Seaweed-based electromagnetorheological fiber and carbon crystal extraction process

Abstract

This invention discloses an algae-based electromagnetic rheological fiber and a carbon crystal extraction process, relating to the fields of functional fiber materials and carbon crystal extraction technology. The process includes organic acid washing of the washed carbonized fiber with citric acid solution, causing some metal residues on both sides of the annular channels to dissolve. Based on the existing annular channels, an easily separable interface is formed between the core carbonized zone and the outer carbonized skeleton. Through a radially layered structure of the core, salt-containing intermediate layer, and outer layer, conductive fillers and magnetic particles are mainly concentrated in the core layer, while water-soluble salt particles are mainly distributed in the salt-containing intermediate layer, avoiding the problem of functional components and salt substances being mixed and distributed within the fiber.

Description

Technical Field

[0001] This invention relates to the field of functional fiber materials and carbon crystal extraction technology, and in particular to an algae-based electromagnetic rheodynamic fiber and carbon crystal extraction process. Background Technology

[0002] Sodium alginate has good fiber-forming properties and metal ion coordination ability, and is often used to prepare wet-spun fibers, composite gel fibers and carbon crystal precursors. In the existing technology, in order to improve the conductivity and magnetic response of sodium alginate fibers, functional components such as carbon nanotubes, graphene, MXene, conductive carbon black, iron oxide particles, and carbonyl iron powder are usually added to the fiber system, and functional composite fibers or carbonized fibers are obtained through cross-linking, drying and carbonization treatment.

[0003] However, existing sodium alginate-based composite fibers mostly use single-layer mixing or simple coating methods, which makes it easy for conductive fillers, magnetic particles, metal ions and soluble salts to be mixed and distributed inside the fiber. After the fiber is carbonized, it is difficult for salt substances to form a continuous liquid inlet channel on the outer periphery of the core layer. Pickling solution and electrolyte are not easy to enter the outer side of the carbonized core layer, resulting in low carbon crystal detachment efficiency, easy breakage of the sheets, and difficulty in separating and collecting magnetic adsorption components and non-magnetic adsorption components. Summary of the Invention

[0004] In a first aspect, the present invention provides an algae-based electromagnetic rheological fiber, comprising a continuous fiber body formed by crosslinking sodium alginate; The continuous fiber body comprises, from the inside out, a core layer, a salt-containing intermediate layer, and an outer layer; The core layer includes an alginate matrix formed by cross-linking sodium alginate, conductive fillers, magnetic particles, and metal ions coordinated with the alginate matrix. The metal ion is an iron ion, a nickel ion, or a cobalt ion; The salt-containing intermediate layer is a continuous annular layer covering the outside of the core layer. The salt-containing intermediate layer includes an alginate matrix formed by cross-linking sodium alginate and water-soluble salt particles dispersed in the alginate matrix. The outer layer is an alginate cross-linked layer that coats the outside of the salt-containing intermediate layer; The conductive filler accounts for 79.2% to 86.9% of the cross-sectional signal in the core layer, and the water-soluble salt particles account for 74.8% to 83.4% of the cross-sectional signal in the salt-containing intermediate layer.

[0005] As a preferred embodiment of the seaweed-based electromagnetic rheotropic fiber of the present invention, the conductive filler is carbon nanotubes, graphene, MXene or conductive carbon black, and the conductive filler and magnetic particles are mixed and distributed in the core layer.

[0006] As a preferred embodiment of the seaweed-based electromagnetic rheotropic fiber of the present invention, the magnetic particles are iron oxide particles, carbonyl iron powder, iron-nickel alloy particles or iron-cobalt oxide particles. The magnetic particles are distributed in an alginate matrix containing coordinating metal ions.

[0007] As a preferred embodiment of the seaweed-based electromagnetic rheotropic fiber of the present invention, the water-soluble salt particles are sodium bicarbonate, potassium bicarbonate, sodium chloride or potassium chloride, and the water-soluble salt particles are dispersed in a salt-containing intermediate layer.

[0008] As a preferred embodiment of the seaweed-based electromagnetic rheological fiber of the present invention, the D50 particle size of the water-soluble salt particles is 6.0 μm to 7.1 μm, and the average thickness of the salt-containing intermediate layer is 31 μm to 46 μm.

[0009] Secondly, the present invention provides a carbon crystal extraction process for seaweed-based electromagnetic rheological fibers, comprising: taking the seaweed-based electromagnetic rheological fibers as raw materials, drying the seaweed-based electromagnetic rheological fibers, and then performing segmented heating carbonization in a nitrogen protective atmosphere, sequentially passing through a dehydration and shaping section, a condensation and conversion section and a carbonization section to obtain carbonized fibers. The carbonized fiber is washed with circulating water to dissolve the soluble salts in the carbonized zone of the salt-containing intermediate layer, forming annular channels for liquid to enter on the outer periphery of the carbonized zone of the core layer. The carbonized fiber after water washing is organically acid-washed with citric acid solution to dissolve some metal residues on both sides of the annular channel. Based on the existing annular channel, an easily separable interface is formed between the core carbonized zone and the outer carbonized skeleton. The organically acid-washed carbonized fibers are placed in a sodium sulfate electrolyte solution, and an intermittent voltage of 8V to 16V is applied. One cycle of power-on and power-off is performed, and the process is repeated for 30 to 50 minutes with power-on for 20 to 40 seconds and power-off for 40 to 90 seconds. The mixture is stirred at 200 to 400 rpm to separate the carbon crystals containing locally graphitized carbon structures in the core carbonization zone from the outer carbonization skeleton along the easily separable interface, thus obtaining a dispersion containing carbon crystals. The dispersion is subjected to magnetic separation, and the magnetically adsorbed carbon crystals and the non-magnetically adsorbed carbon crystals that are not adsorbed by the magnetic field are collected respectively.

[0010] As a preferred embodiment of the carbon crystal extraction process for the seaweed-based electromagnetic rheological fiber described in this invention, the segmented heating carbonization includes: dehydration and shaping at 170°C to 190°C for 40 min, condensation transformation at 390°C to 460°C for 60 min, and carbonization at 780°C to 900°C for 90 min, with a heating rate of 3°C / min for each heating stage.

[0011] As a preferred embodiment of the carbon crystal extraction process for the seaweed-based electromagnetic rheological fiber described in this invention, the water washing is a circulating water washing process, in which the carbonized fiber is added to deionized water at 50°C at a solid-liquid ratio of 1:60 and circulated for 4 times, each time for 15 minutes.

[0012] As a preferred embodiment of the carbon crystal extraction process for the seaweed-based electromagnetic rheological fiber described in this invention, the organic acid washing uses a 1.5wt% to 2.5wt% citric acid solution and is treated at 40°C for 40 min. After being washed with organic acid, the carbonized fibers are separated into solid and liquid phases and then introduced into a sodium sulfate electrolyte solution.

[0013] As a preferred embodiment of the carbon crystal extraction process of the seaweed-based electromagnetic rheological fiber described in this invention, the magnetic separation includes: using a magnet with a surface magnetic induction intensity of 0.20T to 0.50T to adsorb the dispersion liquid for 3min to 10min, collecting the components adsorbed by the magnetic field to obtain magnetically adsorbed carbon crystals. Solid-liquid separation was performed on the dispersion that was not adsorbed by the magnetic field to obtain non-magnetically adsorbed carbon crystals.

