Preparation method of large-tow carbon fiber and obtained large-tow carbon fiber

Abstract

The invention discloses a preparation method of large-tow carbon fibers and the obtained large-tow carbon fibers, and the preparation method comprises the following steps: pre-oxidizing large-tow polyacrylonitrile-based protofilaments for 40-80 minutes at the temperature of 180-300 DEG C, adopting 2-4 temperature zones for pre-oxidation, controlling the cyclization degree difference value of pre-oxidized fibers in adjacent temperature zones to be 10-25% and the oxygen content difference value to be 0.8-2% to prepare pre-oxidized fibers, and carrying out carbonization treatment on the pre-oxidized fiber to prepare the large-tow carbon fiber. In the large-tow polyacrylonitrile-based carbon fiber pre-oxidation stage, a better progressive pre-oxidation fiber structure is obtained through fine control of a cyclization structure, an oxidation structure and a microcrystalline structure, a good foundation is provided for subsequent carbonization, and meanwhile, smaller fiber structure difference is beneficial to reduction of performance dispersion and improvement of fiber quality stability. The tensile strength of the prepared large-tow carbon fibers is larger than or equal to 5.0 GPa, the dispersion coefficient of the tensile strength in batches is smaller than or equal to 3%, and the tensile modulus is larger than or equal to 240 GPa.

Description

Technical Field

[0001] This invention relates to the field of large-tow carbon fiber preparation technology, and more specifically, to a method for preparing large-tow carbon fiber and the resulting large-tow carbon fiber. Background Technology

[0002] Large-tow carbon fiber typically refers to carbon fiber with a tow count ≥48K and a carbon content of over 90%. It possesses both the excellent inherent properties of carbon graphite materials and the good processing capabilities of textile fibers, exhibiting advantages such as high strength, high modulus, good temperature resistance, excellent corrosion resistance, and low density. Large-tow carbon fiber has been widely used in wind turbine blades, bridge construction, sporting goods, and other fields. Pre-oxidation is a crucial intermediate process in the production of polyacrylonitrile-based carbon fiber. It acts as a bridge between the precursor fiber and the carbon fiber, controlling both the quality and yield of the carbon fiber. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned deficiencies of the prior art and to provide a method for preparing large-tow carbon fiber and the resulting large-tow carbon fiber.

[0004] The technical problem solved by this invention is achieved by the following technical solution.

[0005] This invention provides a method for preparing large-tow carbon fiber, comprising: pre-oxidizing large-tow polyacrylonitrile-based precursor fibers at a temperature of 180-300℃ for 40-80 minutes, wherein the pre-oxidation adopts 2-4 temperature zones, and the difference in cyclization degree of pre-oxidized fibers between adjacent temperature zones is controlled to be 10%-25%, and the difference in oxygen content is controlled to be 0.8%-2% to prepare pre-oxidized fibers, wherein the pre-oxidized fibers are then subjected to carbonization treatment to prepare large-tow carbon fiber.

[0006] The present invention also provides a large-tow carbon fiber prepared according to the above-described preparation method.

[0007] The present invention has the following beneficial effects: In the pre-oxidation stage of large-tow polyacrylonitrile-based carbon fibers, the present invention can obtain a superior progressive pre-oxidized fiber structure through precise control of cyclization structure, oxidation structure and microcrystalline structure, which provides a good foundation for subsequent carbonization. At the same time, the smaller fiber structure difference helps to reduce performance dispersion and improve fiber quality stability.

[0008] The large-tow carbon fibers prepared by this invention have excellent properties, with tensile strength ≥5.0GPa, tensile strength intra-batch dispersion coefficient ≤3%, and tensile modulus ≥240GPa. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0010] The following is a detailed description of a method for preparing large-tow carbon fiber and the resulting large-tow carbon fiber provided by an embodiment of the present invention.

