Preparation method of BMC composite material based on pyrolysis recovery of carbon fibers

Abstract

The invention relates to a preparation method of a BMC (bulk molding compound) composite material based on pyrolyzed recycled carbon fibers, which comprises the following steps: pyrolyzing a pretreated waste carbon fiber composite material in an inert atmosphere to obtain recycled carbon fibers. The method comprises the following steps: ultrasonically cleaning recycled carbon fibers for 20-40 minutes by using acetone, performing vacuum drying, impregnating the recycled carbon fibers for 20-40 minutes by using a 1-3wt% silane coupling agent, and drying to obtain pretreated recycled carbon fibers; the recycled carbon fibers are mixed with an epoxy resin system according to the proportion of 30-45 wt% to prepare a BMC material body. And carrying out compression molding on the BMC material body to obtain the BMC composite material. According to the method, nitrogen protection, acetone ultrasonic cleaning and silane coupling agent activation are adopted, a proper epoxy resin system is selected, and the temperature difference between an upper mold and a lower mold is controlled, so that the recovered carbon filaments are effectively re-compounded. On the basis, the performance of the recycled carbon fibers is further improved by combining four procedures of compound catalytic liquid pretreatment, segmented slow cooling, low-temperature plasma decoking and nano coating repairing.

Description

Technical Field

[0001] This invention relates to the technical field of carbon fiber composite materials, and more particularly to a method for preparing BMC composite materials based on pyrolysis-recycled carbon fibers. Background Technology

[0002] Bulk molding compounds (BMCs) are widely used in aerospace, automotive, and electronics industries due to their high strength and lightweight properties. However, the accumulation of large amounts of waste BMCs not only wastes resources but also puts pressure on the environment. Currently, pyrolysis has become the mainstream technology for recycling carbon fibers from waste BMCs due to its moderate investment cost and high fiber strength retention rate. The core idea is to decompose the resin matrix in a high-temperature inert atmosphere, retain the carbon fibers, and then improve the usability of the recycled fibers through decoking and activation treatments.

[0003] In existing technologies, two typical schemes have been developed for optimizing the pyrolysis method for recovering carbon fibers:

[0004] One approach focuses on low-temperature descaling and ozone activation, such as the method disclosed in patent application CN119019757A. This approach effectively reduces energy consumption and fiber damage associated with traditional high-temperature oxidation through low-temperature ozone activation, but it still has limitations: First, the impregnation stage uses only a single zinc acetate catalyst, which, while catalyzing the breaking of CO bonds in the resin, cannot adsorb CO2 and organic acids generated during pyrolysis. Acidic substances easily corrode the carbon fiber surface, leading to a hidden loss of fiber strength. Second, the cooling process after pyrolysis does not mention a temperature control strategy, relying solely on natural cooling from furnace temperature to room temperature. Rapid cooling of high-temperature fibers can easily create internal and external temperature differences, triggering thermal stress microcracks and further reducing fiber mechanical properties. Third, after cleaning, no deep treatment is performed on stubborn semi-coke, relying only on ozone oxidation, which may still leave trace amounts of semi-coke residue, affecting subsequent interfacial bonding with the resin matrix.

[0005] Another type focuses on reducing the pyrolysis temperature through pretreatment, such as the pretreatment method disclosed in patent application CN119307001A. This method effectively reduces the activation energy of resin decomposition through the dual effects of swelling and catalysis of zinc acetate. However, it also has significant shortcomings: First, although high-temperature oxidation decoking can completely remove semi-coke, it leads to disorder of the graphitized layers of carbon fibers and insufficient strength retention. Second, the activation treatment relies solely on air oxidation to introduce oxygen-containing functional groups, without addressing the repair of microcracks on the fiber surface (generated during pyrolysis and oxidation), thus limiting the improvement of the intrinsic strength of the fiber. Third, there is no auxiliary decoking step after cleaning. When the zinc acetate concentration is low, the resin decomposition is incomplete, easily forming small semi-coke particles that adhere to the fiber surface, which are difficult to completely remove in subsequent oxidation, resulting in low interfacial shear strength.

[0006] In summary, existing pyrolysis recycling technologies still suffer from drawbacks such as low performance retention of recycled carbon fibers and incomplete removal of semi-coke. Furthermore, most studies only focus on the stage of thermal cracking to recover carbon fibers, failing to achieve the recombination and molding of carbon filaments. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to provide a method for preparing BMC composite material based on pyrolysis-recovered carbon fiber, which aims to solve the technical problems of low performance retention rate of recovered carbon fiber, incomplete removal of semi-coke, and failure to achieve recombinant molding of carbon filaments in existing pyrolysis recovery technologies.

[0008] Technical Solution: To solve the above technical problems, a method for preparing BMC composite materials based on pyrolysis-recycled carbon fibers is provided, including the following steps:

[0009] (1) The pretreated waste carbon fiber composite material is pyrolyzed in an inert atmosphere to obtain recycled carbon fiber;

[0010] (2) The recycled carbon fiber is ultrasonically cleaned with acetone for 20-40 minutes, vacuum dried, impregnated with 1-3wt% silane coupling agent for 20-40 minutes and dried to obtain pretreated recycled carbon fiber.

[0011] (3) The recycled carbon fiber from step (2) is mixed with the epoxy resin system at a ratio of 30-45 wt% to prepare BMC material;

[0012] (4) The BMC material is molded to obtain the BMC composite material.

[0013] Further, in step (3), the epoxy resin system includes the following components: E51 epoxy resin, ethylene glycol diglycidyl ether, and acid anhydride curing agent.

[0014] Further, by mass percentage, the epoxy resin system comprises the following components: 2-4% ethylene glycol diglycidyl ether, 1-3% acid anhydride curing agent, and the balance E51 epoxy resin.

[0015] Further, step (1) includes:

[0016] The waste carbon fiber composite material is placed in a tube furnace and an inert atmosphere is introduced.

[0017] The tubular furnace is heated from room temperature to 200℃ at a rate of 3-10℃ / min and held for 20-40min. Then, the temperature is increased to 390-420℃ at a rate of 3-6℃ / min and held for 45-90min. The waste carbon fiber composite material after the high-temperature reaction is then cooled to room temperature.

[0018] During the heating process, a slight positive pressure is maintained, and the inert gas flow rate is controlled at 0.8-1.2 L / min.

[0019] Further, in step (3), the mixing includes: first, premixing at a speed of 20-60 rpm; stirring for 3-5 minutes; then, main mixing at a speed of 100-300 rpm for 8-15 minutes, and stopping the machine to scrape the wall for 1 minute every 3-4 minutes during the main mixing process; placing the mixing system in a vacuum environment of -0.08 to -0.095 MPa for 5-10 minutes to degas.

[0020] Further, in step (4), the molding process involves putting the BMC material into a mold cavity preheated to 30-45°C, pre-pressing it with a pressure of 2-3MPa for 30-60 seconds, and after the pre-pressing and venting are completed, raising the temperature to 110-145°C, increasing the pressure to 8-12MPa, and holding the pressure for 4-6 minutes.

