A method for recycling thermosetting carbon fiber prepreg scraps

Abstract

The present application discloses a method for recycling thermosetting carbon fiber prepreg scraps, including: heating and curing the collected thermosetting carbon fiber prepreg scraps in a fluffy state to obtain a carbon fiber prepreg cured product, then crushing the carbon fiber prepreg cured product, and separating the carbon fiber resin matrix cured product through an air separator after crushing the carbon fiber prepreg cured product; the separated carbon fiber resin matrix cured product is subjected to microwave heating under the condition of an oxygen concentration of ≤10%, cracking the resin matrix, and obtaining a carbon fiber with a resin residual rate of less than 10%; finally, by aerobic heating, the remaining resin and residual carbon on the carbon fiber are removed to obtain pure carbon fiber. The present invention can be applied to the recycling of carbon fiber prepreg scraps of different shapes, sizes, and specifications, and all thermosetting carbon fiber prepregs can be uniformly recycled without recycling according to resin sub-categories, and the removal of PE film and release paper is convenient, which is convenient for recycling industrialization.

Description

Technical Field

[0001] The invention belongs to the field of carbon fiber composite materials, and in particular relates to a method for efficiently recycling leftover thermosetting carbon fiber prepreg scraps. Background Art

[0002] Carbon fiber composite materials are a kind of composite materials with resin as the base material, and carbon fiber and resin are mixed and molded to obtain a light and high-strength composite material. Due to its advantages of high strength, light weight, corrosion resistance and designability, it is widely used in the fields of automobiles, aerospace, wind power, sports equipment, etc. In the molding process of carbon fiber composite materials, carbon fiber prepreg is a main material form used to prepare carbon fiber composite materials. Carbon fiber prepreg is made of carbon fiber yarn, epoxy resin, release paper and other materials, and is processed by coating, hot pressing, cooling, PE film coating, winding and other processes, and has a certain width. When using carbon fiber prepreg to prepare carbon fiber composite parts, the carbon fiber prepreg will be cut according to the shape of the part and the sheet laying design. Therefore, a large number of carbon fiber prepreg scraps of different sizes and shapes will be generated and left in the cutting process. These carbon fiber prepreg scraps of different sizes and shapes are difficult to continue to be used to prepare carbon fiber composite parts with a certain configuration, and usually can only be abandoned and landfilled or pressed into plates. Directly abandoning and landfilling pollutes the environment and is not conducive to reducing product costs. If pressed into a plate, for example, CN103121321A discloses a method for utilizing the scraps of continuous fiber reinforced thermoplastic resin composite prepreg tape, which is rolled into a roll, and then tightly wound on an iron plate of required length and width by a winding machine, and then the prepreg tape scraps are placed in a hot press to be pressed into a prepreg sheet of continuous fiber reinforced thermoplastic resin scraps, and then the prepreg sheets are stacked horizontally and vertically on the hot press to be pressed into a plate. Although this method can reproduce the scraps, it has the following disadvantages: (1) It can only be used for thermoplastic prepregs, and cannot adapt to the recycling of the most widely used thermosetting carbon fiber prepreg scraps; (2) The scraps that can be processed are limited to the scraps on the left and right sides of the carbon fiber prepreg width (equal width long strips), and cannot adapt to other scraps of different shapes; (3) The recycling process requires manual tearing of the film (PE film) and paper (release paper), and this method is difficult to achieve mass production.

[0003] CN117885244A discloses a recycling method for carbon fiber prepreg scraps, including: step 1, collection and classification of carbon fiber prepreg scraps; step 2, shredding of carbon fiber prepreg scraps, obtaining prepreg fragments; step 3, ultrasonic dispersion of carbon fiber prepreg scraps; step 4, obtaining uniformly distributed prepreg fragments; step 5, low temperature drying of prepreg fragments, obtaining air-dried prepreg fragments; step 6, spraying chopped carbon fiber and resin mixture on the prepreg surface, obtaining chopped toughened rubber mold prepreg; step 7, chopped toughened rubber mold prepreg multilayer stacking, making composite laminates or profiles. The method also needs to tear film and paper during the recovery process, and it is difficult to achieve mass production; and carbon fiber prepreg fragments also have certain viscosity, poor operability, and poor dispersion effect; in addition, the obtained chopped toughened rubber film prepreg thickness is thicker, which is inconvenient for subsequent paving and use.

