Recycling method of waste carbon fiber composite material

Abstract

The invention provides a waste carbon fiber composite material recovery method, which comprises: sequentially carrying out nitrogen thermal decomposition, cooling and air thermal decomposition on a waste carbon fiber composite material, and recovering to obtain carbon fibers. The carbon fibers obtained through the recycling method are high in recycling rate and performance retention rate which can reach 90% or above, the surfaces of the fibers are smooth and clean, recycling of the recycled carbon fibers is facilitated, the recycling method is suitable for industrial production, chemical reagents are not used in the recycling process, and the recycling method is environmentally friendly, so that sustainable development of composite materials is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling waste carbon fiber reinforced thermosetting epoxy resin composite materials (CF / EP), and relates to a method for recycling waste carbon fiber composite materials, and in particular to a method for recycling carbon fibers from waste carbon fiber reinforced thermosetting resin composite materials in two steps. Background Art

[0002] With the rapid increase in demand for composite materials, the production technology of carbon fiber reinforced thermosetting composite materials has been continuously optimized, and various automated production technologies have been used to further reduce production costs and improve production efficiency. The mass production of thermosetting composite materials will also produce a large amount of scraps, and the service life of thermosetting composite materials is about 20-30 years. As time goes by, various products widely used in this type of composite materials will gradually become scrapped.

[0003] After curing, the thermosetting resin matrix forms a cross-linked network structure that is insoluble, infusible, and not easily decomposed, making the recycling and reuse of discarded carbon fiber reinforced thermosetting resin-based composites very difficult. However, the cost of producing carbon fiber is high. On average, it costs more than 10,000 pounds to produce 1 ton of carbon fiber. If it is directly discarded, it will not only pollute the environment but also increase economic costs. Therefore, the recycling and reuse of carbon fiber from discarded thermosetting composites has extremely important ecological and economic value.

[0004] The existing recycling methods for waste thermosetting composite materials mainly include traditional landfill, mechanical crushing, high-temperature thermal decomposition, solvent recovery, microwave thermal decomposition, electrochemical reaction and catalytic cracking. The traditional landfill method is to bury the waste composite materials directly underground. This method not only seriously pollutes the environment, but also fails to achieve the recycling and reuse of carbon fibers, causing serious harm to economic and social benefits. Therefore, this method is gradually abandoned; the mechanical crushing method is to crush the waste composite materials and use them as raw materials for new materials. This method destroys the performance of each component of the original composite material and cannot recycle the carbon fibers for reuse; the solvent recovery method is to use various chemical solvents to dissolve the matrix resin to recover the carbon fibers therein. This method can effectively recover pure carbon fibers, but it requires the use of strong oxidizing solvents such as nitric acid and needs to be heated to a certain temperature, which is very costly and not suitable for industrial application; the electrochemical reaction method is to use the carbon fiber composite material to be recycled as the anode and the conductive material as the cathode to form an electrochemical reaction system, and the carbon fiber composite material undergoes a chemical reaction to recover the carbon fibers. Although this method is simple and easy to operate and has low pollution, it is costly to form an electrochemical reaction system and is not easy to realize industrial production; the recovered carbon fibers obtained by the catalytic cracking method have a high recovery rate and high resin decomposition efficiency, but it requires the use of a variety of catalysts, oxidants, organic solvents, etc., which is complicated to operate, has great harm, is costly, and is difficult to achieve large-scale application.

[0005] The most industrially applicable existing technology is the high-temperature thermal decomposition method, which includes the inert gas cracking method and the air thermal decomposition method. The inert gas cracking method is a method of placing the waste thermosetting composite material in an inert atmosphere such as nitrogen and helium for thermal decomposition. This method can well protect the surface of the carbon fiber from damage, but the process time is long, and the surface of the recycled carbon fiber is prone to residual carbon from resin decomposition, which affects the reuse of the recycled carbon fiber; and although the air thermal decomposition method has a short process time, the surface of the carbon fiber is easily oxidized at high temperature, resulting in the performance retention rate being maintained at only about 60%, which also affects the reuse of the recycled carbon fiber. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for recycling waste carbon fiber composite materials. The recycling method is simple to operate, has a short process time, can realize the large-scale recycling of waste composite materials, achieve industrial production, and at the same time obtain carbon fiber with good recycling quality, thereby realizing the recycling and reuse of carbon fiber.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for recycling waste carbon fiber composite materials, the recycling method comprising the following steps:

[0009] The waste carbon fiber composite material is subjected to anaerobic thermal decomposition, cooling and air thermal decomposition in sequence to recycle the carbon fiber.

