CN111254521B - Large-diameter high-strength medium-modulus carbon fiber with surface groove structure and preparation method thereof - Google Patents

Large-diameter high-strength medium-modulus carbon fiber with surface groove structure and preparation method thereof Download PDF

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CN111254521B
CN111254521B CN202010174019.3A CN202010174019A CN111254521B CN 111254521 B CN111254521 B CN 111254521B CN 202010174019 A CN202010174019 A CN 202010174019A CN 111254521 B CN111254521 B CN 111254521B
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CN111254521A (en
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王宇
王云峰
徐樑华
王一苇
高爱君
李常清
童元建
赵振文
曹维宇
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Beijing University of Chemical Technology
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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
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/42—Nitriles
    • C08F220/44—Acrylonitrile
    • C08F220/46—Acrylonitrile with carboxylic acids, sulfonic acids or salts thereof
    • 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
    • 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
    • D01D5/253—Formation of filaments, threads, or the like with a non-circular cross section; Spinnerette packs therefor
    • 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
    • D01F6/38—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from copolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds comprising unsaturated nitriles as the major constituent

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Abstract

The invention relates to a large-diameter high-strength medium-modulus carbon fiber with a surface groove structure and a preparation method thereof. The fiber has a surface groove structure, the average diameter is 8.5-11 μm, the strength is 4.9-6.0 GPa, and the modulus is 270-310 GPa. Preparing precursor by adopting a wet spinning technology, controlling the skin-core ratio of pre-oxidized fibers to be more than or equal to 0.85 by regulating the pre-oxidation time ratio of each temperature zone in the pre-oxidation stage, and preparing the large-diameter high-strength medium-modulus carbon fibers with the surface groove structures through low-temperature carbonization and high-temperature carbonization. The prepared large-diameter high-strength medium-mode carbon fiber with the surface groove structure not only improves the collimation of the fiber, but also improves the wettability of resin in the preparation of the composite material, and finally improves the mechanical properties such as compression strength and the like in the application of the composite material.

Description

Large-diameter high-strength medium-modulus carbon fiber with surface groove structure and preparation method thereof
Technical Field
The invention relates to a large-diameter high-strength medium-mode polyacrylonitrile-based carbon fiber with a surface groove structure and a preparation method thereof, belonging to the technical field of fibers.
Background
Polyacrylonitrile (PAN) based carbon fiber is widely used in the fields of aerospace, national defense and military industry, building reinforcement, petrochemical industry, leisure sports and the like due to a series of excellent properties such as light weight, high strength, high modulus and the like, and becomes one of the most influential novel fiber materials in the twenty-first century. Carbon fibers are classified into high-strength types (strength 2000MPa, modulus 250 GPa), high-strength medium-strength models (strength 5300MPa or more and modulus 280GPa or more), high models (modulus 300GPa or more), ultrahigh-strength types (strength greater than 6000MPa), ultrahigh-strength models (modulus greater than 450GPa) and the like according to their mechanical properties such as strength and modulus.
The high-strength medium-modulus carbon fiber is represented by T800-grade carbon fiber due to obvious reinforcing effect, and comprises IM6, IM7, IMS and the like, the fiber diameters of the high-strength medium-modulus carbon fiber and the T800-grade carbon fiber are all 5-6 mu m, the high-strength medium-modulus carbon fiber is mainly used for preparing structural materials, and the prepared composite material becomes an important material in the field of aerospace. The high-strength medium-modulus carbon fiber composite material has very good tensile property, is popular in a plurality of application fields, is used as an important main load-bearing material, and can be used for bearing non-negligible compressive stress in a fiber direction, like an airplane or a rocket body material which bears tensile stress and compressive stress in the steering process of the airplane and a carrier rocket, so that higher and higher requirements on the strength and the compressive strength of the composite material are provided, but the compression strength and the tensile strength of the currently used high-strength medium-modulus carbon fiber are seriously unbalanced.
