Preparation And Research Of Lignin-based Carbon Composites With Electromagnetic Interference Shielding Performance

With the development of the electronics industry,people's requirements for electromagnetic shielding technology are increasing,and new electromagnetic shielding materials with high conductivity and lightness have become a research hotpot in this field.Carbon materials have the advantages of excellent conductivity,low density,high chemical stability and low cost,and have great application potential in the field of electromagnetic shielding.Graphene with excellent electrical conductivity and high specific surface area is an ideal component for preparing carbon-based electromagnetic shielding materials.However,graphene has problems such as easy agglomeration and structure collapse,and it is difficult to exert its electromagnetic shielding performance in the materials.Lignin is natural aromatic polymer with abundant reserves,and has a rigid molecule structure with a three-dimensional network and contains a hydrophobic skeleton and hydrophilic functional groups,which give lignin some amphiphilicity.Based on the above characteristics of lignin,the combination of lignin and graphene is expected to solve the application problem of easy agglomeration and structure collapse of graphene directly as an electromagnetic shielding material.In addition,lignin has a high carbon content,and its carbonized products have excellent conductivity,which can be used as biomass resources to replace part of graphene to achieve the purpose of cut costs.Therefore,in this paper,lignin and graphene are compounded,two lignin-based/graphene composite carbon materials(carbon aerogel and carbon foam)are prepared by carbonization treatment,and the main research results of exploring their application in the field of electromagnetic shielding are as follows:(1)Firstly,the graphene oxide(GO)was dispersed by enzymatic hydrolysis of lignin(EHL)by ultrasonic cavitation method to prepare the EHL/GO composite.Furthermore,through the directional freezing-ice template method and high-temperature(600°C)carbonization,an ordered pore network structure,low density(4.22?12.35 mg/cm³),high conductivity(1.50×10^-2?4.22×10^-2 S·m^-1)composite carbon aerogel was prepared.During the aerogel preparation process,the amphiphilic nature of lignin and the rigid three-dimensional network structure have a synergistic effect,which can inhibit the aerogel volume shrinkage effect,so that the prepared carbon aerogel(D-L30RGA)can maintain 64.3%of the original volume,while the volume of pure graphene carbon aerogel can only be maintained at 34.2%of the original volume.Electrochemical test results show that the interface polarization between the lignin carbon and reduced graphene oxide(RGO)sheets in D-L30RGA can greatly loss incident electromagnetic waves,and exhibits a shielding Effectiveness up to 52.83 d B in the 8.2?12.4 GHz band.,far exceeding the shielding effectiveness of pure graphene carbon aerogel(30.97 d B).(2)Compared with carbon aerogel,the preparation process of composite carbon foam is simpler,lower cost and higher production efficiency.However,the structure of polymer foam is easy to collapse during carbonization process.In this paper,lignin is used to modify the melamine foam to retain complete skeleton and construct a good conductive network.The EHL modified carbon foam was prepared by the two-step method of adsorption-impregnation and high temperature carbonization.In order to improve the adsorption capacity of the melamine foam to EHL molecules and increase the carbon content of the foam material,lignin(DEHL)rich in catechol structure is prepared by demethylation modification.When carbonized at900°C,the electrical conductivity of the DEHL modified carbon foam reached 0.74 S·m^-1,which was 40.5%higher than that of the EHL modified carbon foam,and the electromagnetic shielding effectiveness of the 8.2?12.4 GHz band reached 23.66 d B.The morphology and structure characterization results show that the better electromagnetic shielding effectiveness of DEHL modified carbon foam is mainly due to the lignin carbon layer covering the foam skeleton to form a rigid core-shell structure,which supports the overall structure of the carbon foam material,so that the network structure of the melamine foam remains intact.In order to further improve the electromagnetic shielding effectiveness,the reduced graphene oxide(RGO)was incorporated into the DEHL modified carbon foam to construct the lignin-graphene modified carbon foam,which has high conductivity(1.89 S·m^-1)and low density(20 mg·cm^-3).The RGO introduced in this material builds a scaly plane along the direction of the foam skeleton,forming a dense network structure with continuous carbon skeletons interspersed with the lignin carbon.The interface polarization between the two makes the electromagnetic shielding effectiveness of the composite carbon foam in the 8.2?12.4 GHz band reach 42.39 dB.