Polyacrylonitrile-based pre-oxidized fiber, preparation method thereof and carbon fiber

Abstract

The invention provides a polyacrylonitrile-based pre-oxidized fiber, a preparation method thereof and a carbon fiber, and relates to the technical field of carbon fibers.The preparation method comprises the following steps that polyacrylonitrile precursors are subjected to dipping pretreatment in an antioxidant solution and then subjected to gradient pre-oxidation treatment, and the polyacrylonitrile-based pre-oxidized fiber is obtained; the temperature difference between adjacent pre-oxidation temperature intervals of the gradient pre-oxidation treatment is 20-50 DEG C. The technical problems of oxygen-containing structure regulation and radial structure non-uniformity of the pre-oxidized fiber in the prior art are solved, and the technical effects that the oxygen content is adjustable, the oxygen content is low, and the radial uniformity is good are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fibers, and in particular to a polyacrylonitrile-based pre-oxidized fiber and a preparation method thereof, and a carbon fiber. Background Art

[0002] Carbon fibers with a carbon content of more than 90% have both the excellent inherent properties of carbon graphite materials and the good processing capabilities of textile fibers, such as high strength, high modulus, good temperature resistance, excellent corrosion resistance and low density.

[0003] PAN (polyacrylonitrile) raw silk is pre-oxidized at 200℃-300℃ to obtain pre-oxidized fibers, which are then carbonized and graphitized to obtain carbon fibers. Pre-oxidation is a key link in the preparation of PAN-based carbon fibers; during this process, multiple chemical reactions such as cyclization, dehydrogenation and oxidation occur in the fibers, which transform the linear PAN molecules into a heat-resistant and stable ladder structure, generating a graphite-like structure sp 2 Initial plan structure.

[0004] During the pre-oxidation process, the degree of cyclization and oxidation reaction in the sheath of the fiber is higher than that in the core. The sheath first forms a dense structure, which will hinder the diffusion of oxygen to the core. This causes the pre-oxidized fiber to form different degrees of radial structural differences (skin-core structure); this radially uneven structure will be inherited to the carbon fiber, resulting in reduced mechanical properties of the carbon fiber. At the same time, during the subsequent carbonization process, the oxygen-containing structure is removed as small carbon-containing molecules such as CO and CO2 during thermal cracking. On the one hand, a higher oxygen-containing structure will lead to a lower fiber yield, and on the other hand, the sp 3 The number of disordered carbon atoms and fiber structure defects in the hybrid form will increase, eventually leading to a decrease in the order of the carbon fibers.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] One of the purposes of the present invention is to provide a method for preparing polyacrylonitrile-based pre-oxidized fibers, which can reduce the radial non-uniformity and oxygen-containing structure content of the pre-oxidized fibers.

[0007] The second object of the present invention is to provide a polyacrylonitrile-based pre-oxidized fiber, which has less oxygen-containing structure and less oxygen removal in the subsequent carbonization stage, which is conducive to a more regular carbonization structure.

[0008] A third object of the present invention is to provide a carbon fiber having high strength and modulus.

[0009] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0010] In a first aspect, a method for preparing polyacrylonitrile-based pre-oxidized fibers comprises the following steps:

[0011] The polyacrylonitrile precursor is firstly immersed in an antioxidant solution for pretreatment, and then subjected to a gradient preoxidation treatment to obtain the polyacrylonitrile-based preoxidized fiber;

[0012] The temperature difference between adjacent pre-oxidation temperature intervals in the gradient pre-oxidation treatment is 20°C-50°C.

[0013] Furthermore, the concentration of the antioxidant solution is 2 g / mL-20 g / mL.

[0014] Furthermore, the immersion time is 10s-120s.

[0015] Furthermore, the antioxidant solution includes at least one of an ascorbic acid solution, a tea polyphenol solution and a citric acid solution.

[0016] Furthermore, the pre-oxidation atmosphere includes air.

[0017] Furthermore, the pre-oxidation temperature is 150°C-300°C.

[0018] Furthermore, the pre-oxidation time is 30 min-120 min.

