CN110106585B

CN110106585B - Polyacrylonitrile-based carbon fiber and preparation method thereof

Info

Publication number: CN110106585B
Application number: CN201910420905.7A
Authority: CN
Inventors: 吕春祥; 王飞; 孙同庆; 尹大宇; 李永红
Original assignee: Shanxi Institute of Coal Chemistry of CAS
Current assignee: Shanxi Gangke Carbon Materials Co Ltd
Priority date: 2019-05-20
Filing date: 2019-05-20
Publication date: 2020-08-25
Anticipated expiration: 2039-05-20
Also published as: CN110106585A

Abstract

The invention relates to polyacrylonitrile-based carbon fiber and a preparation method thereof. The main technical scheme adopted is as follows: the preparation method of the polyacrylonitrile-based carbon fiber comprises the following steps: a low-temperature carbonization step, wherein the density is 1.34-1.37 g/cm³Preoxidized fiber ofCarrying out low-temperature carbonization treatment on the fiber body to obtain a low-temperature carbonized fiber body; wherein in the low-temperature carbonization step, the tension of the pre-oxidized fiber body is controlled to be A according to the density of the pre-oxidized fiber body, and A is more than 0 and less than or equal to 5000 CN; a high-temperature carbonization step, namely carbonizing the low-temperature carbonized fiber body at a high temperature to obtain a high-temperature carbonized fiber body; and (4) post-treating, namely performing post-treatment on the high-temperature carbonized fiber body to obtain the polyacrylonitrile-based carbon fiber. The invention is mainly used for further improving the bulk density of the polyacrylonitrile-based carbon fiber on the basis of ensuring the strength and the modulus of the polyacrylonitrile-based carbon fiber.

Description

Polyacrylonitrile-based carbon fiber and preparation method thereof

Technical Field

The invention relates to the technical field of carbon fibers, in particular to a polyacrylonitrile-based carbon fiber and a preparation method thereof.

Background

Since the 50 s of the last century, carbon fibers are continuously researched and developed by researchers, and currently, the carbon fibers mainly comprise viscose fibers, pitch fibers and polyacrylonitrile fibers. Because the polyacrylonitrile-based carbon fiber has light weight, high strength, high modulus, a series of excellent performances such as electric conduction, heat conduction, corrosion resistance, small thermal expansion coefficient and the like, most of the polyacrylonitrile-based carbon fiber is used in the form of carbon fiber reinforced resin matrix composite materials and is widely applied to the fields of aerospace, leisure sports, civil construction and the like.

In the prior art, the preparation method of polyacrylonitrile-based carbon fiber is to perform pre-oxidation stabilization treatment on polyacrylonitrile fiber (i.e., precursor) at 200-.

However, aerospace users need high-bulk-density polyacrylonitrile-based carbon fibers to meet the requirements of special fields, such as winding, layering, structural members and the like, and the high-bulk-density polyacrylonitrile-based carbon fibers are needed, because the improvement of the bulk density of the carbon fibers under the same indexes of strength, modulus and the like can improve the compression strength of the carbon fiber composite material and the tensile-compression ratio of the carbon fiber composite material. Therefore, under the condition of ensuring the strength and the modulus, the improvement of the bulk density of the polyacrylonitrile-based carbon fiber is a difficult problem in the development of the polyacrylonitrile-based carbon fiber.

Disclosure of Invention

In view of the above, the present invention provides a polyacrylonitrile-based carbon fiber and a preparation method thereof, and mainly aims to improve the bulk density of the polyacrylonitrile-based carbon fiber on the basis of ensuring the strength and modulus of the polyacrylonitrile-based carbon fiber.

In order to achieve the purpose, the invention mainly provides the following technical scheme:

in one aspect, an embodiment of the present invention provides a preparation method of a polyacrylonitrile-based carbon fiber, including the following steps:

and (3) low-temperature carbonization: the density of the carbon fiber is 1.34 to 1.37g/cm³Carrying out low-temperature carbonization treatment on the preoxidized fiber body to obtain a low-temperature carbonized fiber body; in the low-temperature carbonization step, the tension of the pre-oxidized fiber body is controlled to be A according to the density of the pre-oxidized fiber body, and A is more than 0 and less than or equal to 5000 CN;

and (3) high-temperature carbonization: and carrying out high-temperature carbonization on the low-temperature carbonized fiber body to obtain the polyacrylonitrile-based carbon fiber.

The object of the present invention and the technical problems solved thereby can be further achieved by the following technical measures.

Preferably, in the low-temperature carbonization step, the tension value a of the pre-oxidized fiber body is approximately in inverse proportion to the density of the pre-oxidized fiber body. Preferably, the density of the pre-oxidized fiber body is 1.34 to 1.355g/cm³The applied tension to the pre-oxidized fiber body is 2500-; if the density of the pre-oxidized fiber body is 1.355 to 1.37g/cm³The tension applied to the pre-oxidized fiber body was 100-2500 CN.

Preferably, in the low-temperature carbonization step:

if the density of the pre-oxidized fiber body is 1.34-1.345 g/cm³Applying a tension to the pre-oxidized fiber body of 4200-5000 CN;

if the density of the pre-oxidized fiber body is 1.345-1.35 g/cm³Applying a tension to the pre-oxidized fiber body of 3500-4200 CN;

if the density of the pre-oxidized fiber body is 1.35 to 1.355g/cm³The tension applied to the pre-oxidized fiber body is 2750-3500 CN;

if the density of the pre-oxidized fiber body is 1.355 to 1.36g/cm³The tension applied to the pre-oxidized fiber body is 2000-2750 CN;

if the density of the pre-oxidized fiber body is 1.36-1.365 g/cm³Applying 1300-2000 CN tension to the pre-oxidized fiber body;

if the density of the pre-oxidized fiber body is 1.365-1.37 g/cm³The tension applied to the pre-oxidized fiber body is 600 to 1300 CN.