[0010] The present invention uses an oxygen-free thermal decomposition process to thermally decompose the resin in the waste carbon fiber composite material, and then uses air thermal decomposition to thermally oxidize and decompose the carbon residue remaining on the surface of the carbon fiber after the resin is decomposed, thereby obtaining pure recycled carbon fiber. The carbon fiber recovered by the present invention has a high recovery rate and a high performance retention rate, which can reach more than 90%, is conducive to the reuse of the recycled carbon fiber, is suitable for industrial production, and does not use chemical reagents in the recycling process, which is green and environmentally friendly, thereby achieving the sustainable development of composite materials.

[0011] As a preferred technical solution of the present invention, the matrix resin of the waste carbon fiber composite material includes a thermosetting resin.

[0012] Preferably, the thermosetting resin includes any one of epoxy resin, unsaturated polyester, phenolic resin or vinyl resin.

[0013] As a preferred technical solution of the present invention, the carbon fiber in the waste carbon fiber composite material includes any one of polyacrylonitrile-based carbon fiber, asphalt-based carbon fiber or viscose-based carbon fiber, or a combination of at least two of them. Typical but non-limiting combinations include a combination of polyacrylonitrile-based carbon fiber and asphalt-based carbon fiber, a combination of asphalt-based carbon fiber and viscose-based carbon fiber, a combination of polyacrylonitrile-based carbon fiber and viscose-based carbon fiber, or a combination of polyacrylonitrile-based carbon fiber, asphalt-based carbon fiber and viscose-based carbon fiber.

[0014] Preferably, the carbon fiber is in the form of any one of continuous fibers, long fibers or carbon fiber fabrics or a combination of at least two thereof. Typical but non-limiting combinations include a combination of continuous fibers and long fibers, a combination of continuous fibers and carbon fiber fabrics, a combination of long fibers and carbon fiber fabrics, or a combination of continuous fibers, long fibers and carbon fiber fabrics.

[0015] As a preferred technical solution of the present invention, the sources of the waste carbon fiber composite materials include scraps generated during the prepreg laying process and / or waste carbon fiber composite material plates and parts.

[0016] The waste carbon fiber composite material of the present invention is a composite material containing both a thermosetting resin and carbon fiber. During the recycling process, the thermosetting resin is first thermally decomposed, and then the impurities remaining after the resin decomposition are decomposed to obtain carbon fiber with a performance retention rate of more than 90%.

[0017] As a preferred technical solution of the present invention, the oxygen-free thermal decomposition includes any one of nitrogen thermal decomposition, helium thermal decomposition or argon thermal decomposition.

[0018] Preferably, the temperature of the anaerobic thermal decomposition is 600-900°C, for example, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C or 900°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0019] Preferably, the flow rate of the gas in the anaerobic thermal decomposition is 20 to 150 mL / min, for example, 20 mL / min, 50 mL / min, 70 mL / min, 100 mL / min, 120 mL / min or 150 mL / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0020] Preferably, the time of the anaerobic thermal decomposition is 1 to 3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] As a preferred technical solution of the present invention, the gas generated by the anaerobic thermal decomposition is connected to an external water tank.

[0022] The purpose of the anaerobic thermal decomposition described in the present invention is to decompose the matrix resin of the carbon fiber reinforced resin composite material by heat. Those skilled in the art can adjust the thermal decomposition temperature and time according to the properties of different resins and the thickness of the composite material to completely decompose the resin by heat. The gas generated by the decomposition of the resin enters an external water tank along with the flowing nitrogen and is not discharged into the atmosphere, thereby avoiding environmental pollution and achieving green recycling.

[0023] As a preferred technical solution of the present invention, the temperature of air thermal decomposition is 450-650°C, for example, it can be 450°C, 500°C, 550°C, 600°C or 650°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] The purpose of air thermal decomposition described in the present invention is to: heat and oxidize the carbon residue remaining on the surface of the carbon fiber after the resin decomposition, so as to obtain pure recycled carbon fiber; when the temperature is lower than 450°C, the residual coke is difficult to absorb enough heat for oxidative decomposition, and the processing time is greatly extended or the coke on the surface cannot be removed at all; when the temperature is higher than 650°C, the oxidative decomposition reaction of the residual coke is too violent, which can easily lead to partial oxidation of the reinforcing carbon fiber, serious loss of mechanical properties, and reduced retention rate of mechanical properties of the recycled carbon fiber.

