Preparation method of high-temperature resistant polyacrylonitrile-based carbon fiber and its application in fireproof fabric

Abstract

The present invention provides a method for preparing high-temperature resistant polyacrylonitrile-based carbon fibers and their application in fireproof fabrics. By adding 2-acrylamido-2-methylpropanesulfonic acid, the limiting oxygen index of the pre-oxidized fibers is increased, enhancing the fireproof performance; by impregnating with perfluorolauryl alcohol polyoxyethylene ether and spraying carbon powder, the coalescence rate of the pre-oxidized fibers is reduced; by spraying basic aluminum chloride, the crimp number of the pre-oxidized fibers is increased, improving the flexibility; by adding hydrogen bromide in oxygen, the oxidation rate and the limiting oxygen index are increased; the pre-oxidation reaction is carried out by means of radiation heating to inhibit the formation of skin-core structure; through the action of ultrasonic waves, the tarry impurities deposited on the surface of the pre-oxidized fibers are removed, improving the quality of the carbon fibers; by treating the pre-oxidized fibers with sodium β-anthraquinonesulfonate, the oxygen absorbed by the pre-oxidized fibers is removed, improving the tensile strength of the carbon fibers; thus, high-temperature resistant and high-strength carbon fibers are prepared and applied to fireproof fabrics.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fibers, and particularly to a preparation method of high-temperature resistant polyacrylonitrile-based carbon fibers and their application in fireproof fabrics. Background Art

[0002] Polyacrylonitrile-based carbon fibers and their composites have the characteristics of high strength and light weight, and are increasingly used as structural materials in fields such as automobiles, sports, aviation, tools, and military equipment. The preparation process of polyacrylonitrile-based carbon fibers mainly includes processes such as monomer polymerization, spinning and solidification, pre-oxidation, and high-temperature carbonization.

[0003] The acrylonitrile-based polymer solidifies from the outside to the inside during the spinning process. The surface layer of the fiber contacts the solidification liquid and solidifies first; the inner core of the fiber solidifies at a slower rate. The previously solidified surface layer further reduces the rate of diffusion of the solidification bath liquid into the inner core of the fiber, and at the same time inhibits the diffusion of the solidification bath liquid from the fiber, resulting in a "skin-core" effect, which causes the fiber to exhibit micron-scale uneven pores and reduces the fiber quality.

[0004] During the pre-oxidation process, linear macromolecular chains undergo reactions such as cyclization, oxidation, and dehydrogenation to form an insoluble and infusible fiber with a heat-resistant ladder structure, which is a crucial link connecting the previous and the next in the preparation of carbon fibers and has an important impact on the structure and properties of the final carbon fibers. The pre-oxidation process usually adopts the method of furnace box heating, heating the spun fiber in hot air at 180°C to 400°C for reaction to achieve the purpose of pre-oxidation. However, the following problems still need to be solved in the pre-oxidation process:

[0005] (1) The pre-oxidation reaction is usually carried out in a high-temperature oven or furnace, with a temperature of 180°C to 400°C and a time of 1 hour to 3 hours, which is energy-consuming, time-consuming, and the manufacturing cost of carbon fibers is relatively high.

[0006] (2) During the pre-oxidation reaction, heat conducts from the surface layer of the fiber to the inner core of the fiber, resulting in excessive oxidation of the fiber surface layer and insufficient oxidation of the inner core of the fiber, presenting a skin-core structure with uneven pre-oxidation degrees on the surface layer and the inner core. The skin-core structure will be inherited by the subsequent carbonization treatment, increasing the structural defects of the carbon fiber and restricting the improvement of mechanical properties.

[0007] (3) Due to the relatively high pre-oxidation temperature, the fibers are prone to coalescence, resulting in poor quality of the carbon fibers.

[0008] (4) When pre-oxidizing at a high temperature, the fibers become brittle and their flexibility decreases. When pre-oxidized and curled, they are prone to breakage and have poor spinnability.

[0009] (5) After the pre-oxidation reaction, tar-like impurities are deposited on the surface of the pre-oxidized fibers, affecting the quality of the carbon fibers.

[0010] The pre-oxidized fibers are carbonized at high temperature to form carbon fibers. Due to the cumulative effects of many factors in process steps such as monomer polymerization, spinning curing, pre-oxidation, and high-temperature carbonization, the quality of carbon fibers still needs to be further improved to meet the requirements of high temperature resistance and high strength in special industries. Summary of the Invention

[0011] To solve the above problems, in the first aspect of the present invention, a method for preparing high-temperature resistant polyacrylonitrile-based carbon fibers is provided, including the following steps:

[0012] Step S1, preparing spinning dope A: Dissolve the polyacrylonitrile-based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile-based copolymer reach 20% - 30% to form spinning dope A;

[0013] Step S2, adding a promoter: Add the promoter 2-acrylamido-2-methylpropanesulfonic acid to spinning dope A to form spinning dope B;

[0014] Step S3, adding polyoxyethylene sorbitan monopalmitate: Add polyoxyethylene sorbitan monopalmitate to spinning dope B to form spinning dope C;

[0015] Step S4, preparing polyacrylonitrile fiber filaments: Use an aqueous solution of dimethylacetamide with a mass concentration of 40% - 50% as the coagulation bath, and spin spinning dope C by the wet spinning method and perform traction stretching to form polyacrylonitrile fiber filaments I;

[0016] Step S5, treatment with perfluorolauryl alcohol polyoxyethylene ether: Immerse polyacrylonitrile fiber filaments I in an aqueous solution of perfluorolauryl alcohol polyoxyethylene ether, and then dry to form polyacrylonitrile fiber filaments II;

[0017] Step S6, spraying basic aluminum chloride: Spray an aqueous solution of basic aluminum chloride on polyacrylonitrile fiber filaments II, and then dry to form polyacrylonitrile fiber filaments III;

[0018] Step S7, spraying carbon powder: Disperse carbon powder in the aqueous solution of perfluorolauryl alcohol polyoxyethylene ether in Step S5 to form solution D, spray solution D on polyacrylonitrile fiber filaments III, and then dry to form polyacrylonitrile fiber filaments IV;

[0019] Step S8, preparing the pre-oxidation gas atmosphere: Replace the gas in the pre-oxidation chamber with a mixed gas of oxygen and hydrogen bromide;

[0020] Step S9, radiation heating pre-oxidation: Place polyacrylonitrile fiber filaments IV in the gas atmosphere in Step S8 and perform pre-oxidation by radiation heating to form pre-oxidized fibers V;

[0021] Step S10, ultrasonic treatment: Immerse the pre-oxidized fiber Ⅴ into the aqueous solution of sodium β -anthraquinone sulfonate, and use ultrasonic treatment to make the pre-oxidized fiber Ⅵ;

[0022] Step S11, perfluorododecyl polyoxyethylene ether treatment: Immerse the pre-oxidized fiber Ⅵ in the aqueous solution of perfluorododecyl polyoxyethylene ether, and then dry it to make the pre-oxidized fiber Ⅶ;

[0023] Step S12, carbonization treatment: Heat and carbonize the pre-oxidized fiber Ⅶ in nitrogen to make the polyacrylonitrile-based carbon fiber.

