Method for recycling composite parts having a thermoplastic organic matrix

Abstract

The present document relates to a method for recycling a composite part made of a recoverable thermoplastic organic matrix, in particular an end-of-life or damaged part, comprising: - introducing (2) the part into a shaping tool; - heating (4) the part in the tool; - applying pressure (5) to the part in the tool; - cooling (6) the part in the tool; and - removing (7) the recycled part from the tool.

Description

Description Title: RECYCLING PROCESS FOR COMPOSITE PARTS WITH A THERMOPLASTIC ORGANIC MATRIX Technical field

[0001] This disclosure relates to the field of parts made of thermoplastic organic matrix composite material. Prior art

[0002] In the aeronautics field in particular, a part made of thermoplastic organic composite material undergoes a certain amount of damage. This damage or degradation can be visible, such as impacts or deformations, or occur within the material during aging, decohesion between the matrix and the fibers, intra-matrix cracks or even during delaminations. This damage or degradation within the material leads to a progressive reduction in the mechanical strength of the part. These phenomena are taken into account in order to carry out appropriate dimensioning of the part. For this, fatigue characterizations of the part material are carried out.

[0003] At the end of its life, a thermoplastic organic matrix composite part can be destroyed, which is environmentally unfavorable, or recycled. Recycling such a part consists of grinding the part to reduce it to chips or granules that can be used in the manufacture of a new part. However, in this case, the mechanical properties of the part material after grinding are degraded compared to those of the original material. Thus, grinding a thermoplastic organic matrix composite part with continuous fibers will result in a recycled part with fibers of dispersed lengths between 1 and 50 mm long. Such treatment therefore modifies the stiffness and strength of the recycled part.

[0004] As a result, currently, end-of-life thermoplastic organic matrix composite parts are not reused for the same function during recycling. The same is true for thermoplastic organic matrix composite parts that are prematurely damaged during use. Summary

[0005] The present disclosure proposes an additional recycling process suitable for parts whose thermoplastic matrix has damaged areas (rupture or delamination) while the fibers or the reinforcing fabric is still in good condition. The process of the present disclosure makes it possible in particular to preserve the same function of the recycled part as the original part.

[0006] A method is proposed for recycling a recoverable thermoplastic organic matrix composite part, in particular a part at the end of its life or damaged, comprising: introducing said part into a shaping tool; heating said part in said tooling; applying pressure to said part in said tooling; cooling said part in said tooling, and removing the recycled part from said tooling.

[0007] This process allows the mechanical properties of a thermoplastic organic matrix composite part to be restored. This part may be at the end of its life or visibly damaged, whether by impact, breakage or deformation, or in a non-visibly damaged manner. The defects concerned are such as debonding of the fiber reinforcement with respect to the thermoplastic resin, local plasticization or internal cracking.

[0008] The application of thermocompression, namely heating and applying pressure to the part, helps promote reconsolidation mechanisms within the part to be recycled.

[0009] In the case where the part is a part with an overmolded part, a step of removing said overmolded part may be carried out before introducing said part into said tooling.

[0010] The removal step may be machining or chemical removal, including chemical stripping with a suitable solvent.

[0011] The PEI Short Fibers part of a part, in PAEK continuous fiber composite, overmolded by a PEI short fiber composite can be solubilized by a chlorine solvent which is ineffective for the PAEK composite.

[0012] In the case of an overmolded part, the process may include overmolding the part before cooling the said part.

[0013] The shaping tool for the part to be recycled can be preheated before introducing the said part.

[0014] Alternatively or additionally, said part may be preheated before introduction into said tool.

[0015] When introducing said part into the shaping tool for the part to be recycled, a thermoplastic film or a thermoplastic organic matrix composite reinforcement ply may be added to said part.

[0016] This step ensures sufficient pressure for the material to flow into areas to be restored without changing the geometry of the part.

[0017] The part comprising an amorphous thermoplastic matrix, the heating of the part to be recycled can be carried out at a temperature higher than the glass transition temperature Tg of said amorphous thermoplastic matrix or, the part comprising a crystalline thermoplastic matrix, the heating of the part to be recycled can be carried out at a temperature higher than the melting temperature Tf of said crystalline thermoplastic matrix.