In practical application, the collimation of the carbon fiber is found to be an important factor influencing the compression performance of the composite material, and the larger the diameter of the carbon fiber is, the better the collimation of the carbon fiber is, which is beneficial to improving the compression strength of the composite material. Meanwhile, the increase of the surface groove structure and the diameter of the carbon fiber is beneficial to improving the resin wettability of the carbon fiber, so that the more easily the tow impregnation is soaked, the higher the forming efficiency is and the higher the compression strength of the composite material is when the carbon fiber is compounded with resin to prepare the composite material. However, the strength of the carbon fiber prepared from the PAN precursor with the surface groove spun by the wet method is difficult to improve compared with the carbon fiber prepared from the PAN precursor with the smooth surface prepared by the dry method and the wet method due to the defect structure of the surface groove, and the problem can be explained by the fact that the ultrahigh-strength carbon fibers sold on the market at present are all prepared from the precursor spun by the dry method and the wet method. Compared with a dry method and a wet method, the difficulty in preparing the large-diameter high-strength medium-mode carbon fiber with the groove structure on the surface is higher. The large-diameter high-strength medium-modulus carbon fiber prepared by adopting the dry-wet method precursor is relatively easy, but the interface performance of the composite material is also reduced due to the smooth surface of the large-diameter high-strength medium-modulus carbon fiber.
The mechanical property of the carbon fiber with the surface groove structure is improved by adopting a diameter reducing method, but the problems of unbalanced tensile-compression ratio of composite materials and the like are also brought, the three are considered, the diameter of the carbon fiber with the surface groove structure is increased on the premise of keeping the performance index of the carbon fiber, and the method is an effective method and has important positive significance on the improvement of the production efficiency of the carbon fiber, the reduction of the production cost and the progress of the carbon fiber preparation technology.
For large-diameter high-strength medium-mode carbon fibers, the patent: CN102766989A discloses a method for preparing a high-strength polyacrylonitrile-based carbon fiber with medium modulus, which comprises the steps of controlling the content of solvent in the fiber step by step in the preparation process of precursor fiber, and effectively drafting the fiber, wherein the properties of the carbon fiber are as follows: 4.2-6.0 GPa, the tensile modulus of 260-310 GPa, and the diameter of the carbon fiber of 4-8 μm; the patent: CN109252251A discloses a large-diameter dry-wet method polyacrylonitrile-based carbon fiber and a preparation method thereof, wherein the method is a dry-jet wet spinning technology and controls the regulation and control of the diameter of a precursor to prepare the large-diameter polyacrylonitrile-based carbon fiber with the carbon fiber performance of 7-20 μm, the tensile strength of 3.8-5.9 GPa and the tensile modulus of 230-300 GPa; the patent: CN109082730A discloses a large-diameter polyacrylonitrile-based carbon fiber and a preparation method thereof, wherein the fiber performance of the large-diameter polyacrylonitrile-based carbon fiber is that the diameter is 10-20 μm, the tensile strength is 3.8-4.6 GPa, and the tensile modulus is 230-260 GPa.
The radial structure difference control technology is one of important technical bottlenecks of large-diameter protofilaments in preparation of high-strength medium-modulus carbon fibers. It has been reported that the radial structural differences of the pre-oxidized fibers are genetic and inherited, and therefore the radial structural differences of the carbon fibers depend to a large extent on the pre-oxidation stage. Many scholars have studied on the radial structure difference regulation and control of polyacrylonitrile pre-oxidized fiber, these regulation and control methods are limited to carbon fiber with diameter less than or equal to 7 μm, and they mostly adopt methods of prolonging pre-oxidation time or impregnating oxidizing solvent, however, the production efficiency is reduced by prolonging time, the process of impregnating oxide is complex and is not beneficial to the improvement of carbon fiber strength. The existing methods for representing the radial structure difference of the pre-oxidized fiber comprise a densitometry and a nano infrared method, and the densitometry is simple, easy to implement and high in efficiency and is favored by researchers.
