A method for producing polyacrylonitrile-based large-tow carbon fibers and the carbon fibers obtained thereby

Abstract

The present application relates to a kind of polyacrylonitrile-based large tow carbon fiber preparation method, mainly solve the existing pre-oxidation process heat concentration, fiber easy fracture, the problem of poor carbon fiber product performance in prior art.The specific steps are as follows: polyacrylonitrile fiber is at least four temperature zones pre-oxidation treatment, by controlling the tension of each temperature zone fiber, and the pre-oxidized fiber is prepared;It is at least three temperature zones low-temperature carbonization treatment and at least three temperature zones high-temperature carbonization treatment, and polyacrylonitrile-based large tow carbon fiber is obtained.In the continuous preparation process of fiber, by controlling the tension of each temperature zone in pre-oxidation stage, and with the temperature of low-temperature carbonization and high-temperature carbonization, draft ratio, residence time are matched, the continuous preparation of large tow carbon fiber is realized, the above problems are preferably solved, and can be used in the industrial production of polyacrylonitrile-based large tow carbon fiber preparation process.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber technology, specifically relating to a method for preparing polyacrylonitrile-based large-tow carbon fiber and the resulting carbon fiber. Background Technology

[0002] Carbon fiber refers to inorganic polymer fibers with a carbon content of over 92%, composed of polymerization precursors or allotropic units of carbon. It is a typical high-performance fiber. It possesses advantages such as high specific strength, high specific modulus, high temperature resistance, corrosion resistance, creep resistance, electrical conductivity, and low specific gravity, making it widely used in automobiles, aircraft, rail transportation, wind power generation, and sporting goods. Carbon fiber is classified into polyacrylonitrile-based, pitch-based, and viscose-based carbon fibers according to its precursor fiber, with polyacrylonitrile-based carbon fiber being the most commercially available.

[0003] Carbon fiber comes in large and small tow sizes, with those of 48K or higher being classified as large tow carbon fiber. Small tow carbon fiber is mainly used in the defense and military industries, while the industrial sector requires large tow carbon fiber more due to its low cost advantage. However, there are many technical problems to be solved in the production and application of large tow carbon fiber. These mainly manifest in the fact that the heat of reaction is concentrated during the pre-oxidation of large tow precursor fibers, making it difficult to dissipate heat. This can easily lead to melting and fiber breakage, or even spontaneous combustion, resulting in reduced production efficiency and poor product performance. Therefore, it is essential to mitigate the concentrated heat release during the pre-oxidation process of large tow precursor fibers and control the smooth passage of the tow through the pre-oxidation stage.

[0004] Currently, methods such as copolymerization to reduce the starting temperature of precursor fiber pre-oxidation or adjusting the pre-oxidation atmosphere (Chinese Patent CN111647973A) are used to achieve control. Although existing technical solutions can increase the pre-oxidation rate, reduce heat release, or optimize the pre-oxidation structure, they are limited to research on small-tow fiber precursors or are difficult to apply on a large scale. Summary of the Invention

[0005] To address the problems of concentrated exothermic reaction during the pre-oxidation process, easy fiber breakage, and poor performance of carbon fiber products in existing technologies, this invention provides a method for preparing polyacrylonitrile pre-oxidized fibers, which features mild exothermic reaction during the pre-oxidation process, less fiber breakage, and superior final product performance.

[0006] One objective of this invention is to provide a method for preparing polyacrylonitrile-based large-tow carbon fibers, comprising: a pre-oxidation treatment of polyacrylonitrile fiber precursors and a carbonization treatment, wherein the relationship between the fiber tension value T and the number of fiber bundles B in the pre-oxidation treatment is as follows:

[0007] T = a × B,

[0008] In the formula, T is the fiber tension value, in N;

[0009] B represents the number of fiber bundles, in thousands;

[0010] a ranges from 0.5 to 1.7, with units of N / thousands.

[0011] In the above relationship, the value of 'a' can be any value in the range of 0.5 to 1.7, for example, it can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 or 1.7, and can be any of the above values ​​or a range between any two values.

