Preparation method of reduced graphene oxide porous chopped fiber

Abstract

The invention discloses a preparation method of a reduced graphene oxide porous chopped fiber wave-absorbing material, and relates to the technical field of preparation of electromagnetic wave absorbing materials. The invention aims to solve the application defects of insufficient dielectric loss performance, limited electromagnetic wave absorption frequency band, low energy attenuation efficiency and the like of a single-component graphene material under a low filling condition. The method comprises the following steps: taking graphene oxide as a main body, constructing a three-dimensional porous fiber structure by combining wet spinning with a freeze-drying process, concentrating a graphene oxide dispersion liquid into a dispersion liquid, performing spinning forming, and performing freeze curing, freeze-drying pore forming, ascorbic acid reduction treatment and cutting to obtain the chopped fiber. According to the invention, efficient dissipation of electromagnetic wave energy and cooperative improvement of broadband absorption performance are realized. The material is simple in technological process, low in cost, high in controllability, capable of being produced in batches and high in wave-absorbing loss strength. The reduced graphene oxide porous chopped fiber wave-absorbing material prepared by the method is applied to the field of electromagnetic wave absorbing materials.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of electromagnetic wave absorbing materials, and particularly relates to a preparation method of reduced graphene oxide porous short fibers. Background Art

[0002] With the rapid development of wireless communication, radar detection, and electronic information technology, the problem of electromagnetic wave radiation pollution has become increasingly serious, which not only interferes with the normal operation of electronic devices but also poses a threat to human health and the safety of the electromagnetic environment. Therefore, the development of lightweight, efficient, and broadband electromagnetic wave absorbing materials has become a research hotspot in the current electromagnetic protection field.

[0003] Carbon-based materials have been widely used in the field of electromagnetic wave absorbing materials due to their low density, high conductivity, large specific surface area, and excellent chemical stability. Especially graphene, due to its unique two-dimensional sheet structure and excellent electrical properties, is considered to be one of the most promising ones. However, the wave absorption performance of pure graphene is often limited by factors such as insufficient dielectric loss, poor impedance matching, and narrow absorption bandwidth, and an ideal wave absorption performance can only be obtained at a relatively high filling amount (>5wt%), which affects its practical application in lightweight electromagnetic protection materials.

[0004] In recent years, in order to improve the wave absorption performance of graphene, researchers have adopted various strategies for structure and component regulation, such as introducing vacancy defects, surface functionalization, heteroatom doping, and constructing three-dimensional networks, etc. Among them, constructing a three-dimensional conductive network of graphene through reasonable structure design can effectively improve the impedance matching characteristics of the material, and enhance the energy attenuation through multi-path scattering and synergistic polarization effects, which is an effective way to achieve lightweight and high efficiency. At the same time, graphene oxide dispersion as a raw material for wet spinning provides a controllable and scalable forming process for constructing a three-dimensional network structure. However, the current research on three-dimensional network graphene still mainly focuses on composite material systems, and there are still many challenges in how to achieve the synergistic optimization of electromagnetic wave absorption performance using single-component graphene materials at low filling amounts. Therefore, developing a three-dimensional conductive network based on single-component graphene, through the synergistic action of microstructural design and multi-stage polarization mechanisms, to endow the material with lightweight, broadband, and efficient electromagnetic wave absorption performance has important research value and application prospects. Summary of the Invention

[0005] The present invention aims to solve the application defects of single-component graphene materials under low filling conditions, such as insufficient dielectric loss performance, limited electromagnetic wave absorption bandwidth, and low energy attenuation efficiency, and proposes a preparation method of reduced graphene oxide porous short fibers.

[0006] A preparation method of reduced graphene oxide porous short fibers is specifically carried out according to the following steps:

[0007] Step 1: Put graphene oxide powder into deionized water and stir it ultrasonically to obtain a graphene oxide dispersion;

[0008] Step 2: Put the graphene oxide dispersion obtained in Step 1 into a constant temperature water bath and stir it magnetically, and then perform concentration treatment to obtain a concentrated graphene oxide dispersion;

[0009] Step 3: Transfer the concentrated graphene oxide dispersion obtained in Step 2 to a syringe, and spin it into a coagulation bath at a constant speed through a micro-injection pump for coagulation, and then transfer it to deionized water for soaking to obtain graphene oxide hydrogel fibers;

[0010] Step 4: Freeze the graphene oxide hydrogel fibers obtained in Step 3 to form a solid, and then transfer it to a freeze dryer for freeze-drying to obtain porous graphene oxide porous fibers;

[0011] Step 5: Immerse the porous graphene oxide porous fibers obtained in Step 4 into an ascorbic acid aqueous solution for reduction in a constant temperature water bath. After reduction, wash and dry them to obtain reduced graphene oxide porous fibers, and then cut them to obtain short-cut fibers, which are the reduced graphene oxide porous short-cut fibers, and the preparation is completed.

