A method for recycling carbon fiber reinforced resin matrix composites based on combustion synthesis

Abstract

The application discloses a method for recycling carbon fiber reinforced resin matrix composite based on combustion synthesis, and belongs to the field of carbon fiber recycling. The application aims at solving the problems of high recycling cost, great environmental risk and low recycling efficiency existing in recycling methods such as mechanical recycling method, chemical recycling method and pyrolysis recycling method. The reducing agent and carbon source are uniformly dispersed on the surface of the carbon fiber reinforced resin matrix composite to be recycled, then combustion synthesis reaction is carried out, then acid pickling, filtration and purification are carried out, and the recycling is completed. The method has the characteristics of simple operation, few technological processes, no need of solvent, low energy consumption and the like.

Description

A method for synthesizing recycled carbon fiber reinforced resin matrix composites based on combustion Technical Field

[0001] This invention belongs to the field of carbon fiber recycling, and more specifically, relates to a method for recycling carbon fiber reinforced resin matrix composites based on combustion synthesis. Background Technology

[0002] Carbon fiber reinforced resin matrix composites (CFRPs) are widely used in sporting goods, automotive, wind power, and aerospace industries due to their excellent specific strength, specific modulus, corrosion resistance, and abrasion resistance. However, with the increasingly widespread application of CFRPs, the amount of waste generated is also rapidly increasing. This waste is difficult to degrade naturally, placing a serious burden on the environment. Furthermore, the production cost of CFRPs is relatively high. Therefore, recycling these materials not only helps reduce environmental pollution but also effectively conserves resources and reduces costs.

[0003] Currently, the main recycling methods include physical recycling, chemical recycling, and pyrolysis recycling.

[0004] Physical recycling methods separate carbon fibers and resins from CFRPs through mechanical cutting, crushing, and screening. These methods are characterized by their simplicity, low cost, and environmental friendliness, but may lead to carbon fiber damage and performance degradation. Roux et al. (ECCM 16-16TH EUROPEAN CONFERENCE ON COMPOSITE MATERIAL, 2014, 22-26) developed an electrodynamic crushing (EDF) technology that generates plasma channels by applying high-voltage pulses to thermoplastic composites in water, achieving effective separation of carbon fibers from the PEEK matrix. The recovered carbon fibers maintained good structural integrity and mechanical properties. However, a universal mechanical recycling strategy is still lacking for CFRPs with commonly used thermosetting epoxy resin matrices. This results in low recycling value for most CFRPs used for mechanical recycling, failing to achieve effective separation of fibers and matrix, and limiting their application.

[0005] Chemical recycling methods utilize solvents or catalysts to degrade the resin matrix in composite materials under high temperature and pressure, thereby separating and recovering fibers from the resin. A key advantage is the ability to recover relatively undamaged fibers, but the process is complex and costly. Ahrens et al. (Nature, 2023, 617, 730) developed a transition metal-catalyzed chemical recycling technology. By using a Ru catalyst in supercritical water, they successfully recovered bisphenol A and intact fibers from epoxy resin composites with high purity, allowing for the production of new epoxy resins, polycarbonates, or polyesters. Simultaneously, the recovered fibers maintained their original high quality, exhibiting mechanical strength comparable to the original fibers. However, chemical recycling methods suffer from low catalytic efficiency, a lack of in-depth understanding and verification of the catalytic mechanism, challenges in scaling up the deconstruction process and cost-effectiveness, and unclear strategies for the reuse and application prospects of the recovered products.

[0006] Pyrolysis recycling is a technology that decomposes thermosetting resin-based composites into smaller molecules through high-temperature pyrolysis. Its key feature is the ability to decompose the resin in an oxygen-free or inert atmosphere, thereby recovering the fibers. However, this process can lead to a decline in fiber performance and generate a certain amount of harmful gases. Hecker et al. (Journal of Cleaner Production, 2023, 428, 139320) developed a technology for recovering carbon fiber reinforced polymer (CFRP) composites using superheated steam. By subjecting CFRP to superheated steam treatment at specific temperatures and pressures, they achieved effective separation of carbon fibers and the resin matrix while preventing oxidative degradation of the recovered fibers. This technology can recover carbon fibers while maintaining approximately 90%-100% of their original tensile modulus and 65%-100% of their tensile strength. Under optimized conditions, the stiffness and strength of the carbon fibers can be recovered without loss. However, pyrolysis recycling requires a long-term, continuous energy input to obtain stable high temperatures, and even the improved superheated steam method still requires a stable steam supply, resulting in significant energy consumption and making it unsuitable for large-scale recycling strategies.

