CN110373729B - Nascent fiber, polyacrylonitrile-based carbon fiber and preparation method thereof - Google Patents
Nascent fiber, polyacrylonitrile-based carbon fiber and preparation method thereof Download PDFInfo
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- CN110373729B CN110373729B CN201910718257.3A CN201910718257A CN110373729B CN 110373729 B CN110373729 B CN 110373729B CN 201910718257 A CN201910718257 A CN 201910718257A CN 110373729 B CN110373729 B CN 110373729B
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D10/00—Physical treatment of artificial filaments or the like during manufacture, i.e. during a continuous production process before the filaments have been collected
- D01D10/02—Heat treatment
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/06—Wet spinning methods
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/12—Stretch-spinning methods
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/12—Stretch-spinning methods
- D01D5/14—Stretch-spinning methods with flowing liquid or gaseous stretching media, e.g. solution-blowing
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
- D01F6/28—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from copolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D01F6/40—Modacrylic fibres, i.e. containing 35 to 85% acrylonitrile
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F9/00—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments
- D01F9/08—Artificial filaments or the like of other substances; Manufacture thereof; Apparatus specially adapted for the manufacture of carbon filaments of inorganic material
- D01F9/12—Carbon filaments; Apparatus specially adapted for the manufacture thereof
- D01F9/14—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments
- D01F9/20—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products
- D01F9/21—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D01F9/22—Carbon filaments; Apparatus specially adapted for the manufacture thereof by decomposition of organic filaments from polyaddition, polycondensation or polymerisation products from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyacrylonitriles
Abstract
The invention relates to a nascent fiber, a polyacrylonitrile-based carbon fiber and a preparation method thereof. The main technical scheme adopted is as follows: the nascent fiber is a strand silk with a fiber form, which is obtained after polyacrylonitrile spinning trickle is formed by a coagulating bath; wherein the light transmittance of the nascent fiber is not less than 60%. The invention mainly provides or prepares the nascent fiber with the light transmittance of more than 60 percent, and the nascent fiber under the light transmittance has a uniform structure, so that the polyacrylonitrile fiber and the polyacrylonitrile-based carbon fiber with uniform structure and excellent performance can be prepared by utilizing the nascent fiber or the preparation method of the nascent fiber.
Description
Technical Field
The invention relates to the technical field of fibers, in particular to nascent fibers, polyacrylonitrile-based carbon fibers and a preparation method thereof.
Background
The polyacrylonitrile-based carbon fiber has excellent properties such as high specific strength and high specific modulus, and the composite material using the polyacrylonitrile-based carbon fiber as a reinforcing fiber is widely applied to aerospace, new energy and the like. With the expansion of the application field of the carbon fiber, the performance requirement of the polyacrylonitrile-based carbon fiber is further improved.
The structural characteristics of polyacrylonitrile fibers (i.e., carbon fiber precursor fibers) determine the basic structure of polyacrylonitrile-based carbon fibers. The performance of polyacrylonitrile-based carbon fibers is greatly affected by the performance of polyacrylonitrile fibers. In particular, when the structure of polyacrylonitrile fiber has a sheath-core structure or is not uniform, the performance of polyacrylonitrile-based carbon fiber is greatly degraded.
And the nascent fiber is the foundation of the polyacrylonitrile fiber structure. The polyacrylonitrile fiber is prepared by coagulating and forming spun fine flow to obtain nascent fiber, and performing post-treatment process and other processes on the nascent fiber. Wherein the nascent fiber is obtained by slowly forming a fiber morphology in a coagulation bath by spinning a trickle. The fiber forming process of the spinning stream in the coagulation bath directly determines the structure of the as-spun fiber.
In the prior art, the spinning trickle enters the coagulation bath and is formed into a nascent fiber form through the phase separation effect; the phase separation process starts from the surface layer of the fiber firstly, so that the surface layer structure and the core layer structure of the fiber are different, so that the so-called skin-core structure exists, the structure of the nascent fiber is uneven, the structures of the polyacrylonitrile fiber and the polyacrylonitrile-based fiber are uneven, and the performances of the polyacrylonitrile fiber and the polyacrylonitrile-based carbon fiber are reduced.
Disclosure of Invention
In view of the above, the present invention provides a nascent fiber, a polyacrylonitrile-based carbon fiber and a preparation method thereof, and mainly aims to improve the structural uniformity of the nascent fiber so as to obtain the polyacrylonitrile fiber and the polyacrylonitrile-based carbon fiber with good structural uniformity and performance.
In order to achieve the purpose, the invention mainly provides the following technical scheme:
in one aspect, embodiments of the present invention provide a nascent fiber, wherein the nascent fiber is a filament with a fiber morphology obtained by forming a polyacrylonitrile spinning trickle through a coagulation bath; wherein the light transmittance of the nascent fiber is not less than 60%.
Preferably, the average pore diameter of the primary fiber at the surface structure is a first average pore diameter; the average pore size at the core structure of the as-spun fiber is a second average pore size; wherein the deviation of the first average pore size and the second average pore size is within 10%. Preferably, the surface structure is a position on the radial section of the fiber, the shortest distance between the surface structure and the outer contour of the fiber is not more than 1 micron; the core layer structure is positioned at the position on the radial section of the fiber, wherein the shortest distance between the fiber and the gravity center of the radial section is not more than 1 micrometer.
On the other hand, the preparation method of the nascent fiber comprises the following steps:
spinning: extruding polyacrylonitrile spinning solution from a spinneret orifice to form polyacrylonitrile spinning trickle;
forming: forming the polyacrylonitrile spinning trickle by a coagulating bath to obtain nascent fiber; wherein the temperature of the coagulating bath is-50-10 ℃.