[0018] This temperature softens the thermoplastic matrix of the part to be recycled.

[0019] Cooling of the part to be recycled can be carried out dynamically and in a controlled manner.

[0020] The removal of the part can be a demolding carried out at a temperature consistent with the temperature recommended for the manufacture of the part.

[0021] The demolding of the part after restoration will thus be carried out at a temperature identical or close to that used during the initial manufacture of the part.

[0022] The thermoplastic material of the part to be recycled can be PAEK, PEI, PPS, PESU, PSU, PC or PA. In the case of thermoplastic resins of the PAEK or PEI type, for simple thermocompression, the preform and therefore the tooling will be heated to a temperature between 350 and 400°C. For operation on a stamping type, the preform can be heated in an oven, for example infrared to a temperature between 350 and 400°C and stamped in a tool heated to a temperature between 150 and 250°C.

[0023] For any other material, refer to the material supplier's data sheets to determine the appropriate temperatures for the restoration cycle.

[0024] The end-of-life aircraft part supplied may be previously manufactured by stamping a stack of thermoplastic organic matrix composite plies, by thermocompression of a long-fiber preform, by thermocompression of a molding compound, or by injection of a resin filled or not with short fibers. Brief description of the drawings

[0025] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which: Fig. 1

[0026] [Fig. 1] represents a first diagram of the recycling process according to the present disclosure. Fig. 2

[0027] [Fig. 2] represents a second diagram of the recycling process according to the present disclosure, comprising a step of preheating the shaping tool. Fig. 3

[0028] [Fig. 3] represents a third diagram of the recycling process according to the present disclosure, comprising a step of preheating the part and a step of preheating the shaping tool.

[0029] [Fig. 4] represents a fourth diagram of the recycling process according to the present disclosure, comprising a step of removing overmolding and a step of overmolding the part. Description of the embodiments

[0030] The present disclosure relates to a method for recycling a recoverable thermoplastic organic matrix composite part. This part is an end-of-life or damaged part. For example, a commercial aircraft seat structure part undergoes, during its use, loads and discharges associated with passenger movements, the various flight phases, but also thermal aging and exposure to the external environment with particular hygrometry and temperatures. During this use, the part may be damaged. The damage may be visible, for example impacts, breakage or deformations, or not visible to the naked eye during decohesion of the fiber reinforcement and the thermoplastic organic matrix, local plasticization or internal cracks. The situation is the same for parts such as supports or bridges made of thermoplastic composite.

[0031] To recycle such parts, the steps of a recycling process will notably include, as shown in Figure 1 after recovery 1 of the end-of-life or damaged part: the introduction 2 of said part into a shaping tool; the heating 4 of said part in said tool; the application of pressure 5 to said part in said tool; the cooling 6 of said part in said tool, and the removal 7 of the recycled part from said tool.

[0032] Such a process aims to repair the stresses or deformations suffered by the part during its subsequent use. This process also aims to restore the initial mechanical properties of damaged areas of the part at the end of its life. This process restores the thermoplastic organic matrix. This process applies in the case where the fiber reinforcement is not damaged, in particular when the fibers are not broken and in the case where the arrangement of the fibers is not modified.

[0033] To do this, the part is introduced into a shaping tool. The shaping tool presents the theoretical shape targeted for the final part. This part undergoes a new cycle of heating and pressure application. This is called thermocompression. These two steps related to thermocompression contribute directly to the restoration of the thermomechanical properties of the part. These three steps of introducing the part into the shaping tool, heating and applying pressure to said part are carried out directly on the part to be treated in its geometric shape obtained at the end of its life or after having suffered damage.

[0034] The end-of-life or damaged part is a thermoplastic matrix composite part. In a first example, this is a monolithic part. Such a part can be manufactured by stamping a stack of thermoplastic matrix composite plies, by thermocompression of a preform with long discontinuous fibers, thermocompression of a bulk molding compound, or by injection of a resin filled or not with short fibers. The process does not apply to parts that have suffered significant damage to the fiber reinforcement, such as fiber breakage or a change in their arrangement.

[0035] We will then distinguish the stages of the process according to the type of initial manufacturing of the end-of-life or damaged part.