[0007] While physical recycling methods are simple to operate, they often fail to completely separate carbon fibers from the resin matrix, resulting in impaired performance of the recycled carbon fibers and making it difficult to meet the performance requirements for reuse. Chemical recycling methods, including pyrolysis and solvent decomposition, offer better separation results, but may use harmful chemicals and consume more energy, posing potential negative environmental impacts. In particular, pyrolysis recycling forms a pyrolytic carbon layer on the carbon fiber surface during resin removal, which reduces the bonding strength between the carbon fibers and the new resin matrix, affecting the final application performance of the recycled material. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this patent proposes a method for synthesizing recycled carbon fiber composites through combustion. This method aims to simultaneously achieve the recycling of CFRPs and graphene modification of the carbon fiber surface through a one-step reaction. This modification not only enhances the surface activity of the recycled carbon fibers, strengthens their interfacial bonding with materials such as resin matrices, metal matrices, ceramic matrices, and carbon matrices, and improves the mechanical properties of the composite material, but also increases the electrical and thermal conductivity of the composite material and reduces its coefficient of thermal expansion. Furthermore, the recycling process of this invention utilizes reactive chemical energy, eliminating the need for large amounts of energy for heating. This invention effectively reduces the generation and use of harmful chemicals, is energy-saving and environmentally friendly, and has low costs. This method can expand the application range of recycled carbon fibers, enhance their market competitiveness, and contribute to the circular economy and sustainable development.

[0009] This invention addresses the problems of high recycling costs, significant environmental risks, and low recycling efficiency associated with traditional recycling methods such as mechanical, chemical, and pyrolysis methods. It proposes a solution for rapidly and efficiently recycling carbon fiber composite materials based on combustion synthesis, while simultaneously modifying the carbon fiber surface.

[0010] To address the aforementioned technical problems, the present invention adopts the following technical solution:

[0011] The purpose of this invention is to provide a method for synthesizing recycled carbon fiber reinforced resin matrix composites through combustion, comprising the following steps:

[0012] The dimensions of the carbon fiber reinforced resin matrix composite material to be recycled are controlled to be ≤500mm in thickness and ≤5000mm in length and width.

[0013] The carbon source is added in a ratio of 1:(0.2-200) of carbon fiber in the carbon fiber composite material to graphene expected to be generated by combustion synthesis reaction, and the reducing agent is added in a ratio of 1:(1.5-3) of oxygen-containing organic matter in the carbon fiber composite material to total oxygen atoms in the carbon source and reducing agent.

[0014] The combustion synthesis reaction is then carried out, and the metal oxides obtained from the reaction are removed with hydrochloric acid for purification. The carbon fibers and graphene powder with covalently linked graphene on the surface obtained from the combustion synthesis are then screened out, thus completing the recycling.

[0015] Further specifying, the combustion synthesis reaction is either a high-pressure combustion synthesis reaction or an atmospheric-pressure combustion synthesis reaction.

[0016] To further specify, the high-pressure combustion synthesis reaction can be carried out according to the following steps:

[0017] Step a: Place the mixed powder in a general-purpose combustion synthesis reaction device with a pressure resistance of 1MPa-30MPa, and then add an igniter above the mixed powder; wherein, the igniter is Fe3O4+Mg or MnO2+Mg from the magnesian reaction or Fe3O4+Al or Cr2O3+Al from the aluminothermic reaction.

[0018] Step b: Evacuate the inside of the combustion synthesis reactor, then introduce carbon dioxide at 0.1-20 MPa into the combustion synthesis reactor, and then seal the reactor.

