CN115044996A

CN115044996A - Superfine aramid fiber and preparation method and application thereof

Info

Publication number: CN115044996A
Application number: CN202210740240.XA
Authority: CN
Inventors: 陈克复; 李金鹏
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-06-28
Filing date: 2022-06-28
Publication date: 2022-09-13
Anticipated expiration: 2042-06-28
Also published as: CN115044996B

Abstract

The invention discloses a preparation method of superfine aramid fiber, which comprises the following steps: adding a modifier into a neutral aramid polymer solution, fully mixing and dispersing, and filtering and defoaming to obtain a spinning stock solution; the modifier is a low-melting-point water-soluble polymer; and (3) conveying the spinning solution to a spinneret plate, and sequentially carrying out spinning, solidification and drafting, washing, drying, hot drafting, heat setting and rolling to prepare the superfine aramid fiber. The invention also discloses the superfine aramid fiber prepared by the preparation method and application. The superfine aramid fiber has small diameter, high strength, linear density less than 1.0dtex, rough surface, large specific surface area and better binding capacity in materials, and is widely applied to the fields of papermaking, filtration, spinning, rubber, flexible circuit boards and the like.

Description

Superfine aramid fiber and preparation method and application thereof

Technical Field

The invention relates to the technical field of aramid fibers, in particular to an ultrafine aramid fiber and a preparation method and application thereof.

Background

The poly (m-phenylene isophthalamide) (m-aramid) is prepared by condensation polymerization of m-phenylene diamine and m-phthaloyl chloride, amide groups in m-aramid macromolecules are connected with each other by m-phenyl, covalent bonds have no conjugation effect, internal rotation potential energy is lower than that of p-aramid fibers, macromolecular chains present flexible structures, and the strength and modulus of the macromolecular chains are equivalent to those of common polyester and nylon. The meta-aramid fiber is a high-tech special fiber, and has excellent mechanical property, stable chemical property and excellent heat resistance.

The ultra-fine aramid fiber is one of the rapidly developed differential fibers in recent years, is called as a new generation synthetic fiber, is outstanding in various varieties of chemical fibers, and is a high-quality and high-technology fiber. The fiber and the fabric have the advantages of soft hand feeling, light weight, softness, air permeability, good drapability, self-extinguishing property and the like, so that the application of the superfine aramid fiber in the fields of textile and clothing, papermaking, filtration and the like is continuously expanded. And the lack of the technology for producing the superfine aramid fiber in China causes that the existing aramid fiber production plants can not meet the market requirements of the superfine aramid fiber in China.

In spite of the prior art, no technology for efficiently producing the superfine aramid meta-fiber exists at present in China. For example, chinese patent 202111349941.2 discloses an aramid fiber and its preparation method and application, wherein the aramid fiber is obtained by drawing and washing the fiber several times, and the linear density of the aramid fiber is 2.7dtex, and the single fiber strength is 3.7 cN/dtex. Chinese patent 202010191376.0 discloses a method for modifying meta-aramid spinning solution, which comprises adding a trace amount of polyethylene glycol (0.1-1%) as a spinning solution modifier into a meta-aramid solution for modification. Chinese patent 202111491249.3 discloses a spinning method of meta-aramid fiber, which obtains a fiber with no skin-core structure or a very weak skin-core structure, the fiber number reaches 1.5dtex, and the single fiber strength reaches 5.10-5.23 cN/dtex at most. It can be known that the single fiber strength value is the most concerned in the current domestic aramid fiber manufacturing technology, and the technology for solving the superfine fiber (less than 1dtex) is not provided.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide the preparation method of the superfine aramid fiber, which realizes the high-efficiency production of the superfine aramid fiber, and the prepared superfine aramid fiber has the linear density of less than 1.0dtex, uniform and compact structure, less defects and large specific surface area.

The invention also aims to provide the superfine aramid fiber prepared by the preparation method of the superfine aramid fiber.

The invention further aims to provide application of the superfine aramid fiber.

The purpose of the invention is realized by the following technical scheme:

a preparation method of superfine aramid fiber comprises the following steps:

adding a modifier into a neutral aramid polymer solution, fully mixing and dispersing, and filtering and defoaming to obtain a spinning stock solution;

the modifier is a low-melting-point water-soluble polymer;

and (3) conveying the spinning solution to a spinneret plate, and sequentially carrying out spinning, solidification and drafting, washing, drying, hot drafting, heat setting and rolling to prepare the superfine aramid fiber.