[0019] Furthermore, the gradient pre-oxidation treatment method comprises the following steps:

[0020] The pre-treated polyacrylonitrile precursor is sequentially treated in a first pre-oxidation temperature zone, a second pre-oxidation temperature zone, a third pre-oxidation temperature zone and a fourth pre-oxidation temperature zone to obtain the polyacrylonitrile-based pre-oxidized fiber;

[0021] The temperature range of the first pre-oxidation temperature zone is 150°C-210°C, the temperature range of the second pre-oxidation temperature zone is 200°C-240°C, the temperature range of the third pre-oxidation temperature zone is 230°C-270°C, and the temperature range of the fourth pre-oxidation temperature zone is 260°C-300°C.

[0022] In a second aspect, a polyacrylonitrile-based pre-oxidized fiber is prepared by any of the preparation methods described above.

[0023] In a third aspect, a carbon fiber is made from the above-mentioned polyacrylonitrile-based pre-oxidized fiber.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] The preparation method of polyacrylonitrile-based preoxidized fiber provided by the present invention comprises the following steps: firstly immersing polyacrylonitrile precursor in an antioxidant solution for pretreatment so that the precursor contains a large amount of antioxidant, and then performing gradient (multi-stage) preoxidation treatment (which may be in an air atmosphere) to form an annular trapezoidal structure; due to the presence of the antioxidant, the oxidation reaction is inhibited, so that the radial unevenness and oxygen-containing structure content of the preoxidized fiber are reduced; the preoxidized fiber with a low oxygen-containing structure has a better microstructure, and the annular trapezoidal structure is arranged more neatly; the less oxidation reaction in the initial stage of preoxidation also helps to improve the radial uniformity of the preoxidized fiber, which is beneficial to reducing the generation of the skin-core structure.

[0026] The polyacrylonitrile-based preoxidized fiber provided by the present invention has a less oxygen-containing structure, and less oxygen is removed in the subsequent carbonization stage, which is conducive to a more regular carbonization structure.

[0027] The carbon fiber provided by the invention has high strength and modulus. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] According to a first aspect of the present invention, there is provided a method for preparing polyacrylonitrile-based pre-oxidized fibers, comprising the following steps:

[0030] The polyacrylonitrile precursor is firstly immersed in an antioxidant solution for pretreatment, and then subjected to gradient preoxidation treatment to obtain polyacrylonitrile-based preoxidized fibers;

[0031] Wherein, the temperature difference between adjacent pre-oxidation temperature intervals of the gradient pre-oxidation treatment may be 20°C-50°C.

[0032] The preparation method of polyacrylonitrile-based preoxidized fiber provided by the present invention comprises the following steps: firstly immersing polyacrylonitrile precursor in an antioxidant solution for pretreatment so that the precursor contains a large amount of antioxidant, and then performing gradient (multi-stage) preoxidation treatment (which may be in an air atmosphere) to form an annular trapezoidal structure; due to the presence of the antioxidant, the oxidation reaction is inhibited, so that the radial unevenness and oxygen-containing structure content of the preoxidized fiber are reduced; the preoxidized fiber with a low oxygen-containing structure has a better microstructure, and the annular trapezoidal structure is arranged more neatly; the less oxidation reaction in the initial stage of preoxidation also helps to improve the radial uniformity of the preoxidized fiber, which is beneficial to reducing the generation of the skin-core structure.

[0033] In summary, compared with the traditional pre-oxidation method, the present invention first immerses the fiber in an antioxidant solution and then performs multi-stage pre-oxidation. With the coordinated cooperation of each step, the oxygen-containing structure of the obtained pre-oxidized fiber is significantly reduced, so that less oxygen is removed in the subsequent carbonization stage, which is conducive to a more regular carbonization structure and effectively improves the strength and modulus of the carbon fiber product.

[0034] In the present invention, typical but non-limiting temperature differences between adjacent pre-oxidation temperature intervals are, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C, which are more conducive to forming a neat annular trapezoidal structure arrangement; if the temperature difference between the pre-oxidation temperature intervals is too large, it will lead to a serious skin-core structure; if the temperature difference between the pre-oxidation temperature intervals is too small, it will lead to incomplete pre-oxidation structure transformation.

