阅读说明：本技术 一种高强耐候聚酰亚胺纤维的制备方法 (Preparation method of high-strength weather-resistant polyimide fiber ) 是由 张清华 董杰 赵昕 王士华 郭涛 郑森森 董晗 张家霖 于 2021-07-28 设计创作，主要内容包括：本发明涉及一种高强耐候聚酰亚胺纤维的制备方法。该方法包括：将含苯并咪唑的二胺单体和含邻羟基二苯甲酮的二胺单体溶解于溶剂中,加入二酐单体,无规共聚反应,然后与锌盐混合,将得到的纺丝原液干法纺丝,再经环化-牵伸一体化处理。该方法可连续化制备、操作简单、工艺环保、原料来源广,具有良好的产业化前景；制备得到的聚酰亚胺纤维具有较好的力学性能、表面活性和耐候性。(The invention relates to a preparation method of a high-strength weather-resistant polyimide fiber. The method comprises the following steps: dissolving a diamine monomer containing benzimidazole and a diamine monomer containing o-hydroxybenzophenone in a solvent, adding a dianhydride monomer, carrying out random copolymerization, mixing with a zinc salt, carrying out dry spinning on the obtained spinning solution, and carrying out cyclization-drafting integrated treatment. The method has the advantages of continuous preparation, simple operation, environment-friendly process, wide raw material source and good industrialization prospect; the prepared polyimide fiber has good mechanical property, surface activity and weather resistance.)

1. A polyimide fiber is characterized in that a dianhydride monomer, a diamine monomer containing benzimidazole and a diamine monomer containing o-hydroxybenzophenone are subjected to random copolymerization, an obtained polyamic acid solution is mixed with a zinc salt, an obtained spinning solution is subjected to dry spinning, and then cyclization-drafting integrated treatment is carried out to obtain the polyimide fiber.

2. The polyimide fiber of claim 1, wherein the dianhydride monomer comprises pyromellitic dianhydride PMDA or biphenyltetracarboxylic dianhydride BPDA; benzimidazole-containing diamine monomers include 2- (4-aminophenyl) -5-aminobenzimidazole BIA; the zinc salt comprises zinc nitrate hexahydrate.

3. The polyimide fiber of claim 1, wherein the ortho-hydroxybenzophenone-containing diamine monomer comprises:

4. a method for preparing a polyimide fiber, comprising:

(1) dissolving a diamine monomer containing benzimidazole and a diamine monomer containing o-hydroxybenzophenone in a solvent according to a molar ratio of 1: 9-8: 2, adding a dianhydride monomer, and performing a random copolymerization reaction to obtain a polyamic acid solution, wherein the molar ratio of the total mole of the diamine monomer containing benzimidazole and the diamine monomer containing o-hydroxybenzophenone to the dianhydride monomer is 1: 1-1: 1.1;

(2) mixing zinc salt with the polyamic acid solution obtained in the step (1), and carrying out ultrasonic treatment to obtain a spinning solution, wherein the mass of the zinc salt accounts for 5-10 wt% of the total mass of the zinc salt and the polyamic acid;

(3) and (3) carrying out dry spinning on the spinning stock solution in the step (2) to obtain nascent fibers, and carrying out cyclization-drafting integrated treatment to obtain the polyimide fibers containing the zinc oxide nanoparticles.

5. The method according to claim 4, wherein the solvent in the step (1) comprises one or both of N, N-dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP); the solid content of the solution for the reaction is 12-20 wt%.

6. The preparation method according to claim 4, wherein the dianhydride monomer is added in step (1) in 3 times, and the addition mass fractions are 65-75%, 20-30% and 1-10% respectively, based on the total mass of the dianhydride monomer.

7. The preparation method according to claim 4, wherein the process parameters of the random copolymerization reaction in the step (1) are as follows: and reacting under the protection of nitrogen, wherein the reaction temperature is 10-50 ℃, and the reaction time is 20-30 h.

