Method for carding short fibers of recycled carbon fibers into strips

Abstract

The invention discloses a short fiber carding and slivering method for recycling carbon fibers. The method comprises the following steps: (1) screening the recycled carbon fibers by using a vibrating screen; (2) soaking the short carbon fibers in a soaking solution for chemical treatment, wherein the soaking solution comprises limonene, turpentine and acrylate modified polyoxyethylene ether; (3) carrying out ultrasonic cleaning on the soaked short carbon fibers; (4) carrying out drying treatment on the cleaned short carbon fibers; and (5) feeding the dried short carbon fibers into a carding machine for carding into strips. The acrylate modified polyoxyethylene ether has good emulsifying, dispersing and solubilizing effects, so that the limonene and the turpentine can be better mixed and dispersed in the soaking solution to form a stable solution system, the uniformity and the stability of the soaking solution are improved, the smell of the turpentine can be reduced, and the cleaning effect of the turpentine is improved. The adverse effects on the environment and operators are reduced, and meanwhile, the dissolving and removing effects of the soaking solution on the resin can be enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fiber recycling, and in particular to a method for carding short fibers of recycled carbon fibers into strips. Background Art

[0002] Carbon fiber has excellent properties such as high strength and low density, and is widely used in many fields such as aerospace, automobile manufacturing, sports equipment, etc. However, with the extensive use of carbon fiber products, its waste is also increasing. Recycling waste carbon fiber can not only reduce resource waste and environmental pollution, but also bring significant economic benefits.

[0003] In the existing process of recycling carbon fiber, combing short fibers into strips is an important step. However, a key technical problem currently faced is that a large amount of resin usually remains on the recycled carbon fiber staple fibers. These resin residues will cause the staple fibers to stick to each other during the combing process, affecting the combing effect and making the quality of the fiber strips unstable. At the same time, the resin residue will also clog the card clothing of the combing equipment, reducing the service life of the equipment and increasing maintenance costs. In addition, the residual resin will also affect the performance of the final product. For example, when used in the preparation of composite materials, it will reduce the strength and stability of the composite material.

[0004] Therefore, there is a need in the prior art to provide a method for combing recycled carbon fiber staple fibers into strips, and to effectively remove the resin residue on the staple fibers to facilitate the use of the recycled carbon fiber staple fibers. Summary of the invention

[0005] The purpose of the present invention is to provide a method for combing recycled carbon fiber staple fibers into strips, so as to solve the problems of poor dissolution rate of residual resin on carbon fiber, low strength retention rate of carbon fiber after recycling treatment, and poor dispersibility of carbon fiber staple fibers after recycling treatment.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for carding short fibers of recycled carbon fibers into strips, comprising the following steps: (1) Using a vibrating screen to screen the recycled carbon fiber, the mesh size of the vibrating screen is 3-12 mm to screen out the carbon fiber short fibers; (2) soaking the carbon fiber staple fibers in a soaking solution for chemical treatment, wherein the soaking solution contains limonene, turpentine, and acrylate-modified polyoxyethylene ether to dissolve the resin residue on the staple fibers; (3) Ultrasonic cleaning of the soaked carbon fiber staple fibers to further remove residual resin and impurities; (4) Drying the cleaned carbon fiber staple fibers; (5) The dried carbon fiber staple fibers are fed into a carding machine to be carded into strips.

[0007] Preferably, in step (1), three layers of screens with different apertures are arranged in a stepped manner in the vibrating screen; wherein the aperture of the first layer of screens is 8-12 mm, which is used to preliminarily screen out impurities and long carbon fiber fibers, and the carbon fiber passing through the first layer of screens enters the second layer of screens for further screening; the aperture of the second layer of screens is 5-8 mm, which is used to further screen out short carbon fiber fibers of moderate length, and the carbon fiber that does not pass through the second layer of screens is collected and used as the raw material for step (2); the carbon fiber that passes through the second layer of screens enters the third layer of screens for further screening; the aperture of the third layer of screens is 3-5 mm, which is used to further finely screen the remaining short carbon fiber fibers, and the carbon fiber that passes through the third layer of screens is too short and does not meet the requirements for short carbon fiber fibers, and is collected and recycled separately; the carbon fiber that does not pass through the second layer of screens is collected and used as the raw material for step (2).

[0008] Preferably, in step (2), limonene, turpentine and acrylate-modified polyoxyethylene ether are mixed in a volume ratio of 4:4:2, the immersion temperature is 50-80° C., and the immersion time is 3-5 h.

