CN117187989A - Carbon fiber and preparation method thereof - Google Patents
Carbon fiber and preparation method thereof Download PDFInfo
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- 229920000049 Carbon (fiber) Polymers 0.000 title claims abstract description 79
- 239000004917 carbon fiber Substances 0.000 title claims abstract description 79
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 65
- 238000002360 preparation method Methods 0.000 title claims abstract description 9
- 238000003763 carbonization Methods 0.000 claims abstract description 220
- 239000000835 fiber Substances 0.000 claims abstract description 166
- 238000011282 treatment Methods 0.000 claims abstract description 88
- 238000012805 post-processing Methods 0.000 claims abstract description 4
- 238000000034 method Methods 0.000 claims description 34
- 238000007254 oxidation reaction Methods 0.000 claims description 28
- 229920002239 polyacrylonitrile Polymers 0.000 claims description 25
- 238000010438 heat treatment Methods 0.000 claims description 16
- 238000004519 manufacturing process Methods 0.000 claims description 13
- 230000003647 oxidation Effects 0.000 claims description 13
- 239000003792 electrolyte Substances 0.000 claims description 12
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Abstract
The application relates to a carbon fiber and a preparation method thereof, belonging to the technical field of carbon fiber production. The preparation method of the carbon fiber comprises the following steps: has a density of 1.34-1.44g/cm 3 Sequentially performing first carbonization treatment, second carbonization treatment and third carbonization treatment on the pre-oxidized fiber body to obtain a carbonized fiber body; post-processing the carbonized fiber body to obtain carbon fibers; wherein, a plurality of first carbonization temperature areas are arranged between 300 ℃ and 500 ℃, a plurality of second carbonization temperature areas are arranged between 1000 ℃ and 1200 ℃, and a plurality of third carbonization temperature areas are arranged between 1300 ℃ and 1600 ℃. The preparation method can smooth the escape rate of products such as gas caused by the reaction of the internal structure of the fiber, and improve the density and the tensile strength of the fiber.
Description
Technical Field
The application relates to the technical field of carbon fiber production, in particular to a carbon fiber and a preparation method thereof.
Background
Carbon fiber is a fibrous inorganic novel material with excellent mechanical properties such as high specific strength and specific modulus. The excellent performance of the carbon fiber makes the carbon fiber an important reinforcement of advanced structural composite materials, is an important strategic substance for national defense and military industry and national economy, is currently applied to the high technical fields of aerospace, aviation, new energy sources and the like, and is widely used in the fields of sports equipment, chemical industry, electronic products, automobile manufacturing, medical treatment and the like. Among carbon fibers prepared from different precursors, carbon fibers using Polyacrylonitrile (PAN) as a precursor are the carbon fiber types with the largest demand and the largest prospect at present due to the advantages of excellent performance, simple process and the like.
The density of the ideal graphite is 2.266g/cm 3 In actual production, the polyacrylonitrile-based carbon fiber produced by the procedures of pre-oxidation, low-temperature carbonization, high-temperature carbonization and the like has a fiber density lower than the value, which indicates that the carbon fiber density consists of a disordered layer structure and pores of carbon. He Fu and the like detect the structural parameter values of different carbon fiber products of the eastern company of japan through the WAXD, and the result shows that as the strength of the carbon fiber is improved, the density of the carbon fiber is also increased, and the porosity is continuously reduced, so that the reduction of the internal void ratio of the carbon fiber and the improvement of the density of the carbon fiber are beneficial to the improvement of the tensile strength of the carbon fiber.
The polyacrylonitrile precursor is subjected to pre-oxidation treatment to form a pre-oxidized fiber with an internal structure and a heat-resistant trapezoid structure, and the pre-oxidized fiber is subjected to low-temperature carbonization and high-temperature carbonization to form a finished carbon fiber with a disordered layer graphite structure. In the whole production of carbon fiber, the composition of elements, the organization structure and the weight of the fiber are changed greatly in the carbonization process, and a large amount of gas products are generated. In the high-temperature carbonization stage, aromatization reaction, intermolecular shrinkage and rearrangement occur, carbon atoms enable the plane of a carbon net to be enlarged through cyclization and crosslinking, carbon fibers with disordered layer graphite structures are formed, meanwhile, along with the removal of non-carbon atoms, a large amount of gaps remain in the carbon fibers along with the escape of a large amount of byproduct nitrogen, so that the density of the carbon fibers is reduced, and the tensile strength is reduced.
Disclosure of Invention
In view of the shortcomings of the prior art, an object of an embodiment of the present application is to provide a method for preparing carbon fibers, so as to improve the density and tensile strength of polyacrylonitrile-based carbon fibers.