The pre-oxidation step is generally divided into three stages, wherein the first stage is a preliminary cyclization stage, the second stage is an oxidation stage, and the third stage is an oxidation later stage. The different stages of the gradient pre-oxidation link have different contributions to the pre-oxidation degree of the fiber, and meanwhile, the different contributions of the temperature zones to the increase of the radial structure difference are different. The first stage reaction is relatively mild, contributing less to the increase in the degree of pre-oxidation of the fibers and the increase in radial structural differences, while the second stage is the opposite. The reason for causing the radial structure of the pre-oxidized fiber is generally considered to be that oxygen enters the pre-oxidized fiber to form a layer of compact oxidation film, so that the inward diffusion of the oxygen is prevented, and a skin-core structure is formed, so that an even gradient temperature rise mode is adopted in the pre-oxidized stage, the oxidation reaction is slowly carried out, and the compact oxidation film is prevented from being formed prematurely, thereby aggravating the radial difference. A large number of experimental researches of the subject group find that oxygen molecules are slowly diffused from the fiber skin layer to the core part, and a large number of active structures of the skin layer meet the oxygen molecules, so that the oxygen molecules are quickly captured, the concentration of the oxygen is reduced, the further inward diffusion rate of the oxygen is reduced, and the inward diffusion of the oxygen is even hindered, which is one of main reasons influencing the inward diffusion of the oxygen. The skin oxidative cyclization structure of the fiber is relatively perfect, while the core oxidative cyclization is insufficient. While the bold prolongation of the pre-oxidation time can achieve homogenization of the radial structure of the pre-oxidized fiber, the production efficiency is extremely low. The invention prolongs the pre-oxidation time of the second-stage temperature zone without increasing the total pre-oxidation time, and shortens the pre-oxidation third stage and properly reduces the temperature to avoid excessive pre-oxidation of the fiber. On one hand, the defect that the radial structure difference of the pre-oxidized fiber is large is made up by the lengthened second stage, the negative effect that the pre-oxidation degree is high due to the long reaction time of the second stage is weakened by reducing the temperature of the third stage, the effect of adjusting the radial structure of the pre-oxidized fiber in the pre-oxidation carbonization process of the large-diameter carbon fiber is obvious, the sheath-core ratio of the pre-oxidized fiber can be effectively controlled, and the performance of the obtained carbon fiber is excellent.
The definition and the structural schematic diagram of the sheath-core ratio (Fs) of the pre-oxidized fiber are shown in FIG. 1:
Figure BDA0002410183010000041
disclosure of Invention
The invention relates to a large-diameter high-strength medium-modulus carbon fiber with a surface groove structure and a preparation method thereof. The fiber has a surface groove structure, the average diameter is 8.5-11 μm, the strength is 4.9-6.0 GPa, and the modulus is 270-310 GPa. Preparing precursor by adopting a wet spinning technology, controlling the skin-core ratio of pre-oxidized fibers to be more than or equal to 0.85 by regulating the pre-oxidation time ratio of each temperature zone in the pre-oxidation stage, and preparing the large-diameter high-strength medium-modulus carbon fibers with surface groove structures through low-temperature carbonization and high-temperature carbonization. The prepared large-diameter high-strength medium-mode carbon fiber with surface grooves not only improves the collimation of the fiber, but also improves the wettability of resin in the preparation of the composite material, and finally improves the compression strength in the application of the composite material.
The invention provides a large-diameter high-strength medium-mode carbon fiber with a surface groove structure, wherein the surface of the fiber has the groove structure, the average diameter is 8.5-11 mu m, the strength is 4.9-6.0 GPa, and the modulus is 270-310 GPa.
The cross section of the fiber is round or nearly round, and the bulk density is 1.76g/cm3～1.81g/cm3。
The invention also provides a preparation method of the large-diameter high-strength medium-modulus carbon fiber with the surface groove structure, which comprises the following steps: the wet spinning is adopted to prepare protofilament, and the protofilament is pre-oxidized, carbonized at low temperature and carbonized at high temperature, and is characterized in that: and controlling the sheath-core ratio of the pre-oxidized fiber to be more than or equal to 0.85 by regulating and controlling the pre-oxidation time ratio of each temperature zone in the pre-oxidation stage.
The temperature zones are divided into 3, and the pre-oxidation time ratio is as follows: (1-3): (4-8): (1-3).
The pre-oxidation is carried out in an air atmosphere by adopting gradient temperature rise, wherein the initial temperature is 225-235 ℃, the intermediate temperature is 240-245 ℃, the final temperature is 250-265 ℃, the total drafting multiplying power is 1.0-1.2 times, and the total time of pre-oxidation treatment is 60-120 minutes.
The low-temperature carbonization is protected by high-purity nitrogen, the oxygen content in the nitrogen is lower than 5PPm, the low-temperature carbonization temperature is 450-850 ℃, the time is 0.5-5 minutes, and the drawing multiplying power is 1.02-1.07 times.
The high-temperature carbonization is protected by high-purity nitrogen, the oxygen content in the nitrogen is lower than 1PPm, the high-temperature carbonization temperature is 1500-1700 ℃, the time is 0.5-3 minutes, and the relative drafting multiplying power is 0.95-0.995 times.
