A mild and efficient method for recycling phenolic resin-based carbon fiber composites

Abstract

The application belongs to the field of recycling of carbon fiber resin matrix composites, and discloses a method for mildly and efficiently recycling phenolic resin matrix carbon fiber composites. The method comprises the following steps: first, cutting the phenolic resin matrix carbon fiber composites into blocks, and then drying the composites; then, immersing the composites in N-methyl pyrrolidone under heating conditions, and pretreating the composites to soften the composites; then, immersing the pretreated sample in an oxidizing agent under heating conditions, and treating the sample to degrade the resin material; and finally, filtering and washing the sample to obtain recycled carbon fibers. The application uses a simple process flow to achieve efficient degradation of the phenolic resin matrix carbon fiber composites under mild conditions, and the recycled carbon fibers have a small degree of damage and a resin degradation rate of up to 98.6%. Compared with the prior art, the application has a simple process, avoids high temperature, high pressure, long time and other reaction conditions, is energy-saving and environmentally friendly, and can recycle high-value-added carbon fibers.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber recycling, and in particular relates to a mild and efficient method for recycling phenolic resin-based carbon fiber composite materials. Background Technology

[0002] Phenolic resin-based carbon fiber composites are a new type of high-performance lightweight composite material. Due to their advantages such as high specific strength, low coefficient of thermal expansion, wear resistance, and low density, they are widely used in aerospace, automotive, sports and other fields.

[0003] With the increasing application of phenolic resin-based carbon fiber composites across various industries, the amount of waste composite materials generated during the manufacturing process, such as scraps and discarded parts, has reached a high level. However, due to the three-dimensional cross-linked network formed by the thermosetting resin in the composite material after curing, which is insoluble and infusible, recycling faces the challenge of complex processes and low recycling value. If this technology can be realized and applied on a large scale, it can bring significant benefits to the social economy.

[0004] Currently, the main methods for recycling carbon fiber are mechanical, pyrolysis, and chemical methods. Mechanical recycling is simple, but the recovered product is a mixture of resin and carbon fiber, which can only be used as a filler material and has very low commercial value. Pyrolysis involves heating to the resin's decomposition temperature under aerobic conditions, degrading the resin into small-molecule gases or solids for separation. While this method can yield industrial-grade products, the enormous energy consumption and damage to the carbon fiber cannot be ignored. Chemical methods involve degrading the composite material using concentrated acids, concentrated alkalis, or organic solvents at temperatures below 200℃ and pressures below 22.1 GPa. However, the reaction conditions still impose a burden on equipment and costs, and the wastewater poses a serious threat to the environment.

[0005] Therefore, it is of great significance to develop a new method for degrading carbon fiber resin composites with mild reaction conditions, simple process, and high recycling efficiency.

[0006] Reference 1, "Chinese Invention Patent Application Publication No. CN 110172177 A," discloses a method for rapidly and efficiently recovering high-performance resin-based carbon fiber composite materials. This method involves pretreating the composite material with glacial acetic acid at 108–112°C, followed by washing and then adding the material to a mixture of dimethyl sulfoxide and potassium hydroxide. The temperature is then raised to 150–180°C, and the reaction is carried out for 40–70 minutes to obtain recovered carbon fibers. Although this method has a short reaction time, the volatilization of organic solvents at this reaction temperature can pollute the environment and threaten human health. Furthermore, the acid and alkali solutions can have certain impacts on the environment and equipment.

[0007] Reference 2, "Chinese Invention Patent Application Publication No. CN 109851848 A," discloses a method for recovering carbon fiber from carbon fiber / phenolic resin composite materials. This method involves mixing the composite material with a solvent, various catalysts, and an oxidant, heating the mixture in a reactor to 100–400°C, and reacting for 0.5–24 hours to obtain recovered carbon fiber. While this method yields carbon fiber of relatively good quality, the solution system is complex, the reaction environment requires a closed reactor, and the high temperature results in high energy consumption.

