Low-resistivity carbon fiber and preparation method thereof

Abstract

The invention belongs to the technical field of carbon fibers, and provides a low-resistivity carbon fiber and a preparation method thereof. The method comprises the following steps: mixing acrylonitrile, itaconic acid, soluble asphalt powder and an organic solvent, then mixing with azobisisoheptonitrile, carrying out polymerization reaction on the obtained mixed solution, and filtering to obtain a spinning solution; carrying out phase separation in a coagulating bath after spinning the spinning solution, and sequentially carrying out water washing, hot water drafting, drying densification and steam drafting on formed nascent fibers to obtain composite fiber precursors; the composite fiber precursor is sequentially subjected to pre-oxidation, carbonization and graphitization treatment. Soluble asphalt is quickly and uniformly introduced into an acrylonitrile copolymer reaction system by adopting an in-situ polymerization method, and the low-resistivity carbon fibers with different asphalt contents can be prepared by regulating and controlling the proportion of the soluble asphalt in the reaction system; in the high-temperature carbonization process, the characteristic that polycyclic aromatic hydrocarbon and alkyl side chains are easy to graphitize can induce graphitization transformation of a fiber matrix, and the conductivity of corresponding carbon fibers is flexibly controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fibers, and in particular to a low-resistivity carbon fiber and a preparation method thereof. Background Art

[0002] With the continuous exploration and advancement of cutting-edge technologies such as low-altitude economy, artificial intelligence, flexible display, smart wearables and green energy, the demand for core component materials such as flexible energy storage devices, electromagnetic shielding materials, electrothermal conversion elements and battery electrodes will continue to grow. Carbon fiber has good electrical conductivity (efficient current transmission), thermal conductivity (rapid heat dispersion), low density (weight reduction and strength preservation), non-toxicity, resistance to chemical solvents and easy processing. It has gradually become a widely recognized popular material in these fields. Polyacrylonitrile-based carbon fiber (PAN-CF) has a relatively simple production process, high quality of finished products and good mechanical properties. Its output has accounted for more than 95% of the total carbon fiber output. It has also introduced a variety of types such as high-strength, high-strength medium modulus, and high-strength high modulus to meet the wide and diverse needs of practical applications. However, its turbostratic graphite structure leads to a weakened responsiveness to electronic conduction. Therefore, improving electrical conductivity has become a key issue that needs to be urgently addressed.

[0003] In order to reduce the large concentration polarization phenomenon of carbon fiber electrodes under high current density, the "Preparation and Application Research of Surface Modified Carbon Fiber Electrodes" (University of Science and Technology of China, 2024) uses a flame method to directly synthesize carbon nanotubes on the surface of carbon fiber to reduce its mass transfer resistance; the patent application number 202211573288.2 treats the PAN-CF surface with ablation oxidation, cathode copper plating, nitrogen annealing and other processes to produce a highly conductive and high-strength copper-plated carbon fiber; the invention patent application number 202111667353.3 introduces graphene slurry into the carbon fiber system to form a graphene coating, which improves the resistance stability of the material in complex environments and generates a large amount of heat at a voltage of 36V. It is not difficult to find that introducing conductive fillers or surface-modified conductive coatings is an effective way to reduce the resistivity of carbon fiber to meet the use standards in the corresponding field.

[0004] High-performance pitch-based carbon fibers contain a highly graphitized microcrystalline structure oriented along the fiber axis. The orderly stacking of microcrystals forms a good conductive path, promoting efficient electron transfer within the fiber. Compared with PAN-CF, pitch-based carbon fibers are prepared by melt spinning, so it is worth exploring how to balance the advantages of both types of carbon fibers. The invention patent with application number 202310380667.8 uses a dual-channel nozzle to prepare composite carbon fiber precursors with a core layer containing mesophase pitch. After carbonization and graphitization, the difference in the degree of graphitization between the skin and core of polyacrylonitrile-based carbon fibers is reduced. However, directly introducing the corresponding components into the spinning solution makes it difficult to achieve their uniform distribution and leads to spinning instability.

[0005] Therefore, it is urgent to develop a functional carbon fiber that can flexibly regulate the "conductive-mechanical" properties to meet the specific requirements of different application scenarios. Summary of the Invention

[0006] The purpose of the present invention is to provide a low-resistivity carbon fiber and a preparation method thereof in order to overcome the deficiencies of the prior art, so as to solve the problems in the prior art that the performance of carbon fiber is difficult to directly match the diverse resistance and heat transfer performance requirements and the high cost.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing low-resistivity carbon fiber, comprising the following steps:

[0009] 1) performing a first mixing of acrylonitrile, itaconic acid, soluble asphalt powder, and an organic solvent, and performing a second mixing of the first mixture and azobisisoheptanenitrile to obtain a mixed solution; performing a polymerization reaction on the mixed solution and then filtering the mixture to obtain a homogeneous asphalt / polyacrylonitrile spinning solution;

[0010] 2) After spinning, the spinning solution phase separates in the coagulation bath to form nascent fibers;

[0011] 3) The raw fibers are sequentially washed, hot water drawn, dried and densified, and steam drawn to obtain asphalt / polyacrylonitrile composite fiber precursors;

[0012] 4) The composite fiber precursor is sequentially subjected to pre-oxidation, carbonization, and graphitization treatments to obtain low-resistivity carbon fibers.

