power generated by the plasma, the plasma application distance, the scanning speed and the number of passes can be determined as a function of a total power per unit area applied during the process, according to these parameters (because it depends on these parameters).

[0063]

[0070] The application parameter selection step may use a machine learning technique.

[0064]

[0071] The invention also relates to a recycling process for a part comprising elements made of composite material having reinforcements included in a first matrix, said elements being included in a second matrix, the recycling process comprising, for all or part of the composite material elements of the part, an extraction of the part according to an extraction process as described above, followed by a step of reusing said element as reinforcement extracted in a new matrix in order to carry out the molding of a new part made of composite material.

[0065]

[0072] This makes it possible to reuse the same elements, potentially many times, to create several composite parts over time. Since the elements are recovered without significant alteration to the properties of the reinforcing fibers, the properties of the parts obtained after recycling remain perfectly predictable.

[0066]

[0073] A method for repairing a part comprising at least one element of composite material having reinforcements included in a first matrix, at least one element being included in a second matrix, at least one element being deteriorated or having to be preventively replaced, the repair method comprising an extraction of at least one element from the part by an extraction method as described above, and the placement of at least one new element in place of the at least one extracted element and the inclusion of said at least one new element in a new matrix.

[0067]

[0074] The proposed process thus enables the repair of certain composite parts, particularly parts formed as described in document FR3130819, and more generally any part formed from elements embedded in a matrix. The quality of the parts after repair remains unchanged, provided that the element(s) are replaced identically, without damaging their surroundings.

[0068] BRIEF DESCRIPTION OF THE FIGURES

[0069]

[0075] Other advantages, purposes and particular features of the present invention will become apparent from the following non-limiting description of at least one particular embodiment of the devices and methods of the present invention, with reference to the accompanying drawings, in which: Figure 1 is a flowchart of an extraction process according to one embodiment of the present invention; Figure 2 is a flowchart of a recycling process according to one embodiment of a second aspect of the present invention; Figure 3 is a flowchart of a repair process for a part comprising an element of composite material, according to one embodiment of a third aspect of the present invention.

[0070] DETAILED DESCRIPTION OF THE INVENTION

[0076] The present description is given as a non-limiting example of implementation.

[0071]

[0077] Figure 1 represents on a flowchart an extraction process according to an embodiment of the present invention.

[0072]

[0078] The process begins with a first step of supplying a part E1 from which an element is to be extracted. This part is made of composite material, which includes elements embedded in a matrix, referred to as the "second matrix". The embedded elements include reinforcements or other elements (for example, sub-components of the part).

[0073]

[0079] The elements include reinforcements, for example carbon fibers, embedded in a matrix, which is called the primary matrix. Other types of reinforcements may be included, notably metallic fibers or meshes, for example copper.

[0074]

[0080] The first matrix can be an epoxy matrix. The second matrix can be an epoxy or polyurethane matrix.

[0075]

[0081] Examples of such parts are described, for example, in document FR3130819.

[0082] The part is positioned and secured on a work surface. Ideally, this work surface can be located within an enclosed space. A fume extraction system can be installed to remove the fumes emitted within the space, for possible treatment and disposal.

[0076]

[0083] In an application step E3, the surface of the part, at the level of the element to be extracted, is scanned with an atmospheric plasma.

[0077]

[0084] Atmospheric plasma, or cold plasma, is generated by a dedicated machine, for example a commercially available machine.

[0078]

[0085] Various methods of generating cold plasma can be implemented by the machine used. Plasma can be generated by thermal, electrical, or light energy. Generally, the discharge required to produce atmospheric plasma is electrically induced. Methods used to produce plasma include dielectric barrier discharge (also known as dielectric barrier controlled discharge, DBD, or silent discharge), atmospheric pressure plasma jet, plasma jet method, corona discharge, plasma needle, and plasma pencil.

[0079]

[0086] The nozzle through which the plasma exits is mounted on an automated means, for example a robotic arm, allowing the desired surface of the part to be scanned very precisely, at a precise and constant speed, and maintaining the nozzle at a constant distance from the surface of the part.

