Regeneration and recovery method of carbon fiber composite material

Abstract

The invention discloses a carbon fiber composite material regeneration and recovery method, which belongs to the technical field of composite material recovery, and comprises the following steps: pretreating a carbon fiber composite material in a pretreatment mixed solution composed of glacial acetic acid and a hydrogen peroxide aqueous solution to swell resin and preliminarily degrade the resin; a salt-acid composite catalyst is introduced into the pretreatment mixed solution, a main treatment mixed solution is constructed, and the pretreated material is subjected to main treatment so as to thoroughly decompose the resin. Through the synergistic effect of glacial acetic acid and hydrogen peroxide, peracetic acid and hydroxyl radicals with strong oxidizing property are generated under mild conditions, and efficient degradation of the resin is realized; through a two-step method and a composite catalyst system, the oxidation reaction process is regulated and controlled, and the mechanical property of the carbon fiber material is effectively protected while the resin is efficiently degraded; the glacial acetic acid in the waste liquid is recovered through atmospheric distillation, a reagent use-recovery-reutilization green closed loop is formed, the cost and the environmental burden are remarkably reduced, and the application range of the method is expanded.

Description

Technical Field

[0001] This invention relates to the field of composite material recycling technology, and in particular to a method for recycling carbon fiber composite materials. Background Technology

[0002] Carbon fiber reinforced plastics (CFRP), an advanced composite material using carbon fiber as reinforcement and thermosetting epoxy resin as the matrix, boasts advantages such as lightweight, high strength, high modulus, and corrosion resistance, and has been widely used in high-end fields such as aerospace, automotive manufacturing, and wind power equipment. However, once the thermosetting matrix of CFRP solidifies, it forms a stable three-dimensional cross-linked network, making secondary processing through melting or dissolution impossible. This results in the difficulty of efficiently recycling discarded CFRP products, such as aircraft parts and wind turbine blade waste, causing not only a serious waste of carbon fiber resources but also significant environmental pressure due to landfill or incineration. Therefore, developing recycling technologies that can efficiently separate carbon fiber from the resin matrix without damaging the properties of the carbon fiber has become crucial for promoting the sustainable development of the CFRP industry.

[0003] Currently, CFRP recycling technologies mainly include mechanical crushing, high-temperature pyrolysis, supercritical fluid decomposition, and chemical oxidation decomposition. While mechanical crushing is simple to operate, it can only break CFRP into low-value fillers and cannot effectively separate carbon fibers from resin. It also damages the original length and mechanical properties of carbon fibers. High-temperature pyrolysis methods, such as fluidized bed pyrolysis and microwave pyrolysis, require inert or oxygen atmospheres at 400-800℃. Although they can recover carbon fibers, the high temperature easily leads to oxidation and etching on the carbon fiber surface, resulting in a tensile strength retention rate that is usually less than 90%. Moreover, the energy consumption is as high as 37-258 MJ / kg, and it is accompanied by the emission of toxic gases. Supercritical fluid methods, such as supercritical water and ethanol, require operation at high temperatures of 300-400℃ and high pressures of 100-220 atm. The equipment investment is large, the scale is difficult to achieve, and the solvent recovery cost is high. Existing chemical oxidation methods, such as those using nitric acid, sodium hypochlorite, and m-chloroperoxybenzoic acid, can decompose resin at medium and low temperatures of 40-100℃. However, some reagents, such as nitric acid, are highly corrosive and easily generate secondary pollution. In addition, the reaction cycle is long, requiring 6-24 hours, making it difficult to balance efficiency and environmental protection.

[0004] Therefore, there is an urgent need for a technology that can rapidly decompose resin under relatively mild conditions and is environmentally friendly, so as to achieve efficient, safe and convenient recycling of fibers in carbon fiber composites. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a method for the recycling of carbon fiber composite materials.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for recycling carbon fiber composite materials, comprising the following steps:

[0007] S1. Mix glacial acetic acid and hydrogen peroxide aqueous solution in a certain proportion and stir evenly at room temperature to prepare a pretreatment mixed solution;

[0008] S2. Immerse the carbon fiber composite material in the pretreatment mixture, heat it for pretreatment, and then wash and dry it.

[0009] S3. Add salt and acid in a mass ratio of 1-3:1 to the pretreatment mixed solution in step S1, stir and mix at room temperature, and then heat and catalyze to prepare the main treatment mixed solution.

[0010] S4. The pretreated and dried carbon fiber composite material is fully immersed in the main treatment mixed solution, heated for main treatment, washed and dried to obtain the recycled carbon fiber material.

[0011] S5. The remaining waste liquid after the pretreatment and main treatment of carbon fiber composite materials is heated, evaporated, condensed, and then glacial acetic acid is recovered.

[0012] In a preferred embodiment of the present invention, in step S1, the mass concentration of hydrogen peroxide is 25-35 wt%.

[0013] In a preferred embodiment of the present invention, in step S1, the pretreated mixed solution contains 80-95% glacial acetic acid and 5%-20% hydrogen peroxide aqueous solution by volume.

[0014] In a preferred embodiment of the present invention, in step S2, the mass ratio of carbon fiber composite material to pretreatment mixed solution is 1:20-50, the heating temperature of the pretreatment is 70-90℃, and the treatment time is 3-5h.

[0015] In a preferred embodiment of the present invention, in step S3, the salt is selected from one or more of potassium chloride, sodium chloride, potassium nitrate, sodium nitrate, ferrous chloride, and tetrabutylammonium bromide.

[0016] In a preferred embodiment of the present invention, in step S3, the acid is selected from one or more of citric acid, ammonium chloride, and sodium bisulfate.

[0017] In a preferred embodiment of the present invention, in step S3, the total mass of salt and acid is 2-4% of the mass of the pretreated mixed solution.

[0018] In a preferred embodiment of the present invention, step S3, the heating catalytic process includes:

[0019] After adding salt and acid to the pretreated mixed solution, heat the mixed solution to 60-70℃ and keep it warm while stirring for 5-10 minutes.

