CN110436923B - Electromagnetic shielding material and preparation method thereof - Google Patents
Electromagnetic shielding material and preparation method thereof Download PDFInfo
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Abstract
The invention provides a preparation method of an electromagnetic shielding material, which comprises the following steps: providing bacterial cellulose, and performing low-temperature carbonization treatment on the bacterial cellulose at the temperature of 200-800 ℃ to obtain the bacterial cellulose with hydrophobic surface; depositing a graphene oxide aqueous solution on the surface of the bacterial cellulose, and drying to remove the solvent to obtain a graphene oxide coated bacterial cellulose complex; and carrying out high-temperature carbonization treatment on the composite body at the temperature of 800-2500 ℃ to obtain the electromagnetic shielding material. According to the preparation method of the electromagnetic shielding material, the bacterial cellulose subjected to low-temperature carbonization is used as a core or middle layer raw material of the electromagnetic shielding material, a graphene oxide aqueous solution is further deposited on the surface of the bacterial cellulose, the bacterial cellulose is completely carbonized after high-temperature carbonization, and meanwhile, graphene oxide on the surface of the bacterial cellulose is reduced to form a compact reduced graphene oxide film.
Description
Technical Field
The invention belongs to the field of electromagnetic shielding materials, and particularly relates to an electromagnetic shielding material and a preparation method thereof.
Background
With the development of the information age, electronic equipment is integrated into the aspects of life. However, electronic devices such as computers, mobile phones, televisions, mobile communication base stations, communication transmitting stations, power transmission and transformation equipment, large power generating stations, radio frequency induction and medium heating equipment, radio frequency and microwave medical equipment, electric processing equipment and other electrical appliances and systems can generate electromagnetic radiation with various forms, different frequencies and different intensities, and invisible and untouchable electromagnetic pollution sources are increasingly concerned by various circles and are called as 'invisible killers', and become the fourth pollution in the lives of people today after water pollution, air pollution and noise pollution. With the development of science and technology, the electromagnetic radiation generated by various electronic devices not only affects the normal operation of the devices, but also harms the natural ecological environment and human health. In order to solve the problem of electromagnetic radiation, the preparation of electromagnetic shielding materials is urgent, and light and efficient shielding are two key technical points for preparing ideal electromagnetic shielding materials.
At present, shielding materials based on metal elements are mostly adopted as the electromagnetic shielding materials, and the electromagnetic shielding materials have good shielding effect, but have large relative weight, high price and no corrosion resistance, so that the application of the electromagnetic shielding materials in electronic equipment, particularly tiny electronic equipment, is limited. The quality of the shielding material can be reduced to a certain extent by depositing metal on the surface of the foam structure to prepare the foam type electromagnetic shielding material (such as conductive foam), but the metal deposition process is complex and the cost is still higher. The carbon material, especially the graphene material, has the characteristics of light weight, high electromagnetic shielding effectiveness and the like. The graphene-based electromagnetic shielding material is prepared by mainly preparing graphene aerogel/foam or compounding graphene and a polymer and the like. Due to poor dispersibility of the graphene sheet in the polymer, the electromagnetic shielding performance of the graphene-based polymer composite material cannot achieve the expected effect, and the preparation of the graphene foam/aerogel usually requires template sacrifice or complex process technology, so that the defects of complex preparation process, high cost, difficulty in realizing industrialization and the like exist.
Disclosure of Invention
The invention aims to provide an electromagnetic shielding material, a preparation method and application thereof, and aims to solve the problems of relatively heavy mass, insufficient shielding effectiveness and the like of the existing electromagnetic shielding material.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a preparation method of an electromagnetic shielding material, which comprises the following steps:
providing bacterial cellulose, and performing low-temperature carbonization treatment on the bacterial cellulose at the temperature of 200-800 ℃ to obtain the bacterial cellulose with hydrophobic surface;
depositing a graphene oxide aqueous solution on the surface of the bacterial cellulose subjected to low-temperature carbonization treatment, and drying to remove a solvent to obtain a graphene oxide-coated bacterial cellulose complex;
and carrying out high-temperature carbonization treatment on the composite body at the temperature of 800-2500 ℃ to obtain the electromagnetic shielding material.
The invention provides an electromagnetic shielding material, which comprises carbonized bacterial cellulose and a reduced graphene oxide layer formed on the outer surface of the carbonized bacterial cellulose, wherein the carbonized bacterial cellulose contains a three-dimensional pore structure.
The preparation method of the electromagnetic shielding material provided by the invention has the following advantages:
firstly, performing low-temperature carbonization treatment on bacterial cellulose at the temperature of 200-800 ℃ to form hydrophobic aerogel, and further, when depositing graphene oxide aqueous solution in the next step, keeping a better cellulose aerogel structure, preventing the foam structure of the aerogel from collapsing and losing multiple reflection shielding lines caused by the porous structure of carbonized bacterial cellulose.
