DE102011081575B4 - Process for recycling fiber-reinforced plastics - Google Patents

Abstract

A process for recycling fiber reinforced plastics, comprising the steps of:
(a) dissolving the polymer matrix of a fiber-reinforced plastic part,
(b) comminuting the fiber structure of the plastic part into sections of an edge length of the order of 1 cm to 20 cm,
(c) scanning each section and evaluating for selected characteristics,
(d) depositing the individual parts according to a suitable storage strategy, for molding a new plastic part, and
(e) infiltrating the new plastic part.

Description

The present invention relates to a process for recycling fiber-reinforced plastics.

Technical background

Fiber-reinforced plastics belong to the class of fiber-reinforced materials (fiber composites), which in turn belong to the class of composite materials. A fiber-reinforced plastic (also: fiber-plastic composite (FKV) or fiber composite plastic, FRP) is a material consisting of reinforcing fibers and a plastic matrix (polymer matrix). The matrix surrounds the fibers which are bonded to the matrix by adhesive or cohesive forces. By using fiber materials, fiber-plastic composites have a direction-dependent elasticity behavior.

Fiber-reinforced plastics generally have high specific stiffnesses and strengths. This makes them suitable materials in lightweight applications. From fiber-reinforced plastics predominantly flat structures are produced.

The mechanical and thermal properties of fiber-plastic composites can be adjusted via a variety of parameters. In addition to the fiber-matrix combination, for example, the fiber angle, the fiber volume fraction, the layer order and much more can be varied.

• • Realisierung einer Faserorientierung (bspw. in Kraftfluss-Richtung),
• • Realisierung eines hohen Faservolumengehaltes, und
• • Einhaltung einer gewissen Mindestfaserlänge zur Kraftübertragung von der Matrix in die Fasern, zur Kraftumleitung und zur Vermeidung von lokalen Spannungsüberhöhungen.

Fiber-reinforced plastics, for example with carbon fiber reinforcement, have a very high potential as a lightweight material. Necessary conditions for use as a high-performance material include the following three criteria:

• Realization of a fiber orientation (eg in force flow direction),
• • realization of a high fiber volume content, and
• • Maintaining a minimum fiber length to transfer force from the matrix to the fibers, to redirect power and to avoid localized voltage buildup.

The current recycling processes of fiber reinforced plastics have a short fiber "casts" or fiber flour as a starting material. This can not be further processed in the form that it would be possible to meet the three criteria mentioned above. Thus, recycled carbon fibers can not currently be used as a raw material for high performance materials (structural components or the like). In reality, so-called downcycling rather than actual recycling is more likely.

Waste fiber reinforced plastic waste, such as carbon fiber reinforced plastic (CFRP), is currently either dumped, thermally disposed of (incinerated, eg using power to generate electricity) or recycled.

The first two alternatives are not an ecologically sound alternative, which is why there is a clear trend towards the latter alternative, ie. H. the preparation, is recognizable. This is also reinforced by social and legal constraints, for example, in the EU through the "Regulation on the disposal, return and environmentally sound disposal of end-of-life vehicles" §5 from 2015, the recovery of at least 95% by weight and the recycling of 85% by weight is required ,

The treatment is done either thermally (pyrolysis) or chemically (solvolysis, hydrolysis, supercritical fluids), in particular, the thermal processes have currently reached an industrially mature state.

However, all methods have in common that they provide a step in which the fibers are shortened. This takes place, for example, in the form of shredding the components before the fibers are released, or else after the separation step on the bare fibers in the form of cutting or shredding. Optionally, an even further shortening to fiber meal can take place.

In addition, in the overall process, for example, by transporting the recyclate on conveyor lines, a separation of the fibers is achieved, so finally there is a wool-like semi-finished fiber. Such a method is used, for example, in JP 2003-033915 described.

Furthermore, there are process variations in which a specific disruption of the fibers (see, for example, US Pat DE 10 2009 023 529 ) is provided. These separated filaments are then combined again in a spinning process to a semi-finished product (yarn / nonwoven).

In the DE 10 2007 058 893 A1 describes a process for the digestion of fiber composite materials.

The DE 10 2008 002 846 B4 relates to a waste treatment process and an arrangement therefor.

In the DE 195 14 543 C1 there is disclosed a method of recovering and recycling waste wastes from fiber reinforced prepreg webs.

There is a need in the art for a process for recycling fiber reinforced plastics where the function of the Reinforcement fibers should be largely retained. The object of the present invention is to provide such a method.

This object is achieved by a method according to claim 1. Further developments of the method are the subject of the dependent claims.

