Carbon fiber and preparation method thereof
By applying tension under an inert atmosphere and performing gradient temperature treatment, the problems of fiber thermal stability and over-oxidation during the pre-oxidation process were solved, enabling the preparation of high-performance carbon fibers while reducing energy consumption and cost.
Patent Information
- Application Number
- CN202511001719.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-21
- Publication Date
- 2025-11-14
AI Technical Summary
Existing technologies struggle to balance fiber thermal stability and avoid defects caused by excessive oxidation during carbon fiber pre-oxidation, resulting in high energy consumption and increased costs.
Polyacrylonitrile precursor fibers were pre-cyclized under an inert atmosphere with a tension of 50MPa-500MPa, followed by gradient temperature pre-oxidation and carbonization. High-purity nitrogen was used as a protective gas to control the oxygen content and temperature gradient in order to optimize the fiber structure.
It improves the thermal stability of fibers, reduces pre-oxidation time and energy consumption, reduces over-oxidation defects, enhances the tensile strength and carbonization yield of carbon fibers, and reduces production costs.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of fibers, and more specifically, this invention relates to a carbon fiber and its preparation method. Background Technology
[0002] Polyacrylonitrile-based carbon fiber, as a high-performance inorganic fiber material, has excellent properties such as high specific strength, high specific modulus, light weight, high temperature resistance, and corrosion resistance. It also has the processability of textile fibers and can be used as a reinforcing material in advanced composite materials. It has been widely used in aerospace, automotive industry, building materials, medical and other fields.
[0003] The pre-oxidation process is a crucial step in carbon fiber production. During this process, chemical reactions such as cyclization, dehydrogenation, oxidation, and cross-linking occur simultaneously, forming a stable pre-oxidized structure that facilitates the formation of disordered graphite structures in the subsequent carbonization stage. In current mainstream processes, the pre-oxidation process typically involves heat-treating polyacrylonitrile precursor fibers in air. This process requires balancing the promotion of molecular chain cyclization to improve thermal stability with the avoidance of fiber defects caused by excessive oxidation. Achieving a balance between these two aspects by simply adjusting process parameters to obtain fibers with high thermal stability is difficult. Summary of the Invention
[0004] To address the aforementioned issues, this invention provides a carbon fiber and its preparation method. This method can balance the thermal stability of the fiber during the pre-oxidation process with avoiding defects caused by excessive oxidation, thereby obtaining high-performance carbon fibers.
[0005] The first aspect of this invention provides a method for preparing carbon fibers, comprising:
[0006] Apply a tension of 50MPa-500MPa and pre-cyclize the polyacrylonitrile precursor fiber under an inert atmosphere to obtain pre-cyclized fiber.
[0007] The pre-cyclized fibers were subjected to pre-oxidation and carbonization treatments in sequence to obtain carbon fibers.
[0008] Furthermore, the tension is 100MPa-350MPa.
[0009] Furthermore, the degree of cyclization of the pre-cyclized fiber is 5%-50%, preferably 8%-35%.
[0010] Furthermore, the pre-cyclization treatment is performed at a temperature of 200℃-260℃ for a time of 3 minutes-30 minutes.
[0011] Furthermore, the pre-cyclized fiber is subjected to gradient temperature pre-oxidation in air at 2-4 temperature zones. The initial temperature of the pre-oxidation is 220℃-230℃, the final temperature is 240℃-260℃, and the total pre-oxidation time is 20-60 minutes.
[0012] Furthermore, the carbonization process includes low-temperature carbonization and high-temperature carbonization.
[0013] Furthermore, the low-temperature carbonization uses high-purity nitrogen as a protective gas, with a temperature of 300℃-700℃ and a residence time of 0.5 minutes-3 minutes.
[0014] Furthermore, the high-temperature carbonization uses high-purity nitrogen as a protective gas, wherein the oxygen content in the high-purity nitrogen is not higher than 3 ppm, preferably not higher than 1 ppm, and the nitrogen dew point is not higher than -60°C.
[0015] Furthermore, the high-temperature carbonization temperature is 1200℃-1550℃, and the residence time is 0.1 minutes-1 minute.
[0016] A second aspect of the present invention provides a carbon fiber prepared using the method described in the first aspect of the present invention. This method can balance the thermal stability of the fiber during the pre-oxidation process with avoiding defects caused by over-oxidation, thereby obtaining high-performance carbon fibers.