[0021] Further, in step (1), the method for preparing the pretreated waste carbon fiber composite material is to cut the waste carbon fiber composite material into 30-50mm pieces, put them into a compound catalytic ethanol impregnation solution, and ultrasonically impregnate them at room temperature for 2 hours; the compound catalytic ethanol impregnation solution contains 1-3mol / L zinc acetate and 0.1-0.3mol / L zinc acetylacetonate hydrate. After ultrasonic impregnation, the material is placed in a normal pressure environment at 60℃ and dried for 24 hours, and the moisture content of the dried material is controlled to be ≤1wt%.

[0022] Further, in step (2), after ultrasonic cleaning with acetone and before vacuum drying, the following steps are taken: a low-temperature plasma generator is used, with a mixed gas of argon and oxygen in a volume ratio of 3-5:1 as the working atmosphere, the gas flow rate is controlled at 30-50 mL / min, and the recycled carbon fiber after ultrasonic cleaning with acetone is treated at a temperature of 60-80℃ for 3-5 min.

[0023] Furthermore, after completing step (2) and before proceeding to step (3), the following steps are also included: immersing the activated recycled carbon fiber in a coating solution and forming a 1-2 μm thick coating by dip coating method. The coating solution includes 10-15 wt% low molecular weight epoxy resin with a solid content of 3-5 wt% nano-SiO2 and anhydrous ethanol. After dip coating, the recycled carbon fiber is pre-cured at 70-90℃ for 25-35 min and then heated to 120-145℃ for final curing for 1 h.

[0024] Furthermore, the step of cooling the waste carbon fiber composite material after the high-temperature reaction to room temperature is as follows: maintaining a nitrogen atmosphere, first cooling the thermally cracked recycled carbon fiber to 180-220℃ at a rate of 4-6℃ / min, holding for 25-35min, then cooling to 90-110℃ at a rate of 7-9℃ / min, holding for 18-22min, and finally naturally cooling to room temperature.

[0025] In this application, a compound catalytic ethanol impregnation solution is prepared using zinc acetate and zinc acetylacetone hydrate. Zinc acetate serves as the core catalyst, supplemented by zinc acetylacetone hydrate. This compound catalytic ethanol impregnation solution can selectively catalyze the breaking of phenolic oxygen bonds and NC bonds in the resin matrix, reducing the resin pyrolysis activation energy and lowering the pyrolysis temperature from the existing 450-550℃ to 380-390℃. This not only reduces the damage to the graphitized layers of carbon fibers caused by high temperatures but also improves the separation effect between resin and carbon fibers, preventing resin carbonization and adhesion to the carbon fiber surface, thus avoiding adverse phenomena such as reduced strength when recycling carbon fibers for reuse. The ethanol solvent softens the resin matrix through penetration, allowing the catalyst components to be uniformly dispersed at the resin-fiber interface and within the polymer chains, laying the foundation for the complete decomposition of the resin during subsequent pyrolysis. The three components work synergistically to achieve an integrated effect of catalytic cooling, corrosion protection, and swelling-assisted decomposition.

[0026] After pyrolysis, carbon fibers are in a high-temperature state. If they are allowed to cool naturally using existing technology, the temperature difference between the inside and outside of the fiber can reach over 200°C, which can easily induce thermal stress and cause microcracks on the surface. This solution uses a segmented temperature control strategy to slowly release thermal stress, effectively suppressing graphite lamellar slippage and microcrack initiation, ensuring the structural integrity of the carbon fiber, and providing a structural basis for maintaining strength.

[0027] In this application, ultrasonic cleaning with acetone can remove most of the surface resin residue, but its effect on removing the dense semi-coke layer formed by resin carbonization is limited. High-energy particles O⁺ and OH⁺ generated by low-temperature plasma have strong oxidizing properties and can rapidly oxidize stubborn semi-coke at low temperatures of 60-80℃, converting it into CO2 for volatilization and removal, which is beneficial for improving the coke removal rate. Simultaneously, plasma treatment can introduce oxygen-containing functional groups such as hydroxyl and carboxyl groups onto the fiber surface, increasing the O / C ratio and significantly improving the fiber surface energy. This provides more active sites for subsequent grafting of silane coupling agents, strengthening the interfacial bonding between the fiber and the resin matrix. Microcracks on the fiber surface, inevitably generated during pyrolysis and treatment, are a key cause of strength loss. Low-molecular-weight epoxy resin has excellent permeability and can fully fill the gaps between microcracks. Its epoxy groups chemically bond with the hydroxyl groups on the fiber surface, forming a strong repair layer. Nano-SiO₂ particles are uniformly dispersed in the epoxy coating, which can improve the coating toughness through dispersion strengthening effect, preventing the repair layer from becoming brittle, while also increasing the surface roughness of the fiber.

[0028] Beneficial effects: Implementing the embodiments of the present invention will have the following beneficial effects:

[0029] This application discloses a method for preparing BMC composite materials based on pyrolysis-recovered carbon fibers. In the pyrolysis recovery stage, a nitrogen-protected tubular furnace and precise temperature control are employed to preserve the composability of the carbon fibers. Subsequent two-step treatment involves acetone ultrasonic cleaning and silane coupling agent activation. During the mixing stage, the proportion of carbon fibers added is controlled, and an epoxy resin system with suitable epoxy value and viscosity is selected as the matrix to adapt to the carbon fibers. A mold design with venting grooves and control of the temperature difference between the upper and lower molds to ≤5℃ eliminate flow dead zones caused by gas resistance and temperature unevenness during filling, ultimately achieving effective recombination of the recovered carbon fibers. Simultaneously, the combination of four steps—pretreatment with a compounding catalyst, segmented slow cooling after pyrolysis, low-temperature plasma decoking after acetone ultrasonic cleaning, and nano-coating repair—further improves the performance of the recovered carbon fibers. The BMC composite material obtained by mixing the recovered carbon fibers and the epoxy resin system exhibits excellent mechanical properties. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0031] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0032] The sources of the raw materials used in the following examples and comparative examples are as follows:

[0033] KH-550 silane coupling agent was used, and HHPA was used as the anhydride curing agent.

[0034] Example 1:

[0035] (1) Cut the waste carbon fiber composite material into 30-50mm pieces and put them into a compound catalytic ethanol impregnation solution. Impregnate the material at 25℃ with an ultrasonic frequency of 100kHz for 2h. The compound catalytic ethanol impregnation solution contains 1-3mol / L zinc acetate and 0.1-0.3mol / L zinc acetylacetone hydrate. After ultrasonic impregnation, dry the material at 60℃ and normal pressure for 24h. Control the moisture content of the material after drying to ≤1wt% to obtain the pretreated waste carbon fiber composite material.

[0036] (2) Place the waste carbon fiber composite material in a tube furnace and introduce nitrogen gas. The flow rate of nitrogen gas is controlled at 0.8-1.2 L / min. The tube furnace is heated from room temperature to 200℃ at a rate of 3-10℃ / min and held for 20-40 min. Then, it is heated to 390-420℃ at a rate of 3-6℃ / min and held for 45-90 min to obtain recycled carbon fiber after thermal cracking. The recycled carbon fiber after thermal cracking is cooled to 180-220℃ at a rate of 4-6℃ / min and held for 25-35 min. Then, it is cooled to 90-110℃ at a rate of 7-9℃ / min and held for 18-22 min. Finally, it is naturally cooled to room temperature. During the reaction, the tube furnace is maintained at a slight positive pressure of 150 Pa to obtain recycled carbon fiber.