8. The preparation method as claimed in claim 4, wherein the temperature of the spinning shaft in the dry spinning in step (3) is 4 stages, the temperature of each stage is 180-330 ℃, and the winding speed is 190-400 m/min.

9. The production method according to claim 4, wherein the process parameters of the cyclization-draft integrated treatment in the step (3) are as follows: and (3) treating the polyamic acid precursor fiber by using a contact hot roller, passing through 3-5 hot rollers, wherein the heating temperature of the hot rollers is 60-500 ℃, and the heat drafting multiple is 1.1-5 times under the protection of nitrogen.

10. Use of the polyimide fiber of claim 1 in aerospace detection equipment.

Technical Field

The invention belongs to the technical field of high-performance fiber preparation, and particularly relates to a preparation method of a polyimide fiber with high strength and high weather resistance, which can meet the application in the field of extreme environments.

Background

In recent years, with the increasing frequency of aerospace detection activities, higher requirements are put on the design service life and stability and reliability of the spacecraft. The high-performance fiber is one of important and preferable materials for aerospace equipment and devices due to the characteristics of light weight, high strength, flexibility, good heat resistance and the like. For example, typical aramid, poly-p-Phenylene Benzoxazole (PBO) fibers, etc. have been used as airbags for "pathfinder" signs, "courage" signs, and "opportunity" signs for Mars detection vehicles. However, in the current Low Earth Orbit (LEO) where space exploration activities are most frequent, the solar spatial short wave Ultraviolet (UVC) intensity can reach 400 μ W/cm²More than 90 times of the ultraviolet intensity reaching the ground. For fibers such as aramid fibers and poly (p-Phenylene Benzobisoxazole) (PBO), amide units and benzoxazole groups in a macromolecular structure have strong absorption to ultraviolet light in two wave bands of 290-310nm and 320-360nm, so that the amide units and the benzoxazole units in the macromolecular chain are in an excited state under UVC radiation, chemical bond breakage is easily caused, and the mechanical properties of the fibers are greatly attenuated (Journal of applied Polymer Science,2012,124,3286; Composite Structures,2006,75, 151; Advances in Space Research,2006,37, 2052). Great potential safety hazard is caused to the space exploration activities. Therefore, the development of a high-performance fiber with excellent mechanical properties, ultraviolet radiation resistance stability, high surface activity and other characteristics has important significance for the research and development of novel aerospace equipment.

As one representative example of high-performance polymers, Polyimide (PI) has a highly rigid molecular structure, which imparts excellent mechanical properties, heat resistance, and the like, to the polyimide, and thus has higher thermal stability than other polyimide polymers in high-temperature, moist-heat, and radioactive environmentsPolymers have greater advantages. The Chinese patent application with the application number of 201110222300.0 discloses a method for preparing a high-strength and high-modulus polyimide fiber containing a benzimidazole structure by adopting a gradient temperature type reaction method and a one-step continuous preparation method, which solves the problem of polymer processing caused by introduction of benzimidazole units; chinese patent application numbers 200710050651.1 and 201010572496.1 also disclose polyimide fibers containing benzimidazole units and a preparation method thereof, and the strength of the prepared fibers reaches 0.73-2.5 GPa. However, the above patent application focuses only on the mechanical properties of the fiber and does not consider the ultraviolet irradiation resistance characteristics of the fiber and the surface activity of the fiber. Compared with other high-performance polymer fibers, the polyimide fiber has flexible molecular structure designability and a spinning forming technology, and can be regulated and controlled by an effective molecular structure design and a fiber forming process to obtain the polyimide fiber with high strength, high weather resistance and high surface reaction activity. For example, substances containing o-hydroxybenzophenone units have excellent ultraviolet radiation resistance, and the mechanism is that carbonyl groups in the molecules of the compounds and hydroxyl groups form intramolecular hydrogen bonds to form a chelate ring structure. After absorbing ultraviolet rays, internal hydrogen bonds oscillate, stable chelate rings are opened, absorbed energy is released in the form of heat energy, and carbonyl groups in molecules are excited by absorbed ultraviolet light energy to generate tautomerism of an enol structure, so that a part of energy is consumed. Therefore, such units have a significant "absorption-conversion" effect on ultraviolet light. In addition, abundant hydroxyl units are beneficial to improving the surface activity of the fiber and forming strong interface composition with a resin matrix. ZnO, TiO₂The nano particles have excellent shielding capability to ultraviolet light, are novel fabric ultraviolet-resistant finishing agents and are widely applied to modern textiles.

