Use of a first matrix material for stabilizing the orientation of fibers during and after a recycling process

Abstract

The invention relates to the use of a first matrix material for stabilizing the mutual orientation of fibers for fiber composite materials, during and after a recycling process for fiber composite materials, the fiber composite material comprising a plurality of fibers that have been stabilized with respect to their mutual orientation by means of the first matrix material and a second matrix material.

Description

[0001] Use of a first matrix material to stabilize the orientation of fibers during and after a recycling process

[0002] The present invention relates to the use of a first matrix material for stabilizing the orientation of fibers for fiber composite materials relative to one another, during and after a recycling process for fiber composite materials, wherein the fiber composite material comprises a plurality of fibers stabilized in their orientation relative to one another by means of the first matrix material and a second matrix material. The present invention also relates to a method for recycling fiber composite components comprising the steps: a) providing a fiber composite, b) disintegrating the second matrix in the fiber composite without disintegrating the first matrix, and c) removing the fibers stabilized relative to one another by means of the first matrix.

[0003] The recycling of common composites (fiber-reinforced plastics), such as glass- or carbon-fiber-reinforced plastics, has not yet been satisfactorily resolved. Although various processes have been developed, which typically involve shortening the fiber lengths or a loss of fiber orientation, these cannot even remotely restore the original fiber composite properties, even with the greatest downstream processing effort. Furthermore, when using thermoset matrices, decomposition or destruction of the matrix is ​​typically required for the reuse of the (degraded) fibers.

[0004] Examples of current processes for disintegrating the matrix include pyrolysis, solvolysis, or incineration of the matrix after a preliminary mechanical comminution process (from sawing to grinding). The remaining fibers are then used as short-fiber reinforcement or filler, for example, in the thermoplastics sector. The production of yarns and technical textiles is technically possible, but very complex.

[0005] What is particularly problematic about the approaches used to date is that when the fiber composite material is disintegrated, not only are the fibers affected, but they also lose their orientation to one another.

[0006] The objective of the present invention was therefore to provide a method by which the fibers of the fiber composite material could be recovered in the best possible condition during a recycling process. In particular, the fibers should be damaged as little as possible by the disintegration process of the fiber composite material, and the orientation of the fibers relative to each other should be preserved as much as possible.

[0007] According to the invention, this object is achieved by the use according to the invention described below and the method according to the invention described below.

[0008] In the first aspect, the object described above is achieved by using a first matrix material for stabilizing the orientation of fibers, in particular for fiber composite materials, relative to one another during and after a recycling process for fiber composite materials, wherein the fiber composite material comprises a plurality of fibers stabilized in their orientation relative to one another by means of the first matrix material and a second matrix material.

[0009] A fiber composite material as defined in this text is a multi-phase or mixed material consisting of two main components: the reinforcing fibers, which in turn may be contacted and / or enclosed by the first matrix material, and a connecting second matrix, which forms the filler or bonding material between the fibers (in contact with the first matrix). Through the mutual interaction of the two components, the overall material acquires superior properties to either of the two components alone. The second matrix thus fulfills two functions: firstly, it fills the gaps between the fibers (including the first matrix), and secondly, it connects the fibers and / or the fibers enclosed by the first matrix through surface adhesion and their internal strength, cohesion.A matrix, as defined in this text, is a spatially extended area within the fiber composite of largely homogeneous material composition. Preferred matrix materials are described below.

[0010] "Stabilizing the orientation of fibers relative to one another" means that several fibers of the matrix material are fixed in their spatial orientation relative to one another. Preferably, the fibers stabilized relative to one another are arranged as bundles of several parallel individual fibers. In particular, the fibers of the individual bundles, and preferably also the respective bundles relative to one another, are stabilized in their orientation.

[0011] For the purposes of the present invention, the first matrix material differs materially from the second matrix material. The person skilled in the art selects the respective matrix materials with regard to the recycling process to be used.

[0012] Accordingly, a use according to the invention is preferred, wherein during the recycling process the second matrix material is disintegrated, preferably dissolved, and the first matrix material is retained.

[0013] The use according to the invention, particularly in the preferred embodiment, makes it possible to recover large portions of the fibers of a fiber composite component in a recycling process with their orientation unchanged. This has the particular advantage that these fiber materials can be used for further applications without a significant change in their properties.