[0012] According to an embodiment of the present invention, the pre-oxidation treatment includes pre-oxidation treatment in at least four temperature zones, preferably,

[0013] In the first temperature zone, the fiber tension value T1 and the number of fiber bundles B satisfy T1 = (0.5~1.2) × B;

[0014] In the second temperature zone, the fiber tension value T2 and the number of fiber bundles B satisfy T2 = (0.7~1.6) × B;

[0015] In the third temperature zone, the fiber tension value T3 and the number of fiber bundles B satisfy T3 = (0.9~1.5) × B;

[0016] In the fourth temperature zone, the fiber tension value T4 and the number of fiber bundles B satisfy T4 = (1.1~1.7) × B.

[0017] More preferably,

[0018] In the first temperature zone, the fiber tension value T1 and the number of fiber bundles B satisfy T1 = (0.6~1.1) × B;

[0019] In the second temperature zone, the fiber tension value T2 and the number of fiber bundles B satisfy T2 = (0.75~1.5) × B;

[0020] In the third temperature zone, the fiber tension value T3 and the number of fiber bundles B satisfy T3 = (1~1.4) × B;

[0021] In the fourth temperature zone, the fiber tension value T4 and the number of fiber bundles B satisfy T4 = (1.1~1.6) × B.

[0022] According to an embodiment of the present invention, the polyacrylonitrile fiber precursor can be any large bundle fiber precursor in the prior art, or it can be prepared by existing preparation processes, for example: the polyacrylonitrile solution is prepared by wet spinning process or dry-wet spinning process, and after the polyacrylonitrile solution is spun out by a spinneret, it is sequentially subjected to coagulation and molding, hot water drawing, water washing, oiling, drying and densification, and steam drawing to obtain polyacrylonitrile fiber precursor;

[0023] Preferably, the number of polyacrylonitrile fiber filaments is at least 48,000, more preferably 48,000 to 360,000; the moisture content of the polyacrylonitrile fiber filaments is less than or equal to 5 wt%, more preferably less than or equal to 2 wt%; the linear density of the polyacrylonitrile fiber filaments is 0.3 to 3.5 dtex, preferably 0.5 to 2.5 dtex.

[0024] According to an embodiment of the present invention, the preparation method specifically includes:

[0025] (1) The polyacrylonitrile fiber precursor is subjected to pre-oxidation treatment in at least four temperature zones using a pre-oxidation furnace. The pre-oxidized fiber is obtained by controlling the tension of the fiber in each temperature zone.

[0026] (2) The obtained pre-oxidized fibers are subjected to low-temperature carbonization and high-temperature carbonization, and finally post-treatment to obtain polyacrylonitrile-based large tow carbon fibers.

[0027] According to a preferred embodiment of the present invention, in the pre-oxidation treatment:

[0028] The temperatures of the first to fourth temperature zones are 160–220℃, 180–240℃, 200–260℃, and 210–280℃, respectively, with the preferred temperatures being 180–200℃, 200–220℃, 220–240℃, and 230–260℃.

[0029] In the aforementioned pre-oxidation treatment, the pre-oxidation residence time in each temperature zone is 5–30 min, preferably 10–20 min.

[0030] According to a preferred embodiment of the present invention, the fibers obtained after pre-oxidation are subjected to carbonization treatment, wherein the carbonization treatment includes low-temperature carbonization treatment and high-temperature carbonization treatment. Specifically, during the carbonization treatment process:

[0031] The low-temperature carbonization includes low-temperature carbonization treatment in at least three temperature zones, wherein the carbonization temperatures of the first to third temperature zones are 350–550°C, 450–650°C, and 650–850°C, respectively, preferably 380–500°C, 480–550°C, and 650–750°C; the draw ratio is 2–7%, preferably 3–5%; and the fiber residence time is 1–15 min, preferably 2–10 min.

[0032] The high-temperature carbonization includes high-temperature carbonization treatment in at least three temperature zones, wherein the carbonization temperatures of the first to third temperature zones are 1000–1250℃, 1200–1350℃, and 1300–1500℃, respectively, preferably 1050–1150℃, 1200–1300℃, and 1350–1450℃; the draw ratio is -5.0 to -0.5%, preferably -3.5 to -0.5%; and the fiber residence time is 1–15 min, preferably 2–10 min.

[0033] The second objective of this invention is to provide a polyacrylonitrile-based large-tow carbon fiber, which is prepared by the above-mentioned preparation method. Preferably, the tensile strength of the carbon fiber is ≥4.0 GPa and the tensile modulus is ≥250 GPa.

