阅读说明：本技术 一种炭纸专用的聚丙烯腈基碳纤维原丝及其制备方法 (Special polyacrylonitrile-based carbon fiber precursor for carbon paper and preparation method thereof ) 是由 敖玉辉 尚垒 宁臣 金琳 杜巍峰 刘宇 马岩 李红龙 于 2021-11-19 设计创作，主要内容包括：本发明提供一种炭纸专用的聚丙烯腈碳纤维原丝及其制备方法,属于有机高分子材料领域。该方法包括：以水为溶剂,过硫酸铵-亚硫酸铵或过硫酸铵-亚硫酸氢铵为氧化还原引发剂,第一单体为丙烯腈、第二单体为衣康酸,第三单体为具有大侧基的乙烯类不饱和酯,在50～60℃下进行反应8～14h,得到PAN聚合物粉末；将得到的PAN聚合物粉末配制成淤浆,得到纺丝原液；设置凝固浴温度为30～60℃,凝固浴牵伸倍数-30％～-5％；采用两段热水牵伸,致密化温度逐级升高,然后进行蒸汽牵伸,最后得到炭纸专用聚丙烯腈基碳纤维原丝。本发明的碳纤维原丝经碳化后,碳含量≥95.6％,电阻率≤1.6mΩ·cm,满足燃料电池扩散层用炭纸的技术指标。(The invention provides polyacrylonitrile carbon fiber precursor special for carbon paper and a preparation method thereof, belonging to the field of organic polymer materials. The method comprises the following steps: taking water as a solvent, ammonium persulfate-ammonium sulfite or ammonium persulfate-ammonium bisulfite as a redox initiator, a first monomer being acrylonitrile, a second monomer being itaconic acid, and a third monomer being ethylene unsaturated ester with a large side group, and reacting at 50-60 ℃ for 8-14 h to obtain PAN polymer powder; preparing the obtained PAN polymer powder into slurry to obtain spinning solution; setting the temperature of a coagulation bath at 30-60 ℃ and the drafting multiple of the coagulation bath to be-30% -5%; and (3) adopting two-stage hot water drafting, gradually increasing the densification temperature, and then carrying out steam drafting to obtain the polyacrylonitrile-based carbon fiber precursor special for carbon paper. After the carbon fiber precursor is carbonized, the carbon content is more than or equal to 95.6 percent, the resistivity is less than or equal to 1.6m omega cm, and the technical indexes of the carbon paper for the diffusion layer of the fuel cell are met.)

1. A preparation method of polyacrylonitrile-based carbon fiber precursor special for carbon paper is characterized by comprising the following steps:

(1) taking water as a solvent, ammonium persulfate-ammonium sulfite or ammonium persulfate-ammonium bisulfite as a redox initiator, a first monomer being acrylonitrile, a second monomer being itaconic acid, and a third monomer being ethylene unsaturated ester with a large side group, and reacting at 50-60 ℃ for 8-14 h to obtain PAN polymer powder;

(2) mixing the PAN polymer powder obtained in the step (1) with a reaction solvent at-18-0 ℃ to prepare a slurry, vacuumizing to 45-90 KPa, and dissolving at 40-55 ℃ for 1-2 hours to obtain a spinning solution; setting the temperature of a coagulation bath at 30-60 ℃ and the drafting multiple of the coagulation bath to be-30% -5%; two sections of hot water are adopted for drafting, and the drafting times are respectively 2.0 and 1.0-5.0; the densification temperature is gradually increased, the temperature range is 100-170 ℃, and the time is gradually prolonged; and then carrying out steam drafting, and finally oiling, sizing and drying the fibers to obtain the polyacrylonitrile-based carbon fiber precursor special for the carbon paper.

2. The preparation method of the polyacrylonitrile-based carbon fiber precursor special for carbon paper as claimed in claim 1, wherein the mass ratio of the acrylonitrile to the itaconic acid to the ethylene unsaturated ester with the large side group is 95-98: 3-1.5: 2-0.5; the total concentration of acrylonitrile, itaconic acid, ethylene unsaturated ester with large side group and water is 18-28 wt%.

