Crystallization-crosslinking structure flame-retardant fiber and preparation method thereof

Abstract

The invention discloses a preparation method of a flame-retardant fiber with a'crystallization-crosslinking 'structure, and belongs to the field of preparation of special flame-retardant fibers.The preparation method comprises the steps that urea and aldehydes are added into a reactor and react for a period of time under the alkaline condition, then a molybdic acid modified linear polymer is added, the pH value is adjusted to be acidic after the reaction, cooling and reduced pressure distillation are conducted after a period of time, and the flame-retardant fiber with the crystallization-crosslinking structure is obtained; and carrying out dry spinning and microwave curing to obtain the urea formaldehyde fiber with the crystal-crosslinking structure. The linear polymer is introduced into the urea formaldehyde fiber, so that the spinning performance of urea formaldehyde resin is improved, a linear polymer crystal-urea formaldehyde cross-linked block ordered structure is constructed, the mechanical property of the fiber is improved, the flame retardant property is ensured, and the application of the urea formaldehyde fiber is facilitated.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of special flame-retardant fibers, and particularly relates to a method for obtaining a spinning solution by modifying a linear polymer block of urea-formaldehyde resin with molybdic acid, dry spinning the solution, microwave curing and cold crystallization to obtain a urea-formaldehyde fiber with a "crystalline-crosslinked" structure and a preparation method thereof. Background Art

[0002] Urea-formaldehyde resin was first synthesized by B. Tollens in 1844. Tollens and Goldschmidt further studied the reaction of urea and formaldehyde, and they believed that an amorphous urea-formaldehyde polymer could be formed through the reaction. In 1896, C. Goldschmidt [GOLDSCHMIDT C. Ueber die einwirkung der muskelthätigkeit aufdie athmung und die herzthätigkeit [J]. Ber Dtsch Chem Ges, 1896] studied and applied for a patent. John [JOHN H. Manufacture of Aldehyde condensation product capable oftechnical utilization [J]. US Patent, 1920] published several patents in 1920, which stimulated the commercial potential of these materials. In 1929, IG Company developed a urea-formaldehyde resin condensation intermediate named KanritLeim that could cure and bond wood at room temperature, which attracted people's attention. From 1930 to 1950, in-depth studies were carried out on formaldehyde resins such as phenolic resin (PF), urea-formaldehyde resin (UF), and melamine-formaldehyde resin (MF).

[0003] The commercial production of urea-formaldehyde resin began in Austria, Germany, and the United States in the early 1920s. Urea-formaldehyde resin reached commercial maturity between 1930 and 1975 and began to penetrate into emerging markets. In particular, the commercial application of UF resin as an adhesive for plywood and particleboard accelerated due to the prosperity of the real estate industry after World War II. By 1975, the commercial production of UF resin adhesives for plywood and particleboard had been fully mature. During this industrial success, Meyer published a monograph on urea-formaldehyde resin in 1979, which was a milestone in the history of urea-formaldehyde resin, comprehensively covering most of the research and patents reported before the mid-1970s. According to the research results of this period, various products were prepared by the condensation of formaldehyde and urea.

[0004] Urea-formaldehyde resin has great potential in intrinsically flame-retardant fibers due to the flame retardancy of UF resin. V. Rogers et al. successfully prepared fibers from urea-formaldehyde resin by wet spinning and successfully cured them. However, due to the poor spinnability and insufficient mechanical properties of urea-formaldehyde fibers, no further research has been reported. The present invention combines the crystallinity of linear polymers and the crosslinkability of urea-formaldehyde resin, conducts block reactions between the two, and then spins and cures to obtain urea-formaldehyde flame-retardant fibers with a "crystalline-crosslinked" structure. Summary of the Invention

[0005] The present invention provides a flame-retardant fiber with a "crystalline-crosslinked" structure and a preparation method thereof. Urea and aldehydes are added to a reactor, and after reacting for a period of time under alkaline conditions, a molybdate-modified linear polymer is added. After the reaction, the pH value is adjusted, and finally, the temperature is lowered and the pressure is reduced for distillation to obtain a urea-formaldehyde spinning solution. Dry spinning and microwave curing are carried out to obtain urea-formaldehyde fibers with a crystalline-crosslinked structure. The fibers exhibit excellent flame retardancy and mechanical properties, which are beneficial to the popularization and application of low-cost, intrinsically flame-retardant urea-formaldehyde fibers.

