Polyacrylonitrile fiber, flame-retardant polyacrylonitrile pre-oxidized fiber and preparation method

Abstract

The present application relates to a kind of polyacrylonitrile fibers, flame-retardant polyacrylonitrile pre-oxidized fibers and preparation method, the polyacrylonitrile fiber is with acrylonitrile, organic silicon modified acrylic and styrene sulfonic acid amine as raw material, carries out homogeneous solution copolymerization, obtains by dry spraying wet spinning;Polyacrylonitrile fiber is obtained by pre-oxidation treatment flame-retardant polyacrylonitrile pre-oxidized fiber.The flame-retardant polyacrylonitrile pre-oxidized fiber prepared by the present application has good flame-retardant effect, and the fiber mechanical property is excellent.

Description

Technical Field

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

[0002] Due to their unique properties, flame-retardant fibers are not only used in flame-retardant textiles for automobiles, trains, and airplanes; decorative textiles for public spaces such as hotels and restaurants; protective clothing and home textiles for hospitals, the military, and forest firefighting; but are also used in flame-retardant composite materials for aerospace applications. Currently, flame-retardant fibers primarily include flame-retardant polyester fibers, flame-retardant polyamide fibers, and flame-retardant regenerated cellulose fibers. Polyacrylonitrile pre-oxidized fibers offer excellent flexibility and high-temperature resistance, and will not burn, melt, soften, or drip. Their Limiting Oxygen Index (LOI) values ​​exceed 45%, significantly higher than those of other fibers. They are flame-retardant grade SA and do not emit toxic gases in flames or under intense radiant heat. They are excellent fire-retardant materials with broad application prospects in civilian, military, and industrial applications.

[0003] Chinese patent CN115478365B discloses a high-temperature-resistant, flame-retardant fiber nonwoven fabric and its preparation method. The high-temperature-resistant, flame-retardant fiber is a modified polyacrylonitrile pre-oxidized fiber. This method involves ammoniation of the polyacrylonitrile fiber, which is then used in the presence of a catalyst to produce an organopolysilazane-composite polyacrylonitrile fiber. This pre-oxidized fiber is then pre-oxidized to obtain the modified polyacrylonitrile pre-oxidized fiber. This method has the advantage of enhancing the strength and cohesion of the pre-oxidized polyacrylonitrile fiber to a certain extent. However, its disadvantages include a complex process, high cost, uneven distribution of ingredients, and the use of multiple dimethyl sulfoxides during the preparation process, which are not environmentally friendly.

[0004] Chinese patent CN116770580A discloses a method for producing post-treatment modified flame-retardant fibers. This method involves spraying a flame retardant solution onto the fibers. After drying and evaporating excess moisture, the flame retardant adheres to the fibers to produce the flame-retardant fibers. This method has the advantages of a one-time spray process, eliminating the need for soaking or circulating rinsing. The flame retardant preparation, fiber drying, and equipment operating power requirements are all lower than with existing technologies. However, this method suffers from uneven distribution of the flame retardant on the fibers, poor washability, and a lack of permanent flame retardancy.

[0005] Chinese patent CN110078861B discloses a polyacrylonitrile spinning solution, a preparation method thereof, and flame-retardant polyacrylonitrile fibers. The method uses a halogen-containing comonomer, which imparts flame retardancy to the resulting fibers and increases the polymerization reaction rate and conversion rate during the preparation of the polyacrylonitrile spinning solution. However, disadvantages include the halogen-containing comonomer's tendency to emit toxic gases at high temperatures, resulting in poor high-temperature resistance of the fibers produced using this method and the high monomer dosage. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a polyacrylonitrile fiber, a flame-retardant polyacrylonitrile pre-oxidized fiber and a preparation method, thereby avoiding the compatibility problem between the flame retardant and the polyacrylonitrile polymer solution in the flame-retardant fiber currently prepared by the post-treatment method, the poor high-temperature stability of the comonomer in the blending method and the poor flame retardancy of the fiber, and overcoming the problems of the existing flame-retardant fiber preparation process being complex, toxic substances polluting the environment, high raw material costs, short service life of the flame-retardant fiber, and uneven composition.

[0007] In order to solve the above technical problems, the present invention provides a polyacrylonitrile fiber, which is obtained by dry-jet wet spinning through homogeneous solution copolymerization of acrylonitrile, organosilicon-modified acrylic acid and styrene sulfonate amide as raw materials.