In a first aspect, an embodiment of the present application provides a method for preparing a carbon fiber, including the steps of: has a density of 1.34-1.44g/cm 3 Sequentially subjecting the pre-oxidized fiber body of (2) to a first carbonPerforming carbonization treatment, second carbonization treatment and third carbonization treatment to obtain a carbonized fiber body; post-processing the carbonized fiber body to obtain carbon fibers; wherein the step of the first carbonization treatment comprises subjecting the pre-oxidized fiber body to gradient heating from 300 to 800 ℃, wherein a plurality of first carbonization temperature zones are arranged between 300 and 500 ℃ so as to have a plurality of temperature gradients between 300 and 500 ℃; the second carbonization treatment step comprises the step of heating the first carbonized fiber body obtained through the first carbonization treatment in a gradient manner from 800 to 1300 ℃, wherein a plurality of second carbonization temperature areas are arranged between 1000 ℃ and 1200 ℃ so as to enable a plurality of temperature gradients between 1000 ℃ and 1200 ℃; the third carbonization treatment step includes subjecting the second carbonized fiber body obtained through the second carbonization treatment to gradient heating from 1300 to 1600 ℃, and a plurality of third carbonization temperature zones are arranged between 1300 and 1600 ℃ so as to have a plurality of temperature gradients between 1300 and 1600 ℃.
Because the exothermic reaction of the fiber at about 400 ℃ is not as intense as the cyclization reaction in the preoxidation process, the concentrated heat release still occurs for a short time, the instantaneous temperature of the fiber is easily increased, the internal structure is damaged, and meanwhile, the decomposition products of the internal reaction of the fiber cannot be instantaneously removed, so that impurities such as tar are adhered to the fiber to cause surface defects, and the fiber performance is reduced. The carbonization temperature is 900-1300 ℃ which is the peak area of denitrification in the fiber, the condensation reaction is aggravated, so that a large amount of nitrogen is intensively escaped in the form of nitrogen, a large amount of void defects are generated in the fiber, and the density of the carbon fiber is reduced. Therefore, the application is provided with a plurality of first carbonization temperature areas between 300 and 500 ℃ and a plurality of second carbonization temperature areas between 1000 and 1200 ℃. That is, a plurality of reaction temperature zones are intensively arranged in the temperature zone with intense reaction in the fiber, so that the temperature gradient in the temperature zone with intense reaction in the fiber is reduced, the carbonization time is prolonged, and the reaction rate of the fiber in the concentrated reaction zone is reduced. Thereby gentle reaction rate can reduce and lead to the fact great hole when nitrogen gas concentrates and escapes from the fibre inside, effectively control nitrogen gas escape rate for the pore channel size that causes reduces, thereby the whole porosity of fibre reduces thereupon, effectively promotes carbon fiber density, and then improves carbon fiber's tensile strength.
In some embodiments of the present application, 3-5 first carbonization temperature zones are provided between 300-500 ℃, and the temperature difference of each first carbonization temperature zone provided between 300-500 ℃ is 30-80 ℃. The exothermic reaction of the fiber at about 400 ℃ is not as intense as the cyclization reaction in the preoxidation process, but the concentrated heat release still occurs for a short time, so that the instantaneous temperature of the fiber is easily increased, the internal structure is damaged, meanwhile, the decomposition products of the internal reaction of the fiber are not instantaneously removed, impurities such as tar are adhered to the fiber to cause surface defects, and the fiber performance is reduced. Therefore, 3-5 first carbonization temperature areas are arranged between 300-500 ℃, and the temperature difference of each temperature area is 30-80 ℃. Thereby reducing the temperature gradient in the temperature zone with intense reaction in the fiber, prolonging the carbonization time and reducing the reaction rate of the fiber in the concentrated reaction zone. The reaction gradient is gentle at about 400 ℃, so that the decomposition rate of the product in the fiber can be reduced, the nitrogen can be timely cleaned by the protection gas, and the pollution risk is reduced.
In some embodiments of the present application, 2-4 second carbonization temperature zones are provided between 1000-1200 ℃, each second carbonization temperature zone being provided between 1000-1200 ℃ with a temperature difference of 30-100 ℃. The carbonization temperature is 900-1300 ℃ which is the peak area of denitrification in the fiber, the condensation reaction is aggravated, so that a large amount of nitrogen is intensively escaped in the form of nitrogen, a large amount of void defects are generated in the fiber, and the density of the carbon fiber is reduced. Therefore, 2-4 second carbonization temperature zones are arranged between 1000-1200 ℃, and the temperature difference of each temperature zone is 30-100 ℃. The fiber is subjected to temperature gradient adjustment in different reaction temperature ranges through a plurality of temperature areas, so that the reaction rate is gentle, larger pores caused when nitrogen gas intensively escapes from the inside of the fiber can be reduced, the escape speed of the nitrogen gas is effectively controlled, the size of a pore channel is reduced, the overall porosity of the fiber is reduced, the density of the carbon fiber is effectively improved, and the tensile strength of the carbon fiber is further improved.
