Low-cost pan-based carbon fiber precursor by inside-outside synergistic plasticization melt spinning and preparation method thereof

Abstract

The application provides a low-cost PAN-based carbon fiber precursor prepared by internal-external synergistic plasticizing melt spinning and a preparation method, the melt-spun PAN fiber is prepared by a synergistic internal-external plasticizing method, a proper amount of a novel comonomer AMPS is added to polymerize with AN to prepare a P(AN-co-AMPS) copolymer as a melt spinning raw material, the molecular interaction between PAN is reduced from the perspective of internal plasticizing method, and the PAN precursor pre-oxidation in the later stage is facilitated; the addition amount of an external plasticizing agent (ethylene carbonate, EC) is reduced from the perspective of external plasticizing method, and the structure defects of the precursor caused in the plasticizing agent removal process are reduced. In addition, the application uses a small amount of solvent, is environment-friendly, has high spinning efficiency, is low in manufacturing cost, helps to promote the large-scale application of carbon fibers in civilian fields, and is a PAN precursor preparation method with wide development prospect. The low-cost PAN-based carbon fiber precursor prepared by the preparation method has a fiber diameter of about 100 mu m, a tensile strength of 108.8 MPa, a tensile modulus of 3267.3 MPa, and a breaking elongation of 43.4%.

Description

Technical Field

[0001] This invention belongs to the field of polyacrylonitrile melt spinning technology, and in particular relates to a low-cost PAN-based carbon fiber precursor and preparation method for melt spinning with synergistic internal and external plasticization. Background Technology

[0002] Carbon fiber has many advantages and is widely used in various fields. Among them, PAN-based carbon fiber dominates the carbon fiber market, with almost 90% of commercially available carbon fiber being made from PAN polymers. The advantages of PAN polymers lie in their fast pyrolysis rate, resulting in carbon fibers with high carbon yield, fewer defects, and higher strength and modulus.

[0003] Currently, industrially, wet spinning and dry-jet wet spinning methods are commonly used to prepare PAN precursor fibers. These processes require large amounts of solvents and multiple operating units. Precursor fiber production accounts for 45-60% of the total cost of carbon fiber production; therefore, reducing precursor fiber production costs is one of the key points to achieving low-cost carbon fiber production. Melt spinning, as a low-cost and environmentally friendly spinning method, has gradually attracted attention. Compared with the two spinning methods mentioned above, melt spinning has the advantages of not requiring large amounts of solvents, having a fast spinning speed, lower equipment requirements, and producing PAN precursor fibers with less difference in core-sheath structure, thus improving the uniformity of heat transfer in subsequent heat treatment processes. However, because PAN homopolymers undergo decomposition followed by melting during heating, it is necessary to lower the melting point of PAN to achieve melt spinning.

[0004] Chinese patent CN101545148A discloses a melt spinning method for polyacrylonitrile (PAN) using imidazole-type ionic liquid as a plasticizer, comprising: (1) mixing polyacrylonitrile powder dried to anhydrous state with the ionic liquid uniformly; (2) adding the mixture to the hopper of a twin-screw spinning machine, adjusting the screw speed to 40-120 r / min, setting the spinning temperature to 170-220℃, and performing melt spinning; the filaments spun by the spinneret are not subjected to a water bath, but are directly subjected to dry heat stretching, wherein the stretching temperature is 80-180℃, and the stretching ratio is 1-8 times; (3) washing the stretched fibers with water, and then heat-setting and winding to obtain polyacrylonitrile fibers. This method is an externally plasticized melt spinning method, which does not consider the high cohesive energy of the PAN homopolymer itself, the high content of the added plasticizer, the complex and costly subsequent extraction process, and the concentrated heat release problem in the later pre-oxidation process of melt-spun PAN homopolymer. Summary of the Invention

[0005] The first objective of this invention is to provide a method for preparing low-cost PAN-based carbon fiber precursor fibers through melt spinning with synergistic internal and external plasticization.

[0006] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution:

[0007] A method for preparing low-cost PAN-based carbon fiber precursor by melt spinning with synergistic internal and external plasticization includes the following steps:

[0008] S1. Preparation of raw materials for melt spinning

[0009] Vacuum-dried P(AN-co-AMPS) copolymer powder and ethylene carbonate were mixed in a certain proportion and then heated in a nitrogen atmosphere for a certain time to obtain melt spinning raw material.

