CN104451961A - Method for preparing superconducting micron fiber - Google Patents

Abstract

The invention discloses a method for preparing superconducting microfibers, which includes: 1) TEMPO oxidized cellulose passes through a micro-fluidizer once to prepare NFC; 2) Hummer's method is used to oxidize graphite to obtain GO; 3) high-strength micron fibers Fiber preparation: Extrude the spinning solution through a needle into an alcohol coagulation bath to form a gel fiber, then pull the gel fiber out of the coagulation bath to dry in the air; during the drying process, apply a certain to improve the orientation of the microfibers; after drying, immerse the microfibers in a 10wt% CaCl ₂ aqueous solution for 1 hour and re-dry; 4) Carbonize the high-strength microfibers to obtain conductive GO+NFC microfibers. The average conductivity of the c(GO+NFC) microfibers obtained in the present invention is 649±60 S/cm, which is the highest conductivity reported so far, and is higher than that of carbonized NFC microfibers and carbonized GO microfibers. At the same time, low-density NFC and GO are used in the preparation, and the raw materials come from a wide range of sources.

Description

A method for preparing superconducting microfibers

technical field

The invention relates to the technical field of ultra-strong micron fibers, in particular to a method for preparing superconductive micron fibers (c(GO+NFC)).

Background technique

Nanocellulose has excellent properties, and has been used to prepare super-strong materials, conductive materials, etc. for electronic equipment, biomedicine, food, packaging and other fields. Fiber is a material with a wide range of uses, and its application fields involve the preparation of textiles, construction, and even aircraft and automobiles. At present, the preparation of high-performance and low-cost micron fibers has attracted widespread attention. Functional microfibers prepared from nanocellulose have gradually become popular.

Synthetic fibers with excellent mechanical properties (such as carbon fibers) play an important role in the preparation of aircraft and wind power turbine blades. But these synthetic fibers are expensive and have limited performance. Therefore, the research on low-cost and high-performance fiber preparation has become a hot spot. Nanocellulose has the characteristics of excellent mechanical properties, wide range of sources, green, etc., and has been used to prepare high-strength materials or reinforcing agents for materials. Two-dimensional nano-graphene oxide (GO) is also a structural unit material with excellent mechanical properties and high specific surface area, which can be used to prepare super-strong materials. The surface and edge of the GO sheet have a large number of hydroxyl, carboxyl and epoxy groups introduced due to chemical reactions. These groups make GO stable in water and form a strong force in the material. The use of low-cost two-dimensional GO for the preparation of one-dimensional microfibers has become a research hotspot. In order to improve the strength of GO microfibers, common methods include chemical crosslinking, polymer coating, ionic bonding, and improving the quality of GO monoliths. The GO micron fiber with the best mechanical strength reported so far has a tensile strength of 442MPa and an elastic modulus of 47GPa. However, in order to replace carbon fibers in practical applications, the strength of GO fibers needs to be further improved.

Cellulose is the most abundant biomacromolecular polymer in nature. It is an important raw material for the preparation of carbon materials. Carbon materials prepared from cellulose have played an important role in energy storage, carbon fiber preparation, water treatment, catalysis and other fields. An important means of preparing carbon materials from cellulose is to carbonize cellulose, which mainly includes heating carbonization and hydrothermal carbonization under a specific atmosphere. During the carbonization process of cellulose, the glucosidic bonds are broken, the fibers are degraded, the gases containing oxygen and hydrogen are released, and finally carbon materials are formed. However, the generally obtained cellulose carbon materials have relatively low conductivity. For example, the conductivity of carbon fiber is about 30S/cm when the carbonization temperature is 1000°C. In order to obtain highly conductive carbon materials, it is usually necessary to increase the carbonization temperature. Because increasing the carbonization temperature can increase the degree of graphitization inside the carbon material, thereby improving the electrical conductivity. When the carbonization temperature is increased to 2000°C, the conductivity of carbon fibers can be increased to 100S/cm. However, the high temperature treatment has extremely high requirements on equipment, which increases the cost of preparing conductive fibers.

