High-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber and method for producing the same

Abstract

The application relates to the technical field of carbon fiber preparation, and discloses high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber and a preparation method thereof. The preparation method comprises the following steps: step 1, polyacrylonitrile fiber is pre-oxidized and low-temperature carbonized to obtain low-temperature carbonized fiber; step 2, the low-temperature carbonized fiber is subjected to six-temperature-zone gradient heating high-temperature carbonization treatment, the total fiber draft ratio during the high-temperature carbonization treatment is -7.0% to -1.0%, and the total treatment time is 4 min to 12 min, thereby obtaining high-temperature carbonized fiber; and step 3, the high-temperature carbonized fiber is subjected to ultrahigh-temperature graphitization treatment to obtain the high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber. Through the multi-temperature-zone treatment of high-temperature carbonization, the final heat treatment temperature is increased, and process parameters such as the draft ratio and the treatment time are optimized, so that the ultrahigh-modulus carbon fiber with a tensile strength greater than or equal to 4000 MPa and a tensile modulus greater than or equal to 640 GPa is prepared, the comprehensive performance of the ultrahigh-modulus carbon fiber is very excellent, and the ultrahigh-modulus carbon fiber has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon fiber preparation, and particularly relates to a high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber and a preparation method thereof. BACKGROUND

[0002] Due to excellent properties such as high specific strength, high specific modulus, low density, corrosion resistance and fatigue resistance, carbon fibers have been widely used in aerospace, sports and leisure, new energy, civil construction and other fields. According to the classification of fiber tensile modulus, carbon fibers can be divided into standard modulus level (230-240 GPa), medium modulus level (290-300 GPa), high modulus level (350-600 GPa) and ultrahigh modulus level (>600 GPa). Due to the excellent ultrahigh modulus, high thermal conductivity and high electrical conductivity of ultrahigh modulus carbon fibers, the composite structure can have ultralow thermal expansion and high stiffness, so it becomes the best material for satellite spacecraft heat dissipation plates. In addition, it can also be used in various industrial zero thermal deformation rollers, robot structure parts, lightweight high-rigid bicycle frames and other industrial fields.

[0003] According to the type of precursor fiber, ultrahigh modulus carbon fibers can be divided into pitch-based ultrahigh modulus carbon fibers and polyacrylonitrile (PAN)-based ultrahigh modulus carbon fibers. Since mesophase pitch has the characteristics of easy graphitization, ultrahigh modulus carbon fibers can be easily prepared by taking pitch fibers as precursors, such as coal-based pitch carbon fibers of Japan Graphite Fiber Corporation and petroleum-based pitch carbon fibers of Mitsubishi Chemical. However, the tensile strength of pitch-based ultrahigh modulus carbon fibers is generally low (significantly lower than 4000 MPa), such as Mitsubishi Chemical K1352U pitch-based ultrahigh modulus carbon fiber with a tensile modulus of 620 GPa and a tensile strength of 3600 MPa. The low strength of ultrahigh modulus carbon fibers leads to high brittleness, which easily causes broken fibers and hair-like fibers during subsequent product processing, thereby affecting the processing workability.

[0004] Compared with mesophase pitch, PAN is a difficult graphitization material, so it is difficult to prepare ultrahigh modulus carbon fibers by taking PAN fibers as precursors. At present, the highest modulus of commercially available PAN-based carbon fibers in the world is M60J carbon fiber of Japan Toray Corporation, which has a tensile modulus of 588 GPa, but its tensile strength is only 3820 MPa.

[0005] CN108286090A discloses a preparation method of PAN-based high-strength high-modulus carbon fiber. The PAN precursor is subjected to conventional pre-oxidation and low-temperature carbonization, and then subjected to high-temperature carbonization by increasing the high-temperature carbonization temperature and matching a certain stretching, or by increasing the high-temperature carbonization stretching ratio, so as to effectively control the orientation of carbon microcrystals, and obtain high-temperature carbonized fibers with an orientation angle of not more than 17.5°. Then, high-temperature graphitization heat drawing treatment is carried out at a relatively low high-temperature graphitization temperature. The prepared fiber has a tensile strength of 3.8-5.0 GPa and a tensile modulus of 500-600 GPa, but cannot exceed 600 GPa.