[0009] Preferably, in step (2), the preparation steps of acrylate-modified polyoxyethylene ether are as follows: S1, using fatty alcohol polyoxyethylene ether and acrylic acid as reaction raw materials, p-toluenesulfonic acid as catalyst, and hydroquinone as inhibitor; S2, adding fatty alcohol polyoxyethylene ether and acrylic acid in a molar ratio of 1:3 into a reaction vessel, adding a catalyst and an inhibitor, the amount of p-toluenesulfonic acid is 1% of the mass of fatty alcohol polyoxyethylene ether, the amount of hydroquinone is 0.05% of the mass of acrylic acid, the reaction temperature is between 70°C and 110°C, and the reaction time is 6h-12h; S3. After the reaction is completed, unreacted acrylic acid, catalyst and impurities are removed to obtain acrylate-modified polyoxyethylene ether.

[0010] Preferably, in step (2), ethanol is added during the preparation of the soaking solution, and the steps are as follows: S1. Add limonene, turpentine and acrylate-modified polyoxyethylene ether into a glass container at a volume ratio of 4:3:3, turn on the stirring device, and stir at a speed of 150-200 r / min for 15-20 min to ensure that the three solvents are fully mixed; S2, weighing anhydrous ethanol accounting for 10% of the total volume of the mixed solution, slowly adding it dropwise to the mixed solution being stirred, and controlling the dropping speed to 2-3 drops per second. After the dropping is completed, continue stirring for 30 minutes, at which time the ethanol is preliminarily dispersed in the mixed solvent; S3, placing the mixed solution containing 10% ethanol in an ultrasonic cleaner, and ultrasonically treating it at a frequency of 40-50 kHz for 20-30 minutes to promote the fusion of ethanol and other solvents; S4. After ultrasonic treatment, weigh anhydrous ethanol accounting for 10% of the total volume of the current solution again, and add it drop by drop at a rate of 1-2 drops per second. During the addition, stir the solution continuously at a rate of 250-300 r / min. After the addition is completed, continue stirring for 1 h to allow the newly added ethanol to fully react with the solution. S5. Transfer the mixed solution to a reactor equipped with a temperature control device, slowly increase the temperature to 40-45°C, and maintain this temperature while continuously stirring at a speed of 180-220 r / min; S6. Weigh 5% of the total volume of the current solution in anhydrous ethanol, add it into the reactor at one time, stir quickly and evenly, increase the stirring speed to 300-350r / min, and continue stirring for 30-40min, so that the ethanol can be quickly diffused into the entire solution system under the action of high temperature and rapid stirring.

[0011] Preferably, in step (2), propylene glycol methyl ether acetate is added during the process of adding ethanol, and the addition of propylene glycol methyl ether acetate is located between steps S5 and S6, and the steps are as follows: Q1. Weigh 3% of the total volume of the current solution of propylene glycol methyl ether acetate; Q2, after S5 is heated and stirred, propylene glycol methyl ether acetate is added into the reactor at one time; Q3. After adding, quickly increase the stirring speed to 320-350r / min, continue stirring for 20-30min, and keep the temperature at 40-45℃. At this time, propylene glycol methyl ether acetate works synergistically with other solvents under high temperature and rapid stirring.

[0012] Preferably, in step (3), the ultrasonic frequency of ultrasonic cleaning is between 40-80 kHz, and the cleaning time is between 30-60 min.

[0013] Preferably, in step (4), the drying temperature is 80-100° C. and the drying time is 1-2 h.

[0014] Preferably, in step (2), the prepared soaking liquid and the carbon fiber staple fibers are placed together in a microwave reactor, the microwave power is set to 300-500 W, the microwave frequency is set to about 2450 MHz, and the processing time is set to 10-20 min.

[0015] Preferably, in step (2), a suitable amount of a surfactant, sodium dodecylbenzene sulfonate, is added to the soaking liquid, and the added amount is 0.5%-1.5% of the total volume of the soaking liquid.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention screens out carbon fiber staple fibers through a multi-stage vibrating screen, and soaks the carbon fiber staple fibers by using limonene and turpentine at the same time to separate the resin from the surface of the carbon fiber, thereby achieving the purpose of removing the resin residue and improving the purity and performance of the carbon fiber.

[0017] 2. The present invention uses acrylate-modified polyoxyethylene ether and its good emulsifying, dispersing and solubilizing effects, so that limonene and turpentine can be better mixed and dispersed in the soaking liquid to form a stable solution system, improve the uniformity and stability of the soaking liquid, reduce the odor of turpentine, reduce the adverse effects on the environment and operators, and enhance the dissolution and removal effect of the soaking liquid on the resin.

