Pre-oxidation method of polyacrylonitrile, application of pre-oxidation method and preparation method of polyacrylonitrile-based high-modulus carbon fiber

Abstract

The invention discloses a polyacrylonitrile pre-oxidation method and application thereof and a preparation method of polyacrylonitrile-based high-modulus carbon fiber, the polyacrylonitrile pre-oxidation method comprises the following steps: pre-oxidizing polyacrylonitrile in at least three temperature zones in sequence in an air atmosphere, the first three temperature zones are controlled according to the sequence of pretreatment: the temperature of the first temperature zone is controlled to be 180-230 DEG C, the temperature of the second temperature zone is controlled to be 210-260 DEG C, and the temperature of the third temperature zone is controlled to be 250-300 DEG C. According to the method, the cyclization degree of the fiber in the pre-oxidation stage is used as a structure control index, and the pre-oxidation fiber with a perfect structure is prepared through regulation and control design of key parameters such as the pre-oxidation temperature, the drafting rate and the retention time, so that the high-model carbon fiber is prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon fiber production, and particularly relates to a method for pre-oxidizing polyacrylonitrile and its application, and a method for preparing polyacrylonitrile-based high-modulus carbon fiber. Background Art

[0002] Polyacrylonitrile (PAN)-based carbon fibers have the advantages of high specific strength, high specific modulus, high temperature resistance, corrosion resistance, creep resistance, conductivity, and low specific gravity, and have been widely used in fields such as automobiles, aircrafts, rail transit, wind power generation, and sports equipment. PAN-based carbon fibers include four categories: high-strength type, high-strength medium-modulus type, high-modulus type, and high-strength high-modulus type. Through further high-temperature treatment of carbon fibers, high-modulus fibers with a carbon content higher than that of carbon fibers can be obtained. High-modulus carbon fibers are obtained by super secondary carbonization treatment on the basis of general-purpose carbon fibers, have extremely high added value, and are widely used. High-modulus fibers have characteristics such as ultra-high modulus, higher thermal conductivity, higher conductivity, and extremely low thermal expansion. They are most suitable for the space environment with large temperature differences between day and night, can be used to prepare structures and functional materials with very small thermal expansion, and are indispensable in the aerospace field. In addition to applications in the space environment, high-modulus fibers have a wide range of applications in many fields, including national defense and military industry, sports goods, textile equipment, battery and power transmission materials, and civil engineering materials.

[0003] In the process of preparing carbon fibers, pre-oxidation is an important intermediate process for preparing carbon fibers, which is the most time-consuming and energy-consuming. In the pre-oxidation stage, the linear molecular chains of the precursor fibers are transformed into heat-resistant ladder structures, which is conducive to infusibility and non-combustibility in the subsequent secondary carbonization environment. The fiber pre-oxidation reaction of acrylonitrile copolymer in an oxygen-containing atmosphere mainly includes three types: cyclization, oxidative crosslinking, and dehydrogenation. The cyclization reaction is exothermic in nature. If the fiber configuration of the pre-oxidized polymer is to be maintained, the cyclization reaction must be controlled. In the prior art, the above-mentioned oxidative crosslinking and cyclization reactions usually lead to the breakage of polymer chains. In order to form a stable pre-oxidized structure, the pre-oxidation must reach a certain temperature, but an excessive oxidized structure will be formed in an oxidizing atmosphere, and the generation of too much oxidized structure will reduce the thermal stability of the pre-oxidized fibers, cause mass loss during thermal cracking during carbonization, greatly affect the carbon yield of polyacrylonitrile fibers, and produce defects in the fibers, affecting the mechanical properties of carbon fibers.

[0004] Moreover, the methods of the prior art are generally time-consuming and cumbersome, and there are still problems in industrial applications. And the present invention takes the cyclization degree of the fibers in each stage of pre-oxidation as the fiber quality index, which is of great significance for preparing high-modulus carbon fibers. Summary of the Invention

[0005] In order to overcome the problems existing in the prior art, the present invention provides a method for pre-oxidizing polyacrylonitrile and its application, as well as a method for preparing polyacrylonitrile-based high-modulus carbon fiber. Among them, taking the fiber cyclization degree in the pre-oxidation stage as the structure control index, through the regulation and design of key parameters such as pre-oxidation temperature, draw ratio, residence time, etc., pre-oxidized fibers with perfect structure are prepared.

[0006] One of the objectives of the present invention is to provide a method for pre-oxidizing polyacrylonitrile, including: pre-oxidizing the polyacrylonitrile in at least three temperature zones in sequence under an air atmosphere. Among them, the following controls are carried out on the first three temperature zones in the order of pretreatment: controlling the temperature of the first temperature zone to be 180-230 °C, controlling the temperature of the second temperature zone to be 210-260 °C, and controlling the temperature of the third temperature zone to be 250-300 °C.

