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

Abstract

The invention relates to a method for recycling composite material and a composite material that forms a material with synergistic properties from two or more base materials, in particular a composite material from the group of fiber-reinforced plastics, which are available, for example, in the form of continuous fiber composites (FRP), sheet molding compounds (SMC), and bulk molding compounds (BMC), wherein the composite material contains at least partially recycled base materials, as well as uses thereof and a power electronic component. The possibilities of nonwoven fabric formation shown here for the first time allow the utilization of fiber reserves that would otherwise not be sustainably available, using recycled fibers, even from different sources, including textile offcuts.

Description

[0001] The invention relates to a method for recycling composite material and 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 fiber-reinforced composite plastics, which are present, for example, in the form of continuous fiber composite "FVK", sheet molding compound "SMC", and bulk molding compound "BMC", wherein the composite material contains at least partially recycled basic materials, as well as uses thereof and a power electronic component.

[0002] 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.

[0003] 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 material-heterogeneous material solution.

[0004] 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 available on the market that can scalably recycle the expensive fibers from fiber reinforcement.

[0005] 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 particularly 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.

[0006] 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, thermal recycling occurs through incineration. Occasionally, the ground recyclate is incorporated into new composite materials as a filler, particularly when it contains thermoset components.

[0007] All fiber composite materials, such as continuous fiber composites (FRP), sheet molding compounds (SMC), and bulk molding compounds (BMC), are generally downcycled because the fibers are shortened during shredding or grinding, significantly losing their performance potential. Fiber-reinforced plastics with thermoset content, in particular, often only result in mixed fractions that are difficult and / or inseparable in standard processes, which can only be recycled thermally by incineration. The valuable fiber reinforcement, because it is often non-combustible, ends up in the slag.

[0008] 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.

[0009] This object is achieved by the subject matter of the present invention as disclosed in the description, the figure and the claims.

[0010] Accordingly, the present invention relates to a process for recycling composite material, comprising the following process steps: - Recycling, i.e. separation of reinforcing fiber and resin matrix - Optional mixing of defined fibers - Production of a mat, a nonwoven or a fibre fabric from recycled fibres by the following process steps: ◯ Standardization of the recycled fiber, in particular by cutting and / or tearing processes ◯ Optional addition of defined fibers ◯ Mat or nonwoven production from the recycled fibers, in particular via e.g. airlay and / or carding technology, wet-laid nonwoven fabric formation and / or, for example, the production of cross-woven nonwovens ◯ Mat or nonwoven bonding, in particular by needling and / or stitching of the cross-woven fabrics produced, for example, in the above process step - Resin impregnation by incorporating the produced mat and / or fleece made of recycled fibres into a resin matrix, in particular comprising recycled and / or renewable components.

[0011] 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, in particular in the form of a nonwoven, and the mat comprises recycled fibers and / or fiber offcuts. The use of such a composite material and, finally, a component comprising such a composite material are also the subject of the present invention.

[0012] The general finding of the invention is that thermoset-embedded fiber reinforcement cannot be recovered for recycling via thermal processes because a fully cured thermoset polymer cannot be melted without decomposition, but that electrical, pyrolytic - by combustion - and / or solvolytic - by dissolving - the thermoset matrix - processes make it possible to separate the fiber reinforcement from the thermoset, possibly destroying the thermoset, 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, even without the admixture of new fibers. However, through a process of fabrication, matting, and / or especially nonwoven production, these fibers can be made available again in their entirety, with or without the admixture of other fibers, as a raw material for the production of a composite material. In the technology of semi-finished textile products, a nonwoven is a special form of mat.

[0013] The term “recycled fibers” used to manufacture the nonwoven material, for example, and subsequently the composite material, generally refers to the sustainably available fiber supply. This term is used to describe all fibers, fiber webs 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 partially thermoset, and that can be obtained by recycling and separating them from the thermoset resin, for example by electrical, pyrolytic (by combustion) and / or solvolytic (by dissolving) processes, which separate the fiber reinforcement from the thermoset, possibly destroying the thermoset. These recycled fibers come from various sources, for example, and / or were embedded in various resin matrices. The fibers can come from a composite material such as SMC or FRP after material separation.Recycled fibers from the process step of separating the reinforcing fibers from the resin matrix are referred to here as fibers with a specific circumference, e.g. fiber length, fiber flakes and / or fiber pile.

[0014] Furthermore, the fiber offcuts from the production of the reinforcing fibers are referred to as "recycled fibers" in the present sense. Accordingly, according to a further advantageous embodiment, in addition to the above definition of recycled fibers, "recycled fibers" also include those that have not yet been embedded in a resin matrix and originate from textile fiber waste.

[0015] In contrast, "defined fibers" generally refer to all types of non-recycled fibers. For example, these can be all common synthetic fibers and / or natural fibers, i.e., renewable fibers, natural or synthetic, non-recycled fibers for nonwoven fabric formation, e.g., knitting threads for stitchbonding, or fibers that impart special properties to a composite material. According to advantageous embodiments, the "defined fibers" are optionally admixed at one or more points in the process according to the invention to the fibers obtained by separating the fiber reinforcement of a product made of composite material from a resin matrix and / or otherwise through recycling to form a mat and / or nonwoven.

[0016] 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 a non-directional and flat manner, thus creating an isotropic reinforcing structure. Alternatively, a zigzag-shaped deposition of a fiber web can be achieved during nonwoven formation using a carding machine.

[0017] The mat and / or fleece formation takes place, for example, via wet nonwoven fabric formation.

[0018] 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.

[0019] 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.