[0008] Reference 3, "Chinese Invention Patent Application Publication No. CN 112876734 A", discloses a method for recycling epoxy resin-based carbon fiber composites under mild conditions. The method uses 1,3-dimethyl-2-imidazolinone and potassium hydroxide to heat the composite material. The reaction conditions are 150℃~180℃ at atmospheric pressure and the reaction time is 3~5h. The method is simple to operate and the conditions are relatively mild, but the required temperature range is still relatively high. Summary of the Invention

[0009] To overcome the problems of complex processes, high recycling temperatures and pressures, long recycling times, and serious environmental pollution caused by existing chemical methods, the primary objective of this invention is to propose a mild and efficient method for recycling phenolic resin-based carbon fiber composite materials.

[0010] This method involves immersing a phenolic resin-based carbon fiber composite material in N-methylpyrrolidone and pretreating it at 60–90°C under normal pressure for 0.2–1 h. The composite material is then placed in an oxidant and heated at 60–90°C under normal pressure for 0.5–3 h until the material degrades, dispersing the carbon fibers. Finally, the solution is filtered and subjected to repeated ultrasonic washing in an ethanol solution to obtain the recovered carbon fibers. This invention features a simple process, low reaction temperature, short reaction time, high resin removal rate, and minimal morphological damage to the recovered product, providing a novel method for recovering carbon fibers from carbon fiber resin composites.

[0011] This invention is achieved through the following technical solution:

[0012] A mild and efficient method for recycling phenolic resin-based carbon fiber composites includes the following steps:

[0013] (1) Cut the phenolic resin-based carbon fiber composite material into blocks and dry them;

[0014] (2) The phenolic resin-based carbon fiber composite material dried in step (1) is immersed in N-methylpyrrolidone and pretreated under heating conditions until the composite material softens.

[0015] (3) The pretreated phenolic resin-based carbon fiber composite material obtained in step (2) is placed in an oxidant solution and reacted under heating conditions until the resin material is degraded to obtain a carbon fiber dispersed solution; (4) The solution obtained in step (3) is filtered, and the solid product is washed and dried to obtain recycled carbon fiber products.

[0016] Preferably, the resin in the phenolic resin-based carbon fiber composite material in step (1) is a thermosetting resin.

[0017] Preferably, the thermosetting resin in step (1) is one or more of the following: phenolic resin, cashew nut shell oil modified phenolic resin, boron modified phenolic resin, melamine-cashew nut shell oil modified phenolic resin, latex modified phenolic resin, or polyvinyl alcohol modified phenolic resin; the resin accounts for 10 to 90 wt% of the composite material.

[0018] Preferably, in the phenolic resin-based carbon fiber composite material of step (1), the carbon fiber is one or more of polyacrylonitrile carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, phenolic carbon fiber, and vapor-grown carbon fiber; the proportion of carbon fiber in the composite material is 10 to 90 wt%.

[0019] Preferably, the pretreatment temperature in step (2) is 60-90°C, the pretreatment time is 0.2-1h, and the mass ratio of N-methylpyrrolidone to the composite material is 100:1-10:1.

[0020] Preferably, the oxidant in step (3) is one or more of hydrogen peroxide, peracetic acid, potassium permanganate, sodium hypochlorite, calcium hypochlorite, or ozone.

[0021] Preferably, the reaction temperature in step (3) is 60-90°C, the treatment time is 0.5-2h, and the mass fraction of the composite material in the solution is 1%-10%.

[0022] Preferably, the washing in step (4) is ultrasonic washing with ethanol for 5-30 minutes, followed by washing with water for 5-30 minutes; the drying in step (4) is drying at 80℃-90℃ for 2-6 hours.

[0023] Preferably, the heating in steps (1) and (3) is performed under normal pressure.

[0024] Preferably, the oxidant in step (3) is hydrogen peroxide, and the concentration of the oxidant solution is 30-40 wt%; or the oxidant is sodium hypochlorite, and the concentration of the oxidant solution is 0.1-0.5 mol / L.

