CN112878036B

CN112878036B - Kevlar-based deprotonation method for preparing aramid nanofibers and nanofibers prepared by using method

Info

Publication number: CN112878036B
Application number: CN202110292740.7A
Authority: CN
Inventors: 马冠香; 刘圆圆; 刘韬; 李文静; 赵英民; 杨洁颖
Original assignee: Aerospace Research Institute of Materials and Processing Technology
Current assignee: Aerospace Research Institute of Materials and Processing Technology
Priority date: 2021-03-18
Filing date: 2021-03-18
Publication date: 2022-07-08
Anticipated expiration: 2041-03-18
Also published as: CN112878036A

Abstract

The invention provides a Kevlar-based deprotonation method for preparing aramid nanofibers, which comprises the following steps: stirring and pretreating a mixed system of aramid fiber, an organic solvent and alkali to obtain an aramid fiber dispersion liquid; and adding a proton donor and/or an ionic reaction auxiliary agent into the aramid fiber dispersion liquid to regulate and control the deprotonation degree, thereby obtaining the aramid nanofiber colloid dispersion liquid. The invention also provides the aramid nano-fiber colloidal dispersion liquid prepared by the method. The method improves the nano-crystallization rate of the aramid fiber (within 1-4 h) and the concentration of a reaction system (more than 4 weight percent), and the prepared aramid fiber nano-fiber has uniform size, high stability (the length is 5-20 microns and 5-30 nanometers), large specific surface area and length-diameter ratio and excellent high-temperature resistance; the method has the advantages of simple equipment and process, strong applicability, solving the problems of long preparation period, low reaction concentration, low production efficiency and the like, and having extremely high practical production and application values.

Description

Kevlar-based deprotonation method for preparing aramid nanofibers and nanofibers prepared by using method

Technical Field

The invention relates to the technical field of polymer nano materials, in particular to a method for rapidly preparing aramid nano fibers in large batch based on deprotonation reaction of Kevlar, the aramid nano fibers prepared by the method and the nano fibers prepared by the method.

Background

Kevlar (Kevlar) is a high-performance para-Aramid fiber which was originally developed and produced by Dupont in the United states in the sixty-seven years of the last century under the trade name of Aramid and under the chemical name of poly-p-phenylene terephthalamide (PPTA) and is called Aramid-1414 in China. Kevlar is a high polymer formed by net-like crosslinking of PPTA long molecular chains which are similar to rigid extended chains. As benzene rings and adjacent amide bonds are linked in a pi-pi conjugated mode, internal rotation energy is high, molecular chains are closely arranged, chain segments are regular and highly oriented, and strong intermolecular hydrogen bonds exist, the factors endow the PPTA fiber with the advantages of high strength, high modulus, high temperature resistance, insulation, flame retardance, chemical corrosion resistance, light weight and the like, and the PPTA fiber is widely applied to the fields of aerospace, special clothing, sports goods and the like.

With respect to the so-called macroscopic aramid fibers having a diameter of micrometer or more, the aramid fibers having a diameter in the nanometer range are generally called aramid nanofibers (hereinafter abbreviated as ANF). Aramid nanofibers are a new nanofiber building block that has emerged in recent years and are often used as reinforcing materials to make composite materials. The aramid nano-fiber is prepared by adopting a deprotonation method based on Kevlar in a Kotov group in 2011 at first, a KOH/DMSO strong base system is utilized to destroy hydrogen bonds among PPTA molecular chains, hydrogen atoms on the PPTA amido bonds are adsorbed and pulled out to carry out deprotonation reaction, nitrogen anions are formed, and therefore electrostatic repulsion force is generated, and macroscopic fiber is degraded into the nano-fiber. It forms balance under the combined action of electrostatic repulsion, pi-pi conjugated acting force, intermolecular hydrogen bond, van der waals force, etc., so that the diameter of ANF is maintained at nanometer level (10-20nm) and it cannot be further dissolved into molecule. The ANF has the advantages of high strength, high modulus, high temperature resistance and the like of macroscopic aramid fibers, has a high specific surface area and a high length-diameter ratio, has abundant polar functional groups such as amide groups on the surface, has a remarkable reinforcing effect on the surface of the nanofiber, can be used for improving the interface bonding strength between the nanofiber and a polymer material, is easier to disperse and convenient to compound with other materials, solves the problem of surface inertia of the macroscopic fibers, has new characteristics which the macroscopic aramid fibers do not have, and has a wider application prospect.

