High-spinnability polyacrylonitrile spinning dope and preparation method thereof

Abstract

The application relates to a high-spinnability polyacrylonitrile spinning solution and a preparation method thereof. The composition of the spinning solution comprises acrylonitrile monomers, second copolymer monomers and third copolymer monomers; wherein the second copolymer monomers are sulfonic acid group type monomers; and the third copolymer monomers are long-chain benzene of olefin type. The raw material composition of the application is low in cost, the preparation process is simple, the hydrophilicity of the obtained spinning solution and the cyclization degree of the pre-oxidized fiber are greatly improved, and the application has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber, and specifically relates to a highly spinnable polyacrylonitrile spinning solution and its preparation method. Background Technology

[0002] Carbon fiber is an inorganic fibrous material composed of incompletely sheet-like graphite crystals stacked along the fiber axis, containing over 90% carbon. Carbon fiber possesses numerous advantages, such as high strength and modulus, good heat resistance, chemical and dimensional stability, and a low coefficient of linear expansion. It is a crucial industrial fiber, commonly used as a reinforcement and insulation material in various composite materials including carbon, resins, and ceramics. The mechanical properties of carbon fiber are almost unaffected by high temperatures. Its earliest applications were in defense and aerospace, playing a vital role in national development. In the sports and leisure industry, carbon fiber is used in bicycles, fishing rods, tennis rackets, golf clubs, and yachts, accounting for approximately 16% of total consumption. Furthermore, global demand for polyacrylonitrile-based carbon fiber continues to grow.

[0003] The quality of carbon fiber is directly determined by the structure and properties of the precursor fiber, and the properties of polyacrylonitrile carbon fiber precursor fiber are closely related to the preparation of the spinning solution. In terms of manufacturing processes, existing carbon fiber spinning solutions mostly employ binary or ternary copolymerization. This is because the homopolymerized acrylonitrile polymer has relatively high rigidity, resulting in poor spinnability of the solution. Furthermore, the exothermic reaction during the subsequent pre-oxidation and carbonization processes tends to be too concentrated, leading to fiber breakage during the oxidation, carbonization, and stretching process, thus reducing the mechanical properties of the carbon fiber. Therefore, comonomers are typically used to improve the spinnability of the polyacrylonitrile solution and mitigate the exothermic reaction during oxidation and carbonization.

[0004] Chinese Patent CN202110434140.X (published on October 25, 2022) discloses a polymer for polyacrylonitrile-based large-tow carbon fibers, a preparation method, and polyacrylonitrile-based large-tow carbon fibers. This invention introduces a fourth comonomer, a long-chain fatty acid ester, which reduces the cohesive energy of the polyacrylonitrile copolymer and improves spinnability. While this method effectively improves the spinnability of polyacrylonitrile, excessive components in the comonomer are detrimental to the formation of cyclic graphite-like structures during carbon fiber preparation. Furthermore, introducing a long-chain fatty acid ester as the fourth comonomer increases structural defects in the carbon fibers, leading to a decrease in their mechanical properties.

[0005] Chinese patent CN201010191644.5 (published on October 20, 2010) discloses a method for preparing a hydrophilic spinning solution for polyacrylonitrile-based carbon fibers. This method uses ammonium itaconic acid ester, which has stronger hydrophilicity, instead of itaconic acid ester as a comonomer, resulting in a spinning solution with higher hydrophilicity than itaconic acid ester. While this method avoids the problem of a looser coagulated fiber structure caused by the increased difference in diffusion rates between solvent and non-solvent in the fiber due to decreased hydrophilicity of the spinning solution, the production cost of this ammonium itaconic acid ester is high because it is an ionic liquid, which is not conducive to subsequent large-scale industrial production. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a high spinnability polyacrylonitrile spinning solution and its preparation method, so as to overcome the defect of poor hydrophilicity of polyacrylonitrile copolymers in the prior art.

[0007] This invention provides a highly spinnable polyacrylonitrile spinning solution, the spinning solution comprising an acrylonitrile monomer, a second comonomer, and a third comonomer; wherein the second comonomer is a sulfonic acid monomer; and the third comonomer is an olefinic long-chain benzene.

[0008] Preferably, the sulfonic acid monomer is at least one of 2-sulfofumaric acid (24674-75-7), (Z)-3-sulfo-2-acrylic acid (875610-90-5), (E)-3-sulfo-2-acrylic acid (875610-88-1), or 2-sulfo-2-butenedioic acid (65319-67-7).