[0008] The present invention provides a method for preparing polyacrylonitrile fiber, comprising the following steps:

[0009] (1) Synthesizing silicone-modified acrylic acid using dichlorotetramethyldisiloxane and hydroxy acrylate as raw materials;

[0010] (2) dissolving acrylonitrile, silicone-modified acrylic acid, and styrenesulfonic acid amine monomers in dimethyl sulfoxide to prepare a homogeneous solution, and then degassing and filtering;

[0011] (3) passing the filtered homogeneous solution into a polymerization kettle for polymerization to prepare a polymerization solution;

[0012] (4) The polymer solution is filtered, degassed, filtered, concentrated, and filtered to obtain a spinning solution;

[0013] (5) The spinning solution is wet-spinned to obtain polyacrylonitrile fiber.

[0014] Preferably, the organosilicon-modified acrylic acid in step (1) is prepared by the following method: adding a dichlorotetramethyldisiloxane mixture to a mixture of hydroxy acrylates at 2-8° C. under nitrogen protection; heating the resulting mixed solution to 22-30° C. for reaction, and after the reaction is completed for 10-12 hours, filtering to finally obtain the organosilicon-modified acrylic acid.

[0015] Preferably, in the hydroxy acrylate mixed solution, the molar ratio of hydroxy acrylate, pyridine and dimethyl sulfoxide is 1:1:3-7; in the dichlorotetramethyldisiloxane mixed solution, the molar ratio of dichlorotetramethyldisiloxane and dimethyl sulfoxide is 1:4-7; in the mixed solution obtained after the addition, the molar ratio of hydroxy acrylate and dichlorotetramethyldisiloxane is 2-2.3:1.

[0016] Preferably, the hydroxy acrylate in step (1) comprises one of hydroxyethyl acrylate, hydroxypropyl acrylate or hydroxybutyl acrylate.

[0017] Preferably, the molar fractions of acrylonitrile, silicone-modified acrylic acid and styrenesulfonic acid amine in step (2) are 96.4% to 98.4%, 0.8% to 1.8% and 0.8% to 1.8%, respectively; and the mass percentage concentration of the monomers in the homogeneous solution prepared in step (2) is 18% to 28%.

[0018] Preferably, the polymerization temperature in step (3) is 55-73° C., the reaction time is 1-8 h, and the stirring speed is 100-350 r / min.

[0019] The present invention provides a flame-retardant polyacrylonitrile pre-oxidized fiber. The flame-retardant polyacrylonitrile pre-oxidized fiber is obtained by subjecting the above-mentioned polyacrylonitrile fiber to a pre-oxidation treatment.

[0020] The present invention also provides a method for preparing flame-retardant polyacrylonitrile pre-oxidized fiber, comprising placing the above-mentioned polyacrylonitrile fiber in a pre-oxidation furnace, setting four temperature zones with a temperature rising gradient, and applying multiple stages of drafting to perform pre-oxidation to obtain flame-retardant polyacrylonitrile pre-oxidized fiber.

[0021] Preferably, the atmosphere in the pre-oxidation furnace is air, and the air flow rate is 1 to 1.5 m / s; the multi-stage drawing includes one temperature zone drawing, two temperature zone drawing, three temperature zone drawing and four temperature zone drawing, and the applied drawing is 1% to 4%; the pre-oxidation temperature is: 220 to 250°C for the first temperature zone, 235 to 260°C for the second temperature zone, 250 to 270°C for the third temperature zone, and 260 to 280°C for the fourth temperature zone, and the insulation time for each temperature zone is 10 to 35 minutes.

[0022] Beneficial effects

[0023] The process of the invention is simple and has good repeatability; the polymerization reaction conversion rate is high, the spinnability is good, and the production cost is low; the prepared flame-retardant polyacrylonitrile pre-oxidized fiber has good flame retardant effect, and the obtained fiber has excellent mechanical properties and has both strength and heat resistance. DETAILED DESCRIPTION

[0024] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0025] Example 1

[0026] The polyacrylonitrile fiber and the flame-retardant polyacrylonitrile pre-oxidized fiber in this embodiment are prepared according to the following method:

[0027] (1) preparing a solution of hydroxybutyl acrylate, pyridine and dimethyl sulfoxide at a molar ratio of 2:2:9; and preparing a solution of dichlorotetramethyldisiloxane and dimethyl sulfoxide at a molar ratio of 1:6;

[0028] (2) adding the prepared dichlorotetramethyldisiloxane mixture to the hydroxybutyl acrylate mixture at 5°C under nitrogen protection, wherein the molar ratio of hydroxybutyl acrylate to dichlorotetramethyldisiloxane in the resulting mixed solution is 2:1;

