Method for recycling composite material, composite material, uses thereof and component

Abstract

The invention relates to a method for recycling composite material and to a composite material which, from two or more base substances, forms a material which has synergistic properties, in particular a composite material from the group of fiber-reinforced composite plastics which exist for example in the form of continuous fibre composites ("FRPs"), sheet molding compounds ("SMCs") and bulk molding compounds ("BMCs"), wherein the composite material contains at least to some extent recycled base substances, and to uses thereof and to a power electronics component. The possible ways of producing nonwovens that are disclosed here for the first time - with recycled fibers, even from different sources and even in the form of textile offcuts - make it possible to use a fiber supply which is otherwise not sustainably available.

Description

[0001] Description

[0002] Process for recycling composite material, composite material, uses thereof and component

[0003] The invention relates to a method for recycling composite material and to a composite material which forms a material with synergistic properties from two or more basic materials, in particular a composite material from the group of fibre-reinforced composite plastics which are present, for example, in the form of continuous fibre composite "FVK", sheet moulding compound "SMC" and bulk moulding compound "BMC", wherein the composite material contains at least partly recycled basic materials, as well as uses thereof and a power electronic component.

[0004] Sustainability is a major issue worldwide. As environmental awareness grows, so does the demand for renewable composite materials, especially given the high costs of valuable fiber reinforcement.

[0005] The increasing ecological, social and political demands on the sustainability of materials and the products made from them represent a significant challenge for composite materials, such as fiber-reinforced plastics, as by definition a heterogeneous material solution.

[0006] The focus is particularly on the recycling of composite materials and sustainably manufactured products made from them. The reuse of high-quality fiber reinforcement after a product's end of life poses particular challenges for the waste disposal industry, as there is currently no technology on the market that can solve the scalable recycling of expensive fibers from fiber reinforcement.

[0007] Thermosetting composites, in particular, are not yet recyclable because, unlike their thermoplastic counterparts, they cannot be remelted and / or plasticized and are therefore not readily amenable to mechanical recycling. Furthermore, the textile processing of reinforcing fibers is technically challenging. There is a risk of a reduction in the reinforcement potential due to general fiber shortening or a heterogeneous property profile of the resulting composite material due to undefined fiber lengths.

[0008] According to the current state of the art, FRPs, which exist, for example, in the form of thermosetting polymer composite components based on continuous, long, and short fiber reinforcement, are recycled by mechanical comminution, pulverization, and grinding. Typically, they are recycled thermally by incineration. Occasionally, the ground recyclate is incorporated into new composite materials as a filler, resulting in the recycling of a composite material—particularly one containing thermosetting components.

[0009] All composite materials and / or fiber-reinforced composites such as continuous fiber composites (FRP), sheet molding compounds (SMC), and bulk molding compounds (BMC) are generally downcycled because the fibers are shortened during comminution and / or grinding and lose a lot of their performance potential. In standard processes, fiber-reinforced plastics with a thermoset content often only arise as mixed fractions that are difficult and / or inseparable and can only be recycled thermally by incineration. The valuable fiber reinforcement ends up in the slag because it is often not combustible.

[0010] The object of the present invention is therefore to create a process for recycling composite materials from the group of fiber-reinforced composite plastics, in which the downcycling of the fibers is minimized. Furthermore, the invention relates to a composite material comprising recycled fibers.

[0011] This object is achieved by the subject matter of the present invention, as disclosed in the description, the figure and the claims. Accordingly, the subject matter of the present invention is a method for recycling composite material, comprising the following process steps:

[0012] - Separation of reinforcing fiber and resin matrix

[0013] - Production of a mat, a nonwoven or a fibre fabric from recycled fibres by the following process steps: o Standardisation of the recycled fibre, o Mat and / or nonwoven production, o Formation of a 3-dimensional laminate and / or bulk material from the mats and / or nonwovens,

[0014] - Embedding by impregnation with impregnating agent the laminates and / or bulk materials made from mats and / or nonwovens made from at least partly recycled fibres into a resin matrix.

