PI / PAN coaxial composite-based carbon fiber as well as preparation method and application thereof

Abstract

The invention provides PI / PAN coaxial composite-based carbon fibers and a preparation method and application thereof.The preparation method comprises the following steps that 1, a polyamide acid polymer solution serves as a core layer spinning solution, a polyacrylonitrile polymer solution serves as a shell layer spinning solution, and PAA / PAN fibers are prepared through a coaxial spinning technology; 2, the PAA / PAN fibers are subjected to pre-oxidation and imidization treatment, and PI / PAN fibers are obtained; and carrying out carbonization treatment or carbonization and graphitization treatment on the PI / PAN fiber to obtain the PI / PAN coaxial composite-based carbon fiber. The PI core layer and the PAN shell layer have a synergistic effect, so that the PI / PAN coaxial composite-based carbon fiber has a higher graphitization degree, thereby having higher heat-conducting property.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fiber composite material preparation, and specifically relates to a PI / PAN coaxial composite-based carbon fiber, a preparation method thereof, and an application thereof. Background Art

[0002] With the wide commercialization of microelectronics, 5G communication, and new energy vehicles, heat dissipation has become a key issue restricting the development of electronic devices and energy. Carbon fiber has the advantages of low density and high thermal conductivity, and has broad application prospects in the field of heat conduction.

[0003] Polyacrylonitrile-based carbon fiber is currently the most widely used and strongest carbon fiber. The Chinese patent application with the publication number CN119753892A pre-oxidizes, low-temperature carbonizes, alkali-soaks, high-temperature carbonizes, and graphitizes polyacrylonitrile-based fibers in sequence to obtain polyacrylonitrile-based carbon fiber, which has a relatively high tensile modulus, with the tensile modulus in the range of 200 GPa to 590 GPa, and has a relatively good tensile strength, with the tensile strength above 2.4 GPa. However, the cross-linked structure formed by the linear molecular chains of polyacrylonitrile-based carbon fiber during the pre-oxidation and carbonization processes is difficult to achieve a highly ordered graphite microcrystal arrangement, and its thermal conductivity is difficult to meet the heat dissipation requirements in fields such as high-power electronic devices. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to provide a PI / PAN coaxial composite-based carbon fiber, a preparation method thereof, and an application thereof, so as to solve the problem that the thermal conductivity of existing polyacrylonitrile-based carbon fiber is difficult to meet the heat dissipation requirements in fields such as high-power electronic devices.

[0005] The present invention is achieved through the following technical solutions: In the first aspect, the present invention provides a preparation method of a PI / PAN coaxial composite-based carbon fiber, including the following steps: Step 1, using a polyamic acid polymerization solution as the core layer spinning solution and a polyacrylonitrile polymerization solution as the shell layer spinning solution, and preparing PAA / PAN fibers through a coaxial spinning process; Step 2, subjecting the PAA / PAN fibers to pre-oxidation and imidization treatments to obtain PI / PAN fibers; subjecting the PI / PAN fibers to carbonization treatment or carbonization and graphitization treatments to obtain PI / PAN coaxial composite-based carbon fibers.

[0006] Preferably, in Step 1, the solid content range of the polyamic acid polymerization solution is 10% to 30%, and more preferably 15% to 20%.

[0007] Preferably, in Step 1, the solid content range of the PAN polymerization solution is 10% to 30%, and more preferably 12% to 20%.

[0008] Preferably, in step 1, the coaxial spinning process is a coaxial wet spinning process or a coaxial electrospinning process.

[0009] Preferably, in step 1, the flow rate ratio of the shell spinning solution to the core spinning solution is (2-4):(1-2).

[0010] Preferably, in step 2, the pre-oxidation and imidization treatments are carried out synchronously, the treatment temperature is 150 °C - 350 °C, more preferably 250 °C - 350 °C; the treatment time is 1 h - 5 h, more preferably 3 h - 5 h.

[0011] Preferably, in step 2, the carbonization temperature is 700 °C - 1800 °C, more preferably 900 °C - 1500 °C, and the carbonization time is 10 min - 1 h.

[0012] Preferably, in step 2, the graphitization temperature is 2000 °C - 3000 °C, more preferably 2500 °C - 3000 °C, and the graphitization time is 10 min - 1 h.

[0013] In a second aspect, the present invention provides a PI / PAN coaxial composite-based carbon fiber obtained by the preparation method as described above.

[0014] In a third aspect, the present invention provides the application of the described PI / PAN coaxial composite-based carbon fiber in the fields of heat conduction, electricity conduction, electromagnetic wave absorption, electromagnetic shielding, sensing or supercapacitors.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses polyamic acid (PAA) and polyacrylonitrile (PAN) as double precursors, and combines a coaxial spinning process to prepare a coaxial composite-based carbon fiber with a core-shell structure; the coaxial composite-based carbon fiber uses polyimide (PI) as the core layer, and its rigid structure is easy to form a graphite microcrystalline structure, providing a highly oriented main heat conduction channel; polyacrylonitrile is used as the shell layer, and the cross-linked network formed by cyano cyclization during high-temperature pyrolysis provides space constraints for the directional rearrangement of the aromatic ring structure in the PI core layer, inhibits the formation of amorphous carbon, and at the same time promotes defect repair, thereby improving the graphitization degree. In addition, the π-π stacking effect at the coaxial interface forms a continuous phonon transmission channel, that is, a heat conduction channel. The above jointly improve the heat conduction performance of the PI / PAN coaxial composite-based carbon fiber. That is, there is a synergistic effect between the PI core layer and the PAN shell layer, making the PI / PAN coaxial composite-based carbon fiber have a higher graphitization degree and also higher heat conduction performance.

