1. The polyimide aerogel fiber is characterized by having a three-dimensional network structure formed by mutually crosslinking polyimide nano fibers, wherein the titer of the polyimide aerogel fiber is 0.07-7D, and the density of the polyimide aerogel fiber is 80-150mg/cm³The thermal conductivity is 0.015W/mK-0.025W/mK, and the pore size of the three-dimensional network structure is 50-200 nm.

2. The preparation method of the polyimide aerogel fiber is characterized by comprising the following steps:

step S1, providing a polyamic acid solution;

step S2, carrying out spinnability treatment on the polyamic acid solution to obtain polyamic acid spinning solution;

step S3, spinning the polyamic acid spinning solution to obtain polyamic acid gel fiber;

step S4, imidizing the polyamic acid gel fiber to obtain polyimide gel fiber with a three-dimensional network structure;

and step S5, performing solvent replacement on the polyimide aerogel fiber, and then performing freeze drying or supercritical drying to obtain the polyimide aerogel fiber.

3. The method according to claim 2, wherein in step S1, the polyamic acid solution is formed by polymerizing a dianhydride monomer, a diamine monomer, and a crosslinking agent in a first organic solvent,

wherein the dianhydride monomer is one or more selected from pyromellitic dianhydride, biphenyl tetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, benzophenone tetracarboxylic anhydride and bisphenol A dianhydride,

the diamine monomer is one or more selected from 4,4 '-diaminodiphenyl ether, 4' -diphenyl ether diamine, p-phenylenediamine, diphenylmethane diisocyanate, toluene diisocyanate, 4 '-diaminobenzanilide and 4,4' -diamino-2, 2 '-dimethyl-1, 1' -biphenyl,

the cross-linking agent is one or more selected from 1,3, 5-tri (4-aminophenoxy) benzene, melamine and derivatives thereof,

the first organic solvent is one selected from the group consisting of N-methylpyrrolidone, N-dimethylformamide and dimethylacetamide.

4. The preparation method according to claim 3, wherein in the polyamic acid solution, the mass concentration of polyamic acid is 15-20 wt%, and the molar ratio of dianhydride monomer, diamine monomer and cross-linking agent is (n +1)/n/m, wherein n is 10-20, and m is 0.5-1.

5. The production method according to claim 1, wherein the spinnability treatment in step S2 includes:

step S21 of subjecting the polyamic acid solution to vacuum degassing treatment;

and step 22, performing ice-water bath on the defoamed polyamic acid solution to prevent gelation.

6. The method according to claim 1, wherein the polyamic acid spinning solution is sprayed into a coagulation bath using a spinneret to form a polyamic acid gel fiber, the coagulation bath is a mixture of a coagulant in a second organic solvent, the coagulant is water, the second organic solvent is one selected from the group consisting of N-methylpyrrolidone, N-dimethylformamide, and dimethylacetamide, and a volume ratio of the second organic solvent in the coagulation bath is 50% or less.

7. The preparation method according to claim 6, wherein the polyamic acid spinning solution is directly sprayed into the coagulating bath through a metering pump and the spinneret by wet spinning to form a solid polyamic acid gel fiber;

or the polyamic acid spinning solution passes through a metering pump and a hollow fiber spinning nozzle, adopts dry-wet spinning, passes through an air gap of 2-5 cm, and is sprayed into the coagulating bath to form the hollow polyamic acid gel fiber.

8. The production method according to claim 1, wherein in the step S4, the imidization is performed by chemical treatment or heat treatment,

wherein the chemical treatment comprises soaking the polyamic acid gel fiber cleaned by clear water in a solution of acetic anhydride/pyridine with the volume ratio of 1:1 for 24-48 hours,

the heat treatment comprises heating the polyamic acid gel fiber cleaned by clear water to 300-350 ℃ for imidization.