[0006] It is understood that currently Toray Company is developing M65J type ultra-high modulus carbon fiber with a tensile modulus of 640 GPa or more and is striving to commercialize it. However, according to the characteristics of the existing carbon fiber brands of the company (the higher the tensile modulus of the carbon fiber, the more obvious the decrease in the tensile strength), it is expected that the tensile strength of the M65J type ultra-high modulus carbon fiber developed by Toray will be lower than 3800 MPa, and may even be only 3600 MPa.

[0007] During the high-temperature carbonization process, the initial two-dimensional turbostratic graphite structure formed inside the fiber gradually changes into a three-dimensional graphite microcrystal structure under the action of high-temperature heat drawing. The graphite microcrystal structure parameters such as microcrystal size and orientation are the key to affecting the final fiber tensile strength and tensile modulus, so the structure regulation at this stage is one of the key ways to prepare ultra-high modulus carbon fiber. Numerous studies have shown that when high-temperature carbonization treatment is carried out on high-modulus level and below (modulus < 600 GPa) carbon fiber, the high-temperature carbonization furnace usually consists of 1-5 temperature zones, and the highest temperature does not exceed 1600℃ (Xu Lianghua et al. <Polyacrylonitrile-based carbon fiber> p134, He Fu <Carbon fiber and graphite fiber> p230).

[0008] In summary, how to continuously and stably prepare high-strength ultra-high modulus carbon fiber with high strength through microstructure control during fiber forming process has become one of the hotspots and difficulties in future research and development. SUMMARY

[0009] The present application is aimed at the typical difficulty of graphitization of polyacrylonitrile (PAN) in the prior art, the high difficulty in preparing ultra-high modulus carbon fiber, and the problems of low tensile strength of existing ultra-high modulus carbon fiber, and the difficulty in achieving ultra-high modulus and high strength. A preparation method of high-strength ultra-high modulus carbon fiber is provided. The internal structure is finely regulated and controlled during the high-temperature carbonization treatment stage of three-dimensional graphite microcrystal structure formation, and PAN-based high-strength ultra-high modulus carbon fiber with excellent comprehensive performance is prepared, and continuous and stable preparation is realized.

[0010] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0011] A method for preparing high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber, comprising the steps of:

[0012] Step 1, pre-oxidizing and low-temperature carbonizing polyacrylonitrile fiber to obtain low-temperature carbonized fiber;

[0013] Step 2, performing six-temperature-zone gradient heating high-temperature carbonization treatment on the low-temperature carbonized fiber, the six-temperature-zone temperatures being 1000℃-1200℃, 1250℃-1350℃, 1300℃-1500℃, 1400℃-1550℃, 1500℃-1650℃, and 1600℃-1800℃ respectively, the total fiber draft ratio during the high-temperature carbonization treatment being -7.0%- -1.0%, and the total treatment time being 4min-12min, to obtain high-temperature carbonized fiber;

[0014] Step 3, performing ultrahigh-temperature graphitization treatment on the high-temperature carbonized fiber to obtain the high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber.

[0015] The high-temperature carbonized fiber obtained in Step 2 has a 002 crystal face spacing d 002 of 0.3485nm-0.3585nm, a carbon element content of 92%-97%, and a bulk density of 1.75g / cm 3 -1.79g / cm 3 .

[0016] In the prior art, when high-temperature carbonization treatment is performed on high-modulus level and below (modulus <600GPa) carbon fiber, the high-temperature carbonization furnace is usually composed of 1-5 temperature zones, and the highest temperature does not exceed 1600℃. However, the present inventors have found through a large number of studies that, if ultrahigh-modulus level, especially modulus higher than 640GPa, ultrahigh-modulus carbon fiber is prepared, the internal structure of the fiber in the high-temperature carbonization stage formed by three-dimensional graphite microcrystals must be precisely controlled.

[0017] It has been found through research that, by adopting six-temperature-zone gradient heating treatment, the fine transformation of the internal two-dimensional disordered layer graphite structure of the fiber to a three-dimensional graphite microcrystal structure is achieved, and the increase of the final heat treatment temperature helps the initial growth of the three-dimensional graphite microcrystal structure. In combination with the matching design of the high-temperature carbonization stage heat treatment temperature, draft process and other parameters, the internal structure of the high-temperature carbonized fiber is controllable, so that the fiber has a 002 crystal face spacing d 002 of 0.3485nm-0.3585nm, a carbon element content of 92%-97%, and a bulk density of 1.75g / cm 3 -1.79g / cm 3 , and after subsequent ultrahigh-temperature graphitization treatment, the fiber has a tensile strength ≥4000MPa, a tensile modulus ≥640GPa, and a bulk density ≥1.95g / cm 3 .

