Preparation method of polyacrylonitrile precursor with high density and mechanical strength
By employing horizontal spinning and multiphase solidification paths, as well as multi-stage drawing and secondary deep densification processes, the structural defects and insufficient densification of polyacrylonitrile precursor fibers in traditional spinning methods have been solved, resulting in the preparation of high-performance polyacrylonitrile precursor fibers and carbon fibers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-29
- Publication Date
- 2026-03-27
AI Technical Summary
Traditional spinning methods are difficult to produce high-purity, high-strength polyacrylonitrile precursor fibers. Problems such as core-sheath structure, surface defects, insufficient fiber densification, and micropores exist, resulting in insufficient carbon fiber performance.
By employing a combination of horizontal spinning and multiphase coagulation path with multi-stage drawing and secondary deep densification processes, and by controlling the fiber turning angle and coagulation bath concentration, polyacrylonitrile precursor fibers with high density and mechanical strength are prepared.
Polyacrylonitrile precursor fibers with uniform and dense structure, smooth surface and circular cross-section were obtained, with the breaking strength increased to over 7.0 cN/dtex. After pre-oxidation and carbonization, the tensile strength of the carbon fibers reached 4.95 GPa, meeting the high performance requirements.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polyacrylonitrile carbon fiber preparation technology, and relates to a method for preparing polyacrylonitrile precursor fibers with high density and mechanical strength. Background Technology
[0002] The performance of polyacrylonitrile (PAN)-based carbon fibers largely depends on the quality of the precursor fiber. High-quality precursor fibers should have high purity, high strength, high orientation, dense microstructure, and uniform circular cross-section, with as few surface defects as possible.
[0003] Currently, traditional wet spinning often faces several problems in the preparation of PAN precursor fibers: the intense double diffusion process in the coagulation bath easily leads to core-sheath structures or surface defects; the fiber cross-sectional shape is difficult to control, easily deviating from a circular shape, resulting in structural inhomogeneity; insufficient fiber densification leads to the presence of micropores, all of which become weak points in subsequent carbon fiber production. While dry-jet wet spinning can improve the cross-sectional shape, the fiber surface is too smooth, which is not conducive to interfacial bonding with the subsequent composite matrix. In addition, existing one-step drying and densification processes sometimes fail to completely eliminate microscopic defects such as micropores inside the fibers, limiting further improvement in the mechanical properties of the precursor fibers. These structural defects and insufficient densification ultimately result in the precursor fibers' breaking strength and the resulting carbon fibers' tensile strength failing to meet higher performance requirements.
[0004] Therefore, developing a spinning method that can precisely control the fiber coagulation process, effectively improve the fiber microstructure, and significantly enhance the densification and mechanical properties of the precursor fiber is crucial for obtaining high-performance carbon fibers. Summary of the Invention
[0005] The purpose of this invention is to provide a method for preparing polyacrylonitrile (PAN) precursor fibers with high density and mechanical strength. This invention utilizes a unique horizontal spinneret and multiphase solidification path, combined with multi-stage drawing and secondary deep densification processes, to produce PAN precursor fibers with uniform and dense structure, excellent surface and cross-sectional morphology, and outstanding mechanical properties. After pre-oxidation and carbonization treatment, carbon fibers with a tensile strength of not less than 4.95 GPa can be obtained from the precursor fibers.
[0006] The technical solution for achieving the objective of this invention is as follows:
[0007] A method for preparing polyacrylonitrile precursor fibers with high density and mechanical strength employs a multiphase solidification path of horizontal spinning-gas phase transition-liquid phase solidification, coupled with multi-stage drawing and secondary deep densification processes, including the following steps:
[0008] (1) Horizontal spinning and multiphase coagulation: The polyacrylonitrile spinning solution is extruded through a horizontal spinneret into the first coagulation bath and run horizontally for 5cm~15cm. Then the fiber turns 90° to vertical downward for the first time and enters the air medium for 1s~3s gas phase coagulation. After that, the fiber turns 90° to horizontal for the second time and is completely immersed in the second coagulation bath to complete the coagulation and obtain the nascent fiber. The first coagulation bath and the second coagulation bath are 25wt%~35wt% dimethyl sulfoxide (DMSO) aqueous solution with the same composition and the temperature is 15℃~25℃.
