Pretreatment process for efficient pre-oxidation of PAN fibers

Abstract

The invention discloses a pretreatment process for efficient pre-oxidation of PAN (polyacrylonitrile) fibers, a pretreatment device is arranged on the inlet side of a pre-oxidation furnace, the pretreatment device comprises an irradiation chamber, and a plurality of under-bundle godets and conveying rollers are arranged in the irradiation chamber along the conveying direction of fiber bundles. And a fiber bundle enters from the inlet, is guided by the godet and the conveying roller in sequence, and then enters the pre-oxidation furnace from the outlet. And the heating unit is used for heating the fiber bundles in the irradiation chamber. The process comprises the following steps of: withdrawing a raw filament on a filament withdrawing frame; a fiber bundle enters the irradiation chamber through the guide wheel and is irradiated under the guide of the godet, and meanwhile, the heating unit assists in heating so as to improve the irradiation effect. The heating mode comprises setting the conveying roller as a heating roller and / or introducing hot air; and after irradiation, the fiber bundles enter a pre-oxidation furnace to complete pre-oxidation. According to the method, irradiation is combined with heating treatment, so that the aromatization efficiency of the PAN fibers is remarkably improved, the pre-oxidation time is shortened, the production cost is reduced, the production efficiency is improved, and the requirements of various industries on the yield of the carbon fibers are met.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber technology, and specifically to a pretreatment process for efficient pre-oxidation of PAN fibers. Background Technology

[0002] Carbon fiber, as a novel carbon material, has become an indispensable key material in aerospace, new energy vehicles, high-end sporting goods, and wind power generation due to its superior lightweight, high specific strength, and high specific modulus properties. Its strength can be several times or even tens of times that of steel, while its density is only about one-fifth that of steel. This unique combination of properties gives it unparalleled advantages in lightweight design. However, despite its broad application prospects, the large-scale popularization of carbon fiber, especially the mainstream polyacrylonitrile (PAN)-based carbon fiber, still faces significant challenges.

[0003] The primary constraint lies in its high cost. This stems mainly from two aspects: first, the high cost of raw materials. Each ton of finished carbon fiber requires approximately 2-2.2 tons of precursor fiber, with the precursor fiber alone costing 40,000-60,000 RMB, which is 4-5 times that of steel materials; second, the complex production process and enormous energy consumption, with electricity consumption accounting for approximately 25%-30% of the total production cost. It is worth noting that the cost of precursor fiber accounts for an extremely high proportion of the total cost, reaching 60.26%, which is one of the core reasons for its persistently high price.

[0004] Secondly, the lengthy preparation cycle is also a bottleneck restricting the improvement of production efficiency. The manufacturing of PAN-based carbon fiber requires multiple processes, including precursor production, pre-oxidation, and carbonization. Among them, the pre-oxidation process, as a crucial link between the preceding and following processes, typically needs to be maintained at a temperature range of 180-300℃ for 50 to 90 minutes. This process accounts for approximately 75% to 90% of the total carbon fiber processing time and consumes about 70% of the total electrical energy. Although current mainstream technologies have shortened the pre-oxidation time to 35-40 minutes through process optimization, this process remains the most time- and energy-intensive part of the entire production chain.

[0005] Currently, further optimization of the pre-oxidation process faces technical bottlenecks. Traditional hot air heating methods, in pursuit of shorter processing times, easily lead to uneven heating inside and outside the fiber, resulting in problems such as insufficient or excessive pre-oxidation. Insufficient pre-oxidation causes the fiber to melt and break during subsequent high-temperature carbonization, while excessive oxidation damages the precursor fiber structure, leading to defects such as holes and cracks in the final carbon fiber product, severely reducing its tensile strength and modulus.