At present, several methods such as electrostatic spinning method, mechanical decomposition method, polymerization assistant assembly fiber forming method, molding powder/in-situ polymerization alkali dissolution method and the like are used for preparing the ANF. For example, in chinese patent CN 106750265 a, a continuous mass preparation method of para-aramid nanofiber dispersion is described, in which an assistant for destroying molecular aggregation is added into a PPTA polymerization system, and the aggregation degree of PPTA is controlled by using the assistant and intermolecular hydrogen bonding, so as to obtain the aramid nanofiber dispersion, which is a preparation method from "small to large" molecular scale to nano scale. In chinese patent CN 110592705 a, it is described that a process of forming a macroscopic fiber skin layer structure is bypassed, and an intermediate PPTA aramid slurry formed directly based on molecular polymerization and not processed by a spinning process is used as a raw material, and a deprotonation process is performed in an alkali solution system to prepare ANF, which is a method for preparing nanofibers from the intermediate PPTA. However, both methods do not pass through a spinning process with high technical content, and have the problems of low orientation degree and crystallinity, more by-products, low intermolecular force and poor reaction controllability, and the obtained ANF has low weight average molecular weight, specific surface area and aspect ratio, large fiber diameter ratio, insufficient uniformity and poor mechanical properties.

Currently, ANF prepared based on the traditional deprotonation method of Kevlar macrofibers is of great interest because of its higher weight average molecular weight, higher specific surface area and aspect ratio, small and uniform diameter of nanofibers, and outstanding mechanical properties. However, the method still has the problems of long preparation period (2-7 days), low concentration (0.2 wt%) of the obtained dispersion, and the like, for example, in chinese patents CN 108424563B, CN 104548968 a, and CN 108265566B all include the traditional deprotonation preparation method of kevlar nanofibers from large to small, the preparation period of the dispersion with the concentration range of 0.2-2 wt% is 2-10 days, and the concentration is not higher than 2.5 wt%; the preparation period is long, and the reaction concentration is low, so that the functionalization, diversification, large-scale preparation and industrial production of the ANF are greatly limited.

Disclosure of Invention

One purpose of the invention is to provide a method for rapidly preparing aramid nano-fibers in large batch based on deprotonation reaction of Kevlar, so as to overcome the defects in the prior art. By controlling the deprotonation reaction process of amide groups of macroscopic Kevlar fibers in a strong alkali system, particularly by adding a proton donor in the middle process of the reaction, the surface structure of the branched nanofibers with negative potential is recovered, and the improvement of the nano-crystallization rate and the reaction system concentration of macroscopic fibers is facilitated; in addition or further, the electric potential of the surface of the fiber and the viscosity of a reaction system thereof are regulated and controlled by adding the ionic reaction auxiliary agent, so that the nano-crystallization rate of the macroscopic fiber and the concentration of the reaction system can be improved or further improved. The method, the equipment and the process provided by the invention are simple, the reaction period is short (the shortest time can be within 1 h), the concentration of the obtained dispersion liquid is high (1-8 wt%), the cost is effectively reduced, the benefit is improved, and the method has extremely high industrial production and application values.

The invention also aims to provide the high-solid-content aramid nanofiber dispersion liquid (1-8 wt%) prepared by the method.

