Composite carbon fiber and preparation method thereof

Abstract

The present invention discloses a composite carbon fiber and a preparation method thereof, the method comprising: (1) providing a nozzle, the nozzle comprising an inner channel and an outer channel, the outer channel being arranged around the periphery of the inner channel, passing a polyacrylonitrile solution into the outer channel, passing a mixed solution comprising polyacrylonitrile and mesophase pitch into the inner channel for spinning, and obtaining a primary fiber having a core layer comprising polyacrylonitrile and mesophase pitch, and a skin layer comprising polyacrylonitrile; (2) subjecting the primary fiber to boiling water drawing, water washing, oiling, drying densification, and steam drawing in sequence, and obtaining a precursor fiber having a skin-core structure; (3) subjecting the precursor fiber to pre-oxidation, carbonization, and graphitization in sequence, and obtaining a composite carbon fiber. The method can be used to prepare a composite carbon fiber having a small radial graphitization difference, and the composite carbon fiber has excellent tensile strength and tensile modulus at a relatively low graphitization temperature.

Description

Technical Field

[0001] The invention belongs to the field of carbon fibers, and in particular relates to a composite carbon fiber and a preparation method thereof. Background Art

[0002] Polyacrylonitrile-based carbon fiber and its composite materials are new materials that are being vigorously developed in the fields of national defense and national economy. With the continuous development of aerospace vehicles, the requirements for carbon fiber performance are constantly increasing. Due to the extremely harsh environment of outer space, the temperature difference can reach hundreds of degrees, and the shape of the aircraft is deformed, and it is likely that the important tasks it performs will not be completed. Therefore, the deformation of the carbon fiber after being stressed is required to be as small as possible, that is, the higher the degree of graphitization of the carbon fiber, the better.

[0003] An effective measure to improve the graphitization degree of carbon fiber is to treat it with high-temperature carbonization and graphitization. Existing studies have confirmed that there are differences in the structure and performance of the cross-section of carbon fiber after high-temperature treatment, such as differences in the size of microcrystals and the degree of graphitization. This is mainly due to the influence of the radial reaction and structural transformation of the PAN carbon fiber cross-section. The degree of radial graphitization transformation of carbon fiber is different, the degree of graphitization of the fiber cortex is high, and the degree of graphitization of the fiber core is low. Therefore, there are skin-core differences in the radial performance of carbon fiber. The mechanical properties of carbon fiber are related to the cross-sectional area of ​​the fiber. Due to the difference in radial structure, the overall mechanical properties are reduced. To improve the mechanical properties of carbon fiber, it is necessary to improve the homogeneity of the radial structure of carbon fiber. Using a relatively low graphitization temperature and a longer treatment time can reduce the difference in the degree of graphitization of the carbon fiber skin and core, but it cannot completely eliminate the inhomogeneous carbon fiber skin-core structure. Summary of the invention

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, one object of the present invention is to provide a composite carbon fiber and a preparation method thereof, by which a composite carbon fiber with a small radial graphitization difference can be prepared, and the composite carbon fiber has excellent tensile strength and tensile modulus at a relatively low graphitization temperature.

[0005] One aspect of the present invention provides a method for preparing composite carbon fiber. According to an embodiment of the present invention, the method comprises:

[0006] (1) providing a nozzle, the nozzle comprising an inner channel and an outer channel, the outer channel being arranged around the periphery of the inner channel, passing a polyacrylonitrile solution into the outer channel, passing a mixed solution comprising polyacrylonitrile and mesophase pitch into the inner channel for spinning, and obtaining a primary fiber having a core layer comprising polyacrylonitrile and mesophase pitch and a skin layer comprising polyacrylonitrile;

[0007] (2) sequentially subjecting the spun fibers to boiling water drawing, water washing, oiling, drying and densification, and steam drawing to obtain precursor fibers having a skin-core structure;

[0008] (3) Pre-oxidizing, carbonizing and graphitizing the precursor fibers in sequence to obtain composite carbon fibers.

[0009] Preferably, the mass concentration of the polyacrylonitrile solution is 10% to 20%.

[0010] Preferably, in the mixed liquid including polyacrylonitrile and mesophase asphalt, the mass ratio of polyacrylonitrile to mesophase asphalt is 1:(2-4).

[0011] Preferably, in the mixed liquid including polyacrylonitrile and mesophase asphalt, the total mass concentration of the polyacrylonitrile and mesophase asphalt is 12% to 24%.

[0012] Preferably, the inner diameter of the inner channel is 0.16-0.19 mm, the outer diameter of the inner channel is 0.30-0.35 mm, the inner diameter of the outer channel is 0.50-0.60 mm, and the outer diameter of the outer channel is 0.70-0.80 mm.

[0013] Preferably, the linear velocity of the polyacrylonitrile solution passing into the outer channel is 60 m / h to 80 m / h.

[0014] Preferably, the linear velocity of the mixed liquid including polyacrylonitrile and mesophase asphalt entering the inner channel is 100 m / h to 120 m / h.