[0012] The prepared reduced graphene oxide porous short-cut fibers are defined as xGPF according to the concentration of the concentrated graphene oxide dispersion, where x is the concentration of the concentrated graphene oxide dispersion. For example, the reduced graphene oxide porous short-cut fibers prepared from a 30 mg / mL concentrated graphene oxide dispersion are defined as 30GPF.

[0013] The present invention combines the strategies of wet spinning and freeze-drying to prepare reduced graphene oxide short-cut fibers with excellent microwave absorption properties. The core advantages of this material are reflected in the synergistic effect of the construction of the three-dimensional conductive network of graphene and the multi-stage polarization mechanism: at the microstructural level, the directionally regulated graphene nanosheets form a continuous three-dimensional conductive network through mutual overlap, significantly enhancing the conduction loss of electromagnetic waves; by regulating the concentration of the graphene oxide dispersion, short-cut fiber pore structures of different sizes are designed, which not only realizes the multi-stage cooperative scattering of electromagnetic waves to broaden the absorption bandwidth, but also improves the impedance matching characteristics of graphene. In terms of the polarization mechanism, the mild reduction strategy of ascorbic acid retains the low reduction degree characteristics of graphene, effectively increasing the formation of in-plane structural defects to form electric dipoles and triggering a strong dipole polarization effect; at the same time, the non-regular overlap of the nanosheets formed by wet spinning and the interlayer stacking distortion during the freeze-drying process jointly induce interface polarization and defect polarization. Through the organic combination of multi-dimensional structural design and multiple loss mechanisms, the material realizes the efficient dissipation of electromagnetic wave energy and the synergistic improvement of broadband absorption performance.

[0014] The beneficial effects of the present invention are:

[0015] The present invention combines a wet spinning and freeze-drying strategy. By constructing a three-dimensional conductive network and regulating the pore structure, a single-component graphene material can achieve the synergistic optimization of loss ability and impedance matching at a low filling content, thereby endowing the material with lightweight, broadband, and efficient electromagnetic wave absorption performance.

[0016] (1) The reduced graphene oxide short fibers developed in the present invention adopt a combined process of wet spinning and freeze-drying, which has the advantages of simple process flow, low cost, strong controllability, and can realize continuous batch production.

[0017] (2) Based on the unique continuous electron transport path characteristics of the graphene three-dimensional conductive network, the pore structure of the short fibers is regulated by controlling the concentration of the graphene oxide dispersion liquid, while solving the problem of impedance mismatch of high-loss materials, a multi-path scattering attenuation channel for electromagnetic waves is constructed.

[0018] (3) The reduced graphene oxide porous short fibers prepared by the method of the present invention form induced electric dipoles through in-plane defects of low-reduced graphene, combined with non-regular lap joints and interlayer stacking distortion of nanosheets, synergistically exciting dipole polarization, interfacial polarization, and defect polarization effects. The construction of the three-dimensional conductive network provides a free electron migration channel to generate conduction loss, realizing the effective coupling of multiple energy dissipation mechanisms.

[0019] (4) The reduced graphene oxide porous short fibers prepared by the method of the present invention have efficient electromagnetic wave absorption performance. For the graphene porous short fibers prepared using a 30 mg / mL graphene oxide dispersion liquid, when their length is 1 mm and the filling content is 2 wt%, the maximum reflection loss reaches -59.09 dB, the effective absorption bandwidth at a matching thickness of 2.36 mm reaches 7.27 GHz, and the matching thickness is 2.41 mm; when their length is 3 mm and the filling content is 1 wt%, the maximum reflection loss reaches -55.95 dB, the effective absorption bandwidth at a matching thickness of 2.65 mm reaches 7.61 GHz, and the matching thickness is 2.92 mm. The present invention provides an important reference for the design and preparation of novel lightweight and efficient electromagnetic wave absorption materials.

[0020] The reduced graphene oxide porous short fibers prepared by the method of the present invention are applied to the field of electromagnetic wave absorption materials. Description of the Drawings

[0021] Figure 1 XRD spectra of the reduced graphene oxide porous short fibers 30GPF-1, 20GPF-1, 40GPF-1, and 50GPF-1 prepared in the examples;

[0022] Figure 2 Raman spectra of the reduced graphene oxide porous short fibers 30GPF-1, 20GPF-1, 40GPF-1, and 50GPF-1 prepared in the examples;

[0023] Figure 3 SEM image of graphene sheets in the cross-section of the reduced graphene oxide porous chopped fiber 30GPF-1 prepared in Example 1;

[0024] Figure 4 SEM images of the cut surfaces of the reduced graphene oxide porous chopped fibers 30GPF-1, 20GPF-1, 40GPF-1, and 50GPF-1 prepared in the examples;

[0025] Figure 5 SEM images of the axial directions of the reduced graphene oxide porous chopped fibers 30GPF-1, 20GPF-1, 40GPF-1, and 50GPF-1 prepared in the examples;