[0010] S2, melt spinning

[0011] Before melt spinning, deionized water is poured into an electric hot water bath and heated to the specified temperature; the vertical extruder is heated to the spinning temperature and preheated at a constant temperature for a certain period of time.

[0012] The molten spinning raw material obtained in step S1 is fed into a vertical extruder. After the melt is extruded, it is stretched by hot water to simultaneously complete the stretching of fibers and the removal of external plasticizers.

[0013] Finally, it is rolled up into threads.

[0014] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0015] As a preferred technical solution of the present invention: In step S1, the P(AN-co-AMPS) copolymer powder is prepared by the following method:

[0016] The free radical solution polymerization method was adopted, and the solvent DMSO, initiator AIBN, reactant AN and AMPS were added into the reactor in a certain ratio: the system was evacuated and purged with nitrogen in sequence, and the process was repeated three times before the system was sealed.

[0017] The reaction begins when the oil bath temperature is raised to 60°C, and the total reaction time at constant temperature is 8 hours.

[0018] After the reaction is complete, the solution is washed in deionized water, then transferred to methanol for soaking, and dried to make powder.

[0019] As a preferred technical solution of the present invention: in step S1, the temperature of vacuum drying is 80°C.

[0020] As a preferred technical solution of the present invention: in step S1, the weight ratio of P(AN-co-AMPS) copolymer powder to ethylene carbonate is 40:60 to 60:40.

[0021] As a preferred technical solution of the present invention: in step S1, heating is carried out in a nitrogen atmosphere for 2 hours.

[0022] As a preferred technical solution of the present invention: in step S2, the deionized water in the electric hot water tank is heated to 50°C.

[0023] As a preferred technical solution of the present invention: in step S2, the spinning temperature is 140℃~160℃.

[0024] As a preferred technical solution of the present invention: in step S2, the diameter of the spinneret hole is 0.3 mm.

[0025] As a preferred technical solution of the present invention: in step S2, the winding speed is 5m / s.

[0026] Another objective of this invention is to provide a low-cost PAN-based carbon fiber precursor.

[0027] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution:

[0028] A low-cost PAN-based carbon fiber precursor is prepared by the low-cost PAN-based carbon fiber precursor prepared by the internal and external synergistic plasticizing melt spinning method described above.

[0029] This invention provides a low-cost PAN-based carbon fiber precursor and its preparation method using synergistic internal and external plasticizing melt spinning. The method involves preparing melt-spun PAN fibers through synergistic internal and external plasticizing. A suitable amount of a novel comonomer, AMPS, is added to polymerize with AN to prepare a P(AN-co-AMPS) copolymer, which serves as the melt spinning raw material. From the perspective of internal plasticizing, this reduces intermolecular forces between PAN fibers and facilitates subsequent pre-oxidation of the PAN precursor. From the perspective of external plasticizing, it reduces the amount of external plasticizer (ethylene carbonate, or EC in this invention) added, minimizing structural defects in the precursor caused during plasticizer removal. Furthermore, this invention uses a small amount of solvent, is environmentally friendly, has high spinning efficiency, and low manufacturing cost, which helps promote the large-scale application of carbon fiber in the civilian sector. It is a PAN precursor preparation method with broad development prospects. The low-cost PAN-based carbon fiber precursor prepared by the internal and external synergistic plasticizing melt spinning method provided by this invention has the following characteristics: fiber diameter of about 100 μm, tensile strength of 108.8 MPa, tensile modulus of 3267.3 MPa, and elongation at break of 43.4%. Attached Figure Description

[0030] Figure 1 The flowchart illustrates the preparation method of low-cost PAN-based carbon fiber precursor by melt spinning with internal and external synergistic plasticization provided by this invention.

[0031] Figure 2This image shows a sample of the low-cost PAN-based carbon fiber precursor obtained by the method for preparing low-cost PAN-based carbon fiber precursor by melt spinning with internal and external synergistic plasticization provided by the present invention.

[0032] Figure 3 The GPC spectrum of the P(AN-co-AMPS) copolymer is shown.

[0033] Figure 4 These are the chemical structural formulas of different external plasticizer molecules.

[0034] Figure 5 Optimized conformations for different external plasticizer molecules.

[0035] Figure 6 DSC curves for P(AN-co-AMPS) / EC mixtures with different ratios.