[0006] To solve the above technical problems, the technical solution of the present invention is as follows: A preparation method of a flame-retardant fiber with a "crystalline-crosslinked" structure, the steps are as follows: (1) An aldehyde compound and urea are added to reactor A, and the pH value is adjusted to 8-10 with an alkali at a temperature of 30-70 °C, and then heated to 90-100 °C for reaction to obtain a branched urea-formaldehyde prepolymer; (2) Molybdic acid and a linear polymer with two terminal hydroxyl groups are added to reactor B to react to obtain a molybdate-modified linear polymer, which is then blended with the branched urea-formaldehyde prepolymer and the pH is adjusted to 3-7 with an acid for reaction, and then the pH is adjusted to 5-8 with triethanolamine and the temperature is lowered to 40-70 °C, and the pressure is reduced for distillation to obtain a viscous and spinnable block urea-formaldehyde resin; (3) The viscous and spinnable block urea-formaldehyde resin enters the spinning channel through the spinneret of a dry spinning machine, and the filaments are heated in the spinning channel to obtain nascent urea-formaldehyde fibers, which are then crosslinked in a microwave, and finally, a flame-retardant urea-formaldehyde fiber with a "crystalline-crosslinked" structure is obtained at a constant temperature of 30-70 °C.

[0007] Among them, in the step (1), the aldehyde compound is one of formaldehyde, paraformaldehyde, acetaldehyde, and glutaraldehyde, and the alkali for adjusting the pH is one of sodium hydroxide, calcium hydroxide, triethanolamine, and ammonia water; the mass ratio of urea to the aldehyde compound is 1:(0.5-1.5).

[0008] Among them, in the step (1), the reaction time after adding the alkali is 0.3-3 hours.

[0009] Among them, the dihydroxy-terminated linear polymer added to reactor B in step (2) is water-soluble PEG or PEG-PCL block polymer, and the molar ratio to molybdic acid is 1:(0.5 - 2). The weight ratio of molybdic acid-modified linear polymer to urea is (0.01 - 2):1, and the reaction time of molybdic acid with the dihydroxy-terminated linear polymer is 0.1 - 2 hours.

[0010] Among them, the acid in step (2) is one of hydrochloric acid, sulfuric acid, formic acid, acetic acid, and benzenesulfonic acid. The reaction time after adding the acid is 0.1 - 2 hours; the reduced pressure distillation time after adding triethanolamine is 0.4 - 4 hours, and the viscosity of the viscous spinnable block urea-formaldehyde resin is 100 - 2000 Pa·s.

[0011] Among them, in step (3), the diameter of the spinneret holes of the dry spinning nozzle is 80 - 300 microns, the length of the spinning channel is 1 - 5 meters, the temperature of the spinning channel is 40 - 130 °C, and the spinning speed is 20 - 400 m / min.

[0012] Among them, in step (3), the microwave power is 500 - 5500 W, the microwave time is 0.01 - 1 hour, and the constant temperature time is 0.1 - 3 hours.

[0013] A "crystalline-crosslinked" structure flame-retardant fiber is made by the above preparation method.

[0014] Compared with the prior art, the present invention has the following beneficial effects: A high proportion of aldehyde to urea ratio is beneficial to the formation of multi-branches, providing a material basis for crosslinking; using a dihydroxy-terminated water-soluble linear polymer to obtain a molybdic acid-coupled triblock copolymer; the linear polymer has no hydroxyl groups on the main chain except at both ends and does not react with urea-formaldehyde to ensure the stability of the straight-chain structure and does not form branched or crosslinked structures, providing a basis for crystallization; using molybdic acid for modification is beneficial to improving the char residue rate and thermal stability of the fiber, and at the same time the flame retardancy is improved; using triethanolamine is beneficial to the adjustment and control of the reaction; using the steps of alkali, acid, and alkali is beneficial to increasing the molecular weight of urea-formaldehyde and reducing the degree of branching, and is beneficial to the formation of a crystalline structure; finally adding alkali to adjust the pH value is beneficial to reducing the polycondensation reaction rate to achieve the risk of reducing gelation; reduced pressure distillation is beneficial to the growth of molecular chains and the increase of viscosity; microwave curing has a fast curing rate and is beneficial to reducing the skin-core structure of the fiber, making the internal and external structures uniform and improving the mechanical properties; cold crystallization after curing is beneficial to the formation of a crystalline structure by the polymer; without adding a flame retardant, a urea-formaldehyde fiber with an excellent flame retardant performance, less toxic and harmful gases released during combustion, flame retardant safety, and high mechanical properties in a "crystalline-crosslinked" ordered structure can be obtained. Specific embodiments

