Low-water-content aramid nanofiber and preparation method thereof

Abstract

The invention provides a preparation method of low-water-content aramid nanofibers, which comprises the following steps: A) in an inert gas protection atmosphere, mixing a calcium chloride solution, p-phenylenediamine and terephthaloyl chloride to react until the viscosity of a system is increased to form a jelly body, and terminating the reaction; b) adding the gel into N-methyl pyrrolidone for dilution, and homogenizing and dispersing to obtain a diluent; c) adding the diluent into a fiber forming solvent, and homogenizing and dispersing to obtain dispersion liquid after fiber forming; the fiber forming solvent is dichloromethane or chloroform; and D) carrying out filter pressing on the fiber-formed dispersion liquid, putting a filter cake into a replacement kettle, adding N-methyl pyrrolidone, cleaning, and carrying out filter pressing again to obtain the aramid nanofiber. No water participates in the preparation process, the water content of the prepared aramid nanofiber is conveniently controlled to be 200 ppm or below, and the nanofiber is dispersed in N-methyl pyrrolidone, is good in stability and can be stored for a long time.

Description

Technical Field

[0001] The present invention relates to the technical field of aramid fibers, and particularly to a low water content aramid nanofiber and a preparation method thereof. Background Art

[0002] Para-aramid nanofibers (ANFs) are aramid fibers with diameters ranging from a dozen to several hundred nanometers and lengths reaching several to dozens of micrometers. Their chemical composition, chemical structure, and crystal structure are identical to those of aramid fibers, inheriting the excellent properties unique to aramid fibers, such as high temperature resistance, high strength, and good insulation performance. At the same time, their unique large aspect ratio structure, huge specific surface area, have received extensive attention in the fields of composite materials, lithium batteries, electronics, etc.

[0003] Currently, there are mainly two routes for the preparation of aramid nanofibers: the top-down method and the bottom-up method. The most common top-down method is to continuously stir aramid fibers or powders in an alkaline solution (KOH / DMSO) to protonate the aramid fibers and split them into nanofibers. This method takes a long time for stirring and has a low yield. In patent CN 110656393A, this method was improved, and the stirring time was minimized to 4h, but it still does not have the ability of continuous production. The bottom-up method, as described in patent CN105153413A: aramid polymers after polycondensation reaction are dispersed by high-speed shear to obtain aramid nanofibers. This method can be continuously produced and has been industrially produced. However, there are still some problems that limit the application of aramid nanofibers: ① In the fields of lithium batteries, electricity, insulation, etc., the water content has a great impact on the product performance, and generally requires the water content of raw materials to be <200 ppm, or even lower. However, water is often used as a fiber-forming or cleaning agent during the processing of aramid nanofibers, and it is difficult to achieve a low water content. ② In the field of composite material reinforcement, aramid nanofibers with water as the dispersion medium are difficult to be compounded with general resin systems, restricting the expansion of their application fields. ③ The recycling process is long, with high energy consumption and cost.

[0004] Therefore, it is very necessary to provide a low water content aramid nanofiber and a preparation method thereof. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a preparation method of a low water content aramid nanofiber. The aramid nanofiber dispersion prepared by the method provided by the present invention has a water content of less than 200 ppm, and the dispersion has good stability and can be stored for a long time without special conditions.

[0006] The present invention provides a preparation method of a low water content aramid nanofiber, comprising the following steps:

[0007] A) Under an inert gas protection atmosphere, calcium chloride solution, p-phenylenediamine and terephthaloyl chloride are mixed and reacted until the viscosity of the system increases and a gel appears, and the reaction is terminated;

[0008] B) The gel is added to N-methylpyrrolidone for dilution and homogenously dispersed to obtain a diluted solution;

[0009] C) The diluted solution is added to a fiber-forming solvent and homogenously dispersed to obtain a fiber-formed dispersion; the fiber-forming solvent is dichloromethane or chloroform;

[0010] D) The fiber-formed dispersion is pressure-filtered, and the filter cake is put into a displacement kettle, added with N-methylpyrrolidone for cleaning and then pressure-filtered again to obtain aramid nanofibers.