[0014] The beneficial effects of this invention are as follows: Through the radial layered structure of the core layer, the salt-containing intermediate layer and the outer layer, the conductive filler and magnetic particles are mainly concentrated in the core layer, while the water-soluble salt particles are mainly distributed in the salt-containing intermediate layer, thus avoiding the problem of functional components and salt substances being mixed and distributed inside the fiber. After fiber carbonization, the salts in the salt-containing intermediate layer are dissolved by water washing, forming annular channels around the core carbonization zone that allow liquid to enter. This allows organic acid washing solution and electrolyte solution to reach the outside of the core carbonization zone. After organic acid washing removes some metal residues on both sides of the annular channels, an easily separable interface is formed between the core carbonization zone and the outer carbonization skeleton. With intermittent voltage and stirring, the carbon crystals to be separated can be efficiently separated from the outer carbonization skeleton along this easily separable interface. Through the synergistic effect of the above structures, combined with magnetic separation treatment, magnetically adsorbed carbon crystals and non-magnetically adsorbed carbon crystals can be collected separately, achieving graded extraction of carbon crystals. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of intermittent voltage processing and magnetic separation grading in Example 1.

[0017] Figure 2 This is a schematic diagram of the formation of the annular channel and easily separable interface in Example 1. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0019] Unless otherwise stated, the salt-containing intermediate layer in this invention refers to a sodium alginate cross-linked layer containing water-soluble salt particles located between the core layer and the outer layer; After carbonization, the salt-containing intermediate layer forms a salt-containing intermediate carbonized zone. After washing with water, the soluble salts in the intermediate layer dissolve out and form annular channels on the outer periphery of the core carbonized zone.

[0020] The electromagnetic rheological fiber in this invention refers to a continuous solid fiber material formed by cross-linking sodium alginate. Under the combined action of an external electric field, magnetic field or electromagnetic field, the storage modulus, bending stiffness or loss factor of the continuous solid fiber material undergoes measurable changes. The electromagnetic rheology in this invention is used to characterize the changes in the viscoelastic mechanical response of fibers under the action of an external field, without using the viscosity or yield stress of liquid materials as necessary evaluation indicators.

[0021] The easily separable interface in this invention refers to the weakened interface region located between the core carbonization zone and the outer carbonization skeleton. The weakened interface region is formed by the dissolution of soluble salts in the carbonized zone of the salt-containing intermediate layer through circulating water washing to form annular channels, and then by the partial dissolution of iron, nickel, or cobalt residues on both sides of the annular channels by citric acid solution.

[0022] Under the process conditions of this invention, the circulating water washing first provides a channel for the citric acid solution to enter the outer periphery of the core carbonization zone; Subsequently, the citric acid solution was treated at 40°C for 40 minutes, causing some metal residues to dissolve from the side of the annular channel adjacent to the core carbonized area and the side adjacent to the outer carbonized skeleton, thereby reducing the connection strength between the core carbonized area and the outer carbonized skeleton. After subsequent intermittent voltage treatment and stirring, the carbon crystals to be separated can detach from the outer carbonized skeleton along the weakened region of the interface.

[0023] In the embodiments, the interface weakening effect was verified by the observability of the annular channel, the metal residue removal rate, the carbon crystal extraction yield, and the sheet integrity rate. Annular channels refer to the void regions formed around the carbonized core zone in the fiber cross-section, resulting from the dissolution of salt substances after water washing. In the embodiment, the observability rate of the annular channel is calculated as follows: at least 30 carbonized fiber cross sections are randomly selected, and the number of cross sections in which annular void regions extending continuously for at least 180° around the carbonized core layer are observed is counted. The proportion of this number to the total number of observed cross sections is taken as the observability rate of the annular channel.

[0024] The carbon crystal in this invention refers to the sheet-like or granular carbon material formed during the carbonization process of sodium alginate matrix and core conductive filler. This carbon material contains a locally graphitized carbon structure and is not required to be a complete single-crystal graphite crystal. Localized graphitized carbon structure refers to the presence of a identifiable 002 diffraction peak in X-ray diffraction (XRD) patterns within the range of 2θ from 24° to 27°, and the presence of this diffraction peak indicates that the carbon material has a locally ordered carbon layer stacking structure.

[0025] In this invention, magnetically adsorbed carbon crystals and non-magnetically adsorbed carbon crystals refer to two types of graded products obtained under the magnetic separation conditions of this invention, based on whether or not they are adsorbed by a magnetic field.

[0026] The cross-sectional signal ratio was determined as follows: Five fibers were randomly selected from the same batch of fibers, and three cross-sections were randomly selected along the length of each fiber, for a total of 15 cross-sections. Scanning electron microscopy was used to observe each cross section, and the core, salt-containing intermediate layer and outer layer regions were delineated by combining the results of Raman surface scanning or EDS energy dispersive spectroscopy.

[0027] The cross-sectional signal ratio of conductive filler in the core layer is calculated as the ratio of the net integral intensity of the characteristic signal of conductive filler in the core layer region to the net integral intensity of the characteristic signal of conductive filler in the entire fiber cross-section.

[0028] The proportion of the cross-sectional signal of water-soluble salt particles in the salt-containing intermediate layer is calculated according to the ratio of the net integral intensity of the characteristic signal of the corresponding salt element in the salt-containing intermediate layer region to the net integral intensity of the characteristic signal of the salt element in the entire fiber cross-section.

[0029] The net integral strength mentioned above is the integral strength after deducting the background. When the conductive filler is carbon nanotube, graphene, or conductive carbon black, the D peak or G peak signal in the Raman spectrum is used as the characteristic signal. When the conductive filler is MXene, the Ti element signal in the EDS energy spectrum is used as the characteristic signal; When the water-soluble salt particles are sodium salts, the Na element signal is used as the characteristic signal; When the water-soluble salt particles are potassium salts, the K element signal is used as the characteristic signal.

[0030] The average value of the calculation results of the 15 cross sections was taken as the cross section signal ratio of the batch of samples.

[0031] The average thickness of the salt-containing interlayer was determined as follows: Five fibers were randomly selected from the same batch of fibers, and three cross-sections were randomly taken along the length of each fiber. After each cross-section was observed by scanning electron microscopy, the thickness of the salt-containing interlayer was measured along four directions: 0°, 45°, 90° and 135°. The average value of 60 measurement data from 15 cross-sections was taken as the average thickness of the salt-containing interlayer of the batch of samples.

[0032] The present invention selects sodium sulfate electrolyte solution as the electrolyte medium because sodium sulfate has good ionic conductivity in water, and sulfate ions are not easy to form insoluble precipitates with iron, nickel or cobalt residues, which is beneficial to maintaining the stability of the electrolyte solution. Compared to chloride electrolytes, sodium sulfate electrolytes reduce the risk of chloride ions participating in side reactions; Compared to acidic electrolytes, sodium sulfate electrolytes have a weaker corrosive effect on plate-like carbon crystal structures.