[0018] 3. In the present invention, in step (2), ethanol is added in batches during the preparation of the soaking solution. Due to the addition of ethanol, the soaking solution can dissolve the resin more fully. In the subsequent ultrasonic cleaning step, the residual resin and impurities can be removed more easily, reducing the difficulty and workload of cleaning and improving the overall recovery efficiency. By gradually adding ethanol, controlling the amount and speed of each addition, and continuously stirring and ultrasonic treatment during the addition process, the violent reaction that may occur when ethanol is mixed with other solvents is avoided, and the safety of the preparation process is guaranteed. After multiple ultrasonic, stirring and heating treatment steps, ethanol and other solvents are fully integrated to form a stable solution system. During the soaking of carbon fiber staple fibers, the performance of the solution will not change significantly due to time or environmental factors, ensuring the stability of the treatment effect. Ethanol and limonene, turpentine, and acrylate-modified polyoxyethylene ether cooperate with each other to enhance the solubility of different types of resins. Ethanol can swell the resin, thereby allowing other solvents to better enter the interior of the resin, destroy the structure of the resin, and make the resin more easily detached from the surface of the carbon fiber staple fibers and dissolved in the soaking solution. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] An embodiment provided by the present invention is a method for carding recycled carbon fiber short fibers into strips, comprising the following steps: (1) Using a vibrating screen to screen the recycled carbon fiber, the mesh size of the vibrating screen is 3-12 mm to screen out the carbon fiber short fibers; (2) soaking the carbon fiber staple fibers in a soaking solution for chemical treatment, wherein the soaking solution contains limonene, turpentine, and acrylate-modified polyoxyethylene ether to dissolve the resin residue on the staple fibers; (3) Ultrasonic cleaning of the soaked carbon fiber staple fibers to further remove residual resin and impurities; (4) Drying the cleaned carbon fiber staple fibers; (5) The dried carbon fiber staple fibers are fed into a carding machine to be carded into strips.

[0021] The present invention provides a method for combing recycled carbon fiber staple fibers into strips. On the one hand, the recycled carbon fiber can be graded and screened according to length or thickness through the different aperture screens of the vibrating screen, and carbon fiber staple fibers that meet the subsequent processing requirements can be accurately obtained to avoid the effects and quality of combing into strips caused by fibers that are too long or too thick. During the screening process, larger impurity particles will be left on the screen, thereby achieving the initial separation of carbon fiber and impurities, improving the purity of carbon fiber staple fibers, providing purer raw materials for subsequent processing, and reducing the adverse effects of impurities on subsequent chemical treatment, cleaning, combing and other processes.

[0022] On the other hand, the good organic solvent formed by the combination of limonene and turpentine has a strong solubility for the resin on the surface of the carbon fiber staple fiber, which can separate the resin from the surface of the carbon fiber, thereby achieving the purpose of removing the resin residue and improving the purity and performance of the carbon fiber. Acrylate-modified polyoxyethylene ether has good emulsification, dispersion and solubilization effects, which can make limonene and turpentine better mixed and dispersed in the soaking liquid to form a stable solution system and improve the uniformity and stability of the soaking liquid. A protective film can also be formed on the surface of the turpentine droplets, which can reduce the volatilization of turpentine molecules. The smell of turpentine is mainly due to its volatile molecules entering the air and being perceived by the human sense of smell. Through this wrapping effect, the amount of turpentine volatilized into the air is reduced, thereby reducing the adverse effects of the smell on the environment and operators, and reducing the smell of turpentine. At the same time, for the resin in the soaking liquid, the acrylate-modified polyoxyethylene ether can dissolve some components of the resin better in the soaking liquid through solubilization; its micellar structure can accommodate some hydrophobic components in the resin, helping to decompose and dissolve the resin; it can also reduce the surface tension between the soaking liquid and the resin, so that the soaking liquid can better wet the resin surface and penetrate into the resin, so that the contact area between the soaking liquid and the resin can be increased, the dissolution and removal process of the resin can be accelerated, and the dissolution and removal effect of the soaking liquid on the resin can be enhanced. Compared with some traditional highly corrosive chemical reagents, the soaking liquid system is relatively mild. While effectively removing the resin residue, it can minimize the damage to the performance of the carbon fiber itself, such as strength, modulus, etc., to ensure the quality and reuse value of the recycled carbon fiber. During the soaking process, the carbon fiber staple fiber is fully in contact with the soaking liquid, so that the resin can be dissolved quickly and evenly, shortening the processing time, improving production efficiency, and providing a good foundation for subsequent ultrasonic cleaning and combing into strips.

[0023] On the other hand, ultrasonic cleaning uses the cavitation effect of ultrasound in liquid to generate strong impact force and micro jets, so that the residual resin and impurities on the surface of carbon fiber staple fibers can be further loosened and removed, and combined with the chemical treatment of the soaking liquid, a more thorough cleaning effect can be achieved, further improving the purity of the carbon fiber. Ultrasonic waves can be evenly propagated throughout the cleaning liquid, so that all parts of the carbon fiber staple fibers can be cleaned, avoiding the problem of uneven cleaning that may occur in traditional cleaning methods, and ensuring the overall quality of the carbon fiber staple fibers. On the other hand, the drying treatment can remove the residual moisture on the surface and inside of the carbon fiber staple fibers after cleaning, so as to avoid the moisture affecting the combing effect and quality of the fibers during the subsequent combing process, such as causing fiber entanglement, agglomeration and other problems. Appropriate drying temperature and time can make the structure and performance of carbon fiber staple fibers more stable, restore their original mechanical properties and physical properties, and provide guarantee for the quality of carbon fiber products after combing into strips. On the other hand, the dried carbon fiber staple fibers are fed into the combing machine for combing into strips, so that the carbon fiber staple fibers are arranged neatly and oriented in a consistent manner, forming fiber strips with a certain strength and uniformity, which is convenient for subsequent processing and application, such as weaving and winding, and improves the processability and utilization rate of carbon fiber. During the combing process, the carding machine can further remove a small amount of impurities and short fibers in the carbon fiber staple fibers, further improving the purity and quality of the carbon fiber, making the final carbon fiber strips of better quality.

