Process for the recycling of thermoplastic composite material scraps

Abstract

The invention relates to a process for valorizing cutting and trimming scraps from parts made of composite material reinforced by continuous fibers in a thermoplastic polymer matrix, the process comprising the steps of: i) obtaining a continuous-reinforced composite preform (110, 500) suitable for obtaining a structural part; ii) obtaining the structural part (200, 400) from the continuous-reinforced composite preform; iii) trimming the structural part (200, 400); iv) recovering (310) the scraps (120, 220) produced in steps i) and iii); v) grinding (320) the scraps to obtain a ground material consisting of composite sections; vi) compounding (330) the ground material obtained in step v) to obtain a compound; vii) obtaining a second composite part (410, 600) by shaping the compound obtained in step vi).

Description

Title of the invention: Method for the recycling of offcuts of thermoplastic composite materials Technical field

[0001] The invention belongs to the field of the implementation of composite materials with a thermoplastic polymer matrix. More particularly, the invention belongs to the field of recycling, in particular, but not exclusively, in the context of a circular economy. Prior art

[0002] Thermoplastic polymer matrix composite materials, more particularly continuous fiber composites, have numerous advantages in terms of implementation and mechanical and chemical characteristics, more particularly, but not exclusively, in aeronautical construction.

[0003] The ability to implement these materials by techniques similar to those for implementing metallic materials, in particular, but not exclusively by stamping, leads to material waste during the initial implementation resulting, for example, from the cutting of arrays of blanks and the trimming of the formed parts.

[0004] These scraps can represent up to 50% of the material used in a large-scale process, or even more when the production flow does not allow for optimization of the ranges.

[0005] While the thermoplastic polymer constituting the matrix is ​​generally considered recyclable, the same is not true for the composite, where the offcuts of said composite mix polymer and fibers.

[0006] However, more particularly in the aeronautical field, both the polymer constituting the matrix and the reinforcing fibers are high-performance and high-cost materials.

[0007] Moreover, specifically in the aeronautical field, the material must be certified and for this purpose must meet quality assurance and traceability rules during its development, which further reinforces the value, or more precisely, the loss of value associated with the landfilling of these scraps, made up of a certified aeronautical material.

[0008] Generally speaking, processes aimed at separating the matrix from the fibers in order to target separate recycling channels are not economically or energetically viable to date.

[0009] In addition, the diversity of fiber rates, matrices and part thicknesses makes difficult open loop recycling, Summary of the invention

[0010] The invention aims to improve the rate of use of the material by recovering the offcuts during implementation.

[0011] To this end, the invention relates to a method for manufacturing two composite parts comprising a structural part made of a composite reinforced by continuous fibers, according to a volume ratio of continuous fibers, in a matrix made of a first thermoplastic polymer with a first melting temperature, and a composite part comprising a fibrous reinforcement comprising sections of the continuous fibers according to a volume ratio of short fibers and a thermoplastic matrix with a second melting temperature and comprising the first thermoplastic polymer, characterized in that it comprises steps consisting of:

[0012] i) obtaining a composite preform with continuous reinforcement suitable for obtaining the structural part;

[0013] ii) obtaining the structural part from the continuously reinforced composite preform;

[0014] iii) to outline the structural part;

[0015] wherein steps i) and iii) produce falls, the method further comprising the steps of:

[0016] iv) recovering the scraps produced in steps i) and iii);

[0017] v) grinding the scraps recovered in step iv) to obtain a ground material;

[0018] vi) carrying out a compounding of the ground material obtained in step v) to obtain a compound;

[0019] vii) obtaining the second composite part by shaping the compound obtained in step vi).

[0020] This process makes it possible to make the best use of the material, in particular material with high added value such as thermoplastic matrix composites and high-performance fibers.

[0021] According to a surprising effect, the method makes it possible to produce the part reinforced by short fibers with a rate of short fibers higher than what is possible to obtain with the methods of the prior art and the commercially available compounds.

[0022] The invention is implemented according to the embodiments and variants set out below, which are to be considered individually or in any technically effective combination.