[0017] Compared with existing technologies, this invention has at least the following beneficial effects: This invention pre-cyclizes polyacrylonitrile precursor fibers under an inert atmosphere and applies a tension of 50MPa-500MPa. This tension promotes the formation and orientation of ring structures within the fiber, preventing the dissociation of the original oriented structures and thus improving the tensile strength of the final carbon fiber. Simultaneously, the pre-cyclization process under this tension can form suitable ring structures within the fiber, improving its thermal stability and thus increasing the pre-oxidation initiation temperature, which helps reduce pre-oxidation time. Furthermore, the ring structures within the fiber can promote the formation of a trapezoidal structure in the subsequent pre-oxidation process, lowering the final pre-oxidation temperature and reducing defects caused by over-oxidation. This results in a reduction of energy consumption in the polyacrylonitrile precursor fiber pre-oxidation process by more than 10%, contributing to a reduction in carbon fiber production costs. In addition, the pre-cyclized fibers obtained under the aforementioned tension reduce radial structural differences caused by oxygen diffusion during the pre-oxidation process, which is beneficial for optimizing the formation of the internal fiber structure during subsequent carbonization, improving carbonization yield and carbon fiber tensile strength. The preparation method employed in this invention is simple and easily industrialized.
[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. The following examples are merely descriptive and not limiting, and should not be used to limit the scope of protection of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0020] The first aspect of this invention discloses a method for preparing carbon fibers, the method comprising:
[0021] S1: Apply a tension of 50MPa-500MPa and pre-cyclize the polyacrylonitrile precursor fiber under an inert atmosphere.
[0022] In this step, a tension of 50MPa-500MPa is applied to pre-cyclize the polyacrylonitrile precursor fiber under an inert atmosphere to obtain pre-cyclized fiber. The inert atmosphere includes any one or a combination of nitrogen, helium, and argon. This invention pre-cyclizes the polyacrylonitrile precursor fiber under an inert atmosphere with a tension of 50MPa-500MPa. This tension promotes the formation and orientation of ring structures within the fiber, prevents the dissociation of existing oriented structures, and thus improves the tensile strength of the final carbon fiber. Simultaneously, the pre-cyclization process under this tension can form suitable ring structures within the fiber, improving its thermal stability and thus increasing the initial temperature of subsequent pre-oxidation, which helps reduce pre-oxidation time. Furthermore, the ring structures within the fiber can promote the formation of a trapezoidal structure during subsequent pre-oxidation, lowering the final pre-oxidation temperature and reducing defects caused by over-oxidation. This results in a reduction of energy consumption in the polyacrylonitrile precursor fiber pre-oxidation process by more than 10%, contributing to a reduction in carbon fiber production costs.
[0023] In some embodiments of the present invention, the tension is 50 MPa-500 MPa. The inventors have found that during the pre-cyclization process, if the applied tension is too small, the effect on the orientation of the ring structure in the fiber is not significant, while too large a tension can cause physical damage to the fiber during the ring structure formation process, resulting in fuzzy or broken fibers, thereby reducing the tensile strength of the final carbon fiber. Therefore, the present invention applies a tension of 50 MPa-500 MPa during the fiber pre-cyclization process, which allows the ring structure in the pre-cyclized fiber to be optimally oriented along the fiber direction, thereby improving fiber performance. In other embodiments of the present invention, the tension is 100 MPa-350 MPa.
[0024] In some embodiments of the present invention, the degree of cyclization of the pre-cyclized fiber is 5%-50%, preferably 8%-35%.
[0025] In some embodiments of the present invention, the temperature of the pre-cyclization treatment is 200℃-260℃, and the time is 3 minutes-30 minutes.
[0026] S2: The pre-cyclized fibers are subjected to pre-oxidation and carbonization treatments in sequence.
[0027] In this step, the pre-cyclized fibers obtained in step S1 are subjected to pre-oxidation and carbonization treatments in sequence to obtain carbon fibers.
[0028] In some embodiments of the present invention, the pre-cyclized fiber is subjected to gradient temperature pre-oxidation in air at 2-4 temperature zones. The initial temperature of the pre-oxidation is 220℃-230℃, the final temperature is 240℃-260℃, and the total pre-oxidation time is 20-60 minutes. Therefore, since the polyacrylonitrile precursor fiber is pre-cyclized under the above conditions in step S1, a suitable cyclized structure can be formed in the fiber, improving the fiber's thermal stability. This increases the initial temperature of the pre-oxidation process, which helps to reduce the pre-oxidation time. Simultaneously, the cyclized structure in the fiber can promote the formation of a trapezoidal structure during the pre-oxidation process, lowering the final pre-oxidation temperature and reducing defects caused by over-oxidation. This results in a reduction of energy consumption of more than 10% in the pre-oxidation process of the polyacrylonitrile precursor fiber, which is beneficial for reducing the cost of carbon fiber production.