[0011] In a first aspect, the present invention provides a method for preparing large-tow carbon fiber, comprising: pre-oxidizing large-tow polyacrylonitrile-based precursor fibers at a temperature of 180-300℃ for 40-80 minutes, wherein the pre-oxidation adopts 2-4 temperature zones, and the difference in cyclization degree of pre-oxidized fibers between adjacent temperature zones is controlled to be 10%-25%, and the difference in oxygen content is controlled to be 0.8%-2% to prepare pre-oxidized fibers, wherein the pre-oxidized fibers are then subjected to carbonization treatment to prepare large-tow carbon fiber.

[0012] In carbon fiber preparation, pre-oxidation is a key process. Industrial production typically employs a series of oxidation furnaces with gradient heating to pre-oxidize polyacrylonitrile (PAC)-based fibers. During this process, PACs undergo complex chemical reactions such as cyclization, oxidation, and dehydrogenation, causing the molecular chains to unwind and develop into a cyclic ladder structure. Further thermal decomposition and thermal condensation occur during carbonization, forming a disordered graphite structure. Therefore, the cyclic ladder structure formed during pre-oxidation forms the basis of the disordered graphite structure and is a crucial factor affecting carbon fiber performance. This invention achieves this by precisely controlling the fiber structure during the pre-oxidation stage, resulting in pre-oxidized fibers with a progressive microstructure and large-tow carbon fibers exhibiting excellent mechanical properties and quality stability.

[0013] In some alternative embodiments, during the pre-oxidation process, the temperature gradient of 2-4 temperature zones increases progressively, the pre-oxidation time of each temperature zone is the same, and the total pre-oxidation time is controlled to be 40-80 min.

[0014] In some specific embodiments, the dry-jet wet-spun large-tow PAN precursor yarn is pre-oxidized at three temperature gradients of 200℃, 230℃, and 250℃, with a pre-oxidation time of 20 min for each temperature zone, and a total pre-oxidation time of 60 min; or, the dry-jet wet-spun large-tow PAN precursor yarn is pre-oxidized at three temperature gradients of 220℃, 250℃, and 270℃, with a pre-oxidation time of 20 min for each temperature zone, and a total pre-oxidation time of 60 min; or, the dry-jet wet-spun large-tow PAN precursor yarn is pre-oxidized at three temperature gradients of 240℃, 270℃, and 290℃. Pre-oxidation can be performed under a temperature gradient, with each temperature zone having a pre-oxidation time of 20 minutes, controlling the total pre-oxidation time to 60 minutes; alternatively, dry-jet wet-spun large-tow PAN precursor fibers can be pre-oxidized under three temperature gradients of 180℃, 210℃, and 230℃, with each temperature zone having a pre-oxidation time of 20 minutes, controlling the total pre-oxidation time to 60 minutes; or dry-jet wet-spun large-tow PAN precursor fibers can be pre-oxidized under three temperature gradients of 200℃, 240℃, and 280℃, with each temperature zone having a pre-oxidation time of 20 minutes, controlling the total pre-oxidation time to 60 minutes. Furthermore, the pre-oxidation method is not limited to the above methods; as long as the difference in cyclization degree between pre-oxidized fibers in adjacent temperature zones is controlled to be 10%-25% and the difference in oxygen content to be 0.8%-2% after pre-oxidation, the pre-oxidized fibers can be prepared.

[0015] In some alternative embodiments, the large tow polyacrylonitrile (PAN) precursor is prepared by one of the following methods: dry-jet wet spinning, wet spinning, or electrospinning. Preferably, the large tow polyacrylonitrile (PAN) precursor is prepared by dry-jet wet spinning.

[0016] In some alternative embodiments, the degree of cyclization of the pre-oxidized fiber ranges from 30% to 80%, and the difference in degree of cyclization between adjacent temperature zones is 10% to 25%. Preferably, the difference in circulatory degree between adjacent temperature zones is 12-20%.

[0017] For example, the degree of cyclization of the pre-oxidized fiber can be any other value between 30%, 40%, 50%, 60%, 70%, 80%, or 30-80%, and the difference in degree of cyclization between adjacent temperature zones can be any other value between 10%, 15%, 20%, 25%, or 10-25%.