Contents of the invention

Purpose of the invention: In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing superconducting micron fibers, combining GO and nanocellulose (NFC) to prepare high-strength micron fibers, which improves the performance of mixed fiber strength, and then carbonized to obtain superconducting micron fibers.

Technical solution: In order to realize the above-mentioned purpose of the invention, the technical solution adopted in the present invention is as follows:

A method for preparing superconducting microfibers, comprising the steps of:

1) NFC is prepared by TEMPO oxidized cellulose passing through a microfluidizer once;

2) Oxidation of graphite by Hummer's method to obtain GO;

3) Preparation of high-strength micron fibers: Extrude the spinning solution through a needle tube into an alcohol coagulation bath to form a gel fiber, and then pull the gel fiber out of the coagulation bath to dry in the air; during the drying process, the micron A force of 0.5N is applied to both ends of the fiber to increase the degree of orientation of the micron fiber; after drying, the micron fiber is immersed in an aqueous solution of 10wt% CaCl for ₁ hour and then dried again;

4) Carbonize high-strength micron fibers to obtain conductive GO+NFC micron fibers.

Step 1): 5g undried absolute-dried softwood pulp, 78mg TEMPO, 514mg NaBr are fully mixed; the reaction is initiated by the addition of 30mL 12%NaClO, and the reaction occurs under stirring at room temperature; the pH value of the system is controlled by NaOH Stable at 10.5; until the reaction of the remaining NaClO in the system is completely completed; the reacted slurry is cleaned by filtration until the pH is neutral; the obtained fiber is made into a concentration of 1% and processed under a pressure of 5-25KPa by a micro-fluidizer ; Obtain a transparent nanocellulose dispersion; store the dispersion in a refrigerator at 4°C.

Step 2): Mix 3.0g graphite flakes and 1.5g NaNO ₃ at 0°C; then add 69mL 98%H ₂ SO ₄ and mix well, and finally add 9.0g KMnO ₄ slowly; when adding KMnO ₄ The temperature of the solution is controlled below 20°C. After adding KMnO ₄ , raise the temperature of the reaction system to 35°C and stir for 30 minutes; then slowly add 138mL of deionized water into the reaction system dropwise, and control the reaction temperature at 98°C for 15 minutes; Immediately after cooling the reaction system to room temperature, add 420 mL of deionized water and 3 mL of 30% C H ₂ O ₂ at the same time; when the reaction mixture is cooled to room temperature, wash the material in a Buchner funnel with deionized water until neutral ; The obtained GO was dispersed in water by ultrasound for use.

In step 3), the spinning solution is a liquid crystal solution with a concentration of 1.1wt% prepared with a mass ratio of GO and NFC of 1:1.

In step 4), the carbonization of high-strength micron fibers is carried out in a mixed atmosphere of 95% argon and 5% hydrogen; the heating program is as follows: first from room temperature to 400°C at a heating rate of 30°C/h, and then at 200°C The heating rate is increased to 1000°C per hour, and finally kept at 1000°C for 2h.

Superconducting microfibers obtained by the method for preparing superconducting microfibers.

The application of the superconducting micron fiber as a conducting material.

Beneficial effects: Compared with the prior art, the present invention has the following advantages and outstanding effects: The average conductivity of the obtained c(GO+NFC) micron fibers is 649±60 S/cm, which is the highest reported by graphite, GO And the highest conductivity of conductive fibers prepared by GO composites is higher than that of carbonized NFC microfibers (average conductivity 33S/cm) and carbonized GO microfibers (average conductivity 137S/cm). At the same time, low-density NFC and GO are used in the preparation, the source of raw materials is extensive, and the fiber preparation method is simple, which has the potential value of large-scale production.