9. The production method according to claim 1, wherein in the step S5,

and the solvent replacement adopts ethanol for multiple replacements, wherein the ethanol: the volume ratio of the polyimide gel fibers is 5-15: 1,

then supercritical drying is carried out, wherein supercritical fluid used in the supercritical drying process is supercritical CO₂And setting the pressure to be 8.5-9 MPa, setting the temperature of a drying kettle to be 40-50 ℃, and preferably setting the drying time to be 12-24 hours to obtain the polyimide aerogel fiber.

10. The production method according to claim 1, wherein in the step S5,

the solvent replacement adopts a mixed solution of tert-butyl alcohol and water for multiple replacements, the volume ratio of the tert-butyl alcohol to the water in the mixed solution of the tert-butyl alcohol and the water is 2:3, and the mixed solution: the volume ratio of the polyimide gel fibers is 5-15: 1,

and then freeze-drying at the temperature of-50 to-30 ℃ under the pressure of 30 to 50Pa for 24 to 36 hours.

Background

Fiber materials have a long history, and have been developed for nearly a hundred years from natural fibers such as cotton and hemp, which have been used by mankind several thousand years ago, to synthetic fibers produced in the 19 th century. Currently, various fields of human life production widely employ various synthetic fibers, such as fibers for everyday clothing cloth, fibers industrially used for filtration and high strength applications, smart fibers used in chips and electronic devices, and the like. Compared with natural fibers, synthetic fibers have qualitative leaps in the aspects of performance, strength, precision and the like, but the heat preservation performance has not been greatly improved. With the improvement of living standard and production level of people, a novel simple and easy fiber material which can be woven and has good heat preservation effect is urgently needed to meet the requirements of people on dress heat preservation and industrial heat preservation.

Aerogel materials have the characteristics of low thermal conductivity, low density and the like due to the special porous network structure, and have been paid attention to for the birth. Over decades of development, aerogel materials have evolved from the original silica aerogel into a vast family of materials possessing a wide variety of species, including graphene aerogels, cellulose aerogels, metal aerogels, carbon aerogels, polyimide aerogels, and the like. Aerogel plates, aerogel plates and the like in the current market are also widely applied to the fields of industrial heat preservation, aerospace and the like. Although aerogel materials have better heat insulation effects than natural fiber materials such as cotton and hemp, most of the aerogel materials are in powder, block or sheet form, and have poor spinnability, which limits better application in the fields of clothes and the like. Therefore, how to prepare aerogel materials into textile aerogel fibers becomes an important factor for the wider application of aerogel materials in the field of thermal insulation.

Among many materials, polyimide is called one of the highest comprehensive performance organic polymer materials. Polyimide can be formed into fibers by spinning techniques, for example, hollow polyimide fibers, which are widely used in the field of membrane separation. While polyimide fibers have good mechanical and fire-retardant properties, traditionally woven polyimide fibers do not have the typical three-dimensional network structure that aerogels possess. Therefore, there is a need to develop a spinnable polyimide aerogel fiber.

Disclosure of Invention

In view of the above, the present invention provides a polyimide aerogel fiber and a method for preparing the same. Compared with the existing polyimide aerogel fiber, the polyimide aerogel fiber has a three-dimensional network structure with a molecular scale by introducing a cross-linking agent, so that the polyimide aerogel fiber has lower thermal conductivity, good air permeability, good mechanical properties and spinnability.

The invention also provides a preparation method of the polyimide aerogel fiber. Compared with the prior art, the method has the advantages of simple process, mild reaction conditions, short reaction time and no need of external energy in the reaction process. And the pollution of reaction raw materials and reaction products is small, and the reaction raw materials are commercially available. The process flow can be continuous and can be used for continuous large-scale production.

The invention comprises the following two aspects:

in a first aspect, the present invention provides a polyimide aerogel fiber, wherein the polyimide aerogel fiber has a three-dimensional network structure formed by mutually crosslinking polyimide nanofibers, the fineness of the polyimide aerogel fiber is 0.07-7D, and the density is 80-150mg/cm³The thermal conductivity is 0.015W/mK-0.025W/mK, and the pore size of the three-dimensional network structure is 50-200 nm.