[0006] Therefore, how to solve these problems existing in the prior art has become the subject of this invention. Summary of the Invention

[0007] The purpose of this invention is to provide a pretreatment process for efficient pre-oxidation of PAN fibers.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A pretreatment process for efficient pre-oxidation of PAN fibers is achieved by a pretreatment device, which is set at the front end corresponding to the inlet side of the pre-oxidation furnace. It includes an irradiation chamber, and multiple fiber guide rollers and conveying rollers are provided in the irradiation chamber corresponding to the fiber bundle conveying direction. The fiber bundle enters through the inlet of the irradiation chamber, passes sequentially through the front guide roller, multiple conveying rollers and the rear guide roller, and then exits through the outlet of the irradiation chamber into the pre-oxidation furnace. It also includes a heating unit, which is provided in relation to the irradiation chamber and is used to heat the fiber bundles in the irradiation chamber; Pretreatment processes include: S1. The fiber bundles are placed on the unwinding frame and unwinding is performed; S2. The fiber bundle enters the irradiation chamber through the guide wheel, and is then irradiated in the irradiation chamber after being guided by the lower guide roller. During irradiation, the fiber bundle is heated by a heating unit to improve the irradiation effect; the heating methods include: The conveying roller is configured as a heating roller, and the operating temperature of the heating roller is set to 60~240℃; or / and, hot air for heating is provided, and the temperature range of the hot air is 20~200℃; S3. The irradiated fiber bundles are fed into a pre-oxidation furnace for pre-oxidation to obtain pre-oxidized fibers.

[0009] A further technical solution is that the irradiation chamber is provided with a hot air circulation area, and the fiber guide roller and the heating roller are provided in the hot air circulation area corresponding to the fiber bundle conveying direction; It also includes a hot air unit, which includes a hot air circulation pipe and a heating element and a fan connected in series in the hot air circulation pipe; the inlet and outlet of the hot air circulation pipe are respectively connected to two different locations in the hot air circulation area for heating the hot air circulation area. The heating unit is the heating roller; Alternatively, the heating unit may be the hot air unit and the hot air circulation area; Alternatively, the heating unit may be a combination of the heating roller, the hot air unit, and the hot air circulation area.

[0010] In the above solution, the heating roller is existing technology, and its heating method can be electromagnetic induction heating, fluid medium (such as hot oil, steam) heating, resistance heating and other heating methods known to those skilled in the art. Since the heating method of the heating roller is not the point of invention of this case, it will not be described in detail here.

[0011] In the above scheme, the heating part of the hot air unit is an electric heating element or heat exchanger that uses the principle of resistance, electromagnetic induction or combustion to heat the air flowing through the hot air circulation pipeline.

[0012] In the above scheme, in the pretreatment process S2, the operating temperature of the heating roller is set to 60~240℃, with the optimal process temperature range being 160~200℃. This temperature range firstly ensures that the fiber bundle precursor can be heated to the starting temperature required for its cyclization reaction (not lower than 160℃); secondly, it effectively avoids operational stability issues that may be caused by excessively high ambient temperatures in the electron beam accelerator irradiation section, eliminating the need to pay additional upgrade and maintenance costs for its high-temperature resistant materials and cooling system.

[0013] The operating temperature range of the hot air unit is 20~220℃, with 120~180℃ being optimal. Compared to heated rollers, the operating temperature of the hot air circulation system is usually set relatively lower. This is mainly due to the differences in their heating principles and thermal efficiencies. Heated rollers (such as those heated by heat transfer oil) transfer heat to the fiber bundle filaments by first heating the heat transfer medium (such as oil) and then conducting the heat through direct contact with the roller body. This direct contact conduction method has relatively high thermal efficiency.

[0014] Hot air circulation requires heating the air first, and then a fan forces the hot air to circulate within the hot air circulation area of ​​the irradiation chamber to achieve convection heating. During this process, some heat is lost from the hot air, so it is only used as an auxiliary heating method.

[0015] Based on energy efficiency and cost considerations, heated rollers are often chosen as the primary method for heating fiber bundles due to their high thermal efficiency and direct heating. However, the heating area of ​​heated rollers is usually limited to the contact zone closely adjacent to the roller body, resulting in a relatively small heating range and potential localized temperature unevenness. Therefore, hot air circulation is introduced as an auxiliary heating method to supplement heating and equalize the temperature of areas that are difficult to cover by the heated rollers or areas prone to temperature fluctuations. Furthermore, hot air circulation can preheat the fiber bundle filaments before they enter the heated rollers, allowing the filament temperature to rise steadily and avoiding drastic temperature jumps that occur when directly contacting the high-temperature roller body. This helps ensure more uniform heating of the fiber bundle and reduces material property fluctuations caused by localized overheating or underheating.