[0024] As a preferred scheme, the molar ratio of acrylonitrile monomer to vinyl acetate in the polyacrylonitrile-based copolymer is 100:1 to 100:10.

[0025] As a preferred scheme, the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid to acrylonitrile monomer is 0.1:100 to 0.2:100.

[0026] As a preferred scheme, the mass ratio of polyoxyethylene sorbitan monopalmitate to the polyacrylonitrile-based copolymer is 0.2:100 to 0.4:100.

[0027] As a preferred scheme, the fineness of the polyacrylonitrile fiber roving Ⅰ is 2D to 5D.

[0028] As a preferred scheme, the mass concentration of the aqueous solution of perfluorododecyl polyoxyethylene ether is 1.5% to 2.5%; the impregnation time is 1 hour to 2 hours; the drying temperature is 110°C to 130°C.

[0029] As a preferred scheme, the mass concentration of the aqueous solution of basic aluminum chloride is 1% to 2%; the drying temperature is 110°C to 130°C.

[0030] As a preferred scheme, the mass concentration of carbon powder in solution D is 5% to 15%, and the particle size of carbon powder is 6 microns to 10 microns; the drying temperature is 110°C to 130°C.

[0031] As a preferred scheme, the volume concentration of hydrogen bromide is 10% to 20%, and the volume concentration of oxygen is 80% to 90%.

[0032] As a preferred scheme, the pre-oxidation temperature is 250°C to 300°C, the time is 20 minutes to 60 minutes; the radiation frequency is 0.3 THz to 400 THz; at the same time, traction is applied, and the stretching length is 2% to 5%.

[0033] As a preferred scheme, the ultrasonic frequency is 100 KHz to 200 KHz; the ultrasonic treatment time is 10 minutes to 30 minutes; the mass concentration of the aqueous solution of sodium β -anthraquinone sulfonate is 15% to 25%.

[0034] As an optimal solution, the carbonization temperature is 800°C to 1200°C; the carbonization time is 1 hour to 2 hours.

[0035] In the second aspect of the present invention, a high-temperature resistant polyacrylonitrile-based carbon fiber is provided, and the high-temperature resistant polyacrylonitrile-based carbon fiber is made by the aforementioned preparation method.

[0036] In the third aspect of the present invention, the high-temperature resistant polyacrylonitrile-based carbon fiber is applied to a fireproof fabric.

[0037] In the fourth aspect of the present invention, the fireproof fabric is applied to fireproof clothing and fireproof appliances.

[0038] Through the above technical solutions, the present invention has the following technical effects:

[0039] (1) By adding polyoxyethylene sorbitan monopalmitate, the void index of the polyacrylonitrile fiber precursor is reduced, and the quality of the precursor is improved.

[0040] (2) By adding 2-acrylamido-2-methylpropanesulfonic acid, the limiting oxygen index of the pre-oxidized fiber is increased, and the fireproof performance is improved.

[0041] (3) By impregnating with perfluorolauryl alcohol polyoxyethylene ether and spraying carbon powder, the coalescence rate of the pre-oxidized fiber is reduced.

[0042] (4) By spraying basic aluminum chloride, the crimp number of the pre-oxidized fiber is increased, and the flexibility is improved.

[0043] (5) After adding hydrogen bromide gas to oxygen, the pre-oxidation reaction can be promoted, the oxidation rate can be increased, and within the same pre-oxidation time, the pre-oxidation degree is higher and the limiting oxygen index is high.

[0044] (6) The pre-oxidation reaction is carried out by means of radiation heating to inhibit the formation of the skin-core structure.

[0045] (7) Through the action of ultrasonic waves, the tarry impurities deposited on the surface of the pre-oxidized fiber are removed, and the quality of the carbon fiber is improved.

[0046] (8) By treating the pre-oxidized fiber with sodium β-anthraquinonesulfonate, the oxygen absorbed by the pre-oxidized fiber is removed, and the tensile strength of the carbon fiber is increased. Specific Embodiments

[0047] To make the above objects, features and advantages of the present invention more obvious and understandable, the applicant illustrates through specific test examples and embodiments.

[0048] Denier is a measure of the fiber size (linear density) used in the textile industry, defined as the weight (in grams) of a fiber for every 9000 meters of fiber length, denoted by the letter D.

[0049] Test Example 1:

[0050] Test Purpose: To investigate the effect of the promoter 2-acrylamido-2-methylpropanesulfonic acid.

[0051] Preparation of Test Sample 1:

[0052] Dissolve the polyacrylonitrile-based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile-based copolymer reach 25% to prepare spinning dope A; the molar ratio of acrylonitrile monomer to vinyl acetate in the polyacrylonitrile-based copolymer is 100:5;

[0053] Use an aqueous solution of dimethylacetamide with a mass concentration of 45% as the coagulation bath, and spin the spinning dope A by the wet spinning method, followed by drawing and stretching to prepare polyacrylonitrile fiber filaments; the fineness of the polyacrylonitrile fiber filaments is 3D;

[0054] Place the polyacrylonitrile fiber filaments in an air atmosphere, heat and pre-oxidize them to prepare pre-oxidized fibers, which are Test Sample 1; the pre-oxidation temperature is 250 °C and the time is 60 minutes; at the same time, draw and the stretching length is 4%.

[0055] Preparation of Test Sample 2:

[0056] Dissolve the polyacrylonitrile-based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile-based copolymer reach 25% to prepare spinning dope A; the molar ratio of acrylonitrile monomer to vinyl acetate in the polyacrylonitrile-based copolymer is 100:5;

[0057] Add the promoter 2-acrylamido-2-methylpropanesulfonic acid to the spinning dope A to prepare spinning dope B; the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid to acrylonitrile monomer is 0.15:100;

[0058] Use an aqueous solution of dimethylacetamide with a mass concentration of 45% as the coagulation bath, and spin the spinning dope B by the wet spinning method, followed by drawing and stretching to prepare polyacrylonitrile fiber filaments; the fineness of the polyacrylonitrile fiber filaments is 3D;

[0059] Place the polyacrylonitrile fiber filaments in an air atmosphere, heat and pre-oxidize them to prepare pre-oxidized fibers, which are Test Sample 2; the pre-oxidation temperature is 250 °C and the time is 60 minutes; at the same time, draw and the stretching length is 4%.

[0060] Determine the limiting oxygen index of Test Sample 1 and Test Sample 2.

[0061] Limiting oxygen index detection method: Determine the limiting oxygen index according to GB / T2406-2009.

[0062] Test results and conclusions: The test results are shown in the following table. The limiting oxygen index of the pre-oxidized fiber prepared after adding 2-acrylamido-2-methylpropanesulfonic acid is significantly higher than that without addition. The limiting oxygen index can reflect the degree of the pre-oxidation reaction. A high limiting oxygen index indicates a high degree of pre-oxidation, while a low limiting oxygen index indicates insufficient pre-oxidation. After adding 2-acrylamido-2-methylpropanesulfonic acid, as a pre-oxidation promoter, 2-acrylamido-2-methylpropanesulfonic acid promotes the cyclization reaction and increases the oxidation rate. At the same pre-oxidation time, the degree of pre-oxidation is higher and the limiting oxygen index is higher.

