Polyacrylonitrile spinning dope, and preparation method and application thereof
A polyacrylonitrile spinning solution with high thermal stability and low viscosity was prepared by copolymerization of N-hydroxymethylacrylamide and phosphorus-containing heterocyclic functional monomers. This solved the problems of poor thermal stability and high production cost in the existing technology, and improved the preparation efficiency and performance of carbon fibers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DONGHUA UNIV
- Filing Date
- 2026-07-06
- Publication Date
- 2026-07-31
AI Technical Summary
Existing polyacrylonitrile spinning solutions have poor thermal stability, high viscosity, high production costs, and cumbersome processes, making it difficult to meet the needs of high-performance carbon fiber preparation.
Polyacrylonitrile spinning solution was prepared by copolymerizing N-hydroxymethylacrylamide and phosphorus-containing heterocyclic functional monomers with acrylonitrile. The introduction of N-hydroxymethylacrylamide promoted the initiation of the pre-oxidation reaction, and the phosphorus-containing heterocyclic functional monomers promoted the uniform progress of the stabilization reaction, forming a staged exothermic characteristic and improving thermal stability.
This method achieves high thermal stability and low viscosity of polyacrylonitrile spinning solution, reduces thermal stress accumulation during pre-oxidation, improves char formation rate and spinning process stability, and reduces production costs.
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Figure CN122483256A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of carbon fiber precursor materials, and specifically relates to a polyacrylonitrile spinning solution, its preparation method, and its application. Background Technology
[0002] Carbon fiber is a new type of high-performance inorganic material with a carbon content exceeding 92%, possessing high specific strength, high specific modulus, and excellent electrical and thermal conductivity, as well as temperature and corrosion resistance. Its regular structure, resembling graphite, combines the properties of traditional carbon materials with the processing flexibility of textile fibers, making it widely used in both defense and civilian fields. Polyacrylonitrile (PA) is currently the most important precursor for carbon fiber, accounting for over 90% of the global market. In the carbon fiber preparation process, the pre-oxidation stage of the precursor fiber significantly affects the final performance. Optimizing the pre-oxidation process and improving the thermal stability of the precursor helps alleviate concentrated exothermic phenomena, reduce fiber damage, and improve production safety. Therefore, one of the keys to preparing high-performance carbon fibers is obtaining acrylonitrile copolymer spinning dopes with high thermal stability. Industrially, binary copolymerization is commonly used to replace homopolymer polyacrylonitrile; however, traditional binary copolymerization systems still have many problems, including concentrated exothermic phenomena in the pre-oxidation process; a narrow stabilization reaction window; insufficient uniformity of the fiber's internal structure; limited improvement in char yield; and difficulty in balancing spinnability and thermal stabilization efficiency. Therefore, developing a novel copolymerization system that can synergistically regulate the pre-oxidation behavior of polyacrylonitrile, reduce concentrated exothermic reactions, and promote the uniform formation of trapezoidal structures is of great significance for the preparation of high-performance carbon fibers.
[0003] Currently, my country's carbon fiber industry still faces technological challenges in its transformation towards high performance and low cost, with precursor fiber quality control being particularly critical. Improving the thermal stability of the spinning solution is an important way to enhance precursor fiber quality. High thermal stability helps lower the cyclization initiation temperature and mitigate concentrated heat release, thereby obtaining high-quality precursor fibers with more uniform structure and fewer defects. A stable solution can also promote the formation of more regular cyclization structures during pre-oxidation, improving process uniformity and efficiency. Therefore, optimizing the thermal stability of polyacrylonitrile spinning solutions is a key step in improving carbon fiber production efficiency, reducing costs, and ensuring high product performance. It not only relates to the continuity of the spinning process but also lays the foundation for preparing high-strength, high-modulus carbon fibers by regulating the fiber microstructure, which is of great significance for applications in aerospace, new energy, and high-end equipment.
[0004] Chinese patent CN201911141138.2 (publication date: January 17, 2020) discloses a method for preparing polyacrylonitrile (PA) spinning dope. First, PA resin is mixed with a solvent to obtain a PA slurry; then, the PA slurry is fed into a twin-screw extruder for dissolution and degassing to obtain the PA spinning dope. Although this method produces a PA spinning dope with high solid content, no bubbles, and no gel, the thermal stability of the PA copolymer is not significantly improved, which may lead to a decrease in the overall performance of the carbon fiber. Furthermore, the production process is complex and unsuitable for practical production.