[0007] For example, controlling the temperature of the first temperature zone to be 180 °C, 190 °C, 200 °C, 210 °C, 220 °C or 230 °C, controlling the temperature of the second temperature zone to be 210 °C, 220 °C, 230 °C, 240 °C, 250 °C or 260 °C, and controlling the temperature of the third temperature zone to be 250 °C, 260 °C, 270 °C, 280 °C, 290 °C or 300 °C.

[0008] Preferably, the temperature of the second temperature zone is higher than that of the first temperature zone, and the temperature of the third temperature zone is higher than that of the second temperature zone.

[0009] In a preferred embodiment, the polyacrylonitrile is an acrylonitrile fiber bundle. Preferably, the number of the acrylonitrile fiber bundles is 1-100K, such as 1K, 10K, 20K, 30K, 40K, 50K, 60K, 70K, 80K, 90K or 100K.

[0010] In a further preferred embodiment, the acrylonitrile fiber bundle is prepared by wet spinning or dry-jet wet spinning.

[0011] In a preferred embodiment, the temperature of the first temperature zone is controlled to be 200-230 °C, preferably 205-230 °C, such as 205 °C, 210 °C, 215 °C, 220 °C, 225 °C or 230 °C.

[0012] In a preferred embodiment, the temperature of the second temperature zone is controlled to be 210-250 °C, preferably 220-250 °C, more preferably 230-250 °C, such as 220 °C, 225 °C, 230 °C, 235 °C, 240 °C, 245 °C or 250 °C.

[0013] In a further preferred embodiment, the temperature of the second temperature zone is controlled to be 15 to 45 °C higher than that of the first temperature zone, preferably 15 to 35 °C higher, more preferably 15 to 30 °C higher, such as 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C or 45 °C higher.

[0014] In a preferred embodiment, the temperature of the third temperature zone is controlled to be 260 to 290 °C, preferably 260 to 280 °C, such as 260 °C, 265 °C, 270 °C, 275 °C or 280 °C.

[0015] In a further preferred embodiment, the temperature of the third temperature zone is controlled to be 15 to 45 °C higher than that of the second temperature zone, preferably 15 to 35 °C higher, more preferably 20 to 30 °C higher, such as 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C or 45 °C higher.

[0016] In a preferred embodiment, the draft ratio of the pre-oxidation is controlled to be -10% to 10%, preferably -5% to 5%.

[0017] In a further preferred embodiment, in the order of the pretreatment, the draft ratio of the first temperature zone is controlled to be 0.5% to 5.0%; and / or, the draft ratio of the second temperature zone is controlled to be -5.0% to -0.5%; and / or, the draft ratio of the third temperature zone is controlled to be -3.0% to -1.0%.

[0018] For example, in the order of the pretreatment, the draft ratio of the first temperature zone is controlled to be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5.0%; and / or, the draft ratio of the second temperature zone is controlled to be -5.0%, -4.5%, -4.0%, -3.5%, -3.0%, -2.5%, -2.0%, -1.5%, -1.0% or -0.5%; and / or, the draft ratio of the third temperature zone is controlled to be -3.0%, -2.5%, -2.0%, -1.5% or -1.0%.

[0019] In a further preferred embodiment, in the order of the pretreatment, the draft ratio of the first temperature zone is controlled to be 1 to 4%; and / or, the draft ratio of the second temperature zone is controlled to be -5.0 to -1%.

[0020] In a preferred embodiment, the total residence time of the three temperature zones is 15 to 150 min, preferably 25 to 120 min, such as 15 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min or 150 min.

[0021] In a further preferred embodiment, the residence time in each temperature zone is independently 5 to 50 min, preferably 8 to 40 min, such as 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min or 50 min.

[0022] In a preferred embodiment, in the order of pretreatment, the cyclization degree (CI) of the fiber after treatment in the first temperature zone is 0.2 to 0.4, the cyclization degree (CI) of the fiber after treatment in the second temperature zone is 0.4 to 0.6, and the cyclization degree (CI) of the fiber after treatment in the first temperature zone is 0.6 to 0.8.

[0023] For example, in the order of pretreatment, the cyclization degree (CI) of the fiber obtained in the first temperature zone is 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38 or 0.4, the cyclization degree (CI) of the fiber obtained in the second temperature zone is 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58 or 0.6, and the cyclization degree (CI) of the fiber obtained in the first temperature zone is 0.6, 0.62, 0.64, 0.66, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78 or 0.8.

[0024] In a further preferred embodiment, in the order of pretreatment, the cyclization degree of the fiber after treatment in the latter temperature zone is higher than that of the fiber after treatment in the previous temperature zone, preferably 0.15 to 0.35 higher, such as 0.15, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34 or 0.35 higher.