3. The preparation method of the polyacrylonitrile-based carbon fiber precursor special for carbon paper as claimed in claim 1, wherein the mass ratio of ammonium persulfate to ammonium sulfite or ammonium bisulfite is 0.1-1: 0.1-0.75;

the mass ratio of the redox initiator to the acrylonitrile is 10-50: 0.1-1.0.

4. The method for preparing polyacrylonitrile-based carbon fiber precursor for carbon paper according to claim 1, wherein the ethylenically unsaturated ester with large side group in step (1) is ethyl methacrylate, n-butyl methacrylate or isobutyl methacrylate.

5. The method for preparing the polyacrylonitrile-based carbon fiber precursor special for carbon paper as claimed in claim 1, wherein the molecular mass of the PAN polymer prepared in the step (1) is 26.2-45.6 ten thousand, and the isotactic ratio of the PAN polymer is 27.4-28%.

6. The method for preparing polyacrylonitrile-based carbon fiber precursor for carbon paper according to claim 1, wherein the reaction solvent in step (2) is DMAC.

7. The preparation method of the polyacrylonitrile-based carbon fiber precursor special for carbon paper as claimed in claim 1, wherein the densification temperature in the step (2) is increased in four stages, the range is 100-170 ℃, and the time is gradually prolonged to 50-70 s.

8. The preparation method of the polyacrylonitrile-based carbon fiber precursor for carbon paper as claimed in claim 7, wherein the four-stage stepwise increase is set as a first-stage temperature of 100-.

9. The method for preparing the polyacrylonitrile-based carbon fiber precursor special for carbon paper according to claim 1, wherein the steam drafting in the step (2) is carried out in two stages, the first stage is a pre-drafting zone, and the second stage is a heating drafting zone; the steam pressure of the second section is 0.2-0.4 mPa higher than that of the first section.

10. The polyacrylonitrile-based carbon fiber precursor special for carbon paper obtained by the preparation method of claim 1 is characterized in that the orientation degree of the carbon fiber precursor is controlled to be 86-89%, the crystallinity is 66-72%, and the precursor strength is 4.72-6.82 CN/dtex.

Technical Field

The invention belongs to the field of organic polymer materials, and particularly relates to polyacrylonitrile-based carbon fiber precursor special for carbon paper and a preparation method thereof.

Background

The carbon paper market for fuel cells and the key raw materials of the carbon paper are monopolized by Dongli companies and West Glry companies all the time, polyacrylonitrile-based carbon fiber (PANCF) belongs to a novel high-performance fiber material, has the excellent performances of low density, high temperature resistance, chemical corrosion resistance, thermal shock resistance, electric conduction, heat conduction and the like, is widely used in the field of carbon paper manufacture at abroad, does not have carbon fiber products of special carbon paper brands at home till now, and the technical blockade of the carbon fiber special for the carbon paper becomes one of the main problems restricting the development of the carbon paper and even the fuel cells in China.

The high-performance PAN-based carbon fiber is mainly obtained by carbonizing PAN-based carbon fiber precursors, high-quality PAN precursors are necessary conditions for manufacturing the high-performance carbon fiber, solution polymerization is homogeneous polymerization reaction, the polymerization solution can be directly spun without separation, the process is simple and easy to operate, a single azo initiator is usually adopted in an initiating system, and commonly used solvents mainly comprise DMSO, DMF, DMAc, NaSCN water solution and the like. Aqueous suspension polymerization is a heterogeneous polymerization. The polymerization medium is water, chain transfer cannot occur, the reaction viscosity in the system is low, the heat exchange rate is high, the reaction temperature is easy to control, and the polymer has the advantages of controllable molecular weight and narrower molecular weight distribution; meanwhile, the method has the advantages of less impurities and high purity, and the influence of micromolecule residues on the performances of the precursor and the carbon fiber is avoided. At present, the polyacrylonitrile precursor for domestic carbon fiber production mostly adopts wet spinning, namely, PAN copolymer with a certain molecular weight is formed into spinning solution in solvents such as dimethylformamide, dimethyl sulfoxide, nitric acid or sodium thiocyanate and the like at a special temperature and in a special atmosphere, then the spinning solution is directly sprayed into solidification bath liquid through holes of a spinneret plate, and then the spinning solution is subjected to drawing, water washing, oiling, drying, densification, steam drawing and steam shaping and then filament winding to obtain the polyacrylonitrile precursor, wherein the final performance of the carbon fiber is influenced by the orientation degree and the crystallinity degree of the precursor.