[0016] Furthermore, the present invention controls the solid content range of the polyamic acid polymerization solution to be 15% - 20%. If the solid content of the polyamic acid polymerization solution is too low, a beaded structure may be formed during the spinning process, affecting the morphology of the coaxial fiber.

[0017] Furthermore, the present invention controls the solid content range of the polyacrylonitrile polymerization solution to be 12% - 20%. If the solid content of the polyacrylonitrile polymerization solution is too high, the needle may be blocked during the spinning process due to too high viscosity.

[0018] Furthermore, the present invention can also further improve the graphitization degree of the PI / PAN coaxial composite-based carbon fiber by increasing the graphitization treatment, making the graphite microcrystalline structure inside the PI / PAN coaxial composite-based carbon fiber gradually perfect, reducing the layer spacing, and having smaller graphite defects. Therefore, the thermal diffusivity and thermal conductivity are higher. The present invention prepares PI / PAN coaxial composite-based carbon fibers with high graphitization degree and high thermal conductivity by controlling the carbonization and graphitization temperatures.

[0019] The PI / PAN coaxial composite-based carbon fiber prepared by the present invention has good thermal conductivity and can be applied in the fields of heat conduction, electricity conduction, electromagnetic wave absorption, electromagnetic shielding, sensing, or supercapacitors. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 It is the TEM image of PI / PAN-GNF-2500 in Example 3 of the present invention; Figure 2 It is the SEM image of PI / PAN-CNF-900 in Example 1 of the present invention; Figure 3 It is the SEM image of PI / PAN-CNF-1400 in Example 2 of the present invention; Figure 4 It is the SEM image of PI / PAN-GNF-2500 in Example 3 of the present invention; Figure 5 It is the Raman and XRD spectra of PI / PAN-CNF-900, PI-CNF-900, and PAN-CNF-900 in Example 1 of the present invention and Comparative Examples 1 - 2; Figure 6 It is the Raman and XRD spectra of PI / PAN-CNF-1400, PI-CNF-1400, and PAN-CNF-1400 in Example 2 of the present invention and Comparative Examples 1 - 2; Figure 7Raman and XRD spectra of PI / PAN-GNF-2500, PI-GNF-2500, and PAN-GNF-2500 in Example 3 and Comparative Examples 1-2 of the present invention; Figure 8 Thermal diffusivity diagrams of all samples in Examples 1-3 and Comparative Examples 1-2 of the present invention; Figure 9 Thermal conductivity diagrams of all samples in Examples 1-3 and Comparative Examples 1-2 of the present invention. Detailed implementation manners

[0022] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0023] It should be noted that the process equipment or devices not specifically specified in the following embodiments all adopt conventional equipment or devices in the art.

[0024] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those clearly listed steps or units, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products, or devices. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, rather than limiting the arrangement order of each method step or the scope in which the present invention can be implemented. The change or adjustment of their relative relationship, without substantial change in technical content, should also be regarded as the scope in which the present invention can be implemented.

[0025] The present invention prepares coaxial fibers with a polyimide core layer and a polyacrylonitrile shell layer through a spinning process, and uses it as a precursor to prepare a PI / PAN coaxial composite-based carbon fiber with high thermal conductivity through carbonization or carbonization and graphitization; the preparation process is simple and convenient, providing a new preparation method for thermal conductive carbon fiber composites, which is of great significance to the thermal conductive field.

[0026] Specifically, the preparation method of the PI / PAN coaxial composite-based carbon fiber described in the present invention includes the following steps: Step 1, using a polyamic acid polymerization solution as the core layer spinning solution and a polyacrylonitrile polymerization solution as the shell layer spinning solution, and preparing PAA / PAN fibers through a coaxial spinning process; Step 2: Pre-oxidize and imidize the PAA / PAN fibers to obtain PI / PAN fibers; then carbonize or carbonize and graphitize the PI / PAN fibers to obtain PI / PAN coaxial composite-based carbon fibers.

[0027] Through the above method of the present invention, PI / PAN coaxial composite-based carbon fibers with a core-shell structure are prepared. Among them, polyimide serves as the core layer, and its rigid structure is prone to form graphite microcrystalline structures, providing a highly oriented main heat conduction channel; polyacrylonitrile (PAN) serves as the shell layer. During high-temperature pyrolysis, the cross-linked network formed by cyano cyclization provides spatial constraints for the directional rearrangement of the aromatic ring structure in the PI core layer, inhibits the formation of amorphous carbon, and at the same time promotes defect repair, thereby increasing the degree of graphitization. And the π-π stacking effect at the coaxial interface forms a continuous phonon transmission channel, that is, a heat conduction channel. The above effects together improve the heat conduction performance of the PI / PAN coaxial composite-based carbon fibers. That is to say, a synergistic effect is generated between the polyimide core layer and the polyacrylonitrile shell layer, making the thermal diffusivity and thermal conductivity of the PI / PAN coaxial composite-based carbon fibers superior to those of pure polyimide carbon fibers and pure polyacrylonitrile carbon fibers.

[0028] In some preferred embodiments of the present invention, the polyamic acid polymerization solution in Step 1 is obtained by polymerizing dianhydride monomers and diamine monomers, and its solid content range is controlled to be 10% - 30%, more preferably 15% - 20%. Further preferably, the solid content of the polyamic acid polymerization solution is controlled to be 18% - 20%. For example, it can be 18%, 19%, 20%; if the solid content of the polyamic acid polymerization solution is too low, a beaded structure may be formed during the spinning process, affecting the morphology of the coaxial fibers. The solid content mentioned in the present invention all refers to the mass content.

[0029] Among them, the dianhydride monomer can be one or more of pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and bisphenol A diether dianhydride, and the diamine monomer can be one or more of 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine, and m-phenylenediamine; the solvent used for the polymerization reaction of the dianhydride monomer and the diamine monomer can be N,N-dimethylformamide or N,N-dimethylacetamide. In a preferred embodiment of the present invention, the dianhydride monomer is selected as pyromellitic dianhydride, the diamine monomer is 4,4'-diaminodiphenyl ether, and the solvent is selected as N,N-dimethylformamide.