[0019] Step c: Ignite the igniter in step a using localized electric ignition or localized high-frequency induction heating to cause the mixed powder to undergo a combustion reaction; wherein, localized electric ignition is achieved by passing a 10A to 30A DC current through a spiral tungsten wire coil to heat the localized reactants and initiate a combustion synthesis reaction; localized high-frequency induction heating is achieved by using a high-frequency induction coil to heat the localized reactants and initiate a combustion synthesis reaction.

[0020] To further specify, the atmospheric pressure combustion synthesis reaction can be carried out according to the following steps:

[0021] Step a: Place the mixed powder in a crucible and add an ignition agent above the mixed powder; wherein, the ignition agent is Fe3O4+Mg or MnO2+Mg from the magnesian reaction or Fe3O4+Al or Cr2O3+Al from the aluminothermic reaction;

[0022] Step b: Then place the crucible at the bottom of the combustion synthesis container; wherein the volume of the combustion synthesis container is 5 to 500 times the volume of the crucible, and the height of the container is 2 to 50 times the height of the crucible;

[0023] Step c: Introduce carbon dioxide or argon into the bottom of the combustion synthesis container to fill the crucible and the inside of the combustion synthesis container with gas;

[0024] Step d: Ignite the igniter using localized electric ignition or localized high-frequency induction heating to initiate a combustion reaction in the mixed powder. During the reaction, carbon dioxide (or argon) is continuously introduced at a rate of 1–1000 L / min. Localized electric ignition involves passing a 10A–30A DC current through a spiral tungsten wire coil to heat the localized reactants and initiate a combustion synthesis reaction. Localized high-frequency induction heating uses a high-frequency induction coil to heat the localized reactants and initiate a combustion synthesis reaction.

[0025] After combustion, the resistance wire can be removed with a magnet. Add 20% hydrochloric acid to a beaker containing the reaction product while stirring to obtain the acid-leached reaction product. Seal the beaker, sonicate for 3 hours, stir magnetically for 12 hours, filter, and dry at 120℃ for 12 hours.

[0026] Further specifying, the resin in the carbon fiber reinforced resin matrix composite to be recycled can be a thermosetting resin or a thermoplastic resin.

[0027] Further specifying, the reducing agent can be magnesium powder or aluminum powder or a mixture of the two.

[0028] Further specified, the magnesium powder has a purity of 95% to 99.999% and an average particle diameter of 0.03 mm to 5 mm;

[0029] Further specified, the purity of the aluminum powder is 90% to 99.9%, and the average particle diameter is 0.01 mm to 5.2 mm.

[0030] Further specifying, the carbon source is one or a mixture of several of the following in any proportion: carbon dioxide, carbonate, oxalate, and organic glycogen.

[0031] Furthermore, the carbonate can be any mixture of one or more of magnesium carbonate, calcium carbonate, and strontium carbonate in any proportion.

[0032] Furthermore, the oxalate is a mixture of one or more of magnesium oxalate, calcium oxalate, and strontium oxalate in any proportion.

[0033] To be further specified, organic glycogen is a mixture of one or more of monosaccharides, disaccharides, and polysaccharides in any proportion.

[0034] Furthermore, the combustion atmosphere can be one or a mixture of several of the following: vacuum, nitrogen, argon, and hydrogen-argon mixture.

[0035] Further specifying, dispersion can be carried out by one or any combination of several of the following methods: ball milling, homogeneous dispersion, mechanical stirring, ultrasonic stirring, and mechanical grinding.

[0036] This invention relates to a combustion synthesis method for recovering carbon fiber reinforced resin matrix composites. This method is simple to operate, has a few steps, requires no solvents, and consumes little energy. Using the method involved in this invention, surface modification of carbon fibers and the preparation of high-value-added graphene can be achieved simultaneously during the recovery process. This is because the ultra-high temperature reaction, reducing atmosphere, and ultra-rapid heating and cooling non-equilibrium process of combustion synthesis allow the resin in the composite material to rapidly decompose, leading to the rearrangement of free radicals or active carbon atoms, forming wrinkled graphene. This transforms the carbon fiber reinforced resin matrix composite into carbon fibers with covalently linked graphene on the surface. Simultaneously, the reaction between the reducing agent and the carbon source in the combustion synthesis reaction generates wrinkled, high-value-added graphene.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] This invention provides a simple and rapid method for high-value recycling of carbon fiber reinforced resin matrix composites. Compared with existing methods for recycling carbon fiber reinforced resin matrix composites, the recycling method proposed in this invention is simple and highly operable.