[0035] In a preferred embodiment, the concentration of the antioxidant solution can be 2g / mL-20g / mL, and its typical but non-limiting concentration is, for example, 2g / mL, 4g / mL, 6g / mL, 8g / mL, 10g / mL, 12g / mL, 14g / mL, 16g / mL, 18g / mL, and 20g / mL, which is more conducive to improving the radial unevenness of the pre-oxidized fiber and reducing the oxygen-containing structure of the pre-oxidized fiber; if the concentration is too high, it will lead to too low oxygen-containing structure, poor thermal stability of the pre-oxidized fiber, and is not conducive to subsequent carbonization; if the concentration is too low, it will lead to poor antioxidant effect and fail to achieve the expected effect.

[0036] In the present invention, the time for the polyacrylonitrile precursor to be immersed in the antioxidant solution can be 10s-120s, for example, 10s, 20s, 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, but not limited to this; the polyacrylonitrile precursor can be immersed at room temperature.

[0037] In a preferred embodiment, the antioxidant solution includes but is not limited to at least one of ascorbic acid solution, tea polyphenol solution and citric acid solution, which is more conducive to inhibiting the oxidation reaction, effectively improving the radial unevenness of the pre-oxidized fiber, and effectively reducing the oxygen-containing structure of the pre-oxidized fiber.

[0038] In the present invention, the atmosphere condition of the pre-oxidation may be an air atmosphere, but is not limited thereto.

[0039] In a preferred embodiment, the pre-oxidation temperature can be 150°C-300°C, and typical but non-limiting temperatures are, for example, 150°C, 200°C, 250°C, and 300°C; the pre-oxidation time can be 30min-120min, and typical but non-limiting times are, for example, 30min, 40min, 50min, 60min, 80min, 100min, and 120min.

[0040] In the present invention, the method of gradient pre-oxidation treatment comprises the following steps:

[0041] The pre-treated polyacrylonitrile precursor is sequentially treated in a first pre-oxidation temperature zone, a second pre-oxidation temperature zone, a third pre-oxidation temperature zone and a fourth pre-oxidation temperature zone to obtain polyacrylonitrile-based pre-oxidation fibers.

[0042] It should be noted that the present invention performs pre-oxidation treatment by gradient temperature increase, and the temperature of the first pre-oxidation temperature zone can be 150℃-210℃, for example, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, but not limited to this; the temperature of the second pre-oxidation temperature zone can be 200℃-240℃, for example, 200℃, 210℃, 220℃, 230℃, 240℃, but not limited to this; the temperature of the third pre-oxidation temperature zone can be 230℃-270℃, for example, 230℃, 240℃, 250℃, 260℃, 270℃, but not limited to this; the temperature of the fourth pre-oxidation temperature zone can be 260℃-300℃, for example, 260℃, 270℃, 280℃, 290℃, 300℃, but not limited to this.

[0043] According to a second aspect of the present invention, there is provided a polyacrylonitrile-based pre-oxidized fiber prepared by any of the preparation methods described above.

[0044] The polyacrylonitrile-based preoxidized fiber provided by the present invention has a less oxygen-containing structure, and less oxygen is removed in the subsequent carbonization stage, which is conducive to a more regular carbonization structure.

[0045] According to a third aspect of the present invention, there is provided a carbon fiber made from the above-mentioned polyacrylonitrile-based pre-oxidized fiber.

[0046] The carbon fiber provided by the invention has high strength and modulus.

[0047] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market.

[0048] Example 1

[0049] This embodiment provides a polyacrylonitrile-based carbon fiber, and its preparation method (process parameters are shown in Table 1) includes the following steps:

[0050] (a) immersing polyacrylonitrile precursor fibers in an ascorbic acid aqueous solution with a concentration of 10 g / mL (at room temperature) for 30 seconds to obtain pretreated precursor fibers;

[0051] (b) subjecting the pretreated raw silk to a gradient preoxidation treatment in an air atmosphere, sequentially passing through four preoxidation temperature zones, wherein the temperatures are 180° C., 220° C., 250° C. and 280° C., respectively, and the total preoxidation time is 90 min, thereby obtaining a polyacrylonitrile-based preoxidized fiber;

[0052] (c) Carbonizing the polyacrylonitrile-based pre-oxidized fibers to obtain carbon fibers.

