Method for improving the surface roughness of dry-jet wet-spun polyacrylonitrile filaments

Abstract

The application discloses a method for improving the surface roughness of dry-jet wet-spun polyacrylonitrile filaments. The method comprises the following steps: after water washing, the expanded fibers are subjected to surface etching in an etching solution, the mass ratio of H2SO4 to DMSO in the etching solution is 4-5:10, the etching tank temperature is 24-30 DEG C, the etching time is 2-4.3 s, then the fibers subjected to surface etching are subjected to water washing, drawing, drying, densification and steam drawing, and finally the polyacrylonitrile filaments with high surface roughness are prepared. The application improves the surface roughness of the filaments by surface etching of the water-containing expanded PAN filaments, prepares the PAN filaments with deep surface gullies, and then improves the surface roughness of the carbon filaments, improves the coupling ability of the dry-jet wet-spun carbon fibers and resin materials, and expands the application scenarios.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber manufacturing technology and relates to a method for improving the surface roughness of dry-jet wet-spun polyacrylonitrile precursor fibers. Background Technology

[0002] Carbon fiber is a high-molecular fiber material with a carbon content of over 90%. It possesses high strength, high modulus, acid and alkali resistance, and corrosion resistance, and is widely used in aerospace, transportation, and new energy fields. High-strength, high-modulus carbon fibers have a tensile strength exceeding 7000 MPa and an elastic modulus exceeding 350 GPa, exhibiting extremely high stiffness, excellent specific modulus, good environmental stability, and dimensional stability. Dry-jet wet spinning is commonly used to prepare high-strength, high-modulus carbon fibers because the polyacrylonitrile (PAN) dope can release stress and allow solvent diffusion when in air, resulting in fibers with smoother surfaces and better mechanical properties, reducing fiber voids and surface collapse caused by solidification. However, the smooth surface of dry-jet wet-spun carbon fibers presents challenges in forming composites with resins, including small contact area, low interlaminar shear strength, and poor interfacial adhesion, which can easily lead to a decline in overall performance.

[0003] Treating the surfaces of carbon fiber precursors and bulk fibers is one way to improve the overall performance of composite materials formed with resins. However, the surface activity of carbon fiber bulk fibers is relatively weak, and methods such as surface chemical modification and irradiation are costly and inefficient. Surface etching of carbon fiber precursors can significantly improve etching efficiency, increase fiber interface contact area, and improve fiber surface roughness. For example, the literature (Gao Q, Jing M, Chen M, et al. Research on PAN Nascent Fiber Interior Microstructure through Ultrasonic Etching and Ultrathin Sectioning[J]. Polymer Science Series A, 2018, 60(5): 594-598. DOI: 10.1134 / S0965545X1805005X.) uses strong acid and a mixed solvent to perform preliminary surface etching and fiber separation of PAN fibers, forming obvious surface trench structures and microfibril structures. However, this method involves etching after the raw yarn has been densified by steaming and winding. Since the raw yarn is highly dense, it is difficult for the etching solvent to penetrate the fiber, resulting in low etching efficiency and insufficient improvement in roughness. Summary of the Invention

[0004] The purpose of this invention is to provide a method for improving the surface roughness of dry-jet wet-spun polyacrylonitrile precursor fibers. This method improves the surface roughness of the precursor fibers by etching the surface of water-swelled PAN precursor fibers, thereby preparing PAN precursor fibers with deep surface grooves, and then preparing carbon fibers with high surface roughness, thus improving the coupling ability between dry-jet wet-spun carbon fibers and resin materials.

[0005] The technical solution for achieving the objective of this invention is as follows:

[0006] A method for improving the surface roughness of dry-jet wet-spun polyacrylonitrile precursor fibers includes the following steps:

[0007] (1) Copolymerization: The spinning solution is prepared by homogeneous free radical solution polymerization in dimethyl sulfoxide (DMSO) using acrylonitrile and itaconic acid as comonomers, one of acrylic acid, methyl acrylate, methyl methacrylate and isobutyl methacrylate as the third monomer, and azobisisobutyronitrile as the initiator.

[0008] (2) De-sing and de-bubbling: The spinning solution is de-singed and de-bubbled and then sent to the spinning unit;

[0009] (3) Coagulation bath: The spinning solution after desizing and defoaming is squeezed into the coagulation bath through the spinneret after being metered by a metering pump, and at the same time, the nascent fibers are drawn in the air.