[0020] In a preferred embodiment of the present invention, in step S4, the mass ratio of the pretreated and dried carbon fiber composite material to the main treatment mixed solution is 1:40-80, the heating temperature of the heat treatment is 90-100℃, and the treatment time is 1-3h.

[0021] In a preferred embodiment of the present invention, step S5, the recycling process specifically includes:

[0022] Under normal pressure, the residual waste liquid after the pretreatment and main treatment of carbon fiber composite materials is heated to 120-125℃ in an oil bath. The evaporated glacial acetic acid vapor is cooled and liquefied by a condenser and then collected, thus completing the recovery of glacial acetic acid.

[0023] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0024] (1) The present invention adopts a two-step method of pretreatment-main treatment to treat carbon fiber composite materials. In the pretreatment stage, epoxy resin is swollen and initially degraded by a mixed solution of glacial acetic acid and hydrogen peroxide, thereby reducing the energy barrier of the main reaction. In the main treatment stage, salt and acid catalysts are introduced to promote the generation of peracetic acid and the yield of hydroxyl radicals by increasing ionic strength and adjusting pH value, thereby achieving efficient degradation of epoxy resin under low temperature and normal pressure conditions.

[0025] (2) This invention introduces a composite catalyst system composed of salt and acid. The acid can lower the pH value of the system, inhibit the hydrolysis of peracetic acid, enhance the electrophilicity of hydrogen peroxide, and increase the steady-state concentration of peracetic acid. The salt can increase the ionic strength of the solution, improve the wetting and penetration of the reaction solution on the carbon fiber composite material, and stabilize the reaction intermediates and reduce the ineffective decomposition of hydrogen peroxide. Combined with the two-step buffer reaction process, the oxidation reaction is made more gentle and uniform, preferentially breaking the CN, CO and other bonds of epoxy resin, avoiding the excessive oxidation and etching of carbon fiber caused by the difficulty in controlling the reaction in the prior art, effectively protecting the original mechanical properties of carbon fiber, facilitating its subsequent reuse as a reinforcing material, and significantly improving the added value of recycled products.

[0026] (3) This invention achieves efficient recovery of glacial acetic acid through atmospheric distillation, eliminating the need for complex purification processes and enabling separation via condensation. The recovered purity meets reuse requirements, and there is no emission of toxic or harmful substances. Compared to existing technologies where glacial acetic acid is used only once and waste liquid treatment costs are high, or where solvent recovery requires high-pressure distillation and multi-stage purification, resulting in complex operations and high energy consumption, this invention constructs a resource recycling model of reagent use-recovery-reuse. This not only reduces the economic cost of the recycling process but also solves the pain point of traditional technologies where environmental protection and economic efficiency are difficult to balance, thus contributing to the green and sustainable development of the carbon fiber recycling industry. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a SEM image of the internal carbon fibers observed after the original CFRP was mechanically crushed;

[0029] Figure 2 This is a SEM image of the original CFRP after preprocessing in Example 1;

[0030] Figure 3 This is a SEM image of carbon fiber after the main treatment of CFRP pretreated in Example 1. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0033] Unless otherwise specified in the following examples, all raw materials are commercially available or prepared using conventional methods in the art.

[0034] A method for recycling carbon fiber composite materials includes the following steps:

[0035] S1. Mix glacial acetic acid and hydrogen peroxide aqueous solution in a certain proportion and stir evenly at room temperature to prepare a pretreatment mixed solution;

[0036] S2. Immerse the carbon fiber composite material in the pretreatment mixture, heat it for pretreatment, and then wash and dry it.

[0037] S3. Add salt and acid in a mass ratio of 1-3:1 to the pretreatment mixed solution in step S1, stir and mix at room temperature, and then heat and catalyze to prepare the main treatment mixed solution.

[0038] S4. The pretreated and dried carbon fiber composite material is fully immersed in the main treatment mixed solution, heated for main treatment, washed and dried to obtain the recycled carbon fiber material.

[0039] S5. The remaining waste liquid after the pretreatment and main treatment of carbon fiber composite materials is heated, evaporated, condensed, and then glacial acetic acid is recovered.

[0040] Each step will be explained in detail below.

[0041] Specifically, step S1 involves the preparation of the pretreatment mixed solution. Glacial acetic acid is mixed with a 25-35% (w / w) aqueous solution of hydrogen peroxide, and the mixture is mechanically stirred at 200-400 rpm for 10-20 minutes at room temperature to obtain a homogeneous and stable pretreatment mixed solution, which provides a dual-effect basis of oxidation and swelling for the preliminary treatment of carbon fiber composite materials.

[0042] In the pretreatment mixed solution, the volume ratio of glacial acetic acid is 80-95%, and the volume ratio of hydrogen peroxide aqueous solution is 5%-20%. This ratio range can ensure the swelling and mediating function of glacial acetic acid, and also provide sufficient raw materials for the generation of peracetic acid and hydroxyl radicals.

[0043] Furthermore, glacial acetic acid, as a reaction medium and swelling agent, not only provides a stable weakly acidic environment for the subsequent oxidation reaction, but its polar characteristics also allow it to efficiently penetrate into the dense three-dimensional cross-linked network of thermosetting epoxy resin. The carboxyl groups interact with the ether bonds, hydroxyl groups and other groups in the epoxy resin through hydrogen bonding, which weakens the molecular forces between the networks and causes the resin to swell. At the same time, the weak acidity of glacial acetic acid can reduce the corrosivity of the system and reduce damage to the carbon fiber surface.