[0080]

[0087] The plasma is applied in one or more passes, with a power level, distance from the workpiece, and scanning speed determined according to the application. Examples of plasma application parameters enabling the local removal of the second matrix to extract the desired element are given in the "Examples" section below. Therefore, an application parameter selection step E2 may precede the application step E3, particularly if the plasma application parameters need to be adapted to the workpiece from which an element is to be extracted.

[0081]

[0088] The step of selecting plasma application parameters can be optimized using advanced machine learning techniques and other artificial intelligence (AI) methodologies.

[0082]

[0089] Machine learning allows a computer system to learn and improve from data without being explicitly programmed for each specific situation. In the context of the present invention, a machine learning algorithm can be trained on a dataset including different combinations of plasma-generated power, application distances, scanning speeds and number of passes, as well as their corresponding extraction efficiency, depending on the constitution of the part considered (in particular the nature of the second matrix as well as the constitution of the included elements, in particular the nature and arrangement of the reinforcements in these elements and the nature of the first matrix).

[0083]

[0090] In this case, the algorithm identifies complex patterns and uncovers causal relationships that may not be obvious to human analysis. Once sufficiently trained, the system can predict the optimal parameters based on the desired total power per unit area for the specific composite materials of the part on which the process is applied.

[0084]

[0091] In addition to machine learning, other artificial intelligence (AI) techniques such as deep neural networks can be used to model the extraction process. Deep neural networks consist of multiple layers of neurons that process information in a hierarchical manner, simulating to some extent the functioning of the human brain. This structure is particularly effective for predicting parameters in complex process situations.

[0085]

[0092] The integration of these AI techniques enables automatic and dynamic selection of plasma application parameters, significantly improving the accuracy, efficiency, and reproducibility of the extraction process for various composite materials. This allows the extraction process to be self-adaptive and self-optimizing.

[0086]

[0093] Once the application step is complete, the element to be extracted is sufficiently detached from the second matrix to be extracted. An extraction step E4 is then performed on the element. The extracted element can thus be retrieved.

[0087]

[0094] Extraction is preferably carried out automatically. A particularly suitable method for this extraction is a robot equipped with a suction cup, which can be an active suction cup, meaning it is connected to a mechanism that generates a vacuum within the cup. The suction cup is placed in contact with the surface of the element to be extracted, and the vacuum is generated within the cup, creating an adhesive force between the cup and the element.

[0088]

[0095] This method allows the element to be extracted without risk of damage. It does not require lifting an edge of the element to be extracted by levering it in order to grasp it.

[0089]

[0096] We have mentioned above the extraction of an element, but it is quite clear that several elements present on the surface of the part, for example side by side, can be extracted after a single application step, if the surface of these elements has been swept during the application step, with appropriate parameters and number of passes.

[0090]

[0097] Figure 2 represents a recycling process according to an embodiment of this second aspect of the invention.

[0091]

[0098] The recycling process in this embodiment includes the extraction, according to the process described with reference to Figure 1, of at least one element of the part that is recycled, and possibly of all the elements included in that part.

[0092]

[0099] Thus, after the extraction step E4, a new plasma application step E3 can be carried out to extract one (or more) other element.

[0093]

[0100] A molding step E5 of the extracted elements is then carried out. This step can directly follow the extraction step E4, or be carried out well after this step, and / or at another site.

[0094]

[0101] The elements used to form the new part may all be derived from an extraction process according to the invention. Alternatively, they may be partly derived from such a process and partly be new elements or elements formed by mechanical cutting of a composite part to be recycled.

[0095]

[0102] During molding, the elements are included in a new matrix (typically a new resin) and are thus used as reinforcement for a new part made of composite material.

[0096]

[0103] To achieve this, the elements can be coated with a resin before being placed in a mold. Resin can also be introduced directly into the mold.

[0097]

[0104] The molding is advantageously carried out under pressure.

[0098]

[0105] A new part is then obtained, in which the recycled elements constitute all or part of the reinforcements of the new part.