[0004] The prior art also discloses the use of organic solvents such as acetone, DMSO, DMF, etc. to dissolve the resin and then recover the carbon fiber, but it is still necessary to tear off the film and paper, and a large amount of waste organic solvents will be generated, causing new pollution and increasing processing costs. Summary of the invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides a method for recycling thermosetting carbon fiber prepreg scraps, which can quickly remove PE film and release paper, especially can effectively remove the release paper, and then further separate the carbon fiber by heating and cracking the resin.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A method for recycling thermosetting carbon fiber prepreg scraps comprises the following steps:

[0008] S1, collecting, collecting different types of thermosetting carbon fiber prepreg scraps to form a scrap mixture; the thermosetting carbon fiber prepreg includes but is not limited to epoxy resin carbon fiber prepreg, bismaleimide resin carbon fiber prepreg, cyanate ester carbon fiber prepreg, phenolic resin carbon fiber prepreg;

[0009] S2, heating and curing, heating and curing the collected thermosetting carbon fiber prepreg scrap material mixture in a fluffy state to obtain a carbon fiber prepreg cured product;

[0010] S3, crushing, crushing the carbon fiber prepreg solidified material of S2 to destroy the adhesion between the release paper, the PE film, and the carbon fiber resin matrix solidified material;

[0011] S4, sorting, passing the carbon fiber prepreg solidified material crushed in S3 through an air separator to remove the release paper and PE film, and retain the carbon fiber resin matrix solidified material;

[0012] S5, oxygen-free heating, subjecting the carbon fiber resin matrix cured product obtained in S4 to microwave heating under the condition of oxygen concentration ≤10%, the heating temperature is 500-800°C, and the heating time is 5-40min to crack the resin matrix to obtain carbon fiber with a resin residual rate of less than 10%;

[0013] S6, aerobic heating, heating the carbon fiber obtained in step S5 under aerobic conditions to remove residual resin and residual carbon to obtain pure carbon fiber.

[0014] In another embodiment, the step S2 heating and curing may be performed by oven curing, and the stacking thickness of the carbon fiber prepreg scrap mixture does not exceed 30 cm. The heating temperature is set based on the carbon fiber prepreg with the highest curing temperature in the mixture, so that all types of carbon fiber prepreg in the mixture can be completely cured.

[0015] In another embodiment, the size range of the carbon fiber prepreg solidified material after crushing in step S3 is controlled within 10 cm, which is conducive to the separation of the release paper, PE film and the carbon fiber resin matrix solidified material. When the size range is within 5 cm, the separation effect of the PE film, release paper and the carbon fiber resin matrix solidified material is best.

[0016] In another embodiment, the wind speed of the winnowing machine in step S4 is set at 3-8 m / s.

[0017] In another embodiment, the step S3 of crushing comprises:

[0018] S31, first crushing, sending the carbon fiber prepreg cured product obtained in step S2 into a crusher for first crushing, and controlling the size of the crushed product to be within 10 cm;

[0019] S32, second crushing, sending the carbon fiber prepreg solidified material crushed in step S31 into a crusher for second crushing, and controlling the size of the crushed solidified material within 5 cm.

[0020] In another embodiment, the step S4 sorting comprises:

[0021] S41, first sorting, sending the carbon fiber prepreg solidified material crushed in S3 to an air separator for first sorting, with the wind speed controlled at 5-8 m / s, to separate the carbon fiber resin matrix solidified material and the mixture A; the mixture A includes release paper, PE film and carbon fiber resin matrix solidified material;

[0022] S42, second sorting, the mixture A in step S41 is sent to the air separator again for second sorting, the wind speed is controlled at 3-5m / s, the carbon fiber resin matrix solidified material is further separated, and the carbon fiber resin matrix solidified material is collected together with the separated carbon fiber resin matrix solidified material in S41.

[0023] In another embodiment, the heating method of the oxygen-free heating in step S5 is any one of ordinary microwave heating, in-phase microwave heating, and in-phase microwave spark discharge heating.

[0024] The conventional microwave heating refers to placing the carbon fiber resin matrix solidified material in a microwave oven heating cavity for microwave pyrolysis.

[0025] During the in-phase microwave heating, based on ordinary microwave heating, the starting phase angles of the microwaves emitted by the microwave generator are the same, and the time and path length of the microwave transmission to the heating cavity are also the same, thereby enhancing the heating effect on the carbon fiber resin matrix cured product and stably reproducing it.

[0026] The in-phase microwave spark discharge heating comprises:

[0027] In a co-phase microwave heating device, a carbon fiber resin matrix cured product is subjected to co-phase microwave heating. At the same time, uniform spark discharge is performed in the co-phase microwave field. The position where the spark discharge occurs is controlled within the same horizontal plane height in the co-phase microwave field, so that the carbon fiber resin matrix cured product is quickly and evenly heated to 500°C within 1-5 minutes. As the microwave and spark discharge time increase, the temperature can continue to increase rapidly to crack the resin, complete the separation of carbon fiber and resin in the carbon fiber resin matrix cured product, and obtain carbon fiber.

