Protein Ultrafine Fibrous Conductive Composites For Electromagnetic Interference Shielding

The rapid development of the modern electronics industry and the large-scale application of electronic equipment have led to the generation of electronic pollution,which is called electronic noise,radio frequency interference(RFI)or electromagnetic interference(EMI).EMI not only hinders the normal operation of nearby electronic equipment,but also affects human health.As people's awareness of EMI shielding continues to increase,the demand for EMI shielding materials has also increased,and the performance requirements have gradually increased.In addition to strong absorption,light weight and flexibility,the current requirements for EMI shielding materials have also become an important development direction for degradable EMI shielding materials in order to reduce damage to the environment.From the perspective of electromagnetic wave absorption induced by microstructure,this topic uses electrospinning technology to prepare a flexible substrate of Zein ultrafine fibers,and introduces conductive polymer polypyrrole(PPy)and metallic phase conductive material silver(Ag)to construct a porous ultrafine fiber composite system.,which has the advantages of simplicity,adjustable structure,and efficient EMI shielding performance.Finally,the degradability of the composites is evaluated.The specific research resultes are as follows:(1)Construction of PPy composite Zein/Epoxy(ZE)ultrafine fibers and evaluation of its electromagnetic interference shielding performanceThis work is based on the excitation effect of the active hydrogen structure of the protein on the epoxy cross-linking reaction and electrospinning technology to prepare a porous ZE-based ultrafine fiber flexible substrate with a stable water phase structure,and then based on the in-situ polymerization method on the surface of the ultrafine fiber,the conductive polymer PPy is introduced to construct a conductivity mismatch induced polarization interface,and an EMI shielding ultrafine fiber composite material is obtained.The EMI shielding performance of the material is related to the polymerization reaction time of PPy,the monomer concentration and the thickness of the substrate,and the comprehensive evaluation time and economic cost are prepared when the substrate thickness is 0.3 mm,the pyrrole monomer concentration is 0.1 M,and the reaction time is 8 h.The prepared composites have good overall performance,its electrical conductivity reaches 386.27±7.09S/m,and the X-band EMI shielding effectiveness(SE)can reach 26.3 d B.When the substrate thickness is increased to 1.2 mm,EMI SE increases to 42.4 d B.The composite of PPy increased the dry tensile strength of the material by 324%to 4.07 MPa,and the elongation at break decreased by 40.4%to 15.4%;after being bent for 5000 times,the EMI SE of the material only dropped by 3.9 d B,and the retention rate 86.5%.The shielding mechanism of the composites are that the micron-scale porous structure of the ZE substrate assists electromagnetic waves to be reflected multiple times inside the material,and the composite of PPy builds an efficient conductive network,and finally realizes the efficient absorption of electromagnetic waves.(2)Construction of Ag/PPy Composite ZE ultrafine fibers and evaluation of its electromagnetic interference shielding performanceIn order to further reduce the thickness of the material and improve the shielding performance of the material,this work introduces the second phase conductive material Ag by Ag NO₃ dipping method,Ag NO₂/Py one-step polymerization method and two-component spray deposition method to provide additional conductive loss and construct a multilayer.The structure introduces interfacial polarization between the Ag/PPy layer and the ZE flexible substrate,and cooperates with the porous ZE substrate to provide more loss paths for the incidence of electromagnetic waves,thereby increasing the chance of absorbing electromagnetic waves.Ag/PPy composite ZE ultra-fine fiber,with a thickness of 0.3 mm,the composite materials prepared by the three composite methods achieve EMI SE of 14.6,12.1,and 33.4 d B,respectively.The two-component spray deposition method has the best effect.As the number of spraying increases(20?100),EMI SE increases significantly.The conductivity of the sample after 60 times of spraying reaches 9969.78±663.25 S/m,and the EMI SE can be increased to 55.6 d B.After 5000 times of bending,the EMI SE drops by 11.5 d B,and the retention rate is 79.3%.(3)Evaluation of the degradation behavior of composite materialsIn view of the slow degradation of Ag-coated composites,this work investigated the degradation performance of PPy/ZE ultrafine fiber composites,which degrade relatively quickly,based on the soil burial method.The composites were buried in the soil for 40 days,and the mechanical properties did not change significantly.After 100 days of burying,the fibers began to break.After 160 days,the weight loss was 41.3±1.7%,and the breaking strength decreased from the initial 4.07 MPa to 0.47 MPa.In summary,the PPy coating and Ag/PPy coating ZE microfiber composites developed in this work not only have high-efficiency EMI shielding performance,but also can be naturally degraded after being discarded.This work not only opens a new application direction for plant proteins,but also forms a degradable,high-performance shielding material based on low-cost natural biomass materials through a reasonable composite structure design for sustainable green EMI shielding applications.