[0063] Table 1 Test results of Test Example 1:

[0064] Sample Name Limiting Oxygen Index (%) Test Sample 1 16 Test Sample 2 41

[0065] Test Example 2:

[0066] Test purpose: To investigate the effect of polyoxyethylene sorbitan monopalmitate.

[0067] Prepare Test Sample 3:

[0068] Dissolve the polyacrylonitrile-based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile-based copolymer reach 25% to form spinning dope A; the molar ratio of acrylonitrile monomer to vinyl acetate in the polyacrylonitrile-based copolymer is 100:5;

[0069] Add the promoter 2-acrylamido-2-methylpropanesulfonic acid to spinning dope A to make spinning dope B; the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid to acrylonitrile monomer is 0.15:100;

[0070] Use an aqueous solution of dimethylacetamide with a mass concentration of 45% as the coagulation bath, and spin spinning dope B by the wet spinning method, followed by drawing and stretching to make polyacrylonitrile fiber filaments, which are Test Sample 3; the fineness of the polyacrylonitrile fiber filaments is 3D.

[0071] Prepare Test Sample 4:

[0072] Dissolve the polyacrylonitrile-based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile-based copolymer reach 25% to form spinning dope A; the molar ratio of acrylonitrile monomer to vinyl acetate in the polyacrylonitrile-based copolymer is 100:5;

[0073] Add the promoter 2-acrylamido-2-methylpropanesulfonic acid to spinning dope A to make spinning dope B; the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid to acrylonitrile monomer is 0.15:100;

[0074] Polyoxyethylene sorbitan monopalmitate is added to the spinning stock solution B to prepare the spinning stock solution C; the mass ratio of the polyoxyethylene sorbitan monopalmitate to the polyacrylonitrile-based copolymer is 0.3:100;

[0075] Using an aqueous solution of dimethylacetamide with a mass concentration of 45% as the coagulation bath, wet spinning is carried out on the spinning stock solution C, followed by drawing and stretching to prepare the polyacrylonitrile fiber precursor, which is the test sample 4; the fineness of the polyacrylonitrile fiber precursor is 3D.

[0076] Measure the void index of test sample 3 and test sample 4.

[0077] Void index detection method: Take 100 g of the test sample with a length of 1 m, weigh the sample, soak the test sample tow in water at 25°C for 10 hours, take it out and drain for 1 hour, weigh the sample, calculate the weight increase value, and take the ratio of the weight increase value to the original weight as the void index. The void index reflects the number of voids in the polyacrylonitrile fiber precursor.

[0078] Test results and conclusions: The test results are shown in the following table. The void index of the polyacrylonitrile fiber precursor prepared after adding polyoxyethylene sorbitan monopalmitate is significantly lower than that without addition.

[0079] During spinning, in the rapid solidification process of the polymer, the surface layer of the filament solidifies first, and the core solidifies at a slower rate, resulting in a "skin-core" effect. The "skin-core" effect reduces the rate of the coagulation bath solution diffusing into the fiber and at the same time inhibits the coagulation bath solution from diffusing out of the fiber, showing pores in the micron range, including uneven micropores and macropores, which affects the fiber quality.

[0080] In the molecular structure of polyoxyethylene sorbitan monopalmitate, sorbitan is used as the hydrophilic group, and the palmitate part endows it with lipophilic characteristics. This structure enables polyoxyethylene sorbitan monopalmitate to be dispersed in the oil phase and dissolved in the water phase.

[0081] During the solidification process, the semi-solidified fiber is in an amorphous state. The present invention utilizes the lipophilic and hydrophilic characteristics of polyoxyethylene sorbitan monopalmitate to reduce the solidification speed difference between the fiber surface and the core by affecting the rate of water and solvent diffusing in and out of the semi-solidified fiber, reducing the "skin-core" effect, and obtaining a structure with low voids and more uniformity in the newly solidified fiber.

[0082] Table 2 Test results of Test Example 2:

[0083] Sample Name Void Index (%) Test Sample 3 6 Test Sample 4 1

[0084] Test Example 3:

[0085] Test purpose: To investigate the effect of perfluorolauryl alcohol polyoxyethylene ether.

[0086] Preparation of Test Sample 5:

[0087] Place the PAN fiber precursor (Test Sample 4) in an air atmosphere, heat and pre-oxidize it to make pre-oxidized fibers, which are Test Sample 5; the pre-oxidation temperature is 250 °C and the time is 60 minutes; at the same time, draw it with a 4% elongation.

[0088] Preparation of Test Sample 6:

[0089] Immerse the PAN fiber precursor (Test Sample 4) in an aqueous solution of perfluorolauryl alcohol polyoxyethylene ether, and then dry it to make a PAN fiber precursor (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the immersion time is 1.5 hours; the drying temperature is 120 °C;

[0090] Place the PAN fiber precursor (2) in an air atmosphere, heat and pre-oxidize it to make pre-oxidized fibers, which are Test Sample 6; the pre-oxidation temperature is 250 °C and the time is 60 minutes; at the same time, draw it with a 4% elongation.

[0091] Measure the fiber coalescence rate of Test Sample 5 and Test Sample 6.

[0092] Method for measuring the fiber coalescence rate: Cut the pre-oxidized fiber bundle into 3 mm lengths, put it into acetone and perform ultrasonic cleaning to remove the surfactant, and count the number of coalesced filaments under a microscope. Calculate the ratio of the number of coalesced filaments to the total number of filaments, which is the coalescence rate.

[0093] Test results and conclusions: The test results are shown in the following table. The coalescence rate of the pre-oxidized fibers prepared after immersion in perfluorolauryl alcohol polyoxyethylene ether is significantly lower than that of the non-immersed ones.

[0094] During pre-oxidation at high temperature, heat accumulates locally in the fibers and causes the pre-oxidized fibers to coalesce with each other, reducing the fiber quality.

[0095] Fluorine is an element with a relatively high electronegativity, having a high oxidation potential and high ionization energy. On the one hand, this property results in a high bond energy of the fluorine-carbon bond (F—C), so the fluorocarbon chain structure is much more stable than the hydrocarbon structure and can withstand extreme high-temperature environments. On the other hand, fluorine atoms are difficult to be polarized, making the fluorocarbon chain less polar than the hydrocarbon chain. It is precisely because of this low polarity that the hydrophobic effect of the fluorocarbon chain is much stronger than that of the hydrocarbon chain, and it also leads to a weak interaction between fluorocarbon chains. The combined action of these two factors makes the fluorocarbon surfactant molecules in the aqueous solution tend to separate from the aqueous solution more strongly than other surfactant molecules, and orient and aggregate on the liquid / solid interface to form a molecular film, forming a layer of fluorocarbon compound on the fiber surface, thus preventing fiber coalescence.

[0096] Table 3 Test Results of Test Example 3:

[0097] Sample Name Coalescence Rate (%) Test Sample 5 6 Test Sample 6 2

[0098] Test Example 4:

[0099] Test purpose: To investigate the effect of basic aluminum chloride.