[0028] In another embodiment, the step S6 is aerobic heating, the temperature is controlled at 450-550° C., and the time is 15-30 minutes.

[0029] The beneficial effects of the present invention include at least: (1) there are no restrictions on the shape, size and specification of the thermosetting carbon fiber prepreg scraps, and all the thermosetting carbon fiber prepregs that need to be recycled can be mixed and recycled in a unified manner. Compared with the prior art that needs to be recycled according to resin sub-categories, the recycling efficiency is high; (2) by first heating and curing, the soft and sticky carbon fiber prepreg is cured in a fluffy state, which is convenient for subsequent physical crushing to break the adhesion between the release paper, PE film and the carbon fiber resin matrix solidified material, and then the release paper and PE film are removed by using a wind separator by utilizing the different densities of the release paper, PE film and the carbon fiber resin matrix solidified material, and the remaining carbon fiber resin matrix solidified material is conducive to the subsequent heating and cracking of the resin matrix; (3) the overall process is simple, the recycling efficiency is high, the recycling cost is low, and it can be industrialized; (4) no new pollutants are introduced during the recycling process, which is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Attached Figure 1 The distance distribution diagram of the crushed carbon fiber prepreg solidified material relative to the wind source at different wind speeds;

[0031] Attached Figure 2 This is the relationship diagram of carbon fiber prepreg cured product size-wind speed-retention rate. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiments in 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. It should be noted that the embodiments in this disclosure and the features in the embodiments can be arbitrarily combined with each other without conflict.

[0033] A method for recycling thermosetting carbon fiber prepreg scraps comprises the following steps:

[0034] S1, collecting, collecting different types of thermosetting carbon fiber prepreg scraps to form a scrap mixture;

[0035] S2, heating and curing, heating and curing the collected thermosetting carbon fiber prepreg scrap mixture in a fluffy state to obtain a carbon fiber prepreg cured product;

[0036] S3, crushing, crushing the carbon fiber prepreg cured product obtained in S2 to destroy the adhesion between the PE film, the release paper, and the carbon fiber resin matrix cured product;

[0037] S4, sorting, sorting the solidified material after being crushed in S3 through a wind separator, removing the release paper and PE film, and retaining the solidified material of the carbon fiber resin matrix;

[0038] S5, oxygen-free heating, subjecting the carbon fiber resin matrix solidified material to microwave heating under the condition of oxygen concentration ≤10%, the heating temperature is 500-800°C, and the heating time is 5-40min to crack the resin matrix to obtain carbon fiber with a resin residual rate of less than 10%;

[0039] S6, aerobic heating, heating the carbon fiber obtained in step 5 under aerobic conditions to remove residual resin and residual carbon to obtain pure carbon fiber.

[0040] In this embodiment, after the carbon fiber prepreg scrap mixture is heated and cured, there will be stacked PE film layers (part of the PE film will also melt), release paper layers and carbon fiber resin matrix cured material layers in the whole cured material. Due to the presence of the release paper, there will be no or only a small amount of adhesion between the layers of the carbon fiber resin matrix cured material. After being crushed, there is basically no mutual adhesion between the release paper, the unmelted PE film and the carbon fiber resin matrix cured material. Thereafter, the PE film, the release paper and the carbon fiber resin matrix cured material are separated by a winnowing machine based on their different densities. The main purpose of this winnowing step is to remove the release paper and part of the PE film, leaving the carbon fiber resin matrix cured material and the part of the PE film that cannot be removed (the PE film is thin and easy to be entangled in the carbon fiber resin matrix cured material). Subsequently, the resin can be cracked by microwave heating to obtain recycled carbon fiber.

[0041] See attached Figure 1 , the size of the crushed carbon fiber prepreg solidified material is controlled within 5cm, and the distance distribution diagram relative to the wind source at different wind speeds. It can be seen from the figure that when the wind speed is less than 3m / s, the release paper, PE film, and carbon fiber resin matrix solidified material are entangled with each other and cannot be effectively separated; when the wind speed reaches 3m / s, the release paper, PE film, and carbon fiber resin matrix solidified material begin to separate significantly; when the wind speed is controlled at 4-6m / s, the separation effect of the release paper, PE film, and carbon fiber resin matrix solidified material is the most obvious; when the wind speed is greater than 8m / s, the release paper, PE film, and carbon fiber resin matrix solidified material begin to entangle with each other again and cannot be effectively separated.