The wet spinning protofilament preparation method comprises the following steps of preparation of a spinning solution, multistage solidification and forming, primary steam drafting, multistage washing, oiling, drying densification, secondary superheated steam drafting and heat setting, the prepared protofilament has a surface groove structure, the diameter is controlled to be 13-17 mu m, the linear density of 1K protofilament is 0.15-0.27 g/m, and the specific steps are as follows:
(1) preparation of the spinning dope
Taking azodiisobutyronitrile as an initiator and dimethyl sulfoxide as a solvent, and mixing acrylonitrile, itaconic acid and methyl acrylate according to the weight ratio of (93-99): (0.5-2.0): (0.0-5.0) and adding the mixture into a polymerization reaction container, wherein the total parts by mole of the substances are 100, the polymerization reaction is carried out for 10-40 hours at the temperature of 50-75 ℃ to obtain a spinning stock solution, and the spinning stock solution is subjected to demonomerization and deaeration to obtain a spinning solution, wherein dimethyl sulfoxide accounts for 75-80% of the mass concentration of the monomers and the dimethyl sulfoxide, azodiisobutyronitrile accounts for 0.1-0.3% of the mole fraction of acrylonitrile, and the viscosity of the spinning stock solution is controlled to be 4500-10000 poise;
(2) multistage coagulation molding of spinning dope
Wet spinning is adopted, the fiber enters a first-stage coagulation bath after leaving a spinneret orifice, the temperature of the first coagulation bath is 10-50 ℃, the coagulation bath adopts a dimethyl sulfoxide aqueous solution, wherein the volume content of a dimethyl sulfoxide solvent is 50-80%, the coagulation time is 0.5-3 minutes, and the coagulation drafting multiplying power is-0.5-3.0; the coagulated strands enter a second coagulation bath after leaving the first coagulation bath, the temperature of the second coagulation bath is 10-50 ℃, the coagulation bath adopts a dimethyl sulfoxide aqueous solution, wherein the volume content of a dimethyl sulfoxide solvent is 30-50%, the coagulation time is 0.5-3 minutes, and the coagulation drafting multiplying power is 1.0-2.0; the coagulated strands enter a third coagulation bath after exiting from the second coagulation bath, the temperature of the third coagulation bath is 10-50 ℃, the coagulation bath adopts a dimethyl sulfoxide aqueous solution, wherein the volume content of a dimethyl sulfoxide solvent is 0-30%, the coagulation time is 0.5-3 minutes, and the coagulation drafting multiplying power is 1.0-3.0;
(3) preparation of the precursor
The solidified fiber is subjected to primary drawing, water washing, oiling, drying densification, superheated steam secondary drawing and heat setting by using a drawing medium of steam with the temperature of 100-110 ℃ to prepare protofilaments. Controlling the primary drafting multiplying power to be 3-10 times, washing the fiber after primary drafting in multiple stages with water, controlling the drafting to be 0.95-1.05 during washing, oiling after washing, and performing multi-stage drying densification treatment at 100-150 ℃, controlling the drafting multiplying power to be 0.95-1.05 during drying densification, performing secondary drafting by superheated steam on the fiber after drying densification, controlling the temperature of the superheated steam to be 120-160 ℃, and controlling the drafting multiplying power to be 1.5-3 times; and (3) performing heat setting on the fiber obtained after the secondary drafting at the temperature of 140-180 ℃ and under the condition that the drafting magnification is 0.9-1.1 times to obtain the precursor.
Advantages and effects of the invention
The large-diameter high-strength medium-modulus carbon fiber prepared by the invention has a surface groove structure, the diameter is 8.5-11 mu m, the tensile strength is 4.9-6.0 GPa, and the tensile modulus is 270-310 GPa. Compared with the prior art, the method adopts wet spinning to prepare the precursor without reducing the production efficiency, and prepares the large-diameter high-strength medium-modulus carbon fiber with the surface groove structure through pre-oxidation, low-temperature carbonization and high-temperature carbonization. On the premise of keeping the mechanical property index of the carbon fiber unchanged or even improving the mechanical property index of the carbon fiber, the diameter of the carbon fiber with the surface groove structure is improved, the collimation of the fiber is greatly improved due to the increase of the diameter, the wettability of the fiber and resin is improved due to the surface groove structure, when the carbon fiber is compounded with the resin to prepare a composite material, the impregnation of a filament bundle is easier to soak, the forming efficiency is higher, and the compression strength of the composite material is finally improved.