[0009] Preferably, the olefinic long-chain benzene is at least one selected from 4-n-octylstyrene, 4-isobutylstyrene, 2-methyl-4-n-butylstyrene, 2-n-pentylstyrene, 3-n-butylstyrene, and 1-methyl-5-n-butylstyrene.

[0010] Preferably, the mass content of acrylonitrile monomer in the spinning solution is 90%-99%, more preferably 95%-98%; the mass content of the second comonomer is 1%-8%, more preferably 1.5%-4%; and the mass content of the third comonomer is 1%-8%, more preferably 1%-4%.

[0011] This invention also provides a method for preparing a highly spinnable polyacrylonitrile spinning solution, comprising the following steps:

[0012] Acrylonitrile monomer, second comonomer, third comonomer and initiator are solution polymerized in a solvent to remove residual monomers and bubbles, resulting in a highly spinnable polyacrylonitrile spinning dope.

[0013] Preferably, the initiator is at least one selected from azobisisobutyronitrile, azobisisovalerate, azobisisoheptanenitrile, dimethyl azobisisobutyrate, and ammonium persulfate; the amount of the initiator is 0.2% to 0.5% of the amount of acrylonitrile, preferably 0.2% to 0.4%.

[0014] Preferably, the solvent is at least one selected from dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

[0015] Preferably, the solution polymerization is carried out in a nitrogen atmosphere at a temperature of 45–65°C, more preferably 50–65°C, for a time of 6–40 h, more preferably 10–25 h.

[0016] Preferably, the process for removing residual monomers is as follows: the solution is distilled under nitrogen protection, and the residual monomer content is controlled to be below 0.15%.

[0017] Preferably, the process for removing air bubbles is as follows: pressure of 8-25 kPa, temperature of 30-100°C, and time of 2-5 days.

[0018] This invention, based on the binary copolymerization of acrylonitrile and sulfonic acid monomers, introduces a third comonomer, olefinic long-chain benzene, and utilizes the volume effect of the side groups to reduce the cohesive energy of the polyacrylonitrile copolymer molecular weight, thereby improving the spinnability of polyacrylonitrile-based carbon fibers. It has the advantages of low cost, good pre-oxidation cyclization performance, easy reaction control, and good hydrophilicity.

[0019] Beneficial effects

[0020] (1) This invention introduces acrylic monomers containing sulfonic acid groups. The sulfonic acid groups can weaken the intramolecular and intermolecular dipole interaction forces of the cyano group in the polyacrylonitrile molecule, thereby reducing the activation energy of the fiber reaction during the preparation of carbon fibers. This is beneficial to promote cyclization and crosslinking, improve the density and uniformity of the fiber, reduce the chance of main chain breakage, and ensure the strength of the carbon fiber.

[0021] (2) By introducing a third comonomer, this invention improves the pre-oxidation process of PAN precursor fibers, enabling cyclization reactions to be initiated at lower temperatures. Furthermore, the introduction of the third comonomer makes the growth reaction exhibit an ionic mechanism, mitigating the exothermic reaction during the pre-oxidation process and making it easier to control the pre-oxidation process and structural transformation.

[0022] (3) The third comonomer used in this invention is an olefinic long-chain benzene with active carbon-carbon double bonds, which is beneficial for forming copolymers with various olefinic monomers. The volume effect of aromatic side groups can be used to reduce the cohesive energy in the polyacrylonitrile copolymer molecule, thereby improving the spinnability of polyacrylonitrile-based carbon fibers.

[0023] (4) The present invention has low cost and simple preparation process. The contact angle between the obtained spinning solution and water after film formation can reach 35° to 50°, and the hydrophilicity of the polymer chain is greatly improved, making it suitable for preparing multifunctional polyacrylonitrile-based carbon fiber precursor. Detailed Implementation

[0024] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0025] Comparative Example 1

[0026] The solvent dimethyl sulfoxide, the main monomer acrylonitrile, the second comonomer 2-sulfofumaric acid, and the free radical initiator azobisisobutyronitrile (AIBN) were added to a reactor equipped with a condenser and a mechanical stirrer. The weight percentage ratio of the added raw materials was as follows: acrylonitrile as the main monomer was 98% of the total monomer weight, 2% of the second comonomer 2-sulfofumaric acid was 2% of the total monomer weight, and AIBN was 0.75% of the total monomer weight, resulting in a total monomer concentration of 25%. The mixture was stirred and mixed at room temperature, bubbled with nitrogen for 20 minutes, and then reacted at a constant temperature of 65°C for 24 hours under nitrogen protection. Residual monomers and bubbles were then removed to obtain a high-spinnable polyacrylonitrile spinning solution. The process for removing residual monomers involved distilling the solution under nitrogen protection, controlling the residual monomer content to below 0.15%. The process for removing bubbles involved a pressure of 8 kPa, a temperature of 30°C, and a time of 5 days. The spinning solution has a weight-average molecular weight of 271,000 and a contact angle with water of 51.6° after film formation.