[0005] Chinese patent CN202111275918.3 (published on May 5, 2023) discloses a method for preparing polyacrylonitrile spinning dope. This method involves mixing polyacrylonitrile resin with a sodium thiocyanate aqueous solution at 10-25°C, dispersing and pulping the mixture at 15-25°C to form a slurry; then mixing the slurry with a sodium thiocyanate aqueous solution at 100-140°C and shearing at high speed at 80-90°C to obtain the polyacrylonitrile spinning dope. While this process produces a polyacrylonitrile spinning dope with high solids content and good fluidity, its production cost is significantly high, and the process is cumbersome. Therefore, the economic limitations of this method restrict its transformation to large-scale industrial production, limiting its commercial prospects. Summary of the Invention
[0006] The technical problem to be solved by this invention is to provide a polyacrylonitrile spinning dope, its preparation method, and its application, so as to overcome the problems of poor thermal stability and high viscosity of polyacrylonitrile spinning dopes in the prior art. The polyacrylonitrile spinning dope prepared by the method of this invention has high thermal stability and low viscosity, and the preparation process has good fluidity, short time, and low cost, and can be used for continuous production.
[0007] This invention provides a method for preparing a polyacrylonitrile spinning solution, comprising:
[0008] Acrylonitrile monomer, comonomer, initiator and solvent are mixed and copolymerized under nitrogen protection. After post-treatment, polyacrylonitrile spinning solution is obtained.
[0009] The comonomers are N-hydroxymethylacrylamide and phosphorus-containing heterocyclic functional monomers; the mass ratio of N-hydroxymethylacrylamide to phosphorus-containing heterocyclic functional monomers is 1~9:9~1.
[0010] Preferably, the phosphorus-containing heterocyclic functional monomer includes one or more of aryloxycyclotriphosphazene, vinylcyclotriphosphazene, phosphazene, 1,3,2-dioxophosphazenecyclopentane, and 1-vinylphosphazene.
[0011] More preferably, the phosphorus-containing heterocyclic functional monomer is vinylcyclotriphosphazene.
[0012] Preferably, the initiator includes one or more of azobisisobutyronitrile, azobisisovalerate, azobisisoheptanenitrile, dimethyl azobisisobutyrate, and azobisisobutyramidine hydrochloride.
[0013] Preferably, the solvent includes one or more of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and sodium thiocyanate aqueous solution.
[0014] More preferably, the solvent is an aqueous solution of sodium thiocyanate.
[0015] Preferably, the mass ratio of N-hydroxymethylacrylamide to phosphorus-containing heterocyclic functional monomer is 1:2 to 2:1.
[0016] Preferably, the acrylonitrile monomer accounts for 85% to 99.9% of the total monomer mass, more preferably 97% to 99.5%.
[0017] Preferably, the comonomer is 0.1 to 15% of the total mass of the monomers, more preferably 0.5 to 3%.
[0018] Preferably, the initiator is 0.3 to 0.5% of the total mass of the monomers.
[0019] Preferably, the total mass percentage concentration of monomers in the reaction system is 20% to 30%.
[0020] The total mass of monomers refers to the sum of the total mass of acrylonitrile monomers and comonomers.
[0021] Preferably, the copolymerization reaction is carried out at 45-65°C for 0.2-12 hours; more preferably, the copolymerization reaction is carried out at 50-65°C for 0.2-1 hours.
[0022] The post-treatment is for removing residual monomers and degassing; wherein the post-treatment process parameters include: pressure of 5~20KPa, temperature of 30~80℃, and time of 2~6 days.
[0023] This invention provides a polyacrylonitrile spinning solution prepared by the method described above.
[0024] The exothermic onset temperature of the polyacrylonitrile copolymer in the polyacrylonitrile spinning solution is 210~240℃.
[0025] This invention provides an application of the polyacrylonitrile spinning solution in the preparation of polyacrylonitrile carbon fibers.