To achieve the above object, the present invention provides in a first aspect a method for preparing aramid nanofibers based on deprotonation of Kevlar, the method comprising the steps of:

(1) stirring a mixed system of aramid fiber, an organic solvent and alkali to uniformly disperse the aramid fiber to obtain an aramid fiber dispersion liquid;

(2) and adding a proton donor and/or an ionic reaction auxiliary agent into the aramid fiber dispersion liquid to regulate and control the deprotonation degree, thereby obtaining the aramid nanofiber colloid dispersion liquid.

The invention provides in a second aspect an aramid nanofiber colloidal dispersion prepared by the method of the first aspect of the invention.

Compared with the prior art, the invention has the advantages that:

1) the invention is based on the deprotonation process of high-performance Kvelar macroscopic fiber, prepare the method of the high-performance aramid fiber nanofiber, on the one hand utilize high shear pre-dispersion of the high-speed disperser of the alkali-soluble system, has improved the contact area of reaction, accelerate the destruction of the surface cortical structure of fiber, make alkali liquor permeate between PPTA fiber and molecular chain fast, has accelerated the deprotonation process; on the other hand, the deprotonation degree of the amido bond is controlled by continuously dropwise adding and/or adding the proton donor, the alkali liquor assistant and/or the ionic reaction assistant in batches in the reaction process, so that the surface structure part of the edge branched negative ion is recovered, the viscosity of the solution is regulated and controlled, the nanocrystallization rate is accelerated, the concentration of a reaction system is improved, the preparation efficiency is obviously improved, the production cost is reduced, and the rapid mass production of the high-concentration aramid nanofiber can be rapidly realized.

2) The aramid nanofiber prepared by the method has higher weight average molecular weight, higher specific surface area and length-diameter ratio, small diameter and good uniformity of the nanofiber, is convenient to compound with other materials and easy to disperse, can be used for improving the interface bonding strength between the aramid nanofiber and a polymer material, can be used as an excellent composite material reinforcement, and has wide application prospects in the fields of high-temperature-resistant filtration, heat insulation, electrical appliance insulating elements, batteries, nanobiology and the like.

Drawings

Fig. 1 is a schematic diagram of rapid preparation of an aramid nanofiber dispersion by controlling the deprotonation process of Kevlar macro-scale fibers as proposed in the present invention.

Fig. 2 is an SEM image of the aramid nanofibers prepared in example 1 of the present invention.

Fig. 3 is a TG diagram of the aramid nanofibers prepared in example 1 of the present invention, in which 1 represents a weight change curve and 2 represents a heat flow change curve.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

As mentioned above, the present invention provides in a first aspect a process for the preparation of aramid nanofibers based on deprotonation of Kevlar, the process comprising the steps of:

(1) stirring a mixed system of macroscopic aramid fibers, an organic solvent and alkali to uniformly disperse the macroscopic aramid fibers to obtain an aramid fiber dispersion liquid;

In the step (2), the deprotonation degree is adjusted, and at the same time, the weak interaction force and viscosity of the reaction system are influenced, so that the subsequent nanocrystallization reaction is facilitated.

In the present invention, the aramid fiber means a macroscopic aramid fiber of an aramid fiber having a diameter of a micrometer or more, unless otherwise specified. For example, the aramid fiber used as a raw material in step (1) of the method of the present invention is such an aramid fiber.

The present invention is not particularly limited to the diameter of the macroscopic aramid fiber as the raw material. However, in some preferred embodiments, the aramid fiber has a filament diameter of 1 to 1000 microns and a length of 0.5 to 20 millimeters. In case the aramid fiber is a macroscopic aramid product, the diameter of the macroscopic aramid product is 1-10 mm.

In contrast to macroscopic aramid fibers, aramid nanofibers mean aramid fibers having diameters in the nanometer scale range, i.e. what is to be produced by the process of the invention is aramid nanofibers, but usually in the form of a colloidal dispersion of aramid nanofibers. Thus, in some preferred embodiments, the aramid nanofibers produced by the process of the present invention are in the form of an aramid nanofiber colloidal dispersion. However, if desired, the aramid nanofibers may be separated from the aramid nanofiber colloidal dispersion.