[0025] After a large number of experimental studies, the inventors found that strictly controlling the temperature, drawing ratio and time in each temperature zone of the pre-oxidation within the scope defined in the present invention, especially within the preferred scope and more preferred scope, can avoid over-pre-oxidation or under-pre-oxidation, and reasonably control the cyclization reaction and oxidation reaction of the fiber during the pre-oxidation process. Taking the cyclization degree of the fiber in the pre-oxidation stage as the structure control index, through the regulation and design of key parameters such as pre-oxidation temperature, drawing ratio and residence time, pre-oxidized fibers with perfect structure are prepared.

[0026] Furthermore, the inventors found that when the cyclization degree of the fiber is controlled within the above range, when applied to carbon fibers, the performance of the final product carbon fiber can be improved. For example, high-modulus carbon fibers with a tensile strength higher than 4.0 GPa and a tensile modulus higher than 300 GPa can be obtained, achieving good technical effects.

[0027] The second object of the present invention is to provide an application of the polyacrylonitrile pre-oxidation method described in the first object of the present invention, preferably an application in the preparation of high-modulus carbon fibers based on polyacrylonitrile.

[0028] The third object of the present invention is to provide a method for preparing high-modulus carbon fibers based on polyacrylonitrile, comprising: polyacrylonitrile pre-oxidation treatment and carbonization treatment under a protective atmosphere, wherein the polyacrylonitrile pre-oxidation treatment is carried out by using the method described in the first object of the present invention.

[0029] In a preferred embodiment, the carbonization treatment includes a first carbonization treatment under a protective atmosphere and a second carbonization treatment under a protective atmosphere, and the temperature of the second carbonization treatment is higher than that of the first carbonization treatment.

[0030] Wherein, the protective atmosphere is selected from at least one of nitrogen and inert gases, preferably nitrogen and / or argon.

[0031] In a further preferred embodiment, the first carbonization treatment includes: under a protective atmosphere, carbonization is carried out in 2 to 7 temperature zones at a draw ratio of 0 to 10% and a temperature of 200 to 1000 °C.

[0032] Preferably, the first carbonization treatment includes: under a protective atmosphere, carbonization is carried out in 4 to 6 temperature zones at a draw ratio of 0 to 8% and a temperature of 300 to 900 °C; more preferably, in the order of treatment, the temperature of the latter temperature zone is higher than that of the former temperature zone.

[0033] For example, the first carbonization treatment includes: the draw ratio is 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7% or 8%, the temperature is 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, 800 °C or 900 °C, and it is divided into 2, 3, 4, 5, 6 or 7 temperature zones.

[0034] In a further preferred embodiment, the second carbonization treatment includes: under a protective atmosphere, carbonization is carried out in 2 to 7 temperature zones at a draw ratio of -10 to 0% and a temperature of 800 to 2000 °C; more preferably, in the order of treatment, the temperature of the latter temperature zone is higher than that of the former temperature zone.

[0035] Preferably, the second carbonization treatment includes: under a protective atmosphere, carbonization is carried out in 4 to 6 temperature zones at a draw ratio of -8 to 0% and a temperature of 1000 to 1800 °C.

[0036] For example, the second carbonization treatment includes: the draw ratio is -8%, -7%, -6%, -5%, -4%, -3%, -2%, -1% or 0%, the temperature is 800 °C, 1000 °C, 1200 °C, 1400 °C, 1600 °C, 1800 °C or 2000 °C, and it is divided into 4, 5 or 6 temperature zones.

[0037] In a preferred embodiment, the time of the first carbonization treatment and the second carbonization treatment are each independently 1 to 30 min, preferably 1 to 20 min, more preferably 1 to 5 min, for example 1 to 4 min, specifically for example 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min or 30 min.

[0038] The fourth object of the present invention is to provide a polyacrylonitrile-based high-modulus carbon fiber obtained by using the preparation method described in the third object of the present invention.

[0039] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. In the following text, in principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be regarded as specifically disclosed herein.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The preoxidation method of the present invention avoids over-preoxidation or under-preoxidation, and reasonably controls the cyclization reaction and oxidation reaction of the fiber during the preoxidation process.

[0042] (2) Taking the cyclization degree of the fiber in the preoxidation stage as the structure control index, through the regulation and design of key parameters such as preoxidation temperature, draw ratio, and residence time, preoxidized fibers with perfect structures are prepared, and thus high-modulus carbon fibers are prepared.