[0015] Preferably, the pre-oxidation treatment is performed at a temperature of 200° C. to 280° C., and the treatment time is 80 minutes to 100 minutes.

[0016] Preferably, the carbonization treatment includes low-temperature carbonization and high-temperature carbonization treatment, the low-temperature carbonization temperature is 350°C to 700°C, the treatment time is 2 minutes to 3 minutes, and the high-temperature carbonization temperature is 1100°C to 1600°C, the treatment time is 1 minute to 2 minutes.

[0017] Preferably, the temperature of the graphitization treatment is 1800° C. to 2400° C., and the treatment time is 40 seconds to 80 seconds.

[0018] The second aspect of the present invention provides a composite carbon fiber, which is prepared by the above method.

[0019] Compared with the prior art, the method for preparing composite carbon fiber of the present application adopts a nozzle with double channels, that is, the outer channel is introduced into the polyacrylonitrile solution, and the inner channel is introduced into the mixed solution including polyacrylonitrile and mesophase asphalt, and then spinning is carried out after the nozzle to obtain the primary fiber with the mixed solution of polyacrylonitrile and mesophase asphalt as the core layer and polyacrylonitrile as the skin layer, and then boiling water drawing, water washing, oiling, drying densification and steam drawing are carried out in sequence to obtain the precursor fiber with skin-core structure, and finally pre-oxidation, carbonization and graphitization are carried out. Since the mesophase asphalt of the core layer is easy to form a graphitized structure, it has a higher tensile modulus, and the polyacrylonitrile located in the skin layer is easy to fiberize and the chaotic layer graphite structure formed by heat treatment has a higher tensile strength. Therefore, after carbonization and graphitization, the precursor fiber with skin-core structure can improve the graphitization degree of the core layer and reduce the radial graphitization difference of the composite carbon fiber, that is, a composite carbon fiber with radial graphitization homogeneity is obtained. Due to the homogeneous radial structure of the fiber, a carbon fiber with a higher tensile modulus can be obtained at a lower graphitization temperature. Due to the low graphitization temperature, the tensile strength of the carbon fiber is higher. At the same time, since polyacrylonitrile carbon fiber is composed of a turbostratic graphite structure with a relatively low degree of graphitization, and this type of carbon fiber has a relatively high tensile strength, and the intermediate phase asphalt carbon fiber has a relatively regular graphite-like structure, it has a higher tensile modulus and electrical and thermal conductivity properties. Therefore, the method of the present application can be used to obtain a composite carbon fiber with excellent tensile strength and tensile modulus at a lower graphitization temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the structure of the nozzle;

[0021] Figure 2 is the Raman spectra of the composite carbon fiber obtained in Example 1 at different radial positions;

[0022] Figure 3 The Raman spectra of the carbon fibers obtained in the comparative example at different radial positions are shown;

[0023] Figure 4 : is a comparison diagram of radial R value distribution of the composite carbon fiber obtained in Example 1 and the carbon fiber of the comparative example;

[0024] Figure 5 is a comparison diagram of radial R value distribution of the composite carbon fiber obtained in Example 2 and the comparative carbon fiber;

[0025] Figure 6 is a comparison diagram of radial R value distribution of the composite carbon fiber obtained in Example 3 and the carbon fiber of the comparative example;

[0026] Figure 7 is a comparison diagram of radial R value distribution of the composite carbon fiber obtained in Example 4 and the carbon fiber of the comparative example;

[0027] Figure 8It is a comparison diagram of the radial R value distribution of the composite carbon fiber obtained in Example 5 and the comparative carbon fiber. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0029] In one aspect of the present invention, the present invention provides a method for preparing composite carbon fiber. According to an embodiment of the present invention, the method comprises:

[0030] S1: providing a nozzle, the nozzle comprising an inner channel and an outer channel, the outer channel being arranged around the periphery of the inner channel, passing a polyacrylonitrile solution into the outer channel, and passing a mixed solution comprising polyacrylonitrile and mesophase asphalt into the inner channel for spinning

[0031] In this step, polyacrylonitrile powder and solvent dimethylformamide are mixed in a mass ratio of 10-20:80-90, stirred evenly, swelled at room temperature for 20-24 hours, and then heated and stirred at 50-60°C for 2-4 hours to obtain a polyacrylonitrile solution with a mass concentration of 10%-20% as an outer channel solution. The inventors found that if the concentration of the polyacrylonitrile solution is lower than 10%, it is easy to form a porous and loose fiber structure, and if the concentration of the polyacrylonitrile solution is higher than 20%, the solution viscosity is too large and the material is difficult to transport, and the macromolecules are easy to entangle and difficult to stretch to orient the fibers. Therefore, the present application uses a polyacrylonitrile solution with a mass concentration of 10%-20% as the outer channel solution, which can improve the tensile strength of the final composite carbon fiber.