[0024] More specifically, in step (1), three layers of screens with different apertures are arranged in a stepped manner in the vibrating screen; Among them, the aperture of the first layer of screen is 8-12mm, which is used to preliminarily screen out impurities and long carbon fiber. The carbon fiber passing through the first layer of screen enters the second layer of screen for further screening; The aperture of the second layer of screen is 5-8 mm, which is used to further screen out short carbon fiber with moderate length. The carbon fiber that does not pass through the second layer of screen is collected and used as the raw material of step (2); the carbon fiber that passes through the second layer of screen enters the third layer of screen for further screening; The aperture of the third layer of screen is 3-5mm, which is used to further finely screen the remaining carbon fiber short fibers. The carbon fibers passing through the third layer of screen are too short and do not meet the requirements of carbon fiber short fibers, so they are collected and recycled separately; the carbon fibers that do not pass through the second layer of screen are collected and used as raw materials for step (2).

[0025] In this embodiment, the aperture of the first layer of screen is 8-12 mm, which can effectively separate the larger impurities in the recycled carbon fiber, such as blocky resin, large foreign particles in the fiber bundle, and the long carbon fiber fibers during the preliminary screening. This can prevent large impurities and long fibers from entering the subsequent process, prevent clogging or damage to the equipment, and ensure the smooth progress of subsequent processing. Through the preliminary screening, the amount of material entering the second layer of screen is reduced, so that the second layer of screen can be more focused on screening the carbon fiber short fibers with moderate length, thereby improving the efficiency and accuracy of the entire screening process. The aperture of the second layer of screen is between 5-8 mm, and this layer of screen is the key link in screening out the carbon fiber short fibers with moderate length. It can further separate the carbon fibers that do not meet the short fiber length requirements, ensuring that the carbon fiber short fibers entering the next process are more uniform in length, which is conducive to the subsequent soaking, cleaning and combing processes, and improving the stability of product quality. The part that has not passed through the intercepted part of the screen, that is, the carbon fiber with shorter length, is collected and used as the raw material of step (2). Although this part of carbon fiber is short in length, it can still be used for subsequent chemical treatment and recycling, which makes full use of resources and avoids waste. The aperture of the third layer of screen is 3-5mm, which further finely screens the carbon fiber that has passed through the second layer of screen. Those carbon fibers that are too short can be screened out to ensure that the carbon fiber staple fibers that are finally used for combing into strips have a suitable length range, thereby improving the performance and quality of the carbon fiber products after combing into strips, so that they can better meet subsequent application requirements. By removing carbon fibers that are too short, the carbon fibers after combing into strips are more uniform in strength, modulus and other properties, which helps to improve the mechanical properties and reliability of the final product and reduce performance fluctuations caused by uneven length of staple fibers.

[0026] More specifically, in step (2), limonene, turpentine and acrylate-modified polyoxyethylene ether are mixed in a volume ratio of 4:4:2, the immersion temperature is 50-80° C., and the immersion time is 3-5 h.

[0027] In this embodiment, within the temperature range of 50-80°C, on the one hand, the solubility of the resin in the soaking liquid can be improved, the dissolution rate of the resin residue can be accelerated, and the treatment process can be made more efficient; on the other hand, this temperature range will not have a significant adverse effect on the performance of the carbon fiber, and avoid the degradation of the mechanical properties of the carbon fiber or structural damage caused by excessively high temperature. The soaking time of 3-5h is sufficient for the effective ingredients in the soaking liquid to fully contact and act with the resin residue on the surface of the carbon fiber staple fiber, ensuring that the resin residue can be dissolved and removed as much as possible. If the soaking time is too short, the ideal removal effect may not be achieved; and if the soaking time is too long, it may increase the production cost and production cycle, and may also have a certain impact on the performance of the carbon fiber.

[0028] More specifically, in step (2), the preparation steps of acrylate-modified polyoxyethylene ether are as follows: S1, using fatty alcohol polyoxyethylene ether and acrylic acid as reaction raw materials, p-toluenesulfonic acid as catalyst, and hydroquinone as inhibitor; S2, adding fatty alcohol polyoxyethylene ether and acrylic acid in a molar ratio of 1:3 into a reaction vessel, adding a catalyst and an inhibitor, the amount of p-toluenesulfonic acid is 1% of the mass of fatty alcohol polyoxyethylene ether, the amount of hydroquinone is 0.05% of the mass of acrylic acid, the reaction temperature is between 70°C and 110°C, and the reaction time is 6h-12h; S3. After the reaction is completed, unreacted acrylic acid, catalyst and impurities are removed to obtain acrylate-modified polyoxyethylene ether.

