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

Abstract

This invention provides a preparation method for high-temperature-resistant polyacrylonitrile-based carbon fiber for fireproof fabric. By incorporating 2-acrylamido-2-methylpropane sulfonic acid, hydrogen bromide, and basic aluminum chloride, the fiber's fire resistance, flexibility, and limiting oxygen index are enhanced. Pre-oxidation via radiation heating inhibits skin-core structures, while ultrasonic cleaning removes impurities. Treatment with sodium β-anthraquinone sulfonate improves tensile strength, yielding high-strength, fire-resistant carbon fiber.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The application claims priority to Chinese patent application No. 202510155065.1, filed on Feb. 12, 2025, the entire contents of which are incorporated herein by reference.TECHNICAL FIELD

[0002] This Invention is related to the technical field of carbon fibre, in particular to a preparation method of high-temperature-resistant polyacrylonitrile-based carbon fibre and its application in fireproof fabric.BACKGROUND

[0003] Polyacrylonitrile-based carbon fibre and its composites are characterized by high strength and light weight, and as structural materials, they are increasingly used in automobile, sports, aviation, tools, military equipment and the like fields. The preparation process of polyacrylonitrile-based carbon fibre mainly includes monomer polymerization, spinning and curing, pre-oxidation, high-temperature carbonization and the like processes.

[0004] Acrylonitrile-based polymers are coagulated from the outside to the inside in the process of spinning. The surface of cellosilk is in contact with the coagulation bath solution and coagulated first; its inner core is cured at a slower rate. The first coagulated surface has further reduced the diffusion speed of coagulation bath solution into the fibre core, and also inhibited the coagulation bath solution from scattering from the fibre, resulting in the “skin core” effect, showing non-uniform voids of micron level and thus reducing the fibre quality.

[0005] In the process of pre-oxidation, the linear macromolecular chain will undergo cyclization, oxidation, dehydrogenation and other reactions, forming insoluble and unmelted fibres with a heat-resistant trapezoidal structure, which is a key link in the preparation of carbon fibres and has an important impact on the structure and performance of the final carbon fibres. For the pre-oxidation process, the furnace box heating method is usually taken to heat the spun silk in hot air at 180° C.~400° C. to achieve the purpose of pre-oxidation. However, the pre-oxidation process still has the following problems to be solved:

[0006] (1) The pre-oxidation reaction is usually taking place in a high-temperature oven and furnace, where the temperature is 180° C.~400° C. and the reaction time is 1 h~3 h. It is a high energy-consuming and time-consuming process, with high cost required for carbon fibre manufacturing.

[0007] (2) During the pre-oxidation reaction, heat is transmitted from the fibre surface to the fibre core, resulting in excessive oxidation of the fibre surface, insufficient oxidation of the fibre core and a skin core structure with uneven degree of pre-oxidation of the surface and core. Skin core structure will be inherited by subsequent carbonization, which will increase the structural defect of carbon fibre and limit the improvement of mechanical properties.

[0008] (3) Due to the high pre-oxidation temperature, the fibre is easy to coalesce, resulting in poor quality of carbon fibre.

[0009] (4) When pre-oxidized at high temperature, the fibre will become brittle and its flexibility will decrease; when pre-oxidized and crimped, it is easy to break and showing poor spinnability.

[0010] (5) After pre-oxidation reaction, tar-like impurities are deposited on the surface of pre-oxidized fibres, thus affecting the quality of carbon fibres.

[0011] The pre-oxidized fibre is carbonized at high temperature to form carbon fibre, and due to the cumulative impact of multitudinous factors in the processing steps such as monomer polymerization, spinning and curing, preoxidation and high-temperature carbonization, the quality of carbon fibre needs to be further improved to meet the requirements of special industries for high-temperature resistance and high strength.SUMMARY

[0012] In order to solve the above problem, the first aspect of the invention provides a preparation method of high-temperature-resistant polyacrylonitrile-based carbon fibre, which comprises the following steps:

[0013] Step S1—prepare Spinning Stock A: dissolve polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of polyacrylonitrile based copolymer reach 20%~30%, and then prepare Spinning Stock A;

[0014] Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B;

[0015] Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C;

[0016] Step S4—prepare polyacrylonitrile fibre precursor: take the aqueous solution of dimethylacetamide with mass concentration of 40%~50% as the coagulation bath, use the wet spinning method to spin Spinning Stock C, draw and stretch to prepare polyacrylonitrile fibre precursor I;

[0017] Step S5—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip polyacrylonitrile fibre precursor I into perfluoro lauryl alcohol polyoxyethylene ether aqueous solution, and then dry to prepare polyacrylonitrile fibre precursor II;

[0018] Step S6—spray basic aluminum chloride: spray the basic aluminum chloride aqueous solution on polyacrylonitrile fibre precursor II, and then dry to make polyacrylonitrile fibre precursor III;

[0019] Step S7—spray carbon powder: disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether of Step S5 to prepare Solution D, spray Solution D on polyacrylonitrile fibre precursor III, and then dry to prepare polyacrylonitrile fibre precursor IV;

[0020] Step S8—prepare preoxidation gas atmosphere: replace the gas in the preoxidation chamber with a mixture of oxygen and hydrogen bromide;

[0021] Step S9—conduct radiation heating preoxidation: place polyacrylonitrile fibre precursor IV in the gas atmosphere of Step S8, and preoxidize by radiation heating to produce pre-oxidized fibre V;

[0022] Step S10—conduct ultrasonication: immerse the pre-oxidized fibre V in the aqueous solution of sodium β-anthraquinone sulfonate, and use ultrasonication to prepare the pre-oxidized fibre VI;

[0023] Step S11—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip the pre-oxidized fibre VI in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare the pre-oxidized fibre VII;

[0024] Step S12—perform carbonization treatment: put the pre-oxidized fibre VII in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre.

[0025] As a preferred embodiment, the molar ratio of the acrylonitrile monomer and vinyl acetate in the polyacrylonitrile-based copolymer is 100:1~100:10.

[0026] As a preferred embodiment, the molar ratio of the 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.1:100~0.2:100.

[0027] As a preferred embodiment, the mass ratio of the polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.2:100~0.4:100.

[0028] As a preferred embodiment, the denier of the polyacrylonitrile fibre precursor I is 2D~5D.

[0029] As a preferred embodiment, the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 1.5%~2.5%; the dipping time is 1 h~2 h; the drying temperature is 110° C.~130° C.

[0030] As a preferred embodiment, the mass concentration of the alkaline aluminum chloride aqueous solution is 1%~2%; the drying temperature is 110° C.~130° C.

[0031] As a preferred embodiment, the mass concentration of carbon powder in Solution D is 5%~15%, and the particle size of carbon powder is 6 μm~10 μm; the drying temperature is 110° C.~130° C.

[0032] As a preferred embodiment, the volume concentration of the hydrogen bromide is 10%-20%, and the volume concentration of oxygen is 80%-90%.

[0033] As a preferred embodiment, the pre-oxidation temperature is 250° C.~300° C. and the time is 20 min~60 min; the radiation frequency is 0.3 THz~400 THz; the fibre is elongated by 2%~5% of its original length under the tension simultaneously applied.

[0034] As a preferred embodiment, the ultrasonic frequency is 100 KHz~200 KHz; the ultrasonication time is 10~30 min; the mass concentration of sodium β-anthraquinone sulfonate aqueous solution is 15%~25%.

[0035] As a preferred embodiment, the carbonization temperature is 800° C.~1200° C.; the carbonization time is 1 h~2 h.

[0036] The second aspect of the invention has provided a high-temperature-resistant polyacrylonitrile-based carbon fibre, which is made with the above preparation method.

[0037] In the third aspect of the invention, the high-temperature resistant polyacrylonitrile-based carbon fibre is applied to the fireproof fabric.

[0038] In the fourth aspect of the invention, the fireproof fabric is applied to fireproof clothing and fireproof equipment.

[0039] Through the above technical solution, the invention has the following technical effects:

[0040] (1) With the addition of polyoxyethylene sorbitan monopalmitate, the void index of polyacrylonitrile fibre precursor is reduced and the quality of precursor is improved.

[0041] (2) With the addition of 2-acrylamido-2-methylpropane sulfonic acid, the limiting oxygen index of pre-oxidized fibre is increased and the fire resistance is improved.

[0042] (3) The coalescence rate of pre-oxidized fibre is reduced through dipping of perfluoroaluminal polyoxyethylene ether and spraying of carbon powder.

[0043] (4) Through spraying of basic aluminum chloride, the crimp number of pre-oxidized fibre is increased and the flexibility is improved.

[0044] (5) The addition of hydrogen bromide gas in oxygen can promote the pre-oxidation reaction and increase the oxidation. In the same pre-oxidation time, the degree of pre-oxidation is high and the limiting oxygen index is high.

[0045] (6) Preoxidation reaction is conducted by means of radiation heating to inhibit the formation of skin core structure.

[0046] (7) The tar-like impurities deposited on the surface of the pre-oxidized fibre are removed by ultrasonic action to improve the quality of the carbon fibre.

[0047] (8) The pre-oxidized fibre was treated with sodium β-anthraquinone sulfonate to remove the oxygen absorbed by the pre-oxidized fibre and improve the tensile strength of the carbon fibre.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In order to make the above purposes, features and advantages of t342 he Invention more obvious and easy to understand, the Applicant has them illustrated through specific test cases and embodiments.

[0049] Denier is a measure of fibre size (linear density) used in the textile industry. It is defined as the fibre weight (grams) per 9000-meter-long fibre, indicated by the letter D.Test Case 1:

[0050] Purpose of Testing: to investigate the effect of accelerator 2-acrylamido-2-methylpropane sulfonic acid.Preparation of Test Sample 1:Dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;

[0052] With 45% dimethylacetamide aqueous solution as the coagulation bath, Spinning Stock A is spun with the wet spinning method and drawn to produce polyacrylonitrile fibre precursor; the polyacrylonitrile fibre precursor size is 3D;

[0053] Put the polyacrylonitrile fibre precursor in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre as Test Sample 1; the pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.Preparation of Test Sample 2:Dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;

[0055] Add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of enoylamino-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.15:100;

[0056] With 45% dimethylacetamide aqueous solution as the coagulation bath, Spinning Stock B is spun with the wet spinning method and drawn to produce polyacrylonitrile fibre precursor; the said polyacrylonitrile fibre precursor size is 3D;

[0057] Put the polyacrylonitrile fibre precursor in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre as Test Sample 2; the said pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.

[0058] Determine the limiting oxygen index of Test Sample 1 and Test Sample 2.

[0059] Detection method of limiting oxygen index: measure the limiting oxygen index as per GB / T2406-2009.