[0025] Preferably, the time for the air thermal decomposition is 0.5 to 1 h, for example, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h or 1 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] The thermal decomposition device in the present invention includes a closed heating furnace for nitrogen thermal decomposition treatment and various forms of heating furnaces or cracking furnaces for air thermal decomposition.

[0027] As a preferred technical solution of the present invention, the recycling method also includes pretreatment of the waste carbon fiber composite material.

[0028] As a preferred technical solution of the present invention, the pretreatment includes: screening, cleaning and crushing the waste carbon fiber composite materials in sequence.

[0029] The purpose of the screening described in the present invention is: to classify and process composite materials with different matrix resins; the present invention removes pollutants such as sludge and oil stains on the surface of the composite materials through a cleaning process; the present invention divides the composite materials into particles of the same volume through a crushing process, so that the composite materials are heated evenly and the thermal decomposition is more thorough.

[0030] As a preferred technical solution of the present invention, the method for recycling waste carbon fiber composite materials of the present invention comprises the following steps:

[0031] (1) Screening, cleaning and crushing the waste carbon fiber composite materials in sequence;

[0032] (2) thermally decomposing the treated waste carbon fiber composite material in a nitrogen atmosphere at 600 to 900° C. for 1 to 3 hours, and obtaining a decomposition product after cooling;

[0033] Wherein, the flow rate of nitrogen in the nitrogen thermal decomposition is 20 to 150 mL / min;

[0034] (3) The decomposition product obtained in step (2) is subjected to air thermal decomposition in an air atmosphere at 450-650° C. for 0.5-1 h to recover the carbon fiber.

[0035] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The carbon fiber recovered by the method provided by the present invention has a high recovery rate and a high performance retention rate, which can reach more than 90%. The fiber surface is smooth, which is conducive to the reuse of the recovered carbon fiber and is suitable for industrial production;

[0038] (2) The recycling method provided by the present invention does not use chemical reagents during the recycling process, which is green and environmentally friendly, thereby achieving the sustainable development of composite materials;

[0039] (3) By adopting the recycling method provided by the present invention, the recovery rate of carbon fiber can reach more than 95%. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0041] Example 1

[0042] This embodiment provides a method for recycling waste carbon fiber composite materials, the recycling method comprising the following steps:

[0043] (1) Screening, cleaning and crushing the waste carbon fiber composite materials in sequence;

[0044] Wherein, the matrix resin of the waste carbon fiber composite material is epoxy resin, and the carbon fiber is viscose-based carbon fiber in the form of continuous fibers;

[0045] (2) thermally decompose the treated waste carbon fiber composite material in a nitrogen atmosphere at 680° C. for 2.5 h, and obtain a decomposition product after cooling;

[0046] Wherein, the flow rate of nitrogen in the nitrogen thermal decomposition is 100 mL / min;

[0047] (3) The decomposition product obtained in step (2) is subjected to air thermal decomposition in an air atmosphere at 500° C. for 0.8 h to recover carbon fiber.

[0048] Example 2

[0049] This embodiment provides a method for recycling waste carbon fiber composite materials, the recycling method comprising the following steps:

[0050] (1) Screening, cleaning and crushing the waste carbon fiber composite materials in sequence;

[0051] Wherein, the matrix resin of the waste carbon fiber composite material is unsaturated polyester, and the carbon fiber is polyacrylonitrile-based carbon fiber in the form of carbon fiber fabric;

[0052] (2) subjecting the treated waste carbon fiber composite material to nitrogen thermal decomposition at 600° C. in a nitrogen atmosphere for 3 h, and obtaining a decomposition product after cooling;

[0053] Wherein, the flow rate of nitrogen in the nitrogen thermal decomposition is 80 mL / min;

[0054] (3) The decomposition product obtained in step (2) is subjected to air thermal decomposition in an air atmosphere at 450° C. for 1 h to recover carbon fiber.

[0055] Example 3

[0056] This embodiment provides a method for recycling waste carbon fiber composite materials, the recycling method comprising the following steps:

[0057] (1) Screening, cleaning and crushing the waste carbon fiber composite materials in sequence;

[0058] Wherein, the matrix resin of the waste carbon fiber composite material is phenolic resin; the carbon fiber is asphalt-based carbon fiber in the form of long fibers;

[0059] (2) thermally decompose the treated waste carbon fiber composite material in a nitrogen atmosphere at 900° C. for 3 h, and obtain a decomposition product after cooling;

[0060] Wherein, the flow rate of nitrogen in the nitrogen thermal decomposition is 20mL / min;

[0061] (3) The decomposition product obtained in step (2) is subjected to air thermal decomposition in an air atmosphere at 650° C. for 0.5 h to recover carbon fiber.