[0099]

[0106] Figure 3 represents an example of a repair method according to a third aspect of the invention.

[0100]

[0107] The repair process involves supplying a part E1. As in the extraction process described above, this part is made of composite material, comprising elements embedded in a matrix (second matrix), and these embedded elements form reinforcements or other components (e.g., sub-components) of the part. These components themselves include conductive reinforcements embedded in a first matrix.

[0101]

[0108] The part to be repaired has one or more damaged components. For the remainder of this description, we assume that only one component is damaged.

[0102]

[0109] The repair process involves the extraction of the damaged element, here according to an extraction process as described with reference to Figure 1.

[0103]

[0110] Once the damaged element has been extracted from the part to be repaired, the process involves supplying a new element E6, the new element corresponding (in terms of shape, dimension, etc.) obviously to the element to be replaced.

[0104]

[0111] A step is then performed to install the new element E7. In this step, the new element is positioned in place of the damaged element that has been extracted and is immobilized in a die that complements the part's die.

[0105]

[0112] After hardening of the matrix around the replaced element, a repaired composite material part is obtained, whose properties are identical or very close to those of the original part.

[0106] EXPERIMENTAL RESULTS

[0107]

[0113] The tests presented below were carried out with a commercially available industrial machine capable of generating an atmospheric plasma jet in the air.

[0108]

[0114] In this case, the tests were carried out with a machine marketed under the Plasmatreat brand, model FG5001S. The nozzle used has the reference PTF 2639-1 12831. It is a stainless steel nozzle with a length of 40 mm and a circular opening of 4 mm in diameter.

[0109]

[0115] To move the nozzle from which a plasma jet is emitted towards the parts on which the tests were conducted, a mobile support was used, namely a 3D printer support from Shenzhen Creality 3D Technology. The relative movement between the nozzle and the part is achieved at constant speed and distance: this is referred to as a plasma scan of the part.

[0110]

[0116] Although such a testing method was used to put the nozzle and the workpiece into relative motion, it is quite clear that any other device, for example a robotic arm, could be used alternatively.

[0111]

[0117] The tests were carried out on composite material plates containing chips as reinforcements included in a matrix.

[0112]

[0118] In particular, each chip is an element with a substantially constant thickness defined between two parallel opposite faces of the chip. Each chip contains carbon fibers embedded or bonded in a primary matrix, namely a resin hardened during an initial curing process to form the recycled part.

[0113]

[0119] The chips were obtained by mechanically cutting a piece of recyclable composite material containing carbon fibers arranged in a bidirectional weave. The chips were cut so that the fibers of the chip extended substantially parallel to opposite faces of the chip.

[0114]

[0120] To form the plate, the shavings were included as reinforcements in a resin which was hardened during a second curing.

[0115]

[0121] The detailed tests below are primarily aimed at demonstrating the feasibility of extracting an element containing electrically conductive reinforcements from a matrix of a composite material part in which its elements constitute reinforcements, using cold plasma.

[0116]

[0122] These tests also illustrate the importance of certain parameters identified by the Applicant in the success of such an extraction.

[0117]

[0123] The tests whose results are described below in Tables 1 to 5 were carried out with a part including in an epoxy matrix (second matrix) chips containing carbon fibers included in an epoxy resin (first matrix).

[0118]

[0124] Table 1 below presents the preliminary results obtained under the aforementioned conditions.

[0119]

[0125] The power generated by the plasma is proportional to the machine's airflow rate. It is the airflow rate parameter that is adjusted on the machine to vary the power generated.

[0120]

[0126] The distance corresponds to the distance between the nozzle from which the plasma jet emerges and the surface of the part exposed to the plasma.

[0121]

[0127] The speed corresponds to the scanning speed, that is, the relative speed between the nozzle and the surface of the part.

[0122]

[0128] The results obtained confirm the ability to remove the matrix from the part using an atmospheric plasma application. These tests also demonstrate the influence of the selected parameters, particularly the power generated by the plasma, on the result in terms of matrix removal from the part.