[0037] (3) The recycled carbon fiber is ultrasonically cleaned with acetone for 20-40 minutes, and then the recycled carbon fiber is reacted with a low temperature plasma generator. The working atmosphere is a mixture of argon and oxygen in a volume ratio of 3-5:1. The gas flow rate is controlled at 30-50 mL / min and treated at 60-80℃ for 3-5 minutes. Finally, the recycled carbon fiber is vacuum dried and then impregnated with 1-3wt% silane coupling agent for 20-40 minutes and dried to obtain the pretreated recycled carbon fiber.

[0038] (4) The pretreated recycled carbon fiber is immersed in the coating solution and a 1-2 μm thick coating is formed by dip coating. The coating solution includes 10-15 wt% low molecular weight epoxy resin with solid content, 3-5 wt% nano SiO2 and anhydrous ethanol. After dip coating, it is first pre-cured at 70-90℃ for 25-35 min, and then heated to 120-145℃ for final curing for 1 h. The cured recycled carbon fiber is then obtained.

[0039] (5) By mass percentage, 2-4% ethylene glycol diglycidyl ether, 1-3% acid anhydride curing agent and the balance E51 epoxy resin are mixed to obtain an epoxy resin system. The recycled carbon fiber is mixed with the epoxy resin system at a ratio of 30-45wt% and premixed at a speed of 20-60rpm for 3-5min. Then, the mixture is mainly mixed at a speed of 100-300rpm for 8-15min. During the main mixing process, the machine is stopped and the wall is scraped for 1min every 3-4min. Finally, the mixture is placed in a vacuum environment of -0.08 to -0.095MPa for 5-10min to degas and obtain BMC material.

[0040] (6) The BMC material is put into the mold cavity preheated to 30-45℃, and pre-pressed at 2-3MPa for 30-60s. After the pre-pressing is completed and the air is exhausted, the temperature is raised to 110-145℃, the pressure is increased to 8-12MPa, and the pressure is held for 4-6min to obtain the BMC composite material.

[0041] In Example 1, the preparation method of BMC composite material based on thermally cracked recycled carbon fiber is as follows:

[0042] (1) The waste carbon fiber composite material was cut into 40 mm pieces and put into a compound catalytic ethanol impregnation solution. It was impregnated at 25°C with an ultrasonic frequency of 100 kHz for 2 h. The compound catalytic ethanol impregnation solution contained 1.5 mol / L zinc acetate and 0.15 mol / L zinc acetylacetone hydrate. After ultrasonic impregnation, the material was dried at 60°C and normal pressure for 24 h. The moisture content of the material after drying was controlled to be ≤1 wt%. The pretreated waste carbon fiber composite material was obtained.

[0043] (2) The waste carbon fiber composite material was placed in a tube furnace and nitrogen was introduced. The flow rate of nitrogen was controlled at 1L / min. The tube furnace was heated from room temperature to 200℃ at a rate of 5℃ / min and held for 30min. Then it was heated to 400℃ at a rate of 5℃ / min and held for 60min to obtain recycled carbon fiber after thermal cracking. The recycled carbon fiber after thermal cracking was cooled to 200℃ at a rate of 5℃ / min and held for 30min. Then it was cooled to 100℃ at a rate of 8℃ / min and held for 20min. Finally, it was naturally cooled to room temperature. During the reaction, the tube furnace was maintained at a slight positive pressure of 150Pa to obtain recycled carbon fiber. The equipment used is a nitrogen-protected tubular furnace with an inner diameter ranging from 80-120 mm, a hot zone length ranging from 300-600 mm, a maximum temperature of 1100-1200℃, and a temperature control accuracy of ±1℃. It supports MFC flow control of 0-5 L / min, 0-2 kPa micro-positive pressure monitoring, and is equipped with exhaust gas condensation and filtration functions. Nitrogen parameters must meet the following requirements: purity ≥99.999%, micro-positive pressure 150 Pa. Before heating, a 12-minute nitrogen purging or 2-3 vacuum / nitrogen purging cycles are required. The resin matrix is ​​removed through pyrolysis, and carbon fibers are recovered with a recovery rate of approximately 55%. Thermogravimetric analysis shows that the residual carbon / ash content of the recovered carbon fibers is ≤0.6 wt%. The pyrolyzed carbon fibers are in a high-temperature state; if naturally cooled using existing technology, the temperature difference between the inside and outside of the fiber can reach over 200℃, easily inducing thermal stress and causing surface micro-cracks. This solution employs a segmented temperature control strategy to slowly release thermal stress, effectively suppressing graphite lamellar slippage and microcrack initiation, ensuring the structural integrity of the carbon fiber, and providing a structural foundation for maintaining strength.

[0044] (3) The recycled carbon fiber was ultrasonically cleaned with acetone for 30 min, and then the recycled carbon fiber was reacted with a low temperature plasma generator. The working atmosphere was a mixture of argon and oxygen in a volume ratio of 4:1. The gas flow rate was controlled at 40 mL / min and the treatment was carried out at 60-80℃ for 3-5 min. Finally, the recycled carbon fiber was vacuum dried and then impregnated with 2wt% silane coupling agent for 30 min and dried to obtain the pretreated recycled carbon fiber.

[0045] (4) The pretreated recycled carbon fibers are immersed in a coating solution to form a 1.5 μm thick coating using an dip-coating method. The coating solution includes 12 wt% low molecular weight epoxy resin with a solid content of 4 wt% nano-SiO2 and anhydrous ethanol. After dip-coating, the mixture is pre-cured at 80°C for 30 min, and then heated to 135°C for final curing for 1 h. The cured recycled carbon fibers are then obtained. For example, the molecular weight range of the selected low molecular weight epoxy resin is 320–340, and the particle size of the nano-SiO2 is 35 nm. The specific implementation steps of the dip-coating method include:

[0046] Step 1, Coating liquid pretreatment: Prepare the nano coating liquid according to the preset formula, put it into a planetary mixer, stir at 150 rpm for 30 minutes to ensure uniform dispersion of nano SiO2, and then let it stand for 10 minutes to eliminate the bubbles generated by stirring.

[0047] Step 2, Preparation of dipping equipment: Use a constant temperature dipping tank made of stainless steel, equipped with a temperature control device with a temperature control accuracy of ±2℃, to stabilize the temperature in the dipping tank at 25℃, so as to avoid the rapid evaporation of ethanol due to excessive temperature, which would affect the uniformity of the coating.

[0048] Step 3, fiber impregnation operation: The recycled carbon fibers, which have been activated by silane and vacuum dried, are evenly spread in a porous basket and slowly immersed in the pretreated nano-coating liquid to ensure that all fibers are completely submerged. The impregnation time is controlled at 2 minutes to ensure that the coating liquid fully penetrates while avoiding excessive adsorption that would result in an overly thick coating.

[0049] Step 4, Removal of excess coating liquid: After impregnation, lift the basket out of the coating liquid at a uniform speed of 5 cm / min and let it stand above the impregnation tank for 30 seconds to drain the excess coating liquid from the surface; then use clean compressed air with a pressure of 0.1 MPa to blow the fiber at a 45° angle for 10 seconds to further remove the excess coating liquid and ensure uniform coating thickness.