[0013] Preferably, in step 1), the mass ratio of acrylonitrile to itaconic acid is 95-97:3-5, the mass ratio of soluble asphalt powder to acrylonitrile is 0.1-0.9:1, and the mass of azobisisoheptanenitrile is 0.65-0.75% of the total mass of acrylonitrile and itaconic acid;

[0014] The organic solvent is dimethyl sulfoxide or N,N-dimethylformamide; the solid content of the spinning solution is 12-30%, and the intrinsic viscosity is 1.2-2.2 dL / g.

[0015] Preferably, in step 1), the temperature of the first mixing is 30-40° C., and the time of the first mixing is 55-65 min;

[0016] The second mixing temperature is 35-45°C, and the second mixing time is 25-35 minutes;

[0017] The polymerization temperature is 45-55°C and the polymerization time is 13-24h;

[0018] The first mixing, the second mixing and the polymerization reaction are carried out under a protective atmosphere;

[0019] The filtration is a two-stage filtration, the precision of the first-stage filtration is 4-6 μm, and the precision of the second-stage filtration is 0.5-1.5 μm.

[0020] Preferably, the preparation process of the soluble asphalt powder in step 1) is: asphalt and solvent are mixed, and then subjected to extraction, centrifugation, filtration, rotary evaporation, and drying in sequence to obtain the soluble asphalt powder;

[0021] The asphalt is one or more of naphthalene asphalt, petroleum asphalt, coal asphalt, modified petroleum asphalt and modified coal asphalt; the solvent is one or more of pyridine, N,N-dimethylformamide, tetrahydrofuran, quinoline, N,N-dimethylacetamide and dimethyl sulfoxide; and the extraction is one or more of ultrasonic-assisted extraction, Soxhlet extraction and magnetic stirring.

[0022] Preferably, the spinning in step 2) is wet spinning or dry-jet wet spinning;

[0023] The process of phase separation of the spinning solution in the coagulation bath after wet spinning is as follows: the spinning solution directly enters the coagulation bath at a speed of 1 to 30 m / min and leaves the coagulation bath at a speed of 0.5 to 45 m / min;

[0024] The process of phase separation of the spinning solution in a coagulation bath after dry-jet wet spinning is as follows: the spinning solution passes through an air gap of 0.1 to 5 cm, enters the coagulation bath at a speed of 1 to 50 m / min, and then leaves the coagulation bath at a speed of 2 to 100 m / min; the temperature of the air gap is 25 to 35°C, and the relative humidity of the air gap is 55 to 65%.

[0025] Preferably, the coagulation bath in step 2) comprises water and an organic solvent, the organic solvent is dimethyl sulfoxide or N,N-dimethylformamide, the mass concentration of the coagulation bath is 30-70%, and the temperature of the coagulation bath is 20-50°C.

[0026] Preferably, the water washing temperature in step 3) is 40-70° C., and the hot water drawing is a two-stage hot water drawing, wherein the temperature of the first stage hot water drawing is 60-80° C., and the drawing ratio is 1.0-1.6; the temperature of the second stage hot water drawing is 80-100° C., and the drawing ratio is 1.5-1.9;

[0027] The drying and densification temperature is 100-180° C., the steam drawing pressure is 0.2-0.4 MPa, and the drawing ratio is 1.8-3.

[0028] Preferably, the pre-oxidation temperature in step 4) is 180-270° C. and the time is 75-130 min;

[0029] The carbonization is a two-stage carbonization, wherein the temperature of the first stage carbonization is 300-600°C and the time is 3-5 minutes; the temperature of the second stage carbonization is 900-1300°C and the time is 2-4 minutes;

[0030] The temperature of the graphitization treatment is 1900-2500°C and the time is 30-60s;

[0031] The carbonization and graphitization treatments are carried out under a protective atmosphere.

[0032] The present invention also provides low-resistivity carbon fibers prepared by the method for preparing the low-resistivity carbon fibers. The low-resistivity carbon fibers have a single-filament diameter of 7 to 11 μm, a tensile strength of 2.5 to 3.8 GPa, a tensile modulus of 322 to 755 GPa, and a resistivity of 6.5 to 22.0 μΩ·m.

[0033] The beneficial effects of the present invention include the following:

[0034] 1) The present invention adopts an in-situ polymerization method to quickly and uniformly introduce soluble asphalt into the acrylonitrile copolymer reaction system. By regulating its proportion in the reaction system, low-resistivity carbon fibers with different asphalt contents can be prepared. Asphalt is an easily graphitized carbon material. The easy graphitization properties of polycyclic aromatic hydrocarbons and alkyl side chains during high-temperature carbonization can induce the graphitization transformation of the fiber matrix, flexibly controlling the conductive properties of the carbon fibers, and can be used as a functional carbon fiber in cutting-edge scientific and technological fields.