In some embodiments of the present application, 5 third carbonization temperature zones are provided between 1300-1600 ℃, each third carbonization temperature zone being provided between 1300-1600 ℃ with a temperature difference of 50-150 ℃. By setting 5 third carbonization temperature areas between 1300 ℃ and 1600 ℃, the temperature difference of each temperature area is 50 ℃ to 150 ℃ so as to finally obtain the carbon fiber with high density and high tensile strength.
In some embodiments of the application, the tension in the first carbonization temperature zone is 5-15N; and/or the tension of the second carbonization temperature zone is 40-60N; and/or the tension of the third carbonization temperature zone is 40-60N. In different carbonization temperature areas, by controlling the tension in the above range, the reaction rate can be gentle, the gas aggregation is reduced, the size of pore channels generated in the fiber is reduced, the overall porosity is reduced, the density of the carbon fiber is improved, and the tensile strength of the carbon fiber is further improved.
In some embodiments of the application, the pre-oxidized fiber body has a line speed of 420-520m/h.
In some embodiments of the application, the first carbonization treatment is performed for a period of 115 to 150 seconds; and/or the second carbonization treatment is performed for 110 to 140 seconds; and/or the time of the third carbonization treatment is 90-110 seconds. By controlling the time of the first carbonization treatment, the second carbonization treatment and the third carbonization treatment within the above ranges, the stability and consistency of the quality of the finally obtained carbon fiber can be realized, the internal structure of the fiber can be optimized, the density and performance of the fiber can be improved, the production efficiency can be improved to a certain extent, and the energy consumption can be saved.
In some embodiments of the application, the preparation of the pre-oxidized fiber body comprises: pre-oxidizing polyacrylonitrile fiber in pre-oxidizing device to obtain polyacrylonitrile fiber with density of 1.34-1.44g/cm 3 Is a pre-oxidized fiber body; wherein the step of pre-oxidation reaction comprises the steps of heating the polyacrylonitrile fiber in a gradient way from 210 ℃ to 260 ℃ and heating the polyacrylonitrile fiber in a gradient way from 15 ℃ to 20 ℃; the pre-oxidation reaction time is 60-90min. By controlling the pre-oxidation temperature and time within the above range, the oxidation reaction of the fiber can be promoted, the fiber structure is improved, the thermal stability and crystallinity of the fiber are enhanced, and an excellent foundation is provided for the subsequent carbonization treatment, so that the high-quality carbon fiber is obtained.
In some embodiments of the present application, the polyacrylonitrile fiber has a running speed of 420-520m/h.
In some embodiments of the present application, the tension applied to the polyacrylonitrile fiber during the pre-oxidation reaction is 15 to 20N. In the tension range, the fiber can be stretched and maintained in shape, so that the uniform distribution of temperature and time in the oxidation process of the fiber is facilitated, the difference of internal structures of the fiber is reduced, and the uniformity of the fiber is maintained.
In some embodiments of the application, the post-processing includes: and sequentially carrying out surface treatment, water washing, sizing, drying and winding on the carbonized fiber body to obtain the carbon fiber.
In some embodiments of the application, the surface treatment comprises: the carbonized fiber body is subjected to anodic oxidation electrochemical treatment.
In some embodiments of the application, the electrolyte used in the electrochemical process comprises an acid electrolyte or an alkaline electrolyte. Wherein the acidic electrolyte contains hydrogen ions (H + ) The ions have higher mobility and can promote the electrolytic reaction, so that the electrolytic process is more rapid. In addition, the acid electrolyte has better chemical stability, can maintain stable electrolysis conditions in a certain range, and is not easy to generate abnormal reaction or unstable compounds.
In a second aspect, an embodiment of the present application provides a carbon fiber manufactured by the above manufacturing method.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The embodiment of the application provides a carbon fiber, which comprises the following steps:
(1) The polyacrylonitrile fiber is subjected to preoxidation reaction by an oxidation furnace, wherein the step of preoxidation reaction comprises the steps of heating the polyacrylonitrile fiber in a gradient from 210 ℃ to 260 ℃, heating the gradient to 15-20 ℃ and the running speed of the polyacrylonitrile fiber to 420-520m/h, the time of the pre-oxidation reaction is 60-90min; in the preoxidation reaction, the tension applied to the polyacrylonitrile fiber is 15-20N, and the density of the obtained preoxidized fiber body is 1.34-1.44g/cm 3 . The temperature of the pre-oxidation reaction is controlled within the range of 210-260 ℃, which is favorable for better oxidation reaction in the fiber, thereby increasing the oxygen content, enhancing the thermal stability and crystallinity of the fiber and laying a foundation for the subsequent carbonization reaction. The pre-oxidation reaction time is controlled to be 60-90min, so that the oxidation reaction can be fully performed, the internal structure of the fiber is better improved, the oxygen content is increased, and a sufficient oxidation structure is provided for the subsequent carbonization treatment, thereby being beneficial to the grain refining and performance improvement of the carbon fiber. The fiber can be stretched and maintained in shape by controlling the tension to 15-20N in the preoxidation process, so that the uniform distribution of temperature and time in the oxidation process of the fiber is facilitated, the difference of internal structures of the fiber is reduced, and the consistency of the fiber is maintained.