[0053] Example 2

[0054] This embodiment provides a polyacrylonitrile-based carbon fiber, and its preparation method (process parameters are shown in Table 1) includes the following steps:

[0055] (a) immersing polyacrylonitrile precursor fibers in an ascorbic acid aqueous solution with a concentration of 10 g / mL (at room temperature) for 60 s to obtain pretreated precursor fibers;

[0056] (b) subjecting the pretreated raw silk to a gradient preoxidation treatment in an air atmosphere, sequentially passing through four preoxidation temperature zones, wherein the temperatures are 180° C., 220° C., 250° C. and 280° C., respectively, and the total preoxidation time is 90 min, thereby obtaining a polyacrylonitrile-based preoxidized fiber;

[0057] (c) Carbonizing the polyacrylonitrile-based pre-oxidized fibers to obtain carbon fibers.

[0058] Example 3

[0059] This embodiment provides a polyacrylonitrile-based carbon fiber, and its preparation method (process parameters are shown in Table 1) includes the following steps:

[0060] (a) immersing polyacrylonitrile precursor fibers in an ascorbic acid aqueous solution with a concentration of 10 g / mL (at room temperature) for 90 s to obtain pretreated precursor fibers;

[0061] (b) subjecting the pretreated raw silk to a gradient preoxidation treatment in an air atmosphere, sequentially passing through four preoxidation temperature zones, wherein the temperatures are 180° C., 220° C., 250° C. and 280° C., respectively, and the total preoxidation time is 90 min, thereby obtaining a polyacrylonitrile-based preoxidized fiber;

[0062] (c) Carbonizing the polyacrylonitrile-based pre-oxidized fibers to obtain carbon fibers.

[0063] Example 4

[0064] This embodiment provides a polyacrylonitrile-based carbon fiber, and its preparation method (process parameters are shown in Table 1) includes the following steps:

[0065] (a) immersing polyacrylonitrile precursor fibers in an ascorbic acid aqueous solution with a concentration of 5 g / mL (at room temperature) for 60 s to obtain pretreated precursor fibers;

[0066] (b) subjecting the pretreated raw silk to a gradient preoxidation treatment in an air atmosphere, sequentially passing through four preoxidation temperature zones, wherein the temperatures are 180° C., 220° C., 250° C. and 280° C., respectively, and the total preoxidation time is 90 min, thereby obtaining a polyacrylonitrile-based preoxidized fiber;

[0067] (c) Carbonizing the polyacrylonitrile-based pre-oxidized fibers to obtain carbon fibers.

[0068] Example 5

[0069] This embodiment provides a polyacrylonitrile-based carbon fiber, and its preparation method (process parameters are shown in Table 1) includes the following steps:

[0070] (a) The polyacrylonitrile precursor was immersed in an ascorbic acid aqueous solution with a concentration of 15 g / mL (room temperature) for 60 s to obtain a pretreated precursor;

[0071] (b) subjecting the pretreated raw silk to a gradient preoxidation treatment in an air atmosphere, sequentially passing through four preoxidation temperature zones, wherein the temperatures are 180° C., 220° C., 250° C. and 280° C., respectively, and the total preoxidation time is 90 min, thereby obtaining a polyacrylonitrile-based preoxidized fiber;

[0072] (c) Carbonizing the polyacrylonitrile-based pre-oxidized fibers to obtain carbon fibers.