[0034] The tension T during the pre-oxidation process of polyacrylonitrile fiber precursor is related to the fiber number B. In this invention, the relationship between tension and fiber number during pre-oxidation is controlled to ensure a relevant proportional relationship, and this relationship is matched with the pre-oxidation temperature, draw ratio, and residence time. By controlling the fiber bundle within a suitable tension range, good heat dissipation is achieved during the oxidation reaction of the large fiber bundle, preventing individual fibers from sticking together and avoiding problems such as smoke and breakage caused by excessively high local temperatures. Simultaneously, the temperature, draw ratio, and residence time of low-temperature carbonization and high-temperature carbonization are matched to achieve continuous preparation of large-tow carbon fibers.

[0035] The technical solution of this invention involves pre-oxidizing polyacrylonitrile fibers in at least four temperature zones using a pre-oxidation furnace. By controlling the tension in each temperature zone of the pre-oxidized fiber, pre-oxidized fibers are obtained. Then, a low-temperature carbonization process is performed in at least three temperature zones using a low-temperature carbonization furnace, followed by a high-temperature carbonization process in at least three temperature zones using a high-temperature carbonization furnace, to obtain polyacrylonitrile-based large-tow carbon fibers. The tensile strength of the large-tow carbon fibers can reach 4.0 GPa, and the tensile modulus can reach 250 GPa, achieving good technical results.

[0036] This invention achieves continuous preparation of large-tow carbon fibers by controlling the tension in each temperature zone of the pre-oxidation stage, and matching it with the temperature, draw ratio, and residence time of low-temperature carbonization and high-temperature carbonization. It effectively solves the above problems and can be used in the industrial production of polyacrylonitrile-based large-tow carbon fibers. Detailed Implementation

[0037] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0038] The testing instruments and conditions used in this embodiment are as follows:

[0039] The tensile strength and tensile modulus of carbon fiber were tested according to GB / T 3362-2017.

[0040] The tension value was tested using an online tension meter.

[0041]

Example 1

[0042] 48K polyacrylonitrile fiber precursor (fineness 1.5dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-temperature zone pre-oxidation furnace. The tension of each temperature zone was controlled at 41N, 57N, 58N, and 67N, respectively, and the pre-oxidation temperatures of the four temperature zones were 190℃, 210℃, 230℃, and 245℃, respectively.

[0043] The pre-oxidized fiber was subjected to low-temperature carbonization treatment in three temperature zones in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each temperature zone were 450℃, 550℃ and 750℃, the fiber draw ratio was 4.5% and the fiber residence time was 3 min.

[0044] High-temperature carbonization of low-density carbon fibers was carried out in a high-temperature carbonization furnace under a nitrogen atmosphere using three temperature zones: 1100℃, 1250℃, and 1400℃. The fiber draw ratio was -3.0%, and the fiber residence time was 3 minutes, thus preparing the large-tow carbon fibers. The carbon fibers had a tensile strength of 4.5 GPa and a tensile modulus of 257 GPa.

[0045]

Example 2

[0046] 48K polyacrylonitrile fiber precursor (fineness 1.5dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-temperature zone pre-oxidation furnace. The tension of each temperature zone was controlled at 29N, 38N, 48N, and 53N, respectively, and the pre-oxidation temperatures of the four temperature zones were 190℃, 210℃, 230℃, and 245℃, respectively.

[0047] The pre-oxidized fiber was subjected to low-temperature carbonization treatment in three temperature zones in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each temperature zone were 450℃, 550℃ and 750℃, the fiber draw ratio was 4.5% and the fiber residence time was 3 min.

[0048] High-temperature carbonization of low-density carbon fibers was performed in a high-temperature carbonization furnace under a nitrogen atmosphere, with three temperature zones: 1100℃, 1250℃, and 1400℃. The fiber draw ratio was -3.0%, and the fiber residence time was 3 minutes, resulting in the large-tow carbon fibers described above. The carbon fibers exhibited a tensile strength of 4.3 GPa and a tensile modulus of 253 GPa.

[0049]

Example 3

[0050] 48K polyacrylonitrile fiber precursor (fineness 1.5dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-temperature zone pre-oxidation furnace. The tension of each temperature zone was controlled at 53N, 70N, 67N, and 77N, respectively, and the pre-oxidation temperatures of the four temperature zones were 190℃, 210℃, 230℃, and 245℃, respectively.

[0051] The pre-oxidized fiber was subjected to low-temperature carbonization treatment in three temperature zones in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each temperature zone were 450℃, 550℃ and 750℃, the fiber draw ratio was 4.5% and the fiber residence time was 3 min.