[0025] The present invention has the following advantages and beneficial effects:

[0026] This invention proposes a mild and efficient method for recycling phenolic resin-based carbon fiber composites. The method involves pretreating the composite material with N-methylpyrrolidone at 60–90°C for 0.2–1 h, followed by dissociation of the composite material using an oxidant at 60–90°C for 0.5–3 h, and finally washing and drying. This method achieves efficient removal of thermosetting resin from the composite material under mild conditions, with a resin degradation rate exceeding 95%. Furthermore, the carbon fiber surface structure remains intact, leaving no impurities and allowing for reuse.

[0027] Compared with existing chemical methods for recycling carbon fiber, this method has the following advantages:

[0028] (1) This method is universal and has a good recycling effect on phenolic resin and its various modified resin composites.

[0029] (2) This method uses N-methylpyrrolidone, a reagent with strong dissolving power and low toxicity, and an easily decomposable oxidant. The selected reagents are more environmentally friendly, as no acids or alkalis are used to treat the composite material. Furthermore, the pretreatment reagent N-methylpyrrolidone can be recycled. After 10 cycles of pretreatment experiments, the resin degradation rate can still reach over 95%. Therefore, it reduces the cost of use and promotes the recycling of resources.

[0030] (3) The reaction conditions of this method are mild, including lower reaction temperature and lower pressure. The temperature is controlled below the flash point of the organic solvent, which greatly suppresses the volatilization of toxic gases. The process is safe and reliable and easy to apply in the process. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of the present invention.

[0032] Figure 2 The images show the morphology of the phenolic resin-based carbon fiber composite material before and after pretreatment. (a), (b), (c), and (d) are the composite material before pretreatment, Example 1 (after pretreatment), Comparative Example 1 (after pretreatment), and Comparative Example 2 (after pretreatment), respectively.

[0033] Figure 3 The image shows the phenolic resin-based carbon fiber composite material in Example 1.

[0034] Figure 4 This is a diagram of the recycled carbon fiber in Example 1.

[0035] Figure 5 This is a scanning electron microscope image of the phenolic resin-based carbon fiber composite material in Example 1.

[0036] Figure 6 This is a scanning electron microscope image of the recovered carbon fiber in Example 1. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. For process parameters not specifically noted, conventional techniques can be referred to.

[0038] The present invention will now be further described with reference to the embodiments:

[0039] Example 1

[0040] Step 1: Select a phenolic resin-based carbon fiber composite material with thermosetting cashew nut shell oil modified phenolic resin as the matrix, cut it into blocks with a mass of 1.5g, of which the resin content is 0.8g.

[0041] Step 2: Immerse the phenolic resin-based carbon fiber composite material from Step 1 in 100g of N-methylpyrrolidone and pretreat it at 80℃ under normal pressure for 30min to obtain a softened phenolic resin-based carbon fiber composite material.

[0042] Step 3: Take out the product from Step 2 and immerse it in 100g of 30% hydrogen peroxide solution, and react it at 80℃ under normal pressure for 2.5h.

[0043] Step 4: Filter the product after step 3, ultrasonically clean it 3 times with anhydrous ethanol for 15 minutes each time, then clean it with deionized water for 15 minutes, and finally dry it in an 80℃ oven for 4 hours to obtain recycled carbon fiber.

[0044] Step 5: Weigh the recycled carbon fiber, which weighs 0.73g, indicating a resin degradation rate of 96.3%.

[0045] Example 2

[0046] Step 1: Select a phenolic resin-based carbon fiber composite material with thermosetting boron-modified phenolic resin as the matrix, cut it into cubes with a mass of 2.3g and a resin content of 0.6g.

[0047] Step 2: Immerse the phenolic resin-based carbon fiber composite material from Step 1 in 70g of N-methylpyrrolidone and pretreat it at 70℃ under normal pressure for 50min to obtain a softened phenolic resin-based carbon fiber composite material.

[0048] Step 3: Take out the product from Step 2 and immerse it in 80g of 30% hydrogen peroxide solution, and react it at 90℃ under normal pressure for 2 hours.

[0049] Step 4: Filter the product after step 3, ultrasonically clean it 3 times with anhydrous ethanol for 15 minutes each time, then clean it with deionized water for 15 minutes, and finally dry it in an 80℃ oven for 4 hours to obtain recycled carbon fiber.