[0023] According to an exemplary implementation, the first polymer is a PPS, the volume rate of continuous fibers is greater than 40% and the volume rate of short fibers is greater than 40%.

[0024] Preferably, a greater length of the composite sections obtained in step v) is between 2 mm and 15 mm, preferably between 4 mm and 8 mm.

[0025] According to one embodiment, step vi) comprises the addition, during compounding, of a second polymer having a second melting temperature and miscible in the first polymer, to the crushed scraps. This addition makes it possible to control both the fiber content in the aggregate and the melting temperature of the aggregate.

[0026] Thus, the melting temperature of the second polymer can be lower, higher or equal to that of the first polymer.

[0027] According to an exemplary embodiment, the first polymer is chosen from PEEK, PEKK and PAEK and in which the second polymer is chosen from PEEK, PEKK, PAEK and LMPAEK, the volume rate of continuous fibers is greater than 50% and the volume rate of short fibers is greater than 40%.

[0028] According to one embodiment, the compound obtained in step vi) is a wound wire and step vii) is carried out by an additive manufacturing process implementing the melting of the wire.

[0029] According to another embodiment, the compound in step vi) is a granule and step vii) is carried out by plastic injection.

[0030] Thus, the process of the invention offers several alternatives for the production of the part reinforced by short fibers.

[0031] According to a particular embodiment, the process comprises, after step vii), a step consisting of:

[0032] viii) link the second composite part to the structural part.

[0033] According to this latter embodiment, steps vii) and viii) are carried out by overmolding the added part onto the structural part.

[0034] According to another variant, step viii) is carried out by welding the added part onto the structural part.

[0035] According to yet another variant, step viii) is carried out by co-consolidation of the added part and the structural part.

[0036] Of course, 2 or more of these variants can be combined when making the same structural part.

[0037] Thus, according to one embodiment, the result of adding a virgin polymer to the ground material before compounding has the effect that the second melting temperature is higher than the first melting temperature. This embodiment is for example suitable for producing an assembly of the second part on the structural part by overmolding or by co-consolidation.

[0038] Alternatively, the result of this addition of virgin polymer is also to obtain a second melting temperature lower than the first melting temperature. This method of implementation is for example suitable for producing the second part in plastic injection molding

[0039] According to an exemplary implementation, the first polymer is a LMPEAK and the second polymer is chosen from PEEK and PEKK.

[0040] According to another embodiment, the first polymer is a PEI and the second polymer is chosen from PEEK, PEKK and LMPAEK.

[0041] These two implementation examples lead to a compound having a melting temperature higher than that of the polymer constituting the matrix of the structural part, these implementation methods being more suitable for overmolding and coconsolidation.

[0042] Alternatively, the reverse combinations produce a compound whose melting temperature is lower than that of the polymer of the structural part matrix. Brief description of the drawings

[0043] The invention is implemented according to the preferred embodiments and examples, which are not limiting, set forth below with reference to Figures 1 to 6 in which: Fig. 1

[0044] [Fig.l] is a top view of an example of blanks cut in a panoply from a consolidated plate reinforced by continuous fibers; Fig.2

[0045] [Fig.2] shows in perspective view simplified examples of clippings made on a structural part obtained by stamping one of the blanks of [Fig.l]; Fig.3

[0046] [Fig.3] is a flowchart summarizing the method of the invention; Fig.4

[0047] [Fig.4] is a perspective and exploded view of an exemplary embodiment of a spar implementing the method of the invention; Fig.5

[0048] [Fig.5] shows in a perspective and exploded view an example of tooling for the production of the spar of [Fig.4]; Fig.6

[0049] [Fig.6] shows in two perspective views from above and below an example of production of a rudder pedal by implementing the method of the invention. Description of the embodiments

[0050] [Fig.l] according to an exemplary embodiment, a composite part with a thermoplastic matrix is ​​obtained from a blank (110), that is to say an essentially flat blank cut out according to an appropriate contour, which blank is stamped between a punch and a die after said blank has been heated to a temperature of the order of the melting temperature of the polymer matrix.

