Hollow composite carbon fiber, hollow composite carbon fiber nonwoven material, and preparation method and application thereof

Abstract

This invention discloses a hollow composite carbon fiber, a hollow composite carbon fiber nonwoven material, its preparation method, and its application, belonging to the field of carbon material technology. This application first adds modified bamboo charcoal powder (m-BC) and ionic liquid to a PAN system in a certain proportion to form a composite spinning system, obtaining m-BC / PAN composite fibers, and determining the optimal addition amount of m-BC. Subsequently, the obtained composite fibers are subjected to pre-oxidation and carbonization treatments to prepare a carbon fiber material with a hollow structure. Further, short-cut hollow carbon fibers are dispersed in an aqueous solution system formed by sodium carboxymethyl cellulose and polyvinyl alcohol. A fiber nonwoven network structure is constructed by filtration, and an aqueous dispersion of graphene oxide is deposited on both sides of the fiber network to obtain a graphene oxide / hollow carbon fiber composite nonwoven material. The resulting composite material forms a continuous conductive network inside, exhibiting good conductivity and electromagnetic shielding properties.

Description

Technical Field

[0001] This invention relates to the field of carbon materials technology, specifically to a hollow composite carbon fiber, a hollow composite carbon fiber nonwoven material, its preparation method, and its application. Background Technology

[0002] Currently, polyacrylonitrile (PAN) fibers are mainly produced using wet spinning, but this requires a large amount of organic solvents, leading to problems such as difficult solvent recovery, high energy consumption, and environmental pollution, which has become a key bottleneck restricting the industry's development. In contrast, melt spinning has advantages such as being solvent-free, having a shorter process, and lower costs, significantly reducing investment and emissions, and has therefore attracted widespread attention. However, the melting temperature of PAN is much higher than its thermal decomposition temperature, making melt processing difficult to achieve under conventional conditions. To solve this problem, ionic liquids (ILs) can be introduced into PAN as green plasticizers, reducing the glass transition temperature and melt viscosity by weakening intermolecular interactions, thus achieving controllable melt spinning. In existing PAN melt spinning research, the reinforcing phase is mostly concentrated on inorganic or petroleum-based carbon materials, while biomass carbon materials are insufficiently dispersed and interfacially bonded in polar PAN systems, limiting their reinforcing effect.

[0003] Meanwhile, with the development of information technology, wireless communication, and high-frequency electronic equipment, electromagnetic interference (EMI) has become a key issue affecting system stability and electromagnetic compatibility. Although traditional metal shielding materials have high conductivity, they are dense, easily corroded, and primarily reflective, limiting their application in wearable, flexible electronics, and lightweight systems.

[0004] Therefore, this application is submitted. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a hollow composite carbon fiber, a hollow composite carbon fiber nonwoven material, its preparation method and application. This invention prepares composite fibers by blending modified bamboo charcoal powder (m-BC) with polyacrylonitrile, and further forms a hollow carbon fiber structure through pre-oxidation and carbonization. Then, it combines graphene oxide (GO) to construct a fiber network structure, thereby improving the shortcomings of existing PAN composite fibers in terms of mechanical properties and thermal stability, while improving the structural stability and electromagnetic shielding performance of carbon fiber-based electromagnetic shielding materials.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing hollow composite carbon fiber includes the following steps: (1) Mix the ionic liquid, polyacrylonitrile and modified bamboo charcoal powder evenly to obtain the precursor; (2) The precursor is placed in a melt spinning device for melt spinning to obtain composite fibers; (3) The composite fiber is pre-oxidized and carbonized to obtain hollow composite carbon fiber.

[0007] This invention first introduces modified bamboo charcoal powder as a functional filler into a polyacrylonitrile (PAC) system. Modified bamboo charcoal powder / PAC composite fibers are then prepared using an ion-solution-assisted melt spinning process. Following pre-oxidation and carbonization treatments, hollow carbon fibers are formed. This achieves synergistic regulation of the biomass carbon material and carbon fiber structure while maintaining the good fiber-forming properties of PAC fibers. The modified bamboo charcoal powder forms a relatively uniform distribution structure within the fiber, resulting in a structurally stable and high-performance hollow carbon fiber material.

[0008] As an embodiment of this application, the ionic liquid is at least one of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium thiocyanate, and 1-ethyl-3-methylimidazolium acetate.

[0009] The modified bamboo charcoal powder mentioned above is the modified bamboo charcoal powder prepared in CN202510706990.9.

[0010] As an embodiment of this application, the modified bamboo charcoal powder is 0-10% of the mass of polyacrylonitrile, preferably 3-5%.

[0011] As an embodiment of this application, the ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is (3~4):2.

[0012] As an embodiment of this application, the melt spinning temperature is 140~150℃ and the take-up speed is 500~1000rpm.

[0013] As an implementation scheme of this application, the pre-oxidation specifically involves: first heating to 95~105℃ and holding for 0.2~2 h; then heating to 125~135℃ and holding for 0.2~2 h; then heating to 155~165℃ and holding for 0.2~2 h; then heating to 185~195℃ and holding for 0.2~2 h; then heating to 215~225℃ and holding for 0.2~2 h; then heating to 245~255℃ and holding for 0.2~2 h; and finally heating to 275~285℃ and holding for 0.2~2 h.

[0014] As an implementation scheme of this application, the carbonization in step (3) specifically involves: first heating to 550~650℃ and holding for 0.2~2 h; then heating to 950~1050℃ and holding for 0.2~2 h.

[0015] As an implementation scheme of this application, the carbonization in step (3) is specifically as follows: first, the temperature is raised to 550~650℃ and held for 0.2~2 h; then the temperature is raised to 950~1050℃ and held for 0.2~2 h; then the temperature is raised to 1500~1700℃ and held for 0.2~2 h; then the temperature is raised to 1950~2000℃ and held for 0.2~2 h.

[0016] As an implementation scheme of this application, the carbonization in step (3) is specifically as follows: first, the temperature is raised to 550~650℃ and held for 0.2~2 h; then the temperature is raised to 950~1050℃ and held for 0.2~2 h; then the temperature is raised to 1500~1700℃ and held for 0.2~2 h; then the temperature is raised to 1950~2000℃ and held for 0.2~2 h; then the temperature is raised to 2450~2550℃ and held for 0.2~2 h; finally the temperature is raised to 2950~3050℃ and held for 0.2~2 h.

[0017] This application also provides a hollow composite carbon fiber, which is prepared by the preparation method described above.