Description of drawings

Fig. 1 is the characterization result figure of TEMPO method oxidized cellulose;

Figure 2 is a diagram of the characterization results of NFC obtained after TEMPO oxidized cellulose passes through the microfluidizer once;

Fig. 3 is the preparation flowchart of GO+NFC micron fiber;

Fig. 4 is the structural representation of high-strength micron fiber;

Fig. 5 is the characterization figure of preparation raw material and mixed solution;

Fig. 6 is a characterization diagram of high-strength microfibers;

Fig. 7 is the characterization diagram of control sample;

Fig. 8 is a stress-strain curve diagram of GO micron fiber, NFC micron fiber and GO+NFC micron fiber;

Fig. 9 is a schematic diagram before and after fiber carbonization;

Fig. 10 is the SEM figure after carbonization;

Figure 11 is the I-V curve of c(GO+NFC) fibers.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the present invention is not limited by the following examples. the

The main reagents and instruments used in the following examples are as follows:

The bleached coniferous wood pulp board is Brazilian Red Fish brand, and the pulp is first beaten by a Wall-E beater to a Canadian freeness of 150mL. Ultraviolet spectrometer UV-Vis Spectrometer Lambda 35 (PerkInElmer, USA); transmission electron microscope (TEM, FEI QUANTA 200, USA); dynamic mechanical analyzer analysis (DMA, Q800); Hitachi (HITACHI) S-510 scanning electron microscope; ultrasonic instrument ( FS 110D, Fisher Scientific).

Example 1 NFC preparation and characterization

5g undried absolute dry softwood pulp, 78mg TEMPO, 514mg NaBr are fully mixed evenly. The reaction was initiated by the addition of 30 mL of 12% NaClO and reacted with stirring at room temperature. The pH value of the system was stabilized at 10.5 by NaOH control. Until the reaction of the remaining NaClO in the system is completely completed. The reacted slurry was washed by filtration until the pH was neutral. The obtained fibers are formulated into a concentration of 1% and processed under a pressure of 5-25KPa by a micro-fluidizer. A transparent nanocellulose (NFC) dispersion was obtained. Store the dispersion in a refrigerator at 4°C until use.

Scanning Electron Microscope (SEM) Observation: After the sample to be tested is vacuum-dried, glued to the table and vacuum-sprayed with gold, the operating condition voltage is 20kV.

The length and width of nanocellulose were characterized by transmission electron microscopy and fiber morphology by atomic force microscopy (AFM). When preparing samples for TEM, drop 10 μL of nanocellulose solution on the carbon grid, absorb the excess liquid with filter paper, and operate at a voltage of 100 kV. When preparing AFM samples, drop 10 μL of nanocellulose solution on a 1 cm × 1 cm silicon wafer, and spread the nanocellulose evenly on the silicon wafer by a spin coater. Visual characterization was performed in tapping mode after drying.

The Zeta potential of the solution was obtained by a Zeta potential tester. During the test, the mass fraction of NFC solution was 0.7 mg/mL, and the pH was 7.8.

The characterization results are shown in Figure 1, where a-c is the SEM image of TEMPO oxidized fiber, d is the transparent paper prepared by TEMPO oxidized fiber, e is the conductive ink written on the paper prepared by TEMPO oxidized fiber, and f is the electric meter test display to write The conductive wire has good conductivity, and g is a diode drawn by a ballpoint pen on paper prepared from TEMPO oxidized fiber. After the fiber is oxidized by TEMPO, the C6 hydroxyl group on the fiber surface is oxidized to a carboxyl group, which increases the charged group content on the fiber. At the same time, due to the oxidation reaction of the fibers and the force of mechanical stirring, the bonding strength between the fibers is reduced, the cell wall is damaged on the fiber surface, and even longitudinal cracks appear (a-b in Figure 1). At the same time, the length and width of the fibers decreased, and the content of fine fibers in the solution increased. Observing the surface of the fiber under a high-power scanning electron microscope (c in Figure 1) shows that the surface contains a large number of fine fibers, which are arranged in a network. This is consistent with the structure of fine fibers in the primary wall of wood. Although most of the fibers oxidized by TEMPO are still micron fibers, the solution has a certain viscosity and transparency. Direct filtration of TEMPO-oxidized fibers can produce transparent paper with a certain degree of haze (d in Figure 1). At the same time, the paper maintains good writing performance and surface smoothness. The surface smoothness may be mainly caused by the deposition of nanofibers generated during the preparation process on the paper surface. e-g in Fig. 1 are writing conductive materials on paper to prepare writable paper-based electronic devices.