Disclosure of Invention

The invention aims to solve the technical problem of providing a preparation method of a high-strength weather-resistant polyimide fiber, so as to overcome the defect that the polyimide fiber in the prior art is difficult to have good mechanical property, weather resistance and surface activity.

The invention provides a high-strength weather-resistant polyimide fiber, which is obtained by carrying out random copolymerization reaction on a dianhydride monomer, a diamine monomer containing benzimidazole and a diamine monomer containing o-hydroxybenzophenone, mixing an obtained polyamic acid solution with zinc salt, carrying out dry spinning on an obtained spinning solution, and then carrying out cyclization-drafting integrated treatment.

The dianhydride monomer comprises pyromellitic dianhydride PMDA or biphenyltetracarboxylic dianhydride BPDA, and the structural formula is as follows:

the benzimidazole-containing diamine monomer comprises 2- (4-aminobenzene) -5-aminobenzimidazole BIA, wherein the structural formula of BIA is as follows:

the zinc salt comprises zinc nitrate hexahydrate.

The o-hydroxybenzophenone-containing diamine monomer includes:

the invention also provides a preparation method of the high-strength weather-resistant polyimide fiber, which comprises the following steps:

(1) dissolving a diamine monomer containing benzimidazole and a diamine monomer containing o-hydroxybenzophenone in a solvent according to a molar ratio of 1: 9-8: 2, adding a dianhydride monomer, and performing a random copolymerization reaction to obtain a polyamic acid solution, wherein the molar ratio of the total mole of the diamine monomer containing benzimidazole and the diamine monomer containing o-hydroxybenzophenone to the dianhydride monomer is 1: 1-1: 1.1;

(2) mixing zinc salt with the polyamic acid solution obtained in the step (1), and performing ultrasonic treatment (to ensure that the zinc salt is uniformly dispersed) to obtain a high-spinnability spinning solution, wherein the mass of the zinc salt accounts for 5-10 wt% of the total mass of the zinc salt and the polyamic acid;

(3) and (3) carrying out dry spinning on the spinning stock solution in the step (2) to obtain nascent fibers, and carrying out cyclization-drafting integrated treatment to obtain the polyimide fibers containing the zinc oxide nanoparticles.

In the step (1), the benzimidazole-containing diamine monomer and the o-hydroxybenzophenone-containing diamine monomer are dissolved in a solvent in a molar ratio of 1: 9-5: 5 in an inert gas atmosphere.

The solvent in the step (1) comprises one or two of N, N-dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP).

When the solvent is a mixed solvent of two solvents, the volume ratio of DMAc to NMP is 9: 1-5: 5.

The solid content of the solution reacted in the step (1) is 12-20 wt%.

The dianhydride monomer is added in the step (1) by 3 times, wherein the dianhydride monomer is added in the amount of 65-75% by mass, 20-30% by mass and 1-10% by mass based on the total mass of the dianhydride monomer.

The technological parameters of the random copolymerization reaction in the step (1) are as follows: and reacting under the protection of nitrogen, wherein the reaction temperature is 10-50 ℃, and the reaction time is 20-30 h.

The temperature section of the spinning channel in the dry spinning in the step (3) is 4 sections, the temperature of each section is 180-330 ℃, and the winding speed is 190-400 m/min.