[0026] Figure 6 SEM image of the fiber cross-section after the reduced graphene oxide porous chopped fiber 30GPF-1 prepared in Example 1 was mixed with paraffin and ultrasonically treated for 15 min in an ultrasonic environment at 65°C;

[0027] Figure 7 Electromagnetic parameter curve of the reduced graphene oxide porous chopped fiber 20GPF-1 prepared in Example 2;

[0028] Figure 8 Absorbing performance curve of the reduced graphene oxide porous chopped fiber 20GPF-1 prepared in Example 2;

[0029] Figure 9 Electromagnetic parameter curve of the reduced graphene oxide porous chopped fiber 40GPF-1 prepared in Example 3;

[0030] Figure 10 Absorbing performance curve of the reduced graphene oxide porous chopped fiber 40GPF-1 prepared in Example 3;

[0031] Figure 11 Electromagnetic parameter curve of the reduced graphene oxide porous chopped fiber 50GPF-1 prepared in Example 4;

[0032] Figure 12 Absorbing performance curve of the reduced graphene oxide porous chopped fiber 50GPF-1 prepared in Example 4;

[0033] Figure 13 Electromagnetic parameter curve of the reduced graphene oxide porous chopped fiber 30GPF-1 prepared in Example 1 (mixed with paraffin at 2 wt%);

[0034] Figure 14 Absorbing performance curve of the reduced graphene oxide porous chopped fiber 30GPF-1 prepared in Example 1 (mixed with paraffin at 2 wt%);

[0035] Figure 15 Electromagnetic parameter curve of the reduced graphene oxide porous short-cut fiber 30GPF-1 prepared in Example 1 (mixed with paraffin at 1 wt%);

[0036] Figure 16 Absorbing performance curve of the reduced graphene oxide porous short-cut fiber 30GPF-1 prepared in Example 1 (mixed with paraffin at 1 wt%);

[0037] Figure 17 Electromagnetic parameter curve of the reduced graphene oxide porous short-cut fiber 30GPF-2 prepared in Example 1;

[0038] Figure 18 Absorbing performance curve of the reduced graphene oxide porous short-cut fiber 30GPF-2 prepared in Example 1;

[0039] Figure 19 Electromagnetic parameter curve of the reduced graphene oxide porous short-cut fiber 30GPF-3 prepared in Example 1;

[0040] Figure 20 Absorbing performance curve of the reduced graphene oxide porous short-cut fiber 30GPF-3 prepared in Example 1. Specific embodiments

[0041] Specific embodiment 1: A preparation method of the reduced graphene oxide porous short-cut fiber in this embodiment is specifically carried out according to the following steps:

[0042] Step 1: Put the graphene oxide powder into deionized water and stir it ultrasonically to obtain a graphene oxide dispersion;

[0043] Step 2: Put the graphene oxide dispersion obtained in Step 1 into a constant temperature water bath and stir it magnetically, and then carry out concentration treatment to obtain a concentrated graphene oxide dispersion;

[0044] Step 3: Transfer the concentrated graphene oxide dispersion obtained in Step 2 to a syringe, and spin it into a coagulation bath at a constant speed through a micro-injection pump for coagulation, and then transfer it to deionized water for soaking to obtain a graphene oxide hydrogel fiber;

[0045] Step 4: Freeze the graphene oxide hydrogel fiber obtained in Step 3 to form a solid, and then transfer it to a freeze dryer for freeze drying to obtain a porous graphene oxide porous fiber;

[0046] Step 5: Immerse the porous graphene oxide porous fiber obtained in Step 4 into an ascorbic acid aqueous solution, perform reduction in a constant-temperature water bath, and after reduction, carry out washing and drying treatments to obtain a reduced graphene oxide porous fiber, and then perform cutting to obtain short-cut fibers, which are the reduced graphene oxide porous short-cut fibers, thus completing the preparation.

[0047] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: during the ultrasonic stirring process in Step 1, the ultrasonic time is controlled to be 6 h, the power is 400 W, magnetic stirring is carried out for 4 h, and the stirring speed is 300 - 500 r / min. Others are the same as Specific Embodiment 1.

[0048] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that: the water bath temperature controlled in Step 2 is 80 °C, the magnetic stirring time is 1 - 4 h, and the stirring speed is 300 - 500 r / min. Others are the same as Specific Embodiment 1 or 2.

[0049] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that: the concentration treatment in Step 2 is: drying in an oven at 60 °C to constant weight; the concentration of the concentrated graphene oxide dispersion is 20 - 50 mg / mL. Others are the same as any one of Specific Embodiments 1 to 3.

[0050] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that: after transferring the concentrated graphene oxide dispersion to a syringe in Step 3, place it in a vacuum drying oven to evacuate, the vacuum time is 3 min, the vacuum degree is 0.1 Pa, and defoaming treatment is carried out. Others are the same as any one of Specific Embodiments 1 to 4.