[0009] (2) Multi-stage drawing: The nascent fibers are subjected to cold drawing, solvent drawing and hot drawing in sequence;
[0010] (3) The drawn fibers are washed, oiled and dried in sequence to densify them;
[0011] (4) Secondary deep densification: The fibers after primary drying and densification are stretched and densified at 135℃~155℃ and tension of 0.05~0.15 cN / dtex, with a stretching ratio of 1.02~1.15 times;
[0012] (5) Steam heat setting and winding.
[0013] Further, in step (1), the diameter of the spinneret orifice of the horizontal spinneret is 0.06mm~0.10mm and the length-to-diameter ratio is 2.5~4.0:1; preferably, the diameter of the spinneret orifice is 0.08mm and the length-to-diameter ratio is 3:1.
[0014] Furthermore, in step (1), both the first coagulation bath and the second coagulation bath are 25wt%~30wt% DMSO aqueous solutions with the same concentration, and the temperature is 15~20℃.
[0015] Further, in step (2), cold drawing is carried out at 20℃~35℃ with a drawing ratio of 1.2~2.0 times; solvent drawing is carried out in a 15 wt%~20 wt% DMSO aqueous solution at 60℃~80℃ with a drawing ratio of 2.0~3.5 times; hot drawing is carried out in hot water at 92℃~98℃ with a drawing ratio of 2.5~4.0 times; and the total drawing ratio is 6.0~28.0 times. Preferably, the drawing ratio of cold drawing is 1.5~1.8 times, the drawing ratio of solvent drawing is 2.8~3.0 times, the drawing ratio of hot drawing is 3.2~3.5 times, and the total drawing ratio is 10~18.9 times.
[0016] Furthermore, in step (3), the temperature for primary drying and densification is 110±5℃.
[0017] Furthermore, in step (4), the secondary deep densification process is carried out on the hot roller, and the surface temperature fluctuation of the hot roller does not exceed ±1℃.
[0018] Furthermore, in step (4), the secondary deep densification temperature is 140~150℃, the tension is 0.10 cN / dtex, and the draw ratio is 1.05~1.08 times.
[0019] Furthermore, in step (5), the steam heat setting is carried out in a saturated steam atmosphere with a pressure of 0.15MPa~0.30MPa, with a pressure fluctuation of no more than ±1%, a time of 1min~3min, and a stretching ratio of 0.95~1.02 times.
[0020] Compared with the prior art, the present invention has the following advantages:
[0021] (1) This invention employs a horizontal spinneret and a multiphase coagulation path of "liquid-gas-liquid," utilizing a gaseous medium as a transition and controlling the angle of the fiber's two turning points to make the double diffusion process smoother and more controllable, which is beneficial for forming a regular circular cross-section and reducing surface defects; the single-concentration coagulation bath system reduces the complexity of the process. These measures together ensure the excellent stability and batch reproducibility of the product performance. Combined with a multi-stage drawing process, the gradual orientation of molecular chains and the refinement of fiber structure are achieved synergistically. Through a two-stage densification process, and by controlling the temperature and tension of the secondary deep drawing densification, internal micropores are further eliminated, promoting the perfection and high orientation of the crystal structure. Finally, heat setting is carried out in a saturated steam atmosphere with precise pressure control to relax the internal stress of the fiber and stabilize the supramolecular structure.
[0022] (2) The cross-section of the polyacrylonitrile precursor fiber prepared by the present invention is a high-roundness circle with a roundness ≥ 0.92 and no visible cracks. The fiber surface forms 3 to 8 regular and clear axial grooves with a depth of 0.1 to 0.3 μm. This not only overcomes the problem of many surface defects in wet spinning, but also improves the disadvantages of excessively smooth surface and weak interfacial bonding of dry and wet spinning fibers, which is beneficial to the penetration of subsequent pre-oxidation process and bonding with resin matrix.