[0029] (3) heating the mixed solution obtained in step (2) to 25° C. for reaction, and after the reaction is completed for 10 hours, filtering to finally obtain organosilicon-modified acrylic acid;

[0030] (4) dissolving acrylonitrile (96.4%, molar fraction), silicone-modified acrylic acid (1.8%, molar fraction) and styrenesulfonamide (1.8%, molar fraction) in dimethyl sulfoxide to prepare a homogeneous solution, wherein the mass percentage concentration of the monomers is 20%, and degassing and filtering are performed. Then, the filtered homogeneous solution is introduced into a polymerization kettle for polymerization. During the polymerization, the temperature is maintained at 58° C., the stirring speed is 150 r / min, and the polymerization time is 6 hours to prepare a polymerization solution; filtering, degassing, filtering, concentrating, and filtering the polymerization solution to obtain a spinning solution; and dry-jet wet spinning is performed to obtain polyacrylonitrile fibers;

[0031] (5) The prepared polyacrylonitrile fiber is oxidized in a pre-oxidation furnace, the atmosphere in the furnace is air, and the air flow rate is 1.2 m / s; the temperature in the furnace is divided into four temperature zones, and different levels of drafting are applied. Specifically, the temperature of the first temperature zone is 230-240°C, kept warm for 30 minutes, and the drafting is 1%; the temperature of the second temperature zone is 240-255°C, kept warm for 30 minutes, and the drafting is 3%; the temperature of the third temperature zone is 255-265°C, kept warm for 25 minutes, and the drafting is 2.5%; the temperature of the fourth temperature zone is 265-280°C, kept warm for 25 minutes, and the drafting is 1.5%; finally, flame-retardant polyacrylonitrile pre-oxidation fiber is obtained.

[0032] Example 2

[0033] The polyacrylonitrile fiber and the flame-retardant polyacrylonitrile pre-oxidized fiber in this embodiment are prepared according to the following method:

[0034] (1) Hydroxypropyl acrylate, pyridine, and dimethyl sulfoxide in a molar ratio of 2:2:10 are prepared into a solution; dichlorotetramethyldisiloxane and dimethyl sulfoxide in a molar ratio of 1:6 are prepared into a solution;

[0035] (2) Under the protection of nitrogen at 5℃, the prepared dichlorotetramethyldisiloxane mixture was added into the hydroxypropyl acrylate mixture, and the molar ratio of hydroxypropyl acrylate to dichlorotetramethyldisiloxane in the obtained mixture was 2:1;

[0036] (3) The mixture obtained in step (2) was warmed to 25℃ for reaction, and after 11h of reaction, filtration was performed, and finally the silicone-modified acrylic acid was obtained;

[0037] (4) Acrylonitrile (97.4%, mole fraction), silicone-modified acrylic acid (1.3%, mole fraction) and styrene sulfonic acid amine (1.3%, mole fraction) were dissolved in dimethyl sulfoxide to prepare a homogeneous solution, wherein the mass percentage concentration of the monomers was 22%, and the homogeneous solution was degassed and filtered, and then introduced into a polymerization kettle for polymerization, and the temperature was maintained at 65℃ and the stirring speed was 200r / min during polymerization, and the polymerization time was 5h, to prepare a polymerization liquid; the polymerization liquid was filtered, degassed, filtered, concentrated and filtered to obtain a spinning stock solution; and a polyacrylonitrile fiber was obtained by dry-jet wet spinning;

[0038] (5) The prepared polyacrylonitrile fiber was oxidized in a pre-oxidation furnace, the atmosphere in the furnace was air, the air flow rate was 1.5m / s; the temperature in the furnace was divided into four temperature zones, and each stage of stretching was applied, specifically, the temperature of the first temperature zone was 230-240℃, the temperature was maintained for 25min, and the stretching was applied at 1.5%; the temperature of the second temperature zone was 240-250℃, the temperature was maintained for 25min, and the stretching was applied at 2.5%; the temperature of the third temperature zone was 250-260℃, the temperature was maintained for 25min, and the stretching was applied at 4%; the temperature of the fourth temperature zone was 260-280℃, the temperature was maintained for 25min, and the stretching was applied at 2%; and finally a flame-retardant polyacrylonitrile pre-oxidized fiber was obtained.