[0039] This invention relates to carbon fibers based on surface covalently linked graphene synthesized and recovered through combustion. Due to the three-dimensional wrinkles of graphene and the high covalent bonding strength between graphene and carbon fiber structures, it is highly beneficial for providing various mechanical, thermal, and electrical properties of carbon fiber composites. It can be used to produce resin-based composites, metal-based composites, ceramic-based composites, and carbon-based composites, and has broad application prospects.

[0040] To further understand the features and technical content of this invention, please refer to the following detailed description and accompanying drawings. However, the accompanying drawings are for reference and illustration only and are not intended to limit the invention. Attached Figure Description

[0041] Figure 1 shows the morphology of graphene covalently linked carbon fibers. (ac) shows a typical morphology of graphene covalently linked carbon fibers. (df) is a magnified view of a typical morphology in (ac).

[0042] Figure 2 shows the Raman spectra of graphene sites on the fiber surface. S3-S6 correspond to the names of carbon fibers prepared from carbon fiber reinforced resin matrix composites recovered under the conditions of 0.049 parts, 0.098 parts, 0.147 parts, and 0.147 parts of reducing agent used to recover 1 part of CFRP, respectively.

[0043] Figure 3 shows the tensile strength stress-strain curve. SRCF is a pyrolytic carbon fiber reinforced resin matrix composite, F1-F4 are resin matrix composites reinforced by carbon fiber samples S3-S6, respectively, and G is a graphene-reinforced resin matrix composite.

[0044] Figure 4 shows the flexural strength stress-strain curve. SRCF is a pyrolytic carbon fiber reinforced resin matrix composite, F1-F4 are resin matrix composites reinforced by carbon fiber samples S3-S6, respectively, and G is a graphene-reinforced resin matrix composite. Detailed Implementation

[0045] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, while not limiting the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0046] Example 1: The surface modification method for carbon fibers recovered through combustion synthesis in this example, which exhibits uniform surface modification morphology, good graphene grafting morphology, and is suitable for resin-based composites, was carried out according to the following steps, wherein the recovered CFRPs consisted of 60% CF and 40% E51 epoxy resin:

[0047] Weigh 1 part CFRP, 2.4 parts magnesium powder, and 5 parts calcium carbonate, and mix them thoroughly. Introduce CO2 into the combustion synthesis reactor, keeping the inlet valve open. Heat the resistance wire with a DC power supply to ignite the reactants, then disconnect the power to begin the combustion synthesis reaction. After the reaction is complete, continue for 5 minutes, then close the inlet valve. Collect the combustion synthesis product after cooling for 30 minutes.

[0048] After removing the resistance wire, 20% hydrochloric acid was added to a beaker containing the reaction product while stirring to obtain the acid-leached reaction product. The beaker was sealed, sonicated for 3 hours, magnetically stirred for 12 hours, filtered, and dried at 120°C for 12 hours to obtain a composite powder containing graphene and surface covalently linked graphene carbon fibers.

[0049] The composite powder was sieved using a 150-mesh sieve to separate the graphene-modified carbon fibers and graphene powder, resulting in carbon fibers with covalently bonded graphene on the surface and combustion-synthesized graphene powder.

[0050] Example 2: In this example, the carbon fibers with surface covalently linked graphene recovered through a combustion-based synthesis method can be used to prepare carbon-based, resin-based, metal-based (copper, aluminum, magnesium-based), and ceramic-based composite materials. The following example demonstrates the preparation of resin-based composite materials, outlining the specific steps:

[0051] According to the formula shown in Table 1, weigh out 2 grams of S3-S6 graphene covalently linked carbon fiber, 2 grams of pyrolytic carbon fiber prepared by ordinary pyrolysis method recovered CFRP, 2 grams of graphene powder, 50 grams of E51 epoxy resin and 50 grams of 593 curing agent.