Preferably, the residence time of the polyacrylonitrile spinning stream in the coagulation bath is 2 to 60 seconds.
Preferably, the polymer in the polyacrylonitrile spinning solution is one or a mixture of two of polyacrylonitrile homopolymer and polyacrylonitrile copolymer. Preferably, the solvent in the polyacrylonitrile spinning solution is one or a mixture of several of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, a lithium chloride solution, an ionic liquid, a sodium thiocyanate solution and a zinc chloride solution.
Preferably, the coagulation bath comprises a mixture of, by mass, 1: 0-2: 8 and a solvent, and the non-solvent has a coagulation value of 2 to 150 relative to the polymer in the polyacrylonitrile spinning dope. The mass ratio of the non-solvent to the solvent is preferably 1: 0-3: 7, more preferably 9: 1-4: 6, more preferably 8: 2-4: 6; preferably, the non-solvent is one or a mixture of more of formic acid, glycerol, ethylene glycol, acetic acid, ethanol, methanol, chloroform, isobutanol, isoamyl alcohol, butanediol, benzyl alcohol, carbon tetrachloride, toluene, acetone, water and dioxane.
Preferably, a wet spinning method is adopted to prepare the polyacrylonitrile spinning solution into the nascent fiber; wherein the drafting multiple of the spinning nozzle is 0.7-1.5 times, preferably 0.75-1.2 times, and more preferably 0.8-1.1 times; or preparing the polyacrylonitrile spinning solution into the nascent fiber by adopting a dry-jet wet spinning method; wherein the draft multiple of the spinneret is 2 to 12 times, preferably 3 to 8 times, and more preferably 4 to 6 times.
On the other hand, the embodiment of the invention also provides the polyacrylonitrile fiber, and the polyacrylonitrile fiber is prepared from the nascent fiber. Preferably, the deviation between the average pore diameter at the surface structure and the average pore diameter at the core structure of the polyacrylonitrile fiber is within 10%; preferably, the tensile strength of the polyacrylonitrile fiber is 900MPa to 1.4GPa, and preferably 950 to 1.5 GPa.
The polyacrylonitrile fiber is used not only for preparing carbon fiber, but also as a reinforcing material of a composite material or an industrial fiber. Specifically, the polyacrylonitrile fiber has good mechanical properties, and can be independently used as a reinforcement fiber except for preparing carbon fiber, such as building reinforcement, reinforced concrete, braided polyacrylonitrile belt as a cable, and the like.
On the other hand, the preparation method of the polyacrylonitrile fiber comprises the following steps:
preparing nascent fiber: preparing the nascent fiber by adopting the preparation method of the nascent fiber;
drawing treatment: drawing the nascent fiber in a gas medium; wherein the as-spun fibers are as described above;
and (3) post-treatment: and (4) carrying out post-treatment on the drawn nascent fiber to obtain the polyacrylonitrile fiber.
Preferably, the post-processing step includes: and (3) carrying out water washing treatment, stretching treatment, oiling treatment and drying treatment on the drawn nascent fiber to obtain the polyacrylonitrile fiber.
Preferably, in the step of the draft treatment:
the drafting treatment is positive drafting treatment; preferably, the draft multiple applied to the nascent fiber is 1.05 to 3.5 times, preferably 1.2 to 3 times, and further preferably 1.5 to 2 times; and/or
The temperature of the gaseous medium is not higher than 25 ℃; the temperature of the gas medium is not lower than the glass transition temperature of the primary fiber and the freezing temperature of the solvent contained in the primary fiber; and/or
The gas medium is any one of air, nitrogen, water vapor, inert gas and carbon dioxide.
On the other hand, the embodiment of the invention also provides polyacrylonitrile-based carbon fiber, and the polyacrylonitrile-based carbon fiber is prepared from the polyacrylonitrile fiber. Preferably, the deviation between the average pore diameter of the polyacrylonitrile-based carbon fiber at the surface layer structure and the average pore diameter of the polyacrylonitrile-based carbon fiber at the core layer structure is within 10%; further preferably, the deviation between the average pore diameter of the polyacrylonitrile-based carbon fiber at the surface layer structure and the average pore diameter of the polyacrylonitrile-based carbon fiber at the core layer structure is within 5%; preferably, the tensile strength of the polyacrylonitrile-based carbon fiber is 7.4-9 GPa.
In another aspect, the preparation method of the polyacrylonitrile-based carbon fiber comprises the following steps: carrying out heat treatment on the polyacrylonitrile fiber to obtain polyacrylonitrile-based carbon fiber;
preferably, the heat treatment comprises: carrying out pre-oxidation, low-temperature carbonization and high-temperature carbonization treatment on the polyacrylonitrile fiber; further preferably, the pre-oxidation temperature is 185-350 ℃; preferably, the temperature of the low-temperature carbonization treatment is 400-850 ℃; preferably, the temperature of the high-temperature carbonization is 1200-3000 ℃.
Compared with the prior art, the nascent fiber, the polyacrylonitrile fiber and the polyacrylonitrile-based carbon fiber and the preparation method thereof have the following beneficial effects:
1. the embodiment of the invention provides a nascent fiber, wherein the light transmittance of the nascent fiber is not lower than 60%; the nascent fiber with the light transmittance of more than or equal to 60 percent of the embodiment of the invention means that the structural uniformity is good.
Further, the average pore diameter at the surface structure of the nascent fiber provided by the embodiment of the invention is a first average pore diameter; the average pore size at the core structure of the as-spun fiber is the second average pore size; wherein the deviation of the first average pore size and the second average pore size is within 10%. Therefore, the nascent fiber provided by the embodiment of the invention has better structural uniformity.