The technological parameters of the cyclization-drafting integrated treatment in the step (3) are as follows: and (3) treating the polyamic acid precursor fiber by using a contact hot roller, passing through 3-5 hot rollers, wherein the heating temperature of the hot rollers is 60-500 ℃, and the heat drafting multiple is 1.1-5 times under the protection of nitrogen.

The size of the zinc oxide nano-particles in the step (3) is 100-300 nm.

The invention also provides application of the high-strength weather-resistant polyimide fiber in space and sky detection equipment.

The cyclization-drafting integrated treatment is carried out in a nitrogen atmosphere, so that zinc salt (such as zinc nitrate hexahydrate) in the fiber is fully ensured to be heated and converted into zinc oxide nano particles which are uniformly dispersed in the fiber.

According to the invention, an o-hydroxybenzophenone unit is introduced into a polyimide fiber main chain, and zinc oxide nanoparticles are further compounded, and the polyimide fiber with high strength, ultraviolet radiation resistance and high surface activity is prepared through dry forming and cyclization-drafting integrated treatment.

Table 1 shows the comparison of the properties of the polyimide fibers of the present invention with those of the polyimide fibers obtained from chinese patents having application nos. 200710050651.1, 201010572496.1 and 201110222300.0 and other high performance fibers of the prior art PI fibers, aramid fibers and PBO fibers from the data reported in fiber manufacturers and literature (Macromolecular Rapid Communication 2018,39,1800141).

TABLE 1

Advantageous effects

(1) The benzimidazole unit and the O-hydroxybenzophenone unit are copolymerized and introduced into the main chain of the polyimide, a C-O-H-N hydrogen bond structure is favorably formed among molecular chains, the intra-molecular/inter-molecular hydrogen bond effect can be effectively improved, the mechanical property of the polyimide fiber is greatly improved, the fiber is endowed with excellent surface activity, and the interface effect with resin is improved;

(2) according to the invention, by means of the unique absorption-conversion effect of the o-hydroxybenzophenone unit on ultraviolet light and the excellent shielding effect of the ZnO nanoparticles on the ultraviolet light, the polyimide fiber is endowed with excellent weather resistance, the extreme application requirement of space can be met, and a new material solution is provided for aerospace detection equipment;

(3) according to the invention, the precursor fiber is subjected to cyclization-drafting integrated treatment, and high-power orientation of macromolecular chains is synchronously generated in cyclization reaction of the precursor fiber, so that the problems of complex preparation process, difficult complete imidization drafting and the like in the traditional process of cyclization before hot drafting are avoided, and the uniformity and batch stability of the fiber are improved. Compared with the traditional process, the integrated process of cyclization-drafting is beneficial to providing production efficiency and is suitable for large-scale development of fibers.

Drawings

FIG. 1 is a SEM photograph of the surface of the polyimide fibers, aramid fibers and PBO fibers in example 1 after 168h irradiation treatment;

FIG. 2 is a s-s curve of the mechanical property test of the polyimide fiber in example 2;

FIG. 3 is a TGA curve of the polyimide fiber of example 3.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Fiber performance test conditions in the examples of the present invention:

mechanical properties: testing by using an Instron3300, wherein the stretching speed is 5cm/min, and the distance between clamps is 2 cm;

ultraviolet irradiation resistance: testing according to the national standard GB/T1452293;

fiber-epoxy interface bond strength test: through the test of a microsphere drawing test, the diameter of the microsphere is 50-100 mu m, the drawing speed is 5m/min, 10 groups of data are tested for each sample, and the average value is taken.