At present, the cost of the domestic universal carbon fiber is higher, the large-scale production technology of the T300-level 25K large-tow carbon fiber is taken as a basis, a polymerization system-microstructure-production process is taken as a main line, the high-performance carbon fiber suitable for the special diffusion layer carbon paper is researched and developed, and the 25K large-tow carbon fiber Polyacrylonitrile (PAN) precursor and protofilament suitable for the carbon paper are prepared through the polymerization system optimization and the correlation research of rheological/crystallization behaviors of spinning stock solution in the water-phase suspension polymerization-wet spinning process.

Disclosure of Invention

The invention aims to provide a polyacrylonitrile-based carbon fiber precursor special for carbon paper and a preparation method thereof, which are characterized in that a low-cost carbon fiber precursor manufacturing technology is adopted to prepare a carbon fiber precursor with high orientation degree and high crystallinity, the cost of carbonized carbon fibers is low, the carbon content is more than or equal to 95.6 percent, the resistivity is less than or equal to 1.6m omega cm, and the prepared carbon paper has the vertical resistivity of less than or equal to 65m omega cm, the parallel resistivity of less than or equal to 4m omega cm and the contact resistance of less than or equal to 5m omega cm by a three-step short-flow production process of' wet paper forming, bonding, crosslinking and graphitizing²。

The invention provides a preparation method of polyacrylonitrile-based carbon fiber precursor special for carbon paper, which comprises the following steps:

(1) taking water as a solvent, ammonium persulfate-ammonium sulfite or ammonium persulfate-ammonium bisulfite as a redox initiator, a first monomer being acrylonitrile, a second monomer being itaconic acid, and a third monomer being ethylene unsaturated ester with a large side group, and reacting at 50-60 ℃ for 8-14 h to obtain PAN polymer powder;

(2) mixing the PAN polymer powder obtained in the step (1) with a reaction solvent at-18-0 ℃ to prepare a slurry, vacuumizing to 45-90 KPa, and dissolving at 40-55 ℃ for 1-2 hours to obtain a spinning solution; setting the temperature of a coagulation bath at 30-60 ℃ and the drafting multiple of the coagulation bath to be-30% -5%; two sections of hot water are adopted for drafting, and the drafting times are respectively 2.0 and 1.0-5.0; the densification temperature is gradually increased, the temperature range is 100-170 ℃, and the time is gradually prolonged; and then carrying out steam drafting, and finally oiling, sizing and drying the fibers to obtain the polyacrylonitrile-based carbon fiber precursor special for the carbon paper.

Preferably, the mass ratio of the acrylonitrile to the itaconic acid to the vinyl unsaturated ester with a large side group is 95-98: 3-1.5: 2-0.5; the total concentration of acrylonitrile, itaconic acid, ethylene unsaturated ester with large side group and water is 18-28 wt%;

preferably, the mass ratio of the ammonium persulfate to the ammonium sulfite or the ammonium bisulfite is 0.1-1: 0.1-0.75;

the mass ratio of the redox initiator to the acrylonitrile is 10-50: 0.1-1.0.

Preferably, the ethylenically unsaturated ester having a large pendant group in step (1) is Ethyl Methacrylate (EMA), n-Butyl Methacrylate (BMA) or isobutyl methacrylate (i-BMA).

Preferably, the molecular mass of the PAN polymer prepared in the step (1) is 26.2 to 45.6 ten thousand, and the isotactic ratio of the PAN polymer is 27.4 to 28%.

Preferably, the reaction solvent of step (2) is DMAC.

Preferably, the densification temperature in the step (2) is increased in four stages, the range is 100-170 ℃, and the time is gradually prolonged to 50-70 s.

Preferably, the four-stage gradual increase is set as the first-stage temperature of 100-.

Preferably, the steam drafting in the step (2) is carried out in two sections, wherein the first section is a pre-drafting zone, and the second section is a heating drafting zone; the steam pressure of the second section is 0.2-0.4 mPa higher than that of the first section.