[0051] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that: the needle orifice diameter of the syringe in Step 3 is 16G, the extrusion speed of the micro-injection pump is 0.3 mL / min, the coagulation bath is 1 wt% CaCl 2 aqueous solution, the coagulation time is 30 min, and the soaking time in deionized water is 30 min. Others are the same as any one of Specific Embodiments 1 to 5.

[0052] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that: the freezing temperature in Step 4 is -20 °C, the freezing time is 24 h, the freeze-drying time in the freeze-dryer is 36 h, the freeze-drying pressure is 0.1 Pa, and the freeze-drying temperature is -60 °C. Others are the same as any one of Specific Embodiments 1 to 6.

[0053] Embodiment VIII: The difference between this embodiment and any one of Embodiments I to VII is that: the concentration of the ascorbic acid aqueous solution in Step V is 0.1 M, the temperature of the constant-temperature water bath reduction is 80 °C, and the reduction time is 12 h. Others are the same as any one of Embodiments I to VII.

[0054] Embodiment IX: The difference between this embodiment and any one of Embodiments I to VIII is that: in the washing process of Step V, the reduced fibers are successively soaked in deionized water and absolute ethanol and washed three times, and the drying process is to transfer the washed fibers to an oven at 60 °C and dry for 12 h. Others are the same as any one of Embodiments I to VIII.

[0055] Embodiment X: The difference between this embodiment and any one of Embodiments I to IX is that: the cutting process in Step V is to cut the fibers aligning with the scale line of the ruler, and the length of the short-cut fibers is 1 - 3 mm. Others are the same as any one of Embodiments I to IX.

[0056] The content of the present invention is not limited to the content of the above embodiments, and the combination of one or several specific embodiments can also achieve the purpose of the invention.

[0057] Example 1:

[0058] A preparation method of reduced graphene oxide porous short-cut fibers (30GPF) in this example is specifically carried out according to the following steps:

[0059] Step 1: Put 1 g of graphene oxide powder into 100 mL of deionized water and ultrasonicate for 6 h, control the ultrasonic power to be 400 W, and then magnetically stir for 4 h, control the stirring speed to be 500 r / min to obtain a graphene oxide dispersion with a concentration of 10 mg / mL;

[0060] Step 2: Put 100 mL of the graphene oxide dispersion obtained in Step 1 into a constant-temperature water bath at 80 °C and magnetically stir, control the stirring speed to be 500 r / min, continuously stir and evaporate the solvent. When the solvent is reduced to 1 / 3 of the original, take out a small amount of the graphene oxide dispersion with a dropper and dry it to constant weight in an oven at 60 °C. Determine the solid content of the graphene oxide by measuring the mass change before and after drying to obtain the concentration of the concentrated graphene oxide dispersion. Through repeated measurement, accurately control the concentration of the concentrated graphene oxide dispersion to be 30 ± 1 mg / mL;

[0061] Step 3: Transfer the concentrated graphene oxide dispersion obtained in Step 2 to a syringe, put it into a vacuum drying oven to evacuate, the vacuum time is 3 min, the vacuum degree is 0.1 Pa, perform defoaming treatment, and then use a needle with a diameter of 16G, through a micro-injection pump, control the uniform extrusion speed to be 0.3 mL / min and spin it into 1 wt% CaCl2 Coagulate in an aqueous solution coagulation bath for 30 min, and then transfer it to deionized water for soaking for 30 min to obtain graphene oxide hydrogel fibers;

[0062] Step 4: Freeze the graphene oxide hydrogel fibers obtained in Step 3 to form a solid. The freezing temperature is -20 °C and the freezing time is 24 h. Then transfer it to a freeze dryer for freeze-drying. The freeze-drying time is 36 h, the freeze-drying pressure is 0.1 Pa, and the freeze-drying temperature is -60 °C to obtain porous graphene oxide porous fibers;

[0063] Step 5: Immerse the porous graphene oxide porous fibers obtained in Step 4 in an aqueous solution of ascorbic acid with a concentration of 0.1 M, and carry out reduction in a constant temperature water bath at 80 °C for 12 h. After reduction, wash it three times alternately with deionized water and absolute ethanol to wash away the residual impurities on the fiber surface, and then put it in a vacuum drying oven at 60 °C for drying for 12 h to obtain reduced graphene oxide porous fibers. Then cut it with a knife to obtain short fibers with a length of 1 mm, which are reduced graphene oxide porous short fibers (30 GPF-1), short fibers with a length of 2 mm, which are reduced graphene oxide porous short fibers (30 GPF-2), and short fibers with a length of 3 mm, which are reduced graphene oxide porous short fibers (30 GPF-3).