2. The embodiment of the invention provides a preparation method of nascent fiber, which controls the light transmittance of the formed nascent fiber to be not less than 60% by controlling the components of a coagulating bath, the temperature of the coagulating bath and the residence time of the fiber in the coagulating bath, and improves the uniformity of the nascent fiber.
3. The embodiment of the invention also provides a polyacrylonitrile fiber and a preparation method of the polyacrylonitrile fiber, wherein the polyacrylonitrile fiber is prepared from the nascent fiber, and the polyacrylonitrile fiber prepared by the embodiment of the invention has a uniform structure and excellent performance due to the uniform structure of the nascent fiber.
Further, in the preparation method of polyacrylonitrile fiber provided by the embodiment of the present invention, after the step of forming the nascent fiber, before the step of performing post-treatment (including washing, stretching, oiling, and drying processes) on the nascent fiber: the step of positively drafting the nascent fiber in a gas medium is added, so that tension can be applied to the nascent fiber, the solvent contained in the sliver is squeezed while the sliver in the nascent fiber shape is lengthened, the solvent contained in the sliver is forced to seep to the surface of the sliver, and the seeped solvent forms liquid drops to leave the sliver, so that the technical effect of removing part of the solvent in the sliver is achieved, and the wastewater amount of the subsequent water washing process is reduced.
4. The embodiment of the invention also provides a polyacrylonitrile-based carbon fiber and a preparation method of the polyacrylonitrile-based carbon fiber, wherein the polyacrylonitrile-based carbon fiber is prepared from the polyacrylonitrile fiber, and the polyacrylonitrile fiber prepared by the embodiment of the invention has a uniform structure and excellent performance due to the uniform structure of the polyacrylonitrile.
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
FIG. 1 is an image of a nascent fiber tow in a coagulation tank during the production of nascent fibers in example 1 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.
In one aspect, embodiments of the present invention provide a nascent fiber; wherein the nascent fiber is a strand silk with a fiber form obtained after polyacrylonitrile spinning trickle passes through a coagulating bath; the light transmittance of the nascent fiber provided in this embodiment is not less than 60%.
Here, the primary fiber (i.e., coagulated fiber) means a filament formed by forming a polyacrylonitrile polymer trickle and having a fiber form; the polymer in the filament may be in a coagulated state, may be in a gel state, or may be partially coagulated or in a gel state.
The inventors of the present invention found that: after the polyacrylonitrile polymer solution enters the coagulation bath, the polyacrylonitrile polymer solution is changed into a non-solution state from a solution state due to mass transfer and/or heat transfer, and the light transmittance of the polymer solution is reduced. When polyacrylonitrile polymer trickle forms a coagulated fiber in a fiber form (i.e., a nascent fiber), if the light transmittance of the coagulated fiber is large, the structure in the coagulated fiber is uniform. Also, the as-spun fibers of the present invention have a light transmittance of greater than or equal to 60% when exiting the coagulation bath. If the transmittance of the as-spun fiber leaving the coagulation bath is less than 60%, the structural uniformity of the as-spun fiber is poor.
Here, it should be noted that: structurally uniform nascent fibers (i.e., coagulated filaments) means that the difference between the surface structure and the core structure of the nascent fiber is within a reasonable range, specifically, the deviation between the average pore size at the surface structure and the average pore size at the core structure is within 10%.
Preferably, the surface structure is a position on the radial section of the fiber, the shortest distance between the surface structure and the outer contour of the fiber is not more than 1 micron; the core layer structure is positioned at the position on the radial section of the fiber, wherein the shortest distance between the fiber and the gravity center of the radial section is not more than 1 micrometer. Specifically, the definition at the skin structure is: the term "cross section" means a range within 1 μm from the outer contour to the inner side in the radial direction of the fiber. The definition at the core structure refers to the range of a circle having a diameter within 1 μm with the center of gravity of the radial cross section as the middle size in the radial cross section of the fiber.
The definitions of the surface layer structure and the core layer structure are not only suitable for nascent fibers, but also suitable for polyacrylonitrile fibers and polyacrylonitrile-based carbon fibers.
Here, the average pore diameter of the surface layer structure and the core layer structure of the nascent fiber was measured by the following method:
1. firstly, drying the nascent fiber by using a freeze-drying method to obtain a dried nascent fiber sample;
2. the section image of the nascent fiber is obtained by using a transmission electron microscope or a scanning electron microscope and the like, and the nascent fiber sample can be subjected to gold spraying treatment before testing, or other pretreatment which can increase the observation effect but does not change the original appearance of the solidified fiber is performed on the nascent fiber;
3. and processing the micro image of the solidified filament by using image processing software to obtain the pore size distribution of different areas. Selecting a circular area with the diameter of 200nm at 1000nm inward from the surface of the primary fiber as a representative area of a surface structure area, calculating the average pore diameter at the surface structure area, and removing the first two large-diameter pores during calculation so as to reduce errors. Selecting a circular area with the diameter of 200nm at the gravity center of the radial section of the nascent fiber as a representative area of the core layer structure, calculating the average pore diameter of the core layer structure, and removing the first two large-diameter pores during calculation so as to reduce errors.
In addition, the light transmittance of the nascent fiber is tested (also can be tested on line) when the nascent fiber leaves the coagulation bath, the light transmittance obtained by testing the nascent fiber on line by using a light transmittance tester is 500 +/-10 nm of the light source wavelength during the test, and the obtained light transmittance is the light transmittance when the stacking thickness of a fiber sample is 1 +/-0.1 mm.