[0044] Furthermore, hydrogen peroxide, as a green oxidant, undergoes a reversible acyl transfer reaction when mixed with glacial acetic acid. A dynamic equilibrium is established during stirring at room temperature, generating highly oxidizing peracetic acid without additional preparation. Simultaneously, hydrogen peroxide undergoes homolytic cleavage in the weakly acidic environment of glacial acetic acid, generating hydroxyl radicals (·OH). Glacial acetic acid, through intermolecular hydrogen bonds, stably binds to hydrogen peroxide molecules, inhibiting the non-selective decomposition of hydrogen peroxide and reducing the ineffective loss of active species. Furthermore, by regulating the pH of the system, it ensures the stable existence of hydroxyl radicals. Peracetic acid and hydroxyl radicals form a synergistic and complementary oxidation system. Peracetic acid specifically attacks key chemical bonds such as CN and CO bonds in the resin crosslinking structure, while hydroxyl radicals efficiently break the molecular chains after initial decomposition, providing sufficient and stable oxidation capacity for resin swelling and initial degradation in subsequent pretreatment stages.

[0045] Furthermore, step S2 is the pretreatment stage of carbon fiber composite material. The core purpose is to weaken the stability of the three-dimensional cross-linked network of epoxy resin through swelling and preliminary degradation, reduce the reaction energy barrier of subsequent main treatment, and create favorable conditions for deep degradation.

[0046] Specifically, the clean and dry carbon fiber composite material is completely immersed in the pretreatment mixed solution prepared in step S1. The carbon fiber composite material is a carbon fiber composite material made of thermosetting epoxy resin and carbon fiber, such as scrap wind turbine blade fragments, aerospace scraps, and experimental waste samples. The resin accounts for 10-90 wt% of the composite material, and the mass ratio of the carbon fiber composite material to the pretreatment mixed solution is 1:20-50. The mixture is heated to 70-90℃ and treated for 3-5 hours. After the reaction is completed, the mixture is washed with water and dried.

[0047] Furthermore, when the carbon fiber composite material is immersed in the pretreatment mixed solution, glacial acetic acid rapidly penetrates into the three-dimensional network of the epoxy resin matrix, causing the resin molecular chains to swell and making the dense resin structure loose, providing channels for the diffusion of active species. Peracetic acid and hydroxyl radicals contact the resin molecules through the channels formed by swelling, selectively attacking the stable CN and CO bonds, and decomposing the macromolecular resin into small molecular fragments through oxidative cleavage of crosslinking bonds, thus achieving the initial degradation and partial stripping of the resin.

[0048] In the pretreatment stage, heating can accelerate the penetration of glacial acetic acid and the swelling of resin, enhance the oxidative activity of hydrogen peroxide, and promote the generation of hydroxyl radicals and the efficiency of cross-linking bond breaking. The water washing step can remove unreacted reagents and some degradation products remaining on the material surface, further increase the fiber gaps, and clear obstacles for the penetration and reaction of the subsequent main treatment solution.

[0049] Furthermore, step S3 involves the preparation of the main treatment mixed solution, which aims to introduce a salt-acid composite catalyst to construct a highly efficient catalytic-oxidation system, enhance the degradation capacity of the reaction system, and ensure the complete decomposition of the resin.

[0050] Specifically, based on the pretreatment mixed solution prepared in step S1, a composite catalyst composed of salt and acid is added. The salt is selected from one or more of potassium chloride, sodium chloride, potassium nitrate, sodium nitrate, ferrous chloride, and tetrabutylammonium bromide, and the acid is selected from one or more of citric acid, ammonium chloride, and sodium bisulfate. The mass ratio of salt to acid is 1-3:1, and the total mass of the two is 2-4% of the mass of the pretreatment mixed solution. The mixture is stirred at room temperature for 15-25 minutes until the solid is completely dissolved. Then, the mixed solution is heated to 60-70°C and stirred for 5-10 minutes to complete the catalytic activation, thus obtaining the main treatment mixed solution.

[0051] Furthermore, the acid moderately lowers the pH of the system, inhibiting the hydrolysis of peracetic acid. Simultaneously, it enhances the electrophilicity of hydrogen peroxide through protonation, promoting its acyl transfer reaction with glacial acetic acid and increasing the steady-state concentration of peracetic acid. The heating catalytic step further activates the catalyst, accelerating the generation of hydroxyl radicals and ensuring the efficient reaction of the subsequent main treatment. Moreover, the weakly acidic environment weakens the polarity of the crosslinking bonds in the epoxy and phenolic resins, aiding in the swelling effect of glacial acetic acid.

[0052] Furthermore, as a neutral strong electrolyte, the addition of salt can increase the ionic strength of the solution, change the interfacial tension between the solution and the carbon fiber composite surface, enhance the wettability of the reaction solution on the carbon fiber composite surface, and reduce local reaction dead zones. Simultaneously, salt ions stabilize hydrogen peroxide molecules by forming hydrogen bonds, reducing their non-selective decomposition, and also weaken the bond energy of the O2O bonds in hydrogen peroxide, lowering its decomposition activation energy and promoting the generation rate of hydroxyl radicals. Ferrous chloride, as a Fenton reaction catalyst, can significantly catalyze the decomposition of hydrogen peroxide to generate highly active hydroxyl radicals, significantly improving the degradation efficiency of the epoxy resin crosslinking network.

[0053] Furthermore, step S4 is the main treatment stage for carbon fiber composite materials, which aims to completely degrade residual epoxy resin, achieve complete separation of carbon fiber from the resin matrix, and at the same time retain the mechanical properties of carbon fiber to the greatest extent.

[0054] Specifically, the pretreated and dried carbon fiber composite material is fully immersed in the main treatment mixed solution prepared in step S3, and the mass ratio of the material to the main treatment mixed solution is controlled at 1:40-80. The mixture is heated to 90-100℃ and maintained for 1-3 hours. After the reaction is completed, the solid product is separated by hot filtration. The solid product is repeatedly washed with water at 50-70℃ until the filtrate is neutral. The solid product is then placed in a forced-air drying oven at 70-90℃ and dried for 3-5 hours to obtain the recovered carbon fiber material.