[0042] In addition, the size of the crushed carbon fiber prepreg solidified material will also affect the separation effect of the release paper, PE film, and carbon fiber resin matrix solidified material. Figure 2 , the carbon fiber prepreg solidified product size-wind speed-retention rate relationship diagram, under the same wind speed, the larger the size of the carbon fiber prepreg solidified product, the less carbon fiber resin matrix solidified product retained after air selection. This is because the larger the size of the carbon fiber prepreg solidified product, the more entangled the release paper, PE film and carbon fiber resin solidified product are, and the more difficult it is to separate the carbon fiber and the release paper. The present invention will be described and compared in detail through specific embodiments below. Example 1

[0043] A method for recycling thermosetting carbon fiber prepreg scraps comprises the following steps:

[0044] S1, collecting, collecting different types of carbon fiber prepreg scraps to form a scrap mixture; in this embodiment, the scraps include epoxy resin carbon fiber prepreg and polyester resin carbon fiber prepreg, with a total weight of 40 kg;

[0045] S2, heating and curing, heating and curing the carbon fiber prepreg scraps mixture collected in S1 in a fluffy state; the heating temperature is set to 180° C., and the stacking thickness of the carbon fiber prepreg scraps is controlled to be 10 cm;

[0046] S3, crushing, crushing the carbon fiber prepreg solidified material obtained in S2 to destroy the adhesion between the PE film, the release paper, and the carbon fiber resin matrix solidified material; the size of the solidified material after crushing is 2-4 cm; specifically including:

[0047] S31, first crushing, sending the carbon fiber prepreg cured product obtained in step S2 into a crusher for first crushing, and controlling the size of the crushed product to be within 10 cm;

[0048] S32, second crushing, sending the carbon fiber prepreg solidified material crushed in step S31 into a crusher for second crushing, and controlling the size of the crushed material to be 2-4 cm;

[0049] S4, sorting, the crushed carbon fiber prepreg solidified material is sorted once by a wind separator, the wind speed is set to 4-6m / s, the release paper and PE film are separated, and the carbon fiber resin matrix solidified material is retained;

[0050] S5, oxygen-free heating, subjecting the carbon fiber resin matrix solidified material to microwave heating under the condition of oxygen concentration ≤ 10% to obtain carbon fiber with a resin residual rate of less than 10%; the oxygen-free heating is carried out by in-phase microwave spark discharge heating, specifically comprising the steps of:

[0051] In a co-phase microwave heating device, the carbon fiber resin matrix solidified material is subjected to co-phase microwave heating, and at the same time, a uniform spark discharge is performed in the co-phase microwave field, and the position where the spark discharge occurs is controlled within the same horizontal plane height in the co-phase microwave field, so that the carbon fiber resin matrix solidified material is quickly and uniformly heated to 500°C within 1-5 minutes, and as the microwave and spark discharge time increase, the temperature can continue to rise rapidly to crack the resin, complete the separation of the carbon fiber and the resin in the carbon fiber resin matrix solidified material, and obtain carbon fiber. S6, aerobic heating, heating the carbon fiber with a resin residual rate of less than 10% obtained in step 5 under aerobic conditions, controlling the temperature at 450-550°C, and the time at 15-30 minutes to obtain pure carbon fiber.

[0052] In this embodiment, through visual observation, the release paper can be basically removed cleanly, and the retention rate of the carbon fiber resin matrix solidified material is good, thereby effectively ensuring the recycling efficiency of the carbon fiber prepreg, and the recycled carbon fiber has a clean surface and a soft feel. Example 2

[0053] A method for recycling thermosetting carbon fiber prepreg scraps comprises the following steps:

[0054] S1, collecting, collecting different types of carbon fiber prepreg scraps to form a scrap mixture; in this embodiment, the scraps include epoxy resin carbon fiber prepreg and polyester resin carbon fiber prepreg, with a total weight of 40 kg;

[0055] S2, heating and curing, heating and curing the carbon fiber prepreg scraps mixture collected in S1 in a fluffy state; the heating temperature is set to 180° C., and the stacking thickness of the carbon fiber prepreg scraps is controlled to be 10 cm;

[0056] S3, crushing, crushing the carbon fiber prepreg solidified material to destroy the adhesion between the PE film, the release paper, and the carbon fiber resin matrix solidified material; the size of the solidified material after crushing is 2-4 cm; specifically including:

[0057] S31, first crushing, sending the carbon fiber prepreg cured product obtained in step S2 into a crusher for first crushing, and controlling the size of the crushed product to be within 10 cm;

