CN111304768B

CN111304768B - High-crystallinity polyacrylonitrile nascent fiber and preparation method thereof

Info

Publication number: CN111304768B
Application number: CN202010296527.9A
Authority: CN
Inventors: 李常清; 杜壮; 徐樑华; 王宇; 高爱君; 童元建; 曹维宇; 赵振文
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2020-04-15
Filing date: 2020-04-15
Publication date: 2021-04-23
Anticipated expiration: 2040-04-15
Also published as: CN111304768A

Abstract

The invention discloses a high-crystallinity polyacrylonitrile nascent fiber and a preparation method thereof, wherein the method comprises the following steps: (1) taking dimethyl sulfoxide as a solvent, copolymerizing acrylonitrile and a comonomer, and then performing demonomerization and deaeration to obtain a polymer spinning solution; (2) and extruding the polymer spinning solution through a spinneret plate, and then, allowing the polymer spinning solution to enter a coagulating bath containing glycerol and ethanol for coagulation forming so as to obtain the polyacrylonitrile nascent fiber. The method adopts glycerol and ethanol which are poor solvents of PAN as a coagulation bath medium, so that PAN keeps metastable double-pitch separation in the phase separation process of coagulation forming, spinning stock solution is uniformly coagulated and formed, the primary fiber structure is compact, the crystallinity of the primary fiber prepared by adopting dimethyl sulfoxide aqueous solution as the coagulation bath medium under the same condition is higher than that of the primary fiber prepared by adopting dimethyl sulfoxide aqueous solution as the coagulation bath medium, and the crystallinity of the polyacrylonitrile primary fiber prepared by the method reaches more than 83.85 percent, so that the carbon fiber with excellent performance can be prepared.

Description

High-crystallinity polyacrylonitrile nascent fiber and preparation method thereof

Technical Field

The invention belongs to the technical field of carbon fiber precursors, and particularly relates to a high-crystallinity polyacrylonitrile nascent fiber and a preparation method thereof.

Background

The polyacrylonitrile-based carbon fiber is a high-performance fiber with carbon content of over 90 percent, which is prepared by taking polyacrylonitrile as a raw material through the working procedures of spinning forming, pre-oxidation, carbonization and the like. Polyacrylonitrile-based carbon fibers are widely used in the fields of aerospace, high-voltage power transmission, automobile parts, engineering plastics and the like because of their own properties such as high specific strength, high specific modulus, excellent heat resistance and electrical conductivity. The carbon fiber material industrial chain develops and matures in multiple fields, and higher requirements are put forward on the performance of polyacrylonitrile carbon fibers.

The structural characteristics of the polyacrylonitrile nascent fiber determine the basic structure of the polyacrylonitrile fiber protofilament, and further influence the structure of the polyacrylonitrile-based carbon fiber. The crystallization behavior and the crystalline structure of the nascent fiber are important influence factors for determining the crystalline structure of the fiber precursor, and the crystalline structure of the precursor determines the diffusion of oxygen in the fiber, further influences the reaction process of thermal oxidation stabilization and also influences the subsequent carbonization process reaction.

The high-quality protofilament is the basis for producing the high-performance polyacrylonitrile carbon fiber, the high crystallinity is the structural characteristic of the high-quality protofilament, the improvement of the crystallinity of the protofilament can be taken as the starting point from the improvement of the crystallinity of the polyacrylonitrile nascent fiber, and the solidification forming process of the stock solution trickle in the solidification bath directly determines the structure of the nascent fiber. The forming process of spinning stock solution trickle in the coagulating bath is based on phase separation and double diffusion, dimethyl sulfoxide water solution which is mostly adopted at present is used as a coagulating bath system, so that the crystallinity of protofilament is low, and the structure and the performance of protofilament and subsequent PAN carbon fiber are limited.

Therefore, the existing process for preparing carbon fiber precursor needs to be further explored.