[0014] Preferably, the fibers are interconnected in lamellae by the first matrix material, wherein the lamellae preferably have a thickness of < 5 mm and a width of > 10 mm and / or are arranged with unidirectional or bidirectional fiber orientation relative to one another. Disintegration within the meaning of the present text preferably occurs by dissolution, but any other suitable chemical, physical, or biological variant of disintegrating the lamellae in contact with the first matrix material is also possible within the meaning of the invention. It is crucial that the second matrix material is sufficiently modified for the selected recycling process so that disintegration of the fiber material connected to the first matrix material is possible.

[0015] The skilled person will – taking into account the recycling process to be used – select the first matrix material and the second matrix material such that, preferably after the disintegration process, the first matrix material is in a state (preferably unchanged) such that no significant damage to the fiber material, and preferably also to the first matrix, occurs during the integration process. The same applies to any subsequent purification process.

[0016] The result is that after the end of the fiber composite component's service life, fiber composite material with unchanged orientation, preferably in the form of lamellae, can be recovered and separated from the original component without damage.

[0017] It is preferred for the use according to the invention that the combination of first matrix and fiber material is produced or can be produced in a pultrusion process.

[0018] According to the invention, a use is preferred wherein the mutually stabilized fibers fill > 25 vol.%, preferably > 40 vol.%, more preferably > 55 vol.% and particularly preferably > 65 vol.% of the volume of the fiber composite material.

[0019] Thus, it is possible that high filling proportions of fibers can be provided for the use according to the invention.

[0020] A use according to the invention is preferred, wherein the first matrix material or the second matrix material fills 5-99 vol.%, preferably 50-99 vol.%, more preferably 90-99 vol.%, based on the total volume less the volume of the fiber composite material occupied by the fibers.

[0021] These ratios of matrix materials to fiber materials have proven to be favorable. A preferred use according to the invention is one in which the fibers are completely enclosed by the first matrix material, compared to the second matrix material.

[0022] This preferred embodiment for the use according to the invention ensures that the fiber material is particularly well protected during the recycling process.

[0023] A preferred use according to the invention is one in which the fibers are present as individual fibers, roving or textile semi-finished product such as a woven fabric or a scrim.

[0024] A roving in the sense of this text is a bundle of a large number of individual fibers (more than 100).

[0025] A semi-finished textile product, as defined in this text, means that the fibers are aligned relative to each other not only in one spatial direction, but in at least two spatial directions. This means that longitudinal and transverse connections are present and that these were produced using textile processes such as knitting, weaving, sewing, or warp-knitting.

[0026] A fabric within the meaning of this text is a textile fabric consisting of at least two thread systems (warp and weft threads) which, when viewed on the fabric surface, intersect at an angle of exactly or approximately 90°.

[0027] A scrim, as defined in this text, is a fabric consisting of one or more layers of parallel, stretched threads. The threads are usually fixed at the intersection points. This fixation is typically achieved by sewing.

[0028] In principle, suitable polymers can be used as matrix materials, e.g., thermosets, thermoplastics, elastomers, or vitrimers. A preferred use according to the invention is one in which the base of the first matrix material and / or the second matrix material is selected from the group consisting of vinyl esters, polyesters, epoxides, silicones, polyurethanes, polyolefins, polyetheretherketone, polyetherketoneketone, polyetherimide, polyphenylene sulfide, polyamides, acrylates, rubber, and caoutchouc, and wherein the first matrix material differs from the second matrix material.Preferably, the first matrix is ​​selected from the group of thermosets, in particular vinyl ester resins, polyester resins, epoxy resins, silicone resins and polyurethane resins or selected from the group of thermoplastics, in particular polypropylene, polyethylene, PEEK, PEKK, PEI, PPS, PA and TPU or selected from the group of elastomers, in particular silicones, polyurethanes, caoutchouc and rubber.

[0029] The second matrix (which is to be disintegrated in the recycling process) is preferably selected from the group of thermosets, in particular vinyl ester resins, polyester resins, epoxy resins, silicone resins and polyurethane resins or selected from the group of thermoplastics, in particular polypropylene, polyethylene, PEEK, PEKK, PEI, PPS, PA and TPU or selected from the group of elastomers, in particular silicones, polyurethanes, caoutchouc and rubber. Matrix resins are preferably selected which differ significantly from the first matrix with regard to the disintegration conditions. Particular preference is given to using matrix resins which have been developed for targeted disintegration (e.g. epoxy resins which use recycled amine as a hardener, in particular Aditia-Bila resins (where mild acid and temperature can be used as drivers for the dissolution of the chemical bonds) or acrylates, in particular ELIUM resins from Arkema).