Preferably, in the low-temperature carbonization step: sequentially carrying out low-temperature carbonization treatment on the preoxidized fiber body through a plurality of low-temperature carbonization temperature regions; wherein the temperature of the latter low-temperature carbonization temperature zone is higher than that of the former low-temperature carbonization temperature zone;

preferably, the temperature of the low-temperature carbonization treatment is 300-900 ℃;

preferably, in the low-temperature carbonization step, the residence time of the fibers is 1-4 min;

preferably, the number of the low-temperature carbonization temperature zones is 5-7.

Preferably, the number of the low-temperature carbonization temperature zones is 6, specifically: a first low-temperature carbonization temperature region of 300-400 ℃, a second low-temperature carbonization temperature region of 400-500 ℃, a third low-temperature carbonization temperature region of 500-600 ℃, a fourth low-temperature carbonization temperature region of 600-700 ℃, a fifth low-temperature carbonization temperature region of 700-800 ℃ and a sixth low-temperature carbonization temperature region of 800-900 ℃.

Preferably, in the high-temperature carbonization step: sequentially passing the low-temperature carbonized fiber body through a plurality of high-temperature carbonization temperature regions to carry out high-temperature carbonization treatment; wherein the content of the first and second substances,

the temperature of the latter high-temperature carbonization temperature zone is higher than that of the former high-temperature carbonization temperature zone; and in the high-temperature carbonization step, the residence time of the fibers is more than 40 seconds;

preferably, in the high-temperature carbonization step, the retention time of the fibers is 0.5-2 min;

preferably, the temperature of the high-temperature carbonization treatment is 1000-1500 ℃.

Preferably, in the high-temperature carbonization step, the tension of the low-temperature carbonized fiber body is controlled to be B, wherein B is more than 0 and less than or equal to 8000 CN.

Preferably, the number of the high-temperature carbonization temperature zones is 3-6; preferably, the first and second liquid crystal materials are,

preferably, the number of the high-temperature carbonization temperature zones is 3 or 4; wherein the content of the first and second substances,

when the high-temperature carbonization temperature zones are 3, the method specifically comprises the following steps: a first high temperature carbonization temperature zone, a second high temperature carbonization temperature zone, and a third high temperature carbonization temperature zone; wherein the temperature of the first high-temperature carbonization temperature zone is 1000-1300 ℃, and is preferably 1100-1300 ℃; the temperature of the second high-temperature carbonization temperature zone is 1150-1400 ℃, and preferably 1200-1400 ℃; the temperature of the third high-temperature carbonization temperature zone is 1300-1500 ℃;

when the high-temperature carbonization temperature zones are 4, the method specifically comprises the following steps: a first high-temperature carbonization temperature region of 900-1000 ℃, a second high-temperature carbonization temperature region of 1000-1100 ℃, a third high-temperature carbonization temperature region of 1100-1300 ℃ and a fourth high-temperature carbonization temperature region of 1300-1500 ℃.

Preferably, before the low-temperature carbonization step, the method further comprises:

pre-oxidation step: carrying out pre-oxidation reaction on polyacrylonitrile fibers in a pre-oxidation device to obtain a pre-oxidized fiber body; wherein the initial temperature of the pre-oxidation reaction is 200-300 ℃, the finishing temperature is 250-280 ℃, and the temperature rise gradient is 8-20 ℃;

preferably, in the pre-oxidation step, the total time of pre-oxidation is 30-70 min;

preferably, in the pre-oxidation step, the tension of the polyacrylonitrile fiber is controlled to be C, and C is more than 0 and less than or equal to 5000 CN;

preferably, in the pre-oxidation step, the running speed of the polyacrylonitrile fiber is 240-400 m/h.

Preferably, when the density of the pre-oxidized fiber body is 1.360-1.370 g/cm³Then, the prepared polyacrylonitrile-based carbon fiber has the tensile strength of 3.5-4.5 GPa, the tensile modulus of 230-250 GPa and the bulk density of 1.760-1.800g/cm³；

When the density of the pre-oxidized fiber body is 1.345-1.355 g/cm³Then, the prepared polyacrylonitrile-based carbon fiber has the tensile strength of 4.9-5.2 GPa, the tensile modulus of 230-250 GPa and the bulk density of 1.780-1.810g/cm³；

When the density of the pre-oxidized fiber body is 1.355-1.360 g/cm³The prepared polyacrylonitrile-based carbon fiber has the tensile strength of 4.3-4.9 GPa, the tensile modulus of 230-250 GPa and the bulk density of 1.770-1.790g/cm³；

When the density of the pre-oxidized fiber body is 1.340-1.345 g/cm³Then, the prepared polyacrylonitrile-based carbon fiber has the tensile strength of 3.0-3.5 GPa, the tensile modulus of 230-250 GPa and the bulk density of 1.790-1.810g/cm³。

On the other hand, the embodiment of the invention provides a polyacrylonitrile-based carbon fiber, wherein the polyacrylonitrile-based carbon fiber is prepared by any one of the preparation methods of the polyacrylonitrile-based carbon fiber; preferably, the density of the polyacrylonitrile-based carbon fiber is 1.760-1.810 g/cm³(ii) a Preferably, the polyacrylonitrile-based carbon fiber has a substantially circular cross section; preferably, the diameter of the polyacrylonitrile-based carbon fiber is 4-8 μm.

Compared with the prior art, the polyacrylonitrile-based carbon fiber and the preparation method thereof have the following beneficial effects:

1. the preparation method of the polyacrylonitrile-based carbon fiber comprises the following steps of firstly controlling the density of a pre-oxidized fiber body to be 1.34-1.37 g/cm³Thereby ensuring the tensile strength and the tensile strength of the polyacrylonitrile-based carbon fiber prepared in the later stageModulus of elongation; further, after the density of the pre-oxidized fiber body is determined, the degree of orientation of the fibers can be increased by determining an appropriate tension to be applied to the pre-oxidized fiber body according to the specific pre-oxidized density, and increasing the degree of orientation of the fibers appropriately increases the bulk density of the polyacrylonitrile-based carbon fibers. Furthermore, the invention adjusts the tension applied to the pre-oxidized fiber body and the density of the pre-oxidized fiber body in a cooperative way (the tension value A applied to the pre-oxidized fiber body and the density of the pre-oxidized fiber body are in an inverse proportion relation) so as to better improve the bulk density of the polyacrylonitrile-based carbon fiber and avoid the carbon fiber from generating broken filaments.