In a second aspect, the present invention provides a method for preparing a polyimide aerogel fiber, which is characterized by comprising the following steps:

step S1, providing a polyamic acid solution;

step S2, carrying out spinnability treatment on the polyamic acid solution to obtain polyamic acid spinning solution;

step S3, spinning the polyamic acid spinning solution to obtain polyamic acid gel fiber;

step S4, imidizing the polyamic acid gel fiber to obtain polyimide gel fiber with a three-dimensional network structure;

and step S5, performing solvent replacement on the polyimide aerogel fiber, and then performing freeze drying or supercritical drying to ensure that the three-dimensional network structure does not collapse to obtain the polyimide aerogel fiber.

The technical scheme of the invention at least has one of the following beneficial effects:

according to the preparation method provided by the embodiment of the invention, a simple preparation method of the polyimide fiber convenient for spinning is provided;

the polyimide aerogel fiber provided by the invention has a typical three-dimensional porous network structure, has low thermal conductivity, good air permeability and good spinnability, and can be applied to the fields of spinning, special clothing, industrial heat preservation and the like;

the preparation method of the polyimide aerogel fiber provided by the invention is simple in process, continuous in process flow and mild in reaction conditions, and can be used for continuous large-scale production.

Drawings

Fig. 1 is an SEM photograph of a polyimide aerogel fiber prepared according to example 2 of the present invention, in which (a) shows a cross-sectional morphology thereof and (b) shows a partial enlarged view thereof.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below. It is to be understood that the described embodiments are merely exemplary of the invention and are not intended to be exhaustive or limiting. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of protection of the invention.

Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs. The use of "first," "second," and similar terms in the present application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another.

The preparation method of the polyimide aerogel fiber comprises the following steps:

step S1, providing a polyamic acid solution;

step S2, carrying out spinnability treatment on the polyamic acid solution to obtain polyamic acid spinning solution;

step S3, spinning the polyamic acid spinning solution to obtain polyamic acid gel fiber with a three-dimensional network structure;

step S4, imidizing the polyamic acid gel fiber to obtain polyimide gel fiber;

and step S5, performing solvent replacement on the polyimide aerogel fiber, and then performing freeze drying or supercritical drying to ensure that the three-dimensional network structure does not collapse to obtain the polyimide aerogel fiber.

Further, in the step S1, the polyamic acid solution is formed by polymerizing a dianhydride monomer, a diamine monomer and a cross-linking agent in a first organic solvent,

wherein the dianhydride monomer is one or more selected from pyromellitic dianhydride, biphenyl tetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, benzophenone tetracarboxylic anhydride and bisphenol A dianhydride,

the diamine monomer is one or more selected from 4,4 '-diaminodiphenyl ether, 4' -diphenyl ether diamine, p-phenylenediamine, diphenylmethane diisocyanate, toluene diisocyanate, 4 '-diaminobenzanilide and 4,4' -diamino-2, 2 '-dimethyl-1, 1' -biphenyl,

the cross-linking agent is one or more selected from 1,3, 5-tri (4-aminophenoxy) benzene, melamine and derivatives thereof,

the first organic solvent is one selected from the group consisting of N-methylpyrrolidone, N-dimethylformamide and dimethylacetamide.

For example, in one embodiment, the polyamic acid solution is obtained by reacting 3,3,4, 4-biphenyltetracarboxylic dianhydride, 4, 4-diaminodiphenyl ether, and 1,3, 5-tris (4-aminophenoxy) benzene in step S1. The reaction mechanism and the reaction route are shown in the following reaction scheme (I):

furthermore, in the polyamic acid solution, the mass concentration of the polyamic acid is 15-20 wt%, and the molar ratio of the dianhydride monomer, the diamine monomer and the cross-linking agent is (n +1)/n/m, wherein the value of n is 10-20, and the value of m is 0.5-1.

Further, the spinnability processing in step S2 includes:

step S21 of subjecting the polyamic acid solution to vacuum degassing treatment;

and step 22, performing ice-water bath on the defoamed polyamic acid solution to prevent gelation.