[0032] At the same time, polyacrylonitrile powder and mesophase asphalt powder are mixed in a mass ratio of 1:2 to 4. The inventors found that if the content of polyacrylonitrile is too high, gel will easily appear in the mixed solution, affecting stable spinning, while the content of mesophase asphalt is too high, affecting the fiberization of the mixed solution. Therefore, the present application mixes polyacrylonitrile powder and mesophase asphalt powder in a mass ratio of 1:2 to 4, which is not only easy to fiberize the mixed solution, but also can be spun stably. Further, a mixed solvent of dimethylformamide and tetrahydrofuran with a volume ratio of 1:1 to 2 is added to the mixture including polyacrylonitrile powder and mesophase asphalt powder, and the total mass of polyacrylonitrile powder and mesophase asphalt powder accounts for 12 to 24% of the mass ratio of the mixed solution, stir evenly, swell at room temperature for 20 to 24 hours, and then heat and stir at 50 to 60°C for 2 to 4 hours to obtain a mixed solution including polyacrylonitrile and mesophase asphalt; finally, the polyacrylonitrile solution and the mixed solution including polyacrylonitrile and mesophase asphalt are degassed at a vacuum absolute pressure of 10 to 30 KPa.

[0033] Specifically, a nozzle 100 is provided, referring to Figure 1The nozzle 100 includes an inner channel 10 and an outer channel 20. The outer channel 20 is arranged around the periphery of the inner channel 10. The inner diameter R1 of the inner channel 10 at the nozzle of the nozzle 100 is 0.16-0.19 mm, the outer diameter R2 of the inner channel 10 is 0.30-0.35 mm, the inner diameter R3 of the outer channel 20 is 0.50-0.60 mm, and the outer diameter R4 of the outer channel 20 is 0.70-0.80 mm.

[0034] The degassed polyacrylonitrile solution is passed into the outer channel 20, and the mixed solution including polyacrylonitrile and intermediate phase asphalt is passed into the inner channel 10 for coaxial spinning. The linear velocity of the polyacrylonitrile solution passing into the outer channel 20 is 60m / h~80m / h, and the linear velocity of the mixed solution including polyacrylonitrile and intermediate phase asphalt passing into the inner channel 10 is 100m / h~120m / h. The linear velocity of the inner channel is greater than that of the outer channel, which is beneficial for the diffusion of the core layer polyacrylonitrile and intermediate phase asphalt mixed solution to the cortex layer, and a transition layer is formed in the interface area between the cortex layer and the core layer. The transition layer can tightly connect the core layer and the cortex layer. Otherwise, it is easy to form interface defects between the cortex layer and the core layer, and they cannot withstand external forces together. For example, by using dry-wet spinning technology, a polyacrylonitrile solution and a mixed solution including polyacrylonitrile and mesophase asphalt are simultaneously metered into a coaxial nozzle and extruded into a coagulation bath including dimethylformamide and water. The mass concentration of the coagulation bath is 50% to 80%, the temperature of the coagulation bath is controlled at 20 to 40°C, the coagulation draft multiple is 3 to 5 times, and coaxial dry-wet spinning is performed to obtain primary fibers whose core layer includes polyacrylonitrile and mesophase asphalt and whose skin layer includes polyacrylonitrile.

[0035] S2: The raw fiber is sequentially subjected to boiling water drawing, water washing, oiling, drying and densification, and steam drawing.

[0036] In this step, the spun fibers obtained above are stretched 4 to 7 times in boiling water at 95 to 100°C, then washed with gradient water at 60 to 80°C, oiled in an oil tank containing modified silicone oil, and then dried and densified at a gradient temperature of 105 to 125°C. Finally, they are stretched 2.5 to 4 times with high-temperature steam at a temperature of 160 to 170°C to obtain precursor fibers with a skin-core structure.

[0037] S3: Pre-oxidation, carbonization and graphitization of the precursor fiber

[0038] In this step, the precursor fiber obtained above is subjected to a pre-oxidation treatment in an air atmosphere, the pre-oxidation treatment temperature is 200°C to 280°C, and the treatment time is 80 minutes to 100 minutes, so as to obtain a pre-oxidized fiber; then, the pre-oxidized fiber is subjected to a low-temperature carbonization and a high-temperature carbonization treatment in a nitrogen atmosphere, the low-temperature carbonization temperature is 350°C to 700°C, the treatment time is 2 minutes to 3 minutes, and the high-temperature carbonization temperature is 1100°C to 1600°C, and the treatment time is 1 minute to 2 minutes, so as to obtain a carbon fiber; finally, the carbon fiber is subjected to a graphitization treatment in an argon atmosphere, the graphitization treatment temperature is 1800°C to 2400°C, and the treatment time is 40 seconds to 80 seconds, so as to obtain a composite carbon fiber.

[0039] Therefore, the method of the present application can be used to obtain radially graphitized homogeneous composite carbon fibers, and the composite carbon fibers have excellent tensile strength and tensile modulus.

[0040] The second aspect of the present invention provides a composite carbon fiber, which is prepared by the above method. It should be noted that the features and advantages described above for the method for preparing the composite carbon fiber are also applicable to the composite carbon fiber, and will not be repeated here.