Secondly, the bacterial cellulose subjected to low-temperature carbonization is used as a core or middle layer raw material of the electromagnetic shielding material, graphene oxide aqueous solution is further deposited on the surface of the bacterial cellulose subjected to low-temperature carbonization, the bacterial cellulose is completely carbonized after high-temperature carbonization, and meanwhile, graphene oxide on the surface of the bacterial cellulose is reduced to reduced graphene oxide to form a compact reduced graphene oxide film. The electromagnetic shielding material formed by the method has triple shielding effectiveness, and can remarkably improve the electromagnetic shielding effect. Specifically, when the electromagnetic wave penetrates through the formed reduced graphene oxide film, a part of the electromagnetic wave is absorbed by the film layer; then, the porous structure of the carbonized bacterial cellulose is used for arranging a multiple reflection barrier for the penetration of electromagnetic waves, so that the loss of the electromagnetic waves is improved; further, after a small amount of electromagnetic waves penetrate through the carbonized bacterial cellulose structure, the electromagnetic waves encounter the reduced graphene oxide film again, electromagnetic wave reflection occurs at the interface, and meanwhile, part of the electromagnetic waves which are not reflected are further collected by the reduced graphene oxide film. Under the coordination of the carbonized bacterial cellulose and the reduced graphene oxide layer, the electromagnetic wave penetrating through the electromagnetic shielding material is reduced sharply, the electromagnetic radiation is obviously reduced, and the electromagnetic shielding performance is improved by utilizing the principles of repeated reflection and absorption of the electromagnetic wave on two interfaces and repeated attenuation in an intermediate foam structure.
In addition, the prepared electromagnetic shielding material does not contain high-density materials such as metal and the like, the bacterial fiber diameter of the bacterial cellulose foam is small, the pores are rich, the density of the whole material is low, and the reduced graphene only forms a thin film layer on the surface, so that the density is not greatly increased, and the electromagnetic shielding material has the advantage of light weight.
According to the electromagnetic shielding material provided by the invention, carbonized bacterial cellulose is used as an inner core or an intermediate layer of the electromagnetic shielding material, reduced graphene oxide is further formed on the surface of the bacterial cellulose, and the carbonized bacterial cellulose contains a three-dimensional pore structure. The electromagnetic shielding material has triple shielding effectiveness and can remarkably improve the electromagnetic shielding effect.
Specifically, when the electromagnetic wave penetrates through the formed reduced graphene oxide film, a part of the electromagnetic wave is absorbed by the film layer; then, the porous structure of the carbonized bacterial cellulose is used for arranging a multiple reflection barrier for the penetration of electromagnetic waves, so that the loss of the electromagnetic waves is improved; further, after a small amount of electromagnetic waves penetrate through the carbonized bacterial cellulose structure, the electromagnetic waves encounter the reduced graphene oxide film again, electromagnetic wave reflection occurs at the interface, and meanwhile, part of the electromagnetic waves which are not reflected are further collected by the reduced graphene oxide film. Under the coordination of the carbonized bacterial cellulose and the reduced graphene oxide layer, the electromagnetic wave penetrating through the electromagnetic shielding material is reduced sharply, the electromagnetic radiation is obviously reduced, and the electromagnetic shielding performance is improved by utilizing the principles of repeated reflection and absorption of the electromagnetic wave on two interfaces and repeated attenuation in an intermediate foam structure.
In addition, the electromagnetic shielding material does not contain high-density materials such as metal, the bacterial cellulose foam has small bacterial fiber diameter and rich pores, so that the density of the whole material is low, and the reduced graphene only forms a thin film layer on the surface, so that the density is not greatly increased, and the electromagnetic shielding material has the advantage of light weight.
Drawings
Fig. 1 is a schematic diagram of the results of graphene oxide-low temperature carbonized bacterial cellulose-graphene oxide provided in embodiment 1 of the present invention;
fig. 2 is a schematic diagram of reduced graphene oxide-high temperature carbonized bacterial cellulose-reduced graphene oxide provided in embodiment 1 of the present invention.
Fig. 3 is a schematic diagram of reduced graphene oxide-pyrocarbon bacterial cellulose provided in comparative example 1 of the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
The weight of the related components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present invention as long as it is in accordance with the description of the embodiments of the present invention. Specifically, the weight described in the description of the embodiment of the present invention may be a unit of mass known in the chemical industry field, such as μ g, mg, g, and kg.
The first aspect of the embodiments of the present invention provides a method for preparing an electromagnetic shielding material, including the following steps:
s01, providing bacterial cellulose, and performing low-temperature carbonization treatment on the bacterial cellulose at the temperature of 200-800 ℃ to obtain the bacterial cellulose with a hydrophobic surface;
s02, depositing a graphene oxide aqueous solution on the surface of the bacterial cellulose subjected to low-temperature carbonization treatment, and drying to remove a solvent to obtain a graphene oxide-coated bacterial cellulose composite;
and S03, carrying out high-temperature carbonization treatment on the composite body at the temperature of 800-2500 ℃ to obtain the electromagnetic shielding material.
The preparation method of the electromagnetic shielding material provided by the embodiment of the invention has the following advantages:
firstly, performing low-temperature carbonization treatment on bacterial cellulose at the temperature of 200-800 ℃ to form hydrophobic aerogel, and further, when depositing graphene oxide aqueous solution in the next step, keeping a better cellulose aerogel structure, preventing the foam structure of the aerogel from collapsing and losing multiple reflection shielding lines caused by the porous structure of carbonized bacterial cellulose.