[0033] Example 1, referring to Figure 1 and Figure 2 This is the first embodiment of the present invention; This embodiment illustrates the preparation method of a three-layer seaweed-based electromagnetic rheological fiber, and the complete process of extracting carbon crystals from the fiber; The core layer slurry was prepared as follows: 3.0 g of sodium alginate was added to 97.0 g of deionized water and stirred at 25℃±5℃ for 6 h to obtain a sodium alginate solution; Add 0.35g of carboxylated carbon nanotubes and 0.60g of iron oxide particles to sodium alginate solution, stir at 600r / min for 30min, and then ultrasonically disperse at 300W ultrasonic power for 20min. Add 0.18g of ferric chloride hexahydrate and continue stirring for 40 minutes to distribute iron ions in the core layer slurry system containing sodium alginate, thus obtaining the core layer slurry. To aid in characterizing the interaction between iron ions and carboxyl groups in sodium alginate segments, Fourier transform infrared spectroscopy was performed on sodium alginate solution without ferric chloride hexahydrate and core layer slurry with ferric chloride hexahydrate. Test results showed that in sodium alginate solution without added iron ions, the asymmetric stretching vibration peak of carboxylates was located at 1595 cm⁻¹. -1 Nearby, in the core slurry after the addition of ferric chloride hexahydrate, the peak shifted to 1608 cm⁻¹. -1 nearby; At the same time, 1420cm -1 The relative intensities of the symmetric stretching vibration peaks of nearby carboxylates change; The peak position shifts and intensity changes of the above-mentioned carboxylate characteristic peaks are consistent with the infrared spectral changes of iron ions participating in the coordination of carboxylate groups; Combined with the results of subsequent EDS analysis of fiber cross-sections showing that the iron element signal is concentrated in the core layer region, it can be concluded that iron ions are retained in the core layer containing the alginate matrix and have a coordination effect with the alginate matrix.

[0034] The salt-containing intermediate layer slurry was prepared as follows: 2.5g of sodium alginate was added to 70.0g of deionized water, and stirred at 600r / min for 4 hours at 25℃±2℃. Then, 30.0g of anhydrous ethanol was added and stirring was continued for 20 minutes to obtain an ethanol-water system sodium alginate solution. Add potassium chloride to the solution and stir at 400 r / min for 30 min at 25℃±2℃ to ensure that undissolved potassium chloride solids are present in the system. Take the supernatant after stirring and determine the potassium ion concentration using ion chromatography or atomic absorption spectrometry. When the relative deviation of potassium ion concentration in three consecutive measurements with an interval of 5 minutes does not exceed ±2%, it is confirmed that potassium chloride has reached saturation in the system. Subsequently, under nitrogen pressure of 0.05MPa to 0.10MPa, the solution was filtered through a 200-mesh stainless steel sieve with an aperture of approximately 74μm to remove undissolved large particles of potassium chloride and mechanical impurities, resulting in a potassium chloride-saturated ethanol-water system sodium alginate solution. 1.20g of dried and sieved potassium chloride particles were moistened with 3.0g of anhydrous ethanol. Before spinning, the potassium chloride saturated ethanol-water system sodium alginate solution was added and stirred at 300r / min for 5min. Spinning was completed within 10min after the addition to obtain a salt-containing intermediate layer slurry. The D50 particle size of potassium chloride microparticles is 6.2 μm; The outer slurry is a 2.5 wt% sodium alginate aqueous solution; The core layer slurry, the salt-containing intermediate layer slurry, and the outer layer slurry are injected into the three-channel coaxial wet spinning head, and the volume flow ratio of the three slurries is 1.00:0.35:0.45. The inner diameter of the core layer outlet of the three-channel coaxial wet spinning head is 0.30 mm, the inner diameter of the middle channel outlet is 0.55 mm, and the inner diameter of the outer channel outlet is 0.85 mm. The distance between the spinning head outlet and the surface of the coagulation bath is 10 mm; The extruded liquid was placed in an aqueous coagulation bath containing 4.0 wt% calcium chloride and 30 wt% ethanol, with a traction speed of 0.8 m / min and a coagulation time of 90 s. The coagulated fibers were continuously drawn through an aqueous washing solution containing 30wt% ethanol and 0.5wt% calcium chloride at a speed of 0.8 m / min. The washing solution temperature was 25℃±2℃ and the rinsing time was 20s. Subsequently, the fibers were dried at 45°C and under a vacuum of -0.08 MPa to -0.095 MPa for 12 hours to obtain three-layer seaweed-based electromagnetic rheological fibers. Cross-sectional testing revealed that the average outer diameter of the obtained fibers was 312 μm, the average diameter of the core layer was 146 μm, the average thickness of the salt-containing intermediate layer was 38 μm, and the average thickness of the outer layer was 45 μm.

[0035] The radial cross-section of the fiber was detected by scanning electron microscopy, energy dispersive spectroscopy, and Raman spectroscopy. The test results showed that the iron signal was concentrated in the core region; The potassium signal is concentrated in the annular region on the outer periphery of the core layer, and corresponds to the location of the salt-containing intermediate layer; The Raman G peak signal corresponding to carbon nanotubes is concentrated in the core layer region; Carboxylated carbon nanotubes, iron oxide particles, and iron ion coordination structures are mainly located in the core layer, while potassium chloride particles are mainly located in the salt-containing intermediate layer.

[0036] The dried three-layer seaweed-based electromagnetic rheological fiber was placed in a tube furnace and carbonized in stages under nitrogen protection at a nitrogen flow rate of 200 mL / min. The carbonization process is carried out under normal pressure nitrogen flow conditions, and nitrogen is continuously discharged from the outlet of the tubular furnace without vacuum carbonization. First, raise the temperature to 180℃ at a rate of 3℃ / min and hold for 40 minutes; Then increase the temperature to 420℃ at a rate of 3℃ / min and hold for 60 minutes; Continue heating at 3℃ / min to 850℃ and hold for 90min to obtain carbonized fiber; The 180℃ heat preservation stage is used to reduce the moisture content in the continuous fiber body and maintain the three-layer radial structure; the 420℃ heat preservation stage is used to promote the condensation and transformation of the sodium alginate skeleton; and the 850℃ heat preservation stage is used to form the core carbonization zone and the outer carbonization skeleton, respectively. During the carbonization process, the core layer is transformed into a core carbonization region containing conductive carbon, magnetic residues, locally graphitized carbon structures, and carbon crystals to be separated; the salt-containing intermediate layer is transformed into a salt-containing intermediate carbonization region; and the outer layer is transformed into an outer carbonization framework.

[0037] The carbonized fiber was added to 50℃ deionized water at a solid-liquid ratio of 1:60 and washed 4 times for 15 minutes each time to dissolve the soluble potassium salt in the carbonized zone of the salt-containing intermediate layer and form annular channels on the outer periphery of the carbonized zone of the core layer. The carbonized fibers after water washing are subjected to organic acid washing using a 2.0wt% citric acid solution at 40℃ for 40 minutes, followed by washing with deionized water until the pH of the washing solution is 6.5 to 7.0. After solid-liquid separation, the organic acid-washed carbonized fibers are obtained.

[0038] The organic acid-washed carbonized fiber was placed in a 0.10 mol / L sodium sulfate solution, wherein the amount of carbonized fiber added was 1.00 g and the volume of sodium sulfate solution was 100 mL; Graphite sheets are used as electrodes. Two graphite sheet electrodes are located on opposite sides of the beaker. The area of ​​the graphite sheet electrodes is 20mm × 30mm and the distance between the electrodes is 25mm. Both graphite sheet electrodes are immersed below the surface of the sodium sulfate solution, and carbonized fiber is located between the two graphite sheet electrodes; An intermittent voltage of 12V was applied, and the process was repeated for 40 minutes with the voltage on for 30 seconds and off for 60 seconds, while stirring at 300 r / min to obtain a dispersion containing carbon crystals. Take 100 mL of dispersion and place it in a beaker. Attach a neodymium iron boron magnet with a surface magnetic induction intensity of 0.30 T to the outer wall of the beaker for magnetic adsorption for 5 min. Collect the components adsorbed by the magnetic field, filter them through a 0.45 μm polytetrafluoroethylene filter membrane, wash them with water 3 times, 20 mL each time, and dry them at 60 °C for 6 h to obtain magnetically adsorbed carbon crystals. The components that were not adsorbed by the magnetic field were filtered through the same filter membrane, washed with water, and dried to obtain non-magnetically adsorbed carbon crystals.