[0011] The preparation method of the aramid nanofibers with low water content provided by the present invention first conducts polymerization: under an inert gas protection atmosphere, calcium chloride solution, p-phenylenediamine and terephthaloyl chloride are mixed and reacted until the viscosity of the system increases and a gel appears, and the reaction is terminated.

[0012] The inert gas described in the present invention includes nitrogen. That is: in a nitrogen protection atmosphere, calcium chloride is dissolved in N-methylpyrrolidone, and then p-phenylenediamine is dissolved at a low temperature.

[0013] The calcium chloride solution is a calcium chloride N-methylpyrrolidone solution, and the mass fraction of calcium chloride in N-methylpyrrolidone is 3.2% - 7.8%; specifically, it can be: 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, 4.2%, 4.4%, 4.6%, 4.8%, 5.0%, 5.2%, 5.4%, 5.6%, 5.8%, 6.0%, 6.2%, 6.4%, 6.6%, 6.8%, 7.0%, 7.2%, 7.4%, 7.6%, 7.8%; or the point values between any two of the above.

[0014] The dissolution temperature of p-phenylenediamine is 0 - 5°C, and the molar concentration of p-phenylenediamine is 0.2M.

[0015] Then terephthaloyl chloride is added, and the mixture is strongly stirred and reacted until the viscosity of the system increases and a gel appears, and the reaction is terminated.

[0016] The molar ratio of terephthaloyl chloride to p-phenylenediamine in the present invention is 1.005 - 1.020; specifically, it can be 1.005, 1.006, 1.007, 1.008, 1.009, 1.010, 1.011, 1.012, 1.013, 1.014, 1.015, 1.016, 1.017, 1.018, 1.019, 1.020; or the point values between any two of the above.

[0017] The frozen colloid is added to N-methylpyrrolidone for dilution and homogenously dispersed to obtain a diluted solution. That is, the frozen colloid is added to N-methylpyrrolidone, and a homogenizer is used for shear dispersion to make it into a flowable solution state.

[0018] According to the present invention, the mass ratio of the frozen colloid to N-methylpyrrolidone is 1:6 to 16. Specifically, it can be 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16; or the point values between any two of the above; or the range values between any two of the above.

[0019] The diluted solution is added to a fiber-forming solvent and homogenously dispersed to obtain a dispersed solution after fiber formation; the fiber-forming solvent is dichloromethane or chloroform.

[0020] According to the present invention, the volume ratio of the diluted solution to the fiber-forming solvent is 1:0.3 to 5, and it can be 1:0.3, 1:0.5, 1:0.8, 1:1, 1:2, 1:3, 1:4, 1:5; or the point values between any two of the above; or the range values between any two of the above.

[0021] The shear linear velocity of the homogenizer is 30 to 34 m / s; specifically, it can be 30 m / s, 31 m / s, 32 m / s, 33 m / s, 34 m / s.

[0022] The dispersed solution after fiber formation is pressure-filtered, and the filter cake enters a displacement kettle, where it is washed with N-methylpyrrolidone and then pressure-filtered again to obtain aramid nanofibers.

[0023] According to the present invention, the pressure of the pressure filter is 0.1 MPa to 1.2 MPa; specifically, it can be 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, 1.1 MPa, 1.2 MPa.

[0024] The solid content of the aramid nanofiber finished product prepared by the present invention is 0.5% to 2%, the average diameter of the nanofibers is 5 nm to 50 nm, and the moisture content is less than 200 ppm.

[0025] After step D) of the present invention, it further includes neutralization and recovery: the filtrates from the two pressure filtrations enter a neutralization kettle, and under the condition of stirring, a neutralizing agent or a mixed slurry of N-methylpyrrolidone is used for neutralization. The neutralized filtrate separates the solvent through an evaporator and enters storage tanks for storage respectively.

[0026] The neutralizing agent according to the present invention is calcium oxide, and the mass fraction of the neutralizing agent is 10% to 15%; specifically, it can be 10%, 11%, 12%, 13%, 14%, 15%.

[0027] The evaporation parameters of the evaporator in the present invention are a vacuum degree of -0.92 to -0.097 MPa and an evaporation temperature of 55°C to 95°C; the solvent obtained by evaporation is dichloromethane or chloroform and enters the fiber-forming solvent storage tank; the solvent obtained by evaporation is N-methylpyrrolidone and enters the dilution solvent storage tank.