According to the method, the sheath-core ratio of the pre-oxidized fiber is effectively controlled to be more than or equal to 0.85 by regulating the pre-oxidation process which is crucial to influence the radial structure difference of the carbon fiber in the carbon fiber production process, and the radial structure difference of the pre-oxidized fiber is reduced. The method regulates the sheath-core ratio of the pre-oxidized fiber by regulating the pre-oxidation time ratio of each temperature zone in the pre-oxidation stage, and is simple and high in feasibility.
The composite material prepared by the large-diameter high-strength medium-modulus carbon fiber with the surface groove structure has the compression strength and the tensile strength of 2200-2700 MPa and 2500-3000 MPa respectively, and the compression-tension ratio is 88.9%.
Drawings
FIG. 1 is a schematic cross-sectional view of a radial structure of a pre-oxidized fiber
FIG. 2 optical microscope photograph of radial cross section of pre-oxidized fiber in example 1
FIG. 3 optical microscope photograph of radial cross section of comparative example 1 pre-oxidized fiber
FIG. 4 optical microscope photograph of radial cross section of pre-oxidized fiber in example 2
FIG. 5 optical microscope photograph of radial cross section of pre-oxidized fiber in example 3
Detailed Description
The present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.
Example 1
(1) Preparation of spinning dope
Taking azobisisobutyronitrile as an initiator and dimethyl sulfoxide as a solvent, and mixing acrylonitrile, itaconic acid and methyl acrylate according to a weight ratio of 98.5: 0.5: 1, the mixture is added into a polymerization reaction vessel, the polymerization reaction temperature is 63 ℃, the polymerization reaction time is 25 hours, the stirring speed is 40rpm, a spinning solution is prepared, the spinning solution is demonomerized and defoamed to obtain a spinning solution, an acrylonitrile copolymer with the polymer molecular weight of 12.5 ten thousand is obtained, wherein, the dimethyl sulfoxide accounts for 78% of the mass percentage concentration weight of the acrylonitrile and the dimethyl sulfoxide, the azobisisobutyronitrile accounts for 0.25% of the mole fraction of the acrylonitrile, and the viscosity of the spinning solution measured by a rotational viscometer at 25 ℃ is 5600 poise.
(2) Coagulation forming of spinning dope
Adopting a spinneret plate with the aperture of 0.10mm, enabling the fiber to enter a first coagulation bath after leaving the spinneret hole, wherein the temperature of the first coagulation bath is 30 ℃, the coagulation bath adopts a dimethyl sulfoxide aqueous solution, the volume content of the dimethyl sulfoxide is 75%, the coagulation time is 2 minutes, and the coagulation drafting multiplying power is-0.4; the coagulated filaments enter a second coagulation bath after leaving the first coagulation bath, the temperature of the second coagulation bath is 30 ℃, the coagulation bath adopts a dimethyl sulfoxide aqueous solution, wherein the volume content of a dimethyl sulfoxide solvent is 50%, the coagulation time is 2 minutes, and the coagulation drawing ratio is 1.0; and (3) enabling the coagulated filaments to enter a third coagulation bath after exiting from the second coagulation bath, wherein the temperature of the third coagulation bath is 25 ℃, the coagulation bath adopts a dimethyl sulfoxide water solution, the volume content of a dimethyl sulfoxide solvent is 20%, the coagulation time is 2 minutes, and the coagulation drawing ratio is 1.2.
(3) Preparation of the precursor
And (3) carrying out primary drawing, washing, oiling, drying densification, secondary drawing of superheated steam and heat setting on the solidified fiber to obtain the precursor. The solidified fiber is subjected to primary drafting under the conditions that the drafting medium is 100 ℃ water vapor and the drafting multiplying factor is 5 times, the fiber subjected to primary drafting is subjected to multistage water washing by water vapor, the drafting multiplying factor is controlled to be 0.99 by water washing, silicone oil is added after residual dimethyl sulfoxide is removed by water washing, drying densification multistage treatment is carried out by a hot roller, the drying densification temperature is 120 ℃, the drying densification drafting multiplying factor is 0.98, the fiber subjected to drying densification is subjected to secondary drafting by superheated water vapor at 140 ℃, and the drafting multiplying factor is 2.0 times. And (3) performing heat setting on the fiber obtained after the secondary drafting at the temperature of 155 ℃ under the condition that the drafting multiplying power is 1.0. And (3) spooling the fiber after heat setting by using a winder, and controlling the total drafting multiplying power to be 10 times in the whole process to obtain the PAN precursor with a compact and uniform structure and a surface groove structure, wherein the diameter of the PAN precursor is 17 mu m, and the linear density of the 1K precursor is 0.26 g/m.