[0030] A preferred use according to the invention is one in which the fibers are selected from the group consisting of carbon fibers; glass fibers; basalt fibers; boron fibers; viscose fibers; polymer fibers, in particular aramid fibers, Dyneema fibers, polypropylene fibers and polyethylene fibers; natural fibers, in particular made of flax, hemp or cotton and metal fibers, in particular made of steel or aluminum.

[0031] These fibers have proven to be particularly suitable for the purposes of the present invention.

[0032] The second aspect of the invention is a method for recycling fiber material components, comprising the steps of: a) providing a fiber composite material as defined above, b) disintegrating the second matrix without disintegrating the first matrix, and c) removing the fibers stabilized to one another by the first matrix. It is preferred that step b) be carried out using chemical, physical, or biological disintegration, in particular by heating and / or using solvents, acids or bases, or microorganisms.

[0033] It goes without saying that a person skilled in the art will design the process according to the invention such that in step b), only the second matrix is ​​disintegrated, without the first matrix being attacked to such an extent that the fiber components of the fiber composite suffer or lose their orientation. Suitable material combinations for the first matrix and the second matrix are readily available to the person skilled in the art, taking into account the disintegration process to be used.

[0034] As already partially indicated above, the advantage of the inventive method and the inventive use is that after the end of use of the fiber composite material or the component formed from it, the individual fiber composites can be removed from the structural component, preferably in the form of lamellae, without damage and separated. The recovered fibers, stabilized in their orientation relative to one another, can be subjected to suitable testing procedures and subsequently reused in equivalent applications as before.

[0035] Fiber composites for the use or method according to the invention can be produced using various manufacturing processes. Infusion processes, fiber patch processes, and 3D printing processes are preferred.

[0036] The fibers to be used according to the invention can form semi-finished products together with the first matrix. These can also be manufactured using different manufacturing processes, with the process selection depending, among other things, on the planned component geometry, the manufacturer's experience, the selected fiber material, and the selected matrix system for the first matrix. For many applications, the production of a semi-finished product to be used according to the invention using pultrusion is particularly preferred. This allows semi-finished products with high fiber volume contents and high fiber stretch to be produced. Alternative preferred manufacturing processes for the preferred semi-finished products to be used according to the invention are vacuum infusion and RTM processes.

[0037] Application examples for the fiber composite materials to be used according to the invention: a) Rotor blade belt: Many of the load-bearing belts of rotor blades are now made from unidirectional pultrudates. These are often deposited in a mold and bonded together using a vacuum infusion process. The production of bi-matrix laminates (fiber composite materials to be used according to the invention) is possible using various processes. In the simplest case, a traditional thermosetting epoxy matrix system is used for pultrusion (together with the fibers) and a recyclable epoxy matrix system is used as the infusion system (e.g., the Recyclamin system from Aditia Bila, the ELIUM system from Arkema, or Vitrimer). However, the combination of thermosetting pultrusion systems with thermoplastic systems (not only, but also infusion systems) is also possible.

[0038] During the recycling process, the matrix resin is dissolved and the pultrudates can be separated from one another. After a cleaning and quality assurance process (and possibly an evaluation process), the pultrudates can be reused. b) Bicycle saddle: Components with a higher complexity in terms of laminate structure and / or geometry must be manufactured with thinner and possibly shorter (fiber) lamellae than rotor blade belts. For example, the so-called fiber patch process can be used. In this process, tape strips (thin lamellae) are deposited in a type of stamping process. The patches can be deposited on a mold and correspondingly complex geometries such as a bicycle saddle can be created. The joining material is applied or activated to the lamella shortly before application. After joining, the joining material should consolidate quickly in order to keep the cycle time in the patch process short.By using a thermosetting matrix system in the consolidated slats and a removable adhesive (either removable thermosetting or thermoplastic systems), the slats can be separated again after the usage phase.