[0026] In this invention, the hydroxymethyl and amide groups in N-hydroxymethylacrylamide can induce ionic cyclization of the polyacrylonitrile nitrile groups, reducing the activation energy and onset temperature of the cyclization reaction. Simultaneously, the P=O groups in the phosphorus-containing heterocyclic functional monomers can form a localized polar induction environment with the heterocyclic structure, promoting the uniform formation of the trapezoidal structure and improving the uniformity of thermal stabilization. The N-hydroxymethylacrylamide and the phosphorus-containing heterocyclic functional monomers form a multi-site synergistic stabilization effect, causing the polyacrylonitrile precursor to exhibit staged stabilization characteristics and dual exothermic peak behavior during pre-oxidation. This reduces thermal stress accumulation and core-sheath structure differences caused by concentrated exothermic reactions, improving thermal stability and carbon yield. This method has advantages such as low cost, easy reaction control, short polymerization time, and good stability of the resulting spinning solution, and has broad application prospects.
[0027] Beneficial effects
[0028] (1) The present invention introduces N-hydroxymethylacrylamide and phosphorus-containing heterocyclic functional monomers to copolymerize with acrylonitrile. N-hydroxymethylacrylamide promotes the initiation of the pre-oxidation reaction of polyacrylonitrile, and phosphorus-containing heterocyclic functional monomers promote the uniform stabilization reaction. The two work together to achieve the staged regulation of the pre-oxidation behavior of polyacrylonitrile, improve the pre-oxidation process of the precursor fiber, and improve the efficiency of trapezoidal structure formation.
[0029] (2) In this invention, N-hydroxymethylacrylamide and phosphorus-containing heterocyclic functional monomers work synergistically to change the exothermic behavior of polyacrylonitrile pre-oxidation process from concentrated release to staged release, so that the system exhibits the characteristics of dual exothermic peaks, realizes heat release uniformity, reduces thermal stress accumulation, and improves the stability of pre-oxidation process.
[0030] (3) The introduction of N-hydroxymethylacrylamide and phosphorus-containing heterocyclic functional monomers in this invention promotes the cyclization reaction, improves the thermal stability uniformity, reduces the difference in the core-shell structure, and promotes the uniform formation of the trapezoidal structure, thereby improving the thermal stability and char formation rate of the polyacrylonitrile precursor. Attached Figure Description
[0031] Figure 1 The DSC curves for poly(acrylonitrile-N-hydroxymethylacrylamide-vinylcyclotriphosphazene) copolymer and poly(acrylonitrile-itaconic acid) at the same feed ratio are shown in Example 4. The DSC curve refers to the differential scanning calorimetry curve. Detailed Implementation
[0032] 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.
[0033] Acrylonitrile was purchased from Shanghai Titan Technology Co., Ltd., and treated by atmospheric distillation, collecting the fraction at 77℃~78℃. N-hydroxymethylacrylamide was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Azobisisobutyronitrile was purchased from Shanghai Bide Pharmaceutical Technology Co., Ltd. Sodium thiocyanate was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Phosphorus-containing heterocyclic functional monomers were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Deionized water was prepared in the laboratory.
[0034] Example 1
[0035] A sodium thiocyanate aqueous solution, acrylonitrile (the main monomer), N-hydroxymethylacrylamide (the comonomer), vinylcyclotriphosphazene (the comonomer), and azobisisobutyronitrile (the free radical initiator) 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 (the main monomer) was 97% of the total monomer weight, N-hydroxymethylacrylamide (the comonomer) was 2% of the total monomer weight, vinylcyclotriphosphazene (the comonomer) was 1% of the total monomer weight, and azobisisobutyronitrile (the azobisisobutyronitrile) was 0.1% of the total monomer weight, resulting in 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 0.2 hours under nitrogen protection. Residual monomers and bubbles were then removed at a pressure of 15 kPa and a temperature of 60°C for 3 days to obtain a polyacrylonitrile spinning solution with high thermal stability.