[0018] The PAN fiber in step 1 is prepared by wet method, dry method or dry spraying wet method, and the fiber tows have specifications of 1K-50K.

[0019] Preferably, the pre-oxidation in step 1 is performed by four to six temperature zone gradient heating treatment in air atmosphere, the pre-oxidation temperature range is 150-280℃, the total fiber draft ratio is 3.0%-8.0%, and the total treatment time is 50-120min. Further preferably, the pre-oxidation temperature range is 180-260℃, the total fiber draft ratio is 5.0%-7.0%, and the treatment time is 80-120min.

[0020] In some embodiments, the pre-oxidation in step 1 is performed by six temperature zone gradient heating treatment, and the temperature ranges of the respective temperature zones are 180-195℃, 195-215℃, 200-220℃, 210-230℃, 225-240℃ and 230-250℃, respectively.

[0021] Preferably, the low-temperature carbonization in step 1 is performed by four to seven temperature zone heating treatment in high-purity nitrogen, the low-temperature carbonization temperature range is 300-1000℃, the total fiber draft ratio is 2.0%-10.0%, and the total treatment time is 3-12min. Further preferably, the low-temperature carbonization temperature range is 350-900℃, the total fiber draft ratio is 3.0%-7.0%, and the treatment time is 3-8min.

[0022] Further preferably, in step 1, the low-temperature carbonization is performed by five to seven temperature zone gradient heating treatment in high-purity nitrogen, the low-temperature carbonization temperature range is 350-900℃, the total fiber draft ratio is 3.0%-7.0%, and the total treatment time is 3-8min.

[0023] The high-temperature carbonization treatment process in step 2 is performed under high-purity nitrogen protection.

[0024] Preferably, the ultra-high temperature graphitization in step 3 is performed by single temperature zone heating treatment, the treatment temperature is 2300-3000℃, the draft ratio is 2.0%-10.0%, and the treatment time is 2-10min. Further preferably, the ultra-high temperature graphitization temperature range is 2500-2800℃, the total fiber draft ratio is 5.0%-8.0%, and the treatment time is 4-6min.

[0025] The ultra-high temperature graphitization treatment in step 3 is performed under high-purity nitrogen and / or argon protection.

[0026] The application also provides the high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber prepared according to the preparation method, which has a tensile strength of greater than or equal to 4000 MPa, a tensile modulus of greater than or equal to 640 GPa, and a bulk density of greater than or equal to 1.95 g / cm 3 .

[0027] Compared with the prior art, the application has the following beneficial effects:

[0028] The application controls the key structural parameters such as the microcrystalline structure, element content and bulk density of the fiber after high-temperature carbonization within a specific range by comprehensive design and optimization of process parameters in the high-temperature carbonization stage, and coupling design of the key process parameters in each stage, so that the polyacrylonitrile-based carbon fiber with both ultrahigh modulus and high strength is finally realized. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A physical map of the carbon fiber sample to be tested for tensile test after being treated by impregnation and reinforcement in Comparative Example 1.

[0030] Figure 2 A stress-strain curve of the carbon fiber prepared in Comparative Example 1 during the tensile test.

[0031] Figure 3 An XRD pattern of the fiber after high-temperature carbonization in Example 1.

[0032] Figure 4 A stress-strain curve of the ultrahigh-modulus carbon fiber prepared in Example 1 during the tensile test. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below with reference to examples. It should be understood that the specific examples described herein are only used to explain the application and not to limit the application. Those skilled in the art can modify or replace the application without departing from the spirit and scope of the application, which should be covered by the protection scope of the application.

[0034] The raw materials used in the following specific embodiments are all purchased from the market. The bulk density of the carbon fiber prepared in the following specific embodiments is tested according to the method for testing the density of carbon fiber in GB-T 30019-2013. The sample is weighed in air, then completely immersed in a liquid with a known density of at least 0.2 g / cm 3 less than the density of the sample, then weighed again. According to Archimedes' principle, the mass value of the sample in the two media is different, and the density of the sample is calculated. The bulk density of the carbon fiber is calculated.