[0030] In some preferred embodiments of the present invention, the polyacrylonitrile polymerization solution in step 1 is obtained by polymerizing acrylonitrile with a small amount of comonomers, and its solid content is controlled in the range of 10% - 30%, more preferably 12% - 20%. Further preferably, the solid content of the polyacrylonitrile polymerization solution is controlled at 12% - 15%, for example, it can be 12%, 13%, 14%, 15%; if the solid content of the polyacrylonitrile polymerization solution is too high, the needle may be blocked during the spinning process due to too high viscosity.

[0031] In the present invention, the polyacrylonitrile polymerization solution in step 1 is obtained by polymerizing acrylonitrile with a small amount of comonomers; the comonomers generally select organic compounds containing acrylate and carboxyl linkages, which are used to promote the pre-oxidation process and cyclization. Specifically, in the examples of the present invention, the polyacrylonitrile polymerization solution used is obtained by polymerizing acrylonitrile with itaconic acid as the comonomer.

[0032] In the preparation method of the above-mentioned PI / PAN coaxial composite-based carbon fiber of the present invention, the coaxial spinning process can be a coaxial wet spinning process or a coaxial electrospinning process, and both spinning processes can be used to prepare PI / PAN coaxial composite-based carbon fiber. Preferably, the coaxial electrospinning process is used in the examples of the present invention.

[0033] In some preferred embodiments of the present invention, in the coaxial spinning process, the flow rate of the shell layer spinning solution is controlled at 0.1 mL / h - 0.5 mL / h, the flow rate of the core layer spinning solution is controlled at 0.05 mL / h - 0.2 mL / h, and the flow rate ratio of the shell layer spinning solution to the core layer spinning solution is (2 - 4):(1 - 2). Preferably, the flow rate of the shell layer spinning solution is controlled at 0.25 mL / h, and the flow rate of the core layer spinning solution is controlled at 0.08 mL / h.

[0034] In some preferred embodiments of the present invention, in step 2, the pre-oxidation and imidization treatments are carried out simultaneously, the treatment temperature is 150 °C - 350 °C, and the time is 1 h - 5 h; more preferably, the temperature of the pre-oxidation and imidization processes is 250 °C - 300 °C, and the time is 3 h - 5 h. In the specific examples of the present invention, the preferred heating program is: keep the temperature at 150 °C, 200 °C, and 300 °C for 1 h each. Stepwise heating can ensure that the reaction proceeds step by step, avoid uneven cyclization caused by local overheating, and thus reduce cracks inside the fiber.

[0035] In some preferred embodiments of the present invention, in step 2, the carbonization temperature is 700 °C - 1800 °C, and the time is 10 min - 1 h; more preferably, the carbonization temperature is 900 °C - 1500 °C, such as 900 °C, 1400 °C, etc.; the carbonization time is, for example, 10 min.

[0036] In the preparation method of the PI / PAN coaxial composite-based carbon fiber of the present invention, the graphitization degree of the PI / PAN coaxial composite-based carbon fiber can be further improved by increasing the graphitization treatment. Specifically, after the carbonization is completed, the graphitization treatment is carried out. The graphitization temperature is 2000 °C to 3000 °C, more preferably 2500 °C to 3000 °C; the graphitization time is 10 min to 1 h, such as 10 min, 20 min, 40 min, 1 h. After the graphitization treatment, the graphite microcrystalline structure inside the PI / PAN coaxial composite-based carbon fiber is gradually improved, the interlayer spacing is reduced, and the graphite defects are small. Therefore, the thermal diffusivity and thermal conductivity are higher.

[0037] The carbonization and graphitization temperatures have a great influence on the thermal conductivity of the carbon fiber. The higher the carbonization and graphitization temperatures, the higher the thermal conductivity of the material. The present invention controls the carbonization and graphitization temperatures to prepare PI / PAN coaxial composite-based carbon fibers with high graphitization degree and high thermal conductivity. As described in an embodiment, PI / PAN coaxial composite-based carbon fibers with a thermal conductivity as high as 226.223 W / m·K are prepared.

[0038] The PI / PAN coaxial composite-based carbon fiber prepared by the present invention through the above method is a functionalized carbon fiber composite material.

[0039] Due to the composite of the polyimide core layer and the polyacrylonitrile shell layer, the graphitization degree is improved; at the same time, through the stress matching effect generated at the core-shell interface, both the high orientation characteristics of the polyimide core layer are maintained, and the lattice of the core layer is further compressed by the shrinkage stress of the polyacrylonitrile shell layer; the π-π stacking effect at the coaxial interface forms a continuous phonon transmission channel, and each effect jointly improves the thermal conductivity of the PI / PAN coaxial composite-based carbon fiber. That is to say, a synergistic effect is generated between the polyimide core layer and the polyacrylonitrile shell layer, making the thermal diffusivity and thermal conductivity of the PI / PAN coaxial composite-based carbon fiber superior to those of pure polyimide carbon fiber and pure polyacrylonitrile carbon fiber.

[0040] The thermal conductivity of the PI / PAN coaxial composite-based carbon fiber obtained in the present invention is 24 W / (m·K) to 230 W / (m·K), and the thermal diffusivity is 14 mm 2 / s to 165 mm 2 / s.

[0041] The PI / PAN coaxial composite-based carbon fiber prepared by the present invention can be applied in multiple fields, such as thermal conduction, electricity conduction, electromagnetic wave absorption, electromagnetic shielding, sensing, supercapacitors and other fields. The present invention is mainly used in the field of thermal conduction.