[0058] S32, the second crushing, the step S31 crushed carbon fiber prepreg cured product is fed into the crusher for a second crushing, the size after crushing is controlled at 2-4cm;

[0059] S4, sorting, sorting the crushed carbon fiber prepreg solidified material twice through a wind separator, specifically including:

[0060] S41, first sorting, sending the carbon fiber prepreg solidified material after crushing in S3 to an air separator for first sorting, with the wind speed controlled at 5-6 m / s, to separate the carbon fiber resin matrix solidified material and the mixture A, wherein the mixture A includes release paper, most of the PE film and a small part of the carbon fiber resin matrix solidified material;

[0061] S42, second sorting, the mixture A in step S42 is again sorted by the air separator for the second time, the wind speed is controlled at 4-5m / s, the carbon fiber resin matrix solidified material is further separated, and the carbon fiber resin matrix solidified material is collected with the separated carbon fiber resin matrix solidified material in S41;

[0062] S5, oxygen-free heating, subjecting the carbon fiber resin matrix solidified material to microwave heating under the condition of oxygen concentration ≤ 10% to obtain carbon fiber with a resin residual rate of less than 10%; the oxygen-free heating is carried out by in-phase microwave spark discharge heating, specifically comprising the steps of:

[0063] In a co-phase microwave heating device, a carbon fiber resin matrix solidified material is subjected to co-phase microwave heating. At the same time, a uniform spark discharge is performed in the co-phase microwave field. The position where the spark discharge occurs is controlled within the same horizontal plane height in the co-phase microwave field, so that the carbon fiber resin matrix solidified material is quickly and uniformly heated to 500° C. within 1-5 minutes. As the microwave and spark discharge time increases, the temperature can continue to increase rapidly to crack the resin, complete the separation of carbon fiber and resin in the carbon fiber resin matrix solidified material, and obtain carbon fiber;

[0064] S6, aerobic heating, heating the carbon fiber with a resin residual rate of less than 10% obtained in step 5 under aerobic conditions, controlling the temperature at 450-550° C. and the time at 15-30 minutes to obtain pure carbon fiber.

[0065] In this embodiment, through visual observation, the carbon fiber resin matrix solidified material obtained by the first air selection basically does not contain release paper, and the carbon fiber resin matrix solidified material obtained by the second air selection is mixed with a small amount of release paper. The recycling efficiency of the carbon fiber prepreg is very high, and the recycled carbon fiber has a clean surface and a soft feel.

[0066] Comparative Example 1

[0067] This comparative example is a comparative example of Example 1, except that the wind speed is controlled during sorting.

[0068] A method for recycling thermosetting carbon fiber prepreg scraps comprises the following steps:

[0069] S1, collecting, collecting different types of carbon fiber prepreg scraps to form a scrap mixture; in this embodiment, the scraps include epoxy resin carbon fiber prepreg and polyester resin carbon fiber prepreg, with a total weight of 40 kg;

[0070] S2, heating and curing, heating and curing the carbon fiber prepreg scraps mixture collected in S1 in a fluffy state; the heating temperature is set to 180° C., and the stacking thickness of the carbon fiber prepreg scraps is controlled to be 10 cm;

[0071] S3, crushing, crushing the carbon fiber prepreg solidified material obtained in S2 to destroy the adhesion between the PE film, the release paper, and the carbon fiber resin matrix solidified material; the size of the solidified material after crushing is 2-4 cm; specifically including:

[0072] S31, first crushing, sending the carbon fiber prepreg cured product obtained in step S2 into a crusher for first crushing, and controlling the size of the crushed product to be within 10 cm;

[0073] S32, second crushing, sending the carbon fiber prepreg solidified material crushed in step S31 into a crusher for second crushing, and controlling the size of the crushed material to 2-4 cm;

[0074] S4, sorting, the crushed carbon fiber prepreg solidified material is sorted once by a wind separator, the wind speed is set to 8-10m / s, the release paper, PE film and other impurities are separated, and the carbon fiber resin matrix solidified material is retained;

[0075] S5, oxygen-free heating, subjecting the carbon fiber resin matrix solidified material to microwave heating under the condition of oxygen concentration ≤ 10% to obtain carbon fiber with a resin residual rate of less than 10%; the oxygen-free heating is carried out by in-phase microwave spark discharge heating; the specific steps include:

[0076] In a co-phase microwave heating device, a carbon fiber resin matrix solidified material is subjected to co-phase microwave heating. At the same time, a uniform spark discharge is performed in the co-phase microwave field. The position where the spark discharge occurs is controlled within the same horizontal plane height in the co-phase microwave field, so that the carbon fiber resin matrix solidified material is quickly and uniformly heated to 500° C. within 1-5 minutes. As the microwave and spark discharge time increases, the temperature can continue to increase rapidly to crack the resin, complete the separation of carbon fiber and resin in the carbon fiber resin matrix solidified material, and obtain carbon fiber;

[0077] S6, aerobic heating, heating the carbon fiber with a resin residual rate of less than 10% obtained in step 5 under aerobic conditions, controlling the temperature at 450-550° C. and the time at 15-30 minutes to obtain pure carbon fiber.

