High-strength medium-modulus polyacrylonitrile precursor for aviation, preparation method and application thereof

Abstract

The application provides a high-strength medium-modulus polyacrylonitrile precursor for aviation, a preparation method and application, and relates to the technical field of carbon fiber precursor preparation. The preparation method of the high-strength medium-modulus polyacrylonitrile precursor for aviation comprises the following steps: first, preparing a spinning solution; after the spinning solution is jetted, the jetted spinning solution is subjected to a coagulation bath to generate a nascent fiber bundle; after the nascent fiber bundle is combined, the combined nascent fiber bundle is subjected to washing and drawing; then, the combined nascent fiber bundle is subjected to blowing, oiling, drying, interlacing treatment and steam drawing in sequence to obtain the polyacrylonitrile precursor. In the washing and drawing process, 1-1.2 times low-temperature drawing treatment and 0.9-1 times low-temperature relaxation treatment are alternately performed, so that the stress of the precursor is homogenized, the replacement speed of the solvent and water in the fiber is accelerated, and the overall performance is improved. The carbon fiber prepared by the method has a strength of greater than or equal to 6600 MPa and a modulus of greater than or equal to 340 GPa.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber precursor preparation technology, specifically relating to a high-strength, medium-modulus aerospace polyacrylonitrile precursor, its preparation method, and its application. Background Technology

[0002] Carbon fiber (CF) is a new type of high-strength, high-modulus fiber material with a carbon content of over 95%. It is a microcrystalline graphite material obtained by stacking organic fibers such as sheet-like graphite microcrystals along the fiber axis and undergoing carbonization and graphitization treatments. Carbon fiber is "flexible on the outside but rigid on the inside," lighter than aluminum but stronger than steel, and possesses corrosion resistance and high modulus properties, making it an important material in both defense and civilian applications. It not only possesses the inherent properties of carbon materials but also combines the flexibility and processability of textile fibers, making it a next-generation reinforcing fiber. With the continuous development of high-end manufacturing, the performance requirements for carbon fiber are becoming increasingly stringent.

[0003] Polyacrylonitrile precursor fiber is the mother of carbon fiber. Carbon fiber can be obtained by pre-oxidation, carbonization, surface treatment, sizing, and drying of the precursor fiber. In the entire carbon fiber preparation process, the performance of the precursor fiber plays a decisive role in the performance of the final carbon fiber.

[0004] Currently, most domestic manufacturers produce general-purpose carbon fibers (such as strength ≥ 5880 MPa and modulus ≥ 324 GPa). However, in order to meet the needs of applications in the aerospace industry and sports and leisure fields, there is an urgent need to develop a high-strength, medium-modulus, high-performance polyacrylonitrile carbon fiber for aerospace (strength ≥ 6600 MPa and modulus ≥ 340 GPa) to improve the widespread application of polyacrylonitrile carbon fiber in aerospace and sports and leisure fields. Summary of the Invention

[0005] In view of the technical problems existing in the prior art, the present invention aims to provide a high-strength medium-modulus polyacrylonitrile precursor fiber for aerospace applications, its preparation method and application.

[0006] One objective of this invention is to provide a method for preparing high-strength, medium-modulus aerospace-grade polyacrylonitrile precursor fibers, the method comprising:

[0007] First, a spinning solution is prepared. After the spinning solution is spun into fibers, it passes through an air layer and then enters a coagulation bath to form nascent fiber bundles. After the nascent fiber bundles are combined, they are washed and stretched with water, and then successively blown dry, oiled, dried, cross-linked and steam stretched to obtain polyacrylonitrile precursor fibers.

[0008] The water washing and stretching process includes low-temperature water washing and stretching at 35-45°C and high-temperature water washing and stretching at 70-90°C.

[0009] The low-temperature water washing and stretching includes multiple low-temperature stretching treatments and multiple low-temperature relaxation treatments, with the low-temperature stretching treatments and the low-temperature relaxation treatments performed alternately. The stretching ratio of the low-temperature stretching treatment is 1 to 1.2 times, and the stretching ratio of the low-temperature relaxation treatment is 0.9 to 1 times.

[0010] Preferably, the time for each low-temperature stretching treatment is 10-13 seconds, and the time for each low-temperature relaxation treatment is 12-15 seconds.

[0011] Preferably, during the low-temperature washing and stretching process, the washing temperature tends to increase along the direction of the merging nascent fiber bundles, with a temperature gradient of 0℃ to 3℃.

[0012] Preferably, the low-temperature water washing and stretching includes 4 to 5 low-temperature stretching treatments and 3 to 4 low-temperature relaxation treatments.

[0013] Preferably, the total low-temperature stretching ratio is 1.05 to 1.8 times, and the high-temperature stretching ratio is 2 to 5 times.