[0036] Molecular weight was determined using a GPC50 gel permeation chromatography system with hexafluoroisopropanol as both solvent and mobile phase at a flow rate of 0.3 mL / min and a column temperature of 45 °C. The copolymer had a weight-average molecular weight of 212,000 and a molecular weight distribution index of 2.77. Under a nitrogen atmosphere, within a temperature range of 50 °C–350 °C and a heating rate of 10 °C / min, the polymer's DSC curve showed an exothermic onset temperature of approximately 235 °C, exhibiting two exothermic peaks with smooth and broad peaks. The carbon yield at 800 °C under a nitrogen atmosphere and a heating rate of 10 °C / min was 53.27%.
[0037] Example 2
[0038] A sodium thiocyanate aqueous solution, acrylonitrile (the main monomer), N-hydroxymethylacrylamide (the comonomer), vinylcyclotriphosphazene (the comonomer), and azobisisobutyronitrile (the free radical initiator) 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 (the main monomer) was 98% of the total monomer weight, N-hydroxymethylacrylamide (the comonomer) was 1% of the total monomer weight, vinylcyclotriphosphazene (the comonomer) was 1% of the total monomer weight, and azobisisobutyronitrile (the azobisisobutyronitrile) was 0.1% of the total monomer weight, resulting in 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 0.2 hours under nitrogen protection. Residual monomers and bubbles were then removed at a pressure of 15 kPa and a temperature of 60°C for 3 days to obtain a polyacrylonitrile spinning solution with high thermal stability.
[0039] Molecular weight was determined using a GPC50 gel permeation chromatography system with hexafluoroisopropanol as both solvent and mobile phase at a flow rate of 0.3 mL / min and a column temperature of 45 °C. The copolymer had a weight-average molecular weight of 204,000 and a molecular weight distribution index of 2.67. Under a nitrogen atmosphere, within a temperature range of 50 °C–350 °C and a heating rate of 10 °C / min, the polymer's DSC curve showed an exothermic onset temperature of approximately 220 °C, exhibiting two exothermic peaks with smooth and broad peaks. The carbon yield at 800 °C under a nitrogen atmosphere and a heating rate of 10 °C / min was 53.14%.
[0040] Example 3
[0041] A sodium thiocyanate aqueous solution, acrylonitrile (the main monomer), N-hydroxymethylacrylamide (the comonomer), vinylcyclotriphosphazene (the comonomer), and azobisisobutyronitrile (the free radical initiator) 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 (the main monomer) was 97% of the total monomer weight, N-hydroxymethylacrylamide (the comonomer) was 1% of the total monomer weight, vinylcyclotriphosphazene (the comonomer) was 2% of the total monomer weight, and azobisisobutyronitrile (the azobisisobutyronitrile) was 0.1% of the total monomer weight, resulting in 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 0.2 hours under nitrogen protection. Residual monomers and bubbles were then removed at a pressure of 15 kPa and a temperature of 60°C for 3 days to obtain a polyacrylonitrile spinning solution with high thermal stability.
[0042] Molecular weight was determined using a GPC50 gel permeation chromatography system with hexafluoroisopropanol as both solvent and mobile phase at a flow rate of 0.3 mL / min and a column temperature of 45 °C. The copolymer had a weight-average molecular weight of 217,000 and a molecular weight distribution index of 2.69. Under a nitrogen atmosphere, within a temperature range of 50 °C–350 °C and a heating rate of 10 °C / min, the polymer's DSC curve showed an exothermic onset temperature of approximately 215 °C, exhibiting two exothermic peaks with smooth and broad peaks. The carbon yield at 800 °C under a nitrogen atmosphere and a heating rate of 10 °C / min was 51.43%.
[0043] Example 4
[0044] A sodium thiocyanate aqueous solution, acrylonitrile (the main monomer), N-hydroxymethylacrylamide (the comonomer), vinylcyclotriphosphazene (the comonomer), and azobisisobutyronitrile (the free radical initiator) 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 (the main monomer) was 99.5% of the total monomer weight, N-hydroxymethylacrylamide (the comonomer) was 0.3% of the total monomer weight, vinylcyclotriphosphazene (the comonomer) was 0.2% of the total monomer weight, and azobisisobutyronitrile (the comonomer) was 0.1% 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 0.2 hours under nitrogen protection. Residual monomers and bubbles were then removed at a pressure of 15 kPa and a temperature of 60°C for 3 days to obtain a polyacrylonitrile spinning solution with high thermal stability.