[0015] Next, in combination with specific embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention. Example 1

[0016] This example provides a method for preparing a flame-retardant fiber with a "crystallization-crosslinking" structure, and the steps are as follows: (1) Formaldehyde and urea, which are aldehyde compounds, are added to a reactor in a certain mass ratio of 1:0.5. At 30 °C, the pH value is adjusted to 8 with sodium hydroxide and heated to 90 °C for 0.3 hours to obtain a branched urea-formaldehyde prepolymer.

[0017] (2) The linear polymer with double-terminal hydroxyl groups added to reactor B reacts with molybdic acid to obtain a molybdic acid-modified polymer. The linear polymer is water-soluble PEG, and the molar ratio of it to molybdic acid is 1:0.5; molybdic acid reacts with the linear polymer with double-terminal hydroxyl groups for 0.1 hour and is blended with the urea-formaldehyde prepolymer. The weight ratio of the molybdic acid-modified linear polymer to urea is 0.01:1; then the pH is adjusted to 3 with hydrochloric acid and reacted for 0.1 hour, and then the pH is adjusted to 5 with triethanolamine and cooled to 40 °C, and vacuum distillation is carried out for 0.4 hours to obtain a spinnable block urea-formaldehyde resin with a viscosity of 100 Pa·s.

[0018] (3) The spinning dope enters the spinning channel through the spinneret of a dry spinning machine. The diameter of the spinneret holes of the spinneret is 80 microns. The filaments are heated in the spinning channel to obtain primary urea-formaldehyde fibers. The length of the dry spinning channel is 1 meter, the temperature of the channel is 40 °C, and the spinning speed is 20 m / min; then it is placed in a microwave with a power of 500 W for crosslinking for 0.01 hour, and finally kept at a constant temperature of 30 °C for 0.1 hour to obtain a flame-retardant urea-formaldehyde fiber with a "crystallization-crosslinking" structure.

[0019] The prepared urea-formaldehyde fiber has a LOI value of 29, a diameter of 7 microns, a tensile strength of 140 MPa, an elongation at break of 10%, a char residue rate at 800 °C of 30%, and the total heat release of a 100 g / m² fabric is 0.05 MJ / m 2 . Example 2

[0020] This example provides a method for preparing a flame-retardant fiber with a "crystallization-crosslinking" structure, and the steps are as follows: (1) Glutaraldehyde and urea, which are aldehyde compounds, are added to a reactor in a certain mass ratio of 1:1.5. At 70 °C, the pH value is adjusted to 10 with ammonia water and heated to 100 °C for 3 hours to obtain a branched urea-formaldehyde prepolymer.

[0021] (2) The dihydroxy-terminated linear polymer added to Reactor B reacts with molybdic acid to obtain a molybdic acid-modified polymer. The linear polymer is a PEG-PCL block polymer, and the molar ratio of the linear polymer to molybdic acid is 1:2. Molybdic acid reacts with the dihydroxy-terminated linear polymer for 2 hours and is blended with the urea-formaldehyde prepolymer. The weight ratio of the molybdic acid-modified linear polymer to urea is 2:1. Then, benzenesulfonic acid is used to adjust the pH to 7 and react for 2 hours, and then triethanolamine is used to adjust the pH to 8 and the temperature is lowered to 70 °C, and vacuum distillation is carried out for 4 hours to obtain a spinnable block urea-formaldehyde resin with a viscosity of 2000 Pa·s.

[0022] (3) The spinning dope enters the spinning channel through the spinneret of a dry spinning machine. The diameter of the spinneret holes of the spinneret is 300 microns. The filaments are heated in the spinning channel to obtain nascent urea-formaldehyde fibers. The length of the dry spinning channel is 5 meters, the temperature of the channel is 130 °C, and the spinning speed is 400 m / min. Then, it is placed in a microwave with a power of 5500 W for crosslinking for 1 hour, and finally, it is kept at a constant temperature of 70 °C for 3 hours to obtain a flame-retardant urea-formaldehyde fiber with a "crystalline-crosslinked" structure.

