Polyacrylonitrile preoxidized yarn and preparation method thereof, polyacrylonitrile carbon fiber

Abstract

The present application relates to a polyacrylonitrile preoxidized yarn and a preparation method thereof, as well as polyacrylonitrile carbon fibers, belonging to the technical field of carbon fiber manufacturing. The preparation method comprises the following steps: copolymerizing acrylonitrile and a modifier to obtain a polyacrylonitrile polymer solution; wherein the modifier is a vinyl phenol compound; spinning the polyacrylonitrile polymer solution to obtain polyacrylonitrile precursor; and preoxidizing the polyacrylonitrile precursor to obtain the polyacrylonitrile preoxidized yarn. By introducing a vinyl phenol compound and copolymerizing with acrylonitrile for modification, the preoxidation cyclization reaction of the polyacrylonitrile precursor fiber can be promoted, the initial exothermic temperature of the polyacrylonitrile precursor can be reduced, the skin-core phenomenon of the polyacrylonitrile preoxidized yarn can be improved, and the strength of the carbon fiber can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of carbon fiber manufacturing, and in particular to a polyacrylonitrile preoxidized yarn and a preparation method thereof, and polyacrylonitrile carbon fiber. Background Art

[0002] Carbon fiber has excellent mechanical properties, especially high specific strength and specific elastic modulus, and is widely used as a reinforcing material in the aerospace industry, the automotive industry, and the leisure products industry. In addition, due to its excellent mechanical properties, it can reduce the weight of aircraft, automobiles, etc., and has received widespread attention as a means of reducing carbon dioxide in aircraft and automobile operation scenarios. At present, most carbon fibers are made from polyacrylonitrile (PAN) as raw material, and are made through stages such as spinning, pre-oxidation, and carbonization. Among them, pre-oxidation is an important stage in the production process of polyacrylonitrile-based carbon fibers. During the pre-oxidation process, the original polyacrylonitrile linear molecular chain is gradually converted into a heat-resistant trapezoidal structure through cyclization, oxidation, and dehydrogenation. The lower the initial exothermic temperature (Ti) in this process, the more likely the polyacrylonitrile precursor will undergo a cyclization reaction at a lower temperature, which can avoid the generation of defects caused by concentrated heat release, thereby improving the mechanical properties of the carbon fiber.

[0003] To reduce the initial exotherm temperature of polyacrylonitrile precursor, most existing studies have adopted the method of impregnation modification of polyacrylonitrile precursor, such as impregnating polyacrylonitrile in boric acid solution. Although this can improve the elastic modulus of carbon fiber to a certain extent, it cannot significantly improve the tensile strength of carbon fiber. This is because during the pre-oxidation process, the fiber sheath soaked in the modifier will gradually form a stable structure. The dense cortex blocks the diffusion of oxygen, resulting in a poor pre-oxidation degree of the core, forming a skin-core structure. The loose core is prone to form holes during the subsequent carbonization process, which seriously reduces the quality of the carbon fiber and thus affects the strength of the carbon fiber. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of the embodiments of the present application includes providing a polyacrylonitrile pre-oxidized yarn and a preparation method thereof, as well as a polyacrylonitrile carbon fiber prepared from the polyacrylonitrile pre-oxidized yarn. By lowering the initial exothermic temperature of the polyacrylonitrile precursor and improving the "skin-core phenomenon" of the polyacrylonitrile pre-oxidized yarn, the strength of the polyacrylonitrile carbon fiber can be effectively improved.

[0005] In a first aspect, the present application provides a method for preparing polyacrylonitrile pre-oxidized yarn, comprising the following steps:

[0006] acrylonitrile and a modifier are copolymerized to obtain a polyacrylonitrile polymer solution; wherein the modifier is a vinyl phenol compound;

[0007] Spinning polyacrylonitrile polymer solution to obtain polyacrylonitrile precursor;

[0008] The polyacrylonitrile precursor is subjected to a pre-oxidation treatment to obtain the polyacrylonitrile pre-oxidized yarn.

[0009] In the above technical solution, the present invention utilizes a modifier to copolymerize with acrylonitrile, distributing the modifier throughout the PAN molecular chain. This modifier, containing phenolic hydroxyl groups, readily forms oxygen anions during pre-oxidation, inducing cyclization of cyano groups at relatively low temperatures and lowering the initial exothermic temperature of the PAN precursor. Furthermore, the copolymerization modification of PAN allows the modifier to penetrate the interior of the precursor fiber, promoting cyclization in the core during pre-oxidation. Furthermore, the presence of the modifier provides a pathway for oxygen molecules to penetrate the core, accelerating the oxidation reaction from the cortex to the core, thereby improving the skin-core structure of the pre-oxidized PAN yarn.