[0062] Example 4

[0063] This embodiment provides a method for recycling waste carbon fiber composite materials, the recycling method comprising the following steps:

[0064] (1) Screening, cleaning and crushing the waste carbon fiber composite materials in sequence;

[0065] Wherein, the matrix resin of the waste carbon fiber composite material is vinyl resin; the carbon fiber is viscose-based carbon fiber in the form of continuous fiber and carbon fiber fabric;

[0066] (2) thermally decomposing the treated waste carbon fiber composite material in a nitrogen atmosphere at 600° C. for 1 to 3 hours, and obtaining a decomposition product after cooling;

[0067] Wherein, the flow rate of nitrogen in the nitrogen thermal decomposition is 150mL / min;

[0068] (3) The decomposition product obtained in step (2) is subjected to air thermal decomposition in an air atmosphere at 550° C. for 0.7 h to recover carbon fiber.

[0069] Example 5

[0070] This embodiment provides a method for recycling waste carbon fiber composite materials, the recycling method comprising the following steps:

[0071] (1) Screening, cleaning and crushing the waste carbon fiber composite materials in sequence;

[0072] Wherein, the matrix resin of the waste carbon fiber composite material is epoxy resin; the carbon fiber is polyacrylonitrile-based carbon fiber in the form of continuous fiber and viscose-based carbon fiber in the form of carbon fiber fabric;

[0073] (2) thermally decompose the treated waste carbon fiber composite material in a nitrogen atmosphere at 650° C. for 2.5 h, and obtain a decomposition product after cooling;

[0074] Wherein, the flow rate of nitrogen in the nitrogen thermal decomposition is 80 mL / min;

[0075] (3) The decomposition product obtained in step (2) is subjected to air thermal decomposition in an air atmosphere at 600° C. for 0.6 h to recover carbon fiber.

[0076] Example 6

[0077] This embodiment provides a method for recycling waste carbon fiber composite materials. The difference between the recycling method and the embodiment 1 is that:

[0078] In this embodiment, the temperature of the air thermal decomposition in step (3) is modified to 400°C.

[0079] Example 7

[0080] This embodiment provides a method for recycling waste carbon fiber composite materials. The difference between the recycling method and the embodiment 1 is that:

[0081] In this embodiment, the temperature of the air thermal decomposition in step (3) is modified to 700°C.

[0082] Example 8

[0083] This embodiment provides a method for recycling waste carbon fiber composite materials. The difference between the recycling method and the embodiment 1 is that:

[0084] In this embodiment, the flow rate of nitrogen in the nitrogen thermal decomposition in step (2) is modified to 0 mL / min, that is, the nitrogen thermal decomposition is carried out in a static nitrogen atmosphere.

[0085] Example 9

[0086] This embodiment provides a method for recycling waste carbon fiber composite materials. The difference between the recycling method and the embodiment 1 is that:

[0087] In this embodiment, the time for the air thermal decomposition in step (3) is modified to 2 hours.

[0088] Example 10

[0089] This embodiment provides a method for recycling waste carbon fiber composite materials. The difference between the recycling method and the embodiment 1 is that:

[0090] In this embodiment, the thermal decomposition of nitrogen in step (2) is modified to thermal decomposition of helium, that is, the thermal decomposition process in step (2) is carried out under a helium atmosphere.

[0091] Comparative Example 1

[0092] This comparative example provides a method for recycling waste carbon fiber composite materials, which differs from Example 1 only in that:

[0093] In this comparative example, nitrogen thermal decomposition was omitted, that is, the waste carbon fiber composite material was only subjected to air thermal decomposition.

[0094] Comparative Example 2

[0095] This comparative example provides a method for recycling waste carbon fiber composite materials, which differs from Example 1 only in that:

[0096] In this comparative example, air thermal decomposition was omitted, that is, the waste carbon fiber composite material was only subjected to nitrogen thermal decomposition.

[0097] The performance of the recycled carbon fibers provided in the above examples and comparative examples was tested, and the performance retention results are shown in Table 1.

[0098] The performance tests include elongation and tensile modulus.