[0043] (3) The method of the present invention is simple and easy to operate and has strong controllability. In particular, high-modulus carbon fibers with a tensile strength higher than 4.0 GPa and a tensile modulus higher than 300 GPa can be obtained through structure control, achieving good technical effects. Specific Embodiments

[0044] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only for further illustration of the present invention and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art to the present invention based on the content of the present invention still fall within the protection scope of the present invention.

[0045] In addition, it should be noted that the various specific technical features described in the following specific embodiments can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0046] Furthermore, any combination can be made among the various different embodiments of the present invention as long as it does not violate the idea of the present invention. The technical solutions thus formed belong to a part of the original public content of this specification and also fall within the protection scope of the present invention.

[0047] The raw materials used in the examples and comparative examples, if not specifically defined, are those publicly disclosed in the prior art. For example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0048] The mechanical properties (tensile strength and tensile modulus) of carbon fiber were measured by referring to the method of GB / T 3362-2017 (Test Method for Tensile Properties of Carbon Fiber Multifilament).

[0049] The cyclization degree of the pre-oxidized fiber at each stage was tested by a Fourier transform infrared spectrometer. The test conditions were as follows: the wave number acquisition range was 4000~650 cm -1 . The cyclization degree CI = 0.29I 1590 / (0.29I 1590 + I 2243 ), where I 1590 and I 2243 are the absorption peak intensities of the sample at 1590 cm -1 and 2243 cm -1 respectively, which are used to judge the degree of the cyclization reaction.

[0050]

Example 1

[0051] Domestic polyacrylonitrile fiber is used (its tow is 12K, and the copolymer composition (wt%) is: acrylonitrile (AN) 95.5%, methyl acrylate (MA) 3.5%, itaconic acid (IA) 1%). In an air medium, three heating furnaces are used as three temperature zones for pre-oxidation treatment. The temperatures of each zone are 210°C, 240°C, and 270°C respectively. The total residence time in the three temperature zones is 60 min (the residence time in each heating furnace is approximately 20 min), and the draw ratios of each section are 3.0%, -3.0%, and -2.0%. After the pre-oxidation three-temperature-zone heat treatment, the CI values of the fiber cyclization degree in each zone are 0.25, 0.51, and 0.71 respectively. The first carbonization is carried out using the first carbonization furnace: the pre-oxidized fiber is subjected to low-temperature carbonization treatment in five temperature zones in the first carbonization furnace under the protection of nitrogen. The temperatures of the low-temperature carbonization treatment in each temperature zone are 350°C, 450°C, 500°C, 600°C, and 750°C respectively. The total residence time in the first carbonization furnace is 3 min, and a draw ratio of 3% is applied; the second carbonization is carried out using the second carbonization furnace: the fiber after the first carbonization treatment is subjected to high-temperature carbonization treatment in five temperature zones in the second carbonization furnace under the protection of nitrogen. The temperatures of the high-temperature carbonization treatment in each temperature zone are 1100°C, 1250°C, 1350°C, 1400°C, and 1500°C respectively. A draw ratio of -3% is applied, and the total residence time in the second carbonization furnace is 3 min to obtain carbon fiber. The tensile strength of the carbon fiber is 5.3 GPa, and the tensile modulus is 310 GPa.

[0052]

Example 2

[0053] Domestic polyacrylonitrile fiber is used (its tow is 12K, and the copolymer composition (wt%) is: acrylonitrile (AN) 95.5%, methyl acrylate (MA) 3.5%, itaconic acid (IA) 1%). In an air medium, three heating furnaces are used as three temperature zones for pre-oxidation treatment. The temperatures of each zone are 220°C, 250°C, and 270°C respectively. The total residence time in the three temperature zones is 40 min (the residence time in each zone is approximately 13 - 14 min respectively), and the draw ratios of each section are 3.0%, -3.0%, and -2.0%. After the pre-oxidation three-temperature-zone heat treatment, the cyclization degree CI values of the fibers in each zone are 0.29, 0.49, and 0.69 respectively. The first carbonization is carried out in the first carbonization furnace: the pre-oxidized fibers are subjected to low-temperature carbonization treatment in five temperature zones in the first carbonization furnace under the protection of nitrogen. The temperatures of the low-temperature carbonization treatment in each zone are 350°C, 450°C, 500°C, 600°C, and 750°C respectively. The total residence time in the first carbonization furnace is 3 min, and a draw ratio of 3% is applied; the second carbonization is carried out in the second carbonization furnace: the fibers after the first carbonization treatment are subjected to high-temperature carbonization treatment in five temperature zones in the second carbonization furnace under the protection of nitrogen. The temperatures of the high-temperature carbonization treatment in each zone are 1100°C, 1250°C, 1350°C, 1400°C, and 1500°C respectively. A draw ratio of -3% is applied, and the total residence time in the second carbonization furnace is 3 min to obtain carbon fibers. The tensile strength of the carbon fibers is 5.1 GPa, and the tensile modulus is 307 GPa.