Summary of the invention

• (a) Auflösen der Polymermatrix eines faserverstärkten Kunststoffteils,
• (b) Zerkleinern der Faserstruktur des Kunststoffteils zu Teilstücken einer Kantenlänge in einer Größenordnung von 1 cm bis 20 cm,
• (c) Einscannen eines jeden Teilstücks und Auswerten hinsichtlich gewählter Kennwerte,
• (d) Ablegen der einzelnen Teilstücke nach einer geeigneten Ablagestrategie, zum Formen eines neuen Kunststoffteils, und
• (e) Infiltrieren des neuen Kunststoffteils.

The present invention relates to a process for recycling fiber-reinforced plastics, comprising the steps:

• (a) dissolving the polymer matrix of a fiber-reinforced plastic part,
• (b) comminuting the fiber structure of the plastic part into sections of an edge length of the order of 1 cm to 20 cm,
• (c) scanning each section and evaluating for selected characteristics,
• (d) depositing the individual parts according to a suitable storage strategy, for molding a new plastic part, and
• (e) infiltrating the new plastic part.

Preferred embodiments of the present invention are described below and in the appended claims.

Brief description of the figures

1 shows a partial step of the claimed method, in which the polymer matrix of the plastic part is removed.

2 shows a partial step of the claimed method, in which partial gap are generated and recorded.

3 shows a partial step of the claimed method in which the sections are scanned, evaluated and stored to a new component.

4 shows a partial step of the claimed method in which the fiber structure of the new component is infected.

Detailed description of the invention

In a first step, the process according to the invention for recycling fiber-reinforced plastics comprises dissolving the polymer matrix. For this purpose, the person skilled in various ways known. For example, the dissolution of the polymer matrix can be carried out thermally by means of pyrolysis, i. H. by a thermo-chemical cleavage of organic compounds at high temperatures of for example 400-900 ° C with the exclusion of oxygen. In another embodiment, the dissolution of the polymer matrix can be carried out chemically by solvolysis, hydrolysis or by means of supercritical fluids. The polymer matrix is removed by means of an organic or aqueous solvent or by means of supercritical fluids. In a preferred embodiment, pyrolysis is used to remove the polymer matrix.

As in 1 shown ( 7 ), according to the present invention, the fiber-reinforced plastic part to be recycled, for example a used component or reject component, is processed in such a way that there is no singling and / or shortening of the fibers. In contrast, in the prior art, recycling processes are used in which the plastic parts are shredded so that the original fiber length is significantly shortened and / or the respective fibers are singulated out of their original environment. Optionally, according to the present invention, a pre-crushing of large structures can be carried out in order to maintain a moderate furnace size, for example during pyrolysis. For example, according to the invention, a rotary kiln or the like need not be used for pyrolysis, but the processing may take place, for example, in batch mode by means of charging racks or in a continuous process by means of conveying equipment (assembly line, etc.) ( 1 ).

After dissolving the polymer matrix of the fiber-reinforced plastic part according to the invention, the fiber layers are present in approximately the same shape as they were used in the original component production ( 8th ).

The present invention is not particularly limited in the reinforcing fibers suitable for the method of the present invention. For example, according to the present invention, fiber-reinforced plastic parts may be recycled with basalt fibers, boron fibers, glass fibers, ceramic fibers, silica fibers, steel fibers, aramid fibers, carbon fibers, polyester fibers, nylon fibers, polyethylene fibers, or Plexiglas fibers. If necessary, care must be taken when removing the polymer matrix that a method is selected in which the respective fibers are not removed. For example, pyrolysis is typically not suitable for organic fibers such as polyester fibers, nylon fibers, polyethylene fibers, or Plexiglas fibers. Preferably, according to the invention, plastic parts reinforced with glass fibers or carbon fibers, more preferably reinforced with carbon fibers, are used.

The present invention is not particularly limited with respect to the polymer matrices which are suitable for the process of the present invention. For example, fiber reinforced Plastic parts with a polymer matrix of polyether ether ketone (PEEK), polyphenylene sulfide (PPS), polysulfone (PSU), polyetherimide (PEI), polytetrafluoroethene (PTFE), epoxy resin (EP), unsaturated polyester resin (UP), vinyl ester resin (VE), phenol-formaldehyde resin ( PF), diallyl phthalate resin (DAP), methacrylate resin (MMA), polyurethane (PUR), melamine resin (MF / MP), urea resin (UF), or rubber. In a preferred embodiment, epoxy resin (EP), phenol-formaldehyde resin (PF), or polyurethane (PUR) is used.