[0041] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0042] Example 1

[0043] The method for preparing composite carbon fiber comprises:

[0044] (1) Mix the polyacrylonitrile powder and solvent dimethylformamide and stir them evenly, swell them at room temperature for 24 hours, and then heat and stir them at 60°C for 4 hours to obtain a polyacrylonitrile solution with a mass concentration of 20%. At the same time, mix the polyacrylonitrile powder and the intermediate phase asphalt powder in a mass ratio of 1:2, add a mixed solvent of dimethylformamide and tetrahydrofuran in a volume ratio of 1:1, and the total mass of the polyacrylonitrile powder and the intermediate phase asphalt powder accounts for 12% of the mass ratio of the mixed solution. Stir them evenly, swell them at room temperature for 24 hours, and then heat and stir them at 60°C for 4 hours to obtain a mixed solution including polyacrylonitrile and intermediate phase asphalt; finally, degas the polyacrylonitrile solution and the mixed solution including polyacrylonitrile and intermediate phase asphalt under a vacuum absolute pressure of 30KPa. Then, provide a reference Figure 1The inner channel 10 has an inner diameter of 0.16 mm and an outer diameter of 0.3 mm, the inner diameter of the outer channel 20 has an inner diameter of 0.55 mm, and the outer diameter of the nozzle 100 is 0.80 mm. The degassed polyacrylonitrile solution is passed into the outer channel 20, and the mixed solution including polyacrylonitrile and mesophase asphalt is passed into the inner channel 10 for coaxial spinning. The linear velocity of the polyacrylonitrile solution passing into the outer channel 20 is 60 m / h, and the linear velocity of the mixed solution including polyacrylonitrile and mesophase asphalt passing into the inner channel 10 is 100 m / h. At the same time, the polyacrylonitrile solution and the mixed solution including polyacrylonitrile and mesophase asphalt are metered into the coaxial nozzle and extruded into a coagulation bath including dimethylformamide and water, the mass concentration of the coagulation bath is 50%, the coagulation bath temperature is controlled at 40°C, the coagulation draft multiple is 3 times, and coaxial dry-wet spinning is performed to obtain primary fibers with a core layer including polyacrylonitrile and mesophase asphalt and a skin layer including polyacrylonitrile;

[0045] (2) The spun fibers obtained above were drawn 5 times in boiling water at 100° C., then washed with gradient water at 60-80° C., oiled in an oil tank containing modified silicone oil, dried at a gradient temperature of 105-125° C. for densification, and finally drawn 3 times with high-temperature steam at a temperature of 160° C. to obtain a precursor fiber with a skin-core structure;

[0046] (3) In an air atmosphere, the precursor fiber obtained above is subjected to a pre-oxidation treatment at a temperature of 250°C for 100 minutes to obtain a pre-oxidized fiber; then, in a nitrogen atmosphere, the pre-oxidized fiber is subjected to a low-temperature carbonization and a high-temperature carbonization treatment at a temperature of 350 to 680°C for 3 minutes, and a high-temperature carbonization temperature of 1500°C for 2 minutes to obtain a carbon fiber; finally, in an argon atmosphere, the carbon fiber is subjected to a graphitization treatment at a temperature of 2000°C for 40 seconds to obtain a composite carbon fiber.

[0047] The radial graphitization degree of the composite carbon fiber obtained in Example 1 was characterized. The Raman spectra at different radial positions of the composite carbon fiber are shown in FIG. Figure 2 (0 position corresponds to the center position of the composite carbon fiber, 1, 2, 3 positions correspond to three positions in the radial direction of the composite carbon fiber away from the center of the circle in one direction, 3 is a position close to the cortex of the composite carbon fiber, and 1, 2, 3 positions are evenly arranged in the radial direction of the composite carbon fiber; -1, -2, -3 positions correspond to positions in the radial direction of the composite carbon fiber in another direction (located on the same radial direction as 1, 2, 3 positions of the composite carbon fiber) and symmetrical to 1, 2, 3 positions), according to the formula R = I D / I G Calculate the R value that characterizes the degree of graphitization of carbon fiber. The larger the R value, the smaller the degree of graphitization of carbon fiber. D 1360cm in the Raman spectrum－1 The integrated intensity at I indicates a disordered carbon structure; G 1580cm in the Raman spectrum －1 The integrated intensity at represents the graphitized carbon structure. The radial R value distribution curve of the composite carbon fiber is as follows: Figure 4 It can be seen that the radial graphitization degree of the composite carbon fibers is basically the same, indicating that this method can be used to obtain radially graphitized homogeneous composite carbon fibers.