[0035] 2) The present invention is based on the prepared homogeneous spinning solution and adopts traditional wet spinning or dry-jet wet spinning process to prepare asphalt / polyacrylonitrile composite fiber precursor, which has good industrial amplification characteristics and lays the foundation for the large-scale preparation of functional carbon fibers.

[0036] 3) The asphalt raw material used in the present invention is abundant in source and has a greater price advantage than the copolymer monomer, which helps to reduce the overall production cost of functional carbon fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a scanning electron microscope image of the cross section of the as-spun fiber of Example 1;

[0038] Figure 2 This is a scanning electron microscope image of the cross section of the as-spun fiber of Example 2;

[0039] Figure 3 This is a scanning electron microscope image of the graphitized carbon fiber surface in Example 3;

[0040] Figure 4 This is a scanning electron microscope image of the cross section of the as-spun fiber of Comparative Example 1;

[0041] Figure 5The XRD spectra of the carbon fibers after graphitization treatment in Example 1 and Comparative Example 1 are shown;

[0042] Figure 6 This is a scanning electron microscope image of the cross section of the as-spun fiber of Comparative Example 2;

[0043] Figure 7 This is a scanning electron microscope image of the graphitized carbon fiber surface in comparative example 3. DETAILED DESCRIPTION

[0044] The present invention provides a method for preparing low-resistivity carbon fiber, comprising the following steps:

[0045] 1) performing a first mixing of acrylonitrile, itaconic acid, soluble asphalt powder, and an organic solvent, and performing a second mixing of the first mixture and azobisisoheptanenitrile to obtain a mixed solution; performing a polymerization reaction on the mixed solution and then filtering the mixture to obtain a homogeneous asphalt / polyacrylonitrile spinning solution;

[0046] 2) After spinning, the spinning solution phase separates in the coagulation bath to form nascent fibers;

[0047] 3) The raw fibers are sequentially washed, hot water drawn, dried and densified, and steam drawn to obtain asphalt / polyacrylonitrile composite fiber precursors;

[0048] 4) The composite fiber precursor is sequentially subjected to pre-oxidation, carbonization, and graphitization treatments to obtain low-resistivity carbon fibers.

[0049] In the present invention, the mass ratio of acrylonitrile and itaconic acid in step 1) is preferably 95-97:3-5, more preferably 95.5-96.5:3.5-4.5, and more preferably 96:4; the mass ratio of soluble asphalt powder and acrylonitrile is preferably 0.1-0.9:1, more preferably 0.2-0.8:1, and more preferably 0.4-0.5:1. The mass of azobisisoheptanenitrile is preferably 0.65-0.75% of the total mass of acrylonitrile and itaconic acid, more preferably 0.68-0.72%, and more preferably 0.7%;

[0050] The organic solvent is preferably dimethyl sulfoxide or N,N-dimethylformamide; the solid content of the spinning solution is preferably 12 to 30%, more preferably 15 to 27%, and more preferably 20 to 25%; the intrinsic viscosity is preferably 1.2 to 2.2 dL / g, more preferably 1.4 to 2.0 dL / g, and more preferably 1.5 to 1.8 dL / g.

[0051] In the present invention, in step 1), the temperature of the first mixing is preferably 30-40°C, more preferably 32-38°C, more preferably 35-36°C, and the time of the first mixing is preferably 55-65min, more preferably 57-63min, more preferably 60min; the temperature of the second mixing is preferably 35-45°C, more preferably 37-43°C, more preferably 40-41°C, and the time of the second mixing is preferably 25-35min, more preferably 27-32min, more preferably 30min; the temperature of the polymerization reaction is preferably 45-55°C, more preferably 47-53°C, more preferably 50-51°C, and the time of the polymerization reaction is preferably 13-24h, more preferably 15-22h, more preferably 18-20h; the first mixing, the second mixing and the polymerization reaction are preferably carried out under a protective atmosphere, and the protective atmosphere is preferably a nitrogen atmosphere;

[0052] The filtration is preferably a two-stage filtration, the precision of the first-stage filtration is preferably 4-6 μm, more preferably 4.5-5.5 μm, more preferably 5 μm; the precision of the second-stage filtration is preferably 0.5-1.5 μm, more preferably 0.8-1.2 μm, more preferably 1 μm.

[0053] In the present invention, the preparation process of the soluble asphalt powder in step 1) is preferably as follows: the asphalt powder and the solvent are mixed and sequentially subjected to extraction, centrifugation, filtration, rotary evaporation, and drying to obtain the soluble asphalt powder;

[0054] The asphalt is preferably one or more of naphthalene asphalt, petroleum asphalt, coal asphalt, modified petroleum asphalt and modified coal asphalt; the solvent is preferably one or more of pyridine, N,N-dimethylformamide, tetrahydrofuran, quinoline, N,N-dimethylacetamide and dimethyl sulfoxide; the extraction is preferably one or more of ultrasonic-assisted extraction, Soxhlet extraction and magnetic stirring.

