Polyimide fiber and preparation method thereof

Abstract

The invention provides a polyimide fiber and a preparation method thereof. The preparation method comprises the following steps: carrying out defoaming, spinning and hot stretching treatment on a polyimide spinning stock solution to obtain the high-temperature-resistant polyimide fiber. Wherein the specific concentration viscosity of polyimide in the polyimide spinning solution is 1.0-1.3 dL / g; the solid content of the polyimide spinning solution is 12-20wt%. The polyimide fiber obtained by the preparation method disclosed by the invention is relatively good in mechanical property, excellent in high-temperature resistance and relatively high in flame retardance.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of polyimide fiber and its preparation method, belong to polyimide fiber field. BACKGROUND

[0002] Polyimide is a kind of high-performance polymer containing imide ring in main chain, and its aromatic heterocyclic structure unit is very stable, so polyimide has excellent mechanical properties, electrical properties and good heat resistance. In addition to the good intrinsic characteristics of its matrix material, polyimide fibers can also be woven into fabrics or made into non-woven fabrics, and used in high temperature, radioactive or high temperature gas / liquid filtration, fireproof felt, fireproof and flame-retardant clothing, and high-performance composite materials, etc.

[0003] Using diamine and dianhydride as raw material is an important method for synthesizing polyimide polymer. This kind of method mainly includes two process routes: one is two-step method, i.e. first, diamine and dianhydride monomers are polycondensed at low temperature to form polyamide acid, and the polyamide acid is directly spun, and the original yarn is washed, dried, and then subjected to second-step high-temperature thermal imidization or chemical imidization to obtain polyimide fiber. For example, CN109295525B and CN116103779B both use two-step method to prepare high-heat-resistant polyimide fiber. This method overcomes the problem of solvent selectivity in the production process of polyimide, and the solvent is easy to remove and recover in the post-processing process. However, polyamide acid fiber will release small molecules of water during imidization, so the fiber is easy to form microporous structure, which destroys the ordered structure and causes the mechanical properties to decrease. The other is one-step method, i.e. directly using soluble polyimide for spinning. The advantage of this method is that the original yarn does not need to go through the imidization process, which can effectively avoid the microporous structure of the fiber caused by the release of water molecules in the two-step process, and the production process is relatively simple. However, due to the large rigidity of polyimide molecular chain, its solubility is poor, so high-toxicity solvents such as m-cresol and p-chlorophenol are usually used, and these solvents are difficult to remove in the spinning and post-processing process, which greatly limits the one-step process research.

[0004] Another important method for synthesizing polyimide polymers is to use diisocyanate and dianhydride as raw materials, which can be used to synthesize soluble polyimides in common aprotic solvents. However, due to the high reactivity, it is usually difficult to obtain high molecular weight polymers by this method. For example, CN105121512B and CN105324415B directly polymerize dianhydride and diisocyanate as raw materials, and only polyimide oligomers can be obtained. The mechanical properties, heat resistance and flame retardant properties of polyimide fibers are all affected by the molecular weight. Patent CN103628172B also uses dianhydride and diisocyanate as raw materials to obtain polyimide solution by one-step polymerization, and then prepares fibers by wet spinning. However, the side reaction cannot be effectively inhibited, resulting in low polymer viscosity and poor spinnability. In addition, this method needs to introduce a large amount of solubilizer, which is easy to cause residue and further affect the performance of the fiber.

[0005] Therefore, it is necessary to provide a new preparation method of polyimide fiber to improve the above problems. SUMMARY

[0006] In order to solve the above technical problems, the purpose of the present application is to provide a polyimide fiber and a preparation method thereof, so that the polyimide fiber obtained has good mechanical properties, excellent high-temperature resistance and high flame retardancy.

[0007] To achieve the above purpose, the present application provides a preparation method of polyimide fiber, which comprises the following steps: subjecting polyimide spinning dope to defoaming, spinning and heat stretching treatment to obtain high-temperature-resistant polyimide fiber. In the polyimide spinning dope, the specific concentration viscosity of polyimide is 1.0-1.3 dL / g; and the solid content of the polyimide spinning dope is 12-20 wt%.

[0008] The present application directly spins the polyimide solution with a specific concentration viscosity of 1.0-1.3 dL / g and a solid content of 12-20 wt% to obtain polyimide fiber with good mechanical properties, excellent high-temperature resistance and high flame retardancy. The method is simple, mild (the polyimide fiber obtained by spinning has been completely imidized, and does not need to be imidized at high temperature / chemically), low in cost and high in production efficiency, which is very beneficial to industrial production.