[0060] Test Results and Conclusions: See the following table for test results. The limiting oxygen index of pre-oxidized fibre prepared with the addition of 2-acrylamido-2-methylpropane sulfonic acid is significantly higher than that of the fibre without the addition of 2-acrylamido-2-methylpropane sulfonic acid. The limiting oxygen index can reflect the degree of preoxidation reaction. A high limiting oxygen index means a high degree of preoxidation, while a low limiting oxygen index means lack of preoxidation. Upon addition of 2-acrylamido-2-methylpropane sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid will act as a pre-oxidation promoter to promote the cyclization reaction and improve the oxidation rate. In the same pre-oxidation time, the degree of pre-oxidation is high and the limiting oxygen index is high.TABLE 1Test Results of Test Case 1:LimitingOxygenSampleIndexDescription(LOI) (%)Test Sample 116Test Sample 241Test Case 2:

[0061] Purpose of Testing: to investigate the effect of polyoxyethylene sorbitan monopalmitate.Preparation of Test Sample 3:

[0062] Dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;

[0063] Add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the said 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.15:100;

[0064] With 45% dimethylacetamide aqueous solution as the coagulation bath, Spinning Stock B is spun with the wet spinning method and drawn to produce polyacrylonitrile fibre precursor as Test Sample 3; the polyacrylonitrile fibre precursor size is 3D;Preparation of Test Sample 4:Dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;

[0066] Add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the said 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.15:100;

[0067] Add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of the said polyoxyethylene sorbitan monopalmitate to polyacrylonitrile based copolymer is 0.3:100;

[0068] With 45% dimethylacetamide aqueous solution as the coagulation bath, Spinning Stock C is spun with the wet spinning method and drawn to produce polyacrylonitrile fibre precursor as Test Sample 4; the polyacrylonitrile fibre precursor size is 3D;

[0069] Measure the void index of Test Sample 3 and Test Sample 4.

[0070] Detection method of void index: take 100 g of test sample with a length of 1 m, weigh the sample, soak the test sample tow in 25° C. water for 10 hours, then take it out and dry for 1 h, weigh the sample weight, calculate the weight gain, and take the ratio of the weight gain to the original weight as the void index. The void index reflects the number of voids in polyacrylonitrile fibre precursor.

[0071] Test Results and Conclusions: See the following table for test results. The void index of polyacrylonitrile fibre precursor prepared with the addition of polyoxyethylene sorbitan monopalmitate is significantly lower than that without the addition of polyoxyethylene sorbitan monopalmitate.

[0072] For spinning, in the process of the rapid coagulation of polymer, the surface of filament will be first coagulated, and the inner core coagulated at a slower rate, resulting in the “skin core” effect, while the “skin core” effect will reduce the diffusion speed of coagulation bath solution into the fibre, and inhibit the coagulation bath solution from escaping from the fibre, showing pores within the micron range, including uneven micropores and macropores, thus affecting the fibre quality.

[0073] In the molecular structure of polyoxyethylene sorbitan monopalmitate, sorbitan is a hydrophilic group and palmitate part will endow it with lipophilic properties. This Structure enables polyoxyethylene sorbitan monopalmitate to be dispersed in the oil phase and dissolved in the water phase.

[0074] In the process of coagulation, the semi-coagulated fibres are amorphous. This Invention utilizes the lipophilic and hydrophilic properties of polyoxyethylene sorbitan monopalmitate to reduce the difference in the coagulation speed between the fibre surface and the inner core, reduce the “skin core” effect and obtain a lower void index and more uniform structure in the newly coagulated fibre by affecting the diffusion rate of water and solvent into and out of the semi-coagulated fibre.TABLE 2Test Results of Test Case 2:SampleVoidDescriptionIndex (%)Test Sample 36Test Sample 41Test Case 3:

[0075] Purpose of Testing: to investigate the effect of perfluoro lauryl alcohol polyoxyethylene ether.Preparation of Test Sample 5:

[0076] Put the polyacrylonitrile fibre precursor (Test Sample 4) in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre as Test Sample 5; the pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.Preparation of Test Sample 6:

[0077] Dip the polyacrylonitrile fibre precursor (Test Sample 4) in the aqueous solution of perfluoroaluminal polyoxyethylene ether, and then have it dried to prepare the polyacrylonitrile fibre precursor (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0078] Put the polyacrylonitrile fibre precursor (2) in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre as Test Sample 6; the pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.

[0079] Determine the fibre coalescence rate of Test Sample 5 and Test Sample 6.

[0080] Determination method of fibre coalescence rate: cut the pre-oxidized fibre bundle into a length of 3 mm, put it into acetone and conduct ultrasonic cleaning to remove the surfactant, count the number of coalescence wires under the microscope, calculate the ratio of the number of coalescence wires to the total number of wires, which is the coalescence rate.

[0081] Test Results and Conclusions: See the following table for test results. The coalescence rate of pre-oxidized fibres impregnated with perfluoroaluminal polyoxyethylene ether is significantly lower than that of the fibres not impregnated.

[0082] When pre-oxidation is conducted at high temperature, heat will accumulate locally in the fibre and cause pre-oxidized fibres to coalesce with each other, thus reducing the fibre quality.

[0083] Fluorine is an element with strong electronegativity, high oxidation potential and high ionization energy, which, on one hand, will result in high energy of fluorine-carbon bond (F-C), so the fluorocarbon chain structure is far more stable than the hydrocarbon structure, and can withstand extreme high temperature; on the other hand, render fluorine atoms difficult to be polarized, making the polarity of fluorocarbon chain lower than that of hydrocarbon chain. It is precisely because of this lower polarity that the hydrophobic effect of fluorocarbon chain is far stronger than that of hydrocarbon chain, thus leading to the weak interaction between fluorocarbon chains. The combined effect of these two factors makes fluorocarbon surfactant molecules in aqueous solution have a stronger tendency to separate from aqueous solution than other surfactant molecules, and directionally assemble and arrange on the liquid / solid interface to form a molecular film, forming a layer of fluorocarbon compounds on the fibre surface, thus preventing fibre coalescence.TABLE 3Test Results of Test Case 3:SampleCoalescenceDescriptionRate (%)Test Sample 56Test Sample 62Test Case 4:

[0084] Purpose of Testing: to investigate the effect of basic aluminum chloride.Preparation of Test Sample 7:Dip the polyacrylonitrile fibre precursor (Test Sample 4) in the aqueous solution of perfluoroaluminal polyoxyethylene ether, and then have it dried to prepare the polyacrylonitrile fibre precursor (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0086] The aqueous solution of basic aluminum chloride is sprayed on the polyacrylonitrile fibre precursor (2), which is then dried to make the polyacrylonitrile fibre precursor (3); the mass concentration of alkaline aluminum chloride aqueous solution is 1.5%; the drying temperature is 120° C.;

[0087] Put the polyacrylonitrile fibre precursor (3) in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre as Test Sample 7; the pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.

[0088] Determine the fibre crimp number of Test Sample 6 and Test Sample 7.

[0089] Determination method of fibre crimp number: at the speed of 100 m / h, the filling pressure of 1 kg / cm2 and the clamping pressure of 2 kg / cm2, respectively make crimps for Test Sample 6 and Test Sample 7, and determine the maximum number of crimps that can be tolerated as per Man-made fibre-Test method for crimping performance of staple fibre (GB / T 14338-2008). Crimp number is the number of crimps per unit length of chemical fibre. One crimp shall be deemed as from one crimp peak of the fibre to the adjacent crimp peak. The larger the maximum crimp number, the higher the fibre flexibility and spinnability.

[0090] Test Results and Conclusions: See the following table for test results. The crimp number of pre-oxidized fibres prepared by spraying basic aluminum chloride is significantly higher than that of the fibres without spraying.

[0091] When preoxidized at high temperature, the fibre will become brittle and its flexibility will decrease; The fibre, once processed into yarn, is easy to break and its spinnability will be reduced.

[0092] The basic aluminum chloride used in this Invention contains hydroxyl groups and is water-soluble. It can not only deposit evenly on the acrylonitrile fibre, but also effectively absorb and diffuse the heat generated in the fibre oxidation process, reduce the excessive heat accumulation or temperature rise inside the fibre, so as to produce uniformly-oxidized fibres, and also has good crimp property.TABLE 4Test Results of Test Case 4:SampleCrimpDescriptionNumberTest Sample 63Test Sample 79Test Case 5:

[0093] Purpose of Testing: to investigate the effect of carbon powder sprayed.Preparation of Test Sample 8:Dip the polyacrylonitrile fibre precursor (Test Sample 4) in the aqueous solution of perfluoroaluminal polyoxyethylene ether, and then have it dried to prepare the polyacrylonitrile fibre precursor (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0095] Spray the aqueous solution of basic aluminum chloride on the polyacrylonitrile fibre precursor (2), which is then dried to make the polyacrylonitrile fibre precursor (3); the mass concentration of alkaline aluminum chloride aqueous solution is 1.5%; the drying temperature is 120° C.;

[0096] Disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether to prepare the carbon powder dispersion liquid, and then spray the carbon powder dispersion liquid on the polyacrylonitrile fibre precursor (3), and then have it dried to prepare the polyacrylonitrile fibre precursor (4); the mass concentration of carbon powder in carbon powder dispersion is 10%, and the particle size of carbon powder is 8 μm; the drying temperature is 120° C.;

[0097] Put the polyacrylonitrile fibre precursor (4) in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre (5) as Test Sample 8; the pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.

[0098] Determine the fibre coalescence rate of Test Sample 7 and Test Sample 8.

[0099] The determination method of fibre coalescence rate is identical with that of Test Case 3.

[0100] Test Results and Conclusions: See the following table for test results. The coalescence rate of pre-oxidized fibres prepared by spraying carbon powder is significantly lower than that of the fibres without spraying.

[0101] When pre-oxidation is conducted at high temperature, heat will accumulate locally in the fibre and uneven reaction will occur, resulting in tar-like substances on the fibre surface, thus affecting the physical properties of the fibre, and also causing mutual adhesion and coalescence. Once the carbon powder is sprayed, tar-like substances will be effectively absorbed by carbon powder, thus reducing the fibre coalescence rate.TABLE 5Test Results of Test Case 5:SampleCoalescenceDescriptionRate (%)Test Sample 71.5Test Sample 8No coalescenceobservedTest Case 6:

[0102] Purpose of Testing: to investigate the effect of hydrogen bromide gas.Preparation of Test Sample 9:Dip the polyacrylonitrile fibre precursor (Test Sample 4) in the aqueous solution of perfluoroaluminal polyoxyethylene ether, and then have it dried to prepare the polyacrylonitrile fibre precursor (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0104] The aqueous solution of basic aluminum chloride is sprayed on the polyacrylonitrile fibre precursor (2), which is then dried to make the polyacrylonitrile fibre precursor (3); the mass concentration of alkaline aluminum chloride aqueous solution is 1.5%; the drying temperature is 120° C.;

[0105] Disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether to prepare the carbon powder dispersion liquid, and spray the carbon powder dispersion liquid on the polyacrylonitrile fibre precursor (3), and then have it dried to prepare the polyacrylonitrile fibre precursor (4); the mass concentration of carbon powder in carbon powder dispersion is 10%, and the particle size of carbon powder is 8 μm; the drying temperature is 120° C.;

[0106] Put the polyacrylonitrile fibre precursor (4) in the mixed atmosphere of oxygen and hydrogen bromide for heating and pre-oxidization to make the pre-oxidized fibre (5) as Test Sample 9; the pre-oxidation temperature is 250° C. and the time is 60 min; the fiber is elongated by 4% of its original length under the tension simultaneously applied; the volume concentration of hydrogen bromide in the mixed gas is 15% and the volume concentration of oxygen is 85%.