NFC can be obtained after TEMPO oxidized cellulose passes through the microfluidizer once, and the results are shown in Figure 2, where the TEM images of NFC are obtained at low magnification a and high magnification b, c is the AFM image of NFC, d is the NFC solution, e The NFC solution is irradiated by the green laser, f is the polarizing microscope picture when the concentration of the NFC solution is 1%, and g is the NFC gel. The higher the pressure through the microfluidizer, the smaller the resulting NFC size. A in Figure 2 is the NFC obtained by the micro-fluidizer with a pressure of 25KPa. Its diameter is less than 10nm and its length is several hundred nanometers. The high-magnification TEM image (b in Figure 2) shows that the NFC has a beautiful crystalline structure. AFM is also used to characterize the NFC morphology (c in Figure 2), and the diameter of NFC shown in the AFM image is slightly larger than the TEM result, which is related to the characterization means. Aqueous solutions of NFC are characterized by their optical transparency (d in Fig. 2), as well as the Tyndall phenomenon of nanosolutions. Since NFC is shown to contain charged groups introduced by TEMPO oxidation, NFC can be stably dispersed in water. The Zeta potential test of the NFC solution shows that the Zeta potential of the solution is -64.9mV, which confirms the good stability of the solution. NFC has the characteristics of self-assembly. When the concentration of NFC solution is 1%, the solution begins to show the liquid crystal form, as shown in e in Figure 2. Further increase the concentration of NFC solution, NFC gel will be formed, as shown in Figure 2 f. The prepared NFC has a diameter of about 10nm and a length in the range of 100-400nm (b in Figure 5), and the liquid crystal phase begins to form when the NFC concentration is 1.0wt%.

Example 2 Preparation of Graphene Oxide (GO)

GO is obtained by oxidation of graphite by Hummer's method. The specific method is as follows: Graphite flakes (3.0g, 1wt. relative mass content) and NaNO ₃ (1.5g, 0.5 wt. relative mass content) were mixed uniformly at 0°C. Then add H ₂ SO ₄ (98%, 69mL) and mix well, and finally add KMnO ₄ (9.0g, 3wt. relative mass content) slowly. When adding KMnO ₄ , the temperature of the solution was controlled below 20°C. After adding KMnO ₄ , the temperature of the reaction system was raised to 35°C and stirred for 30 minutes. Then 138 mL of deionized water was slowly added dropwise into the reaction system, and the reaction temperature was controlled at 98° C. for 15 min. Then the temperature of the reaction system was cooled to room temperature, and at the same time, 420 mL of deionized water and 3 mL of H ₂ O ₂ with a concentration of 30% were added. When the reaction mixture was cooled to room temperature, the material was washed with deionized water in a Buchner funnel until neutral. The obtained GO was dispersed in water by ultrasound for further use. The morphology of GO nanoflakes was observed by atomic force microscopy. The lateral size of GO nanoflakes is about 1.5 μm (as shown in a in Figure 5), and its average lateral size is about 1.2 _μm . The obtained GO is well dispersible in water and forms a liquid crystal form at a concentration of 1.1 wt%.

Example 3 Preparation and Characterization of GO+NFC Micron Fibers

GO+NFC microfibers are prepared by wet spinning. The flow chart is shown in Figure 3, that is, the spinning liquid is extruded through a needle into an alcohol coagulation bath to form gel fibers, and then the gel fibers are pulled out of the coagulation bath. Air dry. During the drying process, a force of 0.5 N is applied to both ends of the microfibers to increase the degree of orientation of the microfibers. After drying, the microfibers were immersed in 10wt% CaCl ₂ aqueous solution for 1 hour and re-dried. In the same way, GO micron fibers and NFC micron fibers were prepared for performance test comparison.

The morphology of the micron fiber is observed by scanning electron microscope (SEM): after the sample to be tested is vacuum-dried, it is glued to the table and vacuum-sprayed with gold.

The tensile strength and elastic modulus of the microfibers were measured on a DMA-800 instrument. The test mode is film/fiber tensile strength test mode.