2. In the high-temperature carbonization step, the preparation method of the polyacrylonitrile-based carbon fiber appropriately increases the effective retention time of the fiber by adjusting the distribution of the high-temperature carbon region (here, the effective retention time refers to the retention time of the fiber in the high-temperature carbonization step when the temperature of the temperature region is sequentially increased), and further can improve the bulk density of the polyacrylonitrile-based carbon fiber (the bulk density and the modulus of the fiber can be increased after the temperature region is increased).

3. The high-density carbon fiber prepared by the preparation method of the polyacrylonitrile-based carbon fiber is beneficial to improving the compression strength of the carbon fiber composite material and improving the tension-compression ratio of the carbon fiber composite material. The invention can realize the preparation of the high-bulk density carbon fiber by optimizing and combining the process conditions without modifying and upgrading the equipment, thereby meeting the requirements of special users. In addition, the preoxidation process, the low-temperature carbonization process and the high-temperature carbonization process do not control drafting but control the tension of the tows like the traditional patent, have higher control precision, are suitable for equipment with different lengths, effectively avoid the generation of fiber broken filaments and broken filaments, and realize industrialized and stable production.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.

Drawings

FIGS. 1A, 1B, 1C and 1D are scanning electron micrographs of polyacrylonitrile-based carbon fiber prepared in example 1 of the present invention;

FIGS. 2A, 2B, 2C and 2D are scanning electron micrographs of polyacrylonitrile-based carbon fiber prepared in example 5 of the present invention;

fig. 3A, 3B, 3C and 3D are scanning electron micrographs of the polyacrylonitrile-based fiber prepared in example 6 of the present invention.

Detailed Description

To further explain the technical means and effects of the present invention adopted to achieve the predetermined object, the following detailed description of the embodiments, structures, features and effects according to the present invention will be made with reference to the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "an embodiment" refers to not necessarily the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

The embodiment of the invention provides a preparation method of polyacrylonitrile-based carbon fibers, which solves the technical problems and has the following conception: the carbon fiber bulk density can be improved under the indexes of the same strength, modulus and the like, so that the compression strength of the carbon fiber composite material can be improved, and the tension-compression ratio of the carbon fiber composite material can be improved.

The specific scheme is as follows:

a preparation method of polyacrylonitrile-based carbon fibers comprises the following steps:

and (3) high-temperature carbonization: carrying out high-temperature carbonization on the low-temperature carbonized fiber body to obtain a high-temperature carbonized fiber body;

and (3) post-treatment: and carrying out post-treatment on the high-temperature carbonized fiber body to obtain the polyacrylonitrile-based carbon fiber.

In the preparation method of the embodiment of the present invention, first, the density of the pre-oxidized fiber body is controlled to be 1.34 to 1.37g/cm³Therefore, the tensile strength and tensile modulus of the polyacrylonitrile-based carbon fiber prepared in the later stage can be ensured. Further, after the density of the pre-oxidized fiber body is determined, the proper tension applied to the pre-oxidized fiber body is determined according to the specific density of the pre-oxidized fiber body, so that the orientation degree of the fiber can be improved, and the proper orientation degree of the fiber can increase the bulk density, modulus and strength of the polyacrylonitrile-based carbon fiber.

Further, in order to better improve the bulk density of the polyacrylonitrile-based carbon fiber and simultaneously reduce and avoid the generation of broken filaments by the carbon fiber, the invention further enables the tension of the pre-oxidized fiber body and the density of the pre-oxidized fiber body to be cooperatively adjusted, and the specific cooperative adjustment method comprises the following steps: the tension value a of the pre-oxidized fiber body is in inverse relation to the density of the pre-oxidized fiber body. Specifically, the density of the pre-oxidized fiber body is 1.34 to 1.355g/cm³The tension applied to the pre-oxidized fiber body is 2500-5000 CN; if the density of the pre-oxidized fiber body is 1.355 to 1.37g/cm³The tension applied to the pre-oxidized fiber body was 100-2500 CN. Further, if the density of the pre-oxidized fiber body is 1.34 to 1.345g/cm³Applying a tension to the pre-oxidized fiber body of 4200-5000 CN; if the density of the pre-oxidized fiber body is 1.345-1.35 g/cm³Applying a tension to the pre-oxidized fiber body of 3500-4200 CN; if the density of the pre-oxidized fiber body is 1.35 to 1.355g/cm³The tension applied to the pre-oxidized fiber body is 2750-3500 CN; if the density of the pre-oxidized fiber body is 1.355 to 1.36g/cm³The tension applied to the pre-oxidized fiber body is 2000-2750 CN; if the density of the pre-oxidized fiber body is 1.36-1.365 g/cm³Applying 1300-2000 CN tension to the pre-oxidized fiber body; if the density of the pre-oxidized fiber body is 1.365-1.37 g/cm³The tension applied to the pre-oxidized fiber body is 600 to 1300 CN.

Preferably, in the low-temperature carbonization step: and (2) feeding the pre-oxidized fiber into a low-temperature carbonization furnace in a high-purity nitrogen environment atmosphere, and performing low-temperature carbonization in 5-7 temperature zones, wherein the temperature is 300-900 ℃, the oxygen content in nitrogen is lower than 2ppm, the residence time is 1-4min, the residence time of each temperature zone is the same (the length of each temperature zone is the same), and the tension of the fiber tows is controlled to be 0-5000 CN. Preferably, 6 temperature zones are selected: the temperature range of the 1-temperature zone is 300-400 ℃, the temperature range of the 2-temperature zone is 400-500 ℃, the temperature range of the 3-temperature zone is 500-600 ℃, the temperature range of the 4-temperature zone is 600-700 ℃, the temperature range of the 5-temperature zone is 700-800 ℃, and the temperature range of the 6-temperature zone is 800-900 ℃.