[0036] Figure 7 SEM images of the surfaces of different melt-spun PAN fiber samples.

[0037] Figure 8 Cross-sectional SEM images of different melt-spun PAN fiber samples.

[0038] Figure 9 Thermogravimetric curves of P(AN-co-AMPS) powder and melt-spun PAN fiber samples are shown.

[0039] Figure 10 Infrared spectra of P(AN-co-AMPS) and melt-spun PAN fiber samples.

[0040] Figure 11 XRD diffraction patterns of different melt-spun PAN fiber samples.

[0041] Figure 12 The graphs show the mechanical properties of different melt-spun PAN fiber samples. Detailed Implementation

[0042] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0043] 1. Preparation Experiment

[0044] 1.1 Preparation of P(AN-co-AMPS) copolymer

[0045] A free radical solution polymerization method was employed. Solvent DMSO, initiator AIBN (azobisisobutyronitrile), reactant AN (acrylonitrile), and AMPS (2-acrylamido-2-methylpropanesulfonic acid) were added to a glass reactor in a specific ratio, and the reaction was carried out under nitrogen balloon closure: vacuuming and nitrogen purging were performed sequentially three times before sealing the system. The reaction began when the temperature was raised to 60°C in an oil bath and remained at this temperature for a total of 8 hours. After the reaction was complete, the solution was washed in deionized water, then transferred to methanol for immersion, dried, and finally powdered and stored in a sealed, dry place.

[0046] The number-average molecular weight (Mn) of the P(AN-co-AMPS) copolymer was determined by gel permeation chromatography. n The molecular weight is 14500 g / mol, and the weight-average molecular weight (M) is 14500 g / mol. w The concentration was 29000 g / mol, the polydispersity index (PDI) was 1.45, and the test curve was as follows: Figure 3 As shown.

[0047] 1.2 Preparation of Ethylene Carbonate (EC) Plasticized Melt-Spun P(AN-co-AMPS) Fibers

[0048] The P(AN-co-AMPS) powder was dried overnight in a vacuum drying oven at 80°C for later use. Ethylene carbonate (EC) is solid at room temperature, so it needs to be heated until completely melted before use to ensure thorough mixing with the P(AN-co-AMPS) powder. After mixing P(AN-co-AMPS) / EC in a specific ratio, the mixture was heated in a nitrogen atmosphere for 2 hours, and then it can be used as a melt spinning raw material.

[0049] Before spinning, deionized water is poured into an electric hot water bath and heated to the specified temperature. The vertical extruder is started and heated to the spinning temperature, and preheated at a constant temperature for half an hour. Spinning begins; the melt is extruded and then passed through a hot water stretching stage, simultaneously completing fiber stretching and removing external plasticizers. It is then wound into filaments. The preparation process is as follows: Figure 1 As shown, the sample is displayed as follows. Figure 2 As shown, Figure 2 The numbers represent the weight ratio of P(AN-co-AMPS) in the P(AN-co-AMPS) / EC mixture. For example, 60, 55, 50, and 45 represent P(AN-co-AMPS) / EC mixture ratios of 60:40, 55:45, 50:50, and 45:55, respectively. During the preparation of different fiber samples, the speed at which the machine pushes the plunger (extrusion speed) remains consistent.

[0050] 2. Research on influencing factors

[0051] 2.1 External plasticizers

[0052] External plasticizer molecules reduce intermolecular forces by binding to the cyano groups on PAN molecules, thereby lowering the melting point of PAN molecules to achieve melt spinning. Stronger forces between the external plasticizer molecules and the cyano groups indicate better bonding and prevent the external plasticizer molecules from being removed during melt processing. Therefore, the binding energy between different external plasticizer molecules and PAN partial units was calculated using Gaussian software, and molecules with higher binding energy were selected as the external plasticizers of this invention.