[0016] In a further technical solution, there are three heating rollers, which are arranged in parallel along the fiber bundle conveying path; the fiber bundle passes through the lower surface of the front heating roller, then through the upper surface of the middle heating roller, and then through the lower surface of the rear heating roller. The irradiation section of the electron beam accelerator is positioned directly above the central heating roller; It is also equipped with a tension sensor and a controller to form a closed-loop control system; the tension sensor monitors the changes in fiber bundle tension in real time and transmits the signal to the controller; the controller, based on the set parameters, adjusts the horizontal spacing or vertical position of the front heating roller and / or the rear heating roller to achieve dynamic and precise compensation of tension.

[0017] This design allows for precise real-time control of fiber bundle tension. By using the front heating roller and / or rear heating roller to regulate tension, tension fluctuations can be effectively suppressed without increasing equipment size, improving system response speed and stability, and ensuring the consistency and reliability of the irradiation process.

[0018] A further technical solution involves providing several parallel, spaced-apart guide grooves on the surface of the fiber bundle guide roller. These guide grooves are positioned around the roller's axis, and their width corresponds to the width of the fiber bundle. The guide grooves are used to position the fiber bundle, ensuring that the fiber bundle's feeding direction does not deviate.

[0019] A further technical solution is to isolate the hot air circulation area from other areas of the irradiation chamber (which can be achieved through heat insulation panels) to ensure the heating efficiency of the fiber bundle in the hot air circulation area.

[0020] A further technical solution includes a temperature closed-loop control unit, which comprises a temperature sensor located in the hot air circulation area of ​​the irradiation chamber, a valve located in the hot air circulation pipeline, and a controller. The control unit is communicatively connected to the temperature sensor and the valve, respectively. The valve is preferably located at the outlet of the hot air circulation pipeline.

[0021] The temperature sensor is used to detect the temperature within the hot air circulation area; the valve is used to regulate the flow rate of hot air entering the hot air circulation area; the control unit is configured to adjust the opening of the valve according to the detection signal of the temperature sensor, so as to control the hot air volume and achieve real-time adjustment of the temperature within the hot air circulation area.

[0022] In a further technical solution, the hot air unit is also equipped with a hot air bypass, which is connected to the pre-oxidation furnace and used to introduce the hot air from the pre-oxidation furnace into the hot air circulation area of ​​the irradiation chamber. This design enables the reuse of the heat source, thereby significantly reducing the energy consumption of the heater and achieving energy saving and consumption reduction.

[0023] A further technical solution involves the following step in the pretreatment process S1: the unwinding is an active unwinding method with a tension of 5-40N and an unwinding speed of 0.5-10 min / s. Active unwinding utilizes a drawing device, reducing fiber damage caused by passive unwinding. Furthermore, active unwinding maintains a stable unwinding speed, further ensuring precise production control.

[0024] In a further technical solution, during the S2 pretreatment process, the energy range of the electron beam accelerator is 0.5–10.0 MeV, the power is 30–400 kW, the current is 5–100 mA, the irradiation dose is 10–10000 Kgy, the irradiation time is 20 s–10 min, and the oxygen volume fraction in the irradiation chamber is 10–24%.

[0025] Irradiation itself promotes the pre-oxidation stage of carbon fibers, accelerating the cross-linking between linear structures to form planar structures. Heating during irradiation further accelerates the cross-linking between the linear structures of PAN fibers, thereby reducing the irradiation dose or shortening the subsequent pre-oxidation time.

[0026] The oxygen volume fraction in the irradiation chamber is controlled within the range of 10% to 24%. This is because oxygen promotes the pre-oxidation reaction during carbon fiber production, enhancing the fiber's thermal stability and ensuring its successful passage through the low-temperature carbonization furnace. However, the introduced oxygen is gradually removed during the subsequent high-temperature carbonization stage, potentially leading to defects within the fiber and consequently reducing its mechanical properties. Therefore, precise control of the oxygen volume fraction in the environment is necessary to manage the amount of oxygen absorbed by the fiber during the pre-oxidation stage and optimize the performance of the final product.