[0009] In some optional embodiments, the coagulation bath used for spinning comprises an aprotic polar solvent and water, and the volume ratio of the aprotic polar solvent to water is (3:7) to (8:2); the temperature of the coagulation bath is 25-40℃; and the aprotic polar solvent is selected from one or more than two combinations of N’N-dimethylacetamide, dimethyl sulfoxide, N’N-dimethylformamide and N-methyl pyrrolidone.

[0010] In a preferred embodiment, the mass concentration of polyimide in the polyimide spinning solution is 16-18 wt%; the volume ratio of aprotic polar solvent to water in the coagulation bath is (3:7) to (6:4). Based on this, the present invention can obtain polyimide fibers with irregular cross-sections. When polyimide fibers are used as high-temperature filtration materials, irregular cross-sections are beneficial for increasing specific surface area and improving filtration efficiency. When spinning with organic solvents, the mass transfer flux ratio is usually greater than 1, and the interface shape depends on the mechanical behavior of the skin layer and the concentration of the spinning solution. When the skin layer is relatively soft, coagulation shrinkage will form a near-circular cross-section; when the skin layer hardness and the spinning solution concentration are moderate, the cross-section collapse will form a non-circular cross-section; when the skin layer is excessively hard, the filament shape is fixed and maintains a circular cross-section, but internal shrinkage will form pores. It can be seen that in order to form fibers with irregular cross-sections, a higher molecular weight (higher specific viscosity means higher molecular weight) is required, so that the mechanical strength of the skin layer during the coagulation process is better and the spinnability at lower spinning solution concentrations is improved.

[0011] Furthermore, the diameter of the spinneret orifice in the spinning process is 0.06~0.22mm.

[0012] Furthermore, the temperature of the polyimide spinning solution is 30~60℃.

[0013] Furthermore, the spinning method is either wet spinning or dry-jet wet spinning. The spinning speed for wet spinning is 15~30m / min; the air layer height for dry-jet wet spinning is 1~5cm, and the spinning speed is 50~80m / min.

[0014] Furthermore, the thermal stretching ratio is 1 to 6 times, the processing temperature is 350 to 500℃, and the processing time is 30 to 120 seconds.

[0015] In a preferred embodiment, the polyimide spinning solution is prepared by the following steps: mixing dianhydride monomers and an aprotic solvent to form a dianhydride monomer solution; first adding an aqueous sodium hydroxide solution to the dianhydride monomer solution for mixing, then adding diisocyanate to carry out a polymerization reaction to obtain the polyimide spinning solution. The diisocyanate is added over a period of 4-5 hours; the molar concentration of the dianhydride monomer in the dianhydride monomer solution is 0.5-0.6 mol / L.

[0016] This invention uses dianhydride and diisocyanate as raw materials and alkaline sodium hydroxide aqueous solution as catalyst to effectively promote the ring opening of acid anhydride and its reaction with isocyanate groups. By controlling the concentration of reactants and the feeding rate, gelation of the system and deactivation of active functional groups are avoided, resulting in polyimide with high specific viscosity and soluble properties. Polyimide fibers are prepared directly by spinning the obtained polyimide solution as spinning dope without post-treatment or re-dissolution.

[0017] In some alternative embodiments, the dianhydride monomer is selected from one or more combinations of pyromellitic dianhydride, 4,4'-oxobisphthalic anhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2'-bis(3,4-dicarboxylic acid)methylene dianhydride, and 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride.

[0018] In some alternative embodiments, the diisocyanate is selected from one or more combinations of 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, isophorone diisocyanate, 1,3-phenyl diisocyanate, dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate, and dimethylbiphenyl diisocyanate.

[0019] Furthermore, the concentration of the sodium hydroxide aqueous solution is 20~30 mol / L.

[0020] Furthermore, the molar ratio of dianhydride monomer to diisocyanate is 1:1 to 1:1.08.

[0021] Furthermore, the molar ratio of the sodium hydroxide aqueous solution to the dianhydride monomer, calculated as hydroxide ions, is 0.01:1 to 0.03:1.

[0022] Furthermore, the polymerization reaction temperature is 60~100℃ and the reaction pressure is 0.1~0.5Mpa; after the diisocyanate is added, the polymerization reaction continues for 20~80min to obtain polyimide spinning solution.

