Preparation method of high-color-fastness polyimide fiber based on molecular entanglement

Abstract

The invention provides a high-color-fastness polyimide fiber preparation method based on molecular entanglement, which comprises the following steps: mixing, stirring and defoaming a polyamide acid solution and a polyacrylonitrile solution to obtain a spinning solution; spinning the spinning solution to obtain polyamide acid / polyacrylonitrile blended gel fibers; and carrying out heat treatment on the polyamide acid / polyacrylonitrile blended gel fiber in an oxygen-containing gas atmosphere to obtain the colored high-color-fastness polyimide fiber. The preparation method has the advantages of being simple in process, good in machinability, free of dyeing associated water pollution and the like. The prepared polyimide fiber is internally porous and uniform in pore size distribution, and has the characteristics of wide color range, high color fastness, high fiber strength and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of textile materials, and particularly relates to a method for preparing polyimide fibers with high color fastness based on molecular entanglement. Background Art

[0002] Polyimide fiber has become one of the representatives of high-performance fiber materials with its excellent performance and is widely used in aerospace, high-temperature protection, electronic communications and other fields. Its unique molecular structure contains highly conjugated aromatic rings and imide rings, which give it excellent thermal stability, mechanical properties and chemical resistance. In addition, this type of fiber also exhibits excellent flame retardant properties and can meet high-demand industrial and defense applications. However, the inherent golden hue of polyimide fiber has become a technical problem in the field of dyeing. Due to the highly conjugated molecular structure of the fiber, its dyeing process not only requires complex processes, but is also easily restricted by the type of dye and process conditions. At present, in order to solve this problem, researchers have tried a variety of dyeing methods, such as disperse dye carrier dyeing, cationic dye carrier dyeing, supercritical dyeing and stock solution dyeing. However, these methods have many shortcomings, such as the need to use a large amount of organic solvents, which complicates the process and brings environmental pollution problems. At the same time, the stock solution dyeing technology is difficult to promote and apply in actual production due to the poor stability of the solution and the discoloration of the pigment during high-temperature treatment. Therefore, the development of an environmentally friendly, efficient and stable intrinsic dyeing technology for polyimide fibers has become the focus and difficulty of current research. Summary of the invention

[0003] In view of the problems existing in the above-mentioned prior art, the object of the present invention is to provide a method for preparing a polyimide fiber with excellent performance and high color fastness. The polyimide fiber prepared by the method of the present invention is porous inside, has uniform pore size distribution, has a wide range of colors, high color fastness, high fiber strength, etc.

[0004] Concept of the invention: The present invention focuses on developing an environmentally friendly, efficient and high color fastness polyimide fiber preparation method based on molecular entanglement to solve the problems of complex dyeing process, serious pollution, single and unstable color system of traditional polyimide fiber. The present invention innovatively introduces polyacrylonitrile into the polyimide system, and utilizes the potential chromophore groups in its molecules. During the subsequent heat treatment process, the nitrile group (-CN) in the polyacrylonitrile molecule will undergo a cyclization reaction during the pre-oxidation process to form a conjugated double bond structure. As the cyclization reaction deepens, the conjugated system continues to expand, and the degree of delocalization of the electron cloud increases. When the conjugated system reaches a certain level, the absorption capacity of the pre-oxidized fiber for visible light is enhanced, and the absorption wavelength moves toward the long-wave direction, so that the pre-oxidized fiber appears black, giving the fiber an intrinsic black color.

[0005] The technical solution adopted by the present invention is as follows:

[0006] In the first aspect of the present invention, there is provided a method for preparing a polyimide fiber with high color fastness based on molecular entanglement, and the preparation method includes the following steps:

[0007] (1) Mix, stir and defoam a polyamic acid solution and a polyacrylonitrile solution to obtain a spinning dope;

[0008] (2) Spinning the spinning dope to obtain a polyamic acid / polyacrylonitrile co - coagulated gel fiber;

[0009] (3) Heat - treat the polyamic acid / polyacrylonitrile co - coagulated gel fiber in an oxygen - containing gas atmosphere.