[0015] In particular, it is a process for recycling composite materials, comprising the following process steps:

[0016] - Recycling, i.e. separation of reinforcing fiber and resin matrix

[0017] - Optional mixing of defined and fresh fibers

[0018] - Production of a laminate, a bulk material and / or another fiber fabric from at least partially recycled fibers by the following process steps: o Standardization of the recycled fiber, in particular by cutting and / or tearing process(es) o Optional admixture of defined fibers o Mat or nonwoven production from the recycled fibers, in particular via e.g. airlay and / or carding technology, wet-laid fabric formation and / or, for example, production of cross-woven fabrics, o Optional mat or nonwoven consolidation, in particular via needling and / or stitch-bonding of the cross-woven fabrics - for example produced in the above process step,

[0019] - Production of a laminate and / or bulk material from the mats, nonwovens and / or fiber fabrics, - Embedding by impregnation with impregnating agent of the produced laminate, fiber fabric and / or bulk material made of at least partly recycled fibers in a resin matrix, in particular comprising recycled and / or renewable components.

[0020] Furthermore, the invention relates to a composite material comprising at least two base materials, fiber reinforcement and a polymer matrix, wherein the fiber reinforcement is at least partially in the form of a mat and / or a nonwoven fabric comprising recycled fibers and / or fiber waste. The use of such a composite material and, finally, a component comprising such a composite material are also the subject of the present invention.

[0021] The general finding of the invention is that duromer-embedded fiber reinforcement cannot be recovered for recycling via thermal processes because a fully cured duromer polymer cannot be melted without decomposition, but that electrical, pyrolytic - by combustion - and / or solvolytic - by dissolving the duromer matrix - processes make it possible to separate the fiber reinforcement from the duromer, possibly destroying the duromer but maintaining the usability of the fiber reinforcement.This recovered fiber reinforcement cannot be reused as fiber reinforcement in its unprocessed form and in many cases not without the addition of new, "fresh" fibers. However, through a process of fabric, mat and / or nonwoven production, these fibers can, in principle, be made available again as a basic material for the production of a composite material, with or without surface fiber treatment, for example application of slip and / or admixture of other fibers. In the technology of semi-finished textile products, a nonwoven is a special form of mat. To produce components from composite material as proposed here according to the invention, the dry fibers are first joined together and then impregnated with a liquid impregnating agent, usually a resin or a resin mixture, i.e. they are cast as completely as possible.It is not only important that all fibers are coated with an impregnating agent, but also that the entire 3-dimensional structure, which is either a laminate made from a stack of laminate layers or as a bulk material, is filled with the impregnating agent and cast to create a stable component with as few air pockets as possible. For this purpose, a subsequent printing process step is often introduced, in which the fibers and the impregnating agent are pressed together.

[0022] When processing the fleece and / or mat into an element or component, the dry fiber material is first formed into a laminate or bulk material in the shape of the component or an element suitable for constructing a component. It is advantageous if the areas containing recycled fibers in the form of a fleece at least partially enclose the areas containing fresh fibers in the form of a woven fabric, scrim, or grid.

[0023] In particular, a sandwich structure in which recycled fibers, for example in the form of a nonwoven fabric, are located on the outside is preferred because the liquid impregnating resin can flow through the disordered and shorter, recycled fibers in the nonwoven fabric better than through the close-meshed fabrics and / or scrims made of fresh fibers in the core of the laminate and / or in the core of the bulk material.

[0024] For example, in a component made of a composite material according to the invention, there is a gradual distribution of the recycled fibers, such that fewer recycled fibers are found in the core and the proportion of recycled fibers in the 3-dimensional element and / or in the component from the inside

[0025] - from the core - outwards - towards the exterior and / or surface

[0026] - increases. For example, a laminate or a sandwich structure can be present in the component, with nonwoven fabric with 100% recycled fiber reinforcement on top and / or bottom, whereby the proportion of fiber reinforcement with recycled fibers decreases towards the inside in the core down to 0% and conversely the fiber reinforcement in the core comprises 100% fresh fibers and on the outside, at least in part, only 0% fresh fibers.

[0027] For example, it is envisaged that the recycled fibers will receive a specific surface treatment, which may include cleaning or coating, or both.

[0028] For example, in a 3-dimensional laminate or bulk material made of mats or nonwovens, the proportion of recycled fibers is intended to increase from the inside to the outside. This increase can occur gradually, in several stages, or in just one stage. In extreme cases, mats and nonwovens are made of 100% virgin fibers in the core and mats and nonwovens are made of 100% recycled fibers in the outer region of the laminate and / or bulk material.