[0052] Table 1 Raw Material Proportioning Table

[0053]

[0054]

[0055] After weighing, the six groups of ingredients were mixed and stirred evenly at room temperature according to the component ratios described in Table 1. Mechanical test samples were prepared using tensile specimen forming molds and placed in a constant temperature oven with the temperature set at 25°C and the time set at 24h.

[0056] The final prepared carbon fiber reinforced resin matrix composite (F1 composite) with surface covalently linked graphene recovered by combustion synthesis method has a maximum flexural strength of 66 MPa and a tensile strength of 40 MPa, which exceeds that of carbon fiber reinforced resin matrix composite (SRCF) recovered by pyrolysis and pure graphene reinforced resin matrix composite (G).

[0057] Figure 1 shows that after combustion synthesis, carbon fiber reinforced epoxy composite material was successfully transformed into carbon fibers with surface covalently linked graphene. Among them, some carbon fibers became monofilaments (a, b, d, e), while some carbon fibers remained in a bundled state (c, f).

[0058] Figure 2 shows that after combustion synthesis, the Raman spectra of carbon fibers recovered under different reducing agent contents all show obvious D peaks, G peaks and 2D peaks, which are typical Raman spectral characteristics of graphene. This indicates that carbon fiber reinforced epoxy composites can be transformed into carbon fibers with surface covalently linked graphene under different reducing agent contents.

[0059] Figure 3 shows that carbon fibers with surface covalently linked graphene recovered through combustion synthesis can exhibit better tensile strength enhancement. Furthermore, some of the prepared composite materials (such as F1 and F2) exhibit greater tensile strength than pyrolysis-recovered carbon fiber reinforced epoxy composites and graphene-reinforced epoxy composites. This indicates that carbon fibers with surface covalently linked graphene recovered through combustion synthesis can be reused as high-performance reinforcing materials, significantly improving the tensile properties of the new matrix.

[0060] Figure 4 shows that carbon fibers with surface covalently linked graphene, which are synthesized and recovered through combustion, can exhibit a better effect on enhancing bending performance. Moreover, the prepared composite materials (F1-F4) all show greater bending strength than the pyrolysis-recovered carbon fiber reinforced epoxy composite material and the graphene-reinforced epoxy composite material. This indicates that carbon fibers with surface covalently linked graphene, which are synthesized and recovered through combustion, can be reused as high-performance reinforcing materials, significantly improving the bending performance of the new matrix.

[0061] The specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for synthesizing recycled carbon fiber reinforced resin matrix composites based on combustion, characterized in that, Includes the following steps: The dimensions of the carbon fiber reinforced resin matrix composite to be recycled are controlled to be ≤500mm in thickness and ≤5000mm in length and width. A carbon source is added at a mass ratio of 1:(0.2-200) of carbon fiber in the carbon fiber composite to the graphene expected to be generated by the combustion synthesis reaction. A reducing agent is added at a mass ratio of 1:(1.5-3) of oxygen-containing organic matter in the carbon fiber composite to the total oxygen atoms in the carbon source and the reducing agent. The combustion synthesis reaction is either a high-pressure combustion synthesis reaction or an atmospheric-pressure combustion synthesis reaction. The reducing agent is magnesium powder or aluminum powder. The carbon source is one or a mixture of several of the following: carbon dioxide, carbonate, oxalate, and organic glycogen in any proportion. The combustion synthesis reaction is then carried out, and the resulting metal oxides are removed with hydrochloric acid for purification. The carbon fibers and graphene powder with surface covalently linked graphene obtained through combustion synthesis are then screened out, thus completing the recycling process.

2. The method according to claim 1, characterized in that, The resin is either a thermosetting resin or a thermoplastic resin.

3. The method according to claim 1, characterized in that, The purity of the magnesium powder is 95% to 99.999%, and the average particle diameter is 0.03 mm to 5 mm.

4. The method according to claim 1, characterized in that, The aluminum powder has a purity of 90% to 99.9% and an average particle diameter of 0.01 mm to 5.2 mm.

5. The method according to claim 1, characterized in that, Carbonates are mixtures of one or more of magnesium carbonate, calcium carbonate, and strontium carbonate in any proportion.

6. The method according to claim 1, characterized in that, The combustion atmosphere is one of the following: vacuum, nitrogen, argon, or a mixture of hydrogen and argon.

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