The form of the aramid fiber as a raw material is not particularly limited in the present invention. For example, in some preferred embodiments, in the step (1), the aramid fiber may be at least one selected from the group consisting of para-aramid fiber, Kevlar strands, Kevlar chopped fiber, and Kevlar fiber product.

In further preferred embodiments, the organic solvent is a polar organic solvent, preferably at least one selected from the group consisting of Dimethylsulfoxide (DMSO), N-Dimethylformamide (DMF), N-Dimethylformamide (DMAC), N-methylpyrrolidone (NMP).

In step (1), the base may be an organic base and/or an inorganic base. However, in other preferred embodiments, the base is selected from at least one of the group consisting of potassium hydroxide, sodium tert-butoxide, potassium hexamethyldisilazide, sodium hexamethyldisilazide, potassium ethoxide, triethylamine, tetramethylethylenediamine, sodium hydride, potassium hydride.

In other preferred embodiments, in step (1), the aramid fiber, the alkali and the organic solvent are used in the following ratio: 1-30: 1-15: 500, wherein the aramid fiber and the alkali are in grams and the organic solvent is in milliliters. For example, the amount ratio may be (1, 2, 5, 10, 15, 20, 25, or 30): (1, 2, 5, 10, or 15): 500.

in other preferred embodiments, in step (1), the stirring pretreatment is magnetic stirring and/or mechanical stirring.

In some more preferred embodiments, the stirring in step (1) is carried out under reaction conditions of 20 to 60 ℃ (e.g., 25, 30, 40, or 50 ℃).

In other preferred embodiments, the stirring speed of the stirring is in the range of 100rpm to 20000rpm (e.g. 100, 200, 500, 1000, 2000, 5000, 10000 or 20000rpm) and the stirring time of the stirring is in the range of 0.5h to 48h (e.g. 0.5, 1.0, 3.0, 6.0, 12.0, 18.0, 24.0 or 48.0 h).

In other preferred embodiments, in step (1), the aramid fiber dispersion is an uncancelled aramid fiber dispersion and/or an at least partially branched aramid nanofiber dispersion.

In other preferred embodiments, in step (2), the proton donor is at least one selected from the group consisting of water, ethanol, methanol, propanol; the ionic reaction auxiliary agent is at least one selected from the group consisting of calcium chloride, sodium chloride, potassium chloride, sodium hydroxide, potassium ethoxide, sodium hydride and potassium hydride. In the invention, the proton donor and/or the ionic reaction auxiliary agent can play a role in providing protons, regulating and controlling the pH value and/or the ion concentration and/or the colloid viscosity of a system, thereby being beneficial to the nanocrystallization of the aramid fiber from large to small.

In other preferred embodiments, in step (2), the proton donor and/or the ionic reaction assistant is added in a manner selected from the group consisting of a one-time addition manner, a batch-wise addition manner, and a continuous dropwise addition manner.

In other preferred embodiments, in step (2), the aramid nanofiber colloidal dispersion is a colloidal dispersion having a tyndall effect; preferably, the solid content concentration of the nanofibers in the aramid nanofiber colloidal dispersion is 0.1 to 8 wt% (e.g., 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, or 8.0 mass%), preferably 0.25 to 8 wt%.

In a second aspect, the invention provides an aramid nanofiber colloidal dispersion prepared by the method of the first aspect of the invention.

Examples

The present invention is further illustrated by the following examples, which are intended to be illustrative rather than restrictive, and the scope of the invention is not limited to these examples.

Example 1

(1) Adding 6g of Kevlar chopped fibers (with the diameter of about 12-20 micrometers and the length of 6 millimeters, purchased from DuPont), 500ml of dimethyl sulfoxide (DMSO) and 1g of KOH into a reaction container, and stirring and pretreating for 5min at the rotation speed of 4000rpm of a high-shear dispersing machine in a normal temperature environment to obtain a faint yellow uniform dispersion liquid of the macroscopic aramid fibers.