Combining GO and NFC to prepare high-strength microfibers, the results are shown in Figure 4, where a is a schematic diagram of the structure of the obtained GO+NFC mixed microfibers. In the mixed microfibers, both GO and NFC are along the fiber The axis has a certain arrangement. The binding force between fibers is mainly composed of hydrogen bonding and ionic bonding increased by the introduction of Ca ²⁺ (b). The introduction of ionic bonds further improves the strength of the hybrid fibers.

The spinning solution in this method is a liquid crystal solution with a concentration of 1.1 wt% prepared by GO and NFC at a mass ratio of 1:1 (as shown in c in Figure 5). At the same concentration, the liquid crystal texture structure of the uniformly mixed GO+NFC spinning solution is obviously different from that of GO alone. The liquid crystal texture gap of the mixed solution is obviously smaller than that of GO liquid crystal texture. After natural drying of the mixed solution and observation under a polarizing microscope, it can be seen that GO has an obvious alignment, which also proves the liquid crystal phase of the mixed solution, as shown in d in Figure 5. In Fig. 5, a is the AFM image of GO, the insert is GO solution, b is the AFM image of NFC, the insert is NFC solution, c is the polarizing microscope image of GO+NFC spinning solution, the insert is GO+NFC spinning Silk solution, d is the polarizing microscope picture of GO+NFC spinning solution after drying.

When preparing high-strength GO+NFC micron fibers by wet spinning, the GO+NFC spinning solution is first extruded into an alcohol coagulation bath. When the GO+NFC spinning solution contacts alcohol, the surface of the micron fiber will first solidify to form a layer, and then slowly through the solvent exchange, the water inside the fiber is also replaced, and finally a stable gel fiber is formed. After the gel fibers are pulled out of the coagulation bath, the alcohol evaporates into dry micron fibers. The results are shown in Figure 6, in which, a shows that four micron fibers are spun simultaneously by wet spinning, b shows that the fibers prepared from 1 mL of spinning solution are wound on a steel column with a diameter of 1.5 cm, and c shows that two fibers are twisted into The SEM picture of a rope, d is the gel fiber just squeezed into the coagulation bath, e is the gel fiber after drying for 10s and f is the polarizing microscope image of the dried fiber. A in Figure 6 shows that four fibers can be extruded at a time, and each fiber can be several meters long. 1mL spinning solution can prepare tens of meters of fiber in a few minutes, and b is the micron fiber entanglement sprayed by 1mL spinning solution. on steel columns. The diameter of the micron fiber prepared by this method is controllable. By changing the diameter of the needle, micron fibers with a diameter ranging from 10 to 40 μm can be obtained. The micron fibers obtained by the wet spinning method have good flexibility and can be knotted or twisted into ropes, as shown in c in Figure 6; Referring to fiber orientation and strength, a force of 0.5 N is applied to both ends of the fiber during drying. During the drying process, the structural unit materials that make up the fibers become more compact, and the diameter of the fibers decreases from about 80 μm for the gel fibers to 10 μm for the final finished fibers. Polarizing microscope is an effective means to observe whether the material has orientation. In order to characterize the orientation of the fiber, observe the fiber under the polarizing microscope. When the orientation direction of the fiber is parallel to the polarized light, only a black background can be seen. When the fiber is rotated, the fiber begins to become bright under the polarizer. When the direction of the fiber is at an angle of 45° to the polarized light, the fiber reaches the brightest state. The d-f fiber in Figure 6 becomes brighter and the texture becomes clearer. It shows that the degree of fiber orientation is getting higher and higher.