[0027] In a further technical solution, in the S3 pretreatment process, the pre-oxidation is carried out by gradient heating. The irradiated fiber bundles pass through 1-3 pre-oxidation temperature zones. The temperature of the first pre-oxidation temperature zone is 160-200℃, the temperature of the second pre-oxidation temperature zone is 200-230℃, and the temperature of the third pre-oxidation temperature zone is 230-260℃. The residence time in each temperature zone is 5-20 minutes.

[0028] A further technical solution also includes S4, which involves carbonizing the pre-oxidized fiber. The carbonization process requires that the pre-oxidized fiber be carbonized at a low temperature of 400-800°C in a low-temperature carbonization furnace under an inert atmosphere, and then carbonized at a high temperature of 900-1600°C in a high-temperature carbonization furnace to obtain polyacrylonitrile-based carbon fiber.

[0029] The terms “include,” “including,” and “have” used in this article are all open-ended, meaning they include but are not limited to.

[0030] Unless otherwise specified, the terms used herein generally have their ordinary meaning in the context of the art, the subject matter, and the specific context. Certain terms used to describe this case will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing the case.

[0031] The working principle and advantages of this invention are as follows: To address the industry bottleneck of excessively long pre-oxidation stages in carbon fiber manufacturing, this application provides a highly efficient pre-oxidation pretreatment process for polyacrylonitrile (PAN)-based carbon fibers. This process significantly enhances the aromatization reaction rate of the fibers by subjecting PAN fibers to electron beam irradiation before pre-oxidation, combined with environmental or bulk heating techniques during the irradiation process. This synergistic treatment effectively induces crosslinking and cyclization between macromolecular chains, thereby accelerating the formation of stable ladder-like structures at the molecular level.

[0032] In the traditional production process of polyacrylonitrile (PAN)-based carbon fiber, pre-oxidation is a critical and time-consuming step. This process has traditionally been carried out in a multi-temperature zone pre-oxidation furnace (early designs may have required 6 or more independent temperature zones), with traditional pre-oxidation times generally ranging from 60 to 100 minutes (1 hour to 1 hour and 40 minutes).

[0033] Through continuous equipment and process innovation (such as optimizing heating methods, precisely controlling the temperature field and stretching tension), the number of temperature zones in the pre-oxidation furnace has been significantly optimized, and the pre-oxidation time in modern industrial production can now be stably controlled at 45-50 minutes. However, there is a clear technical lower limit to further reducing the pre-oxidation time. The fundamental reason is that it is essential to ensure that the PAN precursor fiber can fully and uniformly complete a series of chemical reactions such as cyclization, dehydrogenation, and oxidation to form a sufficiently stable and dense trapezoidal polymer structure. If the degree of pre-oxidation is insufficient, the fiber will be unable to withstand the stress generated by high-temperature thermal decomposition during the subsequent low-temperature carbonization stage due to insufficient thermal stability of the molecular structure, making it prone to melting or fiber breakage, resulting in a decrease in product qualification rate and production interruption.

[0034] The electron beam irradiation pretreatment technology employed in this invention is an effective solution to the aforementioned technical bottlenecks. This technology utilizes a high-energy electron beam to irradiate PAN precursor fibers under heating conditions, which can pre-initiate cross-linking reactions on their molecular chains and promote the formation of early cyclization structures (e.g., through the generation of free radicals). This is equivalent to "pre-positioning" some of the chemical reactions that would otherwise need to be completed in a high-temperature pre-oxidation furnace, significantly improving the initial structural stability of the precursor fibers and their subsequent thermal oxidation reactivity.

[0035] Electron beam irradiation modified precursor fibers exhibit reduced activation energy, accelerated cyclization reaction rate, and a more gradual exothermic peak during subsequent thermal oxidation. This significantly shortens the total pre-oxidation time and reduces stringent requirements on the number, length, or energy consumption of pre-oxidation furnace temperature zones, providing a reliable technical approach to reduce equipment investment, system energy consumption, and production costs.