[0035] Fiber tensile property: The tensile property of the carbon fiber was tested according to the national standard GB-T 3362-2017 Carbon Fiber Filament Tensile Property Test Method.

[0036] Comparative Example 1

[0037] (1) The 6K polyacrylonitrile fiber was subjected to 6-temperature zone pre-oxidation treatment by using a pre-oxidation furnace to obtain pre-oxidized fiber, and the 6-temperature zone pre-oxidation temperatures were 180℃, 205℃, 215℃, 225℃, 230℃ and 245℃, the total draw ratio was 6.5%, the pre-oxidation time of each temperature zone was 16 min, and the total treatment time was 96 min; the pre-oxidized fiber was subjected to five-temperature zone low-temperature carbonization treatment to obtain low-temperature carbonized fiber, and the temperature intervals of each temperature zone were 300℃, 550℃, 650℃, 750℃ and 900℃, the draw ratio was 6.0%, and the total residence time of the fiber was 5 min;

[0038] (2) The low-temperature carbonized fiber was further subjected to four-temperature zone high-temperature carbonization treatment to obtain high-temperature carbonized fiber, and the temperature of each temperature zone was 1100℃, 1300℃, 1450℃ and 1550℃, the draw ratio was -3.0%, and the treatment time of the fiber was 4 min;

[0039] The structure performance indexes such as the 002 crystal plane spacing obtained by microstructure test are shown in Table 10;

[0040] (3) The high-temperature carbonized fiber was further subjected to ultrahigh-temperature graphitization treatment by using a high-temperature graphitization furnace, the treatment temperature was 2700℃, the draw ratio was 6%, the residence time was 4 min, and the carbon fiber was prepared.

[0041] The tensile property and bulk density of the carbon fiber were tested, wherein the main tensile property index was the average value of 6 effective samples, the samples were prepared by dipping the filaments into glue and using paper sheets as reinforcing sheets to bond the two ends of the samples before the tensile test, as shown in Figure 1 , and the test data are shown in Table 1, the tensile strength of the carbon fiber obtained by testing was 3038 MPa, the tensile modulus was 588 GPa, the elongation was 0.52%, and the bulk density was 1.93 g / cm 3 , and the stress-strain curve during the tensile test is shown in Figure 2 .

[0042] Table 1 Main performance indexes of the prepared carbon fiber

[0043] Sample No. Tensile Strength / MPa Tensile Modulus / GPa Elongation / % 1 3320 611 0.54 2 2750 646 0.43 3 2980 543 0.55 4 3010 552 0.55 5 3210 625 0.51 6 2960 551 0.54 Mean 3038 588 0.52

[0044] Comparative Example 2

[0045] The operation process and parameters of step (1) were the same as those of Comparative Example 1

[0046] (2) The low-temperature carbonized fiber is treated by high-temperature carbonization in five temperature zones to obtain high-temperature carbonized fiber, the temperature of each temperature zone is 1100℃, 1300℃, 1450℃, 1550℃, 1700℃ respectively, the drawing ratio is -3.0%, and the fiber treatment time is 5 min;

[0047] The structural performance indexes such as 002 crystal face spacing obtained by microstructure test are shown in Table 10.

[0048] The operation process and parameters of step (3) are the same as those of Comparative Example 1.

[0049] The tensile properties and bulk density of the carbon fiber are tested, wherein the main tensile property index is the average value of 6 effective samples, and the test data are shown in Table 2, and the tensile strength of the carbon fiber is 3405 MPa, the tensile modulus is 618 GPa, the elongation is 0.55%, and the bulk density is 1.94 g / cm 3 .

[0050] Table 2 Main performance indexes of the prepared carbon fiber

[0051] Sample No. Tensile Strength / MPa Tensile Modulus / GPa Elongation / % 1 3730 633 0.59 2 3490 664 0.52 3 3410 596 0.57 4 3130 593 0.53 5 3500 601 0.58 6 3170 621 0.51 Mean 3405 618 0.55

[0052] Comparative Example 3

[0053] The operation process and parameters of step (1) are the same as those of Comparative Example 1

[0054] (2) The low-temperature carbonized fiber is treated by high-temperature carbonization in six temperature zones to obtain high-temperature carbonized fiber, the temperature of each temperature zone is 1100℃, 1300℃, 1450℃, 1500℃, 1600℃, 1700℃ respectively, the drawing ratio is 0.5%, and the fiber treatment time is 5 min;

[0055] The structural performance indexes such as 002 crystal face spacing obtained by microstructure test are shown in Table 10.

