Method for improving electromagnetic shielding performance of PBO paper by grafting graphene

Abstract

The invention belongs to the field of new materials and specialty paper, and particularly relates to a method for improving the electromagnetic shielding performance of PBO paper by grafting graphene, and the method mainly comprises the following steps: (1) preparing carboxylated graphene; (2) preparation of aminated PBO pulp fibers; (3) preparing PBO pulp fiber surface grafted graphene; and (4) preparing the modified PBO composite paper. Through the coupling effect of-COOH and-NH2, the dispersion effect of graphene in the PBO paper can be significantly enhanced, and the defects of uneven dispersion and easy agglomeration are avoided. By adopting the preparation method, the uniformity of the paper is further improved, and the paper has the characteristics of high temperature resistance and acid and alkali corrosion resistance. Meanwhile, the PBO pulp fiber has a large specific surface area and has more site grafted graphene, so that the graphene forms a continuous conductive network and an enhanced network of an interpenetrating system inside and on the surface of the PBO paper, and the electromagnetic shielding performance and the mechanical performance of the PBO paper-based material are improved.

Description

Technical Field

[0001] This invention belongs to the field of new materials and specialty paper, and discloses a method for improving the electromagnetic shielding performance of PBO paper by grafting graphene. Background Technology

[0002] Digital and high-frequency electronic devices, such as mobile phones, communication satellites, and WiFi, are widely used in people's daily lives due to their convenience and efficiency. With the increasing impact of electromagnetic radiation on modern communication, microelectronics, aerospace, and human health, effective protection against electromagnetic radiation is essential. Traditional electromagnetic shielding materials, such as metals, have drawbacks such as susceptibility to corrosion, high density, high cost, and their shielding effectiveness is primarily based on reflection, which can easily cause secondary pollution, limiting their application in some situations. Therefore, it is urgent to research a lightweight, high-strength, corrosion-resistant electromagnetic shielding composite material with good electromagnetic radiation shielding effect to mitigate or eliminate electromagnetic pollution.

[0003] PBO paper-based materials possess a unique three-dimensional network structure, allowing for adjustable composition, structure, and thickness. They are also recyclable, making them an effective and practical material for EMI shielding applications. Furthermore, they are lightweight, high-strength, do not melt or burn at 300°C, and exhibit chemical stability. However, traditional PBO paper-based materials have weak conductivity and poor electromagnetic shielding performance, limiting their application in high-frequency, high-speed, and microwave transmission fields. Therefore, selecting suitable conductive fillers to enhance the electromagnetic shielding performance of PBO paper-based materials is essential.

[0004] Graphene, the thinnest known two-dimensional (2D) material, possesses advantages such as low density, large specific surface area, good chemical stability, and excellent mechanical properties. As a unique two-dimensional carbon-based conductive nanomaterial, graphene and its derivatives have attracted widespread attention due to their outstanding physicochemical properties, such as high surface area, excellent conductivity, and superior chemical, mechanical, and environmental stability. The functional groups and internal defects of graphene possess the potential for dipole and polarization relaxation, which is beneficial for increasing the absorption of electromagnetic radiation. However, the intermolecular forces of graphene result in strong aggregation, making it impossible to achieve uniform dispersion during PBO paper preparation. This leads to deterioration in the performance and stability of graphene composite materials. Solving the problem of graphene aggregation during PBO paper preparation is one of the current challenges that needs to be addressed.

[0005] Patent CN103788395A discloses a method for preparing a graphene polymer composite copolymer film. The method involves amylating graphene and then introducing graphene into the molecular chain of PBO polymer through a co-condensation reaction, so that graphene and PBO molecular chains are covalently linked, and finally PBO composite film is prepared. Although this invention effectively improves the graphene dispersion problem by directly grafting graphene onto the molecular chain, it also changes the structure of PBO molecular chains, which will have a certain impact on the mechanical properties of the fibers.

[0006] Patent CN105908489A discloses a graphene nanoribbon interface-modified PBO fiber and its preparation method. The method uses carboxylated graphene nanoribbons to modify the PBO fiber interface, thus solving the technical problem that existing PBO fiber modification methods result in excessively high reductions in the tensile strength of the PBO fiber itself. However, both the graphene nanoribbons and the PBO fiber undergo carboxylation treatment, limiting the number of grafting sites.