[0020] According to an advantageous embodiment of the process, the recycled fibers are, if possible, transferred into a random layer. Anisotropically oriented fiber layers are less suitable for mat and nonwoven formation. Therefore, aerodynamic treatment of the recycled fibers is preferably performed prior to nonwoven formation, followed by random carding or zigzag storage of the recycled fibers and / or recycled fiber flakes. 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.

[0021] 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.

[0022] Alternatively, or in addition, 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 interlacing the fibers, similar to sewing.

[0023] 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.

[0024] According to an advantageous embodiment of the invention, transverse nonwovens are used for nonwoven bonding. The transverse nonwovens are produced, for example, by wet-bonding.

[0025] In the stitch-bonding process, the base material is preferably 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, which are connected by a large number of parallel or approximately parallel integrated knitting threads.

[0026] 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.

[0027] 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.

[0028] 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 fibers are significantly more stable against chemical acids and / or solvents than an epoxy resin.

[0029] 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 fiber are particularly suitable.

[0030] 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.

[0031] 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 in the process proposed here for the first time, together with the recovered fibers. These are the textile scraps and / or remnants left over from composite processing that must be recycled.

[0032] 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.

[0033] The following basic materials can be used as thermosetting matrices: synthetic resins based on polyester, vinyl ester, epoxy and / or polyurethane resin, 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.

[0034] A polymer matrix as the 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, but 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.

[0035] For example, thermoplastics in the form of PA = polyamide, PET = polyethylene terephthalate, PBT = polybutylene terephthalate, PC = polycarbonate, PPS = polyphenylene sulfide, PES, PPO, PEEK, etc. These 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 within the meaning of the invention.

[0036] 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 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 natural materials (e.g., modified ones) using polyol components.

[0037] According to an advantageous embodiment of the invention, the fiber reinforcement of the composite material also includes naturally occurring fibers.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] According to an advantageous embodiment of the invention, the polymeric resin matrix of the composite material also comprises at least in part a recycled and / or naturally renewable raw material component.

[0042] The textile processing of recycled fibers, with or without the addition of defined fibers, leads to the production of a mat, a fleece or a fiber fabric of the recycled fibers through the following process steps: ◯ Standardization of the recycled fiber, in particular by cutting and / or tearing processes ◯ Optional addition of defined fibers ◯ Mat or nonwoven production from the recycled fibers, in particular using airlay and / or carding technology, for example, producing cross-woven fabrics ◯ Mat or nonwoven bonding, in particular by needling and / or stitching the produced cross-woven fabrics

[0043] 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.

[0044] The semi-finished product subsequently produced by nonwoven fabrication is then directly introduced into the composite production process, for example, by resin impregnation.

[0045] Since the nonwovens are voluminous and have a low basis weight compared to classic nonwovens and fabrics, it is particularly advantageous if a tape-like resin impregnation takes place in the form of a prepreg and / or SMC manufacturing process.

[0046] By adjusting the resin in the B-stage, semi-finished products similar to those of continuous fiber prepregs and / or SMCs are created.

[0047] 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:

[0048] Fig. Figure 1, on the far left, shows 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, especially for the modification of textile waste made from high-performance fibres b) Fibre opening and mixing by bale opener, mixing opener and / or in a mixing chamber, c) Fiber sizing, i.e. application by a spraying process.

[0049] The prepared fibers are fed to the web forming 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.

[0050] In Fig. 1, the arrow 8 finally leads to process block 3, the consolidation methods, inline, i.e. within the fleece.

[0051] 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 - for example, transverse nonwovens, by thread looping.

[0052] According to Fig.1 The consolidated nonwoven fabric obtained 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. From such prepregs, all types of components can be manufactured, 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.

[0053] 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.

[0054] The possibilities demonstrated here for the first time by combining simple material separation with high-quality fiber utilization through nonwoven fabric formation—using recycled fibers, even from various sources, including textile offcuts—make it possible to utilize fiber stocks that would otherwise be unsustainably unavailable. This also enables, for example, composite material strengths that would otherwise only be achievable with valuable and expensive, unsustainably produced continuous fibers and complex surface treatments. In contrast to textile weaving and laying processes, the degree of consolidation in the nonwoven fabric 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

[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: ◯ Standardization of recycled fiber, ◯ Mat and / or fleece production ◯ Mat and / or fleece consolidation - Resin impregnation by incorporating the manufactured mat and / or fleece made of recycled fibers into a resin matrix. [2] A process according to claim 1, additionally comprising a process step of optionally admixing defined fibers. [3] A method according to claim 1 or 2, wherein defined fibers are admixed after separation of the reinforcing fiber from the resin matrix. [4] A process according to any one of the preceding claims, wherein defined fibres are added after standardisation of the recycled fibres. [5] Method according to one of the preceding claims, wherein the step of standardising the recycled fibres 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 fiber and hard matrix results in recycled fibers, recycled fiber flakes and / or recycled fiber web. [7] A method according to any one of the preceding claims, wherein the step of producing the mat or nonwoven fabric results in the random arrangement of the recycled fibers in the nonwoven fabric. [8] A method according to any one of the preceding claims, wherein the step of producing mats or nonwovens results in the formation of at least one transverse nonwoven. [9] Method according to one of the preceding claims, wherein in the mat or nonwoven production step, wet nonwoven fabric formation takes place. [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 nonwovens are used at least in part for the nonwoven consolidation. [13] Composite material obtainable by a process according to one of claims 1 to 12. [14] Use of a composite material according to claim 13 for the production of energy supply and energy distribution elements. [15] Use of a composite material according to claim 13 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 the sanitary area. [16] Component comprising a composite material which can be produced according to one of claims 1 to 12.

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