The invention also provides the polyacrylonitrile-based carbon fiber precursor special for carbon paper, which is prepared by the preparation method, wherein the orientation degree of the carbon fiber precursor is controlled to be 86-89%, the crystallinity is 66-72%, and the strength of the precursor is 4.72-6.82 CN/dtex.

Compared with the prior art, the invention has the beneficial effects that:

1. according to the invention, the low concentration of the polymerization solvent and the initiator is adopted, so that the concentration of chain free radicals is increased at the later stage of aqueous suspension polymerization reaction, the diffusion movement of the chain free radicals is hindered, the meeting probability of the two chain free radicals is reduced, the connection termination probability is reduced, and the automatic acceleration phenomenon is promoted, so that the polymer with the large average molecular weight is prepared, and the preparation of the carbon fiber precursor with the large orientation degree and the large crystallinity is facilitated.

2. The method adopts low polymerization reaction temperature, promotes the head-to-tail bonding mode in the reaction to occupy absolute advantages, is favorable for increasing the proportion of isotactic stereoregular molecular chain segment structures, improves the orientation degree and the crystallinity of protofilaments, and promotes the preoxidation cyclization reaction to be more complete.

3. The coagulating bath solvent content and the drafting ratio adopted in the method are beneficial to improving the polyacrylonitrile content, have more crystal nuclei, easily form a compact three-dimensional network structure and improve the preorientation and crystallization of the polyacrylonitrile.

4. According to the invention, through hot water drafting, drying densification and steam drafting segmentation treatment on the nascent fiber, the synchronous improvement of the crystal region orientation and the molecular chain orientation is realized along with the gradual increase of the drafting multiple. High crystallinity and crystal orientation can be obtained in the later carbonization process, the internal defects of the fiber are reduced, the skin-core structure is reduced, and the carbon fiber with high carbon content and low resistivity is obtained.

5. The carbon fiber prepared by the method has low cost after carbonization, the carbon content is more than or equal to 95.6 percent, the resistivity is less than or equal to 1.6m omega cm, and the prepared carbon paper has the vertical resistivity less than or equal to 65m omega by the three-step short-flow production process of' wet paper making-bonding crosslinking-graphitizationCm, a resistivity in the parallel direction of not more than 4m omega cm, and a contact resistance of not more than 5m omega cm²And the technical index of the carbon paper for the diffusion layer of the fuel cell is met.

Drawings

FIG. 1 is a graph showing the measurement of the degree of orientation of polyacrylonitrile-based carbon fiber strands prepared in examples 2 and 7;

fig. 2 is a graph showing the crystallinity measurement of polyacrylonitrile-based carbon fiber strands prepared in examples 2 and 7.

Detailed Description

The invention provides a preparation method of polyacrylonitrile-based carbon fiber precursor special for carbon paper, which comprises the following steps:

(1) taking water as a solvent, ammonium persulfate-ammonium sulfite or ammonium persulfate-ammonium bisulfite as a redox initiator, a first monomer being acrylonitrile, a second monomer being itaconic acid, and a third monomer being ethylene unsaturated ester with a large side group, and reacting at 50-60 ℃ for 8-14 h to obtain PAN polymer powder;

the mass ratio of the acrylonitrile to the itaconic acid to the vinyl unsaturated ester with the large side group is preferably 95-98: 3-1.5: 2-0.5; the total concentration of acrylonitrile, itaconic acid, large-side-group ethylene unsaturated ester and water is preferably 18-28 wt%;

the mass ratio of the ammonium persulfate to the ammonium sulfite or the ammonium bisulfite is preferably 0.1-1: 0.1-0.75;

the mass ratio of the redox initiator to the acrylonitrile is preferably 10-50: 0.1-1.0.

The ethylene unsaturated ester with the large side group is Ethyl Methacrylate (EMA), n-Butyl Methacrylate (BMA) or isobutyl methacrylate (i-BMA).

The molecular mass of the prepared PAN polymer is preferably 26.2-45.6 ten thousand, and the isotactic ratio of the PAN polymer is preferably 27.4-28%.