[0023] The prepared urea-formaldehyde fiber has a LOI value of 38, a diameter of 28 microns, a tensile strength of 680 MPa, an elongation at break of 41%, a char residue rate at 800 °C of 50%, and a total heat release of 5 MJ / m for a 100 g / m² fabric. 2 。 Example 3

[0024] This example provides a method for preparing a flame-retardant fiber with a "crystalline-crosslinked" structure, and the steps are as follows: (1) Paraformaldehyde and urea, which are aldehyde compounds, are added to the reactor in a certain mass ratio of 1:1. At 50 °C, calcium hydroxide is used to adjust the pH value to 9 and heated to 92 °C for reaction for 2 hours to obtain a branched urea-formaldehyde prepolymer.

[0025] (2) The dihydroxy-terminated linear polymer added to Reactor B reacts with molybdic acid to obtain a molybdic acid-modified polymer. The linear polymer is water-soluble PEG, and the molar ratio of the linear polymer to molybdic acid is 1:1. Molybdic acid reacts with the dihydroxy-terminated linear polymer for 0.6 hours and is blended with the urea-formaldehyde prepolymer. The weight ratio of the molybdic acid-modified linear polymer to urea is 1:1. Then, sulfuric acid is used to adjust the pH to 4 and react for 0.5 hours, and then triethanolamine is used to adjust the pH to 6 and the temperature is lowered to 50 °C, and vacuum distillation is carried out for 3 hours to obtain a spinnable block urea-formaldehyde resin with a viscosity of 300 Pa·s.

[0026] (3) The spinning dope enters the spinning duct through the spinneret of the dry spinning machine. The diameter of the spinneret holes of the spinneret is 200 microns. The filaments are heated in the spinning duct to obtain the nascent urea-formaldehyde fibers. The length of the dry spinning duct is 3 meters, the temperature of the duct is 120 °C, and the spinning speed is 300 m / min; then it is placed in a microwave with a power of 4500 W for crosslinking for 0.4 hours, and finally kept at a constant temperature of 60 °C for 2 hours to obtain the flame-retardant urea-formaldehyde fibers with a "crystallization-crosslinking" structure.

[0027] The prepared urea-formaldehyde fibers have a LOI value of 32, a diameter of 23 microns, a tensile strength of 480 MPa, an elongation at break of 31%, a char residue rate at 800 °C of 32%, and the total heat release of a 100 g / m² fabric is 0.4 MJ / m 2 . Example 4

[0028] This example provides a method for preparing flame-retardant fibers with a "crystallization-crosslinking" structure, and the steps are as follows: (1) The aldehyde compound acetaldehyde and urea are added to the reactor according to a certain mass ratio of 1:1.2. The pH value is adjusted to 8.5 with triethanolamine at 50 °C and heated to 96 °C for reaction for 2 hours to obtain a branched urea-formaldehyde prepolymer. The linear polymer with double-terminal hydroxyl groups added to reactor B reacts with molybdic acid to obtain a molybdic acid-modified polymer. The linear polymer is water-soluble PEG, and the molar ratio of it to molybdic acid is 1:1.5; (2) Molybdic acid reacts with the linear polymer with double-terminal hydroxyl groups for 1 hour and is blended with the urea-formaldehyde prepolymer. The weight ratio of the molybdic acid-modified linear polymer to urea is 1.5:1; then formic acid is used to adjust the pH to 6 for reaction for 0.7 hours, and then triethanolamine is used to adjust the pH to 7 and the temperature is lowered to 50 °C, and vacuum distillation is carried out for 3 hours to obtain a spinnable block urea-formaldehyde resin with a viscosity of 800 Pa·s.

[0029] (3) The spinning dope enters the spinning duct through the spinneret of the dry spinning machine. The diameter of the spinneret holes of the spinneret is 130 microns. The filaments are heated in the spinning duct to obtain the nascent urea-formaldehyde fibers. The length of the dry spinning duct is 4 meters, the temperature of the duct is 60 °C, and the spinning speed is 120 m / min; then it is placed in a microwave with a power of 800 W for crosslinking for 0.6 hours, and finally kept at a constant temperature of 50 °C for 0.9 hours to obtain the flame-retardant urea-formaldehyde fibers with a "crystallization-crosslinking" structure.