[0010] In the present invention, the polyimide fiber is composed of polyimide and polyacrylonitrile, with polyimide as the matrix and polyacrylonitrile as the potential chromophore. In the preparation method of this polyimide fiber, polyacrylonitrile is introduced into the preparation system of the polyimide fiber, and a polyamic acid / polyacrylonitrile co - coagulated gel fiber is obtained by spinning. The polyamic acid / polyacrylonitrile co - coagulated gel fiber is heat - treated in an oxygen - containing gas atmosphere. Among them, under appropriate heating conditions (thermal imidization process), the polyamic acid molecules are thermally cyclized into polyimide, forming a stable imide ring, enhancing the thermal stability and mechanical properties of the fiber; at the same time, when heated in the presence of an oxygen - containing gas (pre - oxidation process), polyacrylonitrile undergoes cyclization, cross - linking and other reactions to form a black conjugated structure, thereby completing in - situ dyeing.

[0011] In the present invention, the molecular weights of the polyamic acid and polyacrylonitrile are not particularly limited, and the polyamic acid and polyacrylonitrile conventionally used in the art for fiber preparation can be adopted. Preferably, the weight - average molecular weight of the polyamic acid is 100,000 - 2,000,000 g / mol, more preferably 1,000,000 - 1,800,000 g / mol; the weight - average molecular weight of the polyacrylonitrile is 100,000 - 1,500,000 g / mol, more preferably 1,000,000 - 1,800,000 g / mol.

[0012] In the above technical solution, in step (1), the polyamic acid solution and the polyacrylonitrile solution are mixed in a mass ratio of polyamic acid to polyacrylonitrile of 5:0 to 5:3, preferably 5:0.5 to 5:2, more preferably 5:1 to 5:2. Further, the mass percentage concentration of polyamic acid in the polyamic acid solution is 10% to 30%, preferably 15% to 25%, more preferably 20%; the mass percentage concentration of polyacrylonitrile in the polyacrylonitrile solution is 1.9% to 7.4%, preferably 3% to 6%, more preferably 5%. In the present invention, polyacrylonitrile is introduced into the preparation system of polyimide fiber, and by adjusting the solid content of polyacrylonitrile, polyimide fibers with different hues and high color fastness can be obtained. By adjusting the ratio of polyacrylonitrile to polyimide, the color range of the fiber can be flexibly controlled (light yellow - dark brown - dark gray - black), which can meet the diverse color requirements of fibers in different fields.

[0013] Preferably, in the above technical solution, the polyamic acid solution and the polyacrylonitrile solution are mixed, and the mixed solution is heated to 50 - 70 °C and stirred at a stirring speed of 800 - 1200 rpm / min for 10 - 18 hours to ensure that the two polymer molecules have sufficient molecular motion ability to be fully mixed and entangled, obtaining a blend solution of polyamic acid / polyacrylonitrile with a molecular entanglement structure. After subjecting this blend solution to vacuum degassing treatment, a spinning dope is obtained. The degassing treatment of the polymer blend solution can be carried out according to conventional devices and methods in the art.

[0014] In the above technical solution, in step (1), the polyamic acid solution and the polyacrylonitrile solution are obtained by dissolving polyamic acid and polyacrylonitrile separately in a co - solvent, and the co - solvent is one or more of dimethylformamide, dimethylacetamide, and dimethyl sulfoxide. The co - solvent can also be a solvent conventionally used in the art for dissolving polyamic acid and polyacrylonitrile.

[0015] In the above technical solution, in step (2), the spinning dope is extruded into coagulation bath I for curing. After phase separation, polyamic acid / polyacrylonitrile co - coagulated gel fibers are obtained. Among them, the composition of coagulation bath I is water and dimethylformamide or dimethylacetamide or dimethyl sulfoxide, and the mass percentage content of water in coagulation bath I is 85% - 100%, and the temperature of coagulation bath I is 0 - 5 °C. Among them, the spinning dope is quantitatively extruded into a low - concentration and low - temperature coagulation bath (coagulation bath I) by wet spinning, so that the extruded fibers can be better cured and entangled, which is beneficial to improving the strength and color fastness of polyimide fibers, and avoiding the collapse of the porous structure inside the fibers, forming a good pore structure.

[0016] In the above technical solution, in step (3), the polyamic acid / polyacrylonitrile co-coagulated gel fibers are subjected to solvent replacement with deionized water. The temperature of the solvent replacement is 0°C to 25°C, and the number of solvent replacement times is 1 to 5 times. Among them, performing solvent replacement on the polyamic acid / polyacrylonitrile co-coagulated gel fibers can further solidify and entangle the polyamic acid / polyacrylonitrile co-coagulated gel fibers, which is beneficial to the formation of a good pore structure.