[0023] (3) Through the synergy of multi-stage drawing and secondary deep densification, the fiber density of this invention is extremely high, and the molecular chain orientation and crystallization perfection are significantly improved. The single filament fineness of the polyacrylonitrile precursor is 0.8 dtex~1.2 dtex, and the breaking strength is stable at above 7.0 cN / dtex, which is a significant improvement over the precursor prepared by traditional methods. After pre-oxidation and carbonization treatment, the carbon fiber obtained has fewer structural defects and the tensile strength is stable at above 4.95 GPa, which meets the application requirements of higher performance fields. Detailed Implementation
[0024] The present invention will be further described in detail below with reference to specific embodiments.
[0025] In the following examples, the polyacrylonitrile spinning solution used is a dimethyl sulfoxide solution of polyacrylonitrile with a solid content of 21 wt%, which is polymerized from 95.5% acrylonitrile, 2.5% acrylic acid and 2.0% methyl acrylate.
[0026] Example 1
[0027] A method for preparing polyacrylonitrile precursor fibers with high density and mechanical strength includes the following steps:
[0028] (1) Horizontal spinning and multiphase coagulation: The polyacrylonitrile spinning solution was extruded through a horizontal spinneret into the first coagulation bath and ran horizontally for 10 cm. Then, the fiber was first turned 90° to vertical downwards and entered the air medium for 2 seconds of gas phase coagulation. After that, the fiber was turned 90° to horizontal again and completely immersed in the second coagulation bath to complete coagulation, obtaining nascent fibers. The spinneret orifice diameter was 0.08 mm and the aspect ratio was 3:1. Both the first and second coagulation baths were 30 wt% DMSO aqueous solutions at a temperature of 20℃.
[0029] (2) Multi-stage stretching: The nascent fiber is first cold stretched at 25°C with a stretching ratio of 1.5 times, then solvent stretched in 70°C and 20% DMSO aqueous solution with a stretching ratio of 2.8 times, and then hot stretched in 95°C hot water with a stretching ratio of 3.2 times. The total stretching ratio is 13.44 times.
[0030] (3) The stretched fibers are washed with water and oiled in sequence, and then dried and densified at 110°C.
[0031] (4) Secondary deep densification: The fibers after primary drying and densification are stretched and densified at 145℃ and a tension of 0.10 cN / dtex, with a stretching ratio of 1.05.
[0032] (5) The fibers that have undergone secondary deep densification are heat-set in saturated steam at 0.22 MPa for 2 min with a draw ratio of 0.98. The fibers are then wound up to obtain polyacrylonitrile precursor fibers.
[0033] The polyacrylonitrile precursor fiber prepared in this embodiment has a single filament fineness of 1.05 dtex, a breaking strength of 7.8 cN / dtex, 5-6 clear axial grooves on the surface, a cross-sectional roundness of 0.95, and no cracks. The carbon fiber obtained by pre-oxidizing and carbonizing the polyacrylonitrile single filament has a tensile strength of 5.05 GPa.
[0034] Example 2
[0035] This embodiment is largely the same as Embodiment 1, except that (2) in the multi-stage stretching, the stretching ratio of cold stretching is 1.8 times, the stretching ratio of solvent stretching is 3.0 times, the stretching ratio of hot stretching is 3.5 times, and the total stretching ratio is increased to 18.9 times; (4) the temperature of secondary deep densification is 150°C, and the stretching ratio is 1.08.
[0036] The polyacrylonitrile precursor fiber prepared in this embodiment has a single filament fineness of 0.88 dtex, a further improved breaking strength of 8.2 cN / dtex, and a cross-sectional roundness as high as 0.94. The carbon fiber obtained by pre-oxidizing and carbonizing the polyacrylonitrile single filament has a tensile strength of 5.18 GPa.
[0037] Example 3
[0038] This embodiment is largely the same as Embodiment 1, except that (1) the first and second coagulation baths are both 25wt% DMSO aqueous solutions and the temperature is 15℃; (2) the total draw ratio in the multi-stage draw is 10 times; (4) the temperature of the secondary deep densification is 140℃.