[0007] Therefore, how to improve the electromagnetic shielding performance and mechanical properties of PBO paper-based materials while solving the problem of graphene dispersion in PBO paper is also a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing a method for improving the electromagnetic shielding performance of PBO paper through graphene grafting. The main steps are as follows: (1) preparation of carboxylated graphene; (2) preparation of aminated PBO pulp fibers; (3) preparation of graphene grafted onto the surface of PBO pulp fibers; (4) preparation of modified PBO composite paper. The coupling effect of -COOH and -NH2 can significantly enhance the dispersion of graphene in PBO paper, avoiding the disadvantages of uneven dispersion and easy agglomeration. Graphene is an electromagnetic shielding reinforcement material and also has excellent mechanical properties. This preparation method further improves the paper uniformity and solves the problem of traditional paper-based materials being unable to withstand high temperatures and acid and alkali corrosion. The prepared electromagnetic shielding composite paper is a flexible material with easy processing characteristics. At the same time, PBO pulp fibers have a large specific surface area and more sites for graphene grafting, realizing the formation of a continuous conductive network and reinforcement network of graphene in the interior and surface of PBO paper, thereby improving the electromagnetic shielding performance and mechanical properties of PBO paper-based materials.

[0009] The specific technical solution of the present invention is as follows: A method for improving the electromagnetic shielding performance of PBO paper by grafting graphene, the specific steps of which are as follows: (1) Preparation of carboxylated graphene Graphene oxide is uniformly dispersed in deionized water by ultrasonic treatment to obtain a graphene oxide suspension. The ultrasonic dispersion time is 1-5 hours and the ultrasonic power is 100-300W. The suspension is cooled to room temperature, sodium hydroxide and bromoacetic acid are added, and ultrasonic treatment is continued for 20-60 minutes. The reaction is continued at room temperature for 2-8 hours to obtain a mixed solution. The mixed solution is centrifuged, washed, filtered, and vacuum dried to obtain carboxylated graphene. The concentration of the graphene oxide suspension is 0.1-0.5 wt%, the amount of sodium hydroxide added is 1-5% of the total mass of the graphene oxide suspension, and the amount of bromoacetic acid added is 3-10% of the total mass of the graphene oxide suspension.

[0010] (2) Preparation of ammoniated PBO pulp fiber PBO pulp fibers were added to a 30-60 wt% sulfuric acid solution and stirred at 50-80°C for 50-150 min to obtain PBO pulp fibers with carboxyl groups on the surface. The PBO pulp fibers with carboxyl groups on the surface were then placed in N-methylpyrrolidone, and 1,3-dicyclohexylcarbodiimide and melamine were added to the reaction system. The reaction was carried out at 60-120°C for 10-43 h. Finally, the fibers were washed with deionized water and vacuum dried to obtain aminated PBO pulp fibers with amino groups on the surface. The average length of PBO pulp fibers is 0.5-1.2 mm, and the freeness is 25-35°SR. The amount of PBO pulp fibers added is 1-10% of the mass of sulfuric acid solution. The amount of PBO pulp fibers with carboxyl groups on the surface added is 2-12% of the mass of N-methylpyrrolidone. The amount of 1,3-dicyclohexylcarbodiimide added is 0.4-2.5 times the mass of PBO pulp fibers with carboxyl groups on the surface. The amount of melamine added is 0.8-1.8 times the mass of 1,3-dicyclohexylcarbodiimide.

[0011] (3) Preparation of graphene grafted onto the surface of PBO pulp fibers The carboxylated graphene obtained in step (1) was ultrasonically dispersed in N-methylpyrrolidone to obtain a uniform carboxylated graphene dispersion. Then, the aminated PBO pulp fiber obtained in step (2) was added. Under nitrogen protection, the mixture was stirred and reacted at 60-100℃ for 10-50h. Then, the graphene-grafted PBO pulp fiber was washed with deionized water until the fiber washing solution was colorless and transparent. After vacuum drying, the graphene-grafted PBO pulp fiber was obtained. The concentration of the carboxylated graphene dispersion is 0.1-0.8wt%, the amount of carboxylated graphene added is 1-10% of the mass of the aminolated PBO pulp fiber, the ultrasonic dispersion time is 1-5h, and the ultrasonic power is 100-300W.