[0055] In the present invention, asphalt powder is obtained by crushing and grinding asphalt raw material and then passing it through a 100-200 mesh sieve; the mass ratio of asphalt powder to solvent is preferably 1:4-7, and more preferably 1:5-6; the extraction temperature is preferably 30-80°C, and more preferably 40-60°C; the extraction time is preferably 10-16h, and more preferably 12-14h; the centrifugal rate is preferably 7500-8500rpm, and more preferably 8000rpm; the centrifugal time is preferably 4-6min, and more preferably 5min; the purpose of rotary evaporation is to remove the solvent; the drying temperature is preferably 55-65°C, and more preferably 60°C; the drying time is preferably 22-26h, and more preferably 23-25h, and more preferably 24h.

[0056] In the present invention, spinning solutions with different asphalt contents are prepared by adjusting the mass ratio of soluble asphalt powder to comonomers (acrylonitrile and itaconic acid); the asphalt content can be changed over a wide range, and there is no problem of small molecular components being easy to agglomerate and difficult to disperse. In addition, asphalt is widely available and has a greater price advantage than comonomers, which helps to reduce overall production costs.

[0057] In the present invention, asphalt is an easily graphitized carbon material. During the high-temperature carbonization process, polycyclic aromatic hydrocarbons and alkyl side chain structures can induce the graphitization transformation of the polyacrylonitrile fiber matrix, thereby flexibly controlling the conductive properties of the corresponding carbon fibers and realizing the differentiated preparation of functional carbon fibers.

[0058] In the present invention, the spinning solution flows into the spinneret assembly through a metering pump, and the spinning stream is extruded to perform conventional spinning.

[0059] In the present invention, the spinning in step 2) is preferably wet spinning or dry-jet wet spinning;

[0060] The process of phase separation of the spinning solution in the coagulation bath after wet spinning is as follows: the spinning solution directly enters the coagulation bath at a speed of 1 to 30 m / min and leaves the coagulation bath at a speed of 0.5 to 45 m / min, the speed of entering the coagulation bath is preferably 5 to 25 m / min, more preferably 10 to 20 m / min, and the speed of leaving the coagulation bath is preferably 2 to 40 m / min, more preferably 10 to 30 m / min;

[0061] The process of phase separation of the spinning solution in the coagulation bath after dry-jet wet spinning is as follows: the spinning solution passes through an air gap of 0.1 to 5 cm, enters the coagulation bath at a speed of 1 to 50 m / min, and then leaves the coagulation bath at a speed of 2 to 100 m / min; the air gap is preferably 0.5 to 4 cm, more preferably 1 to 3 cm, the temperature of the air gap is preferably 25 to 35°C, more preferably 27 to 32°C, more preferably 30°C, the relative humidity of the air gap is preferably 55 to 65%, more preferably 57 to 63%, more preferably 60%; the speed of entering the coagulation bath is preferably 5 to 40 m / min, more preferably 10 to 30 m / min, and the speed of leaving the coagulation bath is preferably 10 to 80 m / min, more preferably 30 to 60 m / min.

[0062] In the present invention, the coagulation bath in step 2) preferably contains water and an organic solvent, the organic solvent is preferably dimethyl sulfoxide or N,N-dimethylformamide, the mass concentration of the coagulation bath (the mass concentration of the organic solvent in the coagulation bath) is preferably 30-70%, more preferably 35-60%, more preferably 40-50%, and the temperature of the coagulation bath is preferably 20-50°C, more preferably 25-40°C, and more preferably 30-35°C.

[0063] In the present invention, the conventional wet spinning or dry-jet wet spinning process is adopted to prepare the asphalt / polyacrylonitrile composite fiber precursor, which has good industrial amplification characteristics and lays the foundation for the large-scale preparation of functional carbon fibers.

[0064] In the present invention, the water washing temperature in step 3) is preferably 40-70° C., more preferably 45-65° C., more preferably 50-60° C., and the hot water drawing is preferably a two-stage hot water drawing. The temperature of the first hot water drawing is preferably 60-80° C., more preferably 65-75° C., more preferably 70° C., and the drawing ratio is preferably 1.0-1.6, more preferably 1.1-1.5, more preferably 1.2-1.4; the temperature of the second hot water drawing is preferably 80-100° C., more preferably 85-95° C., more preferably 90° C., and the drawing ratio is preferably 1.5-1.9, more preferably 1.6-1.8, more preferably 1.7;

[0065] The drying and densification temperature is preferably 100-180°C, more preferably 110-160°C, and more preferably 130-150°C. The steam drawing pressure is preferably 0.2-0.4 MPa, more preferably 0.25-0.35 MPa, and more preferably 0.3 MPa. The drawing ratio is preferably 1.8-3, more preferably 2-2.8, and more preferably 2.3-2.5.