[0078] In this comparative example, through visual observation, the retention rate of the carbon fiber resin matrix solidified material is low, and a large amount of release paper is mixed in the carbon fiber resin matrix solidified material. Therefore, the recycling efficiency of the carbon fiber prepreg is low, which is not conducive to the recycling industrialization, and the release paper mixed in the carbon fiber resin matrix solidified material will form ash after subsequent combustion, which will obviously remain on the carbon fiber and is difficult to remove, affecting the quality of the recycled carbon fiber.

[0079] Comparative Example 2

[0080] This comparative example is a comparative example of Example 2, except that the wind speed is controlled during sorting.

[0081] A method for recycling thermosetting carbon fiber prepreg scraps comprises the following steps:

[0082] S1, collecting, collecting different types of carbon fiber prepreg scraps to form a scrap mixture; in this embodiment, the scraps include epoxy resin carbon fiber prepreg and polyester resin carbon fiber prepreg, with a total weight of 40 kg;

[0083] S2, heating and curing, heating and curing the carbon fiber prepreg scraps mixture collected in S1 in a fluffy state; the heating temperature is set to 180° C., and the stacking thickness of the carbon fiber prepreg scraps is controlled to be 10 cm;

[0084] S3, crushing, crushing the carbon fiber prepreg solidified material to destroy the adhesion between the PE film, the release paper, and the carbon fiber resin matrix solidified material; the size of the solidified material after crushing is 2-4 cm; specifically including:

[0085] S31, first crushing, sending the carbon fiber prepreg cured product obtained in step S2 into a crusher for first crushing, and controlling the size of the crushed product to be within 10 cm;

[0086] S32, second crushing, sending the carbon fiber prepreg solidified material crushed in step S31 into a crusher for second crushing, and controlling the size of the crushed material to 2-4 cm;

[0087] S4, sorting, sorting the crushed carbon fiber prepreg solidified material twice through a wind separator, specifically including:

[0088] S41, first sorting, sending the carbon fiber prepreg solidified material after crushing in S3 to an air separator for first sorting, with the wind speed controlled at 9-10 m / s, to separate the carbon fiber resin matrix solidified material and the mixture A, wherein the mixture A includes release paper, most of the PE film and a small part of the carbon fiber resin matrix solidified material;

[0089] S42, second sorting, the mixture A in step S42 is again sorted by the air separator for the second time, the wind speed is controlled at 8-9m / s, the carbon fiber resin matrix solidified material is further separated, and the carbon fiber resin matrix solidified material is collected with the separated carbon fiber resin matrix solidified material in S41;

[0090] S5, oxygen-free heating, subjecting the cured product of the carbon fiber and the resin matrix to microwave heating under the condition of an oxygen concentration of ≤10%, to obtain a carbon fiber with a resin residual rate of less than 10%; the oxygen-free heating is conducted by in-phase microwave spark discharge heating, specifically comprising the steps of:

[0091] In a co-phase microwave heating device, a carbon fiber resin matrix solidified material is subjected to co-phase microwave heating. At the same time, a uniform spark discharge is performed in the co-phase microwave field. The position where the spark discharge occurs is controlled within the same horizontal plane height in the co-phase microwave field, so that the carbon fiber resin matrix solidified material is quickly and uniformly heated to 500° C. within 1-5 minutes. As the microwave and spark discharge time increases, the temperature can continue to increase rapidly to crack the resin, complete the separation of carbon fiber and resin in the carbon fiber resin matrix solidified material, and obtain carbon fiber;

[0092] S6, aerobic heating, heating the carbon fiber with a resin residual rate of less than 10% obtained in step 5 under aerobic conditions, controlling the temperature at 450-550° C. and the time at 15-30 minutes to obtain pure carbon fiber.

[0093] In this embodiment, after visual observation, the release paper and the carbon fiber resin matrix solidified material cannot be effectively separated, the retention rate of the carbon fiber resin matrix solidified material is very low, and a large amount of release paper is mixed in, resulting in low recycling efficiency of the carbon fiber prepreg, which is not conducive to industrialization, and the mixed release paper will form ash remaining on the carbon fiber after burning, which is difficult to remove, affecting the quality of the recycled carbon fiber.