Preferably, the high-temperature carbonization reaction is carried out in 3-6 temperature zones, high-purity nitrogen is used as protective gas, the oxygen content in the nitrogen is lower than 2ppm, the carbonization temperature is 1000-1500 ℃, the residence time is 0.5-2 min, the residence time of each temperature zone is the same (the temperature zone length is the same), and the fiber tow tension is controlled to be 0-8000 CN. Preferably, three temperature zones are selected: the high carbon temperature 1 temperature zone is 1100-1300 ℃, the 2 temperature zone is 1200-1400 ℃, and the 3 temperature zone is 1300-1500 ℃.

In the high-temperature carbonization step, the effective residence time of the fibers is properly increased by adjusting the distribution of the high-carbon temperature zone (the effective residence time refers to the residence time of the fibers in the high-temperature carbonization step when the temperature of the temperature zone is sequentially increased), so that the bulk density of the polyacrylonitrile-based carbon fibers can be increased, and the bulk density and the modulus of the fibers can be increased after the temperature zone is increased.

Preferably, the method further comprises the following steps of: pre-oxidizing polyacrylonitrile carbon fiber precursor (for the requirement of the polyacrylonitrile-based precursor, the polyacrylonitrile-based carbon fiber precursor can be used as long as the pre-oxidized fiber body with the required density can be prepared) at the initial temperature of 200-230 ℃, controlling the total time of pre-oxidation to be 30-70 min at the temperature rise gradient of 10-20 ℃, carrying out pre-oxidation reaction in 3-5 temperature zones when the temperature rises to the end temperature of 250-280 ℃, controlling the running speed of tows to be 240-400 m/h and the tension of the fiber tows to be 0-5000CN, and controlling the density of the obtained pre-oxidized fiber body to be 1.34-1.37 g/cm³。

Preferably, the post-processing step comprises: and sequentially carrying out surface treatment, washing, sizing, drying and winding on the high-temperature carbonized fiber body to obtain the polyacrylonitrile-based carbon fiber.

The following is further illustrated by the specific examples:

the following examples are set forth to have a density of 1.185 to 1.195g/cm³The polyacrylonitrile-based fiber (protofilament) with the diameter of 10-12 μm is subjected to pre-oxidation, low-temperature carbonization and high-temperature carbonization to concretely illustrate that the scheme of the invention can improve the bulk density of the polyacrylonitrile-based carbon fiber. Of course, the present invention is not limited to the above-mentioned raw yarn, and other types of raw yarn may be used as long as the density of the pre-oxidized fiber obtained after pre-oxidation of the raw yarn is 1.34 to 1.37g/cm³And (4) finishing.

Example 1

Pre-oxidation step: so that the density of the particles is 1.190g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 12 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃, the end temperature is 260 ℃ and the temperature gradient is 10 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; in the pre-oxidation reaction, the tension applied to the filament bundle is 1000CN, and the density of the prepared pre-oxidized fiber body is 1.37g/cm³，

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 300 ℃, a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 500 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 700 ℃ and a low-temperature carbonization temperature region at 900 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2min, and the tension applied to the pre-oxidized fiber body is 600 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

And (3) high-temperature carbonization: and carrying out high-temperature carbonization treatment on the low-temperature carbonized fiber body to obtain the high-temperature carbonized fiber body. Specifically, the low-temperature carbonized fiber body is subjected to high-temperature carbonization treatment sequentially in a high-temperature carbonization temperature region of 1000 ℃, a high-temperature carbonization temperature region of 1200 ℃ and a high-temperature carbonization temperature region of 1300 ℃. In the high-temperature carbonization step, the retention time of the fiber is 1min, and the tension applied to the low-temperature carbonized fiber body is 1200 CN; in the high-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

And (3) post-treatment: and sequentially carrying out surface treatment, washing, sizing, drying and winding on the high-temperature carbonized fiber body to obtain the finished polyacrylonitrile-based carbon fiber.

The polyacrylonitrile-based carbon fiber was tested, and the density of the polyacrylonitrile-based carbon fiber obtained in example 1 was 1.800g/cm³(density gradient test), strength was 4.0GPa and extensometer modulus was 235 GPa.

As can be seen from fig. 1A to 1D: the polyacrylonitrile-based carbon fiber prepared in example 1 has a circular or nearly circular cross section with a diameter of about 7 μm.

Comparative example 1

Pre-oxidation step: to a density of 1.190g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 12 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃, the end temperature is 260 ℃ and the temperature gradient is 10 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; in the pre-oxidation reaction, the tension applied to the filament bundle is 1000CN, and the density of the prepared pre-oxidized fiber body is 1.370g/cm³，

And (3) high-temperature carbonization: and carrying out high-temperature carbonization treatment on the low-temperature carbonized fiber body to obtain the high-temperature carbonized fiber body. Specifically, the low-temperature carbonized fiber body is subjected to high-temperature carbonization treatment sequentially through a high-temperature carbonization temperature region of 1100 ℃ and a high-temperature carbonization temperature region of 1380 ℃. Wherein in the high-temperature carbonization step, the retention time of the fiber is 0.67min, and the tension applied to the low-temperature carbonized fiber body is 1200 CN; in the high-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber is tested, and the density of the polyacrylonitrile-based carbon fiber obtained in comparative example 1 is 1.770g/cm³(density gradient test), strength was 4.0GPa and extensometer modulus was 235 GPa.

By comparing the example 1 with the comparative example 1, in the high-temperature carbonization step, the invention realizes the proper extension of the fiber retention time by adjusting the high-temperature carbonization temperature and the temperature zone distribution, thereby improving the bulk density of the polyacrylonitrile-based carbon fiber.