Disclosure of Invention

The invention aims to solve the technical problem of providing a high-crystallinity polyacrylonitrile nascent fiber and a preparation method thereof, wherein the method adopts glycerol and ethanol which are poor solvents of PAN as a coagulating bath medium, so that the PAN keeps metastable double-node separation in the phase separation process of coagulation forming, spinning stock solution is uniformly coagulated and formed, the nascent fiber structure is compact, the crystallinity of the nascent fiber is higher than that of the nascent fiber prepared by adopting a dimethyl sulfoxide aqueous solution as the coagulating bath medium under the same condition, and the crystallinity of the polyacrylonitrile nascent fiber prepared by the method reaches more than 83.85 percent, so that the carbon fiber with excellent performance can be prepared.

In one aspect of the invention, a method of making high crystallinity polyacrylonitrile as-spun fiber is presented. According to an embodiment of the invention, the method comprises: (1) taking dimethyl sulfoxide as a solvent, copolymerizing acrylonitrile and a comonomer, and then performing demonomerization and deaeration to obtain a polymer spinning solution; (2) and extruding the polymer spinning solution through a spinneret plate, and then, allowing the polymer spinning solution to enter a coagulating bath containing glycerol and ethanol for coagulation forming so as to obtain the polyacrylonitrile nascent fiber.

Preferably, in step (1), the comonomer is at least one selected from the group consisting of itaconic acid, methyl acrylate, methyl methacrylate, methacrylic acid and acrylamide.

Preferably, in the step (1), the molecular weight of the acrylonitrile polymer in the polymer spinning solution is 5 to 50 ten thousand, and preferably 10 to 20 ten thousand.

Preferably, in the step (2), the mass ratio of the glycerol to the ethanol in the coagulation bath is (7-9): (1-3).

Preferably, in the step (2), negative draft is applied in the solidification forming process, and the negative draft is-35% to-25%.

Preferably, in the step (2), the temperature of the coagulating bath is 20-60 ℃, and preferably 20-40 ℃.

Preferably, in step (2), the residence time of the polymer dope in the coagulation bath after extrusion through the spinneret is not less than 30 seconds, preferably not less than 55 seconds.

In another aspect of the invention, the invention provides a high-crystallinity polyacrylonitrile nascent fiber, which is prepared by the method.

The spinning dope trickle undergoes a phase separation process in a coagulation bath to form PAN nascent fibers, which stage determines the crystalline structural characteristics of the nascent fibers. Under the prior art, a phase separation coagulation bath system for regulating and controlling the coagulation forming stage of polyacrylonitrile nascent fiber mostly adopts dimethyl sulfoxide aqueous solution, the coagulation bath system containing glycerol and ethanol is adopted to replace the traditional dimethyl sulfoxide aqueous solution in the application, so that a PAN-DMSO-glycerol/ethanol ternary phase diagram has a larger metastable zone, simultaneously, the ethanol is adopted to improve the fluidity of the system, the action parameters of the ethanol and the PAN are smaller than the action parameters between the glycerol and the PAN, the forming process speed can be slowed down, the fiber skin-core difference is avoided, because the concentration of the PAN in a spinning stock solution is higher, a starting point falls above a critical point, the larger metastable zone ensures that the system still keeps double-node separation when the solid content is changed due to the phase separation, a polymer concentrated phase (high polymer) is always kept as a continuous phase, and a poor phase core is dispersed in the continuous phase and participates in diffusion, finally, the primary fiber with uniform and compact structure is formed, the crystallinity of the primary fiber is higher than that of the primary fiber prepared by adopting dimethyl sulfoxide aqueous solution as a coagulating bath medium under the same condition, and the crystallinity of the polyacrylonitrile primary fiber prepared by the method reaches above 83.85 percent, so that the carbon fiber with excellent performance can be prepared.

Drawings

FIG. 1 is a schematic flow diagram of a method for preparing high crystallinity polyacrylonitrile nascent fiber according to an embodiment of the invention;

FIG. 2 is an X-ray diffraction pattern of PAN nascent fibers prepared in a glycerol-ethanol coagulation bath system of the present invention;

FIG. 3 is a plot of an X-ray diffraction peak fit of PAN nascent fibers prepared in a glycerol-ethanol coagulation bath system of the present invention;

FIG. 4 shows DMSO-H in comparative example₂X-ray diffraction pattern of PAN nascent fiber prepared under O coagulation bath system;

FIG. 5 shows DMSO-H in comparative example₂And (3) preparing a PAN nascent fiber X-ray diffraction peak-splitting fitting graph under an O coagulation bath system.