[0053] Density functional theory (DFT), B3LYP functional theory, and BSSE correction (to remove the overlap effect of basis functions in the complex) were selected. The basis set was set as 6-31+g(d,p) to calculate the binding energy between PAN molecules and different external plasticizer molecules. The structure of PAN molecules was optimized by binding some sites on certain sites with different plasticizers, and the energy of the PAN molecule after binding with each plasticizer was calculated and denoted as E1. The structures of some PAN molecules and one plasticizer molecule were optimized separately, and the energies were calculated and denoted as E2 and E3, respectively. In this part, the binding energy E between PAN molecules and different plasticizers is considered to be equal to the energy after binding minus the individual energies before binding, with BSSE correction, as shown in the following equation:

[0054] E = E1 - E2 - E3 + E BSSE

[0055] Several small molecules with existing research backgrounds or similar structures were selected as external plasticizers for calculation. Figure 4 The chemical structural formulas of all molecules calculated in this figure are shown in the figure: (a) is PAN, (b) is a partial unit of PAN, (c) is acetonitrile, (d) is succinic anionyl nitrile, (e) is ethylene carbonate, (f) is ethylene glycol, (g) is ethanol, (h) is water, and (i) is urea. Figure 5 The figure shows the optimized conformations of PAN partial units and plasticizer molecules. In the figure: (a) is PAN partial unit, (b) is acetonitrile, (c) is succinic acid, (d) is ethylene carbonate, (e) is ethylene glycol, (f) is ethanol, (g) is water, and (h) is urea.

[0056] The calculated binding energy between PAN molecules and plasticizer molecules is shown in Table 1. The results show that succinic anionylene, urea, and ethylene carbonate have relatively high binding energies with PAN molecules. To achieve low-cost preparation of melt-spun PAN fibers and efficient removal of external plasticizers, water was selected as the coagulation bath solvent. Among the molecules with high binding energies with PAN molecules, succinic anionylene is slightly soluble in water, which is not conducive to complete removal; urea heated to the range of 150-160℃ will deaminate to form biuret, which may fall within the melt-spinning temperature range, meaning that urea molecules may undergo chemical changes during melt-spinning, potentially affecting the quality of the melt-spun PAN fibers; ethylene carbonate has a melting point of 35-38℃ and a boiling point above 240℃ (below the melt-spinning temperature) and is easily soluble in water. Therefore, it was heated and melted, and then premixed with P(AN-co-AMPS) powder. The mixture was fed into a vertical spinning machine for extrusion tests, and the results showed that spinning could proceed smoothly. Therefore, ethylene carbonate (EC) was selected as the external plasticizer used in this invention.

[0057] Table 1. Binding energies of different molecules to PAN molecules

[0058]

[0059] 2.2P(AN-co-AMPS) / EC melt spinning process

[0060] The spinning temperature range should be above the melting point of the P(AN-co-AMPS) / EC mixture and below the decomposition temperature of P(AN-co-AMPS). Taking a P(AN-co-AMPS) / EC mixture with a ratio of 50:50 as an example, the spinning effect at different temperatures was studied, as shown in Table 2. It can be seen that the spinning effect is best at 150℃, so 150℃ is used as the melt spinning temperature parameter.

[0061] Table 2. Melt spinning effect at different temperatures

[0062]

[0063] The spinneret orifice diameter is also one of the important parameters in the spinning process. If the orifice diameter is too small, it will be difficult to extrude the melt and may even cause melt fracture. If the orifice diameter is too large, the resulting melt-spun fiber will have a large fineness and be prone to too many defect structures, resulting in poor fiber strength and easy breakage. Therefore, a spinneret orifice diameter of 0.3 mm is selected, as the fiber quality and fineness are the best at this orifice diameter.

[0064] The melt spinning test results of P(AN-co-AMPS) / EC mixtures with different ratios are shown in Table 3. When the proportion of P(AN-co-AMPS) reaches 65% or more, melt extrusion is difficult. When the proportion of P(AN-co-AMPS) drops to 40%, the fibers are prone to breakage when removed from the roller, possibly due to excessive defect structures. Therefore, mixtures with P(AN-co-AMPS) / EC ratios of 60:40, 55:45, 50:50, and 45:55 were selected as experimental subjects for melt spinning. The resulting melt-spun PAN fibers were labeled as P... 60 P 55 P 50 P 45 .

[0065] Table 3. Melt spinning effect of P(AN-co-AMPS) / EC mixtures with different ratios

[0066]

[0067] 2.3 Effect of external plasticizer content on the glass transition temperature of P(AN-co-AMPS)

[0068] The feasibility of melt processing of P(AN-co-AMPS) / EC mixtures was studied by DSC to determine the effect of external plasticizer EC on the glass transition temperature of P(AN-co-AMPS).