[0094] Comparative Example 3

[0095] This comparative example is a comparative example of Example 2, except that the size of the carbon fiber prepreg cured product after crushing is controlled differently.

[0096] A method for recycling thermosetting carbon fiber prepreg scraps comprises the following steps:

[0097] S1, classification and collection, the carbon fiber prepreg scraps are classified and collected; in this embodiment, the thermosetting carbon fiber prepreg includes epoxy resin and polyester resin, with a total weight of 40 kg;

[0098] S2, heating and curing, heating and curing the thermosetting carbon fiber prepreg scrap material mixture collected in S1 in a fluffy state; setting the heating and curing temperature at 180° C.; and controlling the thickness of the cured carbon fiber prepreg to be 10 cm;

[0099] S3, crushing, crushing the carbon fiber prepreg solidified material once, and controlling the size of the crushed material within 10 cm;

[0100] S4, sorting, sorting the crushed carbon fiber prepreg solidified material twice through a wind separator, specifically including:

[0101] S41, first sorting, sending the carbon fiber prepreg solidified material after crushing in S3 to an air separator for first sorting, with the wind speed controlled at 5-6 m / s, to separate the carbon fiber resin matrix solidified material and the mixture A, wherein the mixture A includes release paper, most of the PE film and a small part of the carbon fiber resin matrix solidified material;

[0102] S42, second sorting, the mixture A in step S42 is again sorted by the air separator for the second time, the wind speed is controlled at 4-5m / s, the carbon fiber resin matrix solidified material is further separated, and the carbon fiber resin matrix solidified material is collected with the separated carbon fiber resin matrix solidified material in S41;

[0103] S5, oxygen-free heating, subjecting the cured product of the carbon fiber and the resin matrix to microwave heating under the condition of an oxygen concentration of ≤10%, to obtain a carbon fiber with a resin residual rate of less than 10%; the oxygen-free heating is conducted by in-phase microwave spark discharge heating, specifically comprising the steps of:

[0104] In a co-phase microwave heating device, a carbon fiber resin matrix solidified material is subjected to co-phase microwave heating. At the same time, a uniform spark discharge is performed in the co-phase microwave field. The position where the spark discharge occurs is controlled within the same horizontal plane height in the co-phase microwave field, so that the carbon fiber resin matrix solidified material is quickly and uniformly heated to 500° C. within 1-5 minutes. As the microwave and spark discharge time increases, the temperature can continue to increase rapidly to crack the resin, complete the separation of carbon fiber and resin in the carbon fiber resin matrix solidified material, and obtain carbon fiber;

[0105] S6, aerobic heating, heating the carbon fiber with a resin residual rate of less than 10% obtained in step 5 under aerobic conditions, controlling the temperature at 450-550° C. and the time at 15-30 minutes to obtain pure carbon fiber.

[0106] In this embodiment, after visual observation, it is found that during the air separation process, the carbon fiber resin matrix solidified material and the release paper cannot be well separated, resulting in a low retention rate of the carbon fiber resin matrix solidified material, which is not conducive to industrialization, and there is a lot of release paper mixed in the carbon fiber resin matrix solidified material, so that the recovery efficiency of the carbon fiber prepreg is low, and the mixed release paper will form ash after burning and remain on the carbon fiber, which is difficult to remove, affecting the quality of the recycled carbon fiber.

[0107] In the present invention, the release paper removal rate and the carbon fiber resin matrix solidified material retention rate in the embodiments and comparative examples are actually measured and calculated. The calculation is based on: taking samples and weighing them from the carbon fiber prepreg solidified material before sorting, manually sorting out the release paper and the carbon fiber resin matrix solidified material, weighing and calculating the weight ratio of the release paper and the carbon fiber resin matrix solidified material, and the PE film is very light and can be ignored. Similarly, taking samples and weighing them from the carbon fiber resin matrix solidified material that is finally retained or collected after sorting, manually sorting out the release paper and the carbon fiber resin matrix solidified material, and then weighing and calculating the weight ratio of the release paper and the carbon fiber resin matrix solidified material, thereby calculating the release paper removal rate and the carbon fiber resin matrix solidified material retention rate after air selection in each embodiment and comparative example. The calculation results are specifically shown in Table 1.