[0048] Example 2

[0049] The method for preparing composite carbon fiber comprises:

[0050] (1) Mix the polyacrylonitrile powder and solvent dimethylformamide and stir them evenly, swell them at room temperature for 24 hours, and then heat and stir them at 60°C for 4 hours to obtain a polyacrylonitrile solution with a mass concentration of 10%. At the same time, mix the polyacrylonitrile powder and the intermediate phase asphalt powder in a mass ratio of 1:4, add a mixed solvent of dimethylformamide and tetrahydrofuran in a volume ratio of 1:1, and the total mass of the polyacrylonitrile powder and the intermediate phase asphalt powder accounts for 24% of the mass ratio of the mixed solution. Stir them evenly, swell them at room temperature for 24 hours, and then heat and stir them at 60°C for 4 hours to obtain a mixed solution including polyacrylonitrile and intermediate phase asphalt; finally, degas the polyacrylonitrile solution and the mixed solution including polyacrylonitrile and intermediate phase asphalt under a vacuum absolute pressure of 30KPa. Then, provide a reference Figure 1 The inner channel 10 has an inner diameter of 0.16 mm and an outer diameter of 0.3 mm, the inner diameter of the outer channel 20 has an inner diameter of 0.55 mm, and the outer diameter of the nozzle 100 is 0.80 mm. The degassed polyacrylonitrile solution is passed into the outer channel 20, and the mixed solution including polyacrylonitrile and mesophase asphalt is passed into the inner channel 10 for coaxial spinning. The linear velocity of the polyacrylonitrile solution passing into the outer channel 20 is 60 m / h, and the linear velocity of the mixed solution including polyacrylonitrile and mesophase asphalt passing into the inner channel 10 is 100 m / h. At the same time, the polyacrylonitrile solution and the mixed solution including polyacrylonitrile and mesophase asphalt are metered into the coaxial nozzle and extruded into a coagulation bath including dimethylformamide and water, the mass concentration of the coagulation bath is 50%, the coagulation bath temperature is controlled at 40°C, the coagulation draft multiple is 3 times, and coaxial dry-wet spinning is performed to obtain primary fibers with a core layer including polyacrylonitrile and mesophase asphalt and a skin layer including polyacrylonitrile;

[0051] (2) The spun fibers obtained above were drawn 5 times in boiling water at 100° C., then washed with gradient water at 60-80° C., oiled in an oil tank containing modified silicone oil, dried at a gradient temperature of 105-125° C. for densification, and finally drawn 3 times with high-temperature steam at a temperature of 160° C. to obtain a precursor fiber with a skin-core structure;

[0052] (3) In an air atmosphere, the precursor fiber obtained above is subjected to a pre-oxidation treatment at a temperature of 250°C for 100 minutes to obtain a pre-oxidized fiber; then, in a nitrogen atmosphere, the pre-oxidized fiber is subjected to a low-temperature carbonization and a high-temperature carbonization treatment at a temperature of 350 to 680°C for 3 minutes, and a high-temperature carbonization temperature of 1500°C for 2 minutes to obtain a carbon fiber; finally, in an argon atmosphere, the carbon fiber is subjected to a graphitization treatment at a temperature of 2000°C for 40 seconds to obtain a composite carbon fiber.

[0053] The radial graphitization degree of the composite carbon fiber obtained in Example 2 was characterized by referring to the method of Example 1. The radial R value distribution curve of the composite carbon fiber obtained is as follows: Figure 5 It can be seen that the radial graphitization degree of the composite carbon fibers is basically the same, indicating that this method can be used to obtain radially graphitized homogeneous composite carbon fibers.

[0054] Example 3

[0055] The method for preparing composite carbon fiber comprises:

[0056] (1) Mix the polyacrylonitrile powder and solvent dimethylformamide and stir them evenly, swell them at room temperature for 24 hours, and then heat and stir them at 60°C for 4 hours to obtain a polyacrylonitrile solution with a mass concentration of 15%. At the same time, mix the polyacrylonitrile powder and the intermediate phase asphalt powder in a mass ratio of 1:3, add a mixed solvent of dimethylformamide and tetrahydrofuran in a volume ratio of 1:1, and the total mass of the polyacrylonitrile powder and the intermediate phase asphalt powder accounts for 18% of the mass ratio of the mixed solution. Stir them evenly, swell them at room temperature for 24 hours, and then heat and stir them at 60°C for 4 hours to obtain a mixed solution including polyacrylonitrile and intermediate phase asphalt; finally, degas the polyacrylonitrile solution and the mixed solution including polyacrylonitrile and intermediate phase asphalt under a vacuum absolute pressure of 30KPa. Then, provide a reference Figure 1The inner channel 10 has an inner diameter of 0.16 mm and an outer diameter of 0.3 mm, the inner diameter of the outer channel 20 has an inner diameter of 0.55 mm, and the outer diameter of the nozzle 100 is 0.80 mm. The degassed polyacrylonitrile solution is passed into the outer channel 20, and the mixed solution including polyacrylonitrile and mesophase asphalt is passed into the inner channel 10 for coaxial spinning. The linear velocity of the polyacrylonitrile solution passing into the outer channel 20 is 60 m / h, and the linear velocity of the mixed solution including polyacrylonitrile and mesophase asphalt passing into the inner channel 10 is 100 m / h. At the same time, the polyacrylonitrile solution and the mixed solution including polyacrylonitrile and mesophase asphalt are metered into the coaxial nozzle and extruded into a coagulation bath including dimethylformamide and water, the mass concentration of the coagulation bath is 50%, the coagulation bath temperature is controlled at 40°C, the coagulation draft multiple is 3 times, and coaxial dry-wet spinning is performed to obtain primary fibers with a core layer including polyacrylonitrile and mesophase asphalt and a skin layer including polyacrylonitrile;