[0039] In this embodiment, the salt-containing intermediate layer is carbonized to form a salt-containing intermediate layer carbonized region. After being washed with circulating water, soluble potassium salt is dissolved and forms annular channels, allowing citric acid solution and sodium sulfate electrolyte to enter the outer periphery of the core layer carbonized region. After the citric acid solution removes some of the iron residue on both sides of the annular channel, an easily separable interface is formed between the core carbonized zone and the outer carbonized skeleton. Intermittent voltage treatment refers to alternating between applying and de-energizing the sodium sulfate electrolyte solution. During the energizing stage, an electric field and local ion migration are formed near the annular channel and easily separable interface, which further weakens the connection between the carbon crystal to be separated and the outer carbonized framework. During the power-off phase, the local ion concentration difference and interfacial stress are mitigated, reducing local impact and lamellar breakage caused by continuous power supply. Compared with constant voltage treatment, intermittent voltage treatment is beneficial for gradually separating carbon crystals along easily separable interfaces and reduces the risk of widening of the particle size distribution.

[0040] In this embodiment, a neodymium iron boron magnet with a surface magnetic induction intensity of 0.30T is used for magnetic field adsorption in order to stably collect carbon crystals with high magnetic residue within 5 minutes, while reducing the non-magnetically adsorbed carbon crystals carried along with the magnetically adsorbed components. When the magnetic field adsorption time is less than 3 minutes, the magnetic adsorption components are not collected sufficiently. When the adsorption time is longer than 10 min, the amount of non-magnetic adsorption components entrained increases; In actual operation, the magnetic field adsorption can be adjusted within 3 to 10 minutes according to the volume of the dispersion liquid and the carbon crystal content. In this embodiment, 5 minutes is selected as the detection condition.

[0041] Set up comparative examples 1 to 3; Comparative Example 1: Single-layer mixed fibers: Except that the spinning sizing agent is changed to a single-layer homogeneous sizing agent, the other steps are the same as in Example 1; The single-layer homogeneous slurry was prepared by dispersing 3.0g sodium alginate, 0.35g carboxylated carbon nanotubes, 0.60g iron oxide particles, 0.18g ferric chloride hexahydrate and 1.20g potassium chloride particles in a mixed solvent composed of deionized water and ethanol. The mass ratio of deionized water to ethanol, the wetting method of potassium chloride particles and the spinning time after addition were the same as in Example 1. This comparative example is used to evaluate the effect of the three-layer radially distributed structure on subsequent carbon crystal extraction; Comparative Example 2: Salt-free intermediate layer fibers: Except for the elimination of the salt-containing intermediate layer slurry channel, the remaining steps are the same as in Example 1; The core layer slurry and the outer layer slurry enter the coaxial wet spinning head separately, and the volumetric flow rate ratio of the core layer slurry to the outer layer slurry is 1.00:0.45; This comparative example is used to evaluate the effect of the salt-containing intermediate layer on the formation of annular channels and the detachment of carbon crystals.

[0042] For Comparative Examples 1 and 2, since they do not have the same salt-containing intermediate layer structure as Example 1, in order to compare the distribution of salt elements at the same radial position, an equivalent salt-containing statistical region is defined according to the relative position of the salt-containing intermediate layer in the fiber radial direction in Example 1, and the proportion of the salt element signal intensity in this region to the salt element signal intensity of the entire fiber cross section is calculated in the same way. The delineation of the equivalent salt-containing statistical region is only used to compare the distribution of salt substances in different fibers within the same radial location range, in order to evaluate the impact of the presence or absence of a salt-containing intermediate layer on the spatial distribution of salt elements. This equivalent region does not represent the actual existence of a salt-containing intermediate layer structure in Comparative Example 1 and Comparative Example 2; it is only used for comparative analysis.

[0043] Comparative Example 3: Constant Voltage Processing Technology Except for the electrolysis treatment being changed to a constant voltage of 12V for 40 minutes, the other steps are the same as in Example 1; This comparative example is used to evaluate the effects of constant voltage treatment and intermittent voltage treatment on carbon crystal detachment yield and lamellar integrity. The carbonization yield was calculated as the ratio of the dry weight of the carbonized fiber to the dry weight of the three-layer seaweed-based electromagnetic rheotropic fiber after drying. The carbon crystal extraction yield is calculated as the ratio of the sum of the dry masses of magnetically adsorbed carbon crystals and non-magnetically adsorbed carbon crystals to the dry mass of carbonized fibers. The integrity of carbon crystal sheets is determined by randomly observing no less than 200 carbon crystal particles using transmission electron microscopy. The ratio of the particle's projected area to the area of ​​its smallest circumscribed ellipse is no less than 85%, and the number of particles with no protrusions or depressions on their surface larger than 10% of the particle's minor axis length is expressed as the proportion of the total number of observed particles. The carbon crystal particle size distribution was measured using a laser particle size analyzer, and the D90 / D10 value was used to evaluate the width of the particle size distribution. The Raman graphitization peak intensity ratio IG / ID is the ratio of the G peak intensity to the D peak intensity, used to evaluate the degree of order in carbon structure. The Fe content was determined using inductively coupled plasma atomic emission spectrometry. After magnetic separation, the difference in Fe content is calculated as the difference between the Fe content in the magnetically adsorbed component and the Fe content in the non-magnetically adsorbed component, in percentage points. The larger the difference, the more obvious the difference in metal residue between magnetically adsorbed carbon crystals and non-magnetically adsorbed carbon crystals; The fiber length is defined as the total length of continuous fibers collected in each batch of spinning solution within the same spinning time. In this example and the comparative example, continuous spinning is performed for 30 minutes. Table 1: Comparison of performance parameters of fibers and carbon crystals obtained in Example 1 and Comparative Examples 1-3

[0044] The data in the table shows that the cross-sectional signal ratio of the conductive filler in the core layer of Example 1 is 84.6%, and the cross-sectional signal ratio of the salt element in the equivalent salt-containing statistical region is 81.7%, indicating that the carboxylated carbon nanotubes are mainly located in the core layer, and the potassium chloride particles are mainly located in the salt-containing intermediate layer. Comparative Example 1 uses a single-layer mixed fiber. The proportion of the conductive filler cross-section signal in the core layer is reduced to 31.2%, the proportion of the salt element cross-section signal in the equivalent salt statistical region is reduced to 18.5%, and the observability of the annular channel is 18.6%. This indicates that the single-layer mixing method cannot form a stable radial partition and it is difficult to obtain the liquid inlet channel located on the outer periphery of the core layer after water washing. In Comparative Example 2, after the salt-containing intermediate layer was removed, the cross-sectional signal ratio of the conductive filler in the core layer was 82.8%, but the cross-sectional signal ratio of the salt element in the equivalent salt-containing statistical region was 3.6%, the observable rate of the annular channel was 12.4%, and the carbon crystal extraction yield was 34.7%. The conductive filler and magnetic particles in the core layer could not replace the salt-containing intermediate layer. The liquid inlet channel formed after carbonization and water washing of the salt-containing intermediate layer is an important condition for the smooth progress of organic acid washing and electrolytic separation; Comparative Example 3 retains the same three-layer fiber structure as Example 1, but is treated with a constant voltage. The observable rate of annular channels in this group of samples was 89.7%, but the carbon crystal extraction yield was 50.6%, the carbon crystal D90 / D10 particle size distribution ratio was 6.7, and the carbon crystal lamellar integrity rate was 61.4%. Compared with Example 1, the carbon crystal yield obtained by constant voltage treatment was lower, the particle size distribution was wider, and the lamellar integrity rate was lower, indicating that intermittent voltage treatment was more conducive to the detachment of carbon crystals along the easily separable interface formed after organic acid washing. The carbon crystal extraction yield of Example 1 was 62.4%, the carbon crystal sheet integrity rate was 76.8%, and the Raman graphitization peak intensity ratio IG / ID was 1.31. The Fe content in the magnetic adsorption component is 12.6%, while the Fe content in the non-magnetic adsorption component is 2.1%. The difference in Fe content between the two is 10.5 percentage points, indicating that the iron oxide particles and iron ion coordination structure in the core layer form carbon crystal components that can be separated by a magnetic field after carbonization. Example 1 uses a three-layer fiber structure to control the position of functional components, followed by segmented heating carbonization, water washing, citric acid washing, intermittent voltage stripping and magnetic separation, to obtain carbon crystals with high extraction yield, high sheet integrity and magnetic segregation.