(2) Mixing the PAN polymer powder obtained in the step (1) with a reaction solvent at the temperature of-18-0 ℃ to prepare slurry, wherein the reaction solvent is preferably DMAC, vacuumizing to 45-90 KPa, and dissolving at the temperature of 40-55 ℃ for 1-2 hours to obtain a spinning stock solution; setting the temperature of a coagulation bath at 30-60 ℃ and the drafting multiple of the coagulation bath to be-30% -5%; two sections of hot water are adopted for drafting, and the drafting times are respectively 2.0 and 1.0-5.0; the densification temperature is gradually increased, the temperature range is 100-170 ℃, and the time is gradually prolonged; and then carrying out steam drafting, and finally oiling, sizing and drying the fibers to obtain the polyacrylonitrile-based carbon fiber precursor special for the carbon paper.

In the step (2), the densification temperature is gradually increased in four stages, the range is 100-170 ℃, the time is gradually prolonged, the time of each stage is 50-70 s, and specifically, the preferable first-stage temperature is 100-plus-120 ℃, the time is 50s, the second-stage temperature is 120-plus-140 ℃, the time is 55s, the third-stage temperature is 140-plus-150 ℃, the time is 60s, and the fourth-stage temperature is 160-plus-165 ℃, and the time is 65 s.

The steam drafting in the step (2) is carried out by two sections, wherein the first section is a pre-drafting area, and the second section is a heating drafting area; the steam pressure of the second section is 0.2-0.4 mPa higher than that of the first section.

The invention also provides the polyacrylonitrile-based carbon fiber precursor special for carbon paper, which is prepared by the preparation method, wherein the orientation degree of the carbon fiber precursor is controlled to be 86-89%, the crystallinity is 66-72%, and the strength of the precursor is 4.72-6.82 CN/dtex.

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example 1

According to the test, an acrylonitrile monomer solution is added into a polymerization kettle according to the proportion of 95 percent (wt%) and the proportion of 3 percent (wt%) of second monomer itaconic acid and 2 percent (wt%) of third monomer ethyl methacrylate by a metering pump, ammonium persulfate and ammonium bisulfite are respectively added into the polymerization kettle according to the proportion of 0.10 percent (wt%) and 0.75 percent (wt%) and respectively corresponding deionized water, the temperature is kept at 55 ℃, the reaction time is 8 hours, and the prepared PAN polymer has the relative molecular weight of 35.9 ten thousand.

Mixing the PAN polymer powder with a reaction solvent DMAC (dimethylacetamide) at-18 ℃ to prepare slurry, vacuumizing to 65KPa, and dissolving at 45 ℃ for 2 hours to obtain spinning solution; the temperature of the coagulating bath is 40 ℃, and the drafting multiple of the coagulating bath is-30%; hot water drafting is divided into two sections, and the drafting multiple of the first section is 2.0; the second section draft multiple is 3.0; the densification temperature is gradually increased in four stages, namely 100℃ +50s/120℃ +55s/140℃ +60s/160℃ +65 s; the steam drafting is carried out in two sections, the first section is a pre-drafting area, and the vapor pressure is 1 mPa; the second section is a carbon fiber precursor special for carbon paper, which is prepared by oiling, sizing and drying the fiber with the steam pressure of 1.2mPa in a heating and drafting zone. The orientation degree of the prepared carbon fiber protofilament is controlled to be 86 percent, the crystallinity is controlled to be 66 percent, and the protofilament strength is 6.82 CN/dtex.

The carbon content of the carbonized carbon fiber of the precursor prepared in the embodiment 1 is more than or equal to 95.6 percent, the resistivity is less than or equal to 1.6m omega cm, and the prepared carbon paper has the resistivity which is less than or equal to 65m omega cm in the vertical direction, less than or equal to 4m omega cm in the parallel direction and less than or equal to 5m omega cm in the contact resistance through the three-step short-flow production process of wet paper forming, bonding, crosslinking and graphitization²。

Example 2

An acrylonitrile monomer solution is added into a polymerization kettle through a metering pump according to the proportion of 96 percent (wt%), a second monomer of itaconic acid of 3 percent (wt%) and a third monomer of n-butyl methacrylate of 1 percent (wt%), ammonium persulfate and ammonium bisulfite are respectively added into the polymerization kettle according to the proportion of 0.10 percent (wt%) and 0.75 percent (wt%) and respectively corresponding deionized water, the temperature is kept at 58 ℃, the reaction time is 8 hours, and the prepared PAN polymer has the relative molecular weight of 43.8 ten thousand through tests.