[0018] In some alternative embodiments, the oxygen content of the pre-oxidized fiber ranges from 3% to 10%, and the oxygen content difference between adjacent temperature zones is 0.8% to 2%. Preferably, the oxygen content difference between adjacent temperature zones is 1.0%-1.5%.

[0019] For example, the oxygen content of the pre-oxidized fiber can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any other value between 3% and 10%, and the oxygen content difference between adjacent temperature zones can be 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0% or any other value between 0.8% and 2%.

[0020] In some alternative embodiments, the crystallinity of the pre-oxidized fiber ranges from 5% to 70%, and the crystallinity difference between adjacent temperature zones is 15% to 35%. Preferably, the crystallinity difference between adjacent temperature zones is 20-30%.

[0021] For example, the crystallinity of the pre-oxidized fiber can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any other value between 5% and 70%, and the crystallinity difference between adjacent temperature zones can be 15%, 20%, 25%, 30%, 35%, or any other value between 15% and 35%.

[0022] In some alternative embodiments, the total pre-oxidation time is 50-70 min.

[0023] For example, the total pre-oxidation time can be 50 min, 55 min, 60 min, 65 min, 70 min, or any other value between 50 and 70 min.

[0024] In some alternative embodiments, the carbonization process includes low-temperature carbonization and high-temperature carbonization, wherein: low-temperature carbonization uses six temperature zones with a temperature of 500-800°C, and high-temperature carbonization uses nine temperature zones with a temperature of 900°C-1600°C.

[0025] For example, low-temperature carbonization uses six temperature zones with temperatures of 500℃, 560℃, 620℃, 680℃, 740℃, and 800℃, while high-temperature carbonization uses nine temperature zones with temperatures of 900℃, 987.5℃, 1075℃, 1162.5℃, 1250℃, 1337.5℃, 1425℃, 1512.5℃, and 1600℃.

[0026] Secondly, the present invention also provides a large-tow carbon fiber prepared according to the preparation method described above.

[0027] In some alternative embodiments, the large tow carbon fiber tow specification is ≥48K.

[0028] In some alternative embodiments, the prepared large-tow carbon fibers have a tensile strength ≥ 5.0 GPa, a tensile strength intra-batch dispersion coefficient ≤ 3%, and a tensile modulus ≥ 240 GPa.

[0029] The following detailed description of a method for preparing large-tow carbon fiber provided by the present invention, in conjunction with embodiments, should not be construed as limiting the scope of protection of the present invention.

[0030] The chemical structure of the pre-oxidized fibers was characterized using Fourier transform infrared spectroscopy (FT-IR), with a scanning range of 4000-500 cm⁻¹, 32 scans, and a resolution of 4 cm⁻¹. At least three infrared spectra were acquired for each sample. The degree of cyclization (CR) of the pre-oxidized fibers was calculated using the following formula.

[0031]

[0032] Where ƒ is the ratio of the molar absorption coefficients of the cyano group to the cyclic structure, 0.29; I abs（1590） 1590cm -1 The characteristic absorption peak intensity near (-C=N-); Iabs (2240) is 2240 cm⁻¹. -1 The intensity of the characteristic absorption peak near (-C≡N).

[0033] The content of oxygen (O) in the fiber was analyzed using an elemental analyzer. The principle is to bring the sample into contact with activated carbon at high temperature to generate carbon monoxide, and then quantitatively analyze the O content by detecting the carbon monoxide content.

[0034] The crystal structure of the pre-oxidized fibers was analyzed using wide-angle X-ray diffraction (XRD) with CuKa as the radiation source, an accelerating voltage of 45 kV, and an operating current of 200 mA. The scanning range of the pre-oxidized fibers was 10°–50°, and the scanning speed was 20° / min. The XRD patterns of the pre-oxidized fibers were analyzed using JADE6 software to obtain the corresponding parameters. The crystallinity was calculated using the following formula.

[0035]

[0036] The tensile strength, intra-batch dispersion of tensile strength Cv, and tensile modulus of carbon fiber were determined in accordance with GB 3362.