[0028] In the preparation process of the present invention, the selected dilution solvent and the fiber-forming solvent have a large difference in boiling point, are easy to separate, have a short recovery process, and low energy consumption. The solvents used are common solvents in the aramid industry, without introducing new reagents, which is conducive to the unified integration of the production of various aramid products. This dispersion can be well matched with the existing technologies in multiple industries (such as lithium battery separator coating, composite material reinforcement, etc.).

[0029] A low-water-content aramid nanofiber of the present invention is prepared by the preparation method described in any one of the above.

[0030] The preparation process of the present invention does not involve water, and the water content of the prepared aramid nanofibers can be conveniently controlled below 200 ppm. The nanofibers are dispersed in N-methylpyrrolidone and have good stability and can be stored for a long time.

[0031] The fiber-forming solvents (dichloromethane, chloroform) used in the present invention have low boiling points, are easy to separate from N-methylpyrrolidone, have a short recovery process, and low energy consumption; and they are all common solvents in the aramid industry, without introducing new reagents, which is conducive to the unified integration of the production of various aramid products. Description of the Drawings

[0032] Figure 1 is a process flow chart;

[0033] Figure 2 is a transmission electron microscope photograph of the aramid nanofibers in Example 1;

[0034] Figure 3 is a diameter distribution diagram of the aramid nanofibers in Example 1.

[0035] Figure 4 is a transmission electron microscope photograph of the product obtained by the process treatment in Comparative Example 2.

[0036] Figure 5 is a diameter distribution diagram of the aramid nanofibers in Comparative Example 3. Detailed Embodiments

[0037] The present invention provides a kind of aramid nanofibers with low water content and a preparation method thereof. Those skilled in the art can draw on the content of this article and appropriately improve the process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they all fall within the protection scope of the present invention. The method and application of the present invention have been described through preferred embodiments. It is obvious that relevant personnel can make changes or appropriate alterations and combinations to the methods and applications in this article without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0038] It should be understood that the expression "one or more of..." individually includes each object recited after the said expression and various different combinations of two or more of the recited objects, unless otherwise understood from the context and usage. The expression "and / or" combined with three or more recited objects should be understood to have the same meaning, unless otherwise understood from the context.

[0039] The terms "comprising", "having" or "containing", including the use of their grammatical synonyms, should generally be understood as open and non-restrictive, for example, not excluding other unrecited elements or steps, unless specifically stated otherwise or otherwise understood from the context.

[0040] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Wherein A and B can be singular or plural.

[0041] In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one of the following (items)" or its similar expressions refer to any combination of these items, including any combination of single item (s) or plural item (s).

[0042] It should be understood that as long as the present invention is still operable, the order of steps or the order of performing certain actions is not important. In addition, two or more steps or actions can be carried out simultaneously.

[0043] The use of any and all examples or exemplary languages such as "for example" or "including" in this article is only intended to better illustrate the present invention and does not limit the scope of the present invention unless a claim is made. No language in this specification should be construed as indicating that any unclaimed element is essential for the practice of the present invention.

[0044] In addition, the numerical ranges and parameters used to define the present invention are approximate values. Here, the relevant values in the specific embodiments have been presented as precisely as possible. However, any numerical value inherently inevitably contains standard deviations caused by individual testing methods. Therefore, unless otherwise clearly stated, it should be understood that all ranges, quantities, numerical values, and percentages used in this disclosure are modified by "about". Here, "about" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specific numerical value or range.

[0045] It should be understood that in various embodiments of the present application, the magnitude of the serial numbers of the above processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0046] Some cases are recorded in the embodiments and comparative examples of the present invention, and the embodiments show certain implementation manners of the present invention. However, this does not mean that the effects of the present invention can only be achieved in these cases.

[0047] To further illustrate the present invention, a low water content aramid nanofiber and its preparation method provided by the present invention will be described in detail below in conjunction with embodiments.