[0029] More specifically, in step (2), ethanol is added during the preparation of the soaking solution, and the steps are as follows: S1. Add limonene, turpentine and acrylate-modified polyoxyethylene ether into a glass container at a volume ratio of 4:3:3, turn on the stirring device, and stir at a speed of 150-200 r / min for 15-20 min to ensure that the three solvents are fully mixed; S2, weighing anhydrous ethanol accounting for 10% of the total volume of the mixed solution, slowly adding it dropwise to the mixed solution being stirred, and controlling the dropping speed to 2-3 drops per second. After the dropping is completed, continue stirring for 30 minutes, at which time the ethanol is preliminarily dispersed in the mixed solvent; S3, placing the mixed solution containing 10% ethanol in an ultrasonic cleaner, and ultrasonically treating it at a frequency of 40-50 kHz for 20-30 minutes to promote the fusion of ethanol and other solvents; S4. After ultrasonic treatment, weigh anhydrous ethanol accounting for 10% of the total volume of the current solution again, and add it drop by drop at a rate of 1-2 drops per second. During the addition, stir the solution continuously at a rate of 250-300 r / min. After the addition is completed, continue stirring for 1 h to allow the newly added ethanol to fully react with the solution. S5. Transfer the mixed solution to a reactor equipped with a temperature control device, slowly increase the temperature to 40-45°C, and maintain this temperature while continuously stirring at a speed of 180-220 r / min; S6. Weigh 5% of the total volume of the current solution in anhydrous ethanol, add it into the reactor at one time, stir quickly and evenly, increase the stirring speed to 300-350r / min, and continue stirring for 30-40min, so that the ethanol can be quickly diffused into the entire solution system under the action of high temperature and rapid stirring.

[0030] In the present embodiment, in S2 and S4, by slowly dropping ethanol, and controlling the dropping speed, ethanol can be more evenly dispersed in the mixed solution, avoiding a large amount of one-time addition causing excessive local concentration, affecting the overall performance of the solution. Ultrasonic treatment and long-term stirring in S3 and S4 can further promote the interaction between ethanol and other solvent molecules, so that ethanol is better integrated into the solution system, ensuring the uniformity of the solution. This uniformly mixed soaking liquid can more comprehensively contact the resin residue on the surface of carbon fiber staple fibers, and improve the dissolution effect. Ethanol has good solubility and permeability, and can adjust the properties such as polarity and dielectric constant of the soaking liquid after addition, so that it is more conducive to dissolving the resin residue on the carbon fiber staple fibers. Under a specific volume ratio and addition mode, ethanol and limonene, turpentine, and acrylate-modified polyoxyethylene ether cooperate with each other, and enhance the solubility of different types of resins. Ethanol can swell the resin, thereby allowing other solvents to better enter the interior of the resin, destroying the structure of the resin, and making the resin more easily detached from the surface of the carbon fiber staple fibers and dissolved in the soaking liquid. In S5 and S6, the temperature is increased and the stirring speed is accelerated, so that the diffusion speed of ethanol in the solution is accelerated, and the movement rate and reaction activity of other solvent molecules are also increased, which accelerates the process of resin dissolution, thereby improving the efficiency of the entire carbon fiber short fiber processing and reducing the soaking time. Because the addition method of ethanol makes the soaking liquid dissolve the resin more fully, in the subsequent ultrasonic cleaning step, the residual resin and impurities can be removed more easily, reducing the difficulty and workload of cleaning, and improving the overall recovery efficiency. By gradually adding ethanol, and controlling the amount and speed of each addition, and continuously stirring and ultrasonic treatment during the addition process, the violent reaction that may be produced when ethanol is mixed with other solvents is avoided, and the safety of the preparation process is guaranteed. After multiple ultrasonic, stirring and heating steps, ethanol and other solvents are fully fused and a stable solution system is formed. In the process of soaking carbon fiber short fibers, the performance of the solution will not change significantly due to time or environmental factors, ensuring the stability of the treatment effect.

[0031] More specifically, in step (2), propylene glycol methyl ether acetate is added during the process of adding ethanol, and the addition of propylene glycol methyl ether acetate is located between steps S5 and S6, and the steps are as follows: Q1. Weigh 3% of the total volume of the current solution of propylene glycol methyl ether acetate; Q2, after S5 is heated and stirred, propylene glycol methyl ether acetate is added into the reactor at one time; Q3. After adding, quickly increase the stirring speed to 320-350r / min, continue stirring for 20-30min, and keep the temperature at 40-45℃. At this time, propylene glycol methyl ether acetate works synergistically with other solvents under high temperature and rapid stirring.