[0052] High-temperature carbonization of low-density carbon fibers was performed in a high-temperature carbonization furnace under a nitrogen atmosphere, with three temperature zones: 1100℃, 1250℃, and 1400℃. The fiber draw ratio was -3.0%, and the fiber residence time was 3 minutes, resulting in the large-tow carbon fibers described above. The carbon fibers exhibited a tensile strength of 4.1 GPa and a tensile modulus of 251 GPa.

[0053]

Example 4

[0054] 120K polyacrylonitrile fiber precursor (fineness 1.5dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-temperature zone pre-oxidation furnace. The tension of each temperature zone was controlled at 96N, 144N, 144N, and 168N, respectively, and the pre-oxidation temperatures of the four temperature zones were 190℃, 210℃, 230℃, and 245℃, respectively.

[0055] The pre-oxidized fiber was subjected to low-temperature carbonization treatment in three temperature zones in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each temperature zone were 450℃, 550℃ and 750℃, the fiber draw ratio was 4.5% and the fiber residence time was 3 min.

[0056] High-temperature carbonization of low-density carbon fibers was performed in a high-temperature carbonization furnace under a nitrogen atmosphere, with three temperature zones: 1100℃, 1250℃, and 1400℃. The fiber draw ratio was -3.0%, and the fiber residence time was 3 minutes, resulting in the large-tow carbon fibers described above. The carbon fibers exhibited a tensile strength of 4.0 GPa and a tensile modulus of 254 GPa.

[0057]

Example 5

[0058] 360K polyacrylonitrile fiber precursor (fineness 2.0 dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-temperature zone pre-oxidation furnace. The tension of each temperature zone was controlled at 252N, 324N, 396N, and 468N, respectively, and the pre-oxidation temperatures of the four temperature zones were 190℃, 210℃, 230℃, and 245℃, respectively.

[0059] The pre-oxidized fiber was subjected to low-temperature carbonization treatment in three temperature zones in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each temperature zone were 450℃, 550℃ and 750℃, the fiber draw ratio was 4.5% and the fiber residence time was 3 min.

[0060] High-temperature carbonization of low-density carbon fibers was performed in a high-temperature carbonization furnace under a nitrogen atmosphere, with three temperature zones: 1100℃, 1250℃, and 1400℃. The fiber draw ratio was -3.0%, and the fiber residence time was 3 minutes, resulting in the large-tow carbon fibers described above. The carbon fibers exhibited a tensile strength of 4.0 GPa and a tensile modulus of 251 GPa.

[0061]

Example 6

[0062] 48K polyacrylonitrile fiber precursor (fineness 1.5dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-temperature zone pre-oxidation furnace. The tension of each temperature zone was controlled at 41N, 30N, 77N, and 67N, respectively, and the pre-oxidation temperatures of the four temperature zones were 190℃, 210℃, 230℃, and 245℃, respectively.

[0063] The pre-oxidized fiber was subjected to low-temperature carbonization treatment in three temperature zones in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each temperature zone were 450℃, 550℃ and 750℃, the fiber draw ratio was 4.5% and the fiber residence time was 3 min.

[0064] High-temperature carbonization of low-density carbon fibers was performed in a high-temperature carbonization furnace under a nitrogen atmosphere, with three temperature zones: 1100℃, 1250℃, and 1400℃. The fiber draw ratio was -3.0%, and the fiber residence time was 3 minutes, resulting in the large-tow carbon fibers described above. The carbon fibers exhibited a tensile strength of 3.8 GPa and a tensile modulus of 255 GPa.

[0065]

Example 7

[0066] 48K polyacrylonitrile fiber precursor (fineness 1.5dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-temperature zone pre-oxidation furnace. The tension of each temperature zone was controlled at 41N, 57N, 58N, and 67N, respectively, and the pre-oxidation temperatures of the four temperature zones were 190℃, 210℃, 230℃, and 245℃, respectively.

[0067] The pre-oxidized fiber was subjected to low-temperature carbonization treatment in three temperature zones in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each temperature zone were 450℃, 550℃ and 750℃, the fiber draw ratio was 4.5% and the fiber residence time was 3 min.

[0068] High-temperature carbonization of low-density carbon fibers was performed in a high-temperature carbonization furnace under a nitrogen atmosphere, with three temperature zones: 1100℃, 1350℃, and 1500℃. The fiber draw ratio was -3.0%, and the fiber residence time was 3 minutes, resulting in the large-tow carbon fibers described above. The carbon fibers exhibited a tensile strength of 3.5 GPa and a tensile modulus of 265 GPa.