Preferably, the low-melting-point water-soluble polymer is at least one of polyethylene glycol, polyvinylpyrrolidone, N-vinyl pyrrolidone and polyoxyethylene lauryl ether.

Preferably, the molecular weight of the polyethylene glycol is 400-1500, but the polyethylene glycol is not limited thereto, and the invention can be realized if the molecular weight is 4000 or more.

Preferably, the oven dry mass ratio of the modifier to the aramid polymer is (5-40) - (60-95), and the mixing temperature is 60-150 ℃.

Preferably, the aperture of the spinneret plate is 0.03-0.10 mm.

Preferably, the coagulation drawing comprises a first-stage coagulation bath drawing and a second-stage coagulation bath drawing, and specifically comprises the following steps:

the primary coagulation bath drafting magnification is 1.1-1.8 times, and the temperature is 20-80 ℃; the drafting ratio of the secondary coagulating bath is 1.1-2.5 times, and the temperature is 20-80 ℃.

Preferably, the hot drawing is, in particular: the drafting multiplying power is 1.1-2.0 times, and the temperature is 70-150 ℃.

The water washing specifically comprises the following steps:

the water washing process comprises two stages of water washing: the temperature of the first-stage water washing is 50-100 ℃; the temperature of the second-stage washing water is 20-50 ℃;

the drying specifically comprises the following steps:

the drying temperature is 80-120 ℃;

the heat setting specifically comprises the following steps:

the heat setting temperature is 280-320 ℃.

Preferably, the preparation method of the neutral aramid polymer solution comprises the following steps:

dissolving a cosolvent and m-phenylenediamine in N, N-dimethylacetamide at the temperature of 0-20 ℃ under the nitrogen protection atmosphere, and then adding m-phthaloyl chloride in several times to obtain a reaction solution; with the reaction, the temperature of the reaction liquid is gradually increased, and after the treatment of heat preservation at 50-80 ℃ for 0.5-10 h, an alkaline agent is added for neutralization to prepare a neutral aramid polymer solution;

the mol ratio of the m-phenylenediamine to the isophthaloyl dichloride is 100: (90-120);

the cosolvent is more than one of lithium bromide, lithium chloride, calcium chloride and calcium bromide;

the alkaline agent is more than one of calcium oxide, calcium hydroxide, magnesium hydroxide, sodium hydroxide and organic amine.

The superfine aramid fiber prepared by the preparation method of the superfine aramid fiber has the linear density less than 1.0 dtex.

The superfine aramid fiber is applied to papermaking, filtering, spinning, rubber and flexible circuit boards.

The principle of the invention is as follows:

the supermolecule fine structure of aramid fiber is characterized by high orientation degree and has regularly arranged long chains, while the conventional flexible chain or medium-stiffness polymer fiber is usually of a folding chain supermolecule structure. The invention obviously improves the rheological property of the aramid polymer by adding the modifier, and is beneficial to dry-wet spinning. After the modified spinning solution enters a coagulation bath through a spinneret plate, a solvent in the aramid fiber precursor is dissolved in hot water while the solvent is subjected to double diffusion in the coagulation bath, the modifier is gradually dissolved out of the aramid fiber precursor along with the aramid fiber precursor gradually passes through a multi-stage coagulation bath and a water washing bath, and finally the aramid fiber macromolecules are highly oriented and arranged by combining a multi-stage multi-time drafting process. The above characteristics make the proportion of molecular chains in the fiber which bear tensile load high, and the difference in length between these molecular chains small, and thus have excellent mechanical properties. Under the synergistic action of solidification and stretching, the acting force between molecules is increased along with the gradual solidification of the aramid fiber, the free volume of the molecules is relatively reduced, the orientation and the transition diffusion motion of molecular chains are obviously influenced, a highly ordered and regular chain structure is formed, and the macromolecules are arranged along the fiber axis in an oriented manner, so that the strength of the aramid fiber is greatly improved. In addition, by controlling different coagulation bath compositions and process temperatures, the dissolution rate of the modifier can be adjusted, and finally the superfine high-strength aramid fiber with rough and adjustable surface is prepared.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) according to the preparation method of the superfine aramid fiber, the superfine aramid fiber is prepared by adding the modifier and changing spinning parameters, and the superfine fiber with small density, uniform and compact structure, less defects and large specific surface area can be efficiently prepared.