[0023] Furthermore, it is speculated that the polyimide prepared by this invention has the following structural formula:

[0024]

[0025] Where n is an integer from 100 to 1000, and Ar1 is one or more of the following structures:

[0026]

[0027] Ar2 can be one or more of the following structures:

[0028]

[0029] The present invention also provides a polyimide fiber, which is prepared by the aforementioned preparation method.

[0030] Based on the reasons mentioned above, the polyimide fiber of this invention has good mechanical properties, excellent high temperature resistance, and high flame retardancy, and can be better applied in fields such as protective clothing and high temperature filter materials. The temperature conditions for the high temperature filter material can reach up to 280°C. Attached Figure Description

[0031] Figure 1 This is a cross-sectional SEM image of the polyimide fiber in Example 1.

[0032] Figure 2 This is a cross-sectional SEM image of the polyimide fiber in Example 2.

[0033] Figure 3 This is a cross-sectional SEM image of the polyimide fiber in Example 3.

[0034] Figure 4 This is a cross-sectional SEM image of the polyimide fiber in Comparative Example 1.

[0035] Figure 5 This is a cross-sectional SEM image of the polyimide fiber in Comparative Example 2.

[0036] Figure 6 The TGA curves of polyimide fibers in Examples 1-5 and Comparative Examples 1-3 are shown. Detailed Implementation

[0037] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0038] Example 1

[0039] This embodiment provides a method for preparing polyimide fibers, which includes the following steps:

[0040] (1) Under nitrogen protection, 0.1 mol of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) powder and 200 mL of N'N-dimethylacetamide (DMAc) solvent were added to a three-necked flask. The mixture was heated to 80 °C. After the BTDA was completely dissolved, 0.08 mL of NaOH aqueous solution (25 mol / L) was added as a catalyst. Then, a mixture containing 0.084 mol of toluene diisocyanate (TDI) and 0.021 mol of 4,4-diphenylmethane diisocyanate (MDI) was added dropwise to the reaction system at a uniform rate over a period of 5 h. After the addition was complete, the reaction was continued for 80 min to obtain a homogeneous and transparent polyimide solution with a solid content of 20 wt%.

[0041] (2) Using the polyimide solution obtained in step (1) as the spinning solution, let it stand to remove bubbles, and then use wet spinning method to prepare polyimide nascent fibers (spinning process conditions: spinning solution temperature is 40℃, spinneret diameter is 0.06mm, volume ratio of DMAc and water in coagulation bath is 8:2, coagulation bath temperature is 30℃, spinning speed is 30m / min); continue to dry the obtained nascent fibers and then perform hot stretching treatment, the hot stretching ratio is 3.2 times, the treatment temperature is 360℃, and the treatment time is 45s.

[0042] The specific viscosity of the polyimide obtained in step (1) is 1.177 dL / g; the SEM image of the polyimide fiber obtained in step (2) is shown below. Figure 1 As shown, the thermal decomposition temperature is 595.8℃. Figure 6 The tensile strength is 4.21 cN / dtex, the tensile modulus is 30.13 cN / dtex, the elongation at break is 19.8%, and the limiting oxygen index is 39%.

[0043] Example 2

[0044] This embodiment provides a method for preparing polyimide fibers, which includes the following steps:

[0045] Add 50 mL of DMAc solution to the polyimide solution prepared in Example 1 to adjust the solid content of the polyimide solution to 16 wt%. Then use it as the spinning solution, let it stand to remove bubbles, and then prepare polyimide nascent fibers by wet spinning (spinning process conditions: spinning solution temperature 40°C, spinneret diameter 0.06 mm, volume ratio of DMAc to water in the coagulation bath 3:7, coagulation bath temperature 30°C, spinning speed 25 m / min). After drying the obtained nascent fibers, perform hot stretching treatment with a stretching ratio of 3.5 times, a treatment temperature of 360°C, and a treatment time of 45 s.

[0046] The SEM image of the polyimide fiber obtained in this embodiment is as follows: Figure 2 As shown, it is a polyimide fiber with an irregular cross-section and a thermal decomposition temperature of 593.4℃. Figure 6 The tensile strength is 3.83 cN / dtex, the tensile modulus is 27.72 cN / dtex, the elongation at break is 21.3%, and the limiting oxygen index is 39%.