[0027] Example 1

[0028] The solvent dimethyl sulfoxide, the main monomer acrylonitrile, the second comonomer 2-sulfono-2-butenedioic acid, and the free radical initiator azobisisobutyronitrile (AIBN) were added to a reactor equipped with a condenser and a mechanical stirrer. The weight percentage ratio of the added raw materials was as follows: acrylonitrile as the main monomer was 97% of the total monomer weight, 2-sulfono-2-butenedioic acid as the second comonomer was 3% of the total monomer weight, and azobisisobutyronitrile was 0.75% of the total monomer weight, resulting in a total monomer concentration of 25%. The mixture was stirred at room temperature, bubbled with nitrogen for 20 minutes, and then reacted at a constant temperature of 65°C for 24 hours under nitrogen protection. Residual monomers and bubbles were then removed to obtain a high-spinnable polyacrylonitrile spinning solution. The process for removing residual monomers involved distilling the solution under nitrogen protection, controlling the residual monomer content to below 0.15%. The process for removing bubbles involved a pressure of 8 kPa, a temperature of 40°C, and a time of 5 days. The spinning solution has a weight-average molecular weight of 265,000 and a contact angle of 40.0° with water after film formation.

[0029] Example 2

[0030] The solvent dimethyl sulfoxide, the main monomer acrylonitrile, the second comonomer 2-sulfofumaric acid, the third comonomer 4-n-octylstyrene, and the free radical initiator azobisisobutyronitrile (AIBN) were added to a reactor equipped with a condenser and a mechanical stirrer. The weight percentage ratio of the added raw materials was as follows: acrylonitrile as the main monomer was 98% of the total monomer weight, 2-sulfofumaric acid as the second comonomer was 1% of the total monomer weight, 4-n-octylstyrene as the third comonomer was 1% of the total monomer weight, and azobisisobutyronitrile was 0.75% of the total monomer weight, resulting in a total monomer concentration of 25%. The mixture was stirred at room temperature, bubbled with nitrogen for 20 minutes, and then reacted at a constant temperature of 65°C for 24 hours under nitrogen protection. Residual monomers and bubbles were then removed to obtain a high-spinnable polyacrylonitrile spinning solution. The process for removing residual monomers involved distilling the solution under nitrogen protection, controlling the residual monomer content to below 0.15%. The degassing process is as follows: pressure 10 kPa, temperature 50°C, time 4 days. The spinning solution has a weight-average molecular weight of 242,000, and the contact angle with water after film formation is 38.0°.

[0031] Example 3

[0032] The solvent dimethyl sulfoxide, the main monomer acrylonitrile, the second comonomer 2-sulfofumaric acid, the third comonomer 4-n-octylstyrene, and the free radical initiator azobisisobutyronitrile (AIBN) were added to a reactor equipped with a condenser and a mechanical stirrer. The weight percentage ratio of the added raw materials was as follows: acrylonitrile as the main monomer was 99% of the total monomer weight, 2-sulfofumaric acid as the second comonomer was 0.75% of the total monomer weight, 4-n-octylstyrene as the third comonomer was 0.25% of the total monomer weight, and AIBN was 0.25% of the total monomer weight, resulting in a total monomer concentration of 23.5%. The mixture was stirred at room temperature, bubbled with nitrogen for 20 minutes, and then reacted at a constant temperature of 50°C for 36 hours under nitrogen protection. Residual monomers and bubbles were then removed to obtain a high-spinnable polyacrylonitrile spinning solution. The process for removing residual monomers involved distilling the solution under nitrogen protection, controlling the residual monomer content to below 0.15%. The degassing process is as follows: pressure 15 kPa, temperature 60°C, time 4 days. The spinning solution has a weight-average molecular weight of 562,000, and the contact angle with water after film formation is 46.0°.