On the other hand, the embodiment of the invention also provides a preparation method of the nascent fiber, which comprises the following steps:
1) spinning: extruding the polyacrylonitrile spinning solution from the spinneret orifice to form polyacrylonitrile spinning trickle.
In this step, the polymer in the polyacrylonitrile spinning dope may be a blend of acrylonitrile homopolymer, or a copolymer having acrylonitrile as a main component, and a polymer having acrylonitrile homopolymer or a copolymer having acrylonitrile as a main component.
In this step, the solvent in the polyacrylonitrile spinning solution (referred to as polyacrylonitrile solvent); selecting any one or a mixture of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, lithium chloride/ionic liquid, sodium thiocyanate solution and zinc chloride solution.
In this step, the molecular weight and the distribution of the polymer in the polyacrylonitrile spinning solution are not particularly limited, and the smaller the molecular weight, the poorer the mechanical properties of the carbon fiber precursor fiber and the carbon fiber obtained, and therefore the polymer molecular weight is preferably 10 ten thousand or more. The carbon fiber precursor fiber and the carbon fiber obtained with a larger molecular weight have better mechanical properties, but the polymer having a large molecular weight is less soluble in a solvent, and therefore the upper limit of the molecular weight of the polymer is not particularly limited as long as the polymer can be dissolved in the solvent, and the polymer is usually 150 ten thousand or less.
2) Forming: forming the polyacrylonitrile spinning trickle by a coagulating bath to obtain nascent fiber; .
In the step, the temperature of the coagulation bath is-50 to 10 ℃. Under the condition, the polymer solution has a low coagulation speed in a coagulation bath, and a nascent fiber with uniform inside and outside and high light transmittance is easily formed.
In the step, the bath liquid of the coagulating bath comprises the following components in a mass ratio of 1: 0-2: 8 (polyacrylonitrile non-solvent: solvent incapable of dissolving polyacrylonitrile) and a solvent (polyacrylonitrile solvent: solvent capable of dissolving polyacrylonitrile), and the non-solvent has a coagulation value of 2 to 150 with respect to the polymer in the polyacrylonitrile spinning dope. The mass ratio of the non-solvent to the solvent is preferably 1: 0-3: 7, more preferably 9: 1-4: 6, more preferably 8: 2-4: 6; preferably, the non-solvent is any one or a mixture of several of formic acid, glycerol, ethylene glycol, acetic acid, ethanol, methanol, chloroform, isobutanol, isoamyl alcohol, butanediol, benzyl alcohol, carbon tetrachloride, toluene, acetone, water and dioxane; preferably, the solvent in the coagulation bath is a polyacrylonitrile solvent, and any one or a mixture of several of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, lithium chloride/ionic liquid, a sodium thiocyanate solution and a zinc chloride solution is selected.
In this case, the components in the coagulation bath may contain other components besides the solvent and the non-solvent, which do not impair the effect of the present invention, that is, other components may be present in the coagulation bath besides the listed solvents and non-solvents.
Here, the light transmittance of the formed nascent fiber is controlled to be not less than 60% by controlling the components of the coagulation bath and the temperature of the coagulation bath, and the uniformity of the nascent fiber is improved.
Under the conditions, the polyacrylonitrile spinning stream can be preferentially formed into a gel state before phase separation occurs in a coagulation bath, or the phase separation and the gelation process are simultaneously carried out, so that the formed primary fiber has basically the same internal and external structures, and thus, the homogeneous primary fiber without a sheath-core structure is obtained (wherein, the gelation process refers to the process that a polymer solution is converted into the gel state from a solution state; the loss modulus of the polymer solution is larger than the storage modulus; and the gel state refers to the state that the loss modulus of the polymer solution is equal to or smaller than the storage modulus in a certain conversion process, but part of the polymer solution still does not undergo phase separation.).
Here, it should be noted that: the "coagulation value" referred to above refers to the volume of solution required for the turbidity titration of a dilute solution of polymer. The specific method comprises the following steps: 1. firstly, dissolving a polymer by using a solvent to obtain a uniform solution with the concentration of 1 wt%; 2. dropwise adding other solutions into the polymer solution obtained in the step 1 with a certain volume amount under the conditions of stirring and 20 ℃, and recording the volume of the dropwise added solution when the cloud point appears in the system for the first time; 3. by calculation, a volume value of the solution to be added dropwise at which the cloud point first appears in 100ml of the polymer solution was obtained, and the volume value (i.e., 100) was defined as a coagulation value of the solution to this polymer. Here, the solvent used for determining the coagulation value is dimethylformamide.
Preferably, the residence time of the polyacrylonitrile spinning stream in the coagulation bath is between 2 and 60 seconds, the residence time of the polyacrylonitrile spinning stream in the coagulation bath is more than 60 seconds, and the residence time of the polymer solution in the coagulation bath is too long, so that the production efficiency is reduced. When the residence time of the polyacrylonitrile spinning trickle in the coagulation bath is less than 2 seconds, the fibers are easy to be adhered after the coagulated filaments are discharged from the coagulation tank.
The process for producing the nascent fiber may be any of wet spinning and dry-jet wet spinning. When wet spinning is adopted, the drafting multiple of a spinning nozzle can be 0.7-1.5 times, preferably 0.75-1.2 times, and further preferably 0.8-1.1 times; when the dry jet wet spinning method is adopted, the draft multiple of the spinning nozzle can be 2-12 times, preferably 3-8 times, and more preferably 4-6 times.
Herein, in the present application, the term "spinneret draft ratio" refers to, for those skilled in the art: after spinning, the ratio of the speed of the first driving transmission roller to the speed of the spinning solution trickles flowing out of the spinning holes.