Secondly, the bacterial cellulose subjected to low-temperature carbonization is used as a core or middle layer raw material of the electromagnetic shielding material, graphene oxide aqueous solution is further deposited on the surface of the bacterial cellulose subjected to low-temperature carbonization, the bacterial cellulose is completely carbonized after high-temperature carbonization, and meanwhile, graphene oxide on the surface of the bacterial cellulose is reduced to reduced graphene oxide to form a compact reduced graphene oxide film. The electromagnetic shielding material formed by the method has triple shielding effectiveness, and can remarkably improve the electromagnetic shielding effect. Specifically, when the electromagnetic wave penetrates through the formed reduced graphene oxide film, a part of the electromagnetic wave is absorbed by the film layer; then, the porous structure of the carbonized bacterial cellulose is used for arranging a multiple reflection barrier for the penetration of electromagnetic waves, so that the loss of the electromagnetic waves is improved; further, after a small amount of electromagnetic waves penetrate through the carbonized bacterial cellulose structure, the electromagnetic waves encounter the reduced graphene oxide film again, electromagnetic wave reflection occurs at the interface, and meanwhile, part of the electromagnetic waves which are not reflected are further collected by the reduced graphene oxide film. Under the coordination of the carbonized bacterial cellulose and the reduced graphene oxide layer, the electromagnetic wave penetrating through the electromagnetic shielding material provided by the embodiment of the invention is reduced sharply, the electromagnetic radiation is reduced remarkably, and the electromagnetic shielding performance is improved by utilizing the principles of repeated reflection and absorption of the electromagnetic wave on two interfaces and repeated attenuation in an intermediate foam structure.
In addition, the prepared electromagnetic shielding material does not contain high-density materials such as metal and the like, the bacterial fiber diameter of the bacterial cellulose foam is small, the pores are rich, the density of the whole material is low, and the reduced graphene only forms a thin film layer on the surface, so that the density is not greatly increased, and the electromagnetic shielding material has the advantage of light weight.
Specifically, in step S01, the bacterial cellulose is a generic term for cellulose synthesized by any of microorganisms belonging to the genera Acetobacter (Acetobacter), Agrobacterium (Agrobacterium), Rhizobium (Rhizobium), Sarcina (Sarcina), and the like under different conditions. Compared with common cellulose, the bacterial cellulose has better biocompatibility, better tension and less impurities, and has better conductivity and electromagnetic shielding effect under a proper pore diameter. The graphene oxide in the graphene oxide aqueous solution is an oxide of graphene, and the surface of the graphene oxide aqueous solution contains more oxygen-containing functional groups such as hydroxyl groups and carboxyl groups due to oxidation, and the graphene oxide aqueous solution is more active than graphene. The graphene oxide can be reduced into reduced graphene oxide with conductivity and electromagnetic shielding effectiveness by high temperature, chemical reduction and other methods.
Before the bacterial cellulose is used for preparing the electromagnetic shielding material, in order to avoid interference of introduction of other impurities on the electromagnetic shielding effect of the bacterial cellulose, the bacterial cellulose is washed, and preferably deionized water is used for washing. Further, the cellulose after washing is frozen, and after freezing, freeze-drying is performed. The freeze drying is adopted, and is based on that when the bacterial cellulose material is heated and dried, the structure, particularly the pore structure, of the material can be damaged, so that the multiple reflection shielding performance brought by the porous structure is influenced, and the electromagnetic shielding effect is influenced. As a particularly preferred embodiment, the washed cellulose mass is frozen in liquid nitrogen and, after freezing, placed in a freeze dryer until completely dried.
Since the bacterial cellulose has good hydrophilicity, if the graphene oxide aqueous solution is directly deposited on the surface of the bacterial cellulose, the graphene oxide aqueous solution is deposited on the surface of the bacterial cellulose and permeates into the pore diameter structure of the bacterial cellulose along with the pore structure, so that the foam structure of the non-carbonized bacterial cellulose is directly collapsed in the aqueous solution. Therefore, before the step of depositing the graphene oxide aqueous solution on the surface of the bacterial cellulose, the bacterial cellulose is subjected to low-temperature carbonization treatment at a temperature of 200-800 ℃ to obtain the bacterial cellulose with a hydrophobic surface (to form a hydrophobic aerogel). In this case, the carbonization treatment at a low temperature of 200 to 800 ℃ can remove at least the surface active functional group hydroxyl of the bacterial cellulose, thereby improving the surface hydrophobicity of the bacterial cellulose. Further, in the process of depositing the graphene oxide aqueous solution on the surface of the bacterial cellulose, the graphene oxide aqueous solution cannot penetrate into the inside of the cellulose due to the hydrophobic surface of the bacterial cellulose, but a compact film is formed on the surface of the carbonized bacterial cellulose, so that the influence on the porous structure inside the bacterial cellulose is avoided.