[0048] Example 1:

[0049] In a nitrogen atmosphere, calcium chloride was dissolved at high temperature in N-methylpyrrolidone, and the mass fraction of calcium chloride was 6.6%. It was cooled to 3 °C, and p-phenylenediamine was dissolved at low temperature, and its concentration was 0.2 mol / L. According to a molar ratio of 1.015:1, terephthaloyl chloride was added, and the reaction was carried out for 11 minutes until the climbing rod phenomenon occurred. The frozen colloid was added to N-methylpyrrolidone according to a mass ratio of 1:10, and stirred for 5 minutes. The dilution was added to dichloromethane with high-speed shear dispersion, and the volume ratio of the dilution to dichloromethane was 1:2, and the shear linear velocity was 32 m / s, and dispersed for 15 minutes to form aramid nanofibers. The dispersion entered the filter press 1 for pressure filtration, and the filter cake entered the cleaning kettle and was dispersed again in N-methylpyrrolidone to replace the solvent. After dispersing for 15 minutes, it entered the filter press 2 for pressure filtration, with a pressure of 0.2 MPa. The obtained finished product had a solid content of 0.8%, an average diameter of the nanofibers of 11.47 nm, and a water content of 187 ppm. The filtrate entered the neutralization kettle, and 10% calcium oxide / NMP slurry was added for neutralization. After the filtrate was filtered to remove excess calcium oxide after neutralization, it entered the evaporator to evaporate and separate dichloromethane and NMP, etc. The dichloromethane gas was cooled by deep cooling and entered the storage tank for reuse. NMP entered the NMP solvent storage tank and could be reused in the dilution section. The transmission electron microscope image of the nanofibers in this example is shown in the appendix Figure 2 and the diameter distribution is shown in the appendix Figure 3 .

[0050] Example 2:

[0051] In a nitrogen atmosphere, N-methylpyrrolidone was added to dissolve calcium chloride at high temperature, and the mass fraction of calcium chloride was 3.4%. It was cooled to 3 °C, and p-phenylenediamine was dissolved at low temperature with a concentration of 0.2 mol / L. According to the molar ratio of 1.015:1, terephthaloyl chloride was added and reacted for 9 minutes until the "climbing rod" phenomenon occurred. The frozen colloid was added to N-methylpyrrolidone according to the mass ratio of 1:8 and stirred for 5 minutes. The dilution was added to chloroform under high-speed shear dispersion, and the volume ratio of the dilution to dichloromethane was 1:3, with a shear linear velocity of 30 m / s, and dispersed for 15 minutes to form aramid nanofibers. The dispersion entered filter press 1 for pressure filtration, and the filter cake entered the cleaning kettle and was dispersed again in N-methylpyrrolidone to replace the solvent. After dispersing for 15 minutes, it entered filter press 2 for pressure filtration at a pressure of 0.2 MPa. The obtained finished product had a solid content of 1.1%, an average nanofiber diameter of 7.36 nm, and a moisture content of 167 ppm. The filtrate entered the neutralization kettle, and 10% calcium oxide / NMP slurry was added for neutralization. After neutralization, the filtrate was filtered to remove excess calcium oxide and then entered the evaporator to evaporate and separate chloroform and NMP, etc. The gas passed through cooling and entered the storage tank for reuse. N-methylpyrrolidone entered the N-methylpyrrolidone solvent storage tank and could be reused in the dilution section.

[0052] Example 3:

[0053] In a nitrogen atmosphere, N-methylpyrrolidone was added to dissolve calcium chloride at high temperature, and the mass fraction of calcium chloride was 5.5%. It was cooled to 3 °C, and p-phenylenediamine was dissolved at low temperature with a concentration of 0.2 mol / L. According to the molar ratio of 1.015:1, terephthaloyl chloride was added and reacted for 11 minutes until the "climbing rod" phenomenon occurred. The frozen colloid was added to N-methylpyrrolidone according to the mass ratio of 1:12 and stirred for 5 minutes. The dilution was added to dichloromethane under high-speed shear dispersion, and the volume ratio of the dilution to dichloromethane was 2:1, with a shear linear velocity of 32 m / s, and dispersed for 15 minutes to form aramid nanofibers. The dispersion entered filter press 1 for pressure filtration, and the filter cake entered the cleaning kettle and was dispersed again in N-methylpyrrolidone to replace the solvent. After dispersing for 15 minutes, it entered filter press 2 for pressure filtration at a pressure of 0.2 MPa. The obtained finished product had a solid content of 0.8%, an average nanofiber diameter of 19.37 nm, and a moisture content of 192 ppm. The filtrate entered the neutralization kettle, and 10% calcium oxide / NMP slurry was added for neutralization. After neutralization, the filtrate was filtered to remove excess calcium oxide and then entered the evaporator to evaporate and separate dichloromethane and NMP, etc. The dichloromethane gas passed through deep cooling and entered the storage tank for reuse. NMP entered the NMP solvent storage tank and could be reused in the dilution section.