In another aspect, the embodiment of the present invention further provides a polyacrylonitrile fiber, where the polyacrylonitrile fiber is prepared from the nascent fiber. Preferably, the preparation method of the polyacrylonitrile fiber comprises the following steps:
1) preparing nascent fiber: preparing the nascent fiber by adopting the method;
2) drawing treatment: drawing the nascent fiber in a gas medium;
3) and (3) post-treatment: and (4) carrying out post-treatment on the drawn nascent fiber to obtain the polyacrylonitrile fiber.
Here, in the step of the draft treatment: the drafting treatment is positive drafting treatment; preferably, the draft multiple applied to the nascent fiber is 1.05 to 3.5 times, preferably 1.2 to 3 times, and further preferably 1.5 to 2 times; and/or the temperature of the gaseous medium is not higher than 25 ℃; the temperature of the gas medium is not lower than the glass transition temperature of the primary fiber and the freezing temperature of the solvent contained in the primary fiber; and/or the gas medium is any one of air, nitrogen, water vapor, inert gas and carbon dioxide.
Before the primary fiber is subjected to post-treatment (including the processes of washing, stretching, oiling and drying), the primary fiber is subjected to positive drafting treatment in a gas medium, namely tension is applied to the primary fiber, when the primary fiber is in a filament shape, the solvent contained in the filament forms an extrusion effect while the filament is lengthened, the solvent contained in the filament is forced to permeate to the surface of the filament, and the permeated solvent forms liquid drops to leave the filament, so that the technical effect of removing part of the solvent in the filament is achieved; thereby reducing the wastewater amount of the subsequent water washing process.
Preferably, the post-processing step includes: and (3) carrying out water washing treatment, stretching treatment, oiling treatment and drying treatment on the drawn nascent fiber to obtain the polyacrylonitrile fiber. It is further preferable to add a dry densification process, a steam drawing process, and a dry heat drawing process to the post-treatment drying process. Here, the post-treatment processes (water washing, drawing in a bath, oiling process, drying process, dry densification process, steam drawing process, dry heat drawing process, etc.) described in the present invention may adjust the process sequence according to process optimization. Preferably, after drawing in the bath, the drawn fiber strands are preferably oiled in order to prevent inter-fiber adhesion, reduce static electricity, and increase the bundling property and the fiber separation property of the fiber bundle. When the draft multiple is increased, molecules are easily aligned along the axial direction of the fiber, and the performance of the fiber is increased. Therefore, in the production process of the polyacrylonitrile-based fiber, the total draft ratio is preferably 10 times or more and less than 350 times, and more preferably 25 times or more and less than 150 times.
In another aspect, embodiments of the present invention further provide a polyacrylonitrile-based carbon fiber; wherein the polyacrylonitrile-based carbon fiber is prepared from the polyacrylonitrile fiber.
Preferably, the method for manufacturing polyacrylonitrile-based carbon fiber preferably includes the following steps: and carrying out heat treatment on the polyacrylonitrile-based fibers. The heat treatment process described herein is not particularly limited as long as the carbon fiber precursor fiber can be heated to become a carbon fiber, and examples thereof include a pre-oxidation process, a low-temperature carbonization process, and a high-temperature carbonization process.
Preferably, the polyacrylonitrile fiber is subjected to the following processes in sequence to obtain the polyacrylonitrile-based carbon fiber: a pre-oxidation process, namely pre-oxidizing the obtained polyacrylonitrile-based fiber in an oxidizing atmosphere at the temperature of 185-350 ℃; a low-temperature carbonization process, wherein the fibers obtained in the pre-oxidation process are carbonized at low temperature in an inert atmosphere at the temperature of 400-850 ℃; and (3) a high-temperature carbonization process, namely carbonizing the fibers obtained in the low-temperature carbonization process at the temperature of 1200-3000 ℃ in an inert atmosphere.
In order to increase the bonding strength of the polyacrylonitrile-based carbon fiber with the matrix in the composite material, the surface of the carbon fiber may be treated by electrolysis. After the electrolytic treatment, in order to increase the bundling property and subsequent use performance of the carbon fiber, sizing treatment can be carried out on the carbon fiber. The sizing agent used in the sizing treatment is selected according to the type of the matrix in the composite material.
The deviation between the average pore diameter at the surface layer structure and the average pore diameter at the core layer structure of the polyacrylonitrile fiber prepared by the above method is within 10%, so that the polyacrylonitrile fiber has a uniform structure. And the tensile strength of the polyacrylonitrile fiber is more than 800 MPa; preferably greater than 1GPa, preferably between 950 MPa and 1.5 GPa. It should be noted that, because the mechanical properties of the polyacrylonitrile fiber are good, the polyacrylonitrile fiber can be used alone as a reinforcement fiber besides preparing carbon fiber, such as building reinforcement, reinforced concrete, weaving polyacrylonitrile tape as a cable, and the like.
The deviation between the average pore diameter of the surface layer structure and the average pore diameter of the core layer structure of the polyacrylonitrile-based carbon fiber prepared by the method is within 10 percent, so that the polyacrylonitrile-based carbon fiber has a uniform structure. Preferably, the tensile strength of the polyacrylonitrile-based carbon fiber is 7.4-9 GPa.