[0055] Compared to the pretreatment stage, a higher bath ratio ensures sufficient contact between the material and the main treatment solution, avoiding incomplete degradation due to insufficient reagents in certain areas; the heating temperature of 90-100℃ further enhances the catalyst activity and free radical generation rate, strengthens the synergistic effect of peracetic acid and hydroxyl radicals, efficiently breaks residual cross-linking bonds, and achieves complete degradation of the resin; the cleaning step can efficiently remove degradation products and catalyst residues adhering to the carbon fiber surface, and after drying, a clean and stable carbon fiber material is obtained.

[0056] Furthermore, the synergistic effect of the composite catalyst makes the oxidation reaction more gentle and uniform, preferentially attacking the chemical bonds of the resin while avoiding excessive oxidation and etching of the carbon fiber body, effectively protecting the original mechanical properties of the carbon fiber.

[0057] Furthermore, step S5 involves the recycling and reuse of glacial acetic acid, with the aim of constructing a green closed loop of reagent use-recycling-reuse, reducing process costs and environmental burden, and achieving efficient resource utilization.

[0058] Specifically, the remaining waste liquid after the pretreatment and main treatment of carbon fiber composite materials is combined and then subjected to atmospheric distillation. The waste liquid is heated to 120-125℃ in an oil bath, and the evaporated glacial acetic acid vapor is collected after being cooled and liquefied by a condenser, thus completing the recovery of glacial acetic acid.

[0059] The atmospheric pressure heating method eliminates the need for special high-pressure equipment, resulting in low equipment investment costs and safe and simple operation. The temperature of 120-125℃ ensures complete evaporation of glacial acetic acid and allows for precise separation from degradation products and catalyst residues in the waste liquid. The recovered glacial acetic acid meets the purity requirements for reuse and can be directly used in the preparation of subsequent pretreatment and main treatment mixtures. This step not only improves reagent utilization, reduces chemical reagent consumption, and lowers production costs, but also significantly reduces waste liquid discharge, alleviating environmental pressure. Furthermore, the remaining resin degradation products after distillation can be centrally processed by specialized institutions, achieving efficient resource utilization across the entire industrial chain, from reagent recycling to product recovery.

[0060] Example 1:

[0061] Step S1: Mix 900 mL of glacial acetic acid with 100 mL of 30 wt% hydrogen peroxide aqueous solution and mechanically stir at 300 rpm for 15 min at room temperature to obtain 1 L of pretreated mixed solution, wherein the volume percentage of glacial acetic acid is 90% and the volume percentage of hydrogen peroxide aqueous solution is 10%.

[0062] Step S2: Weigh 20.00g of epoxy resin-based carbon fiber composite (CFRP) block sample and immerse it completely in 600g of pretreatment mixed solution. The mass ratio of carbon fiber composite to pretreatment mixed solution is 1:30. Reflux the sample in an 80℃ constant temperature water bath for 4h. After the reaction is complete, remove the pretreated CFRP sample, wash it with water until the filtrate is neutral, and air dry it for later use.

[0063] Step S3: Add 6.00g of potassium chloride and 3.00g of citric acid to 300g of the pretreatment mixed solution from step S1, stir at room temperature for 20min until completely dissolved, then heat to 65℃ and stir for 8min to obtain the main treatment mixed solution. The total mass of potassium chloride and citric acid is 3% of the mass of the pretreatment mixed solution, and the mass ratio of potassium chloride to citric acid is 2:1.

[0064] Step S4: Weigh 5.00g of the CFRP sample pretreated in step S2 and immerse it completely in the main treatment mixed solution. The mass ratio of the sample to the main treatment mixed solution is 1:60. The sample is refluxed at 95°C for 2 hours. After the reaction is completed, the solid product is separated by hot filtration. The solid product is washed with water at 60°C until the filtrate is neutral. The solid product is dried at 80°C for 4 hours to obtain the recovered carbon fiber material.

[0065] Example 2:

[0066] Compared with Example 1, in this embodiment, 6.00g of sodium chloride and 3.00g of citric acid are added to 300g of the pretreatment mixed solution from Step S1 in step S3, and the remaining steps are the same.

[0067] Example 3:

[0068] Compared with Example 1, in this embodiment, 6.00g of ferrous chloride and 3.00g of citric acid are added to 300g of the pretreatment mixed solution from Step S1 in step S3, and the remaining steps are the same.

[0069] Example 4:

[0070] Compared with Example 1, in this embodiment, 6.00g of tetrabutylammonium bromide and 3.00g of citric acid are added to 300g of the pretreatment mixed solution from Step S1 in step S3, and the remaining steps are the same.

[0071] Example 5:

[0072] Compared with Example 1, in this embodiment, 6.00g of potassium chloride and 3.00g of sodium bisulfate are added to 300g of the pretreatment mixed solution from Step S1 in step S3, and the remaining steps are the same.

[0073] Example 6:

[0074] Compared with Example 1, in this embodiment, 6.00g of potassium chloride and 3.00g of ammonium chloride are added to 300g of the pretreatment mixed solution from Step S1 in step S3, and the remaining steps are the same.

[0075] Example 7:

[0076] Compared with Example 1, in this embodiment, in step S3, 4.50g of potassium chloride and 4.50g of citric acid are added to 300g of the pretreatment mixed solution from step S1, that is, the mass ratio of potassium chloride to citric acid is 1:1, and the remaining steps are the same.

[0077] Example 8:

[0078] Compared with Example 1, in this embodiment, in step S3, 6.75g of potassium chloride and 2.25g of citric acid are added to 300g of the pretreatment mixed solution from step S1, that is, the mass ratio of potassium chloride to citric acid is 3:1, and the remaining steps are the same.

[0079] Example 9:

[0080] Compared with Example 1, in this embodiment, in step S3, 4.00g of potassium chloride and 2.00g of citric acid are added to 300g of the pretreatment mixed solution from step S1, that is, the total mass of potassium chloride and citric acid is 2% of the mass of the pretreatment mixed solution, and the remaining steps are the same.