[0012] (4) Preparation of modified PBO composite paper Graphene-grafted PBO pulp fibers, PBO chopped fibers, and meta-aramid precipitated fibers were added to water, and dispersants were added to prepare dispersions. Fiber dispersions with concentrations of 0.2-5 wt% were prepared. The three dispersions were added to a pulping machine in a certain proportion for pulping, then wired and pressed into shape. After vacuum drying, PBO base paper was obtained. Finally, the PBO base paper was hot-pressed to obtain graphene-modified PBO composite paper.

[0013] The mass ratio of PBO chopped fibers to graphene-grafted PBO pulp fibers is 1-4:5-9; the amount of meta-aramid precipitated fibers is 7-15% of the total mass of PBO chopped fibers and graphene-grafted PBO pulp fibers.

[0014] The advantage of using meta-aramid precipitated fibers as a binder is that it avoids the poor dimensional stability or limited application scenarios that can result from using adhesives or resins.

[0015] The dispersant is any one of polyoxyethylene ether, hydroxyethyl cellulose, sodium lignosulfonate, and maleic acid-acrylic acid copolymer, preferably polyoxyethylene ether; wherein the amount of dispersant used is 0.1-1.5% of the oven-dry weight of PBO chopped fibers, graphene-grafted PBO pulp fibers, and meta-aramid precipitated fibers; the fiber dispersion method is to add the dispersant while stirring, and continue stirring for 10-50 minutes after the dispersant is added.

[0016] Dispersants can reduce the friction between PBO fibers, decrease the degree of freedom of fiber movement in water, prevent fibers from contacting each other, thereby reducing fiber aggregation and improving fiber dispersion in water.

[0017] The average length of the PBO chopped fibers is 2-5 mm; the average length of the meta-aramid precipitated fibers is 0.8-1.3 mm, and the freeness is 23-32°SR.

[0018] The hot pressing conditions are: pressure 12-18MPa, temperature 200-300℃, hot pressing 1-4 times, and hot pressing time 20-80s for each time.

[0019] This hot-pressing process reduces the rough particles on the paper surface and increases the paper's density. After hot pressing, graphene constructs a more stable 3D interconnected conductive network on the PBO fiber chopped skeleton, improving the interfacial and mechanical properties of the PBO material while obtaining high-performance electromagnetic shielding composite paper.

[0020] Compared with the prior art, the beneficial effects of this invention are: (1) This preparation method overcomes the problem of uneven dispersion and easy agglomeration of graphene in paper. Melamine plays the role of molecular bridge to combine PBO fiber and graphene, so that graphene can be evenly distributed on the surface of PBO pulp fiber. The modified fiber surface has highly active amino functional groups, which can form hydrogen bonds with the carboxyl groups on the modified graphene surface under appropriate conditions, thereby enhancing the direct grafting effect between graphene and fiber surface, firmly grafting graphene onto the surface of PBO fiber, and enhancing the interaction force between PBO pulp fiber and graphene.

[0021] (2) This electromagnetic shielding PBO composite paper cleverly integrates the excellent conductivity, mechanical properties, high dielectric loss, wave absorption, and shielding performance of graphene. Electromagnetic waves are continuously reflected and transmitted in the PBO composite paper, and the continuous attenuation generates multiple reflections and transmission losses, thus achieving the purpose of resisting electromagnetic interference. Graphene constructs a more stable 3D interconnected conductive network on the PBO chopped fiber skeleton. When graphene enters the interior of the paper, the adhesion between fibers is improved, enhancing the mechanical and electromagnetic shielding properties of the paper. This preparation method solves the problems of traditional paper-based electromagnetic shielding materials being unable to withstand high temperatures and acid and alkali corrosion, and having poor flexibility. It effectively improves the electromagnetic shielding and mechanical properties of paper-based materials and expands the application range of PBO electromagnetic shielding composite paper.

[0022] (3) During the hot pressing process, the meta-aramid precipitated fibers soften under heat, the gaps between the fibers become smaller and fewer, and the fibers are more tightly bonded, which can improve the paper uniformity and better bond the short fibers together. It plays a "bridging and bonding" role between the fibers, making the maximum use of the fiber length to transfer stress, giving full play to the performance of PBO short fibers and pulp fibers, and improving the strength of PBO paper.