[0054]

Example 3

[0055] Domestic polyacrylonitrile fiber is used (its tow is 12K, and the copolymer composition (wt%) is respectively: acrylonitrile (AN) 95.5%, methyl acrylate (MA) 3.5%, itaconic acid (IA) 1%). In an air medium, three heating furnaces are used as three temperature zones for pre-oxidation treatment. The temperatures of each zone are 210°C, 235°C, and 260°C respectively. The total residence time in the three temperature zones is 40 min (the residence time in each zone is approximately 13 - 14 min respectively), and the draw ratios in each zone are 3.0%, -3.0%, and -2.0%. After the pre-oxidation three-temperature-zone heat treatment, the cyclization degree CI values of the fibers in each zone are 0.24, 0.43, and 0.63 respectively. The first carbonization is carried out in the first carbonization furnace: the pre-oxidized fibers are subjected to low-temperature carbonization treatment in five temperature zones in the first carbonization furnace under the protection of nitrogen. The temperatures of the low-temperature carbonization treatment in each zone are 350°C, 450°C, 500°C, 600°C, and 750°C respectively. The total residence time in the first carbonization furnace is 3 min, and a draw ratio of 3% is applied; the second carbonization is carried out in the second carbonization furnace: the fibers after the first carbonization treatment are subjected to high-temperature carbonization treatment in five temperature zones in the second carbonization furnace under the protection of nitrogen. The temperatures of the high-temperature carbonization treatment in each zone are 1100°C, 1250°C, 1350°C, 1400°C, and 1500°C respectively. A draw ratio of -3% is applied, and the total residence time in the second carbonization furnace is 3 min to obtain carbon fibers. The tensile strength of the carbon fibers is 4.8 GPa, and the tensile modulus is 305 GPa.

[0056]

Example 4

[0057] Domestic polyacrylonitrile fiber is used (its tow is 12K, and the copolymer composition (wt%) is respectively: acrylonitrile (AN) 95.5%, methyl acrylate (MA) 3.5%, itaconic acid (IA) 1%). In an air medium, three heating furnaces are used as three temperature zones for pre-oxidation treatment. The temperatures of the three temperature zones are 225°C, 250°C, and 280°C respectively. The total residence time in the three temperature zones is 40 min (the residence time in each temperature zone is about 13 - 14 min respectively). The draw ratios of each section are 4.0%, -3.0%, and -2.0%. After the pre-oxidation three-temperature-zone heat treatment, the cyclization degree CI values of the fibers in each zone are 0.33, 0.55, and 0.76 respectively. The first carbonization is carried out using the first carbonization furnace: The pre-oxidized fibers are subjected to low-temperature carbonization treatment in five temperature zones in the first carbonization furnace under the protection of nitrogen. The temperatures of the low-temperature carbonization treatment in each temperature zone are 350°C, 450°C, 500°C, 600°C, and 750°C respectively. The total residence time in the first carbonization furnace is 3 min, and a draw ratio of 3% is applied; The second carbonization is carried out using the second carbonization furnace: The fibers after the first carbonization treatment are subjected to high-temperature carbonization treatment in five temperature zones in the second carbonization furnace under the protection of nitrogen at a temperature of 1000 - 1800°C. The temperatures of the high-temperature carbonization treatment in each temperature zone are 1100°C, 1250°C, 1350°C, 1400°C, and 1500°C respectively. A draw ratio of -3% is applied, and the total residence time in the second carbonization furnace is 3 min to obtain carbon fiber. The tensile strength of the carbon fiber is 4.7 GPa, and the tensile modulus is 307 GPa.

[0058]

Example 5

[0059] Domestic polyacrylonitrile fiber is used (the tow is 3K, and the copolymer composition (wt%) is: acrylonitrile (AN) 97.5%, itaconic acid (IA) 2.5%). In an air medium, three heating furnaces are used as three temperature zones for pre-oxidation treatment. The temperatures of each zone are 215°C, 235°C, and 265°C respectively. The total residence time in the three temperature zones is 60 min (the residence time in each zone is approximately 20 min). The draw ratios of each section are 4.0%, -3.0%, and -2.0%. After the pre-oxidation three-temperature zone heat treatment, the cyclization degree CI values of the fibers in each zone are 0.27, 0.50, and 0.68 respectively. The first carbonization is carried out using the first carbonization furnace: The pre-oxidized fibers are subjected to low-temperature carbonization treatment in five temperature zones in the first carbonization furnace under the protection of nitrogen. The temperatures of the low-temperature carbonization treatment in each zone are 350°C, 450°C, 500°C, 600°C, and 720°C respectively. The total residence time in the first carbonization furnace is 3 min, and a draw ratio of 3% is applied; The second carbonization is carried out using the second carbonization furnace: The fibers after the first carbonization treatment are subjected to high-temperature carbonization treatment in the second carbonization furnace under the protection of nitrogen. The temperatures are 1100°C, 1250°C, 1350°C, 1400°C, and 1480°C respectively, and a draw ratio of -3% is applied. The total residence time in the second carbonization furnace is 3 min to obtain carbon fiber. The tensile strength of the carbon fiber is 5.7 GPa, and the tensile modulus is 309 GPa.