[0081] Example 10:

[0082] Compared with Example 1, in this embodiment, in step S3, 8.00g of potassium chloride and 4.00g of citric acid are placed in 300g of the pretreatment mixed solution from step S1, that is, the total mass of potassium chloride and citric acid is 4% of the mass of the pretreatment mixed solution, and the remaining steps are the same.

[0083] Example 11:

[0084] The experiment was conducted according to the steps of Example 1, and all remaining waste liquid from steps S2 and S4 was collected. The waste liquid was distilled and glacial acetic acid was recovered under normal pressure and 120°C oil bath. All steps of Example 1 were repeated using the glacial acetic acid recovered in this example.

[0085] Comparative Example 1:

[0086] The difference between Comparative Example 1 and Example 1 is that water was used instead of glacial acetic acid in the preparation of the pretreatment mixed solution. Specifically, the steps include:

[0087] Step S1: Mix 900 mL of water with 100 mL of 30 wt% hydrogen peroxide aqueous solution and mechanically stir at 300 rpm for 15 min at room temperature to obtain 1 L of pretreated mixed solution, wherein the volume percentage of water is 90% and the volume percentage of hydrogen peroxide aqueous solution is 10%.

[0088] Step S2: Weigh 20.00g of epoxy resin-based carbon fiber composite (CFRP) block sample and completely immerse it in 600g of pretreatment mixed solution. The mass ratio of carbon fiber composite to pretreatment mixed solution is 1:30. Reflux the sample in an 80℃ constant temperature water bath for 4h. After the reaction is complete, remove the pretreated CFRP sample, wash it with water until the filtrate is neutral, and air dry it for later use.

[0089] Step S3: Add 6.00g potassium chloride and 3.00g citric acid to 300g of the pretreatment mixed solution from step S1, stir at room temperature for 20min until completely dissolved, then heat to 65℃ and stir for 8min to obtain the main treatment mixed solution. The total mass of potassium chloride and citric acid is 3% of the mass of the pretreatment mixed solution, and the mass ratio of potassium chloride to citric acid is 2:1.

[0090] Step S4: Weigh 5.00g of the CFRP sample that has been pretreated and dried in step S2, and completely immerse it in the main treatment mixed solution. The mass ratio of the sample to the main treatment mixed solution is 1:60. The sample is refluxed at 95°C for 2 hours. After the reaction is completed, the solid product is separated by hot filtration. The solid product is washed with water at 60°C until the filtrate is neutral. The solid product is dried at 80°C for 4 hours to obtain the recovered carbon fiber material.

[0091] Comparative Example 2:

[0092] Comparative Example 2 differs from Example 1 in that it did not include a pretreatment stage. Specifically, it includes the following steps:

[0093] Step S1: Mix 900 mL of glacial acetic acid with 100 mL of 30 wt% hydrogen peroxide aqueous solution and mechanically stir at 300 rpm for 15 min at room temperature to obtain 1 L of pretreatment mixed solution, wherein the volume percentage of glacial acetic acid is 90% and the volume percentage of hydrogen peroxide aqueous solution is 10%.

[0094] Step S2: Add 6.00g potassium chloride and 3.00g citric acid to 300g of the pretreatment mixed solution from step S1, stir at room temperature for 20min until completely dissolved, then heat to 65℃ and stir for 8min to obtain the main treatment mixed solution. The total mass of potassium chloride and citric acid is 3% of the mass of the pretreatment mixed solution, and the mass ratio of potassium chloride to citric acid is 2:1.

[0095] Step S3: Weigh 5.00g of epoxy resin-based carbon fiber composite (CFRP) block sample and completely immerse it in the main treatment mixed solution prepared in step S2. The mass ratio of the sample to the main treatment mixed solution is 1:60. The mixture is refluxed at 95℃ for 2h. After the reaction is completed, the solid product is separated by hot filtration. The solid product is washed with water at 60℃ until the filtrate is neutral. The solid product is dried at 80℃ for 4h to obtain the recovered carbon fiber material.

[0096] Comparative Example 3:

[0097] Comparative Example 3 differs from Example 1 in that it only uses a pretreatment mixed solution to treat the epoxy resin-based carbon fiber composite block sample, without adding a salt and acid composite catalyst. Specifically, it includes the following steps:

[0098] Step S1: Mix 900 mL of glacial acetic acid with 100 mL of 30 wt% hydrogen peroxide aqueous solution and mechanically stir at 300 rpm for 15 min at room temperature to obtain 1 L of pretreatment mixed solution, wherein the volume percentage of glacial acetic acid is 90% and the volume percentage of hydrogen peroxide aqueous solution is 10%.

[0099] Step S2: Weigh 20.00g of epoxy resin-based carbon fiber composite (CFRP) block sample and completely immerse it in 600g of pretreatment mixed solution. The mass ratio of carbon fiber composite to pretreatment mixed solution is 1:30. Reflux the sample in an 80℃ constant temperature water bath for 4h. After the reaction is complete, remove the pretreated CFRP sample, wash it with water until the filtrate is neutral, and air dry it for later use.

[0100] Step S3: Weigh 5.00g of the CFRP sample after the pretreatment in step S2, and completely immerse it in 300g of the pretreatment mixed solution. The mass ratio of the sample to the pretreatment mixed solution is 1:60. The sample is refluxed at 95℃ for 2 hours. After the reaction is completed, the solid product is separated by hot filtration. The solid product is washed with water at 60℃ until the filtrate is neutral. The solid product is dried at 80℃ for 4 hours to obtain the recovered carbon fiber material.

[0101] Comparative Example 4:

[0102] The difference between Comparative Example 4 and Example 1 is that only 6.00 g of potassium chloride was added to the main treatment mixture of Comparative Example 4, and citric acid was not added; the remaining steps were the same. Specifically, step S3 is as follows:

[0103] Add 6.00g of potassium chloride to 300g of the pretreatment mixed solution from step S1, stir at room temperature for 20min until completely dissolved, then heat to 65℃ and stir for 8min to obtain the main treatment mixed solution.