[0023] (4) The surface of PBO pulp fibers after graphene grafting becomes rough and contains a large number of polar functional groups. At the same time, the surface is activated, which can increase the interweaving and bonding ability between fibers, improve the wettability of the fiber surface, improve the dispersion effect of fibers in water, and improve the interfacial adhesion between chopped fibers and pulp fibers, making the paper stronger and further improving the mechanical properties of PBO paper. In addition, strict control of the fiber dispersion process in papermaking greatly reduces the aggregation of fibers in the dispersion process in water, which is also conducive to improving the uniformity of papermaking. Detailed Implementation

[0024] The following will provide a further detailed description of the above-described contents of the present invention. The following are merely preferred embodiments of the present invention, and should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described contents of the present invention fall within the scope of the present invention. Unless otherwise specified, the following embodiments are all implemented using conventional prior art.

[0025] Example 1: Preparation of carboxylated graphene and aminoated PBO pulp fiber, the specific steps are as follows: (1) 1.1 g of graphene oxide was uniformly dispersed in 260 mL of deionized water by ultrasonic treatment to obtain a graphene oxide suspension. The ultrasonic dispersion time was 3 h and the ultrasonic power was 200 W. After the suspension was cooled to room temperature, 12.1 g of sodium hydroxide and 23.2 g of bromoacetic acid were added. After ultrasonic dispersion for 30 min, the reaction was continued at room temperature for 6 h to obtain a mixed solution. The mixed solution was centrifuged, washed, filtered, and dried under vacuum at 85 °C to obtain carboxylated graphene. (2) 12g of PBO pulp fiber was added to 200g of sulfuric acid solution with a concentration of 60wt%, and stirred at 70℃ for 100min to obtain PBO pulp fiber with carboxyl groups on the surface, wherein the average length of PBO pulp fiber was 0.6mm and the freeness was 30°SR. 10g of PBO pulp fiber with carboxyl groups on its surface was placed in 125g of N-methylpyrrolidone, and then 24g of 1,3-dicyclohexylcarbodiimide and 26g of melamine were added to the reaction system. The reaction was carried out at 100℃ for 38h. The fiber was then washed 5 times with deionized water and dried under vacuum at 85℃ to obtain PBO pulp fiber with amino groups on its surface.

[0026] The following examples all use the carboxylated graphene and aminated PBO pulp fiber prepared in Example 1 above.

[0027] Example 2: A method for improving the electromagnetic shielding performance of PBO paper by grafting graphene, the specific steps of which are as follows: (1) 0.54g of carboxylated graphene was ultrasonically dispersed in 120g of N-methylpyrrolidone solvent for 1.5h of ultrasonic dispersion and 200W of ultrasonic power to obtain a uniform carboxylated graphene dispersion. Then, 9.0g of PBO pulp fiber with amino groups on the surface was added. Under nitrogen protection, the mixture was stirred and reacted at 90°C for 40h. The graphene-grafted PBO pulp fiber was then washed with deionized water until the fiber washing solution was colorless and transparent. After vacuum drying at 85°C, PBO pulp fiber grafted on the graphene surface was obtained. (2) 7.2g of graphene-grafted PBO pulp fiber, 7.2g of chopped fiber, and 7.2g of meta-aramid precipitated fiber were added to 472.8g of water, and 0.1g of polyoxyethylene ether dispersant was added to each to prepare three dispersions. The fiber dispersion was carried out by adding the dispersant while stirring, and stirring was continued for 35min after the dispersant was added. The average length of the PBO chopped fiber was 4mm, the average length of the meta-aramid precipitated fiber was 0.9mm, and the freeness was 28°SR. Fiber dispersions with a concentration of 1.5wt% were prepared. The three dispersions were added to a delamination machine and beating for 30min according to the following ratio, where the mass ratio of graphene-grafted PBO pulp fiber to chopped fiber was 6:4, and the amount of meta-aramid precipitated fiber added was 9% of the total mass of graphene-grafted PBO pulp fiber and chopped fiber. After that, the paper was pressed onto a wire and vacuum dried at 110℃ to obtain modified PBO composite base paper.