[0014] Preferably, the spinning solution is prepared by solution polymerization of acrylonitrile as the first monomer, itaconic acid as the second monomer, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile as the initiator, and then successively undergoing monomer removal, concentration and amination.

[0015] Preferably, the spinning solution has a solid content of 18% to 22%, a rotational viscosity of 700 to 800 P at 45°C, and an intrinsic viscosity of 1.7 to 1.8 dL / g.

[0016] Preferably, the spinning solution is spun using a spinneret with a spinneret size of ≤4K, the height of the air layer is 2-4mm, the draw ratio of the air layer is 3-5 times, the coagulation bath is a dimethyl sulfoxide aqueous solution with a mass concentration of 30-35% and a pH value of 8-10, the temperature of the coagulation bath is 0-5℃, and the residence time in the coagulation bath is 10-20s.

[0017] Preferably, the oiling step first uses a dispersing device to disperse the bundled fibers at a frequency of ≥20 Hz, and then applies oil with an amino-modified silicone oil aqueous solution with a concentration of 3.0-3.8%; the drying step is a multi-stage distributed hot roller drying with a steam pressure of 0.8-1.0 MPa, a temperature of 140-180℃, and a drying time of 20-40 s; the interlocking is done with compressed air interlocking at a pressure of 0.20-0.30 MPa; the steam pressure during steam drawing is 0.5-0.6 MPa, and the drawing ratio is 3-5 times.

[0018] The second objective of this invention is to provide a high-strength, medium-modulus polyacrylonitrile precursor fiber for aerospace applications. The polyacrylonitrile precursor fiber has a total draw ratio of 10–15 times, a fineness of 0.70–0.80 dtex, a single filament strength of ≥9.0 CN / dtex, a modulus of ≥150 CN / dtex, and an elongation of ≥10%; the fiber density is ≥1.18 g / cm³. 3 The raw silk contains 0.9% to 1.5% oil.

[0019] The third objective of this invention is to provide an application of high-strength, medium-modulus aerospace polyacrylonitrile precursor fiber, which, after carbonization, can be used to prepare aerospace-grade high-strength, medium-modulus carbon fiber with a strength ≥6600MPa and a modulus ≥340GPa.

[0020] Beneficial effects of the invention

[0021] In the preparation of high-strength, medium-modulus aerospace-grade polyacrylonitrile precursor fibers, this invention employs a low-temperature water washing and stretching process at 35–45°C, involving multiple low-temperature stretching and relaxation treatments. Alternating between 1–1.2 times low-temperature stretching and 0.9–1 times low-temperature relaxation gradually homogenizes the fiber stress. During stretching, the 1.0–1.2 times stretching effectively elongates the fiber, allowing the molecular chains to fully extend. Subsequently, the 0.9–1.0 times relaxation allows the fiber to recover to some extent, alleviating internal stress. This alternation between stretching and relaxation reduces stress concentration within the fiber. By controlling the alternation between 1.0–1.2 times stretching and 0.90–1.0 times relaxation, the molecular chain arrangement of the carbon fiber becomes more ordered, further optimizing the fiber's crystallinity and orientation, increasing its modulus, strength, and resistance to deformation. The 0.90–1.0 times relaxation also allows for some self-repair and adjustment of the fiber. The alternating stretching and relaxation reduces defects in the microstructure, effectively decreasing the probability of fiber breakage and further ensuring fiber continuity and consistency. Meanwhile, when the fiber is in a tense state with a stretch of 1.0 to 1.2 times, the water in the fiber is squeezed out, and when it is in a relaxed state with a stretch of 0.9 to 1.0 times, it is conducive to the water entering the fiber. The alternation of stretching and relaxation accelerates the replacement rate of solvent and water inside the fiber and improves the washing efficiency. Detailed Implementation

[0022] This invention provides a method for preparing high-strength, medium-modulus polyacrylonitrile precursor fibers for aerospace applications, characterized in that the preparation method includes:

[0023] First, a spinning solution is prepared. After the spinning solution is spun into fibers, it passes through an air layer and then enters a coagulation bath to form nascent fiber bundles. After the nascent fiber bundles are combined, they are washed and stretched with water, and then successively blown dry, oiled, dried, cross-linked and steam stretched to obtain polyacrylonitrile precursor fibers.

[0024] The water washing and stretching process includes low-temperature water washing and stretching at 35-45°C and high-temperature water washing and stretching at 70-90°C.

[0025] The low-temperature water washing and stretching includes multiple low-temperature stretching treatments and multiple low-temperature relaxation treatments, with the low-temperature stretching treatments and the low-temperature relaxation treatments performed alternately. The stretching ratio of the low-temperature stretching treatment is 1 to 1.2 times, and the stretching ratio of the low-temperature relaxation treatment is 0.9 to 1 times.