[0054] Comparative Example 1:

[0055] In a nitrogen atmosphere, N-methylpyrrolidone was added to dissolve calcium chloride at high temperature, and the mass fraction of calcium chloride was 6.3%. The temperature was lowered to 1 °C, and p-phenylenediamine was dissolved at low temperature, with a concentration of 0.2 mol / L. According to the molar ratio of 1.015:1, terephthaloyl chloride was added and the reaction was carried out for 11 minutes until the "climbing rod" phenomenon occurred. The frozen colloid was added to N-methylpyrrolidone according to the mass ratio of 1:10 and stirred for 5 minutes. The diluent was added to acetone under high-speed shear dispersion, and the volume ratio of the diluent to acetone was 1:2, with a shear linear velocity of 32 m / s, and dispersed for 15 minutes to form aramid nanofibers. The dispersion entered filter press 1 for pressure filtration, and the filter cake entered the cleaning kettle and was dispersed again by adding N-methylpyrrolidone to replace the solvent. After dispersing for 15 minutes, it entered filter press 2 for pressure filtration at a pressure of 0.2 MPa. The obtained finished product had a solid content of 0.9%, an average nanofiber diameter of 14.21 nm, and a moisture content of 2900 ppm, which could not meet the requirement of a water content lower than 200 ppm.

[0056] The filtrate entered the neutralization kettle, and 10% calcium oxide / NMP slurry was added for neutralization. After neutralization, the filtrate was filtered to remove excess calcium oxide and then entered the evaporator to evaporate and separate acetone, NMP, etc.

[0057] Comparative Example 2:

[0058] In a nitrogen atmosphere, N-methylpyrrolidone was added to dissolve calcium chloride at high temperature, and the mass fraction of calcium chloride was 6.6%. The temperature was lowered to 3 °C, and p-phenylenediamine was dissolved at low temperature, with a concentration of 0.2 mol / L. According to the molar ratio of 1.015:1, terephthaloyl chloride was added and the reaction was carried out for 11 minutes until the "climbing rod" phenomenon occurred. The frozen colloid was added to N-methylpyrrolidone according to the mass ratio of 1:10 and stirred for 5 minutes. The diluent was added to dichloromethane under high-speed shear dispersion, and the volume ratio of the diluent to dichloromethane was 1:0.2, with a shear linear velocity of 32 m / s, and dispersed for 15 minutes. The dispersion entered filter press 1 for pressure filtration, and the filter cake entered the cleaning kettle and was dispersed again by adding N-methylpyrrolidone to replace the solvent. After dispersing for 15 minutes, it entered filter press 2 for pressure filtration at a pressure of 0.2 MPa. The obtained finished product had a solid content of 1.5%, and the obtained product morphology was film-like and could not become nanofibers, as Figure 4 shown: Transmission electron microscope photograph of the product obtained by the process of this comparative example; It can be seen from Figure 4 this that the fiber-forming ratio of the diluent to dichloromethane is lower than the range, and nanofibers cannot be obtained.

[0059] Comparative Example 3:

[0060] In a nitrogen atmosphere, N-methylpyrrolidone was added to dissolve calcium chloride at high temperature, and the mass fraction of calcium chloride was 6.6%. It was cooled to 3 °C, and p-phenylenediamine was dissolved at low temperature, with a concentration of 0.2 mol / L. According to a molar ratio of 1.015:1, terephthaloyl chloride was added and reacted for 11 minutes until the "climbing rod" phenomenon occurred. The frozen colloid was added to N-methylpyrrolidone according to a mass ratio of 1:10 and stirred for 5 minutes. The dilution was added to dichloromethane under high-speed shear dispersion, and the volume ratio of the dilution to dichloromethane was 1:2, with a shear linear velocity of 24 m / s, and dispersed for 15 minutes to form aramid nanofibers. The dispersion entered filter press 1 for pressure filtration, and the filter cake entered the cleaning kettle and was dispersed again by adding N-methylpyrrolidone to replace the solvent. After dispersing for 15 minutes, it entered filter press 2 for pressure filtration at a pressure of 0.2 MPa. The obtained finished product had a solid content of 1.1%, an average nanofiber diameter of 31.53 nm, a maximum diameter of 143.23 nm, and a moisture content of 193 ppm. Here, the fiber diameter was too large.

[0061] The filtrate entered the neutralization kettle, and 10% calcium oxide / NMP slurry was added for neutralization. After neutralization, the filtrate was filtered to remove excess calcium oxide and then entered the evaporator to evaporate and separate dichloromethane, NMP, etc. The dichloromethane gas passed through deep cooling and entered the storage tank for reuse. NMP entered the NMP solvent storage tank and could be reused in the dilution section. The diameter distribution of this comparative example is shown in Figure 5 ; It can be seen from Figure 5 that the shear rate is too low and the fiber diameter is too large.

[0062] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing aramid nanofibers with low water content, characterized in that, It includes the following steps: A) Under the protection of an inert gas atmosphere, calcium chloride solution, p-phenylenediamine and terephthaloyl chloride are mixed and reacted until the viscosity of the system increases and a gel appears, and the reaction is terminated; B) The gel is added to N-methylpyrrolidone for dilution and homogenously dispersed to obtain a diluted solution; C) The diluted solution is added to a fiber-forming solvent and homogenously dispersed to obtain a fiber-formed dispersion; the fiber-forming solvent is dichloromethane or chloroform; D) The fiber-formed dispersion is pressure-filtered, and the filter cake enters a displacement kettle, where it is washed with N-methylpyrrolidone and then pressure-filtered again to obtain aramid nanofibers.

2. The preparation method according to claim 1, characterized in that, The inert gas includes nitrogen; the calcium chloride solution is a calcium chloride N-methylpyrrolidone solution, and the mass fraction of calcium chloride in N-methylpyrrolidone is 3.2% - 7.8%; The dissolution temperature of p-phenylenediamine is 0 - 5°C, the molar concentration of p-phenylenediamine is 0.2M, and the molar ratio of terephthaloyl chloride to p-phenylenediamine is 1.005 - 1.

020.

3. The preparation method according to claim 1, wherein In step B), the mass ratio of the gel to N-methylpyrrolidone is 1:6 - 16.

4. The preparation method according to claim 1, characterized in that, In step C), the volume ratio of the diluted solution to the fiber-forming solvent is 1:0.3 - 5, and the shear linear velocity of the homogenizer is 30 - 34 m / s.

5. The preparation method according to claim 1, characterized in that, The pressure of the pressure filter is 0.1 MPa - 1.2 MPa.

6. The preparation method according to claim 1, wherein The solid content of the aramid nanofiber product is 0.5% - 2%, the average diameter of the nanofibers is 5 nm - 50 nm, and the moisture content is less than 200 ppm.

7. The preparation method according to claim 1, characterized in that, After step D), it also includes neutralization and recovery: the filtrates from the two pressure filtrations enter a neutralization kettle, where they are neutralized with a neutralizing agent or a mixed slurry of N-methylpyrrolidone under stirring conditions. The neutralized filtrate separates the solvent through an evaporator and enters storage tanks respectively for storage.

8. The preparation method according to claim 7, characterized in that, The neutralizing agent is calcium oxide, and the mass fraction of the neutralizing agent is 10% - 15%.

9. The preparation method according to claim 7, characterized in that, The evaporation parameters of the evaporator are a vacuum degree of -0.92 - -0.097 MPa and an evaporation temperature of 55°C - 95°C; the solvent obtained by evaporation is dichloromethane or chloroform and enters the fiber-forming solvent storage tank; the solvent obtained by evaporation is N-methylpyrrolidone and enters the dilution solvent storage tank.

10. A low water content aramid nanofiber, characterized in that, Prepared by the preparation method according to any one of claims 1 - 9.

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