[0064] Example 2:

[0065] The difference between this example and Example 1 is that the concentration of the concentrated graphene oxide dispersion obtained in Step 2 is 20 mg / mL; short fibers with a length of 1 mm are obtained, which are reduced graphene oxide porous short fibers (20 GPF-1), short fibers with a length of 2 mm, which are reduced graphene oxide porous short fibers (20 GPF-2), and short fibers with a length of 3 mm, which are reduced graphene oxide porous short fibers (20 GPF-3).

[0066] Example 3:

[0067] The difference between this example and Example 1 is that the concentration of the concentrated graphene oxide dispersion obtained in Step 2 is 40 mg / mL; short fibers with a length of 1 mm are obtained, which are reduced graphene oxide porous short fibers (40 GPF-1), short fibers with a length of 2 mm, which are reduced graphene oxide porous short fibers (40 GPF-2), and short fibers with a length of 3 mm, which are reduced graphene oxide porous short fibers (40 GPF-3).

[0068] Example 4:

[0069] The differences between this embodiment and Embodiment 1 are as follows: the concentration of the concentrated graphene oxide dispersion obtained in Step 2 is 50 mg / mL; short fibers with a length of 1 mm are obtained, which are reduced graphene oxide porous short fibers (50GPF-1), short fibers with a length of 2 mm are reduced graphene oxide porous short fibers (50GPF-2), and short fibers with a length of 3 mm are reduced graphene oxide porous short fibers (50GPF-3).

[0070] Preparation of test samples:

[0071] Put the reduced graphene oxide porous short fibers prepared in the embodiment into paraffin at 2 wt%, and ultrasonicate for 15 min in an ultrasonic environment at 65 °C to allow the paraffin to penetrate into the interior of the 30GPF-1 porous short fibers. Place the sample in a mold to finally obtain a coaxial ring with an outer diameter of 7 mm, an inner diameter of 3.04 mm, and a height of 2.5 mm.( Figures 7 to 14 )

[0072] Meanwhile, preparation of test samples:

[0073] Mix the reduced graphene oxide porous short fibers prepared in the embodiment with paraffin at 1 wt%, and ultrasonicate for 15 min in an ultrasonic environment at 65 °C to allow the paraffin to penetrate into the interior of the 30GPF-1 porous short fibers. Place the sample in a mold to finally obtain a coaxial ring with an outer diameter of 7 mm, an inner diameter of 3.04 mm, and a height of 2.5 mm.( Figures 15 to 20 )

[0074] Test the reduced graphene oxide porous short fibers and test samples prepared in the embodiment.

[0075] Figure 1 XRD spectra of the reduced graphene oxide porous short fibers 30GPF-1, 20GPF-1, 40GPF-1, and 50GPF-1 prepared in the embodiment. It can be seen from the figure that the characteristic peaks of the samples mainly show the typical "bread-like peak" of RGO, indicating that the crystallinity of the carbon material is low and it mainly exists in the form of amorphous carbon. There is a graphite peak in the XRD at 42.3°, corresponding to the (100) crystal plane of graphite. Usually, in single-layer or few-layer graphene, if there is local multi-layer stacking or in-plane ordered structure, a weak diffraction peak may appear at this angle, and the multi-layer stacking may be due to the growth of ice crystals during the freezing of the fibers, inducing the multi-layer stacking of graphene sheets through physical extrusion.

[0076] Figure 2Raman spectra of the reduced graphene oxide porous short cut fibers 30GPF-1, 20GPF-1, 40GPF-1, and 50GPF-1 prepared for the examples. The ID / IG values of all the products of the examples are stable within the range of 1.21 ± 0.01. This is because when the same reducing agent (ascorbic acid) and treatment conditions are used, the removal rate of oxygen-containing groups and the sp 2 The carbon domain reconstruction process is repeatable. And when the pores are constructed through the ice crystal template during the freeze-drying process, no forces that would damage the integrity of the graphene lattice, such as chemical etching or mechanical shearing, are applied. Therefore, the change in pore size will not significantly change the density of micro-defects, indicating that the control of the reduction degree has process stability.

[0077] Figure 3 SEM image of the graphene sheets in the cross-section of the reduced graphene oxide porous short cut fiber 30GPF-1 prepared for Example 1. It can be seen that the graphene sheets with a lateral size of up to 35 μm have clear edges and significant surface wrinkles, and form a three-dimensional porous network with adjacent sheets through π-π stacking.

[0078] Figure 4 SEM images of the cut surfaces of the reduced graphene oxide porous short cut fibers 30GPF-1, 20GPF-1, 40GPF-1, and 50GPF-1 prepared for the examples, where (a) 20GPF-1, (b) 30GPF-1, (c) 40GPF-1, and (d) 50GPF-1. When the concentration of the concentrated graphene oxide dispersion increases from 20 mg / mL to 50 mg / mL, the average pore diameter of the porous fibers decreases regularly from 200 μm to 30 μm. The pore diameter of the fibers decreases with the decrease in concentration. This is because when the concentration of the graphene oxide dispersion is high, there are more graphene oxide solutes, which may limit the growth space of ice crystals during the freezing process, resulting in a decrease in ice crystal size. And the interaction between graphene oxide sheets is enhanced at high concentrations, thus hindering the expansion of ice crystals.