(4) Preoxidation
Performing thermal stabilization and pre-oxidation treatment on the PAN precursor obtained in the step (3) in a pre-oxidation furnace, wherein the initial speed of filament running is 20m/h, a gradual heating method is adopted, the PAN precursor is divided into 3 temperature zones, the temperature is 230 ℃, 245 ℃ and 265 ℃, the drafting multiplying power is 1.05 times, the total time of the pre-oxidation treatment is 120 minutes, and the time distribution of the three temperature zones is as follows: 1:6:1. The obtained pre-oxidized fiber has a sheath-core ratio of 0.86, as shown in FIG. 2
(5) Low temperature carbonization
And (3) introducing the PAN pre-oxidized fiber obtained in the step (4) into a low-carbon furnace in a high-purity nitrogen environment atmosphere for low-temperature carbonization treatment, wherein the oxygen content in nitrogen is 5PPm, the temperature is 650 ℃, the retention time is 2 minutes, and the drawing multiplying power is 1.05 times.
(6) High temperature carbonization
And (3) putting the PAN low-carbon fiber obtained in the step (5) into a high-carbon furnace in a high-purity nitrogen environment atmosphere for high-temperature carbonization treatment, wherein the oxygen content in nitrogen is 1PPm, the temperature is 1600 ℃, the retention time is 2 minutes, and the drafting multiplying power is 0.97 times, so that the large-diameter high-strength medium-mode carbon fiber with a surface groove structure is obtained. The prepared carbon fiber and unidirectional carbon fiber composite material is subjected to performance tests (the same below) by adopting GB3362-3366-82, GB T3354-: fiber section circular or near circular, strength 5.60GPa, modulus 294GPa, fiber diameter 11 μm, bulk density: 1.79g/cm3The compressive strength and the tensile strength of the unidirectional composite material are respectively as follows: 2650MPa and 2850MPa, and the compression-tension ratio is: 93 percent.
Comparative example 1
(1) Preparation of spinning dope
Same as example 1
(2) Multistage coagulation molding of spinning dope
Same as example 1
(3) Preparation of precursor
Same as example 1
(4) Preoxidation
Carrying out thermal stabilization and pre-oxidation treatment on the PAN precursor (the diameter of which is 17 mu m) obtained in the step (3) in a pre-oxidation furnace, wherein the filament running initial speed is 20m/h, the PAN precursor is divided into 6 temperature zones by adopting a gradual heating method, the temperature is respectively 200 ℃, 222 ℃, 238 ℃, 245 ℃, 255 ℃ and 260 ℃, the drafting ratio is 1.05 times, the total time of the pre-oxidation treatment is 120 minutes, and the time distribution proportion of the six temperature zones is as follows: 1:2:2:2:2:1. The sheath-core ratio for the pre-oxidized fiber was 0.81 as shown in FIG. 2
(5) Low temperature carbonization
And (3) introducing the PAN pre-oxidized fiber obtained in the step (4) into a low-carbon furnace in a high-purity nitrogen environment atmosphere for low-temperature carbonization treatment, wherein the oxygen content in nitrogen is 5PPm, the temperature is 650 ℃, the retention time is 2 minutes, and the drawing multiplying power is 1.05 times.
(6) High temperature carbonization
And (3) putting the PAN low-carbon fiber obtained in the step (5) into a high-carbon furnace in a high-purity nitrogen environment atmosphere for high-temperature carbonization treatment, wherein the oxygen content in nitrogen is 1PPm, the temperature is 1600 ℃, the retention time is 2 minutes, and the drafting multiplying power is 0.99 times, so that the large-diameter carbon fiber with the surface groove structure is prepared.