[0028] (3) The modified PBO composite paper is hot-pressed at a pressure of 16 MPa and a temperature of 270°C for 3 times, with each hot-pressing time being 30 seconds, to obtain the modified PBO composite paper.

[0029] Testing revealed that the unmodified PBO composite paper had a tensile strength of 113.5 MPa, an electrical conductivity of 54 S / m, and an electromagnetic shielding effectiveness of 18.3 dB in the 8.2-12.4 GHz (X-band) range. The graphene-modified PBO composite paper had a tensile strength of 125.6 MPa, an electrical conductivity of 463 S / m, and an electromagnetic shielding effectiveness of 42.3 dB in the 8.2-12.4 GHz (X-band) range. The unmodified PBO composite paper was prepared by replacing the graphene-grafted PBO pulp fibers with ordinary PBO pulp fibers.

[0030] Example 3: A method for improving the electromagnetic shielding performance of PBO paper by grafting graphene. The method is the same as described in Example 2, except that in step (1), 0.63g of carboxylated graphene is ultrasonically dispersed in 120g of N-methylpyrrolidone solvent, and the rest is the same as described in Example 2.

[0031] Testing revealed that the unmodified PBO composite paper had a tensile strength of 113.5 MPa, an electrical conductivity of 54 S / m, and an electromagnetic shielding effectiveness of 18.3 dB in the 8.2-12.4 GHz (X-band) range. The graphene-modified PBO composite paper had a tensile strength of 136.3 MPa, an electrical conductivity of 582 S / m, and an electromagnetic shielding effectiveness of 48.3 dB in the 8.2-12.4 GHz (X-band) range. The unmodified PBO composite paper was prepared by replacing the graphene-grafted PBO pulp fibers with ordinary PBO pulp fibers.

[0032] Example 4: A method for improving the electromagnetic shielding performance of PBO paper by grafting graphene. The method is the same as described in Example 3, except that in step (1), 0.72g of carboxylated graphene is ultrasonically dispersed in 120g of N-methylpyrrolidone solvent, and in step (2), the mass ratio of PBO pulp fiber to chopped fiber is 7:3, and the amount of meta-aramid precipitated fiber added is 12% of the total mass of PBO pulp fiber and chopped fiber. The rest is the same as described in Example 3.

[0033] Testing revealed that the unmodified PBO composite paper had a tensile strength of 118.3 MPa, an electrical conductivity of 65 S / m, and an electromagnetic shielding effectiveness of 19.4 dB in the 8.2-12.4 GHz (X-band) range. The graphene-modified PBO composite paper had a tensile strength of 151.3 MPa, an electrical conductivity of 735 S / m, and an electromagnetic shielding effectiveness of 57.6 dB in the 8.2-12.4 GHz (X-band) range. The unmodified PBO composite paper was prepared by replacing the graphene-grafted PBO pulp fibers with ordinary PBO pulp fibers.

[0034] Example 5: A method for improving the electromagnetic shielding performance of PBO paper by grafting graphene. The method is the same as that described in Example 4, except that in step (1), 0.81g of carboxylated graphene is ultrasonically dispersed in 120g of N-methylpyrrolidone solvent, and the rest is the same as that described in Example 4.

[0035] Testing revealed that the unmodified PBO composite paper had a tensile strength of 118.3 MPa, an electrical conductivity of 65 S / m, and an electromagnetic shielding effectiveness of 19.4 dB in the 8.2-12.4 GHz (X-band) range. The graphene-modified PBO composite paper had a tensile strength of 158.2 MPa, an electrical conductivity of 829 S / m, and an electromagnetic shielding effectiveness of 65.3 dB in the 8.2-12.4 GHz (X-band) range. The unmodified PBO composite paper was prepared by replacing the graphene-grafted PBO pulp fibers with ordinary PBO pulp fibers.

[0036] A comparative example is a method for preparing PBO composite paper modified with graphene blending, the specific steps of which are as follows: (1) 0.8g of graphene oxide was uniformly dispersed in 200mL of deionized water by ultrasonic treatment to obtain a graphene oxide suspension, wherein the ultrasonic dispersion time was 3h and the ultrasonic power was 200W.