[0036] Case of a part at the end of its life or damaged initially manufactured by stamping:

[0037] In this case, the end-of-life or damaged part is not obtained by overmolding.

[0038] As illustrated in Figure 1, in such a configuration, the recycling process is as mentioned above, namely that the end-of-life or damaged part is subjected in particular to a heating and pressure application step. The shaping tooling may have the shape of the initial part or be adapted to the shape of the end-of-life or damaged part.

[0039] As shown schematically in the process of Figure 2, the shaping tooling of the part to be recycled can be preheated 8 before introducing said part. The preheating temperature of the mold is chosen to facilitate the introduction of the end-of-life or damaged part into the shaping tooling. This temperature also makes it possible to optimize the restoration / repair cycle. Two particular preheating temperature values ​​are to be considered with interest: the temperature set for the restoration cycle in accordance with the temperature recommended for the manufacture of the part, the ejection temperature of the part at demolding in accordance with the temperature recommended for the manufacture of the part.

[0040] The tooling temperature and the exposure time of the part in the tooling are established so that the thermoplastic organic matrix is ​​brought to the target temperature throughout the part. This step is carried out at a sufficient time to allow the mobility of the polymer chains in the areas to be restored or repaired. This time depends on the thickness of the part to be heated. For example, in the case of thermoplastic resins such as PAEK or PEI, for simple thermocompression, the forming tooling is heated to a temperature between 350 and 400°C. For operation on a stamping type, the tooling is heated to a temperature between 150 and 250°C. For any other material, refer to the material suppliers' data sheets to set the appropriate temperatures for the restoration cycle.

[0041] The forming tooling can be equipped with dynamic thermal control technology. For example, this dynamic thermal control technology can be the technology proposed by the company Surface Generation ltd (UK) based on regulation by pulsed air or technology based on induction.

[0042] The shaping tool may include at least one pressure sensor. This pressure sensor makes it possible to verify that the material is being pressurized. The restoration operation requires, in fact, applying sufficient pressure to the material to promote the material's reconsolidation mechanisms. This minimum pressure must be ensured by the implementation means during the restoration / repair cycle.

[0043] As shown in Figure 2, when introducing said part into the shaping tool of the part to be recycled, a thermoplastic film or a thermoplastic organic matrix composite ply for reinforcement 9 can be added to said part. This thermoplastic film or thermoplastic organic matrix composite ply makes it possible to ensure sufficient pressure for the material to flow in the areas to be restored without changing the geometry of the part.

[0044] Said part can be preheated 10 before introduction into said tool. This tool can, as mentioned above, also be preheated 8. Such a method is schematically represented in Figure 3.

[0045] The preheating temperatures of the tool and the part are chosen to facilitate the introduction of the part into the preheated tool and to optimize the restoration / repair cycle. The part can be preheated to a temperature up to the glass transition temperature Tg - 10°C for amorphous thermoplastic matrices. The part can be preheated to a melting temperature Tf - 10°C for semi-crystalline thermoplastic matrices. This preheating method allows the part to be introduced without plastically deforming it.

[0046] The part comprising an amorphous thermoplastic matrix, the heating of the part to be recycled can be carried out at a temperature higher than the glass transition temperature Tg of said amorphous thermoplastic matrix or for which, the part comprising a crystalline thermoplastic matrix, the heating of the part to be recycled can be carried out at a temperature higher than the melting temperature Tf of said crystalline thermoplastic matrix.

[0047] This specific heat treatment softens the thermoplastic organic matrix.

[0048] Opening the forming tool and the part heating step before applying pressure to said part can be dynamically controlled. This dynamic control makes it possible to control the expansion of the material before applying pressure to said part. Expansion means a recovery in thickness, an increase in the thickness of the treated part compared to the part at the end of its life that has not yet been treated. The expansion of the preform during the part heating step alone allows good reconsolidation when closing the forming tool.

[0049] Pressure application can be achieved by a vacuum tank, a membrane or in an autoclave.

[0050] The thickness of the part can be reduced during the thermocompression operation. This ensures that the part is pressurized.

[0051] Cooling of the part to be recycled can be carried out dynamically and in a controlled manner.