[0104] Comparative Example 5:

[0105] Compared with Example 1, Comparative Example 5 differs in that only 3.00 g of citric acid was added to the main treatment mixture solution of Comparative Example 5, and potassium chloride was not added; the remaining steps were the same. Specifically, step S3 is as follows:

[0106] Add 3.00g of citric acid to 300g of the pretreatment mixture from step S1, stir at room temperature for 20min until completely dissolved, then heat to 65℃ and stir for 8min to obtain the main treatment mixture.

[0107] Experimental Example 1:

[0108] The recycled carbon fiber materials were obtained by following the recycling methods for carbon fiber composite materials provided in Examples 1-11 and Comparative Examples 1-5, respectively.

[0109] The resin removal efficiency in each example and comparative example was quantified using a resin degradation rate test. Specifically, the mass of the original carbon fiber composite sample was weighed and recorded as W0 (g); the mass of the carbon fiber material sample dried to constant weight was weighed and recorded as W... r (g); Using the high-temperature calcination method, another sample of the original carbon fiber composite material from the same batch was placed in a muffle furnace and calcined at 600°C for 2 hours in an air atmosphere to ensure complete oxidation and decomposition of the resin matrix. After cooling, the mass loss was calculated to obtain the initial mass W of the resin. c (g); Calculate the resin degradation rate DR (%). Among them,

[0110] .

[0111] The surface morphology of raw CFRP, pretreated and recycled carbon fiber materials after mechanical crushing was observed using a JSM-6360LV scanning electron microscope (SEM). The resin residue, surface smoothness and presence of fractures and damage on the carbon fiber surface were recorded. Three images of different fields of view were taken and saved at each magnification.

[0112] An MTS Criterion Model 42 electronic universal testing machine was used to measure the average tensile strength σ1 (MPa) of the recovered carbon fiber monofilaments and the average tensile strength σ2 (MPa) of the original carbon fiber composite monofilaments, based on the national standard GB / T31290-2022 "Determination of Tensile Properties of Carbon Fiber Monofilaments". The tensile strength retention rate A (%) was then calculated.

[0113] .

[0114] The results of the above tests are as follows Figure 1-3 As shown in Table 1.

[0115]

[0116] As shown in Table 1, in Example 1, using potassium chloride-citric acid as a composite catalyst and glacial acetic acid-hydrogen peroxide as a pretreatment mixture, under the conditions of pretreatment at 80℃ for 4 hours and main treatment at 95℃ for 2 hours, a resin degradation rate of 97.2% was achieved, and the tensile strength of the recovered carbon fiber material monofilament reached 3850 MPa, with a strength retention rate of 92.1%.

[0117] Specifically, glacial acetic acid, with its strong polarity and penetrating power, forms hydrogen bonds with the ether and hydroxyl groups in the epoxy resin through its carboxyl groups, deeply penetrating into the three-dimensional cross-linked network, causing resin swelling and loosening the dense structure. Simultaneously, hydrogen peroxide undergoes a reversible acyl transfer reaction with glacial acetic acid to generate highly oxidizing peracetic acid, which undergoes homolytic cleavage in the weakly acidic environment of glacial acetic acid, producing hydroxyl radicals. Both work together to complete the initial degradation of the resin, lowering the reaction energy barrier in the main treatment. In the main treatment stage, potassium chloride, as a neutral strong electrolyte, significantly increases the ionic strength of the solution, reduces the surface tension of the reaction solution, enhances the wettability of the resin, and reduces local reaction dead zones. It also stabilizes hydrogen peroxide molecules through the ionic environment, reducing their non-selective decomposition. Citric acid regulates the pH of the system, inhibiting the hydrolysis of peracetic acid, and enhances the electrophilicity of hydrogen peroxide through protonation, promoting an increase in the steady-state concentration of peracetic acid. The synergistic effect of both makes the oxidation reaction uniform and efficient, preferentially attacking the CN and CO bonds of the epoxy resin, avoiding localized excessive oxidation that damages the carbon fiber matrix.

[0118] like Figure 1 As shown, after the original CFRP is mechanically rolled, the carbon fibers are wrapped in a large amount of dense resin, and there are no obvious gaps between the fibers. Figure 2 The image shows the SEM image after pretreatment in Example 1. It can be seen that the resin has been partially peeled off, and a small amount of resin remains on the fiber surface. However, the gaps between the fibers have increased significantly. This is the result of the combined effect of swelling by glacial acetic acid and initial oxidation by peracetic acid, which creates a channel for the penetration and deep degradation of the subsequent main treatment solution. Figure 3 The SEM image of the carbon fiber after primary treatment shows that the resin on the fiber surface has been completely removed, and the surface is smooth without obvious etching damage, which directly confirms the core effectiveness of the two-step method and the composite catalyst.

[0119] Examples 2-6 further verified the universality of the process by replacing the salt and acid composite catalyst components. The resin degradation rate was maintained at 95.5-96.8%, the tensile strength was 3650-3780 MPa, and the strength retention rate was 87.4-90.3%. Although slightly lower than Example 1, they were all significantly better than the comparative examples.

