Preparation And Prperties Of Low Reflection Impact Resistant Electromagnetic Shielding Composites

With the rapid development of information technology and digital intelligent electronic equipment,electromagnetic radiation pollution has become an increasingly serious problem,The electromagnetic radiation generated by electronic equipment will affect the normal operation of the surrounding precision electronic instruments and cause harm to human health.Therefore,the development of high-performance electromagnetic shielding materials has become a research hotspot in recent years.Conductive polymer composite is the ideal choice of high performance electromagnetic shielding composite because of its advantages of light weight,easy-machining and adjustable performance.According to the principle of impedance mismatch,composite materials with high electrical conductivity show excellent electromagnetic shielding performance based on their strong electromagnetic reflection ability.Therefore,according to the properties of the materials and the design of the composite structure,the use of interfacial polarization,dielectric loss and magnetic loss for multiple attenuation of electromagnetic waves,reduce the reflection of electromagnetic waves,become an effective way to prepare electromagnetic shielding materials with low reflection characteristics.In addition,electronic equipment is inevitably affected by the collision and impact of external objects in the process of daily use.These collisions and violent impact will cause serious injuries to electronic equipment and users,affecting the normal use of electronic equipment and endangering personal safety.Most electromagnetic shielding materials are difficult to resist external impact and collision while shielding electromagnetic waves,so the development of electromagnetic shielding composite materials with low reflection and impact resistance has become an urgent problem to be solved.In this paper,low reflection impact resistant electromagnetic shielding material is taken as the research target,and the defects of high reflectivity and poor impact resistance of electromagnetic shielding material in existing studies are solved through the structural design of asymmetric layered composite material,and the impact resistance electromagnetic shielding material with significant low reflection characteristics is finally obtained.Relevant research contents are as follows:(1)The CNT/STG fiber cloth(UHMWPE fiber cloth,Aramid fiber cloth)with different electrical conductivity was prepared by spraying technology to load conductive filler on the surface of fiber cloth and control the proportion of CNT and STG.The asymmetric composite material with gradient conductive network was obtained by hot pressing.Thanks to the uniform distribution of CNT/STG on the surface of fiber cloth,a perfect conductive network can be built on the surface of fiber cloth,and the friction force of fiber pulling out when the fiber cloth is impacted is enhanced.The design of gradient layered structure is beneficial to multiple reflection and attenuation of electromagnetic wave and energy dissipation during impact process.Based on the design of the gradient asymmetric layered structure,the EMI SE reaches31.2 d B,the R value is 0.64,and the absorption energy is 26.44 J when the material is 1mm thick(3-layer fiber cloth).By increasing the number of fiber cloth layers in the upper absorbing layer and conductive layer,the R value can be as low as 0.47,and the effective EMI of 43 d B can be obtained SE,the absorbed energy is 20.11 J.(2)With carbon black(CB)as conductive filler and Aramid honeycomb as structural material for reinforcing mechanics,the blend of CB and STG was filled into aramid fiber honeycomb by mechanical pressing.The laminated sandwich board of UHMWPE fiber cloth/(CB/STG)honeycomb sandwich/carbon fiber cloth was prepared by hot pressing.The top layer of UHMWPE fiber cloth is used as the wave transmitting layer,the middle CB/STG aramid fiber honeycomb is used as the conductive loss layer,and the bottom layer of carbon fiber cloth is used as the reflective layer.The conductive loss of electromagnetic wave in incident path can be improved by regulating the content of CB in aramid honeycomb and the shear thickening effect of core layer STG is used to absorb shock energy,so that the material has good electromagnetic wave absorption and energy dissipation ability.Based on the design of sandwich structure,the R value of composite material can be reduced to 0.34,while the EMI SE increases to 51.52 d B,and the absorption capacity of composite material can reach 31.19 J when resisting impact.(3)The conductive filler CB in the aramid honeycomb in the previous chapter is replaced by electromagnetic doped Fe₃O₄@r GO particles,and the same preparation process was adopted to prepare Fe₃O₄@r GO/STG honeycomb sandwich panel composites.The magnetic and dielectric losses along the incident direction of electromagnetic wave were enhanced by adjusting the content of Fe₃O₄@r GO in the aramid fiber honeycomb.At the same time,the addition of Fe₃O₄@r GO further increases the variation range of STG's energy storage modulus and loss modulus,improves the material's energy dissipation ability,and further enhances the impact resistance of the material under the low reflection electromagnetic shielding efficiency.When the absorption rate of sandwich layer is the highest,the EMI SE of composite material increases to 43.20 d B,while the R value decreases to 0.41,and the absorption energy reaches36.71 J.