[0050] Step 5, Coating thickness control: By adjusting the viscosity of the coating liquid and the lifting speed within the range of 80-120 mPa・s, the coating thickness on the fiber surface can be precisely controlled to 1.5 μm. 3-5 fibers can be randomly sampled using a coating thickness gauge to ensure that the thickness meets the requirements.

[0051] Step 6, Curing and Bonding: Immediately transfer the coated fibers into a hot air drying oven. Pre-curing is performed at 80℃ for 30 minutes, followed by a final curing at 120℃ for 1 hour. The pre-curing stage removes the ethanol solvent from the coating and initially fixes its shape. The final curing stage achieves chemical bonding between the E44 epoxy resin and the hydroxyl groups on the fiber surface, forming a strong composite repair layer.

[0052] (5) By mass percentage, 3% ethylene glycol diglycidyl ether, 2% acid anhydride curing agent, and the balance E51 epoxy resin are mixed to obtain an epoxy resin system. The recycled carbon fiber is mixed with the epoxy resin system at a ratio of 40wt%. First, it is premixed at a speed of 40rpm for 4min, and then the main mixing is carried out at a speed of 200rpm for 12min. During the main mixing process, the machine is stopped and the wall is scraped for 1min every 3min. Finally, it is placed in a vacuum environment of -0.09MPa for 8min to degas and obtain BMC material. The epoxy resin system has the following requirements: the epoxy value range is 0.45~0.55eq / 100g, preferably 0.50±0.02eq / 100g, and the epoxy viscosity range is 10000~16000mPa·s, preferably 13000mPa·s. The mixing equipment uses a 10-30L vacuum planetary mixer, double planetary mixer, or Z-type kneader, with a vacuum degree of −0.08 to −0.095 MPa and a jacket temperature control of 20-40℃. During mixing, chopped recycled carbon fibers are added to the epoxy resin system at a ratio of 30-45 wt%, preferably 40 wt%, and stirred until homogeneous under conditions of an internal temperature of 25-30℃ and a system temperature difference ≤5℃. For viscosity control, Brookfield RV is used to record the viscosity every 5 minutes to ensure that the composite viscosity of the mixed system is 150-250 Pa·s, preferably 200 Pa·s, to obtain the BMC material.

[0053] (6) The BMC material is placed into a mold cavity preheated to 40°C. It is first pre-pressed at 3MPa for 45s. After the pre-pressing and venting are completed, the temperature is raised to 135°C, the pressure is increased to 10MPa, and the pressure is maintained for 5min to obtain the BMC composite material. The pre-pressing is used to remove the trace gas remaining in the BMC material. The mold temperature is required to be controlled at 30-45°C, and the temperature difference between the upper and lower molds is ≤5°C. The mold is equipped with venting grooves with a depth of 0.02-0.05mm, the surface roughness Ra≤0.2μm, and is treated with a fluorocarbon release agent. The molding process includes: placing the BMC material into a mold cavity preheated to 40°C, and using a staged pressurization process: first, pre-pressing at 2.5MPa for 45 seconds to vent, then raising the temperature to 135°C, then increasing the pressure to 10MPa, maintaining the pressure at 135°C for 5min, and demolding after the material is completely cured to obtain a high-mechanical-performance BMC composite material product based on recycled carbon fiber. For thick-walled or high-resin-content workpieces, the heat preservation time can be appropriately extended. After the pressure holding is completed, allow it to cool naturally to ≤100℃ before demolding to obtain a composite product with a smooth surface and high density.

[0054] Example 2:

[0055] (1) The waste carbon fiber composite material was cut into 40 mm pieces and put into a compound catalytic ethanol impregnation solution. It was impregnated at 25°C with an ultrasonic frequency of 100 kHz for 2 h. The compound catalytic ethanol impregnation solution contained 1 mol / L zinc acetate and 0.1 mol / L zinc acetylacetone hydrate. After ultrasonic impregnation, the material was placed in a normal pressure environment at 60°C and dried for 24 h. The moisture content of the material after drying was controlled to be ≤1 wt%, and the pretreated waste carbon fiber composite material was obtained.

[0056] (2) Place the waste carbon fiber composite material in a tube furnace and introduce nitrogen gas, with the nitrogen flow rate controlled at 1L / min;

[0057] The tubular furnace was heated from room temperature to 200°C at a rate of 5°C / min and held for 30 min, then heated to 400°C at a rate of 5°C / min and held for 60 min to obtain thermally cracked recycled carbon fibers. The thermally cracked recycled carbon fibers were cooled to 200°C at a rate of 5°C / min and held for 30 min, then cooled to 100°C at a rate of 8°C / min and held for 20 min, and finally cooled naturally to room temperature. During the reaction, the tubular furnace was maintained at a slight positive pressure of 150 Pa to obtain recycled carbon fibers.

[0058] (3) The recycled carbon fiber was ultrasonically cleaned with acetone for 30 min, and then the recycled carbon fiber was reacted with a low temperature plasma generator. The working atmosphere was a mixture of argon and oxygen in a volume ratio of 3:1. The gas flow rate was controlled at 40 mL / min and the treatment was carried out at 60-80℃ for 3-5 min. Finally, the recycled carbon fiber was vacuum dried and then impregnated with 1wt% silane coupling agent for 30 min and dried to obtain the pretreated recycled carbon fiber.

[0059] (4) The pretreated recycled carbon fibers are immersed in a coating solution to form a 1 μm thick coating using an dip-coating method. The coating solution includes 10 wt% low molecular weight epoxy resin with a solid content of 3 wt% nano-SiO2 and anhydrous ethanol. After dip-coating, the recycled carbon fibers are pre-cured at 80°C for 30 min, and then the temperature is raised to 135°C for final curing for 1 h. The cured recycled carbon fibers are then obtained. For example, the molecular weight range of the selected low molecular weight epoxy resin is 320-340, and the particle size of the nano-SiO2 is 35 nm.

[0060] (5) By mass percentage, 2% ethylene glycol diglycidyl ether, 1% acid anhydride curing agent and the balance E51 epoxy resin are mixed to obtain an epoxy resin system. The recycled carbon fiber is mixed with the epoxy resin system at a ratio of 30wt%. First, it is premixed at a speed of 40rpm for 4min. Then, it is main mixed at a speed of 200rpm for 12min. During the main mixing process, the machine is stopped and scraped for 1min every 3min. Finally, it is placed in a vacuum environment of -0.09MPa for 8min to degas and obtain BMC material.

[0061] (6) The BMC material is placed into the mold cavity preheated to 40°C, and pre-pressed at 3MPa for 45s. After the pre-pressing is completed and the gas is exhausted, the temperature is raised to 135°C, the pressure is increased to 10MPa, and the pressure is maintained for 5min to obtain the BMC composite material. The pre-pressing is used to remove the trace amounts of gas remaining in the BMC material.

[0062] Example 3:

[0063] (1) The waste carbon fiber composite material was cut into 40 mm pieces and put into a compound catalytic ethanol impregnation solution. It was impregnated at 25°C with an ultrasonic frequency of 100 kHz for 2 h. The compound catalytic ethanol impregnation solution contained 3 mol / L zinc acetate and 0.3 mol / L zinc acetylacetone hydrate. After ultrasonic impregnation, the material was placed in a normal pressure environment at 60°C and dried for 24 h. The moisture content of the material after drying was controlled to be ≤1 wt%, and the pretreated waste carbon fiber composite material was obtained.