[0039] Example 3

[0040] The polyacrylonitrile fiber and the flame-retardant polyacrylonitrile pre-oxidized fiber in this example were prepared as follows:

[0041] (1) Hydroxyethyl acrylate, pyridine and dimethyl sulfoxide were prepared into a solution with a molar ratio of 2:2:10; dichlorotetramethyldisiloxane and dimethyl sulfoxide were prepared into a solution with a molar ratio of 1:6;

[0042] (2) Under the protection of nitrogen at 2℃, the prepared dichlorotetramethyldisiloxane mixture was added into the hydroxyethyl acrylate mixture, and the molar ratio of hydroxyethyl acrylate to dichlorotetramethyldisiloxane in the obtained mixture was 2:1;

[0043] (3) heating the mixed solution obtained in step (2) to 28° C. for 12 h. After the reaction is completed, filtering is performed to obtain organosilicon-modified acrylic acid;

[0044] (4) dissolving acrylonitrile (98.4%, molar fraction), silicone-modified acrylic acid (0.8%, molar fraction) and styrenesulfonic acid amine (0.8%, molar fraction) in dimethyl sulfoxide to prepare a homogeneous solution, wherein the mass percentage concentration of the monomers is 25%, and degassing and filtering are performed. Then, the filtered homogeneous solution is introduced into a polymerization kettle for polymerization. During the polymerization, the temperature is maintained at 68° C., the stirring speed is 150 r / min, and the polymerization time is 6 hours to prepare a polymerization solution; filtering, degassing, filtering, concentrating, and filtering the polymerization solution to obtain a spinning solution; and dry-jet wet spinning is performed to obtain polyacrylonitrile fibers;

[0045] (5) The prepared polyacrylonitrile fiber is oxidized in a pre-oxidation furnace, the atmosphere in the furnace is air, and the air flow rate is 1.3 m / s; the temperature in the furnace is divided into four temperature zones, and different levels of drafting are applied. Specifically, the temperature of the first temperature zone is 230-250°C, kept warm for 28 minutes, and the drafting is 1.5%; the temperature of the second temperature zone is 250-260°C, kept warm for 28 minutes, and the drafting is 2.5%; the temperature of the third temperature zone is 260-270°C, kept warm for 28 minutes, and the drafting is 4%; the temperature of the fourth temperature zone is 270-280°C, kept warm for 28 minutes, and the drafting is 2%; finally, flame-retardant polyacrylonitrile pre-oxidation fiber is obtained.

[0046] Example 4

[0047] The polyacrylonitrile fiber and the flame-retardant polyacrylonitrile pre-oxidized fiber in this embodiment are prepared according to the following method:

[0048] (1) preparing a solution of hydroxyethyl acrylate, pyridine and dimethyl sulfoxide at a molar ratio of 2:2:9; and preparing a solution of dichlorotetramethyldisiloxane and dimethyl sulfoxide at a molar ratio of 1:4.5;

[0049] (2) Add the prepared dichlorotetramethyldisiloxane mixture to the hydroxyethyl acrylate mixture at 2°C under nitrogen protection, and the molar ratio of hydroxyethyl acrylate to dichlorotetramethyldisiloxane in the resulting mixed solution is 2:1.

[0050] (3) heating the mixed solution obtained in step (2) to 30° C. and reacting for 12 hours. After the reaction is completed, filtering is performed to finally obtain organosilicon-modified acrylic acid;

[0051] (4) dissolving acrylonitrile (98%, molar fraction), silicone-modified acrylic acid (1%, molar fraction) and styrenesulfonic acid amine (1%, molar fraction) in dimethyl sulfoxide to prepare a homogeneous solution, wherein the mass percentage concentration of the monomers is 28%, and degassing and filtering are performed. Then, the filtered homogeneous solution is introduced into a polymerization kettle for polymerization. During the polymerization, the temperature is maintained at 60° C., the stirring speed is 250 r / min, and the polymerization time is 4 hours to prepare a polymerization solution; filtering, degassing, filtering, concentrating, and filtering the polymerization solution to obtain a spinning solution; and dry-jet wet spinning is performed to obtain polyacrylonitrile fibers;

[0052] (5) The polyacrylonitrile fiber is placed in a pre-oxidation furnace for oxidation. The atmosphere in the furnace is air and the air flow rate is 1.3 m / s. The temperature in the furnace is divided into four temperature zones, and different levels of drafting are applied. Specifically, the temperature of the first temperature zone is 220-240°C, kept warm for 35 minutes, and the drafting is 1.5%; the temperature of the second temperature zone is 240-250°C, kept warm for 35 minutes, and the drafting is 2.5%; the temperature of the third temperature zone is 250-265°C, kept warm for 22 minutes, and the drafting is 4%; the temperature of the fourth temperature zone is 265-280°C, kept warm for 22 minutes, and the drafting is 2%; and finally, flame-retardant polyacrylonitrile pre-oxidation fiber is obtained.