[0010] Secondly, the modifier in the molecular chain can promote the cyclization reaction to occur in advance, so that the exothermic range in the pre-oxidation process is widened, the exothermic reaction of pre-oxidation is alleviated, the sudden temperature rise and local heat accumulation of the fiber are avoided, the chance of main bond rupture and chain breakage is reduced, the uniformity and integrity of the fiber structure are maintained, and the cyclization oxidation structure is more perfect, thereby improving the quality and mechanical properties of the fiber.

[0011] Thirdly, the tensile strength of carbon fiber mainly depends on the degree of intramolecular chemical reaction, intramolecular bonding force, molecular chain orientation and the number of defects produced during the pre-oxidation treatment of the precursor. After modification, the pre-oxidation process is relatively mild, the molecular structure and grain structure are relatively complete, and fewer defects are produced during the carbonization process, thereby greatly improving the tensile strength of the fiber.

[0012] In some embodiments of the present application, the vinylphenol compound includes at least one of 2-methoxy-4-vinylphenol, 4-vinylphenol, resveratrol, salvianolic acid, or 6-vinyl-2-naphthol.

[0013] In the above technical solution, specific monomers with double bonds and phenolic hydroxyl groups are selected, which are more likely to form oxygen anions during pre-oxidation, inducing cyclization reaction of cyano groups, and the larger groups provide double diffusion channels, which is beneficial to improving the degree of internal pre-oxidation.

[0014] In some embodiments of the present application, the amount of the modifier used is 0.2 wt%-5.0 wt% of the total weight of the monomers.

[0015] In the above technical solution, by controlling the amount of the modifier within a certain range, the modification effect and cost can be effectively regulated.

[0016] In some embodiments of the present application, a method for preparing a polyacrylonitrile polymerization solution includes: copolymerizing acrylonitrile, a modifier, a comonomer, and an initiator in a solvent;

[0017] Wherein, the comonomer is a vinyl ester compound;

[0018] The initiator includes at least one of azobisisobutyronitrile or azobisisoheptanenitrile;

[0019] Optionally, the solvent includes at least one of dimethyl sulfoxide, dimethylformamide or dimethylacetamide.

[0020] In some embodiments of the present application, the added amount of the comonomer accounts for 8 wt%-12 wt% of the total mass of acrylonitrile, the modifier and the comonomer.

[0021] In the above technical solution, by introducing a comonomer and carrying out copolymerization reaction together with acrylonitrile and a modifier, a double diffusion channel can be provided during pre-oxidation, which can effectively control the exothermic reaction during the pre-oxidation process.

[0022] In some embodiments of the present application, the temperature of the pre-oxidation treatment is 200-260° C., and the time is 80-110 minutes.

[0023] In some embodiments of the present application, the pre-oxidation treatment includes:

[0024] The polyacrylonitrile precursor is passed through the first pre-oxidation temperature zone, the second pre-oxidation temperature zone and the third pre-oxidation temperature zone in sequence; wherein, the temperature of the first pre-oxidation temperature zone is 200-220°C, and the residence time is 30-40min; the temperature of the second pre-oxidation temperature zone is 220-240°C, and the residence time is 30-40min; the temperature of the third pre-oxidation temperature zone is 245-255°C, and the residence time is 20-30min.

[0025] In some embodiments of the present application, the spinning method is wet spinning or dry-jet wet spinning. Preferably, the spinning method is dry-jet wet spinning.

[0026] In some embodiments of the present application, after the copolymerization reaction, the further step includes: performing desinging and degassing treatment on the polyacrylonitrile polymerization liquid to obtain a homogeneous polyacrylonitrile polymerization liquid.

[0027] Through the removal of monomers and degassing treatment, the unreacted monomers remaining in the copolymerization reaction can be removed and the structural defects of the polyacrylonitrile precursor can be reduced.

[0028] In a second aspect, an embodiment of the present application provides a polyacrylonitrile pre-oxidized yarn prepared by the above-mentioned preparation method.

[0029] In a third aspect, an embodiment of the present application further provides a polyacrylonitrile carbon fiber, which is prepared by carbonizing the above-mentioned polyacrylonitrile pre-oxidized yarn.