[0056] The operation process and parameters of step (3) are the same as those of Comparative Example 1.

[0057] The tensile properties and bulk density of the carbon fiber are tested, wherein the main tensile property index is the average value of 6 effective samples, and the test data are shown in Table 3, and the tensile strength of the carbon fiber is 3855 MPa, the tensile modulus is 639 GPa, the elongation is 0.60%, and the bulk density is 1.95 g / cm 3 .

[0058] Table 3 Main performance indexes of the prepared carbon fiber

[0059] Sample No. Tensile Strength / MPa Tensile Modulus / GPa Elongation / % 1 3550 666 0.53 2 3910 605 0.65 3 4090 660 0.62 4 3890 643 0.60 5 3610 620 0.58 6 4080 639 0.64 Mean 3855 639 0.60

[0060] Comparative Example 4

[0061] The operation process and parameters of step (1) are the same as those of Comparative Example 1.

[0062] (2) The low-temperature carbonized fiber is subjected to six-zone high-temperature carbonization treatment to obtain a high-temperature carbonized fiber, the temperature of each zone is 1100℃, 1300℃, 1450℃, 1500℃, 1650℃, and 1700℃ respectively, the draw ratio is -8.0%, and the fiber treatment time is 4 min;

[0063] The structural performance indexes such as the 002 crystal face spacing obtained through the microscopic structure test are shown in Table 10.

[0064] The operation process and parameters of step (3) are the same as those of Comparative Example 1.

[0065] The tensile properties and bulk density of the carbon fiber are tested, wherein the main tensile property index is the average value of 6 effective samples, and the test data are shown in Table 4. The tensile strength of the carbon fiber is 4132 MPa, the tensile modulus is 610 GPa, the elongation is 0.68%, and the bulk density is 1.94 g / cm 3 .

[0066] Table 4 Main performance indexes of the prepared carbon fiber

[0067] Sample No. Tensile Strength / MPa Tensile Modulus / GPa Elongation / % 1 3930 614 0.64 2 4190 607 0.69 3 4120 616 0.67 4 4280 583 0.73 5 4120 630 0.65 6 4150 607 0.68 Mean 4132 610 0.68

[0068] Example 1

[0069] The preparation method of the high-strength ultrahigh-modulus carbon fiber in this example comprises the following steps:

[0070] (1) The 6K polyacrylonitrile fiber is subjected to six-zone pre-oxidation treatment by using a pre-oxidation furnace to obtain a pre-oxidized fiber, the pre-oxidation temperature of each zone is 180℃, 205℃, 215℃, 225℃, 230℃, and 245℃ respectively, the total draw ratio is 6.5%, the pre-oxidation time of each zone is 16 min, and the total treatment time is 96 min; the pre-oxidized fiber is subjected to five-zone low-temperature carbonization treatment to obtain a low-temperature carbonized fiber, the temperature of each zone is 300℃, 550℃, 650℃, 750℃, and 900℃ respectively, the draw ratio is 6.0%, and the total fiber residence time is 5 min;

[0071] (2) The low-temperature carbonized fiber is subjected to six-zone high-temperature carbonization treatment to obtain a high-temperature carbonized fiber, the temperature of each zone is 1050℃, 1300℃, 1400℃, 1450℃, 1550℃, and 1750℃ respectively, the draw ratio is -4.0%, and the fiber treatment time is 4 min;

[0072] The XRD pattern of the fiber after high-temperature carbonization is shown in Figure 3As shown, there is an obvious 002 peak near 2θ = 25° as a structural characteristic peak of carbon material, the smaller the half-height width, the higher the graphitization degree, and the 002 interplanar spacing and other structural performance indicators obtained by microstructure test are shown in Table 10.

[0073] (3) Further, the high-temperature carbonized fiber is subjected to ultrahigh-temperature graphitization treatment by using a high-temperature graphitization furnace, the treatment temperature is 2700℃, the drawing ratio is 6%, and the residence time is 4 min, to prepare the ultrahigh-modulus carbon fiber.