[0047] Example 3

[0048] This embodiment provides a method for preparing polyimide fibers, which includes the following steps:

[0049] Using the polyimide solution prepared in Example 1 as the spinning solution, the solution was allowed to stand to remove bubbles, and then polyimide nascent fibers were prepared by dry-jet wet spinning (spinning process conditions: spinning solution temperature 40℃, spinneret diameter 0.06mm, air layer length 1.5cm, volume ratio of DMAc to water in the coagulation bath 8:2, coagulation bath temperature 30℃, spinning speed 60m / min); the obtained nascent fibers were then dried and subjected to hot stretching treatment with a stretching ratio of 4 times, a treatment temperature of 360℃, and a treatment time of 45s.

[0050] The SEM image of the polyimide fiber obtained in this embodiment is as follows: Figure 3 As shown, the thermal decomposition temperature is 598℃. Figure 6 The tensile strength is 4.41 cN / dtex, the tensile modulus is 32.14 cN / dtex, the elongation at break is 18.5%, and the limiting oxygen index is 40%.

[0051] Example 4

[0052] 190 mL of DMAc solution was added to the polyimide solution prepared in Example 1 to adjust the solid content of the polyimide solution to 12 wt%. This solution was then used as the spinning dosing solution and allowed to stand to remove bubbles. Subsequently, polyimide nascent fibers were prepared by wet spinning (spinning process conditions: spinning dosing solution temperature 40°C, spinneret diameter 0.06 mm, volume ratio of DMAc to water in the coagulation bath 8:2, coagulation bath temperature 30°C, spinning speed 30 m / min). The obtained nascent fibers were then dried and subjected to hot stretching treatment with a stretching ratio of 3.2 times, a treatment temperature of 360°C, and a treatment time of 45 s.

[0053] The thermal decomposition temperature of the polyimide fiber obtained in this embodiment is 596.5℃. Figure 6 The tensile strength is 3.72 cN / dtex, the tensile modulus is 26.93 cN / dtex, the elongation at break is 17.2%, and the limiting oxygen index is 39%.

[0054] Example 5

[0055] The polyimide solution prepared in Example 1 was used as the spinning solution. After standing to remove bubbles, polyimide nascent fibers were prepared by wet spinning (spinning process conditions: spinning solution temperature was 40℃, spinneret diameter was 0.22mm, volume ratio of DMAc to water in the coagulation bath was 8:2, coagulation bath temperature was 30℃, and spinning speed was 30m / min). The obtained nascent fibers were then dried and subjected to hot stretching treatment with a stretching ratio of 3.2 times, a treatment temperature of 360℃, and a treatment time of 45s.

[0056] The thermal decomposition temperature of the polyimide fiber obtained in this embodiment is 597.1℃. Figure 6 The tensile strength is 4.06 cN / dtex, the tensile modulus is 29.34 cN / dtex, the elongation at break is 23.7%, and the limiting oxygen index is 39%.

[0057] Example 6

[0058] This embodiment provides a method for preparing polyimide fibers, which includes the following steps:

[0059] (1) Under nitrogen protection, 0.09 mol of BTDA powder, 0.01 mol of pyromellitic anhydride (PMDA) powder, and 200 mL of solvent DMAc were added to a three-necked flask. The mixture was heated to 80 °C. After BTDA and PMDA were completely dissolved, 0.08 mL of NaOH aqueous solution (25 mol / L) was added as a catalyst. Then, a mixture containing 0.084 mol of TDI and 0.021 mol of MDI was added dropwise to the reaction system at a uniform rate over a period of 5 h. After the addition was complete, the reaction was continued for 80 min to obtain a homogeneous and transparent polymer solution with a solid content of 19 wt%.

[0060] (2) Using the polyimide solution obtained in step (1) as the spinning solution, let it stand to remove bubbles, and then use wet spinning method to prepare polyimide nascent fibers (spinning process conditions: spinning solution temperature is 40℃, spinneret diameter is 0.06mm, volume ratio of DMAc and water in coagulation bath is 8:2, coagulation bath temperature is 30℃, spinning speed is 30m / min); continue to dry the obtained nascent fibers and then perform hot stretching treatment, the hot stretching ratio is 3.2 times, the treatment temperature is 360℃, and the treatment time is 45s.

[0061] The specific viscosity of the polyimide obtained in step (1) is 1.223 dL / g; the thermal decomposition temperature of the polyimide fiber obtained in step (2) is 611.3℃. Figure 6 The tensile strength is 4.35 cN / dtex, the tensile modulus is 37.38 cN / dtex, the elongation at break is 14.3%, and the limiting oxygen index is 42%.