As a reference sample, GO microfibers and NFC microfibers were prepared in the same way, as shown in Figure 7, where a is the POM map of GO spinning solution, b-d is the extrusion of GO spinning solution into ethanol, GO Diffusion into GO belts, and with the increase of storage time, GO gradually dissolves into ethanol, e is the preparation of GO microfibers in 1% NaOH ethanol coagulation bath, f is the POM map of GO microfibers, g is the NFC spinning solution The POM map of , h is the NFC micron fiber prepared in the ethanol coagulation bath, the fiber in the figure is dyed with blue dye, and i is the POM map of the NFC micron fiber. A in Figure 7 is the GO spinning solution, which shows an obvious liquid crystal phase when observed under a polarizer. Since GO is soluble in ethanol, fibers cannot be formed when the GO spinning solution is directly extruded into ethanol, but GO bands appear. The strength of the GO band is poor, and it cannot be guaranteed to be completely removed from ethanol; as the storage time increases, the GO band gradually dissolves and finally dissolves in ethanol (b-d in Figure 7). To prepare GO microfibers, 1% NaOH ethanol solution was used as the coagulation bath. e in Figure 7 shows that GO microfibers can be formed in the 1% NaOH ethanol coagulation bath and can be fished out. Obtained GO microfibers were observed under a polarizing fiberscope (f in Fig. 7), which indicated that the fibers had a high degree of orientation. NFC is insoluble in ethanol, and NFC microfibers can be easily obtained by using ethanol as a coagulation bath. The g in Figure 7 is the POM diagram of the NFC spinning solution with a concentration of 1 wt%, indicating that the NFC spinning solution is a liquid crystal phase. When the NFC spinning solution was extruded into ethanol, the NFC spinning solution immediately formed gel fibers, as shown in h in Fig. 7. The NFC microfibers in the picture are dyed with a blue dye to reveal the NFC microfibers in ethanol solution. NFC has self-assembly properties. During the drying process of NFC microfibers, NFC is arranged along the fiber direction. Polarizing microscope observation of NFC microfibers shows that NFC microfibers have a good degree of orientation.

a-b in Figure 8 are the stress-strain curves of GO microfibers, NFC microfibers and GO+NFC microfibers. The average elastic modulus and average tensile strength of the obtained GO+NFC microfibers are 20.6±0.9GPa and 274.6 ±22.4MPa. The strength is higher than that of pure NFC microfibers (15.5±4.5GPa, 139.1±28.7MPa) and GO microfibers (2.3±2GPa, 84.0±2.8MPa).

In order to further improve the strength of the microfibers, the microfibers were impregnated with Ca ²⁺ , and ionic bonds were introduced into the fibers to increase the bonding strength between the fibers. During the impregnation process, the fiber will re-wet and swell, and Ca ²⁺ will enter the interior of the fiber, and after drying, it will change back to form an ionic bond. b in Figure 8 is the stress-strain curve after impregnation of GO micron fiber, NFC micron fiber and GO+NFC micron fiber. After impregnation, the elastic modulus and tensile strength of GO microfibers increased to 9.7 GPa and 96.3 MPa, respectively. The elastic modulus and tensile strength of NFC microfibers were increased to 20.7GPa and 272MPa, respectively. The elastic modulus and tensile strength of GO+NFC microfibers were increased to 31.6 ± 2.5 GPa and 416.6 ± 25.8 MPa, respectively. The elastic modulus and tensile strength of GO+NFC micron fibers can reach up to 34.1GPa and 442.4MPa, and the elongation at break is 2%.

The purposes of embodiment 4GO+NFC micron fiber

GO+NFC micron fibers have excellent mechanical properties and can be used in the preparation of super-strength structural materials. The results are shown in Figure 9, a is a 12.5g magnetic stirring bar lifted by a GO+NFC micron fiber, b is the GO+NFC micron fiber on the needle, c-d is sewing different patterns of GO+NFC micron fiber on the cloth, e is using GO+NFC micron fiber to weave the net, the net woven for GO+NFC micron fiber can be bent arbitrarily , supporting a magnetic stirring bar for the GO+NFC micron fiber web. It vividly shows the strength of GO+NFC micron fiber. In the figure, a GO+NFC microfiber with a diameter of about 80 μm is tied and lifted to a magnetic stirring bar with a mass of 12.5 g. GO+NFC micron fibers not only have excellent mechanical properties, but also have good flexibility, and can be sewn on clothes like threads. It shows that GO+NFC micron fibers can be worn on ordinary needles to sew different patterns on clothes. It is shown that GO+NFC microfibers can be woven into a mesh with certain strength. This net can be bent or even folded arbitrarily, and can also support a weight 100 times its own mass. GO+NFC micro fiber has low density and high strength, which is a good choice for the preparation of high-strength materials.