[0018] This application also provides a method for preparing hollow composite carbon fiber nonwoven material, including the following steps: S1. Cut the hollow composite carbon fiber, place the cut hollow composite carbon fiber in a dispersion system and stir, filter, and obtain pretreated hollow composite carbon fiber. S2. Graphene oxide aqueous dispersion was dropped onto the two surfaces of the pretreated hollow composite carbon fiber, and then dried to obtain hollow composite carbon fiber nonwoven material. The hollow composite carbon fiber is the hollow composite carbon fiber described above.

[0019] This application involves cutting hollow carbon fibers into short fibers and dispersing them in an aqueous solution of sodium carboxymethyl cellulose and polyvinyl alcohol. A fiber network structure is constructed through filtration, and then an aqueous dispersion of graphene oxide is deposited on the fiber surface to obtain a graphene oxide / cut hollow carbon fiber composite nonwoven material. This method, by constructing a three-dimensional conductive network structure synergistically formed by hollow carbon fibers and graphene oxide, improves the structural stability and interfacial bonding of the material, while enhancing the multiple scattering and energy dissipation capabilities of electromagnetic waves within the material, resulting in a material with excellent electromagnetic shielding performance. This preparation method has a simple process flow, widely available raw materials, and can be continuously prepared, showing promising application prospects in the fields of electromagnetic shielding materials and functional composite materials.

[0020] As an embodiment of this application, the dispersion system includes sodium carboxymethyl cellulose, polyvinyl alcohol and water; the solid-liquid ratio of sodium carboxymethyl cellulose, polyvinyl alcohol and water is (1~5) g: (0.02~0.1) g: (400~600) mL.

[0021] As an embodiment of this application, the method for preparing the dispersion system is as follows: dissolving 1-4 g of sodium carboxymethyl cellulose in 400-600 mL of water to obtain a sodium carboxymethyl cellulose solution; dissolving 0.02-0.1 g of polyvinyl alcohol in 2-10 mL of water to obtain a polyvinyl alcohol solution; and mixing the sodium carboxymethyl cellulose solution and the polyvinyl alcohol solution prepared above evenly to obtain the dispersion system.

[0022] As an embodiment of this application, the mass concentration of graphene oxide in the graphene oxide aqueous dispersion is 0.5~2%.

[0023] This application also provides a hollow composite carbon fiber nonwoven material, which is prepared by the preparation method described above.

[0024] This application also provides an application of hollow composite carbon fiber nonwoven material in the preparation of electromagnetic shielding materials.

[0025] The beneficial effects of this invention are as follows: First, the melt spinning ratio of polyacrylonitrile (PAN) is determined in an ionic liquid-assisted system. Modified bamboo charcoal powder (m-BC) is added to the PAN system in a certain proportion to form a composite spinning system. The composite fiber is then extruded using a melt spinning process, and collected by winding and adjusting the winding speed to obtain m-BC / PAN composite fibers. The optimal addition amount of m-BC is determined. Subsequently, the obtained composite fibers are subjected to pre-oxidation and carbonization treatments to prepare carbon fiber materials with a hollow structure. Further, chopped hollow carbon fibers are dispersed in an aqueous solution system formed by sodium carboxymethyl cellulose and polyvinyl alcohol. A nonwoven fiber network structure is constructed by filtration, and an aqueous dispersion of graphene oxide is deposited on both sides of the fiber network to obtain a graphene oxide / hollow carbon fiber composite nonwoven material. The resulting composite material forms a continuous conductive network inside, exhibiting good conductivity and electromagnetic shielding properties. The method of this invention is simple, uses widely available raw materials, and has good repeatability, showing promising prospects for industrial application. It can be applied to fields such as electromagnetic shielding materials and electronic device protection. Attached Figure Description

[0026] Figure 1 (a) XRD diffraction pattern and (b) diffraction parameter diagram of composite fibers prepared by different ratios of m-BC / PAN in Examples 1-6.

[0027] Figure 2 The images show SEM images of the m-BC / PAN fiber surfaces in Examples 1-6 at different ratios.

[0028] Figure 3 The graph shows the effects of different m-BC contents on the tensile strength and modulus of the composite fibers in Examples 1-6; and the diameter and elongation at break.

[0029] Figure 4 The images show cross-sectional SEM images of PAN composite fibers (a, b, c) and 3 wt% composite fibers (d, e, f) at carbonization temperatures of 1000℃, 2000℃, and 3000℃, respectively, in Examples 7-12.

[0030] Figure 5 The images show the Raman spectra of 3 wt% composite fibers carbonized at 1000~3000℃ and the Raman spectra of PAN composite fibers carbonized at 3000℃ for Examples 7-12.

[0031] Figure 6 This is a flowchart illustrating the preparation process of the hollow composite carbon fiber nonwoven material of this application.

[0032] Figure 7 The image shows a cross-sectional SEM image of the 3000-GO / 3 wt%SCF composite material from Example 15.

[0033] Figure 8 The optimal EMI SE parameters in the X-band for the 2000-GO / 3 wt%SCF, 3000-GO / SCF, and 3000-GO / 3 wt%SCF samples of Examples 13-15 are shown. Figure 9 The attenuation constant (a) and effective absorption rate (b) of the 2000-GO / 3 wt%SCF, 3000-GO / SCF, and 3000-GO / 3 wt%SCF samples from Examples 13-15 are shown. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0036] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0037] In this application, there are no particular restrictions on the specific dispersion and mixing methods.

[0038] Unless otherwise specified, all components, raw materials, or instruments used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0039] The following embodiments are provided to facilitate understanding of the invention. These embodiments are not intended to limit the scope of the claims. Example 1

[0040] A method for preparing composite fibers includes the following steps: (1) The ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile (brand name: P303197, Mw≈150000, Shanghai Aladdin Biochemical Technology Co., Ltd., the same below) were mixed evenly to obtain the precursor; The mass ratio of polyacrylonitrile to ionic liquid is 3:2.

