| Graphene is a honeycomb-like sheet of carbon just one atom thick with a number of unique physical properties,such as absorbing properties,electrical conductivity,adjustable performance of its working surface,boundary effects and so on.It is for these reasons that graphene is widely used in the field of preparation of absorbing materials.The absorbing mechanism of graphene is mainly dielectric loss.It has been found that it is difficult for the absorbing material prepared by using only graphene to provide four properties of thin,light,wide and strong simultaneously.In order to prepare a kind of absorbing material with more comprehensive functions,we can adopt the method of compositing various absorbing materials with different characteristics.The electromagnetic parameters of the absorbing material prepared by the method of compositing the materials with different loss mechanism and different absorption frequency band will be more convenient for being controlled,thus making it easier to meet the requirements of impedance matching.Moreover,compared with the materials prepared by graphene alone,the materials prepared by composite method will be lighter in mass.For these reasons,the method of compositing graphene with other functional particles in the preparation step of absorbing materials has become an important research direction in the field of electromagnetic protection materials development.In this study,the coating fabric samples was prepared by using a scraping coating method,with polyester/cotton blended fabrics(P/C)as the base fabrics,polyurethane resins as the binder,graphene doped with polyaniline(electric loss type)and metal iron powder(magnetic loss type)as the functional particles respectively.This study could be divided into three steps,the first step was to explore the optimum preparation conditions of the polyaniline particles.Because powdery polyaniline is not suitable for the electromagnetic property testing,in this study,the polyaniline particles were firstly loaded on a piece of P/C fabric.Then the electromagnetic properties of the polyaniline-P/C sample were tested to reflect the optimum preparation conditions of the polyaniline particles.In this step,the effects of the concentration of the polyaniline,the dopant and oxidant type and the concentration of the dopant and oxidant to the shielding effectiveness,surface resistance,real and imaginary parts of dielectric constant and tangent of loss Angle of the composite fabric samples were studied.The second step was to prepare the coating fabric samples.In this step,polyaniline/graphene coating fabric samples and iron powder/graphene coating fabric samples were prepared,and the effects of graphene content,polyaniline content,iron powder content,iron particle size and coating thickness on the shielding effectiveness,real and imaginary parts of dielectric constant and tangent of loss Angle of the samples were investigated.The third step was the performance characterization of the coating fabric samples.In this step,the properties of the samples were tested with the help of some scientific experimental apparatus such as XRD,XPS,VSM and so on.Results showed that,in the research of exploring the optimum technological conditions for the preparation of polyaniline,when the concentration of aniline was 0.2mol/L,the concentration of dopant(p-toluene sulfonic acid)was 0.4 mol/L,the concentration of oxidant(ammonium persulfate)was 0.4 mol/L,and the test frequency was 1.81×10~7 Hz,the shielding efficiency of the samples reached a maximum value(9.84 d B).When the concentration of aniline was 0.4 mol/L,the concentration of dopant(p-toluene sulfonic acid)was 0.4 mol/L,the concentration of oxidant(ammonium persulfate)was 0.4 mol/L,and the test frequency was between 10~6?10~9 Hz,the real and imaginary parts of the dielectric constant and the tangential value of the loss Angle reached maximum values were 6.10,2.00 and 0.60 respectively.In the preparation of polyaniline/graphene coating fabrics,when the graphene content was 4%,the polyaniline content was 5%,the coating thickness was 1.1mm,and the test frequency was 2.31×10~7 Hz,the shielding efficiency of the samples reached the maximum value(10.69 d B).In the range of the studied frequency,the real and imaginary parts of the dielectric constant and the tangential value of the loss Angle reached the maximum values were 4.95,0.40 and 0.13,respectively.In the experiment of preparing iron powder/graphene coating fabric,when the graphene content was 4%,the iron powder content was 20%,the coating thickness was 1.1mm,and the test frequency was1.23×10~7 Hz,the shielding efficiency of the samples reached the maximum value(14.61d B).In the range of the studied frequency,the real and imaginary parts of the dielectric constant and the tangential value of the loss Angle reached the maximum values were4.80,0.50 and 0.12,respectively.The mechanical properties and electromagnetic shielding properties of iron powder/graphene coating fabric samples are better than those of polyaniline/graphene coating fabric samples. |
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