(2) And (2) adding 18g of deionized water and 2g of KOH solution into the pre-dispersion liquid obtained in the step (1) at one time to obtain a mixed liquid, adjusting the rotating speed, and continuously stirring for reacting for 1h to obtain the black-red uniform transparent aramid nano-fiber colloid dispersion liquid. Fig. 2 shows an SEM image of the aramid nanofibers prepared in this example; FIG. 3 shows a simultaneous thermal analysis (TG/DSC) chart of the aramid nanofibers prepared in this example; table 1 shows the properties of the prepared aramid nanofibers.

Example 2

(1) 10g of Kevlar chopped fibers used in example 1, 600ml of dimethyl sulfoxide (DMSO), 1g of KOH and 1g of potassium ethoxide are added into a reaction container, and stirring pretreatment is carried out for 5min under the conditions of normal temperature and the rotation speed of a high-shear disperser of 4000rpm, so as to obtain a faint yellow uniform dispersion liquid of macroscopic aramid fibers.

(2) Respectively adding 15g of deionized water and 3g of KOH solution into the pre-dispersion liquid obtained in the step (1), and continuously stirring for reaction for 0.5 h; then adding 10ml of ethanol and 1g of potassium ethoxide, adjusting the rotating speed to 3000rpm and continuously stirring for 1h to obtain the black-red uniform transparent aramid nano-fiber colloid dispersion liquid.

Example 3

(1) 6g of Kevlar chopped fibers used in example 1, 500ml of N, N-Dimethylformamide (DMF) and 1g of potassium tert-butoxide are added into a reaction vessel and stirred and pretreated for 5min at the rotation speed of 4000rpm of a high-shear disperser in a normal temperature environment to obtain a light yellow uniform dispersion liquid of macroscopic aramid fibers.

(2) And (2) adding 18g of deionized water, 3g of KOH and 6g of propanol into the pre-dispersion liquid obtained in the step (1) at one time, adjusting the rotating speed to 3000rpm, and continuously stirring for reacting for 2 hours to obtain a black-red uniform transparent aramid nanofiber dispersion liquid.

Example 4

(1) 30g of Kevlar chopped fibers used in example 1, 1000ml of dimethyl sulfoxide (DMSO) and 5g of KOH are added into a reaction vessel, and stirring pretreatment is carried out for 5min under the normal temperature environment at the rotation speed of 4000rpm of a high-shear dispersion machine, so as to obtain a light yellow uniform dispersion liquid of macroscopic aramid fibers.

(2) And (2) adding a solution of 30g of deionized water and 5g of KOH into the pre-dispersion liquid obtained in the step (1) at one time, adjusting the rotation speed to 5000rpm, and continuously stirring for reacting for 3 hours to obtain a black-red uniform transparent aramid nanofiber dispersion liquid.

Example 5

(1) 50g of Kevlar chopped fibers used in example 1, 1000ml of dimethyl sulfoxide (DMSO) and 5g of KOH are added into a reaction vessel, and stirred and pretreated for 5min at the rotation speed of 4000rpm of a high-shear disperser in a normal-temperature environment to obtain a light yellow uniform dispersion liquid of macroscopic aramid fibers.

(2) And (2) adding 30g of deionized water and 5g of KOH solution into the pre-dispersion liquid obtained in the step (1) at one time, simultaneously dropwise adding 20ml of 1mol/L sodium hydroxide solution, adjusting the rotation speed to 5000rpm, keeping the temperature at 40 ℃, and continuously stirring at a high speed for reacting for 4 hours to obtain the black-red uniform transparent aramid nanofiber dispersion liquid.