[0029] In some embodiments of the present invention, the carbonization process includes low-temperature carbonization and high-temperature carbonization. The low-temperature carbonization uses high-purity nitrogen as a protective gas, with an initial temperature of 300°C, a maximum temperature of 700°C, and a residence time of 0.5 to 3 minutes. The high-temperature carbonization uses high-purity nitrogen as a protective gas, wherein the oxygen content in the high-purity nitrogen is not higher than 3 ppm, preferably not higher than 1 ppm, and the nitrogen dew point is not higher than -60°C. The high-temperature carbonization temperature is 1200°C to 1550°C, and the residence time is 0.1 to 1 minute.
[0030] Therefore, this invention pre-cyclizes polyacrylonitrile precursor fibers under an inert atmosphere and applies a tension of 50MPa-500MPa. This tension promotes the formation and orientation of ring structures within the fiber, prevents the dissociation of the original oriented structure, and thus improves the tensile strength of the final carbon fiber. Simultaneously, the pre-cyclization process under this tension can form suitable ring structures within the fiber, improving its thermal stability and thus increasing the starting temperature of subsequent pre-oxidation, which helps reduce pre-oxidation time. Furthermore, the ring structures within the fiber can promote the formation of a trapezoidal structure during subsequent pre-oxidation, lowering the final pre-oxidation temperature and reducing defects caused by over-oxidation. This results in a reduction of energy consumption in the polyacrylonitrile precursor fiber pre-oxidation process by more than 10%, contributing to a reduction in carbon fiber production costs. In addition, the pre-cyclized fibers obtained under the aforementioned tension reduce radial structural differences caused by oxygen diffusion during pre-oxidation, which is beneficial for optimizing the formation of the internal fiber structure during subsequent carbonization, improving carbonization yield and carbon fiber tensile strength.
[0031] A second aspect of the present invention discloses a carbon fiber prepared by the method described in the first aspect. This carbon fiber exhibits high carbonization yield and tensile strength.
[0032] It should be noted that the features and advantages described above for the method of preparing carbon fiber also apply to this carbon fiber, and will not be repeated here.
[0033] The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.
[0034] Example 1
[0035] 1) Pre-circulation treatment
[0036] Polyacrylonitrile precursor fibers were pre-cyclized in a nitrogen atmosphere at a temperature of 210°C for 20 minutes and a tension of 350 MPa, resulting in fibers with a degree of cyclization of 9.5%.
[0037] The degree of cyclization of the pre-cyclized fiber is calculated by formula (1) based on the intensity of the C≡N and C=N peaks in its infrared spectrum (the same applies below).
[0038]
[0039] In the formula, I 1590 and I 2243 The fiber samples were at 1590 cm⁻¹. -1 (C=N and C=C) and 2243cm -1The absorption peak intensity at (-C≡N); f is the absorption ratio constant of -C≡N, -C=N and C=C groups, with a value of 0.29.
[0040] 2) Pre-oxidation treatment
[0041] The pre-cyclized fibers obtained above were subjected to gradient temperature pre-oxidation in air atmosphere. The pre-oxidation start temperature was 220℃ and the pre-oxidation end temperature was 260℃. The pre-oxidation treatment of the pre-cyclized fibers was carried out in two temperature zones, and the total pre-oxidation time was 60 minutes.
[0042] 3) Low-temperature carbonization treatment
[0043] The pre-oxidized fibers obtained above are fed into a low-temperature carbonization furnace for carbonization treatment using gradient heating and high-purity nitrogen as a protective gas. The initial temperature of the low-temperature carbonization is 300℃, the maximum temperature is 700℃, and the residence time is 3 minutes.
[0044] 4) High-temperature carbonization treatment
[0045] The fibers that have undergone low-temperature carbonization are then fed into a high-temperature carbonization furnace for high-temperature carbonization. High-purity nitrogen is used as the protective gas, with an oxygen content of 0.5 ppm and a nitrogen dew point of -65°C. The high-temperature carbonization temperature is 1350°C, and the residence time is 0.5 minutes.
[0046] Example 2
[0047] 1) Pre-circulation treatment
[0048] Polyacrylonitrile precursor fibers were pre-cyclized in a nitrogen atmosphere at a temperature of 230°C for 10 minutes and a tension of 250 MPa, resulting in fibers with a degree of cyclization of 18.5%.