[0069] like Figure 6 As shown in the figure, the vertical dashed line represents the glass transition temperature. After the introduction of EC, the glass transition temperature (Tg) of P(AN-co-AMPS) decreased. The Tg values ​​of different samples are shown in Table 4. As the EC content increases, the glass transition temperature of P(AN-co-AMPS) decreases more significantly. This is because more EC molecules combine with the cyano groups on the PAN molecules, reducing the dipole force between the cyano groups. This allows the PAN molecular chains and their segments to move at lower temperatures, resulting in a decrease in the glass transition temperature of the P(AN-co-AMPS) / EC mixture.

[0070] Table 4 Glass transition temperatures of P(AN-co-AMPS) / EC mixtures with different ratios

[0071]

[0072] 2.4 Morphology of melt-spun P(AN-co-AMPS) fibers

[0073] The surface and cross-sectional morphology of four melt-spun PAN fiber samples were observed by SEM testing to study the effect of different plasticizer contents on the morphology of melt-spun PAN fibers. The diameter of multiple melt-spun PAN fibers was measured by surface photographs, and the average value was used as the diameter data of melt-spun PAN fibers. The results are shown in Table 5.

[0074] Table 5 Diameter data of melt-spun PAN fibers

[0075]

[0076] like Figure 7 As shown, Figure 7 SEM images of the surfaces of different melt-spun PAN fiber samples are shown. In the figure: (a) is P 60 (b) is P 55 (c) is P 50 , (d) is P 45 As shown in the figure, the surface roughness of P60 fibers is likely due to the low EC content, resulting in poor melt drawability. Simultaneously, all fiber surfaces exhibit groove structures, possibly related to the pore defects left by EC escaping from the fiber interior during drawing. These pores become elongated or close during drawing, forming grooves on the fiber surface. With increasing EC content, the surface roughness decreases because more EC molecules combine with the cyano groups in PAN molecules, resulting in weaker intermolecular forces and greater mobility of PAN molecular chain segments. Therefore, nascent fibers extruded through the spinneret can achieve greater drawing during hot water drawing to eliminate grooves.

[0077] like Figure 8 As shown, Figure 8 Cross-sectional SEM images of different melt-spun PAN fiber samples are shown. In the figure: (a) is P 60 (b) is P 55 (c) is P 50 , (d) is P 45 As shown in the figure, the cross-sections of the four melt-spun PAN fiber samples are relatively dense, without any porous structures or defects, and are generally round in shape. PAN precursor fibers with these characteristics tend to have good uniformity and are less prone to defects in subsequent pre-oxidation and carbonization processes.

[0078] 2.5 Thermogravimetric analysis of melt-spun P(AN-co-AMPS) fibers

[0079] Figure 9 In Figures (a) and (b), the thermogravimetric curves and differential curves of P(AN-co-AMPS) powder and melt-spun PAN fibers are shown, respectively. Figure 9As shown, both P(AN-co-AMPS) powder and the four types of PAN fibers experienced slight weight loss before 140℃, which may be due to the volatilization of moisture, low-molecular-weight volatiles, and residual plasticizers within the fibers upon heating. In the 160–270℃ range, the weight loss rate of P(AN-co-AMPS) powder was higher than that of the other melt-spun PAN fibers, indicating that the thermal stability of melt-spun PAN fibers was higher than that of P(AN-co-AMPS) powder in this temperature range. The 270–350℃ range is the stage where PAN decomposes upon heating, transforming from a linear structure to a trapezoidal structure and beginning to release small molecule gases such as H2O, HCN, and NH3. The temperature corresponding to the maximum weight loss rate of the four melt-spun PAN fibers in this stage is approximately 20℃ higher than that of P(AN-co-AMPS) powder. In the 350–800℃ range, cross-linking occurs between adjacent PAN molecular chains, releasing various small molecule gases. In this range, the weight loss rate of P(AN-co-AMPS) powder is higher than that of the other melt-spun PAN fibers. The carbon yield of the four melt-spun PAN fibers was slightly higher than that of P(AN-co-AMPS) powder, indicating that melt processing improves the thermal stability of P(AN-co-AMPS) to some extent.