[0074] The tensile properties and bulk density of the carbon fiber are tested, wherein the main tensile property index is the average value of 6 effective samples, and the test data are shown in Table 5, the tensile strength of the ultrahigh-modulus carbon fiber is 4210 MPa, the tensile modulus is 646 GPa, the elongation is 0.66%, and the bulk density is 1.96 g / cm 3 The stress-strain curve during the tensile test is shown in Figure 4 .

[0075] Table 5 Main performance indexes of the high-strength ultrahigh-modulus carbon fiber prepared

[0076] Sample No. Tensile Strength / MPa Tensile Modulus / GPa Elongation / % 1 4340 641 0.68 2 4170 662 0.63 3 4070 601 0.68 4 4170 676 0.62 5 4430 676 0.66 6 4080 620 0.66 Mean 4210 646 0.66

[0077] Example 2

[0078] The preparation method of the high-strength high-modulus carbon fiber in this example comprises the following steps:

[0079] The operation process and parameters of step (1) are the same as those of Example 1.

[0080] (2) The low-temperature carbonized fiber is subjected to six-zone high-temperature carbonization treatment to obtain a high-temperature carbonized fiber, the temperature of each zone is 1100℃, 1300℃, 1400℃, 1450℃, 1600℃, and 1780℃ respectively, the drawing ratio is-5.5%, and the fiber treatment time is 5 min;

[0081] The 002 interplanar spacing and other structural performance indicators obtained by microstructure test are shown in Table 10;

[0082] The operation process and parameters of step (3) are the same as those of Example 1.

[0083] The tensile properties and bulk density of the carbon fiber are tested, wherein the main tensile property index is the average value of 6 effective samples, and the test data are shown in Table 6, the tensile strength of the ultrahigh-modulus carbon fiber is 4277 MPa, the tensile modulus is 655 GPa, the elongation is 0.66%, and the bulk density is 1.97 g / cm 3 .

[0084] Table 6 Main performance indexes of the high-strength ultrahigh-modulus carbon fiber prepared

[0085] Sample No. Tensile Strength / MPa Tensile Modulus / GPa Elongation / % 1 4250 666 0.64 2 4420 672 0.66 3 4650 677 0.69 4 4170 619 0.67 5 4020 675 0.60 6 4150 623 0.67 Mean 4277 655 0.66

[0086] Example 3

[0087] The preparation method of the high-strength high-modulus carbon fiber of the present embodiment comprises the following steps:

[0088] The operation process and parameters of step (1) are the same as those of Example 1.

[0089] (2) The low-temperature carbonized fiber is subjected to six-zone high-temperature carbonization treatment to obtain a high-temperature carbonized fiber, the temperature of each zone is 1100℃, 1300℃, 1450℃, 1500℃, 1600℃, 1700℃, the drawing ratio is -3.0%, and the fiber treatment time is 5min;

[0090] The structural performance indexes such as the 002 crystal face spacing obtained through the microstructure test are shown in Table 10;

[0091] The operation process and parameters of step (3) are the same as those of Example 1.

[0092] The tensile properties and bulk density of the carbon fiber are tested, wherein the main tensile property index is the average value of 6 effective samples, and the test data are shown in Table 7. The tensile strength of the ultra-high modulus carbon fiber is 4138MPa, the tensile modulus is 640GPa, the elongation is 0.65%, and the bulk density is 1.96g / cm 3 .

[0093] Table 7 Main performance indexes of the high-strength ultra-high modulus carbon fiber prepared

[0094] Sample No. Tensile Strength / MPa Tensile Modulus / GPa Elongation / % 1 4030 606 0.67 2 4010 631 0.63 3 4460 683 0.65 4 4180 672 0.62 5 3870 618 0.63 6 4280 630 0.68 Mean 4138 640 0.65

[0095] Example 4

[0096] The preparation method of the high-strength high-modulus carbon fiber of the present embodiment comprises the following steps:

[0097] The operation process and parameters of step (1) are the same as those of Example 1.

[0098] (2) The low-temperature carbonized fiber is subjected to six-zone high-temperature carbonization treatment to obtain a high-temperature carbonized fiber, the temperature of each zone is 1100℃, 1300℃, 1450℃, 1550℃, 1650℃, 1750℃, the drawing ratio is -3.0%, and the fiber treatment time is 6min;

[0099] The structural performance indexes such as the 002 crystal face spacing obtained through the microstructure test are shown in Table 10;

[0100] The operation process and parameters of step (3) are the same as those of Example 1.