[0045] Example 2 is the second embodiment of the present invention; Based on Example 1, this embodiment adjusts the raw material dosage, spinning flow rate, coagulation conditions, organic acid washing concentration, and carbonization temperature to investigate the fiber formation state, radial distribution, and carbon crystal extraction under a lower parameter combination. Except for the differences mentioned above, the other preparation steps, electrolysis methods, magnetic separation methods, and detection methods are the same as in Example 1; corresponding Comparative Examples 2-1 to 2-3 were prepared. In the core layer slurry, the amount of sodium alginate is 2.6g, the amount of deionized water is 97.4g, the amount of carboxylated carbon nanotubes is 0.18g, the amount of iron oxide particles is 0.32g, and the amount of ferric chloride hexahydrate is 0.08g. In the salt-containing intermediate layer slurry, the amount of sodium alginate is 2.2g, the amount of deionized water is 70.0g, the amount of anhydrous ethanol is 30.0g, the amount of potassium chloride microparticles is 0.60g, and the D50 particle size of the potassium chloride microparticles is 6.5μm; Potassium chloride microparticles were added using the short-time dispersion method described in Example 1, which utilizes a potassium chloride saturated ethanol-water system. In this embodiment, the potassium chloride saturated ethanol-water system is used to reduce the dissolution rate of the added potassium chloride particles before spinning. The amount of potassium chloride microparticles used is calculated based on the mass of dried and sieved potassium chloride microparticles added shortly before spinning; The outer slurry is a 2.2 wt% sodium alginate aqueous solution; The volumetric flow rate ratio of the three slurries is 1.00:0.30:0.40; The calcium chloride content in the coagulation bath was 3.5 wt%, the traction speed was 0.7 m / min, and the coagulation time was 100 s; The average outer diameter of the obtained fibers is 286 μm, the average diameter of the core layer is 132 μm, the average thickness of the salt-containing intermediate layer is 31 μm, and the average thickness of the outer layer is 39 μm. In the segmented heating carbonization process, the dehydration and shaping temperature is 170°C, the condensation conversion temperature is 390°C, the carbonization temperature is 780°C, and the holding time for each segment is the same as in Example 1. Organic acid washing uses a 1.5wt% citric acid solution; Using the sample obtained in this embodiment as Example 2, Comparative Example 2-1, Comparative Example 2-2 and Comparative Example 2-3 were also prepared. Comparative Example 2-1 is a lower limit single-layer mixed fiber, wherein the amounts of carboxylated carbon nanotubes, iron oxide particles, ferric chloride hexahydrate and potassium chloride particles are all the lower limit amounts corresponding to this example, and they are dispersed together in a single layer of sodium alginate slurry; Comparative Example 2-2: The salt-containing intermediate layer was removed; Comparative Examples 2-3 used three-layer fibers with lower limit parameters, but the electrolytic treatment was changed to a constant voltage of 12V for 40 minutes; Table 2: Comparison of performance parameters of fibers and carbon crystals obtained in Example 2 and Comparative Examples 2-1 to 2-3

[0046] As shown in Table 2, under the lower limit parameter combination, Example 2 can still maintain the positioning of the core conductive filler and the salt element positioning of the salt-containing intermediate layer, and form annular channels after water washing. Compared with Comparative Examples 2-1 and 2-2, the carbon crystal extraction yield and sheet integrity rate of Example 2 were significantly improved, indicating that the single-layer homogenization method or the elimination of the salt-containing intermediate layer is not conducive to subsequent extraction. Compared with Comparative Examples 2-3, Example 2 showed better extraction yield and sheet integrity under intermittent voltage treatment, indicating that intermittent voltage treatment can still be effective under lower limit parameter conditions.

[0047] Example 3 is the third embodiment of the present invention; Based on Example 1, this embodiment increases the amount of conductive filler, magnetic particles, metal ion source and water-soluble salt particles, and adjusts the spinning flow rate, coagulation conditions, organic acid washing concentration and carbonization temperature to investigate the fiber formation state and carbon crystal extraction under higher parameter combinations. Except for the differences mentioned above, the other preparation steps, electrolysis methods, magnetic separation methods, and detection methods are the same as in Example 1; Prepare comparative examples 3-1 to 3-3; In the core layer slurry, the amount of sodium alginate is 3.4g, the amount of deionized water is 96.6g, the amount of carboxylated carbon nanotubes is 0.52g, the amount of iron oxide particles is 0.90g, and the amount of ferric chloride hexahydrate is 0.30g. In the salt-containing intermediate layer slurry, the amount of sodium alginate is 2.8g, the amount of deionized water is 70.0g, the amount of anhydrous ethanol is 30.0g, the amount of potassium chloride microparticles is 1.80g, and the D50 particle size of the potassium chloride microparticles is 7.1μm; The outer slurry is a 2.8 wt% sodium alginate aqueous solution; The volumetric flow rate ratio of the three slurries is 1.00:0.40:0.50; The calcium chloride content in the coagulation bath was 4.5 wt%, the traction speed was 0.6 m / min, and the coagulation time was 110 s; The rinsing method was the same as in Example 1, using an aqueous washing solution containing 30 wt% ethanol and 0.5 wt% calcium chloride for a rapid rinsing of 20 seconds; The resulting fibers had an average outer diameter of 346 μm, an average core diameter of 162 μm, an average thickness of 46 μm for the salt-containing intermediate layer, and an average thickness of 50 μm for the outer layer. In the segmented heating carbonization process, the dehydration and shaping temperature is 190°C, the condensation conversion temperature is 460°C, the carbonization temperature is 900°C, and the holding time for each segment is the same as in Example 1. Organic acid washing uses a 2.5 wt% citric acid solution; Under the upper limit parameter combination in this embodiment, by increasing the calcium chloride content in the coagulation bath, reducing the traction speed and extending the coagulation time, the resulting fibers can still form a radially layered structure. Using the sample obtained in this embodiment as Example 3, Comparative Examples 3-1, 3-2, and 3-3 were also prepared. Comparative Example 3-1 is an upper limit single-layer mixed fiber, in which the amounts of carboxylated carbon nanotubes, iron oxide particles, ferric chloride hexahydrate and potassium chloride particles are all the upper limit amounts corresponding to this example, and they are dispersed together in a single layer of sodium alginate slurry; Comparative Example 3-2: The salt-containing intermediate layer was removed; Comparative Example 3-3 uses three-layer fibers with the upper limit parameters, but the electrolysis treatment is changed to a constant voltage of 12V for 40 minutes; Table 3: Comparison of performance parameters of fibers and carbon crystals obtained in Example 3 and Comparative Examples 3-1 to 3-3

[0048] As shown in Table 3, under the upper limit parameter combination, Example 3 can still form the core layer conductive filler positioning and the salt element positioning of the salt-containing intermediate layer, and the observability of the annular channel remains at a high level. Compared with Comparative Examples 3-1 and 3-2, Example 3 showed higher carbon crystal extraction yield, sheet integrity rate, and metal content difference after magnetic separation, indicating that the three-layer structure and salt-containing intermediate layer are still necessary even with higher filler content. Compared with Comparative Example 3-3, intermittent voltage treatment can reduce the risk of particle size distribution broadening and lamellar breakage; Based on Examples 1 to 3, it can be seen that under the conditions of 2.0wt%, 1.5wt%, and 2.5wt% citric acid solutions and treatment at 40℃ for 40 min, the observable rate of annular channels was 91.3%, 84.7%, and 92.5%, respectively; the metal residue removal rates before electrolysis were 48.5%, 41.3%, and 52.6%, respectively; and the carbon crystal extraction yields were 62.4%, 54.6%, and 64.8%, respectively. The above results show that, under the combined action of the three-layer fiber structure, circulating water washing conditions, and citric acid washing conditions defined in this invention, an easily separable interface can be formed for subsequent intermittent voltage separation.