The properties of the obtained carbon fiber and the unidirectional composite material are as follows: fiber cross section near circular, strength 4.60GPa, modulus 245GPa, fiber diameter 11 μm, bulk density: 1.77g/cm3The compressive strength and the tensile strength of the unidirectional composite material are respectively as follows: 1650MPa and 1890 MPa.
Compared with the comparative example 1, the tensile strength of the carbon fiber of the example 1 is improved by 21.7%, the tensile modulus is improved by 20%, and the compressive strength and the tensile strength of the composite material are respectively improved by 60.1% and 50.8%.
Example 2
(1) Preparation of the dope As in example 1
(2) Coagulation forming of spinning dope
Adopting a spinneret plate with the aperture of 0.075mm, enabling the fiber to enter a first coagulation bath after leaving a spinneret orifice, wherein the temperature of the first coagulation bath is 25 ℃, the coagulation bath adopts a dimethyl sulfoxide aqueous solution, the volume content of a dimethyl sulfoxide solvent is 74%, the coagulation time is 2.5 minutes, and the coagulation drafting multiplying power is-0.35; the coagulated filaments enter a second coagulation bath after leaving the first coagulation bath, the temperature of the second coagulation bath is 25 ℃, the coagulation bath adopts dimethyl sulfoxide water solution, wherein the volume content of dimethyl sulfoxide solvent is 50%, the coagulation time is 2 minutes, and the coagulation drawing multiplying power is 1.0; and (3) enabling the coagulated filaments to enter a third coagulation bath after exiting from the second coagulation bath, wherein the temperature of the third coagulation bath is 20 ℃, the coagulation bath adopts a dimethyl sulfoxide aqueous solution, the volume content of a dimethyl sulfoxide solvent is 20%, the coagulation time is 2 minutes, and the coagulation drawing ratio is 1.0.
(3) The raw yarn was produced in the same manner as in example 1 except that the total draft number in one-drawing and two-drawing was controlled to 13 times, and raw yarn having a diameter of 13.5 μm and a linear density of 1K raw yarn was 0.17 g/m.
(4) Preoxidation
And (3) carrying out thermal stabilization and pre-oxidation treatment on the PAN precursor obtained in the step (3) in a pre-oxidation furnace, wherein the initial speed of filament running is 20m/h, a gradual heating method is adopted, the PAN precursor is divided into 3 temperature zones, the temperature is 230 ℃, 240 ℃ and 260 ℃, the drafting ratio is 1.05 times, the total time of the pre-oxidation treatment is 90 minutes, and the time distribution of the three temperature zones is 1:8: 1. The sheath-core ratio of the prepared pre-oxidized fiber was 0.90, as shown in FIG. 4
(5) Examples (6) to (6) are the same as example 1.
The prepared fiber and the unidirectional composite material have the following properties: fiber cross section near circular, strength 5.91GPa, modulus 310GPa, fiber diameter 8.6 μm, bulk density: 1.79g/cm3The compressive strength and the tensile strength of the unidirectional composite material are respectively as follows: 2240MPa and 2900MPa, and the compression-tension ratio is: 77.2 percent. .
Example 3
(1) Preparation of spinning dope
Taking azobisisobutyronitrile as an initiator and dimethyl sulfoxide as a solvent, and mixing acrylonitrile, itaconic acid and methyl acrylate according to a weight ratio of 98.5: 0.5: 1, the mixture is added into a polymerization reaction vessel, the polymerization reaction temperature is 65 ℃, the polymerization reaction time is 23 hours, the stirring speed is 40rpm, a spinning solution is prepared, the spinning solution is demonomerized and defoamed to obtain a spinning solution, an acrylonitrile copolymer with the polymer molecular weight of 11 ten thousand is obtained, wherein, the mass percentage concentration weight of dimethyl sulfoxide is 79 percent of that of acrylonitrile and dimethyl sulfoxide, the molar fraction of azobisisobutyronitrile is 0.25 percent of that of acrylonitrile, and the viscosity of the spinning solution measured by rotational viscosity at 25 ℃ is controlled at 4800 poise.