[0037] In the following examples, both low-temperature carbonization and high-temperature carbonization use the same process: low-temperature carbonization uses six temperature zones with a temperature of 500-800℃, and high-temperature carbonization uses nine temperature zones with a temperature of 900℃-1600℃.

[0038] Example 1 The dry-jet wet-spun large-tow PAN precursor fibers were pre-oxidized at three temperature gradients of 200℃, 230℃, and 250℃, with a total pre-oxidation time of 60 min. The cyclization degree of the pre-oxidized fibers in the three temperature zones was 35.1%, 58.4%, and 74.8%, respectively; the oxygen content of the pre-oxidized fibers in the three temperature zones was 4.86%, 6.57%, and 7.85%, respectively; and the crystallinity of the pre-oxidized fibers in the three temperature zones was 65.4%, 41.3%, and 18.6%, respectively.

[0039] Large-tow carbon fibers were prepared by pre-oxidized fibers through low-temperature carbonization and high-temperature carbonization. The tensile strength was 5629 MPa, the intra-batch dispersion Cv of the tensile strength was 1.87%, and the tensile modulus was 275 GPa.

[0040] Example 2 The dry-jet wet-spun large-tow PAN precursor fibers were pre-oxidized at three temperature gradients of 220℃, 250℃, and 270℃, with a total pre-oxidation time of 60 min. The cyclization degree of the pre-oxidized fibers in the three temperature zones was 39.6%, 67.6%, and 77.1%, respectively; the oxygen content of the pre-oxidized fibers in the three temperature zones was 5.03%, 6.87%, and 8.35%, respectively; and the crystallinity of the pre-oxidized fibers in the three temperature zones was 62.9%, 36.6%, and 10.4%, respectively.

[0041] Large-tow carbon fibers were prepared by pre-oxidized fibers through low-temperature carbonization and high-temperature carbonization. The tensile strength was 5129 MPa, the intra-batch dispersion Cv of the tensile strength was 2.54%, and the tensile modulus was 263 GPa.

[0042] Example 3 The dry-jet wet-spun large-tow PAN precursor fibers were pre-oxidized at three temperature gradients of 240℃, 270℃, and 290℃, with a total pre-oxidation time of 60 min. The cyclization degree of the pre-oxidized fibers in the three temperature zones was 42.1%, 71.5%, and 79.5%, respectively; the oxygen content of the pre-oxidized fibers in the three temperature zones was 5.83%, 7.24%, and 8.64%, respectively; and the crystallinity of the pre-oxidized fibers in the three temperature zones was 57.6%, 30.2%, and 6.5%, respectively.

[0043] Large-tow carbon fibers were prepared by pre-oxidized fibers through low-temperature carbonization and high-temperature carbonization. The tensile strength was 5066 MPa, the intra-batch dispersion Cv of tensile strength was 2.83%, and the tensile modulus was 258 GPa.

[0044] Example 4 The dry-jet wet-spun large-tow PAN precursor fibers were pre-oxidized at three temperature gradients of 180℃, 210℃, and 230℃, with a total pre-oxidation time of 60 min. The cyclization degree of the pre-oxidized fibers in the three temperature zones was 28.5%, 50.1%, and 67.4%, respectively; the oxygen content of the pre-oxidized fibers in the three temperature zones was 3.73%, 5.97%, and 7.34%, respectively; and the crystallinity of the pre-oxidized fibers in the three temperature zones was 69.4%, 47.2%, and 23.2%, respectively.

[0045] Large-tow carbon fibers were prepared by pre-oxidized fibers through low-temperature carbonization and high-temperature carbonization. The tensile strength was 5314 MPa, the intra-batch dispersion Cv of the tensile strength was 2.06%, and the tensile modulus was 257 GPa.

[0046] Example 5 The dry-jet wet-spun large-tow PAN precursor fibers were pre-oxidized at three temperature gradients of 200℃, 240℃, and 280℃, with a total pre-oxidation time of 60 min. The cyclization degree of the pre-oxidized fibers in the three temperature zones was 35.4%, 64.1%, and 76.2%, respectively; the oxygen content of the pre-oxidized fibers in the three temperature zones was 4.87%, 7.03%, and 7.91%, respectively; and the crystallinity of the pre-oxidized fibers in the three temperature zones was 65.5%, 36.8%, and 10.2%, respectively.