[0045] Molecular weight was determined using a GPC50 gel permeation chromatography system with hexafluoroisopropanol as both solvent and mobile phase at a flow rate of 0.3 mL / min and a column temperature of 45 °C. The copolymer had a weight-average molecular weight of 219,000 and a molecular weight distribution index of 2.80. Under a nitrogen atmosphere, within a temperature range of 50 °C–350 °C and a heating rate of 10 °C / min, the polymer's DSC curve showed an exothermic onset temperature of approximately 236 °C, exhibiting two exothermic peaks with smooth and broad peaks. The carbon yield at 800 °C under a nitrogen atmosphere and a heating rate of 10 °C / min was 51.77%.
[0046] Example 5
[0047] A sodium thiocyanate aqueous solution, acrylonitrile (the main monomer), N-hydroxymethylacrylamide (the comonomer), vinylcyclotriphosphazene (the comonomer), and azobisisobutyronitrile (the free radical initiator) 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 (the main monomer) was 99.5% of the total monomer weight, N-hydroxymethylacrylamide (the comonomer) was 0.3% of the total monomer weight, vinylcyclotriphosphazene (the comonomer) was 0.2% of the total monomer weight, and azobisisobutyronitrile (the free radical initiator) was 0.1% 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 65°C for 0.2 hours under nitrogen protection. Residual monomers and bubbles were then removed at a pressure of 15 kPa, a temperature of 60°C, and a time of 3 days to obtain a polyacrylonitrile spinning solution with high thermal stability.
[0048] Molecular weight was determined using a GPC50 gel permeation chromatography system with hexafluoroisopropanol as both solvent and mobile phase at a flow rate of 0.3 mL / min and a column temperature of 45 °C. The copolymer had a weight-average molecular weight of 215,000 and a molecular weight distribution index of 2.87. Under a nitrogen atmosphere, within a temperature range of 50 °C–350 °C and a heating rate of 10 °C / min, the polymer's DSC curve showed an exothermic onset temperature of approximately 228 °C, exhibiting two exothermic peaks with smooth and broad peaks. The carbon yield at 800 °C under a nitrogen atmosphere and a heating rate of 10 °C / min was 53.46%.
[0049] Example 6
[0050] A sodium thiocyanate aqueous solution, acrylonitrile (the main monomer), N-hydroxymethylacrylamide (the comonomer), vinylcyclotriphosphazene (the comonomer), and azobisisobutyronitrile (the free radical initiator) 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 (the main monomer) was 99.5% of the total monomer weight, N-hydroxymethylacrylamide (the comonomer) was 0.3% of the total monomer weight, vinylcyclotriphosphazene (the comonomer) was 0.2% of the total monomer weight, and azobisisobutyronitrile (the azobisisobutyronitrile) was 0.1% 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 55°C for 0.2 hours under nitrogen protection. Residual monomers and bubbles were then removed at a pressure of 15 kPa, a temperature of 60°C, and a time of 3 days to obtain a polyacrylonitrile spinning solution with high thermal stability.
[0051] Molecular weight was determined using a GPC50 gel permeation chromatography system with hexafluoroisopropanol as both solvent and mobile phase at a flow rate of 0.3 mL / min and a column temperature of 45 °C. The copolymer had a weight-average molecular weight of 212,000 and a molecular weight distribution index of 2.73. Under a nitrogen atmosphere, within a temperature range of 50 °C–350 °C and a heating rate of 10 °C / min, the polymer's DSC curve showed an exothermic onset temperature of approximately 218 °C, exhibiting two exothermic peaks with smooth and broad peaks. The carbon yield at 800 °C under a nitrogen atmosphere and a heating rate of 10 °C / min was 54.25%.
[0052] Example 7
[0053] A sodium thiocyanate aqueous solution, acrylonitrile (the main monomer), N-hydroxymethylacrylamide (the comonomer), vinylcyclotriphosphazene (the comonomer), and azobisisobutyronitrile (the free radical initiator) 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 (the main monomer) was 99.5% of the total monomer weight, N-hydroxymethylacrylamide (the comonomer) was 0.3% of the total monomer weight, vinylcyclotriphosphazene (the comonomer) was 0.2% of the total monomer weight, and azobisisobutyronitrile (the azobisisobutyronitrile) was 0.1% 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 50°C for 0.2 hours under nitrogen protection. Residual monomers and bubbles were then removed at a pressure of 15 kPa, a temperature of 60°C, and a time of 3 days to obtain a polyacrylonitrile spinning solution with high thermal stability.