[0033] Example 4

[0034] The solvent dimethyl sulfoxide, the main monomer acrylonitrile, the second comonomer 2-sulfofumaric acid, the third comonomer 4-n-octylstyrene, and the free radical initiator azobisisobutyronitrile (AIBN) were added to a reactor equipped with a condenser and a mechanical stirrer. The weight percentage ratio of the added raw materials was as follows: acrylonitrile as the main monomer was 90% of the total monomer weight, 2-sulfofumaric acid as the second comonomer was 5% of the total monomer weight, 4-n-octylstyrene as the third comonomer was 5% of the total monomer weight, and azobisisobutyronitrile was 0.5% of the total monomer weight, with a total monomer concentration of 20%. The mixture was stirred at room temperature, bubbled with nitrogen for 20 minutes, and then reacted at a constant temperature of 60°C for 24 hours under nitrogen protection. Residual monomers and bubbles were then removed to obtain a high-spinnable polyacrylonitrile spinning solution. The process for removing residual monomers involved distilling the solution under nitrogen protection, controlling the residual monomer content to below 0.15%. The degassing process is as follows: pressure 18 kPa, temperature 65°C, time 3 days. The spinning solution has a weight-average molecular weight of 104,000, and the contact angle with water after film formation is 34.5°.

[0035] Example 5

[0036] The solvent dimethylformamide, the main monomer acrylonitrile, the second comonomer (Z)-3-sulfono-2-acrylic acid, the third comonomer 2-methyl-4-n-butylstyrene, and the free radical initiator azobisisobutyronitrile (AIBN) were added to a reactor equipped with a condenser and a mechanical stirrer. The weight percentage ratio of the added raw materials was as follows: acrylonitrile as the main monomer was 97% of the total monomer weight, the second comonomer (Z)-3-sulfono-2-acrylic acid was 1.5% of the total monomer weight, the third comonomer 2-methyl-4-n-butylstyrene was 1.5% of the total monomer weight, and the amount of AIBN was 0.75% of the total monomer weight, with a total monomer concentration of 20%. The mixture was stirred and mixed at room temperature, bubbled with nitrogen for 20 minutes, and then reacted at a constant temperature of 60°C for 24 hours under nitrogen protection. Residual monomers and bubbles were then removed to obtain a high-spinnable polyacrylonitrile spinning solution. The process for removing residual monomers involved distilling the solution under nitrogen protection, controlling the residual monomer content to below 0.15%. The degassing process is as follows: pressure 20 kPa, temperature 50°C, time 3 days. The spinning solution has a weight-average molecular weight of 243,000, and the contact angle with water after film formation is 47.5°.

[0037] Example 6

[0038] The solvent dimethylformamide, the main monomer acrylonitrile, the second comonomer (Z)-3-sulfono-2-acrylic acid, the third comonomer 2-n-pentylstyrene, and the free radical initiator azobisisovalerate were added to a reactor equipped with a condenser and a mechanical stirrer. The weight percentage ratio of the added raw materials was as follows: acrylonitrile as the main monomer was 97% of the total monomer weight, the second comonomer (Z)-3-sulfono-2-acrylic acid was 1.5% of the total monomer weight, the third comonomer 2-n-pentylstyrene was 1.5% of the total monomer weight, and the azobisisovalerate was 0.75% of the total monomer weight, with a total monomer concentration of 20%. The mixture was stirred at room temperature, bubbled with nitrogen for 20 minutes, and then reacted at a constant temperature of 60°C for 24 hours under nitrogen protection. Residual monomers and bubbles were then removed to obtain a high-spinnable polyacrylonitrile spinning solution. The process for removing residual monomers involved distilling the solution under nitrogen protection, controlling the residual monomer content to below 0.15%. The degassing process is as follows: pressure 20 kPa, temperature 70°C, time 3 days. The spinning solution has a weight-average molecular weight of 234,000, and the contact angle with water after film formation is 47.0°.