[0073] Example 6

[0074] This embodiment provides a polyacrylonitrile-based carbon fiber, and its preparation method (process parameters are shown in Table 1) includes the following steps:

[0075] (a) immersing polyacrylonitrile precursor fibers in an ascorbic acid aqueous solution with a concentration of 10 g / mL (at room temperature) for 60 s to obtain pretreated precursor fibers;

[0076] (b) subjecting the pretreated raw silk to a gradient preoxidation treatment in an air atmosphere, sequentially passing through four preoxidation temperature zones, wherein the temperatures are 150° C., 200° C., 230° C. and 270° C., respectively, and the total preoxidation time is 90 min, thereby obtaining polyacrylonitrile-based preoxidized fibers;

[0077] (c) Carbonizing the polyacrylonitrile-based pre-oxidized fibers to obtain carbon fibers.

[0078] Example 7

[0079] This embodiment provides a polyacrylonitrile-based carbon fiber, and its preparation method (process parameters are shown in Table 1) includes the following steps:

[0080] (a) immersing polyacrylonitrile precursor fibers in an ascorbic acid aqueous solution with a concentration of 10 g / mL (at room temperature) for 60 s to obtain pretreated precursor fibers;

[0081] (b) subjecting the pretreated raw silk to a gradient preoxidation treatment in an air atmosphere, sequentially passing through four preoxidation temperature zones, wherein the temperatures are 200° C., 230° C., 260° C. and 290° C., respectively, and the total preoxidation time is 90 min, thereby obtaining a polyacrylonitrile-based preoxidized fiber;

[0082] (c) Carbonizing the polyacrylonitrile-based pre-oxidized fibers to obtain carbon fibers.

[0083] Example 8

[0084] This embodiment provides a polyacrylonitrile-based carbon fiber, and its preparation method (process parameters are shown in Table 1) includes the following steps:

[0085] (a) The polyacrylonitrile precursor was immersed in a 10 g / mL tea polyphenol aqueous solution (at room temperature) for 60 s to obtain a pretreated precursor;

[0086] (b) subjecting the pretreated raw silk to a gradient preoxidation treatment in an air atmosphere, sequentially passing through four preoxidation temperature zones, wherein the temperatures are 180° C., 220° C., 250° C. and 280° C., respectively, and the total preoxidation time is 90 min, thereby obtaining a polyacrylonitrile-based preoxidized fiber;

[0087] (c) Carbonizing the polyacrylonitrile-based pre-oxidized fibers to obtain carbon fibers.

[0088] Example 9

[0089] This embodiment provides a polyacrylonitrile-based carbon fiber, and its preparation method (process parameters are shown in Table 1) includes the following steps:

[0090] (a) The polyacrylonitrile precursor was immersed in a citric acid aqueous solution with a concentration of 10 g / mL (room temperature) for 60 s to obtain a pretreated precursor;

[0091] (b) subjecting the pretreated raw silk to a gradient preoxidation treatment in an air atmosphere, sequentially passing through four preoxidation temperature zones, wherein the temperatures are 180° C., 220° C., 250° C. and 280° C., respectively, and the total preoxidation time is 90 min, thereby obtaining a polyacrylonitrile-based preoxidized fiber;

[0092] (c) Carbonizing the polyacrylonitrile-based pre-oxidized fibers to obtain carbon fibers.

[0093] Table 1

[0094]

[0095] Comparative Example 1

[0096] The difference between this comparative example and Example 2 is that the polyacrylonitrile precursor is not subjected to an impregnation pretreatment, but the polyacrylonitrile precursor is directly subjected to a gradient preoxidation treatment;

[0097] The remaining steps and process parameters are the same as those in Example 1 to obtain carbon fiber.

[0098] Compared with Example 1, the defects of the carbon fiber obtained in this comparative example are that the radial structure difference is large and the tensile strength of the carbon fiber is low.

[0099] Comparative Example 2

[0100] The difference between this comparative example and Example 2 is that the pretreated raw silk is not subjected to a gradient pre-oxidation treatment, but a one-step pre-oxidation treatment, and the temperature of the one-step pre-oxidation treatment is 230°C;

[0101] The remaining steps and process parameters are the same as those in Example 1 to obtain carbon fiber.

[0102] Compared with Example 1, the defect of the carbon fiber obtained in this comparative example is that the tensile strength of the carbon fiber is extremely low.