[0036] In summary, the introduction of irradiation technology can effectively stimulate the activity of PAN molecular chains, enhance their cross-linking ability, and promote the faster formation of stable aromatized structures in fibers, thereby significantly shortening the pre-oxidation time. This invention, through the aforementioned heated irradiation pretreatment process, not only significantly improves pre-oxidation efficiency but also helps reduce overall production energy consumption and costs, while simultaneously improving the yield and quality consistency of carbon fibers, better meeting the growing demand for high-performance carbon fibers in various downstream application fields. Attached Figure Description

[0037] Appendix Figure 1 This is a schematic diagram of the pretreatment device according to an embodiment of the present invention; Appendix Figure 2 This is a top view of the lower wire guide roller according to an embodiment of the present invention; Appendix Figure 3 This is a process flow diagram of an embodiment of the present invention; Appendix Figure 4 This is a schematic diagram of the system structure according to an embodiment of the present invention; Appendix Figure 5 Infrared images of PAN fibers after different irradiation treatments according to the present invention.

[0038] In the above figures: 1. Fiber bundle; 2. Irradiation chamber; 3. Pre-oxidation furnace; 4. Hot air circulation area; 5. Guide roller below the bundle; 6. Heating roller; 6a. Front heating roller; 6b. Middle heating roller; 6c. Rear heating roller; 7. Hot air circulation pipeline; 8. Heating section; 9. Irradiation section of electron beam accelerator; 10. Guide groove; 11. Unwinding frame; 12. Guide wheel; 13. Low-temperature carbonization furnace; 14. High-temperature carbonization furnace; 15. Drawing machine; 16. Winding machine; 17. Surface treatment tank; 18. Sizing tank; 19. Drying equipment; 20. Hot air bypass; 21. Fan; 22. Valve. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments: The present invention will be clearly described below with illustrations and detailed description. Any person skilled in the art who understands the embodiments of the present invention can make changes and modifications based on the technology taught in the present invention without departing from the spirit and scope of the present invention.

[0040] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of this work. Singular forms such as “a,” “this,” “this,” “the,” and “the” as used herein also include plural forms.

[0041] This invention provides a pretreatment process for highly efficient pre-oxidation of PAN fibers, such as... Figure 1As shown, this is achieved through a pretreatment device, which is located at the front end of the inlet side of the pre-oxidation furnace 3. It includes an irradiation chamber 2, and a hot air circulation area 4 is provided in the irradiation chamber 2. In the hot air circulation area 4, a plurality of fiber guide rollers 5 and heating rollers 6 are provided in the direction of fiber bundle 1.

[0042] The fiber bundle 1 enters through the inlet of the irradiation chamber 2, passes sequentially through the front end guide roller 5, multiple heating rollers 6 and the rear end guide roller 5, and then exits through the outlet of the irradiation chamber 2 and enters the pre-oxidation furnace 3.

[0043] It also includes a hot air unit, which includes a hot air circulation pipe 7 and a heating part 8 and a fan 21 connected in series in the hot air circulation pipe 7; the inlet and outlet of the hot air circulation pipe 7 are respectively connected to two different positions of the hot air circulation area 4 for heating the hot air circulation area 4.

[0044] Preferably, there are three heating rollers 6, which are arranged in parallel along the conveying path of the fiber bundle 1; the fiber bundle 1 passes through the lower surface of the front heating roller 6a, then through the upper surface of the middle heating roller 6b, and then through the lower surface of the rear heating roller 6c.

[0045] The irradiation section 9 of the electron beam accelerator is positioned directly above the central heating roller 6b.

[0046] It is also equipped with a tension sensor and a controller (not shown in the figure) to form a closed-loop control system; the tension sensor monitors the tension change of the fiber bundle 1 in real time and transmits the signal to the controller; the controller adjusts the horizontal spacing or vertical position of the front heating roller 6a and / or the rear heating roller 6c according to the set parameters to achieve dynamic and precise compensation of tension.

[0047] Preferred, such as Figure 2 As shown, the surface of the fiber guide roller 5 is provided with several parallel and spaced guide grooves 10. The guide grooves 10 are arranged around the axis of the roller, and the width of the grooves corresponds to the width of the fiber bundle 1.

[0048] Preferably, the hot air circulation area 4 is relatively isolated from other areas of the irradiation chamber 2 (this can be achieved through a heat insulation plate, which is not shown in the figure).