[0100] Prepare test sample 7:

[0101] Immerse the PAN fiber raw yarn (test sample 4) in an aqueous solution of perfluorolauryl alcohol polyoxyethylene ether, and then dry it to obtain the PAN fiber raw yarn (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the immersion time is 1.5 hours; the drying temperature is 120 °C;

[0102] Spray the basic aluminum chloride aqueous solution onto the PAN fiber raw yarn (2), and then dry it to obtain the PAN fiber raw yarn (3); the mass concentration of the basic aluminum chloride aqueous solution is 1.5%; the drying temperature is 120 °C;

[0103] Place the PAN fiber raw yarn (3) in an air atmosphere, heat and pre-oxidize it to obtain the pre-oxidized fiber, which is test sample 7; the pre-oxidation temperature is 250 °C and the time is 60 minutes; at the same time, draw it with a 4% elongation.

[0104] Measure the fiber crimp number of test sample 6 and test sample 7.

[0105] Method for measuring fiber crimp number: At a speed of 100 m / h, a filling pressure of 1 kg / cm 2 and a clamping pressure of 2 kg / cm 2 , create crimps for test sample 6 and test sample 7 respectively, and measure the maximum crimp number they can withstand according to the test method for the crimp properties of chemical fiber staple fibers in GB / T 14338-2008. The crimp number is the number of bends per unit length of the chemical fiber. From one crimp peak of the fiber to the adjacent one is one crimp. The larger the maximum crimp number, the higher the fiber flexibility and the stronger the spinnability.

[0106] Test results and conclusions: The test results are shown in the following table. The crimp number of the pre-oxidized fiber prepared after spraying basic aluminum chloride is significantly higher than that of the unsprayed one.

[0107] During pre-oxidation at high temperature, the fiber becomes brittle and the flexibility decreases. When using the fiber to process into yarn, it is easy to break and the spinnability decreases.

[0108] The basic aluminum chloride used in the present invention contains hydroxyl groups and is water-soluble. It can not only be evenly deposited on the acrylonitrile fiber, but also effectively absorb and dissipate the heat generated during the fiber oxidation process, reducing the excessive heat accumulation or temperature rise inside the fiber, thereby producing uniformly oxidized fibers, and also having good crimpability.

[0109] Table 4 Test Example 4 Test Results:

[0110] Sample Name Number of Crimps Test Sample 6 3 Test Sample 7 9

[0111] Test Example 5:

[0112] Test Purpose: To investigate the effect of carbon powder spraying.

[0113] Preparation of Test Sample 8:

[0114] The polyacrylonitrile fiber tow (Test Sample 4) was immersed in an aqueous solution of perfluorolauryl alcohol polyoxyethylene ether, and then dried to obtain a polyacrylonitrile fiber tow (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution was 2.0%; the immersion time was 1.5 hours; the drying temperature was 120 °C;

[0115] The basic aluminum chloride aqueous solution was sprayed on the polyacrylonitrile fiber tow (2), and then dried to obtain a polyacrylonitrile fiber tow (3); the mass concentration of the basic aluminum chloride aqueous solution was 1.5%; the drying temperature was 120 °C;

[0116] The carbon powder was dispersed in an aqueous solution of perfluorolauryl alcohol polyoxyethylene ether to prepare a carbon powder dispersion, and the carbon powder dispersion was sprayed on the polyacrylonitrile fiber tow (3), and then dried to obtain a polyacrylonitrile fiber tow (4); the mass concentration of the carbon powder in the carbon powder dispersion was 10%, and the carbon powder particle size was 8 microns; the drying temperature was 120 °C;

[0117] The polyacrylonitrile fiber tow (4) was placed in an air atmosphere and heated for pre-oxidation to obtain pre-oxidized fiber (5), which was Test Sample 8; the pre-oxidation temperature was 250 °C and the time was 60 minutes; at the same time, it was tractioned and the stretching length was 4%.

[0118] Measure the fiber coalescence rate of Test Sample 7 and Test Sample 8.

[0119] The method for measuring the fiber coalescence rate is the same as that in Test Example 3.

[0120] Test Results and Conclusions: The test results are shown in the following table. The fiber coalescence rate of the pre-oxidized fiber prepared after spraying carbon powder is significantly lower than that of the non-sprayed one.

[0121] During pre-oxidation at high temperature, heat accumulates locally in the fibers, resulting in non-uniform reactions, which cause tarry substances to form on the fiber surface, affecting the physical properties of the fibers and also leading to adhesion and coalescence with each other. After spraying carbon powder, the tarry substances will be effectively adsorbed by the carbon powder, thereby reducing the fiber coalescence rate.

[0122] Table 5 Test Example 5 Test Results:

[0123] Sample Name Coalescence Rate (%) Test Sample 7 1.5 Test Sample 8 No coalescence was observed

[0124] Test Example 6:

[0125] Test Purpose: To investigate the effect of hydrogen bromide gas.

[0126] Preparation of Test Sample 9:

[0127] The polyacrylonitrile fiber filaments (Test Sample 4) are immersed in an aqueous solution of perfluorolauryl alcohol polyoxyethylene ether and then dried to obtain polyacrylonitrile fiber filaments (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the immersion time is 1.5 hours; the drying temperature is 120 °C;

[0128] An aqueous solution of basic aluminum chloride is sprayed onto the polyacrylonitrile fiber filaments (2) and then dried to obtain polyacrylonitrile fiber filaments (3); the mass concentration of the basic aluminum chloride aqueous solution is 1.5%; the drying temperature is 120 °C;

[0129] Carbon powder is dispersed in an aqueous solution of perfluorolauryl alcohol polyoxyethylene ether to prepare a carbon powder dispersion. The carbon powder dispersion is sprayed onto the polyacrylonitrile fiber filaments (3) and then dried to obtain polyacrylonitrile fiber filaments (4); the mass concentration of carbon powder in the carbon powder dispersion is 10%, and the carbon powder particle size is 8 microns; the drying temperature is 120 °C;

[0130] The polyacrylonitrile fiber filaments (4) are placed in a mixed gas atmosphere of oxygen and hydrogen bromide, heated for pre-oxidation to obtain pre-oxidized fibers (5), which are Test Sample 9; the pre-oxidation temperature is 250 °C, the time is 60 minutes; at the same time, traction is applied, and the stretching length is 4%; the volume concentration of hydrogen bromide in the mixed gas is 15%, and the volume concentration of oxygen is 85%.

[0131] Determine the limiting oxygen index of Test Sample 8 and Test Sample 9.

[0132] Limiting Oxygen Index Detection Method: Determine the limiting oxygen index in accordance with GB / T2406-2009.

[0133] Test results and conclusions: The test results are shown in the following table. The limiting oxygen index of the pre-oxidized fiber prepared in the mixed gas atmosphere of oxygen and hydrogen bromide is significantly higher than that in air. The limiting oxygen index can reflect the degree of pre-oxidation. A high limiting oxygen index indicates a high degree of pre-oxidation, while a low limiting oxygen index indicates insufficient pre-oxidation. After adding hydrogen bromide gas to oxygen, the pre-oxidation reaction can be promoted and the oxidation rate can be increased. At the same pre-oxidation time, the degree of pre-oxidation is higher and the limiting oxygen index is higher; to reach the same limiting oxygen index, the pre-oxidation time is shorter.