[0107] Determine the limiting oxygen index of Test Sample 8 and Test Sample 9.

[0108] Detection method of limiting oxygen index: measure the limiting oxygen index as per GB / T2406-2009.

[0109] Test Results and Conclusions: See the following table for test results. The limiting oxygen index of pre-oxidized fibre prepared in the mixed gas atmosphere of oxygen and hydrogen bromide is significantly higher than that of air. The limiting oxygen index can reflect the degree of preoxidation reaction. A high limiting oxygen index means a high degree of preoxidation, while a low limiting oxygen index means lack of preoxidation. The addition of hydrogen bromide gas in oxygen can promote the pre-oxidation reaction and increase the oxidation. In the same pre-oxidation time, the degree of pre-oxidation is high and the limiting oxygen index is high; when the same limiting oxygen index is reached, the pre-oxidation time will be shortened.TABLE 6Test Results of Test Case 6:LimitingOxygenSampleIndexDescription(LOI) (%)Test Sample 845Test Sample 961Test Case 7:

[0110] Purpose of Testing: to investigate the effect of radiation heating in preoxidation.Preparation of Test Sample 10:Dip the polyacrylonitrile fibre precursor (Test Sample 4) in the aqueous solution of perfluoroaluminal polyoxyethylene ether, and then have it dried to prepare the polyacrylonitrile fibre precursor (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0112] Spray the aqueous solution of basic aluminum chloride on the polyacrylonitrile fibre precursor (2), which is then dried to make the polyacrylonitrile fibre precursor (3); the mass concentration of alkaline aluminum chloride aqueous solution is 1.5%; the drying temperature is 120° C.;

[0113] Disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether to prepare the carbon powder dispersion liquid, and spray the carbon powder dispersion liquid on the polyacrylonitrile fibre precursor (3), and then have it dried to prepare the polyacrylonitrile fibre precursor (4); the mass concentration of carbon powder in carbon powder dispersion is 10%, and the particle size of carbon powder is 8 μm; the drying temperature is 120° C.;

[0114] Put the polyacrylonitrile fibre precursor (4) in a mixed 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%;

[0115] Preoxidized by means of radiation heating to make pre-oxidized fibre (5) as Test Sample 10; the pre-oxidation temperature is 250° C. and the time is 60 min; the radiation frequency is 200 THz; the fiber is elongated by 4% of its original length under the tension simultaneously applied.

[0116] Determine the skin core ratio of Test Sample 9 and Test Sample 10.

[0117] Determine the skin core ratio with the method of optical microscope: the test sample is first embedded in a mixture of epoxy resin: curing agent=15:2 (mass ratio), cured at 60° C. for 2 h, and then sliced with EM TRIM2 ultrathin microtome of Leica (Germany); the thickness of the sample is approx. 400 nm; then under the BX53M high-power optical microscope of Olympus (Japan), slices are observed with 20× object lens; and then according to the different transmittance of the cortex and the inner core, the optical density value is analyzed with ImageJ software and the skin core ratio is calculated with the formula of the skin area of the cross section of the fibre / the total area*100%.

[0118] Test Results and Conclusions: See the following table for test results. After pre-oxidation reaction by means of radiation heating, the skin core structure has disappeared and the radiation heating effectively inhibited the formation of skin core structure.

[0119] Equipment such as ovens are mostly used for traditional pre-oxidation reaction heating, as a result, both heat and oxygen diffuse from the fibre surface to the inner core, and both are the promoter of the pre-oxidation reaction, leading to excessive pre-oxidation of the fibre surface, forming a dense trapezoidal structure, thus hindering the diffusion of oxygen to the interior of the fibre, resulting in a low degree of pre-oxidation reaction of the fibre core and forming a skin core structure.

[0120] The heat transfer mode of radiation heating is different from that of traditional oven heating. The radiation heating has a strong penetration force, so that heat is generated inside and on the surface of the fibre at the same time, and the pre-oxidation reaction is conducted at the same time; once released from pre-oxidation reaction, the heat is diffused from the inner core of the fibre to the surface, resulting in high temperature of the inner core and low temperature of the surface, accelerating the inner core cyclization reaction, thus reducing the difference between the pre-oxidation reaction of the inner core and the surface, preventing the formation of the skin core structure, thus improving the fibre uniformity and the fibre quality.

[0121] By controlling the frequency of the radiation wave, it is kept consistent with the absorption wave of the polyacrylonitrile fibre precursor, and their resonance achieved can make the temperature of fibre surface and inner core identical at the initial stage of heating, so as to avoid the temperature difference effect of traditional heating.

[0122] In addition, radiation heating has the advantages of convenient and accurate temperature control and high thermal efficiency.TABLE 7Test Results of Test Case 7:SampleSkin CoreDescriptionRatio (%)Test Sample 989.1Test Sample 1099.9Test Case 8:

[0123] Purpose of Testing: to investigate the effect of ultrasonication.Preparation of Test Sample 11:

[0124] Dip Test Sample 10 in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then have it dried to prepare pre-oxidized fibre (7); the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 2%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0125] Put the pre-oxidized fibre (7) in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre as Test Sample 11; the carbonization temperature is 1,000° C.; the carbonization time is 1.5 h.Preparation of Test Sample 12:Dip Test Sample 10 in the aqueous solution for ultrasonication to make pre-oxidized fibre (6); the said ultrasonic frequency is 1500 KHz; the ultrasonication time is 20 min;

[0127] Dip the pre-oxidized fibre (6) in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then have it dried to prepare pre-oxidized fibre (7); the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 2%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0128] Put the pre-oxidized fibre (7) in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre as Test Sample 12; the carbonization temperature is 1,000° C.; the carbonization time is 1.5 h.

[0129] Determine the tensile strength of Test Sample 11 and Test Sample 12. The method for determination of tensile strength is an existing technology and will not be described here.

[0130] Test Results and Conclusions: See the following table for test results. Through ultrasonication, the tensile strength of pre-oxidized carbon fibre is increased significantly after carbonization reaction.

[0131] The tar-like carbon powder deposited on the surface of pre-oxidized fibre can be removed through ultrasonication; when the pre-oxidized fibre is carbonized, high-quality carbon fibre can be obtained.TABLE 8Test Results of Test Case 8:SampleTensileDescriptionStrength (MPa)Test Sample 11268Test Sample 12353Test Case 9:

[0132] Purpose of Testing: to investigate the effect of sodium β-anthraquinone sulfonate.Preparation of Test Sample 13:Dip Test Sample 10 in the aqueous solution of sodium β-anthraquinone sulfonate for ultrasonication to make pre-oxidized fibre (6); the said ultrasonic frequency is 1,500 KHz; the ultrasonication time is 20 min; the mass concentration of sodium β-anthraquinone sulfonate aqueous solution is 20%;

[0134] Dip the pre-oxidized fibre (6) in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then have it dried to prepare pre-oxidized fibre (7); the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 2%; the dipping time is 1.5 h; the said drying temperature is 120° C.;

[0135] Put the pre-oxidized fibre (7) in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre as Test Sample 13; the carbonization temperature is 1,000° C.; the carbonization time is 1.5 h.

[0136] Determine the tensile strength of Test Sample 12 and Test Sample 13. The method for determination of tensile strength is an existing technology and will not be described here.

[0137] Test Results and Conclusions: See the following table for test results. The tensile strength of pre-oxidized carbon fibre is increased significantly after carbonization reaction through treatment with sodium β-anthraquinone sulfonate.

[0138] Have the pre-oxidized fibre carbonized to obtain carbon fibre in an oxygen-free and high-temperature environment, and the oxygen will reduce the quality of carbon fibre in the process of carbonization. However, the pre-oxidized fibre prepared from an oxygen-containing environment will inevitably contain a small amount of oxygen, which will then affect the quality of carbon fibre.

[0139] This Invention has used sodium β-anthraquinone sulfonate reducing solution to treat the pre-oxidized fibre, remove the oxygen absorbed by the pre-oxidized fibre, and then treated the fibre at high temperature in a non oxidizing atmosphere, so as to eliminate the impact of oxygen oxidation on the carbonization reaction, thus significantly improve the tensile strength of the carbon fibre, and further increase the limiting oxygen index.TABLE 9Test Results of Test Case 9:LimitingOxygenSampleTensileIndexDescriptionStrength (MPa)(LOI) (%)Test Sample 1235363Test Sample 1346675Embodiment 1

[0140] The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:

[0141] Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 20%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:1;

[0142] Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.1:100;

[0143] Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.2:100;

[0144] Step S4—prepare polyacrylonitrile fibre precursor: take the aqueous solution of dimethylacetamide with mass concentration of 40% as the coagulation bath, use the wet spinning method to spin Spinning Stock C, draw and stretch to prepare polyacrylonitrile fibre precursor I; the size of polyacrylonitrile fibre precursor I is 2D;

[0145] Step S5—treat with perfluoro lauryl alcohol polyoxyethylene ether: dip polyacrylonitrile fibre precursor I into the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare polyacrylonitrile fibre precursor II; the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 1.5%; the dipping time is 1 h; the drying temperature is 110° C.;

[0146] Step S6—spray basic aluminum chloride: spray the basic aluminum chloride aqueous solution on polyacrylonitrile fibre precursor II, and then dry to make polyacrylonitrile fibre precursor III; the mass concentration of the aqueous solution of alkaline aluminum chloride is 1%; the drying temperature is 110° C.;

[0147] Step S7—spray carbon powder: disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether in Step S5 to prepare Solution D, spray Solution D on polyacrylonitrile fibre precursor III, and then dry to prepare polyacrylonitrile fibre precursor IV; the mass concentration of carbon powder in Solution D is 5% and the particle size of carbon powder is 6 μm; the said drying temperature is 110° C.;

[0148] Step S8—prepare preoxidation gas atmosphere: replace the gas in the preoxidation chamber with a mixture of oxygen and hydrogen bromide, where the hydrogen bromide volume concentration is 10% and the oxygen volume concentration is 90%;

[0149] Step S9—conduct radiation heating preoxidation: place polyacrylonitrile fibre precursor IV in the gas atmosphere of Step S8, and preoxidize by means of radiation heating to produce pre-oxidized fibre V; the pre-oxidation temperature is 250° C. and the time is 20 min; the radiation frequency is 0.3 THz; the fiber is elongated by 2% of its original length under the tension simultaneously applied;

[0150] Step S10—conduct ultrasonication: immerse the pre-oxidized fibre V in the aqueous solution of sodium β-anthraquinone sulfonate, and use ultrasonication to prepare the pre-oxidized fibre VI; the ultrasonic frequency is 100 KHz; the ultrasonication time is 10 min; the mass concentration of sodium β-anthraquinone sulfonate aqueous solution is 15%;