[0049] Example 4 is the fourth embodiment of the present invention; This embodiment is used to verify that when conductive fillers, magnetic particles, metal ion sources and water-soluble salt particles are replaced by material combinations, the three-layer seaweed-based electromagnetic rheological fibers can still form a radially layered structure and obtain carbon crystals through carbonization, water washing, organic acid washing, electrolysis and magnetic separation. This embodiment is based on Embodiment 1, only changing the material combinations listed in Table 4; The amounts of other raw materials, spinning flow rate, coagulation conditions, rinsing method, drying conditions, segmented heating carbonization conditions, water washing conditions, organic acid washing conditions, electrolysis conditions, magnetic separation conditions, and detection methods are all the same as in Example 1; The amount of conductive filler added is 0.35g, the amount of magnetic particles added is 0.60g, and the amount of water-soluble salt particles added is 1.20g. The metal ion source was added according to the molar amount of metal ions corresponding to 0.18g of ferric chloride hexahydrate in Example 1; Ferric chloride is ferric chloride hexahydrate, nickel chloride is nickel chloride hexahydrate, and cobalt chloride is cobalt chloride hexahydrate; Different water-soluble salt particles were added using a short-term dispersion method in an ethanol-water system saturated with the corresponding water-soluble salt. For sodium bicarbonate and potassium bicarbonate samples, a sodium alginate solution in a saturated ethanol-water system corresponding to the bicarbonate was prepared at 25℃±2℃. Then, the dried and sieved bicarbonate particles wetted with anhydrous ethanol were added before spinning, and spinning was completed within 10 minutes after addition. For sodium chloride and potassium chloride samples, the potassium chloride saturated ethanol-water system was treated using the short-time dispersion method described in Example 1. Table 4: Samples and Test Results of Material Combinations in Example 4

[0050] In this embodiment, the proportion of the cross-sectional signal of salt elements in the salt-containing intermediate layer is evaluated according to the detection method in Example 1; For sodium bicarbonate, potassium bicarbonate and sodium chloride samples, the determination is made by combining EDS surface scanning of fiber cross section, changes in porosity of salt-containing intermediate layer region before and after water washing, and sodium or potassium ion content in water washing solution. For potassium chloride samples, the potassium element signal intensity is used for determination; The corresponding metal content in the magnetic adsorption component and the non-magnetic adsorption component refers to the content of iron, nickel or cobalt elements used in the sample; As shown in Table 4, after the conductive filler, magnetic particles, metal ion source and water-soluble salt particles were combined and replaced, samples 4-1 to 4-6 were still able to maintain the positioning of the conductive filler in the core layer and the salt enrichment in the salt-containing intermediate layer, and were able to complete the subsequent carbon crystal extraction and magnetic classification process.

[0051] Verification Example 1; This validation example is used to comprehensively evaluate the combined effects of water washing, organic acid washing, intermittent voltage treatment, and magnetic separation. The same batch of carbonized fibers obtained in Example 1 were divided into five treatment groups, each with a dry weight of 2.00g. Processing group 1 is processed according to the circulating water washing, organic acid washing, intermittent voltage treatment and magnetic separation process of Example 1, as a complete process group; Treatment group 2 did not undergo independent water washing, but directly underwent organic acid washing, intermittent voltage treatment and magnetic separation to evaluate the impact of omitting the water washing channel opening step on the formation of annular channels and subsequent carbon crystal detachment. After water washing, treatment group 3 did not undergo organic acid washing, but directly entered intermittent voltage treatment and magnetic separation to evaluate the effect of organic acid washing on the formation of easily separable interfaces and the detachment of carbon crystals. After water washing and organic acid washing, the electrolytic treatment in treatment group 4 was changed to a constant voltage of 12V for 40 minutes to evaluate the effect of continuous energization treatment on the integrity of carbon crystal sheets and particle size distribution compared with intermittent voltage treatment. After water washing, organic acid washing and intermittent voltage treatment, the entire dispersion of treatment group 5 was directly filtered and dried without magnetic adsorption separation, in order to evaluate the effect of magnetic separation on the fractional collection of magnetically adsorbed carbon crystals and non-magnetically adsorbed carbon crystals. Except for the differences in treatment mentioned above, the water washing temperature, organic acid washing concentration, electrolyte solution, stirring speed, treatment time and detection method of each group were the same as in Example 1; The metal residue removal rate before entering electrolysis was calculated based on the change in Fe content of the samples in each treatment group before entering the electrolysis step; Treatment group 5 did not undergo magnetic field adsorption separation, and the resulting product was mixed carbon crystals. The Fe content of treatment group 5 in Table 5 is expressed as the average Fe content of the mixed carbon crystals, and the difference in Fe content after magnetic separation is taken as 0. Table 5: Comprehensive Validation Results of Process Nodes

[0052] It should be noted that although treatment group 2 did not undergo independent water washing, the organic acid washing solution was an aqueous system during the subsequent organic acid washing process. Some soluble salts could still be partially dissolved during the organic acid washing process, so a small number of annular channels could still be observed in the cross section of the carbonized fiber. However, the observable rate of its annular channels was much lower than that of the treatment group 1 which was treated with independent water washing, indicating that the independent water washing step is the key step to fully form annular channels and improve the subsequent carbon crystal detachment effect.

[0053] As shown in Table 5, when the complete process was used in treatment group 1, the observability rate of the annular channel was 91.0%, the metal residue removal rate before electrolysis was 48.1%, the carbon crystal extraction yield was 62.1%, the sheet integrity rate was 76.4%, and the difference in Fe content after magnetic separation was 10.2 percentage points. This indicates that there is a continuous synergistic effect between water washing, organic acid washing, intermittent voltage treatment and magnetic separation. When treatment group 2 was not subjected to independent water washing, the observability rate of the annular channels dropped to 13.5%, the carbon crystal extraction yield dropped to 26.8%, and the sheet integrity rate dropped to 31.7%. This indicates that the soluble salts in the carbonized zone of the salt-containing intermediate layer need to be fully dissolved by independent water washing before annular channels can be formed on the periphery of the carbonized zone of the core layer for subsequent treatment liquid to enter. When treatment group 3 was washed with water but not with organic acid, the observability rate of the annular channel was 90.4%, but the metal residue removal rate before electrolysis was only 8.4%, the carbon crystal extraction yield was 39.5%, and the sheet integrity rate was 49.6%. This indicates that the liquid inlet channel alone is insufficient to form a stable and easily separable interface. Organic acid washing removes some metal residues on both sides of the annular channel, which helps to weaken the connection between the core carbonization zone and the outer carbonization skeleton. When constant voltage was used for treatment group 4, the observability of the annular channel and the removal rate of metal residues before electrolysis were close to those of treatment group 1. However, the carbon crystal extraction yield dropped to 51.4%, the D90 / D10 particle size distribution ratio increased to 6.9, and the sheet integrity rate dropped to 60.8%. This indicates that under the same conditions of total treatment time and voltage value, continuous power supply treatment tends to widen the carbon crystal particle size distribution and reduce the sheet integrity rate. When no magnetic separation was performed in treatment group 5, the carbon crystal extraction yield and sheet integrity rate were close to those of the complete process group. However, the product obtained was a mixed carbon crystal, and it was not possible to obtain two types of graded products: magnetically adsorbed carbon crystal and non-magnetically adsorbed carbon crystal. This indicates that magnetic separation was mainly used for product grading rather than to increase the total extraction yield.