[0064] (2) The waste carbon fiber composite material was placed in a tube furnace and nitrogen was introduced. The flow rate of nitrogen was controlled at 1L / min. The tube furnace was heated from room temperature to 200℃ at a rate of 5℃ / min and held for 30min. Then it was heated to 400℃ at a rate of 5℃ / min and held for 60min to obtain recycled carbon fiber after thermal cracking. The recycled carbon fiber after thermal cracking was cooled to 200℃ at a rate of 5℃ / min and held for 30min. Then it was cooled to 100℃ at a rate of 8℃ / min and held for 20min. Finally, it was naturally cooled to room temperature. During the reaction, the tube furnace was maintained at a slight positive pressure of 150Pa to obtain recycled carbon fiber.

[0065] (3) The recycled carbon fiber was ultrasonically cleaned with acetone for 30 min, and then the recycled carbon fiber was reacted with a low temperature plasma generator. The working atmosphere was a mixture of argon and oxygen in a volume ratio of 5:1. The gas flow rate was controlled at 40 mL / min and the treatment was carried out at 60-80℃ for 3-5 min. Finally, the recycled carbon fiber was vacuum dried and then impregnated with 3wt% silane coupling agent for 30 min and dried to obtain the pretreated recycled carbon fiber.

[0066] (4) The pretreated recycled carbon fibers are immersed in a coating solution to form a 2μm thick coating using an dip-coating method. The coating solution includes 15wt% low molecular weight epoxy resin with a solid content of 5wt% nano-SiO2 and anhydrous ethanol. After dip-coating, the recycled carbon fibers are pre-cured at 80℃ for 30min, and then the temperature is raised to 135℃ for final curing for 1h. The cured recycled carbon fibers are then obtained. For example, the molecular weight range of the selected low molecular weight epoxy resin is 320-340, and the particle size of the nano-SiO2 is 35nm.

[0067] (5) By mass percentage, 4% ethylene glycol diglycidyl ether, 3% acid anhydride curing agent and the balance E51 epoxy resin are mixed to obtain an epoxy resin system. The recycled carbon fiber is mixed with the epoxy resin system at a ratio of 45wt%. First, it is premixed at a speed of 40rpm for 4min. Then, it is main mixed at a speed of 200rpm for 12min. During the main mixing process, the machine is stopped and the wall is scraped for 1min every 3min. Finally, it is placed in a vacuum environment of -0.09MPa for 8min to degas and obtain BMC material.

[0068] (6) The BMC material is placed into the mold cavity preheated to 40°C, and pre-pressed at 3MPa for 45s. After the pre-pressing is completed and the gas is exhausted, the temperature is raised to 135°C, the pressure is increased to 10MPa, and the pressure is maintained for 5min to obtain the BMC composite material. The pre-pressing is used to remove the trace amounts of gas remaining in the BMC material.

[0069] Comparative Example 1:

[0070] (1) The waste carbon fiber composite material is cut into 40mm pieces to obtain the waste carbon fiber composite material.

[0071] (2) The waste carbon fiber composite material was placed in a tube furnace and nitrogen was introduced. The flow rate of nitrogen was controlled at 1L / min. The tube furnace was heated from room temperature to 200℃ at a rate of 5℃ / min and held for 30min. Then it was heated to 400℃ at a rate of 5℃ / min and held for 60min to obtain recycled carbon fiber after thermal cracking. The recycled carbon fiber after thermal cracking was cooled to 200℃ at a rate of 5℃ / min and held for 30min. Then it was cooled to 100℃ at a rate of 8℃ / min and held for 20min. Finally, it was naturally cooled to room temperature. During the reaction, the tube furnace was maintained at a slight positive pressure of 150Pa to obtain recycled carbon fiber.

[0072] (3) The recycled carbon fiber was ultrasonically cleaned with acetone for 30 min, and then the recycled carbon fiber was reacted with a low temperature plasma generator. The working atmosphere was a mixture of argon and oxygen in a volume ratio of 4:1. The gas flow rate was controlled at 40 mL / min and the treatment was carried out at 60-80℃ for 3-5 min. Finally, the recycled carbon fiber was vacuum dried and then impregnated with 2wt% silane coupling agent for 30 min and dried to obtain the pretreated recycled carbon fiber.

[0073] (4) The pretreated recycled carbon fibers are immersed in a coating solution to form a 1.5 μm thick coating using an dip-coating method. The coating solution includes 12 wt% low molecular weight epoxy resin with a solid content of 4 wt% nano-SiO2 and anhydrous ethanol. After dip-coating, the recycled carbon fibers are pre-cured at 80°C for 30 min, and then the temperature is raised to 135°C for final curing for 1 h. The cured recycled carbon fibers are then obtained. For example, the molecular weight range of the selected low molecular weight epoxy resin is 320-340, and the particle size of the nano-SiO2 is 35 nm.

[0074] (5) Mix 3% ethylene glycol diglycidyl ether, 2% acid anhydride curing agent and the balance of E51 epoxy resin by mass percentage to obtain an epoxy resin system. Mix the recycled carbon fiber with the epoxy resin system at a ratio of 40wt%. First, premix at a speed of 40rpm for 4min. Then, perform main mixing at a speed of 200rpm for 12min. During the main mixing process, stop the machine every 3min to scrape the wall for 1min. Finally, place it in a vacuum environment of -0.09MPa for 8min to degas and obtain BMC material.

[0075] (6) The BMC material is placed into the mold cavity preheated to 40°C, and pre-pressed at 3MPa for 45s. After the pre-pressing is completed and the gas is exhausted, the temperature is raised to 135°C, the pressure is increased to 10MPa, and the pressure is maintained for 5min to obtain the BMC composite material. The pre-pressing is used to remove the trace amounts of gas remaining in the BMC material.

[0076] Comparative Example 2:

[0077] (1) The waste carbon fiber composite material was cut into 40 mm pieces and put into a compound catalytic ethanol impregnation solution. It was impregnated at 25°C with an ultrasonic frequency of 100 kHz for 2 h. The compound catalytic ethanol impregnation solution contained 1.5 mol / L zinc acetate and 0.15 mol / L zinc acetylacetone hydrate. After ultrasonic impregnation, the material was dried at 60°C and normal pressure for 24 h. The moisture content of the material after drying was controlled to be ≤1 wt%. The pretreated waste carbon fiber composite material was obtained.

[0078] (2) The waste carbon fiber composite material was placed in a tube furnace and nitrogen was introduced. The flow rate of nitrogen was controlled at 1L / min. The tube furnace was heated from room temperature to 200℃ at a rate of 5℃ / min and held for 30min. Then it was heated to 400℃ at a rate of 5℃ / min and held for 60min to obtain recycled carbon fiber after thermal cracking. The recycled carbon fiber after thermal cracking was cooled to 200℃ at a rate of 5℃ / min and held for 30min. Then it was cooled to 100℃ at a rate of 8℃ / min and held for 20min. Finally, it was naturally cooled to room temperature. During the reaction, the tube furnace was maintained at a slight positive pressure of 150Pa to obtain recycled carbon fiber.