[0151] Step S11—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip the pre-oxidized fibre VI in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare the pre-oxidized fibre VII; the mass concentration of the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether is 1.5%; the dipping time is 1 h; the drying temperature is 110° C.;

[0152] Step S12—perform carbonization treatment: put the pre-oxidized fibre VII in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre; the carbonization temperature is 800° C.; the carbonization time is 1 h.Embodiment 2

[0153] The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:

[0154] Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;

[0155] Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the said 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.15:100;

[0156] Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of said polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.3:100;

[0157] Step S4—prepare polyacrylonitrile fibre precursor: take the aqueous solution of dimethylacetamide with mass concentration of 45% as the coagulation bath, use the wet spinning method to spin Spinning Stock C, draw and stretch to prepare polyacrylonitrile fibre precursor I; the size of polyacrylonitrile fibre precursor I is 3D;

[0158] Step S5-treat with perfluoro lauryl alcohol polyoxyethylene ether: dip polyacrylonitrile fibre precursor I into the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare polyacrylonitrile fibre precursor II; the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the said dipping time is 1.5 h; the said drying temperature is 120° C.;

[0159] Step S6—spray basic aluminum chloride: spray the basic aluminum chloride aqueous solution on polyacrylonitrile fibre precursor II, and then dry to make polyacrylonitrile fibre precursor III; the mass concentration of the aqueous solution of alkaline aluminum chloride is 1.5%; the drying temperature is 120° C.;

[0160] Step S7—spray carbon powder: disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether in Step S5 to prepare Solution D, spray Solution D on polyacrylonitrile fibre precursor III, and then dry to prepare polyacrylonitrile fibre precursor IV; the mass concentration of carbon powder in Solution D is 10% and the particle size of carbon powder is 6 μm; the said drying temperature is 120° C.;

[0161] Step S8—prepare preoxidation gas atmosphere: replace the gas in the preoxidation chamber with a mixture of oxygen and hydrogen bromide, where the hydrogen bromide volume concentration is 15% and the oxygen volume concentration is 85%;

[0162] Step S9—conduct radiation heating preoxidation: place polyacrylonitrile fibre precursor IV in the gas atmosphere of Step S8, and preoxidize by means of radiation heating to produce pre-oxidized fibre V; the pre-oxidation temperature is 270° C. and the time is 40 min; the radiation frequency is 200 THz; the fiber is elongated by 3% of its original length under the tension simultaneously applied;

[0163] Step S10—conduct ultrasonication: immerse the pre-oxidized fibre V in the aqueous solution of sodium β-anthraquinone sulfonate, and use ultrasonication to prepare the pre-oxidized fibre VI; the ultrasonic frequency is 150 KHz; the ultrasonication time is 20 min; the mass concentration of sodium β-anthraquinone sulfonate aqueous solution is 20%;

[0164] Step S11—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip the pre-oxidized fibre VI in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare the pre-oxidized fibre VII; the mass concentration of the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether is 2.0%; the dipping time is 1.5 h; the said drying temperature is 120° C.;

[0165] Step S12—perform carbonization treatment: put the pre-oxidized fibre VII in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre; the carbonization temperature is 1,000° C.; the carbonization time is 1.5 h.Embodiment 3

[0166] The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:

[0167] Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 30%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:10;

[0168] Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.2:100;

[0169] Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.4:100;

[0170] Step S4—prepare polyacrylonitrile fibre precursor: take the aqueous solution of dimethylacetamide with mass concentration of 50% as the coagulation bath, use the wet spinning method to spin Spinning Stock C, draw and stretch to prepare polyacrylonitrile fibre precursor I; the size of polyacrylonitrile fibre precursor I is 5D;

[0171] Step S5—treat with perfluoro lauryl alcohol polyoxyethylene ether: dip polyacrylonitrile fibre precursor I into the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare polyacrylonitrile fibre precursor II; the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 2.5%; the dipping time is 2 h; the drying temperature is 130° C.;

[0172] Step S6—spray basic aluminum chloride: spray the basic aluminum chloride aqueous solution on polyacrylonitrile fibre precursor II, and then dry to make polyacrylonitrile fibre precursor III; the mass concentration of the aqueous solution of alkaline aluminum chloride is 2%; the rying temperature is 130° C.;

[0173] Step S7—spray carbon powder: disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether in Step S5 to prepare Solution D, spray Solution D on polyacrylonitrile fibre precursor III, and then dry to prepare polyacrylonitrile fibre precursor IV; the mass concentration of carbon powder in Solution D is 15% and the particle size of carbon powder is 10 μm; the drying temperature is 130° C.;

[0174] Step S8—prepare preoxidation gas atmosphere: replace the gas in the preoxidation chamber with a mixture of oxygen and hydrogen bromide, where the hydrogen bromide volume concentration is 20% and the oxygen volume concentration is 90%;

[0175] Step S9—conduct radiation heating preoxidation: place polyacrylonitrile fibre precursor IV in the gas atmosphere of Step S8, and preoxidize by means of radiation heating to produce pre-oxidized fibre V; the pre-oxidation temperature is 300° C. and the time is 60 min; the radiation frequency is 400 THz; the fiber is elongated by 5% of its original length under the tension simultaneously applied;

[0176] Step S10—conduct ultrasonication: immerse the pre-oxidized fibre V in the aqueous solution of sodium β-anthraquinone sulfonate, and use ultrasonication to prepare the pre-oxidized fibre VI; the ultrasonic frequency is 200 KHz; the ultrasonication time is 30 min; the mass concentration of sodium β-anthraquinone sulfonate aqueous solution is 25%;

[0177] Step S11—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip the pre-oxidized fibre VI in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare the pre-oxidized fibre VII; the mass concentration of the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether is 12.5%; the dipping time is 2 h; the drying temperature is 130° C.;

[0178] Step S12—perform carbonization treatment: put the pre-oxidized fibre VII in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre; the said carbonization temperature is 1,200° C.; the carbonization time is 2 h.

[0179] The void index, crimp number, coalescence rate, limiting oxygen index and skin core ratio of the pre-oxidized fibre Vin Embodiment 1, Embodiment 2 and Embodiment 3 are tested and the results are shown in the following table.

[0180] The pre-oxidized fibre V prepared by the invention has extremely low void index and coalescence rate, and high skin core ratio, which is conducive to the quality control of such pre-oxidized fibre and the quality improvement of any subsequent carbon fibre. The pre-oxidized fibre V prepared with this Invention has high crimp number and good flexibility, which can improve the spinnability in the production process and reduce the risk of fibre breakage. The pre-oxidized fibre Vprepared with this Invention has high limiting oxygen index, high-temperature resistance and good flame retardancy.TABLE 10Pre-oxidized Fibre V Test Results of the Embodiments:LimitingVoidCrimpCoales-OxygenSkinSampleIndexNumbercenceIndexCoreDescription(%)(Nr. / cm)Rate (%)(LOI) (%)Ratio (%)Embodi-1.09No6099.9ment 1coalescenceobservedEmbodi-1.09No6299.9ment 2coalescenceobservedEmbodi-0.910No6199.9ment 3coalescenceobserved

[0181] The coalescence rate, limiting oxygen index and tensile strength of polyacrylonitrile-based carbon fibre in Embodiment 1, Embodiment 2 and Embodiment 3 are tested and the results are shown in the following table.

[0182] The polyacrylonitrile-based carbon fibre prepared with this Invention has extremely low coalescence rate and this Invention has improved the acceptability of carbon fibre with high limiting oxygen index, high temperature resistance, good flame retardancy, high tensile strength and high quality.TABLE 11Test Results of Polyacrylonitrile-basedCarbon Fibre in the Embodiments:LimitingCoales-OxygenTensileSamplecenceIndexStrengthDescriptionRate (%)(LOI) (%)(MPa)Embodi-No73465ment 1coalescenceobservedEmbodi-No75470ment 2coalescenceobservedEmbodi-No75471ment 3coalescenceobserved

Examples

embodiment 1

[0140]The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:[0141]Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 20%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:1;[0142]Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.1:100;[0143]Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.2:100;[0144]Step S4—prepare polyacrylonitrile fibre precursor: ...

embodiment 2

[0153]The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:[0154]Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;[0155]Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the said 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.15:100;[0156]Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of said polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.3:100;[0157]Step S4—prepare polyacrylonitrile fibre ...

embodiment 3

[0166]The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:[0167]Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 30%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:10;[0168]Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.2:100;[0169]Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.4:100;[0170]Step S4—prepare polyacrylonitrile fibre precursor:...

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The application claims priority to Chinese patent application No. 202510155065.1, filed on Feb. 12, 2025, the entire contents of which are incorporated herein by reference.TECHNICAL FIELD

[0002] This Invention is related to the technical field of carbon fibre, in particular to a preparation method of high-temperature-resistant polyacrylonitrile-based carbon fibre and its application in fireproof fabric.BACKGROUND

[0003] Polyacrylonitrile-based carbon fibre and its composites are characterized by high strength and light weight, and as structural materials, they are increasingly used in automobile, sports, aviation, tools, military equipment and the like fields. The preparation process of polyacrylonitrile-based carbon fibre mainly includes monomer polymerization, spinning and curing, pre-oxidation, high-temperature carbonization and the like processes.

[0004] Acrylonitrile-based polymers are coagulated from the outside to the inside in the process of spinning. The surface of cellosilk is in contact with the coagulation bath solution and coagulated first; its inner core is cured at a slower rate. The first coagulated surface has further reduced the diffusion speed of coagulation bath solution into the fibre core, and also inhibited the coagulation bath solution from scattering from the fibre, resulting in the “skin core” effect, showing non-uniform voids of micron level and thus reducing the fibre quality.

[0005] In the process of pre-oxidation, the linear macromolecular chain will undergo cyclization, oxidation, dehydrogenation and other reactions, forming insoluble and unmelted fibres with a heat-resistant trapezoidal structure, which is a key link in the preparation of carbon fibres and has an important impact on the structure and performance of the final carbon fibres. For the pre-oxidation process, the furnace box heating method is usually taken to heat the spun silk in hot air at 180° C.~400° C. to achieve the purpose of pre-oxidation. However, the pre-oxidation process still has the following problems to be solved:

[0006] (1) The pre-oxidation reaction is usually taking place in a high-temperature oven and furnace, where the temperature is 180° C.~400° C. and the reaction time is 1 h~3 h. It is a high energy-consuming and time-consuming process, with high cost required for carbon fibre manufacturing.

[0007] (2) During the pre-oxidation reaction, heat is transmitted from the fibre surface to the fibre core, resulting in excessive oxidation of the fibre surface, insufficient oxidation of the fibre core and a skin core structure with uneven degree of pre-oxidation of the surface and core. Skin core structure will be inherited by subsequent carbonization, which will increase the structural defect of carbon fibre and limit the improvement of mechanical properties.

