Characteristic Of Porous Carbon Fiber And Study On Its Microwave Absorption As A Filler For Composite

Nowadays, the stealth technology has played more and more important role in the modernwar. As the key of stealth technology, the radar absorbing material has been received widelyattention. Among many kinds of absorbing materials, porous carbon fibers (PCFs) meet highrequirements for the future absorbing material due to its developed pore structure and highconductivity, temperature resistance and other properties. Therefore, it’s significant to prepareporous carbon fibers and study their radar absorbing properties.In this paper, porous carbon fibers (PCFs) were prepared through a novel and simplemethod—polymer blend technique. And then these fibers were employed as the radar absorbingfillers and the epoxy as the matrix to prepare single-layered radar absorbing composites. Theinfluence of several factors, such as carbonization temperature, the amount of pores, as well as thelength of PCFs, on the absorbing properties of composites was studied. Besides, the magneticFe3O4particles were also introduced on the surface of PCFs and acted as absorbing agent togetherwith PCFs.Polyacrylonitrile (PAN) was used as carbon precursor polymer (CPP), while polymethylmethacrylate (PMMA) as thermally decomposed polymer (TDP). They were both dissolved in N,N-dimethylformamide (DMF) with PAN/PMMA(70/30,80/20,90/10,100/0) to prepare theblending solution. The blend fibers were prepared by wet-spinning technique and carbonized athigh temperature under a nitrogen atmosphere, which removed TDP component and got PCFs.The morphology of blend fibers with various content ratio of PAN/PMMA impregnated in acetonewas observed by SEM. The results showed that pores appeared and existed on the cross section offibers, while the PMMA phase vanished. The quantity of these cylinder-shaped pores became more with the increase of PMMA content and there was no pore in blend fibers without PMMA.This phenomenon also could be found in the morphology of cross section for porous carbon fibersprepared from blend fibers with various content ratio of PAN/PMMA.The blend fibers of PAN/PMMA(70/30) were carbonized with different temperature(1000℃、1200℃、1400℃)and the crystalline structure of the obtained porous carbon fibers duringthis process were investigated through Raman spectra and XRD. The results showed that with theincrease of carbonization temperature, the degree of the graphitization and conductivity becamehigher and the graphite structure gradually transformed into three-dimensionally ordered lamellarstructure. When carbonization temperature was chosen as1400℃, the conductivity of PCFsreached to339S/cm.The PCFs prepared from different blend fibers (70/30,80/20,100/0) were employed as theradar absorbing filler and the epoxy as the matrix to prepare the flat composites with6wt%addition of the filler, which were used to discuss the influence of different content ratio ofPAN/PMMA on microwave absorbing performance. The results showed that the performancebecame better with the increase of PMMA content and the composites with PCFs prepared from70/30blend fibers got the best absorbing performance, whose peak reflection loss could reach-24.5dB and the band with reflection loss below-10dB could reach1.9GHz. The PCFs preparedfrom70/30blend fibers were used to prepare the composites as the same way to discuss theinfluence of different carbonization temperature and length on microwave absorbing performance.For carbonization temperature, the composites got the best performance when the PCFs wascarbonized at1200℃. Because this kind of PCFs got proper conductivity, which meanscomposites could produce enough consumption of electromagnetic and avoid reflections ofelectromagnetic waves like metal at the same time. For length of PCFs, the composites got thebest performance when the length was0.2mm. Because0.2mm PCFs could disperse well incomposites and keep the fiber morphology.Magnetic Fe3O4as a kind of magnetic loss material can adjust the electromagneticparameters of PCFs/Epoxy composite material well through the magnetization modification ofPCFs, making composite material have better performance on wave absorption such as strongerabsorption, wider frequency band. The PCFs prepared from70/30blend fibers were coated byFe3O4through wet chemical methods and then PCFs after treatment were employed as filler andthe paraffin as the matrix to prepare the flat composites with11wt%. By XRD, EDS and SEM, themorphology and property of fibers coated were characterized. Besides, we used electromagneticparameters to test absorbing properties of composites. The experimental results indicated thatPCFs were successfully coated by Fe3O4and the microwave absorption of composites withFe3O4@PCFs was greatly improved, whose peak reflection loss could reach-20.7dB and the band with reflection loss below-10dB became wider. In addition, the absorbing performance ofcomposites filled with Fe3O4@PCFs was better than that filled with Fe3O4/PCFs.