[0030] The prepared urea-formaldehyde fibers have a LOI value of 32, a diameter of 22 microns, a tensile strength of 580 MPa, an elongation at break of 21%, a char residue rate at 800 °C of 34%, and the total heat release of a 100 g / m² fabric is 4 MJ / m 2 . Example 5

[0031] This example provides a method for preparing flame-retardant fibers with a "crystallization-crosslinking" structure, and the steps are as follows: (1) Aldehyde compounds formaldehyde and urea are added to a reactor at a certain mass ratio of 1:1.4. The pH value is adjusted to 9 with ammonia water at 65 °C and heated to 93 °C for reaction for 1.6 hours to obtain a branched urea-formaldehyde prepolymer.

[0032] (2) The linear polymer with two terminal hydroxyl groups added to reactor B reacts with molybdic acid to obtain a molybdic acid-modified polymer. The linear polymer is water-soluble PEG, and the molar ratio of it to molybdic acid is 1:1.3. Molybdic acid reacts with the linear polymer with two terminal hydroxyl groups for 0.4 hours and is blended with the urea-formaldehyde prepolymer. The weight ratio of the molybdic acid-modified linear polymer to urea is 0.5:1. Then acetic acid is used to adjust the pH to 4 for reaction for 0.6 hours, and then triethanolamine is used to adjust the pH to 8 and the temperature is lowered to 60 °C, and vacuum distillation is carried out for 2 hours to obtain a spinnable block urea-formaldehyde resin with a viscosity of 1200 Pa·s.

[0033] (3) The spinning dope enters the spinning channel through the spinneret of a dry spinning machine. The diameter of the spinneret holes of the spinneret is 80 microns. The filaments are heated in the spinning channel to obtain nascent urea-formaldehyde fibers. The length of the dry spinning channel is 3 meters, the temperature of the channel is 110 °C, and the spinning speed is 30 m / min. Then it is placed in a microwave with a power of 3500 W for crosslinking for 0.7 hours, and finally kept at a constant temperature of 40 °C for 2 hours to obtain a flame-retardant urea-formaldehyde fiber with a "crystallization-crosslinking" structure.

[0034] The prepared urea-formaldehyde fiber has a LOI value of 35, a diameter of 23 microns, a tensile strength of 380 MPa, an elongation at break of 40%, a char residue rate at 800 °C of 40%, and a total heat release of 0.7 MJ / m for a fabric of 100 g / m² 2 。 Example 6

[0035] This example provides a method for preparing a flame-retardant fiber with a "crystallization-crosslinking" structure, and the steps are as follows: (1) Glutaraldehyde and urea, which are aldehyde compounds, are added to a reactor at a certain mass ratio of 1:0.9. The pH value is adjusted to 8.5 with ammonia water at 60 °C and heated to 97 °C for reaction for 0.9 hours to obtain a branched urea-formaldehyde prepolymer.

[0036] (2) The linear polymer with two terminal hydroxyl groups added to reactor B reacts with molybdic acid to obtain a molybdic acid-modified polymer. The linear polymer is water-soluble PEG, and the molar ratio of it to molybdic acid is 1:1.4. Molybdic acid reacts with the linear polymer with two terminal hydroxyl groups for 1.4 hours and is blended with the urea-formaldehyde prepolymer. The weight ratio of the molybdic acid-modified linear polymer to urea is 1:1. Then acetic acid is used to adjust the pH to 5 for reaction for 0.6 hours, and then triethanolamine is used to adjust the pH to 6 and the temperature is lowered to 60 °C, and vacuum distillation is carried out for 0.8 hours to obtain a spinnable block urea-formaldehyde resin with a viscosity of 400 Pa·s.

[0037] (3) The spinning dope enters the spinning channel through the spinneret of the dry spinning machine. The diameter of the spinneret holes of the spinneret is 210 microns. The fine filaments are heated in the spinning channel to obtain the nascent urea-formaldehyde fibers. The length of the dry spinning channel is 4 meters, the temperature of the channel is 60 °C, and the spinning speed is 250 m / min. Then it is placed in a microwave with a power of 3300 W for crosslinking for 0.5 hours, and finally kept at a constant temperature of 60 °C for 0.7 hours to obtain the flame-retardant urea-formaldehyde fibers with a "crystallization-crosslinking" structure.