[0041] (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to make the powder melt. Then, the melt is driven by the screw to be extruded through the die and pulled through the roller to the take-up device. The take-up speed is 800 rpm. The powder is cleaned in ultrasound for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-1 (PANComposite fiber). Example 2

[0042] A method for preparing composite fibers includes the following steps: (1) The ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile are mixed evenly, and then modified bamboo charcoal powder is added and mixed evenly to obtain the precursor; the modified bamboo charcoal powder is the modified bamboo charcoal powder of Example 5 in Patent 202510706990.9. The ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is 3:2. The modified bamboo charcoal powder accounts for 3% of the mass of polyacrylonitrile. (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to heat the powder to a molten state. Then, the melt is driven by a screw to be extruded through a die and pulled through a roller to a take-up device. The take-up speed is 800 rpm. The powder is cleaned in an ultrasonic environment for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-2 (3wt% PAN Composite fiber). Example 3

[0043] A method for preparing composite fibers includes the following steps: (1) The ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile are mixed evenly, and then modified bamboo charcoal powder is added and mixed evenly to obtain the precursor; the modified bamboo charcoal powder is the modified bamboo charcoal powder of Example 5 in Patent 202510706990.9. The ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is 3:2. The modified bamboo charcoal powder comprises 5% of the mass of polyacrylonitrile. (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to make the powder melt. Then, the melt is driven by the screw to be extruded through the die and pulled through the roller to the take-up device. The take-up speed is 800 rpm. The powder is cleaned in ultrasound for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-3 (5wt% PANComposite fiber). Example 4

[0044] A method for preparing composite fibers includes the following steps: (1) The ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile are mixed evenly, and then modified bamboo charcoal powder is added and mixed evenly to obtain the precursor; the modified bamboo charcoal powder is the modified bamboo charcoal powder of Example 5 in Patent 202510706990.9. The ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is 3:2. The modified bamboo charcoal powder accounts for 7% of the mass of polyacrylonitrile. (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to make the powder melt. Then, the melt is driven by the screw to be extruded through the die and pulled through the roller to the take-up device. The take-up speed is 800 rpm. The powder is cleaned in ultrasound for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-4 (7wt% PANComposite fiber). Example 5

[0045] A method for preparing composite fibers includes the following steps: (1) The ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile are mixed evenly, and then modified bamboo charcoal powder is added and mixed evenly to obtain the precursor; the modified bamboo charcoal powder is the modified bamboo charcoal powder of Example 5 in Patent 202510706990.9. The ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is 3:2. The modified bamboo charcoal powder comprises 9% of the mass of polyacrylonitrile. (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to make the powder melt. Then, the melt is driven by the screw to be extruded through the die and pulled through the roller to the take-up device. The take-up speed is 800 rpm. The powder is cleaned in ultrasound for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-5 (9wt% PANComposite fiber). Example 6

[0046] A method for preparing composite fibers includes the following steps: (1) The ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile are mixed evenly, and then modified bamboo charcoal powder is added and mixed evenly to obtain the precursor; the modified bamboo charcoal powder is the modified bamboo charcoal powder of Example 5 in Patent 202510706990.9. The ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is 3:2. The modified bamboo charcoal powder comprises 10% of the mass of polyacrylonitrile. (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to make the powder melt. Then, the melt is driven by the screw to be extruded through the die and pulled through the roller to the take-up device. The take-up speed is 800 rpm. The powder is cleaned in ultrasound for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-6 (10wt% PANComposite fiber).

[0047] The XRD diffraction patterns and (b) diffraction parameters of the composite fibers-1 to composite fibers-6 prepared in Examples 1 to 6 are shown below. Figure 1 (a) Figure 1 As shown in (b).

[0048] Figure 1(a) It is found that the melt-spun PAN composite fiber (composite fiber-1) exhibits diffraction signals at 2θ≈17° and 26°, corresponding to the (100) and (110) crystal planes of the PAN composite fiber, respectively. A relatively wide diffuse peak is visible between 2θ≈22~27°, reflecting the presence of a side-order disordered amorphous phase. The main peak of PAN is located at 17.05°. With the introduction and increase of m-BC, the main peak shifts to a lower angle overall, indicating that the interlayer spacing increases and the compactness of chain segment stacking is disturbed.

[0049] Figure 1 (b) The changes in grain size and crystallinity are shown. The grain size of each sample on the (100) crystal plane generally falls within the range of 3-4 nm, showing a trend of first decreasing and then increasing with the increase of m-BC (modified bamboo charcoal powder) content. The grain sizes of 3wt% and 5wt% composite fibers (Examples 2 and 3) are 3.44 nm and 3.33 nm, respectively, both lower than those of PAN composite fibers, indicating that a small amount of m-BC as heterogeneous nucleation sites can increase the nucleus density and generate more but smaller grains. When the content of modified bamboo charcoal powder continues to increase, the crystal size rebounds due to uneven crystallization and defect accumulation.

[0050] The crystallinity of the PAN composite fiber was 37.21%, with little difference between the 3 wt% and 5 wt% composite fibers. This indicates that the low m-BC content resulted in good interfacial bonding with the PAN matrix and had no significant impact on the overall crystallinity. As the m-BC content increased to 9% and 10%, the crystallinity decreased to 32.43% and 31.15%, respectively. This suggests that interparticle interactions and localized agglomeration hindered crystal growth and orientation, leading to a continuous decrease in crystallinity. This change typically results in reduced mechanical properties, making the material more brittle.

[0051] The surface SEM images of composite fibers-1 to composite fibers-6 prepared in Examples 1 to 6 are shown below. Figure 2 (a) ~ Figure 2 As shown in (f). Figure 2 (a) The surface of the PAN composite fiber is smooth and dense, with no obvious particles, indicating that the molecular chains are fully oriented and form a continuous phase during the melt spinning-drawing process, which is consistent with its high crystallinity. When the m-BC content increases to 3 wt% and 5 wt%, ( Figure 2 (b) and (c) show that although a few fine lines appear on the fiber surface, it still maintains a high degree of smoothness and no obvious agglomeration is observed, indicating that the filler is relatively uniformly dispersed in the matrix. When the m-BC content continues to increase, its surface roughness increases and grooves, stripes and local defects appear, indicating that the introduction of high filler enhances the interference with melt flow and tensile orientation, which may be accompanied by local phase separation and stress concentration.

[0052] Figure 3Figures (a) and (b) show the changes in the mechanical properties of the composite fiber with the addition of m-BC. The tensile strength and modulus of the PAN composite fiber in the figures are 153.52 MPa and 5.58 GPa, respectively. When 3 wt% m-BC is added, the tensile strength and modulus of the 3 wt% composite fiber are 204.32 MPa and 6.81 GPa, respectively, representing increases of 33.09% and 22.04% compared to the PAN composite fiber. This indicates that a small amount of m-BC is beneficial for interfacial load transfer and chain segment orientation, thereby enhancing mechanical properties. When the m-BC content increases to 5 wt%, the strength decreases to 154.59 MPa. When the filler content is continuously increased to 7-10 wt%, both the tensile strength and modulus decrease significantly, indicating that high filler content easily leads to agglomeration, causing stress concentration and a decrease in strength.