Example 5 Preparation and Characterization of Conductive Micron Fibers

Conductive GO+NFC microfibers (c(GO+NFC)) were prepared by carbonizing GO+NFC precursor fibers. The carbonization of GO+NFC precursor fibers was carried out in a mixed atmosphere of 95% argon and 5% hydrogen. The heating program is as follows: first from room temperature to 400°C at a rate of 30°C/h, then to 1000°C at a rate of 200°C/h, and finally at 1000°C for 2 hours. NFC and GO fibers were treated with the same procedure as a comparison sample.

The morphology of the micron fibers is characterized by SEM. After the sample to be tested is vacuum-dried, it is bonded and vacuum-sprayed with gold.

The carbon structure of the carbonized fibers was characterized by TEM. When preparing samples for TEM, ultrasonically disperse the carbonized fibers in the aqueous solution, then drop 10 μL of the solution on the carbon mesh, and absorb the excess liquid with filter paper.

The conductivity of the micron fiber is obtained by testing the I-V curve of the micron fiber. The two ends of the conductive microfibers were fixed with silver glue, and the length and average diameter of the microfibers were tested with an optical microscope. When calculating the conductivity of microfibers, treat microfibers as standard solid cylinders.

Using the carbonization method to prepare high-conductivity micron fibers, the results are shown in Figure 9, where, a-b shows that after carbonization, the NFC changes from fibrous to spherical, and c-d shows that after carbonization of NFC containing GO, there are only flake materials, spherical The material disappears, and e is a schematic diagram of the structure of GO+NFC fibers after carbonization. It can be seen from Figure 9 that a-b are the morphology changes before and after NFC carbonization. The figure shows that the fibrous NFC is carbonized to form spherical carbon particles. Carbonization products with similar GO morphology, e shows the morphology of c(GO+NFC) microfibers after carbonization. The structural unit materials are arranged in the fiber along the axial direction of the fiber, and the inside of the micro-fibers has a hollow structure due to the shrinkage during the carbonization process and the rearrangement of the structural unit materials.

The SEM image after carbonization is shown in Figure 10, where a-b is the SEM image of NFC fiber after carbonization, c-d is the SEM image of GO fiber after carbonization, and e-f is the SEM image of GO+NFC fiber after carbonization. The morphology of NFC microfibers after carbonization is shown in Figure 10 a-b. The surface of the fibers is composed of many carbon microspheres with a diameter of about 1 μm. The average conductivity of NFC microfibers is 33 S/cm, which is similar to that of carbon fibers. . The carbonized GO microfibers become rough and porous, but GO still exists in the form of flakes (c-d in Figure 10). The average conductivity of carbonized GO microfibers is 137 S/cm, which is higher than that of carbonized NFC microfibers. Figure 10 e-f shows the morphology of GO+NFC microfibers after carbonization, and the structure is similar to that of carbonized GO microfibers: the fibers have a porous structure without carbonized NFC microspheres. Because GO is a model agent for NFC carbonization, the NFC carbonization material is coated on the carbonized GO sheet. This carbon coating repairs the vacancies and topological defects generated during heat treatment of GO, thereby improving the conductivity. In addition, this carbon coating also acts as a carbon glue, connecting the carbonized GO sheets, increasing the contact between the sheets, reducing the electron transmission resistance, and further improving the conductivity of the fiber.

The average conductivity of c(GO+NFC) fibers after carbonization is 649±60 S/cm, which is the highest conductivity reported so far for conductive fibers prepared from graphite, GO and GO composites. Figure 11 is the I-V curve of c(GO+NFC) micron fibers at room temperature, the test fiber length is 35mm, and the average fiber diameter is 18μm.