Mixing the PAN polymer powder with a reaction solvent DMAC (dimethylacetamide) at-15 ℃ to prepare slurry, vacuumizing to 65KPa, and dissolving at 48 ℃ for 2 hours to obtain spinning solution; the temperature of the coagulating bath is 40 ℃, and the drafting multiple of the coagulating bath is-30%; hot water drafting is divided into two sections, and the drafting multiple of the first section is 2.0; the second section draft multiple is 3.0; the densification temperature is gradually increased in four stages, namely 120 ℃, 50s/140 ℃, 55s/150 ℃, 60s/160 ℃ and 65 s; the steam drafting is carried out in two sections, the first section is a pre-drafting area, and the vapor pressure is 1 mPa; the second section is a carbon fiber precursor special for carbon paper, which is prepared by oiling, sizing and drying the fiber with the steam pressure of 1.2mPa in a heating and drafting zone. The orientation degree of the prepared carbon fiber precursor is controlled to be 89.1 percent, the crystallinity is controlled to be 71.62 percent, and the strength of the precursor is 5.23 CN/dtex.

The orientation degree measurement curve and the crystallinity degree measurement curve of the polyacrylonitrile-based carbon fiber strand prepared in example 2 are shown in fig. 1 and 2.

The carbon content of the carbonized carbon fiber of the precursor prepared in the embodiment 2 is more than or equal to 95.6 percent, the resistivity is less than or equal to 1.6m omega cm, and the prepared carbon paper has the resistivity which is less than or equal to 65m omega cm in the vertical direction, less than or equal to 4m omega cm in the parallel direction and less than or equal to 5m omega cm in the contact resistance through the three-step short-flow production process of wet paper forming, bonding, crosslinking and graphitization²。

Example 3

An acrylonitrile monomer solution is added into a polymerization kettle through a metering pump according to the proportion of 97 percent (wt%), a second monomer of itaconic acid 2 percent (wt%) and a third monomer of n-butyl methacrylate 1 percent (wt%), ammonium persulfate and ammonium bisulfite are respectively added into the polymerization kettle according to the proportion of 0.10 percent (wt%) and 0.75 percent (wt%) and respectively corresponding deionized water, the temperature is kept at 55 ℃, the reaction time is 10 hours, and the prepared PAN polymer has the relative molecular weight of 38.2 ten thousand through tests.

Mixing the PAN polymer powder with a reaction solvent DMAC (dimethylacetamide) at-13 ℃ to prepare slurry, vacuumizing to 65KPa, and dissolving at 45 ℃ for 2 hours to obtain spinning solution; the temperature of the coagulating bath is 40 ℃, and the drafting multiple of the coagulating bath is-30%; hot water drafting is divided into two sections, and the drafting multiple of the first section is 2.0; the second section draft multiple is 2.5; the densification temperature is gradually increased in four stages, namely 120 ℃, 50s/130 ℃, 55s/145 ℃, 60s/160 ℃ and 65 s; the steam drafting is carried out in two sections, the first section is a pre-drafting area, and the vapor pressure is 1 mPa; the second section is a carbon fiber precursor special for carbon paper, which is prepared by oiling, sizing and drying the fiber with the steam pressure of 1.3mPa in a heating and drafting zone. The orientation degree of the prepared carbon fiber precursor is controlled to be 87 percent, the crystallinity is controlled to be 68 percent, and the strength of the precursor is 5.51 CN/dtex.

The carbon content of the carbonized carbon fiber of the precursor prepared in the embodiment 3 is more than or equal to 95.6 percent, the resistivity is less than or equal to 1.6m omega cm, and the prepared carbon paper is vertical through a three-step short-flow production process of wet paper forming, bonding crosslinking and graphitizationThe resistivity in the direction is less than or equal to 65m omega cm, the resistivity in the parallel direction is less than or equal to 4m omega cm, and the contact resistance is less than or equal to 5m omega cm²。

Example 4

An acrylonitrile monomer solution is added into a polymerization kettle through a metering pump according to the proportion of 97 percent (wt%), a second monomer of itaconic acid 2 percent (wt%) and a third monomer of isobutyl methacrylate 1 percent (wt%), ammonium persulfate and ammonium bisulfite are respectively added into the polymerization kettle according to the proportion of 0.10 percent (wt%) and 0.75 percent (wt%) and respectively corresponding deionized water, the temperature is kept at 56 ℃, the reaction time is 11 hours, and the prepared PAN polymer has the relative molecular weight of 37.5 ten thousand through tests.