[0049] Preferably, it also includes a temperature closed-loop control unit, which includes a temperature sensor disposed in the hot air circulation area 4 of the irradiation chamber 2, a valve 22 disposed in the hot air circulation pipeline 7, and a control unit. The control unit is communicatively connected to the temperature sensor and the valve 22, respectively. The valve 22 is preferably disposed at the outlet of the hot air circulation pipeline 7.

[0050] The temperature sensor is used to detect the temperature within the hot air circulation zone 4; the valve is used to regulate the flow rate of hot air entering the hot air circulation zone 4; the control unit is configured to adjust the opening of the valve according to the detection signal of the temperature sensor, so as to control the hot air volume and achieve real-time adjustment of the temperature within the hot air circulation zone 4.

[0051] Preferably, the hot air unit is further provided with a hot air bypass 20, which is connected to the pre-oxidation furnace 3 and is used to introduce the hot air in the pre-oxidation furnace 3 into the hot air circulation area 4 of the irradiation chamber 2.

[0052] like Figure 3 As shown, the pretreatment process includes: S1. The fiber bundle 1 raw filament is placed on the unwinding frame 11 and unwinding is performed; the unwinding is preferably active unwinding, with a tension of 5-40N and an unwinding speed of 0.5-10min / s.

[0053] S2. Fiber bundle 1 enters the irradiation chamber through guide wheel 12, and after being guided by the lower guide roller 5, it is irradiated in irradiation chamber 2. During irradiation, the energy range of the electron beam accelerator is 0.5-10.0 MeV, the power is 30-400 kW, the current is 5-100 mA, the irradiation dose is 200-500 Kgy, the irradiation time is 5s-60s, and the oxygen volume fraction in irradiation chamber 2 is 10-24%.

[0054] During the irradiation process, heating roller 6 and hot air circulation are used for simultaneous heating to improve the irradiation effect; the working temperature of heating roller 6 is set to 160~200℃, and the temperature range of the hot air output by the hot air unit is 120~180℃.

[0055] S3. The irradiated fiber bundle 1 enters the pre-oxidation furnace 3 for pre-oxidation to obtain pre-oxidized fibers. The pre-oxidation is carried out by gradient heating. The irradiated fiber bundle 1 passes through 1-3 pre-oxidation temperature zones. The temperature of the first pre-oxidation temperature zone is 160-200℃, the temperature of the second pre-oxidation temperature zone is 200-230℃, and the temperature of the third pre-oxidation temperature zone is 230-260℃. The residence time in each temperature zone is 5-20 minutes.

[0056] Preferably, the process further includes S4, which involves carbonizing the pre-oxidized fiber. The carbonization process requires that the pre-oxidized fiber be carbonized at a low temperature of 400-800°C in a low-temperature carbonization furnace 13 under an inert atmosphere, and then carbonized at a high temperature of 900-1600°C in a high-temperature carbonization furnace 14 to obtain polyacrylonitrile-based carbon fiber.

[0057] like Figure 4As shown, the system includes a low-temperature carbonization furnace 13 and a high-temperature carbonization furnace 14 located behind the pre-oxidation furnace 3, and the three are arranged in sequence from front to back according to the fiber bundle 1 feeding direction.

[0058] During the modification process, the fiber bundle 1 is given traction force by the drawing machine 15 in the production line, and the fiber is fed and wound up by the unwinding frame 11 and the winding machine 16 at both ends.

[0059] After being irradiated in irradiation chamber 2, fiber bundle 1 is sequentially processed in pre-oxidation furnace 3, low-temperature carbonization furnace 13, high-temperature carbonization furnace 14, surface treatment tank 17, and sizing tank 18. Finally, it is dried in drying equipment 19 to complete the modification process and then the fibers are collected.

[0060] The carbonization process requires the following steps: Under an inert atmosphere, the pre-oxidized fibers are carbonized at a low temperature of 400-800℃ in a low-temperature carbonization furnace 13, followed by high-temperature carbonization at 900-1600℃ in a high-temperature carbonization furnace 14 to obtain polyacrylonitrile-based carbon fibers. The pre-oxidation, surface treatment, sizing, and drying processes can follow conventional carbon fiber processing requirements and will not be elaborated upon in this document.