[0008] (3) Due to the high pre-oxidation temperature, the fibre is easy to coalesce, resulting in poor quality of carbon fibre.

[0009] (4) When pre-oxidized at high temperature, the fibre will become brittle and its flexibility will decrease; when pre-oxidized and crimped, it is easy to break and showing poor spinnability.

[0010] (5) After pre-oxidation reaction, tar-like impurities are deposited on the surface of pre-oxidized fibres, thus affecting the quality of carbon fibres.

[0011] The pre-oxidized fibre is carbonized at high temperature to form carbon fibre, and due to the cumulative impact of multitudinous factors in the processing steps such as monomer polymerization, spinning and curing, preoxidation and high-temperature carbonization, the quality of carbon fibre needs to be further improved to meet the requirements of special industries for high-temperature resistance and high strength.SUMMARY

[0012] In order to solve the above problem, the first aspect of the invention provides a preparation method of high-temperature-resistant polyacrylonitrile-based carbon fibre, which comprises the following steps:

[0013] Step S1—prepare Spinning Stock A: dissolve polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of polyacrylonitrile based copolymer reach 20%~30%, and then prepare Spinning Stock A;

[0014] Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B;

[0015] Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C;

[0016] Step S4—prepare polyacrylonitrile fibre precursor: take the aqueous solution of dimethylacetamide with mass concentration of 40%~50% as the coagulation bath, use the wet spinning method to spin Spinning Stock C, draw and stretch to prepare polyacrylonitrile fibre precursor I;

[0017] Step S5—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip polyacrylonitrile fibre precursor I into perfluoro lauryl alcohol polyoxyethylene ether aqueous solution, and then dry to prepare polyacrylonitrile fibre precursor II;

[0018] Step S6—spray basic aluminum chloride: spray the basic aluminum chloride aqueous solution on polyacrylonitrile fibre precursor II, and then dry to make polyacrylonitrile fibre precursor III;

[0019] Step S7—spray carbon powder: disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether of Step S5 to prepare Solution D, spray Solution D on polyacrylonitrile fibre precursor III, and then dry to prepare polyacrylonitrile fibre precursor IV;

[0020] Step S8—prepare preoxidation gas atmosphere: replace the gas in the preoxidation chamber with a mixture of oxygen and hydrogen bromide;

[0021] Step S9—conduct radiation heating preoxidation: place polyacrylonitrile fibre precursor IV in the gas atmosphere of Step S8, and preoxidize by radiation heating to produce pre-oxidized fibre V;

[0022] Step S10—conduct ultrasonication: immerse the pre-oxidized fibre V in the aqueous solution of sodium β-anthraquinone sulfonate, and use ultrasonication to prepare the pre-oxidized fibre VI;

[0023] Step S11—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip the pre-oxidized fibre VI in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare the pre-oxidized fibre VII;

[0024] Step S12—perform carbonization treatment: put the pre-oxidized fibre VII in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre.

[0025] As a preferred embodiment, the molar ratio of the acrylonitrile monomer and vinyl acetate in the polyacrylonitrile-based copolymer is 100:1~100:10.

[0026] As a preferred embodiment, the molar ratio of the 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.1:100~0.2:100.

[0027] As a preferred embodiment, the mass ratio of the polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.2:100~0.4:100.

[0028] As a preferred embodiment, the denier of the polyacrylonitrile fibre precursor I is 2D~5D.

[0029] As a preferred embodiment, the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 1.5%~2.5%; the dipping time is 1 h~2 h; the drying temperature is 110° C.~130° C.

[0030] As a preferred embodiment, the mass concentration of the alkaline aluminum chloride aqueous solution is 1%~2%; the drying temperature is 110° C.~130° C.

[0031] As a preferred embodiment, the mass concentration of carbon powder in Solution D is 5%~15%, and the particle size of carbon powder is 6 μm~10 μm; the drying temperature is 110° C.~130° C.

[0032] As a preferred embodiment, the volume concentration of the hydrogen bromide is 10%-20%, and the volume concentration of oxygen is 80%-90%.

[0033] As a preferred embodiment, the pre-oxidation temperature is 250° C.~300° C. and the time is 20 min~60 min; the radiation frequency is 0.3 THz~400 THz; the fibre is elongated by 2%~5% of its original length under the tension simultaneously applied.

[0034] As a preferred embodiment, the ultrasonic frequency is 100 KHz~200 KHz; the ultrasonication time is 10~30 min; the mass concentration of sodium β-anthraquinone sulfonate aqueous solution is 15%~25%.

[0035] As a preferred embodiment, the carbonization temperature is 800° C.~1200° C.; the carbonization time is 1 h~2 h.

[0036] The second aspect of the invention has provided a high-temperature-resistant polyacrylonitrile-based carbon fibre, which is made with the above preparation method.

[0037] In the third aspect of the invention, the high-temperature resistant polyacrylonitrile-based carbon fibre is applied to the fireproof fabric.

[0038] In the fourth aspect of the invention, the fireproof fabric is applied to fireproof clothing and fireproof equipment.

[0039] Through the above technical solution, the invention has the following technical effects:

[0040] (1) With the addition of polyoxyethylene sorbitan monopalmitate, the void index of polyacrylonitrile fibre precursor is reduced and the quality of precursor is improved.

[0041] (2) With the addition of 2-acrylamido-2-methylpropane sulfonic acid, the limiting oxygen index of pre-oxidized fibre is increased and the fire resistance is improved.

[0042] (3) The coalescence rate of pre-oxidized fibre is reduced through dipping of perfluoroaluminal polyoxyethylene ether and spraying of carbon powder.

[0043] (4) Through spraying of basic aluminum chloride, the crimp number of pre-oxidized fibre is increased and the flexibility is improved.

[0044] (5) The addition of hydrogen bromide gas in oxygen can promote the pre-oxidation reaction and increase the oxidation. In the same pre-oxidation time, the degree of pre-oxidation is high and the limiting oxygen index is high.

[0045] (6) Preoxidation reaction is conducted by means of radiation heating to inhibit the formation of skin core structure.

[0046] (7) The tar-like impurities deposited on the surface of the pre-oxidized fibre are removed by ultrasonic action to improve the quality of the carbon fibre.

[0047] (8) The pre-oxidized fibre was treated with sodium β-anthraquinone sulfonate to remove the oxygen absorbed by the pre-oxidized fibre and improve the tensile strength of the carbon fibre.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In order to make the above purposes, features and advantages of t342 he Invention more obvious and easy to understand, the Applicant has them illustrated through specific test cases and embodiments.

[0049] Denier is a measure of fibre size (linear density) used in the textile industry. It is defined as the fibre weight (grams) per 9000-meter-long fibre, indicated by the letter D.Test Case 1:

[0050] Purpose of Testing: to investigate the effect of accelerator 2-acrylamido-2-methylpropane sulfonic acid.Preparation of Test Sample 1:Dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;

[0052] With 45% dimethylacetamide aqueous solution as the coagulation bath, Spinning Stock A is spun with the wet spinning method and drawn to produce polyacrylonitrile fibre precursor; the polyacrylonitrile fibre precursor size is 3D;

[0053] Put the polyacrylonitrile fibre precursor in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre as Test Sample 1; the pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.Preparation of Test Sample 2:Dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;

[0055] Add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of enoylamino-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.15:100;

[0056] With 45% dimethylacetamide aqueous solution as the coagulation bath, Spinning Stock B is spun with the wet spinning method and drawn to produce polyacrylonitrile fibre precursor; the said polyacrylonitrile fibre precursor size is 3D;

[0057] Put the polyacrylonitrile fibre precursor in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre as Test Sample 2; the said pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.

[0058] Determine the limiting oxygen index of Test Sample 1 and Test Sample 2.

[0059] Detection method of limiting oxygen index: measure the limiting oxygen index as per GB / T2406-2009.

[0060] Test Results and Conclusions: See the following table for test results. The limiting oxygen index of pre-oxidized fibre prepared with the addition of 2-acrylamido-2-methylpropane sulfonic acid is significantly higher than that of the fibre without the addition of 2-acrylamido-2-methylpropane sulfonic acid. The limiting oxygen index can reflect the degree of preoxidation reaction. A high limiting oxygen index means a high degree of preoxidation, while a low limiting oxygen index means lack of preoxidation. Upon addition of 2-acrylamido-2-methylpropane sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid will act as a pre-oxidation promoter to promote the cyclization reaction and improve the oxidation rate. In the same pre-oxidation time, the degree of pre-oxidation is high and the limiting oxygen index is high.TABLE 1Test Results of Test Case 1:LimitingOxygenSampleIndexDescription(LOI) (%)Test Sample 116Test Sample 241Test Case 2:

[0061] Purpose of Testing: to investigate the effect of polyoxyethylene sorbitan monopalmitate.Preparation of Test Sample 3:

[0062] Dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;

[0063] Add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the said 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.15:100;

[0064] With 45% dimethylacetamide aqueous solution as the coagulation bath, Spinning Stock B is spun with the wet spinning method and drawn to produce polyacrylonitrile fibre precursor as Test Sample 3; the polyacrylonitrile fibre precursor size is 3D;Preparation of Test Sample 4:Dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;

[0066] Add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the said 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.15:100;

[0067] Add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of the said polyoxyethylene sorbitan monopalmitate to polyacrylonitrile based copolymer is 0.3:100;

[0068] With 45% dimethylacetamide aqueous solution as the coagulation bath, Spinning Stock C is spun with the wet spinning method and drawn to produce polyacrylonitrile fibre precursor as Test Sample 4; the polyacrylonitrile fibre precursor size is 3D;

[0069] Measure the void index of Test Sample 3 and Test Sample 4.

[0070] Detection method of void index: take 100 g of test sample with a length of 1 m, weigh the sample, soak the test sample tow in 25° C. water for 10 hours, then take it out and dry for 1 h, weigh the sample weight, calculate the weight gain, and take the ratio of the weight gain to the original weight as the void index. The void index reflects the number of voids in polyacrylonitrile fibre precursor.

[0071] Test Results and Conclusions: See the following table for test results. The void index of polyacrylonitrile fibre precursor prepared with the addition of polyoxyethylene sorbitan monopalmitate is significantly lower than that without the addition of polyoxyethylene sorbitan monopalmitate.

[0072] For spinning, in the process of the rapid coagulation of polymer, the surface of filament will be first coagulated, and the inner core coagulated at a slower rate, resulting in the “skin core” effect, while the “skin core” effect will reduce the diffusion speed of coagulation bath solution into the fibre, and inhibit the coagulation bath solution from escaping from the fibre, showing pores within the micron range, including uneven micropores and macropores, thus affecting the fibre quality.

[0073] In the molecular structure of polyoxyethylene sorbitan monopalmitate, sorbitan is a hydrophilic group and palmitate part will endow it with lipophilic properties. This Structure enables polyoxyethylene sorbitan monopalmitate to be dispersed in the oil phase and dissolved in the water phase.

