Process for the production of hollow cross-section polyacrylonitrile dry-jet wet-spun carbon fibers

Abstract

The application discloses a preparation method of hollow-section polyacrylonitrile dry-jet wet-spun carbon fiber. The method extrudes the spinning dope through a spinneret with an annular cavity, enters a coagulation bath, and then is washed by multiple stages of desalted water, hot water drawing, oiling, drying densification, steam drawing, and finally is wound to obtain a hollow-section precursor fiber. The hollow-section precursor fiber is then pre-oxidized, carbonized in a low-temperature furnace and a high-temperature furnace to obtain the dry-jet wet-spun carbon fiber with a hollow section. The preparation method is simple, the structure of the spinneret with the annular cavity and the subsequent process conditions are controlled to effectively control the structure of the hollow-section polyacrylonitrile carbon fiber, and the prepared hollow-section carbon fiber has the advantages of high specific surface area, low skin-core ratio and low cost, and has a wide application prospect in the fields of wave-absorbing materials, electromagnetic shielding materials, resin-based composite materials, carbon / carbon composite materials and the like.

Description

Technical Field

[0001] This invention relates to a method for preparing hollow cross-section polyacrylonitrile dry-jet wet-spun carbon fibers, belonging to the field of carbon fiber preparation technology. Background Technology

[0002] Hollow fibers are fibers with cavities along their axial cross-section. Due to their unique cross-sectional shape, hollow fibers have a significantly increased surface area compared to circular cross-section fibers, potentially leading to improved composite properties with the matrix. The cavities in hollow fibers provide still air, enhancing their warmth retention and increasing surface area per unit volume, thus improving their bulkiness. The ability of hollow fibers to absorb water, air, blood, and other media, as well as their bonding ability with the matrix material when used as composites, not only improves their stiffness and rigidity but also enhances their bending resistance and abrasion resistance. Filling their interior with hollow elements could potentially create hollow fibers with specific functionalities. Currently, hollow fiber cross-sections are mainly produced through melt spinning, electrospinning, and wet spinning. Hollow fibers primarily include polyester fibers, glass fibers, carbon fibers, and nanofibers. Polypropylene (PP), polyester, polyamide, polyacrylonitrile, polystyrene, polyethylene, nylon, cellulose acetate, and various nylon, polyester, acrylic, and polypropylene fibers can all be processed into hollow fibers using appropriate spinning techniques.

[0003] Dry-jet wet spinning technology can effectively improve the mechanical properties and spinning speed of polyacrylonitrile fibers and is an engineering-feasible technology. However, the dry-jet wet spinning process is extremely cumbersome. Under the influence of surface tension, the forming process of the spinning solution with viscoelastic properties after passing through a special hollow spinneret is far more complex than that after passing through a circular spinneret. The spinning solution undergoes extrusion and expansion after passing through the special hollow spinneret, but due to the difference in the structure of the hollow spinneret, the shear force on the solution is uneven, which can easily lead to the breakage of the fine stream. Moreover, the design of the inner and outer diameters of the spinneret is crucial. However, if the difference between the inner and outer diameters is too small, the solution is prone to breakage after extrusion under a large N2 pressure, and the hollow fibers cannot withstand the strong driving force of the coagulation bath process, resulting in poor compactness. If the difference between the inner and outer diameters is too large, the solution is prone to bonding into a circular solid filament after extrusion through the air layer, resulting in excessive deviation of the hollow fibers. Therefore, the prepared hollow carbon fibers are required to have a suitable inner-outer diameter ratio, E. i Defined as:

[0004]

[0005] The relative deviation S is represented by the ratio of the absolute value of the fiber inner-outer diameter ratio Ei and the difference between the inner and outer diameters E of the spinneret to the inner and outer diameters E of the spinneret:

[0006]