Mixing the PAN polymer powder with a reaction solvent DMAC (dimethylacetamide) at-18 ℃ to prepare slurry, vacuumizing to 65KPa, and dissolving at 50 ℃ for 2 hours to obtain spinning solution; the temperature of the coagulating bath is 40 ℃, and the drafting multiple of the coagulating bath is-30%; hot water drafting is divided into two sections, and the drafting multiple of the first section is 2.0; the second section draft multiple is 2.5; the densification temperature is gradually increased in four stages, namely 125℃ +50s/135℃ +55s/145℃ +60s/165℃ +65 s; the steam drafting is carried out in two sections, the first section is a pre-drafting area, and the vapor pressure is 1 mPa; the second section is a carbon fiber precursor special for carbon paper, which is prepared by oiling, sizing and drying the fiber with the steam pressure of 1.2mPa in a heating and drafting zone. The orientation degree of the prepared carbon fiber protofilament is controlled at 88 percent, the crystallinity degree is controlled at 71 percent, and the protofilament strength is 4.91 CN/dtex.

The carbon content of the carbonized carbon fiber of the precursor prepared in the embodiment 4 is more than or equal to 95.6 percent, the resistivity is less than or equal to 1.6m omega cm, and the prepared carbon paper has the resistivity which is less than or equal to 65m omega cm in the vertical direction, less than or equal to 4m omega cm in the parallel direction and less than or equal to 5m omega cm in the contact resistance through the three-step short-flow production process of wet paper forming, bonding, crosslinking and graphitization²。

Example 5

An acrylonitrile monomer solution is added into a polymerization kettle through a metering pump according to the proportion of 97 percent (wt%), a second monomer of itaconic acid 2.5 percent (wt%) and a third monomer of isobutyl methacrylate 0.5 percent (wt%), ammonium persulfate and ammonium bisulfite are respectively added into the polymerization kettle according to the proportion of 0.10 percent (wt%) and 0.75 percent (wt%) and respectively corresponding deionized water, the temperature is kept at 56 ℃, the reaction time is 11 hours, and the prepared PAN polymer has the relative molecular weight of 43.3 ten thousand through tests.

Mixing the PAN polymer powder with a reaction solvent DMAC (dimethylacetamide) at-18 ℃ to prepare slurry, vacuumizing to 65KPa, and dissolving for 2 hours at 48 ℃ to obtain spinning solution; the temperature of the coagulating bath is 40 ℃, and the drafting multiple of the coagulating bath is-30%; hot water drafting is divided into two sections, and the drafting multiple of the first section is 2.0; the second section draft multiple is 2.5; the densification temperature is gradually increased in four stages, namely 120 ℃, 50s/135 ℃, 55s/145 ℃, 60s/160 ℃ and 65 s; the steam drafting is carried out in two sections, the first section is a pre-drafting area, and the vapor pressure is 1 mPa; the second section is a carbon fiber precursor special for carbon paper, which is prepared by oiling, sizing and drying the fiber with the steam pressure of 1.3mPa in a heating and drafting zone. The orientation degree of the prepared carbon fiber precursor is controlled to be 89 percent and the crystallinity degree is controlled to be 72 percent, and the strength of the precursor is 4.72 CN/dtex.

The carbon content of the carbonized carbon fiber of the precursor prepared in the embodiment 5 is more than or equal to 95.6 percent, the resistivity is less than or equal to 1.6m omega cm, and the prepared carbon paper has the resistivity which is less than or equal to 65m omega cm in the vertical direction, less than or equal to 4m omega cm in the parallel direction and less than or equal to 5m omega cm in the contact resistance through the three-step short-flow production process of wet paper forming, bonding, crosslinking and graphitization²。

Example 6

An acrylonitrile monomer solution is added into a polymerization kettle through a metering pump according to the proportion of 96 percent (wt%), a second monomer of itaconic acid 2.5 percent (wt%) and a third monomer of n-butyl methacrylate 1.5 percent (wt%), ammonium persulfate and ammonium bisulfite are respectively added into the polymerization kettle according to the proportion of 0.10 percent (wt%) and 0.75 percent (wt%) and respectively corresponding deionized water, the temperature is kept at 52 ℃, the reaction time is 8 hours, and the prepared PAN polymer has the relative molecular weight of 40.5 ten thousand through testing.