[0010] (4) Washing: The nascent fibers are washed with desalinated water in multiple stages to remove the solvent, so that the PAN filaments reach an expanded and porous state;

[0011] (5) Surface etching: The water-washed and expanded fibers are placed in an etching tank and immersed in an etching solution for surface etching. The mass ratio of etchant H2SO4 to DMSO in the etching solution is 4-5:10. The temperature of the etching tank is 24-30℃ and the etching time is 2.0-4.3s. After etching, the residual etching solution on the fibers is removed by squeezing with extrusion rollers.

[0012] (6) Water washing and stretching: After surface etching and extrusion, the fibers are washed with desalinated water in multiple stages to remove the solvent. After washing, they are passed through hot water at 60-80℃ and stretched 1-2 times.

[0013] (7) Drying and densification: After washing and stretching, the fiber is coated with 1-3% silicone oil agent and then dried and densified. The hot roller pressure is 0.45-0.65 MPa, the temperature range is 145-180℃, and the load is 1.0-2.0 times the stretch.

[0014] (8) Steam drawing: After drying and densification, the fiber is drawn by steam at a steam pressure of 0.30 to 0.60 MPa, and drawn by 2.0 to 3.5 times to obtain dry-jet wet-spun PAN precursor yarn with high surface roughness.

[0015] Furthermore, in step (1), the homogeneous free radical solution polymerization reaction temperature is 60-65℃, the spinning solution temperature is 40-70℃, and the solid content is 14-25%.

[0016] Further, in step (1), with the total mass of monomers being 100%, the proportions of each monomer are: 92-99.8 wt.% acrylonitrile, 0.1-4 wt.% itaconic acid, and 0.1-4 wt.% third monomer.

[0017] Further, in step (2), the specific method for removing monofilaments and bubbles is as follows: the spinning solution is subjected to removal of monofilaments under a pressure of -60 to -78 kPa, and then subjected to a first-stage filtration of 3 μm. The solution after the first-stage filtration is subjected to degassing under a pressure of -78 to -100 kPa, and then subjected to a second-stage filtration of 1 μm before being sent to the spinning unit.

[0018] Furthermore, in step (3), the concentration of DMSO in the coagulation bath is 55-70 wt%, the temperature is 5-25 °C, and the stretching ratio in the air is 1-2.5 times.

[0019] Furthermore, in step (4) or (6), the water washing temperature is controlled at 33-36°C.

[0020] Furthermore, in step (6), the DMSO content in the fiber after washing is ≤0.1%.

[0021] Furthermore, in step (7), the silicone oil agent is a silicone oil agent commonly used in the oiling section of the polyacrylonitrile precursor fiber preparation process, such as a silicone oil agent composed of amino-modified silicone oil, polyether-modified silicone oil, antistatic agent and emulsifier and other additives.

[0022] Furthermore, in step (7), the pressure of the hot roller is 0.45 to 0.55 MPa, and the temperature range is 146 to 167 °C.

[0023] Furthermore, in step (8), the stretching is 3.3 to 3.5 times.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) The present invention improves the surface roughness of the PAN precursor by etching the surface of the water-swellable porous PAN precursor, thereby preparing a PAN precursor with deep surface grooves, and then preparing a carbon filament with high surface roughness.

[0026] (2) Carbon filaments with high surface roughness can effectively improve the coupling ability between dry-spun and wet-spun carbon fibers and resin materials, thus expanding their application scenarios. Attached Figure Description

[0027] Figure 1 SEM image of the PAN precursor fiber obtained in Example 1;

[0028] Figure 2 SEM image of the PAN precursor fiber obtained in Example 2;

[0029] Figure 3 This is a SEM image of the PAN precursor fiber prepared in Comparative Example 4. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] Example 1

[0032] (1) Copolymerization: Free radical solution polymerization was carried out on a mixed solution of 92 wt.% acrylonitrile, 4 wt.% itaconic acid and 4 wt.% methyl methacrylate in dimethyl sulfoxide to obtain a polyacrylonitrile polymer spinning solution with a solid content of 18.5%.

[0033] (2) De-sing and de-bubbling: The spinning solution is first de-singled in a de-singling kettle at a pressure of -76Kpa, then filtered through a 3μm primary filter, and then de-bubbled in a de-bubbling kettle at a pressure of -97KPa before being sent to a 1μm secondary filter for further processing.

[0034] (3) Coagulation bath: The spinning solution after desizing and defoaming is pressurized and transported to the spinning unit, and the temperature of the spinning solution is maintained at 45°C. The spinning solution passes through an air layer and then goes to the coagulation bath for coagulation and molding. The air layer is 2mm, the concentration of DMSO in the coagulation bath is 45wt%, the temperature of the coagulation bath is 5°C, and a draw ratio of 1.1 is applied to obtain nascent fibers.