[0039] The polyacrylonitrile precursor fiber prepared in this embodiment has a breaking strength of 7.3 cN / dtex, with the clearest and most regular surface grooves, averaging 6-7 grooves with a depth of approximately 0.25 μm, and a cross-sectional roundness as high as 0.96. The carbon fiber obtained by pre-oxidizing and carbonizing the polyacrylonitrile monofilament has a tensile strength of 4.95 GPa. Due to its excellent surface structure and interfacial properties, it performs outstandingly in the interfacial shear strength test of composite materials.
[0040] Comparative Example 1
[0041] (1) Horizontal spinning and multiphase coagulation: The polyacrylonitrile spinning solution is extruded through a horizontal spinneret into the coagulation bath, running horizontally for 10 cm, then turning 37° once to vertically downwards, entering the air medium for 2 seconds of gas-phase coagulation, and then turning 37° again to the horizontal direction, obtaining nascent fibers in the coagulation bath. The spinneret orifice diameter is 0.08 mm, and the aspect ratio is 3:1. The coagulation is performed in 4 stages: the concentration of the first coagulation bath is 78 wt%, and the temperature of the first coagulation bath is 65 °C; the concentration of the second coagulation bath is 48 wt%, and the temperature of the second coagulation bath is 55 °C; the concentration of the third coagulation bath is 25 wt%, and the temperature of the third coagulation bath is 70 °C; the concentration of the fourth coagulation bath is 15 wt%, and the temperature of the fourth coagulation bath is 45 °C.
[0042] (2) Multi-stage stretching: The nascent fiber is first cold stretched at 25°C with a stretching ratio of 1.5 times, then solvent stretched in 70°C and 20% DMSO aqueous solution with a stretching ratio of 2.8 times, and then hot stretched in 95°C hot water with a stretching ratio of 3.2 times. The total stretching ratio is 13.44 times.
[0043] (3) The stretched fibers are washed with water and oiled in sequence, and then dried and densified at 110°C.
[0044] (4) Secondary deep densification: The fibers after primary drying and densification are stretched and densified at 145℃ and a tension of 0.10 cN / dtex, with a stretching ratio of 1.05.
[0045] (5) The fibers that have undergone secondary deep densification are heat-set in 0.22 MPa saturated steam for 2 min, and then the fibers are collected to obtain polyacrylonitrile precursor fibers.
[0046] The polyacrylonitrile precursor fibers prepared in this comparative example exhibited a breaking strength of 7.0 cN / dtex, a cross-sectional roundness of 0.90, and surface grooves that were present but not very regular. Some fibers showed slight signs of a core-sheath structure. The carbon fibers obtained from the polyacrylonitrile monofilaments after pre-oxidation and carbonization had a tensile strength of 4.70 GPa. The coagulation bath used in this comparative example was complex to manage, had a high load on the solvent recovery system, and resulted in excessive energy consumption and cost.
[0047] Comparative Example 2
[0048] This comparative example is largely the same as Example 1, except that (4) secondary deep densification is not performed. The breaking strength of the polyacrylonitrile precursor prepared in this comparative example decreased to 7.0 cN / dtex, and the cross-sectional roundness was 0.94. The tensile strength of the carbon fiber obtained by pre-oxidizing and carbonizing the polyacrylonitrile monofilament decreased significantly to 4.60 GPa. In addition, electron microscopy showed that the internal density of the fiber was worse than that of Example 1, and a small number of micropores were present.
[0049] Comparative Example 3
[0050] This comparative example is roughly the same as Example 1, except that (1) after horizontal spinning, all solidification is completed directly in the same solidification bath without turning or gas phase solidification.
[0051] The polyacrylonitrile precursor fiber prepared in this comparative example has a breaking strength of 6.5 cN / dtex, a cross-sectional roundness of only 0.87, a slightly oval shape, and shallow and indistinct surface grooves. The carbon fiber obtained by pre-oxidizing and carbonizing polyacrylonitrile monofilament has a tensile strength of only 4.40 GPa.