[0039] Example 7

[0040] The solvent dimethylformamide, the main monomer acrylonitrile, the second comonomer (E)-3-sulfono-2-acrylic acid, the third comonomer 4-isobutylstyrene, and the free radical initiator azobisisovalerate were added to a reactor equipped with a condenser and a mechanical stirrer. The weight percentage ratio of the added raw materials was as follows: acrylonitrile as the main monomer was 97% of the total monomer weight, the second comonomer (E)-3-sulfono-2-acrylic acid was 1.5% of the total monomer weight, the third comonomer 4-isobutylstyrene was 1.5% of the total monomer weight, and the azobisisovalerate was 0.75% of the total monomer weight, with a total monomer concentration of 20%. The mixture was stirred at room temperature, bubbled with nitrogen for 20 minutes, and then reacted at a constant temperature of 60°C for 24 hours under nitrogen protection. Residual monomers and bubbles were then removed to obtain a high-spinnable polyacrylonitrile spinning solution. The process for removing residual monomers involved distilling the solution under nitrogen protection, controlling the residual monomer content to below 0.15%. The degassing process is as follows: pressure 22 kPa, temperature 80°C, time 2 days. The spinning solution has a weight-average molecular weight of 276,000, and the contact angle with water after film formation is 46.5°.

[0041] Example 8

[0042] The solvent dimethylformamide, the main monomer acrylonitrile, the second comonomer 2-sulfono-2-butenedioic acid, the third comonomer 1-methyl-5-n-butylstyrene, and the free radical initiator azobisisoheptanenitrile were added to a reactor equipped with a condenser and a mechanical stirrer. The weight percentage ratio of the added raw materials was as follows: acrylonitrile as the main monomer was 97% of the total monomer weight, 2-sulfono-2-butenedioic acid as the second comonomer was 1.5% of the total monomer weight, 1-methyl-5-n-butylstyrene as the third comonomer was 1.5% of the total monomer weight, and azobisisoheptanenitrile was 0.75% of the total monomer weight, with a total monomer concentration of 20%. The mixture was stirred at room temperature, bubbled with nitrogen for 20 minutes, and then reacted at a constant temperature of 60°C for 24 hours under nitrogen protection. Residual monomers and bubbles were then removed to obtain a high-spinnable polyacrylonitrile spinning solution. The process for removing residual monomers is as follows: the solution is distilled under nitrogen protection, and the residual monomer content is controlled below 0.15%. The process for removing bubbles is as follows: pressure 25 kPa, temperature 100℃, time 2 days. The spinning solution has a weight-average molecular weight of 298,000, and the contact angle with water after film formation is 45.5°.

[0043] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A highly spinnable polyacrylonitrile spinning solution, characterized in that: The spinning solution comprises an acrylonitrile monomer, a second comonomer, and a third comonomer; wherein the second comonomer is a sulfonic acid monomer; the third comonomer is an olefinic long-chain benzene; the sulfonic acid monomer is at least one of 2-sulfofumaric acid, (Z)-3-sulfo-2-acrylic acid, (E)-3-sulfo-2-acrylic acid, or 2-sulfono-2-butenedioic acid; and the olefinic long-chain benzene is at least one of 4-n-octylstyrene, 4-isobutylstyrene, 2-methyl-4-n-butylstyrene, 2-n-pentylstyrene, 3-n-butylstyrene, and 1-methyl-5-n-butylstyrene.

2. The high spinnability polyacrylonitrile spinning solution according to claim 1, characterized in that: The spinning solution contains 90%-99% acrylonitrile monomer, 1%-8% second comonomer, and 1%-8% third comonomer.

3. A method for preparing a highly spinnable polyacrylonitrile spinning solution as described in any one of claims 1-2, comprising the following steps: Acrylonitrile monomer, second comonomer, third comonomer and initiator are solution polymerized in a solvent to remove residual monomers and bubbles, resulting in a highly spinnable polyacrylonitrile spinning dope.

4. The preparation method according to claim 3, characterized in that: The initiator is at least one selected from azobisisobutyronitrile, azobisisovalerate, azobisisoheptanenitrile, dimethyl azobisisobutyrate, and ammonium persulfate; the amount of the initiator is 0.2% to 0.5% of the amount of acrylonitrile.

5. The preparation method according to claim 3, characterized in that: The solvent is at least one of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

6. The preparation method according to claim 3, characterized in that: The total concentration of the acrylonitrile monomer, the second comonomer, and the third comonomer is 20%-25%.

7. The preparation method according to claim 3, characterized in that: The solution polymerization was carried out under a nitrogen atmosphere at a temperature of 45–65°C for 6–40 hours.

8. The preparation method according to claim 3, characterized in that: The process for removing residual monomers is as follows: the solution is distilled under nitrogen protection, and the residual monomer content is controlled below 0.15%; the process for removing bubbles is as follows: pressure is 8-25 kPa, temperature is 30-100℃, and time is 2-5 days.