[0053] Figure 3 (b) The diameter of the composite fibers fluctuates between 49 and 55 μm. The diameters of the PAN composite fibers and the 3 wt% composite fibers are similar, indicating that their melt flowability and tensile orientation are consistent. However, the diameters of the 9 wt% and 10 wt% samples are significantly larger, indicating that excessive m-BC induces agglomeration, leading to increased system viscosity and inhibiting melt flow and the stretching orientation process. The results of the elongation at break are also consistent with this. However, the 3 wt% composite fiber exhibits the best toughness, indicating that the addition of an appropriate amount of m-BC does not disrupt the chain movement of PAN. Example 7

[0054] A method for preparing hollow composite carbon fiber includes the following steps: (1) Mix the ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile evenly to obtain the precursor; The mass ratio of polyacrylonitrile to ionic liquid is 3:2.

[0055] (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to make the powder melt. Then, the melt is driven by the screw to be extruded through the die and pulled through the roller to the take-up device. The take-up speed is 800 rpm. The powder is cleaned in ultrasound for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-1 (PANComposite fiber).

[0056] (3) The composite fiber-1 was pre-oxidized in an air atmosphere in a muffle furnace. The temperature was increased from room temperature to 100℃ at 1℃ / min and held for 0.5 h; then increased to 130℃ at 1℃ / min and held for 0.5 h; then increased to 160℃ at 1℃ / min and held for 0.5 h; then increased to 190℃ at 1℃ / min and held for 0.5 h; then increased to 220℃ at 1℃ / min and held for 0.5 h; then increased to 250℃ at 1℃ / min and held for 0.5 h; and finally increased to 280℃ at 1℃ / min and held for 0.5 h.

[0057] (4) After the pre-oxidation is completed, the fiber is transferred to a high-temperature graphitization furnace. Under N2 atmosphere, the temperature is first raised to 600℃ at 5℃ / min and held for 0.5 h; then the temperature is raised to 1000℃ at 5℃ / min and held for 0.5 h. The hollow carbon fiber obtained is named 1000-CF. Example 8

[0058] A method for preparing hollow composite carbon fiber includes the following steps: (1) Mix the ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile evenly to obtain the precursor; The mass ratio of polyacrylonitrile to ionic liquid is 3:2.

[0059] (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to make the powder melt. Then, the melt is driven by the screw to be extruded through the die and pulled through the roller to the take-up device. The take-up speed is 800 rpm. The powder is cleaned in ultrasound for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-1 (PANComposite fiber).

[0060] (3) The composite fiber-1 was pre-oxidized in an air atmosphere in a muffle furnace. The temperature was increased from room temperature to 100℃ at 1℃ / min and held for 0.5 h; then increased to 130℃ at 1℃ / min and held for 0.5 h; then increased to 160℃ at 1℃ / min and held for 0.5 h; then increased to 190℃ at 1℃ / min and held for 0.5 h; then increased to 220℃ at 1℃ / min and held for 0.5 h; then increased to 250℃ at 1℃ / min and held for 0.5 h; and finally increased to 280℃ at 1℃ / min and held for 0.5 h.

[0061] (4) After the pre-oxidation is completed, the fiber is transferred to a high-temperature graphitization furnace. Under N2 atmosphere, the temperature is first increased to 600℃ at 5℃ / min and held for 0.5 h; then increased to 1000℃ at 5℃ / min; then increased to 1600℃ at 10℃ / min and held for 0.5 h; then increased to 2000℃ at 4℃ / min and held for 1 h. The hollow carbon fiber obtained is named 2000-CF. Example 9

[0062] A method for preparing hollow composite carbon fiber includes the following steps: (1) Mix the ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile evenly to obtain the precursor; The mass ratio of polyacrylonitrile to ionic liquid is 3:2.

[0063] (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to make the powder melt. Then, the melt is driven by the screw to be extruded through the die and pulled through the roller to the take-up device. The take-up speed is 800 rpm. The powder is cleaned in ultrasound for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-1 (PANComposite fiber).

[0064] (3) The composite fiber-1 was pre-oxidized in an air atmosphere in a muffle furnace. The temperature was increased from room temperature to 100℃ at 1℃ / min and held for 0.5 h; then increased to 130℃ at 1℃ / min and held for 0.5 h; then increased to 160℃ at 1℃ / min and held for 0.5 h; then increased to 190℃ at 1℃ / min and held for 0.5 h; then increased to 220℃ at 1℃ / min and held for 0.5 h; then increased to 250℃ at 1℃ / min and held for 0.5 h; and finally increased to 280℃ at 1℃ / min and held for 0.5 h.

[0065] (4) After the pre-oxidation is completed, the fiber is transferred to a high-temperature graphitization furnace. Under N2 atmosphere, the temperature is first increased to 600℃ at 5℃ / min and held for 0.5 h; then increased to 1000℃ at 5℃ / min; then increased to 1600℃ at 10℃ / min and held for 0.5 h; then increased to 2000℃ at 4℃ / min and held for 1 h; then increased to 2500℃ at 10℃ / min and held for 1 h; and finally increased to 3000℃ at 10℃ / min and held for 2 h. The hollow carbon fiber obtained is named 3000-CF. Example 10

[0066] A method for preparing hollow composite carbon fiber includes the following steps: (1) The ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile are mixed evenly, and then modified bamboo charcoal powder is added and mixed evenly to obtain the precursor; the modified bamboo charcoal powder is the modified bamboo charcoal powder of Example 5 in Patent 202510706990.9. The ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is 3:2. The modified bamboo charcoal powder accounts for 3% of the mass of polyacrylonitrile. (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to heat the powder to a molten state. Then, the melt is driven by a screw to be extruded through a die and pulled through a roller to a take-up device. The take-up speed is 800 rpm. The powder is cleaned in an ultrasonic environment for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-2 (3wt% PAN Composite fiber).

[0067] (3) The composite fiber-2 was pre-oxidized in an air atmosphere in a muffle furnace. The temperature was increased from room temperature to 100℃ at 1℃ / min and held for 0.5 h; then increased to 130℃ at 1℃ / min and held for 0.5 h; then increased to 160℃ at 1℃ / min and held for 0.5 h; then increased to 190℃ at 1℃ / min and held for 0.5 h; then increased to 220℃ at 1℃ / min and held for 0.5 h; then increased to 250℃ at 1℃ / min and held for 0.5 h; and finally increased to 280℃ at 1℃ / min and held for 0.5 h.