[0038] The LOI value of the prepared urea-formaldehyde fibers is 35, the diameter is 7 microns, the tensile strength is 680 MPa, the elongation at break is 40%, the char residue rate at 800 °C is 42%, and the total heat release of the 100 g / m² fabric is 4.2 MJ / m 2 .

[0039] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a flame-retardant fiber with a "crystallization-crosslinking" structure, characterized in that The steps are as follows: (1) An aldehyde compound and urea are added into reactor A, the pH value is adjusted to 8 - 10 with an alkali at a temperature of 30 - 70 °C, and then heated to 90 - 100 °C for reaction to obtain a branched urea - formaldehyde prepolymer; (2) Molybdic acid and a linear polymer with two - terminal hydroxyl groups are added into reactor B to react to obtain a molybdenum - acid - modified linear polymer, and then it is blended with the branched urea - formaldehyde prepolymer and the pH is adjusted to 3 - 7 with an acid for reaction. Then, triethanolamine is used to adjust the pH to 5 - 8 and the temperature is lowered to 40 - 70 °C, and then vacuum distillation is carried out to obtain a viscous and spinnable block urea - formaldehyde resin; (3) The viscous and spinnable block urea - formaldehyde resin enters the spinning channel through the spinneret of a dry - spinning machine, the filaments are heated in the spinning channel to obtain nascent urea - formaldehyde fibers, then placed in a microwave for cross - linking, and finally kept at a constant temperature of 30 - 70 °C to obtain flame - retardant urea - formaldehyde fibers with a "crystalline - cross - linked" structure.

2. The preparation method of a flame-retardant fiber with a "crystallization-crosslinking" structure according to claim 1, characterized in that: In the step (1), the aldehyde compound is one of formaldehyde, paraformaldehyde, acetaldehyde, and glutaraldehyde, and the alkali for adjusting the pH is one of sodium hydroxide, calcium hydroxide, triethanolamine, and ammonia water; the mass ratio of urea to the aldehyde compound is 1:(0.5 - 1.5).

3. The preparation method of a flame-retardant fiber with a "crystallization-crosslinking" structure according to claim 1, characterized in that: In the step (1), the reaction time after adding the alkali is 0.3 - 3 hours.

4. The preparation method of a flame retardant fiber with a "crystallization-crosslinking" structure according to claim 1, characterized in that: In the step (2), the linear polymer with two - terminal hydroxyl groups added into reactor B is a water - soluble PEG or a PEG - PCL block polymer, the molar ratio of it to molybdic acid is 1:(0.5 - 2), the weight ratio of the molybdenum - acid - modified linear polymer to urea is (0.01 - 2):1, and the reaction time of molybdic acid and the linear polymer with two - terminal hydroxyl groups is 0.1 - 2 hours.

5. The preparation method of a flame retardant fiber with a "crystallization-crosslinking" structure according to claim 1, characterized in that: In the step (2), the acid is one of hydrochloric acid, sulfuric acid, formic acid, acetic acid, and benzenesulfonic acid, the reaction time after adding the acid is 0.1 - 2 hours; the vacuum distillation time after adding triethanolamine is 0.4 - 4 hours, and the viscosity of the viscous and spinnable block urea - formaldehyde resin is 100 - 2000 Pa·s.

6. The preparation method of a flame-retardant fiber with a "crystallization-crosslinking" structure according to claim 1, characterized in that: In the step (3), the diameter of the spinneret holes of the dry - spinning nozzle is 80 - 300 microns, the length of the spinning channel is 1 - 5 meters, the temperature of the spinning channel is 40 - 130 °C, and the spinning speed is 20 - 400 m / min.

7. The preparation method of a flame-retardant fiber with a "crystallization-crosslinking" structure according to claim 1, characterized in that: In the step (3), the microwave power is 500 - 5500 W, the microwave time is 0.01 - 1 hour, and the constant - temperature time is 0.1 - 3 hours.

8. A flame retardant fiber with a "crystallization-crosslinking" structure, characterized in that It is made by the preparation method according to any one of claims 1 - 7.