[0080] 2.6 Chemical structure of melt-spun P(AN-co-AMPS) fibers

[0081] Figure 10 Infrared spectra of P(AN-co-AMPS) powder and four types of melt-spun PAN fibers. The cyano group -CN on the PAN main chain is located at 2243 cm⁻¹. -1 The methine -CH is located at 1454 cm⁻¹ -1 The methylene group (CH2) is located at 1357 cm⁻¹. -1 The characteristic absorption peaks on the surface, and the carbonyl group -C=O on the comonomer AMPS located at 1654 cm⁻¹ -1 The imino-NH group is located at 1552 cm⁻¹. -1 The sulfinyl group -S=O is located at 1186 cm⁻¹ -1 The S-O-C bond is located at 1035 cm⁻¹ -1 The intensity of the characteristic absorption peak did not change significantly before and after P(AN-co-AMPS) melt spinning. Since the temperature used in PAN plasticizing melt spinning is much lower than the decomposition temperature of PAN molecules, PAN molecules will not decompose significantly at this temperature. After P(AN-co-AMPS) powder is melt-extruded into PAN fibers, it can still retain its molecular structure relatively intact.

[0082] 2.7 Crystalline structure of melt-spun P(AN-co-AMPS) fibers

[0083] The XRD pattern of melt-spun PAN fibers is as follows: Figure 11 As shown, the diffraction parameters are listed in Table 6. Figure 11 It can be seen that the melt-spun PAN fibers have diffraction peaks near 2θ = 17° and 29°, which correspond to the (100) and (110) crystal planes of PAN, with interplanar spacings of 0.52 nm and 0.30 nm, respectively. There are broad and gentle diffuse peaks between 2θ = 22° and 27°, indicating that the melt-spun PAN fibers have amorphous regions with side order.

[0084] As the plasticizer content decreases, the intensity of the diffraction peak near 2θ = 17° gradually increases, while the peak half-width and height gradually decrease. This indicates that the crystallinity and grain size of the sample increase accordingly, suggesting that the crystallinity of melt-spun PAN fibers is improving. When the proportion of plasticizer in the melt decreases, fewer cyano groups bind with the plasticizer molecules, while more cyano groups interact with each other through dipole interactions. This results in a higher degree of regularity in the arrangement of PAN molecules and increased crystallinity, which is beneficial for improving the tensile strength of the fiber sample.

[0085] Table 6. XRD diffraction parameters of melt-spun PAN fibers

[0086]

[0087] 2.8 Mechanical properties of melt-spun P(AN-co-AMPS) fibers

[0088] The stress-strain curves, tensile strength, Young's modulus, and elongation at break of the four melt-spun PAN fiber samples are as follows: Figure 12 As shown in (a), (b), (c), and (d), the stress-strain curves reveal that the four fibers underwent elastic deformation, yielding, and necking stages during the stretching process, indicating that the drawing process used to prepare the fiber samples was reasonable. Melt-spun PAN fiber sample P 60 P 55 P 50 P 45 The tensile strengths were 108.8±2.7 MPa, 99.1±13.8 MPa, 75.9±7.2 MPa, and 75.0±12.0 MPa, respectively. The tensile strength of the fiber increased with decreasing EC content. This is because EC is removed during hot water stretching, and the space occupied by EC during removal leaves micropores and other defects in the fiber. Therefore, when the EC content is low, the chance of leaving defects during removal is smaller, resulting in a denser internal structure of the PAN fiber, which helps to improve the tensile strength of the fiber. Melt-spun PAN fiber sample P 60 P 55 P 50 P 45The Young's moduli of the samples were 3267.3±326.3 MPa, 3172.1±683.4 MPa, 2168.5±326.3 MPa, and 839.5±175.9 MPa, respectively. The modulus is related to the crystallinity of the fiber sample because the intermolecular forces generated by the regularly arranged PAN molecular chains provide rigidity to the PAN molecules. Therefore, fiber samples with higher crystallinity have higher moduli. Melt-spun PAN fiber sample P 60 P 55 P 50 P 45 The elongation at break were 43.4%, 8.8%, 13.6%, and 10.7%, respectively. There was no clear pattern in the elongation at break among the four fiber samples. This is because the viscoelasticity of different P(AN-co-AMPS) / EC ratios varies, meaning their stretchability under the same conditions is inconsistent. Therefore, the elongation at break here can only be used as a reference indicator for the difference between the fiber's draw ratio and its natural draw ratio. For example, P... 60 The fiber sample exhibited a high elongation at break. Comparison of its stress-strain curves with other fiber samples revealed a longer necking development and overall stretching stage. This phenomenon is likely due to the higher glass transition temperature of the mixture at this formulation. Under the same temperature conditions, the PAN molecular chains exhibit poor mobility, leading to a reduced draw ratio during spinning to prevent fiber breakage. This results in the PAN produced from the mixture exhibiting a lower elongation at break. 60 The fiber has a small tensile strength, thus exhibiting a high elongation at break in tensile tests.