[0068] (4) After the pre-oxidation is completed, the fiber is transferred to a high-temperature graphitization furnace. Under N2 atmosphere, the temperature is first raised to 600℃ at 5℃ / min and held for 0.5 h; then the temperature is raised to 1000℃ at 5℃ / min and held for 0.5 h. The hollow carbon fiber obtained is named 1000-3. Example 11

[0069] A method for preparing hollow composite carbon fiber includes the following steps: (1) The ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile are mixed evenly, and then modified bamboo charcoal powder is added and mixed evenly to obtain the precursor; the modified bamboo charcoal powder is the modified bamboo charcoal powder of Example 5 in Patent 202510706990.9. The ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is 3:2. The modified bamboo charcoal powder accounts for 3% of the mass of polyacrylonitrile. (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to heat the powder to a molten state. Then, the melt is driven by a screw to be extruded through a die and pulled through a roller to a take-up device. The take-up speed is 800 rpm. The powder is cleaned in an ultrasonic environment for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-2 (3wt% PAN Composite fiber).

[0070] (3) The composite fiber-2 was pre-oxidized in an air atmosphere in a muffle furnace. The temperature was increased from room temperature to 100℃ at 1℃ / min and held for 0.5 h; then increased to 130℃ at 1℃ / min and held for 0.5 h; then increased to 160℃ at 1℃ / min and held for 0.5 h; then increased to 190℃ at 1℃ / min and held for 0.5 h; then increased to 220℃ at 1℃ / min and held for 0.5 h; then increased to 250℃ at 1℃ / min and held for 0.5 h; and finally increased to 280℃ at 1℃ / min and held for 0.5 h.

[0071] (4) After the pre-oxidation is completed, the fiber is transferred to a high-temperature graphitization furnace. Under N2 atmosphere, the temperature is first increased to 600℃ at 5℃ / min and held for 0.5 h; then increased to 1000℃ at 5℃ / min; then increased to 1600℃ at 10℃ / min and held for 0.5 h; then increased to 2000℃ at 4℃ / min and held for 1 h. The hollow carbon fiber obtained is named 2000-3. Example 12

[0072] A method for preparing hollow composite carbon fiber includes the following steps: (1) The ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile are mixed evenly, and then modified bamboo charcoal powder is added and mixed evenly to obtain the precursor; the modified bamboo charcoal powder is the modified bamboo charcoal powder of Example 5 in Patent 202510706990.9. The ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is 3:2. The modified bamboo charcoal powder accounts for 3% of the mass of polyacrylonitrile. (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to heat the powder to a molten state. Then, the melt is driven by a screw to be extruded through a die and pulled through a roller to a take-up device. The take-up speed is 800 rpm. The powder is cleaned in an ultrasonic environment for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-2 (3wt% PAN Composite fiber).

[0073] (3) The composite fiber-2 was pre-oxidized in an air atmosphere in a muffle furnace. The temperature was increased from room temperature to 100℃ at 1℃ / min and held for 0.5 h; then increased to 130℃ at 1℃ / min and held for 0.5 h; then increased to 160℃ at 1℃ / min and held for 0.5 h; then increased to 190℃ at 1℃ / min and held for 0.5 h; then increased to 220℃ at 1℃ / min and held for 0.5 h; then increased to 250℃ at 1℃ / min and held for 0.5 h; and finally increased to 280℃ at 1℃ / min and held for 0.5 h.

[0074] (4) After the pre-oxidation is completed, the fiber is transferred to a high-temperature graphitization furnace. Under N2 atmosphere, the temperature is first increased to 600℃ at 5℃ / min and held for 0.5h; then increased to 1000℃ at 5℃ / min; then increased to 1600℃ at 10℃ / min and held for 0.5h; then increased to 2000℃ at 4℃ / min and held for 1h; then increased to 2500℃ at 10℃ / min and held for 1h; and finally increased to 3000℃ at 10℃ / min and held for 2h. The hollow carbon fiber obtained is named 3000-3.

[0075] The inventors of this application discovered that high-temperature carbonization and graphitization determine the continuous evolution process of "defect-disordered layers-graphite microcrystals" in carbon materials, thereby affecting electrical conductivity, electromagnetic parameters, and the dominant electromagnetic shielding mechanism. Cross-sectional morphology shows that as the carbonization temperature increases from 1000℃ to 3000℃ for graphitization, the hollow tube structures of both systems exhibit an evolutionary trend from unstable to stable and from irregular to regular. The cross-sectional SEM images of the hollow composite fibers in Examples 7-12 are shown below. Figure 4 As shown in (a) to (f).

[0076] like Figure 4 As shown in (a), the hollow cavity of the PAN composite fiber is relatively irregular after carbonization at 1000℃, and cracks are visible inside the wall layer; when the carbonization temperature is raised to 2000℃ ( Figure 4 b) and at 3000℃ ( Figure 4 c) The hollow structure gradually becomes clearer, forming a more typical concentric hollow tube structure. The inner cavity is more rounded, and the wall layers are denser and smoother, indicating that high-temperature treatment promotes carbon layer rearrangement and densification. In contrast, such as Figure 4 As shown in (d, e), the 3 wt% composite fiber exhibits a hollow structure and relatively rough wall texture at 1000℃ and 2000℃; when the temperature rises to 3000℃, as... Figure 4As shown in (f), the hollow feature is more pronounced, and the inner cavity is larger, forming a morphology of "hollow cavity-rough wall layer" coexisting. This structure, on the one hand, extends the propagation path of electromagnetic waves in the cavity and enhances multiple reflections; on the other hand, the rough wall layer provides abundant interfaces and defect sites, which is beneficial for multi-scale scattering and polarization loss. At the same time, the introduction of m-BC brings additional carbonaceous heterogeneous interfaces and structural perturbations, which participate in microstructure rearrangement at high temperatures, making it easier for fibers to form rough wall layers, thus providing a favorable structural basis for electromagnetic wave reflection-scattering-dissipation.

[0077] The Raman spectra of the hollow composite fibers in Examples 7-12 are as follows: Figure 5 As shown. From Figure 5 Typical D bands (≈1350 cm) can be observed in the middle. -1 ) and G-band (≈1580cm cm) -1 Characteristic peaks. As the carbonization temperature increases, the G peak gradually narrows and its shape changes from broad and blunt to sharp, while the relative intensity of the D peak decreases significantly, and the I peak... D / I G The value gradually decreases, indicating that the defect content continues to decline. 2 The degree of ordering of the carbon framework was significantly improved. Among them, 3000-3% of sample I D / I G The value of 0.045 indicates that it has the lowest defect density, the most fully developed graphite microcrystals, and a structure that is closest to a highly ordered disordered graphite structure.