[0061] The technical effects of the present invention will be further illustrated below through multiple sets of embodiments, multiple sets of comparative examples, and blank samples: Table 1. Effects of different irradiation processes process Irradiation dose / kgy Irradiation heating method Irradiation temperature / ℃ Irradiation time / s Oxygen content in irradiated environment / % Pre-oxidation time / min <![CDATA[Pre-oxidized bulk density / g / cm 3 > Oxygen content after pre-oxidation / % Carbonization strength / MPa Modulus after carbonization / GPa blank sample 0 none none none 21 45 1.36 5.3 4921 231 Comparative Example 1 100 none none 10 21 30 1.36 5.3 4987 241 Comparative Example 2 200 none none 10 21 30 1.36 5.6 4911 235 Comparative Example 3 400 none none 10 21 30 1.37 6.0 4722 233 Example 1 200 Heating rollers 160 7 21 20 1.37 5.7 4922 235 Example 2 200 thermal cycle 160 7 21 20 1.37 5.8 4889 235 Example 3 (Best) 200 Heating roller + heat circulation 160 5 21 20 1.37 6.4 4941 239 Example 4 200 Heating rollers 160 7 19 20 1.36 5.8 5001 231 Example 5 200 Heating rollers 160 7 16 20 1.36 5.4 4732 230 Example 6 200 Heating rollers 160 7 13 20 1.35 5.1 4642 230 As shown in Table 1, due to the lack of heating in Examples 1-3, the irradiation method effectively shortened the pre-oxidation time compared to the traditional method, although there is still room for further reduction. Example 1 used a heating roller, effectively reducing the pre-oxidation time; Example 2 used hot air circulation heating, effectively shortening the pre-oxidation time; Example 3 used a composite heating method, resulting in the shortest pre-oxidation time and better fiber mechanical properties. Examples 4-6 irradiated PAN fibers in environments with different oxygen concentrations, finding that the irradiated fibers showed a certain improvement in mechanical strength at a 19% oxygen concentration.

[0062] like Figure 5 As shown, 2240cm -1 Represents the cyano peak, 1680 cm⁻¹ -1 Represents the -C=N peak, 2240 cm⁻¹ -1 The weakening of the peak at position 1360 cm⁻¹ indicates that some of the cyano groups have undergone cyclization, producing a stable cross-linked structure. -1 and 1454cm -1The dehydrogenation index represents the PAN fiber. The higher the value, the more -CC- is converted into -C=C-, resulting in a stable cross-linked structure. The data comparison shows that, with appropriate heating and appropriate oxygen concentration atmosphere control, the cross-linking effect of irradiation on the fiber can be effectively improved in Examples 3 and 4.

[0063] As can be seen from the above examples and comparative examples, Example 3 is an irradiation process for T700 precursor fibers, which can save more than 50% of the pre-oxidation time.

[0064] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A pretreatment process for efficient pre-oxidation of PAN fibers, characterized in that: This is achieved through a pretreatment device, which is set at the front end of the inlet side of the pre-oxidation furnace. It includes an irradiation chamber, and multiple fiber guide rollers and conveying rollers are provided in the irradiation chamber in the direction of fiber bundle conveying. The fiber bundle enters through the inlet of the irradiation chamber, passes sequentially through the front guide roller, multiple conveying rollers and the rear guide roller, and then exits through the outlet of the irradiation chamber into the pre-oxidation furnace. It also includes a heating unit, which is provided in relation to the irradiation chamber and is used to heat the fiber bundles in the irradiation chamber; Pretreatment processes include: S1. The fiber bundles are placed on the unwinding frame and unwinding is performed; S2. The fiber bundle enters the irradiation chamber through the guide wheel, and is then irradiated in the irradiation chamber after being guided by the lower guide roller. During irradiation, the fiber bundle is heated by a heating unit to improve the irradiation effect; the heating methods include: The conveying roller is configured as a heating roller, and the operating temperature of the heating roller is set to 60~240℃; or / and, hot air for heating is provided, and the temperature range of the hot air is 20~200℃; S3. The irradiated fiber bundles are fed into a pre-oxidation furnace for pre-oxidation to obtain pre-oxidized fibers.