Further, in step S3, the polyamic acid spinning solution is sprayed into a coagulation bath using a spinneret to form a polyamic acid gel fiber, the coagulation bath is a mixture of a coagulant in a second organic solvent, the coagulant is water, the second organic solvent is any one selected from N-methylpyrrolidone, N-dimethylformamide, and dimethylacetamide, and a volume ratio of the second organic solvent in the coagulation bath is 50% or less.

Further, the polyamic acid spinning solution passes through a metering pump and the spinneret and is directly sprayed into the coagulating bath by wet spinning to form solid polyamic acid gel fiber;

or the polyamic acid spinning solution passes through a metering pump and a hollow fiber spinning nozzle, adopts dry-wet spinning, passes through an air gap of 2-5 cm, and is sprayed into the coagulating bath to form the hollow polyamic acid gel fiber.

Further, in the step S4, the imidization is performed by chemical treatment or heat treatment,

wherein the chemical treatment comprises soaking the polyamic acid gel fiber cleaned by clear water in a solution of acetic anhydride/pyridine with the volume ratio of 1:1 for 24-48 hours,

the heat treatment comprises heating the polyamic acid gel fiber cleaned by clear water to 300-350 ℃ for imidization.

For example, in one embodiment, the reaction mechanism for the formation of the imide by the amide acid thermal imidization or chemical imidization is shown in the following reaction scheme (two):

further, in step S5, the following two schemes may be adopted:

and the solvent replacement adopts ethanol for multiple replacements, wherein the ethanol: the volume ratio of the polyimide gel fibers is 5-15: 1, thereafter carrying out supercritical drying in which supercritical CO is used as a supercritical fluid₂The pressure is set to be 8.5-9 MPa, the temperature of the drying kettle is 40-50 ℃, and the drying time is preferably 12-24 h.

Or, the solvent replacement is carried out for multiple times by using a mixed solution of tert-butyl alcohol and water, the volume ratio of tert-butyl alcohol to water in the mixed solution of tert-butyl alcohol and water is 2:3, and the mixed solution: the volume ratio of the polyimide gel fibers is 5-15: and 1, freeze-drying at the temperature of minus 50 to minus 30 ℃ under the pressure of 30 to 50Pa for 24 to 36 hours.

The polyimide aerogel fiber prepared by the preparation method has a three-dimensional network structure formed by mutually crosslinking polyimide nano fibers, wherein the titer of the polyimide nano fibers is 0.07-7D, and the density of the polyimide nano fibers is 80-150mg/cm³The thermal conductivity is 0.015W/mK-0.025W/mK, and the pore size of the three-dimensional network structure is 50-200 nm.

Polyimide aerogel fibers and a method for preparing the same according to embodiments of the present invention are illustrated below by specific examples.

Example 1

28.125g (0.1406mol) of diamine monomer 4, 4-diaminodiphenyl ether was taken and dissolved in 250ml of a first organic solvent, N-methylpyrrolidone. After stirring uniformly, 44.063g (0.1497mol) of dianhydride monomer 3,3,4, 4-biphenyltetracarboxylic dianhydride was added to the above mixed solution, and stirred at room temperature for ten minutes. And obtaining the polyamic acid solution after the solution is completely transparent. Adding 2.5g (0.00625mol) of cross-linking agent 1,3, 5-tri (4-aminophenoxy) benzene into the polyamic acid solution, and stirring for ten minutes at normal temperature to obtain the polyamic acid solution with the three-dimensional network molecular structure.

The molar ratio of the diamine monomer to the cross-linking agent is 16:15: 0.67.

In the polyamic acid solution with the three-dimensional network molecular structure, the mass fraction of the polyamic acid is 18 wt%.