Example 2

Pre-oxidation step: so that the density of the particles is 1.185g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 11 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃, the end temperature is 254 ℃, and the temperature gradient is 12 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; in the pre-oxidation reaction, the tension applied to the filament bundle is 1000CN, and the density of the prepared pre-oxidized fiber body is 1.364g/cm³。

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 300 ℃, a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 500 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 700 ℃ and a low-temperature carbonization temperature region at 800 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2min, and the tension applied to the pre-oxidized fiber body is 1300 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

And (3) high-temperature carbonization: and carrying out high-temperature carbonization treatment on the low-temperature carbonized fiber body to obtain the high-temperature carbonized fiber body. Specifically, the low-temperature carbonized fiber body is subjected to high-temperature carbonization treatment sequentially in a high-temperature carbonization temperature region of 1000 ℃, a high-temperature carbonization temperature region of 1150 ℃ and a high-temperature carbonization temperature region of 1300 ℃. In the high-temperature carbonization step, the retention time of the fiber is 1min, and the tension applied to the low-temperature carbonized fiber body is 1200 CN; in the high-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber was tested, and the density of the polyacrylonitrile-based carbon fiber obtained in example 2 was 1.790g/cm³(density gradient test), strength was 4.0GPa and extensometer modulus was 235 GPa.

Example 3

Pre-oxidation step: so that the density of the particles is 1.185g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 11 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃, the end temperature is 250 ℃ and the temperature gradient is 10 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; in the pre-oxidation reaction, the tension applied to the filament bundle is 1000CN, and the density of the prepared pre-oxidized fiber body is 1.362g/cm³。

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 300 ℃, a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 500 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 700 ℃ and a low-temperature carbonization temperature region at 800 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2min, and the tension applied to the pre-oxidized fiber body is 1400 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber was tested, and the density of the polyacrylonitrile-based carbon fiber obtained in example 3 was 1.795g/cm³(density gradient test), strength was 4.0GPa and extensometer modulus was 235 GPa.

Example 4

Pre-oxidation step: so that the density of the particles is 1.185g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 10 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 230 ℃, and the final temperature is 248 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; in the pre-oxidation reaction, the tension applied to the filament bundle is 1000CN, and the density of the prepared pre-oxidized fiber body is 1.360g/cm³。

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 300 ℃, a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 500 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 700 ℃ and a low-temperature carbonization temperature region at 800 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2min, and the tension applied to the pre-oxidized fiber body is 1600 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber was tested, and the density of the polyacrylonitrile-based carbon fiber obtained in example 4 was 1.800g/cm³(density gradient test), strength was 4.0GPa and extensometer modulus was 235 GPa.

Comparative example 2

Pre-oxidation step: so that the density of the particles is 1.185g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 10 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃ and the final temperature is 260 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; in the pre-oxidation reaction, the tension applied to the filament bundle is 1000CN, and the density of the prepared pre-oxidized fiber body is 1.367g/cm³。

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 300 ℃, a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 500 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 700 ℃ and a low-temperature carbonization temperature region at 800 ℃. In the low-temperature carbonization step, the retention time of the fiber is 2min, and the tension applied to the pre-oxidized fiber body is 400 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber was tested, and the density of the polyacrylonitrile-based carbon fiber obtained in comparative example 2 was 1.780g/cm³(density gradient test), strength was 4.0GPa and extensometer modulus was 235 GPa.

By combining the examples 2, 3, 4 and 2, it can be seen that the fiber orientation degree can be effectively adjusted and the carbon fiber bulk density can be increased by matching the low-temperature carbonization reaction tension with the pre-oxidized fiber bulk density.

Example 5

Pre-oxidation step: has a density of 1.190g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 12 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃, the end temperature is 250 ℃, and the temperature gradient is 8 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 50 min; in the pre-oxidation reaction, the tension applied to the filament bundle is 2000CN, and the density of the prepared pre-oxidized fiber body is 1.345g/cm³，

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 450 ℃, a low-temperature carbonization temperature region at 520 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 750 ℃ and a low-temperature carbonization temperature region at 780 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2.4min, and the tension applied to the pre-oxidized fiber body is 4200 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

And (3) high-temperature carbonization: and carrying out high-temperature carbonization treatment on the low-temperature carbonized fiber body to obtain the high-temperature carbonized fiber body. Specifically, the low-temperature carbonized fiber body is subjected to high-temperature carbonization treatment sequentially in a high-temperature carbonization temperature region of 900 ℃, a high-temperature carbonization temperature region of 1100 ℃, a high-temperature carbonization temperature region of 1300 ℃ and a high-temperature carbonization temperature region of 1400 ℃. In the high-temperature carbonization step, the retention time of the fiber is 1.4min, and the tension applied to the low-temperature carbonized fiber body is 1600 CN; in the high-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber was tested, and the density of the polyacrylonitrile-based carbon fiber obtained in example 5 was 1.810g/cm³(density gradient test), strength was 5.02GPa, and extensometer modulus was 238 GPa.

As can be seen from fig. 2A to 2D: the polyacrylonitrile-based carbon fiber prepared in example 5 has a circular or nearly circular cross section with a diameter of about 7 μm.

Comparative example 3

And (3) high-temperature carbonization: and carrying out high-temperature carbonization treatment on the low-temperature carbonized fiber body to obtain the high-temperature carbonized fiber body. Specifically, the low-temperature carbonized fiber body is subjected to high-temperature carbonization treatment sequentially in a high-temperature carbonization temperature region of 900 ℃, a high-temperature carbonization temperature region of 1100 ℃ and a high-temperature carbonization temperature region of 1400 ℃. Wherein in the high-temperature carbonization step, the retention time of the fiber is 1.05min, and the tension applied to the low-temperature carbonized fiber body is 1600 CN; in the high-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber is tested, and the density of the polyacrylonitrile-based carbon fiber obtained in the comparative example 3 is 1.770g/cm³(density gradient test), strength was 5.02GPa, and extensometer modulus was 238 GPa.