[0078] A method for preparing hollow composite carbon fiber nonwoven fabric material includes the following steps: (1) The ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile are mixed evenly, and then modified bamboo charcoal powder is added and mixed evenly to obtain the precursor; the modified bamboo charcoal powder is the modified bamboo charcoal powder of Example 5 in Patent 202510706990.9. The ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is 3:2. The modified bamboo charcoal powder accounts for 3% of the mass of polyacrylonitrile. (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to make the powder melt. Then, the melt is driven by the screw to be extruded through the die and pulled through the roller to the take-up device. The take-up speed is 800 rpm. The powder is cleaned in ultrasound for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-2 (3 wt% PAN Composite fiber).

[0079] (3) The composite fiber-2 was pre-oxidized in an air atmosphere in a muffle furnace. The temperature was increased from room temperature to 100℃ at 1℃ / min and held for 0.5 h; then increased to 130℃ at 1℃ / min and held for 0.5 h; then increased to 160℃ at 1℃ / min and held for 0.5 h; then increased to 190℃ at 1℃ / min and held for 0.5 h; then increased to 220℃ at 1℃ / min and held for 0.5 h; then increased to 250℃ at 1℃ / min and held for 0.5 h; and finally increased to 280℃ at 1℃ / min and held for 0.5 h.

[0080] (4) After the pre-oxidation is completed, the fiber is transferred to a high-temperature graphitization furnace. Under N2 atmosphere, the temperature is first increased to 600℃ at 5℃ / min and held for 0.5 h; then increased to 1000℃ at 5℃ / min; then increased to 1600℃ at 10℃ / min and held for 0.5 h; then increased to 2000℃ at 4℃ / min and held for 1 h. The hollow carbon fiber obtained is named 2000-3.

[0081] (5) Cut the hollow fibers mentioned above into short hollow carbon fibers of 3-6 mm; (6) Dissolve 2 g of sodium carboxymethyl cellulose (model: 1500-3100 mpa.s, Shanghai Maclean Biochemical Technology Co., Ltd., the same below) in 500 mL of water to obtain sodium carboxymethyl cellulose solution; dissolve 0.05 g of polyvinyl alcohol (model: 1788, 98%, Tianjin Huasheng Chemical Reagent Co., Ltd., the same below) in 5 mL of water to obtain polyvinyl alcohol solution; mix the sodium carboxymethyl cellulose solution and polyvinyl alcohol solution prepared above evenly to obtain a dispersion system.

[0082] Add 0.5 g of short-cut hollow carbon fibers in batches to the above dispersion system and stir for 0.5 h; (7) Transfer the obtained slurry to a vacuum filter and perform vacuum filtration for 4 hours until the deionized water is completely drained, so that a fiber network is formed on the surface of the filter membrane. (8) During the filtration process of the composite hollow carbon fiber skeleton, 5 mL of 0.5 wt% graphene oxide (model: 300 mesh 1%, Beijing Carbon Century Technology Co., Ltd., the same below) aqueous dispersion was added to both sides of the fiber skeleton simultaneously to promote inter-fiber bridging and network stability. (9) After vacuum filtration and molding, the wet film was dried at 40°C for 48 h to obtain graphene oxide / chopped hollow carbon fiber nonwoven material (GO / SCF). The sample was named 2000-GO / 3wt%SCF.

[0083] Preparation process as follows Figure 6 As shown. Example 14

[0084] A method for preparing hollow composite carbon fiber nonwoven fabric material includes the following steps: (1) Mix the ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile evenly to obtain the precursor; The mass ratio of polyacrylonitrile to ionic liquid is 3:2.

[0085] (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to make the powder melt. Then, the melt is driven by the screw to be extruded through the die and pulled through the roller to the take-up device. The take-up speed is 800 rpm. The powder is cleaned in ultrasound for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-1 (PANComposite fiber).

[0086] (3) The composite fiber-1 was pre-oxidized in an air atmosphere in a muffle furnace. The temperature was increased from room temperature to 100℃ at 1℃ / min and held for 0.5 h; then increased to 130℃ at 1℃ / min and held for 0.5 h; then increased to 160℃ at 1℃ / min and held for 0.5 h; then increased to 190℃ at 1℃ / min and held for 0.5 h; then increased to 220℃ at 1℃ / min and held for 0.5 h; then increased to 250℃ at 1℃ / min and held for 0.5 h; and finally increased to 280℃ at 1℃ / min and held for 0.5 h.

[0087] (4) After the pre-oxidation is completed, the fiber is transferred to a high-temperature graphitization furnace. Under N2 atmosphere, the temperature is first increased to 600℃ at 5℃ / min and held for 0.5 h; then increased to 1000℃ at 5℃ / min; then increased to 1600℃ at 10℃ / min and held for 0.5 h; then increased to 2000℃ at 4℃ / min and held for 1 h; then increased to 2500℃ at 10℃ / min and held for 1 h; and finally increased to 3000℃ at 10℃ / min and held for 2 h. The hollow carbon fiber obtained is named 3000.

[0088] (5) Cut the hollow fibers mentioned above into short hollow carbon fibers of 3-6 mm; (6) Dissolve 2 g of sodium carboxymethyl cellulose in 500 mL of water to obtain a sodium carboxymethyl cellulose solution; dissolve 0.05 g of polyvinyl alcohol in 5 mL of water to obtain a polyvinyl alcohol solution; mix the sodium carboxymethyl cellulose solution and the polyvinyl alcohol solution prepared above evenly to obtain a dispersion system.

[0089] Add 0.5 g of short-cut hollow carbon fibers in batches to the above dispersion system and stir for 0.5 h; (7) Transfer the obtained slurry to a vacuum filter and perform vacuum filtration for 4 hours until the deionized water is completely drained, so that a fiber network is formed on the surface of the filter membrane. (8) During the filtration process of the composite hollow carbon fiber skeleton, 5 mL of 0.5 wt% graphene oxide aqueous dispersion was added to both sides of the fiber skeleton simultaneously to promote inter-fiber bridging and network stability. (9) After vacuum filtration and molding, the wet film was dried at 40°C for 48 h to obtain graphene oxide / chopped hollow carbon fiber nonwoven material (GO / SCF). The sample was named 3000-GO / SCF. Example 15

[0090] A method for preparing hollow composite carbon fiber nonwoven fabric material includes the following steps: (1) The ionic liquid (1-butyl-3-methylimidazolium chloride) and polyacrylonitrile are mixed evenly, and then modified bamboo charcoal powder is added and mixed evenly to obtain the precursor; the modified bamboo charcoal powder is the modified bamboo charcoal powder of Example 5 in Patent 202510706990.9. The ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is 3:2. The modified bamboo charcoal powder accounts for 3% of the mass of polyacrylonitrile. (2) The mixed powder is placed in a melt spinning device and heated for 0.2 h (temperature is 145℃) to heat the powder to a molten state. Then, the melt is driven by a screw to be extruded through a die and pulled through a roller to a take-up device. The take-up speed is 800 rpm. The powder is cleaned in an ultrasonic environment for 0.5 h and dried at 80℃ for 12 h to obtain composite fiber-2 (3wt% PAN Composite fiber).