[0042] The raw materials and equipment used in the embodiments of the present invention are all known products and are obtained by purchasing commercially available products.

[0043] Example 1 In this example, the preparation method of PI / PAN coaxial composite-based carbon fiber includes the following steps: Step 1, under a nitrogen atmosphere, 0.02 mol of 4,4-diaminodiphenyl ether and N,N-dimethylformamide were added to a three-necked flask. After stirring thoroughly until 4,4-diaminodiphenyl ether was completely dissolved, 0.02 mol of pyromellitic dianhydride was added. An ice-water bath reaction was carried out in a water bath, with the temperature controlled below 10 °C. The polymerization solution was mechanically stirred for 12 h to obtain a PAA polymerization solution, which was used as the core-layer spinning solution (the intrinsic viscosity of the PAA polymerization solution was 0.98 dL / g, and the solid content was 18%). A PAN polymerization solution with a solid content of 15% was used as the shell-layer spinning solution.

[0044] Step 2, the core-layer spinning solution and the core-layer spinning solution were respectively filled into two 5 mL syringes, and then placed in an oven at 50 °C for 5 h of static defoaming treatment. Using an electrospinning device, a 19 G coaxial electrospinning needle was selected, and a silicon oil paper was pasted on the roller receiver to facilitate obtaining a complete nanofiber membrane. The roller rotation speed was set to 2000 rpm, the spinning positive pressure was set to 22 kv, the negative pressure was 3 kv, the flow rate of the shell-layer spinning solution was adjusted to 0.25 mL / h, the flow rate of the core-layer spinning solution was 0.08 mL / h, the distance between the syringe and the roller was 15 cm, the temperature setting value was 50 °C, and the humidity setting value was 30%. Continuous electrospinning was carried out for 15 h to obtain a PAA / PAN coaxial fiber membrane with a certain thickness. To ensure complete volatilization of the solvent, it was placed in a vacuum oven at 50 °C for 12 h of drying treatment.

[0045] Step 3, the PAA / PAN coaxial fiber membrane was placed in a high-temperature oven for pre-oxidation and imidization treatment at a heating rate of 5 °C / min. The specific heating program was: holding at 150 °C, 200 °C, and 300 °C for 1 h each to obtain a sample PI / PAN coaxial fiber membrane.

[0046] Step 4, under nitrogen protection, the PI / PAN coaxial fiber membrane was clamped between graphite plates and placed in a tubular furnace for carbonization treatment. The carbonization temperature was 900 °C, the heating rate was 5 °C / min, and it was held for 10 min, and then cooled naturally to obtain a sample PI / PAN-CNF-900.

[0047] Example 2 In this example, the preparation method of PI / PAN coaxial composite-based carbon fiber includes the following steps: Step 1, under a nitrogen atmosphere, 0.02 mol of 4,4-diaminodiphenyl ether and N,N-dimethylformamide were added to a three-necked flask. After stirring thoroughly until 4,4-diaminodiphenyl ether was completely dissolved, 0.02 mol of pyromellitic dianhydride was added. An ice-water bath reaction was carried out in a water bath, with the temperature controlled below 10 °C. The polymerization solution was mechanically stirred for 12 h to obtain a PAA polymerization solution, which was used as the core layer spinning solution (the intrinsic viscosity of the PAA polymerization solution was 0.98 dL / g, and the solid content was 18%). A PAN polymerization solution with a solid content of 15% was used as the shell layer spinning solution.

[0048] Step 2, the core layer spinning solution and the core layer spinning solution were respectively filled into two 5 mL syringes, and then placed in an oven at 50 °C for 5 h of static defoaming treatment. Using an electrospinning device, a 19 G coaxial electrospinning needle was selected, and siliconized paper was pasted on the drum receiver to facilitate obtaining a complete nanofiber membrane. The drum rotation speed was set to 2000 rpm, the positive spinning pressure was set to 22 kv, the negative pressure was set to 3 kv, the flow rate of the shell layer spinning solution was adjusted to 0.25 mL / h, the flow rate of the core layer spinning solution was adjusted to 0.08 mL / h, the distance between the syringe and the drum was 15 cm, the temperature setting value was 50 °C, and the humidity setting value was 30%. Continuous electrospinning was carried out for 15 h to obtain a PAA / PAN coaxial fiber membrane with a certain thickness. To ensure complete volatilization of the solvent, it was placed in a vacuum oven at 50 °C for 12 h of drying treatment.

[0049] Step 3, the PAA / PAN coaxial fiber membrane was placed in a high-temperature oven for pre-oxidation and imidization treatment at a heating rate of 5 °C / min. The specific heating program was: keep warm at 150 °C, 200 °C, and 300 °C for 1 h each to obtain a sample PI / PAN coaxial fiber membrane.

[0050] Step 4, under nitrogen protection, the PI / PAN coaxial fiber membrane was sandwiched between graphite plates and placed in a tube furnace for carbonization treatment. The carbonization temperature was 1400 °C, the heating rate was 5 °C / min, keep warm for 10 min, and then naturally cool down to obtain a sample PI / PAN-CNF-1400.

[0051] Example 3 In this example, the preparation method of the PI / PAN coaxial composite-based carbon fiber includes the following steps: Step 1, under a nitrogen atmosphere, 0.02 mol of 4,4-diaminodiphenyl ether and N,N-dimethylformamide were added to a three-necked flask. After stirring thoroughly until 4,4-diaminodiphenyl ether was completely dissolved, 0.02 mol of pyromellitic dianhydride was added. The reaction was carried out in an ice-water bath in a water bath, with the temperature controlled below 10 °C. The polymerization solution was mechanically stirred for 12 h to obtain a PAA polymerization solution, which was used as the core layer spinning solution (the intrinsic viscosity of the PAA polymerization solution was 0.98 dL / g, and the solid content was 18%). A PAN polymerization solution with a solid content of 15% was used as the shell layer spinning solution.