[0079] Figure 5 SEM images of the axial directions of the reduced graphene oxide porous short cut fibers 30GPF-1, 20GPF-1, 40GPF-1, and 50GPF-1 prepared for the examples, where (a) 20GPF-1, (b) 30GPF-1, (c) 40GPF-1, and (d) 50GPF-1. The statistical distribution of the fiber diameters shows that the diameter of 20GPF-1 is 643 μm, which is much smaller than that of 30GPF-1 (1032 μm), 40GPF-1 (1021 μm), and 50GPF-1 (1046 μm). This may be because there are fewer graphene oxide solutes in the spinning solution of 20 mg / mL, and cross-linking cannot be formed between graphene oxide sheets during the freeze-drying of the fibers, resulting in the collapse of the pore structure framework and the reduction of the fiber diameter.

[0080] Figure 6 SEM image of the cross-section of the reduced graphene oxide porous short-cut fibers 30GPF-1 prepared in Example 1 after being mixed with paraffin and ultrasonically treated for 15 min in an ultrasonic environment at 65°C. It can be clearly seen that during the ultrasonic treatment at 65°C, the paraffin melted and penetrated into the pore structure of the reduced graphene oxide porous short-cut fibers under the action of ultrasonic waves, playing a supporting role for the pore structure.

[0081] Figure 7 Electromagnetic parameter curve of the reduced graphene oxide porous short-cut fibers 20GPF-1 prepared in Example 2. From the electromagnetic parameters, it shows a dielectric dispersion trend. The real and imaginary parts of the magnetic permeability are 1 and 0 respectively, indicating no magnetic loss.

[0082] Figure 8 Absorbing performance curve of the reduced graphene oxide porous short-cut fibers 20GPF-1 prepared in Example 2. Curve 1 represents a thickness of 1.0 mm, curve 2 represents a thickness of 1.5 mm, curve 3 represents a thickness of 2.0 mm, curve 4 represents a thickness of 2.34 mm, curve 5 represents a thickness of 2.68 mm, curve 6 represents a thickness of 3.0 mm, curve 7 represents a thickness of 3.5 mm, curve 8 represents a thickness of 4.0 mm, curve 9 represents a thickness of 4.5 mm, and curve 10 represents a thickness of 5.0 mm. When the matching thickness is 2.68 mm, the filling amount is 2 wt%, and the frequency is 12.815 GHz, the maximum reflection loss is -17.09 dB.

[0083] Figure 9 Electromagnetic parameter curve of the reduced graphene oxide porous short-cut fibers 40GPF-1 prepared in Example 3. From the electromagnetic parameters, it shows a dielectric dispersion trend. The real and imaginary parts of the dielectric constant are correspondingly higher compared to 20GPF-1.

[0084] Figure 10 Absorbing performance curve of the reduced graphene oxide porous short-cut fibers 40GPF-1 prepared in Example 3. Curve 1 represents a thickness of 1.0 mm, curve 2 represents a thickness of 1.5 mm, curve 3 represents a thickness of 2.0 mm, curve 4 represents a thickness of 2.28 mm, curve 5 represents a thickness of 2.69 mm, curve 6 represents a thickness of 3.0 mm, curve 7 represents a thickness of 3.5 mm, curve 8 represents a thickness of 4.0 mm, curve 9 represents a thickness of 4.5 mm, and curve 10 represents a thickness of 5.0 mm. Compared with the 20GPF-1 comparison sample, the absorbing performance is slightly improved. When the matching thickness is 2.69 mm, the filling amount is 2 wt%, and the frequency is 12.39 GHz, the maximum reflection loss is -36.02 dB.

[0085] Figure 11Electromagnetic parameter curve of the reduced graphene oxide porous short cut fiber 50GPF-1 prepared in Example 4. Judging from the electromagnetic parameters, it shows a dielectric dispersion trend. The real part and imaginary part of the dielectric increase correspondingly compared with 20GPF-1. The real part of the dielectric is close to 40GPF-1, and the imaginary part of the dielectric is slightly lower than 40GPF-1.

[0086] Figure 12 Absorbing performance curve of the reduced graphene oxide porous short cut fiber 50GPF-1 prepared in Example 4. Curve 1 represents a thickness of 1.0 mm, Curve 2 represents a thickness of 1.5 mm, Curve 3 represents a thickness of 2.0 mm, Curve 4 represents a thickness of 2.5 mm, Curve 5 represents a thickness of 3.06 mm, Curve 6 represents a thickness of 3.2 mm, Curve 7 represents a thickness of 3.5 mm, Curve 8 represents a thickness of 4.0 mm, Curve 9 represents a thickness of 4.5 mm, Curve 10 represents a thickness of 5.0 mm. Compared with the 40GPF-1 comparison sample, the absorbing performance decreases slightly. When the matching thickness is 3.20 mm, the filling amount is 2 wt%, and the frequency is 10.65 GHz, the maximum reflection loss is -27.13 dB.