Mixing the PAN polymer powder with a reaction solvent DMAC (dimethylacetamide) at-15 ℃ to prepare slurry, vacuumizing to 65KPa, and dissolving at 55 ℃ for 2 hours to obtain spinning solution; the temperature of the coagulating bath is 40 ℃, and the drafting multiple of the coagulating bath is-30%; hot water drafting is divided into two sections, and the drafting multiple of the first section is 2.0; the second section draft multiple is 2.5; the densification temperature is gradually increased in four stages, namely 120 ℃, 50s/135 ℃, 55s/150 ℃, 60s/165 ℃ and 65 s; the steam drafting is carried out in two sections, the first section is a pre-drafting area, and the vapor pressure is 1 mPa; the second section is a carbon fiber precursor special for carbon paper, which is prepared by oiling, sizing and drying the fiber with the steam pressure of 1.3mPa in a heating and drafting zone. The orientation degree of the prepared carbon fiber protofilament is controlled to be 86 percent and the crystallinity degree is controlled to be 69 percent, and the strength of the protofilament is 4.82 CN/dtex.

The carbon content of the carbonized carbon fiber of the precursor prepared in the embodiment 6 is more than or equal to 95.6 percent, the resistivity is less than or equal to 1.6m omega cm, and the prepared carbon paper has the resistivity which is less than or equal to 65m omega cm in the vertical direction, less than or equal to 4m omega cm in the parallel direction and less than or equal to 5m omega cm in the contact resistance through the three-step short-flow production process of wet paper forming, bonding, crosslinking and graphitization²。

Example 7

An acrylonitrile monomer solution is added into a polymerization kettle through a metering pump according to the proportion of 96 percent (wt%), a second monomer of itaconic acid of 3 percent (wt%) and a third monomer of ethyl methacrylate of 1 percent (wt%), ammonium persulfate and ammonium bisulfite are respectively added into the polymerization kettle according to the proportion of 0.10 percent (wt%) and 0.75 percent (wt%) and respectively corresponding deionized water, the temperature is kept at 55 ℃, the reaction time is 12 hours, and the prepared PAN polymer has the relative molecular weight of 34.9 ten thousand through tests.

Mixing the PAN polymer powder with a reaction solvent DMAC (dimethylacetamide) at-18 ℃ to prepare slurry, vacuumizing to 65KPa, and dissolving at 50 ℃ for 2 hours to obtain spinning solution; the temperature of the coagulating bath is 40 ℃, and the drafting multiple of the coagulating bath is-30%; hot water drafting is divided into two sections, and the drafting multiple of the first section is 2.0; the second section draft multiple is 2.5; the densification temperature is gradually increased in four stages, namely 120 ℃, 50s/130 ℃, 55s/140 ℃, 60s/160 ℃ and 65 s; the steam drafting is carried out in two sections, the first section is a pre-drafting area, and the vapor pressure is 1 mPa; the second section is a carbon fiber precursor special for carbon paper, which is prepared by oiling, sizing and drying the fiber with the steam pressure of 1.4mPa in a heating and drafting zone. The orientation degree of the prepared carbon fiber precursor is controlled to be 87.9 percent, the crystallinity is controlled to be 68.18 percent, and the strength of the precursor is 5.31 CN/dtex.

The orientation degree measurement curve and the crystallinity degree measurement curve of the polyacrylonitrile-based carbon fiber strand prepared in example 7 are shown in fig. 1 and 2.

The carbon content of the carbonized carbon fiber of the precursor prepared in the embodiment 7 is more than or equal to 95.6 percent, the resistivity is less than or equal to 1.6m omega cm, and the prepared carbon paper has the resistivity which is less than or equal to 65m omega cm in the vertical direction, less than or equal to 4m omega cm in the parallel direction and less than or equal to 5m omega cm in the contact resistance through the three-step short-flow production process of wet paper forming, bonding, crosslinking and graphitization²。