[0052] Step 2, the core layer spinning solution and the core layer spinning solution were respectively filled into two 5 mL syringes, and then placed in an oven at 50 °C for 5 h of static defoaming treatment. Using an electrospinning device, a 19 G coaxial electrospinning needle was selected, and a silicone oil paper was pasted on the roller receiver to facilitate obtaining a complete nanofiber membrane. The roller rotation speed was set to 2000 rpm, the spinning positive pressure was set to 22 kv, the negative pressure was set to 3 kv, the flow rate of the shell layer spinning solution was adjusted to 0.25 mL / h, the flow rate of the core layer spinning solution was adjusted to 0.08 mL / h, the distance between the syringe and the roller was 15 cm, the temperature setting value was 50 °C, and the humidity setting value was 30%. Continuous electrospinning was carried out for 15 h to obtain a PAA / PAN coaxial fiber membrane with a certain thickness. To ensure complete volatilization of the solvent, it was placed in a vacuum oven at 50 °C for 12 h of drying treatment.

[0053] Step 3, the PAA / PAN coaxial fiber membrane was placed in a high-temperature oven for pre-oxidation and imidization treatment at a heating rate of 5 °C / min. The specific heating program was: keep warm at 150 °C, 200 °C, and 300 °C for 1 h each to obtain a sample PI / PAN coaxial fiber membrane.

[0054] Step 4, under nitrogen protection, the PI / PAN coaxial fiber membrane was clamped between graphite plates and placed in a tube furnace for carbonization treatment. The carbonization temperature was 900 °C, the heating rate was 5 °C / min, keep warm for 10 min, and then graphitization treatment was carried out. The graphitization temperature was 2500 °C, the heating rate was 10 °C / min, keep warm for 1 h, and then it was naturally cooled to obtain a sample PI / PAN-GNF-2500.

[0055] Example 4 In this example, the preparation method of the PI / PAN coaxial composite-based carbon fiber includes the following steps: Step 1, under a nitrogen atmosphere, 0.02 mol of 4,4-diaminodiphenyl ether and N,N-dimethylformamide were added to a three-necked flask. After stirring thoroughly until 4,4-diaminodiphenyl ether was completely dissolved, 0.02 mol of pyromellitic dianhydride was added. An ice-water bath reaction was carried out in a water bath, with the temperature controlled below 10 °C. The polymerization solution was mechanically stirred for 12 h to obtain a PAA polymerization solution, which was used as the core layer spinning solution (the intrinsic viscosity of the PAA polymerization solution was 0.98 dL / g, and the solid content was 18%). A PAN polymerization solution with a solid content of 13% was used as the shell layer spinning solution.

[0056] Step 2, the core layer spinning solution and the core layer spinning solution were respectively filled into two 5 mL syringes, and then placed in an oven at 50 °C for 5 h of static defoaming treatment. Using an electrospinning device, a 19 G coaxial electrospinning needle was selected, and a silicon oil paper was pasted on the drum receiver to facilitate obtaining a complete nanofiber membrane. The drum rotation speed was set to 2000 rpm, the positive spinning pressure was set to 22 kv, the negative pressure was 3 kv, the flow rate of the shell layer spinning solution was adjusted to 0.18 mL / h, the flow rate of the core layer spinning solution was 0.06 mL / h, the distance between the syringe and the drum was 15 cm, the temperature setting value was 50 °C, and the humidity setting value was 30%. Continuous electrospinning was carried out for 15 h to obtain a PAA / PAN coaxial fiber membrane with a certain thickness. To ensure complete volatilization of the solvent, it was placed in a vacuum oven at 50 °C for 12 h of drying treatment.

[0057] Step 3, the PAA / PAN coaxial fiber membrane was placed in a high-temperature oven for pre-oxidation and imidization treatment at a heating rate of 5 °C / min. The specific heating program was: holding at 150 °C, 200 °C, and 300 °C for 3 h each to obtain a sample PI / PAN coaxial fiber membrane.

[0058] Step 4, under nitrogen protection, the PI / PAN coaxial fiber membrane was clamped between graphite plates and placed in a tube furnace for carbonization treatment. The carbonization temperature was 1100 °C, the heating rate was 5 °C / min, held for 10 min, and cooled naturally to obtain a sample PI / PAN-CNF-1100.

[0059] Example 5 In this example, the preparation method of the PI / PAN coaxial composite-based carbon fiber includes the following steps: Step 1, under a nitrogen atmosphere, 0.02 mol of 4,4-diaminodiphenyl ether and N,N-dimethylformamide were added to a three-necked flask. After stirring well until the 4,4-diaminodiphenyl ether was completely dissolved, 0.02 mol of pyromellitic dianhydride was added. The reaction was carried out in an ice-water bath in a water bath, with the temperature controlled below 10 °C. The polymerization solution was mechanically stirred for 12 h to obtain a PAA polymerization solution, which was used as the core layer spinning solution (the intrinsic viscosity of the PAA polymerization solution was 0.98 dL / g, and the solid content was 18%). A PAN polymerization solution with a solid content of 15% was used as the shell layer spinning solution.

[0060] Step 2, the core layer spinning solution and the core layer spinning solution were respectively filled into two 5 mL syringes, and then placed in an oven at 50 °C for 5 h of static defoaming treatment. Using an electrospinning device, a 19 G coaxial electrospinning needle was selected, and a silicon oil paper was pasted on the drum receiver to facilitate obtaining a complete nanofiber membrane. The drum rotation speed was set to 2000 rpm, the spinning positive pressure was set to 22 kv, the negative pressure was 3 kv, the flow rate of the shell layer spinning solution was adjusted to 0.25 mL / h, the flow rate of the core layer spinning solution was 0.08 mL / h, the distance between the syringe and the drum was 15 cm, the temperature setting value was 50 °C, and the humidity setting value was 30%. Continuous electrospinning was carried out for 15 h to obtain a PAA / PAN coaxial fiber membrane with a certain thickness. To ensure complete volatilization of the solvent, it was placed in a vacuum oven at 50 °C for 12 h of drying treatment.