[0129] Table 2 below presents the results of tests aimed at showing the influence of the scanning speed on the removal of the part's matrix. part matrix. With the power and distance parameters adopted for this test, a satisfactory result is obtained at a scanning speed of 5 mm / s. However, significant removal of the resin constituting the second matrix is ​​obtained at much higher speeds, on the order of 40 mm / s to 50 mm / s. It is therefore conceivable to carry out the process of the present invention with a scanning speed compatible with high efficiency (i.e., a high element extraction speed), by modifying the other parameters, i.e., by increasing the power or decreasing the distance. See, for example, Table 5 below.

[0123]

[0131] Table 3 below presents the results of tests aimed at showing the influence of the number of passes (i.e., of the passage of the plasma over the surface of the part along the same trajectory) on the result obtained.

[0124] 132] With the parameters proposed above, the removal of the workpiece elements (chips) is successfully achieved by performing five plasma passes on the chip surface. With too few passes, the workpiece matrix is ​​not satisfactorily removed. With too many passes, the chip matrix is ​​damaged, and chip cohesion is no longer guaranteed.

[0125]

[0133] Table 4 below presents the results of tests aimed at showing the influence of the distance between the nozzle from which the plasma exits and the workpiece.

[0126]

[0134] With the parameters proposed above, detachment of the workpiece elements (chips) is achieved in 5 passes (and potentially fewer, as shrinkage is observed after 5 passes) by moving the plasma nozzle 5 mm to 7 mm away from the workpiece surface. However, resin shrinkage is greater when the nozzle is closer to the workpiece. At 10 mm, chip detachment from the workpiece is no longer achieved in 5 passes.

[0127]

[0135] After demonstrating the feasibility of extracting a chip or other element with conductive reinforcements, embedded in a matrix to form a part, the

[0128] The Applicant evaluated various sets of parameters. Some results are described in Table 5 below. to enable the extraction of a chip and its recovery using an automated gripping device, in particular a suction cup gripping robot.

[0129]

[0137] The influence of the part's matrix (called "second matrix") was also studied.

[0130]

[0138] Table 6 below describes tests carried out with different resins as the matrix of the part from which the elements are to be extracted.

[0131]

[139] In Table 6 above, “SR Epoxy Resin” refers to the resin marketed by Sicomin Composite under the name SR 8160 resin, used with the same company’s SD 815 B4 hardener. “Resoltech™ Epoxy Resin” refers to the resin marketed by Resoltech under reference 1600, used with the same company’s hardener under reference 1606. “Polyurethane Resin” refers to the resin marketed by Sika under the reference SikaBiresin CR690 (A) used with the same company’s CH690 (B) hardener.

[0132]

[0140] The extraction process is thus applicable to many resins, a priori at least to all epoxy and polyurethane resins. It has been observed that polyurethane resin reacts strongly to plasma, so that the extraction of elements embedded in such a resin is efficient. It is therefore possible to extract a chip or other element with a low loss of matrix for that element (first matrix).

[0133]

[0141] Furthermore, preliminary tests show that the extraction process can be successfully carried out on parts whose matrix is ​​a thermoplastic resin. It should be noted that in this case, the plasma does not merely melt the resin, but that it is destroyed by physicochemical degradation caused by the application of the plasma.

[0134]

[0142] Table 7 below describes tests carried out with chips including glass fibers in an epoxy resin.

[0135]

[0143] Table 7 above thus shows that, under experimental conditions similar to those carried out with parts containing carbon fibers, the process does not allow, with glass fibers, the selective removal of the matrix. More specifically, tests 38 to 40 carried out on individual chips show that the plasma causes deterioration of both the matrix and the fibers, leading, for all sets of parameters tested, to deterioration of the fibers simultaneously with the matrix. The chips tested are three identical chips obtained as described above with regard to chips including carbon fibers, but from a composite material element containing glass fibers. Parts 1 to 3 correspond to plates formed as explained above, but with chips including glass fibers.On these plates, the application of plasma led to the formation of a mass of burnt fibers and resin, leaving no possibility of recovering a chip with the proposed process.