Example 6

(1) 6g of Kevlar chopped fibers used in example 1, 500ml of dimethyl sulfoxide (DMSO) and 1g of KOH are added into a reaction vessel, and stirring pretreatment is carried out for 5min at the rotation speed of 4000rpm of a high-shear disperser in a normal-temperature environment, so as to obtain a light yellow uniform dispersion liquid of macroscopic aramid fibers.

(2) And (2) adding 18g of deionized water and 3g of KOH solution into the pre-dispersion liquid obtained in the step (1) at one time, heating to 60 ℃, keeping the temperature, stirring and reacting at the rotating speed of 1000rpm for 6 hours to obtain a black-red uniform transparent aramid nanofiber colloid dispersion liquid.

Example 7

(1) 60g of Kevlar chopped fibers used in example 1, 1000ml of dimethyl sulfoxide (DMSO) and 5g of KOH are added into a reaction vessel, and stirring pretreatment is carried out for 20min at the rotating speed of 5000rpm of a high-shear disperser in a normal temperature environment, so as to obtain a light yellow uniform dispersion liquid of macroscopic aramid fibers.

(2) And (2) adding 40g of deionized water and 10g of KOH solution into the pre-dispersion liquid obtained in the step (1) twice (every time, 20g of deionized water and 5g of KOH are added at intervals of 1 hour), continuously reacting for 2 hours, adding 2g of sodium chloride, adjusting the rotating speed, and continuously stirring and reacting for 2 hours to obtain the black-red uniform and transparent aramid nano-fiber colloid dispersion liquid.

Example 8

(1) 80g of Kevlar chopped fibers used in example 1, 1000ml of dimethyl sulfoxide (DMSO), 5g of KOH and 20g of water are added into a reaction container, and stirring pretreatment is carried out for 5min under the normal temperature environment and the rotation speed of a high-shear disperser 10000rpm, so as to obtain a faint yellow uniform dispersion liquid of macroscopic aramid fibers.

(2) And (2) adding a mixed solution of 10g of water, 10g of ethanol, 2g of KOH and 2g of potassium tert-butoxide into the pre-dispersion liquid obtained in the step (1), then gradually dripping 30 ml of 2mol/L KOH aqueous solution within 5min, heating to 60 ℃, keeping the temperature, stirring at 3000rpm at a high speed, adding an auxiliary agent sodium chloride after 2h, and continuing to react for 8h to obtain the black-red uniform and transparent aramid nanofiber colloid dispersion liquid.

Comparative example 1

(1) A round-bottomed flask was charged with 1g of Kevlar fiber, 1g of potassium hydroxide, and 100ml of dimethyl sulfoxide, and magnetically stirred (1000rpm) at 25 ℃ for 7 days at normal temperature to form a nanofiber dispersion having a concentration of 1% (w/v).

Comparative example 2: a round-bottomed flask was charged with 8g of Kevlar fiber, 8g of potassium hydroxide, and 100ml of dimethyl sulfoxide, and magnetically stirred at 25 ℃ at normal temperature (1000rpm) for 10 days to form a nanofiber dispersion having a concentration of 8% (w/v).

Note:

(a) the time represents the stirring pretreatment time of step (1) of the example plus the stirring reaction time of step (2), or the stirring reaction time of step (1) of the comparative example plus the stirring reaction time of step (2).

(b) High temperature resistance is expressed; temperature at 10% weight loss.

(c) The concentration ratio indicates: weight percentage of aramid nanofibers to total volume of organic solvent such as DMSO (m/V).

As can be seen from the results in table 1, the Kevlar nanofibers prepared in this example have high temperature resistance, temperature higher than 520 ℃, aspect ratio greater than 500, and small diameter of nanofibers (about 15 nm) at 10% weight loss. In examples 1 to 8, the preparation time was greatly shortened, and when the dispersion concentration ratio was 1%, the time was less than 2 hours, whereas in comparative example 1, a time of 7 days was required; when the concentration ratio of the dispersion liquid is 5%, the time is less than 5 hours; when the concentration ratio of the dispersion was 8%, the time required was less than 12 hours, whereas in comparative example 2, a time as long as 10 days was required. In the invention, a method of regulating and controlling the reaction by adopting the proton donor and/or the ionic reaction auxiliary agent is adopted, and the changes of stirring speed, reaction temperature, material adding mode and the like are combined, so that the reaction period is greatly shortened, and the concentration of a reaction system is improved.