When the temperature is increased to the low-temperature carbonization treatment temperature, the slow heating treatment is preferable. Specifically, the heating rate is 5-30 ℃/min. Under the condition of the heating rate, active hydroxyl on the surface of the bacterial cellulose can be completely removed, and the surface hydrophobic property is realized; and the material ashing caused by too high temperature rise rate and too large instant temperature difference can be avoided.
In the step S02, a graphene oxide aqueous solution is deposited on the hydrophobic surface of the bacterial cellulose subjected to the low-temperature carbonization treatment, and graphene oxide is adsorbed on the surface of the bacterial cellulose. The graphene oxide film layer coated with the bacterial cellulose can be formed on the surface of the bacterial cellulose by depositing the graphene oxide aqueous solution on the surface of the bacterial cellulose. And carrying out high-temperature carbonization treatment on the graphene oxide film layer, and reducing oxygen-containing functional groups on the surface to finally form the reduced graphene oxide film. The carbonized reduced graphene oxide film has good conductivity and electromagnetic wave absorption capacity, so that the composite material is endowed with an excellent electromagnetic shielding effect.
Preferably, the concentration of the graphene oxide aqueous solution is 0.05-20 mg/ml. The concentration of the graphene oxide aqueous solution is in the range, a graphene oxide film layer with a proper film thickness (1-100 mu m) can be formed through one-time deposition and drying treatment, and the deposition efficiency is improved.
In some embodiments, depositing an aqueous graphene oxide solution on the surface of the bacterial cellulose may be achieved by immersing the bacterial cellulose in the aqueous graphene oxide solution. The mode can deposit graphene oxide on the surface of the bacterial cellulose rapidly, and the adsorption of the bacterial cellulose to the graphene oxide is promoted.
In the step of depositing the graphene oxide aqueous solution on the surface of the bacterial cellulose, the graphene oxide aqueous solution is dripped or sprayed on the surface of the bacterial cellulose with hydrophobic surface, and the outer surface of the bacterial cellulose is coated with the graphene oxide. Because the surface of the bacterial cellulose is hydrophobic, the graphene oxide solution can be remained on the surface of the hydrophobic aerogel in a mild mode of dripping or spraying, and a graphene oxide film coated on the surface of the bacterial cellulose is formed after drying treatment.
Depositing a graphene oxide aqueous solution on the surface of the bacterial cellulose, and removing a solvent in the graphene oxide aqueous solution through drying treatment, wherein the temperature of the drying treatment is preferably 10-200 ℃. Under the temperature condition, the solvent such as water in the graphene oxide aqueous solution deposited on the surface of the bacterial cellulose can be removed, and the influence of high-temperature treatment on the structure and the performance of the bacterial cellulose material can be avoided. In the drying process, a partial region deposition and partial region drying method can be adopted, and the bacterial cellulose deposited with the graphene oxide aqueous solution is completely dried through multiple deposition-drying processes.
According to the embodiment of the invention, after drying treatment, the graphene oxide coated bacterial cellulose complex is obtained. The shape of the composite varies depending on the shape of the bacterial cellulose, but the composite should be coated at least on the surface of the electromagnetic wave passing through the composite material. When the bacterial cellulose is layered, the graphene oxide is at least coated on the upper surface and the lower surface of the bacterial cellulose, namely the two surfaces through which electromagnetic waves pass, and further, the graphene oxide can be also coated on the four side surfaces of the bacterial cellulose; when the bacterial cellulose is layered, the graphene oxide at least coats two surfaces of the bacterial cellulose penetrated by electromagnetic waves, and further, the four side surfaces of the bacterial cellulose can also be coated with the graphene oxide; when the bacterial cellulose is spherical or irregular, the graphene oxide is coated at least on the surface of the bacterial cellulose through which the electromagnetic waves pass, and preferably on all the surface of the bacterial cellulose.
In a specific embodiment, the bacterial cellulose is layered hydrophobic bacterial cellulose, and at this time, two dense graphene oxide films are formed on the upper and lower surfaces of the hydrophobic bacterial cellulose, so that not only is the porous structure inside the bacterial cellulose not affected, but also most of electromagnetic waves are absorbed firstly when the electromagnetic waves pass through as reduced graphene oxide is an absorption shielding material, and a small part of the electromagnetic waves penetrating through the reduced graphene oxide is partially lost by multiple reflection of the porous structure of the carbonized bacterial cellulose, and is finally absorbed by the reduced graphene oxide layer on the other surface side of the bacterial cellulose.
In step S03, the composite is subjected to a high-temperature carbonization treatment at a temperature of 800 to 2500 ℃. Through high-temperature carbonization at 800-2500 ℃, the graphene oxide is reduced into reduced graphene oxide with excellent electromagnetic shielding effect, and the crystal crystallization property is improved, so that the reduced graphene oxide is endowed with excellent electrical conductivity and electromagnetic shielding property; and the bacterial cellulose is carbonized at a high temperature of 800-2500 ℃ to form carbonized bacterial cellulose, so that the bacterial cellulose has excellent conductivity and electromagnetic shielding effectiveness. When the electromagnetic wave passes through the shielding material obtained by the method, the reduced graphene oxide film on the surface layer can firstly absorb most of the electromagnetic wave, the electromagnetic wave penetrating through the reduced graphene oxide film can lose a part of the electromagnetic wave through multiple reflection of the porous structure of the carbonized bacterial cellulose, and finally the electromagnetic wave is reflected and absorbed by the reduced graphene oxide layer on the other side to realize the shielding of the electromagnetic wave.