[0051] According to an exemplary embodiment, the blank (110) is for example cut from a consolidated composite plate (100) reinforced by fibers comprising continuous fibers (101), that is to say fibers extending continuously from one edge to another of the consolidated plate (100) and which, after cutting the blank, extend from one edge to another of the blank (110).

[0052] As non-limiting examples, the plate (100) is made of a thermoplastic polymer PEEK (polyetheretherketone), PEKK (polyetherketoneketone), PAEK (polyaryletherketone), PEI (polyetherimide), PPS (polyphenylene sulfide) or any other thermoplastic polymer.

[0053] The fiber reinforcements are carbon, glass or aramid fibers, without these examples being limiting.

[0054] The blank is cut, for example, using a high-pressure abrasive water jet.

[0055] Several blanks, organized in a panoply, are cut from such a plate (100). However, even by optimizing the nesting of the blanks cut from the plate, there remains a waste in the form of a skeleton (120, filled in dotted lines in the figure) which represents a significant part of the mass of the initial plate, typically between 30% and 50% of the volume of the consolidated plate before trimming the panoply,

[0056] [Fig.2] after stamping, the part obtained is trimmed on its edges to eliminate an unconsolidated part inherent in the stamping process and is also trimmed in current section according to various trajectories (211, 212), in particular to create lights there.

[0057] These trimmings are for example carried out by milling and also produce offcuts (220) made of the same material as the structural part (200).

[0058] These offcuts, both the skeletons of the panoply and those resulting from the cutting of the raw stamping part, are discarded and must be treated according to a specific process in a waste disposal center, which results in additional costs.

[0059] To date, there is no recycling system for the offcuts of these composite materials reinforced by continuous fibers.

[0060] At best, these scraps are burned in a process known as energy recovery, which emits greenhouse gases.

[0061] The recycling difficulties are due in particular to the fact of the mixing of the polymer constituting the matrix with fibrous reinforcements and, on the other hand, on the scale of an industrial production installation, to the diversity of the materials treated both from the point of view of the matrices and the reinforcing fibers as well as the thicknesses.

[0062] Given the sorting operations that would be necessary, the difficulty of visually differentiating the nature of the waste and the low value of the waste as such, such recycling operations using conventional channels have too significant an impact on production costs, to the point that, to date, it remains more profitable to pay for special waste treatment than to set up processes allowing external recycling.

[0063] Furthermore, the methods for obtaining composite parts with a thermoplastic matrix and continuous fiber reinforcement are not limited to the stamping of blanks taken from consolidated plates but can implement other methods such as partially consolidated blanks obtained by placing fibers, consolidation in the form of unconsolidated folds, etc. without these examples being either exhaustive or limiting.

[0064] However, whatever the process, the scraps are produced, these scraps being made up of materials having undergone different thermal histories with equivalent compositions, functions of the process implemented for the production of the part reinforced by continuous fibers, thermal histories which result in cohesion and in particular different porosity rates, even if these remain within strict acceptable limits.

[0065] The invention aims at a recycling described as internal in which the scraps are used, after appropriate treatment as explained below, as material for the production of parts with non-continuous reinforcement.

[0066] The method of the invention also has the advantage of being able to combine scraps of the same material but from different implementation processes by erasing the thermal histories associated with these processes and providing a homogeneous material.

[0067] However, surprisingly, the process of the invention takes advantage of the prior implementation of the material by making it possible to achieve reinforcement rates higher than what is possible to obtain using a raw material not derived from the process of the invention.

[0068] In industrial fields where the material must be prequalified, particularly in the aeronautical field, the material resulting from the process of the invention benefits, at least partially, from the qualification of the material from which the scraps are derived, thus facilitating this process.

[0069] In certain embodiments, for the manufacture of parts comprising a structural part (200) reinforced by continuous fibers on which other parts such as supports or cleats are attached, these attached parts, obtained from scraps from the manufacture of the structural part, are particularly suitable for being integrated into said structural part, or into a structural part from the same batch, in an integral manner, without fixing, by methods such as welding, co-consolidation or overmolding, with perfect miscibility of the polymers present.