[0053] Comparative Example 1

[0054] To further illustrate that the present invention can effectively improve the flame retardant properties of the fiber by using silicone-modified acrylic acid and styrene sulfonamide as comonomers, the polymerization reaction is carried out by replacing the comonomers, and the steps are as follows:

[0055] (1) A homogeneous solution of three monomers, acrylonitrile (96.4%, molar fraction), methyl acrylate (1.8%, molar fraction) and styrenesulfonamide (1.8%, molar fraction), was prepared by dissolving them in dimethyl sulfoxide, wherein the mass percentage concentration of the monomers was 20%, and the solution was degassed and filtered. The filtered homogeneous solution was then introduced into a polymerization kettle for polymerization. During the polymerization, the temperature was maintained at 65°C, the stirring speed was 300 r / min, and the polymerization time was 8 hours to prepare a polymerization solution. The polymerization solution was filtered, degassed, filtered, concentrated, and filtered to obtain a spinning solution. The polyacrylonitrile fiber was obtained by dry-jet wet spinning.

[0056] (2) The polyacrylonitrile fiber is placed in a pre-oxidation furnace for oxidation. The oxidation conditions are the same as those in Example 1. The atmosphere in the furnace is air and the air flow rate is 1.2 m / s. The temperature in the furnace is divided into four temperature zones, and different levels of drafting are applied. Specifically, the temperature of the first temperature zone is 230-240°C, kept warm for 30 minutes, and the drafting is 1%; the temperature of the second temperature zone is 240-255°C, kept warm for 30 minutes, and the drafting is 3%; the temperature of the third temperature zone is 255-265°C, kept warm for 25 minutes, and the drafting is 2.5%; the temperature of the fourth temperature zone is 265-280°C, kept warm for 25 minutes, and the drafting is 1.5%; and finally, the polyacrylonitrile pre-oxidized fiber is obtained.

[0057] After testing, the polyacrylonitrile pre-oxidized fiber prepared in this comparative example was measured by an LOI 901 limiting oxygen index instrument, and its limiting oxygen index test value was 47, while the LOI values ​​of Examples 1 to 4 were all greater than 53.

[0058] Comparative Example 2

[0059] In order to further illustrate that the pre-oxidation process adopted in the present invention can effectively improve the flame retardant properties of the flame retardant fiber, polyacrylonitrile fiber without pre-oxidation was used as a control.

[0060] The manufacturing steps of this polyacrylonitrile fiber are as follows:

[0061] (1) preparing a solution of hydroxyethyl acrylate, pyridine and dimethyl sulfoxide at a molar ratio of 2:2:9; and preparing a solution of dichlorotetramethyldisiloxane and dimethyl sulfoxide at a molar ratio of 1:4.5;

[0062] (2) adding the prepared dichlorotetramethyldisiloxane mixture to the hydroxyethyl acrylate mixture at 5°C under nitrogen protection, wherein the molar ratio of hydroxyethyl acrylate to dichlorotetramethyldisiloxane in the resulting mixed solution is 2:1;

[0063] (3) heating the mixed solution obtained in step (2) to 28° C. and reacting for 12 hours. After the reaction is completed, filtering is performed to finally obtain organosilicon-modified acrylic acid;

[0064] (4) The obtained acrylonitrile (97.4%, molar fraction), silicone-modified acrylic acid (1.3%, molar fraction) and styrenesulfonic acid amine (1.3%, molar fraction) three monomers are dissolved in dimethyl sulfoxide to prepare a homogeneous solution, wherein the mass percentage concentration of the monomers is 23%, and the solution is degassed and filtered. The filtered homogeneous solution is then introduced into a polymerization kettle for polymerization. During the polymerization, the temperature is maintained at 58°C, the stirring speed is 150 r / min, and the polymerization time is 6 hours to prepare a polymerization solution; the polymerization solution is filtered, degassed, filtered, concentrated, and filtered to obtain a spinning solution; and polyacrylonitrile fibers are obtained by dry-jet wet spinning.

[0065] After testing, it was found that the polyacrylonitrile fiber prepared in this comparative example burned out upon ignition and did not have flame retardancy.