[0099] Table 1

[0100]

[0101]

[0102] Table 1 shows the following points:

[0103] (1) Comprehensive analysis of Example 1 and Comparative Examples 1-2 shows that the performance retention rate of the carbon fiber obtained by anaerobic pyrolysis or air pyrolysis alone is good, but the surface of the recycled carbon fiber has more residues and undecomposed resin (furthermore, the residues and undecomposed resin on the surface of the carbon fiber obtained in Comparative Example 2 are more than those in Comparative Example 1). Therefore, the carbon fiber obtained by the methods provided in Comparative Examples 1 and 2 cannot achieve the purpose of recycling;

[0104] (2) Comprehensive analysis of Example 1 and Example 6 shows that when the temperature is too high during the air thermal decomposition process, the surface of the recovered carbon fiber is oxidized, thereby affecting the performance retention rate of the carbon fiber; when the temperature is too low during the air thermal decomposition process, residues will accumulate on the surface of the carbon fiber, affecting its recycling;

[0105] (3) Comprehensive analysis of Example 1 and Example 8 shows that in anaerobic thermal decomposition, the lack of nitrogen flow will cause residual value to accumulate on the surface of carbon fiber, affecting its recycling, but will not affect the strength and modulus of the fiber;

[0106] (4) Analysis of Example 1 and Example 9 shows that when the air thermal decomposition time is too long, the carbon fiber is oxidized, thereby affecting the performance retention rate of the carbon fiber.

[0107] In summary, the carbon fiber recovery rate obtained by the recycling method provided by the present invention is high, and the performance retention rate is high, which can reach more than 90%. The fiber surface is smooth, which is conducive to the reuse of the recycled carbon fiber and is suitable for industrial production. In addition, no chemical reagents are used in the recycling process, which is green and environmentally friendly, thereby realizing the sustainable development of composite materials.

[0108] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for recycling waste carbon fiber composite materials, characterized in that: The recovery method comprises the following steps: The waste carbon fiber composite material is subjected to anaerobic thermal decomposition, cooling and air thermal decomposition in sequence to recycle the carbon fiber.

2. The recycling method according to claim 1, characterized in that: The matrix resin of the waste carbon fiber composite material includes a thermosetting resin; Preferably, the thermosetting resin includes any one of epoxy resin, unsaturated polyester, phenolic resin or vinyl resin.

3. The recovery method according to claim 1 or 2, characterized in that: The carbon fiber in the waste carbon fiber composite material includes any one of polyacrylonitrile-based carbon fiber, asphalt-based carbon fiber or viscose-based carbon fiber, or a combination of at least two thereof; Preferably, the carbon fiber is in the form of any one of continuous fiber, long fiber or carbon fiber fabric, or a combination of at least two of them.

4. The recycling method according to any one of claims 1 to 3, characterized in that: The sources of the waste carbon fiber composite materials include scraps generated during the prepreg laying process and / or waste carbon fiber composite material plates and parts.

5. The recycling method according to any one of claims 1 to 4, characterized in that: The oxygen-free thermal decomposition includes any one of nitrogen thermal decomposition, helium thermal decomposition or argon thermal decomposition; Preferably, the temperature of the anaerobic thermal decomposition is 600-900°C; Preferably, the flow rate of the gas in the anaerobic thermal decomposition is 20 to 150 mL / min; Preferably, the time of the anaerobic thermal decomposition is 1 to 3 hours.

6. The recycling method according to any one of claims 1 to 5, characterized in that: The gas generated by the anaerobic thermal decomposition is connected to an external water tank.

7. The recycling method according to any one of claims 1 to 6, characterized in that: The temperature of the air thermal decomposition is 450-650°C; Preferably, the time for the air thermal decomposition is 0.5 to 1 h.

8. The recycling method according to any one of claims 1 to 7, characterized in that: The recycling method also includes pre-processing the waste carbon fiber composite material.

9. The recycling method according to claim 8, characterized in that: The pretreatment includes: screening, cleaning and crushing the waste carbon fiber composite materials in sequence.

10. The recycling method according to any one of claims 1 to 9, characterized in that: The recovery method comprises the following steps: (1) Screening, cleaning and crushing the waste carbon fiber composite materials in sequence; (2) performing anaerobic thermal decomposition of the treated waste carbon fiber composite material in an oxygen-free atmosphere at 600 to 900° C. for 1 to 3 hours, and obtaining a decomposition product after cooling; Wherein, the flow rate of the gas in the anaerobic thermal decomposition is 20 to 150 mL / min; (3) The decomposition product obtained in step (2) is subjected to air thermal decomposition in an air atmosphere at 450-650° C. for 0.5-1 h to recover the carbon fiber.

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