[0037] (2) 7.2g of PBO chopped fibers, 7.2g of PBO pulp fibers, and 7.2g of meta-aramid precipitated fibers were added to 472.8g of water, and 0.1g of polyoxyethylene ether dispersant was added to each to prepare a dispersion. The fibers were dispersed by adding the dispersant while stirring. After the dispersant was added, stirring was continued for 35min. The average length of PBO pulp fibers was 0.6mm and the freeness was 30°SR. The average length of PBO chopped fibers was 4mm. The average length of meta-aramid precipitated fibers was 0.9mm and the freeness was 28°SR. Fiber dispersions with a concentration of 1.5wt% were prepared for each.

[0038] The three dispersions were added to a pulping machine in the following proportions and pulped for 5 minutes, wherein the mass ratio of PBO pulp fiber to chopped fiber was 7:3, and the amount of meta-aramid precipitated fiber added was 12% of the total mass of PBO pulp fiber and chopped fiber. After adding the graphene oxide suspension, pulping was continued for 30 minutes. Then, the paper was wired and pressed into shape, and vacuum dried at 110°C to obtain graphene-modified PBO composite base paper; wherein the amount of graphene oxide added was 9% of the mass of PBO pulp fiber.

[0039] The modified PBO composite paper was hot-pressed at a pressure of 16 MPa and a temperature of 270°C for 3 times, with each hot-pressing time being 30 seconds, to obtain graphene-blended modified PBO composite paper.

[0040] The graphene-modified PBO composite paper obtained above has a tensile strength of 121.7 MPa, an electrical conductivity of 315 S / m, and an electromagnetic shielding effectiveness of 36.5 dB in the 8.2-12.4 GHz (X band) range.

[0041] Comparison of test results shows that the electromagnetic shielding performance of the graphene-modified PBO paper obtained in Examples 2-5 is significantly higher than that of the unmodified PBO composite paper and the graphene blend-modified PBO composite paper prepared in the comparative example. Furthermore, its tensile strength and electrical conductivity are also significantly higher than those of the unmodified PBO composite paper. Therefore, it is feasible to reduce the electromagnetic shielding of PBO paper using the method of this invention, and this method also has a certain effect on improving the tensile strength of PBO paper, representing a significant improvement over existing technologies.

[0042] In the comparative example, graphene was added to PBO paper through blending. Although this reduced the electromagnetic shielding performance of PBO paper, the graphene in the PBO paper prepared by blending was not evenly dispersed in the paper, resulting in a decrease in the mechanical properties of the PBO paper. The performance was not as good as that of the PBO paper prepared by the method of this invention.

[0043] The above embodiments illustrate and describe the basic principles, product features, and advantages of the method of the present invention. The present invention is not limited to the above embodiments; various changes and modifications can be made without departing from the scope of the invention, and all such changes and modifications are claimed to be included within the scope of protection.

Claims

1. A method for improving the electromagnetic shielding performance of PBO paper by grafting graphene, characterized in that, The specific steps are as follows: (1) Preparation of carboxylated graphene Graphene oxide is uniformly dispersed in deionized water by ultrasonic treatment to obtain a graphene oxide suspension. The ultrasonic dispersion time is 1-5 hours and the ultrasonic power is 100-300W. The suspension is cooled to room temperature, sodium hydroxide and bromoacetic acid are added, and ultrasonic treatment is continued for 20-60 minutes. The reaction is continued at room temperature for 2-8 hours to obtain a mixed solution. The mixed solution is centrifuged, washed, filtered, and vacuum dried to obtain carboxylated graphene. (2) Preparation of aminated PBO pulp fiber PBO pulp fibers were added to a sulfuric acid solution and stirred for 50-150 min to obtain PBO pulp fibers with carboxyl groups on the surface. The PBO pulp fibers with carboxyl groups on the surface were placed in N-methylpyrrolidone, and then 1,3-dicyclohexylcarbodiimide and melamine were added to the reaction system. The reaction was carried out at 60-120℃ for 10-43 h. Finally, the fibers were washed with deionized water and vacuum dried to obtain PBO pulp fibers with amino groups on the surface. (3) Preparation of graphene grafted onto the surface of PBO pulp fibers The carboxylated graphene obtained in step (1) was ultrasonically dispersed in N-methylpyrrolidone to obtain a uniform carboxylated graphene dispersion. Then, the aminated PBO pulp fiber obtained in step (2) was added. Under nitrogen protection, the mixture was stirred and reacted at 60-100℃ for 10-50h. Then, the graphene-grafted PBO pulp fiber was washed with deionized water until the fiber washing solution was colorless and transparent. After vacuum drying, the graphene-grafted PBO pulp fiber was obtained. (4) Preparation of modified PBO composite paper Graphene-grafted PBO pulp fibers, PBO chopped fibers, and meta-aramid precipitated fibers were added to water, and dispersants were added to prepare dispersions. Fiber dispersions with concentrations of 0.2-5 wt% were prepared. The three dispersions were added to a pulping machine in a certain proportion for pulping, then wired and pressed into shape. After vacuum drying, PBO base paper was obtained. Finally, the PBO base paper was hot-pressed to obtain graphene-modified PBO composite paper.