(2) The superfine aramid fiber has small linear density and small diameter, and the fiber has good structural uniformity and high compactness; the specific surface area of the fiber is increased by thinning the fiber, and the combination effect of the fiber and the fiber is increased; the refining of the aramid fiber reduces the defect content of fiber protofilament in unit area and improves the strength.

(3) The superfine aramid fiber has the linear density of less than 1.0dtex, rough surface, large specific surface area and better binding capacity in materials, and is widely applied to the fields of papermaking, filtration, spinning, rubber, flexible circuit boards and the like.

Drawings

Fig. 1 is a schematic view of a manufacturing apparatus for implementing a method for manufacturing an ultrafine aramid fiber according to an embodiment of the present invention.

Fig. 2 is a cross-sectional SEM image of an ultra-fine aramid fiber prepared in example 5 of the present invention.

Fig. 3 is a surface SEM image of the ultra-fine aramid fiber prepared in example 5 of the present invention.

Fig. 4 is a surface SEM image of the ultra-fine aramid fiber prepared in example 6 of the present invention.

Fig. 5 is a surface SEM image of the ultra-fine aramid fiber prepared in example 7 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1

As shown in fig. 1, the manufacturing apparatus for implementing the method for manufacturing an aramid microfiber of this embodiment includes a spinneret 1, a collecting device 2, a first-stage coagulation bath drafting device 3, a second-stage coagulation bath drafting device 4, a first-stage washing device 5, a second-stage washing device 6, a drying device 7, a hot drafting device 8, a heat setting device 9, and a winding device 10.

The preparation method of the superfine aramid fiber of the embodiment is as follows:

(1) preparing an aramid polymer: dissolving m-phenylenediamine in N, N-dimethylacetamide under the conditions of low temperature of 15 ℃ and nitrogen protection atmosphere, adding lithium chloride, and then adding isophthaloyl dichloride for 1 time, wherein the molar ratio of the m-phenylenediamine to the isophthaloyl dichloride is controlled to be 100: 90. the temperature is gradually increased to 50 ℃ as the reaction proceeds, and the holding time is 10 h. And (3) adding calcium oxide for neutralization after heat preservation treatment to prepare a neutral aramid polymer solution.

(2) Preparing an aramid fiber stock solution: adding a proper amount of polyoxyethylene lauryl ether into the neutral aramid polymer obtained in the step (1), wherein the absolute dry mass ratio of the modifier to the aramid polymer is 5:95, and the mixing temperature is 80 ℃. And filtering and defoaming after fully mixing and dispersing to obtain the spinning solution.

(3) Preparing superfine aramid fibers: and (3) conveying the spinning solution obtained in the step (2) to a spinneret plate, and finally preparing the superfine aramid fiber through spinning, solidification drafting, water washing, drying, hot drafting, heat setting and rolling in sequence, wherein the specific parameters are as follows:

and (3) spinning: the aperture range of the spinneret plate is 0.03mm, and the number of holes is 20000; the distance between the spinneret and the coagulation bath is 5 cm;

and (3) solidification and drawing process: the first-stage coagulating bath comprises the following components in percentage by mass: n, N-dimethylacetamide: glycerol: water, etc. 60:20: 20; the temperature of the coagulation bath is 20 ℃, and the drafting ratio is 1.1 times; the secondary coagulating bath comprises the following components in percentage by mass: n, N-dimethylacetamide: 50:50 of water, 50 ℃ of coagulation bath temperature and 1.5 times of secondary coagulation bath drafting ratio;

and (3) water washing process: the first-stage washing water temperature is 20 ℃, and the drafting multiplying power is 1.5 times; the water temperature of the second-stage washing is 50 ℃;

and (3) drying: the drying temperature is 80 ℃;

and (3) hot drawing process: the hot drawing temperature is 200 ℃, and the drawing multiplying power is 1.5 times;

and (3) heat setting process: the heat setting temperature was 280 ℃.