Detailed Description

The present invention will be further described in detail with reference to the following examples and fig. 1-5 thereof, which are illustrative and not restrictive, and the scope of the present invention is not limited thereto.

It should be noted that the PAN nascent fiber crystallinity is calculated herein using the following method: firstly, carrying out desolventizing treatment on PAN nascent fiber, airing at room temperature, shearing into powder, carrying out XRD analysis, carrying out peak-splitting fitting on a scanning curve of the PAN nascent fiber to obtain a crystalline region peak area (Ac) and an amorphous region peak area (Aa), and calculating the crystallinity of the PAN nascent fiber by adopting a crystallinity (Xc) formula (the crystallinity Xc is Ac/(Ac + Aa) × 100%).

In one aspect of the invention, a method of making high crystallinity polyacrylonitrile as-spun fiber is presented. According to an embodiment of the invention, with reference to fig. 1, the method comprises:

s100: uses dimethyl sulfoxide as solvent, makes acrylonitrile and comonomer implement copolymerization, then makes the above-mentioned material undergo the processes of demonomerization and defoaming

In the step, dimethyl sulfoxide (DMSO) is used as a solvent, acrylonitrile and a comonomer are copolymerized to obtain a polymer spinning solution, and then the polymer spinning solution is demonomerized to obtain a polymer spinning stock solution. Specifically, in the process, dimethyl sulfoxide is used as a solvent, Azodiisobutyronitrile (AIBN) is used as an initiator to carry out copolymerization on acrylonitrile and a comonomer at the temperature of 60-70 ℃, preferably 65 ℃, for 12-36 hours, preferably 24 hours, so as to obtain a polymer spinning solution, wherein the comonomer is at least one selected from itaconic acid, methyl acrylate, methyl methacrylate, methacrylic acid and acrylamide, unreacted monomers in the polymer spinning solution are removed under the conditions of stirring at the temperature of 60-70 ℃, preferably 65 ℃ and the vacuum degree of more than 0.095MPa, the stirring is stopped after 7-9 hours, preferably 8 hours, and the polymer spinning solution is kept still and defoamed under the same vacuum condition of 55-65 ℃, preferably 60 ℃. Preferably, the molecular weight of the acrylonitrile polymer in the polymer spinning solution is 5 to 50 ten thousand, and preferably 10 to 20 ten thousand. The inventor finds that if the molecular weight of the acrylonitrile polymer in the polymer spinning solution is too large, the flexibility of PAN molecular chains is enhanced, so that the crystallization process of fibers is slow, the crystallization capacity is poor, and the crystallinity of the nascent fibers prepared in the same solidification time is low, and if the molecular weight of the acrylonitrile polymer in the polymer spinning solution is too small, the performance of the obtained nascent fibers is poor, and the strength of the final PAN carbon fiber product is influenced.

S200: extruding the polymer spinning solution by a spinneret plate, and then putting the extruded polymer spinning solution into a coagulating bath containing glycerol and ethanol for coagulation forming

In the step, the obtained polymer spinning solution is extruded by a spinneret plate and then enters a coagulating bath containing glycerol and ethanol for coagulation forming, so that the polyacrylonitrile nascent fiber is obtained. The inventor finds that, different from the traditional phase separation coagulation bath system for regulating and controlling the coagulation forming stage of polyacrylonitrile nascent fiber by adopting dimethyl sulfoxide aqueous solution, the invention adopts the coagulation bath system containing glycerol and ethanol to replace the traditional dimethyl sulfoxide aqueous solution, so that a PAN-DMSO-glycerol/ethanol ternary phase diagram has a larger metastable zone, simultaneously adopts ethanol to improve the fluidity of the system, and the action parameters of the ethanol and the PAN are smaller than those of the glycerol and the PAN, so that the forming process speed can be slowed down, the generation of sheath-core difference of the fiber can be avoided, because the concentration of the PAN in the spinning stock solution is higher, the starting point falls above a critical point, the larger metastable zone ensures that the system still keeps double-node separation when the solid content is changed due to phase separation, a polymer concentrated phase (high polymer) is always kept as a continuous phase, and a poor phase core is dispersed in the continuous phase and participates in diffusion, finally, the primary fiber with uniform and compact structure is formed, the crystallinity of the primary fiber is higher than that of the primary fiber prepared by adopting dimethyl sulfoxide aqueous solution as a coagulating bath medium under the same condition, and the crystallinity of the polyacrylonitrile primary fiber prepared by the method reaches above 83.85 percent.