[0054] Molecular weight was determined using a GPC50 gel permeation chromatography system with hexafluoroisopropanol as both solvent and mobile phase at a flow rate of 0.3 mL / min and a column temperature of 45 °C. The copolymer had a weight-average molecular weight of 216,000 and a molecular weight distribution index of 2.67. Under a nitrogen atmosphere, within a temperature range of 50 °C–350 °C and a heating rate of 10 °C / min, the polymer's DSC curve showed an exothermic onset temperature of approximately 224 °C, exhibiting two exothermic peaks with smooth and broad peaks. The carbon yield at 800 °C under a nitrogen atmosphere and a heating rate of 10 °C / min was 52.26%.
[0055] Example 8
[0056] A sodium thiocyanate aqueous solution, acrylonitrile (the main monomer), N-hydroxymethylacrylamide (the comonomer), vinylcyclotriphosphazene (the comonomer), and azobisisobutyronitrile (the free radical initiator) 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 (the main monomer) was 99.5% of the total monomer weight, N-hydroxymethylacrylamide (the comonomer) was 0.3% of the total monomer weight, vinylcyclotriphosphazene (the comonomer) was 0.2% of the total monomer weight, and azobisisobutyronitrile (the azobisisobutyronitrile) was 0.1% 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 65°C for 0.3 hours under nitrogen protection. Residual monomers and bubbles were then removed at a pressure of 15 kPa and a temperature of 60°C for 3 days to obtain a polyacrylonitrile spinning solution with high thermal stability.
[0057] Molecular weight was determined using a GPC50 gel permeation chromatography system with hexafluoroisopropanol as both solvent and mobile phase at a flow rate of 0.3 mL / min and a column temperature of 45 °C. The copolymer had a weight-average molecular weight of 219,000 and a molecular weight distribution index of 2.74. Under a nitrogen atmosphere, within a temperature range of 50 °C–350 °C and a heating rate of 10 °C / min, the polymer's DSC curve showed an exothermic onset temperature of approximately 220 °C, exhibiting two exothermic peaks with smooth and broad peaks. The carbon yield at 800 °C under a nitrogen atmosphere and a heating rate of 10 °C / min was 51.29%.
[0058] Example 9
[0059] A sodium thiocyanate aqueous solution, acrylonitrile (the main monomer), N-hydroxymethylacrylamide (the comonomer), vinylcyclotriphosphazene (the comonomer), and azobisisobutyronitrile (the free radical initiator) 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 (the main monomer) was 99.5% of the total monomer weight, N-hydroxymethylacrylamide (the comonomer) was 0.3% of the total monomer weight, vinylcyclotriphosphazene (the comonomer) was 0.2% of the total monomer weight, and azobisisobutyronitrile (the azobisisobutyronitrile) was 0.1% 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 65°C for 0.4 hours under nitrogen protection. Residual monomers and bubbles were then removed at a pressure of 15 kPa and a temperature of 60°C for 3 days to obtain a polyacrylonitrile spinning solution with high thermal stability.
[0060] Molecular weight determination was performed using a GPC50 gel permeation chromatography system with hexafluoroisopropanol as both solvent and mobile phase at a flow rate of 0.3 mL / min and a column temperature of 45 °C. The copolymer had a weight-average molecular weight of 221,000 and a molecular weight distribution index of 2.74. Under a nitrogen atmosphere, within a temperature range of 50 °C–350 °C and a heating rate of 10 °C / min, the polymer's DSC curve showed an exothermic onset temperature of approximately 220 °C, exhibiting two exothermic peaks with smooth and broad peaks. The carbon yield at 800 °C under a nitrogen atmosphere and a heating rate of 10 °C / min was 53.25%.