[0070] Also, the parts obtained from recycled material from scraps are generally parts with high added value, due to their high reinforcement rate and the nature of their polymer matrix, and directing the scraps towards a perfectly identified use in a production unit greatly increases the profitability of the operation.

[0071] [Fig.3], to this end, the invention relates to a method comprising a first step of collecting the offcuts (310).

[0072] According to a particular, non-limiting embodiment, the offcuts are assigned to the same production process as that of the structural part so that they remain, for example, referenced in the ERP in the same general range.

[0073] According to a grinding step (320) the scraps are ground, possibly after having been pre-cut, in particular the skeletons of panoplies, so as to obtain a ground material consisting of sections whose greatest average length is statistically of the order of 6 mm, typically between 2 mm and 15 mm and preferably 4 mm and 8 mm at + / - 3 standard deviations from the average. The ground material comprises both polymer and sections of fibers from the continuous fibers of the structural part.

[0074] The creation of the scraps results from cutting or trimming, consolidated plates for the sets of blanks or semi-finished parts having been the subject of consolidation for example during stamping, consolidation in shape or at least partial consolidation during draping by placing fibers at high speed. In fact, the material included in the scraps has already undergone a thermomechanical cycle of melting of the polymer constituting the matrix, compression and degassing for impregnation and intimate bonding of the reinforcements and the matrix and porosity rates of less than 5% or commonly less than 2%.

[0075] Grinding is preferably carried out by a slow speed knife mill, producing clean cuts of the sections without crushing and without delamination away from the edges of the sections.

[0076] According to a compounding step (330) the ground material is placed in an extruder in order to carry out compounding.

[0077] Compounding is a process known from the prior art consisting of passing the ground material through a screw extruder in order to extrude a substantially cylindrical wire through a die.

[0078] Said yarn is a composite yarn comprising a thermoplastic polymer and short fibers corresponding to the portions of reinforcing fibers initially continuous and included in the structural part then present in the sections of the ground material.

[0079] According to embodiments, the composite yarn thus extruded is wound to be ul previously used, for example, in a wire fusion additive manufacturing process.

[0080] According to another embodiment, the extruded wire is cut into sections, for example of a length of the order of 2 mm, in order to constitute granules suitable for plastic injection, said granules comprising short fibers.

[0081] The achievable fiber content depends on the viscosity of the polymer at the compounding temperature, and on the ability of said polymer to impregnate the fibers so that the extruded yarn is cohesive.

[0082] Without being bound by any theory, it appears that the impregnation of the fibers by the polymer and the cohesion of the composite in them is, at least in part, inherited in the extruded yarn, allowing the latter to retain its cohesion up to volume rates of fibers in the yarn or granule which can reach 60%.

[0083] Such volume rates of short fibers are well beyond those obtained in commercially available granules which are not produced by the process of the invention.

[0084] The fiber content in the extruded yarn can be controlled by adding virgin polymer granules or chips to the ground material prior to compounding, so as to achieve a fiber content lower than that included in the scraps.

[0085] The polymer added before compounding can be the same as that constituting the matrix of the scraps, or be of a different nature, provided that it is miscible with the original polymer, or even a combination of the two.

[0086] The addition of a different polymer, miscible in the first, also makes it possible to adjust the melting point of the wire or granule.

[0087] Thus if (325), after grinding, the fiber rate x of the ground material is equal to the fiber rate X targeted in the granule and if the melting temperature tf of the ground material is equal to the melting temperature Tf targeted for the granule then the compounding is carried out directly from the ground material. Otherwise during an adjustment step (335), a polymer is added to the ground material before the compounding step.

[0088] The polymer added during the adjustment step must be miscible with the first polymer constituting the matrix of the scraps, it can be the same polymer, in this case only the fiber rate of the extruded yarn is modified, or it can be another polymer, in this case, both the fiber rate and the melting temperature of the yarn are modified compared to the composite constituting the structural part.

[0089] Thus, according to an exemplary embodiment if the matrix of the scraps is made up of a low melting temperature PAEK (LMPAEK®) the addition of PEEK or PEKK to the ground material prior to compounding makes it possible to increase the melting temperature of the granule.