2. The pretreatment process for efficient pre-oxidation of PAN fibers according to claim 1, characterized in that: The irradiation chamber is provided with a hot air circulation area, and the fiber guide roller and the heating roller are provided in the hot air circulation area corresponding to the fiber bundle conveying direction. It also includes a hot air unit, which includes a hot air circulation pipe and a heating element and a fan connected in series in the hot air circulation pipe; the inlet and outlet of the hot air circulation pipe are respectively connected to two different locations in the hot air circulation area for heating the hot air circulation area. The heating unit is the heating roller; Alternatively, the heating unit may be the hot air unit and the hot air circulation area; Alternatively, the heating unit may be a combination of the heating roller, the hot air unit, and the hot air circulation area.

3. The pretreatment process for efficient pre-oxidation of PAN fibers according to claim 1 or 2, characterized in that: There are three heating rollers, which are arranged in parallel along the fiber bundle conveying path; the fiber bundle passes through the lower surface of the front heating roller, then through the upper surface of the middle heating roller, and then through the lower surface of the rear heating roller. The irradiation section of the electron beam accelerator is positioned directly above the central heating roller; It is also equipped with a tension sensor and a controller to form a closed-loop control system; the tension sensor monitors the changes in fiber bundle tension in real time and transmits the signal to the controller; the controller, based on the set parameters, adjusts the horizontal spacing or vertical position of the front heating roller and / or the rear heating roller to achieve dynamic and precise compensation of tension.

4. The pretreatment process for efficient pre-oxidation of PAN fibers according to claim 1, characterized in that: The surface of the fiber guide roller is provided with several parallel and spaced guide grooves, which are arranged around the axis of the roller and the width of the grooves corresponds to the width of the fiber bundle.

5. The pretreatment process for efficient pre-oxidation of PAN fibers according to claim 2, characterized in that: The hot air circulation area is relatively isolated from other areas of the irradiation chamber.

6. The pretreatment process for efficient pre-oxidation of PAN fibers according to claim 2, characterized in that: It also includes a temperature closed-loop control unit, which includes a temperature sensor located in the hot air circulation area of ​​the irradiation chamber, a valve located in the hot air circulation pipeline, and a control unit, the control unit being communicatively connected to the temperature sensor and the valve respectively.

7. The pretreatment process for efficient pre-oxidation of PAN fibers according to claim 2, characterized in that: The hot air unit is also provided with a hot air bypass, which is connected to the pre-oxidation furnace and is used to introduce the hot air in the pre-oxidation furnace into the hot air circulation area of ​​the irradiation chamber.

8. The pretreatment process for efficient pre-oxidation of PAN fibers according to claim 1, characterized in that: In S2, during irradiation, the energy range of the electron beam accelerator is 0.5–10.0 MeV, the power is 30–400 kW, the current is 5–100 mA, the irradiation dose is 10–10000 Kgy, the irradiation time is 20 s–10 min, and the oxygen volume fraction in the irradiation chamber is 10–24%.

9. The pretreatment process for efficient pre-oxidation of PAN fibers according to claim 1, characterized in that: In S3, pre-oxidation is carried out by gradient heating. The irradiated fiber bundles pass through 1-3 pre-oxidation temperature zones. The temperature of the first pre-oxidation temperature zone is 160-200℃, the temperature of the second pre-oxidation temperature zone is 200-230℃, and the temperature of the third pre-oxidation temperature zone is 230-260℃. The residence time in each temperature zone is 5-20 minutes.

10. The pretreatment process for efficient pre-oxidation of PAN fibers according to claim 1, characterized in that: It also includes S4, which involves carbonizing the pre-oxidized fibers, wherein the requirements for the carbonization treatment are as follows: Under an inert atmosphere, the pre-oxidized fibers are subjected to low-temperature carbonization treatment at 400-800℃ in a low-temperature carbonization furnace, and then subjected to high-temperature carbonization treatment at 900-1600℃ in a high-temperature carbonization furnace to obtain polyacrylonitrile-based carbon fibers.

Images