[0120] Specifically, in Example 2, sodium chloride-citric acid was used. Because sodium and chloride ions have smaller radii than potassium ions, the increase in ionic strength of the solution was slightly lower, resulting in a slight decrease in the wettability and mass transfer efficiency of the reaction solution, and a lower degradation rate than in Example 1. In Example 3, ferrous chloride-citric acid was used. Although ferrous ions can catalyze the generation of more hydroxyl radicals from hydrogen peroxide through the Fenton reaction, they themselves have weak reducing properties and will consume hydrogen peroxide, leading to a slight decrease in the amount of peracetic acid generated. The resin degradation rate dropped to 95.5%, but it was still much higher than the system without a catalyst. In Example 4, tetrabutylammonium bromide was used as a quaternary ammonium salt. Although its hydrophobic groups have a good effect on the resin surface wettability... While the wettability is somewhat improved, the degree of ionic dissociation is lower than that of inorganic salts, resulting in limited improvement in ionic strength. Therefore, the resin degradation rate and strength retention rate remain at a moderate level. In Example 5, sodium bisulfate, an inorganic acid salt, was used instead of citric acid. Although its acidity is stronger and it can increase the concentration of peracetic acid, it did not cause significant corrosion to the carbon fiber surface. Since sodium bisulfate also has pH regulation function, the stability of active species is slightly reduced only due to the difference in acid strength, and the tensile strength retention rate still reaches 87.4%. In Example 6, ammonium chloride is used, which has both acid regulation and weak electrolyte properties. It works synergistically with potassium chloride to improve ionic strength while regulating pH value, and its performance is similar to that of Example 1. Therefore, the salt-acid composite catalyst selected in this invention has good versatility. Different types of salts and acids can exert catalytic effects through ionic strength regulation and pH control, with only slight fluctuations in performance due to differences in ionic radius, degree of dissociation, and acid strength.

[0121] Examples 7-10 optimized the ratio and total amount of the composite catalyst. The results showed that the resin degradation rate was reduced to 93.8%-95.2%, the tensile strength was 3520-3620 MPa, and the strength retention rate was 84.8%-87.0%.

[0122] Specifically, in Example 7, the salt-to-acid mass ratio was 1:1, with excess citric acid. While this promoted peracetic acid formation, the excess hydrogen ions slightly etched the carbon fiber surface, reducing the carbon fiber tensile strength retention rate to 86.2%. In Example 8, the salt-to-acid mass ratio was 3:1, with excess potassium chloride. The enhanced interionic interaction inhibited free radical generation, leading to a decrease in resin degradation rate. In Example 9, the total addition amount of the salt and acid composite catalyst was too low, at 2%, resulting in insufficient catalytic activity, a decreased hydroxyl free radical generation rate, and a lower steady-state concentration of peracetic acid, which failed to completely break the resin cross-links, thus reducing the resin degradation rate. In Example 10, the total addition amount of the salt and acid composite catalyst was 4%. Due to the excessively high salt concentration, the enhanced interionic interaction inhibited the homolytic cracking reaction of hydrogen peroxide, and compared to Example 1, the resin degradation rate did not increase with the increase in addition amount. Therefore, the salt-to-acid mass ratio and total addition amount in Example 1 ensured a balance between ionic strength and pH while avoiding mass transfer resistance or fiber corrosion problems, making it the optimal choice that balances efficiency and fiber protection.

[0123] Example 11 used distilled glacial acetic acid for repeated experiments. The resin degradation rate was 92.5%, the tensile strength was 3480 MPa, and the strength retention rate was 83.9%. Although these figures were slightly lower than those of other examples using fresh glacial acetic acid, the core performance was still within the high-efficiency recovery range. Gas chromatography analysis showed that the purity of the recovered glacial acetic acid reached 98.5%, and the degradation rate remained stable above 90% after three consecutive cycles. This demonstrates the feasibility of the glacial acetic acid distillation recovery process, which solves the cost and environmental problems associated with single-use solvents in traditional chemical recycling, while also preventing the introduction of impurities during the recovery process.

[0124] In Comparative Example 1, a pretreatment solution prepared using water instead of glacial acetic acid resulted in a resin degradation rate of only 45.3%, a tensile strength of 2850 MPa, and a strength retention rate of 68.3%, with a large amount of blocky resin residue remaining on the surface. The main reason is that water's polarity and penetrating power are far weaker than glacial acetic acid, making it unable to form hydrogen bonds with the ether and hydroxyl groups in the epoxy resin. This hinders its penetration into the dense three-dimensional cross-linked network, only wetting the sample surface. Simultaneously, the water system cannot provide a stable weakly acidic environment for hydrogen peroxide, leading to its non-selective decomposition. This results in low hydroxyl radical generation and short lifespan, degrading only a small amount of surface resin while the internal resin remains tightly wrapped around the carbon fibers. Under stress, stress concentration causes fiber breakage, significantly reducing the strength retention rate. This highlights the irreplaceable role of glacial acetic acid as both a swelling medium and a medium.

[0125] Comparative Example 2 omitted the pretreatment step and directly treated the raw CFRP with the main treatment mixed solution. The resin degradation rate was 68.7%, the tensile strength was 3210 MPa, and the strength retention rate was 77.1%, which was better than Comparative Example 1, but much lower than Example 1. The main reason is that the untreated epoxy resin network is dense, and the glacial acetic acid in the main treatment mixed solution cannot penetrate quickly. Peracetic acid and hydroxyl radicals can only act on the surface resin, and the internal resin cannot be completely degraded due to the hindered mass transfer. This results in more resin residue on the fiber surface, reduced inter-fiber bonding force, and easy fiber slippage during stretching, reducing the strength retention rate by 15%. Therefore, the pretreatment stage is crucial for reducing the energy barrier of the main treatment reaction and improving the degradation efficiency.

[0126] In Comparative Example 3, no salt and acid composite catalyst was added during the main treatment stage. The resin degradation rate was 72.4%, the tensile strength was 3350 MPa, and the strength retention rate was 80.7%. There were still many dot-like residues on the surface, indicating that without a catalyst, the pH of the system could not be precisely controlled, peracetic acid was prone to hydrolysis, the homolytic cracking rate of hydrogen peroxide was slowed down, and the amount of hydroxyl radicals generated was insufficient and unevenly distributed, resulting in incomplete resin degradation. At the same time, the wettability of the reaction solution on the resin was poor, and there were local reaction dead zones. Some resin was not completely decomposed and adhered to the fiber surface, affecting the force transmission. This further confirms the core role of the composite catalyst in enhancing the oxidation reaction.