In the high-temperature carbonization process, the higher the carbonization temperature is, the higher the carbonization (or graphitization) degree of the bacterial cellulose and the graphene oxide is, the more complete the crystal structure is, and the better the conductivity and the electromagnetic shielding performance are. However, if the temperature of the carbonization treatment is too high, exceeding 2500 ℃, the structure of the obtained electromagnetic shielding material becomes loose and brittle, the mechanical properties are deteriorated, and it is difficult to maintain the original shape. In addition, the higher the carbonization temperature, the higher the requirements for equipment and energy consumption, and the higher the cost.
The electromagnetic shielding material is obtained after high-temperature carbonization, and in a material penetrated by electromagnetic waves, two layers of reduced graphene oxide form two layers of compact films on the surface of carbonized bacterial cellulose, so that the porous structure in the bacterial cellulose cannot be influenced.
In some embodiments, in the step of subjecting the composite body to high-temperature carbonization treatment at a temperature of 800 ℃ to 2500 ℃, the temperature rise rate of heating the composite body to the carbonization treatment temperature is 5 to 30 ℃/min. Under the condition of the heating rate, the bacterial cellulose can be fully carbonized, the graphene oxide is completely reduced to the reduced graphene oxide, the electromagnetic shielding material with the upper and lower surfaces of the carbonized bacterial cellulose coated by the reduced graphene oxide is formed, and the material ashing caused by too high temperature rise rate and too large instant temperature difference can be avoided.
In a specific embodiment, the method for preparing the electromagnetic shielding material comprises the following steps:
providing bacterial cellulose, and performing low-temperature carbonization treatment on the bacterial cellulose at the temperature of 350 ℃ to obtain the bacterial cellulose with hydrophobic surface;
soaking the bacterial cellulose in a graphene oxide aqueous solution, depositing graphene oxide on the surface of the bacterial cellulose, and drying to remove a solvent to obtain a graphene oxide coated bacterial cellulose complex;
and carrying out high-temperature carbonization treatment on the composite body at the temperature of 1000 ℃ to obtain the electromagnetic shielding material.
The second aspect of the embodiment of the invention provides an electromagnetic shielding material, which comprises carbonized bacterial cellulose and a reduced graphene oxide layer formed on the outer surface of the carbonized bacterial cellulose, wherein the carbonized bacterial cellulose contains a three-dimensional pore structure.
According to the electromagnetic shielding material provided by the embodiment of the invention, carbonized bacterial cellulose is used as an inner core or an intermediate layer of the electromagnetic shielding material, reduced graphene oxide is further formed on the surface of the bacterial cellulose, and the carbonized bacterial cellulose contains a three-dimensional pore structure. The electromagnetic shielding material has triple shielding effectiveness and can remarkably improve the electromagnetic shielding effect.
Specifically, when the electromagnetic wave penetrates through the formed reduced graphene oxide film, a part of the electromagnetic wave is absorbed by the film layer; then, the porous structure of the carbonized bacterial cellulose is used for arranging a multiple reflection barrier for the penetration of electromagnetic waves, so that the loss of the electromagnetic waves is improved; further, after a small amount of electromagnetic waves penetrate through the carbonized bacterial cellulose structure, the electromagnetic waves encounter the reduced graphene oxide film again, electromagnetic wave reflection occurs at the interface, and meanwhile, part of the electromagnetic waves which are not reflected are further collected by the reduced graphene oxide film. Under the coordination of the carbonized bacterial cellulose and the reduced graphene oxide layer, the electromagnetic wave penetrating through the electromagnetic shielding material provided by the embodiment of the invention is reduced sharply, the electromagnetic radiation is reduced remarkably, and the electromagnetic shielding performance is improved by utilizing the principles of repeated reflection and absorption of the electromagnetic wave on two interfaces and repeated attenuation in an intermediate foam structure.
In addition, the electromagnetic shielding material does not contain high-density materials such as metal, the bacterial cellulose foam has small bacterial fiber diameter and rich pores, so that the density of the whole material is low, and the reduced graphene only forms a thin film layer on the surface, so that the density is not greatly increased, and the electromagnetic shielding material has the advantage of light weight.
In the embodiment of the present invention, the electromagnetic shielding material may be prepared by the method for carbonizing bacterial cellulose at a low temperature to form the corresponding electromagnetic shielding material in the embodiment of the present invention. The pore structure of the carbonized bacterial cellulose does not contain the reduced graphene oxide.
In some embodiments, the carbonized bacterial cellulose has a thickness of 2mm or more, and the reduced graphene oxide layer has a thickness of 1 μm to 100 μm. The obtained electromagnetic shielding material has obvious electromagnetic shielding effect.