[0069]

Comparative Example 1

[0070] 48K polyacrylonitrile fiber precursor (fineness 1.5dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-temperature zone pre-oxidation furnace. The tension of each temperature zone was controlled at 20N, 30N, 42N, and 47N, respectively, and the pre-oxidation temperatures of the four temperature zones were 190℃, 210℃, 230℃, and 245℃, respectively.

[0071] The pre-oxidized fiber was subjected to low-temperature carbonization treatment in three temperature zones in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each temperature zone were 450℃, 550℃ and 750℃, the fiber draw ratio was 4.5% and the fiber residence time was 3 min.

[0072] High-temperature carbonization of low-density carbon fibers was performed in a high-temperature carbonization furnace under a nitrogen atmosphere, with three temperature zones: 1100℃, 1250℃, and 1400℃. The fiber draw ratio was -3.0%, and the fiber residence time was 3 minutes, resulting in the large-tow carbon fibers described above. The carbon fibers exhibited a tensile strength of 3.4 GPa and a tensile modulus of 246 GPa.

[0073] [Comparative Example 2]

[0074] 48K polyacrylonitrile fiber precursor (fineness 1.5dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-temperature zone pre-oxidation furnace. The tension of each temperature zone was controlled at 58N, 80N, 82N, and 83N, respectively, and the pre-oxidation temperatures of the four temperature zones were 190℃, 210℃, 230℃, and 245℃, respectively.

[0075] The pre-oxidized fiber was subjected to low-temperature carbonization treatment in three temperature zones in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each temperature zone were 450℃, 550℃ and 750℃, the fiber draw ratio was 4.5% and the fiber residence time was 3 min.

[0076] High-temperature carbonization of low-density carbon fibers was performed in a high-temperature carbonization furnace under a nitrogen atmosphere, with three temperature zones: 1100℃, 1250℃, and 1400℃. The fiber draw ratio was -3.0%, and the fiber residence time was 3 minutes, resulting in the large-tow carbon fibers described above. The carbon fibers exhibited a tensile strength of 2.9 GPa and a tensile modulus of 237 GPa.

[0077] [Comparative Example 3]

[0078] 48K polyacrylonitrile fiber precursor (fineness 1.5dtex, moisture content 2%) was pre-oxidized in an air atmosphere in a four-temperature zone pre-oxidation furnace. The tension of each temperature zone was controlled at 41N, 57N, 77N, and 83N, respectively, and the pre-oxidation temperatures of the four temperature zones were 190℃, 210℃, 230℃, and 245℃, respectively.

[0079] The pre-oxidized fiber was subjected to low-temperature carbonization treatment in three temperature zones in a low-temperature carbonization furnace under a nitrogen atmosphere. The temperatures of each temperature zone were 450℃, 550℃ and 750℃, the fiber draw ratio was 4.5% and the fiber residence time was 3 min.

[0080] High-temperature carbonization of low-density carbon fibers was performed in a high-temperature carbonization furnace under a nitrogen atmosphere, with three temperature zones: 1100℃, 1250℃, and 1400℃. The fiber draw ratio was -3.0%, and the fiber residence time was 3 minutes, resulting in the large-tow carbon fibers described above. The carbon fibers exhibited a tensile strength of 3.1 GPa and a tensile modulus of 247 GPa.

[0081] Obviously, by adopting the technical solution of the present invention, the concentrated exothermic process can be slowed down, avoiding the problem of melting and fiber breakage caused by concentrated exothermic heat. Moreover, the final product has better performance and is convenient for subsequent applications. It has great technical advantages and can be used in the industrial production of polyacrylonitrile-based large tow carbon fiber preparation process.

Claims

1. A method for preparing polyacrylonitrile-based large-tow carbon fibers, comprising: The steps of pre-oxidation treatment and carbonization treatment of polyacrylonitrile fiber precursor are as follows: In the pre-oxidation treatment, the relationship between the fiber tension value T and the number of fiber bundles B is: T=a×B, where T is the fiber tension value in N; B is the number of fiber bundles in thousands; and a is 0.5~1.7 in N / thousand. The pre-oxidation treatment includes pre-oxidation treatment in four temperature zones: In the first temperature zone, the fiber tension value T1 and the number of fiber bundles B satisfy T1 = (0.5~1.2) × B; In the second temperature zone, the fiber tension value T2 and the number of fiber bundles B satisfy T2 = (0.7~1.6) × B; In the third temperature zone, the fiber tension value T3 and the number of fiber bundles B satisfy T3 = (0.9~1.5) × B; In the fourth temperature zone, the fiber tension value T4 and the number of fiber bundles B satisfy T4 = (1.1~1.7) × B.