[0057] (2) The spun fibers obtained above were drawn 5 times in boiling water at 100° C., then washed with gradient water at 65-80° C., oiled in an oil tank containing modified silicone oil, dried at a gradient temperature of 105-125° C. for densification, and finally drawn 3 times with high-temperature steam at a temperature of 160° C. to obtain a precursor fiber with a skin-core structure;

[0058] (3) In an air atmosphere, the precursor fiber obtained above is subjected to a pre-oxidation treatment at a temperature of 250°C for 100 minutes to obtain a pre-oxidized fiber; then, in a nitrogen atmosphere, the pre-oxidized fiber is subjected to a low-temperature carbonization and a high-temperature carbonization treatment at a temperature of 350 to 680°C for 3 minutes, and a high-temperature carbonization temperature of 1500°C for 2 minutes to obtain a carbon fiber; finally, in an argon atmosphere, the carbon fiber is subjected to a graphitization treatment at a temperature of 2000°C for 40 seconds to obtain a composite carbon fiber.

[0059] The radial graphitization degree of the composite carbon fiber obtained in Example 3 was characterized by referring to the method of Example 1. The radial R value distribution curve of the composite carbon fiber obtained is as follows: Figure 6 It can be seen that the radial graphitization degree of the composite carbon fibers is basically the same, indicating that this method can be used to obtain radially graphitized homogeneous composite carbon fibers.

[0060] Example 4

[0061] The method for preparing composite carbon fiber comprises:

[0062] (1) Mix the polyacrylonitrile powder and solvent dimethylformamide and stir them evenly, swell them at room temperature for 24 hours, and then heat and stir them at 60°C for 4 hours to obtain a polyacrylonitrile solution with a mass concentration of 15%. At the same time, mix the polyacrylonitrile powder and the intermediate phase asphalt powder in a mass ratio of 1:3, add a mixed solvent of dimethylformamide and tetrahydrofuran in a volume ratio of 1:1, and the total mass of the polyacrylonitrile powder and the intermediate phase asphalt powder accounts for 18% of the mass ratio of the mixed solution. Stir them evenly, swell them at room temperature for 24 hours, and then heat and stir them at 60°C for 4 hours to obtain a mixed solution including polyacrylonitrile and intermediate phase asphalt; finally, degas the polyacrylonitrile solution and the mixed solution including polyacrylonitrile and intermediate phase asphalt under a vacuum absolute pressure of 30KPa. Then, provide a reference Figure 1 The inner channel 10 has an inner diameter of 0.16 mm and an outer diameter of 0.3 mm, the inner diameter of the outer channel 20 has an inner diameter of 0.55 mm, and the outer diameter of the nozzle 100 is 0.80 mm. The degassed polyacrylonitrile solution is passed into the outer channel 20, and the mixed solution including polyacrylonitrile and mesophase asphalt is passed into the inner channel 10 for coaxial spinning. The linear velocity of the polyacrylonitrile solution passing into the outer channel 20 is 80 m / h, and the linear velocity of the mixed solution including polyacrylonitrile and mesophase asphalt passing into the inner channel 10 is 120 m / h. At the same time, the polyacrylonitrile solution and the mixed solution including polyacrylonitrile and mesophase asphalt are metered into the coaxial nozzle and extruded into a coagulation bath including dimethylformamide and water. The mass concentration of the coagulation bath is 50%, the temperature of the coagulation bath is controlled at 40° C., and the coagulation draft multiple is 3 times. Coaxial dry-wet spinning is performed to obtain primary fibers with a core layer including polyacrylonitrile and mesophase asphalt and a skin layer including polyacrylonitrile.

[0063] (2) The spun fibers obtained above were drawn 5 times in boiling water at 100° C., then washed with gradient water at 65-80° C., oiled in an oil tank containing modified silicone oil, dried at a gradient temperature of 105-125° C. for densification, and finally drawn 3 times with high-temperature steam at a temperature of 160° C. to obtain a precursor fiber with a skin-core structure;

[0064] (3) In an air atmosphere, the precursor fiber obtained above is subjected to a pre-oxidation treatment at a temperature of 250°C for 100 minutes to obtain a pre-oxidized fiber; then, in a nitrogen atmosphere, the pre-oxidized fiber is subjected to a low-temperature carbonization and a high-temperature carbonization treatment at a temperature of 350 to 680°C for 3 minutes, and a high-temperature carbonization temperature of 1500°C for 2 minutes to obtain a carbon fiber; finally, in an argon atmosphere, the carbon fiber is subjected to a graphitization treatment at a temperature of 2000°C for 40 seconds to obtain a composite carbon fiber.

[0065] The radial graphitization degree of the composite carbon fiber obtained in Example 4 was characterized by referring to the method of Example 1. The radial R value distribution curve of the composite carbon fiber obtained is as follows: Figure 7 It can be seen that the radial graphitization degree of the composite carbon fibers is basically the same, indicating that this method can be used to obtain radially graphitized homogeneous composite carbon fibers.