[0066] In the present invention, the temperature of the pre-oxidation in step 4) is preferably 180-270°C, more preferably 200-260°C, more preferably 220-240°C, and the time is preferably 75-130 min, more preferably 80-120 min, more preferably 100-110 min;

[0067] The carbonization is preferably a two-stage carbonization, wherein the temperature of the first stage carbonization is preferably 300-600°C, more preferably 350-550°C, more preferably 450-500°C, and the time is preferably 3-5 minutes, more preferably 4 minutes; the temperature of the second stage carbonization is preferably 900-1300°C, more preferably 1000-1200°C, more preferably 1100°C, and the time is preferably 2-4 minutes, more preferably 3 minutes;

[0068] The temperature of the graphitization treatment is preferably 1900-2500°C, more preferably 2000-2400°C, more preferably 2100-2300°C, and the time is preferably 30-60s, more preferably 40-50s, more preferably 45s;

[0069] The carbonization and graphitization treatments are preferably carried out under a protective atmosphere.

[0070] The present invention also provides low-resistivity carbon fibers prepared by the method for preparing the low-resistivity carbon fibers. The low-resistivity carbon fibers have a single-filament diameter of 7 to 11 μm, a tensile strength of 2.5 to 3.8 GPa, a tensile modulus of 322 to 755 GPa, and a resistivity of 6.5 to 22.0 μΩ·m.

[0071] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0072] Example 1

[0073] The petroleum asphalt was crushed and ground in a crusher at a speed of 800 rpm for 5 minutes and then sieved through a 100-mesh sieve to obtain petroleum asphalt powder; the petroleum asphalt powder was mixed with pyridine in a mass ratio of 1:5 and extracted with magnetic stirring at a speed of 500 rpm at 80°C for 10 hours, and then centrifuged at a speed of 8000 rpm for 5 minutes. The filtered extract was rotary evaporated at a speed of 100 rpm at 60°C and finally dried at 60°C for 24 hours to obtain soluble asphalt powder.

[0074] Under a nitrogen atmosphere, acrylonitrile, itaconic acid, soluble asphalt powder and dimethyl sulfoxide are mixed in a monomer reactor, with the mass ratio of acrylonitrile to itaconic acid being 96:4, and the mass ratio of soluble asphalt powder to acrylonitrile being 0.2:1, and the mixture is stirred at 35°C for 60 minutes; azobisisoheptanenitrile accounting for 0.7% of the total mass of acrylonitrile and itaconic acid is added to the reactor and stirred at 40°C for 30 minutes; the mixed solution is polymerized at a kettle temperature of 50°C for 18 hours; after two-stage filtration (the precision of the first filter is 5 μm, and the precision of the second filter is 1 μm), removal of unreacted monomers and degassing, a homogeneous asphalt / polyacrylonitrile spinning solution with a solid content of 20% is obtained.

[0075] The spinning solution flows into the spinneret through a metering pump to extrude a spinning stream for wet spinning. The spinning stream directly enters the coagulation bath at a speed of 4 m / min, and leaves the coagulation bath at a speed of 3.2 m / min after being guided by a roller (the coagulation bath is dimethyl sulfoxide and deionized water, the mass concentration of dimethyl sulfoxide in the coagulation bath is 40%, and the temperature of the coagulation bath is 50°C), and phase separation occurs in the coagulation bath to form nascent fibers; the nascent fibers are washed at 60°C and then subjected to two-stage hot water drawing, the temperature of the first hot water drawing is 70°C, the drawing ratio is 1.1 times, the temperature of the second hot water drawing is 80°C, the drawing ratio is 1.5 times, and then dried and densified at 130°C, and steam drawn twice at 0.3 MPa to obtain asphalt / polyacrylonitrile composite fiber precursors.

[0076] In an air atmosphere, the composite fiber precursor was pre-oxidized at 270°C for 80 minutes; then, it was subjected to two-stage carbonization and graphitization treatments in a nitrogen atmosphere, with the first-stage carbonization temperature at 500°C for 4 minutes and the second-stage carbonization temperature at 1000°C for 2 minutes; the graphitization treatment temperature was 2200°C for 60 seconds to obtain low-resistivity carbon fibers.

[0077] The microstructure of the cross section of the as-spun fiber formed by phase separation in the coagulation bath in this embodiment is as follows: Figure 1 As shown by Figure 1 It can be seen that the outline of the as-spun fiber is close to circular, but there are a few micropores in the cross section; the soluble petroleum asphalt powder does not affect the phase separation of the polyacrylonitrile matrix.

[0078] Example 2

[0079] Naphthalene asphalt was crushed and ground in a crusher at a speed of 600 rpm for 5 minutes and then sieved through a 100-mesh sieve to obtain naphthalene asphalt powder; the naphthalene asphalt powder was mixed with N,N-dimethylformamide in a mass ratio of 1:4 and extracted with magnetic stirring at a speed of 500 rpm at 80°C for 16 hours, and then centrifuged at a speed of 8000 rpm for 5 minutes. The filtered extract was rotary evaporated at a speed of 140 rpm at 90°C and finally dried at 60°C for 24 hours to obtain soluble asphalt powder.