Further, the mass ratio of glycerol to ethanol in the coagulation bath containing glycerol and ethanol is (7-9): (1-3). The inventor finds that a proper ratio of glycerol to ethanol is beneficial to preparing PAN nascent fibers with higher crystallinity, if the ratio of glycerol is too high, the system has too strong PAN precipitation capacity, and a phase separation path rapidly passes through a metastable zone from a starting point to generate spinodal line separation so as to form a compact skin layer and a loose porous core layer structure; if the proportion of ethanol is too high, the polymer-poor phase nuclei become droplets in the fibers, and voids are formed, resulting in a decrease in the crystallinity of the fibers. Meanwhile, negative draft is applied in the solidification forming process, and the negative draft is-35% to-25%, preferably-30%. The inventor finds that the spinning efficiency can be effectively improved by adopting a proper draft ratio in the spinning process, molecular chains are oriented, and the fiber crystallinity is improved, but if the draft ratio is too low, the orientation capability of the PAN molecular chains is poor, especially the PAN molecular chains in the nascent fiber are tangled and arranged loosely, and the yarn breakage phenomenon is easily caused by a higher draft ratio. In addition, the temperature of the coagulating bath is 20-60 ℃, preferably 20-40 ℃, and the retention time of the polymer spinning solution in the coagulating bath after being extruded by a spinneret plate is not less than 30 seconds, preferably not less than 55 seconds.

In a second aspect of the invention, a high crystallinity polyacrylonitrile as-spun fiber is presented. According to the embodiment of the invention, the high-crystallinity polyacrylonitrile nascent fiber is prepared by adopting the method. Therefore, the crystallinity of the polyacrylonitrile nascent fiber reaches above 83.85 percent, so that the carbon fiber with excellent performance can be prepared.

The invention will now be described with reference to specific examples, which are intended to be illustrative only and not to be limiting in any way.

Example 1

(1) Taking azobisisobutyronitrile as an initiator, acrylonitrile as a monomer, itaconic acid as a comonomer and dimethyl sulfoxide as a solvent (having good dissolving capacity for polyacrylonitrile), and carrying out free radical polymerization at 65 ℃ to obtain a mixture of acrylonitrile and itaconic acid with a molar ratio of 99: 1, obtaining a polymer spinning solution (the molecular weight of an acrylonitrile polymer in the polymer spinning solution is 15 ten thousand) after 8 hours of demonomerization and 8 hours of defoaming procedures;

(2) in the spinning stage, the linear speed of spinning fine flow passing through a spinneret orifice is controlled to be 44.59m/h by controlling the supply amount of a metering pump, the number of the spinneret orifice and the aperture (1000-orifice spinneret and 0.065mm aperture), the speed of a first driving transmission wheel after the nascent fiber leaves a coagulation bath is 31.21m/h, the coagulation negative draft is kept to be-30%, the coagulation bath adopts a mixed solution containing glycerol and ethanol (the mass ratio of the glycerol to the ethanol is 8:2), the temperature of the coagulation bath is kept to be 20 ℃, the spinning fine flow is extruded by spinning until the spinning fine flow leaves the coagulation bath, the coagulation time is 92.3s, and the spinning fine flow is obtainedPAN nascent fiber. Using wide-angle X-ray diffractometer to PANⁱThe primary fiber is subjected to X-ray scanning, as shown in fig. 2, subjected to peak-splitting fitting, and the fitted curve is as shown in fig. 3, and the crystallinity of the primary fiber is calculated. As can be seen from fig. 2 and 3, a strong crystal diffraction peak appears at about 16.9 ° 2 θ, and a weaker crystal diffraction peak appears at about 29 ° 2 θ, indicating that two crystal diffraction peaks at 16.9 ° 2 θ and 29 ° 2 θ exist in the as-spun fiber; a broad diffraction peak exists around 25 ° at 2 θ, and represents an amorphous region having a random structure.