And (3) placing the polyamic acid solution with the three-dimensional network molecular structure in an ice-water bath, and then defoaming for 2 hours in a vacuum environment. During the spinning process, the low-temperature environment of the polyamic acid spinning solution with the three-dimensional network molecular structure is maintained to slow down the gel. The polyamic acid spinning solution with the three-dimensional network molecular structure adopts wet spinning. Specifically, a 50-hole spinneret with a diameter of 50 μm and a diameter of 1.8cm is adopted³And (3) spinning at an extrusion speed of/min, and carrying out gel curing on the polyamic acid trickle in a coagulating bath at 25 ℃ to form the polyamic acid gel fiber, wherein the coagulating bath is a 50% N-methyl pyrrolidone aqueous solution, the curing time is 3min, and the drawing speed of the gel bath is 2 times. The polyamide acid gel fiber is pulled to a clean water bath at 25 ℃ by a guide roller for cleaning, and the residual N-methyl pyrrolidone on the surface is cleaned in the clean water bath for 1 min. And drawing the washed polyamic acid gel fiber into a mixed solution of pyridine and acetic anhydride through a guide roller, soaking for 24 hours, and carrying out chemical imidization to obtain the polyimide gel fiber. The ratio of pyridine to acetic anhydride in the mixed solution of pyridine and acetic anhydride is 1:1, and the temperature is controlled at 25 ℃.

The polyimide gel fiber is subjected to solvent replacement for 4 times in ethanol solution with 10 times of volume per se, and each time is 6 hours. And carrying out supercritical drying on the polyimide aerogel fiber after the solvent replacement to obtain the polyimide aerogel fiber with the three-dimensional network structure. The supercritical fluid used in the supercritical drying process is supercritical CO₂The pressure of the drying kettle is controlled to be 8.5-9 MPa, the temperature of the drying kettle is controlled to be 40-50 ℃, and the drying time is 15 hours. The density of the obtained polyimide aerogel fiber was 100mg/cm³Specific surface area of 370m²(ii)/g, porosity 95%, thermal conductivity 0.02W/m.K.

Example 2

28.125g (0.1406mol) of diamine monomer 4, 4-diaminodiphenyl ether was taken and dissolved in 250ml of a first organic solvent, N-methylpyrrolidone. After stirring uniformly, 44.063g (0.1497mol) of dianhydride monomer 3,3,4, 4-biphenyltetracarboxylic dianhydride was added to the above mixed solution, and stirred at room temperature for ten minutes. And obtaining the polyamic acid solution after the solution is completely transparent. Adding 2.5g (0.00625mol) of cross-linking agent 1,3, 5-tri (4-aminophenoxy) benzene into the polyamic acid solution, and stirring for ten minutes at normal temperature to obtain the polyamic acid solution with the three-dimensional network molecular structure.

The molar ratio of the diamine monomer to the cross-linking agent is 16:15: 0.67.

In the polyamic acid solution with the three-dimensional network molecular structure, the mass fraction of the polyamic acid is 18%.

And (3) placing the polyamic acid solution with the three-dimensional network molecular structure in an ice-water bath, and then defoaming for 2 hours in a vacuum environment. During the spinning process, the low-temperature environment of the polyamic acid spinning solution with the three-dimensional network molecular structure is maintained to slow down the gel. The polyamic acid spinning solution with the three-dimensional network molecular structure adopts wet spinning. Specifically, a 50-hole spinneret with a diameter of 50 μm and a diameter of 1.8cm is adopted³And (3) spinning at an extrusion speed of/min, and carrying out gel curing on the polyamic acid trickle in a coagulating bath at 25 ℃ to form the polyamic acid gel fiber, wherein the coagulating bath is a 50% N-methyl pyrrolidone aqueous solution, the curing time is 3min, and the drawing speed of the gel bath is 2 times. The polyamide acid gel fiber is pulled to a clean water bath at 25 ℃ by a guide roller for cleaning, and the residual N-methyl pyrrolidone on the surface is cleaned in the clean water bath for 1 min. And drawing the washed polyamic acid gel fiber into a mixed solution of pyridine and acetic anhydride through a guide roller, soaking for 24 hours, and carrying out chemical imidization to obtain the polyimide gel fiber. The ratio of pyridine to acetic anhydride in the mixed solution of pyridine and acetic anhydride is 1:1, and the temperature is controlled at 25 ℃.