[0039] Component manufactured from pultruded composite lamellae using a chemically resistant epoxy matrix (first matrix material) and recycled amine as the joining material (second matrix material). a) General cleaning of the used component and, if necessary, removal of attachments. b) Place the component in a bath containing a slightly acidic solution. Heat the bath to approx.

[0040] 80 °C and the component remaining in the bath for several hours. The residence time depends on the component's dimensions. Movement of the component in the bath or movement of the solution can influence the residence time. The use of a component carrier may be useful. c) Removal of the "component", separation of the lamellae, and washing and drying of the lamellae d) (if necessary, surface treatment of the lamellae) e) Quality assurance of the lamellae using NDT methods and, if necessary, supplementary and random destructive methods

[0041] Another example:

[0042] Several fiber-containing carbon fibers, semi-finished products with a first matrix (with high chemical / thermal resistance, such as RTM6 (cf. RTM6_RTM62_HexFlow_DataSheet.pdf (hexcel.com)) or alternatively RIM 135 (cf. TDS RIMH 137.pdf (metyx.com)) are bonded to a comparatively easily degraded / soluble second matrix or interface (e.g. with low chemical / thermal resistance, as second matrix B) such as Recyclamine (Epotec® YDL 5540G resin with Epotec® THR 9163 hardener (cf. Briozen YDL 5540G - Briozen THR 9163 | Recyclamine Technology (abg-am.com)) or ELIUM 191 (cf. liquid-thermoplastic-resin- for-tougher-composites.pdf (arkema.com)) and bonded together. The respective process windows are maintained to ensure sufficient crosslinking of the matrix systems.After the component's useful life and any necessary cleaning processes, the semi-finished products can be recovered from the component in a recycling process. For example, if a second matrix based on recycled amine is used, storing the component in a mild acid at 80 °C for 2 hours can achieve sufficient degradation of the second matrix, allowing the semi-finished products to be separated from the first matrix without damage. The storage conditions must be adapted to the specific component and the specific semi-finished products.

Claims

1 . Use of a first matrix material for stabilizing the orientation of fibers for fiber composite materials to one another, during and after a recycling process for fiber composite materials, wherein the fiber composite material comprises a plurality of fibers stabilized in their orientation to one another by means of the first matrix material and a second matrix material.

2. Use according to claim 1, wherein during the recycling process the second matrix material is disintegrated, preferably dissolved, and the first matrix material is retained.

3. Use according to claim 1 or 2, wherein the mutually stabilized fibers fill > 25 vol.%, preferably > 40 vol.%, more preferably > 55 vol.% and particularly preferably > 65 vol.% of the volume of the fiber composite material.

4. Use according to one of the preceding claims, wherein the first matrix material or the second matrix material fills 5-99 vol.%, preferably 50-99 vol.%, more preferably 90-99 vol.%, based on the total volume less the volume of the fiber composite material occupied by the fibers.

5. Use according to one of the preceding claims, wherein the fibers are completely enclosed by the first matrix material relative to the second matrix material.

6. Use according to one of the preceding claims, wherein the fibers are in the form of a roving or a textile semi-finished product such as a woven fabric or a scrim.

7. Use according to one of the preceding claims, wherein the base of the first matrix material and / or the second matrix material is selected from the group consisting of vinyl esters, polyesters, epoxies, silicones, polyurethanes, polypropylene, polyethylene, polyetheretherketone, polyetherketoneketone, polyetherimide, polyphenylene sulfide, polyamides, acrylates, vitrimers, rubber and rubber and wherein the first matrix material differs from the second matrix material.

8. Use according to one of the preceding claims, wherein the fibers are selected from the group consisting of carbon fibers; glass fibers; basalt fibers; boron fibers; viscose fibers; polymer fibers, in particular aramid fibers, Dyneema fibers, polypropylene fibers and polyethylene fibers; natural fibers, in particular made of flax, hemp or cotton and metal fibers, in particular made of steel or aluminum.

9. A method for recycling fiber composite components, comprising the steps of: a) providing a fiber composite as defined in any one of claims 1-9, b) disintegrating the second matrix without disintegrating the first matrix, and c) removing the fibers stabilized to one another by the first matrix.

10. The method according to claim 9, wherein step b) is carried out using chemical, physical or biological disintegration, in particular by heating and / or using microorganisms.

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