[0017] The so-called "solidification and entanglement" means that the spinning dope solidifies in the coagulation bath or during the solvent replacement process, and double diffusion occurs under the action of the concentration gradient, that is, the coagulant diffuses into the spinning dope, and the co-solvent in the spinning dope diffuses into the coagulant. When the content of the coagulant in the spinning dope reaches a certain level, the high-concentration polyamic acid and polyacrylonitrile molecular chains are highly entangled, and gelation occurs due to phase separation, realizing the solidification and shaping of the fibers, and winding to obtain PAA / PAN wet fibers.

[0018] In the above technical solution, in step (3), the oxygen-containing gas is air or an oxygen-nitrogen mixed gas with an oxygen content of 10 to 21%. In the presence of the oxygen-containing gas, polyacrylonitrile undergoes an oxidation reaction, that is, polyacrylonitrile undergoes cyclization, cross-linking, etc. to form a black conjugated structure, thereby completing in-situ dyeing. In the present invention, by adjusting the solid content of polyacrylonitrile, polyimide fibers with different hues and high color fastness are obtained.

[0019] In the above technical solution, in step (3), the heat treatment includes: putting the polyamic acid / polyacrylonitrile co-coagulated gel fibers into a device, introducing an oxygen-containing gas, and gradually raising the temperature of the device to 270°C to 350°C. Among them, the flow rate of the oxygen-containing gas is 0.2 to 0.6 L / min, and the heating rate of the device is 2 to 5°C / min. At this time, under appropriate heating conditions, the polyamic acid in the polyamic acid / polyacrylonitrile co-coagulated gel fibers undergoes thermal cyclization to become polyimide, and the nitrile group (-CN) in the polyacrylonitrile molecule undergoes a cyclization reaction under the combined action of heat and oxygen to form a conjugated double bond structure, resulting in an increase in the delocalization degree of the electron cloud, an enhanced ability to absorb visible light, a shift of the absorption wavelength towards the long-wave direction, presenting a black color, and finally obtaining colored and high-color-fastness polyimide fibers. In the present invention, by adjusting the solid content of polyacrylonitrile and the heat treatment temperature, etc., polyimide fibers with different hues and high color fastness can be obtained.

[0020] In the method for preparing polyimide fiber provided by the present invention, polyacrylonitrile is introduced into the preparation system of polyimide fiber, and polyamic acid / polyacrylonitrile co - coagulation gel fiber is prepared by wet phase separation spinning technology. By adjusting the solid content of polyacrylonitrile and combining synchronous thermal imidization and pre - oxidation during the heat treatment process, a uniform pore structure is formed inside the fiber, realizing the optimization of the molecular structure and the synchronous generation of color. During the thermal imidization process, polyamic acid molecules are transformed into polyimide, forming stable imide rings, enhancing the thermal stability and mechanical properties of the fiber. At the same time, under the action of pre - oxidation, polyacrylonitrile undergoes cyclization, cross - linking and other reactions to form a black conjugated structure, thus completing in - situ dyeing. By adjusting the ratio of polyacrylonitrile to polyimide, the color range of the fiber can be flexibly controlled (light yellow - dark brown - dark gray - black fiber), meeting the diverse color requirements of different fields for the fiber. The entire preparation process is green and environmentally friendly, abandoning the use of a large amount of organic solvents in the traditional dyeing process, effectively avoiding the generation of dyeing wastewater, and conforming to the concept of sustainable development. The in - situ intrinsically black polyimide porous fiber prepared has a uniform pore size distribution, ensuring its stability and reliability in applications; its high - strength characteristics make it have broad application prospects in fields such as aerospace and high - performance composite materials; the adjustable hue further expands its application scope in fields such as textiles and decoration, providing high - performance and environmentally friendly new fiber materials for the development of related industries.

[0021] In the second aspect of the present invention, a polyimide fiber is provided. The polyimide fiber is prepared by the preparation method of high - color - fastness polyimide fiber based on molecular entanglement as described above. Among them, the hue of the polyimide fiber is black series, brown series, gray series or yellow series, and the inside of the polyimide fiber is porous.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) By introducing polyacrylonitrile as a potential chromophore and combining wet phase separation spinning, synchronous thermal imidization and pre - oxidation processes, the present invention realizes in - situ dyeing of polyimide fiber, effectively avoiding the complex processes of using a large amount of organic solvents and dyes in the traditional dyeing process, significantly reducing wastewater discharge and environmental pollution. The color of the fiber prepared by the present invention is stable and can be flexibly controlled from dark brown to black by adjusting the raw material ratio, overcoming the dependence on dyes and process conditions in traditional dyeing, and meeting the current requirements of green and sustainable development.