[0032] In the present embodiment, propylene glycol methyl ether acetate molecules have both ether bonds and carbonyl and ester structures, and have certain solubility for non-polar substances and polar substances. In the soaking liquid, it can cooperate with solvents such as limonene, turpentine, and acrylate-modified polyoxyethylene ether to better dissolve the resin residue on the carbon fiber staple fibers and improve the resin removal effect. It is helpful to further improve the compatibility between each solvent in the soaking liquid, make the whole soaking liquid system more stable and uniform, avoid the phenomenon of solvent stratification or local uneven concentration during the soaking process, thereby ensuring that the carbon fiber staple fibers can fully contact the effective ingredients in the soaking liquid, and improve the effect and efficiency of chemical treatment. Under high temperature and rapid stirring, propylene glycol methyl ether acetate can be better dispersed in the solution, and its unique molecular structure can interact with other solvents to prevent the agglomeration of certain components that may occur in the solution, so that the effective ingredients in the soaking liquid can be more evenly distributed on the surface of the carbon fiber staple fibers, giving full play to its chemical action.

[0033] On the other hand, at higher temperatures, propylene glycol methyl ether acetate can reduce the surface tension of the solution, increase the fluidity of the solution, help stabilize the entire soaking liquid system, reduce the problems of solvent volatilization and component precipitation that may be caused by temperature changes or long-term stirring, and extend the service life and stability of the soaking liquid. The addition of propylene glycol methyl ether acetate can reduce the surface tension of the soaking liquid, making it easier for the soaking liquid to spread on the surface of the carbon fiber staple fiber, so that the effective ingredients in the soaking liquid can more fully contact and react with the resin residue on the surface of the carbon fiber staple fiber, thereby improving the thoroughness of the resin removal. Due to its good dispersion and stabilization effect, as well as the optimization of the solution system, the physical and chemical effects on the carbon fiber staple fiber during the soaking process are more uniform, reducing the damage to the carbon fiber staple fiber that may be caused by excessive local solvent concentration or uneven action, and protecting the mechanical properties of the carbon fiber. By enhancing the synergistic effect of the solvent, optimizing the solution system, and improving the surface properties of the carbon fiber, the chemical treatment process of the carbon fiber staple fiber in the soaking liquid is more efficient, so that the soaking time can be shortened to a certain extent, and the production efficiency of the entire recycled carbon fiber staple fiber combing into strips can be improved. Due to the shortened processing time and improved solution stability, the energy consumption required for long-term heating and stirring is reduced, and the replacement frequency and amount of the soaking solution are also reduced, thereby reducing production costs and energy consumption to a certain extent.

[0034] More specifically, in step (3), the ultrasonic frequency of ultrasonic cleaning is between 40-80 kHz, and the cleaning time is between 30-60 min.

[0035] More specifically, in step (4), the drying temperature is 80-100° C. and the drying time is 1-2 h.

[0036] More specifically, in step (2), the prepared soaking liquid and carbon fiber staple fibers are placed in a microwave reactor together, the microwave power is set to 300-500 W, the microwave frequency is set to about 2450 MHz, and the processing time is set to 10-20 min.

[0037] In this embodiment, under the action of microwaves, the movement of solvent molecules in the soaking liquid is accelerated, and they can more quickly penetrate into the interface between the carbon fiber staple fibers and the resin residue, promoting the dissolution of the resin. At the same time, the heat generated by the microwaves can rapidly increase the temperature of the soaking liquid, further accelerating the dissolution rate of the resin. However, it is necessary to control the microwave power and processing time to avoid affecting the performance of the carbon fiber staple fibers. More specifically, in step (2), a suitable amount of a surfactant, sodium dodecylbenzene sulfonate, is added to the soaking liquid, and the added amount is 0.5%-1.5% of the total volume of the soaking liquid.

[0038] In this embodiment, sodium dodecylbenzene sulfonate can reduce the surface tension between the resin and the carbon fiber staple fibers, making it easier for the resin to be peeled off from the surface of the carbon fiber staple fibers and dissolved in the soaking liquid, thereby improving the dissolution efficiency of the resin residue. After adding the surfactant, the soaking liquid is stirred at a speed of 200-300 r / min for 30-40 minutes to allow the surfactant to be fully dispersed and function.

[0039] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that in step 2, only limonene is used.

[0040] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is only that in step 2, only turpentine oil is used.

[0041] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that in step 2, limonene and turpentine are used together, but acrylate-modified polyoxyethylene ether is not used.

[0042] Comparative Example 4: The only difference between Comparative Example 4 and Example 1 is that in step 2, when ethanol is added during the preparation of the soaking solution, it is completed at one time.