[0030] By copolymerizing and modifying polyacrylonitrile, the initial exothermic temperature of the polyacrylonitrile precursor is reduced, and the pre-oxidation cyclization reaction is promoted. The cyclization degree of the prepared polyacrylonitrile pre-oxidized yarn is significantly increased, and the skin-core structure is significantly improved. The tensile strength of the polyacrylonitrile carbon fiber prepared from the polyacrylonitrile pre-oxidized yarn is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 A process flow chart of the method for preparing polyacrylonitrile pre-oxidized yarn provided in an embodiment of the present application;

[0033] Figure 2 This is a scanning electron microscope cross-sectional view of the polyacrylonitrile pre-oxidized yarn prepared in Example 1 of the present application at a magnification of 5000;

[0034] Figure 3 This is a scanning electron microscope cross-sectional view of the polyacrylonitrile pre-oxidized yarn prepared in Example 2 of the present application at a magnification of 5000;

[0035] Figure 4 This is a scanning electron microscope cross-sectional view of the polyacrylonitrile pre-oxidized yarn prepared in Example 3 of the present application at a magnification of 5000;

[0036] Figure 5 This is a scanning electron microscope cross-sectional view of the polyacrylonitrile pre-oxidized yarn prepared in Example 4 of the present application at a magnification of 5000;

[0037] Figure 6 This is a scanning electron microscope cross-sectional view of the polyacrylonitrile pre-oxidized yarn prepared in Example 5 of the present application at a magnification of 5000;

[0038] Figure 7 This is a scanning electron microscope cross-sectional view of the polyacrylonitrile pre-oxidized yarn prepared in Example 6 of the present application at a magnification of 5000;

[0039] Figure 8 This is a scanning electron microscope cross-sectional view of the polyacrylonitrile pre-oxidized yarn prepared in Comparative Example 1 of the present application at a magnification of 5000. DETAILED DESCRIPTION

[0040] Figure 1 This is a process flow chart of the method for preparing polyacrylonitrile pre-oxidized yarn provided in the embodiment of this application. Figure 1The method for preparing polyacrylonitrile pre-oxidized yarn provided in this application comprises the following steps:

[0041] S110, copolymerizing acrylonitrile and a modifier to obtain a polyacrylonitrile polymerization liquid; wherein the modifier is a vinyl phenol compound.

[0042] The vinylphenol compound includes at least one of 2-methoxy-4-vinylphenol, 4-vinylphenol, resveratrol, salvianolic acid or 6-vinyl-2-naphthol. Preferably, the vinylphenol compound is 4-vinylphenol or 2-methoxy-4-vinylphenol.

[0043] The amount of the modifier used is 0.2 wt% to 5.0 wt% of the total mass of the modifier and acrylonitrile. For example, the mass concentration of the modifier in the copolymerization reaction system can be 0.2 wt%, 0.5 wt%, 2.5 wt%, or 5.0 wt%.

[0044] In the embodiment of the present application, the preparation process of the polyacrylonitrile polymerization solution may specifically include: copolymerizing acrylonitrile, a modifier, a comonomer and an initiator in a solvent.

[0045] The comonomer is a vinyl ester compound. For example, the comonomer may be vinyl acetate, methyl methacrylate, etc. The amount of the comonomer added accounts for 8wt%-12wt% of the total weight of the monomers.

[0046] By introducing a comonomer, the exothermic reaction during the pre-oxidation process can be effectively controlled. The comonomer used in the embodiments of the present application has a large side group, which can provide a dual diffusion channel during pre-oxidation, facilitating the core pre-oxidation reaction and heat removal.

[0047] It can be understood that when the copolymerization system further includes a comonomer, the amount of the modifier used accounts for 0.2 wt% to 5.0 wt% of the total mass of acrylonitrile, the modifier and the comonomer.

[0048] The initiator may include at least one of azobisisobutyronitrile or azobisisoheptanenitrile, and the solvent may include at least one of dimethyl sulfoxide, dimethylformamide, or dimethylacetamide. The initiator and solvent may be selected from the above raw materials, one or more of which may be selected. Preferably, azobisisobutyronitrile is the initiator, and dimethyl sulfoxide is the solvent.

[0049] As an example, the copolymerization reaction may be: using dimethyl sulfoxide as a solvent, azobisisobutyronitrile as an initiator, and acrylonitrile, methyl methacrylate and 4-vinylphenol to carry out a copolymerization reaction.