By comparing the example 5 with the comparative example 3, in the high-temperature carbonization step, the invention realizes the proper extension of the fiber retention time by adjusting the high-temperature carbonization temperature and the temperature zone distribution, thereby improving the bulk density of the polyacrylonitrile-based carbon fiber.

Example 6

Pre-oxidation step: the density of the product is 1.185g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 10 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃, the end temperature is 250 ℃, and the temperature gradient is 8 ℃; the running speed of the polyacrylonitrile fiber tows is 240 m/h; the pre-oxidation retention time is 50 min; in the pre-oxidation reaction, the tension applied to the filament bundle is 2000CN, and the density of the prepared pre-oxidized fiber body is 1.350g/cm³，

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 450 ℃, a low-temperature carbonization temperature region at 520 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 750 ℃ and a low-temperature carbonization temperature region at 780 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2.4min, and the tension applied to the pre-oxidized fiber body is 3500 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

And (3) high-temperature carbonization: and carrying out high-temperature carbonization treatment on the low-temperature carbonized fiber body to obtain the high-temperature carbonized fiber body. Specifically, the low-temperature carbonized fiber body is subjected to high-temperature carbonization treatment sequentially in a high-temperature carbonization temperature region of 1200 ℃, a high-temperature carbonization temperature region of 1350 ℃ and a high-temperature carbonization temperature region of 1500 ℃. Wherein in the high-temperature carbonization step, the retention time of the fiber is 1.05min, and the tension applied to the low-temperature carbonized fiber body is 4000 CN; in the high-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber was tested, and the polyacrylonitrile-based carbon fiber obtained in example 6 had a density of 1.809g/cm³(density gradient test), strength 5.07GPa, extensometer modulus 295 GPa.

As can be seen from fig. 3A to 3D: the polyacrylonitrile-based carbon fiber prepared in example 6 has a circular or nearly circular cross section with a diameter of about 5 μm.

Comparative example 4

And (3) high-temperature carbonization: and carrying out high-temperature carbonization treatment on the low-temperature carbonized fiber body to obtain the high-temperature carbonized fiber body. Specifically, the low-temperature carbonized fiber body is subjected to high-temperature carbonization treatment sequentially through a high-temperature carbonization temperature region of 1200 ℃ and a high-temperature carbonization temperature region of 1500 ℃. Wherein in the high-temperature carbonization step, the retention time of the fiber is 1.07min, and the tension applied to the low-temperature carbonized fiber body is 4000 CN; in the high-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

When polyacrylonitrile-based carbon fiber was tested, the density of the polyacrylonitrile-based carbon fiber obtained in example 6 was 1.770g/cm³(density gradient test), strength was 5.66GPa and extensometer modulus was 235 GPa.

By comparing the example 6 with the comparative example 4, in the high-temperature carbonization step, the invention realizes the proper extension of the fiber retention time by adjusting the high-temperature carbonization temperature and the temperature zone distribution, thereby improving the bulk density of the polyacrylonitrile-based carbon fiber.

Example 7

Pre-oxidation step: has a density of 1.195g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 11 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃, the end temperature is 254 ℃, and the temperature gradient is 12 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; tension applied to the tow during pre-oxidation1000CN, the density of the obtained pre-oxidized fiber body is 1.354g/cm³。

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 300 ℃, a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 500 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 700 ℃ and a low-temperature carbonization temperature region at 800 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2min, and the tension applied to the pre-oxidized fiber body is 3000 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

And (3) high-temperature carbonization: and carrying out high-temperature carbonization treatment on the low-temperature carbonized fiber body to obtain the high-temperature carbonized fiber body. Specifically, the low-temperature carbonized fiber body is subjected to high-temperature carbonization treatment sequentially in a high-temperature carbonization temperature region of 1100 ℃, a high-temperature carbonization temperature region of 1300 ℃ and a high-temperature carbonization temperature region of 1400 ℃. In the high-temperature carbonization step, the retention time of the fiber is 1min, and the tension applied to the low-temperature carbonized fiber body is 1200 CN; in the high-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber was tested, and the density of the polyacrylonitrile-based carbon fiber obtained in example 7 was 1.790g/cm³(density gradient test), strength was 5.05GPa and extensometer modulus was 235 GPa.

Example 8

Pre-oxidation step: has a density of 1.195g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 11 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃, the end temperature is 250 ℃ and the temperature gradient is 10 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; in the pre-oxidation reaction, the tension applied to the tow was 1000CN, and the density of the obtained pre-oxidized fiber body was 1000CN1.352g/cm³。

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 300 ℃, a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 500 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 700 ℃ and a low-temperature carbonization temperature region at 800 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2min, and the tension applied to the pre-oxidized fiber body is 3300 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber was tested, and the density of the polyacrylonitrile-based carbon fiber obtained in example 8 was 1.800g/cm³(density gradient test), strength was 5.02GPa and extensometer modulus was 235 GPa.

Example 9

Pre-oxidation step: has a density of 1.195g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 11 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 230 ℃, and the final temperature is 248 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; in the pre-oxidation reaction, the tension applied to the filament bundle is 1000CN, and the density of the prepared pre-oxidized fiber body is 1.350g/cm³。

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 300 ℃, a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 500 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 700 ℃ and a low-temperature carbonization temperature region at 800 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2min, and the tension applied to the pre-oxidized fiber body is 3500 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

When polyacrylonitrile-based carbon fiber was tested, the density of the polyacrylonitrile-based carbon fiber obtained in example 9 was 1.810g/cm³(density gradient test), strength was 5.06GPa, and extensometer modulus was 235 GPa.