The following are further illustrated by specific experimental examples:
example 1
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber, and the preparation steps are as follows:
1) preparing a spinning solution: a polymer solution obtained by solution polymerization using dimethyl sulfoxide as a solvent and acrylonitrile and itaconic acid as comonomers is a polyacrylonitrile spinning solution, and the weight average molecular weight is 13 ten thousand and the viscosity is 90pa.s (here, this example and the following examples mainly use a polyacrylonitrile spinning solution with a viscosity average molecular weight of 14 ten thousand and a viscosity of 90pa.s as an example, but not limited thereto, and any polyacrylonitrile spinning solution is suitable for the present invention).
2) Preparing nascent fiber: preparing a nascent fiber by adopting a dry-jet wet spinning method (wherein the drafting multiple of a spinning nozzle is 3.5); in this step. The temperature of the coagulating bath is controlled to be-15 ℃, the bath liquid of the coagulating bath comprises dimethyl sulfoxide and methanol (the mass percentage is 2: 8), and the residence time of polyacrylonitrile-based spinning trickle in the coagulating bath is 60 seconds in the process of preparing the nascent fiber.
And (3) carrying out online measurement on the light transmittance of the nascent fiber leaving the coagulation bath by using a light transmittance tester, wherein the light source wavelength is 500 +/-10 nm during measurement, and the obtained light transmittance is the light transmittance when the stacking thickness of the fiber sample is 1 +/-0.1 mm.
3) Drawing treatment: the nascent fiber is subjected to drafting treatment in air, and the drafting multiple is 1.2 times.
4) Post-treatment: washing and drafting the drafted fiber by using a water bath, oiling the drafted fiber by using the water bath fiber, then performing drying densification treatment by using a drying roller, and drafting the fiber in high-temperature steam; therefore, the total drafting multiple applied to the fiber in the preparation process of the polyacrylonitrile fiber is 30 times, and the polyacrylonitrile fiber with the single fiber fineness of 0.94dtex is obtained.
5) A heat treatment step: and pre-oxidizing the obtained polyacrylonitrile fiber in air with a temperature gradient in a temperature range of 185-350 ℃ to obtain the pre-oxidized fiber. And carbonizing the obtained pre-oxidized fiber at a low temperature in a nitrogen atmosphere at the temperature of 400-850 ℃ to obtain the low-temperature carbonized fiber. And (2) carbonizing the low-temperature carbonized fiber at high temperature in a nitrogen atmosphere with the maximum temperature of 1500 ℃, performing electrolytic treatment by using an ammonium bisulfate solution as an electrolyte, washing with water, drying, and then performing sizing treatment to obtain the polyacrylonitrile-based carbon fiber.
Example 2
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 2 differs from example 1 in that:
preparing nascent fiber: the drafting multiple of the spinning jet is 2 times; the temperature of the coagulation bath was 2 ℃; the coagulating bath consists of ethanol and water in a mass ratio of 1: 9; the residence time of the polyacrylonitrile spinning trickle in the coagulating bath is 2 seconds;
drawing treatment: the draft was 1.5 times.
The other steps are exactly the same as those of example 1.
Example 3
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 3 differs from example 1 in that:
preparing nascent fiber: the drafting multiple of the spinning jet is 3 times; the temperature of the coagulation bath is-50 ℃; the coagulating bath is composed of ethanol; the residence time of the polyacrylonitrile spinning trickle in the coagulating bath is 5 seconds;
drawing treatment: the draft was 1.4 times.
The other steps are exactly the same as those of example 1.
Example 4
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 4 differs from example 1 in that:
preparing nascent fiber: the drafting multiple of the spinning jet is 8 times; the temperature of the coagulation bath is 0 ℃; the composition of the coagulation bath was methanol; the residence time of the polyacrylonitrile spinning trickle in the coagulating bath is 10 seconds;
drawing treatment: the draft was 1.6 times.
The other steps are exactly the same as those of example 1.
Example 5
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 5 differs from example 1 in that:
preparing nascent fiber: the drafting multiple of the spinning jet is 4 times; the temperature of the coagulation bath is-12 ℃; the coagulating bath consists of formic acid and ethylene glycol in a mass ratio of 1: 9; the residence time of the polyacrylonitrile spinning trickle in the coagulating bath is 30 seconds;
drawing treatment: the draft was 2 times.
The other steps are exactly the same as those of example 1.
Example 6
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 6 differs from example 1 in that:
preparing nascent fiber: the drafting multiple of the spinning jet is 6 times; the temperature of the coagulation bath is-18 ℃; the coagulating bath comprises the following components in percentage by mass: 4 isobutanol and dimethylformamide; the residence time of the polyacrylonitrile spinning trickle in the coagulating bath is 20 seconds;
drawing treatment: the draft was 1.1 times.
The other steps are exactly the same as those of example 1.
Example 7
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 7 differs from example 1 in that:
preparing nascent fiber: adopting a wet spinning method, wherein the drawing multiple of a spinning nozzle is 0.7 times; the temperature of the coagulation bath was 5 ℃; the coagulating bath comprises the following components in percentage by mass: 2 isoamyl alcohol and water; the residence time of the polyacrylonitrile spinning trickle in the coagulation bath is 35 seconds;
drawing treatment: the draft was 1.1 times.
The other steps are exactly the same as those of example 1.
Example 8
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 8 differs from example 1 in that:
preparing nascent fiber: adopting a wet spinning method, wherein the drawing multiple of a spinning nozzle is 0.75 times; the temperature of the coagulating bath is-25 ℃; the coagulating bath comprises the following components in percentage by mass of 3:7 dimethyl sulfoxide and ethanol; the residence time of the polyacrylonitrile spinning trickle in the coagulating bath is 25 seconds;
drawing treatment: the draft was 1.3 times.
The other steps are exactly the same as in example 1.
