Structure Control And Performance Of Polyurethane-based Flexible Electromagnetic Shielding Films

With the continuous development of electronic communication and intelligent interconnection,the radiation pollution of electromagnetic wave is becoming more and more serious.These electromagnetic waves will not only interfere with other nearby electronic devices,but also endanger human health.Electromagnetic interference(EMI)shielding materials can effectively solve electromagnetic pollution problems because it is able to efficiently reduce the degree of electromagnetic wave conduction between electronic devices.However,due to the continuous upgrading of electronic devices,it presents higher requirements for the comprehensive performance of the EMI shielding materials.Polymer-based EMI shielding materials have a critical application in electromagnetic shielding,owing to the advantages of high stability,easy processing and light weight.With the rapid development of flexible electronics towards flexibility,integration,and multifunctionality,electromagnetic shielding materials are often required to have diversified performance in flexibility and other functionalities simultaneously.In this thesis,polymer composites with flexible,high stability and excellent electromagnetic shielding effectiveness are constructed by conductive materials(metal nanomaterials,graphene,etc.)and flexible polymer matrix(polyurethane).Firstly,the relationship between the content and morphology of conductive fillers,microstructures of composites,and EMI shielding performances are investigated.With the compounding of different conductive fillers with flexible polymer,we prepared flexible EMI shielding films with various merits of excellent electromagnetic shielding performance,light weight,excellent flexibility and stability performance.The specific research contents and conclusions are discussed as follows:(1)Preparation and properties of graphene(GN)/silver nanowires(AgNWs)/thermoplastic polyurethane(TPU)electromagnetic shielding films:We prepare a flexible and ultra-thin(0.05 mm)GN/AgNWs/TPU shielding film by the scratch coating technique.The film has excellent thermal conductivity(33.6 W/(m·K))and EMI shielding performance(57 dB).In this work,we systematacially investigated the effect of the ratio of GN:AgNWs on the hybrid filler structure,electrically conductive,thermally conductive,and EMI shielding properties of the resulting composite films.In addition,the EMI shielding mechanism and contributions of different fillers are also investigated.(2)Preparation and properties of transparent silver nanowire/ionic liquid/TPU electromagnetic shielding films:In this work,we designed a simple and effective method to prepare flexible,transparent EMI shielding films based on silver nanowires/ionic liquids(ILs)/thermoplastic polyurethane ternary composites.Based on the formation of a low-density but highly interconnected AgNW network and the synergistic effect of AgNWs and ILs on the conductivity of the composites,the prepared AgNWs/ILs/TPU films achieved an EMI shielding effectiveness of～26.8 dB at 10 GHz,and the EMI shielding efficiency reduced thickness(SSE/t)reached 1.32 x 10~6 dB.The prepared EMI films also showed good durability and stability in EMI shielding performance after 1000 uninterrupted bending cycles and long-term immersion tests in strong acidic and alkaline solutions.