[0079] (3) The recycled carbon fiber was ultrasonically cleaned with acetone for 30 min, the gas flow rate was controlled at 40 mL / min, and it was treated at 60-80℃ for 3-5 min. Finally, the recycled carbon fiber was vacuum dried and then impregnated with 2wt% silane coupling agent for 30 min and dried to obtain the pretreated recycled carbon fiber.

[0080] (4) The pretreated recycled carbon fibers are immersed in a coating solution to form a 1.5 μm thick coating using an dip-coating method. The coating solution includes 12 wt% low molecular weight epoxy resin with a solid content of 4 wt% nano-SiO2 and anhydrous ethanol. After dip-coating, the recycled carbon fibers are pre-cured at 80°C for 30 min, and then the temperature is raised to 135°C for final curing for 1 h. The cured recycled carbon fibers are then obtained. For example, the molecular weight range of the selected low molecular weight epoxy resin is 320-340, and the particle size of the nano-SiO2 is 35 nm.

[0081] (5) Mix 3% ethylene glycol diglycidyl ether, 2% acid anhydride curing agent and the balance of E51 epoxy resin by mass percentage to obtain an epoxy resin system. Mix the recycled carbon fiber with the epoxy resin system at a ratio of 40wt%. First, premix at a speed of 40rpm for 4min. Then, perform main mixing at a speed of 200rpm for 12min. During the main mixing process, stop the machine every 3min to scrape the wall for 1min. Finally, place it in a vacuum environment of -0.09MPa for 8min to degas and obtain BMC material.

[0082] (6) The BMC material is placed into the mold cavity preheated to 40°C, and pre-pressed at 3MPa for 45s. After the pre-pressing is completed and the gas is exhausted, the temperature is raised to 135°C, the pressure is increased to 10MPa, and the pressure is maintained for 5min to obtain the BMC composite material. The pre-pressing is used to remove the trace amounts of gas remaining in the BMC material.

[0083] Comparative Example 3:

[0084] (1) The waste carbon fiber composite material was cut into 40 mm pieces and put into a compound catalytic ethanol impregnation solution. It was impregnated at 25°C with an ultrasonic frequency of 100 kHz for 2 h. The compound catalytic ethanol impregnation solution contained 1.5 mol / L zinc acetate and 0.15 mol / L zinc acetylacetone hydrate. After ultrasonic impregnation, the material was dried at 60°C and normal pressure for 24 h. The moisture content of the material after drying was controlled to be ≤1 wt%. The pretreated waste carbon fiber composite material was obtained.

[0085] (2) The waste carbon fiber composite material was placed in a tube furnace and nitrogen was introduced. The flow rate of nitrogen was controlled at 1L / min. The tube furnace was heated from room temperature to 200℃ at a rate of 5℃ / min and held for 30min. Then it was heated to 400℃ at a rate of 5℃ / min and held for 60min to obtain recycled carbon fiber after thermal cracking. The recycled carbon fiber after thermal cracking was cooled to 200℃ at a rate of 5℃ / min and held for 30min. Then it was cooled to 100℃ at a rate of 8℃ / min and held for 20min. Finally, it was naturally cooled to room temperature. During the reaction, the tube furnace was maintained at a slight positive pressure of 150Pa to obtain recycled carbon fiber.

[0086] (3) The recycled carbon fiber was ultrasonically cleaned with acetone for 30 min, and then the recycled carbon fiber was reacted with a low temperature plasma generator. The working atmosphere was a mixture of argon and oxygen in a volume ratio of 4:1. The gas flow rate was controlled at 40 mL / min and the treatment was carried out at 60-80℃ for 3-5 min. Finally, the recycled carbon fiber was vacuum dried and then impregnated with 2wt% silane coupling agent for 30 min and dried to obtain the pretreated recycled carbon fiber.

[0087] (4) Mix 3% ethylene glycol diglycidyl ether, 2% acid anhydride curing agent and the balance of E51 epoxy resin by mass percentage to obtain an epoxy resin system. Mix the recycled carbon fiber with the epoxy resin system at a ratio of 40wt%. First, premix at a speed of 40rpm for 4min. Then, perform main mixing at a speed of 200rpm for 12min. During the main mixing process, stop the machine every 3min to scrape the wall for 1min. Finally, place it in a vacuum environment of -0.09MPa for 8min to degas and obtain BMC material.

[0088] (5) The BMC material is put into the mold cavity preheated to 40°C, and pre-pressed at 3MPa for 45s. After the pre-pressing is completed and the gas is exhausted, the temperature is raised to 135°C, the pressure is increased to 10MPa, and the pressure is held for 5min to obtain the BMC composite material. The pre-pressing is used to remove the trace gas remaining in the BMC material.

[0089] Comparative Example 4:

[0090] (1) The waste carbon fiber composite material was cut into 40 mm pieces and put into a compound catalytic ethanol impregnation solution. It was impregnated at 25°C with an ultrasonic frequency of 100 kHz for 2 h. The compound catalytic ethanol impregnation solution contained 3 mol / L zinc acetate and 0.5 mol / L zinc acetylacetone hydrate. After ultrasonic impregnation, the material was placed in a normal pressure environment at 60°C and dried for 24 h. The moisture content of the material after drying was controlled to be ≤1 wt%, and the pretreated waste carbon fiber composite material was obtained.

[0091] (2) The waste carbon fiber composite material was placed in a tube furnace and nitrogen was introduced. The flow rate of nitrogen was controlled at 1L / min. The tube furnace was heated from room temperature to 200℃ at a rate of 5℃ / min and held for 30min. Then it was heated to 400℃ at a rate of 5℃ / min and held for 60min to obtain recycled carbon fiber after thermal cracking. The recycled carbon fiber after thermal cracking was cooled to 200℃ at a rate of 5℃ / min and held for 30min. Then it was cooled to 100℃ at a rate of 8℃ / min and held for 20min. Finally, it was naturally cooled to room temperature. During the reaction, the tube furnace was maintained at a slight positive pressure of 150Pa to obtain recycled carbon fiber.

[0092] (3) The recycled carbon fiber was ultrasonically cleaned with acetone for 30 min, and then the recycled carbon fiber was reacted with a low temperature plasma generator. The working atmosphere was a mixture of argon and oxygen in a volume ratio of 4:1. The gas flow rate was controlled at 40 mL / min and the treatment was carried out at 60-80℃ for 3-5 min. Finally, the recycled carbon fiber was vacuum dried and then impregnated with 2wt% silane coupling agent for 30 min and dried to obtain the pretreated recycled carbon fiber.

[0093] (4) The pretreated recycled carbon fibers are immersed in a coating solution to form a 1.5 μm thick coating using an dip-coating method. The coating solution includes 12 wt% low molecular weight epoxy resin with a solid content of 4 wt% nano-SiO2 and anhydrous ethanol. After dip-coating, the recycled carbon fibers are pre-cured at 80°C for 30 min, and then the temperature is raised to 135°C for final curing for 1 h. The cured recycled carbon fibers are then obtained. For example, the molecular weight range of the selected low molecular weight epoxy resin is 320-340, and the particle size of the nano-SiO2 is 35 nm.