[0029] In particular, it is intended that recycled and / or cleaned fibers are surface-treated, for example with a coating, such as an amphoteric coating, so that these fibers promote good flow behavior with respect to the respective impregnating agent.

[0030] For example, the amphoteric coating can comprise surfactants that adhere well to the fiber at one end—in the case of carbon fiber, to the carbon—and have, for example, epoxy groups at the other end. For example, silanes, siloxanes, alcohols, and / or corresponding sulfur or phosphorus compounds, as well as any combinations and / or mixtures, with or without adhesion promoters, can be used to treat the surface of the recycled fiber.

[0031] For example, the coating of the reinforcing fibers in the nonwoven fabric is intended to exert or enhance a capillary effect on the impregnating agent, so that the impregnating agent is absorbed through the nonwoven fabric made of recycled fibers into the core of the laminate and / or bulk material. The capillary effect can be created and / or enhanced by the arrangement and / or type of fibers in the nonwoven fabric, by the functional groups of the surface coating of the reinforcing fibers in the nonwoven fabric, or by both.

[0032] It is therefore also advantageous to use the nonwovens made from recycled fibres as a covering or at least partly as an outer skin for the laminate or the bulk material, because this promotes the completeness of the impregnation also in the core of the laminate and / or bulk material.

[0033] A resin embedding and / or impregnation with resin that is as complete as possible for the production of the composite material is essential for the quality of the component produced from it in mechanical, electrical and / or insulating terms.

[0034] The term “recycled fibers” used to manufacture the nonwoven material, for example, and subsequently the composite material, generally refers to the sustainably available fiber stock. This initially refers to all fibers, fiber piles and / or fiber flakes that have already been processed as fiber reinforcement in a composite material with a resin matrix, in particular with a resin matrix that is at least partly thermoset, and that are obtainable by recycling and separation from the thermoset resin, e.g. by electrical, pyrolytic (by combustion) and / or solvolytic (by dissolving) processes, a separation of the fiber reinforcement from the thermoset, possibly with destruction of the thermoset. These recycled fibers come, for example, from different sources and / or were embedded in different resin matrices. The fibers can come from a composite material such as SMC, BMC and / or FVK after material separation.In the present case, recycled fibers from the process step of separating the reinforcing fibers from the resin matrix are referred to as fibers with a specific circumference, for example, fiber flakes of the same and / or measurable fiber length, fiber pile and / or fiber nap. In addition, the fiber offcuts from the production of the reinforcing fibers are referred to as "recycled fiber" in the present sense. Accordingly, according to a further advantageous embodiment, in addition to the above definition of recycled fiber, "recycled fibers" also include those that have not yet been embedded in a resin matrix and originate from textile fiber waste.

[0035] In contrast, the term “defined fibers” generally refers to all types of non-recycled, fresh fibers. For example, these can be all common synthetic fibers and / or natural fibers, i.e. renewable fibers, natural or synthetic, fresh and non-recycled fibers for nonwoven formation, e.g. knitting threads for stitchbonding, or fibers that impart special properties to a composite material. According to advantageous embodiments, the “fresh and defined fibers” are optionally admixed at one or more points in one embodiment of the method to the fibers obtained by separating the fiber reinforcement of a product made from a composite material from a resin matrix and / or otherwise by recycling to form a mat and / or nonwoven.

[0036] During mat and / or nonwoven formation, inter alia, cut threads or fibers with lengths preferably greater than 2 mm, in particular greater than 10 mm, and particularly preferably greater than 20 mm, or in lengths ranging from 1 mm to 150 mm, preferably in the range from 2 to 120 mm, particularly preferably in the range from 10 mm to 100 mm, are laid down in an undirected and flat manner, thus creating an isotropic reinforcing structure. Alternatively, a zigzag-shaped laying of a fiber web can be achieved during nonwoven formation using a carding machine.

[0037] The mat and / or fleece formation takes place, for example, via wet-laid nonwoven fabric formation.

[0038] The fibers can be bonded mechanically by needling and / or knitting, or alternatively or additionally by a binder, which is applied prior to deposition and bonds the fibers together during drying. For better impregnation, the binder can be soluble in the matrix, for example.