(2) Sequentially performing first carbonization treatment, second carbonization treatment and third carbonization treatment on the pre-oxidized fiber body in the step (1) to obtain a carbonized fiber body; wherein the step of the first carbonization treatment comprises the step of heating the pre-oxidized fiber body in a gradient from 300 to 800 ℃, wherein 3 to 5 first carbonization temperature areas are arranged between 300 and 500 ℃ so as to have a plurality of temperature gradients between 300 and 500 ℃, and the temperature difference of each first carbonization temperature area is 30 to 80 ℃; the second carbonization treatment comprises the steps of heating the first carbonized fiber body obtained through the first carbonization treatment in a gradient manner from 800 ℃ to 1200 ℃, wherein 2-4 second carbonization temperature areas are arranged between 1000 ℃ and 1200 ℃ so as to enable a plurality of temperature gradients to exist between 1000 ℃ and 1200 ℃, and the temperature difference of each second carbonization temperature area is 30-100 ℃; the third carbonization treatment step comprises the step of heating the second carbonized fiber body obtained through the second carbonization treatment in a gradient manner from 1300 to 1600 ℃, wherein 5 third carbonization temperature areas are arranged between 1300 and 1600 ℃ so as to enable a plurality of temperature gradients between 1300 and 1600 ℃, and the temperature difference of each third carbonization temperature area is 50 to 150 ℃.
The first carbonization treatment, the second carbonization treatment, and the third carbonization treatment are performed in carbonization furnaces, which are classified into a low-temperature furnace (performing the first carbonization treatment), a medium-temperature furnace (performing the second carbonization treatment), and a high-temperature furnace (performing the third carbonization treatment) for carbonizing the fiber according to the set temperature of each furnace body. The residence time of the fiber carbonization process in each temperature zone and the temperature gradient of the carbonization process are controlled by three carbonization furnaces. The high-temperature furnace is a graphite furnace which is continuously opened to maintain a certain temperature and is used for producing graphite carbon fibers, the temperature is reduced when non-graphite fibers (such as polyacrylonitrile-based carbon fibers) are produced, the running graphite furnace is used, the temperature of the graphite furnace is reduced to serve as the high-temperature furnace, the temperature of the high-temperature furnace is reduced, the medium-temperature furnace is filled, the energy consumption of equipment in production can be reduced, the production resources are fully utilized, and the production cost is reduced.
The carbonization process of the pre-oxidized filaments spans a temperature range exceeding thousands of degrees celsius, during which a number of complex chemical reactions and structural changes occur within the fiber, not only with regard to material exchange but also with regard to energy. The inside of the carbonization equipment is provided with high-purity nitrogen as a protective atmosphere in the carbonization process, and pyrolysis products in the fiber carbonization process can be taken away. In the application, in the first carbonization treatment, namely, 7-9 unevenly distributed first carbonization temperature areas are arranged in the temperature of 300-800 ℃, the exothermic reaction of the fiber at about 400 ℃ is not as intense as the cyclization reaction in the preoxidation process, but the concentrated heat release still occurs in a short time, the instantaneous temperature of the fiber is easily increased, the internal structure is easily damaged, meanwhile, the decomposition products of the internal reaction of the fiber are not instantaneously removed, so that impurities such as tar are adhered to the fiber to cause surface defects, and the fiber performance is reduced. Therefore, 3-5 first carbonization temperature areas are arranged between 300 and 500 ℃, the temperature difference of each temperature area is 30-80 ℃, and the decomposition rate of products in the fiber can be reduced by gradually reacting at about 400 ℃ so that the nitrogen can be timely cleaned by the protection gas, and the pollution risk is reduced. A plurality of first carbonization temperature areas are also arranged in the temperature range of 500-800 ℃, and the temperature difference of each temperature area arranged in the temperature range of 500-800 ℃ is 50-150 ℃. In the second carbonization treatment, namely, 5-7 unevenly distributed second carbonization temperature areas are arranged in 800-1300 ℃, and the carbonization temperature is a peak area for denitrification in the fiber in the range of 900-1300 ℃, so that condensation reaction is aggravated, a large amount of nitrogen intensively escapes in the form of nitrogen, a large amount of void defects appear in the fiber, and the density of the carbon fiber is reduced. Therefore, 2-4 second carbonization temperature areas are arranged between 1000-1200 ℃, and the temperature difference of each temperature area is 30-100 ℃; a plurality of second carbonization temperature zones are also arranged between 800 and 1000 ℃ and between 1200 and 1300 ℃, and the temperature difference of each temperature zone arranged between 800 and 1000 ℃ and between 1200 and 1300 ℃ is 50 to 150 ℃. The reaction rate of the fiber in the concentrated reaction zone is reduced by reducing the temperature gradient in the temperature zone where the reaction in the fiber is severe, thereby prolonging the carbonization time. Thereby gentle reaction rate can reduce and lead to the fact great hole when nitrogen gas concentrates and escapes from the fibre inside, effectively control nitrogen gas escape rate for the pore channel size that causes reduces, thereby the whole porosity of fibre reduces thereupon, effectively promotes carbon fiber density, and then improves carbon fiber's tensile strength. Further, by setting 5 third carbonization temperature zones between 1300 ℃ and 1600 ℃, the temperature difference of each third carbonization temperature zone is 50 ℃ to 150 ℃ so as to finally obtain the carbon fiber with high density and high tensile strength.