[0074] In the process of coagulation, the semi-coagulated fibres are amorphous. This Invention utilizes the lipophilic and hydrophilic properties of polyoxyethylene sorbitan monopalmitate to reduce the difference in the coagulation speed between the fibre surface and the inner core, reduce the “skin core” effect and obtain a lower void index and more uniform structure in the newly coagulated fibre by affecting the diffusion rate of water and solvent into and out of the semi-coagulated fibre.TABLE 2Test Results of Test Case 2:SampleVoidDescriptionIndex (%)Test Sample 36Test Sample 41Test Case 3:

[0075] Purpose of Testing: to investigate the effect of perfluoro lauryl alcohol polyoxyethylene ether.Preparation of Test Sample 5:

[0076] Put the polyacrylonitrile fibre precursor (Test Sample 4) in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre as Test Sample 5; the pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.Preparation of Test Sample 6:

[0077] Dip the polyacrylonitrile fibre precursor (Test Sample 4) in the aqueous solution of perfluoroaluminal polyoxyethylene ether, and then have it dried to prepare the polyacrylonitrile fibre precursor (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0078] Put the polyacrylonitrile fibre precursor (2) in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre as Test Sample 6; the pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.

[0079] Determine the fibre coalescence rate of Test Sample 5 and Test Sample 6.

[0080] Determination method of fibre coalescence rate: cut the pre-oxidized fibre bundle into a length of 3 mm, put it into acetone and conduct ultrasonic cleaning to remove the surfactant, count the number of coalescence wires under the microscope, calculate the ratio of the number of coalescence wires to the total number of wires, which is the coalescence rate.

[0081] Test Results and Conclusions: See the following table for test results. The coalescence rate of pre-oxidized fibres impregnated with perfluoroaluminal polyoxyethylene ether is significantly lower than that of the fibres not impregnated.

[0082] When pre-oxidation is conducted at high temperature, heat will accumulate locally in the fibre and cause pre-oxidized fibres to coalesce with each other, thus reducing the fibre quality.

[0083] Fluorine is an element with strong electronegativity, high oxidation potential and high ionization energy, which, on one hand, will result in high energy of fluorine-carbon bond (F-C), so the fluorocarbon chain structure is far more stable than the hydrocarbon structure, and can withstand extreme high temperature; on the other hand, render fluorine atoms difficult to be polarized, making the polarity of fluorocarbon chain lower than that of hydrocarbon chain. It is precisely because of this lower polarity that the hydrophobic effect of fluorocarbon chain is far stronger than that of hydrocarbon chain, thus leading to the weak interaction between fluorocarbon chains. The combined effect of these two factors makes fluorocarbon surfactant molecules in aqueous solution have a stronger tendency to separate from aqueous solution than other surfactant molecules, and directionally assemble and arrange on the liquid / solid interface to form a molecular film, forming a layer of fluorocarbon compounds on the fibre surface, thus preventing fibre coalescence.TABLE 3Test Results of Test Case 3:SampleCoalescenceDescriptionRate (%)Test Sample 56Test Sample 62Test Case 4:

[0084] Purpose of Testing: to investigate the effect of basic aluminum chloride.Preparation of Test Sample 7:Dip the polyacrylonitrile fibre precursor (Test Sample 4) in the aqueous solution of perfluoroaluminal polyoxyethylene ether, and then have it dried to prepare the polyacrylonitrile fibre precursor (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0086] The aqueous solution of basic aluminum chloride is sprayed on the polyacrylonitrile fibre precursor (2), which is then dried to make the polyacrylonitrile fibre precursor (3); the mass concentration of alkaline aluminum chloride aqueous solution is 1.5%; the drying temperature is 120° C.;

[0087] Put the polyacrylonitrile fibre precursor (3) in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre as Test Sample 7; the pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.

[0088] Determine the fibre crimp number of Test Sample 6 and Test Sample 7.

[0089] Determination method of fibre crimp number: at the speed of 100 m / h, the filling pressure of 1 kg / cm2 and the clamping pressure of 2 kg / cm2, respectively make crimps for Test Sample 6 and Test Sample 7, and determine the maximum number of crimps that can be tolerated as per Man-made fibre-Test method for crimping performance of staple fibre (GB / T 14338-2008). Crimp number is the number of crimps per unit length of chemical fibre. One crimp shall be deemed as from one crimp peak of the fibre to the adjacent crimp peak. The larger the maximum crimp number, the higher the fibre flexibility and spinnability.

[0090] Test Results and Conclusions: See the following table for test results. The crimp number of pre-oxidized fibres prepared by spraying basic aluminum chloride is significantly higher than that of the fibres without spraying.

[0091] When preoxidized at high temperature, the fibre will become brittle and its flexibility will decrease; The fibre, once processed into yarn, is easy to break and its spinnability will be reduced.

[0092] The basic aluminum chloride used in this Invention contains hydroxyl groups and is water-soluble. It can not only deposit evenly on the acrylonitrile fibre, but also effectively absorb and diffuse the heat generated in the fibre oxidation process, reduce the excessive heat accumulation or temperature rise inside the fibre, so as to produce uniformly-oxidized fibres, and also has good crimp property.TABLE 4Test Results of Test Case 4:SampleCrimpDescriptionNumberTest Sample 63Test Sample 79Test Case 5:

[0093] Purpose of Testing: to investigate the effect of carbon powder sprayed.Preparation of Test Sample 8:Dip the polyacrylonitrile fibre precursor (Test Sample 4) in the aqueous solution of perfluoroaluminal polyoxyethylene ether, and then have it dried to prepare the polyacrylonitrile fibre precursor (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0095] Spray the aqueous solution of basic aluminum chloride on the polyacrylonitrile fibre precursor (2), which is then dried to make the polyacrylonitrile fibre precursor (3); the mass concentration of alkaline aluminum chloride aqueous solution is 1.5%; the drying temperature is 120° C.;

[0096] Disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether to prepare the carbon powder dispersion liquid, and then spray the carbon powder dispersion liquid on the polyacrylonitrile fibre precursor (3), and then have it dried to prepare the polyacrylonitrile fibre precursor (4); the mass concentration of carbon powder in carbon powder dispersion is 10%, and the particle size of carbon powder is 8 μm; the drying temperature is 120° C.;

[0097] Put the polyacrylonitrile fibre precursor (4) in the air atmosphere for heating and pre-oxidization to make the pre-oxidized fibre (5) as Test Sample 8; the pre-oxidation temperature is 250° C. and the time is 60 min; the fibre is elongated by 4% of its original length under the tension simultaneously applied.

[0098] Determine the fibre coalescence rate of Test Sample 7 and Test Sample 8.

[0099] The determination method of fibre coalescence rate is identical with that of Test Case 3.

[0100] Test Results and Conclusions: See the following table for test results. The coalescence rate of pre-oxidized fibres prepared by spraying carbon powder is significantly lower than that of the fibres without spraying.

[0101] When pre-oxidation is conducted at high temperature, heat will accumulate locally in the fibre and uneven reaction will occur, resulting in tar-like substances on the fibre surface, thus affecting the physical properties of the fibre, and also causing mutual adhesion and coalescence. Once the carbon powder is sprayed, tar-like substances will be effectively absorbed by carbon powder, thus reducing the fibre coalescence rate.TABLE 5Test Results of Test Case 5:SampleCoalescenceDescriptionRate (%)Test Sample 71.5Test Sample 8No coalescenceobservedTest Case 6:

[0102] Purpose of Testing: to investigate the effect of hydrogen bromide gas.Preparation of Test Sample 9:Dip the polyacrylonitrile fibre precursor (Test Sample 4) in the aqueous solution of perfluoroaluminal polyoxyethylene ether, and then have it dried to prepare the polyacrylonitrile fibre precursor (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0104] The aqueous solution of basic aluminum chloride is sprayed on the polyacrylonitrile fibre precursor (2), which is then dried to make the polyacrylonitrile fibre precursor (3); the mass concentration of alkaline aluminum chloride aqueous solution is 1.5%; the drying temperature is 120° C.;

[0105] Disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether to prepare the carbon powder dispersion liquid, and spray the carbon powder dispersion liquid on the polyacrylonitrile fibre precursor (3), and then have it dried to prepare the polyacrylonitrile fibre precursor (4); the mass concentration of carbon powder in carbon powder dispersion is 10%, and the particle size of carbon powder is 8 μm; the drying temperature is 120° C.;

[0106] Put the polyacrylonitrile fibre precursor (4) in the mixed atmosphere of oxygen and hydrogen bromide for heating and pre-oxidization to make the pre-oxidized fibre (5) as Test Sample 9; the pre-oxidation temperature is 250° C. and the time is 60 min; the fiber is elongated by 4% of its original length under the tension simultaneously applied; the volume concentration of hydrogen bromide in the mixed gas is 15% and the volume concentration of oxygen is 85%.

[0107] Determine the limiting oxygen index of Test Sample 8 and Test Sample 9.

[0108] Detection method of limiting oxygen index: measure the limiting oxygen index as per GB / T2406-2009.

[0109] Test Results and Conclusions: See the following table for test results. The limiting oxygen index of pre-oxidized fibre prepared in the mixed gas atmosphere of oxygen and hydrogen bromide is significantly higher than that of air. The limiting oxygen index can reflect the degree of preoxidation reaction. A high limiting oxygen index means a high degree of preoxidation, while a low limiting oxygen index means lack of preoxidation. The addition of hydrogen bromide gas in oxygen can promote the pre-oxidation reaction and increase the oxidation. In the same pre-oxidation time, the degree of pre-oxidation is high and the limiting oxygen index is high; when the same limiting oxygen index is reached, the pre-oxidation time will be shortened.TABLE 6Test Results of Test Case 6:LimitingOxygenSampleIndexDescription(LOI) (%)Test Sample 845Test Sample 961Test Case 7:

[0110] Purpose of Testing: to investigate the effect of radiation heating in preoxidation.Preparation of Test Sample 10:Dip the polyacrylonitrile fibre precursor (Test Sample 4) in the aqueous solution of perfluoroaluminal polyoxyethylene ether, and then have it dried to prepare the polyacrylonitrile fibre precursor (2); the mass concentration of the lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0112] Spray the aqueous solution of basic aluminum chloride on the polyacrylonitrile fibre precursor (2), which is then dried to make the polyacrylonitrile fibre precursor (3); the mass concentration of alkaline aluminum chloride aqueous solution is 1.5%; the drying temperature is 120° C.;

[0113] Disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether to prepare the carbon powder dispersion liquid, and spray the carbon powder dispersion liquid on the polyacrylonitrile fibre precursor (3), and then have it dried to prepare the polyacrylonitrile fibre precursor (4); the mass concentration of carbon powder in carbon powder dispersion is 10%, and the particle size of carbon powder is 8 μm; the drying temperature is 120° C.;

[0114] Put the polyacrylonitrile fibre precursor (4) in a mixed 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%;

[0115] Preoxidized by means of radiation heating to make pre-oxidized fibre (5) as Test Sample 10; the pre-oxidation temperature is 250° C. and the time is 60 min; the radiation frequency is 200 THz; the fiber is elongated by 4% of its original length under the tension simultaneously applied.