[0103] Comparative Example 3

[0104] The difference between this comparative example and Example 2 is that the temperatures of the four pre-oxidation temperature zones through which the pre-treated raw silk passes are 180°C, 190°C, 250°C and 310°C respectively;

[0105] The remaining steps and process parameters are the same as those in Example 1 to obtain carbon fiber.

[0106] Compared with Example 1, the defects of the carbon fiber obtained in this comparative example are that the radial structure difference is large and the tensile strength of the carbon fiber is low.

[0107] Comparative Example 4

[0108] The difference between this comparative example and Example 2 is that the temperatures of the four pre-oxidation temperature zones through which the pre-treated raw silk passes are 180°C, 240°C, 250°C and 260°C respectively;

[0109] The remaining steps and process parameters are the same as those in Example 1 to obtain carbon fiber.

[0110] Compared with Example 1, the defects of the carbon fiber obtained in this comparative example are that the radial structure difference is large and the tensile strength of the carbon fiber is low.

[0111] Test example

[0112] The data of oxygen content, skin-core structure and tensile strength of the pre-oxidized fibers obtained in Examples 1-9 and Comparative Examples 1-4 are shown in Table 2.

[0113] Test method for oxygen content of pre-oxidized fiber: the pre-oxidized fiber is made into powdered short fiber, and the test amount is between 2-3 mg; the O mode of the Thermo FlashSmart elemental analyzer is used to determine the percentage content of elemental oxygen.

[0114] Testing method for the skin-core structure of pre-oxidized fibers: Epoxy resin embedding section method is used to observe and measure the skin-core structure of the fiber under an optical microscope at a magnification of 1000 times.

[0115] Test standard for tensile strength of carbon fiber: refer to GB / T 3362.

[0116] Table 2 Comparison of pre-oxidized fiber and carbon fiber

[0117]

[0118] It can be seen that the preparation method of polyacrylonitrile-based pre-oxidized fibers with controllable oxygen content provided by the present invention can achieve the effects of adjustable oxygen content and good radial uniformity, and solves the problems of oxygen-containing structure regulation and radial structural unevenness of pre-oxidized fibers.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing polyacrylonitrile-based pre-oxidized fiber, characterized in that: The following steps are involved: The polyacrylonitrile precursor is firstly immersed in an antioxidant solution for pretreatment, and then subjected to a gradient preoxidation treatment to obtain the polyacrylonitrile-based preoxidized fiber; The temperature difference between adjacent pre-oxidation temperature intervals in the gradient pre-oxidation treatment is 20°C-50°C.

2. The preparation method according to claim 1, characterized in that: The concentration of the antioxidant solution is 2 g / mL-20 g / mL.

3. The preparation method according to claim 2, characterized in that: The immersion time is 10s-120s.

4. The preparation method according to claim 2, characterized in that: The antioxidant solution includes at least one of an ascorbic acid solution, a tea polyphenol solution and a citric acid solution.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The pre-oxidation atmosphere includes air.

6. The preparation method according to claim 5, characterized in that: The pre-oxidation temperature is 150°C-300°C.

7. The preparation method according to claim 6, characterized in that: The pre-oxidation time is 30 min-120 min.

8. The preparation method according to claim 7, characterized in that: The method for gradient pre-oxidation treatment comprises the following steps: The pre-treated polyacrylonitrile precursor is sequentially treated in a first pre-oxidation temperature zone, a second pre-oxidation temperature zone, a third pre-oxidation temperature zone and a fourth pre-oxidation temperature zone to obtain the polyacrylonitrile-based pre-oxidized fiber; The temperature range of the first pre-oxidation temperature zone is 150°C-210°C, the temperature range of the second pre-oxidation temperature zone is 200°C-240°C, the temperature range of the third pre-oxidation temperature zone is 230°C-270°C, and the temperature range of the fourth pre-oxidation temperature zone is 260°C-300°C.

9. A polyacrylonitrile-based pre-oxidized fiber prepared by the preparation method according to any one of claims 1 to 8.

10. A carbon fiber, characterized in that: It is made from the polyacrylonitrile-based pre-oxidized fiber described in claim 9.

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