[0094] (5) Mix 3% ethylene glycol diglycidyl ether, 2% acid anhydride curing agent and the balance of E51 epoxy resin by mass percentage to obtain an epoxy resin system. Mix the recycled carbon fiber with the epoxy resin system at a ratio of 40wt%. First, premix at a speed of 40rpm for 4min. Then, perform main mixing at a speed of 200rpm for 12min. During the main mixing process, stop the machine every 3min to scrape the wall for 1min. Finally, place it in a vacuum environment of -0.09MPa for 8min to degas and obtain BMC material.

[0095] (6) The BMC material is placed into the mold cavity preheated to 40°C, and pre-pressed at 3MPa for 45s. After the pre-pressing is completed and the gas is exhausted, the temperature is raised to 135°C, the pressure is increased to 10MPa, and the pressure is maintained for 5min to obtain the BMC composite material. The pre-pressing is used to remove the trace amounts of gas remaining in the BMC material.

[0096] Comparative Example 5:

[0097] (1) The waste carbon fiber composite material was cut into 40 mm pieces and put into a compound catalytic ethanol impregnation solution. It was impregnated at 25°C with an ultrasonic frequency of 100 kHz for 2 h. The compound catalytic ethanol impregnation solution contained 1.5 mol / L zinc acetate and 0.15 mol / L zinc acetylacetone hydrate. After ultrasonic impregnation, the material was dried at 60°C and normal pressure for 24 h. The moisture content of the material after drying was controlled to be ≤1 wt%. The pretreated waste carbon fiber composite material was obtained.

[0098] (2) The waste carbon fiber composite material was placed in a tube furnace and nitrogen was introduced. The flow rate of nitrogen was controlled at 1L / min. The tube furnace was heated from room temperature to 200℃ at a rate of 5℃ / min and held for 30min. Then it was heated to 400℃ at a rate of 5℃ / min and held for 60min to obtain recycled carbon fiber after thermal cracking. The recycled carbon fiber after thermal cracking was cooled to 200℃ at a rate of 5℃ / min and held for 30min. Then it was cooled to 100℃ at a rate of 8℃ / min and held for 20min. Finally, it was naturally cooled to room temperature. During the reaction, the tube furnace was maintained at a slight positive pressure of 150Pa to obtain recycled carbon fiber.

[0099] (3) The recycled carbon fiber was ultrasonically cleaned with acetone for 30 min, and then the recycled carbon fiber was reacted with a low temperature plasma generator. The working atmosphere was a mixture of argon and oxygen in a volume ratio of 1:1. The gas flow rate was controlled at 40 mL / min and the treatment was carried out at 60-80℃ for 3-5 min. Finally, the recycled carbon fiber was vacuum dried and then impregnated with 2wt% silane coupling agent for 30 min and dried to obtain the pretreated recycled carbon fiber.

[0100] (4) The pretreated recycled carbon fibers are immersed in a coating solution to form a 1.5 μm thick coating using an dip-coating method. The coating solution includes 12 wt% low molecular weight epoxy resin with a solid content of 4 wt% nano-SiO2 and anhydrous ethanol. After dip-coating, the recycled carbon fibers are pre-cured at 80°C for 30 min, and then the temperature is raised to 135°C for final curing for 1 h. The cured recycled carbon fibers are then obtained. For example, the molecular weight range of the selected low molecular weight epoxy resin is 320-340, and the particle size of the nano-SiO2 is 35 nm.

[0101] (5) Mix 3% ethylene glycol diglycidyl ether, 2% acid anhydride curing agent and the balance of E51 epoxy resin by mass percentage to obtain an epoxy resin system. Mix the recycled carbon fiber with the epoxy resin system at a ratio of 40wt%. First, premix at a speed of 40rpm for 4min. Then, perform main mixing at a speed of 200rpm for 12min. During the main mixing process, stop the machine every 3min to scrape the wall for 1min. Finally, place it in a vacuum environment of -0.09MPa for 8min to degas and obtain BMC material.

[0102] (6) The BMC material is placed into the mold cavity preheated to 40°C, and pre-pressed at 3MPa for 45s. After the pre-pressing is completed and the gas is exhausted, the temperature is raised to 135°C, the pressure is increased to 10MPa, and the pressure is maintained for 5min to obtain the BMC composite material. The pre-pressing is used to remove the trace amounts of gas remaining in the BMC material.

[0103] Comparative Example 6:

[0104] (1) The waste carbon fiber composite material was cut into 40 mm pieces and put into a compound catalytic ethanol impregnation solution. It was impregnated at 25°C with an ultrasonic frequency of 100 kHz for 2 h. The compound catalytic ethanol impregnation solution contained 1.5 mol / L zinc acetate and 0.15 mol / L zinc acetylacetone hydrate. After ultrasonic impregnation, the material was dried at 60°C and normal pressure for 24 h. The moisture content of the material after drying was controlled to be ≤1 wt%. The pretreated waste carbon fiber composite material was obtained.

[0105] (2) The waste carbon fiber composite material was placed in a tube furnace and nitrogen was introduced. The flow rate of nitrogen was controlled at 1L / min. The tube furnace was heated from room temperature to 200℃ at a rate of 5℃ / min and held for 30min. Then it was heated to 400℃ at a rate of 5℃ / min and held for 60min to obtain recycled carbon fiber after thermal cracking. The recycled carbon fiber after thermal cracking was cooled to 200℃ at a rate of 5℃ / min and held for 30min. Then it was cooled to 100℃ at a rate of 8℃ / min and held for 20min. Finally, it was naturally cooled to room temperature. During the reaction, the tube furnace was maintained at a slight positive pressure of 150Pa to obtain recycled carbon fiber.

[0106] (3) The recycled carbon fiber was ultrasonically cleaned with acetone for 30 min, and then the recycled carbon fiber was reacted with a low temperature plasma generator. The working atmosphere was a mixture of argon and oxygen in a volume ratio of 4:1. The gas flow rate was controlled at 40 mL / min and the treatment was carried out at 60-80℃ for 3-5 min. Finally, the recycled carbon fiber was vacuum dried and then impregnated with 2wt% silane coupling agent for 30 min and dried to obtain the pretreated recycled carbon fiber.

[0107] (4) The pretreated recycled carbon fibers are immersed in a coating solution to form a 1.5 μm thick coating using an dip-coating method. The coating solution includes 7 wt% low molecular weight epoxy resin with a solid content of 2 wt% nano-SiO2 and anhydrous ethanol. After dip-coating, the carbon fibers are pre-cured at 80°C for 30 min, and then the temperature is raised to 135°C for final curing for 1 h. The cured recycled carbon fibers are then obtained. For example, the molecular weight range of the selected low molecular weight epoxy resin is 320-340, and the particle size of the nano-SiO2 is 35 nm.

[0108] (5) Mix 3% ethylene glycol diglycidyl ether, 2% acid anhydride curing agent and the balance of E51 epoxy resin by mass percentage to obtain an epoxy resin system. Mix the recycled carbon fiber with the epoxy resin system at a ratio of 40wt%. First, premix at a speed of 40rpm for 4min. Then, perform main mixing at a speed of 200rpm for 12min. During the main mixing process, stop the machine every 3min to scrape the wall for 1min. Finally, place it in a vacuum environment of -0.09MPa for 8min to degas and obtain BMC material.

[0109] (6) The BMC material is placed into the mold cavity preheated to 40°C, and pre-pressed at 3MPa for 45s. After the pre-pressing is completed and the gas is exhausted, the temperature is raised to 135°C, the pressure is increased to 10MPa, and the pressure is maintained for 5min to obtain the BMC composite material. The pre-pressing is used to remove the trace amounts of gas remaining in the BMC material.

