Preparation And Electromagnetic Properties Of Three-dimensional Woven Spacer Fabric Reinforced Carbon Nanotube Epoxy Foam Composites

The electromagnetic properties of a material are determined by electromagnetic parameters,of which the complex dielectric constant is a key part.Effective regulation of the complex dielectric constant of the material can greatly improve its electromagnetic properties,which is important for the development and design of future electromagnetic absorbing materials and electromagnetic shielding materials.The development of structurally and functionally integrated composites with both functional and load-bearing capabilities is a major trend in future materials research.How to regulate the dielectric properties of the material while providing good loadbearing capacity is of great significance.In this paper,multi-walled carbon nanotubes are used as the material dielectric property regulating factor to prepare carbon nanotube/epoxy foam with adjustable dielectric properties,and three-dimensional woven spacer fabric is used as the backbone to develop three-dimensional woven spacer fabric-reinforced carbon nanotube epoxy foam composites with load-bearing capacity and adjustable dielectric properties.Meanwhile,to facilitate the application of 3D woven spacer fabric-reinforced carbon nanotube epoxy foam composites in electromagnetic wave absorption and other fields,the overall dielectric properties are predicted and analyzed using the single cell model formulation method and the rectangular waveguide resonant cavity method,and the application of 3D woven spacer fabric-reinforced carbon nanotube epoxy foam composites in the direction of actual electromagnetic wave absorption is simulated using CST electromagnetic field simulation。The main research elements and findings of this paper:(1)Modulation of material complex dielectric constant:multi-walled carbon nanotubes were doped into the epoxy resin foaming system as a modulating factor of material dielectric properties,and the effects of carbon nanotube content on foam structure,mechanical properties and dielectric properties were investigated.The results showed that the doped carbon nanotubes could maintain a good bubble structure,although some of the carbon nanotubes were agglomerated,resulting in blemishes on the foam surface.The carbon nanotubes/epoxy foam showed better mechanical properties,and the compressive modulus increased from 49.1 MPa to 190.4 MPa(287.7%);the compressive strength of the foam increased from 5.2 MPa to 15.2 MPa(192.3%).The dielectric constant and dielectric loss of the foam increased nearly linearly with the increase of CNT filler content,and the fitted equations for the dielectric constant ε^’ and dielectric loss ε^" of the foam in the range of 0～3%of CNT content were obtained as:ε’=1.244+1.614x and:ε"=0.24+0.194x.(2)Enhancement of material load-bearing capacity:In order to make the material have better load-bearing capacity and meet the needs of practical applications in the future,3D woven spacer fabric was used as the backbone to prepare 3D woven spacer fabric-reinforced carbon nanotube epoxy foam composites(3DWSC-carbon nanotube/epoxy foam plates),and the effect of carbon nanotubes on the mechanical properties of 3DWSC-carbon nanotube/epoxy foam plates relative to 3D woven spacer fabric/epoxy hollow composites and 3D woven spacer fabric-reinforced epoxy foam composites was investigated.The results showed that the flat compressive modulus of 3DWSC-carbon nanotube/epoxy foam sheet increased from 25.8 MPa to 65.3 MPa,153.1%,and the flat compressive modulus increased from 332 MPa to 635 MPa,91.3%,relative to 3DWSC-epoxy foam sheet;the impact properties were relatively similar,but tended to exhibit the characteristics of a high-strength but brittle material.Compared to 3DWSC-hollow compound,it shows more obviously superior mechanical properties than 3DWSC-carbon nanotube/epoxy foam sheet.(3)Theoretical modeling of dielectric constant:The single-cell model formulation method and the rectangular waveguide resonant cavity method were used to establish the theoretical modeling of the overall dielectric properties of 3DWSC-carbon nanotube/epoxy foam plates,and the results of their dielectric constants were obtained for different carbon nanotube contents.Compared with the actual dielectric constant measurement results of 3DWSC-carbon nanotube/epoxy foam plates,the error of both prediction methods does not exceed 15%,which has good reliability and is a guide for the development and design of 3D woven spacer fabricreinforced carbon nanotube epoxy foam composites in fields such as electromagnetic wave absorbing materials.(4)Material electromagnetic performance analysis:The electromagnetic simulation of 3DWSC-carbon nanotube/epoxy foam plate was completed by using CST electromagnetic field simulation software,and the effect of CNT content on the electromagnetic performance of 3DWSC-carbon nanotube/epoxy foam plate was investigated.The results show that the increase of CNT content effectively improves the dielectric loss of 3DWSC-carbon nanotube/epoxy foam plates,which greatly improves the electromagnetic properties of the material and enhances the ability of the material to consume electromagnetic wave energy.However,at the same time,the increase of its dielectric constant causes impedance mismatch,which affects the electromagnetic wave entry inside the absorbing material.