[0116] Determine the skin core ratio of Test Sample 9 and Test Sample 10.

[0117] Determine the skin core ratio with the method of optical microscope: the test sample is first embedded in a mixture of epoxy resin: curing agent=15:2 (mass ratio), cured at 60° C. for 2 h, and then sliced with EM TRIM2 ultrathin microtome of Leica (Germany); the thickness of the sample is approx. 400 nm; then under the BX53M high-power optical microscope of Olympus (Japan), slices are observed with 20× object lens; and then according to the different transmittance of the cortex and the inner core, the optical density value is analyzed with ImageJ software and the skin core ratio is calculated with the formula of the skin area of the cross section of the fibre / the total area*100%.

[0118] Test Results and Conclusions: See the following table for test results. After pre-oxidation reaction by means of radiation heating, the skin core structure has disappeared and the radiation heating effectively inhibited the formation of skin core structure.

[0119] Equipment such as ovens are mostly used for traditional pre-oxidation reaction heating, as a result, both heat and oxygen diffuse from the fibre surface to the inner core, and both are the promoter of the pre-oxidation reaction, leading to excessive pre-oxidation of the fibre surface, forming a dense trapezoidal structure, thus hindering the diffusion of oxygen to the interior of the fibre, resulting in a low degree of pre-oxidation reaction of the fibre core and forming a skin core structure.

[0120] The heat transfer mode of radiation heating is different from that of traditional oven heating. The radiation heating has a strong penetration force, so that heat is generated inside and on the surface of the fibre at the same time, and the pre-oxidation reaction is conducted at the same time; once released from pre-oxidation reaction, the heat is diffused from the inner core of the fibre to the surface, resulting in high temperature of the inner core and low temperature of the surface, accelerating the inner core cyclization reaction, thus reducing the difference between the pre-oxidation reaction of the inner core and the surface, preventing the formation of the skin core structure, thus improving the fibre uniformity and the fibre quality.

[0121] By controlling the frequency of the radiation wave, it is kept consistent with the absorption wave of the polyacrylonitrile fibre precursor, and their resonance achieved can make the temperature of fibre surface and inner core identical at the initial stage of heating, so as to avoid the temperature difference effect of traditional heating.

[0122] In addition, radiation heating has the advantages of convenient and accurate temperature control and high thermal efficiency.TABLE 7Test Results of Test Case 7:SampleSkin CoreDescriptionRatio (%)Test Sample 989.1Test Sample 1099.9Test Case 8:

[0123] Purpose of Testing: to investigate the effect of ultrasonication.Preparation of Test Sample 11:

[0124] Dip Test Sample 10 in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then have it dried to prepare pre-oxidized fibre (7); the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 2%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0125] Put the pre-oxidized fibre (7) in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre as Test Sample 11; the carbonization temperature is 1,000° C.; the carbonization time is 1.5 h.Preparation of Test Sample 12:Dip Test Sample 10 in the aqueous solution for ultrasonication to make pre-oxidized fibre (6); the said ultrasonic frequency is 1500 KHz; the ultrasonication time is 20 min;

[0127] Dip the pre-oxidized fibre (6) in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then have it dried to prepare pre-oxidized fibre (7); the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 2%; the dipping time is 1.5 h; the drying temperature is 120° C.;

[0128] Put the pre-oxidized fibre (7) in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre as Test Sample 12; the carbonization temperature is 1,000° C.; the carbonization time is 1.5 h.

[0129] Determine the tensile strength of Test Sample 11 and Test Sample 12. The method for determination of tensile strength is an existing technology and will not be described here.

[0130] Test Results and Conclusions: See the following table for test results. Through ultrasonication, the tensile strength of pre-oxidized carbon fibre is increased significantly after carbonization reaction.

[0131] The tar-like carbon powder deposited on the surface of pre-oxidized fibre can be removed through ultrasonication; when the pre-oxidized fibre is carbonized, high-quality carbon fibre can be obtained.TABLE 8Test Results of Test Case 8:SampleTensileDescriptionStrength (MPa)Test Sample 11268Test Sample 12353Test Case 9:

[0132] Purpose of Testing: to investigate the effect of sodium β-anthraquinone sulfonate.Preparation of Test Sample 13:Dip Test Sample 10 in the aqueous solution of sodium β-anthraquinone sulfonate for ultrasonication to make pre-oxidized fibre (6); the said ultrasonic frequency is 1,500 KHz; the ultrasonication time is 20 min; the mass concentration of sodium β-anthraquinone sulfonate aqueous solution is 20%;

[0134] Dip the pre-oxidized fibre (6) in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then have it dried to prepare pre-oxidized fibre (7); the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 2%; the dipping time is 1.5 h; the said drying temperature is 120° C.;

[0135] Put the pre-oxidized fibre (7) in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre as Test Sample 13; the carbonization temperature is 1,000° C.; the carbonization time is 1.5 h.

[0136] Determine the tensile strength of Test Sample 12 and Test Sample 13. The method for determination of tensile strength is an existing technology and will not be described here.

[0137] Test Results and Conclusions: See the following table for test results. The tensile strength of pre-oxidized carbon fibre is increased significantly after carbonization reaction through treatment with sodium β-anthraquinone sulfonate.

[0138] Have the pre-oxidized fibre carbonized to obtain carbon fibre in an oxygen-free and high-temperature environment, and the oxygen will reduce the quality of carbon fibre in the process of carbonization. However, the pre-oxidized fibre prepared from an oxygen-containing environment will inevitably contain a small amount of oxygen, which will then affect the quality of carbon fibre.

[0139] This Invention has used sodium β-anthraquinone sulfonate reducing solution to treat the pre-oxidized fibre, remove the oxygen absorbed by the pre-oxidized fibre, and then treated the fibre at high temperature in a non oxidizing atmosphere, so as to eliminate the impact of oxygen oxidation on the carbonization reaction, thus significantly improve the tensile strength of the carbon fibre, and further increase the limiting oxygen index.TABLE 9Test Results of Test Case 9:LimitingOxygenSampleTensileIndexDescriptionStrength (MPa)(LOI) (%)Test Sample 1235363Test Sample 1346675Embodiment 1

[0140] The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:

[0141] Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 20%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:1;

[0142] Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.1:100;

[0143] Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.2:100;

[0144] Step S4—prepare polyacrylonitrile fibre precursor: take the aqueous solution of dimethylacetamide with mass concentration of 40% as the coagulation bath, use the wet spinning method to spin Spinning Stock C, draw and stretch to prepare polyacrylonitrile fibre precursor I; the size of polyacrylonitrile fibre precursor I is 2D;

[0145] Step S5—treat with perfluoro lauryl alcohol polyoxyethylene ether: dip polyacrylonitrile fibre precursor I into the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare polyacrylonitrile fibre precursor II; the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 1.5%; the dipping time is 1 h; the drying temperature is 110° C.;

[0146] Step S6—spray basic aluminum chloride: spray the basic aluminum chloride aqueous solution on polyacrylonitrile fibre precursor II, and then dry to make polyacrylonitrile fibre precursor III; the mass concentration of the aqueous solution of alkaline aluminum chloride is 1%; the drying temperature is 110° C.;

[0147] Step S7—spray carbon powder: disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether in Step S5 to prepare Solution D, spray Solution D on polyacrylonitrile fibre precursor III, and then dry to prepare polyacrylonitrile fibre precursor IV; the mass concentration of carbon powder in Solution D is 5% and the particle size of carbon powder is 6 μm; the said drying temperature is 110° C.;

[0148] Step S8—prepare preoxidation gas atmosphere: replace the gas in the preoxidation chamber with a mixture of oxygen and hydrogen bromide, where the hydrogen bromide volume concentration is 10% and the oxygen volume concentration is 90%;

[0149] Step S9—conduct radiation heating preoxidation: place polyacrylonitrile fibre precursor IV in the gas atmosphere of Step S8, and preoxidize by means of radiation heating to produce pre-oxidized fibre V; the pre-oxidation temperature is 250° C. and the time is 20 min; the radiation frequency is 0.3 THz; the fiber is elongated by 2% of its original length under the tension simultaneously applied;

[0150] Step S10—conduct ultrasonication: immerse the pre-oxidized fibre V in the aqueous solution of sodium β-anthraquinone sulfonate, and use ultrasonication to prepare the pre-oxidized fibre VI; the ultrasonic frequency is 100 KHz; the ultrasonication time is 10 min; the mass concentration of sodium β-anthraquinone sulfonate aqueous solution is 15%;

[0151] Step S11—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip the pre-oxidized fibre VI in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare the pre-oxidized fibre VII; the mass concentration of the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether is 1.5%; the dipping time is 1 h; the drying temperature is 110° C.;

[0152] Step S12—perform carbonization treatment: put the pre-oxidized fibre VII in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre; the carbonization temperature is 800° C.; the carbonization time is 1 h.Embodiment 2

[0153] The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:

[0154] Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;

[0155] Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the said 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.15:100;

[0156] Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of said polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.3:100;

[0157] Step S4—prepare polyacrylonitrile fibre precursor: take the aqueous solution of dimethylacetamide with mass concentration of 45% as the coagulation bath, use the wet spinning method to spin Spinning Stock C, draw and stretch to prepare polyacrylonitrile fibre precursor I; the size of polyacrylonitrile fibre precursor I is 3D;

[0158] Step S5-treat with perfluoro lauryl alcohol polyoxyethylene ether: dip polyacrylonitrile fibre precursor I into the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare polyacrylonitrile fibre precursor II; the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 2.0%; the said dipping time is 1.5 h; the said drying temperature is 120° C.;

[0159] Step S6—spray basic aluminum chloride: spray the basic aluminum chloride aqueous solution on polyacrylonitrile fibre precursor II, and then dry to make polyacrylonitrile fibre precursor III; the mass concentration of the aqueous solution of alkaline aluminum chloride is 1.5%; the drying temperature is 120° C.;

[0160] Step S7—spray carbon powder: disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether in Step S5 to prepare Solution D, spray Solution D on polyacrylonitrile fibre precursor III, and then dry to prepare polyacrylonitrile fibre precursor IV; the mass concentration of carbon powder in Solution D is 10% and the particle size of carbon powder is 6 μm; the said drying temperature is 120° C.;

[0161] Step S8—prepare preoxidation gas atmosphere: replace the gas in the preoxidation chamber with a mixture of oxygen and hydrogen bromide, where the hydrogen bromide volume concentration is 15% and the oxygen volume concentration is 85%;

[0162] Step S9—conduct radiation heating preoxidation: place polyacrylonitrile fibre precursor IV in the gas atmosphere of Step S8, and preoxidize by means of radiation heating to produce pre-oxidized fibre V; the pre-oxidation temperature is 270° C. and the time is 40 min; the radiation frequency is 200 THz; the fiber is elongated by 3% of its original length under the tension simultaneously applied;