[0066] Example 5

[0067] The method for preparing composite carbon fiber comprises:

[0068] (1) Mix the polyacrylonitrile powder and solvent dimethylformamide and stir them evenly, swell them at room temperature for 24 hours, and then heat and stir them at 60°C for 4 hours to obtain a polyacrylonitrile solution with a mass concentration of 15%. At the same time, mix the polyacrylonitrile powder and the intermediate phase asphalt powder in a mass ratio of 1:3, add a mixed solvent of dimethylformamide and tetrahydrofuran in a volume ratio of 1:1, and the total mass of the polyacrylonitrile powder and the intermediate phase asphalt powder accounts for 18% of the mass ratio of the mixed solution. Stir them evenly, swell them at room temperature for 24 hours, and then heat and stir them at 60°C for 4 hours to obtain a mixed solution including polyacrylonitrile and intermediate phase asphalt; finally, degas the polyacrylonitrile solution and the mixed solution including polyacrylonitrile and intermediate phase asphalt under a vacuum absolute pressure of 30KPa. Then, provide a reference Figure 1 The inner channel 10 has an inner diameter of 0.16 mm and an outer diameter of 0.3 mm, the inner diameter of the outer channel 20 has an inner diameter of 0.55 mm, and the outer diameter of the nozzle 100 is 0.80 mm. The degassed polyacrylonitrile solution is passed into the outer channel 20, and the mixed solution including polyacrylonitrile and mesophase asphalt is passed into the inner channel 10 for coaxial spinning. The linear velocity of the polyacrylonitrile solution passing into the outer channel 20 is 70 m / h, and the linear velocity of the mixed solution including polyacrylonitrile and mesophase asphalt passing into the inner channel 10 is 110 m / h. At the same time, the polyacrylonitrile solution and the mixed solution including polyacrylonitrile and mesophase asphalt are metered into the coaxial nozzle and extruded into a coagulation bath including dimethylformamide and water. The mass concentration of the coagulation bath is 50%, the coagulation bath temperature is controlled at 40° C., and the coagulation draft multiple is 3 times. Coaxial dry-wet spinning is performed to obtain primary fibers with a core layer including polyacrylonitrile and mesophase asphalt and a skin layer including polyacrylonitrile.

[0069] (2) The spun fibers obtained above were drawn 5 times in boiling water at 100° C., then washed with gradient water at 65-80° C., oiled in an oil tank containing modified silicone oil, dried at a gradient temperature of 105-125° C. for densification, and finally drawn 3 times with high-temperature steam at a temperature of 160° C. to obtain a precursor fiber with a skin-core structure;

[0070] (3) In an air atmosphere, the precursor fiber obtained above is subjected to a pre-oxidation treatment at a temperature of 250°C for 100 minutes to obtain a pre-oxidized fiber; then, in a nitrogen atmosphere, the pre-oxidized fiber is subjected to a low-temperature carbonization and a high-temperature carbonization treatment at a temperature of 350 to 680°C for 3 minutes, and a high-temperature carbonization temperature of 1500°C for 2 minutes to obtain a carbon fiber; finally, in an argon atmosphere, the carbon fiber is subjected to a graphitization treatment at a temperature of 2000°C for 40 seconds to obtain a composite carbon fiber.

[0071] The radial graphitization degree of the composite carbon fiber obtained in Example 5 was characterized by referring to the method of Example 1. The radial R value distribution curve of the composite carbon fiber obtained is as follows: Figure 8 It can be seen that the radial graphitization degree of the composite carbon fibers is basically the same, indicating that this method can be used to obtain radially graphitized homogeneous composite carbon fibers.

[0072] Comparative Example

[0073] The method for preparing carbon fiber comprises:

[0074] (1) Mix polyacrylonitrile powder and solvent dimethylformamide and stir evenly, swell at room temperature for 24 hours, and then heat and stir at 60°C for 4 hours to obtain a polyacrylonitrile solution with a mass concentration of 20%. Degas the polyacrylonitrile solution under a vacuum absolute pressure of 30KPa. Then pass the degassing polyacrylonitrile solution into a common spinning nozzle for wet spinning, the coagulation bath is a mixed solution of dimethylformamide and water, the mass concentration of the coagulation bath is 50%, and the coagulation bath temperature is controlled at 40°C to obtain the primary fiber of polyacrylonitrile;

[0075] (2) The spun fibers obtained above were drawn 5 times in boiling water at 100° C., then washed with gradient water at 65-80° C., oiled in an oil tank containing modified silicone oil, dried at a gradient temperature of 105-125° C. for densification, and finally drawn 3 times with high-temperature steam at a temperature of 160° C. to obtain precursor fibers;

[0076] (3) In an air atmosphere, the precursor fiber obtained above is subjected to a pre-oxidation treatment at a temperature of 250°C for 100 minutes to obtain a pre-oxidized fiber; then, in a nitrogen atmosphere, the pre-oxidized fiber is subjected to a low-temperature carbonization treatment and a high-temperature carbonization treatment, wherein the low-temperature carbonization temperature is 350-680°C for 3 minutes, and the high-temperature carbonization temperature is 1500°C for 2 minutes to obtain a carbon fiber; finally, in an argon atmosphere, the carbon fiber is subjected to a graphitization treatment at a temperature of 2400°C for 40 seconds to obtain a carbon fiber.