[0090] Conversely, if the polymer constituting the matrix of the scraps is a PEEK, the addition of LMPAEK or PEI to the ground material during the compounding operation allows to lower the melting temperature of the granule in comparison with the melting temperature of the polymer constituting the matrix of the scraps.

[0091] The extruded wire or granule is used to produce a part reinforced with short fibers during a manufacturing step (340), by additive manufacturing or by a plastic injection molding process.

[0092] According to an exemplary embodiment, the part produced during this manufacturing step (340) is assembled to a structural part during an integration step (350), preferably by a method without fixing.

[0093] As non-limiting examples of such methods are:

[0094] - overmolding, during which the added part is injected directly onto the structural part, in this case the adjustment step (335) preferably aims to obtain a granule having a melting temperature higher than that of the polymer constituting the matrix of the structural part;

[0095] - the co-consolidation in this case the adjustment step (335) preferably aims to obtain a granule having a melting temperature higher than that of the polymer constituting the matrix of the structural part;

[0096] - The welding, in this case the adjustment step (335) possibly aims to lower the rate of short fibers in the granule without changing the melting temperature.

[0097] According to an exemplary embodiment, the structural part is an aircraft frame and the added part is an accessory support ("bracket") or a cleat linked to this frame.

[0098] Compounding subjects the ground material to severe thermo-mechanical stress bringing the material to a state of melting. This stress eliminates even slight cohesion defects present in the scraps due to the processing methods including trimming, eliminating, for example, porosities and delaminations, although surprisingly the process of the invention takes advantage of the impregnation of the fibers and the homogeneity of the material obtained during previous processing such as consolidation, stamping, etc.

[0099] [Fig.4] according to another example, the structural part is a spar (400) made of a composite with a reduced melting temperature PAEK thermoplastic matrix (LMPAEK®) and comprising a continuous fibrous reinforcement of carbon fibers corresponding to 60% by volume of fibers (66% by mass).

[0100] Said spar comprises a plurality of ribs (410i...4105). According to an exemplary embodiment, said ribs are produced by plastic injection molding with a granule obtained from trimming offcuts of said spar (400), in practice, from one or more similar spars produced and trimmed previously.

[0101] Said scraps are ground and added with a virgin polymer of PEEK type or PEKK, miscible in LMPAEK®, so as to increase the melting temperature of the polymer matrix and to reduce the fiber content in the granule to a rate of between 40% and 55% by mass. The high fiber content achievable by the method of the invention makes it possible to achieve the mechanical characteristics targeted for the ribs.

[0102] [Fig.5] according to an exemplary embodiment, the ribs (410i.. .4105) are placed in a mandrel tool (590), assembled, such that the soles of said ribs to be assembled with wings of the spar are flush with the surface of the mandrel tool.

[0103] A preform (500) of the spar is draped over the mandrel tool (590), for example by automatic placement of fibers or by manual draping of non-woven plies. The plies produced come into contact with the soles of the ribs placed in the mandrel tool (590).

[0104] The assembly is then bagged in a sealed manner, drawn under vacuum and heated to a temperature equal to or greater than the melting temperature of the preform matrix (500).

[0105] This temperature is lower than the melting temperature of the polymer (modified during compounding) constituting the matrix of the ribs, but remains sufficient to activate self-hesion and welding phenomena at the interfaces between said preform (500) and the ribs (410i...4105) without the latter losing their cohesion and deforming excessively.

[0106] The preform (500) thus undergoes a pressure-temperature cycle capable of consolidating the spar and integrating the ribs.

[0107] After demolding, the spar is trimmed to give it its final profile; the offcuts from this trimming are used to make a granule suitable for plastic injection molding of the ribs.

[0108] It should be noted that [Fig.4] and [Fig.5] represent a composite spar demonstrator. Those skilled in the art understand that the length of the wing is nearly 2 orders of magnitude greater than the width of the ribs, and that consequently the volume of scrap collected during the final trimming is sufficient to produce one or more of these ribs.

