Preparation Of Graphene-based Films And Their Electromagnetic Interference Shielding Applications

With the development of information industry and the popularization of electronic equipment,electromagnetic wave pollution has gradually become a hot issue of social and scientific concern.An effective solution to electromagnetic wave pollution is the application of electromagnetic interference（EMI）shielding materials.Traditional EMI shielding products are made of metals as their intrinsic high conductivity,the inevitable shortcomings such as high density and corrosion promote the development of chemically inert carbon-based EMI shielding materials.As a new two-dimensional planar carbon material with many excellent properties,graphene and its derivatives made considerable progress as an EMI shielding materials.With the increase of production capacity of pan-graphene materials in recent years,it is of practical significance to realize the industrialization of high-performance graphene materials.This paper aims to explore the feasibility of large-scale preparation of EMI shielding films using graphene oxide（GO）as the main raw material,and to regulate the EMI shielding efficiency（SE）of the final product through formulation improvement and process optimization.The main contents and achievements of this study are as follows:（1）The feasibility of large-scale continuous production of GO film by coating method was verified.High solid content GO slurry with good stability was prepared by high-speed dispersion of GO solid（45 wt%）with double-planetary agitator.The viscosity of the slurry increased exponentially with the increase of solid content,and the solid content suitable for the coating process ranged from 3.5%to 5.5%.GO coating can be continuously prepared on a pilot-scale coating machine,smooth dry GO film can be obtained by adjusting the process parameters,which is convenient for subsequent transport and processing.The thickness of dry film prepared by single coating ranges from 30 μm to 150 μm,and the width can be adjusted according to matrix size or process requirements.The production capacity of single coating line（calculated by GO）can reach 500 g·h-1,which has good industrial potential.（2）The optimization of thermal process enhanced the conductivity of reduced GO（rGO）.Thermal reduction process contains several stages,in previous stages with low temperature the volatilization and escape of residual solvent occurred,and the decomposition of oxygen-containing groups on the GO sheets arose in the latter stages with high temperature.The conductivity of rGO film increased to 500 S·cm^-1 with the peak heating temperature higher than 700℃.The EMI SE of rGO was significantly improved with the increase of its conductivity,rGO film treated at 1000℃ showed SE value higher than 50 dB in x-band（8.2-12.4 GHz）.with initial GO thickness of 50 μm.（3）The polyimide material with high heat resistance can form graphite-like structure after thermal decomposition,which can be used to doping the GO film to improve electromagnetic shielding performance.Polyimide precursor/GO slurry with high solid content was prepared by strong polar organic solvent,and composite GO membrane was successfully prepared by small coating machine.The conductivity of rGO composite film is 500 S·cm^-1 after multi-stage thermal treatment（peak temperature 800℃）,and the EMI SE of composite film reaching an average of 65 dB in x-band,is significantly higher than pure rGO film.（4）Two-dimensional material MXene and uniform particle size polystyrene（PS）nanospheres were respectively used to construct micromorphology in GO film to improve the overall EMI SE.The monolayer MXene made by etching aluminum titanium carbide in LiF/HCl mixed solution showed good dispersion in water.Thin MXene/GO composite films with hierarchical structure were prepared by vacuum filter,and their EMI SE varied by their internal structure.For films with same compositions,G-M film（single thick MXene layer）got the highest EMI SE,and M-G-M film（double thin MXene layers）showed lower EMI SE value,while the M/G film（mixed）were the worst.After heat treatment,the EMI SE of all composite films were improved by the reduction of GO.The EMI SE of porous rGO foam prepared by template method with PS nanospheres was little improved compared with control group,although the simple compounding of GO/PS destroy the integrity of dry coating which indicated its incompatibility to pilot-scale fabrication of GO film.