[0007] In the formula, d is the inscribed circle diameter of the hollow cross-section carbon fiber, A1 is the area of ​​the shaded portion of the hollow cross-section carbon fiber, D is the circumscribed circle diameter of the hollow cross-section carbon fiber, and A0 is the circumscribed circle area of ​​the fiber. The unique surface morphology of hollow cross-section fibers allows oxygen to penetrate more easily into the interior during the pre-oxidation process. This alleviates radial non-uniformity of the fiber, improves the uniformity of pre-oxidized filaments, and reduces the core-sheath ratio of the carbon fiber. Furthermore, it increases the reaction rate, reduces the fiber travel time, lowers the reactor operating temperature, and enables rapid carbon fiber preparation, thus reducing production costs. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing hollow cross-section polyacrylonitrile dry-jet wet-spun carbon fibers. The method first involves spraying the spinning solution through a spinneret with an annular cavity into a coagulation bath to form nascent fibers with a hollow cross-section. The fibers undergo multi-stage desalination washing, water drawing, oiling, drying, steam drawing, and then winding to obtain a hollow cross-section precursor fiber. This precursor fiber is then pre-oxidized and carbonized to obtain carbon fibers with a hollow cross-section.

[0009] The technical solution for achieving the objective of this invention is as follows:

[0010] A method for preparing hollow cross-section polyacrylonitrile dry-jet wet-spun carbon fibers includes the following steps:

[0011] (1) Using 95-99 wt.% acrylonitrile as the first monomer and 1-5 wt.% acrylic acid, methyl acrylate, methyl methacrylate or isobutyl methacrylate as the second monomer, solution polymerization is carried out in dimethyl sulfoxide to obtain spinning solution. The temperature of spinning solution is controlled at 40-70℃ and the solid content is 10-25%.

[0012] (2) After degassing and de-soaking, the spinning solution is pressurized and extruded through a spinneret with an annular cavity at a speed of 10-20 m / min. It then passes through an air layer and enters a dimethyl sulfoxide coagulation bath for phase separation to form gel strips. Simultaneously, it is stretched to obtain nascent fibers with a hollow cross-section. The coagulation bath concentration is 30-50 wt%, and the coagulation bath temperature is 5-20 °C. The spinneret with an annular cavity includes a first plate 1 and a second plate 2. The first plate 1 has several through holes 4 and several needle-containing cylinders 8, with an annular groove 3 at the top and an annular groove 5 at the bottom. The second plate 2 has several through holes 9 containing micropores. A plate 1 and a second plate 2 are bonded together to form a slurry inlet channel 6; the needle-containing cylinder 8 on the first plate and the micro-perforated through hole 9 on the second plate correspond one-to-one to form an annular cavity 7; the through hole 4 connects to the slurry inlet channel 6, and the slurry inlet channel 6 connects to the annular cavity 7; rubber rings are installed on the annular groove 3 and annular groove 5; the top of the first plate 1 abuts against the raw liquid feed pipe, and the top of the second plate 2 abuts against the bottom of the first plate 1; the needle length of the needle-containing cylinder 8 is the same as the micro-perforation length in the micro-perforated through hole 9, the needle diameter of the needle-containing cylinder 8 is 0.5-0.6 mm, and the micro-perforation diameter in the micro-perforated through hole 9 is 1.0-1.5 mm; the length-to-diameter ratio of the spinneret is 3-4:1;

[0013] (3) The nascent fibers are washed with desalinated water in multiple stages to remove the solvent, and then washed with hot desalinated water and stretched.

[0014] (4) After being stretched in hot water, the fibers are oiled and then dried and densified by hot rollers.

[0015] (5) The dried and densified fibers are steam drawn, and after steam drawing, they are wound into shape to obtain hollow cross-section filaments.