[0077] The radial graphitization degree of the carbon fiber obtained in the comparative example was characterized by the method of Example 1. The Raman spectra of the carbon fiber at different radial positions are as follows: Figure 3 According to the formula R = I D / I G Calculate the R value that characterizes the degree of graphitization of carbon fiber. The larger the R value, the smaller the degree of graphitization of carbon fiber. D 1360cm in the Raman spectrum －1 The integrated intensity at I indicates a disordered carbon structure; G 1580cm in the Raman spectrum －1 The integrated intensity at represents the graphitized carbon structure. The carbon fiber radial R value distribution curve is as follows Figure 4-8 It can be seen that there is an obvious difference in the degree of graphitization of the carbon fiber in the radial direction, and the degree of graphitization in the core is lower, indicating that the radial graphitization uniformity of the obtained carbon fiber is poor.

[0078] The tensile strength and tensile modulus of the composite carbon fibers obtained in Examples 1-5 and the carbon fibers obtained in the comparative example were characterized. The characterization results are shown in Table 1.

[0079] Table 1 Tensile strength and tensile modulus of the composite carbon fibers of Examples 1-5 and the carbon fibers of the comparative example

[0080] Tensile strength / GPa Tensile modulus / GPa Example 1 5.80 389 Example 2 5.42 378 Example 3 5.68 383 Example 4 5.61 375 Example 5 5.70 385 Comparative Example 5.02 364

[0081] Conclusion, by Figure 4-8 It can be seen that the radial graphitization degree of the composite carbon fibers obtained in Examples 1-5 is basically the same. At the same time, referring to the data in Table 1, it can be seen that the tensile strength and tensile modulus of the composite fibers obtained in Examples 1-5 are higher than the tensile strength and tensile modulus of the carbon fibers obtained in the comparative example, indicating that radially graphitized homogeneous composite carbon fibers can be obtained by the method of the present application, and the obtained composite carbon fibers have excellent tensile strength and tensile modulus.

[0082] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as not within the scope of protection of the invention.

Claims

1. A method for preparing composite carbon fiber, characterized in that: include: (1) providing a nozzle, the nozzle comprising an inner channel and an outer channel, the outer channel being arranged around the periphery of the inner channel, passing a polyacrylonitrile solution into the outer channel, passing a mixed solution comprising polyacrylonitrile and mesophase pitch into the inner channel for spinning, and obtaining a primary fiber having a core layer comprising polyacrylonitrile and mesophase pitch and a skin layer comprising polyacrylonitrile; (2) sequentially subjecting the spun fibers to boiling water drawing, water washing, oiling, drying and densification, and steam drawing to obtain precursor fibers having a skin-core structure; (3) Pre-oxidizing, carbonizing and graphitizing the precursor fibers in sequence to obtain composite carbon fibers.

2. The method according to claim 1, characterized in that The mass concentration of the polyacrylonitrile solution is 10% to 20%.

3. The method according to claim 1, characterized in that In the mixed liquid including polyacrylonitrile and mesophase asphalt, the mass ratio of polyacrylonitrile to mesophase asphalt is 1:(2-4).

4. The method according to claim 1 or 3, characterized in that: In the mixed liquid including polyacrylonitrile and mesophase asphalt, the total mass concentration of the polyacrylonitrile and mesophase asphalt is 12% to 24%.

5. The method according to claim 1, characterized in that The inner diameter of the inner channel at the nozzle orifice is 0.16-0.19 mm, the outer diameter of the inner channel is 0.30-0.35 mm, the inner diameter of the outer channel is 0.50-0.60 mm, and the outer diameter of the outer channel is 0.70-0.80 mm.

6. The method according to claim 1, characterized in that The linear velocity of the polyacrylonitrile solution passing into the outer channel is 60 m / h to 80 m / h.

7. The method according to claim 1, characterized in that The linear velocity of the mixed liquid including polyacrylonitrile and mesophase asphalt entering the inner channel is 100m / h to 120m / h.

8. The method according to claim 1, characterized in that The temperature of the pre-oxidation treatment is 200° C. to 280° C., and the treatment time is 80 minutes to 100 minutes.

9. The method according to claim 1, characterized in that: The carbonization treatment includes low-temperature carbonization and high-temperature carbonization. The low-temperature carbonization temperature is 350° C. to 700° C., and the treatment time is 2 minutes to 3 minutes. The high temperature carbonization temperature is 1100° C. to 1600° C., and the processing time is 1 minute to 2 minutes.

10. The method according to claim 1, characterized in that The temperature of the graphitization treatment is 1800° C. to 2400° C., and the treatment time is 40 seconds to 80 seconds.

11. A composite carbon fiber, characterized in that: The composite carbon fiber is prepared by the method according to any one of claims 1 to 10.

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