[0062] Example 7

[0063] This embodiment provides a method for preparing polyimide fibers, which includes the following steps:

[0064] (1) Under nitrogen protection, 0.1 mol of BTDA powder and 200 mL of solvent DMAc were added to a three-necked flask and heated to 80 °C. After the BTDA powder was completely dissolved, 0.08 mL of NaOH aqueous solution (25 mol / L) was added as a catalyst. Then, a mixture containing 0.0945 mol of TDI and 0.0105 mol of MDI was added dropwise to the reaction system at a uniform rate over a period of 5 h. After the addition was complete, the reaction was continued for 80 min to obtain a homogeneous and transparent polymer solution with a solid content of 19 wt%.

[0065] (2) Using the polyimide solution obtained in step (1) as the spinning solution, let it stand to remove bubbles, and then use wet spinning method to prepare polyimide nascent fibers (spinning process conditions: spinning solution temperature is 40℃, spinneret diameter is 0.06mm, volume ratio of DMAc and water in coagulation bath is 8:2, coagulation bath temperature is 30℃, spinning speed is 30m / min); continue to dry the obtained nascent fibers and then perform hot stretching treatment, the hot stretching ratio is 3.2 times, the treatment temperature is 360℃, and the treatment time is 45s.

[0066] The specific viscosity of the polyimide obtained in step (1) is 1.054 dL / g; the thermal decomposition temperature of the polyimide fiber obtained in step (2) is 584.8℃. Figure 6 The tensile strength is 3.62 cN / dtex, the tensile modulus is 28.17 cN / dtex, the elongation at break is 23.5%, and the limiting oxygen index is 41%.

[0067] Comparative Example 1

[0068] This comparative example provides a method for preparing polyimide fibers, which includes the following steps:

[0069] (1) Under nitrogen protection, 0.5 mol of BTDA was added to 640 mL of solvent DMAc and stirred until completely dissolved. Then, 0.15 mL of NaOH aqueous solution (25 mol / L) was added as a catalyst, and 60 g of anhydrous LiCl was added as a solubilizer to form a mixed system. The mixed system was heated to 80 °C, and a mixture of 0.4 mol of TDI and 0.1 mol of MDI was added dropwise to the mixed system, with the addition time controlled at 2 h 40 min. After the addition was complete, the reaction continued until no CO2 gas was produced. The reaction pressure was 0.1 MPa, and a homogeneous and transparent polyimide solution with a solid content of about 30 wt% was obtained.

[0070] (2) Using the polyimide solution obtained in step (1) as the spinning solution, let it stand to remove bubbles, and then use wet spinning method to prepare polyimide nascent fibers (spinning process conditions: spinning solution temperature is 40℃, spinneret diameter is 0.06mm, volume ratio of DMAc and water in coagulation bath is 8:2, coagulation bath temperature is 30℃, spinning speed is 30m / min); continue to dry the obtained nascent fibers and then perform hot stretching treatment, the hot stretching ratio is 3.2 times, the treatment temperature is 360℃, and the treatment time is 45s.

[0071] The polyimide obtained in step (1) has a specific viscosity of 0.6384 dL / g. The SEM image of the polyimide fiber obtained in step (2) is shown below. Figure 4 As shown, the thermal decomposition temperature is 577.3℃. Figure 6 The tensile strength is 2.79 cN / dtex, the tensile modulus is 27.13 cN / dtex, the elongation at break is 16.3%, and the limiting oxygen index is 36%.

[0072] Comparative Example 2

[0073] This comparative example provides a method for preparing polyimide fibers, which includes the following steps:

[0074] DMAc solution was added to the polyimide solution prepared in Comparative Example 1 to adjust the solid content of the solution to 16 wt%, and then used as the spinning solution for static degassing. Subsequently, polyimide nascent fibers were prepared by wet spinning (spinning process conditions: spinning solution temperature 40℃, spinneret diameter 0.06 mm, volume ratio of DMAc to water in the coagulation bath 3:7, coagulation bath temperature 30℃, spinning speed 25 m / min); the obtained nascent fibers were then dried and subjected to hot stretching treatment with a stretching ratio of 3.5 times, a treatment temperature of 360℃, and a treatment time of 45 s.

[0075] The SEM image of the polyimide fiber obtained in this comparative example is shown below. Figure 5 As shown, due to the low hardness of the cortex, irregularly shaped cross-section fibers cannot be obtained; furthermore, due to the low viscosity of the spinning solution and poor spinnability, the resulting fibers have many defects, and the thermal decomposition temperature is only 561.7℃. Figure 6 The tensile strength is 1.83 cN / dtex, the tensile modulus is 20.35 cN / dtex, the elongation at break is 16.3%, and the limiting oxygen index is 34%.