[0108] Table 1

[0109] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Release paper removal rate (%) 95 90 65 50 50 Carbon fiber resin matrix solidification retention rate (%) 82 95 40 60 80

[0110] By comparing the above embodiments with the comparative examples, it can be seen that when the size of the carbon fiber prepreg solidified material after crushing is controlled at 2-4 cm and the wind speed of the winnowing machine is controlled at 4-6 m / s, the removal rate of the release paper can be better taken into account, and the retention rate of the carbon fiber resin matrix solidified material can be maximized, thereby improving the carbon fiber recycling efficiency and recycling quality.

Claims

1. A method for recycling thermosetting carbon fiber prepreg scraps, characterized in that: The following steps are involved: S1, collecting, collecting different types of thermosetting carbon fiber prepreg scraps to form a scrap mixture; S2, heating and curing, heating and curing the collected carbon fiber prepreg scrap mixture in a fluffy state to obtain a carbon fiber prepreg cured product; S3, crushing, crushing the carbon fiber prepreg solidified material of S2 to destroy the adhesion between the release paper, the PE film, and the carbon fiber resin matrix solidified material; S4, sorting, passing the carbon fiber prepreg solidified material crushed in S3 through an air separator to remove the release paper and PE film, and retain the carbon fiber resin matrix solidified material; S5, oxygen-free heating, subjecting the carbon fiber resin matrix solidified material to microwave heating under the condition of oxygen concentration ≤10%, the heating temperature is 500-800°C, and the heating time is 5-40min to crack the resin matrix to obtain carbon fiber with a resin residual rate of less than 10%; S6, aerobic heating, heating the carbon fiber obtained in step S5 under aerobic conditions to remove residual resin and residual carbon to obtain pure carbon fiber.

2. The method for recycling thermosetting carbon fiber prepreg scraps according to claim 1, characterized in that: In the heating and curing of step S2, the stacking thickness of the carbon fiber prepreg scrap mixture does not exceed 30 cm, and the heating temperature is set based on the carbon fiber prepreg with the highest curing temperature in the mixture.

3. The method for recycling thermosetting carbon fiber prepreg scraps according to claim 1, characterized in that: The size range of the carbon fiber prepreg cured product after the crushing in step S3 is controlled within 10 cm.

4. The method for recycling thermosetting carbon fiber prepreg scraps according to claim 3, characterized in that: The size range of the carbon fiber prepreg cured product after the crushing in step S3 is controlled within 5 cm.

5. The method for recycling thermosetting carbon fiber prepreg scraps according to claim 1, characterized in that: The wind speed of the air separator in step S4 is set to 3-8 m / s.

6. The method for recycling thermosetting carbon fiber prepreg scraps according to claim 4, characterized in that: The step S3 of crushing comprises: S31, first crushing, sending the carbon fiber prepreg cured product obtained in step S2 into a crusher for first crushing, and controlling the size of the crushed product to be within 10 cm; S32, second crushing, sending the carbon fiber prepreg solidified material crushed in step S31 into a crusher for second crushing, and controlling the size of the crushed solidified material within 5 cm.

7. The method for recycling thermosetting carbon fiber prepreg scraps according to claim 1, characterized in that: The step S4 sorting includes the following steps: S41, first sorting, sending the carbon fiber prepreg solidified material crushed in S3 into a wind separator for first sorting, with the wind speed controlled at 5-8 m / s, to separate the carbon fiber resin matrix solidified material and the mixture A, wherein the mixture A includes release paper, PE film and a small portion of the carbon fiber resin matrix solidified material; S42, second sorting, the mixture A obtained in step S41 is sent to the air separator again for second sorting, the wind speed is controlled at 3-5m / s, the carbon fiber resin matrix solidified material is further separated, and the mixture is collected with the carbon fiber resin matrix solidified material separated in S41.

8. The method for recycling thermosetting carbon fiber prepreg scraps according to claim 1, characterized in that: The heating method of the oxygen-free heating in step S5 is in-phase microwave spark discharge heating, which specifically includes: In a co-phase microwave heating device, the carbon fiber resin matrix solidified material is subjected to co-phase microwave heating. At the same time, uniform spark discharge is performed in the co-phase microwave field. The position where the spark discharge occurs is controlled within the same horizontal plane height in the co-phase microwave field, so that the carbon fiber resin matrix solidified material is rapidly and uniformly heated to 500°C within 1-5 minutes. As the microwave and spark discharge time increase, the temperature continues to rise rapidly to crack the resin, complete the separation of the carbon fiber and the resin in the carbon fiber matrix solidified material, and obtain the carbon fiber.

9. The method for recycling thermosetting carbon fiber prepreg scraps according to claim 1, characterized in that: The step S6 is aerobic heating, the temperature is controlled at 450-550° C., and the time is 15-30 minutes.

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