Example 2

The present embodiment (2) differs from embodiment 1 in that: and regulating the speed of a metering pump, controlling the linear speed of the spinning trickle passing through a spinneret orifice to be 74.30m/h, and controlling the speed of a first driving wheel after the nascent fiber leaves the coagulating bath to be 52.01m/h, namely, the coagulating negative draft is kept to be-30%, so that the coagulating time of the PAN solution trickle is 55.4 s. The rest of the process parameters and the implementation steps are the same as in example 1.

Example 3

This example differs from example 1 in that: and regulating the speed of a metering pump, controlling the linear speed of the spinning trickle passing through a spinneret orifice to be 118.89m/h, and controlling the speed of a first driving wheel after the nascent fiber leaves the coagulating bath to be 83.22m/h, namely, the coagulating negative draft is kept to be-30%, so that the coagulating time of the PAN solution trickle is 34.6 s. The rest of the process parameters and the implementation steps are the same as in example 1.

Example 4

This example differs from example 1 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 30 ℃, and the remaining process parameters and the implementation steps were the same as in example 1.

Example 5

This example differs from example 2 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 30 ℃, and the remaining process parameters and the implementation steps were the same as those of example 2.

Example 6

This example differs from example 3 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 30 ℃, and the remaining process parameters and the implementation steps were the same as those in example 3.

Example 7

This example differs from example 1 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 40 ℃, and the remaining process parameters and the implementation steps were the same as in example 1.

Example 8

This example differs from example 2 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 40 ℃, and the remaining process parameters and the implementation steps were the same as those of example 2.

Example 9

This example differs from example 3 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 40 ℃, and the remaining process parameters and the implementation steps were the same as those in example 3.

Example 10

This example differs from example 1 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 50 ℃, and the remaining process parameters and the implementation steps were the same as in example 1.

Example 11

This example differs from example 2 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 50 ℃, and the remaining process parameters and the implementation steps were the same as those of example 2.

Example 12

This example differs from example 3 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 50 ℃, and the remaining process parameters and the implementation steps were the same as those in example 3.

Example 13

This example differs from example 1 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 60 ℃, and the remaining process parameters and the implementation steps were the same as in example 1.

Example 14

This example differs from example 2 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 60 ℃, and the remaining process parameters and the implementation steps were the same as those of example 2.

Example 15

This example differs from example 3 in that: the temperature of the coagulation bath containing glycerol and ethanol was controlled to 60 ℃, and the remaining process parameters and the implementation steps were the same as those in example 3.

Example 16

This example differs from example 4 in that: the mass ratio of glycerol to ethanol in the coagulation bath containing glycerol and ethanol was controlled to 7:3, and the remaining process parameters and the implementation steps were the same as in example 1.

Example 17

This example differs from example 5 in that: the mass ratio of glycerol to ethanol in the coagulation bath containing glycerol and ethanol was controlled to 7:3, and the remaining process parameters and the implementation steps were the same as in example 2.

Example 18

This example differs from example 6 in that: the mass ratio of glycerol to ethanol in the coagulation bath containing glycerol and ethanol was controlled to 7:3, and the remaining process parameters and the implementation steps were the same as in example 3.

Example 19

This example differs from example 4 in that: the mass ratio of glycerol to ethanol in the coagulation bath containing glycerol and ethanol was controlled to 9:1, and the remaining process parameters and the implementation steps were the same as in example 1.

Example 20

This example differs from example 5 in that: the mass ratio of glycerol to ethanol in the coagulation bath containing glycerol and ethanol was controlled to 9:1, and the remaining process parameters and the implementation steps were the same as those in example 2.

Example 21

This example differs from example 6 in that: the mass ratio of glycerol to ethanol in the coagulation bath containing glycerol and ethanol was controlled to 9:1, and the remaining process parameters and the implementation steps were the same as in example 3.

Comparative example 1

The difference from example 1 is that: an aqueous solution with the mass concentration of the dimethyl sulfoxide of 76 percent is adopted as a coagulating bath system.