[0039] A binder can bond fibers, rovings, fiber composites and / or fiber fabrics; it can be present before or with the impregnation and in liquid or solid form.

[0040] According to an advantageous embodiment of the process, the recycled fibers are, if possible, tangled. Anisotropically oriented fiber layers are less suitable for mat and nonwoven formation. Therefore, prior to nonwoven formation, the recycled fibers are preferably subjected to aerodynamic treatment, followed by random carding or zigzag storage of the recycled fibers and / or recycled fiber flocks. This tangles the recycled fibers according to an aerodynamic principle, i.e., they are arranged as homogeneously and isotropically oriented as possible in all spatial directions.

[0041] A homogeneous, random arrangement of the recycled fibers in all spatial directions is essential for nonwoven formation. So-called airlay lines, i.e. lines with random nonwoven carding, have proven particularly effective.

[0042] Alternatively or additionally, the fibers can be needled. In this process, the fiber mats are pierced with pins in the form of needles with additional barbs, creating a mechanical connection, e.g., by physically entangling the fibers, similar to sewing.

[0043] An example of stitchbonding is the so-called Maliwatt process. Maliwatt is a brand name for a nonwoven stitchbonded fabric, but also for a system used to carry out the process and produce textile fabrics.

[0044] According to an advantageous embodiment of the invention, transverse nonwovens are used for web consolidation. The transverse nonwovens are produced, for example, by wet-bonding.

[0045] In the stitch-bonding process, the base material used is preferably

[0046] Cross-woven fabrics, e.g. made of wool fibre, polymer fibre, shredded fibre, including recycled fibre, glass fibre, glass mat and any mixtures thereof and with other fibres, connected by a multitude of parallel or approximately parallel integrated knitted threads.

[0047] Nonwovens made from recycled fibers, which usually form the cross-woven fabrics, using a Maliwatt process or needle-punched, can be processed into composite materials using all types of resins.

[0048] Nonwovens are special forms of mats that are characterized by significantly lower surface weights and are often used as surface nonwovens for components with high-quality surfaces, for example in automotive engineering.

[0049] The separation of the reinforcing fibers from the resin matrix is ​​achieved, for example, by carefully dissolving the duromeric matrix, whereby the fiber reinforcement, which is usually not only stronger than the surrounding duromeric matrix, but also chemically represents the more stable compound, for example glass, basalt, sisal, aramid, jute, cotton, flax, hemp and / or carbon fiber are significantly more stable against chemical acids and / or solvents than an epoxy resin.

[0050] All of the above-mentioned fibers can be processed into mats and nonwovens in any blend. Synthetic fibers such as glass, basalt, and / or carbon fibers are particularly suitable.

[0051] A fiber extracted using state-of-the-art technology may or may not be damaged on the surface depending on the separation process. Furthermore, the fibers usually have highly variable morphologies, orientations, and / or lengths, making their return to technical use as a composite with properties defined by fiber reinforcement not only difficult but virtually impossible.

[0052] Apart from that, there are other fibers from the fiber manufacturing process that are difficult to use as raw materials for a composite material, but which can be utilized together with the recovered fibers in the process proposed here for the first time. These are the textile scraps and / or remnants left over from composite processing that must be recycled.

[0053] This particularly refers to the waste of semi-finished fiber products, up to 20% and more of which is discarded as offcuts during the processing of a continuous fiber composite material into a composite component.

[0054] The following basic materials can be used as impregnating agents and / or as thermosetting matrices: synthetic resins based on polyester, vinyl ester, epoxy and / or polyurethane resins, as well as other, possibly less common "exotic" resins based on imides, e.g. phenolically bonded as polyetherimide, such as pyromellitic dianhydride and 4,4'-diaminodiphenyl ether.

[0055] An impregnating agent and / or a polymer matrix as a base material for a composite material within the meaning of the present invention does not necessarily comprise only thermosetting, thermoplastic, or elastic polymer components, but can certainly be present as a blend and / or even a copolymer of various thermosetting, thermoplastic, and elastic resin components. All possible combinations are conceivable here; however, the separation of the fiber reinforcement from the thermosetting components is the most technically challenging because it cannot be achieved simply by heating and melting.