The structural formula of diamine a in the examples is:the structural formula of diamine B is:the structural formula of the diamine C is

Example 1

Under the protection of nitrogen, two diamine monomers are dissolved in NMP solvent according to the molar ratio of BPDA to BIA to diamine A being 10:5:5 in advance, after the two diamine monomers are completely dissolved, BPDA is added in batches under the protection of nitrogen (the addition is divided into 3 times, the addition mass fractions are respectively 70%, 25% and 5%, based on the total mass of dianhydride monomers), the solid content is controlled to be 17 wt%, and the mixture is fully stirred and reacted for 24 hours at room temperature to obtain the solution with the intrinsic viscosity of 3.3 dl/g. And (3) blending and adding zinc nitrate hexahydrate into the polymerization solution, wherein the mass fraction of the zinc nitrate hexahydrate is 5 wt% (based on the total mass of solids in the spinning solution), and uniformly mixing the zinc nitrate hexahydrate and the spinning solution by ultrasonic dispersion. The fiber is prepared by dry forming, namely spinning solution is measured and extruded by a metering pump after being filtered and defoamed and enters a spinning channel through a spinning hole (168 holes, the aperture is 100 mu m), the temperature section of the spinning channel is 4 sections, the temperature of each section of the channel is 300 ℃, and the winding speed is 200 m/min. And (2) carrying out cyclization-drafting integrated treatment on the obtained nascent fiber, namely, carrying out cyclization-drafting integrated treatment on the nascent fiber by five hot rollers at the temperature of 280, 320, 380, 420 and 450 ℃ respectively and at the drafting ratio of 1.3, 1.5, 2.0 and 2.3, wherein the process is carried out under the protection of nitrogen, and zinc nitrate hexahydrate is converted into ZnO nanoparticles through heat treatment. And finally, winding to obtain the polyimide/ZnO composite fiber. The fiber strength was 3.58GPa, the modulus 123GPa, and the elongation at break 3.2%. After 168 hours of ultraviolet irradiation, the strength retention rate is 93.5%, and as can be seen from fig. 1, the fibers of the embodiment are basically unchanged after the ultraviolet irradiation treatment, and the surfaces of the PBO and aramid fibers are obviously etched. In addition, the interface bonding strength of the fiber and the epoxy resin reaches 42 MPa.

Example 2

Under the protection of nitrogen, two diamine monomers are dissolved in NMP solvent according to the molar ratio of BPDA to BIA to diamine C being 10 to 7 to 3 in advance, after the two diamine monomers are completely dissolved, BPDA is added in batches under the protection of nitrogen (the addition weight fractions are respectively 70 percent, 25 percent and 5 percent based on the total weight of dianhydride monomers) and the solid content is controlled to be 15 weight percent, and the mixture is fully stirred and reacted for 24 hours at room temperature to obtain the solution with the intrinsic viscosity of 3.5 dl/g. And (3) blending and adding zinc nitrate hexahydrate into the polymerization solution, wherein the mass fraction of the zinc nitrate hexahydrate is 8 wt% (based on the total mass of solids in the spinning solution), and uniformly mixing the zinc nitrate hexahydrate and the spinning solution by ultrasonic dispersion. The fiber is prepared by dry forming, namely spinning solution is measured and extruded by a metering pump after being filtered and defoamed and enters a spinning channel through a spinning hole (168 holes, the aperture is 100 mu m), the temperature section of the spinning channel is 4 sections, the temperature of each section of the channel is 320 ℃, and the winding speed is 190 m/min. And (2) carrying out cyclization-drafting integrated treatment on the obtained nascent fiber, namely, carrying out cyclization-drafting integrated treatment on the nascent fiber by five hot rollers at the temperatures of 300, 320, 350, 420 and 460 ℃ respectively and at the drafting ratios of 1.1, 1.3, 1.5, 2.0 and 2.3, wherein the process is carried out under the protection of nitrogen, and zinc nitrate hexahydrate is converted into ZnO nanoparticles through heat treatment. And finally, winding to obtain the polyimide/ZnO composite fiber. The fiber strength is 3.70GPa, the modulus is 135GPa, the elongation at break is 3.0 percent, and the s-s curve of the mechanical property of the fiber is shown in figure 2. After ultraviolet irradiation for 168 hours, the strength retention rate is 95%. In addition, the interface bonding strength of the fiber and the epoxy resin reaches 47 MPa.