[0101] The tensile properties and bulk density of the carbon fiber were tested, wherein the main tensile property index was the average value of 6 effective samples, and the test data were shown in Table 8. The tensile strength of the ultra-high modulus carbon fiber was 4145 MPa, the tensile modulus was 644 GPa, the elongation was 0.66%, and the bulk density was 1.96 g / cm 3 .

[0102] Table 8 Main performance indexes of the high-strength ultra-high modulus carbon fiber prepared

[0103] Sample No. Tensile Strength / MPa Tensile Modulus / GPa Elongation / % 1 4420 627 0.70 2 3990 659 0.63 3 3990 664 0.63 4 4380 624 0.69 5 3910 662 0.62 6 4180 630 0.66 Mean 4145 644 0.66

[0104] Example 5

[0105] The preparation method of the high-strength high-modulus carbon fiber in the embodiment comprises the following steps:

[0106] The operation process and parameters of step (1) were the same as those of Example 1.

[0107] (2) The low-temperature carbonized fiber was treated by high-temperature carbonization in six temperature zones to obtain a high-temperature carbonized fiber, the temperature of each temperature zone was 1100℃, 1300℃, 1450℃, 1500℃, 1600℃, and 1750℃, the drawing ratio was -1.5%, and the fiber treatment time was 5 min;

[0108] The structural performance indexes such as the 002 crystal plane spacing obtained by the microstructure test were shown in Table 10;

[0109] The operation process and parameters of step (3) were the same as those of Example 1.

[0110] The tensile properties and bulk density of the carbon fiber were tested, wherein the main tensile property index was the average value of 6 effective samples, and the test data were shown in Table 9. The tensile strength of the ultra-high modulus carbon fiber was 4012 MPa, the tensile modulus was 641 GPa, the elongation was 0.63%, and the bulk density was 1.96 g / cm 3 .

[0111] Table 9 Main performance indexes of the high-strength ultra-high modulus carbon fiber prepared

[0112] Sample No. Tensile Strength / MPa Tensile Modulus / GPa Elongation / % 1 3990 606 0.66 2 3860 655 0.59 3 3970 624 0.64 4 3840 609 0.63 5 4200 724 0.58 6 4210 630 0.67 Mean 4012 641 0.63

[0113] Table 10 Structural parameters of the high-temperature carbonized fiber of the comparative example and the embodiment and main performance indexes of the fiber after graphitization

[0114]

[0115]

[0116] The above Comparative Example 1 and Comparative Example 2 show that the fiber structure transformation in the high-temperature carbonization stage can be controlled to a certain extent by optimizing the number of temperature intervals. In Comparative Example 1, the temperature intervals are set less, the temperature range is unevenly distributed, and the high-temperature carbonization termination temperature is lower, which leads to insufficient formation of the three-dimensional graphite microcrystalline structure in the fiber. This is reflected in the higher interplanar spacing of the high-temperature carbonized fiber, and the lower carbon content and bulk density.

[0117] In Comparative Example 2, the temperature zones are increased and the high-temperature carbonization termination temperature is increased to 1700℃. After the two-dimensional turbostratic graphite structure in the fiber is transformed into a three-dimensional graphite microcrystalline structure, the increase in the termination temperature is beneficial to the growth of the graphite microcrystalline structure, thereby facilitating the improvement of the subsequent fiber performance. Therefore, the tensile strength and tensile modulus of the fiber after graphitization are higher than those in Comparative Example 1, indicating that the reasonable setting of the temperature intervals has a significant impact on the mechanical properties of the final graphitized fiber. However, due to the wide temperature distribution in each temperature zone, the fine structure in the fiber is not well controlled, so the bulk density of the fiber after high-temperature carbonization is low and the densification degree is low, resulting in a lower tensile strength of the final fiber despite a higher tensile modulus of 600GPa.

[0118] In Comparative Example 3, the temperature zones in the high-temperature carbonization stage are reasonably designed and distributed. However, due to the use of 0.5% positive draft ratio, the stacking structure in the fiber is tightly arranged under the action of tension during the high-temperature carbonization stage, resulting in a high bulk density. However, the high draft tension can easily cause fiber breakage and produce lint, resulting in a decrease in the tensile strength of the final fiber.

[0119] In Comparative Example 4, the draft ratio is only -8.0%. Due to the low draft tension, the escape of non-carbon elements during the high-temperature carbonization stage causes the fiber to shrink and the bulk density to decrease. Moreover, it can lead to poor orientation of the fiber during the forming process. After subsequent graphitization, the fiber has a low tensile modulus.