[0054] Verification Example 2; To evaluate the effect of the type of organic acid washing solution on the extraction effect of carbon crystals, the same batch of carbonized fibers washed with water in Example 1 were taken and divided into two groups, with a dry weight of 2.00g in each group. The first group uses a 2.0wt% citric acid solution and is treated at 40℃ for 40 min, serving as the pickling group of this invention; The second group used a 2.0wt% acetic acid solution and was treated at 40℃ for 40 min as a reference pickling group. Both groups of samples were washed with organic acid and then washed with deionized water until the pH of the washing solution was 6.5 to 7.0, and then treated according to the electrolysis and magnetic separation conditions in Example 1. To evaluate the effect of intermittent voltage parameters on the carbon crystal detachment effect, another batch of carbonized fibers from the same batch after organic acid washing in Example 1 was taken and divided into three groups, with each group having a dry weight of 1.00g. All three groups of samples were placed in a 0.10 mol / L sodium sulfate solution, with a volume of 100 mL for each group. The electrode arrangement was the same as in Example 1. The first group was subjected to an intermittent voltage of 8V, with power on for 20 seconds and power off for 40 seconds, and was cyclically processed for 30 minutes, while being stirred at 200r / min. The second group was subjected to an intermittent 12V voltage, with power on for 30 seconds and power off for 60 seconds, and was cyclically processed for 40 minutes, while being stirred at 300r / min. The third group was subjected to an intermittent voltage of 16V, with power on for 40 seconds and power off for 90 seconds, and was cyclically processed for 50 minutes, while being stirred at 400r / min. All three groups of samples were collected and tested according to the magnetic separation method in Example 1 after processing; Table 6: Effects of organic acid washing solution and intermittent voltage parameters on carbon crystal extraction efficiency

[0055] Table 6 shows that the metal residue removal rate, carbon crystal extraction yield, sheet integrity rate and Fe content difference after magnetic separation of the reference pickling group are all lower than those of the pickling group of the present invention. This indicates that citric acid pickling under the three-layer fiber structure and circulating water washing conditions specified in the present invention is more suitable for forming an easily separable interface for subsequent intermittent voltage separation. Within the range of 8V to 16V intermittent voltage, 20s to 40s of power-on, 40s to 90s of power-off, 30min to 50min of cyclic treatment, and 200r / min to 400r / min of stirring speed, all three groups of samples were able to separate the carbon crystals containing locally graphitized carbon structures from the outer carbonized skeleton along the easily separable interface. It should be noted that the voltage value, power-on and power-off time, circulation processing time and stirring speed were adjusted simultaneously in the above three sets of experiments. The results are used to illustrate that the parameter combination within the scope of the present invention is operable, and are not used to distinguish the contribution of a single parameter to the carbon crystal extraction yield or the sheet integrity rate. The results in Table 6 show that under the conditions of 12V, 30s of power-on, 60s of power-off, 40min of cyclic treatment, and 300r / min of stirring, the carbon crystal extraction yield and the integrity of the lamellae are relatively balanced.

[0056] Verification Example 3; To evaluate the effect of magnetic separation conditions on the fractionation effect, the same batch of dispersion obtained after intermittent voltage treatment in Example 1 was taken and divided into three groups, each with a volume of 100 mL. The first group was attracted by a magnet with a surface magnetic induction intensity of 0.20T for 3 minutes; The second group was adsorbed for 5 minutes using a neodymium iron boron magnet with a surface magnetic induction intensity of 0.30T; The third group was attracted by a magnet with a surface magnetic induction intensity of 0.50T for 10 minutes; The components adsorbed by the magnetic field were collected from all three groups of samples and then filtered, washed, and dried to obtain magnetically adsorbed carbon crystals. The dispersion that was not adsorbed by the magnetic field was filtered, washed and dried using the same filter membrane to obtain non-magnetically adsorbed carbon crystals; Table 7: Effect of magnetic separation conditions on carbon crystal fractionation

[0057] Table 7 shows that within the range of surface magnetic induction intensity of 0.20T to 0.50T and adsorption time of 3min to 10min, carbon crystals in the dispersion can be divided into magnetically adsorbed carbon crystals and non-magnetically adsorbed carbon crystals. Under the conditions of 0.20T and 3min, the amount of magnetically adsorbed components collected was relatively small, indicating that the magnetic field adsorption strength and the reaction time were insufficient. Under the conditions of 0.50T and 10min, the amount of magnetically adsorbed components collected increased, but the Fe content in the non-magnetically adsorbed components remained at 3.1%, indicating that the fractionation selectivity was not further improved under these conditions. Under the conditions of 0.30T and 5min, the difference in Fe content after magnetic separation is relatively high, which can achieve a good balance between the collection of magnetic adsorption components and the purification of non-magnetic adsorption components.

[0058] Verification Example 4; To evaluate the mechanical response changes of the three-layer seaweed-based electromagnetic rheotropic fiber under the action of an applied electric field and magnetic field, dried fibers obtained in Example 1, Comparative Example 1 and Comparative Example 2 were used. Fiber bundles with a length of 50 mm and a mass of 0.20 g were taken from each fiber bundle and equilibrated in an environment of 25°C and 50% ± 5% relative humidity for 24 h before dynamic mechanical and electrical response tests were conducted. In the magnetic field response test, the fiber bundle was fixed in the fixture of the dynamic mechanical analyzer, and the test frequency was 1Hz. The storage modulus, bending stiffness and loss factor were measured under no magnetic field and 0.30T magnetic field respectively. In the electric field response test, the fiber bundle was placed between parallel plate electrodes with an electric field strength of 1.0 kV / mm. The change in energy storage modulus in the 1 Hz compression mode was tested, and the volume resistivity was measured simultaneously. In the electromagnetic field interaction test, a magnetic field of 0.30T and an electric field of 1.0kV / mm were applied simultaneously. Each sample group was tested three times. The test results in Table 8 are the arithmetic mean of the three test results. Table 8: Test Results of External Field Mechanical Response Performance of Three-Layer Fiber

[0059] Table 8 shows that the fiber obtained in Example 1 exhibits measurable changes in energy storage modulus under the combined action of magnetic field, electric field and electromagnetic field. The energy storage modulus increase rate under the combined action of electromagnetic field is 50.6%, which is higher than that of Comparative Example 1 and Comparative Example 2. The volume resistivity of Example 1 is lower than that of Comparative Examples 1 and 2, indicating that after the conductive filler, magnetic particles and metal ion coordination structure in the core layer are concentrated and distributed, the fiber has a measurable mechanical response change under the applied electric field and magnetic field, which can support its property of generating a measurable mechanical response under the applied electric field and magnetic field.