The polyimide gel fiber was solvent-substituted with 10 times its volume of t-butanol/water solution 4 times for 6 hours each time. The ratio of tert-butanol/water in the tert-butanol/water solution is 2: 3. Mixing the solventAnd freeze-drying the replaced polyimide gel fiber to obtain the polyimide aerogel fiber with the three-dimensional network structure. In the freeze drying process, the temperature is controlled to be between minus 50 ℃ and minus 30 ℃, the pressure is controlled to be between 30 Pa and 50Pa, and the drying time is 24 hours. The density of the obtained polyimide aerogel fiber was 100mg/cm³Specific surface area of 400m²(ii) a porosity of 96% and a thermal conductivity of 0.02W/m.K. Fig. 1 shows a cross-sectional morphology SEM image (as shown in (a)) and a partially enlarged SEM image (as shown in (b)) of the prepared polyimide aerogel fiber. As can be seen from fig. 1, the prepared polyimide aerogel fiber has a uniform three-dimensional network structure.

Example 3

28.125g (0.1406mol) of diamine monomer 4, 4-diaminodiphenyl ether was taken and dissolved in 250ml of a first organic solvent, N-methylpyrrolidone. After stirring uniformly, 44.063g (0.1497mol) of dianhydride monomer 3,3,4, 4-biphenyltetracarboxylic dianhydride was added to the above mixed solution, and stirred at room temperature for ten minutes. And obtaining the polyamic acid solution after the solution is completely transparent. Adding 2.5g (0.00625mol) of cross-linking agent 1,3, 5-tri (4-aminophenoxy) benzene into the polyamic acid solution, and stirring for ten minutes at normal temperature to obtain the polyamic acid solution with the three-dimensional network molecular structure.

The molar ratio of the diamine monomer to the cross-linking agent is 16:15: 0.67.

In the polyamic acid solution with the three-dimensional network molecular structure, the mass fraction of the polyamic acid is 18%.

And (3) placing the polyamic acid solution with the three-dimensional network molecular structure in an ice-water bath, and then defoaming for 2 hours in a vacuum environment. During the spinning process, the low-temperature environment of the polyamic acid spinning solution with the three-dimensional network molecular structure is maintained to slow down the gel. The polyamic acid spinning solution with the three-dimensional network molecular structure adopts wet spinning. Specifically, a 50-hole spinneret with a diameter of 50 μm and a diameter of 1.8cm is adopted³Spinning at extrusion speed/min, and gel-curing the polyamic acid stream in a 25 deg.C coagulating bath to form polyamic acid gel fiber, wherein the coagulating bath is 50% N-methyl pyrrolidone water solutionThe melting time is 3min, and the drawing speed of the gel bath is 2 times. The polyamide acid gel fiber is pulled to a clean water bath at 25 ℃ by a guide roller for cleaning, and the residual N-methyl pyrrolidone on the surface is cleaned in the clean water bath for 1 min.

The washed polyamic acid gel fiber was solvent-replaced 4 times in 10 volumes of ethanol solution per se for 6 hours each time. And carrying out supercritical drying on the polyamic acid gel fiber after solvent replacement to obtain the polyamic acid aerogel fiber with a three-dimensional network structure. In the supercritical drying process, supercritical fluid is supercritical CO2, the pressure of a drying kettle is controlled to be 8.5-9 MPa, the temperature of the drying kettle is controlled to be 40-50 ℃, and the drying time is 15 hours.

And heating the polyamic acid aerogel fiber with the three-dimensional network structure to 300 ℃ for 6 hours under the protection of nitrogen atmosphere to carry out thermal imidization, and finally forming the polyimide aerogel fiber with the three-dimensional network structure. The density of the obtained polyimide aerogel fiber was 100mg/cm³Specific surface area of 390m²(ii)/g, porosity 94%, thermal conductivity 0.02W/m.K.

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.