[0056] For example, thermoplastics in the form of PA = polyamide, PET = polyethylene terephthalate, PBT = polybutylene terephthalate, PC = polycarbonate, PPS = polyphenylene sulfide, PES, PPO, PEEK, etc. The abbreviations correspond to the internationally recognized abbreviations for polymers. Bio-based matrix systems can also be used as a base material for the composite material in accordance with the invention.

[0057] Suitable thermosets include, for example, "UP resins" = unsaturated polyesters, vinyl esters and / or epoxy resins. Renewable, sustainable materials for the resin matrix in the field of epoxy resins include, for example, epoxidized vegetable oils and / or glycidyl ethers from glycerin-based epichlorohydrin. For example, UP resins can be obtained from PET recycling, such as textiles and / or bottles, or can be made from, for example, modified, natural substances using polyol components.

[0058] According to an advantageous embodiment of the invention, the fiber reinforcement of the composite material also includes naturally occurring fibers.

[0059] Renewable resins can be considered as a biologically based resin matrix. Examples of suitable natural resins include turpentine, balsam, gum lac, furan resin, rosin, sandarac, and mastic.

[0060] Chemical recycling continues to utilize residual materials that cannot be mechanically processed as raw materials for the resin matrix. These are then, for example, fed into the standard steam cracking process after pyrolysis and are found—in certain proportions—in the basic chemicals that form the basis for all polymer chemistry.

[0061] According to an advantageous embodiment of the invention, the fibers or the fiber mixture used for nonwoven formation, for example, have a fiber length of at least 2 mm, preferably at least 10 mm and very preferably at least 20 mm.

[0062] According to an advantageous embodiment of the invention, the polymeric resin matrix of the composite material also comprises at least partly a recycled and / or naturally renewable raw material component.

[0063] The textile processing of the recycled fibers, with or without the addition of defined fibers, leads to the production of a mat, a nonwoven or a fiber fabric of the recycled fibers through the following process steps: o Standardization of the recycled fibers, in particular by cutting and / or tearing process o Optional admixture of defined fibers o Mat or nonwoven production from the recycled fibers, in particular via e.g. airlay and / or carding technology, for example production of cross-woven fabrics o Mat or nonwoven consolidation, in particular via needling and / or stitch-bonding of the produced cross-woven fabrics

[0064] In the process step of standardizing the recycled fibers through cutting and / or tearing, the recycled fibers are standardized, for example, in their morphology and / or length. The extent and type of standardization varies and is adaptable depending on the quality requirements of the nonwoven.

[0065] The semi-finished product subsequently produced by nonwoven fabrication is then, for example, directly introduced into the composite production process by resin impregnation.

[0066] Since the nonwovens are voluminous and have a low basis weight compared to classic fabrics and wovens, it is particularly advantageous if a tape-like resin impregnation takes place in the form of a prepreg and / or SMC manufacturing process.

[0067] By adjusting the resin in the B-stage, semi-finished products similar to those of continuous fiber prepregs and / or SMCs are created.

[0068] In the following, the invention is explained in more detail with reference to a figure which shows a diagram of an exemplary embodiment of the method:

[0069] Figure 1 shows, on the far left as 1, process step 1, the preparation and opening of the recycled fibers, with explanation 4. Explanation 4 explains that the following preparation and opening techniques are used alone or in any combination: a) cutting and tearing technology, in particular for modifying textile waste made from high-performance fibers b) fiber opening and mixing by bale openers, mixing openers and / or in a mixing chamber c) fiber sizing, i.e. application by a spraying process.

[0070] The prepared fibers are fed to the web formation process 2 according to arrow 7. As explained in more detail in Figure 5, aerodynamic web formation with fiber deposition in the air stream and random fiber deposition, forming an isotropic web structure, can be used here. Alternatively or additionally, web formation can be carried out using a carding machine, whereby after the fiber flock is opened and parallelized, fiber web formation takes place using a drum, worker and / or turner pairs, which finally follows a zigzag-shaped deposition of the fiber web using a crosslapper.

[0071] In Figure 1, the arrow 8 finally leads to process block 3, the consolidation methods, inline, i.e. within the fleece.