Various properties of the obtained aramid fiber were measured, and the test results are shown in table 1.

Example 2

(1) preparing an aramid polymer: dissolving m-phenylenediamine in N, N-dimethylacetamide under the conditions of low temperature of 10 ℃ and nitrogen protection atmosphere, adding lithium chloride, and then adding isophthaloyl chloride 5 times, wherein the molar ratio of the m-phenylenediamine to the isophthaloyl chloride is controlled to be 100: 110. the temperature is gradually increased to 60 ℃ as the reaction proceeds, and the holding time is 8 h. And (3) adding calcium hydroxide for neutralization after heat preservation treatment to prepare a neutral aramid polymer solution.

(2) Preparing aramid fiber stock solution: adding a proper amount of polyethylene glycol-400 into the neutral aramid polymer obtained in the step (1), wherein the absolute dry mass ratio of the modifier to the aramid polymer is 10:90, and the mixing temperature is 60 ℃. And filtering and defoaming after fully mixing and dispersing to obtain the spinning solution.

and (3) spinning: the aperture range of the spinneret plate is 0.08mm, and the number of holes is 5000; the distance between the spinneret and the coagulation bath was 10 cm.

And (3) solidification and drawing process: the first-stage coagulating bath comprises the following components in percentage by mass: n, N-dimethylacetamide: glycerol: water, etc. 70:20: 10; the temperature of the coagulation bath is 50 ℃ and the drawing ratio is 1.5 times. The secondary coagulating bath comprises the following components in percentage by mass: n, N-dimethylacetamide: water is 60:40, the temperature of the coagulation bath is 80 ℃, and the drafting ratio of the secondary coagulation bath is 1.7 times;

and (3) water washing process: the first-stage washing water temperature is 40 ℃, and the drafting multiplying power is 1.3 times; the temperature of second-stage washing water is 60 ℃;

and (3) drying: the drying temperature is 100 ℃;

and (3) hot drawing process: the hot drawing temperature is 260 ℃ and the drawing multiplying power is 1.9 times;

and (3) heat setting process: the heat setting temperature is 290 ℃;

Example 3

(1) preparing an aramid polymer: dissolving m-phenylenediamine in N, N-dimethylacetamide under the conditions of low temperature of 5 ℃ and nitrogen protection atmosphere, adding lithium chloride, and then adding isophthaloyl dichloride 3 times, wherein the molar ratio of the m-phenylenediamine to the isophthaloyl dichloride is controlled to be 100: 105. the temperature is gradually increased to 70 ℃ as the reaction proceeds, and the holding time is 5 h. And (3) adding calcium oxide for neutralization after heat preservation treatment to prepare a neutral aramid polymer solution.

(2) Preparing aramid fiber stock solution: adding a proper amount of polyethylene glycol-400 into the neutral aramid polymer obtained in the step (1), wherein the absolute dry mass ratio of the modifier to the aramid polymer is 25:75, and the mixing temperature is 70 ℃. And filtering and defoaming after fully mixing and dispersing to obtain the spinning solution.

spinning: the aperture range of the spinneret plate is 0.05mm, and the number of holes is 8000; the distance between the spinneret and the coagulation bath is 20 cm;

and (3) solidification process: the secondary coagulating bath comprises the following components in percentage by mass: n, N-dimethylacetamide: water 60:40, the temperature of the coagulating bath is 80 ℃;

and (3) drafting: the first-stage coagulating bath comprises the following components in percentage by mass: n, N-dimethylacetamide: glycerol: water, etc. 70:15: 15; the temperature of the coagulation bath is 60 ℃, and the drawing ratio is 1.8 times. The secondary coagulating bath comprises the following components in percentage by mass: n, N-dimethylacetamide: water is 60:40, the temperature of the coagulation bath is 80 ℃, and the drafting ratio of the secondary coagulation bath is 1.8 times; the three-stage drafting is hot drafting, the hot drafting temperature is 275 ℃, and the drafting multiplying power is 2.2 times;

and (3) water washing process: the water temperature of the first-stage water washing is 50 ℃, and the drafting multiplying power is 1.1 times; the temperature of the second-stage washing water is 80 ℃;

and (3) drying: the drying temperature is 105 ℃;

and (3) heat setting process: the heat-setting temperature was 320 ℃.