[0035] (4) Washing: The nascent fibers are desalinated in multiple stages at 33-36℃ to remove the solvent, so that the PAN filaments reach an expanded and porous state.

[0036] (5) Surface etching: The water-washed and expanded fibers are placed in the etching tank and immersed in the etching solution for surface etching. The mass ratio of H2SO4 to DMSO in the etching solution is 4:10, the temperature of the etching tank is 30℃, and the immersion time is 4.3s.

[0037] (6) Water washing and stretching: After etching, the fiber is desalinated in multiple stages at 33-36℃ to remove the solvent, and after washing, it is placed in hot water at 60-80℃ and stretched by 1.1 times.

[0038] (7) Drying and densification: After being drawn by hot water, the fibers are passed through a 1.1% silicone oil bath. The oiled raw fibers are then dried and densified by hot rollers with a certain temperature gradient. The drying roller pressure is maintained at 0.45 MPa, there are 25 drying rollers, the temperature gradient of the drying rollers is 4℃, and the temperature range is 146~165℃.

[0039] (8) Steam drawing: The dried fiber bundles were steam drawn at a saturated steam pressure of 0.45 MPa and a steam drawing ratio of 3.5 to obtain polyacrylonitrile precursor fibers. The surface morphology was tested, and the precursor fibers showed obvious longitudinal surface grooves, such as... Figure 1 As shown.

[0040] Example 2

[0041] This embodiment is basically the same as Embodiment 1, except that in step (5) surface etching: the mass ratio of H2SO4 to DMSO is 5:10, polyacrylonitrile precursor fibers are prepared and their surface morphology is tested. The precursor fiber surface shows obvious grooves and contains fiber separation and a lot of gel impurities, such as Figure 2 As shown.

[0042] Comparative Example 1

[0043] This comparative example is basically the same as Example 1, except that in step (5) surface etching: the mass ratio of H2SO4 to DMSO is 3:10, polyacrylonitrile precursor is obtained and the surface morphology is tested. The precursor surface is smooth and without grooves.

[0044] Comparative Example 2

[0045] This comparative example is basically the same as Example 1, except that in step (5) surface etching: the mass ratio of HCl and H3PO4 to DMSO in the etching solution is 2:2:10, polyacrylonitrile precursor fiber is obtained and the surface morphology is tested. The surface of the precursor fiber becomes rough but has no longitudinal grooves.

[0046] Comparative Example 3

[0047] This comparative example is basically the same as Example 1, except that in step (5) surface etching: the mass ratio of HNO3 to DMSO in the etching solution is 4:10. After etching, the raw silk showed obvious dissolution, and the raw silk was washed with water and could not be dried and steamed.

[0048] Comparative Example 4

[0049] This comparative example is basically the same as Example 1, except that no surface etching step is performed. Polyacrylonitrile precursor fibers were obtained, and their surface morphology was tested. The precursor fiber surface was smooth and without grooves. Figure 3 As shown.

[0050] Comparative Example 5

[0051] This comparative example is largely the same as Example 1, except that the surface of the steam-drawn and wound filament is etched, as detailed below:

[0052] (1) Copolymerization: Free radical solution polymerization was carried out on a mixed solution of 92 wt.% acrylonitrile, 4 wt.% itaconic acid and 4 wt.% methyl methacrylate in dimethyl sulfoxide to obtain a polyacrylonitrile polymer spinning solution with a solid content of 18.5%.

[0053] (2) De-sing and de-bubbling: The spinning solution is first de-singled in a de-singling kettle at a pressure of -76Kpa, then filtered through a 3μm primary filter, and then de-bubbled in a de-bubbling kettle at a pressure of -97KPa before being sent to a 1μm secondary filter for further processing.

[0054] (3) Coagulation bath: The spinning solution after desizing and defoaming is pressurized and transported to the spinning unit, and the temperature of the spinning solution is maintained at 45°C. The spinning solution passes through an air layer and then goes to the coagulation bath for coagulation and molding. The air layer is 2mm, the concentration of DMSO in the coagulation bath is 45wt%, the temperature of the coagulation bath is 5°C, and a draw ratio of 1.1 is applied to obtain nascent fibers.

[0055] (4) Washing and stretching: The nascent fibers are desalinated in multiple stages at 33-36℃ to remove the solvent, and after washing, they are placed in hot water at 60-80℃ and stretched by 1.1 times.