[0080] Under a nitrogen atmosphere, acrylonitrile, itaconic acid, soluble asphalt powder and N,N-dimethylformamide are mixed in a monomer reactor, with the mass ratio of acrylonitrile to itaconic acid being 96:4, and the mass ratio of soluble asphalt powder to acrylonitrile being 0.8:1, and the mixture is stirred at 35°C for 60 minutes; azobisisoheptanenitrile accounting for 0.7% of the total mass of acrylonitrile and itaconic acid is added to the reactor and stirred at 40°C for 30 minutes; the mixed solution is polymerized at a kettle temperature of 50°C for 20 hours; after two-stage filtration (the precision of the first filter is 5μm, and the precision of the second filter is 1μm), removal of unreacted monomers and degassing, a homogeneous asphalt / polyacrylonitrile spinning solution with a solid content of 27% is obtained.

[0081] The spinning solution flows into the spinneret through a metering pump to extrude a spinning stream for dry-jet wet spinning. After the spinning stream passes through a 1 cm air gap (the temperature of the air gap is 30°C and the relative humidity is 60%), it directly enters the coagulation bath at a speed of 6 m / min. After being guided by a roller, it leaves the coagulation bath at a speed of 10 m / min (the coagulation bath is N,N-dimethylformamide and deionized water, the mass concentration of N,N-dimethylformamide in the coagulation bath is 70%, and the temperature of the coagulation bath is 50°C), and phase separates in the coagulation bath to form nascent fibers; the nascent fibers are washed at 60°C and then subjected to two-stage hot water drawing, the temperature of the first hot water drawing is 70°C, the drawing ratio is 1.3 times, the temperature of the second hot water drawing is 90°C, the drawing ratio is 1.6 times, and then dried and densified at 150°C, and steam drawn 1.8 times at 0.4 MPa to obtain asphalt / polyacrylonitrile composite fiber precursors.

[0082] In an air atmosphere, the composite fiber precursor was pre-oxidized at 250°C for 130 minutes; then, it was subjected to two-stage carbonization and graphitization treatments in a nitrogen atmosphere, with the first-stage carbonization temperature at 600°C for 4 minutes and the second-stage carbonization temperature at 1300°C for 2 minutes; the graphitization temperature was 2400°C for 30 seconds to obtain low-resistivity carbon fibers.

[0083] The microstructure of the cross section of the as-spun fiber formed by phase separation in the coagulation bath in this embodiment is as follows: Figure 2 As shown by Figure 2 It can be seen that the outline of the primary fiber is circular, and no obvious micropores appear when the cross section is locally enlarged; the soluble naphthalene pitch powder does not affect the phase separation of the polyacrylonitrile matrix, and the fiber cross section is smooth.

[0084] Example 3

[0085] The modified coal tar was crushed and ground in a crusher at a speed of 800 rpm for 5 minutes and then sieved through a 100-mesh sieve to obtain modified coal tar powder; the modified coal tar powder was mixed with tetrahydrofuran at a mass ratio of 1:7 and extracted with magnetic stirring at a speed of 500 rpm at 30°C for 16 hours, and then centrifuged at a speed of 8000 rpm for 5 minutes. The filtered extract was rotary evaporated at a speed of 80 rpm at 40°C and finally dried at 60°C for 24 hours to obtain soluble asphalt powder.

[0086] Under a nitrogen atmosphere, acrylonitrile, itaconic acid, soluble asphalt powder and N,N-dimethylformamide are mixed in a monomer reactor, with the mass ratio of acrylonitrile to itaconic acid being 96:4, and the mass ratio of soluble asphalt powder to acrylonitrile being 0.5:1, and the mixture is stirred at 35°C for 60 minutes; azobisisoheptanenitrile accounting for 0.7% of the total mass of acrylonitrile and itaconic acid is added to the reactor and stirred at 37°C for 30 minutes; the mixed solution is polymerized at a kettle temperature of 50°C for 20 hours; after two-stage filtration (the precision of the first filter is 5μm, and the precision of the second filter is 1μm), removal of unreacted monomers and degassing, a homogeneous asphalt / polyacrylonitrile spinning solution with a solid content of 22% is obtained.

[0087] The spinning solution flows into the spinneret through a metering pump to extrude a spinning stream for wet spinning. The spinning stream directly enters the coagulation bath at a speed of 3 m / min, and leaves the coagulation bath at a speed of 3 m / min after being guided by a roller (the coagulation bath is N,N-dimethylformamide and deionized water, the mass concentration of N,N-dimethylformamide in the coagulation bath is 50%, and the temperature of the coagulation bath is 35°C), and phase separation occurs in the coagulation bath to form nascent fibers; the nascent fibers are washed at 60°C and then subjected to two-stage hot water drawing, the temperature of the first hot water drawing is 75°C, the drawing ratio is 1.2 times, the temperature of the second hot water drawing is 100°C, and the drawing ratio is 1.7 times, and then dried and densified at 140°C, and steam drawn 2.2 times at 0.4 MPa to obtain asphalt / polyacrylonitrile composite fiber precursors.

[0088] In an air atmosphere, the composite fiber precursor was pre-oxidized at 240°C for 130 minutes; then, it was subjected to two-stage carbonization and graphitization treatments in a nitrogen atmosphere, with the first-stage carbonization temperature at 450°C for 5 minutes and the second-stage carbonization temperature at 1100°C for 3 minutes; the graphitization treatment temperature was 2000°C for 50 seconds to obtain low-resistivity carbon fibers.