[0024] (2) The preparation method of the polyimide of the present invention has the advantages of simple process and high efficiency. The whole preparation process is stable and easy to operate, suitable for industrial promotion, and significantly reduces the production cost. The prepared fibers have a uniform pore size distribution, high strength and excellent comprehensive properties, and can be widely used in fields such as aerospace, high-performance composite materials, and textile decoration, providing a new direction for the development of high-performance environmental protection materials and showing broad market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a physical photograph of the high color fastness polyimide fiber prepared in the present invention.

[0026] Figure 2 is an SEM image of the high color fastness polyimide fiber prepared in the present invention.

[0027] Figure 3 is a K / S graph of the high color fastness polyimide fiber prepared in the present invention.

[0028] Figure 4 is a graph of the breaking strength and elongation at break of the high color fastness polyimide fiber prepared in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] To make the technical solutions of the present application clearer, the following further details the present application in conjunction with the drawings and embodiments. The specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0030] In the following embodiments, unless otherwise specified, the experimental methods used are all conventional methods, and the reagents used can be purchased from chemical or biological reagent companies.

[0031] In the following embodiments, the mass percentage content ratio of the polyamic acid solution is 20% and is obtained by dissolving polyamic acid in dimethylformamide, and the mass percentage content of the polyacrylonitrile solution is 5% and is obtained by dissolving polyacrylonitrile in dimethylformamide. In the wet spinning of step (2), the spinning dope is extruded into the coagulation bath using a conventional propeller in the art such as a sterile syringe and a 21-gauge needle.

[0032] Example 1

[0033] The high color fastness polyimide fiber was prepared according to the following method:

[0034] (1) The polyacrylonitrile solution and the polyamic acid solution were mixed at a solute mixing ratio of 5:0.5, and stirred at a speed of 1000 rpm / min for 12 hours at 60 °C to obtain a blend solution of polyamic acid / polyacrylonitrile with a molecular entanglement structure. The blend solution was degassed under vacuum to obtain a spinning dope.

[0035] (2) Load the above spinning dope into a 20 mL syringe, extrude it into coagulation bath I for solidification. After phase separation, polyamic acid / polyacrylonitrile co - coagulated gel fibers are obtained. The extrusion speed is 20 mL / h, the coagulation bath I is deionized water, the temperature of the coagulation bath is 2 °C, and the fiber collection speed during phase separation is 0.06 mm / s.

[0036] (3) Carry out solvent replacement on the above polyamic acid / polyacrylonitrile gel fibers. The replacement reagent is deionized water, the replacement temperature is 25 °C, and the number of replacement times is 3 times to further solidify and entangle. Then, put the polyamic acid / polyacrylonitrile co - coagulated gel fibers after solvent replacement into a heating device, introduce air, and gradually raise the temperature of the device to 320 °C at a speed of 5 °C / min, hold for 30 minutes, and then naturally cool to room temperature. Air is introduced throughout the process, and the air flow rate is 0.5 L / min.

[0037] Example 2

[0038] Prepare high - color - fastness polyimide fibers according to the following method:

[0039] (1) Mix the polyacrylonitrile solution and the polyamic acid solution according to a solute mixing ratio of 5:1, stir at a speed of 1000 rpm / min for 12 hours at 60 °C to obtain a blended solution of polyamic acid / polyacrylonitrile with a molecular entangled structure. Carry out vacuum degassing on the blended solution to obtain the spinning dope.

[0040] (2) Load the above spinning dope into a 20 mL syringe, extrude it into coagulation bath I for solidification. After phase separation, polyamic acid / polyacrylonitrile co - coagulated gel fibers are obtained. The extrusion speed is 20 mL / h, the coagulation bath I is deionized water, the temperature of the coagulation bath is 2 °C, and the fiber collection speed during phase separation is 0.06 mm / s.

[0041] (3) Carry out solvent replacement on the above polyamic acid / polyacrylonitrile gel fibers. The replacement reagent is deionized water, the replacement temperature is 25 °C, and the number of replacement times is 3 times to further solidify and entangle. Then, put the polyamic acid / polyacrylonitrile co - coagulated gel fibers after solvent replacement into a heating device, introduce air, and gradually raise the temperature of the device to 320 °C at a speed of 5 °C / min, hold for 30 minutes, and then naturally cool to room temperature. Air is introduced throughout the process, and the air flow rate is 0.5 L / min.