[0056] (5) Drying and densification: After being drawn by hot water, the fibers are passed through a 1.1% silicone oil bath. The oiled raw fibers are then dried and densified by hot rollers with a certain temperature gradient. The drying roller pressure is maintained at 0.45 MPa, there are 25 drying rollers, the temperature gradient of the drying rollers is 4℃, and the temperature range is 146~165℃.

[0057] (6) Steam drawing: The dried fiber bundles are steam drawn with a saturated steam pressure of 0.45 MPa and a steam drawing ratio of 3.5.

[0058] (7) Surface etching: The wound raw wire is put into the etching tank and immersed in the etching solution for surface etching. The mass ratio of H2SO4 to DMSO in the etching solution is 4:10, the temperature of the etching tank is 30℃, and the immersion time is 4.3s.

[0059] (8) Water washing and stretching: The etched fiber is washed with desalinated water at 33-36℃ in multiple stages to remove the solvent, and polyacrylonitrile precursor fiber is obtained and its surface morphology is tested. The precursor fiber surface is smooth and without grooves.

Claims

1. A method for improving the surface roughness of dry-jet wet-spun polyacrylonitrile filaments, characterized in that, The method comprises the following steps: (1) copolymerization: acrylonitrile and itaconic acid are used as comonomers, one of acrylic acid, methyl acrylate, methyl methacrylate and isobutyl methacrylate is used as a third monomer, and azobisisobutyronitrile is used as an initiator to perform homogeneous radical solution polymerization in DMSO to obtain a spinning dope; (2) single removal and degassing: the spinning dope is sent to a spinning unit after single removal and degassing; (3) coagulation bath: the spinning dope after single removal and degassing is extruded into a coagulation bath through a metering pump after a spinneret, and is drawn in air to obtain a nascent fiber; (4) water washing: the nascent fiber is washed by multiple stages of desalting water to remove solvents, so that the PAN precursor reaches a swelling porous state; (5) surface etching: the water-washed and swollen fiber is immersed in an etching solution in an etching tank to perform surface etching, the mass ratio of etchant H2SO4 to DMSO in the etching solution is 4-5:10, the etching tank temperature is 24-30 DEG C, the etching time is 2.0-4.3 s, and the etching solution remaining on the fiber is removed by extrusion after etching is completed; (6) water washing and drawing: the fiber after surface etching and extrusion is washed by multiple stages of desalting water to remove solvents, is drawn by 1-2 times after water washing in hot water at 60-80 DEG C; (7) drying and densification: the fiber after water washing and drawing is applied with 1-3% silicon oil agent and is dried and densified, the hot roller pressure is 0.45-0.65 MPa, the temperature range is 145-180 DEG C, and the fiber is drawn by 1.0-2.0 times; (8) steam drawing: the fiber after drying and densification is drawn in steam at a steam pressure of 0.30-0.60 MPa by 2.0-3.5 times to obtain a dry-jet wet-spun PAN precursor with high surface roughness.

2. The method of claim 1, wherein, In step (1), the homogeneous radical solution polymerization reaction temperature is 60-65 DEG C, the temperature of the spinning dope is 40-70 DEG C, and the solid content is 14-25%.

3. The method of claim 1, wherein, In step (1), the total mass of monomers is 100%, and the mass fraction of each monomer is: 92-99.8 wt.% acrylonitrile, 0.1-4 wt.% itaconic acid and 0.1-4 wt.% third monomer.

4. The method of claim 1, wherein, In step (2), the specific method for single removal and degassing is: the spinning dope is subjected to single removal under a pressure of-60--78 KPa, is subjected to primary filtration through a 3-micron filter, is subjected to degassing treatment under a pressure of-78--100 KPa after primary filtration, and is sent to the spinning unit after secondary filtration through a 1-micron filter.

5. The method of claim 1, wherein, In step (3), the concentration of DMSO in the coagulation bath is 55-70 wt%, and the temperature is 5-25 DEG C, and the drawing multiple in air is 1-2.5 times.

6. The method of claim 1, wherein, In step (4) or (6), the water washing temperature is controlled at 33-36 DEG C.

7. The method of claim 1, wherein, In step (6), the DMSO content in the fiber after water washing is ≤0.1%.

8. The method of claim 1, wherein, In step (7), the silicon oil agent is composed of amino-modified silicon oil, polyether-modified silicon oil, antistatic agent and emulsifier.

9. The method of claim 1, wherein, In step (7), the hot roller pressure is 0.45-0.55 MPa, and the temperature range is 146-167 DEG C.

10. The method of claim 1, wherein, In step (8), the drawing multiple is 3.3-3.5.

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