[0049] 2) Pre-oxidation treatment
[0050] The pre-cyclized fibers obtained above were subjected to gradient temperature pre-oxidation in air atmosphere. The pre-oxidation start temperature was 225℃ and the pre-oxidation end temperature was 250℃. The pre-cyclized fibers were pre-oxidized in four temperature zones, with temperatures of 225℃, 235℃, 245℃ and 250℃ respectively. The total pre-oxidation time was 40 minutes.
[0051] 3) Low-temperature carbonization treatment
[0052] The pre-oxidized fibers obtained above are fed into a low-temperature carbonization furnace for carbonization treatment using gradient heating and high-purity nitrogen as a protective gas. The low-temperature carbonization starts at 300℃, reaches a maximum temperature of 700℃, and has a residence time of 2 minutes.
[0053] 4) High-temperature carbonization treatment
[0054] The fibers that have undergone low-temperature carbonization are then fed into a high-temperature carbonization furnace for high-temperature carbonization. High-purity nitrogen is used as the protective gas, with an oxygen content of 0.5 ppm and a nitrogen dew point of -70°C. The high-temperature carbonization temperature is 1450°C, and the residence time is 0.3 minutes.
[0055] Example 3
[0056] 1) Pre-circulation treatment
[0057] Polyacrylonitrile precursor fibers were pre-cyclized in a nitrogen atmosphere at a temperature of 250°C for 5 minutes and a tension of 100 MPa, resulting in fibers with a degree of cyclization of 28.5%.
[0058] 2) Pre-oxidation treatment
[0059] The pre-cyclized fibers obtained above were subjected to gradient temperature pre-oxidation in air atmosphere. The pre-oxidation start temperature was 220℃ and the pre-oxidation end temperature was 250℃. The pre-cyclized fibers were pre-oxidized in four temperature zones, with temperatures of 220℃, 230℃, 240℃ and 250℃ respectively. The total pre-oxidation time was 30 minutes.
[0060] 3) Low-temperature carbonization treatment
[0061] The pre-oxidized fibers obtained above are fed into a low-temperature carbonization furnace for carbonization treatment using gradient heating and high-purity nitrogen as a protective gas. The low-temperature carbonization starts at 300°C, reaches a maximum temperature of 700°C, and has a residence time of 1 minute.
[0062] 4) High-temperature carbonization treatment
[0063] The fibers that have undergone low-temperature carbonization are then fed into a high-temperature carbonization furnace for high-temperature carbonization. High-purity nitrogen is used as the protective gas, with an oxygen content of 0.5 ppm and a nitrogen dew point of -70°C. The high-temperature carbonization temperature is 1500°C, and the residence time is 0.1 minutes.
[0064] Example 4
[0065] 1) Pre-circulation treatment
[0066] Polyacrylonitrile precursor fibers were pre-cyclized in a nitrogen atmosphere at a temperature of 250°C for 15 minutes and a tension of 200 MPa, resulting in fibers with a degree of cyclization of 32.0%.
[0067] 2) Pre-oxidation treatment
[0068] The pre-cyclized fibers obtained above were subjected to gradient temperature pre-oxidation in air atmosphere. The pre-oxidation start temperature was 220℃ and the pre-oxidation end temperature was 250℃. The pre-cyclized fibers were pre-oxidized in four temperature zones, with temperatures of 220℃, 230℃, 240℃ and 250℃ respectively. The total pre-oxidation time was 30 minutes.
[0069] 3) Low-temperature carbonization treatment
[0070] The pre-oxidized fibers obtained above are fed into a low-temperature carbonization furnace for carbonization treatment using gradient heating, with high-purity nitrogen as the protective gas. The low-temperature carbonization starts at 300℃, stabilizes at a maximum of 700℃, and has a residence time of 1 minute.
[0071] 4) High-temperature carbonization treatment
[0072] The fibers that have undergone low-temperature carbonization are then fed into a high-temperature carbonization furnace for high-temperature carbonization. High-purity nitrogen is used as the protective gas, with an oxygen content of 0.5 ppm and a nitrogen dew point of -70°C. The high-temperature carbonization temperature is 1500°C, and the residence time is 0.1 minutes.
[0073] Comparative Example 1
[0074] 1) Pre-oxidation treatment
[0075] The polyacrylonitrile precursor fiber was subjected to gradient temperature pre-oxidation in air atmosphere. The pre-oxidation start temperature was 220℃ and the pre-oxidation end temperature was 250℃. The pre-cyclized fiber was pre-oxidized in four temperature zones, with temperatures of 220℃, 230℃, 240℃ and 250℃ respectively. The total pre-oxidation time was 80 minutes.