[0061] Step 3, the PAA / PAN coaxial fiber membrane was placed in a high-temperature oven for pre-oxidation and imidization treatment at a heating rate of 5 °C / min. The specific heating program was: keep warm at 150 °C, 200 °C, and 250 °C for 2 h each to obtain a sample PI / PAN coaxial fiber membrane.

[0062] Step 4, under nitrogen protection, the PI / PAN coaxial fiber membrane was clamped between graphite plates and placed in a tube furnace for carbonization treatment. The carbonization temperature was 1400 °C, the heating rate was 5 °C / min, keep warm for 10 min, and then cool down naturally to obtain a sample PI / PAN-CNF-1400.

[0063] Example 6 The preparation method of the PI / PAN coaxial composite-based carbon fiber in this example includes the following steps: Step 1, under a nitrogen atmosphere, 0.02 mol of 4,4-diaminodiphenyl ether and N,N-dimethylformamide were added to a three-necked flask. After stirring thoroughly until 4,4-diaminodiphenyl ether was completely dissolved, 0.02 mol of pyromellitic dianhydride was added. An ice-water bath reaction was carried out in a water bath, with the temperature controlled below 10 °C. The polymerization solution was mechanically stirred for 12 h to obtain a PAA polymerization solution, which was used as the core-layer spinning solution (the intrinsic viscosity of the PAA polymerization solution was 0.98 dL / g, and the solid content was 18%). A PAN polymerization solution with a solid content of 15% was used as the shell-layer spinning solution.

[0064] Step 2, the core-layer spinning solution and the core-layer spinning solution were respectively filled into two 5 mL syringes, and then placed in an oven at 50 °C for 5 h of static defoaming treatment. Using an electrospinning device, a 19 G coaxial electrospinning needle was selected, and a silicone oil paper was pasted on the drum receiver to facilitate obtaining a complete nanofiber membrane. The drum rotation speed was set at 2000 rpm, the spinning positive pressure was set at 22 kv, the negative pressure was set at 3 kv, the flow rate of the shell-layer spinning solution was adjusted to 0.50 mL / h, the flow rate of the core-layer spinning solution was adjusted to 0.17 mL / h, the distance between the syringe and the drum was 15 cm, the temperature setting value was 50 °C, and the humidity setting value was 30%. Continuous electrospinning was carried out for 15 h to obtain a PAA / PAN coaxial fiber membrane with a certain thickness. To ensure complete volatilization of the solvent, it was placed in a vacuum oven at 50 °C for 12 h of drying treatment.

[0065] Step 3, the PAA / PAN coaxial fiber membrane was placed in a high-temperature oven for pre-oxidation and imidization treatment at a heating rate of 5 °C / min. The specific heating program was: holding at 150 °C, 200 °C, and 300 °C for 1 h each to obtain a sample PI / PAN coaxial fiber membrane.

[0066] Step 4, under nitrogen protection, the PI / PAN coaxial fiber membrane was clamped between graphite plates and placed in a tubular furnace for carbonization treatment. The carbonization temperature was 1500 °C, the heating rate was 5 °C / min, it was held for 10 min, and then cooled naturally to obtain a sample PI / PAN-CNF-1500.

[0067] Example 7 The preparation method of the PI / PAN coaxial composite-based carbon fiber in this example includes the following steps: Step 1, under a nitrogen atmosphere, 0.02 mol of 4,4-diaminodiphenyl ether and N,N-dimethylformamide were added to a three-necked flask. After stirring thoroughly until 4,4-diaminodiphenyl ether was completely dissolved, 0.02 mol of pyromellitic dianhydride was added. An ice-water bath reaction was carried out in a water bath, with the temperature controlled below 10 °C. The polymerization solution was mechanically stirred for 12 h to obtain a PAA polymerization solution, which was used as the core layer spinning solution (the intrinsic viscosity of the PAA polymerization solution was 0.98 dL / g, and the solid content was 18%). A PAN polymerization solution with a solid content of 12% was used as the shell layer spinning solution.

[0068] Step 2, the core layer spinning solution and the core layer spinning solution were respectively filled into two 5 mL syringes, and then placed in an oven at 50 °C for 5 h of static defoaming treatment. Using an electrospinning device, a 19 G coaxial electrospinning needle was selected, and a silicon oil paper was pasted on the roller receiver to facilitate obtaining a complete nanofiber membrane. The roller speed was set at 2000 rpm, the positive spinning pressure was set at 22 kv, the negative pressure was 3 kv, the flow rate of the shell layer spinning solution was adjusted to 0.25 mL / h, the flow rate of the core layer spinning solution was 0.08 mL / h, the distance between the syringe and the roller was 15 cm, the temperature setting value was 50 °C, and the humidity setting value was 30%. Continuous electrospinning was carried out for 15 h to obtain a PAA / PAN coaxial fiber membrane with a certain thickness. To ensure complete volatilization of the solvent, it was placed in a vacuum oven at 50 °C for 12 h of drying treatment.

[0069] Step 3, the PAA / PAN coaxial fiber membrane was placed in a high-temperature oven for pre-oxidation and imidization treatment at a heating rate of 5 °C / min. The specific heating program was: holding at 150 °C, 200 °C, and 300 °C for 1 h each to obtain a sample PI / PAN coaxial fiber membrane.

