Preparation And Electromagnetic Shielding Properties Of Graphene Hybrid Particles/glass-fiber Composites

The increasingly serious electromagnetic interference and pollution have caused a serious hazard to people's health,information and communication,and national defense security.Therefore,the new electromagnetic shielding protective materials have been widely concerned.Surface metalized glass fiber mat can be used in the development of electromagnetic shielding or absorbing materials by its characteristics of high temperature resistance,flexible lightweight,machinability and adjustable electromagnetic function.Since most studies on conductive fiber electromagnetic shielding materials usually adopt the method of improving the conductivity to increase the reflection and reduce the transmission of electromagnetic waves,its high reflectivity will cause potential secondary pollution.Magnetic graphene hybrid material is a kind of electromagnetic wave absorption material with excellent performance.It mainly reduces the reflection of electromagnetic waves by improving the impedance match between the material and air,the single material has a limited blocking effect on electromagnetic waves.Considering the excellent conductivity and mechanical stability of silver-coated glass fiber,the multifunctional electromagnetic shielding material,combining the shielding reflection and absorption,is a composite of fiber reinforced matrix and absorbent,which can effectively overcome the adverse effects caused by impedance mismatch.Here,in order to realize the integration of electromagnetic shielding and absorbing,silver-coated glass fiber mat material was used as shielding matrix,and graphene hybrid particles were selected as wave-absorbent.The composition optimization,regulation of structures and electromagnetic performance were investigated respectively,and then the shielding layer and matching absorbing layer were composite by casting technology.Our goal was to achieve the effective integration of strong absorption and high shielding efficiency in the same band,reduce the reflection intensity of electromagnetic wave at the air-material interface,improve the impedance matching ability and electromagnetic loss,and develop lightweight and high strength electromagnetic shielding/absorbing composite materials.The main work contents and research results are as follows:(1)Spherical magnetic ferric oxide(Fe₃O₄)particles were synthesized on the surface of graphene nanoplates(f-GNPs)by solvothermal method,and Fe₃O₄@f-GNPs absorbing agent was prepared.The particle size of hybrid particles and the ratio of graphene to Fe₃O₄(also known as carbon magnetic ratio)were relatively controllable.The growth process and regulation methods of Fe₃O₄ particles were probed in depth,and the structure-activity relationship among the microstructure,electromagnetic parameters and wave absorption performance of nano-hybrid particles was established.The result showed that the absorbing effect increases with the increase of particle size.The hybrid material with magnetic particle size of 422.3nm had the best absorbing efficiency among all the samples.When the thickness of the composite material was 1.5mm,the maximum reflection loss was-30.2dB in the frequency range of 2-18GHz.In addition,the electromagnetic parameters and microwave absorption effect of Fe₃O₄@f-GNPs samples were adjusted by changing the carbon magnetic ratio and thickness.When the carbon/magnetic ratio is 1.4:1,the reflection loss of the absorber with a thickness of 1.5mm reached-48.34 dB,and the effective frequency bandwidth(RL<-10dB)was 2.56GHz(covering 11.12-13.68GHz).It was confirmed that the introduction of magnetic particles optimized the impedance matching of hybrid materials,and the carbon magnetic heterostructure further promoted the attenuation of electromagnetic waves by polarization relaxation.(2)Electromagnetic shielding glass mat(GM)was prepared by using polydopamine(PDA)modification as a secondary functionalized platform and silver plating on the fiber surface.Adjusting the concentration of dopamine and the concentration of silver plating solution was the main method to optimize the conductivity and shielding performance of silver-coated glass fiber mat.The results showed that the silver layer was uniform and the adhesion was strong after the oxidation and self-polymerization of 3g/L dopamine on the surface of the fiber.When the concentration of silver nitrate was 10g/L,the silver-plated glass fiber had the highest weight gain rate and the best electrical conductivity,and its shielding efficiency was up to 68.10 dB.The high shielding performance of the material was attributed to the three-dimensional porous macrostructure of the conductive fiberglass mat,which enhanced the conductivity and multiple scattering loss simultaneously.(3)The homemade Fe₃O₄@f-GNPs hybrid particles were used as the functional filler of impedance matching and absorption layer.After mixing with waterborne polyurethane,it was compounded with silver-plated glass fiber mat by casting method.The magnetic absorbent was concentrated on the compound side under the induction of magnetic field,forming a two-layer structure of absorbing and shielding.The conductive glass fiber mat composite without absorbing agent had a higher dielectric constant and a lower absorption rate.The impedance matching ability and the absorption and attenuation of electromagnetic waves of the composites containing absorbing agent were improved,and it exhibited a unique multiple shielding mechanism of"absorption-reflection-absorption".When the functional filler content was20%,the average electromagnetic shielding value of the composite was 21.81 dB,and the absorption rate was 0.41.Meanwhile,the excellent mechanical properties displayed that the glass fiber composite has stable and reliable electromagnetic shielding ability.