[0050] The reaction temperature of the copolymerization reaction may be 60-80° C. and the reaction time may be 10-20 hours to promote the polymerization reaction to proceed fully. For example, the reaction temperature may be 80° C. and the reaction time may be 15 hours.

[0051] After the copolymerization reaction, the method may further include: performing desing and degassing treatments on the polyacrylonitrile polymerization liquid to obtain a homogeneous polyacrylonitrile polymerization liquid.

[0052] The deaeration and degassing process involves transferring the polyacrylonitrile polymer solution to a deaeration reactor to remove unreacted acrylonitrile, followed by a degassing reactor to remove air bubbles. Through meticulous control of the deaeration and degassing processes, a high-quality, homogeneous polymer solution can be obtained, minimizing gels and impurities that can cause structural defects in the precursor yarn.

[0053] Preferably, the solid content of the homogeneous polyacrylonitrile polymer solution after the desing and degassing treatment is 18 wt%-20 wt%, which is more conducive to subsequent spinning.

[0054] S120, spinning the polyacrylonitrile polymer solution to obtain polyacrylonitrile precursor.

[0055] The spinning process can be wet spinning or dry-jet wet spinning. Preferably, the spinning process is dry-jet wet spinning. The fiber precursor produced by the dry-jet wet spinning process has a smooth surface and few defects, which is the basis of high-strength carbon fiber.

[0056] Specifically, a dry-wet spray forming process can be used to spin a homogeneous polymer solution, and polyacrylonitrile precursor can be obtained through the following process steps: water washing, hot water drawing, drying, steam drawing and oiling.

[0057] S130, pre-oxidizing the polyacrylonitrile precursor to obtain pre-oxidized polyacrylonitrile yarn.

[0058] The pre-oxidation process includes treating the polyacrylonitrile precursor at 200-260°C for 80-110 minutes. Preferably, the polyacrylonitrile precursor undergoes a first pre-oxidation, a second pre-oxidation, and a third pre-oxidation in sequence. The first pre-oxidation treatment is performed at a temperature of 200-220°C for 30-40 minutes; the second pre-oxidation treatment is performed at a temperature of 220-240°C for 30-40 minutes; and the third pre-oxidation treatment is performed at a temperature of 245-255°C for 20-30 minutes.

[0059] It should be noted that the pre-oxidation temperature and its distribution are key process parameters that affect the degree of fiber pre-oxidation, which in turn affects mechanical properties such as tensile strength and modulus of the carbon fiber. The present embodiment controls the specific temperature and gradient distribution during the pre-oxidation process to ensure sufficient fiber pre-oxidation, complete the molecular structure of the ladder polymer, and improve the performance of the polyacrylonitrile pre-oxidized yarn.

[0060] The above preparation method uses a specific modifier to copolymerize with acrylonitrile to modify the modifier so that the modifier is distributed in the PAN molecular chain, which can reduce the initial exothermic temperature of PAN pre-oxidation, alleviate the exothermic reaction of pre-oxidation, and improve the skin-core structure of PAN pre-oxidation fiber, thereby effectively improving the strength of carbon fiber.

[0061] In addition, the present application also provides a polyacrylonitrile pre-oxidized yarn prepared by the above preparation method. The polyacrylonitrile pre-oxidized yarn can be subjected to carbonization treatment and post-treatment to prepare polyacrylonitrile carbon fibers, and the prepared carbon fibers have excellent mechanical properties.

[0062] The carbonization treatment may be a multi-stage carbonization, such as sequentially performing low-temperature carbonization and high-temperature carbonization. The temperature range of the low-temperature carbonization may be 300-900°C, and the temperature range of the high-temperature carbonization may be 1000-1600°C.

[0063] It can be understood that after the carbonization treatment, the carbonized fibers may be subjected to surface treatment and some other post-treatment processes.

[0064] The surface treatment may be conventional electrochemical anodizing. Other post-treatment processes may include washing, sizing, drying, winding, etc.

[0065] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0066] Example 1

[0067] This embodiment provides a polyacrylonitrile preoxidized yarn and a preparation method thereof, as well as a polyacrylonitrile carbon fiber prepared from the polyacrylonitrile preoxidized yarn. The preparation method includes the following steps:

[0068] (1) Using dimethyl sulfoxide as solvent and azobisisobutyronitrile as initiator, acrylonitrile, methyl methacrylate, and 0.2 wt% of 4-vinylphenol, based on the total weight of the monomers, were mixed and copolymerized in a polymerization reactor at 80°C for 15 h to produce a polyacrylonitrile polymerization solution having a solid content of 17 wt%. The polyacrylonitrile polymerization solution was directly transferred to a deaeration reactor to remove unreacted acrylonitrile, and finally to a degassing reactor to remove bubbles, thereby producing a homogeneous polyacrylonitrile polymerization solution having a solid content of 18 wt%.