[0109] [Fig.6] according to another embodiment, scraps of a PPS matrix composite reinforced with continuous carbon fibers with a volume rate of 50% (57% by mass) are ground then formed into granules without adding virgin polymer before compounding.

[0110] These granules are used, for example, to obtain by injection molding a rudder control pedal for an aircraft. This part is traditionally made of aluminum alloy, the shape of this part makes its production in composite with continuous reinforcement difficult or even impossible, and its production by injection plastic from a commercially available granule on the one hand does not allow sufficient reinforcement rates to be achieved and would require qualification of the material. The use of a granule obtained from scrap aeronautical parts makes it possible to resolve these two problems, with an injected part (600) comprising 57% fibers by mass (50% by volume) and made from an already qualified material.

[0111] The above examples show that the invention achieves the intended aim and makes it possible to enhance using a high value-added process for composite manufacturing waste previously treated as ultimate waste.

Claims

Claims

1. Method for manufacturing two composite parts comprising a structural part (200, 400) made of a composite reinforced by continuous fibers, according to a volume ratio of continuous fibers, in a matrix made of a first thermoplastic polymer with a first melting temperature, and a composite part (410, 600) comprising a fibrous reinforcement comprising sections of the continuous fibers according to a volume ratio of short fibers and a thermoplastic matrix with a second melting temperature and comprising the first thermoplastic polymer, characterized in that it comprises steps consisting of: i) obtaining a composite preform (110, 500) with continuous reinforcement suitable for obtaining the structural part; ii) obtaining the structural part (200, 400) from the composite preform with continuous reinforcement; iii) trimming the structural part (200, 400);in which steps i) and iii) produce scraps (120, 220) and which further comprises the steps of: iv) recovering (310) the scraps (120, 220) produced in steps i) and iii); v) grinding (320) the scraps recovered in step iv) to obtain a ground material consisting of composite sections; vi) carrying out a compounding (330) of the ground material obtained in step v) to obtain a compound; vii) obtaining the second composite part (410, 600) by shaping the compound obtained in step vi).;

2. The method of claim 1, wherein the first polymer is a PPS, the volume ratio of continuous fibers is greater than 40% and the volume ratio of short fibers is greater than 40%.

3. Method according to claim 1, in which a greater length of the composite sections obtained in step v) is between 2 mm and 15 mm, preferably between 4 mm and 8 mm.

4. The method of claim 1, wherein step vi) comprises an adjustment step (335) comprising adding, before compounding, a second polymer having a second melting temperature and miscible in the first polymer, to the ground scraps.

5. The method of claim 4, wherein the first polymer is selected from PEEK, PEKK and PAEK and wherein the second polymer is selected from PEEK, PEKK, PAEK and LMPAEK, the volume ratio of continuous fibers is greater than 50% and the volume ratio of short fibers is greater than 40%.

6. Method according to claim 1, in which the compound obtained in step vi) is a wound wire and step vii) is carried out by an additive manufacturing method implementing the melting of the wire.

7. Method according to claim 1, in which the compound obtained in step vi) is a granule and step vii) is carried out by plastic injection.

8. A method according to claim 1, comprising after step vii) a step of: viii) bonding the second composite part to the structural part.

9. Method according to claim 8, in which steps vii) and viii) are carried out by overmolding the second composite part onto the structural part (200).

10. The method of claim 8, wherein step viii) is performed by welding the second composite part to the structural part (200).

11. The method of claim 8, wherein step viii) is performed by co-consolidation of the second composite part and the structural part (400).

12. The method of claim 4, wherein the second melting temperature is higher than the first melting temperature.

13. The method of claim 4, wherein the second melting temperature is lower than the first melting temperature.

14. The method of claim 12, wherein the first polymer is a LMPEAK and the second polymer is selected from PEEK and PEKK.

15. The method of claim 12, wherein the first polymer is a PEI and the second polymer is selected from PEEK, PEKK and LMPAEK.

16. The method of claim 13, wherein the first polymer is selected from PEEK and PEKK and the second polymer is a LMPEAK.

17. A method according to claim 13, wherein the first polymer is selected from PEEK, PEKK and LMPAEK and the second polymer is a PEI.

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