[0060] Verification Example 5; To further characterize the locally graphitized carbon structure in the carbon crystals of the dispersion, X-ray diffraction tests were performed on the carbon crystals in the dispersions obtained in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3. The test used Cu Kα radiation, with a tube voltage of 40 kV, a tube current of 40 mA, a scanning range of 10° to 60°, and a scanning rate of 5° / min. The interlayer spacing d002 is calculated based on the position of the 002 diffraction peak, and the ordered stacking size Lc along the c-axis is estimated based on the half-peak width of the 002 diffraction peak. Lc is only used to compare the relative degree of order of locally graphitized carbon structures in different samples, and is not used to limit carbon crystals to single-crystal structures or complete graphite crystals; Table 9: XRD characterization results of carbon crystals in the dispersion

[0061] As shown in Table 9, the carbon crystals in the dispersion obtained in Example 1 show a 002 diffraction peak near 2θ of 26.1° and a 100 / 101 diffraction peak near 43.2°, indicating that there is a locally graphitized carbon structure inside. The d002 interlayer spacing of Example 1 is 0.341 nm, which is lower than that of Comparative Example 1 (0.359 nm) and Comparative Example 2 (0.362 nm). Furthermore, Example 1 has a smaller half-peak width of 002 and a larger Lc ordered stacking size, indicating that the three-layer salt-containing separation structure combined with water washing, organic acid washing, and intermittent voltage treatment is more conducive to obtaining carbon crystals in a dispersion with locally ordered carbon structure. Comparative Example 1 uses a single-layer mixed fiber with mixed distribution of functional components and salt substances. The position of the 002 peak in the XRD is low and the peak width is large, indicating that the local graphitized carbon structure in the detachment product has a low degree of order. After removing the salt-containing intermediate layer in Comparative Example 2, it was difficult to form stable annular channels after water washing, and the 002 peak of the obtained product became wider, indicating that the carbon structure had a low degree of order. Although Comparative Example 3 retains the three-layer structure, it is treated with constant voltage. Its d002 layer spacing and Lc ordered stacking size are between those of Example 1 and Comparative Examples 1 and 2. This shows that constant voltage treatment can obtain carbon crystals with partially localized graphitized carbon structures, but its layer integrity and degree of order are not as good as those obtained by intermittent voltage treatment. The XRD results are consistent with the trend of the Raman graphitization peak intensity ratio IG / ID, which further proves that the detachment product obtained in this invention contains a locally graphitized carbon structure.

Claims

1. A seaweed-based electromagnetic rheological fiber, characterized in that, Includes a continuous fiber body formed by cross-linking sodium alginate; The continuous fiber body comprises, from the inside out, a core layer, a salt-containing intermediate layer, and an outer layer; The core layer includes an alginate matrix formed by cross-linking sodium alginate, conductive fillers, magnetic particles, and metal ions coordinated with the alginate matrix. The metal ion is an iron ion, a nickel ion, or a cobalt ion; The salt-containing intermediate layer is a continuous annular layer covering the outside of the core layer. The salt-containing intermediate layer includes an alginate matrix formed by cross-linking sodium alginate and water-soluble salt particles dispersed in the alginate matrix. The outer layer is an alginate cross-linked layer that coats the outside of the salt-containing intermediate layer; The conductive filler accounts for 79.2% to 86.9% of the cross-sectional signal in the core layer, and the water-soluble salt particles account for 74.8% to 83.4% of the cross-sectional signal in the salt-containing intermediate layer.

2. The seaweed-based electromagnetic rheological fiber as described in claim 1, characterized in that: The conductive filler is carbon nanotube, graphene, MXene, or conductive carbon black, and the conductive filler and magnetic particles are mixed and distributed in the core layer.

3. The seaweed-based electromagnetic rheological fiber as described in claim 1, characterized in that: The magnetic particles are iron oxide particles, carbonyl iron powder, iron-nickel alloy particles, or iron-cobalt oxide particles. The magnetic particles are distributed in an alginate matrix containing coordinating metal ions.

4. The seaweed-based electromagnetic rheological fiber as described in claim 1, characterized in that: The water-soluble salt particles are sodium bicarbonate, potassium bicarbonate, sodium chloride, or potassium chloride, and the water-soluble salt particles are dispersed in a salt-containing intermediate layer.

5. The seaweed-based electromagnetic rheological fiber as described in claim 1, characterized in that: The water-soluble salt particles have a D50 particle size of 6.0 μm to 7.1 μm, and the average thickness of the salt-containing intermediate layer is 31 μm to 46 μm.

6. A carbon crystal extraction process for seaweed-based electromagnetic rheological fibers as described in any one of claims 1 to 5, characterized in that, include: The seaweed-based electromagnetic rheological fiber was used as raw material. After drying the seaweed-based electromagnetic rheological fiber, it was subjected to segmented heating and carbonization in a nitrogen protective atmosphere. The fiber passed through a dehydration and shaping section, a condensation and conversion section and a carbonization section in sequence to obtain carbonized fiber. The carbonized fiber is washed with circulating water to dissolve the soluble salts in the carbonized zone of the salt-containing intermediate layer, forming annular channels for liquid to enter on the outer periphery of the carbonized zone of the core layer. The carbonized fiber after water washing is organically acid-washed with citric acid solution to dissolve some metal residues on both sides of the annular channel. Based on the existing annular channel, an easily separable interface is formed between the core carbonized zone and the outer carbonized skeleton. The organically acid-washed carbonized fibers are placed in a sodium sulfate electrolyte solution, and an intermittent voltage of 8V to 16V is applied. One cycle of power-on and power-off is performed, and the process is repeated for 30 to 50 minutes with power-on for 20 to 40 seconds and power-off for 40 to 90 seconds. The mixture is stirred at 200 to 400 rpm to separate the carbon crystals containing locally graphitized carbon structures in the core carbonization zone from the outer carbonization skeleton along the easily separable interface, thus obtaining a dispersion containing carbon crystals. The dispersion is subjected to magnetic separation, and the magnetically adsorbed carbon crystals and the non-magnetically adsorbed carbon crystals that are not adsorbed by the magnetic field are collected respectively.

7. The carbon crystal extraction process for seaweed-based electromagnetic rheological fibers as described in claim 6, characterized in that: The segmented heating carbonization includes: holding at 170℃ to 190℃ for 40 min for dehydration and shaping, holding at 390℃ to 460℃ for 60 min for condensation transformation, and holding at 780℃ to 900℃ for 90 min for carbonization. The heating rate for each heating stage is 3℃ / min.

8. The carbon crystal extraction process for seaweed-based electromagnetic rheological fibers as described in claim 6, characterized in that: The water washing is a circulating water washing, in which the carbonized fiber is added to deionized water at 50°C at a solid-liquid ratio of 1:60 and washed 4 times, each time for 15 minutes.

9. The carbon crystal extraction process for seaweed-based electromagnetic rheological fibers as described in claim 6, characterized in that: The organic acid washing uses a 1.5wt% to 2.5wt% citric acid solution, treated at 40°C for 40 min; After being washed with organic acid, the carbonized fibers are separated into solid and liquid phases and then introduced into a sodium sulfate electrolyte solution.

10. The carbon crystal extraction process for seaweed-based electromagnetic rheological fibers as described in claim 6, characterized in that: The magnetic separation includes: using a magnet with a surface magnetic induction intensity of 0.20T to 0.50T to adsorb the dispersion for 3 min to 10 min, collecting the components adsorbed by the magnetic field to obtain magnetically adsorbed carbon crystals; and performing solid-liquid separation on the dispersion that was not adsorbed by the magnetic field to obtain non-magnetically adsorbed carbon crystals.

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