Example 9
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 9 differs from example 1 in that:
preparing nascent fiber: adopting a wet spinning method, wherein the drawing multiple of a spinning nozzle is 0.8 times; the temperature of the coagulation bath was 10 ℃; the coagulating bath comprises the following components in percentage by mass: 3: 1 dimethyl sulfoxide: ethanol: water; the residence time of the polyacrylonitrile spinning trickle in the coagulating bath is 60 seconds;
drawing treatment: the draft was 1.4 times.
The other steps are exactly the same as in example 1.
Example 10
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 10 differs from example 1 in that:
preparing nascent fiber: adopting a wet spinning method, wherein the drafting multiple of a spinning nozzle is 1.1 times; the temperature of the coagulating bath is-10 ℃; the coagulating bath consists of butanediol and dimethylacetamide in a mass ratio of 3: 7; the residence time of the polyacrylonitrile spinning trickle in the coagulating bath is 20 seconds;
drawing treatment: the draft was 1.4 times.
The other steps are exactly the same as in example 1.
Example 11
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 11 differs from example 1 in that:
preparing nascent fiber: adopting a wet spinning method, wherein the drawing multiple of a spinning nozzle is 1.2 times; the temperature of the coagulating bath is-5 ℃; the composition of the coagulation bath was propanol; the residence time of the polyacrylonitrile spinning trickle in the coagulating bath is 25 seconds;
drawing treatment: the draft was 1.3 times.
The other steps are exactly the same as in example 1.
Example 12
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 12 differs from example 1 in that:
preparing nascent fiber: adopting a wet spinning method, wherein the drawing multiple of a spinning nozzle is 1.5 times; the temperature of the coagulation bath is-20 ℃; the coagulating bath is composed of ethylene glycol; the residence time of the polyacrylonitrile spinning trickle in the coagulating bath is 10 seconds;
drawing treatment: the draft was 1.1 times.
The other steps are exactly the same as in example 1.
Example 13
The embodiment is mainly used for preparing nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, example 13 differs from example 1 in that:
preparing nascent fiber: the drafting multiple of the spinneret is 12 times; the temperature of the coagulation bath is-10 ℃; the composition of the coagulating bath is butanediol; the residence time of the polyacrylonitrile spinning trickle in the coagulating bath is 6 seconds;
drawing treatment: the draft was 1.5 times.
The other steps are exactly the same as in example 1.
Comparative example 1
Comparative example 1 was mainly used for the preparation of nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, comparative example 1 is different from example 1 in that: the same procedure as in example 1 was repeated except that the temperature of the coagulation bath was 15 ℃.
Comparative example 2
Comparative example 2 was mainly used for the preparation of nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, comparative example 2 is different from example 2 in that: the polyacrylonitrile spinning stream was allowed to stay in the coagulation bath for 65 seconds, and the operation was otherwise the same as in example 2.
Comparative example 3
Comparative example 3 was mainly used for the preparation of nascent fiber, polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber; among them, comparative example 3 differs from example 7 in that: the same procedure as in example 7 was repeated except that the spinneret draft was 0.55.
FIG. 1 is an image of the as-spun fiber tow in the coagulation tank when making as-spun fibers of example 1. The coagulating bath is provided with a temperature control pipeline 3, a coagulating bath 1, a temperature measuring device 4 (thermocouple) and nascent fiber 2. As can be seen from fig. 1: the light transmission of the as-spun fibers 2 (see the positions between the dashed lines) is particularly good; because of its excellent light transmission, the whole is transparent, and is not easy to be seen clearly under the contrast of the coagulating bath 1.
The structural performance parameters of the as-spun fibers, polyacrylonitrile fibers, and polyacrylonitrile-based carbon fibers prepared in examples 1 to 13 and comparative examples 1 to 3 are shown in table 1.
Table 1 shows the process parameters and the structural properties of the fibers prepared in examples 1 to 13 and comparative examples 1 to 3
As can be seen from table 1: the nascent fiber prepared by the embodiment of the invention has high light transmittance, and polyacrylonitrile fiber and polyacrylonitrile-based carbon fiber prepared by the nascent fiber have uniform structures and good performance.
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 (17)
1. The preparation method of the polyacrylonitrile-based carbon fiber is characterized in that the deviation between the average pore diameter of the polyacrylonitrile-based carbon fiber at the surface layer structure and the average pore diameter of the polyacrylonitrile-based carbon fiber at the core layer structure is within 10 percent; the tensile strength of the polyacrylonitrile-based carbon fiber is 7.4-9 GPa;
the preparation method of the polyacrylonitrile-based carbon fiber comprises the following steps: carrying out heat treatment on polyacrylonitrile fibers to obtain polyacrylonitrile-based carbon fibers; wherein the heat treatment comprises: carrying out pre-oxidation, low-temperature carbonization and high-temperature carbonization treatment on the polyacrylonitrile fiber; wherein the deviation between the average pore diameter at the surface structure and the average pore diameter at the core structure of the polyacrylonitrile fiber is within 10%;
the preparation method of the polyacrylonitrile fiber comprises the following steps:
preparing nascent fiber;
drawing treatment: drawing the nascent fiber in a gas medium;
and (3) post-treatment: post-treating the drafted nascent fiber to obtain polyacrylonitrile fiber;
the nascent fiber is a strand silk with a fiber form, which is obtained by forming polyacrylonitrile spinning trickle through a coagulating bath; wherein the content of the first and second substances,
the light transmittance of the nascent fiber is not lower than 60%;
the average pore diameter of the surface structure of the nascent fiber is a first average pore diameter; the average pore size at the core structure of the as-spun fiber is a second average pore size; wherein the deviation between the first average pore size and the second average pore size is within 10%;
the preparation method of the nascent fiber comprises the following steps:
spinning: extruding polyacrylonitrile spinning solution from a spinneret orifice to form polyacrylonitrile spinning trickle;
forming: forming the polyacrylonitrile spinning trickle by a coagulating bath to obtain nascent fiber;
wherein the temperature of the coagulating bath is-50 to-5 ℃;
wherein the coagulating bath comprises the following components in a mass ratio of 1: 0 to 2: 8, non-solvent and solvent; wherein the non-solvent has a coagulation value of 2 to 150 relative to the polymer in the polyacrylonitrile spinning dope;
wherein the residence time of the polyacrylonitrile spinning trickle in the coagulation bath is 2-35 seconds;
preparing polyacrylonitrile spinning solution into the nascent fiber by a wet spinning method; wherein the drafting multiple of the spinneret is 0.7-1.5 times; or preparing the polyacrylonitrile spinning solution into the nascent fiber by adopting a dry-jet wet spinning method; wherein, the drafting multiple of the spinneret is 2 to 12 times.