Finally, it should be noted that: the unexplained part of the present invention is a technique known to those skilled in the art, and the above embodiments are only used to illustrate the technical solution of the present invention, not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A method for producing aramid nanofibers based on deprotonation of Kevlar, characterized in that the method comprises the following steps:

(2) adding a proton donor and an ionic reaction auxiliary agent into the aramid fiber dispersion liquid to regulate and control the deprotonation degree, thereby obtaining an aramid nanofiber colloid dispersion liquid; the solid content concentration of the nano-fibers in the aramid nano-fiber colloid dispersion liquid is 1-8 wt%;

the time for preparing the aramid nano-fiber colloid dispersion liquid is less than 12 hours.

2. The method of claim 1, wherein:

in the step (1), the aramid fiber is at least one selected from the group consisting of para-aramid fiber, Kevlar strands, Kevlar chopped fiber, and Kevlar fiber products;

the organic solvent is a polar organic solvent.

3. The method of claim 2, wherein:

the monofilament diameter of the aramid fiber is 1-1000 microns, and the length of the aramid fiber is 0.5-20 millimeters.

4. The method of claim 3, wherein:

the Kevlar fiber product has a diameter of 1 to 10 mm.

5. The method of claim 2, wherein:

the organic solvent is at least one selected from the group consisting of dimethyl sulfoxide (DMSO), N-Dimethylformamide (DMF), N-Dimethylformamide (DMAC), and N-methylpyrrolidone (NMP).

6. The method of claim 1, wherein:

in the step (1), the base is an organic base and/or an inorganic base.

7. The method of claim 6, wherein:

the base is at least one selected from the group consisting of potassium hydroxide, sodium tert-butoxide, potassium hexamethyldisilazide, sodium hexamethyldisilazide, potassium ethoxide, triethylamine, tetramethylethylenediamine, sodium hydride, and potassium hydride.

8. The method of claim 1, wherein: in the step (1), the dosage ratio of the aramid fiber, the alkali and the organic solvent is as follows: 1-30: 1-15: 500, wherein the aramid fiber and the alkali are in grams and the organic solvent is in milliliters.

9. The method of claim 1, wherein:

in the step (1), the stirring pretreatment is magnetic stirring and/or mechanical stirring.

10. The method of claim 9, wherein:

the stirring is carried out under the reaction condition of 20-60 ℃.

11. The method of claim 10, wherein:

the stirring speed of the stirring is in the range of 100rpm-20000rpm, and the stirring time of the stirring is 5min or 20 min.

12. The method of claim 1, wherein:

in the step (1), the aramid fiber dispersion liquid is an uncancelled aramid fiber dispersion liquid and/or an at least partially branched aramid nanofiber dispersion liquid.

13. The method of claim 1, wherein:

in the step (2), the proton donor is selected from deionized water, ethanol, methanol, propanol, and the ionic reaction auxiliary agent is selected from at least one of the group consisting of calcium chloride, sodium chloride, potassium chloride, sodium hydroxide, potassium ethoxide, sodium hydride, and potassium hydride.

14. The method of claim 1, wherein:

in the step (2), the proton donor and/or the ionic reaction auxiliary is added in a manner selected from the group consisting of a one-time addition manner, a batch-wise addition manner, and a continuous dropwise addition manner.

15. The method of claim 1, wherein:

in the step (2), the aramid nanofiber colloidal dispersion liquid is a colloidal dispersion with a tyndall effect.

16. An aramid nanofiber colloidal dispersion prepared by the method of any one of claims 1 to 15.