It is worth mentioning that the reduced graphene oxide is not contained in the pore structure of the carbonized bacterial cellulose, so that the porous structure inside the bacterial cellulose is not affected, and the reduced graphene oxide is an absorption shielding material, so that most of electromagnetic waves are absorbed firstly when the electromagnetic waves pass through, and a part of the electromagnetic waves penetrating through the reduced graphene oxide are lost by multiple reflection of the porous structure of the carbonized bacterial cellulose, and are finally absorbed by the reduced graphene oxide layer on the other surface side of the bacterial cellulose.
The following description will be given with reference to specific examples.
Example 1
A preparation method of an electromagnetic shielding material comprises the following steps:
bacterial cellulose 20mm thick was cut into 10cm × 5cm pieces and washed with deionized water. And (3) freezing the washed bacterial cellulose blocks in liquid nitrogen, and drying in a freeze dryer for 3-4 days until the bacterial cellulose blocks are completely dried. Putting the dried cellulose block into a tubular furnace, and carbonizing for 2 hours at the temperature of 350 ℃ to obtain bacterial cellulose with hydrophobic surface;
uniformly dropwise adding 2.0mg/ml of graphene oxide aqueous solution to one surface of the low-temperature carbonized bacterial cellulose until the thickness of the graphene oxide layer is 10 microns, and baking for 2 hours at the temperature of 80 ℃. Taking out the dried sample, dropwise adding the same amount of graphene oxide aqueous solution on the opposite side, and drying at the temperature of 80 ℃ for 2 hours to obtain a graphene oxide coated bacterial cellulose complex; in this case, the obtained composite is sandwiched between two graphene oxide layers as shown in fig. 1, and thus has a sandwich structure.
And (3) placing the composite body in a tube furnace, and carrying out high-temperature carbonization treatment for 2 hours at the temperature of 800 ℃ to obtain the electromagnetic shielding material. As shown in fig. 2, the electromagnetic shielding material prepared in embodiment 1 has high conductivity and electromagnetic shielding effectiveness due to both the high-temperature carbonized bacterial cellulose and the reduced graphene oxide.
Example 2
A preparation method of an electromagnetic shielding material comprises the following steps:
bacterial cellulose 20mm thick was cut into 10cm × 5cm pieces and washed with deionized water. And (3) freezing the washed bacterial cellulose blocks in liquid nitrogen, and drying in a freeze dryer for 3-4 days until the bacterial cellulose blocks are completely dried. Putting the dried cellulose block into a tubular furnace, and carbonizing at 550 ℃ for 1.5 hours to obtain bacterial cellulose with hydrophobic surface;
uniformly dropwise adding 2.0mg/ml of graphene oxide aqueous solution to one surface of the low-temperature carbonized bacterial cellulose until the thickness of the graphene oxide layer is 10 microns, and baking for 2 hours at the temperature of 80 ℃. Taking out the dried sample, dropwise adding the same amount of graphene oxide aqueous solution on the opposite side, and drying at the temperature of 80 ℃ for 2 hours to obtain a graphene oxide coated bacterial cellulose complex; in this case, the obtained composite is sandwiched between two graphene oxide layers as shown in fig. 1, and thus has a sandwich structure.
And (3) putting the composite body into a tubular furnace, and carrying out high-temperature carbonization treatment for 2 hours at the temperature of 1000 ℃ to obtain the electromagnetic shielding material.
Example 3
A preparation method of an electromagnetic shielding material comprises the following steps:
bacterial cellulose 20mm thick was cut into 10cm × 5cm pieces and washed with deionized water. And (3) freezing the washed bacterial cellulose blocks in liquid nitrogen, and drying in a freeze dryer for 3-4 days until the bacterial cellulose blocks are completely dried. Putting the dried cellulose block into a tubular furnace, and carbonizing at 750 ℃ for 1.2 hours to obtain bacterial cellulose with hydrophobic surface;
uniformly dropwise adding 2.0mg/ml of graphene oxide aqueous solution to one surface of the low-temperature carbonized bacterial cellulose until the thickness of the graphene oxide layer is 10 microns, and baking for 2 hours at the temperature of 80 ℃. Taking out the dried sample, dropwise adding the same amount of graphene oxide aqueous solution on the opposite side, and drying at the temperature of 80 ℃ for 2 hours to obtain a graphene oxide coated bacterial cellulose complex; in this case, the obtained composite is sandwiched between two graphene oxide layers as shown in fig. 1, and thus has a sandwich structure.
And (3) placing the composite body in a tube furnace, and carrying out high-temperature carbonization treatment for 2 hours at the temperature of 1500 ℃ to obtain the electromagnetic shielding material.