[0120] From the observation of Examples 1-5, it can be seen that through the coupling design of the number of temperature intervals, draft tension and processing time and other key parameters in the high-temperature carbonization stage, the internal structure of the fiber in the high-temperature carbonization stage is optimized and controlled. Based on this, a high-strength ultra-high modulus carbon fiber with a tensile strength of more than 4000MPa, a tensile modulus of more than 640GPa and a bulk density of more than 1.95g / cm 3 is prepared after subsequent graphitization.

[0121] The above-described examples are only preferred embodiments of the present application and do not limit the present application in any way. Any simple modification, change and equivalent change made to the above examples according to the technical essence of the present application are still within the protection scope of the technical solution of the present application.

Claims

1. A method for preparing high-strength, ultra-high-modulus polyacrylonitrile-based carbon fibers, characterized in that, The method comprises the steps of: Step 1: pre-oxidizing and low-temperature carbonizing polyacrylonitrile fibers to obtain low-temperature carbonized fibers; Step 2: high-temperature carbonizing the low-temperature carbonized fibers in six temperature zones, wherein the temperatures of the six temperature zones are 1000-1200, 1250-1350, 1300-1500, 1400-1550, 1500-1650 and 1600-1800 DEG C respectively, the total drawing ratio of the fibers during the high-temperature carbonizing process is -7.0% to -1.0%, and the total processing time is 4-12 min, to obtain high-temperature carbonized fibers; Step 3: super-high-temperature graphitizing the high-temperature carbonized fibers to obtain the high-strength and high-modulus polyacrylonitrile-based carbon fibers.

2. The process for producing high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber according to claim 1, characterized by, The interplanar spacing d of the high-temperature carbonized fiber obtained in Step 2 is 0.3485 nm to 0.3585 nm 002 0.3485 nm to 0.3585 nm, the carbon content is 92% to 97%, and the bulk density is 1.75 g / cm 3 to 1.79 g / cm 3 .

3. The process for producing high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber according to claim 1, characterized by, The polyacrylonitrile fibers in step 1 are prepared by wet method, dry method or dry-spraying-wet method, and the fiber tows have a specification of 1K-50K.

4. The process for producing high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber according to claim 1, characterized by, The pre-oxidation in step 1 is performed by four to six temperature zones of gradient heating and in an air atmosphere, the pre-oxidation temperature ranges from 150 DEG C to 280 DEG C, the total drawing ratio of the fibers is 3.0% to 8.0%, and the total processing time is 50-120 min.

5. The process for producing high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber according to claim 1, characterized by, The low-temperature carbonization in step 1 is performed by four to seven temperature zones of gradient heating and in high-purity nitrogen, the low-temperature carbonization temperature ranges from 300 DEG C to 1000 DEG C, the total drawing ratio of the fibers is 2.0% to 10.0%, and the total processing time is 3-12 min.

6. The process for producing high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber according to claim 1, characterized by, The super-high-temperature graphitization in step 3 is performed by single temperature zone of heat treatment, the processing temperature is 2300 DEG C to 3000 DEG C, the drawing ratio is 2.0% to 10.0%, and the processing time is 2-10 min.

7. The process for producing high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber according to claim 1, characterized by, The high-temperature carbonizing process in step 2 is performed under the protection of high-purity nitrogen.

8. The process for producing high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber according to claim 1, characterized by, The super-high-temperature graphitizing process in step 3 is performed under the protection of high-purity nitrogen and / or argon.

9. The process for producing high-strength ultrahigh-modulus polyacrylonitrile-based carbon fiber according to claim 1, characterized by, In step 1, the low-temperature carbonization is performed by five to seven temperature zones of gradient heating and in high-purity nitrogen, the low-temperature carbonization temperature ranges from 350 DEG C to 900 DEG C, the total drawing ratio of the fibers is 3.0% to 7.0%, and the total processing time is 3-8 min.

10. The high-strength, ultrahigh-modulus polyacrylonitrile-based carbon fiber produced according to the production method of any one of claims 1 to 9, characterized by The tensile strength is ≥ 4000 MPa, the tensile modulus is ≥ 640 GPa, and the bulk density is ≥ 1.95 g / cm 3 .

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