Electromagnetic Shielding And Mechanical Properties Of Coated Flexible Composites

In recent decades,the extensive usage of electrical equipment and portable electronics leads to serious electromagnetic interference(EMI)pollutions.With the development of modern science and technology,the requirements for materials are further improved.Single-function materials can no longer meet the requirements,and will gradually be replaced by multi-functional materials.In order to meet application requirements,electromagnetic shielding materials not only need good electromagnetic shielding properties,but their materials also often need to be flexible and have excellent mechanical properties.This thesis combines the excellent mechanical properties,flexible characteristics of fabrics and the functional advantages of composite materials,the mechanism of the fabric coating on electromagnetic shielding performance was calculated and analyzed,and the coating textile material is designed.Multifunctional textile materials with high mechanical and electromagnetic shielding properties were prepared by in-situ polymerization and coating.The main research content of this paper is as follow.(1)This thesis is based on electromagnetic wave propagation theory and electromagnetic simulation model of coated fabric.The influence of the conductive property,dielectric property and the thickness of the coated textiles on the electromagnetic shielding property of the coated fabric was discussed by simulation.(2)Polypyrrole preoxidized felt were prepared by in-situ polymerization with polypyrrole as functional particle and preoxidized felt as the main substrate.At the same time,cotton,basalt fiber fabrics and nylon were selected as the control group base material.Multilayer flexible polypyrrole reinforced preoxygenated felt materials were prepared by in-situ polymerization of preoxygenated felt with good porosity to generate conductive polypyrrole.By changing the concentration of pyrrole monomer,oxidant,dopant and reaction time,the influence of single factor on the final properties of the materials was studied.It was found that the electrical conductivity and electromagnetic shielding properties of the materials increased with the increase of polypyrrole production rate.Due to the multi-layer structure and the introduction of conductive polypyrrole,the conductivity of the materials was increased by five times.In addition,the high conductivity and light weight of this material make it an efficient and practical material for electromagnetic shielding materials.In the 0-800 mhz frequency band,the electromagnetic shielding efficiency increases from 13 dB to about 24 dB,and the tensile property of the composite material increases by 43.5%.Based on the far-field theory of electromagnetic shielding,the shielding mechanism is studied deeply.(3)In order to further improve the mechanical and electromagnetic shielding properties of materials and meet the requirements of strong and light,graphite and graphene reinforced materials with good chemical stability,easy processing,low density,good electrical conductivity and high temperature resistance were introduced.Carbon-based/polyurethane composite materials were prepared by blending method.The effects of functional particle coating thickness,drying temperature and coating viscosity on the electromagnetic and mechanical properties of graphite coated preoxygenated felt were analyzed.The multilayer coated textileshave the highest shielding efficiency of 32 dB in the 0-200 MHZ band.Finally,the effects of different absorbing functional particles(graphene and graphite)on the electromagnetic and mechanical properties of preoxygenated felt with single-layer coating were analyzed and compared.It is found that under the same technological conditions,the shielding ability of graphene-coated preoxygen felt material is better than that of graphene-coated preoxygen felt material,and the graphene-coated preoxygen felt material has better mechanical performance.