[0050] Step 5: Weigh the recycled carbon fiber, which weighs 1.71g, indicating a resin degradation rate of 98.3%.

[0051] Example 3

[0052] Step 1: Select a phenolic resin-based carbon fiber composite material with thermosetting phenolic resin as the matrix, cut it into cubes with a mass of 5.5g, of which the resin content is 2.5g.

[0053] Step 2: Immerse the phenolic resin-based carbon fiber composite material from Step 1 in 120g of N-methylpyrrolidone and pretreat it at 80℃ under normal pressure for 1h to obtain a softened phenolic resin-based carbon fiber composite material.

[0054] Step 3: Take out the product from Step 2 and immerse it in 120g of sodium hypochlorite solution with a concentration of 0.1mol / L. React at 90℃ under normal pressure for 30min.

[0055] Step 4: Filter the product after step 3, ultrasonically clean it 3 times with anhydrous ethanol for 15 minutes each time, then clean it with deionized water for 15 minutes, and finally dry it in an 80℃ oven for 4 hours to obtain recycled carbon fiber.

[0056] Step 5: Weigh the recycled carbon fiber, which weighs 3.12g, indicating a resin degradation rate of 95.2%.

[0057] Experiments show that phenolic resin-based carbon fiber composites can be efficiently recycled by pretreating with N-methylpyrrolidone at 60–90°C for 0.2–1 h, followed by treatment with an oxidant at 60–90°C for 0.5–3 h. The experimental process is simple and the conditions are mild, the degradation rate of resin reaches more than 95%, and there is no obvious resin residue on the surface of the recycled carbon fiber.

[0058] The degradation rate of the resin is calculated using the following formula:

[0059] Resin degradation rate = (mass of phenolic resin-based carbon fiber composite material - mass of recycled carbon fiber) / mass of resin in phenolic resin-based carbon fiber composite material × 100%

[0060] Comparative Example 1

[0061] Step 1: Select a phenolic resin-based carbon fiber composite material with thermosetting cashew nut shell oil modified phenolic resin as the matrix, cut it into cubes with a mass of 1.6g and a resin content of 0.85g.

[0062] Step 2: Immerse the phenolic resin-based carbon fiber composite material from Step 1 in 70g of N-methylpyrrolidone and pretreat it at 50℃ under normal pressure for 50min.

[0063] Step 3: Take out the product from Step 2 and immerse it in 80g of 30% hydrogen peroxide solution, and react it at 90℃ under normal pressure for 2 hours.

[0064] Step 4: Filter the product after step 3, ultrasonically clean it 3 times with anhydrous ethanol for 15 minutes each time, then clean it with deionized water for 15 minutes, and finally dry it in an 80℃ oven for 4 hours to obtain recycled carbon fiber.

[0065] Step 5: Weigh the recycled carbon fiber, which weighs 1.11g, and calculate its resin degradation rate as 57.6%.

[0066] Comparative Example 2

[0067] Step 1: Select a phenolic resin-based carbon fiber composite material with thermosetting cashew nut shell oil modified phenolic resin as the matrix, cut it into cubes with a mass of 1.5g and a resin content of 0.8g.

[0068] Step 2: Immerse the phenolic resin-based carbon fiber composite material from Step 1 in 70g of dimethyl sulfoxide and pretreat it at 80℃ under normal pressure for 50min.

[0069] Step 3: Take out the product from Step 2 and immerse it in 80g of 30% hydrogen peroxide solution, and react it at 90℃ under normal pressure for 2 hours.

[0070] Step 4: Filter the product after step 3, ultrasonically clean it 3 times with anhydrous ethanol for 15 minutes each time, then clean it with deionized water for 15 minutes, and finally dry it in an 80℃ oven for 4 hours to obtain recycled carbon fiber.

[0071] Step 5: Weigh the recycled carbon fiber, which has a mass of 0.81g, and calculate its resin degradation rate to be 86.3%.