[0026] In this invention, alternating between 1.0–1.2 times low-temperature stretching and 0.90–1.0 times low-temperature relaxation is used to keep the fiber in a state of tension and relaxation, gradually homogenizing the fiber stress. During stretching, 1.0–1.2 times stretching effectively extends the fiber, allowing the molecular chains to fully extend; subsequently, 0.9–1.0 times relaxation allows the fiber to recover to some extent, relieving internal stress. By controlling the alternation of stretching and relaxation, the molecular chains of the carbon fiber are arranged more orderly, the crystallinity and orientation of the fiber are further optimized, the fiber modulus is improved, and the fiber strength and resistance to deformation are increased. During the alternation of stretching and relaxation, the fiber also undergoes a certain degree of self-repair and adjustment, reducing defects in the microstructure and improving the overall performance of the fiber. The alternating 0.9–1.0 times relaxation relieves the high stress state of the fiber after stretching, preventing fiber breakage caused by overstretching, effectively reducing the probability of fiber breakage, and further ensuring the continuity and consistency of the fiber. Meanwhile, when the fiber is in a tense state with a stretch of 1.0 to 1.2 times, the water in the fiber is squeezed out, and when it is in a relaxed state with a stretch of 0.9 to 1.0 times, it is conducive to the water entering the fiber. The alternation of stretching and relaxation accelerates the replacement rate of solvent and water inside the fiber and improves the washing efficiency.

[0027] When the overstretch ratio exceeds 1.2 times, the molecular chains are excessively stretched, leading to damage to the internal structure of the fiber, reducing its mechanical properties, and subjecting the fiber to excessive stress, increasing the risk of breakage. When the relaxation ratio is below 0.9 times, it causes excessive fiber shrinkage, affecting its final dimensional and morphological stability.

[0028] In this invention, the draw ratio is, for example, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, or 1.20; and the relaxation ratio is, for example, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or 1.00.

[0029] In a preferred embodiment of the present invention, the time for each low-temperature stretching treatment is 10-13 seconds, and the time for each low-temperature relaxation treatment is 12-15 seconds.

[0030] In a preferred embodiment of the present invention, during the low-temperature washing and stretching process, the washing temperature tends to rise along the direction of the merging nascent fiber bundles, with a temperature gradient of 0°C to 3°C.

[0031] In this invention, the upward trend along the direction of the merging nascent fiber bundles means that the temperature of the last slot is higher than that of the first slot, and each slot is 0°C to 3°C higher than the previous slot.

[0032] In this invention, the temperature gradient is, for example, 0°C, 1°C, 2°C or 3°C.

[0033] In this invention, the temperature of the low-temperature water bath is set, for example, to 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 35℃, 37℃, 39℃, 41℃, 41℃, 42℃, 43℃, 44℃, 45℃, 35℃, 35℃, 38℃, 38℃, 40℃, 40℃, 42℃, 45℃, 45℃, or 35℃, 35℃, 35℃, 40℃, 40℃, 40℃, 40℃, 42℃, 42℃, 45℃.

[0034] In this invention, the low-temperature washing and stretching includes 4 to 5 low-temperature stretching treatments and 3 to 4 low-temperature relaxation treatments. In the entire low-temperature washing and stretching process, the merged nascent fiber bundles are alternately subjected to low-temperature stretching and low-temperature relaxation, that is, the process is set to alternately perform low-temperature stretching, low-temperature relaxation, low-temperature stretching, low-temperature relaxation, low-temperature stretching, ...

[0035] For example, when the low-temperature stretching treatment is set to 4 times and the low-temperature relaxation treatment is set to 3 times, the low-temperature washing and stretching process includes sequentially performing low-temperature stretching, low-temperature relaxation, low-temperature stretching, low-temperature relaxation, low-temperature stretching, low-temperature relaxation, and low-temperature stretching on the merged nascent fiber bundles.

[0036] For example, when the low-temperature stretching treatment is set to 4 times and the low-temperature relaxation treatment is set to 4 times, the low-temperature washing and stretching process includes sequentially performing low-temperature stretching, low-temperature relaxation, low-temperature stretching, low-temperature relaxation, low-temperature stretching, low-temperature relaxation, low-temperature stretching, and low-temperature relaxation on the merged nascent fiber bundles.

[0037] For example, when the low-temperature stretching treatment is set to 5 times and the low-temperature relaxation treatment is set to 4 times, the low-temperature washing and stretching process includes sequentially performing low-temperature stretching, low-temperature relaxation, low-temperature stretching, low-temperature relaxation, low-temperature stretching, low-temperature relaxation, low-temperature stretching, low-temperature relaxation, and low-temperature stretching on the merged nascent fiber bundles.