[0087] Figure 13 Electromagnetic parameter curve of the reduced graphene oxide porous short cut fiber 30GPF-1 prepared in Example 1 (mixed with paraffin at 2 wt%); Judging from the electromagnetic parameters, it shows a dielectric dispersion trend. The real part and imaginary part of the dielectric increase correspondingly compared with 20GPF-1. The real part of the dielectric is close to 40GPF-1 and 50GPF-1, and the imaginary part of the dielectric is slightly higher than 40GPF-1 and 50GPF-1, with the strongest dielectric loss ability.

[0088] Figure 14 Absorbing performance curve of the reduced graphene oxide porous short cut fiber 30GPF-1 prepared in Example 1 (mixed with paraffin at 2 wt%). Curve 1 represents a thickness of 1.0 mm, Curve 2 represents a thickness of 1.5 mm, Curve 3 represents a thickness of 2.0 mm, Curve 4 represents a thickness of 2.36 mm, Curve 5 represents a thickness of 2.41 mm, Curve 6 represents a thickness of 3.0 mm, Curve 7 represents a thickness of 3.5 mm, Curve 8 represents a thickness of 4.0 mm, Curve 9 represents a thickness of 4.5 mm, Curve 10 represents a thickness of 5.0 mm. It can be seen that when the short cut fiber length is 1 mm and the filling amount is 2 wt%, 30GPF-1 has a strong absorbing intensity. When the matching thickness is 2.36 mm and the frequency is 14.09 GHz, the maximum reflection loss is -59.09 dB, and the effective absorption bandwidth is 7.27 GHz (10.33 - 18 GHz).

[0089] Figure 15Electromagnetic parameter curve of the reduced graphene oxide porous short-cut fiber 30GPF-1 prepared in Example 1 (mixed with paraffin at 1 wt%). From the perspective of electromagnetic parameters, its dielectric parameter phase exhibits dielectric dispersion characteristics, but the real and imaginary parts of the dielectric constant are relatively low. The real and imaginary parts of the magnetic permeability are 1 and 0 respectively, proving no magnetic loss.

[0090] Figure 16 Absorbing wave performance curve of the reduced graphene oxide porous short-cut fiber 30GPF-1 prepared in Example 1 (mixed with paraffin at 1 wt%). Curve 1 represents a thickness of 1.0 mm, Curve 2 represents a thickness of 1.5 mm, Curve 3 represents a thickness of 2.0 mm, Curve 4 represents a thickness of 2.5 mm, Curve 5 represents a thickness of 2.86 mm, Curve 6 represents a thickness of 3.0 mm, Curve 7 represents a thickness of 3.5 mm, Curve 8 represents a thickness of 4.0 mm, Curve 9 represents a thickness of 4.5 mm, Curve 10 represents a thickness of 5.0 mm; no absorbing wave performance is shown at thicknesses of 1.0 - 5.0 mm, and the reflection loss values are all greater than -10 dB.

[0091] Figure 17 Electromagnetic parameter curve of the reduced graphene oxide porous short-cut fiber 30GPF-2 prepared in Example 1; it can be seen that its dielectric parameter phase exhibits obvious dielectric dispersion characteristics. With the construction of the conductive network, the dielectric constant of 30GPF-2 has been improved compared with that of 30GPF-1, and the dielectric loss ability has been enhanced.

[0092] Figure 18 Absorbing wave performance curve of the reduced graphene oxide porous short-cut fiber 30GPF-2 prepared in Example 1. Curve 1 represents a thickness of 1.0 mm, Curve 2 represents a thickness of 1.5 mm, Curve 3 represents a thickness of 2.0 mm, Curve 4 represents a thickness of 2.68 mm, Curve 5 represents a thickness of 3.0 mm, Curve 6 represents a thickness of 3.22 mm, Curve 7 represents a thickness of 3.5 mm, Curve 8 represents a thickness of 4.0 mm, Curve 9 represents a thickness of 4.5 mm, Curve 10 represents a thickness of 5.0 mm. Compared with 30GPF-1, the absorbing wave performance is significant. When the matching thickness is 3.22 mm, the filling amount is 1 wt%, and the frequency is 11.965 GHz, the maximum reflection loss is -35.96 dB.

[0093] Figure 19 Electromagnetic parameter curve of the reduced graphene oxide porous short-cut fiber 30GPF-3 prepared in Example 1; it can be seen that its dielectric parameter phase exhibits obvious dielectric dispersion characteristics. With the construction of the conductive network, the dielectric constant of 30GPF-3 has been improved compared with that of 30GPF-1 and 30GPF-2, and the dielectric loss ability has been significantly enhanced.