[0066] By comparing Comparative Example 1 and Examples 1 to 4, it can be seen that the present invention uses silicone-modified acrylic acid and styrene sulfonamide as comonomers to effectively improve the flame retardant properties of the fiber.

[0067] By comparing Comparative Example 2 and Examples 1 to 4, it can be seen that the pre-oxidation process of the present invention can effectively improve the flame retardant properties of the fiber.

Claims

1. A flame-retardant polyacrylonitrile pre-oxidized fiber, characterized in that: The flame-retardant polyacrylonitrile pre-oxidized fiber is obtained by pre-oxidizing polyacrylonitrile fiber. The polyacrylonitrile fiber is obtained by homogeneous solution copolymerization of acrylonitrile, organosilicon-modified acrylic acid and styrene sulfonate amine as raw materials, and dry-jet wet spinning. The organosilicon-modified acrylic acid is prepared by the following method: adding a dichlorotetramethyldisiloxane mixed solution to an acrylic acid hydroxy ester mixed solution at 2-8° C. under nitrogen protection; heating the obtained mixed solution to 22-30° C. for reaction, and after reacting for 10-12 hours, filtering to finally obtain the organosilicon-modified acrylic acid.

2. A method for preparing the flame-retardant polyacrylonitrile pre-oxidized fiber according to claim 1, comprising the following steps: (1) Synthesizing silicone-modified acrylic acid using dichlorotetramethyldisiloxane and hydroxy acrylate as raw materials; (2) dissolving acrylonitrile, silicone-modified acrylic acid, and styrenesulfonic acid amine monomers in dimethyl sulfoxide to prepare a homogeneous solution, and then degassing and filtering; (3) passing the filtered homogeneous solution into a polymerization kettle for polymerization to prepare a polymerization solution; (4) The polymer solution is filtered, degassed, filtered, concentrated, and filtered to obtain a spinning solution; (5) obtaining polyacrylonitrile fiber by dry-jet wet spinning of the spinning solution; (6) The polyacrylonitrile fiber is placed in a pre-oxidation furnace, four temperature zones are set with a temperature gradient, and multiple stretching steps are applied to perform pre-oxidation to obtain flame-retardant polyacrylonitrile pre-oxidized fiber.

3. The method for preparing flame-retardant polyacrylonitrile pre-oxidized fiber according to claim 2, characterized in that: In the hydroxy acrylate mixed solution, the molar ratio of hydroxy acrylate, pyridine and dimethyl sulfoxide is 1:1:3-7; in the dichlorotetramethyldisiloxane mixed solution, the molar ratio of dichlorotetramethyldisiloxane and dimethyl sulfoxide is 1:4-7; in the mixed solution obtained after the addition, the molar ratio of hydroxy acrylate and dichlorotetramethyldisiloxane is 2-2.3:

1.

4. The method for preparing flame-retardant polyacrylonitrile pre-oxidized fiber according to claim 2, characterized in that: The hydroxy acrylate in step (1) includes one of hydroxyethyl acrylate, hydroxypropyl acrylate or hydroxybutyl acrylate.

5. The method for preparing flame-retardant polyacrylonitrile pre-oxidized fiber according to claim 2, characterized in that: The molar fractions of acrylonitrile, organosilicon-modified acrylic acid and styrenesulfonic acid amine in step (2) are 96.4% to 98.4%, 0.8% to 1.8% and 0.8% to 1.8% respectively; the mass percentage concentration of the monomers in the homogeneous solution prepared in step (2) is 18% to 28%.

6. The method for preparing flame-retardant polyacrylonitrile pre-oxidized fiber according to claim 2, characterized in that: The polymerization temperature in step (3) is 55-73° C., the reaction time is 1-8 hours, and the stirring speed is 100-350 r / min.

7. The method for preparing flame-retardant polyacrylonitrile pre-oxidized fiber according to claim 2, characterized in that: In the step (6), the atmosphere in the pre-oxidation furnace is air, and the air flow rate is 1 to 1.5 m / s; the multi-stage stretching includes one temperature zone stretching, two temperature zone stretching, three temperature zone stretching and four temperature zone stretching, and the applied stretching is 1% to 4%; the pre-oxidation temperature is: 220 to 250°C for the first temperature zone, 235 to 260°C for the second temperature zone, 250 to 270°C for the third temperature zone, and 260-280°C for the fourth temperature zone, and the insulation time of each temperature zone is 10 to 35 minutes.