Compared with the conventional polyacrylonitrile-based carbon fiber production, the application only uses two carbonization devices, namely a high-temperature furnace and a low-temperature furnace, and the graphite furnace is fully utilized to reduce the temperature of the furnace body, prolong the carbonization overall time so as to optimize the overall carbonization temperature interval, reduce the temperature gradient of the temperature interval with intense reaction in the fiber, prolong the carbonization time, reduce the reaction rate of the fiber in the concentrated reaction interval, reduce the precipitation rate of substances such as nitrogen, reduce the damage degree of the fiber structure, fully fine-crystallize the internal structure of the fiber, and further improve the fiber density and the tensile strength.
In the first carbonization treatment, 3-5 first carbonization temperature areas are arranged between 300 and 500 ℃, and the temperature difference of each temperature area is 30-80 ℃. The number of the first carbonization temperature areas arranged between 300 ℃ and 500 ℃ can be 3, 4 and 5, and the application is not limited. The temperature difference of each temperature zone includes, but is not limited to, 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃.
In the second carbonization treatment, 2-4 second carbonization temperature areas are arranged between 1000 and 1200 ℃, and the temperature difference of each temperature area is 30-100 ℃. The number of the second carbonization temperature areas arranged between 1000 ℃ and 1200 ℃ can be 2, 3 and 4, and the application is not limited. The temperature difference of each temperature zone includes, but is not limited to, 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃,100 ℃.
In the third carbonization treatment, 5 third carbonization temperature areas are arranged between 1300 ℃ and 1600 ℃, and the temperature difference of each temperature area is 50 ℃ to 150 ℃. The temperature difference of each temperature zone includes, but is not limited to, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃,100 ℃,110 ℃,120 ℃, 130 ℃,140 ℃,150 ℃.
In an embodiment of the application, the tension of the first carbonization temperature zone is 5-15N, the tension of the second carbonization temperature zone is 40-60N, and the tension of the third carbonization temperature zone is 40-60N. In different carbonization temperature areas, the tension of the fibers can be uniformly distributed by controlling the tension in the above range, so that the reaction of the internal structure of the fibers in the carbonization process is more uniform and stable, the damage degree of the fiber structure is reduced, the structural heterogeneity is reduced, and the consistency and the reliability of the fibers are improved. And the aggregation of gas can be reduced, so that the size of a pore channel generated in the fiber is reduced, the overall porosity is reduced, and the density of the carbon fiber is improved. Because the density of the fiber is related to the tensile strength, the density of the carbon fiber is effectively improved by controlling the tension in the carbonization process, and the tensile strength of the carbon fiber is further improved. The increased density means more bonds between carbon atoms, enhancing the chemical bond connections within the fiber, giving it higher tensile strength and stiffness.
In an embodiment of the application, the pre-oxidized fiber body is operated at a line speed of 420-520m/h, the first carbonization treatment is performed for 115-150 seconds, the second carbonization treatment is performed for 110-140 seconds, and the third carbonization treatment is performed for 90-110 seconds. By controlling the time of the carbonization process within the above-described range, fibers of different batches or locations may be subjected to similar time and temperature conditions during carbonization, thereby providing stability and consistency in the quality of the carbon fibers. Different time treatments may result in structural differences in the fibers, while treatments within a specified time frame help unify the properties of the fibers. And the gas is more fully discharged from the inside of the carbon fiber, so that the formation of pores is reduced, and the density of the carbon fiber is improved. The carbonization reaction rates in different temperature areas are different, and the microstructure of the carbon fiber can be optimized by processing in the time range, so that the carbon fiber is more compact in crystallization and more uniform in crystal size. This helps to improve properties of the carbon fiber such as tensile strength, elastic modulus, heat resistance, and the like. The carbonization treatment time is strictly controlled, so that the production period can be shortened as much as possible, the production efficiency is improved, and the production cost is reduced.