2. The preparation method according to claim 1, characterized in that, The aforementioned pre-oxidation treatment: In the first temperature zone, the fiber tension value T1 and the number of fiber bundles B satisfy T1 = (0.6~1.1) × B; In the second temperature zone, the fiber tension value T2 and the number of fiber bundles B satisfy T2 = (0.75~1.5) × B; In the third temperature zone, the fiber tension value T3 and the number of fiber bundles B satisfy T3 = (1~1.4) × B; In the fourth temperature zone, the fiber tension value T4 and the number of fiber bundles B satisfy T4 = (1.1~1.6) × B.

3. The preparation method according to claim 1, characterized in that, The number of polyacrylonitrile fiber filaments is at least 48,000; and / or, The moisture content of the polyacrylonitrile fiber precursor is less than or equal to 5 wt%; and / or, The linear density of the polyacrylonitrile fiber precursor is 0.3~3.5 dtex.

4. The preparation method according to claim 3, characterized in that, The number of polyacrylonitrile fiber precursors is 48,000 to 360,000; and / or, The moisture content of the polyacrylonitrile fiber precursor is less than or equal to 2 wt%; and / or, The linear density of the polyacrylonitrile fiber precursor is 0.5~2.5 dtex.

5. The preparation method according to claim 1, characterized in that, The preparation method specifically includes: (1) The polyacrylonitrile fiber precursor was subjected to a four-temperature zone pre-oxidation treatment using a pre-oxidation furnace. The pre-oxidized fiber was obtained by controlling the tension of the fiber in each temperature zone. (2) The obtained pre-oxidized fibers are subjected to low-temperature carbonization and high-temperature carbonization to obtain polyacrylonitrile-based large-tow carbon fibers.

6. The preparation method according to claim 5, characterized in that, In the aforementioned pre-oxidation treatment, the temperatures of the first to fourth temperature zones are 160–220℃, 180–240℃, 200–260℃, and 210–280℃, respectively; and / or, In the aforementioned pre-oxidation treatment, the pre-oxidation residence time in each temperature zone is 5–30 min.

7. The preparation method according to claim 6, characterized in that, In the aforementioned pre-oxidation treatment, the temperatures of the first to fourth temperature zones are 180–200℃, 200–220℃, 220–240℃, and 230–260℃, respectively; and / or, In the aforementioned pre-oxidation treatment, the pre-oxidation residence time in each temperature zone is 10–20 min.

8. The preparation method according to claim 5, characterized in that, The aforementioned low-temperature carbonization includes low-temperature carbonization treatment in three temperature zones; and / or, The high-temperature carbonization includes high-temperature carbonization treatment in three temperature zones.

9. The preparation method according to claim 8, characterized in that, In the aforementioned low-temperature carbonization, the carbonization temperatures in the first to third temperature zones are 350–550℃, 450–650℃, and 650–850℃, respectively; the draw ratio is 2–7%; and the fiber residence time is 1–15 min; and / or, The carbonization temperatures of the first to third temperature zones of the high-temperature carbonization are 1000–1250℃, 1200–1350℃, and 1300–1500℃, respectively; the draw ratio is -5.0 to -0.5%; and the fiber residence time is 1–15 min.

10. The preparation method according to claim 9, characterized in that, In the low-temperature carbonization, the carbonization temperatures in the first to third temperature zones are 380–500℃, 480–550℃, and 650–750℃, respectively; the draw ratio is 3–5%; the fiber residence time is 2–10 min; and / or, The carbonization temperatures of the first to third high-temperature carbonization zones are 1050–1150℃, 1200–1300℃, and 1350–1450℃, respectively; the draw ratio is -3.5 to -0.5%; and the fiber residence time is 2–10 min.

11. The preparation method according to any one of claims 1 to 10, characterized in that, The tensile strength of the polyacrylonitrile-based large-tow carbon fiber is ≥4.0 GPa, and the tensile modulus is ≥250 GPa.