[0089] The surface micromorphology of the carbon fiber graphitized at 2000℃ in this embodiment is as follows Figure 3 As shown by Figure 3 It can be seen that there are surface grooves inherent in wet spinning and coagulation forming on the surface of carbon fiber; the soluble modified coal tar powder does not affect the fiber surface, and the overall morphology is relatively smooth.

[0090] Example 4

[0091] The mass ratio of soluble asphalt powder to acrylonitrile was 0.8:1, and other process conditions were the same as those in Example 3.

[0092] Comparative Example 1

[0093] In this comparative example, the soluble petroleum asphalt powder is omitted based on Example 1, and other process conditions are the same as those in Example 1.

[0094] The microstructure of the cross section of the primary fiber formed by phase separation in the coagulation bath is as follows: Figure 4 As shown by Figure 4 It can be seen that the outline of the as-spun fiber is bean-shaped and there are micropores in the cross section; Figure 1 In contrast, the spinnability of the pitch / polyacrylonitrile spinning solution of Example 1 is relatively high under the same conditions.

[0095] The XRD spectra of the carbon fibers after graphitization treatment in this comparative example and Example 1 are as follows: Figure 5 As shown by Figure 5 It can be seen that under the same graphitization treatment conditions, after the introduction of asphalt, the diffraction peak of carbon fiber at (002) changes from a broader peak to a sharp peak, the peak intensity increases, the peak width becomes narrower, and the peak position shifts to the right, indicating that the degree of graphitization of the matrix induced by asphalt is improved.

[0096] Comparative Example 2

[0097] This comparative example omits the soluble naphthalene pitch powder on the basis of Example 2, and is an equal-composition copolymer system. Other preparation methods are the same as those in Example 2.

[0098] The cross-sectional microstructure of the primary fiber formed by phase separation in the coagulation bath is as follows: Figure 6 As shown by Figure 6 It can be seen that the outline of the as-spun fiber is circular, and no obvious micropores appear when the cross section is partially enlarged, and the cross section is flat; Figure 2 In comparison, the cross-sectional morphologies of the primary fibers of the two systems are similar, indicating that the soluble naphthalene pitch does not affect the phase separation of the polyacrylonitrile matrix.

[0099] Comparative Example 3

[0100] In this comparative example, the soluble modified coal tar powder is omitted on the basis of Example 3, and a copolymer system of equal composition is obtained; the graphitization temperature is adjusted to 2500° C., and the other preparation methods are the same as those in Example 3.

[0101] The surface micromorphology of the carbon fiber graphitized at 2500℃ in this embodiment is as follows: Figure 7 As shown, the carbon fiber surface has inherent surface grooves formed by wet spinning coagulation; Figure 3 In comparison, the surface morphologies of graphitized fibers in the two systems are similar, and the soluble asphalt component does not affect the surface roughness of the carbon fibers.

[0102] The performance test results of the carbon fibers prepared in Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1.

[0103] Table 1 Performance data of carbon fibers prepared in different embodiments and comparative examples

[0104] serial number Diameter / μm Tensile strength / GPa Tensile modulus / GPa Resistivity / μΩ·m Example 1 10.2 2.7 325 19.7 Example 2 7.4 3.3 653 5.2 Example 3 9.3 3.0 482 10.9 Example 4 10.5 3.5 727 4.1 Comparative Example 1 — 1.8 165 35.6 Comparative Example 2 6.9 2.6 232 29.5 Comparative Example 3 7.6 3.0 264 27.6

[0105] As can be seen from Table 1, the resistivity of the carbon fiber prepared based on the asphalt / polyacrylonitrile spinning solution in the embodiment can be controlled in a large range, and the value is lower than the resistivity of the polyacrylonitrile-based carbon fiber; compared with Example 3, even if the graphitization temperature of the polyacrylonitrile-based carbon fiber is increased, its resistivity is still significantly higher than that of the carbon fiber in Example 3; compared with Comparative Examples 1 to 3, the spinning process and heat treatment temperature have limited effects on the resistivity change range of the polyacrylonitrile-based carbon fiber; compared with Examples 1 to 4, the type and content of asphalt have a greater influence on the resistivity and mechanical properties of the corresponding carbon fiber, that is, after the introduction of the soluble asphalt component, the controllable range of the resistivity and mechanical properties of the carbon fiber becomes wider.

[0106] The easy graphitization property of asphalt in the heat treatment process of the present invention can form a large-scale graphite microcrystalline structure with high regularity, induce the graphitization transformation of the polyacrylonitrile fiber matrix during the high-temperature carbonization process, improve the graphitization degree and microcrystalline size of the matrix, so as to prepare low-resistivity carbon fibers based on asphalt / polyacrylonitrile and realize flexible control of the "conductive-mechanical" properties.