[0072] Example 1 was experimentally compared with Comparative Examples 1 and 2. Under different pretreatment conditions, the morphology of the resulting composite material products differed. Figure 2It can be seen that the pretreated sample of Example 1 swelled, becoming softer and more fluffy in shape. The sample of Comparative Example 1 showed almost no change in shape before and after pretreatment, while the pretreated sample of Comparative Example 2, although exhibiting material distortion, had greater hardness and showed no swelling. Furthermore, the resin degradation rate of Example 1 was 67.2% and 11.6% higher than that of Comparative Examples 1 and 2, respectively. This indicates that the pretreatment conditions under the present invention can dissolve some of the crosslinking products of the phenolic resin-based carbon fiber composite material, reduce the hardness of the cured product, and have a significant swelling effect on the interface layer, thus promoting subsequent degradation reactions. Moreover, at a lower temperature (50°C), N-methylpyrrolidone has almost no effect. In addition, dimethyl sulfoxide has a weaker solubility than N-methylpyrrolidone, and an ideal resin degradation rate cannot be obtained.

[0073] Figure 3 , 4 The morphology of the phenolic resin-based carbon fiber composite material in Example 1 before and after degradation is shown. Figure 5 , 6 The microstructure of the phenolic resin-based carbon fiber composite material and recycled carbon fiber in Example 1 is shown. It can be seen that the surface morphology of the recycled carbon fiber is intact and there are few resin particles bonded to the surface, indicating that this system can not only have a good degradation effect on the resin, but also restore the carbon fiber structure to a large extent.

[0074] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A mild and efficient method for recycling phenolic resin-based carbon fiber composite materials, characterized in that, Includes the following steps: (1) Cut the phenolic resin-based carbon fiber composite material into blocks and dry them; (2) The phenolic resin-based carbon fiber composite material dried in step (1) is immersed in N-methylpyrrolidone and pretreated under heating conditions until the composite material softens. (3) The pretreated phenolic resin-based carbon fiber composite material obtained in step (2) is placed in an oxidant solution and reacted under heating conditions until the resin material is degraded, resulting in a carbon fiber dispersed solution. (4) The solution obtained in step (3) is filtered, and the solid product is washed and dried to obtain recycled carbon fiber products; The pretreatment temperature in step (2) is 60–90°C; The oxidant in step (3) is hydrogen peroxide or sodium hypochlorite, and the reaction temperature is 60-90°C.

2. The method according to claim 1, characterized in that, In step (1), the resin in the phenolic resin-based carbon fiber composite material is a thermosetting resin.

3. The method according to claim 2, characterized in that, The thermosetting resin in step (1) is one or more of the following: phenolic resin, cashew nut shell oil modified phenolic resin, boron modified phenolic resin, melamine-cashew nut shell oil modified phenolic resin, latex modified phenolic resin, or polyvinyl alcohol modified phenolic resin; the resin accounts for 10 to 90 wt% of the composite material.

4. The method according to claim 1, characterized in that, In step (1), the carbon fiber in the phenolic resin-based carbon fiber composite material is one or more of polyacrylonitrile carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, phenolic carbon fiber, and vapor-grown carbon fiber; the proportion of carbon fiber in the composite material is 10 to 90 wt%.

5. The method according to claim 1, characterized in that, The pretreatment time in step (2) is 0.2 to 1 hour, and the mass ratio of N-methylpyrrolidone to the composite material is 100:1 to 10:

1.

6. The method according to claim 1, characterized in that, The processing time in step (3) is 0.5 to 2 hours, and the mass fraction of the composite material in the solution is 1% to 10%.

7. The method according to claim 1, characterized in that, The washing in step (4) involves ultrasonication with ethanol for 5-30 minutes, followed by washing with water for 5-30 minutes; the drying in step (4) involves drying at 80℃-90℃ for 2-6 hours.

8. The method according to claim 1, characterized in that, The heating described in steps (1) and (3) is performed under normal pressure.

9. The method according to claim 1, characterized in that, The oxidant in step (3) is hydrogen peroxide, and the concentration of the oxidant solution is 30-40 wt%; or the oxidant is sodium hypochlorite, and the concentration of the oxidant solution is 0.1-0.5 mol / L.

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