[0136]

[0144] The Applicant has thus developed, within the scope of the present invention, a method for extracting, from a composite material part, an element comprising electrically conductive reinforcements by scanning the part with an atmospheric plasma (cold plasma). This method allows for the recycling of composite material parts themselves derived from the recycling of composite material parts mechanically cut into elements, such as chips, used as reinforcements. This method also allows for the repair of composite material parts including elements themselves made of composite material, by replacing the damaged element(s) with an identical one.

Claims

Demands 1. Method for extracting from a part an element made of composite material having electrically conductive reinforcements included in a first matrix, comprising the steps of: supplying the part (E1), the part having said composite material element, said composite material element being included in a second matrix; applying (E3) on said element, by scanning a surface of the part, an atmospheric plasma, in one or more passes, so as to eliminate said second matrix around said element, and extraction (E4) and recovery of the element from said part.

2. A method for extracting a composite material element according to claim 1, wherein the atmospheric plasma used is a dielectric barrier discharge plasma, an atmospheric pressure plasma jet, a corona discharge generated plasma, a plasma needle generated plasma, or a plasma pencil generated plasma.

3. Extraction method according to claim 1 or claim 2, wherein the extraction step (E4) is carried out using a gripper robot.

4. Extraction method according to claim 3, wherein the gripping robot includes a means of gripping by suction, for example by suction cup, or by adhesion to the composite material element.

5. Extraction method according to any one of the preceding claims, wherein the element is a chip having a substantially constant thickness defined between two parallel opposite faces of the chip, the chip comprising carbon fibers at least partly included in an adhesive hardened during a first hardening prior to the formation of said part, said hardened adhesive constituting the first matrix, at least a majority of said fibers of the chip extending substantially parallel to said opposite faces of the chip.

6. Method for extracting a composite material element according to claim 5, wherein the second matrix is ​​a thermosetting or thermoplastic resin having been hardened to constitute the part.

7. Method for extracting a composite material element according to any one of the preceding claims, wherein the first matrix and / or the second matrix is ​​an epoxy resin.

8. Method for extracting a composite material element according to any one of claims 1 to 6, wherein the first matrix and / or the second matrix is ​​a polyurethane resin.

9. Method for extracting a composite material element according to any one of claims 1 to 6, wherein the first matrix and / or the second matrix is ​​a thermoplastic.

10. A method for extracting a composite material element according to any one of the preceding claims, comprising application parameters such as: the power generated by the plasma is between 200 W and 900 W, preferably between 570 W and 770 W; the plasma application distance is between 3 mm and 20 mm, preferably between 5 mm and 7 mm; the scanning is carried out at a speed between 4 mm / s and 50 mm / s, preferably between 5 mm / s and 7 mm / s; and the number of passes is between 1 and 20.

11. Method for extracting a composite material element according to claim 9, further comprising a step of selecting the application parameters (E2) of the plasma before the application step (E3), during which the power generated by the plasma, the plasma application distance, the scanning speed and the number of passes are determined.

12. A method for extracting a composite material element according to claim 10, wherein the power generated by the plasma, the plasma application distance, the scanning speed and the number of passes are determined as a function of a total power per unit area applied during the process according to these parameters.

13. Method for extracting a composite material element according to claim 10 or claim 11, wherein the step of selecting the application parameters uses a machine learning technique.

14. A recycling process for a part comprising elements of composite material including reinforcements included in a first matrix, said elements being included in a second matrix, the recycling process comprising, for all or part of the composite material elements of the part, an extraction of the part according to an extraction process according to one of the preceding claims, followed by a step of reusing said recovered element as an extracted reinforcement in a new matrix in order to carry out the molding (E5) of a new part of composite material.

15. A method for repairing a part comprising at least one element of composite material having reinforcements included in a first matrix, at least one element being included in a second matrix, at least one element being damaged or having to be preventively replaced, the repair method comprising an extraction (E4) of at least one element of the part by an extraction method according to any one of claims 1 to 12, and the placement of at least one new element (E7) in place of the at least one extracted element and the inclusion of said at least one new element in a new matrix.

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