2. The method for producing polyacrylonitrile-based carbon fiber according to claim 1,
the surface structure is a position on the radial section of the fiber, wherein the shortest distance between the surface structure and the outer contour of the fiber is not more than 1 micrometer;
the core layer structure is positioned at the position on the radial section of the fiber, wherein the shortest distance between the fiber and the gravity center of the radial section is not more than 1 micrometer.
3. The method for producing polyacrylonitrile-based carbon fiber according to claim 1,
the polymer in the polyacrylonitrile spinning solution is one or a mixture of two of polyacrylonitrile homopolymer and polyacrylonitrile copolymer.
4. The method for producing polyacrylonitrile-based carbon fiber according to claim 1,
the mass ratio of the non-solvent to the solvent is 1: 0 to 3: 7.
5. the method for producing polyacrylonitrile-based carbon fiber according to claim 4, characterized in that
The mass ratio of the non-solvent to the solvent is 9: 1-4: 6.
6. the method for producing polyacrylonitrile-based carbon fiber according to claim 4,
the mass ratio of the non-solvent to the solvent is 8: 2-4: 6.
7. the method for producing polyacrylonitrile-based carbon fiber according to claim 1,
the non-solvent is one or a mixture of more of formic acid, glycerol, ethylene glycol, acetic acid, ethanol, methanol, chloroform, isobutanol, isoamylol, butanediol, benzyl alcohol, carbon tetrachloride, toluene, acetone, water and dioxane; and/or
The solvent in the coagulating bath is a solvent capable of dissolving polyacrylonitrile, wherein the solvent is one or a mixture of more of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, a lithium chloride solution, an ionic liquid, a sodium thiocyanate solution and a zinc chloride solution.
8. The method for producing polyacrylonitrile-based carbon fiber according to claim 1,
if a wet spinning method is adopted to prepare the polyacrylonitrile spinning solution into the nascent fiber; wherein the drafting multiple of the spinneret is 0.75-1.2 times;
if a dry-jet wet spinning method is adopted, preparing the polyacrylonitrile spinning solution into the nascent fiber; wherein, the drafting multiple of the spinneret is 3-8 times.
9. The method for producing polyacrylonitrile-based carbon fiber according to claim 1,
if a wet spinning method is adopted to prepare the polyacrylonitrile spinning solution into the nascent fiber; wherein the drafting multiple of the spinneret is 0.8-1.1 times;
if a dry-jet wet spinning method is adopted, preparing the polyacrylonitrile spinning solution into the nascent fiber; wherein, the drafting multiple of the spinneret is 4-6 times.
10. The method for producing polyacrylonitrile-based carbon fiber according to claim 1, characterized in that the post-treatment step includes: and (3) carrying out water washing treatment, stretching treatment, oiling treatment and drying treatment on the drawn nascent fiber to obtain the polyacrylonitrile fiber.
11. The method for preparing polyacrylonitrile-based carbon fiber according to claim 1, wherein the tensile strength of the polyacrylonitrile fiber is 900MPa-1.5 GPa.
12. The method for preparing polyacrylonitrile-based carbon fiber according to claim 11, wherein the tensile strength of the polyacrylonitrile fiber is 950 MPa-1.5 Gpa.
13. The method for producing polyacrylonitrile-based carbon fiber according to claim 1, characterized in that, in the step of the drawing treatment:
the drafting treatment is positive drafting treatment; wherein the draft multiple applied to the nascent fiber is 1.05-3.5 times; and/or
The temperature of the gaseous medium is not higher than 50 ℃; the temperature of the gas medium is not lower than the glass transition temperature of the primary fiber and the freezing temperature of the solvent contained in the primary fiber.
14. The method for producing polyacrylonitrile-based carbon fiber according to claim 13, characterized in that, in the step of the drawing treatment: the draft multiple applied to the nascent fiber is 1.2-3 times.
15. The method for producing polyacrylonitrile-based carbon fiber according to claim 14, characterized in that, in the step of the drawing treatment: the draft multiple applied to the nascent fiber is 1.5-2 times.
16. The method for producing polyacrylonitrile-based carbon fiber according to claim 1,
the deviation between the average pore diameter of the polyacrylonitrile-based carbon fiber at the surface layer structure and the average pore diameter of the polyacrylonitrile-based carbon fiber at the core layer structure is within 5%.
17. The method for producing polyacrylonitrile-based carbon fiber according to claim 1,
the pre-oxidation temperature is 185-350 ℃; and/or
The temperature of the low-temperature carbonization treatment is 400-850 ℃; and/or
The temperature of the high-temperature carbonization is 1200-3000 ℃.
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