[0076] Comparative Example 3

[0077] This comparative example provides a method for preparing polyimide fibers, which includes the following steps:

[0078] (1) Under nitrogen protection, 0.45 mol of BTDA and 0.05 mol of PMDA were added to 640 mL of solvent DMAc and stirred until completely dissolved. Then, 0.15 mL of NaOH aqueous solution (25 mol / L) was added as a catalyst, and 60 g of anhydrous LiCl was added as a solubilizer to form a mixed system. The mixed system was heated to 80 °C, and a mixture of 0.4 mol of TDI and 0.1 mol of MDI was added dropwise to the mixed system, with the addition time controlled at 2 h 40 min. After the addition was complete, the reaction continued until no CO2 gas was produced. The reaction pressure was 0.1 MPa, and a homogeneous and transparent polyimide solution with a solid content of about 28 wt% was obtained.

[0079] (2) Using the polyimide solution obtained in step (1) as the spinning solution, let it stand to remove bubbles, and then use wet spinning method to prepare polyimide nascent fibers (spinning process conditions: spinning solution temperature is 40℃, spinneret diameter is 0.06mm, volume ratio of DMAc and water in coagulation bath is 8:2, coagulation bath temperature is 30℃, spinning speed is 30m / min); continue to dry the obtained nascent fibers and then perform hot stretching treatment, the hot stretching ratio is 3.2 times, the treatment temperature is 360℃, and the treatment time is 45s.

[0080] The specific viscosity of the polyimide obtained in step (1) is 0.6112 dL / g. The thermal decomposition temperature of the polyimide fiber obtained in step (2) is 585.4℃. Figure 6 The tensile strength is 3.12 cN / dtex, the tensile modulus is 32.34 cN / dtex, the elongation at break is 13.1%, and the limiting oxygen index is 37%.

[0081] In summary, this invention utilizes a polyimide solution with a polyimide specific viscosity of 1.0–1.3 dL / g and a solid content of 12–20 wt% as the spinning dosing to directly spin polyimide fibers with excellent mechanical properties, superior high-temperature resistance, and high flame retardancy. This method is simple, operates under mild conditions (the polyimide fibers obtained through spinning are already fully imidized, eliminating the need for further high-temperature / chemical imidization), has low cost, and high production efficiency, making it a promising candidate for industrial application.

Claims

1. A method for preparing polyimide fibers, wherein, Includes the following steps: High-temperature resistant polyimide fibers are obtained by degassing, spinning, and hot stretching of the polyimide spinning solution; among which, The specific viscosity of polyimide in the polyimide spinning solution is 1.0~1.3 dL / g; The solid content of the polyimide spinning solution is 12~20wt%.

2. The method for preparing polyimide fibers according to claim 1, wherein, The coagulation bath used for spinning includes an aprotic polar solvent and water, and the volume ratio of the aprotic polar solvent to the water is (3:7) to (8:2).

3. The method for preparing polyimide fibers according to claim 2, wherein, The polyimide spinning solution has a polyimide mass concentration of 16-18 wt%; the coagulation bath has a volume ratio of (3:7) to (6:4) of aprotic polar solvent to water.

4. The method for preparing polyimide fibers according to claim 2, wherein, The temperature of the coagulation bath is 25~40℃.

5. The method for preparing polyimide fibers according to claim 2, wherein, The aprotic polar solvent is selected from one or more combinations of dimethyl sulfoxide, N'N-dimethylformamide, N'N-dimethylacetamide, and N-methylpyrrolidone.

6. The method for preparing polyimide fibers according to claim 1, wherein, The diameter of the spinneret orifice in the spinning process is 0.06~0.22mm.

7. The method for preparing polyimide fibers according to claim 1, wherein, The spinning method is wet spinning or dry-jet wet spinning.

8. The method for preparing polyimide fibers according to claim 7, wherein, The spinning speed of the wet spinning process is 15~30m / min; The air layer height in the dry-jet wet spinning process is 1-5 cm, and the spinning speed is 50-80 m / min.

9. The method for preparing polyimide fibers according to claim 1, wherein, The thermal stretching ratio is 1 to 6 times, the processing temperature is 350 to 500°C, and the processing time is 30 to 120 seconds.

10. A polyimide fiber, wherein, It is prepared by the preparation method according to any one of claims 1 to 9.

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