[0047] Large-tow carbon fibers were prepared by pre-oxidized fibers through low-temperature carbonization and high-temperature carbonization. The tensile strength was 5129 MPa, the intra-batch dispersion Cv of tensile strength was 2.46%, and the tensile modulus was 256 GPa.

[0048] Table 1 Comparison of Pre-oxidation Temperature Gradients and Characteristic Values

[0049] Table 2 Comparison of Mechanical Properties of Large-Tow Carbon Fibers

[0050] As can be seen from the above, in the pre-oxidation stage of large-tow polyacrylonitrile-based carbon fibers, this invention achieves a superior progressive pre-oxidized fiber structure through precise control of the cyclization structure, oxidation structure, and microcrystalline structure, providing a good foundation for subsequent carbonization. Simultaneously, the smaller differences in fiber structure help reduce performance dispersion and improve fiber quality stability. The prepared large-tow carbon fibers exhibit excellent properties, with a tensile strength ≥5.0 GPa, a batch-to-batch variation coefficient of tensile strength ≤3%, and a tensile modulus ≥240 GPa.

[0051] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing large-tow carbon fibers, characterized in that, include: Large-tow polyacrylonitrile precursor fibers are pre-oxidized at 180-300℃ for 40-80 minutes. The pre-oxidation is carried out in 2-4 temperature zones, and the difference in cyclization degree between adjacent temperature zones is controlled to be 10%-25%, and the difference in oxygen content is controlled to be 0.8%-2%. The pre-oxidized fibers are then carbonized to prepare large-tow carbon fibers.

2. The preparation method according to claim 1, characterized in that, During the pre-oxidation process, the temperature gradient increases in 2-4 temperature zones, the pre-oxidation time is the same in each temperature zone, and the total pre-oxidation time is controlled to be 40-80 min.

3. The preparation method according to claim 1, characterized in that, The large tow polyacrylonitrile (PAN) precursor yarn is prepared by one of the following methods: dry-jet wet spinning, wet spinning, or electrospinning. Preferably, the large-tow polyacrylonitrile (PAN) precursor yarn is prepared by dry-jet wet spinning; Preferably, the obtained large-tow carbon fiber filaments have a specification of ≥48K.

4. The preparation method according to claim 1, characterized in that, The degree of cyclization of the pre-oxidized fiber ranges from 30% to 80%, and the difference in degree of cyclization between adjacent temperature zones is 10% to 25%. Preferably, the difference in circulatory degree between adjacent temperature zones is 12-20%.

5. The preparation method according to claim 1, characterized in that, The oxygen content of the pre-oxidized fiber ranges from 3% to 10%, and the oxygen content difference between adjacent temperature zones is 0.8% to 2%. Preferably, the oxygen content difference between adjacent temperature zones is 1.0%-1.5%.

6. The preparation method according to claim 1, characterized in that, The crystallinity of the pre-oxidized fiber ranges from 5% to 70%, and the crystallinity difference between adjacent temperature zones is 15% to 35%. Preferably, the crystallinity difference between adjacent temperature zones is 20-30%.

7. The preparation method according to claim 1, characterized in that, The total pre-oxidation time is 50-70 min.

8. The preparation method according to claim 1, characterized in that, Carbonization treatment includes low-temperature carbonization and high-temperature carbonization. Low-temperature carbonization uses six temperature zones with a temperature of 500-800℃, while high-temperature carbonization uses nine temperature zones with a temperature of 900℃-1600℃.

9. A large-tow carbon fiber prepared by any one of claims 1-8.

10. The large-tow carbon fiber according to claim 9, characterized in that, The tensile strength of the large-tow carbon fiber is ≥5.0 GPa, the batch-specific dispersion coefficient of tensile strength is ≤3%, and the tensile modulus is ≥240 GPa.

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