[0061] Example 10
[0062] A sodium thiocyanate aqueous solution, acrylonitrile (the main monomer), N-hydroxymethylacrylamide (the comonomer), vinylcyclotriphosphazene (the comonomer), and azobisisobutyronitrile (the free radical initiator) 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 (the main monomer) was 99.5% of the total monomer weight, N-hydroxymethylacrylamide (the comonomer) was 0.3% of the total monomer weight, vinylcyclotriphosphazene (the comonomer) was 0.2% of the total monomer weight, and azobisisobutyronitrile (the azobisisobutyronitrile) was 0.1% 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 65°C for 0.5 hours under nitrogen protection. Residual monomers and bubbles were then removed at a pressure of 15 kPa, a temperature of 60°C, and a time of 3 days to obtain a polyacrylonitrile spinning solution with high thermal stability.
[0063] Molecular weight was determined using a GPC50 gel permeation chromatography system with hexafluoroisopropanol as both solvent and mobile phase at a flow rate of 0.3 mL / min and a column temperature of 45 °C. The copolymer had a weight-average molecular weight of 214,000 and a molecular weight distribution index of 2.75. Under a nitrogen atmosphere, within a temperature range of 50 °C–350 °C and a heating rate of 10 °C / min, the polymer's DSC curve showed an exothermic onset temperature of approximately 226 °C, exhibiting two exothermic peaks with a smooth and gradual transition. The carbon yield at 800 °C under a nitrogen atmosphere and a heating rate of 10 °C / min was 51.19%.
[0064] Comparative Example 1
[0065] Compared with Example 4, the only difference is that the comonomer is replaced with itaconic acid, while the experimental and testing methods are the same.
[0066] like Figure 1As shown, the curves of poly(acrylonitrile-N-hydroxymethylacrylamide-vinylcyclotriphosphazene) copolymer and poly(acrylonitrile-itaconic acid) at the same feed ratio indicate that poly(acrylonitrile-N-hydroxymethylacrylamide-vinylcyclotriphosphazene) significantly reduces the initial exothermic temperature of the cyclization reaction and endows the copolymer with a unique two-stage exothermic peak characteristic, reducing the risk of thermal stress accumulation during the thermal stabilization process and exhibiting better thermal performance.
Claims
1. A method for preparing a polyacrylonitrile spinning solution, characterized in that, include: Acrylonitrile monomer, comonomer, initiator and solvent are mixed and copolymerized under nitrogen protection. After post-treatment, polyacrylonitrile spinning solution is obtained. The comonomers are N-hydroxymethylacrylamide and phosphorus-containing heterocyclic functional monomers; the mass ratio of N-hydroxymethylacrylamide to phosphorus-containing heterocyclic functional monomers is 1~9:9~1.
2. The preparation method according to claim 1, characterized in that, The phosphorus-containing heterocyclic functional monomers include one or more of aryloxycyclotriphosphazene, vinylcyclotriphosphazene, phosphazene, 1,3,2-dioxophosphazenecyclopentane, and 1-vinylphosphazene.
3. The preparation method according to claim 1, characterized in that, The initiator includes one or more of azobisisobutyronitrile, azobisisovalerate, azobisisoheptanenitrile, dimethyl azobisisobutyrate, and azobisisobutyramidine hydrochloride; the solvent includes one or more of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and sodium thiocyanate aqueous solution.
4. The preparation method according to claim 1, characterized in that, The mass ratio of the N-hydroxymethylacrylamide to the phosphorus-containing heterocyclic functional monomer is 1:2 to 2:
1.
5. The preparation method according to claim 1, characterized in that, The acrylonitrile monomer accounts for 85% to 99.9% of the total monomer mass; the comonomer accounts for 0.1% to 15% of the total monomer mass; and the initiator accounts for 0.3% to 0.5% of the total monomer mass.
6. The preparation method according to claim 1, characterized in that, The total mass percentage concentration of monomers in the reaction system is 20%~30%.
7. The preparation method according to claim 1, characterized in that, The copolymerization reaction is carried out at 45~65℃ for 0.2~12h.
8. The preparation method according to claim 1, characterized in that, The post-processing includes the removal of residual monomers and defoaming. The post-processing parameters include: pressure of 5~20 kPa, temperature of 30~80℃, and time of 2~6 days.
9. A polyacrylonitrile spinning solution prepared by the method of claim 1.
10. The application of the polyacrylonitrile spinning solution of claim 9 in the preparation of polyacrylonitrile carbon fibers.