Example 4
A preparation method of an electromagnetic shielding material comprises the following steps:
bacterial cellulose 20mm thick was cut into 10cm × 5cm pieces and washed with deionized water. And (3) freezing the washed bacterial cellulose blocks in liquid nitrogen, and drying in a freeze dryer for 3-4 days until the bacterial cellulose blocks are completely dried. Putting the dried cellulose block into a tubular furnace, and carbonizing for 2 hours at the temperature of 400 ℃ to obtain bacterial cellulose with hydrophobic surface;
uniformly dropwise adding 2.0mg/ml of graphene oxide aqueous solution to one surface of the low-temperature carbonized bacterial cellulose until the thickness of the graphene oxide layer is 10 microns, and baking for 2 hours at the temperature of 80 ℃. Taking out the dried sample, dropwise adding the same amount of graphene oxide aqueous solution on the opposite side, and drying at the temperature of 80 ℃ for 2 hours to obtain a graphene oxide coated bacterial cellulose complex; in this case, the obtained composite is sandwiched between two graphene oxide layers as shown in fig. 1, and thus has a sandwich structure.
And (3) putting the composite body into a tubular furnace, and carrying out high-temperature carbonization treatment for 2 hours at the temperature of 2000 ℃ to obtain the electromagnetic shielding material.
Example 5
A preparation method of an electromagnetic shielding material comprises the following steps:
bacterial cellulose 20mm thick was cut into 10cm × 5cm pieces and washed with deionized water. And (3) freezing the washed bacterial cellulose blocks in liquid nitrogen, and drying in a freeze dryer for 3-4 days until the bacterial cellulose blocks are completely dried. Putting the dried cellulose block into a tubular furnace, and carbonizing for 2 hours at the temperature of 600 ℃ to obtain bacterial cellulose with hydrophobic surface;
uniformly dropwise adding 2.0mg/ml of graphene oxide aqueous solution to one surface of the low-temperature carbonized bacterial cellulose until the thickness of the graphene oxide layer is 10 microns, and baking for 2 hours at the temperature of 80 ℃. Taking out the dried sample, dropwise adding the same amount of graphene oxide aqueous solution on the opposite side, and drying at the temperature of 80 ℃ for 2 hours to obtain a graphene oxide coated bacterial cellulose complex; in this case, the obtained composite is sandwiched between two graphene oxide layers as shown in fig. 1, and thus has a sandwich structure.
And (3) placing the composite in a tubular furnace, and carrying out high-temperature carbonization treatment for 2 hours at the temperature of 2500 ℃ to obtain the electromagnetic shielding material.
Example 6
A preparation method of an electromagnetic shielding material comprises the following steps:
bacterial cellulose 20mm thick was cut into 10cm × 5cm pieces and washed with deionized water. And (3) freezing the washed bacterial cellulose blocks in liquid nitrogen, and drying in a freeze dryer for 3-4 days until the bacterial cellulose blocks are completely dried. Putting the dried cellulose block into a tubular furnace, and carbonizing for 2 hours at 550 ℃ to obtain bacterial cellulose with hydrophobic surface;
uniformly dropwise adding 2.0mg/ml of graphene oxide aqueous solution to one surface of the low-temperature carbonized bacterial cellulose until the thickness of the graphene oxide layer is 15 microns, and baking for 2 hours at the temperature of 80 ℃. Taking out the dried sample, dropwise adding the same amount of graphene oxide aqueous solution on the opposite side, and drying at the temperature of 80 ℃ for 2 hours to obtain a graphene oxide coated bacterial cellulose complex; in this case, the obtained composite is sandwiched between two graphene oxide layers as shown in fig. 1, and thus has a sandwich structure.
And (3) placing the composite body in a tube furnace, and carrying out high-temperature carbonization treatment for 2 hours at the temperature of 1500 ℃ to obtain the electromagnetic shielding material.
Example 7
A preparation method of an electromagnetic shielding material comprises the following steps:
bacterial cellulose 20mm thick was cut into 10cm × 5cm pieces and washed with deionized water. And (3) freezing the washed bacterial cellulose blocks in liquid nitrogen, and drying in a freeze dryer for 3-4 days until the bacterial cellulose blocks are completely dried. Putting the dried cellulose block into a tubular furnace, and carbonizing for 2 hours at the temperature of 350 ℃ to obtain bacterial cellulose with hydrophobic surface;
uniformly dropwise adding 2.0mg/ml of graphene oxide aqueous solution to one surface of the low-temperature carbonized bacterial cellulose until the thickness of the graphene oxide layer is 20 microns, and baking for 2 hours at the temperature of 80 ℃. Taking out the dried sample, dropwise adding the same amount of graphene oxide aqueous solution on the opposite side, and drying at the temperature of 80 ℃ for 2 hours to obtain a graphene oxide coated bacterial cellulose complex; in this case, the obtained composite is sandwiched between two graphene oxide layers as shown in fig. 1, and thus has a sandwich structure.
And (3) placing the composite body in a tube furnace, and carrying out high-temperature carbonization treatment for 2 hours at the temperature of 1500 ℃ to obtain the electromagnetic shielding material.
Comparative example 1
Bacterial cellulose 20mm thick was cut into 10cm × 5cm pieces and washed with deionized water. And (3) freezing the washed bacterial cellulose blocks in liquid nitrogen, and drying in a freeze dryer for 3-4 days until the bacterial cellulose blocks are completely dried. And (3) putting the dried cellulose block into a tubular furnace, and carbonizing for 2 hours at the temperature of 800 ℃ to obtain the high-temperature carbonized bacterial cellulose.