[0134] Table 6 Test results of Test Example 6:

[0135] Sample Name Limiting Oxygen Index (%) Test Sample 8 45 Test Sample 9 61

[0136] Test Example 7:

[0137] Test purpose: To investigate the role of the radiation heating method in pre-oxidation.

[0138] Prepare test sample 10:

[0139] Immerse the PAN fiber tow (test sample 4) in an aqueous solution of perfluorolauryl alcohol polyoxyethylene ether, and then dry it to make a PAN fiber tow (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the immersion time is 1.5 hours; the drying temperature is 120 °C;

[0140] Spray the aqueous solution of basic aluminum chloride on the PAN fiber tow (2), and then dry it to make a PAN fiber tow (3); the mass concentration of the basic aluminum chloride aqueous solution is 1.5%; the drying temperature is 120 °C;

[0141] Disperse carbon powder in an aqueous solution of perfluorolauryl alcohol polyoxyethylene ether to make a carbon powder dispersion liquid. Spray the carbon powder dispersion liquid on the PAN fiber tow (3), and then dry it to make a PAN fiber tow (4); the mass concentration of carbon powder in the carbon powder dispersion liquid is 10%, and the particle size of carbon powder is 8 microns; the drying temperature is 120 °C;

[0142] Place the PAN fiber tow (4) in the mixed gas atmosphere of oxygen and hydrogen bromide, and the volume concentration of hydrogen bromide in the mixed gas is 15% and the volume concentration of oxygen is 85%;

[0143] Pre-oxidize by radiation heating to make a pre-oxidized fiber (5), which is test sample 10; the pre-oxidation temperature is 250 °C, the time is 60 minutes; the radiation frequency is 200 THz; at the same time, draw, at the same time, draw, and the draw length is 4%.

[0144] Measure the skin-core ratio of test sample 9 and test sample 10.

[0145] Determination of skin-core ratio by optical microscopy: The test samples were embedded with a mixed solution of epoxy resin:curing agent = 15:2 (mass ratio). After curing at 60 °C for 2 h, the samples were sectioned using an EM TRIM2 ultra-thin microtome from Leica, Germany. The sample thickness was approximately 400 nm. Then, under a BX53M high-power optical microscope from Olympus, Japan, using a 20X objective lens, the sections were observed. According to the different light transmittances of the cortex and the core, the ImageJ software was used for optical density value analysis to calculate the skin-core ratio. The calculation formula is the cortex area of the fiber cross-section / total area * 100%.

[0146] Test results and conclusions: The test results are shown in the following table. After the pre-oxidation reaction was carried out by radiation heating, the skin-core structure disappeared, and the radiation heating method effectively inhibited the formation of the skin-core structure.

[0147] In traditional pre-oxidation reaction heating, equipment such as ovens is mostly used. Heat and oxygen both diffuse from the fiber surface to the core. Since both heat and oxygen are promoting factors for the pre-oxidation reaction, it leads to excessive pre-oxidation of the fiber surface, forming a dense ladder structure, which in turn hinders the diffusion of oxygen into the fiber interior, resulting in a lower degree of pre-oxidation reaction in the fiber core and the formation of a skin-core structure.

[0148] The heat transfer method of the radiation heating method is different from that of traditional oven heating. Radiation heating has strong penetration, generating heat simultaneously inside and on the surface of the fiber, and carrying out the pre-oxidation reaction at the same time. After the pre-oxidation reaction releases heat, the heat diffuses from the fiber core to the surface, resulting in a higher temperature in the core and a lower temperature on the surface, accelerating the cyclization reaction in the core, thereby reducing the difference in pre-oxidation reaction between the core and the surface, preventing the formation of the skin-core structure, improving the fiber uniformity, and enhancing the fiber quality.

[0149] By controlling the radiation wave frequency to be consistent with the absorption wave of the PAN fiber filament, resonance occurs between the two, enabling the temperatures of the fiber surface and core to be consistent at the initial stage of heating, avoiding the temperature difference effect of traditional heating.

[0150] In addition, radiation heating has the advantages of convenient and accurate temperature control and high thermal efficiency.

[0151] Table 7 Test results of Test Example 7:

[0152] Sample Name Skin-Core Ratio (%) Test Sample 9 89.1 Test Sample 10 99.9

[0153] Test Example 8:

[0154] Test purpose: To investigate the effect of ultrasonic treatment.

[0155] Preparation of test sample 11:

[0156] The test sample 10 was immersed in an aqueous solution of polyoxyethylene perfluorolauryl ether, and then dried to prepare a pre-oxidized fiber (7); the mass concentration of the aqueous solution of polyoxyethylene perfluorolauryl ether was 2%; the immersion time was 1.5 hours; the drying temperature was 120 °C;

[0157] The pre-oxidized fiber (7) was placed in nitrogen and heated for carbonization to prepare a polyacrylonitrile-based carbon fiber, which was the test sample 11; the carbonization temperature was 1000 °C; the carbonization time was 1.5 hours.

[0158] Preparation of test sample 12:

[0159] The test sample 10 was immersed in an aqueous solution and treated with ultrasonic waves to prepare a pre-oxidized fiber (6); the ultrasonic frequency was 1500 KHz; the ultrasonic treatment time was 20 minutes;

[0160] The pre-oxidized fiber (6) was immersed in an aqueous solution of polyoxyethylene perfluorolauryl ether, and then dried to prepare a pre-oxidized fiber (7); the mass concentration of the aqueous solution of polyoxyethylene perfluorolauryl ether was 2%; the immersion time was 1.5 hours; the drying temperature was 120 °C;

[0161] The pre-oxidized fiber (7) was placed in nitrogen and heated for carbonization to prepare a polyacrylonitrile-based carbon fiber, which was the test sample 12; the carbonization temperature was 1000 °C; the carbonization time was 1.5 hours.

[0162] The tensile strengths of the test sample 11 and the test sample 12 were measured. The method for measuring the tensile strength is a prior art and will not be elaborated here.

[0163] Test results and conclusions: The test results are shown in the following table. After the ultrasonic treatment and the carbonization reaction of the pre-oxidized fiber, the tensile strength of the carbon fiber increased significantly.

[0164] Through the action of ultrasonic waves, the carbon powder-tar deposited on the surface of the pre-oxidized fiber can be removed, and high-quality carbon fibers can be obtained when the pre-oxidized fiber is carbonized.

[0165] Table 8 Test results of Test Example 8:

[0166] Sample Name Tensile Strength (ksi) Test Sample 11 268 Test Sample 12 353

[0167] Test Example 9:

[0168] Test purpose: To investigate the role of sodium β-anthraquinone sulfonate.