[0091] (3) The composite fiber-2 was pre-oxidized in an air atmosphere in a muffle furnace. The temperature was increased from room temperature to 100℃ at 1℃ / min and held for 0.5 h; then increased to 130℃ at 1℃ / min and held for 0.5 h; then increased to 160℃ at 1℃ / min and held for 0.5 h; then increased to 190℃ at 1℃ / min and held for 0.5 h; then increased to 220℃ at 1℃ / min and held for 0.5 h; then increased to 250℃ at 1℃ / min and held for 0.5 h; and finally increased to 280℃ at 1℃ / min and held for 0.5 h.

[0092] (4) After the pre-oxidation is completed, the fiber is transferred to a high-temperature graphitization furnace. Under N2 atmosphere, the temperature is first increased to 600℃ at 5℃ / min and held for 0.5 h; then increased to 1000℃ at 5℃ / min; then increased to 1600℃ at 10℃ / min and held for 0.5 h; then increased to 2000℃ at 4℃ / min and held for 1 h; then increased to 2500℃ at 10℃ / min and held for 1 h; and finally increased to 3000℃ at 10℃ / min and held for 2 h. The hollow carbon fiber obtained is named 3000-3.

[0093] (5) Cut the hollow fibers mentioned above into short hollow carbon fibers of 3-6 mm; (6) Dissolve 2 g of sodium carboxymethyl cellulose in 500 mL of water to obtain a sodium carboxymethyl cellulose solution; dissolve 0.05 g of polyvinyl alcohol in 5 mL of water to obtain a polyvinyl alcohol solution; mix the sodium carboxymethyl cellulose solution and the polyvinyl alcohol solution prepared above evenly to obtain a dispersion system.

[0094] Add 0.5 g of short-cut hollow carbon fibers in batches to the above dispersion system and stir for 0.5 h; (7) Transfer the obtained slurry to a vacuum filter and perform vacuum filtration for 4 hours until the deionized water is completely drained, so that a fiber network is formed on the surface of the filter membrane. (8) During the filtration process of the composite hollow carbon fiber skeleton, 5 mL of 0.5 wt% graphene oxide aqueous dispersion was added to both sides of the fiber skeleton simultaneously to promote inter-fiber bridging and network stability. (9) After vacuum filtration and molding, the wet film was dried at 40°C for 48 h to obtain graphene oxide / chopped hollow carbon fiber nonwoven material (GO / SCF). The sample was named 3000-GO / 3wt%SCF.

[0095] Preparation process as follows Figure 6 As shown.

[0096] The cross-sectional SEM images of the hollow composite carbon fiber nonwoven fabric material prepared in Example 15 are shown below. Figure 7 As shown in (a) to (c), the prepared hollow composite carbon fiber nonwoven fabric material exhibits a typical sandwich structure of sheet attachment-fiber skeleton-sheet attachment. Figure 6 (a) shows that GOene is attached to the surface of SCF, and the internal SCF randomly overlaps to form a three-dimensional interconnected porous network. Figure 6 (b) It can be seen that the internal SCFs are all hollow structures arranged in an alternating pattern. Figure 6(c) clearly shows the hollow cavity and tube wall structure at the fiber ends, proving the existence of a large number of hierarchical channels with short fiber cavities in the composite. Based on the consensus theory and extensive research in the field of electromagnetic shielding, multi-level channel structures provide more interfaces and propagation paths for electromagnetic waves incident into the material, causing multiple reflections and scatterings in the pore walls and fiber network, thereby increasing the effective propagation distance inside the material and improving the attenuation opportunity. This multi-reflection-scattering-dissipation effect has been repeatedly emphasized in the review of porous lightweight shielding materials and the study of carbon-based porous systems. On the other hand, GO, as a two-dimensional sheet structure with oxygen-containing functional groups on its surface, is often used to construct high specific surface area interfaces on the surface of carbon-based skeletons. This is because the sheet coating and bridging of GO can significantly increase the number of multiphase interfaces and the area of ​​interface charge accumulation, providing a structural basis for interface polarization and dipole polarization. The layered interface formed by its sheets and fiber skeleton will enhance the interface scattering and internal reflection of electromagnetic waves.

[0097] like Figure 7 As shown, the GO / SCF nonwoven three-dimensional conductive network itself facilitates multiple scattering and reflection of electromagnetic waves within the material. When m-BC is introduced and subjected to high-temperature treatment, the heterogeneity of the heterogeneous interface and microstructure increases, synergistically enhancing multiple scattering and interface dissipation. Ultimately, 3000-GO / 3 wt%SCF achieves the highest SE under the combined effect of the highly graphitized conductive network and polarization loss sites. T (58.55 dB), of which SE A The electromagnetic shielding efficiency (SE) reached 49.57 dB, and the SER was 7.99 dB, indicating that the absorption-dominated electromagnetic shielding mechanism of this system is more prominent. Under carbonization conditions of 3000 °C, the carbon structure of 3000-GO / SCF tends to be highly ordered, with a relative decrease in the number of lattice defects and heterogeneous interfaces. Although high graphitization is beneficial to improving conductivity, the reduction in polarization centers weakens the dipole polarization and interfacial polarization loss channels, thereby limiting SE. A The improvement in performance is consistent with the high graphitization and low polarization loss characteristics of carbon-based electromagnetic shielding materials. In comparison, 2000-GO / 3 wt%SCF outperforms 3000-GO / SCF, primarily because m-BC, as a carbonaceous heterogeneous filler, can pre-build conductive contacts and increase polarization centers, enabling the system to achieve strong carrier response and dielectric loss at 2000 °C. Simultaneously, the defects and polar functional groups introduced by P / N co-modification can further enhance dipole and interfacial polarization, thereby improving SE. A .