Example 4

(1) preparing an aramid polymer: dissolving m-phenylenediamine in N, N-dimethylacetamide under the conditions of low temperature of 5 ℃ and nitrogen protection atmosphere, adding lithium chloride, and then adding isophthaloyl dichloride 2 times, wherein the molar ratio of the m-phenylenediamine to the isophthaloyl dichloride is controlled to be 100: 103. the temperature is gradually increased to 80 ℃ as the reaction proceeds, and the holding time is 3 h. After heat preservation treatment, adding calcium oxide for neutralization to prepare a neutral aramid polymer solution;

(2) preparing aramid fiber stock solution: adding a proper amount of polyethylene glycol-800 into the neutral aramid polymer obtained in the step (1), wherein the absolute dry mass ratio of the modifier to the aramid polymer is 40:60, and the mixing temperature is 70 ℃. Fully mixing, dispersing, filtering and defoaming to obtain spinning stock solution;

(3) preparing superfine aramid fibers: and (3) conveying the spinning solution obtained in the step (2) to a spinneret plate, and carrying out spinning, solidification and drafting, washing, drying, hot drafting, heat setting and rolling in sequence to finally prepare the superfine aramid fiber. The specific parameters are as follows:

and (3) spinning: the aperture range of the spinneret plate is 0.1mm, and the number of holes is 500; the distance between the spinneret and the coagulation bath was 30 cm.

And (3) solidification and drawing process: the first-stage coagulating bath comprises the following components in percentage by mass: n, N-dimethylacetamide: glycerol: water, etc. 65:25: 10; the temperature of the coagulation bath is 80 ℃, and the drawing magnification is 1.6 times. The secondary coagulating bath comprises the following components in percentage by mass: n, N-dimethylacetamide: water is 50:50, the temperature of the coagulation bath is 70 ℃, and the drafting ratio of the secondary coagulation bath is 2.0 times;

and (3) water washing process: the first-stage washing water temperature is 45 ℃, and the drafting magnification is 2.0 times; the water temperature of the second-stage water washing is 90 ℃;

and (3) hot drawing process: the hot drawing temperature is 280 ℃, and the drawing multiplying power is 2.4 times;

and (3) heat setting process: the heat setting temperature was 300 ℃.

Example 5

(1) preparing an aramid polymer: dissolving m-phenylenediamine in N, N-dimethylacetamide under the conditions of low temperature of 5 ℃ and nitrogen protection atmosphere, adding calcium bromide, and then adding isophthaloyl chloride for 3 times, wherein the molar ratio of the m-phenylenediamine to the isophthaloyl chloride is controlled to be 100: 103. the temperature is gradually increased to 80 ℃ as the reaction proceeds, and the holding time is 3 h. And (3) adding calcium oxide for neutralization after heat preservation treatment to prepare a neutral aramid polymer solution.

(2) Preparing aramid fiber stock solution: adding a proper amount of polyethylene glycol-800 into the neutral aramid polymer obtained in the step (1), wherein the absolute dry mass ratio of the modifier to the aramid polymer is 30:70, and the mixing temperature is 70 ℃. And filtering and defoaming after fully mixing and dispersing to obtain the spinning solution.

spinning: the aperture range of the spinneret plate is 0.05mm, and the number of holes is 8000; the distance between the spinneret and the coagulation bath is 15 cm;

and (3) solidification and drawing process: the first-stage coagulating bath comprises the following components in percentage by mass: n, N-dimethylacetamide: glycerol: water, etc. 70:15: 15; the temperature of the coagulation bath is 70 ℃, and the drawing ratio is 1.6 times. The secondary coagulating bath comprises the following components in percentage by mass: n, N-dimethylacetamide: water is 60:40, the temperature of the coagulation bath is 70 ℃, and the drafting ratio of the secondary coagulation bath is 2.5 times;

and (3) water washing process: the first-stage washing water temperature is 40 ℃, and the drafting multiplying power is 1.5 times; the temperature of second-stage washing water is 85 ℃;

and (3) drying: the drying temperature is 110 ℃;

and (3) hot drawing process: the hot drawing temperature is 285 ℃, and the drawing multiplying power is 2.9 times;

and (3) heat setting process: the heat setting temperature was 295 ℃.