As in 2 shown, the obtained fiber layers are further comminuted into suitable sections ( 2 ). The crushing is preferably carried out by cutting by means known in the prior art cutting device. According to the invention, the edge length of the sections is from about 1 cm to about 20 cm, preferably about 2 cm to about 10 cm. In a preferred embodiment, the sizes of the sections is about 2 × 2 cm ² to about 10 × 10 cm ² ( 14 ). These can be picked up individually from the original fiber structure after comminution ( 3 ), for example by means of a conventional FPP head ( 10 ) (Fiber Patch Preforming).

As in 3 each section is then scanned in with suitable methods ( 11 ). In principle, any imaging process is suitable. For example, a laser or the like may be used to scan the sections. When scanning, characteristic values are recorded, such as: As fiber orientation, Faserondulationen, fiber length, basis weight or geometric structure ( 15 ). Subsequently, either a Zwischenablagerung the individual cuts or a direct processing. This processing then takes place with the aid of a suitable filing strategy ( 4 ), as explained in more detail below.

The filing strategy is used to produce a new component out of the obtained sections of fiber layers that meets the requirements of fiber-reinforced plastic parts. The choice of a suitable storage strategy initially serves to match the geometric contours of the sections with the new, desired component, for example to reduce waste ( 16 ). In addition, taking into account a material database, favorable fiber orientations, layer structure, laminate thickness and other requirements of the component can be taken into account ( 17 ). In fiber-reinforced plastic parts, for example, an orientation of the fibers along the expected force flows is of considerable importance for the specific strength and rigidity of the components obtained by the recycling. The filing strategy is therefore developed in such a way that the individual sections are deposited in the new component to be formed in such a way that the fiber orientation coincides with the expected fluxes. Further in-depth partial aspects of the filing strategy are conceivable, for example the consideration of correction factors for fiber discharges, or the like ( 18 ). In a preferred embodiment, the filing strategy can be developed using computerized methods.

• (a) Auswählen von Teilstücken, die geeignet sind die gewünschte Struktur eines neu zu bildenden Bauteils auszufüllen, wobei vorzugsweise möglichst wenig Verschnitt anfallen soll; und/oder
• (b) Auswählen von Teilstücken hinsichtlich ihrer Faserorientierung, wobei die Teilstücke gemäß ihrer Faserorientierung entlang der Kraftlinien des neu zu bildenden Bauteils anzuordnen sind;
• (c) Auswählen von bestimmten Teilstücken, um Faserondulationen anderer Teilstücke auszugleichen; und/oder
• (d) Auswählen von Teilstücken hinsichtlich ihres Flächengewichts, wobei die Teilstücke hinsichtlich des gewünschten Flächengewichts des neu zu bildenden Bauteils anzuordnen sind.

In a specific embodiment, the filing strategy comprises:

• (A) selecting portions that are suitable to fill the desired structure of a newly formed component, preferably as little waste as possible should occur; and or
• (b) selecting sections in terms of their fiber orientation, wherein the sections are to be arranged along the lines of force of the newly formed component according to their fiber orientation;
• (c) selecting particular sections to compensate for fiber soundings of other sections; and or
• (d) selecting sections in terms of their basis weight, the sections being arranged with respect to the desired basis weight of the component to be formed.

An additional variant, which is possible according to the invention, consists in the production of hybrid materials: In this case, the portions of the fiber layers obtained after removal of the polymer matrix and the cutting can be combined with parts of another type to obtain the material characteristics corresponding to a target application to influence. For example, the additional sections may be virgin material to improve specific rigidity; Furthermore, the addition of waste residues is conceivable to provide a value-added and resource-saving recovery for this. In addition, other types of material can be introduced. For example, aramid carbon fiber hybrids are well known in the art and are feasible with the present method. Likewise, the insertion of thickenings (eg metals or plastics) is possible according to the invention and provides sufficient material for threads for attachment to superordinate support structures. The integration of other, additional functionalities is also possible.

All the above-described variations of the method can be easily combined with each other.

The storage of the individual parts to form a new component ( 5 ) is effected, for example, by means of the above-described FPP head or with the aid of comparable methods until a near-net shape fiber preform of corresponding laminate thickness is produced ( 12 ).