[0163] Step S10—conduct ultrasonication: immerse the pre-oxidized fibre V in the aqueous solution of sodium β-anthraquinone sulfonate, and use ultrasonication to prepare the pre-oxidized fibre VI; the ultrasonic frequency is 150 KHz; the ultrasonication time is 20 min; the mass concentration of sodium β-anthraquinone sulfonate aqueous solution is 20%;

[0164] Step S11—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip the pre-oxidized fibre VI in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare the pre-oxidized fibre VII; the mass concentration of the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether is 2.0%; the dipping time is 1.5 h; the said drying temperature is 120° C.;

[0165] Step S12—perform carbonization treatment: put the pre-oxidized fibre VII in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre; the carbonization temperature is 1,000° C.; the carbonization time is 1.5 h.Embodiment 3

[0166] The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:

[0167] Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 30%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:10;

[0168] Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.2:100;

[0169] Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.4:100;

[0170] Step S4—prepare polyacrylonitrile fibre precursor: take the aqueous solution of dimethylacetamide with mass concentration of 50% as the coagulation bath, use the wet spinning method to spin Spinning Stock C, draw and stretch to prepare polyacrylonitrile fibre precursor I; the size of polyacrylonitrile fibre precursor I is 5D;

[0171] Step S5—treat with perfluoro lauryl alcohol polyoxyethylene ether: dip polyacrylonitrile fibre precursor I into the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare polyacrylonitrile fibre precursor II; the mass concentration of the perfluoro lauryl alcohol polyoxyethylene ether aqueous solution is 2.5%; the dipping time is 2 h; the drying temperature is 130° C.;

[0172] Step S6—spray basic aluminum chloride: spray the basic aluminum chloride aqueous solution on polyacrylonitrile fibre precursor II, and then dry to make polyacrylonitrile fibre precursor III; the mass concentration of the aqueous solution of alkaline aluminum chloride is 2%; the rying temperature is 130° C.;

[0173] Step S7—spray carbon powder: disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether in Step S5 to prepare Solution D, spray Solution D on polyacrylonitrile fibre precursor III, and then dry to prepare polyacrylonitrile fibre precursor IV; the mass concentration of carbon powder in Solution D is 15% and the particle size of carbon powder is 10 μm; the drying temperature is 130° C.;

[0174] Step S8—prepare preoxidation gas atmosphere: replace the gas in the preoxidation chamber with a mixture of oxygen and hydrogen bromide, where the hydrogen bromide volume concentration is 20% and the oxygen volume concentration is 90%;

[0175] Step S9—conduct radiation heating preoxidation: place polyacrylonitrile fibre precursor IV in the gas atmosphere of Step S8, and preoxidize by means of radiation heating to produce pre-oxidized fibre V; the pre-oxidation temperature is 300° C. and the time is 60 min; the radiation frequency is 400 THz; the fiber is elongated by 5% of its original length under the tension simultaneously applied;

[0176] Step S10—conduct ultrasonication: immerse the pre-oxidized fibre V in the aqueous solution of sodium β-anthraquinone sulfonate, and use ultrasonication to prepare the pre-oxidized fibre VI; the ultrasonic frequency is 200 KHz; the ultrasonication time is 30 min; the mass concentration of sodium β-anthraquinone sulfonate aqueous solution is 25%;

[0177] Step S11—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip the pre-oxidized fibre VI in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare the pre-oxidized fibre VII; the mass concentration of the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether is 12.5%; the dipping time is 2 h; the drying temperature is 130° C.;

[0178] Step S12—perform carbonization treatment: put the pre-oxidized fibre VII in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre; the said carbonization temperature is 1,200° C.; the carbonization time is 2 h.

[0179] The void index, crimp number, coalescence rate, limiting oxygen index and skin core ratio of the pre-oxidized fibre Vin Embodiment 1, Embodiment 2 and Embodiment 3 are tested and the results are shown in the following table.

[0180] The pre-oxidized fibre V prepared by the invention has extremely low void index and coalescence rate, and high skin core ratio, which is conducive to the quality control of such pre-oxidized fibre and the quality improvement of any subsequent carbon fibre. The pre-oxidized fibre V prepared with this Invention has high crimp number and good flexibility, which can improve the spinnability in the production process and reduce the risk of fibre breakage. The pre-oxidized fibre Vprepared with this Invention has high limiting oxygen index, high-temperature resistance and good flame retardancy.TABLE 10Pre-oxidized Fibre V Test Results of the Embodiments:LimitingVoidCrimpCoales-OxygenSkinSampleIndexNumbercenceIndexCoreDescription(%)(Nr. / cm)Rate (%)(LOI) (%)Ratio (%)Embodi-1.09No6099.9ment 1coalescenceobservedEmbodi-1.09No6299.9ment 2coalescenceobservedEmbodi-0.910No6199.9ment 3coalescenceobserved

[0181] The coalescence rate, limiting oxygen index and tensile strength of polyacrylonitrile-based carbon fibre in Embodiment 1, Embodiment 2 and Embodiment 3 are tested and the results are shown in the following table.

[0182] The polyacrylonitrile-based carbon fibre prepared with this Invention has extremely low coalescence rate and this Invention has improved the acceptability of carbon fibre with high limiting oxygen index, high temperature resistance, good flame retardancy, high tensile strength and high quality.TABLE 11Test Results of Polyacrylonitrile-basedCarbon Fibre in the Embodiments:LimitingCoales-OxygenTensileSamplecenceIndexStrengthDescriptionRate (%)(LOI) (%)(MPa)Embodi-No73465ment 1coalescenceobservedEmbodi-No75470ment 2coalescenceobservedEmbodi-No75471ment 3coalescenceobserved

Examples

embodiment 1

[0140]The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:[0141]Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 20%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:1;[0142]Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.1:100;[0143]Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.2:100;[0144]Step S4—prepare polyacrylonitrile fibre precursor: ...

embodiment 2

[0153]The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:[0154]Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 25%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:5;[0155]Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the said 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.15:100;[0156]Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of said polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.3:100;[0157]Step S4—prepare polyacrylonitrile fibre ...

embodiment 3

[0166]The high-temperature-resistant polyacrylonitrile-based carbon fibre is prepared with the following method:[0167]Step S1—prepare Spinning Stock A: dissolve the polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of the polyacrylonitrile based copolymer reach 30%, and then make Spinning Stock A; the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:10;[0168]Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B; the molar ratio of the 2-acrylamido-2-methylpropane sulfonic acid to acrylonitrile monomer is 0.2:100;[0169]Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C; the mass ratio of polyoxyethylene sorbitan monopalmitate to polyacrylonitrile-based copolymer is 0.4:100;[0170]Step S4—prepare polyacrylonitrile fibre precursor:...

Claims

1. A preparation method of high-temperature-resistant polyacrylonitrile-based carbon fibre, which is characterized in that it includes the following steps:Step S1—prepare Spinning Stock A: dissolve polyacrylonitrile based copolymer in dimethylacetamide to make the mass concentration of polyacrylonitrile based copolymer reach 20%~30%, and then prepare Spinning Stock A;Step S2—add accelerator: add accelerator 2-acrylamido-2-methylpropane sulfonic acid to Spinning Stock A to prepare Spinning Stock B;Step S3—add polyoxyethylene sorbitan monopalmitate: add polyoxyethylene sorbitan monopalmitate to Spinning Stock B to prepare Spinning Stock C;Step S4—prepare polyacrylonitrile fibre precursor: take the aqueous solution of dimethylacetamide with mass concentration of 40%~50% as the coagulation bath, use the wet spinning method to spin Spinning Stock C, draw and stretch to prepare polyacrylonitrile fibre precursor I;Step S5—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip polyacrylonitrile fibre precursor I into perfluoro lauryl alcohol polyoxyethylene ether aqueous solution, and then dry to prepare polyacrylonitrile fibre precursor II;Step S6—spray basic aluminum chloride: spray the basic aluminum chloride aqueous solution on polyacrylonitrile fibre precursor II, and then dry to make polyacrylonitrile fibre precursor III;Step S7—spray carbon powder: disperse the carbon powder in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether of Step S5 to prepare Solution D, spray Solution D on polyacrylonitrile fibre precursor III, and then dry to prepare polyacrylonitrile fibre precursor IV;Step S8—prepare preoxidation gas atmosphere: replace the gas in the preoxidation chamber with a mixture of oxygen and hydrogen bromide;Step S9—conduct radiation heating preoxidation: place polyacrylonitrile fibre precursor IV in the gas atmosphere of Step S8, and preoxidize by radiation heating to produce pre-oxidized fibre V;Step S10—conduct ultrasonication: immerse the pre-oxidized fibre V in the aqueous solution of sodium β-anthraquinone sulfonate, and use ultrasonication to prepare the pre-oxidized fibre VI; wherein an ultrasonic frequency is 100 KHz-200 KHz; an ultrasonic treatment time is 10 min-30 min; a mass concentration of an aqueous solution of sodium beta-anthraquinone sulfonate is 15%-25%;Step S11—perform perfluoro lauryl alcohol polyoxyethylene ether treatment: dip the pre-oxidized fibre VI in the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether, and then dry to prepare the pre-oxidized fibre VII;Step S12—perform carbonization treatment: place the pre-oxidized fibre VII in nitrogen for heating and carbonization to produce polyacrylonitrile-based carbon fibre, wherein a carbonization temperature is 800° C.-1200° C.; a carbonization time is 1 h-2 h.

2. The preparation method stated in claim 1, which is characterized in that the molar ratio of acrylonitrile monomer and vinyl acetate in the polyacrylonitrile based copolymer is 100:1~100:10.

3. The preparation method stated in claim 2, which is characterized in that the molar ratio of 2-acrylamido-2-methylpropane sulfonic acid and acrylonitrile monomer is 0.1:100~0.2:100.

4. The preparation method stated in claim 3, which is characterized in that the mass ratio of the polyoxyethylene sorbitan monopalmitate and polyacrylonitrile based copolymer is 0.2:100~0.4:100.

5. The preparation method stated in claim 4, which is characterized in that the size of the polyacrylonitrile fibre precursor I is 2D~5D.

6. The preparation method stated in claim 5, which is characterized in that the mass concentration of the aqueous solution of perfluoro lauryl alcohol polyoxyethylene ether is 1.5%~2.5%; the dipping time is 1 h~2 h; the drying temperature is 110° C.~130° C.

7. The preparation method stated in claim 6, which is characterized in that the mass concentration of the alkaline aluminum chloride aqueous solution is 1%~2%; the drying temperature is 110° C.~130° C.

8. The preparation method stated in claim 7, which is characterized in that the mass concentration of the carbon powder in Solution Dis 5%~15%, and the particle size of the carbon powder is 6 μm~10 μm; the drying temperature is 110° C.~130° C.

9. A high-temperature-resistant polyacrylonitrile-based carbon fibre, which is characterized in that the high-temperature-resistant polyacrylonitrile-based carbon fibre is fabricated with the preparation method stated in claim 8.

10. The application of high-temperature-resistant polyacrylonitrile-based carbon fibre in fireproof fabric stated in claim 9.