Various properties of the obtained aramid fiber are measured, and the test results are listed in table 1; SEM of the fiber cross section and surface are shown in FIGS. 2-3.

Example 6

This embodiment is different from embodiment 4 in that: in the step (1), the modifier polyethylene glycol-800 is replaced by polyvinylpyrrolidone k 30. The SEM of the fiber surface is shown in fig. 4.

Example 7

The present embodiment is different from embodiment 3 in that: in step (1), the calcium oxide is replaced by diethylamine. The SEM of the fiber surface is shown in fig. 5.

Example 8

The present embodiment is different from embodiment 3 in that: in the step (1), the components and the mass ratio of the primary coagulating bath are changed into N, N-dimethylacetamide: ethylene glycol: water 70:15: 15.

Comparative example 1

The comparative example differs from example 1 in that: no modifier is added in the step (2).

Detection method

The tensile strength and the elongation at break are detected by reference (GB/T14337-; the linear density was measured as GB/T6100-2007.

TABLE 1 summary table of test results of ultra-fine aramid fibers

Examples	Line Density (dtex)	Tension (cN/dtex)	Elongation (%)
				Example 1	0.98	3.86	28.5
Example 2	0.75	4.15	30.4
				Example 3	0.62	4.83	34.1
Example 4	0.41	5.26	37.5
				Example 5	0.13	5.69	40.6
Example 6	0.55	4.96	35.2
				Example 7	0.65	4.58	33.5
Example 8	0.59	5..03	35.0
				Comparative example 1	2.75	2.82	20.4

As can be seen from table 1, compared with comparative example 1 in which no modifier is added, the ultrafine aramid fiber added with the modifier of the present invention can significantly reduce the diameter of the aramid fiber and improve the strength of the aramid fiber. As is clear from the graphs 2-5, the aramid fiber prepared by the method has the advantages of rough surface, compact structure and no collapse or cavity generation.

The modifier of the present invention is not limited to the polyethylene glycol and polyoxyethylene lauryl ether in the above-mentioned examples, and other modifiers such as polyvinylpyrrolidone and N-vinylpyrrolidone can also implement the present invention.

The invention can be adjusted according to actual production and is suitable for wet spinning or dry-wet spinning; the aramid polymer raw material can be meta-aramid polymer, para-aramid polymer, heterocyclic aramid polymer and the like.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. The preparation method of the superfine aramid fiber is characterized by comprising the following steps of:

the modifier is a low-melting-point water-soluble polymer;

2. The method for preparing the ultra-fine aramid fiber according to claim 1, wherein the low melting point water-soluble polymer is at least one of polyethylene glycol, polyvinylpyrrolidone, N-vinylpyrrolidone, and polyoxyethylene lauryl ether.

3. The method for preparing the ultra-fine aramid fiber according to claim 1, wherein the absolute dry mass ratio of the modifier to the aramid polymer is (5-40) - (60-95), and the mixing temperature is 60-150 ℃.

4. The method for preparing the ultra-fine aramid fiber according to claim 1, wherein the diameter of the spinneret plate is 0.03 to 0.10 mm.

5. The method for preparing the ultra-fine aramid fiber according to claim 1, wherein the coagulation drawing includes a primary coagulation bath drawing and a secondary coagulation bath drawing, and specifically comprises:

6. The method for preparing the ultra-fine aramid fiber according to claim 1, wherein the hot drawing is specifically: the drafting multiplying power is 1.1-2.0 times, and the temperature is 70-150 ℃.

7. The method for producing an ultrafine aramid fiber according to claim 1,

the water washing specifically comprises the following steps:

the drying specifically comprises the following steps:

the drying temperature is 80-120 ℃;

the heat setting specifically comprises the following steps:

the heat setting temperature is 280-320 ℃.

8. The method for preparing the ultra-fine aramid fiber according to claim 1, wherein the method for preparing the neutral aramid polymer solution comprises the following steps:

9. The ultra-fine aramid fiber obtained by the method of any one of claims 1 to 8, characterized in that the linear density is less than 1.0 dtex.

10. Use of the ultra-fine aramid fiber of claim 9 in papermaking, filtration, textile, rubber, flexible circuit board.