[0016] (6) The hollow cross-section raw filaments are pre-oxidized in the pre-oxidation furnace after passing through the unwinding frame to obtain pre-oxidized filaments;

[0017] (7) The pre-oxidized fiber is carbonized in a low-temperature furnace and a high-temperature furnace in sequence to prepare carbon fiber with a hollow cross section; the temperature of the low-temperature furnace is 580-650℃ and the draw ratio of the low-temperature furnace is 1.0-1.1 times; the temperature of the high-temperature furnace is 1450-1600℃ and the draw ratio of the high-temperature furnace is 0.95-1.05 times.

[0018] Further, in step (2), the method for removing monofilaments and degassing is as follows: first, the spinning solution is removed from the monofilaments under a pressure of -76Kpa in the monofilament removal kettle, then filtered through a 3μm primary filter, and then degassed through a degassing kettle at a pressure of -97KPa before being sent to a 1μm secondary filter for further processing.

[0019] Further, in step (2), the air layer height is 1-5 mm, and the air stretching ratio is 1-2 times. Preferably, the coagulation bath concentration is 45 wt%, and the coagulation bath temperature is 5 °C.

[0020] Further, in step (2), the number of holes in the through hole 4 is 1 to 2K, the number of holes in the needle cylinder 8 and the through hole 9 containing micropores is the same, both being 1 to 5K, the needle length in the needle cylinder 8 and the length of the micropore in the through hole 9 are both 0.3 to 1.0 mm; the length of the cylinder in the needle cylinder 8 is 10 to 15 mm, and the diameter of the cylinder is 3 to 5 mm; the length of the through hole in the through hole 9 containing micropores is 5 to 8 mm, the diameter of the through hole is 4 to 6 mm, and the hole spacing is 1 to 3 mm.

[0021] Furthermore, in step (2), the spinneret with an annular cavity is made of Hastelloy C276, 3161L alloy, 1Cr18Ni9Ti austenitic stainless steel, AISI316 or AISI630.

[0022] Furthermore, in step (3), the washing tank is of grade 3 to 7, the washing temperature is 20 to 36°C, and the stretching ratio is 1 to 1.5 times; the hot desalination water washing and stretching are of grade 1 to 3, the temperature is 60 to 80°C, and the stretching ratio is 1 to 2.0 times.

[0023] Furthermore, in step (4), the temperature of the hot roller is level 3 to 7, the temperature range is 100 to 185°C, and the pressure of the hot roller is 0.30 to 1.10 MPa.

[0024] Furthermore, in step (5), the steam pressure is 0.30 to 0.80 MPa, the steam draw ratio is 3.0 to 5.0 times, and the winding speed is 350 to 500 m / min.

[0025] Further, in step (6), the pre-oxidation temperature is 200℃~300℃, and the pre-oxidation draw ratio is 0.9~1.05 times. Preferably, the pre-oxidation temperature is 220℃~240℃.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] (1) This invention designs a spinneret with an annular cavity and successfully applies it to the dry-jet wet spinning method to prepare hollow cross-section polyacrylonitrile carbon fibers.

[0028] (2) The present invention achieves effective control of hollow cross-section polyacrylonitrile carbon fiber structure by controlling the size of needle-containing cylinders and micro-holes in spinnerets with annular cavities and the length-to-diameter ratio of spinnerets, while matching appropriate coagulation bath conditions.

[0029] (3) The hollow cross-section carbon fiber prepared by the method of the present invention has advantages such as high specific surface area, high density, low core-skin ratio, high filling ratio, high wave absorption performance, high tensile strength and low cost. When used as a two-dimensional reinforcing material, it can load other media to improve the comprehensive performance of composite materials. It is suitable for preparing wave absorbing materials, electromagnetic shielding materials, radar wave absorbing materials, resin-based composite materials, carbon / carbon composite materials, functional materials, structural materials and stealth weapons. Attached Figure Description

[0030] Figure 1 This is a schematic cross-sectional diagram of the overall structure of the spinneret;

[0031] Figure 2 for Figure 1 Enlarged anatomical view of section I in the middle;

[0032] Figure 3 This is a schematic structural view of the first plate.