[0042] Example 3

[0043] Prepare high - color - fastness polyimide fibers according to the following method:

[0044] (1) Mix the polyacrylonitrile solution and the polyamic acid solution at a solute mixing ratio of 5:2, stir at a speed of 1000 rpm / min for 12 hours at 60 °C to obtain a blended solution of polyamic acid / polyacrylonitrile with a molecular entanglement structure, and subject the blended solution to vacuum degassing to obtain a spinning dope.

[0045] (2) Load the above spinning dope into a 20 mL syringe, extrude it into coagulation bath I for curing, and after phase separation, obtain polyamic acid / polyacrylonitrile co-gel fibers, where the extrusion speed is 20 mL / h, coagulation bath I is deionized water, the coagulation bath temperature is 2 °C, and the fiber collection speed during phase separation is 0.06 mm / s.

[0046] (3) Perform solvent replacement on the above polyamic acid / polyacrylonitrile gel fibers, the replacement reagent is deionized water, the replacement temperature is 25 °C, and the replacement is carried out 3 times to further cure the entanglement. Then, place the polyamic acid / polyacrylonitrile co-gel fibers after solvent replacement into a heating device, introduce air, and gradually increase the temperature of the device to 320 °C at a rate of 5 °C / min, hold for 30 minutes, and then naturally cool to room temperature. Air is introduced throughout the process, and the air flow rate is 0.5 L / min.

[0047] Comparative Example 1

[0048] Preparation of pure polyimide fibers: The preparation method is basically the same as that of Example 1, the difference is that in step (1) of Comparative Example 1, no polyacrylonitrile solution is added.

[0049] Example 4

[0050] Characterization of the polyimide fibers prepared in Examples 1-3 and Comparative Example 1: The appearance colors of the polyimide fibers with high color fastness to molecular entanglement structure were compared, and the structural morphology, color depth, color fastness, and mechanical strength of the fibers were characterized using a scanning electron microscope (SEM), color matching system K / S value test, wash fastness tester, and single fiber strength tester. The results are as follows:

[0051] (1) Appearance color comparison and results:

[0052] Appearance color comparison: Dry the prepared polyimide fibers under normal temperature and pressure conditions and observe their colors with the naked eye.

[0053] As Figure 1 shown, the appearance colors of the high color fastness polyimide fibers prepared in the present invention are obvious. The fibers prepared in Comparative Example 1 are light yellow, and as the solid content of polyacrylonitrile increases, the porous fibers gradually show dark brown, dark gray, and black in turn. Figure 1Among them, (a) is the polyimide prepared in Comparative Example 1, and (b) to (d) are the high color fastness polyimide fibers prepared in Examples 1 to 3 in sequence.

[0054] (2) SEM test results: As Figure 2 shown, the interior of the high color fastness polyimide fibers prepared in the present invention presents a honeycomb-like and uniformly distributed porous structure. Compared with pure polyimide fibers, as the solid content of polyacrylonitrile increases, the cross-section of the porous fibers gradually changes from oval to circular.

[0055] (3) K / S value test and results:

[0056] K / S value test method: The K / S value is a key parameter used in textile and materials science to quantify the color depth of fibers or fabrics. Among them, K is the colorant absorption coefficient and S is the colorant scattering coefficient. The larger the K / S value, the stronger the ability of the material to absorb light and the darker the color. The K / S value and CIELab chromaticity value of the prepared polyimide fibers were measured using a Color-Eye 7000A spectrophotometer in the range of 360 - 750 nm. The CIELab chromaticity value is based on a comparative color system and is used to determine the numerical information of a certain color.

[0057] Figure 3 (a) represents the specific CIELab chromaticity values of the polyimide fibers prepared in Examples 1 to 3. It can be seen from the figure that the colors of the fibers show different brightness, hue, and saturation, and their color distributions can be intuitively seen, indicating that polyacrylonitrile with different solid contents has successfully imparted different hues to the polyimide fibers.

[0058] Figure 3 (b) represents the measurement results of the K / S values of the polyimide fibers prepared in Comparative Example 1 and Examples 1 to 3 at different visible light wavelengths. The K / S value of the high color fastness polyimide fibers prepared in the present invention is significantly greater than that of pure polyimide fibers, and the K / S value is Example 3 > Example 2 > Example 1, indicating that the color depth of the polyimide fibers in Examples 1 to 3 gradually increases in sequence.

[0059] (4) Color fastness test and results:

[0060] Washing fastness: According to "GB / T 3921 - 2008 Textiles - Tests for color fastness - Color fastness to soaping".