(3) The carbonized carbon fiber body is used as an anode and placed in an electrolytic bath. An acidic electrolyte or an alkaline electrolyte is prepared and injected into the electrolytic tank to fully soak the fibers in the electrolyte. Then, the anodes are connected by using a direct current power supply, and the anodes are electrified to carry out anodic oxidation treatment. During the anodization process, an oxide layer is formed on the surface of the fibers, which helps to enhance the surface properties and adhesion of the fibers. Taking out the carbon fiber body subjected to anodic oxidation treatment, and washing with water. The purpose of the water washing is to wash away residual electrolyte and other impurities generated during the anodic oxidation process to avoid adverse effects on the next operation. And immersing the washed carbon fiber body in a polymer sizing agent. Drying the sized carbon fiber body to evaporate water in the sizing agent, solidifying the sizing agent on the surface of the fiber and forming a layer of film. The temperature and time of drying may be determined according to the actual situation, and the present application is not limited thereto. The dried carbon fiber body is wound according to a specific specification and length to be long or roll-shaped. The carbon fiber finished product obtained in this way can be stored and used conveniently, and can also be used as a reinforcing material of a composite material.
The features and capabilities of the present application are described in further detail below in connection with the examples.
Example 1
The embodiment provides a carbon fiber, and the preparation method thereof comprises the following steps:
(1) Density of 1.18g/cm 3 Performing a pre-oxidation reaction on polyacrylonitrile fibers with the monofilament diameter of 8.6 mu m to obtain a pre-oxidized fiber body; wherein the initial temperature of the pre-oxidation reaction is 220 ℃ and the final temperature isThe temperature is 250 ℃ and the temperature gradient is 15 ℃; the running speed of the polyacrylonitrile fiber tows is 520m/h; the pre-oxidation residence time is 60min; in the pre-oxidation reaction, the tension applied to the filament bundle was 18N, and the density of the resulting pre-oxidized fiber body was 1.385g/cm 3 。
(2) The pre-oxidized fiber body in the step (1) is subjected to a first carbonization treatment by a low-temperature furnace (first carbonization temperature zone), specifically, the pre-oxidized fiber body is subjected to a first carbonization treatment by sequentially passing through a first carbonization temperature zone of 380 ℃, a first carbonization temperature zone of 420 ℃, a first carbonization temperature zone of 440 ℃, a first carbonization temperature zone of 480 ℃, a first carbonization temperature zone of 560 ℃, a first carbonization temperature zone of 660 ℃ and a first carbonization temperature zone of 780 ℃. Wherein in the first carbonization treatment, the residence time of the fibers was 115 seconds, and the tension applied to the pre-oxidized fiber body was 8N; introducing nitrogen into the low-temperature furnace, wherein the oxygen content in the nitrogen in the low-temperature furnace is lower than 2ppm.
And then the first carbonized fiber body obtained after the first carbonization treatment is subjected to the second carbonization treatment by a medium temperature furnace (a second carbonization temperature zone), specifically, the first carbonized fiber body is subjected to the second carbonization treatment by sequentially passing through a second carbonization temperature zone of 860 ℃, a second carbonization temperature zone of 1000 ℃, a second carbonization temperature zone of 1050 ℃, a second carbonization temperature zone of 1150 ℃, a second carbonization temperature zone of 1200 ℃ and a second carbonization temperature zone of 1280 ℃. Wherein in the first carbonization treatment, the residence time of the fibers is 110 seconds, and the tension applied to the pre-oxidized fiber body is 50N; introducing nitrogen into the medium temperature furnace, wherein the oxygen content in the nitrogen in the medium temperature furnace is lower than 1ppm.
And then subjecting the second carbonized fiber body obtained through the second carbonization treatment to a third carbonization treatment by a high temperature furnace (third carbonization temperature zone), specifically, subjecting the second carbonized fiber body to a third carbonization treatment by sequentially passing through a third carbonization temperature zone of 1350 ℃, a third carbonization temperature zone of 1400 ℃, a third carbonization temperature zone of 1450 ℃, a third carbonization temperature zone of 1500 ℃ and a third carbonization temperature zone of 1550 ℃. Wherein in the first carbonization treatment, the residence time of the fibers was 90 seconds, and the tension applied to the pre-oxidized fiber body was 55N; introducing nitrogen into the high-temperature furnace, wherein the oxygen content in the nitrogen in the high-temperature furnace is lower than 1ppm.
(3) And sequentially carrying out surface treatment, water washing, sizing, drying and winding on the carbonized fiber body subjected to the third carbonization treatment to obtain a polyacrylonitrile-based carbon fiber finished product.
The pre-oxidized fiber body sequentially passes through a low-temperature furnace, a medium-temperature furnace and a high Wen Lushi furnace, the temperature of each temperature zone in each furnace is preset, the temperature of each temperature zone reaches a preset value, and then the pre-oxidized fiber body starts to run at a constant linear speed (520 m/h) and sequentially passes through the low-temperature furnace, the medium-temperature furnace and the high-temperature furnace.