[0038] Specifically, in the low-temperature washing and stretching process, the low-temperature stretching treatment is carried out in a low-temperature water tank. Four to five low-temperature stretching water tanks and three to four low-temperature relaxation water tanks are set up. The low-temperature stretching water tanks and the low-temperature relaxation water tanks are arranged alternately, that is, the arrangement is low-temperature stretching water tank, low-temperature relaxation water tank, low-temperature stretching water tank, low-temperature relaxation water tank, low-temperature stretching water tank, low-temperature relaxation water tank, ... The nascent fiber bundles are sequentially passed through the alternately arranged low-temperature stretching water tanks and the low-temperature relaxation water tanks. The nascent fiber bundles are stretched by 1 to 1.2 times in the low-temperature stretching water tanks and relaxed by 0.9 to 1 times in the low-temperature relaxation water tanks.

[0039] For example, when four low-temperature stretching water tanks and three low-temperature relaxation water tanks are set, the low-temperature water tanks are arranged in the following order: low-temperature stretching water tank, low-temperature relaxation water tank, low-temperature stretching water tank, low-temperature relaxation water tank, low-temperature stretching water tank, low-temperature relaxation water tank, and low-temperature stretching water tank.

[0040] For example, when four low-temperature stretching water tanks and four low-temperature relaxation water tanks are set, the low-temperature water tanks are arranged in the following order: low-temperature stretching water tank, low-temperature relaxation water tank, low-temperature stretching water tank, low-temperature relaxation water tank, low-temperature stretching water tank, low-temperature relaxation water tank, low-temperature stretching water tank, and low-temperature relaxation water tank.

[0041] For example, when five low-temperature drawing tanks and four low-temperature relaxation tanks are set, the low-temperature tanks are arranged in the following order: low-temperature drawing tank, low-temperature relaxation tank, low-temperature drawing tank, low-temperature relaxation tank, low-temperature drawing tank, low-temperature relaxation tank, low-temperature drawing tank, low-temperature relaxation tank, low-temperature drawing tank, low-temperature relaxation tank, and low-temperature drawing tank.

[0042] In a preferred embodiment of the present invention, the total low-temperature stretching ratio is 1.05 to 1.8 times, and the high-temperature stretching ratio is 2 to 5 times.

[0043] In this invention, the total low-temperature stretching ratio is, for example, 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or 1.8; and the high-temperature stretching ratio is, for example, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0.

[0044] In a preferred embodiment of the present invention, during the washing step, the water is in a flowing state, and the flow direction is opposite to the direction of the merging of the nascent fiber bundles.

[0045] In this invention, the residual rate of dimethyl sulfoxide in the fibers after washing is ≤0.1%.

[0046] In a preferred embodiment of the present invention, the spinning solution is prepared by solution polymerization of acrylonitrile as the first monomer, itaconic acid as the second monomer, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile initiator, followed by monomer removal, concentration and amination.

[0047] In a preferred embodiment of the present invention, the spinning solution has a solid content of 18% to 22%, a rotational viscosity of 700 to 800 P at 45°C, and an intrinsic viscosity of 1.7 to 1.8 dL / g.

[0048] Preferably, the concentration of azobisisobutyronitrile is 0.001–0.01 mol / L; the mass ratio of acrylonitrile to itaconic acid is 10–35:1; and the mass ratio of azobisisobutyronitrile to acrylonitrile is 10–30:1.

[0049] In this invention, the concentration of azobisisobutyronitrile is, for example, 0.001 mol / L, 0.002 mol / L, 0.003 mol / L, 0.004 mol / L, 0.005 mol / L, 0.006 mol / L, 0.007 mol / L, 0.008 mol / L, 0.009 mol / L, or 0.010 mol / L; the mass ratio of acrylonitrile to itaconic acid is, for example, 10:1, 15:1, 20:1, 25:1, 30:1, or 35:1; and the mass ratio of azobisisobutyronitrile to acrylonitrile is 10:1, 15:1, 20:1, 25:1, or 30:1.

[0050] In this invention, the solid content of the spinning solution is, for example, 18.0%, 18.5%, 19.0%, 19.5%, 20.0%, 20.5%, 21.0%, 21.5%, or 22.0%. The rotational viscosity is, for example, 700P, 710P, 720P, 730P, 740P, 750P, 760P, 770P, 780P, 790P, or 800P. The intrinsic viscosity is, for example, 1.70 dL / g, 1.72 dL / g, 1.74 dL / g, 1.76 dL / g, 1.78 dL / g, or 1.80 dL / g.