Example 5 Application of Conductive Micron Fibers

Flexible electrical appliances and wearable electrical appliances have attracted much attention because of their portability and good integration. As a major building block of such electronic devices, highly conductive fibers are being studied more and more because of their ease of being woven into textile products or integrated into other mechanisms. The conductive fibers prepared in Example 4 are widely used in wearable nanogenerators, supercapacitors, batteries, actuators, and flexible solar cells. For example: using c(GO+NFC) micron fibers as electrode materials for the assembly of sodium-ion batteries, the results show that the efficiency of the first cycle is low, the discharge capacity of the second cycle of the battery is 317.3mAh/g, and the efficiency is 62.2%. After 63 cycles, the discharge capacity of the battery was 312 mAh/g which was basically the same as that of the second cycle. This good electrochemical reaction is mainly attributed to the high conductivity of the fibers. At the same time, c(GO+NFC) microfibers exhibit certain flexibility, which has potential application in the preparation of flexible and wearable electronic devices.

Claims (7)

1. prepare a method for superconduct micrometer fibers, it is characterized in that, comprise the following steps:

1) TEMPO oxycellulose is once by preparing NFC after microfluidizer;

2) Hummer ' s method is adopted to be oxidized graphite and to obtain GO;

3) preparation of high strength micrometer fibers: spinning solution is expressed in alcohol coagulating bath by needle tubing and separates out, form gelatinous fibre, then gelatinous fibre is pulled out coagulating bath dry in atmosphere; In dry run, apply the active force of 0.5N at micrometer fibers two ends, to improve the degree of orientation of micrometer fibers; After drying, micrometer fibers is placed in 10wt% CaCl ₂the aqueous solution in dipping again dry after 1 hour;

4) charing is carried out to high strength micrometer fibers and obtain conduction GO+NFC micrometer fibers.

2. the method preparing superconduct micrometer fibers according to claim 1, is characterized in that: in step 1): the over dry softwood pulp that 5g is not dried and 78mg TEMPO, 514mg NaBr fully mix; Reaction adds initiation by 30mL 12%NaClO, and reacts under stirring at room temperature; The pH value of system controls to be stabilized in 10.5 by NaOH; The end until system interior residue NaClO reacts completely; Reacted slurry is clean by filtration washing, to pH in neutral; The concentration fiber obtained being made into 1% is processed under 5 ~ 25KPa pressure by microfluidizer; Obtain transparent nanofiber element dispersion liquid; Dispersion liquid storage and 4 DEG C of refrigerators.

3. the method preparing superconduct micrometer fibers according to claim 1, is characterized in that: step 2) in: by 3.0g graphite flakes, 1.5g NaNO ₃mix at 0 DEG C; Then 69mL 98%H ₂sO ₄add mixing and stirring, finally slowly add 9.0g KMnO ₄; Add KMnO ₄time solution temperature control, lower than 20 DEG C, to add KMnO ₄after temperature of reaction system is elevated to 35 DEG C and stirs 30min; Then 138mL deionized water is slowly dripped and enter reaction system, and control reaction temperature at 98 DEG C of maintenance 15min; And then reaction system is cooled to room temperature, interpolation 420mL deionized water and 3mL concentration are the H of 30 % in addition simultaneously ₂o ₂; Deng reactant mixture cool to room temperature time, material is spent in Buchner funnel deionized water to neutral; The GO ultrasonic disperse obtained is stand-by in water.

4. the method preparing superconduct micrometer fibers according to claim 1, is characterized in that: in step 3), and described spinning solution is the concentration that GO and NFC mass ratio 1:1 prepares is the liquid crystal solution of 1.1wt%.

5. the method preparing superconduct micrometer fibers according to claim 1, is characterized in that: in step 4), and the charing of high strength micrometer fibers is carried out in 95% argon gas and 5% hydrogen mixed gas atmosphere; Heating schedule is as follows: be first raised to 400 DEG C from room temperature to the heating rate of 30 DEG C/h, be raised to 1000 DEG C afterwards, finally at 1000 DEG C, be incubated 2h with the heating rate of 200 DEG C/h.

6. the superconduct micrometer fibers that the method preparing superconduct micrometer fibers described in any one of claim 1-5 obtains.

7. superconduct micrometer fibers according to claim 6 is as the application of conductive material.