[0069] (2) The homogeneous polyacrylonitrile polymer solution is spun by dry-jet wet spinning technology to produce polyacrylonitrile raw yarn with a fineness of 0.76 dtex.

[0070] (3) The polyacrylonitrile precursor is sequentially subjected to pre-oxidation treatment in a first pre-oxidation temperature zone, a second pre-oxidation temperature zone, and a third pre-oxidation temperature zone. The temperature in the first pre-oxidation temperature zone is 215°C, the residence time is 30 minutes, the temperature in the second pre-oxidation temperature zone is 230°C, the residence time is 30 minutes, and the temperature in the third pre-oxidation temperature zone is 245°C, the residence time is 25 minutes, and the polyacrylonitrile pre-oxidation yarn is obtained.

[0071] (4) The polyacrylonitrile pre-oxidized filaments prepared above are subjected to carbonization treatment to obtain polyacrylonitrile carbon fibers.

[0072] Example 2

[0073] This embodiment provides a polyacrylonitrile preoxidized yarn and a preparation method thereof, as well as a polyacrylonitrile carbon fiber prepared from the polyacrylonitrile preoxidized yarn. The preparation method is substantially the same as that in Example 1, except that the mass concentration of the modifier 4-vinylphenol in step (1) is 0.5 wt%.

[0074] Example 3

[0075] This embodiment provides a polyacrylonitrile preoxidized yarn and a preparation method thereof, as well as a polyacrylonitrile carbon fiber prepared from the polyacrylonitrile preoxidized yarn. The preparation method is substantially the same as that in Example 1, except that the mass concentration of the modifier 4-vinylphenol in step (1) is 2.5 wt%.

[0076] Example 4

[0077] This embodiment provides a polyacrylonitrile preoxidized yarn and a preparation method thereof, as well as a polyacrylonitrile carbon fiber prepared from the polyacrylonitrile preoxidized yarn. The preparation method is substantially the same as that in Example 1, except that the mass concentration of the modifier 4-vinylphenol in step (1) is 5.0 wt%.

[0078] Example 5

[0079] This embodiment provides a polyacrylonitrile preoxidized yarn and a preparation method thereof, as well as a polyacrylonitrile carbon fiber prepared from the polyacrylonitrile preoxidized yarn. The preparation method is substantially the same as that of Example 4, except that the modifier in step (1) is 2-methoxy-4-vinylphenol.

[0080] Example 6

[0081] This embodiment provides a polyacrylonitrile preoxidized yarn and a preparation method thereof, as well as a polyacrylonitrile carbon fiber prepared from the polyacrylonitrile preoxidized yarn. The preparation method is substantially the same as that of Example 4, except that methyl methacrylate is not added in step (1).

[0082] Comparative Example 1

[0083] This comparative example provides a polyacrylonitrile preoxidized yarn and a preparation method thereof, as well as a polyacrylonitrile carbon fiber prepared from the polyacrylonitrile preoxidized yarn. The preparation method is substantially the same as that in Example 1, except that the modifier 4-vinylphenol is not added in step (1).

[0084] Test example

[0085] The polyacrylonitrile precursors prepared in the examples and comparative examples were tested for their initial exothermic temperature, cyclization degree, and cross-sectional morphology. The tensile strength of the polyacrylonitrile carbon fibers was also tested. The specific test methods are as follows:

[0086] (1) Onset exotherm temperature: Differential scanning calorimetry (DSC) was used to measure the heat release. A 3-5 mg polyacrylonitrile precursor sample was heated from 30°C to 450°C at a rate of 10°C / min in an air atmosphere at 60 mL / min, and the heat flow was recorded as a function of temperature.

[0087] (2) Cyclization degree: After the dried polyacrylonitrile pre-oxidized silk was chopped, KBr and polyacrylonitrile pre-oxidized silk were mixed and ground at a mass ratio of 200:5 to prepare KBr pellets for infrared analysis. IC≡N is the characteristic absorption peak intensity of cyano group, corresponding to the wave number 2240 cm -1 IC=N is the characteristic absorption peak intensity of C=N, corresponding to the wave number 1580cm -1 .