[0110] Table 1. Performance test results of Examples 1-3, Comparative Examples 1-6, and commercial native BMCs.

[0111] Performance indicators Tensile strength / MPa Bending strength / MPa Flexural modulus / GPa Impact strength / kJ·m⁻² Volume resistivity / Ω·cm Heat distortion temperature / °C Commercial Native BMC (Comparison) 205 340 11.0 28 <![CDATA[2.10×10 5 ]]> 195 Example 1 208.6 342.2 11.6 30.5 <![CDATA[2.23×10 5 ]]> 199.6 Example 2 201.1 332.0 11.3 28.8 <![CDATA[2.25×10 5 ]]> 194.0 Example 3 205.2 338.8 11.8 28.2 <![CDATA[2.52×10 5 ]]> 197.7 Comparative Example 1 174.5 270.9 9.2 24.8 <![CDATA[5.80×10 5 ]]> 180.5 Comparative Example 2 192.4 267.0 9.0 25.5 <![CDATA[5.26×10 5 ]]> 176.3 Comparative Example 3 189.8 315.6 10.2 27.6 <![CDATA[2.55×10 5 ]]> 185.8 Comparative Example 4 193.7 298.5 9.7 21.6 <![CDATA[3.84×10 5 ]]> 187.6 Comparative Example 5 186.2 287.2 9.4 23.4 <![CDATA[4.58×10 5 ]]> 180.6 Comparative Example 6 190.0 306.7 10.3 26.7 <![CDATA[3.05×10 5 ]]> 189.8

[0112] Example 1 is the preferred embodiment of this application. Comparative Example 1 lacks pretreatment with the compound catalytic ethanol impregnation solution, Comparative Example 2 lacks low-temperature plasma decoking, Comparative Example 3 lacks nano-coating repair, Comparative Example 4 increases the content of zinc acetate and zinc acetylacetone hydrate, Comparative Example 5 reduces the argon content during low-temperature plasma treatment, and Comparative Example 6 increases the content of low molecular weight epoxy resin and nano-SiO2. Comparative Examples 1-6 demonstrate that the four processes—compound catalytic solution pretreatment, staged slow cooling after pyrolysis, acetone ultrasonic cleaning followed by low-temperature plasma decoking, and nano-coating repair—complement each other, improving the performance of the recycled carbon fiber through their combined action.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for producing a BMC composite material based on pyrolytic recycled carbon fibers, characterized in that, The method comprises the following steps: (1) pyrolyzing the pretreated waste carbon fiber composite material in an inert atmosphere to obtain recycled carbon fiber; (2) ultrasonically cleaning the recycled carbon fiber with acetone for 20-40 minutes, vacuum drying, then immersing in 1-3wt% silane coupling agent for 20-40 minutes and drying to obtain pretreated recycled carbon fiber; (3) mixing the recycled carbon fiber in step (2) with an epoxy resin system at a proportion of 30-45wt% to prepare a BMC material body; (4) molding the BMC material body to obtain a BMC composite material.

2. The method for producing a BMC composite material based on pyrolytic recycled carbon fibers according to claim 1, characterized in that, In step (3), the epoxy resin system comprises the following components: E51 epoxy resin, ethylene glycol diglycidyl ether, and anhydride curing agent.

3. The method for producing a BMC composite material based on pyrolytic recycled carbon fibers according to claim 2, characterized in that, In terms of mass percentage, the epoxy resin system comprises the following components: 2-4% ethylene glycol diglycidyl ether, 1-3% anhydride curing agent, and the balance of E51 epoxy resin.

4. The method for preparing BMC composite material based on pyrolysis-recycled carbon fiber according to claim 1, characterized in that, The step (1) comprises: placing the waste carbon fiber composite material in a tube furnace and introducing an inert atmosphere; heating the tube furnace from room temperature to 200℃ at a rate of 3-10℃ / min, maintaining for 20-40min, then heating to 390-420℃ at a rate of 3-6℃ / min, maintaining for 45-90min, and cooling the waste carbon fiber composite material after high-temperature reaction to room temperature; maintaining a slight positive pressure during the heating process, and controlling the inert gas flow at 0.8-1.2L / min.

5. The method for preparing BMC composite material based on pyrolysis-recycled carbon fiber according to claim 1, characterized in that, In step (3), the mixing comprises: first premixing at a speed of 20-60rpm; stirring for 3-5min, then main mixing at a speed of 100-300rpm, stirring for 8-15min, and stopping every 3-4min during the main mixing process to scrape the wall for 1min.

6. The method for preparing BMC composite material based on pyrolysis-recycled carbon fiber according to claim 1, characterized in that, In step (4), the molding step is to put the BMC material body into a mold cavity preheated to 30-45℃, first pre-pressing at a pressure of 2-3MPa for 30-60s, then heating to 110-145℃, increasing the pressure to 8-12MPa, and maintaining for 4-6min after the pre-pressing exhaust.

7. The method for preparing BMC composite material based on pyrolysis-recycled carbon fiber according to claim 1, characterized in that, In step (1), the preparation method of the pretreated waste carbon fiber composite material is to cut the waste carbon fiber composite material into 30-50mm material, immerse in a compounded catalytic ethanol immersion liquid at room temperature for 2h; the compounded catalytic ethanol immersion liquid contains 1-3mol / L zinc acetate and 0.1-0.3mol / L zinc acetylacetone hydrate, after ultrasonic immersion, the material is dried at 60℃ in a normal pressure environment for 24h, and the water content of the dried material is controlled to be ≤1wt%.

8. The method for preparing BMC composite material based on pyrolysis-recycled carbon fiber according to claim 1, characterized in that, In step (2), after acetone ultrasonic cleaning, the following steps are taken before vacuum drying: using a low-temperature plasma generator, using a mixed gas of argon and oxygen at a volume ratio of 3-5:1 as the working atmosphere, controlling the gas flow at 30-50mL / min, and treating the recycled carbon fiber after acetone ultrasonic cleaning at a temperature of 60-80℃ for 3-5min.

9. The method of producing a BMC composite material based on pyrolytic recycled carbon fibers according to claim 1, characterized in that, After the step (2) is performed, before the step (3) is entered, the following step is further included: immersing the pretreated recycled carbon fiber into a coating liquid to form a 1-2 μm thick coating layer by dip coating, the coating liquid including 10-15 wt% solid content of low molecular weight epoxy resin and 3-5 wt% nano-SiO2 and anhydrous ethanol; after dip coating, pre-curing at 70-90 ℃ for 25-35 min, and then final curing at 120-145 ℃ for 1 h, the recycled carbon fiber after curing.

10. The method of producing a BMC composite material based on pyrolytic recycled carbon fibers according to claim 4, characterized in that, The step of cooling the waste carbon fiber composite material after high temperature reaction to room temperature is: maintaining a nitrogen atmosphere, first cooling the heat-cracked recycled carbon fiber to 180-220 ℃ at a rate of 4-6 ℃ / min, holding for 25-35 min, then cooling to 90-110 ℃ at a rate of 7-9 ℃ / min, holding for 18-22 min, and finally naturally cooling to room temperature.