[0060]

Example 6

[0061] Domestic polyacrylonitrile fiber is used (its tow is 48K, and the copolymer composition (wt%) is respectively: acrylonitrile (AN) 91.0%, methyl acrylate (MA) 4.5%, itaconic acid (IA) 4.5%). In an air medium, three heating furnaces are used as three temperature zones for pre-oxidation treatment. The temperatures of each zone are 205°C, 235°C, and 265°C respectively. The total residence time in the three temperature zones is 80 min (the residence time in each zone is approximately 26 - 27 min respectively), and the draw ratios of each section are 3.0%, -3.0%, and -2.0%. After the pre-oxidation three-temperature-zone heat treatment, the cyclization degree CI values of the fibers in each zone are 0.23, 0.49, and 0.69 respectively. The first carbonization is carried out using the first carbonization furnace: The pre-oxidized fibers are subjected to low-temperature carbonization treatment in five temperature zones in the first carbonization furnace under the protection of nitrogen. The temperatures of the low-temperature carbonization treatment in each zone are 350°C, 450°C, 500°C, 600°C, and 680°C respectively. The total residence time in the first carbonization furnace is 3 min, and a 3% draw ratio is applied; The second carbonization is carried out using the second carbonization furnace: The fibers after the first carbonization treatment are subjected to high-temperature carbonization treatment in five temperature zones in the second carbonization furnace under the protection of nitrogen. The temperatures of the high-temperature carbonization treatment in each zone are 1100°C, 1250°C, 1350°C, 1400°C, and 1450°C respectively, and a -3% draw ratio is applied. The total residence time in the second carbonization furnace is 3 min to obtain carbon fibers. The tensile strength of the carbon fibers is 4.5 GPa, and the tensile modulus is 306 GPa.

[0062]

Example 7

[0063] Domestic polyacrylonitrile fiber is used (its tow is 12K, and the copolymer composition (wt%) is respectively: acrylonitrile (AN) 95.5%, methyl acrylate (MA) 3.5%, itaconic acid (IA) 1%). In an air medium, three heating furnaces are used as three temperature zones for pre-oxidation treatment. The temperatures of each zone are 210°C, 240°C, and 270°C respectively. The total residence time in the three temperature zones is 60 min (the residence time in each heating furnace is approximately 20 min respectively), and the draw ratios of each section are 3.0%, -5.0%, and -1.0%. After the pre-oxidation heat treatment in the three-temperature zone, the cyclization degree CI values of the fibers in each zone are 0.25, 0.52, and 0.72 respectively. The first carbonization is carried out using the first carbonization furnace: The pre-oxidized fibers are subjected to low-temperature carbonization treatment in five temperature zones in the first carbonization furnace under the protection of nitrogen. The temperatures of the low-temperature carbonization treatment in each temperature zone are 350°C, 450°C, 500°C, 600°C, and 750°C respectively. The total residence time in the first carbonization furnace is 3 min, and a draw ratio of 3% is applied; The second carbonization is carried out using the second carbonization furnace: The fibers after the first carbonization treatment are subjected to high-temperature carbonization treatment in five temperature zones in the second carbonization furnace under the protection of nitrogen. The temperatures of the high-temperature carbonization treatment in each temperature zone are 1100°C, 1250°C, 1350°C, 1400°C, and 1500°C respectively. A draw ratio of -3% is applied, and the total residence time in the second carbonization furnace is 3 min to obtain carbon fiber. The tensile strength of the carbon fiber is 5.2 GPa, and the tensile modulus is 311 GPa.