[0061] Rubbing fastness: According to "GB / T 3920 - 2008 Textiles - Tests for color fastness - Color fastness to rubbing".

[0062] The color fastness test results of the polyimide fibers prepared in Comparative Example 1 and Examples 1 to 3 are shown in Table 1.

[0063] Table 1. Results of color fastness determination of polyimide fibers

[0064]

[0065] As can be seen from Table 1, the soaping and rubbing resistance of the polyimide fibers with high color fastness prepared in Comparative Example 1 and the present invention are good, and the color fastness levels are all 4-5, indicating that the introduction of polyacrylonitrile in the present invention endows the fibers with multiple color systems, and the prepared fibers all have high color fastness.

[0066] (5) Mechanical property testing and results:

[0067] Mechanical property testing method: The YG004 single fiber strength tester was used for testing. The tensile speed was 15 mm / min. The breaking strength and breaking elongation of single fibers were measured. Each sample was tested 10 times and the average value was taken.

[0068] The measurement results are as Figure 4 shown. The mechanical properties of the high color fastness polyimide fibers prepared in the present invention are excellent. Compared with pure polyimide fibers, the breaking strength and breaking elongation of the fibers added with polyacrylonitrile increase. Among them, when the mass ratio of polyimide to polyacrylonitrile is 5:1 (Example 2), the mechanical properties are the best ( Figure 4 (a)). Figure 4 (b) shows the tensile curves of the polyimide fibers of Comparative Example 1 and Examples 1 to 3 tested 10 times.

[0069] The above embodiments are only illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A preparation method of high color fastness polyimide fibers based on molecular entanglement, comprising the following steps: (1) Mix, stir and degas a polyamic acid solution and a polyacrylonitrile solution to obtain a spinning dope; (2) Spin the spinning dope to obtain polyamic acid / polyacrylonitrile co - coagulation gel fibers; (3) Heat - treat the polyamic acid / polyacrylonitrile co - coagulation gel fibers in an oxygen - containing gas atmosphere.

2. The preparation method according to claim 1, wherein: In step (1), the polyamic acid solution and the polyacrylonitrile solution are mixed according to a mass ratio of polyamic acid to polyacrylonitrile of 5:0.5 - 5:

3.

3. The preparation method according to claim 1, wherein: In step (1), the mass percentage concentration of polyamic acid in the polyamic acid solution is 10% - 30%, and the mass percentage concentration of polyacrylonitrile in the polyacrylonitrile solution is 1.9% - 7.4%.

4. The preparation method according to claim 1, wherein: In step (1), the polyamic acid solution and the polyacrylonitrile solution are obtained by dissolving polyamic acid and polyacrylonitrile respectively in a co - solvent, and the co - solvent is one or more of dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

5. The preparation method according to claim 1, wherein: In step (2), the spinning dope is extruded into a coagulation bath I for curing, and after phase separation, polyamic acid / polyacrylonitrile co - coagulation gel fibers are obtained. Among them, the composition of the coagulation bath I is water and dimethylformamide or dimethylacetamide or dimethyl sulfoxide, and the mass percentage content of water in the coagulation bath I is 85% - 100%, and the temperature of the coagulation bath I is 0 - 5°C.

6. The preparation method according to claim 1, wherein: In step (3), the polyamic acid / polyacrylonitrile co - coagulation gel fibers are subjected to solvent replacement with deionized water. The temperature of the solvent replacement is 0 - 25°C, and the number of solvent replacement times is 1 - 5 times.

7. The preparation method according to claim 1, wherein: In step (3), the oxygen - containing gas is air or an oxygen - nitrogen mixed gas with an oxygen content of 10% - 21%.

8. The preparation method according to claim 1, wherein: In step (3), the heat treatment comprises the following steps: Put the polyamic acid / polyacrylonitrile co - coagulation gel fibers into a device, introduce an oxygen - containing gas, and gradually raise the temperature of the device to 270 - 350°C. Among them, the flow rate of the oxygen - containing gas is 0.2 - 0.6 L / min, and the heating rate of the device is 2 - 5°C / min.

9. A polyimide fiber, characterized in that, The polyimide fibers are prepared by the preparation method of high color fastness polyimide fibers based on molecular entanglement according to any one of claims 1 - 8.

10. The polyimide fiber according to claim 9, characterized in that, The hue of the polyimide fibers is black, brown, gray or yellow, and the interior of the polyimide fibers is porous.

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