Comparative example 5

Pre-oxidation step: has a density of 1.195g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 11 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃, the end temperature is 254 ℃, and the temperature gradient is 12 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; in the pre-oxidation reaction, the tension applied to the filament bundle was 1000CN, and the density of the obtained pre-oxidized fiber body was 1.354g/cm³。

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 300 ℃, a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 500 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 700 ℃ and a low-temperature carbonization temperature region at 800 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2min, and the tension applied to the pre-oxidized fiber body is 600 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber was tested, and the polyacrylonitrile-based carbon fiber obtained in comparative example 5 had a density of 1.780g/cm³(density gradient test), strength was 5.0GPa, and extensometer modulus was 235 GPa.

By combining example 7, example 8, example 9 and comparative example 5, it can be seen that the degree of fiber orientation can be effectively adjusted and the bulk density of the carbon fiber can be increased by matching the low-temperature carbonization reaction tension with the bulk density of the pre-oxidized fiber.

Example 10

Pre-oxidation step: so that the density of the particles is 1.185g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 10 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃, the end temperature is 260 ℃ and the temperature gradient is 10 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; in the pre-oxidation reactionIn this case, a tensile force of 1000CN was applied to the tow, and the density of the obtained pre-oxidized fiber body was 1.356g/cm³，

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 300 ℃, a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 500 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 700 ℃ and a low-temperature carbonization temperature region at 900 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2min, and the tension applied to the pre-oxidized fiber body is 2500 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber was tested, and the polyacrylonitrile-based carbon fiber obtained in example 10 had a density of 1.785g/cm³(density gradient test), strength was 4.7GPa and extensometer modulus was 235 GPa.

Comparative example 6

Pre-oxidation step: so that the density of the particles is 1.185g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 10 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 ℃, the end temperature is 260 ℃ and the temperature gradient is 10 ℃; the running speed of the polyacrylonitrile fiber tows is 360 m/h; the pre-oxidation retention time is 54 min; in the pre-oxidation reaction, the tension applied to the tow was 1000CN,the density of the obtained pre-oxidized fiber body is 1.356g/cm³，

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 300 ℃, a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 500 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 700 ℃ and a low-temperature carbonization temperature region at 900 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2min, and the tension applied to the pre-oxidized fiber body is 1000 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber is tested, and the density of the polyacrylonitrile-based carbon fiber obtained in the comparative example 6 is 1.770g/cm³(density gradient test), strength was 4.3GPa and extensometer modulus was 235 GPa.

Combining example 10 and comparative example 6, it can be seen that by matching the low-temperature carbonization reaction tension with the bulk density of the pre-oxidized fiber, the degree of fiber orientation can be effectively adjusted, and the bulk density of the polyacrylonitrile-based carbon fiber can be increased.

Example 11

Pre-oxidation step: the density of the product is 1.186g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 12 mu m to obtain pre-oxidized fiber bodies; wherein the initial temperature of the pre-oxidation reaction is 220 DEG CThe finishing temperature is 250 ℃, and the temperature rise gradient is 8 ℃; the running speed of the polyacrylonitrile fiber tows is 240 m/h; the pre-oxidation retention time is 50 min; in the pre-oxidation reaction, the tension applied to the filament bundle is 2000CN, and the density of the prepared pre-oxidized fiber body is 1.344g/cm³，

And (3) low-temperature carbonization: carrying out low-temperature carbonization treatment on the pre-oxidized fiber body to obtain a low-temperature carbonized fiber body; specifically, the preoxidized fiber body is subjected to low-temperature carbonization treatment sequentially through a low-temperature carbonization temperature region at 400 ℃, a low-temperature carbonization temperature region at 450 ℃, a low-temperature carbonization temperature region at 520 ℃, a low-temperature carbonization temperature region at 600 ℃, a low-temperature carbonization temperature region at 750 ℃ and a low-temperature carbonization temperature region at 780 ℃. Wherein in the low-temperature carbonization step, the retention time of the fiber is 2.4min, and the tension applied to the pre-oxidized fiber body is 4500 CN; in the low-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

Polyacrylonitrile-based carbon fiber was tested, and the polyacrylonitrile-based carbon fiber obtained in example 11 had a density of 1.803g/cm³(density gradient test), strength was 3.5GPa, and extensometer modulus was 235 GPa.

Comparative example 7

Pre-oxidation step: the density of the product is 1.186g/cm³Carrying out pre-oxidation reaction on polyacrylonitrile-based fibers with the diameter of 12 mu m to obtain pre-oxidized fiber bodies; wherein the pre-oxidation reaction has a temperature rise initial temperature of 220 ℃, an end temperature of 250 ℃ and a temperature rise gradient of8 ℃; the running speed of the polyacrylonitrile fiber tows is 240 m/h; the pre-oxidation retention time is 50 min; in the pre-oxidation reaction, the tension applied to the filament bundle is 2000CN, and the density of the prepared pre-oxidized fiber body is 1.344g/cm³，

And (3) high-temperature carbonization: and carrying out high-temperature carbonization treatment on the low-temperature carbonized fiber body to obtain the high-temperature carbonized fiber body. Specifically, the low-temperature carbonized fiber body is subjected to high-temperature carbonization treatment sequentially through a high-temperature carbonization temperature zone at 1300 ℃ and a high-temperature carbonization temperature zone at 1450 ℃. Wherein in the high-temperature carbonization step, the retention time of the fiber is 35s, and the tension applied to the low-temperature carbonized fiber body is 4000 CN; in the high-temperature carbonization device, nitrogen is introduced, and the oxygen content in the nitrogen is less than 2 ppm.

The polyacrylonitrile-based carbon fiber was tested, and the density of the polyacrylonitrile-based carbon fiber obtained in comparative example 7 was 1.790g/cm³(density gradient test), strength was 3.4GPa, and extensometer modulus was 235 GPa.