[0051] In a preferred embodiment of the present invention, the spinning solution is filtered by a metering pump and a high-precision filter of 1μm to 3μm before entering the spinneret for spinning; the spun filaments are drawn 3 to 5 times while passing through an air layer of 2 to 4 mm in height; the coagulation bath is a dilute dimethyl sulfoxide solution with a mass concentration of 30 to 35% and a pH value of 8 to 10, and the coagulation bath temperature is 0 to 5°C, in which nascent fibers are formed by double diffusion coagulation.

[0052] In this invention, the high-precision filter has a filtration accuracy of, for example, 1μm, 2μm, or 3μm; an air layer height of, for example, 2mm, 3mm, or 4mm; a draw ratio of, for example, 3 times, 4 times, or 5 times; and a spinneret specification of, for example, 1K, 2K, 3K, or 4K.

[0053] In this invention, the temperature of the dimethyl sulfoxide desalting aqueous solution is 0°C, 1°C, 2°C, 3°C, 4°C, or 5°C; the mass concentration of the dimethyl sulfoxide desalting aqueous solution is, for example, 30%, 31%, 32%, 33%, 34%, or 35%; and the pH value is, for example, 8, 8.5, 9, 9.5, or 10.

[0054] In a preferred embodiment of the present invention, small filament bundles of ≤4K are combined to obtain nascent fiber bundles of ≤24K.

[0055] In this invention, the small tow nascent fibers are, for example, 1K, 2K, 3K or 4K nascent fibers; the nascent fibers are, for example, 2K, 3K, 4K, 6K, 8K, 10K, 12K, 14K, 15K, 16K, 18K, 20K, 22K or 24K nascent fibers.

[0056] In a preferred embodiment of the present invention, the oiling step first uses a dispersing device to disperse the bundled fibers at a frequency of ≥20 Hz, and then applies oil with an aqueous solution of amino-modified silicone oil with a concentration of 3.0-3.8%.

[0057] In this invention, the bundled fibers are patted and dispersed to ensure that the amount of oil adhering to individual fibers is minimally different. The concentration of amino-modified silicone oil is, for example, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, or 3.8%.

[0058] In a preferred embodiment of the present invention, the drying step is a multi-stage hot roller drying with a steam pressure of 0.8 to 1.0 MPa, a temperature of 140 to 180°C, and a drying time of 20 to 40 seconds.

[0059] In this invention, drying is used to quickly remove a large amount of moisture from the fibers to achieve densification; the steam pressure is, for example, 0.80 MPa, 0.85 MPa, 0.90 MPa, 0.95 MPa or 1.0 MPa; the drying temperature is, for example, 140°C, 150°C, 160°C, 170°C or 180°C; the drying time is, for example, 20s, 25s, 30s, 35s or 40s.

[0060] In a preferred embodiment of the present invention, the interlocking is a compressed air interlocking with a pressure of 0.20 to 0.30 MPa.

[0061] In this invention, the interlacing process ensures uniform distribution of the precursor fibers after merging, resulting in uniform stress during subsequent drawing and carbonization processes. The air interlacing pressure is, for example, 0.20 MPa, 0.22 MPa, 0.24 MPa, 0.26 MPa, 0.28 MPa, or 0.30 MPa.

[0062] In a preferred embodiment of the present invention, the steam stretching pressure is 0.5 to 0.6 MPa, and the stretching ratio is 3 to 5 times.

[0063] In this invention, the steam stretching pressure is, for example, 0.50 MPa, 0.52 MPa, 0.54 MPa, 0.56 MPa, 0.58 MPa, or 0.60 MPa; and the stretching ratio is, for example, 3.0 times, 3.2 times, 3.4 times, 3.6 times, 3.8 times, 4.0 times, 4.2 times, 4.4 times, 4.6 times, 4.8 times, or 5.0 times.

[0064] In a preferred embodiment of the present invention, the preparation method specifically includes:

[0065] Solution polymerization was carried out using dimethyl sulfoxide as solvent, acrylonitrile as the first monomer, itaconic acid as the second monomer, and azobisisobutyronitrile (AIOBT) at a concentration of 0.001–0.01 mol / L as initiator. The mass ratio of acrylonitrile to itaconic acid was 10–35:1. The spinning solution was prepared after monomer removal, concentration, and amination.

[0066] The solid content of the spinning solution is 18%–22%, the rotational viscosity at 45℃ is 700–800P, and the intrinsic viscosity is 1.7–1.8 dL / g.

[0067] The spinning solution is filtered by a metering pump and a high-precision filter of 1μm to 3μm before entering the spinneret for spinning. The spinneret specification is ≤4K.