[0169] Preparation of test sample 13:

[0170] Immerse the test sample 10 in an aqueous solution of sodium β - anthraquinone sulfonate, and use ultrasonic treatment to make the pre - oxidized fiber (6); the ultrasonic frequency is 1500 KHz; the ultrasonic treatment time is 20 minutes; the mass concentration of the aqueous solution of sodium β - anthraquinone sulfonate is 20%;

[0171] Immerse the pre - oxidized fiber (6) in an aqueous solution of perfluorolauryl alcohol polyoxyethylene ether, and then dry it to make the pre - oxidized fiber (7); the mass concentration of the aqueous solution of perfluorolauryl alcohol polyoxyethylene ether is 2%; the impregnation time is 1.5 hours; the drying temperature is 120 °C;

[0172] Place the pre - oxidized fiber (7) in nitrogen and heat it for carbonization to make the polyacrylonitrile - based carbon fiber, which is the test sample 13; the carbonization temperature is 1000 °C; the carbonization time is 1.5 hours.

[0173] Measure the tensile strength of test sample 12 and test sample 13. The method for measuring the tensile strength is a prior art and will not be elaborated here.

[0174] Test results and conclusions: The test results are shown in the following table. After treatment with sodium β - anthraquinone sulfonate, after the carbonization reaction of the pre - oxidized fiber, the tensile strength of the carbon fiber increases significantly.

[0175] The pre - oxidized fiber is carbonized in an oxygen - free and high - temperature environment to obtain carbon fiber. Oxygen during carbonization will reduce the quality of the carbon fiber. However, the pre - oxidized fiber is prepared from an oxygen - containing environment and inevitably contains a small amount of oxygen itself, which affects the quality of the carbon fiber.

[0176] The present invention uses a sodium β - anthraquinone sulfonate reducing solution to treat the pre - oxidized fiber, removes the oxygen absorbed by the pre - oxidized fiber, and then subjects the fiber to high - temperature treatment in a non - oxidizing atmosphere, thus eliminating the influence of oxygen oxidation on the carbonization reaction, significantly improving the tensile strength of the carbon fiber, and further increasing the limiting oxygen index.

[0177] Table 9 Test results of Test Example 9:

[0178] Sample Name Tensile Strength (ksi) Limiting Oxygen Index (%) Test Sample 12 353 63 Test Sample 13 466 75

[0179] Example 1:

[0180] Prepare high - temperature - resistant polyacrylonitrile - based carbon fiber according to the following method:

[0181] Step S1, prepare the spinning dope A: Dissolve the polyacrylonitrile - based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile - based copolymer reach 20% to make the spinning dope A; the molar ratio of acrylonitrile monomer to vinyl acetate in the polyacrylonitrile - based copolymer is 100:1;

[0182] Step S2, adding accelerator: Add 2-acrylamido-2-methylpropanesulfonic acid as an accelerator to the spinning dope A to make spinning dope B; the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid to acrylonitrile monomer is 0.1:100;

[0183] Step S3, adding polyoxyethylene sorbitan monopalmitate: Add polyoxyethylene sorbitan monopalmitate to the spinning dope B to make spinning dope C; the mass ratio of polyoxyethylene sorbitan monopalmitate to the polyacrylonitrile-based copolymer is 0.2:100;

[0184] Step S4, preparing polyacrylonitrile fiber tow: Using an aqueous solution of dimethylacetamide with a mass concentration of 40% as a coagulation bath, spin the spinning dope C by the wet spinning method, and perform traction and stretching to make polyacrylonitrile fiber tow I; the fineness of the polyacrylonitrile fiber tow I is 2D;

[0185] Step S5, treating with perfluorododecanol polyoxyethylene ether: Immerse the polyacrylonitrile fiber tow I in an aqueous solution of perfluorododecanol polyoxyethylene ether, and then dry it to make polyacrylonitrile fiber tow II; the mass concentration of the perfluorododecanol polyoxyethylene ether aqueous solution is 1.5%; the immersion time is 1 hour; the drying temperature is 110°C;

[0186] Step S6, spraying basic aluminum chloride: Spray an aqueous solution of basic aluminum chloride on the polyacrylonitrile fiber tow II, and then dry it to make polyacrylonitrile fiber tow III; the mass concentration of the basic aluminum chloride aqueous solution is 1%; the drying temperature is 110°C;

[0187] Step S7, spraying carbon powder: Disperse the carbon powder in the perfluorododecanol polyoxyethylene ether aqueous solution in Step S5 to make solution D, spray solution D on the polyacrylonitrile fiber tow III, and then dry it to make polyacrylonitrile fiber tow IV; the mass concentration of the carbon powder in solution D is 5%, and the particle size of the carbon powder is 6 microns; the drying temperature is 110°C;

[0188] Step S8, preparing the pre-oxidation gas atmosphere: Replace the gas in the pre-oxidation chamber with a mixed gas of oxygen and hydrogen bromide, the volume concentration of hydrogen bromide is 10%, and the volume concentration of oxygen is 90%;

[0189] Step S9, radiation heating pre-oxidation: Place the polyacrylonitrile fiber tow IV in the gas atmosphere in Step S8, and pre-oxidize it by radiation heating to make pre-oxidized fiber V; the pre-oxidation temperature is 250°C, and the time is 20 minutes; the radiation frequency is 0.3 THz; at the same time, perform traction, and the stretching length is 2%;

[0190] Step S10, ultrasonic treatment: Immerse the pre-oxidized fiber Ⅴ in an aqueous solution of sodium β -anthraquinone sulfonate, and use ultrasonic treatment to make the pre-oxidized fiber Ⅵ; the ultrasonic frequency is 100KHz; the ultrasonic treatment time is 10 minutes; the mass concentration of the aqueous solution of sodium β -anthraquinone sulfonate is 15%;

[0191] Step S11, perfluorododecanol polyoxyethylene ether treatment: Immerse the pre-oxidized fiber Ⅵ in an aqueous solution of perfluorododecanol polyoxyethylene ether, and then dry it to make the pre-oxidized fiber Ⅶ; the mass concentration of the aqueous solution of perfluorododecanol polyoxyethylene ether is 1.5%; the immersion time is 1 hour; the drying temperature is 110°C;

[0192] Step S12, carbonization treatment: Heat and carbonize the pre-oxidized fiber Ⅶ in nitrogen to make the polyacrylonitrile-based carbon fiber; the carbonization temperature is 800°C; the carbonization time is 1 hour.