[0043] The following are the experimental methods and data provided by the present invention, which reflect the dissolution of residual resin on the carbon fiber staple fibers in Example 1 and each comparative example, the strength retention rate of the carbon fiber staple fibers, the observation of the surface state of the treated carbon fiber staple fibers, and the dispersion test comparison results of the treated carbon fiber staple fibers. The specific experimental methods and data are as follows: 1. Comparison of residual resin dissolution rate The weight method is used to determine the change in resin content of carbon fiber staple fibers before and after treatment, and then the residual resin dissolution rate is calculated. The calculation formula is: Residual resin dissolution rate = (resin mass before treatment - resin mass after treatment) ÷ resin mass before treatment × 100%.

[0044] 2. Comparison of carbon fiber staple fiber strength retention rate The tensile strength of the carbon fiber staple fibers before and after treatment was tested using a tensile testing machine, and the strength retention rate was calculated using the formula: Strength retention rate = tensile strength of the carbon fiber staple fibers after treatment ÷ tensile strength of the carbon fiber staple fibers before treatment × 100%.

[0045] 3. Observation of the surface state of carbon fiber staple fibers after treatment (observation by scanning electron microscope SEM) Example 1: The surface of the carbon fiber staple fibers is relatively smooth, with very little resin residue, good dispersion between the fibers, and no obvious agglomeration phenomenon.

[0046] Comparative Example 1: There is still some resin residue attached to the surface of the carbon fiber staple fibers, the fiber surface is relatively rough, and some small resin particles are aggregated.

[0047] Comparative Example 2: Similar to the situation in Comparative Example 1, there is more resin residue on the surface, the fiber dispersion is not as good as in Example 1, and there is local fiber adhesion.

[0048] Comparative Example 3: The surface resin residue is between Comparative Examples 1 and 2 and Example 1, but compared with Example 1, more obvious traces of resin residue can still be seen, and the fiber dispersion is average.

[0049] Comparative Example 4: The surface state is slightly worse than that of Example 1, with a small amount of resin residue and slightly inferior dispersion uniformity between fibers. This may be due to the change in the method of adding ethanol affecting the overall treatment effect.

[0050] 4. Dispersion test of treated carbon fiber staple fibers (through specific dispersion test methods, such as measuring the sedimentation of fibers in liquid over a certain period of time, etc.) Example 1: The fibers are evenly dispersed in the test liquid and settle slowly after being placed for a long time, indicating that the fibers have good dispersion and are not easy to agglomerate.

[0051] Comparative Example 1: The dispersibility is general, the sedimentation speed is faster than that of Example 1, and some fibers agglomerate and sink.

[0052] Comparative Example 2: The dispersion is poor, and many fibers agglomerate and settle in a short period of time, indicating that the dispersion effect between the fibers is not good.

[0053] Comparative Example 3: The dispersibility is between Comparative Example 1 and Example 1, with a certain degree of fiber agglomeration, and the sedimentation rate is also between the two.

[0054] Comparative Example 4: The dispersibility is slightly inferior to that of Example 1, with a small amount of fiber agglomeration, and the sedimentation rate is slightly faster than that of Comparative Example 1.

[0055] Experimental data: It can be seen from the above experimental data that compared with the various comparative examples, Example 1 has better overall performance in terms of dissolution of residual resin in carbon fiber staple fibers, fiber strength retention, surface state, dispersibility, etc. Although the total electrical energy consumed in each step may be higher, the overall treatment effect is better, reflecting the advantages of the combination of multiple reagents and specific process operations in each step.

[0056] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for carding short fibers of recycled carbon fibers into slivers, characterized in that: The following steps are involved: (1) Using a vibrating screen to screen the recycled carbon fiber, the mesh size of the vibrating screen is 3-12 mm to screen out the carbon fiber short fibers; (2) soaking the carbon fiber staple fibers in a soaking solution for chemical treatment, wherein the soaking solution contains limonene, turpentine, and acrylate-modified polyoxyethylene ether to dissolve the resin residue on the staple fibers; (3) Ultrasonic cleaning of the soaked carbon fiber staple fibers to further remove residual resin and impurities; (4) Drying the cleaned carbon fiber staple fibers; (5) The dried carbon fiber staple fibers are fed into a carding machine to be carded into strips.

2. The method for carding short fibers of recycled carbon fibers into slivers according to claim 1, characterized in that: In the step (1), three layers of screens with different apertures are arranged in a stepped manner in the vibrating screen; Among them, the aperture of the first layer of screen is 8-12mm, which is used to preliminarily screen out impurities and long carbon fiber. The carbon fiber passing through the first layer of screen enters the second layer of screen for further screening; The aperture of the second layer of screen is 5-8 mm, which is used to further screen out short carbon fiber with moderate length. The carbon fiber that does not pass through the second layer of screen is collected and used as the raw material of step (2); the carbon fiber that passes through the second layer of screen enters the third layer of screen for further screening; The aperture of the third layer of screen is 3-5mm, which is used to further finely screen the remaining carbon fiber short fibers. The carbon fibers passing through the third layer of screen are too short and do not meet the requirements of carbon fiber short fibers, so they are collected and recycled separately; the carbon fibers that do not pass through the second layer of screen are collected and used as raw materials for step (2).