[0033] Figure 4 Here are three schematic views of the second plate structure;

[0034] The figures are labeled as follows: 1 First plate, 2 Second plate, 3 Annular groove, 4 Through hole, 5 Annular groove, 6 Slurry inlet channel, 7 Annular cavity, 8 Needle-containing cylinder, 9 Through hole containing micropores. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] like Figures 1-4 As shown, the spinneret used in this invention includes a first plate body 1 and a second plate body 2. The first plate body 1 has several through holes 4 and several needle-containing cylinders 8, with an annular groove 3 at the top and an annular groove 5 at the bottom. The second plate body 2 has several through holes containing micropores 9. The first plate body 1 and the second plate body 2 are fitted together to form a slurry inlet channel 6. The needle-containing cylinders 8 on the first plate body and the micropore-containing through holes 9 on the second plate body correspond one-to-one to form an annular cavity 7. The through holes 4 connect to the slurry inlet channel 6, and the slurry inlet channel 6 connects to the annular cavity 7. Rubber rings are installed in the annular grooves 3 and 5. The top of the second plate body 2 abuts against the bottom of the first plate body 1. The top of the first plate body 1 abuts against the raw material feed pipe.

[0037] Specifically, the first plate 1 is circular in shape. Through holes 4 are evenly distributed along the circumference of the first plate 1, and the number of through holes 4 is 1 to 2K. Needle-containing cylinders 8 are located within the through holes 4 and are evenly distributed along the center of the first plate 1. The number of needle-containing cylinders 8 is 1 to 5K, the length of the cylinder is 10 to 15 mm, the diameter of the cylinder is 3 to 5 mm, the needle length is 0.3 to 1.0 mm, and the needle diameter is 0.3 to 0.8 mm.

[0038] Specifically, the second plate 2 is circular in shape. The number of micro-holes 9 is 1 to 5K, the length is 5 to 8 mm, the diameter is 4 to 6 mm, and the spacing between the holes is 1 to 3 mm. The length of the micro-holes in the micro-holes 9 is the same as the length of the needle in the needle cylinder 8, which is 0.3 to 1.0 mm. The diameter of the micro-holes is 0.5 to 1.5 mm, and the length-to-diameter ratio of the spinneret is 3 to 5:1.

[0039] Specifically, a rubber ring is installed in the annular groove 3 to seal the connection between the first plate 1 and the raw liquid inlet pipe to prevent leakage.

[0040] Specifically, a rubber ring is installed in the annular groove 5 to seal the connection between the first plate 1 and the second plate 2 to prevent leakage.

[0041] In this invention, the top of the first spinneret 1 rests against the spinning solution feed pipe. The spinning solution flows into the through hole 4 through the feed pipe, passes through the first spinneret 1, then flows into the slurry inlet channel 6, and then into the annular cavity 7. It then passes through the second spinneret 2 and is extruded to obtain a spinning solution with a hollow cross-section. The hollow cross-section spinning solution is then solidified and drawn to form nascent fibers with a hollow cross-section, such as... Figure 2 As shown, hollow cross-section carbon fibers are then produced through subsequent processes.