[0070] Step 4, under nitrogen protection, the PI / PAN coaxial fiber membrane was sandwiched between graphite plates and placed in a tube furnace for carbonization treatment. The carbonization temperature was 900 °C, the heating rate was 5 °C / min, and it was held for 10 min. Then, graphitization treatment was carried out. The graphitization temperature was 2500 °C, the heating rate was 10 °C / min, and it was held for 1 h. It was cooled naturally to obtain a sample PI / PAN-CNF-900.

[0071] Comparative Example 1 Comparative Example 1 was a PAN carbon fiber membrane obtained by treating a PAN spinning solution with a solid content of 15% under the same electrospinning conditions and the same pre-oxidation temperature as in Example 1, followed by carbonization at 900 °C, carbonization at 1400 °C, and carbonization at 900 °C and graphitization at 2500 °C. The samples were named PAN-CNF-900, PAN-CNF-1400, and PAN-GNF-2500 respectively.

[0072] Comparative Example 2 Comparative Example 2 is a PI carbon fiber membrane obtained by treating a PAA spinning solution with a solid content of 18% under the same electrospinning conditions and the same imidization temperature, and then carbonizing at 900 °C, carbonizing at 1400 °C, and carbonizing at 900 °C and graphitizing at 2500 °C, respectively. The samples are named PI-CNF-900, PI-CNF-1400, and PI-GNF-2500, respectively.

[0073] Figure 1 The TEM image of the sample obtained in Example 3 is shown. Figures 2 to 4 The SEM micrographs of the samples obtained in Examples 1 to 3 are shown respectively. Figures 5 to 7 The Raman and XRD diagrams of the samples obtained in Examples 1 to 3 and Comparative Examples 1 to 2 are shown respectively. Figure 8 The thermal diffusivity diagrams of the samples obtained in Examples 1 to 3 and Comparative Examples 1 to 2 of the present invention are shown. Figure 9 The thermal conductivity diagrams of the samples obtained in Examples 1 to 3 and Comparative Examples 1 to 2 of the present invention are shown. A more detailed description will be given below with reference to the accompanying drawings.

[0074] 1. Micrograph: Figure 1 The TEM image of the sample obtained in Example 3 is shown. It can be seen that the sample obtained in Example 3 has a core-shell structure, and the core layer is graphitized PI (G PI ), and the shell layer is graphitized PAN (G PAN ).

[0075] Figures 2 to 4 The SEM micrographs of the PI / PAN-CNF-900, PI / PAN-CNF-1400, and PI / PAN-GNF-2500 samples obtained in Examples 1 to 3 are shown respectively.

[0076] It can be seen from the SEM images that PI / PAN-CNF-900 maintains good alignment and has a smooth surface, and the diameter uniformity of the nanofibers is good. This regular morphology is due to the use of a flow rate ratio of the shell spinning solution to the core spinning solution close to 3:1 during the coaxial spinning process, forming a stable Taylor cone through the needle, eliminating the beaded structure commonly found in electrospinning. During the carbonization stage, as the temperature increases continuously, the surface morphology of the CNF changes significantly: as small molecules such as NH3 and CO2 escape, the diameter of the PI / PAN-CNF shrinks uniformly. After high-temperature graphitization treatment, the graphite microcrystalline structure grows and undergoes longitudinal contraction, and non-carbon elements are gradually removed. Wrinkled shrinkage patterns are observed on the surface of PI / PAN-GNF-2500, which is due to the rearrangement of the carbon layer and sp 2This is caused by the stress release phenomenon resulting from hybridization enhancement. It should be noted that even after high-temperature carbonization and graphitization treatments, PI / PAN-CNF-1400 and PI / PAN-GNF-2500 still maintain good alignment and orientation, and the core-shell structure remains intact, without obvious crack or pore structures.

[0077] 2. Raman and XRD Spectra: Figures 5 to 7 The Raman and XRD spectra of PI / PAN-CNF-900, PI / PAN-CNF-1400, and PI / PAN-GNF-2500 obtained in Examples 1 to 3, PAN-CNF-900, PAN-CNF-1400, and PAN-CNF-2500 obtained in Comparative Examples 1 to 2, and PI-CNF-900, PI-CNF-1400, and PI-CNF-2500 obtained in Comparative Examples 1 to 2 are respectively shown.

[0078] Taking Figure 5 in (A) as an example, the Raman curve of PI / PAN-CNF-900 obtained in Example 1 has a smaller D peak and a sharper G peak compared with the Raman curves of the samples obtained in Comparative Examples 1 and 2. Among them, the D peak and the G peak respectively represent the lattice defects of carbon atoms and the characteristic vibration modes of sp 2 hybrid carbon atoms. In other words, the lattice defects of the carbon atoms in PI / PAN-CNF-900 obtained in Example 1 are less than those of PAN-CNF-900 in Comparative Example 1 and PI-CNF-900 in Comparative Example 2, and the graphitization degree of PI / PAN-CNF-900 obtained in Example 1 is higher than that of PAN-CNF-900 in Comparative Example 1 and PI-CNF-900 in Comparative Example 2. The comparison rules between other examples and comparative examples are the same as those between Example 1 and comparative examples. However, the I D / I G of PI / PAN-GNF-2500 obtained in Example 3 is less than that of the samples in Example 1 and Example 2, indicating that PI / PAN-GNF-2500 obtained in Example 3 of the present invention has a relatively high graphitization degree compared with the samples obtained in Example 1 and Example 2.