Example 2
This embodiment is substantially the same as embodiment 1 except that: the temperature, number and temperature gradient of each temperature zone of the first carbonization treatment are different.
Specifically, the pre-oxidized fiber body was subjected to a first carbonization treatment by passing through a first carbonization temperature zone of 400 ℃, a first carbonization temperature zone of 420 ℃, a first carbonization temperature zone of 440 ℃, a first carbonization temperature zone of 480 ℃, a first carbonization temperature zone of 560 ℃, a first carbonization temperature zone of 660 ℃, and a first carbonization temperature zone of 780 ℃ in this order.
Example 3
This embodiment is substantially the same as embodiment 1 except that: the temperature, number and temperature gradient of each temperature zone of the first carbonization treatment are different.
Specifically, the pre-oxidized fiber body was subjected to a first carbonization treatment by passing through a first carbonization temperature zone of 400 ℃, a first carbonization temperature zone of 440 ℃, a first carbonization temperature zone of 480 ℃, a first carbonization temperature zone of 560 ℃, a first carbonization temperature zone of 660 ℃, and a first carbonization temperature zone of 780 ℃.
Example 4
This embodiment is substantially the same as embodiment 1 except that: the temperature, the number and the temperature gradient of each temperature zone of the second carbonization treatment are different.
Specifically, the first carbonized fiber body is subjected to the second carbonization treatment in this order of a second carbonization temperature zone of 860 ℃, a second carbonization temperature zone of 1000 ℃, a second carbonization temperature zone of 1100 ℃, a second carbonization temperature zone of 1200 ℃, and a second carbonization temperature zone of 1280 ℃.
Example 5
This embodiment is substantially the same as embodiment 1 except that: the temperature, the number and the temperature gradient of each temperature zone of the second carbonization treatment are different.
Specifically, the first carbonized fiber body is subjected to the second carbonization treatment by passing through a second carbonization temperature zone of 860 ℃, a second carbonization temperature zone of 1060 ℃, and a second carbonization temperature zone of 1180 ℃ in this order, the second carbonization temperature zone of 1280 ℃.
Example 6
This embodiment is substantially the same as embodiment 1 except that: the reaction violent area inside the fiber is not distinguished during the low temperature, medium temperature and high temperature carbonization, and the temperature is increased isothermally at 70 ℃ in the range of 300-1600 ℃.
Specifically, the pre-oxidized fiber body is carbonized by sequentially passing through an isothermal heating carbonization temperature zone with a temperature gradient of 70 ℃ from 300 ℃.
Comparative example 1
This comparative example is substantially the same as example 1, except that: the pre-oxidized fiber body is subjected to only the first carbonization treatment and the third carbonization treatment without performing the second carbonization treatment.
Test example 1
The carbon fiber products provided in examples 1-6 and comparative example 1 were tested for density and tensile strength with reference to GB/T30019 and tensile strength with reference to GB/T3362. The density and tensile strength test results are shown in table 1.
TABLE 1
In the embodiment 1, 5 first carbonization temperature areas are arranged in the range of 300-500 ℃, in the embodiment 2, 4 first carbonization temperature areas are arranged in the range of 300-500 ℃, in the embodiment 3, 6 first carbonization temperature areas are arranged in the range of 300-500 ℃, as can be seen from comparison of the embodiment 1-3, in the low-temperature carbonization process, the number of different temperature areas arranged in the range of 300-500 ℃ has a large difference on the gentle effect of the temperature gradient, the density and the strength of the finished product fiber increase along with the increase of the number of the temperature areas in the range of 300-500 ℃, and in the low-carbon fiber reaction area around 400 ℃, too few temperature areas are arranged to lead the carbonization temperature gradient in the temperature area to increase, thus the performance of the finished product carbon fiber is easy to be reduced, and the gentle temperature gradient strength of a medium-temperature furnace cannot be improved after the subsequent increase.
In the embodiment 1, 4 second carbonization temperature areas are arranged in the temperature range of 1000-1200 ℃, in the embodiment 4, 3 second carbonization temperature areas are arranged in the temperature range of 1000-1200 ℃, in the embodiment 5, 2 second carbonization temperature areas are arranged in the temperature range of 1000-1200 ℃, and as can be seen from the comparison of the embodiments 1 and 4-5, in the middle-temperature carbonization process, the reaction is severe in the inside of the fiber, the number of the temperature increasing areas is gentle in the temperature range of nitrogen removal, the thinning of nitrogen removal channels is facilitated, and the fiber performance is improved.
