Study On The Epoxy-based Electromagnetic Interference Shielding Materials With High Strength And High Toughness

Electromagnetic radiation not only affects the normal operation of equipment,but also seriously threatens human health.Electromagnetic interference(EMI)shielding materials based on conductive polymer composites(CPCs),which have the advantages of light weight,good chemical stability,and excellent corrosion resistance,have gradually replaced traditional metal-based EMI shielding materials.Due to its excellent mechanical properties,epoxy resin is the preferred matrix material for the preparation of CPCs with high mechanical properties.A lot of conductive fillers are needed to improve the conductivity of epoxy resi.However,the introduction of a great deal of conductive fillers will significantly reduce the tensile strength and elongation at break(toughness)of epoxy resin,while the EMI shielding effectiveness(SE)cannot be effectively inproved if the adding amount of conductive fillers is limited.Therefore,how to construct the conductive network in the epoxy matrix with low filler loading and ensure the excellent mechanical properties of epoxy resin is a vital problem.In this paper,the epoxy-based composites with excellent EMI shielding performance and high mechanical properties can be prepared by designing the conductive network structure.The main results are as follows:(1)Tetrapod-like ZnO coated with silver(T-ZnO/Ag)nanoparticles with special spatial structures were prepared by chemical deposition method and the conductivity of the T-ZnO/Ag fillers can be as high as 81700 S/m.Next,the T-ZnO/Ag/EP composites with uniform structure can be obtained by curing the mixture of T-ZnO/Ag and EP curing systems.The effect of the T-ZnO/Ag content on the final properties of the composites was systematically studied.The results show that the conductivity and EMI SE can be increased with the increasing content of T-ZnO/Ag fillers,while tensile strength and elongation at break will be decreased with the increasing content of T-ZnO/Ag fillers.When the content of T-ZnO/Ag fillers reaches 25 wt%,the conductivity,EMI SE,and tensile strength of the composites can reach 22.4 S/cm,21d B,and 35.4 MPa,respectively.(2)In order to further improve the EMI SE and mechanical properties of the composites,modified in-situ polymerization(MISP)method was used to prepare T-ZnO/Ag/EP composites with deposited conductive network structure.The EMI SE value in X band can reach 36.8 d B when the T-ZnO/Ag content is only 5 wt%,while the EMI SE value of T-ZnO/Ag/EP composites prepared by traditional in-situ polymerization(ISP)method and solvent blending(SB)method can only reach 21d B when the T-ZnO/Ag content is as high as 30wt%.Besides,the EMI SE of the EP_T-X systems prepared by MISP method can be increased with the increasing content of the T-ZnO/Ag fillers,and the average EMI SE value of the EP_T-20sample can reach 76.7 d B(in 2-18 GHz)and 80.1 d B(in X band).At the same time,Tg of the EP_T-X systems can be increased from 108.1 ^oC to 116.1 ^oC.Though the tensile strength of the EP_T-X systems can be decreased with the increasing content of T-ZnO/Ag,the tensile strength of the EP_T-20 sample can still remain 50.4 MPa.(3)On the basis of the above research,T-ZnO/Ag fillers mixed with MWCNTs that have ultra-high aspect ratio and large specific surface area were used as the hybrid conducive fillers,and flexible side chain butyl glycidyl ether(BGE)was introduced into the epoxy matrix to further improve the mechanical properties of the composites.The ternary T-ZnO/Ag/MWCNTs/EP EMI shielding composites(EP_BD-X systems)with deposited conductive network structure were prepared by a facile solvent-assistant in-situ polymerization(SAISP)method.Due to the fact that 3D T-ZnO/Ag fillers are entangled by the intertwined 1D MWCNTs,the incident EM wave can go through multiple interfacial reflection events in the heterogeneous interphases between T-ZnO/Ag and intertwined MWCNTs,and 9:1 was verified as the proper mass ratio of T-ZnO/Ag and MWCNTs.The synergistic effect of the deposited conductive network structure and the synergy of the multidimensional hybrid fillers can provide remarkable EMI SE of 85.9 d B for the EP_BD-15sample and 88.1 d B for the EP_BD-20 sample,which can still possess high tensile strength of72.4 MPa and Tg of 113.6 ^oC due to the synergistic effect of deposited structure and the self-assembly effect of butyl glycidyl ether(BGE)soft chains in the epoxy curing network.In comparison,the tensile strength of the EP_D-20 sample(without BGE)can only reach 56.3MPa.