[0079] From Figure 5 in (B), by comparing the curves of PI / PAN-CNF-900 obtained in Example 1 with the XRD curves of its corresponding comparative examples, it is found that after carbonization at 900 °C, the diffraction peak 2θ values of the (002) crystal plane of PI / PAN-CNF-900 obtained in Example 1, PAN-CNF-900 in Comparative Example 1, and PI-CNF-900 in Comparative Example 2 are distributed in the range of 23.8 to 24.8°, and the corresponding interlayer spacing d 002The value is between 0.35 and 0.38 nm, the full width at half maximum (FWHM) does not differ much, being between 5.27 and 5.66°, and the interplanar spacing (L c ), which is between 1.42 and 1.53 nm, indicates that the carbon materials inside the sample are mainly amorphous carbon at this time. Among them, the (002) diffraction peak of PI / PAN-CNF-900 obtained in Example 1 is sharper than the (002) diffraction peaks of PAN-CNF-900 in Comparative Example 1 and PI-CNF-900 in Comparative Example 2, indicating that PI / PAN-CNF-900 obtained in Example 1 has a higher degree of carbonization. In addition, from Figure 6 and Figure 7 it can be seen that the comparison between other examples and comparative examples follows the same pattern as the comparison between Example 1 and comparative examples, and PI / PAN-GNF-2500 obtained in Example 3 exhibits more excellent graphite lattice parameters. The lattice parameters of different examples and comparative examples are shown in Table 1 in detail.

[0080] Table 1 Lattice parameter table of examples and comparative examples

[0081] 3. Thermal conductivity: Figure 8 and 9 respectively characterize the thermal diffusivity and thermal conductivity of the samples obtained in Examples 1 to 3 and Comparative Examples 1 to 2. It can be clearly seen that the thermal diffusivity and thermal conductivity of the samples obtained in Examples 1 to 3 are higher than those of the corresponding samples in Comparative Examples 1 to 2, that is, the thermal diffusivity and thermal conductivity of PI / PAN-CNF-900 are higher than those of PAN-CNF-900 and PI-CNF-900, and the thermal diffusivity and thermal conductivity of PI / PAN-CNF-1400 are higher than those of PAN-CNF-1400 and PI-CNF-1400, and the thermal diffusivity and thermal conductivity of PI / PAN-GNF-2500 are higher than those of PAN-GNF-2500 and PI-GNF-2500. This is because of the stress matching effect generated at the core-shell interface of PI / PAN coaxial composite carbon fibers, which not only maintains the high orientation characteristics of the polyimide core layer but also further compresses the core layer lattice through the shrinkage stress of the polyacrylonitrile core layer, reducing the formation of graphite defects. In addition, the π-π stacking effect at the coaxial interface forms a continuous phonon transmission channel, increasing its thermal conductivity. Therefore, the samples obtained in Examples 1 to 3 have higher thermal conductivity compared with the corresponding samples in Comparative Examples 1 to 2. That is, a synergistic effect is generated between the polyimide core layer and the polyacrylonitrile core layer, making the thermal diffusivity and thermal conductivity of PI / PAN coaxial composite carbon fibers superior to those of pure PI carbon fibers and pure PAN carbon fibers. In addition, the thermal diffusivity and thermal conductivity of the sample in Example 3 with the best thermal conductivity are 165.018 mm 2 / s and 226.223 W / (m·K). This is because after the graphitization treatment at 2500 °C, the internal graphite microcrystalline structure of Example 3 is gradually improved, the interlayer spacing is reduced, and the graphite defects are small. Therefore, the thermal diffusivity and thermal conductivity are much higher than those of Example 1 and Example 2.

[0082] The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the disclosed form. Many modifications and variations are obvious to one of ordinary skill in the art. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention and design various embodiments with various modifications suited to particular uses.

Claims

1. A method for preparing PI / PAN coaxial composite-based carbon fiber, characterized in that, It includes the following steps: Step 1: Using the polyamic acid polymerization solution as the core layer spinning solution and the polyacrylonitrile polymerization solution as the shell layer spinning solution, through the coaxial spinning process, PAA / PAN fibers are prepared; Step 2: The PAA / PAN fibers are subjected to pre-oxidation and imidization treatments to obtain PI / PAN fibers; the PI / PAN fibers are subjected to carbonization treatment or carbonization and graphitization treatments to obtain PI / PAN coaxial composite base carbon fibers.

2. The preparation method of the PI / PAN coaxial composite base carbon fiber according to claim 1, wherein, In Step 1, the solid content range of the polyamic acid polymerization solution is 10% - 30%.

3. The preparation method of the PI / PAN coaxial composite-based carbon fiber according to claim 1, wherein, In Step 1, the solid content range of the PAN polymerization solution is 10% - 30%.

4. The preparation method of the PI / PAN coaxial composite-based carbon fiber according to claim 1, characterized in that, In Step 1, the coaxial spinning process is a coaxial wet spinning process or a coaxial electrospinning process.

5. The preparation method of the PI / PAN coaxial composite-based carbon fiber according to claim 1, wherein, In Step 1, the flow rate ratio of the shell layer spinning solution to the core layer spinning solution is (2 - 4):(1 - 2).

6. The preparation method of the PI / PAN coaxial composite-based carbon fiber according to claim 1, wherein, In Step 2, the pre-oxidation and imidization treatments are carried out synchronously, and the treatment temperature is 150 °C - 350 °C.

7. The preparation method of the PI / PAN coaxial composite-based carbon fiber according to claim 1, characterized in that, In Step 2, the carbonization temperature is 700 °C - 1800 °C, and the carbonization time is 10 min - 1 h.

8. The preparation method of the PI / PAN coaxial composite-based carbon fiber according to claim 1, characterized in that, In Step 2, the graphitization temperature is 2000 °C - 3000 °C, and the graphitization time is 10 min - 1 h.

9. The PI / PAN coaxial composite base carbon fiber obtained by using the preparation method according to any one of claims 1 - 8.

10. The application of the PI / PAN coaxial composite base carbon fiber according to claim 9 in the fields of heat conduction, electricity conduction, electromagnetic wave absorption, electromagnetic shielding, sensing or supercapacitors.

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