[0127] Comparative Examples 4 and 5, using salt or acid as catalysts alone, showed resin degradation rates of 83.1% and 81.5%, respectively, tensile strengths of 3420 MPa and 3380 MPa, and strength retention rates of 82.4% and 81.5%, respectively. While these were higher than the group without catalyst, they were lower than the group with the composite catalyst. This is mainly because Comparative Example 4 only added potassium chloride, which, although improving the ionic strength and wettability of the solution, could not adjust the pH value of the system, leading to easy hydrolysis of peracetic acid, increased non-selective decomposition of hydrogen peroxide, and low utilization of active species. Comparative Example 5 only added citric acid, which, although adjusting the pH value and stabilizing peracetic acid, could not improve the ionic strength, resulting in insufficient wettability and mass transfer efficiency of the reaction solution and incomplete internal degradation of the resin. The absence of either of these two components weakens the catalytic effect, fully demonstrating the irreplaceable role of the synergistic effect of salt and acid in the composite catalyst. Only through the combined action of both can a highly efficient and mild balance of oxidation reactions be achieved.

[0128] This invention achieves the mild and efficient recycling of epoxy resin-based carbon fiber composites through a complete process of pretreatment swelling, main treatment catalytic oxidation, and solvent recovery. In the pretreatment stage, glacial acetic acid, with its strong permeability and polarity, penetrates into the three-dimensional cross-linked network of the epoxy resin, inducing resin swelling and weakening structural stability. Simultaneously, glacial acetic acid undergoes a reversible acyl transfer reaction with hydrogen peroxide in a weakly acidic environment, generating highly oxidizing peracetic acid in situ. This peracetic acid, along with hydroxyl radicals generated by the homolytic cleavage of hydrogen peroxide, forms a synergistic oxidation system, initially breaking the CN and CO cross-links in the resin and completing the initial degradation of the resin. In the main treatment stage, a salt-acid composite catalyst is introduced into the pretreatment mixed solution. The acid moderately lowers the pH of the system, stabilizing and promoting the formation of peracetic acid, while the salt increases the ionic strength of the solution, enhancing the wetting and penetration of the reaction solution onto the fiber bundles, reducing reaction dead zones. Simultaneously, the electrostatic interaction stabilizes the reaction intermediates, synergistically increasing the generation rate and uniform distribution of hydroxyl radicals, thereby completely decomposing residual epoxy resin under low temperature and normal pressure conditions. Furthermore, this invention recovers glacial acetic acid through atmospheric pressure distillation, achieving a green closed loop of reagent use-recovery-reuse, fundamentally reducing processing costs and environmental impact. The method provided by this invention has a simple process, requiring no high pressure or special complex equipment, offering an efficient, economical, and sustainable reliable path for the high-value, large-scale recycling of carbon fiber composite materials.

[0129] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for regenerating and recycling carbon fiber composite materials, characterized in that, Includes the following steps: S1. Mix glacial acetic acid and hydrogen peroxide aqueous solution in a certain proportion and stir evenly at room temperature to prepare a pretreatment mixed solution; S2. Immerse the carbon fiber composite material in the pretreatment mixture, heat it for pretreatment, and then wash and dry it. S3. Add salt and acid in a mass ratio of 1-3:1 to the pretreatment mixed solution in step S1, stir and mix at room temperature, and then heat and catalyze to prepare the main treatment mixed solution. S4. The pretreated and dried carbon fiber composite material is fully immersed in the main treatment mixed solution, heated for main treatment, washed and dried to obtain the recycled carbon fiber material. S5. The remaining waste liquid after the pretreatment and main treatment of carbon fiber composite materials is heated, evaporated, condensed, and then glacial acetic acid is recovered.

2. The method for regenerating and recycling carbon fiber composite materials according to claim 1, characterized in that: In step S1, the mass concentration of hydrogen peroxide is 25-35 wt%.

3. The method for recycling carbon fiber composite materials according to claim 1, characterized in that: In step S1, the pretreated mixed solution contains 80-95% glacial acetic acid and 5-20% hydrogen peroxide aqueous solution by volume.

4. The method for recycling carbon fiber composite materials according to claim 1, characterized in that: In step S2, the mass ratio of carbon fiber composite material to pretreatment mixed solution is 1:20-50, the heating temperature for pretreatment is 70-90℃, and the treatment time is 3-5h.

5. The method for recycling carbon fiber composite materials according to claim 1, characterized in that: In step S3, the salt is selected from one or more of potassium chloride, sodium chloride, potassium nitrate, sodium nitrate, ferrous chloride, and tetrabutylammonium bromide.

6. The method for recycling carbon fiber composite materials according to claim 1, characterized in that: In step S3, the acid is selected from one or more of citric acid, ammonium chloride, and sodium bisulfate.

7. The method for recycling carbon fiber composite materials according to claim 1, characterized in that: In step S3, the total mass of salt and acid is 2-4% of the mass of the pretreated mixed solution.

8. The method for recycling carbon fiber composite materials according to claim 1, characterized in that: In step S3, the heating catalytic process includes: After adding salt and acid to the pretreated mixed solution, heat the mixed solution to 60-70℃ and keep it warm while stirring for 5-10 minutes.

9. The method for recycling carbon fiber composite materials according to claim 1, characterized in that: In step S4, the mass ratio of the pretreated and dried carbon fiber composite material to the main treatment mixed solution is 1:40-80, the heating temperature of the heat treatment is 90-100℃, and the treatment time is 1-3h.

10. A method for recycling carbon fiber composite materials according to claim 1, characterized in that: In step S5, the recycling process is as follows: Under normal pressure, the residual waste liquid after the pretreatment and main treatment of carbon fiber composite materials is heated to 120-125℃ in an oil bath. The evaporated glacial acetic acid vapor is cooled and liquefied by a condenser and then collected, thus completing the recovery of glacial acetic acid.

Images