[0094] Figure 20 Absorbing performance curve of the reduced graphene oxide porous chopped fibers 30GPF-3 prepared in Example 1. Curve 1 represents a thickness of 1.0 mm, curve 2 represents a thickness of 1.5 mm, curve 3 represents a thickness of 2.0 mm, curve 4 represents a thickness of 2.5 mm, curve 5 represents a thickness of 2.65 mm, curve 6 represents a thickness of 2.92 mm, curve 7 represents a thickness of 3.5 mm, curve 8 represents a thickness of 4.0 mm, curve 9 represents a thickness of 4.5 mm, and curve 10 represents a thickness of 5.0 mm. It can be seen that when the chopped fiber length is 3 mm and the filling amount is 1 wt%, 30GPF-3 has strong absorbing intensity. When the matching thickness is 2.36 mm and the frequency is 14.09 GHz, the maximum reflection loss is -59.09 dB, and the effective absorption bandwidth is 7.27 GHz (10.33 - 18 GHz).

Claims

1. A method for preparing reduced graphene oxide porous chopped fibers, characterized in that The method is specifically carried out in the following steps: Step 1: placing graphene oxide powder in deionized water and ultrasonically stirring to obtain a graphene oxide dispersion; Step 2: placing the graphene oxide dispersion obtained in step 1 into a constant temperature water bath for magnetic stirring, and then concentrating the dispersion to obtain a concentrated graphene oxide dispersion; Step 3: transferring the concentrated graphene oxide dispersion obtained in step 2 into a syringe, spinning it into a coagulation bath at a uniform speed through a micro-injection pump for coagulation, and then transferring it to deionized water for immersion to obtain graphene oxide hydrogel fibers; Step 4: freezing the graphene oxide hydrogel fiber obtained in step 3 to form a solid, and then transferring it to a freeze dryer for freeze drying to obtain porous graphene oxide porous fibers; Step 5: immerse the porous graphene oxide porous fiber obtained in step 4 in an aqueous solution of ascorbic acid, reduce it in a constant temperature water bath, wash and dry it after reduction to obtain the reduced graphene oxide porous fiber, and then cut it to obtain chopped fibers, namely the reduced graphene oxide porous chopped fibers, to complete the preparation.

2. The method for preparing a reduced graphene oxide porous chopped fiber according to claim 1, characterized in that In the ultrasonic stirring process of step 1, the ultrasonic time is controlled to be 6 hours, the power is 400W, the magnetic stirring is 4 hours, and the stirring speed is 300-500r / min.

3. The method for preparing a reduced graphene oxide porous chopped fibers according to claim 1, characterized in that In step 2, the water bath temperature is controlled to be 80° C., the magnetic stirring time is 1 to 4 hours, and the stirring speed is 300 to 500 r / min.

4. The method for preparing a reduced graphene oxide porous chopped fibers according to claim 1, characterized in that The concentration treatment in step 2 is: drying in a drying oven at 60° C. to constant weight; the concentration of the concentrated graphene oxide dispersion is 20 to 50 mg / mL.

5. The method for preparing a reduced graphene oxide porous chopped fibers according to claim 1, characterized in that Step 3: After the concentrated graphene oxide dispersion is transferred to a syringe, it is placed in a vacuum drying oven for evacuation. The vacuum time is 3 minutes and the vacuum degree is 0.1 Pa for defoaming treatment.

6. The method for preparing a reduced graphene oxide porous chopped fibers according to claim 1, characterized in that Step 3: The needle caliber of the syringe is 16G, the extrusion speed of the microinjection pump is 0.3mL / min, the coagulation bath is a 1wt% CaCl2 aqueous solution, the coagulation time is 30min, and the immersion time in deionized water is 30min.

7. The method for preparing a reduced graphene oxide porous chopped fiber according to claim 1, characterized in that The freezing temperature in step 4 is -20°C, the freezing time is 24h, the freeze-drying time in the freeze dryer is 36h, the freeze-drying pressure is 0.1Pa, and the freeze-drying temperature is -60°C.

8. The method for preparing a reduced graphene oxide porous chopped fiber according to claim 1, characterized in that The concentration of the ascorbic acid aqueous solution in step 5 is 0.1 M, the temperature of the constant temperature water bath reduction is 80° C., and the reduction time is 12 h.

9. The method for preparing a reduced graphene oxide porous chopped fiber according to claim 1, characterized in that The washing process described in step five is to soak the reduced fiber in deionized water and anhydrous ethanol three times in sequence, and the drying process is to transfer the washed fiber to an oven at 60° C. and dry it for 12 hours.

10. The method for preparing reduced graphene oxide porous chopped fibers according to claim 1, characterized in that The cutting process described in step five is to align the fiber with the scale line of the ruler and cut it, and the length of the cut short fiber is 1 to 3 mm.

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