[0042] Example 1

[0043] Using 96 wt% acrylonitrile as the first monomer and 5 wt% methyl acrylate as the second monomer, free radical solution polymerization was carried out in dimethyl sulfoxide to obtain the spinning solution. The temperature of the spinning solution was controlled at 60℃, and the solid content was 20%. The spinning solution was first demonstrated in a demonstration reactor at a pressure of -76 kPa, then filtered through a 3 μm primary filter, and then degassed in a degassing reactor at a pressure of -97 kPa. After that, it was sent to a 1 μm secondary filter for further treatment. The refined spinning solution was then pressurized and transported to the spinning unit. The spinning solution was passed through a 1 μm wick filter, pressurized, and extruded through a spinneret with an annular cavity at an extrusion speed of 15.49 m / min. The spinneret with an annular cavity was made of 316L alloy. The first plate contained 3K needle cylinders with a needle diameter of 0.5 mm, and the second plate contained 3K micropores with a micropore diameter of 1.0 mm. The aspect ratio of the spinneret orifices was 3:1. The spinning solution, after passing through a 1mm air layer, enters a coagulation bath for coagulation and shaping. The coagulation bath concentration is 45wt%, and the coagulation bath temperature is 5℃, while a draw ratio of 1.05 is applied to obtain nascent fibers. The nascent fibers are descaled in a multi-stage desalination bath at 35℃ to remove the solvent, washed with water, and then subjected to hot water at 70℃, while being drawn at a draw ratio of 1.3. The fibers after hot water drawing are passed through an oil bath with a concentration of 1.10%. The oiled fibers are then dried and densified using hot rollers with a temperature gradient of 100–185℃, maintaining a drying roller pressure of 0.55MPa, with 25 drying rollers. The dried and densified fiber bundles are then steam drawn at a saturated steam pressure of 0.45MPa and a steam draw ratio of 3.55. After steam drawing, the fibers are wound to obtain hollow cross-section precursor yarn. The precursor yarn is then passed through a unwinding rack and pre-oxidized in a pre-oxidation furnace at a pre-oxidation temperature of 240℃ and a pre-oxidation draw ratio of 0.98. Pre-oxidized fibers were sequentially carbonized in a low-temperature furnace and a high-temperature furnace to prepare carbon fibers with a hollow cross-section. The low-temperature furnace temperature was controlled at 600℃ with a draw ratio of 1.02, while the high-temperature furnace temperature was controlled at 1500℃ with a draw ratio of 1.01. The prepared carbon fibers had a core-sheath ratio of 3% and an inner-outer diameter ratio E. i The percentage was 58%, with a relative deviation of 16%.

[0044] Example 2

[0045] Using 96 wt% acrylonitrile as the first monomer and 4 wt% acrylic acid as the second monomer, free radical solution polymerization was carried out in dimethyl sulfoxide to obtain the spinning solution. The temperature of the spinning solution was controlled at 60℃, and the solid content was 20%. The spinning solution was first demonstrated in a demonstration reactor at a pressure of -76 kPa, then filtered through a 3 μm primary filter, and then degassed in a degassing reactor at a pressure of -97 kPa. After that, it was sent to a 1 μm secondary filter for further treatment. The refined spinning solution was then pressurized and transported to the spinning unit. The spinning solution was passed through a 1 μm wick filter, pressurized, and then extruded through a spinneret with an annular cavity at an extrusion speed of 15.49 m / min. The spinneret with an annular cavity was made of 316L alloy. The first plate contained 3K needle cylinders with a needle diameter of 0.6 mm, and the second plate contained 3K micropores with a micropore diameter of 1.2 mm. The aspect ratio of the spinneret orifices was 4:1. The spinning solution, after passing through a 1mm air layer, enters a coagulation bath for coagulation and shaping. The coagulation bath concentration is 45wt%, and the coagulation bath temperature is 5℃, while a draw ratio of 1.05 is applied to obtain nascent fibers. The nascent fibers are descaled in a multi-stage desalination bath at 35℃ to remove the solvent, washed with water, and then subjected to hot water at 70℃, while being drawn at a draw ratio of 1.3. The fibers after hot water drawing are passed through an oil bath with a concentration of 1.10%. The oiled fibers are then dried and densified using hot rollers with a temperature gradient of 100–185℃, maintaining a drying roller pressure of 0.55MPa, with 25 drying rollers. The dried and densified fiber bundles are then steam drawn at a saturated steam pressure of 0.45MPa and a steam draw ratio of 3.55. After steam drawing, the fibers are wound to obtain hollow cross-section precursor yarn. The precursor yarn is then passed through a unwinding rack and pre-oxidized in a pre-oxidation furnace at a pre-oxidation temperature of 240℃ and a pre-oxidation draw ratio of 0.98. Pre-oxidized fibers were sequentially carbonized in a low-temperature furnace and a high-temperature furnace to prepare carbon fibers with a hollow cross-section. The low-temperature furnace temperature was controlled at 600℃ with a draw ratio of 1.02, while the high-temperature furnace temperature was controlled at 1500℃ with a draw ratio of 1.01. The prepared carbon fibers had a core-sheath ratio of 0% and an inner-outer diameter ratio E. i The percentage was 55%, with a relative deviation of 10%.