Example 3

Under the protection of nitrogen, two diamine monomers are dissolved in NMP solvent according to the molar ratio of BPDA to BIA to diamine C being 10.1:5:5 in advance, after the two diamine monomers are completely dissolved, BPDA is added in batches under the protection of nitrogen (the addition weight fractions are 70%, 25% and 5% respectively based on the total weight of dianhydride monomers) and the solid content is controlled to be 16 wt%, and the mixture is fully stirred and reacted for 24 hours at room temperature to obtain the solution with the intrinsic viscosity of 3.8 dl/g. And (3) blending and adding zinc nitrate hexahydrate into the polymerization solution, wherein the mass fraction of the zinc nitrate hexahydrate is 10 wt% (based on the total mass of solids in the spinning solution), and uniformly mixing the zinc nitrate hexahydrate and the spinning solution by ultrasonic dispersion. The fiber is prepared by dry forming, namely spinning solution is measured and extruded by a metering pump after being filtered and defoamed and enters a spinning channel through a spinning hole (168 holes, the aperture is 100 mu m), the temperature section of the spinning channel is 4 sections, the temperature of each section of the channel is 330 ℃, and the winding speed is 200 m/min. And (2) carrying out cyclization-drafting integrated treatment on the obtained nascent fiber, namely, carrying out cyclization-drafting integrated treatment on the nascent fiber by five hot rollers at the temperature of 270, 320, 370, 420 and 490 ℃ respectively and at the drafting ratio of 1.4, 1.7, 1.5 and 2.1, wherein the process is carried out under the protection of nitrogen, and zinc nitrate hexahydrate is converted into ZnO nanoparticles through heat treatment. And finally, winding to obtain the polyimide/ZnO composite fiber. The fiber strength was 4.20GPa, the modulus 140GPa, and the elongation at break 2.5%. After 168 hours of ultraviolet irradiation, the strength retention rate is 94.6%. In addition, the interface bonding strength of the fiber and the epoxy resin reaches 44 MPa. As shown in fig. 3, the initial decomposition temperature of the fiber reached 580 ℃ under a nitrogen atmosphere.

Example 4

Under the protection of nitrogen, two diamine monomers are dissolved in NMP solvent in advance according to the molar ratio of PMDA to BIA to diamine B being 10 to 8 to 2, after the two diamine monomers are completely dissolved, PMDA is added in batches under the protection of nitrogen (the addition is carried out by 3 times, the addition mass fractions are respectively 70 percent, 25 percent and 5 percent, and the total mass of dianhydride monomers is taken as a reference), the solid content is controlled to be 13 weight percent, and the solution is fully stirred and reacted for 24 hours at room temperature to obtain the intrinsic viscosity of the solution of 3.5 dl/g. And (3) blending and adding zinc nitrate hexahydrate into the polymerization solution, wherein the mass fraction of the zinc nitrate hexahydrate is 10 wt% (based on the total mass of solids in the spinning solution), and uniformly mixing the zinc nitrate hexahydrate and the spinning solution by ultrasonic dispersion. The fiber is prepared by dry forming, namely spinning solution is measured and extruded by a metering pump after being filtered and defoamed and enters a spinning channel through a spinning hole (168 holes, the aperture is 100 mu m), the temperature of the spinning channel is 4 sections, the temperature of each section of the channel is 300 ℃, and the winding speed is 220 m/min. And (2) carrying out cyclization-drafting integrated treatment on the obtained nascent fiber, namely, carrying out cyclization-drafting integrated treatment on the nascent fiber by five hot rollers at the temperatures of 300, 320, 390, 450 and 490 ℃ respectively, wherein the drafting ratio is 1.3, 1.1, 1.3, 1.7 and 2.1, the process is carried out under the protection of nitrogen, and zinc nitrate hexahydrate is converted into ZnO nanoparticles through heat treatment. And finally, winding to obtain the polyimide/ZnO composite fiber. The fiber strength was 3.50GPa, the modulus 220GPa, and the elongation at break 2.3%. After 168 hours of ultraviolet irradiation, the strength retention rate is 93 percent. In addition, the interface bonding strength of the fiber and the epoxy resin reaches 44 MPa.