[0107] 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 principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing low-resistivity carbon fiber, characterized in that: The following steps are included: 1) performing a first mixing of acrylonitrile, itaconic acid, soluble asphalt powder, and an organic solvent, and performing a second mixing of the first mixture and azobisisoheptanenitrile to obtain a mixed solution; performing a polymerization reaction on the mixed solution and then filtering the mixture to obtain a homogeneous asphalt / polyacrylonitrile spinning solution; 2) After spinning, the spinning solution phase separates in the coagulation bath to form nascent fibers; 3) The raw fibers are sequentially washed, hot water drawn, dried and densified, and steam drawn to obtain asphalt / polyacrylonitrile composite fiber precursors; 4) The composite fiber precursor is sequentially subjected to pre-oxidation, carbonization, and graphitization treatments to obtain low-resistivity carbon fibers.

2. The method for preparing low-resistivity carbon fiber according to claim 1, wherein: Step 1) The mass ratio of acrylonitrile to itaconic acid is 95-97:3-5, the mass ratio of soluble asphalt powder to acrylonitrile is 0.1-0.9:1, and the mass of azobisisoheptanenitrile is 0.65-0.75% of the total mass of acrylonitrile and itaconic acid; The organic solvent is dimethyl sulfoxide or N,N-dimethylformamide; the solid content of the spinning solution is 12-30%, and the intrinsic viscosity is 1.2-2.2 dL / g.

3. The method for preparing low-resistivity carbon fiber according to claim 1 or 2, characterized in that: Step 1) the temperature of the first mixing is 30-40° C., and the time of the first mixing is 55-65 min; The second mixing temperature is 35-45°C, and the second mixing time is 25-35 minutes; The polymerization temperature is 45 to 55° C., and the polymerization time is 13 to 24 hours. The first mixing, the second mixing and the polymerization reaction are carried out under a protective atmosphere; The filtration is a two-stage filtration, the precision of the first-stage filtration is 4-6 μm, and the precision of the second-stage filtration is 0.5-1.5 μm.

4. The method for preparing low-resistivity carbon fiber according to claim 3, characterized in that: Step 1) The preparation process of the soluble asphalt powder is as follows: asphalt and a solvent are mixed, and then subjected to extraction, centrifugation, filtration, rotary evaporation, and drying in sequence to obtain the soluble asphalt powder; The asphalt is one or more of naphthalene asphalt, petroleum asphalt, coal asphalt, modified petroleum asphalt and modified coal asphalt; the solvent is one or more of pyridine, N,N-dimethylformamide, tetrahydrofuran, quinoline, N,N-dimethylacetamide and dimethyl sulfoxide; and the extraction is one or more of ultrasonic-assisted extraction, Soxhlet extraction and magnetic stirring.

5. The method for preparing low-resistivity carbon fiber according to claim 3, characterized in that: Step 2) the spinning is wet spinning or dry-jet wet spinning; The process of phase separation of the spinning solution in the coagulation bath after wet spinning is as follows: the spinning solution directly enters the coagulation bath at a speed of 1 to 30 m / min and leaves the coagulation bath at a speed of 0.5 to 45 m / min; The process of phase separation of the spinning solution in a coagulation bath after dry-jet wet spinning is as follows: the spinning solution passes through an air gap of 0.1 to 5 cm, enters the coagulation bath at a speed of 1 to 50 m / min, and then leaves the coagulation bath at a speed of 2 to 100 m / min; the temperature of the air gap is 25 to 35°C, and the relative humidity of the air gap is 55 to 65%.

6. The method for preparing low-resistivity carbon fiber according to claim 4 or 5, characterized in that: Step 2) The coagulation bath comprises water and an organic solvent, wherein the organic solvent is dimethyl sulfoxide or N,N-dimethylformamide, the mass concentration of the coagulation bath is 30-70%, and the temperature of the coagulation bath is 20-50°C.

7. The method for preparing low-resistivity carbon fiber according to claim 6, characterized in that: Step 3) the water washing temperature is 40-70° C., and the hot water drawing is a two-stage hot water drawing, wherein the first stage hot water drawing temperature is 60-80° C., and the drawing ratio is 1.0-1.6; the second stage hot water drawing temperature is 80-100° C., and the drawing ratio is 1.5-1.9; The drying and densification temperature is 100-180° C., the steam drawing pressure is 0.2-0.4 MPa, and the drawing ratio is 1.8-3.

8. The method for preparing low-resistivity carbon fiber according to claim 7, characterized in that: Step 4) the pre-oxidation temperature is 180-270° C. and the time is 75-130 min; The carbonization is a two-stage carbonization, wherein the temperature of the first stage carbonization is 300-600°C and the time is 3-5 minutes; the temperature of the second stage carbonization is 900-1300°C and the time is 2-4 minutes; The temperature of the graphitization treatment is 1900-2500°C and the time is 30-60s; The carbonization and graphitization treatments are carried out under a protective atmosphere.

9. The low-resistivity carbon fiber prepared by the method for preparing low-resistivity carbon fiber according to any one of claims 1 to 8, characterized in that: The single fiber diameter of the low-resistivity carbon fiber is 7 to 11 μm, the tensile strength is 2.5 to 3.8 GPa, the tensile modulus is 322 to 755 GPa, and the resistivity is 6.5 to 22.0 μΩ·m.

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