[0193] Example 2:

[0194] Prepare the high-temperature resistant polyacrylonitrile-based carbon fiber according to the following method:

[0195] Step S1, prepare spinning dope A: Dissolve the polyacrylonitrile-based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile-based copolymer reach 25% to make spinning dope A; the molar ratio of acrylonitrile monomer to vinyl acetate in the polyacrylonitrile-based copolymer is 100:5;

[0196] Step S2, add accelerator: Add the accelerator 2-acrylamido-2-methylpropanesulfonic acid to the spinning dope A to make spinning dope B; the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid to acrylonitrile monomer is 0.15:100;

[0197] Step S3, add polyoxyethylene sorbitan monopalmitate: Add polyoxyethylene sorbitan monopalmitate to the spinning dope B to make spinning dope C; the mass ratio of polyoxyethylene sorbitan monopalmitate to the polyacrylonitrile-based copolymer is 0.3:100;

[0198] Step S4, prepare polyacrylonitrile fiber tow: Use an aqueous solution of dimethylacetamide with a mass concentration of 45% as the coagulation bath, and use the wet spinning method to spin the spinning dope C, and perform drawing and stretching to make the polyacrylonitrile fiber tow Ⅰ; the fineness of the polyacrylonitrile fiber tow Ⅰ is 3D;

[0199] Step S5, perfluorododecanol polyoxyethylene ether treatment: Immerse the polyacrylonitrile fiber tow Ⅰ in an aqueous solution of perfluorododecanol polyoxyethylene ether, and then dry it to make the polyacrylonitrile fiber tow Ⅱ; the mass concentration of the aqueous solution of perfluorododecanol polyoxyethylene ether is 2.0%; the immersion time is 1.5 hours; the drying temperature is 120°C;

[0200] Step S6, spraying basic aluminum chloride: Spraying an aqueous solution of basic aluminum chloride onto the polyacrylonitrile fiber precursor II, and then drying to obtain the polyacrylonitrile fiber precursor III; the mass concentration of the aqueous solution of basic aluminum chloride is 1.5%; the drying temperature is 120°C;

[0201] Step S7, spraying carbon powder: Dispersing carbon powder in the aqueous solution of perfluorolauryl alcohol polyoxyethylene ether in Step S5 to prepare Solution D, spraying Solution D onto the polyacrylonitrile fiber precursor III, and then drying to obtain the polyacrylonitrile fiber precursor IV; the mass concentration of carbon powder in Solution D is 10%, and the particle size of the carbon powder is 8 μm; the drying temperature is 120°C;

[0202] Step S8, preparing the pre-oxidation gas atmosphere: Replacing the gas in the pre-oxidation chamber with a mixed gas of oxygen and hydrogen bromide, the volume concentration of hydrogen bromide is 15%, and the volume concentration of oxygen is 85%;

[0203] Step S9, radiation heating pre-oxidation: Placing the polyacrylonitrile fiber precursor IV in the gas atmosphere of Step S8 and pre-oxidizing it by radiation heating to obtain the pre-oxidized fiber V; the pre-oxidation temperature is 270°C, and the time is 40 minutes; the radiation frequency is 200 THz; at the same time, traction is applied, and the stretching length is 3%;

[0204] Step S10, ultrasonic treatment: Immersing the pre-oxidized fiber V in an aqueous solution of β-anthraquinone sulfonate and performing ultrasonic treatment to obtain the pre-oxidized fiber VI; the ultrasonic frequency is 150 KHz; the ultrasonic treatment time is 20 minutes; the mass concentration of the aqueous solution of β-anthraquinone sulfonate is 20%;

[0205] Step S11, perfluorolauryl alcohol polyoxyethylene ether treatment: Immersing the pre-oxidized fiber VI in an aqueous solution of perfluorolauryl alcohol polyoxyethylene ether, and then drying to obtain the pre-oxidized fiber VII; the mass concentration of the aqueous solution of perfluorolauryl alcohol polyoxyethylene ether is 2.0%; the immersion time is 1.5 hours; the drying temperature is 120°C;

[0206] Step S12, carbonization treatment: Heating and carbonizing the pre-oxidized fiber VII in nitrogen to obtain the polyacrylonitrile-based carbon fiber; the carbonization temperature is 1000°C; the carbonization time is 1.5 hours.

[0207] Example 3:

[0208] Prepare the high-temperature resistant polyacrylonitrile-based carbon fiber according to the following method:

[0209] Step S1, preparation of spinning dope A: Dissolve the polyacrylonitrile-based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile-based copolymer reach 30% to prepare spinning dope A; the molar ratio of acrylonitrile monomer to vinyl acetate in the polyacrylonitrile-based copolymer is 100:10;

[0210] Step S2, addition of accelerator: Add the accelerator 2-acrylamido-2-methylpropanesulfonic acid to spinning dope A to prepare spinning dope B; the molar ratio of 2-acrylamido-2-methylpropanesulfonic acid to acrylonitrile monomer is 0.2:100;

[0211] Step S3, addition of polyoxyethylene sorbitan monopalmitate: Add polyoxyethylene sorbitan monopalmitate to spinning dope B to prepare spinning dope C; the mass ratio of polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.4:100;

[0212] Step S4, preparation of polyacrylonitrile fiber tow: Using an aqueous solution of dimethylacetamide with a mass concentration of 50% as the coagulation bath, spin spinning dope C by the wet spinning method and perform drawing and stretching to prepare polyacrylonitrile fiber tow I; the fineness of the polyacrylonitrile fiber tow I is 5 D;

[0213] Step S5, treatment with perfluorododecanol polyoxyethylene ether: Immerse polyacrylonitrile fiber tow I in an aqueous solution of perfluorododecanol polyoxyethylene ether, and then dry it to prepare polyacrylonitrile fiber tow II; the mass concentration of the aqueous solution of perfluorododecanol polyoxyethylene ether is 2.5%; the immersion time is 2 hours; the drying temperature is 130 °C;

[0214] Step S6, spraying with basic aluminum chloride: Spray an aqueous solution of basic aluminum chloride on polyacrylonitrile fiber tow II, and then dry it to prepare polyacrylonitrile fiber tow III; the mass concentration of the aqueous solution of basic aluminum chloride is 2%; the drying temperature is 130 °C;

[0215] Step S7, spraying with carbon powder: Disperse carbon powder in the aqueous solution of perfluorododecanol polyoxyethylene ether in Step S5 to prepare solution D, spray solution D on polyacrylonitrile fiber tow III, and then dry it to prepare polyacrylonitrile fiber tow IV; the mass concentration of carbon powder in solution D is 15%, and the particle size of the carbon powder is 10 microns; the drying temperature is 130 °C;

[0216] Step S8, preparation of pre-oxidation gas atmosphere: Replace the gas in the pre-oxidation chamber with a mixed gas of oxygen and hydrogen bromide, the volume concentration of hydrogen bromide is 20%, and the volume concentration of oxygen is 90%;

[0217] Step S9, radiation heating pre-oxidation: Place the PAN fiber roving Ⅳ in the gas atmosphere of step S8, and pre-oxidize it by radiation heating to produce the pre-oxidized fiber Ⅴ; the pre-oxidation temperature is 300 °C, the time is 60 minutes; the radiation frequency is 400 THz; at the same time, draw it, and the stretching length is 5%;

[0218] Step S10, ultrasonic treatment: Immerse the pre-oxidized fiber Ⅴ in an aqueous solution of sodium β - anthraquinone sulfonate, and use ultrasonic treatment to produce the pre-oxidized fiber Ⅵ; the ultrasonic frequency is 200 KHz; the ultrasonic treatment time is 30 minutes; the mass concentration of the aqueous solution of sodium β - anthraquinone sulfonate is 25%;

[0219] Step S11, perfluorododecanol polyoxyethylene ether treatment: Immerse the pre-oxidized fiber Ⅵ in an aqueous solution of perfluorododecanol polyoxyethylene ether, and then dry it to produce the pre-oxidized fiber Ⅶ; the mass concentration of the aqueous solution of perfluorododecanol polyoxyethylene ether is 12.5%; the immersion time is 2 hours; the drying temperature is 130 °C;

[0220] Step S12, carbonization treatment: Heat and carbonize the pre-oxidized fiber Ⅶ in nitrogen to produce PAN-based carbon fiber; the carbonization temperature is 1200 °C; the carbonization time is 2 hours.