[0076] 2) Low-temperature carbonization treatment
[0077] The pre-oxidized fibers obtained above are fed into a low-temperature carbonization furnace for carbonization treatment using gradient heating, with high-purity nitrogen as the protective gas. The low-temperature carbonization starts at 300℃, stabilizes at a maximum of 700℃, and has a residence time of 4 minutes.
[0078] 3) High-temperature carbonization treatment
[0079] The fibers that have undergone low-temperature carbonization are then fed into a high-temperature carbonization furnace for high-temperature carbonization. High-purity nitrogen is used as the protective gas, with an oxygen content of 0.5 ppm and a nitrogen dew point of -70°C. The high-temperature carbonization temperature is 1500°C, and the residence time is 1 minute.
[0080] Comparative Example 2
[0081] The method for preparing carbon fibers is the same as in Example 1, except that the pre-cyclization tension is 30 MPa, and the degree of cyclization of the pre-cyclized fibers is 11.3%.
[0082] Comparative Example 3
[0083] The method for preparing carbon fibers is the same as in Example 1, except that the pre-cyclization tension is 550 MPa, and the degree of cyclization of the pre-cyclized fibers is 8.6%.
[0084] It should be noted that the polyacrylonitrile precursor fibers used in Examples 1-4 and Comparative Examples 1-3 were from the same batch of samples.
[0085] The carbon yield and tensile strength of the carbon fibers obtained in Examples 1-4 and Comparative Examples 1-3 are shown in Table 1.
[0086] Table 1
[0087] Group Carbonization yield (%) Tensile strength (MPa) Example 1 50.35 5381 Example 2 52.63 6083 Example 3 52.75 6525 Example 4 54.90 5697 Comparative Example 1 48.02 5025 Comparative Example 2 50.48 5124 Comparative Example 3 49.86 4944
[0088] As shown in Table 1, the carbon yield and tensile strength of the carbon fibers obtained in Examples 1-4 are higher than those obtained by the methods in Comparative Examples 1-3. Furthermore, the pre-oxidation process time in Examples 1-4 is shorter than that in Comparative Example 1. This indicates that pre-cyclizing polyacrylonitrile precursor fibers under an inert atmosphere and applying a tension of 50 MPa-500 MPa can form a suitable cyclized structure in the fiber, taking into account the thermal stability of the fiber during the pre-oxidation process and avoiding defects caused by excessive oxidation, thereby facilitating the acquisition of high-performance carbon fibers.
[0089] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0090] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.
Claims
1. A method for preparing carbon fiber, characterized in that, include: Apply a tension of 50MPa-500MPa and pre-cyclize the polyacrylonitrile precursor fiber under an inert atmosphere to obtain pre-cyclized fiber. The pre-cyclized fibers were subjected to pre-oxidation and carbonization treatments in sequence to obtain carbon fibers.
2. The method according to claim 1, characterized in that, The tension is 100MPa-350MPa.
3. The method according to claim 1 or 2, characterized in that, The degree of cyclization of the pre-cyclized fiber is 5%-50%, preferably 8%-35%.
4. The method according to claim 1 or 2, characterized in that, The pre-cyclization treatment is performed at a temperature of 200℃-260℃ for 3 minutes to 30 minutes.
5. The method according to claim 1, characterized in that, The pre-cyclized fiber is subjected to gradient temperature pre-oxidation in air at 2-4 temperature zones. The initial temperature of the pre-oxidation is 220℃-230℃, the final temperature is 240℃-260℃, and the total pre-oxidation time is 20-60 minutes.
6. The method according to claim 1 or 5, characterized in that, The carbonization process includes low-temperature carbonization and high-temperature carbonization.
7. The method according to claim 6, characterized in that, The low-temperature carbonization process uses high-purity nitrogen as a protective gas, with an initial temperature of 300℃, a maximum temperature of 700℃, and a residence time of 0.5 minutes to 3 minutes.
8. The method according to claim 6, characterized in that, The high-temperature carbonization process uses high-purity nitrogen as a protective gas, wherein the oxygen content in the high-purity nitrogen is not higher than 3 ppm, preferably not higher than 1 ppm, and the nitrogen dew point is not higher than -60°C.
9. The method according to claim 6, characterized in that, The high-temperature carbonization temperature is 1200℃-1550℃, and the residence time is 0.1 minutes-1 minute.
10. A carbon fiber, characterized in that, It is prepared by any one of claims 1-9.