3. The method for carding short fibers of recycled carbon fibers into slivers according to claim 2, characterized in that: In the step (2), limonene, turpentine and acrylate-modified polyoxyethylene ether are mixed in a volume ratio of 4:4:2, the soaking temperature is 50-80° C., and the soaking time is 3-5 hours.

4. The method for carding short fibers of recycled carbon fibers into slivers according to claim 2, characterized in that: In the step (2), the preparation steps of acrylate-modified polyoxyethylene ether are as follows: S1, using fatty alcohol polyoxyethylene ether and acrylic acid as reaction raw materials, p-toluenesulfonic acid as catalyst, and hydroquinone as inhibitor; S2, adding fatty alcohol polyoxyethylene ether and acrylic acid in a molar ratio of 1:3 into a reaction vessel, adding a catalyst and an inhibitor, the amount of p-toluenesulfonic acid is 1% of the mass of fatty alcohol polyoxyethylene ether, the amount of hydroquinone is 0.05% of the mass of acrylic acid, the reaction temperature is between 70°C and 110°C, and the reaction time is 6h-12h; S3. After the reaction is completed, unreacted acrylic acid, catalyst and impurities are removed to obtain acrylate-modified polyoxyethylene ether.

5. The method for carding short fibers of recycled carbon fibers into slivers according to claim 4, characterized in that: In the step (2), ethanol is added during the preparation of the soaking solution, and the steps are as follows: S1. Add limonene, turpentine and acrylate-modified polyoxyethylene ether into a glass container at a volume ratio of 4:3:3, turn on the stirring device, and stir at a speed of 150-200 r / min for 15-20 min to ensure that the three solvents are fully mixed; S2, weighing anhydrous ethanol accounting for 10% of the total volume of the mixed solution, slowly adding it dropwise to the mixed solution being stirred, and controlling the dropping speed to 2-3 drops per second. After the dropping is completed, continue stirring for 30 minutes, at which time the ethanol is preliminarily dispersed in the mixed solvent; S3, placing the mixed solution containing 10% ethanol in an ultrasonic cleaner, and ultrasonically treating it at a frequency of 40-50 kHz for 20-30 minutes to promote the fusion of ethanol and other solvents; S4. After ultrasonic treatment, weigh anhydrous ethanol accounting for 10% of the total volume of the current solution again, and add it drop by drop at a rate of 1-2 drops per second. During the addition, stir the solution continuously at a rate of 250-300 r / min. After the addition is completed, continue stirring for 1 h to allow the newly added ethanol to fully react with the solution. S5. Transfer the mixed solution to a reactor equipped with a temperature control device, slowly increase the temperature to 40-45°C, and maintain this temperature while continuously stirring at a speed of 180-220 r / min; S6. Weigh 5% of the total volume of the current solution in anhydrous ethanol, add it into the reactor at one time, stir quickly and evenly, increase the stirring speed to 300-350r / min, and continue stirring for 30-40min, so that the ethanol can be quickly diffused into the entire solution system under the action of high temperature and rapid stirring.

6. A method for carding recycled carbon fiber staple fibers into slivers according to claim 5, characterized in that: In the step (2), propylene glycol methyl ether acetate is added during the process of adding ethanol, and the addition of propylene glycol methyl ether acetate is located between steps S5 and S6, and the steps are as follows: Q1. Weigh 3% of the total volume of the current solution of propylene glycol methyl ether acetate; Q2, after S5 is heated and stirred, propylene glycol methyl ether acetate is added into the reactor at one time; Q3. After adding, quickly increase the stirring speed to 320-350r / min, continue stirring for 20-30min, and keep the temperature at 40-45℃. At this time, propylene glycol methyl ether acetate works synergistically with other solvents under high temperature and rapid stirring.

7. A method for carding recycled carbon fiber staple fibers into slivers according to claim 6, characterized in that: In step (3), the ultrasonic frequency of ultrasonic cleaning is between 40-80 kHz, and the cleaning time is between 30-60 min.

8. The method for carding recycled carbon fiber staple fibers into slivers according to claim 7, characterized in that: In the step (4), the drying temperature is 80-100° C. and the drying time is 1-2 hours.

9. A method for carding recycled carbon fiber short fibers into slivers according to claim 8, characterized in that: In the step (2), the prepared soaking liquid and the carbon fiber staple fibers are placed in a microwave reactor together, the microwave power is set to 300-500 W, the microwave frequency is set to about 2450 MHz, and the processing time is set to 10-20 min.

10. A method for carding recycled carbon fiber short fibers into slivers according to claim 9, characterized in that: In the step (2), a proper amount of the surfactant sodium dodecylbenzene sulfonate is added to the soaking liquid, and the added amount is 0.5%-1.5% of the total volume of the soaking liquid.