[0098] Figure 9(a) shows that the attenuation constant α of the three-component samples increases slowly with frequency in the X band. Among them, 3000-GO / 3wt%SCF maintains the highest value in the entire frequency band, indicating that it has the strongest internal attenuation capability for electromagnetic waves; 2000-GO / 3wt%SCF is the second highest, while 3000-GO / SCF is the lowest. Figure 9 In (b), the effective absorption rate A_eff shows the same trend, with 3000-GO / 3 wt%SCF being closest to 1, 2000-GO / 3 wt%SCF being slightly lower, and 3000-GO / SCF being the lowest, consistent with the aforementioned changes in SEA and SET, indicating that the shielding difference mainly originates from internal absorption and dissipation within the material. It is noteworthy that although the heat treatment temperature of 2000-GO / 3 wt%SCF is lower than that of 3000-GO / SCF, its α is higher, indicating enhanced interfacial polarization and multiple scattering in the system, thereby improving the internal attenuation capability of electromagnetic waves.

[0099] In summary, this invention employs an ionic liquid-assisted melt spinning process to prepare modified bamboo charcoal powder / polyacrylonitrile (m-BC / PAN) composite fibers, and further constructs graphene oxide / chopped hollow carbon fiber (GO / SCF) composite nonwoven materials. During the composite fiber preparation process, modified bamboo charcoal powder and polyacrylonitrile are thoroughly mixed to form a stable spinning system. Continuous extrusion and drawing are achieved through melt spinning, and the influence of key process parameters on the structure and properties of the composite fibers is investigated. The study shows that by rationally controlling the addition ratio of modified bamboo charcoal powder, the filler can be uniformly distributed within the fiber while ensuring good fiber formability, thereby obtaining composite fibers with stable structure and excellent performance. The obtained composite fibers are further heat-treated and carbonized to form chopped carbon fibers with a hollow structure, which serve as a conductive framework and are synergistically assembled with graphene oxide (GO) to construct composite nonwoven materials. Through solution dispersion and forming processes, GO sheets and SCF form an interconnected conductive network structure within the system. The results show that an appropriate SCF content helps to construct a stable three-dimensional conductive pathway within the material, while GO sheets provide abundant interfacial polarization sites, thereby enhancing the attenuation and dissipation capabilities of electromagnetic waves within the material. With increasing heat treatment temperature, the structural order of the carbon material is further improved, and the conductive network gradually becomes more complete, enabling the material to exhibit excellent electromagnetic shielding performance in the X-band. Compared with traditional single carbon filler systems, the composite structure constructed in this invention has significant advantages in conductive network formation and multi-interfacial polarization, providing a new technical approach for the design and fabrication of lightweight and efficient electromagnetic shielding materials.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing hollow composite carbon fibers, characterized in that, Includes the following steps: (1) Mix the ionic liquid, polyacrylonitrile and modified bamboo charcoal powder evenly to obtain the precursor; (2) The precursor is placed in a melt spinning device for melt spinning to obtain composite fibers; (3) The composite fibers are pre-oxidized and carbonized to obtain hollow composite carbon fibers.

2. The method for preparing hollow composite carbon fiber according to claim 1, characterized in that, Satisfy at least one of the following conditions (a) to (c): (a) The ionic liquid is at least one of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium thiocyanate, and 1-ethyl-3-methylimidazolium acetate; (b) The modified bamboo charcoal powder comprises 0-10% of the mass of polyacrylonitrile, preferably 3-5%; (c) The ratio of the sum of the masses of the ionic liquid and polyacrylonitrile to the mass of the ionic liquid is (3~4):

2.

3. The method for preparing hollow composite carbon fiber according to claim 1, characterized in that, The temperature of melt spinning in step (2) is 140~150℃ and the winding speed is 500~900 rpm.

4. The method for preparing hollow composite carbon fiber according to claim 1, characterized in that, The pre-oxidation in step (3) is as follows: first, heat to 95~105℃ and hold for 0.2~2 h; then heat to 125~135℃ and hold for 0.2~2 h; then heat to 155~165℃ and hold for 0.2~2 h; then heat to 185~195℃ and hold for 0.2~2 h; then heat to 215~225℃ and hold for 0.2~2 h; then heat to 245~255℃ and hold for 0.2~2 h; finally heat to 275~285℃ and hold for 0.2~2 h.

5. The method for preparing hollow composite carbon fiber according to claim 1, characterized in that, The carbonization in step (3) specifically involves: first heating to 550~650℃ and holding for 0.2~2 h; then heating to 950~1050℃ and holding for 0.2~2 h; or First, raise the temperature to 550~650℃ and hold for 0.2~2 hours; then raise the temperature to 950~1050℃ and hold for 0.2~2 hours; then raise the temperature to 1500~1700℃ and hold for 0.2~2 hours; then raise the temperature to 1950~2000℃ and hold for 0.2~2 hours; or First, raise the temperature to 550~650℃ and hold for 0.2~2 h; then raise the temperature to 950~1050℃ and hold for 0.2~2 h; then raise the temperature to 1500~1700℃ and hold for 0.2~2 h; then raise the temperature to 1950~2000℃ and hold for 0.2~2 h; then raise the temperature to 2450~2550℃ and hold for 0.2~2 h; finally, raise the temperature to 2950~3050℃ and hold for 0.2~2 h.

6. A hollow composite carbon fiber, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 5.

7. A method for preparing a hollow composite carbon fiber nonwoven material, characterized in that, Includes the following steps: S1. Cut the hollow composite carbon fiber, place the cut hollow composite carbon fiber in a dispersion system and stir, then filter to obtain pretreated hollow composite carbon fiber. S2. Graphene oxide aqueous dispersion was dropped onto the two surfaces of the pretreated hollow composite carbon fiber, and then dried to obtain hollow composite carbon fiber nonwoven material. The hollow composite carbon fiber is the hollow composite carbon fiber as described in claim 6.

8. The method for preparing hollow composite carbon fiber nonwoven material according to claim 7, characterized in that, Satisfy at least one of the following conditions (d) to (e): (d) The dispersion system comprises sodium carboxymethyl cellulose, polyvinyl alcohol, and water; the solid-liquid ratio of sodium carboxymethyl cellulose, polyvinyl alcohol, and water is (1~5) g : (0.02~0.1) g : (400~600) mL; (e) The mass concentration of graphene oxide in the graphene oxide aqueous dispersion is 0.5~2%.

9. A hollow composite carbon fiber nonwoven material, characterized in that, It is prepared by any one of the preparation methods described in claims 7 to 8.

10. The application of the hollow composite carbon fiber nonwoven material according to claim 9 in the preparation of electromagnetic shielding materials.

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