2. The method for improving the electromagnetic shielding performance of PBO paper by grafting graphene according to claim 1, characterized in that, In step (1), the concentration of the graphene oxide suspension is 0.1-0.5 wt%, the amount of sodium hydroxide added is 1-5% of the total mass of the graphene oxide suspension, and the amount of bromoacetic acid added is 3-10% of the total mass of the graphene oxide suspension.

3. The method for improving the electromagnetic shielding performance of PBO paper by grafting graphene according to claim 1, characterized in that, The average length of the PBO pulp fiber mentioned in step (2) is 0.5-1.2 mm, and the beating degree is 25-35°SR. The amount of PBO pulp fiber added is 1-10% of the mass of sulfuric acid solution. The amount of PBO pulp fiber with carboxyl groups on the surface added is 2-12% of the mass of N-methylpyrrolidone. The amount of 1,3-dicyclohexylcarbodiimide added is 0.4-2.5 times the mass of PBO pulp fiber with carboxyl groups on the surface. The amount of melamine added is 0.8-1.8 times the mass of 1,3-dicyclohexylcarbodiimide.

4. The method for improving the electromagnetic shielding performance of PBO paper by grafting graphene according to claim 1, characterized in that, In step (3), the concentration of carboxylated graphene dispersion is 0.1-0.8 wt%, and the amount of carboxylated graphene added is 1-10% of the mass of aminated PBO pulp fiber.

5. The method for improving the electromagnetic shielding performance of PBO paper by grafting graphene according to claim 1, characterized in that, In step (3), the ultrasonic dispersion time is 1-5 hours and the ultrasonic power is 100-300W.

6. The method for improving the electromagnetic shielding performance of PBO paper by grafting graphene according to claim 1, characterized in that, In step (4), the mass ratio of PBO chopped fibers to graphene-grafted PBO pulp fibers is 1-4:5-9; the amount of meta-aramid precipitated fibers used is 7-15% of the total mass of PBO chopped fibers and graphene-grafted PBO pulp fibers.

7. The method for improving the electromagnetic shielding performance of PBO paper by grafting graphene according to claim 1, characterized in that, The dispersant mentioned in step (4) is any one of polyoxyethylene ether, hydroxyethyl cellulose, sodium lignosulfonate, and maleic acid-acrylic acid copolymer; the amount of dispersant used is 0.1-1.5% of the oven-dry weight of PBO chopped fiber, graphene-grafted PBO pulp fiber, and meta-aramid precipitated fiber, respectively. The fiber dispersion method is to add the dispersant while stirring, and continue stirring for 10-50 minutes after the dispersant is added.

8. The method for improving the electromagnetic shielding performance of PBO paper by grafting graphene according to claim 1 or 7, characterized in that, The dispersant mentioned in step (4) is polyoxyethylene ether.

9. The method for improving the electromagnetic shielding performance of PBO paper by grafting graphene according to claim 1 or 6, characterized in that, The PBO chopped fiber length in step (4) is 2-5 mm, the average length of the meta-aramid precipitated fiber is 0.8-1.3 mm, and the freeness is 23-32°SR.

10. The method for improving the electromagnetic shielding performance of PBO paper by grafting graphene according to claim 1, characterized in that, The hot pressing conditions described in step (4) are: pressure 12-18MPa, temperature 200-300℃, hot pressing 1-4 times, and hot pressing time 20-80s each time.