[0068] The extruded filaments are stretched 3 to 5 times while passing through an air layer 2 to 4 mm high; then they are placed in a dimethyl sulfoxide desalination aqueous solution with a temperature of 0 to 5°C, a concentration of 30 to 35%, and a pH of 8 to 10 for 10 to 20 seconds of coagulation bath treatment to obtain small bundles of nascent fibers.

[0069] After the small bundles of nascent fibers are combined, they undergo 4 to 5 low-temperature stretching treatments and 3 to 4 low-temperature relaxation treatments. Each low-temperature stretching treatment lasts for 10 to 13 seconds, and each low-temperature relaxation treatment lasts for 12 to 15 seconds. The low-temperature relaxation treatment time should be 0 to 3 seconds longer than the previous low-temperature stretching treatment time. After cleaning, the residual dimethyl sulfoxide content of the fibers should be ≤0.1%.

[0070] After being washed and stretched at a high temperature of 70-90℃, the stretching ratio is 2-5 times;

[0071] Then, use a dispersing device to disperse the bundled fibers at a frequency of ≥20 Hz, and then apply oil with an amino-modified silicone oil aqueous solution of 3.0-3.8% concentration.

[0072] Then it is dried by hot rollers with multi-stage steam pressure of 0.8 to 1.0 MPa for 20 to 40 seconds;

[0073] The dried fibers are interlaced by an air processor with a pressure of 0.20-0.30 MPa, and then stretched 3-5 times in saturated steam with a pressure of 0.5-0.6 MPa.

[0074] The final raw yarn has a total draw ratio of 10–15, a fineness of 0.70–0.80 dtex, a single filament strength of ≥9.0 CN / dtex, a modulus of ≥150 CN / dtex, an elongation of ≥10%, and a density of ≥1.18 g / cm³. 3 The raw silk contains 0.9% to 1.5% oil.

[0075] Example 1

[0076] Using dimethyl sulfoxide as solvent, solution polymerization was carried out with 25 parts acrylonitrile as the first monomer, 1 part itacron as the second monomer, and azobisisobutyronitrile at a concentration of 0.005 mol / L as the initiator. The spinning solution was prepared after monomer removal, concentration and amination.

[0077] The spinning solution has a solid content of 19.4%, a rotational viscosity of 750P (45℃), and an intrinsic viscosity of 1.80 dL / g.

[0078] The spinning solution is metered and filtered through a 1μm high-precision filter before entering the 4K spinneret for spinning.

[0079] The extruded filaments are stretched 4.0 times while passing through a 3mm high air layer; then they are placed in a dimethyl sulfoxide desalination aqueous solution at a temperature of 3℃, a concentration of 30%, and a pH of 9 for 15 seconds of coagulation bath treatment to obtain small bundles of nascent fibers.

[0080] Three bundles of 4K small filament bundles of nascent fibers are combined to obtain a bundle of 12K nascent fibers.

[0081] 12K nascent fiber bundles were subjected to 1.02 times stretching, 1.0 times relaxation, 1.04 times stretching, 0.97 times relaxation, 1.08 times stretching, 0.95 times relaxation, 1.15 times stretching, 0.9 times relaxation, and 1.05 times stretching. The water bath temperatures were 35℃, 35℃, 38℃, 38℃, 40℃, 40℃, 42℃, 45℃, and 45℃. The low-temperature stretching treatment time for each bath was 10–13 seconds, and the low-temperature relaxation treatment time was 12–15 seconds. After cleaning, the residual dimethyl sulfoxide content of the fibers was ≤0.1%.

[0082] After being washed and stretched at 75℃, the stretching ratio is 2.5 times.

[0083] Then, use a dispersing device to disperse the bundled fibers at a frequency of ≥20 Hz, and then apply oil with 3.5% amino-modified silicone oil.

[0084] Then it is dried by hot rollers with a multi-stage steam pressure of 0.8 MPa for 30 seconds;

[0085] The dried fibers are interlaced by a 0.25MPa air processor and then stretched 4.38 times in saturated steam at a pressure of 0.52MPa.

[0086] The final raw yarn had a total draw ratio of 12.32, a fineness of 0.75 dtex, a single filament strength of 9.4 CN / dtex, a modulus of 163 CN / dtex, an elongation of 10.8%, and a density of 1.2 g / cm³. 3 The precursor fiber contains 1.2% oil. After carbonization, the carbon fiber prepared from this 12K precursor fiber has a strength of 6740MPa and a modulus of 342GPa.

[0087] Example 2

[0088] The 12k nascent fiber bundles were subjected to alternating cycles of 1.06 times stretching, 1.0 times relaxation, 1.06 times stretching, 1.0 times relaxation, 1.06 times stretching, 1.0 times relaxation, 1.06 times stretching, 1.0 times relaxation, 1.06 times stretching, 1.0 times relaxation, and 1.06 times stretching. After cleaning, the residual dimethyl sulfoxide content of the fibers was ≤0.1%.