[0046] Example 3

[0047] Using 95 wt% acrylonitrile as the first monomer and 5 wt% isobutyl methacrylate as the second monomer, free radical solution polymerization was carried out in dimethyl sulfoxide to obtain the spinning solution. The temperature of the spinning solution was controlled at 60℃, and the solid content was 20%. The spinning solution was first demonstrated in a demonstration reactor at a pressure of -76 kPa, then filtered through a 3 μm primary filter, and then degassed in a degassing reactor at a pressure of -97 kPa. After that, it was sent to a 1 μm secondary filter for further treatment. The refined spinning solution was then pressurized and transported to the spinning unit. The spinning solution was passed through a 1 μm wick filter, pressurized, and extruded through a spinneret with an annular cavity at an extrusion speed of 15.49 m / min. The spinneret with an annular cavity was made of 316L alloy. The first plate contained 3K needle cylinders with a needle diameter of 0.5 mm, and the second plate contained 3K micropores with a micropore diameter of 1.5 mm. The aspect ratio of the spinneret orifices was 3:1. The spinning solution, after passing through a 1mm air layer, enters a coagulation bath for coagulation and shaping. The coagulation bath concentration is 45wt%, and the coagulation bath temperature is 5℃, while a draw ratio of 1.05 is applied to obtain nascent fibers. The nascent fibers are descaled in a multi-stage desalination bath at 35℃ to remove the solvent, washed with water, and then subjected to hot water at 70℃, while being drawn at a draw ratio of 1.3. The fibers after hot water drawing are passed through an oil bath with a concentration of 1.10%. The oiled fibers are then dried and densified using hot rollers with a temperature gradient of 100–185℃, maintaining a drying roller pressure of 0.55MPa, with 25 drying rollers. The dried and densified fiber bundles are then steam drawn at a saturated steam pressure of 0.45MPa and a steam draw ratio of 3.55. After steam drawing, the fibers are wound to obtain hollow cross-section precursor yarn. The precursor yarn is then passed through a unwinding rack and pre-oxidized in a pre-oxidation furnace at a pre-oxidation temperature of 240℃ and a pre-oxidation draw ratio of 0.98. Pre-oxidized fibers were sequentially carbonized in a low-temperature furnace and a high-temperature furnace to prepare carbon fibers with a hollow cross-section. The low-temperature furnace temperature was controlled at 650℃ with a draw ratio of 1.02, while the high-temperature furnace temperature was controlled at 1600℃ with a draw ratio of 1.01. The prepared carbon fibers had a core-sheath ratio of 0% and an inner-outer diameter ratio E. i The percentage was 40%, with a relative deviation of 17.6%.

[0048] Example 4

[0049] This embodiment is largely the same as Embodiment 3, except that the precursor fiber is pre-oxidized in a pre-oxidation furnace after passing through a de-firing frame. The pre-oxidation temperature is 220°C, and the pre-oxidation draw ratio is 0.98. The pre-oxidized fiber is then carbonized sequentially in a low-temperature furnace and a high-temperature furnace to prepare carbon fibers with a hollow cross-section. The low-temperature furnace temperature is controlled at 580°C, and the low-temperature furnace draw ratio is 1.02. The high-temperature furnace temperature is controlled at 1450°C, and the high-temperature furnace draw ratio is 1.01. The prepared carbon fiber has a core-sheath ratio of 0% and an inner-outer diameter ratio E. i The percentage was 40%, with a relative deviation of 8%.