By comparing example 11 with comparative example 7, in the high-temperature carbonization step, the present invention realizes appropriate extension of the fiber residence time by adjusting the high-temperature carbonization temperature and the temperature zone distribution, thereby increasing the bulk density of the polyacrylonitrile-based carbon fiber.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and any simple modification, equivalent change and modification made to the above embodiment according to the technical spirit of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A preparation method of polyacrylonitrile-based carbon fibers is characterized by comprising the following steps:

and (3) post-treatment: carrying out post-treatment on the high-temperature carbonized fiber body to obtain polyacrylonitrile-based carbon fiber;

in the low-temperature carbonization step, wherein the tension value A of the pre-oxidized fiber body is in an inverse relationship with the density of the pre-oxidized fiber body;

if the density of the pre-oxidized fiber body is 1.365-1.37 g/cm³Then to the pre-oxidationThe tension applied by the fiber body is 600-1300 CN.

2. The method for producing polyacrylonitrile-based carbon fibers according to claim 1, characterized in that, in the low-temperature carbonization step: sequentially carrying out low-temperature carbonization treatment on the preoxidized fiber body through a plurality of low-temperature carbonization temperature regions; wherein the latter low-temperature carbonization temperature zone has a higher temperature than the former low-temperature carbonization temperature zone.

3. The method for preparing polyacrylonitrile-based carbon fiber according to claim 2, characterized in that

The temperature of the low-temperature carbonization treatment is 300-900 ℃; and/or

In the low-temperature carbonization step, the residence time of the fibers is 1-4 min.

4. The method for producing polyacrylonitrile-based carbon fiber according to claim 2,

the number of the low-temperature carbonization temperature zones is 5-7.

5. The method for producing polyacrylonitrile-based carbon fiber according to claim 4,

the number of the low-temperature carbonization temperature zones is 6, and specifically comprises the following steps: a first low-temperature carbonization temperature region of 300-400 ℃, a second low-temperature carbonization temperature region of 400-500 ℃, a third low-temperature carbonization temperature region of 500-600 ℃, a fourth low-temperature carbonization temperature region of 600-700 ℃, a fifth low-temperature carbonization temperature region of 700-800 ℃ and a sixth low-temperature carbonization temperature region of 800-900 ℃.

6. The production method of a polyacrylonitrile-based carbon fiber according to any one of claims 1 to 5, characterized in that, in the high-temperature carbonization step: sequentially passing the low-temperature carbonized fiber body through a plurality of high-temperature carbonization temperature regions to carry out high-temperature carbonization treatment; wherein the content of the first and second substances,

the temperature of the latter high-temperature carbonization temperature zone is higher than that of the former high-temperature carbonization temperature zone; and the residence time of the fibers in the high temperature carbonization step is more than 40 seconds.

7. The method for preparing polyacrylonitrile-based carbon fiber according to claim 6, wherein in the high temperature carbonization step, the residence time of the fiber is 0.5 to 2 min.

8. The method for producing polyacrylonitrile-based carbon fiber according to claim 6,

the temperature of the high-temperature carbonization treatment is 1000-1500 ℃.

9. The method for producing polyacrylonitrile-based carbon fiber according to claim 6,

in the high-temperature carbonization step, the tension of the low-temperature carbonized fiber body is controlled to be B, wherein B is more than 0 and less than or equal to 8000 CN.

10. The preparation method of polyacrylonitrile-based carbon fiber according to claim 6, characterized in that the number of the high temperature carbonization temperature zones is 3-6.

11. The method for producing polyacrylonitrile-based carbon fiber according to claim 10,

the number of the high-temperature carbonization temperature zones is 3 or 4; wherein the content of the first and second substances,

when the high-temperature carbonization temperature zones are 3, the method specifically comprises the following steps: a first high temperature carbonization temperature zone, a second high temperature carbonization temperature zone, and a third high temperature carbonization temperature zone; wherein the temperature of the first high-temperature carbonization temperature zone is 1000-1300 ℃; the temperature of the second high-temperature carbonization temperature zone is 1150-1400 ℃; the temperature of the third high-temperature carbonization temperature zone is 1300-1500 ℃;

12. The method for producing a polyacrylonitrile-based carbon fiber according to any one of claims 1 to 5 and 7 to 11, characterized by further comprising, before the low-temperature carbonization step:

pre-oxidation step: carrying out pre-oxidation reaction on polyacrylonitrile fibers in a pre-oxidation device to obtain a pre-oxidized fiber body; wherein the initial temperature of the pre-oxidation reaction is 200-300 ℃, the finishing temperature is 250-280 ℃, and the temperature gradient is 8-20 ℃.

13. The method for producing polyacrylonitrile-based carbon fiber according to claim 12, characterized in that,

in the pre-oxidation step, the total time of pre-oxidation is 30-70 min.

14. The method for producing polyacrylonitrile-based carbon fiber according to claim 12, characterized in that,

in the pre-oxidation step, the tension of the polyacrylonitrile fiber is controlled to be C, and C is more than 0 and less than or equal to 5000 CN.

15. The method for producing polyacrylonitrile-based carbon fiber according to claim 12, characterized in that,

in the pre-oxidation step, the operation speed of the polyacrylonitrile fiber is 240-400 m/h.

16. The production method of a polyacrylonitrile-based carbon fiber according to any one of claims 1 to 5, 7 to 11, 13 to 15, characterized in that the post-treatment step comprises: and sequentially carrying out surface treatment, washing, sizing, drying and winding on the high-temperature carbonized fiber body to obtain the polyacrylonitrile-based carbon fiber.

17. The method for producing polyacrylonitrile-based carbon fiber according to any one of claims 1 to 5, 7 to 11, and 13 to 15, wherein when the pre-oxidized fiber bulk density is 1.360 to 1.370g/cm³The method comprises the following steps: the prepared polyacrylonitrile-based carbon fiber has the tensile strength of 3.5-4.5 GPa, the tensile modulus of 230-250 GPa and the bulk density of 1.760-1.800g/cm³；

When the density of the pre-oxidized fiber body is 1.355-1.360 g/cm³The prepared polyacrylonitrile-based carbon fiber has the tensile strength of 4.3-4.9 GPa, the tensile modulus of 230-250 GPa and the bulk density of 1.770-1.790g/cm³。