[0089] In summary, this invention uses density functional theory to simulate and calculate the binding energy between different external plasticizer molecules and PAN molecules, selecting EC with a higher binding energy value as the external plasticizer. DSC testing of the P(AN-co-AMPS) / EC mixture shows that EC has a plasticizing effect on P(AN-co-AMPS), and the glass transition temperature of the mixture decreases with increasing EC content. Furthermore, the influence of the external plasticizer EC content on the structure and properties of melt-spun PAN fibers was studied, leading to the following conclusions: the surface roughness of melt-spun PAN fibers decreases with decreasing EC content in the mixture; the cross-section of all fibers is... The fibers are round, without obvious pores or defects, and the difference between the core and sheath is not obvious. No significant chemical structure changes occurred in P(AN-co-AMPS) before and after melt spinning, and P(AN-co-AMPS) copolymer plasticized melt spinning was successfully achieved. The melt-spun PAN fibers have excellent thermal stability. Reducing the EC content is beneficial to improving the crystallinity and tensile properties of melt-spun PAN fibers. Among them, the crystallinity of P60 fiber sample with EC content of 40% reached 49.6%, and the tensile strength and modulus reached 108.8±2.7MPa and 3267.3±326.3MPa, respectively. This invention develops the application of AMPS in the melt spinning preparation of PAN precursor fibers.

[0090] The above specific embodiments are used to explain and illustrate the present invention, and are only preferred embodiments of the present invention, not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing low-cost PAN-based carbon fiber precursor by melt spinning with synergistic internal and external plasticization, characterized in that: The preparation method includes the following steps: S1. Preparation of raw materials for melt spinning Vacuum-dried P(AN-co-AMPS) copolymer powder and ethylene carbonate were mixed in a certain proportion and then heated in a nitrogen atmosphere for a certain time to obtain melt spinning raw material. S2, melt spinning Before melt spinning, deionized water is poured into an electric hot water bath and heated to the specified temperature; the vertical extruder is heated to the spinning temperature and preheated at a constant temperature for a certain period of time. The molten spinning raw material obtained in step S1 is fed into a vertical extruder. After the melt is extruded, it is stretched by hot water to simultaneously complete the stretching of fibers and the removal of external plasticizers. Finally, it is rolled up into threads; In step S1, the vacuum drying temperature is 80°C; In step S1, the weight ratio of P(AN-co-AMPS) copolymer powder to ethylene carbonate is 40:60 to 60:

40. In step S1, heating is carried out in a nitrogen atmosphere for 2 hours; In step S2, the deionized water in the electric hot water tank is heated to 50°C; In step S2, the spinning temperature is 140℃~160℃.

2. The method for preparing low-cost PAN-based carbon fiber precursor by internal and external synergistic plasticizing melt spinning according to claim 1, characterized in that: In step S1, the P(AN-co-AMPS) copolymer powder is prepared by the following method: The free radical solution polymerization method was adopted, and the solvent DMSO, initiator AIBN, reactant AN and AMPS were added into the reactor in a certain ratio: the system was evacuated and purged with nitrogen in sequence, and the process was repeated three times before the system was sealed. The reaction begins when the oil bath temperature is raised to 60°C, and the total reaction time at constant temperature is 8 hours. After the reaction is complete, the solution is washed in deionized water, then transferred to methanol for soaking, and dried to make powder.

3. The method for preparing low-cost PAN-based carbon fiber precursor by melt spinning with internal and external synergistic plasticization according to claim 1, characterized in that: In step S2, the diameter of the spinneret orifice is 0.3 mm.

4. The method for preparing low-cost PAN-based carbon fiber precursor by melt spinning with internal and external synergistic plasticization according to claim 1, characterized in that: In step S2, the winding speed is 5 m / s.

5. A low-cost PAN-based carbon fiber precursor, characterized in that: The low-cost PAN-based carbon fiber precursor is prepared by the method for preparing low-cost PAN-based carbon fiber precursor by melt spinning with internal and external synergistic plasticization as described in any one of claims 1-4.

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