[0050] Comparative Example 1

[0051] This comparative example is largely the same as Example 3, except that the coagulation bath concentration is 55 wt% and the coagulation bath temperature is 23°C. The prepared precursor fiber has a flat structure with an inner-outer diameter ratio E. i The percentage was 58%, with a relative deviation of 67%.

[0052] Comparative Example 2

[0053] This comparative example is largely the same as Example 3, except that the needle diameter in the needle-containing cylinder is 0.8 mm, the micropore diameter in the microporous through-hole is 1.2 mm, and the length-to-diameter ratio of the spinneret is 5:1. The prepared precursor fiber has a flat structure with an inner-outer diameter ratio E. i The percentage was 53%, with a relative deviation of 20.9%.

[0054] Comparative Example 3

[0055] This comparative example is largely the same as Example 3, except that the needle diameter in the needle-containing cylinder is 0.3 mm, the micropore diameter in the microporous through-hole is 0.5 mm, and the length-to-diameter ratio of the spinneret is 4:1. The prepared precursor fiber has a flat structure with an inner-outer diameter ratio E. i The percentage was 34%, with a relative deviation of 43.3%.

[0056] Comparative Example 4

[0057] This comparative example is largely the same as Example 3, except that the needle diameter in the needle-containing cylinder is 0.3 mm, the micropore diameter in the microporous through-hole is 1.5 mm, and the length-to-diameter ratio of the spinneret is 3:1. The prepared carbon filament has a solid structure with a core-sheath ratio of 11.6%.

[0058] Comparative Example 5

[0059] This comparative example is largely the same as Example 3, except that the pre-oxidized fiber is sequentially carbonized in a low-temperature furnace and a high-temperature furnace to prepare carbon fibers with a hollow cross-section. The low-temperature furnace temperature is controlled at 650°C with a draw ratio of 1.02, while the high-temperature furnace temperature is controlled at 1650°C with a draw ratio of 1.01. The prepared carbon fiber has a core-sheath ratio of 2% and an inner-outer diameter ratio E. i The percentage was 40%, with a relative deviation of 43%.

Claims

1. A process for the production of hollow cross-section polyacrylonitrile dry-jet wet- spun carbon fibers, characterized in that, The method comprises the following steps: (1) solution polymerization is carried out in dimethyl sulfoxide by taking 95-99 wt.% acrylonitrile as a first monomer and 1-5 wt.% acrylic acid, methyl acrylate, methyl methacrylate or isobutyl methacrylate as a second monomer, so as to obtain a spinning dope, and the temperature of the spinning dope is controlled to be 40-70 ℃ and the solid content is controlled to be 10-25%; (2) after the spinning dope is defibered and defoamed, the spinning dope is extruded through a spinneret with an annular cavity under pressure, the extrusion speed is 10-20 m / min, the gel fine strip is formed by phase separation in a dimethyl sulfoxide coagulation bath through an air layer, and the gel fine strip is simultaneously drawn to obtain a primary fiber with a hollow cross section, the concentration of the coagulation bath is 30-50 wt%, and the temperature of the coagulation bath is 5-20 ℃; the spinneret with the annular cavity comprises a first plate body (1) and a second plate body (2); the first plate body (1) is provided with a plurality of through holes (4), a plurality of needle-containing cylinders (8), a top annular groove (3) and a bottom annular groove (5); the second plate body (2) is provided with a plurality of micro-hole-containing through holes (9); the first plate body (1) and the second plate body (2) are attached to form a pulp feeding channel (6); the needle-containing cylinder (8) on the first plate body (1) and the micro-hole-containing through hole (9) on the second plate body (2) correspond to each other to form an annular cavity (7); the through hole (4) is connected to the pulp feeding channel (6), and the pulp feeding channel (6) is connected to the annular cavity (7); the annular groove (3) and the annular groove (5) are provided with rubber rings; the top of the first plate body (1) abuts against a dope feeding pipeline, and the top of the second plate body (2) abuts against the bottom of the first plate body (1); the length of the needle of the needle-containing cylinder (8) is the same as the length of the micro-hole in the micro-hole-containing through hole (9), the diameter of the needle of the needle-containing cylinder (8) is 0.5-0.6 mm, and the diameter of the micro-hole in the micro-hole-containing through hole (9) is 1.0-1.5 mm; the length-diameter ratio of the spinneret is 3-4:1; (3) the primary fiber is washed by multiple stages of desalting water to remove the solvent, and then the primary fiber is washed by hot desalting water and drawn; (4) the fiber after being drawn by hot water is oiled and then dried and densified by a hot roller; (5) the fiber after being dried and densified is subjected to steam drawing, and then wound to form a hollow cross section of the original yarn; (6) the original yarn with the hollow cross section is fed into a pre-oxidation furnace through a yarn unwinding frame to be pre-oxidized, and a pre-oxidized yarn is obtained; (7) the pre-oxidized yarn is sequentially subjected to carbonization in a low-temperature furnace and a high-temperature furnace to prepare a carbon fiber with a hollow cross section; the temperature of the low-temperature furnace is 580-650 ℃, the drawing ratio of the low-temperature furnace is 1.0-1.1 times, the temperature of the high-temperature furnace is 1450-1600 ℃, and the drawing ratio of the high-temperature furnace is 0.95-1.05 times.