[0089] The remaining steps and parameters are the same as in Example 1.

[0090] The final obtained precursor fiber had a total draw ratio of 14.65, a fineness of 0.71 dtex, a single filament strength of 9.9 CN / dtex, a modulus of 168 CN / dtex, an elongation of 10.2%, and a density of 1.2 g / cm³. 3 The precursor fiber contains 1.2% oil. After carbonization, the carbon fiber prepared from this 12K precursor fiber has a strength of 6773MPa and a modulus of 347GPa.

[0091] Example 3

[0092] The 12k nascent fiber bundles were subjected to alternating stretching cycles of 1.1 times, 1.0 times, 1.1 times, 0.96 times, 1.08 times, 0.95 times, 1.08 times, 0.94 times, and 1.05 times. After cleaning, the residual dimethyl sulfoxide content of the fibers was ≤0.1%.

[0093] The remaining steps and parameters are the same as in Example 1.

[0094] The final obtained precursor fiber had a total draw ratio of 13.91, a fineness of 0.72 dtex, a single filament strength of 10.0 CN / dtex, a modulus of 167 CN / dtex, an elongation of 10.4%, and a density of 1.2 g / cm³. 3 The precursor fiber contains 1.2% oil. After carbonization, the carbon fiber prepared from this 12K precursor fiber has a strength of 6840MPa and a modulus of 349GPa.

[0095] Example 4

[0096] The 12k nascent fiber bundles were subjected to alternating stretching cycles of 1.15 times, 1.0 times, 1.1 times, 0.96 times, 1.05 times, 0.94 times, 1.04 times, 0.94 times, and 1.02 times. After cleaning, the residual dimethyl sulfoxide content of the fibers was ≤0.1%.

[0097] The remaining steps and parameters are the same as in Example 1.

[0098] The final obtained precursor fiber had a total draw ratio of 13.08, a fineness of 0.73 dtex, a single filament strength of 9.8 CN / dtex, a modulus of 167 CN / dtex, an elongation of 10.6%, and a density of 1.2 g / cm³. 3 The precursor fiber contains 1.2% oil. After carbonization, the carbon fiber prepared from this 12K precursor fiber has a strength of 6759MPa and a modulus of 343GPa.

[0099] Example 5

[0100] The 12k nascent fiber bundles were subjected to alternating stretching processes of 1.05 times, 0.98 times, 1.1 times, 0.96 times, 1.15 times, 0.94 times, 1.2 times, 0.9 times, and 1.05 times. After cleaning, the residual dimethyl sulfoxide content of the fibers was ≤0.1%.

[0101] The remaining steps and parameters are the same as in Example 1.

[0102] The final raw yarn had a total draw ratio of 14.58, a fineness of 0.70 dtex, a single filament strength of 9.8 CN / dtex, a modulus of 169 CN / dtex, an elongation of 10.3%, and a density of 1.2 g / cm³. 3 The precursor fiber contains 1.2% oil. After carbonization, the carbon fiber prepared from this 12K precursor fiber has a strength of 6767MPa and a modulus of 348GPa.

[0103] Comparative Example 1

[0104] After 12k nascent fiber bundles were stretched by 1.05 times, 1.02 times, 1.06 times, 1.02 times, and 1.05 times, the residual dimethyl sulfoxide content of the fibers after cleaning was ≤0.1%.

[0105] The remaining steps and parameters are the same as in Example 1.

[0106] The final raw yarn had a total draw ratio of 13.31, a fineness of 0.72 dtex, a single filament strength of 8.2 CN / dtex, a modulus of 142 CN / dtex, an elongation of 7.3%, and a density of 1.2 g / cm³. 3 The precursor fiber contains 1.2% oil. After carbonization, the carbon fiber prepared from this 12K precursor fiber has a strength of 6621MPa and a modulus of 310GPa.

[0107] Comparative Example 2

[0108] The 12k nascent fiber bundles were subjected to alternating stretching times of 1.05, 1.1, 1.2, 1.1, 1.04, 0.98, 0.96, 0.9, and 0.94. After cleaning, the residual dimethyl sulfoxide content of the fibers was ≤0.1%.

[0109] The remaining steps and parameters are the same as in Example 1.

[0110] The final obtained precursor fiber had a total draw ratio of 13.81, a fineness of 0.71 dtex, a single filament strength of 8.4 CN / dtex, a modulus of 143 CN / dtex, an elongation of 7.5%, and a density of 1.2 g / cm³. 3 The precursor fiber contains 1.2% oil. After carbonization, the carbon fiber prepared from this 12K precursor fiber has a strength of 6628MPa and a modulus of 312GPa.