After the filing of the necessary patches has taken place, an infiltration of the component takes place. This step is in 4 shown ( 6 ). Methods of infiltration in the manufacture of fiber reinforced plastic parts are well known to a person skilled in the art. An example of a suitable infiltration process is Liquid Composite Molding (LCM). In this method, the fibrous structure is placed in a tool (e.g., upper and lower dies) and a resin is injected into the fibrous structure, optionally using elevated or reduced pressure. Subsequently, the resin is cured, for example thermally. Variants of this method are for example Resin Transfer Molding (RTM), Vacuum Assisted RTM (VARTM) or Vacuum Assisted Resin Infusion (VARI). In the RTM process, resin is injected into the fiber reinforcements to wet the preform, and then the part is cured, for example by thermal curing or another suitable curing process. When injecting the resin, additional vacuum can be applied to optimize the filling of the mold (VARTM). The VARI method is a modification of the VARTM method in which a flexible vacuum bag is used as the upper tool. The reinforcing fibers are placed on the lower tool. The assembly is sealed with a flexible vacuum film and vacuum applied. The resin flows over the fibers and infiltrates them. A subsequent curing can be carried out as usual in the prior art, for example thermally at about 180 ° C, depending on the structure and the resin system used.

The plastic part formed ( 13 ) removed from the tool (demolding). The further post-processing and system integration of the finished component take place as usual in the prior art.

In the manner described above, a plastic part can be produced, which on the one hand based on recycled fiber material and on the other hand can still realize the advantages of fiber-reinforced plastic as before. So there is a real recycling instead of in contrast to downcycling, which is customary in the prior art.

In particular, the illustrated method causes in the recycling process of fiber reinforced structures, such as with carbon fiber reinforced plastic, no shortening of the filaments below the described minimum size of the cuts and no fiber separation takes place. In this way, the actual and original purpose of the reinforcing fibers remains intact. The fibers, z. As carbon fibers, are usually produced with high technical complexity and high energy consumption, and can be obtained according to the present invention during recycling.

The specific strength and rigidity of the fiber material obtained according to the invention qualifies this as a potential-intensive reinforcing structure of plastics. The resulting composites are thus well suited for lightweight material applications. The gain in the target application (fuel savings through lower structural weight in aircraft or automotive, faster acceleration through lower moment of inertia, etc.) justifies the use of these complex raw materials in many different areas and can also achieve a positive ecological balance compared to other materials. This use in high-quality applications, ie in those which exploit the properties of the carbon fibers to a great extent, requires that a minimum fiber length is given and a fiber orientation is adjustable. In contrast to the prior art, recycled fibers also have the potential to be used in such high-quality applications with the new process shown. The recycled fibers according to the prior art, however, rely on new applications, the majority could not even be identified and no significant sales markets are seen and exploit the fiber potential only very limited.

Claims (9)

A process for recycling fiber reinforced plastics, comprising the steps of: (a) dissolving the polymer matrix of a fiber-reinforced plastic part, (b) comminuting the fiber structure of the plastic part into sections of an edge length of the order of 1 cm to 20 cm, (c) scanning each section and evaluating for selected characteristics, (d) depositing the individual parts according to a suitable storage strategy, for molding a new plastic part, and (e) infiltrating the new plastic part. A method according to claim 1, wherein the dissolution of the polymer matrix takes place thermally by means of pyrolysis or chemically by solvolysis, hydrolysis or by means of supercritical fluids, preferably by means of pyrolysis. A method according to claim 1 or 2, wherein the fiber-reinforced plastic part is reinforced with basalt fibers, boron fibers, glass fibers, ceramic fibers, silica fibers, steel fibers, aramid fibers, carbon fibers, polyester fibers, nylon fibers, polyethylene fibers, or Plexiglas fibers, preferably reinforced with glass fibers or carbon fibers, more preferably reinforced with carbon fibers. A method according to any one of claims 1-3, wherein the polymer matrix of the fiber reinforced plastic part is selected from polyetheretherketone (PEEK), polyphenylene sulphide (PPS), polysulphone (PSU), polyetherimide (PEI), polytetrafluoroethene (PTFE), epoxy resin (EP), unsaturated polyester resin (UP), vinyl ester resin (VE), phenol-formaldehyde resin (PF), diallyl phthalate resin (DAP), methacrylate resin (MMA), polyurethane (PUR), melamine resin (MF / MP), urea resin (UF), rubber and polyurethane (PUR). Method according to one of claims 1-4, wherein in step (b) the fiber structure of the plastic part is comminuted into sections of an edge length of 2 cm to 10 cm, preferably into sections of an area of 2 × 2 cm ² to 10 × 10 cm ² . A method according to any one of claims 1-5, wherein in step (c) said selected characteristics are selected from fiber orientation, fiber dulness, fiber length, basis weight and geometric structure. A method according to claim 6, wherein the deposition takes place taking into account the characteristic values. Method according to one of claims 1-7, wherein the scanning takes place by means of a laser. A method according to any one of claims 1-8, wherein step (d) further comprises establishing a suitable filing strategy, preferably by computer-aided methods.

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