In example 6, the severe reaction temperature zone is not distinguished, and the isothermal gradient is set, so that the temperature range of the severe reaction zone in the fiber is not distinguished, and after the carbonization temperature is uniformly increased at 70 ℃, the carbon fiber performance is negatively affected, the fiber density is not obviously changed, and the strength is similar or even slightly reduced, as can be seen from the data in table 1.
In comparative example 1, the second carbonization treatment, that is, the intermediate temperature furnace treatment was not performed, and as can be seen from table 1, after carbonization was performed using only the low temperature furnace and the high temperature furnace, the total temperature zone was reduced relative to the total temperature zone using the intermediate temperature furnace, the temperature zone set in the different severe reaction stages of the fiber was correspondingly reduced, and the performance was lower than that of the fiber after the mild temperature gradient in the severe reaction zone of the fiber using the intermediate temperature furnace, and the comparative results showed that: the number of temperature zones in the carbonization process is added in a mode of adding the medium-temperature furnace, so that the temperature gradient in the temperature zone with severe fiber reaction is gentle, and the performances such as the density and the strength of the carbon fiber body can be effectively improved.
The embodiments described above are some, but not all embodiments of the application. The detailed description of the embodiments of the application is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
Claims (10)
1. A method for preparing carbon fibers, comprising the steps of:
has a density of 1.34-1.44g/cm 3 Sequentially performing first carbonization treatment, second carbonization treatment and third carbonization treatment on the pre-oxidized fiber body to obtain a carbonized fiber body; post-processing the carbonized fiber body to obtain the carbon fiber;
wherein the step of the first carbonization treatment comprises subjecting the pre-oxidized fiber body to gradient heating from 300 to 800 ℃, wherein a plurality of first carbonization temperature zones are arranged between 300 and 500 ℃ so as to have a plurality of temperature gradients between 300 and 500 ℃; the second carbonization treatment step comprises the step of heating the first carbonized fiber body obtained through the first carbonization treatment in a gradient manner from 800 to 1300 ℃, wherein a plurality of second carbonization temperature areas are arranged between 1000 and 1200 ℃ so as to enable a plurality of temperature gradients to be arranged between 1000 and 1200 ℃; the third carbonization treatment step includes performing gradient heating from 1300 to 1600 ℃ on the second carbonized fiber body obtained through the second carbonization treatment, wherein a plurality of third carbonization temperature areas are arranged between 1200 and 1600 ℃ so as to have a plurality of temperature gradients between 1300 and 1600 ℃.
2. The method of claim 1, wherein 3 to 5 first carbonization temperature zones are provided between 300 to 500 ℃, and a temperature difference of each first carbonization temperature zone provided between 300 to 500 ℃ is 30 to 80 ℃.
3. The method of claim 1, wherein 2-4 second carbonization temperature zones are provided between 1000-1200 ℃, and a temperature difference of each second carbonization temperature zone provided between 1000-1200 ℃ is 30-100 ℃.
4. The method of claim 1, wherein 4-5 third carbonization temperature zones are provided between 1300-1600 ℃, and a temperature difference between 1300-1600 ℃ for each third carbonization temperature zone is 50-150 ℃.
5. The method of any one of claims 1-4, wherein the first carbonization temperature zone has a tension of 5-15N; and/or the tension of the second carbonization temperature zone is 40-60N; and/or the tension of the third carbonization temperature zone is 40-60N.
6. The method according to any one of claims 1 to 4, wherein the pre-oxidized fiber body has a running line speed of 420 to 520m/h;
optionally, the first carbonization treatment is performed for 115-150 seconds; and/or the second carbonization treatment is performed for 110-140 seconds; and/or the time of the third carbonization treatment is 90-110 seconds.
7. The method of any one of claims 1-4, wherein the preparation of the pre-oxidized fiber body comprises:
pre-oxidizing polyacrylonitrile fiber in pre-oxidizing device to obtain polyacrylonitrile fiber with density of 1.34-1.44g/cm 3 Is a pre-oxidized fiber body; wherein the step of pre-oxidation reaction comprises the step of heating the polyacrylonitrile fiber in a gradient way from 210 ℃ to 260 ℃ with a heating gradient of 15-20 ℃; the time of the pre-oxidation reaction is 60-90min;
optionally, the running speed of the polyacrylonitrile fiber is 420-520m/h;
optionally, in the pre-oxidation reaction, the tension applied to the polyacrylonitrile fiber is 15 to 20N.
8. The method of any one of claims 1-4, wherein the post-treatment comprises:
and sequentially carrying out surface treatment, water washing, sizing, drying and winding on the carbonized fiber body to obtain the carbon fiber.
9. The method of manufacturing according to claim 8, wherein the surface treatment comprises: performing anodic oxidation electrochemical treatment on the carbonized fiber body;
preferably, the electrolyte used in the electrochemical treatment includes an acid electrolyte or an alkaline electrolyte.
10. A carbon fiber produced by the production method according to any one of claims 1 to 9.
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