And (3) carrying out X-ray scanning on the PAN nascent fiber by adopting a wide-angle X-ray diffractometer, carrying out peak-splitting fitting on the PAN nascent fiber as shown in figure 4, and calculating the crystallinity of the PAN nascent fiber by using a fitting curve as shown in figure 5. As can be seen from fig. 4 and 5, a strong crystal diffraction peak appears around 16.9 ° at 2 θ, and a broader diffraction peak representing an amorphous structure exists around 25 ° at 2 θ, but no crystal diffraction peak is observed around 29 ° at 2 θ.

Comparative example 2

The difference from example 2 is that: an aqueous solution with the mass concentration of the dimethyl sulfoxide of 76 percent is adopted as a coagulating bath system.

Comparative example 3

The difference from example 3 is that: an aqueous solution with the mass concentration of the dimethyl sulfoxide of 76 percent is adopted as a coagulating bath system.

Comparative example 4

The difference from example 1 is that: glycerol was used as the coagulation bath system.

Comparative example 5

The difference from example 2 is that: glycerol was used as the coagulation bath system.

Comparative example 6

The difference from example 3 is that: glycerol was used as the coagulation bath system.

Comparative example 7

The difference from example 1 is that: ethanol was used as the coagulation bath system.

Comparative example 8

The difference from example 2 is that: ethanol was used as the coagulation bath system.

Comparative example 9

The difference from example 3 is that: ethanol was used as the coagulation bath system.

Comparative example 10

The difference from example 1 is that: the mass ratio of the glycerol to the ethanol in the coagulating bath containing the glycerol and the ethanol is controlled to be 6: 4.

Comparative example 11

The difference from example 2 is that: the mass ratio of the glycerol to the ethanol in the coagulating bath containing the glycerol and the ethanol is controlled to be 6: 4.

Comparative example 12

The difference from example 3 is that: the mass ratio of the glycerol to the ethanol in the coagulating bath containing the glycerol and the ethanol is controlled to be 6: 4.

The crystallinity of the polyacrylonitrile-formed fibers obtained in examples 1 to 21 and comparative examples 1 to 12 is shown in Table 1.

TABLE 1 crystallinity of Polyacrylonitrile nascent fibers obtained in examples 1-21 and comparative examples 1-12

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the technical principle of the present invention, and these modifications and decorations should not be regarded as the protection scope of the invention.

Claims

1. A method for preparing high-crystallinity polyacrylonitrile nascent fiber is characterized by comprising the following steps:

(1) taking dimethyl sulfoxide as a solvent, copolymerizing acrylonitrile and a comonomer, and then performing demonomerization and deaeration to obtain a polymer spinning solution;

(2) extruding the polymer spinning solution by a spinneret plate, then putting the extruded polymer spinning solution into a coagulating bath containing glycerol and ethanol for coagulation forming so as to obtain polyacrylonitrile nascent fiber,

wherein in the step (2), the mass ratio of the glycerol to the ethanol in the coagulation bath is (7-9): (1-3).

2. The method according to claim 1, wherein in step (1), the comonomer is at least one selected from the group consisting of itaconic acid, methyl acrylate, methyl methacrylate, methacrylic acid and acrylamide.

3. The method according to claim 1 or 2, wherein in the step (1), the molecular weight of the acrylonitrile polymer in the polymer dope is 5 to 50 ten thousand.

4. The method according to claim 1 or 2, wherein in the step (1), the molecular weight of the acrylonitrile polymer in the polymer dope is 10 to 20 ten thousand.

5. The method according to claim 1, wherein in step (2), the coagulation forming process applies a negative draft, the negative draft being-35% to-25%.

6. The method according to claim 1 or 5, wherein in the step (2), the temperature of the coagulation bath is 20 to 60 ℃.

7. The method according to claim 1 or 5, wherein in the step (2), the temperature of the coagulation bath is 20 to 40 ℃.

8. The method of claim 1, wherein in step (2), the polymer dope solution is extruded through a spinneret and then stays in the coagulation bath for a time of not less than 30 seconds.

9. The method of claim 1 or 8, wherein in step (2), the polymer dope solution is extruded through the spinneret plate and then stays in the coagulation bath for not less than 55 seconds.

10. A high crystallinity polyacrylonitrile as-spun fiber prepared by the method of any one of claims 1 to 9.