Comparative example 1

Under the protection of nitrogen, diamine monomer is dissolved in NMP solvent in advance according to the molar ratio of BPDA to BIA being 1:1, after the diamine monomer is completely dissolved, BPDA is added in batches under the protection of nitrogen (the addition mass fractions are respectively 70%, 25% and 5%, based on the total mass of dianhydride monomer) and the solid content is controlled to be 16 wt%, and the mixture is fully stirred and reacted for 24 hours at room temperature, so that the intrinsic viscosity of the solution is 3.0 dl/g. And (3) blending and adding zinc nitrate hexahydrate into the polymerization solution, wherein the mass fraction of the zinc nitrate hexahydrate is 10 wt% (based on the total mass of solids in the spinning solution), and uniformly mixing the zinc nitrate hexahydrate and the spinning solution by ultrasonic dispersion. The fiber is prepared by dry forming, namely spinning solution is measured and extruded by a metering pump after being filtered and defoamed and enters a spinning channel through a spinning hole (168 holes, the aperture is 100 mu m), the temperature section of the spinning channel is 4 sections, the temperature of each section of the channel is 330 ℃, and the winding speed is 200 m/min. And (3) subjecting the obtained nascent fiber to cyclization-drafting integrated treatment, namely subjecting the nascent fiber to five hot rollers at the temperatures of 270, 320, 370, 420 and 490 ℃ respectively and the drafting ratios of 1.4, 1.7, 1.5 and 2.1, carrying out the process under the protection of nitrogen, and finally winding to obtain the polyimide fiber. Compared with the fiber of the example 3, the fiber without the o-hydroxybenzophenone-containing monomer has the strength of 3.30GPa, the modulus of 120GPa and the elongation at break of 3.5 percent. After 168 hours of ultraviolet irradiation, the strength retention rate is 90%. In addition, the interface bonding strength of the fiber and the epoxy resin reaches 38 MPa.

Comparative example 2

Under the protection of nitrogen, two diamine monomers are dissolved in NMP solvent according to the molar ratio of BPDA to BIA to diamine C being 10 to 7 to 3 in advance, after the two diamine monomers are completely dissolved, BPDA is added in batches under the protection of nitrogen (the addition weight fractions are respectively 70 percent, 25 percent and 5 percent based on the total weight of dianhydride monomers) and the solid content is controlled to be 15 weight percent, and the mixture is fully stirred and reacted for 24 hours at room temperature to obtain the solution with the intrinsic viscosity of 3.5 dl/g. The fiber is prepared by dry forming, namely spinning solution is measured and extruded by a metering pump after being filtered and defoamed and enters a spinning channel through a spinning hole (168 holes, the aperture is 100 mu m), the temperature section of the spinning channel is 4 sections, the temperature of each section of the channel is 320 ℃, and the winding speed is 190 m/min. And (2) subjecting the obtained nascent fiber to cyclization-drafting integrated treatment, namely subjecting the nascent fiber to five hot rollers at the temperatures of 300, 320, 350, 420 and 460 ℃ respectively and at the drafting ratios of 1.1, 1.3, 1.5, 2.0 and 2.3, carrying out the process under the protection of nitrogen, and finally winding to obtain the polyimide fiber. Compared with the embodiment 2, the fiber strength is 3.90GPa, the modulus is 130GPa, the elongation at break is 3.2% without adding zinc nitrate hexahydrate, the strength retention rate is 87% after ultraviolet irradiation for 168h, and the interface bonding strength of the fiber and the epoxy resin reaches 40 MPa.