[0052] Case of parts initially manufactured by stamping - overmolding:

[0053] We now consider the case of a part composed of several materials and initially produced by stamping and overmolding. The part may have been produced in one step if stamping and overmolding take place in the same tool, or in two steps if the part is first stamped and then a preform is introduced into an injection tool to carry out the overmolding.

[0054] In this case, the recycling process is the same as before. The only difference in this type of configuration is that it is not possible to preheat the part. It is therefore not possible to use an infrared oven at the risk of melting an overmolded part and losing the shape. The part must be introduced cold into a cold shaping tool, i.e. not preheated.

[0055] As illustrated in Figure 4, the part being a part with an overmolded part, a step of removing said overmolded part 11 can be carried out before introducing said part into said tooling.

[0056] The removal step can be machining or chemical removal. Chemical removal can be carried out using a solvent specific to the thermoplastic matrix used for the overmolded part.

[0057] The process may then include overmolding of the part 12 before cooling said part.

[0058] The overmolded part can be made from new material. Alternatively, the overmolded part can be made from the previously removed overmolded part. In the latter case, it is necessary to grind the overmolded elements to reconstitute granules that can be injected.

[0059] The overmolded part can be produced in the forming tool or in a dedicated tool.

[0060] Case of a hybrid part:

[0061] A hybrid part is a part made from two composite materials that differ in terms of the nature of the fiber reinforcement and / or thermoplastic resin matrix. An example of a hybrid part is a PAEK composite with continuous fibers and a PEI composite with short fibers.

[0062] The short fiber thermoplastic overmolded part can be thermally removed.

[0063] We study the case of an overmolded hybrid part. This overmolded hybrid part comprises a material A comprising continuous fibers with a softening temperature higher than a material B used for overmolding. This scenario allows the material to be melted and evacuated in the overmolded areas without affecting the continuous fibers which are treated according to the aforementioned process.

[0064] For example, a hybrid part will be defined in which the continuous fiber part is made of PAEK, PEEK or PEKK and the overmolded area will be made of PEI material filled with short fibers. The short fiber component of PEI can be melted off by heating the part to a temperature above the glass transition temperature Tg of PEI, i.e. 210 °C, and below the melting temperature Tm of PEEK, 300 °C. Thanks to this process step, only the PEI part will become molten and can thus be removed from the continuous fiber PEEK part.

[0065] The short fiber thermoplastic overmolded part can be chemically removed.

[0066] We study the case of an overmolded hybrid part comprising a material A comprising continuous fibers insensitive to a chemical agent and a material B used for overmolding configured to dissolve with the chemical agent. This chemical removal allows material B to be removed from the part without affecting the continuous fiber material A. Material A is then treated according to the aforementioned method.

Claims

Claims

1. Method for recycling a recoverable thermoplastic organic matrix composite part, in particular a part at the end of its life or damaged, comprising: the introduction (2) of said part into a shaping tool; the heating (4) of said part in said tool; the application of pressure (5) to said part in said tool; the cooling (6) of said part in said tool, and the removal (7) of the recycled part from said tool, and, for which the part being a part with an overmolded part, a step of removing said overmolded part (11) is carried out before the introduction of said part into said tool.

2. A method according to claim 1, wherein the step of removing said overmolded portion (11) is machining or chemical removal.

3. Method according to claim 1 or 2, comprising overmolding the part (12) before cooling said part.

4. Method according to any one of the preceding claims, in which the tool for shaping the part to be recycled is preheated (8) before introduction of said part.

5. A method according to any preceding claim, wherein said part is preheated (10) before introduction into said tooling.

6. Method according to any one of the preceding claims, in which, when introducing said part into the tool for shaping the part to be recycled, a thermoplastic film or a composite ply with a thermoplastic organic matrix for reinforcement (9) is added to said part.

7. Method according to any one of the preceding claims, for which, the part comprising an amorphous thermoplastic matrix, the heating of the part to be recycled is carried out at a temperature above the glass transition temperature Tg of said amorphous thermoplastic matrix or for which, the part comprising a crystalline thermoplastic matrix, the heating of the part to be recycled is carried out at a temperature above the melting temperature Tf of said crystalline thermoplastic matrix.

8. Method according to any one of the preceding claims, in which the cooling (6) of the part to be recycled is carried out dynamically and in a controlled manner.

Images