Comparative example 2
A preparation method of an electromagnetic shielding material comprises the following steps:
bacterial cellulose 20mm thick was cut into 10cm × 5cm pieces and washed with deionized water. And (3) freezing the washed bacterial cellulose blocks in liquid nitrogen, and drying in a freeze dryer for 3-4 days until the bacterial cellulose blocks are completely dried. Putting the dried cellulose block into a tubular furnace, and carbonizing for 2 hours at the temperature of 350 ℃ to obtain bacterial cellulose with hydrophobic surface;
uniformly dropwise adding 2.0mg/ml of graphene oxide aqueous solution to the surface of the low-temperature carbonized bacterial cellulose until the thickness of a graphene oxide layer is 10 microns, and drying at the temperature of 80 ℃ for 2 hours to obtain a graphene oxide coated bacterial cellulose composite (only one surface of an electromagnetic wave passing route is coated with the graphene oxide aqueous solution); the resulting composite is shown in FIG. 3.
And (3) placing the composite body in a tube furnace, and carrying out high-temperature carbonization treatment for 2 hours at the temperature of 1500 ℃ to obtain the electromagnetic shielding material.
The electromagnetic shielding materials prepared in examples 1 to 7 and the electromagnetic shielding materials provided in comparative examples 1 to 2 were subjected to performance tests, the test methods were:
shielding effectiveness: and connecting the material with a vector network analyzer by using a waveguide adapter, and carrying out electromagnetic shielding effectiveness test in the range of 8.2GHz-12.5 GHz.
The test results are shown in table 1 below.
TABLE 1
| Test results | Shielding effectiveness (dB) |
| Example 1 | 21.5 |
| Example 2 | 36.4 |
| Example 3 | 48.9 |
| Example 4 | 60.8 |
| Example 5 | 74.5 |
| Example 6 | 51.3 |
| Example 7 | 54.1 |
| Comparative example 1 | 14.2 |
| Comparative example 2 | 18.5 |
As can be seen from the above table, the electromagnetic shielding material prepared by the embodiment of the invention has excellent electromagnetic shielding performance.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (9)
1. The preparation method of the electromagnetic shielding material is characterized by comprising the following steps of:
providing bacterial cellulose, and performing low-temperature carbonization treatment on the bacterial cellulose at the temperature of 200-800 ℃ to enable the bacterial cellulose to form hydrophobic aerogel so as to obtain the bacterial cellulose with hydrophobic surface;
depositing a graphene oxide aqueous solution on the surface of the bacterial cellulose subjected to low-temperature carbonization treatment, and drying to remove a solvent to obtain a graphene oxide-coated bacterial cellulose complex;
carrying out high-temperature carbonization treatment on the composite at the temperature of 800-2500 ℃ to obtain an electromagnetic shielding material;
and in the step of carrying out high-temperature carbonization treatment on the composite body at the temperature of 800-2500 ℃, the temperature is heated to the carbonization treatment temperature at the temperature rise rate of 5-30 ℃/min.
2. The method for preparing an electromagnetic shielding material according to claim 1, wherein the concentration of the graphene oxide aqueous solution is 0.05-20 mg/ml.
3. The method for preparing an electromagnetic shielding material according to any one of claims 1 to 2, wherein the drying temperature is 10 ℃ to 200 ℃.
4. The method for preparing an electromagnetic shielding material according to any one of claims 1 to 3, wherein in the step of depositing the aqueous solution of graphene oxide on the surface of the bacterial cellulose, the aqueous solution of graphene oxide is dipped, dripped or sprayed on the surface of the bacterial cellulose with hydrophobic surface, and the outer surface of the bacterial cellulose is coated with graphene oxide.
5. A method for preparing an electromagnetic shielding material as claimed in any one of claims 1 to 3, comprising the steps of:
providing bacterial cellulose, and performing low-temperature carbonization treatment on the bacterial cellulose at the temperature of 350 ℃ to obtain the bacterial cellulose with hydrophobic surface;
soaking the bacterial cellulose in a graphene oxide aqueous solution, depositing graphene oxide on the surface of the bacterial cellulose, and drying to remove a solvent to obtain a graphene oxide coated bacterial cellulose complex;
and carrying out high-temperature carbonization treatment on the composite body at the temperature of 1000 ℃ to obtain the electromagnetic shielding material.
6. An electromagnetic shielding material, wherein the electromagnetic shielding material is prepared by the preparation method according to any one of claims 1 to 5, the electromagnetic shielding material comprises carbonized bacterial cellulose, and a reduced graphene oxide layer formed on an outer surface of the carbonized bacterial cellulose, and the carbonized bacterial cellulose contains a three-dimensional porous structure.
7. The electromagnetic shielding material of claim 6, wherein the layer of reduced graphene oxide has a thickness of 1 μm to 100 μm.
8. The electromagnetic shielding material of claim 6, wherein the carbonized bacterial cellulose has a thickness of 2mm or more.
9. The electromagnetic shielding material according to any one of claims 6 to 8, wherein the reduced graphene oxide is not contained in the pore structure of the carbonized bacterial cellulose.
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