[0052] In summary, a comparison between Example 1 and Comparative Example 3 shows that the vapor-phase solidification stage is crucial for obtaining a high-roundness cross-section and a regular surface structure. Comparison with Comparative Example 2 shows that secondary deep densification is beneficial for further improving the strength of the precursor fiber and obtaining high-performance carbon fibers. A comparison between Example 1 and Comparative Example 1 shows that the present invention employs precise path control with horizontal spinning and two 90° turns, combined with a single-concentration solidification bath, which simplifies the process, reduces system complexity and cost, while achieving superior fiber structure and final product performance.
Claims
1. A method for preparing polyacrylonitrile precursor fibers with high density and mechanical strength, characterized in that, Includes the following steps: (1) Horizontal spinning and multiphase coagulation: The polyacrylonitrile spinning solution is extruded through a horizontal spinneret into the first coagulation bath and runs horizontally for 5cm~15cm. Then the fiber turns 90° to vertical downward for the first time and enters the air medium for 1s~3s gas phase coagulation. After that, the fiber turns 90° to horizontal for the second time and is completely immersed in the second coagulation bath to complete the coagulation and obtain the nascent fiber. The first coagulation bath and the second coagulation bath are 25wt%~35wt% DMSO aqueous solution with the same composition and the temperature is 15℃~25℃. (2) Multi-stage drawing: The nascent fibers are subjected to cold drawing, solvent drawing and hot drawing in sequence; (3) The drawn fibers are washed, oiled and dried in sequence to densify them; (4) Secondary deep densification: The fibers after primary drying and densification are stretched and densified at 135℃~155℃ and tension of 0.05~0.15cN / dtex, with a stretching ratio of 1.02~1.15 times; (5) Steam heat setting and winding.
2. The preparation method according to claim 1, characterized in that, In step (1), the diameter of the spinneret orifice of the horizontal spinneret is 0.06mm~0.10mm and the length-to-diameter ratio is 2.5~4.0:
1.
3. The preparation method according to claim 1, characterized in that, In step (1), the horizontal spinneret has an orifice diameter of 0.08 mm and a length-to-diameter ratio of 3:
1.
4. The preparation method according to claim 1, characterized in that, In step (1), both the first coagulation bath and the second coagulation bath are 25wt%~30wt% DMSO aqueous solutions with the same concentration, and the temperature is 15~20℃.
5. The preparation method according to claim 1, characterized in that, In step (2), cold drawing is carried out at 20℃~35℃ with a drawing ratio of 1.2~2.0 times; solvent drawing is carried out in 15 wt%~20 wt% DMSO aqueous solution at 60℃~80℃ with a drawing ratio of 2.0~3.5 times; hot drawing is carried out in hot water at 92℃~98℃ with a drawing ratio of 2.5~4.0 times; the total drawing ratio is 6.0~28.0 times.
6. The preparation method according to claim 1, characterized in that, In step (2), the stretching ratio of cold stretching is 1.5 to 1.8 times, the stretching ratio of solvent stretching is 2.8 to 3.0 times, the stretching ratio of hot stretching is 3.2 to 3.5 times, and the total stretching ratio is 10 to 18.9 times.
7. The preparation method according to claim 1, characterized in that, In step (3), the temperature for primary drying and densification is 110±5℃.
8. The preparation method according to claim 1, characterized in that, In step (4), the secondary deep densification process is carried out on the hot roller, and the surface temperature of the hot roller fluctuates by no more than ±1℃.
9. The preparation method according to claim 1, characterized in that, In step (4), the secondary deep densification temperature is 140~150℃, the tension is 0.10 cN / dtex, and the draw ratio is 1.05~1.08 times.
10. The preparation method according to claim 1, characterized in that, In step (5), the steam heat setting is carried out in a saturated steam atmosphere with a pressure of 0.15MPa~0.30MPa, with a pressure fluctuation of no more than ±1%, a time of 1min~3min, and a stretching ratio of 0.95~1.02 times.