[0088] (3) Cross-sectional morphology: Dry polyacrylonitrile pre-oxidized wire was broken and fixed to a cylindrical sample holder using an appropriate amount of conductive adhesive. The pre-oxidized wire was gold-sprayed using an ion sputtering apparatus with a current of 12 μA and a duration of 70 s, and then subjected to scanning electron microscopy (SEM) testing.

[0089] (4) Tensile strength: tested according to GB / T3362 test standard.

[0090] The above performance test results are shown in Table 1 and Figure 2-8 .

[0091] Table 1

[0092]

[0093]

[0094] As can be seen from Table 1, compared with the unmodified comparative example 1, the pre-oxidation initial exothermic temperature of Examples 1-6 is lower, which promotes the cyclization reaction of the precursor and increases the corresponding cyclization degree. Figures 2 to 7From the scanning electron microscope cross-sectional view of the polyacrylonitrile pre-oxidized yarn, it can be seen that compared with the unmodified polyacrylonitrile pre-oxidized yarn in Comparative Example 1, the skin-core phenomenon of the copolymerized modified polyacrylonitrile pre-oxidized yarn in Examples 1-6 is significantly improved, and the core is denser. And as the amount of modifier increases, the improvement effect is better. In addition, the tensile strength of the polyacrylonitrile carbon fiber prepared from the polyacrylonitrile pre-oxidized yarn by carbonization treatment is significantly improved. Among them, compared with the unmodified polyacrylonitrile carbon fiber prepared in Comparative Example 1, the tensile strength of the polyacrylonitrile carbon fiber in Example 4 is increased by about 20%.

[0095] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A method for preparing polyacrylonitrile pre-oxidized yarn, characterized in that: The steps include: A polyacrylonitrile and a modifier are copolymerized to obtain a polyacrylonitrile polymer solution; wherein the modifier is a vinyl phenol compound, and the vinyl phenol compound includes at least one of 2-methoxy-4-vinylphenol, 4-vinylphenol, resveratrol, salvianolic acid, or 6-vinyl-2-naphthol; Spinning the polyacrylonitrile polymer solution to obtain polyacrylonitrile precursor; The polyacrylonitrile precursor is subjected to a pre-oxidation treatment to obtain the polyacrylonitrile pre-oxidized yarn.

2. The preparation method according to claim 1, characterized in that The amount of the modifier used accounts for 0.2 wt% to 5.0 wt% of the total mass of the acrylonitrile and the modifier.

3. The preparation method according to claim 1, characterized in that The preparation method of the polyacrylonitrile polymerization liquid comprises: copolymerizing the acrylonitrile, the modifier, the comonomer and the initiator in a solvent; Wherein, the comonomer is a vinyl ester compound, and the vinyl ester compound includes at least one of vinyl acetate or methyl methacrylate; The initiator includes at least one of azobisisobutyronitrile and azobisisoheptanenitrile.

4. The preparation method according to claim 3, characterized in that The solvent includes at least one of dimethyl sulfoxide, dimethylformamide or dimethylacetamide.

5. The preparation method according to claim 3, characterized in that The added amount of the comonomer accounts for 8 wt % to 12 wt % of the total mass of the acrylonitrile, the modifier and the comonomer.

6. The preparation method according to claim 1, characterized in that The temperature of the pre-oxidation treatment is 200-260° C., and the time is 80-110 minutes.

7. The preparation method according to claim 6, characterized in that The pre-oxidation treatment comprises: The polyacrylonitrile precursor is sequentially passed through a first pre-oxidation temperature zone, a second pre-oxidation temperature zone and a third pre-oxidation temperature zone; wherein, the temperature of the first pre-oxidation temperature zone is 200-220°C, and the residence time is 30-40 minutes; the temperature of the second pre-oxidation temperature zone is 220-240°C, and the residence time is 30-40 minutes; the temperature of the third pre-oxidation temperature zone is 245-255°C, and the residence time is 20-30 minutes.

8. The preparation method according to claim 1, characterized in that The spinning method is wet spinning or dry-jet wet spinning.

9. A polyacrylonitrile pre-oxidized yarn, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. A polyacrylonitrile carbon fiber, characterized in that: The polyacrylonitrile pre-oxidized fiber is prepared by carbonizing the polyacrylonitrile pre-oxidized fiber described in claim 9.

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