(2) Coagulation forming of spinning dope
Adopting a spinneret plate with the aperture of 0.10mm, enabling the fiber to enter a first coagulation bath after leaving the spinneret hole, wherein the temperature of the first coagulation bath is 25 ℃, the coagulation bath adopts a dimethyl sulfoxide aqueous solution, the volume content of a dimethyl sulfoxide solvent is 75%, the coagulation time is 2.5 minutes, and the coagulation drafting multiplying power is-0.37; the coagulated filaments enter a second coagulation bath after leaving the first coagulation bath, the temperature of the second coagulation bath is 25 ℃, the coagulation bath adopts dimethyl sulfoxide water solution, wherein the volume content of dimethyl sulfoxide solvent is 50%, the coagulation time is 2 minutes, and the coagulation drawing multiplying power is 1.0; and (3) enabling the coagulated filaments to enter a third coagulation bath after exiting from the second coagulation bath, wherein the temperature of the third coagulation bath is 20 ℃, the coagulation bath adopts a dimethyl sulfoxide aqueous solution, the volume content of a dimethyl sulfoxide solvent is 20%, the coagulation time is 2 minutes, and the coagulation drawing ratio is 1.05.
(3) Preparation process of raw yarn
As in example 1, except that the total draft number of one draw and two draws was controlled to be 9.5 times, a strand having a diameter of 15 μm was produced, and the linear density of the 1K strand was 0.21 g/m.
(4) Preoxidation
And (3) carrying out thermal stabilization and pre-oxidation treatment on the PAN precursor (the diameter of which is 15 mu m) obtained in the step (3) in a pre-oxidation furnace, wherein the filament moving initial speed is 20m/h, a gradual heating method is adopted, the filament moving initial speed is divided into 3 temperature zones, the temperature is respectively 235 ℃, 245 ℃ and 260 ℃, the drawing magnification is 1.05 times, the total time of the pre-oxidation treatment is 120 minutes, and the time ratio of the three temperature zones is 3:6: 1. The sheath-core ratio for the pre-oxidized fiber was 0.88, as shown in FIG. 4
(5) EXAMPLES (6) As in example 1
The properties of the large-diameter high-strength medium-model carbon fiber and the unidirectional composite material thereof are as follows: fiber cross section: round or near round, strength 5.73GPa, modulus 298GPa, fiber diameter 9.4 μm, bulk density: 1.80g/cm3The compressive strength and the tensile strength of the unidirectional composite material are respectively as follows: 2500MPa and 2930MPa, and the compression-tension ratio is: 85.3 percent.

Claims (6)

1. A preparation method of large-diameter high-strength medium-modulus carbon fiber with a surface groove structure comprises the following steps: the large-diameter protofilament is prepared by wet spinning, and is prepared by pre-oxidation, low-temperature carbonization and high-temperature carbonization, and is characterized in that: the pre-oxidation is carried out in an air atmosphere by adopting gradient temperature rise, the total time of pre-oxidation treatment is 60-120 minutes, the gradient temperature rise is carried out for 3 temperature zones, and the ratio of the pre-oxidation time of the 3 temperature zones is as follows: (1-3): (4-8): (1-3), the initial temperature is 225-235 ℃, the intermediate temperature is 240-245 ℃, the final temperature is 250-265 ℃, the total drafting multiplying power is 1.0-1.2 times, and the sheath-core ratio of the pre-oxidized fiber is controlled to be more than or equal to 0.85; the low-temperature carbonization time is 0.5-5 minutes, and the drafting multiplying power is 1.02-1.07 times; the high-temperature carbonization time is 0.5-3 minutes, and the drafting multiplying power is 0.95-0.995 times.
2. The method of claim 1, wherein: the low-temperature carbonization temperature is 450-850 ℃.
3. The method of claim 1, wherein: the high-temperature carbonization is protected by high-purity nitrogen, and the high-temperature carbonization temperature is 1500-1700 ℃.
4. The method of claim 1, wherein: the wet spinning preparation of the precursor comprises the steps of preparation of spinning solution, multistage solidification and forming, primary drawing, multistage washing, oiling, drying and densification, secondary gas drawing and heat setting, and the prepared precursor has a groove structure on the surface and the diameter is controlled to be 13-17 mu m.
5. A large-diameter high-strength medium-modulus carbon fiber having a surface groove structure prepared by any one of the preparation methods according to claims 1 to 4, characterized in that: the fiber surface has a groove structure, the average diameter is 8.5-11 μm, the strength is 5.6-6.0 GPa, and the modulus is 294-310 GPa.
6. The carbon fiber according to claim 5, characterized in that: the cross-section of the fiber is circular or near circular.
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