[0072] As explained in more detail in Figure 6, needling is performed here, for example, by vertical needle penetrations, e.g., with barbed needles, and reorientation of the fibers in the z-direction. Alternatively or in addition, a stitch-bonding process, e.g., Maliwatt®, involves the insertion of a knitting thread and / or sewing thread and consolidation of the nonwovens, for example, by thread looping.

[0073] The consolidated nonwoven obtained according to Figure 1 forms a so-called "nonwoven" which can be used in a resin matrix to produce the composite material, in particular in the form of a prepreg, e.g. as a single layer. It can then be used in SMC production and SMC processing together with the resin matrix, e.g. based on epoxy and / or vinyl ester, to produce prepregs. All types of components can be produced from such prepregs, for example housings, circuit breakers, electric motors, generators, transformers, components for power electronics and / or any elements and components of interior fittings, for the sanitary sector, including vehicles, on land, rail and / or road, vehicles for air and water, as well as elements in all types of real estate.

[0074] The nonwoven fabric formation from recycled fibers for use in composite materials, disclosed here for the first time, makes it possible to produce a high-quality power electronic component from recycled fibers, where previously only use as a filler was conceivable.

[0075] The possibilities demonstrated here for the first time of combining simple material separation with high-quality fiber utilization through nonwoven formation - with recycled fibers, even from different sources, including textile offcuts - make it possible to utilize fiber stocks that would otherwise not be sustainably available. This also makes it possible, for example, to achieve strengths in composite materials that would otherwise only be possible with valuable and expensive continuous fibers that cannot be produced sustainably and with complex surface treatments. In contrast to textile weaving and laying processes, the degree of consolidation in the nonwoven production process can be adjusted over a wide range. This enables high degrees of forming for three-dimensional components and mass-production press processing, which can also be used for SMC production.

Claims

Patent claims 1 . Process for recycling composite material, comprising the following process steps: - Separation of reinforcing fiber and resin matrix - Production of a mat, a nonwoven or a fibre fabric from recycled fibres by the following process steps: o Standardisation of the recycled fibre, o Mat and / or nonwoven production, o Formation of a 3-dimensional laminate and / or bulk material from the mats and / or nonwovens, - Embedding by impregnation with impregnating agent the laminates and / or bulk materials made from mats and / or nonwovens made from at least partly recycled fibres into a resin matrix.

2. A process according to claim 1, additionally comprising a process step of optionally admixing defined fresh fibers prior to mat and / or nonwoven formation.

3. Method according to claim 1 or 2, additionally comprising a method step of consolidating the mat and / or the fleece. 4 . Method according to one of the preceding claims, additionally comprising a method step of at least partially surface treating the recycled fibers.

5. Method according to one of the preceding claims, wherein the method step of standardizing the recycled fibers is carried out in particular by cutting and / or tearing process(es).

6. A method according to any one of the preceding claims, wherein the step of separating reinforcing fibers and hard matrix results in recycled fibers, recycled fiber flocks and / or recycled fiber pile.

7. A method according to any one of the preceding claims, wherein the step of producing a mat or nonwoven fabric results in the recycled fibers being arranged randomly in the nonwoven fabric.

8. A method according to any one of the preceding claims, wherein the step of producing a mat or nonwoven fabric results in the formation of at least one transverse nonwoven fabric.

9. A method according to any one of the preceding claims, wherein the mat or nonwoven fabric production step comprises wet nonwoven fabric formation.

10. A method according to any one of the preceding claims, wherein the mat or nonwoven bonding step comprises needling.

11. A method according to any one of the preceding claims, wherein the mat or nonwoven bonding step comprises a stitch-bonding step.

12. Method according to one of claims 10 or 11, wherein transverse webs are used at least in part for the web consolidation.

13. Method according to one of the preceding claims, wherein in the 3-dimensional laminate and / or bulk material the proportion of recycled fibers increases from the inside to the outside. 14 . Composite material obtainable by a process according to one of claims 1 to 13 . 15 . Use of a composite material according to claim 14 for the production of elements for energy supply and energy distribution.

16. Use of a composite material according to claim 14 for the manufacture of housings, electric motors, circuit breakers, generators, transformers, in power electronics, elements of the interior fittings of rooms, of vehicles and / or elements of Sanitary area.

17. Component comprising a composite material which can be produced according to one of claims 1 to 13.

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