[0111] Comparative Example 3

[0112] After washing, the residual dimethyl sulfoxide content of the 12k nascent fiber bundles was ≤0.1% after being stretched by 1.05 times, 1.1 times, 0.98 times, 0.96 times, 1.15 times, 1.2 times, 0.9 times, 0.94 times, and 1.05 times.

[0113] The remaining steps and parameters are the same as in Example 1.

[0114] The final obtained precursor fiber had a total draw ratio of 14.58, a fineness of 0.69 dtex, a single filament strength of 8.8 N / dtex, a modulus of 148 CN / dtex, an elongation of 6.7%, and a density of 1.2 g / cm³. 3The precursor fiber contains 1.2% oil. After carbonization, the carbon fiber prepared from this 12K precursor fiber has a strength of 6631MPa and a modulus of 315GPa.

[0115] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for preparing high-strength, medium-modulus polyacrylonitrile precursor for aerospace applications, characterized in that, The preparation method includes: First, a spinning solution is prepared. After the spinning solution is spun into fibers, it passes through an air layer and then enters a coagulation bath to form nascent fiber bundles. After the nascent fiber bundles are combined, they are washed and drawn with water, and then successively blown dry, oiled, dried, cross-linked and steam drawn to obtain polyacrylonitrile precursor fibers. During the water washing and stretching process, the water is in a flowing state, and the flow direction is opposite to the direction of the merging nascent fiber bundles. The water washing and stretching process includes low-temperature water washing and stretching at 35-45°C and high-temperature water washing and stretching at 70-90°C. The low-temperature water washing and stretching includes 4 to 5 low-temperature stretching treatments and 3 to 4 low-temperature relaxation treatments, with the low-temperature stretching treatments and the low-temperature relaxation treatments being performed alternately. The draw ratio of the low-temperature drawing treatment is 1 to 1.2 times, and the draw ratio of the low-temperature relaxation treatment is 0.9 to 1 times; The total stretching ratio of the low-temperature water washing is 1.05 to 1.8 times; The total multiple of the high-temperature water washing stretching is 2 to 5 times; The duration of each low-temperature stretching treatment is 10-13 seconds, and the duration of each low-temperature relaxation treatment is 12-15 seconds. During the low-temperature washing and stretching process, the washing temperature tends to increase along the direction of the merging nascent fiber bundles, with a temperature gradient of 0℃ to 3℃.

2. The preparation method according to claim 1, characterized in that, The spinning solution is prepared by solution polymerization of acrylonitrile as the first monomer, itaconic acid as the second monomer, dimethyl sulfoxide as the solvent, and azobisisobutyronitrile initiator, followed by monomer removal, concentration and amination. The solid content of the spinning solution is 18%~22%, the rotational viscosity at 45℃ is 700~800P, and the intrinsic viscosity is 1.7~1.8dL / g.

3. The preparation method according to claim 1, characterized in that, The spinning solution is spun using a spinneret with a spinneret size of ≤4K. The height of the air layer is 2~4mm, the draw ratio of the air layer is 3~5 times, the coagulation bath is a dimethyl sulfoxide aqueous solution with a mass concentration of 30~35% and a pH value of 8~10, the temperature of the coagulation bath is 0~5℃, and the residence time in the coagulation bath is 10~20s.

4. The preparation method according to claim 1, characterized in that, The oiling step first uses a dispersing device to disperse the bundled fibers at a frequency of ≥20 Hz, and then applies oil with an amino-modified silicone oil aqueous solution with a concentration of 3.0~3.8%; the drying step is a multi-stage distributed hot roller drying with a steam pressure of 0.8~1.0 MPa, a temperature of 140~180℃, and a drying time of 20~40s; the interlocking is done with compressed air interlocking at a pressure of 0.20~0.30 MPa; the steam pressure during steam drawing is 0.5~0.6 MPa, and the drawing ratio is 3~5 times.

5. The polyacrylonitrile precursor fiber prepared by the preparation method according to any one of claims 1 to 4, characterized in that, The polyacrylonitrile precursor fiber has a total draw ratio of 10-15 times, a fineness of 0.70-0.80 dtex, a single filament strength of ≥9.0 CN / dtex, a modulus of ≥150 CN / dtex, and an elongation of ≥10%; the density of the precursor fiber is ≥1.18 g / cm³. 3 The raw silk contains 0.9-1.5% oil.

6. The application of the polyacrylonitrile precursor fiber as described in claim 5, characterized in that, The polyacrylonitrile precursor fiber can be carbonized to prepare aerospace-grade high-strength medium-modulus carbon fiber with a strength ≥6600MPa and a modulus ≥340GPa.