[0064]

Example 8

[0065] Domestic polyacrylonitrile fiber is used (its tow is 48K, and the copolymer composition (wt%) is respectively: acrylonitrile (AN) 91.0%, methyl acrylate (MA) 4.5%, itaconic acid (IA) 4.5%). In an air medium, three heating furnaces are used as three temperature zones for pre-oxidation treatment. The temperatures of each zone are 205°C, 235°C, and 265°C respectively. The total residence time in the three temperature zones is 80 min (the residence time in each zone is about 26 - 27 min respectively), and the draw ratios of each section are 3.0%, -0.5%, and -3.0%. After the pre-oxidation three-temperature-zone heat treatment, the cyclization degree CI values of the fibers in each zone are 0.23, 0.47, and 0.66 respectively. The first carbonization is carried out using the first carbonization furnace: The pre-oxidized fibers are subjected to low-temperature carbonization treatment in five temperature zones in the first carbonization furnace under the protection of nitrogen. The temperatures of the low-temperature carbonization treatment in each zone are 350°C, 450°C, 500°C, 600°C, and 680°C respectively. The total residence time in the first carbonization furnace is 3 min, and a draw ratio of 3% is applied; The second carbonization is carried out using the second carbonization furnace: The fibers after the first carbonization treatment are subjected to high-temperature carbonization treatment in five temperature zones in the second carbonization furnace under the protection of nitrogen. The temperatures of the high-temperature carbonization treatment in each zone are 1100°C, 1250°C, 1350°C, 1400°C, and 1450°C respectively, and a draw ratio of -3% is applied. The total residence time in the second carbonization furnace is 3 min to obtain carbon fibers. The tensile strength of the carbon fibers is 4.3 GPa, and the tensile modulus is 303 GPa.

[0066]

Comparative Example 1

[0067] Domestic polyacrylonitrile fiber is used (its tow is 12K, and the copolymer composition (wt%) is respectively: acrylonitrile (AN) 95.5%, methyl acrylate (MA) 3.5%, itaconic acid (IA) 1%). In an air medium, three heating furnaces are used as three temperature zones for pre-oxidation treatment. The temperatures of each zone are 210°C, 225°C, and 240°C respectively. The total residence time in the three temperature zones is 60 minutes (the residence time in each zone is approximately 20 minutes), and the draw ratios of each section are 3.0%, -3.0%, and -2.0%. After the pre-oxidation three-temperature zone heat treatment, the cyclization degree CI values of the fibers in each zone are 0.24, 0.37, and 0.53 respectively. The first carbonization is carried out using the first carbonization furnace: the pre-oxidized fibers are subjected to low-temperature carbonization treatment in five temperature zones in the first carbonization furnace under the protection of nitrogen. The temperatures of the low-temperature carbonization treatment in each zone are 350°C, 450°C, 500°C, 600°C, and 750°C respectively. The total residence time in the first carbonization furnace is 3 minutes, and a draw ratio of 3% is applied; the second carbonization is carried out using the second carbonization furnace: the fibers after the first carbonization treatment are subjected to high-temperature carbonization treatment in five temperature zones in the second carbonization furnace under the protection of nitrogen. The temperatures of the high-temperature carbonization treatment in each zone are 1100°C, 1250°C, 1350°C, 1400°C, and 1500°C respectively. A draw ratio of -3% is applied, and the total residence time in the second carbonization furnace is 3 minutes to obtain carbon fiber. The tensile strength of the carbon fiber is 3.9 GPa, and the tensile modulus is 290 GPa.

[0068]

Comparative Example 2

[0069] Domestic polyacrylonitrile fiber is used (its tow is 12K, and the copolymer composition (wt%) is respectively: acrylonitrile (AN) 95.5%, methyl acrylate (MA) 3.5%, itaconic acid (IA) 1%). In an air medium, three heating furnaces are used as three temperature zones for pre-oxidation treatment. The temperatures of each zone are 175°C, 235°C, and 285°C respectively. The total residence time in the three temperature zones is 60 min (the residence time in each zone is approximately 20 min respectively), and the draw ratios in each zone are 3.0%, -3.0%, and -2.0%. After the pre-oxidation heat treatment in the three temperature zones, the cyclization degree CI values of the fibers in each zone are 0.11, 0.29, and 0.55 respectively. The first carbonization is carried out using the first carbonization furnace: the pre-oxidized fibers are subjected to low-temperature carbonization treatment in five temperature zones in the first carbonization furnace under the protection of nitrogen. The temperatures of the low-temperature carbonization treatment in each zone are 350°C, 450°C, 500°C, 600°C, and 750°C respectively. The total residence time in the first carbonization furnace is 3 min, and a 3% draw ratio is applied; the second carbonization is carried out using the second carbonization furnace: the fibers after the first carbonization treatment are subjected to high-temperature carbonization treatment in each zone under the protection of nitrogen. The temperatures of the high-temperature carbonization treatment in each zone are 1100°C, 1250°C, 1350°C, 1400°C, and 1500°C respectively, and a -3% draw ratio is applied. The total residence time in the second carbonization furnace is 3 min to obtain carbon fibers. The tensile strength of the carbon fibers is 3.3 GPa, and the tensile modulus is 275 GPa.

