Study On The Preparation Of Layerby-Layer Assembled For Flexible Rubber-Based Composite Foam And Its Electromagnetic Microwave Absorption Property

In recent years,the exploration of electromagnetic absorption materials with excellent wave absorption performance to cope with the increasingly serious problem of electromagnetic environmental pollution has become a hot topic in the current research.The ideal electromagnetic absorbing material should not only meet the needs of"strong,wide,thin and light"but also meet the practical application needs of flexibility,stretchability,and lightweight.At present,single-component magnetic metals often have shortcomings such as high density,easy corrosion,and narrow effective absorption frequency band,which seriously restrict their development in the field of electromagnetic wave absorption.To this end,this paper prepares a flexible rubber-based composite foam by spontaneous foam and layer assembly with conductive carbon nanotubes（CNTs）and magnetic Fe₃O₄as fillers,discarded tire chips（CR）as the matrix,and polyurethane as the reinforcing phase.The influence of morphological structure,multilayer assembly,and temperature on the magnetic properties,conductivity,wave absorption,and mechanical tensile properties of composite foam were systematically studied.The specific research content is as follows:（1）CNT/Fe₃O₄nanocomposite particles were synthesized by hydrothermal method,and then CR was used as the matrix to prepare CR@CNT/Fe₃O₄composite materials by microwave auxiliary method.The effect of the addition of CNT/Fe₃O₄on the composites’dielectric properties and microwave absorption properties was studied to alleviate the problems of black pollution and electromagnetic pollution effectively.The 2.3 mm thick CR@CNT/Fe₃O₄exhibits a minimum reflection loss of-60.46 d B（RLmin）and a wide effective absorption band（5.5 GHz）,thanks to coordinated dielectric and magnetic losses,good interfacial impedance matching,and synergy between multiple internal reflections.（2）A one-component moisture-cured polyurethane was introduced into the CR@CNT/Fe₃O₄ composite,and a PU/CR@CNT/Fe₃O₄composite flexible foam was successfully prepared through a spontaneous foaming process.The introduction of conductive magnetic CNT/Fe₃O₄enables the construction of an efficient electronic transmission path inside the composite foam.At a thickness of 2.0 mm for composite foam samples,the RLmin value can reach-48.67 d B,which means that more than 99%of electromagnetic waves can be effectively absorbed.Composite magnetic foam exhibits good multi-tensile deformation recovery,and its maximum tensile strength can reach 2.5 MPa.In addition,increasing the temperature can significantly increase the absorbing strength of the magnetic foam,and the composite foam exhibits an enhanced RLmin value（-51.04 d B）at 40°C.（3）Based on the first two parts,a series of composite foams with a double/triple structure were prepared using the layer-by-layer pouring method.Through the study of foam morphology, electromagnetic parameters,and wave absorption performance,it is found that each layer’s dielectric characteristics,thickness,and multi-layer microstructure will have an important impact on the electromagnetic absorption performance of the composite foam.The multilayer structure design allows for better adjustment of the impedance matching of the material,resulting in better absorption and dissipation of electromagnetic waves.The results show that compared with the single-layer foam with the same component,the double-layer structure can effectively improve the electromagnetic absorption intensity of the composite foam,such as compared with the single-layer composite foam,the wave absorption performance of the T3 sample is improved by 159%.The electromagnetic absorption performance of the three-layer composite foam is excellent,as the three-layer F7 sample is 182%higher than the double-layer T4.At the same time,the effect of the three-layer foam in broadening the effective absorption bandwidth is also more obvious.Through the observation of the morphological structure of the composite foam fault,it is found that there will be a binding zone with almost no gap between the foam layers,which also improves the tensile performance of the multi-layer foam.In addition,the increase in temperature not only enhances the absorbing strength of the composite foam but also helps to reduce the matching thickness,such as the RLmin value generated by the three-layer F2 sample at 60°C is-65.66 d B,and the minimum matching thickness is reduced to 3.0 mm.