2. The production method according to claim 1, characterized by, In step (2), the defibered and defoamed spinning dope is first defibered in a defibering kettle under a pressure of-76 Kpa, then subjected to a first-stage filtration treatment through a 3 μm filter, and then subjected to a defoaming treatment in a defoaming kettle under a pressure of-97 KPa, and finally subjected to a second-stage filtration treatment through a 1 μm filter.

3. The production method according to claim 1, characterized by, In step (2), the height of the air layer is 1-5 mm, and the air drawing ratio is 1-2 times.

4. The production method according to claim 1, characterized by, In step (2), the concentration of the coagulation bath is 45 wt%, and the temperature of the coagulation bath is 5 ℃.

5. The preparation method according to claim 1, characterized in that, In step (2), the number of holes of the through hole (4) is 1~2K, the number of holes of the needle-containing cylinder (8) and the micro-hole-containing through hole (9) is the same, and is 1~5K, the length of the needle of the needle-containing cylinder (8) and the length of the micro-hole of the micro-hole-containing through hole (9) is 0.3~1.0mm; the length of the cylinder of the needle-containing cylinder (8) is 10~15mm, and the diameter of the cylinder is 3~5mm; the length of the through hole of the micro-hole-containing through hole (9) is 5~8mm, the diameter of the through hole is 4~6mm, and the hole spacing is 1~3mm; the material of the spinneret with an annular cavity is Hastelloy C276, 316L alloy, 1Cr18Ni9Ti austenitic stainless steel, AISI316 or AISI630.

6. The method of claim 1, wherein, In step (3), the water washing tank is 3~7 levels, the water washing temperature is 20~36℃, and the draft ratio is 1~1.5 times; the hot desalination water washing and drafting is 1~3 stages, the temperature is 60~80℃, and the draft ratio is 1~2.0 times.

7. The preparation method according to claim 1, characterized in that, In step (4), the hot roller temperature is 3~7 levels, the temperature range is 100~185℃, and the hot roller pressure is 0.30~1.10MPa.

8. The method of claim 1, wherein, In step (5), the steam pressure is 0.30~0.80MPa, the steam draft ratio is 3.0~5.0 times, and the winding speed is 350~500m / min.

9. The method of claim 1, wherein, In step (6), the pre-oxidation temperature is 200℃~300℃, and the pre-oxidation draft ratio is 0.9~1.05 times.

10. The method of claim 9, wherein, The pre-oxidation temperature is 220℃~240℃.

Images