[0070]

Comparative Example 3

[0071] Domestic polyacrylonitrile fiber is used (its tow is 12K, and the copolymer composition (wt%) is respectively: acrylonitrile (AN) 95.5%, methyl acrylate (MA) 3.5%, itaconic acid (IA) 1%). In an air medium, three heating furnaces are used as three temperature zones for pre-oxidation treatment. The temperatures of each zone are 235°C, 265°C, and 295°C respectively. The total residence time in the three temperature zones is 60 min (the residence time in each zone is approximately 20 min respectively), and the draw ratios in each section are 3.0%, -3.0%, and -2.0%. The tow cannot operate continuously and stably during the pre-oxidation stage.

[0072] By adopting the technical solution of the present invention, the cyclization reaction and oxidation reaction of the fiber during pre-oxidation can be reasonably controlled. Through the regulation and design of key parameters such as pre-oxidation temperature, draw ratio, and residence time, pre-oxidized fibers with perfect structures can be prepared, thereby preparing high-modulus carbon fibers, which have great technical advantages and can be used in the industrial production of polyacrylonitrile-based high-modulus carbon fibers.

[0073] The present invention has been described in detail above in connection with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solutions and their implementation manners of the present invention, and these all fall within the scope of the present invention. The protection scope of the present invention shall be subject to the appended claims.

Claims

1. A method for pre-oxidizing polyacrylonitrile, comprising: Pre-oxidizing the polyacrylonitrile in at least three temperature zones in an air atmosphere. Among them, the first three temperature zones are controlled as follows according to the order of pretreatment: the temperature of the first temperature zone is controlled at 180-230 °C, the temperature of the second temperature zone is controlled at 210-260 °C, and the temperature of the third temperature zone is controlled at 250-300 °C.

2. The method for pre-oxidizing polyacrylonitrile according to claim 1, characterized in that the polyacrylonitrile is an acrylonitrile fiber bundle, and preferably the number of the acrylonitrile fiber bundles is 1-100K.

3. The method for pre-oxidizing polyacrylonitrile according to claim 1, characterized in that the temperature of the first temperature zone is controlled at 200-230 °C; and / or, the temperature of the second temperature zone is controlled at 210-250 °C; and / or, the temperature of the third temperature zone is controlled at 260-290 °C.

4. The method for pre-oxidizing polyacrylonitrile according to claim 1, characterized in that the draw ratio of the pre-oxidation is controlled at -10% to 10%, preferably -5% to 5%.

5. The method for pre-oxidizing polyacrylonitrile according to claim 4, characterized in that According to the order of pretreatment, the draw ratio of the first temperature zone is controlled at 0.5% to 5.0%; and / or, the draw ratio of the second temperature zone is controlled at -5.0% to -0.5%; and / or, the draw ratio of the third temperature zone is controlled at -3.0% to -1.0%.

6. The method for pre-oxidizing polyacrylonitrile according to any one of claims 1-5, characterized in that According to the order of pretreatment, the fiber cyclization degree after treatment in the first temperature zone is 0.2-0.4, the fiber cyclization degree after treatment in the second temperature zone is 0.4-0.6, and the fiber cyclization degree after treatment in the first temperature zone is 0.6-0.

8.

7. The method for pre-oxidizing polyacrylonitrile according to claim 6, characterized in that According to the order of pretreatment, the fiber cyclization degree after treatment in the latter temperature zone is higher than that after treatment in the previous temperature zone.

8. The application of the method for pre-oxidizing polyacrylonitrile according to any one of claims 1-7, preferably the application in the preparation of polyacrylonitrile-based high-modulus carbon fiber.

9. A method for preparing polyacrylonitrile-based high-modulus carbon fiber, comprising: Pre-oxidation treatment of polyacrylonitrile and carbonization treatment under a protective atmosphere, wherein the pre-oxidation treatment of polyacrylonitrile is carried out by using the method according to any one of claims 1-7.

10. The preparation method according to claim 9, characterized in that the carbonization treatment includes a first carbonization treatment under a protective atmosphere and a second carbonization treatment under a protective atmosphere, and the temperature of the second carbonization treatment is higher than that of the first carbonization treatment; preferably, the protective atmosphere is selected from at least one of nitrogen and inert gas.

11. The preparation method according to claim 10, characterized in that the first carbonization treatment includes: under a protective atmosphere, carbonization is carried out in 2-7 temperature zones at a draw ratio of 0-10% and a temperature of 200-1000 °C; and / or, The second carbonization treatment includes: carbonizing in 2 to 7 temperature zones at a draw ratio of -10 to 0% and a temperature of 1000 to 1800°C under a protective atmosphere; and / or, The time of the first carbonization treatment and the second carbonization treatment are each independently 1 to 30 minutes, preferably 1 to 20 minutes, more preferably 1 to 5 minutes.