[0221] Detect the void index, crimp number, coalescence rate, limiting oxygen index, and skin-core ratio of the pre-oxidized fiber Ⅴ in Example 1, Example 2, and Example 3. The results are shown in the following table.

[0222] The pre-oxidized fiber Ⅴ prepared by the present invention has extremely low void index and coalescence rate, and a relatively high skin-core ratio, which is beneficial to the quality control of the pre-oxidized fiber and the improvement of the quality of subsequent carbon fiber. The pre-oxidized fiber Ⅴ prepared by the present invention has a relatively high crimp number and good flexibility, which can improve the spinnability during the production process and reduce the risk of fiber breakage. The pre-oxidized fiber Ⅴ prepared by the present invention has a relatively high limiting oxygen index, can withstand high temperatures, and has good flame retardancy.

[0223] Table 10 Detection results of the pre-oxidized fiber Ⅴ in the examples:

[0224] Sample Name Void Index (%) Number of Crimps (per cm) Coalescence Rate (%) Limiting Oxygen Index (%) Skin-Core Ratio (%) Example 1 1.0 9 No coalescence was observed 60 99.9 Example 2 1.0 9 No coalescence was observed 62 99.9 Example 3 0.9 10 No coalescence was observed 61 99.9

[0225] Detect the coalescence rate, limiting oxygen index, and tensile strength of the PAN-based carbon fiber in Example 1, Example 2, and Example 3. The results are shown in the following table.

[0226] The PAN-based carbon fiber prepared by the present invention has an extremely low coalescence rate, which improves the qualified rate of the carbon fiber; the limiting oxygen index is relatively high, can withstand high temperatures, and has good flame retardancy; the tensile strength is relatively high, and it has relatively high quality.

[0227] Table 11 Detection results of the PAN-based carbon fiber in the examples:

[0228] Sample Name Coalescence Rate (%) Limiting Oxygen Index (%) Tensile Strength (ksi) Example 1 No coalescence was observed 73 465 Example 2 No coalescence was observed 75 470 Example 3 No coalescence was observed 75 471

Claims

1. A method for preparing high temperature resistant polyacrylonitrile-based carbon fiber, characterized in that: The following steps are involved: Step S1, preparing spinning stock A: dissolving a polyacrylonitrile-based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile-based copolymer reach 20% to 30%, to prepare a spinning stock A; Step S2, adding an accelerator: adding an accelerator 2-acrylamido-2-methylpropanesulfonic acid to the spinning stock A to prepare the spinning stock B; Step S3, adding polyoxyethylene sorbitan monopalmitate: adding polyoxyethylene sorbitan monopalmitate to spinning stock B to prepare spinning stock C; Step S4, preparing polyacrylonitrile fiber precursor: using a dimethylacetamide aqueous solution with a mass concentration of 40% to 50% as a coagulation bath, spinning the spinning stock C by wet spinning, pulling and stretching, and preparing polyacrylonitrile fiber precursor I; Step S5, perfluorolauryl alcohol polyoxyethylene ether treatment: immersing the polyacrylonitrile fiber precursor I in a perfluorolauryl alcohol polyoxyethylene ether aqueous solution, and then drying to prepare the polyacrylonitrile fiber precursor II; Step S6, spraying basic aluminum chloride: spraying a basic aluminum chloride aqueous solution on the polyacrylonitrile fiber precursor II, followed by drying to prepare the polyacrylonitrile fiber precursor III; Step S7, carbon powder spraying: dispersing carbon powder in the aqueous solution of perfluorolauryl alcohol polyoxyethylene ether in step S5 to prepare solution D, spraying solution D on polyacrylonitrile fiber precursor III, and then drying to prepare polyacrylonitrile fiber precursor IV; Step S8, preparing a pre-oxidation gas atmosphere: replacing the gas in the pre-oxidation chamber with a mixed gas of oxygen and hydrogen bromide; Step S9, radiation heating preoxidation: placing the polyacrylonitrile fiber precursor IV in the gas atmosphere of step S8, and preoxidizing by radiation heating to produce preoxidized fiber V; Step S10, ultrasonic treatment: immersing the pre-oxidized fiber V in an aqueous solution of sodium β-anthraquinone sulfonate and using ultrasonic treatment to prepare pre-oxidized fiber VI; the ultrasonic frequency is 100KHz to 200KHz; the ultrasonic treatment time is 10 minutes to 30 minutes; the mass concentration of the aqueous solution of sodium β-anthraquinone sulfonate is 15% to 25%; Step S11, perfluorolauryl alcohol polyoxyethylene ether treatment: immersing the pre-oxidized fiber VI in a perfluorolauryl alcohol polyoxyethylene ether aqueous solution, and then drying to prepare the pre-oxidized fiber VII; Step S12, carbonization treatment: placing the pre-oxidized fiber VII in nitrogen for heating and carbonization to prepare polyacrylonitrile-based carbon fiber; the carbonization temperature is 800° C. to 1200° C.; the carbonization time is 1 hour to 2 hours.

2. The preparation method according to claim 1, characterized in that: The molar ratio of acrylonitrile monomer to vinyl acetate in the polyacrylonitrile-based copolymer is 100:1 to 100:

10.

3. The preparation method according to claim 2, characterized in that: The molar ratio of the 2-acrylamido-2-methylpropanesulfonic acid to the acrylonitrile monomer is 0.1:100 to 0.2:

100.

4. The preparation method according to claim 3, characterized in that: The mass ratio of the polyoxyethylene sorbitan monopalmitate to the polyacrylonitrile-based copolymer is 0.2:100 to 0.4:

100.

5. The preparation method according to claim 4, characterized in that: The fineness of the polyacrylonitrile fiber precursor I is 2D-5D.

6. The preparation method according to claim 5, characterized in that: The mass concentration of the perfluorolauryl alcohol polyoxyethylene ether aqueous solution is 1.5% to 2.5%; the immersion time is 1 hour to 2 hours; and the drying temperature is 110° C. to 130° C.

7. The preparation method according to claim 6, characterized in that: The mass concentration of the basic aluminum chloride aqueous solution is 1% to 2%; the drying temperature is 110° C. to 130° C.

8. The preparation method according to claim 7, characterized in that: The mass concentration of the carbon powder in solution D is 5% to 15%, and the particle size of the carbon powder is 6 microns to 10 microns; the drying temperature is 110° C. to 130° C.

9. A high temperature resistant polyacrylonitrile-based carbon fiber, characterized in that: The high temperature resistant polyacrylonitrile-based carbon fiber is made by the preparation method described in claim 8.

10. Use of the high temperature resistant polyacrylonitrile-based carbon fiber according to claim 9 in fireproof fabrics.