The Preparation Of Polyaniline Composites And The Research On Their Radar Absorbing Properties

Microwave absorbing materials have shown great potential in the fields of electromagnetic shielding and stealth technology. At the present time, the researching interests have focused on the materials with strong absorbing, wide frequency band and light weight. Polyaniline(PANI) has been a promising absorbing material due to its easy synthesis, low density, controllable conductivity and multi-morphologies. Therefore, to get the higher wave absorbing performance of polyaniline and its composite materials has become one of the main research directions in the study of polyaniline.In this paper, the PANI/montmorillonite(MMT) composites and PANI/porous carbon ftber(PCFs) composites were separately prepared and were employed as absorbing fillers for the production of wave absorbing composites. The properties and morphologies of obtained PANI/MMT and PANI/PCFs were studied. The main content of this paper is as follow:In the presence of MMT, the PANI/MMT composites were prepared by chemically oxidation polymerization, where ammonium persulfate (APS) was as oxidant, hydrochloric acid(HCl) and dodecylbenzene sulfonic acid (DBSA) were respectively as acid dopant with the content of MMT from10%to70%. By infrared spectroscopy(FT-IR), X-ray diffraction(XRD), thermal gravimetric analysis(TGA), scanning electron microscopy (SEM) and the conductivity test, the morphology and the property of the composite were characterized. From the results, it was found that PANI was intercalated into the MMT galleries and led to an increase of distance in MMT interlayer spacing. The thermal stability of the composites was improved obviously and the conductivity of the composite is higher than the pristine PANI when the content of MMT reached to a certain value(10%-30%). The flake-like morphology of PANI was observed in PANI/MMT with HC1doped, which was different from the granular particle form of PANI without MMT. And the flake-like morphology of PANI was retained after removing MMT totally via hydrofluoric acid etching. The network-like morphology was observed in PANI/MMT with DBS A doped. And the neddle-like morphology of PANI was observed by removing MMT totally.The PANI/MMT composite as a microwave absorber was mixed with paraffin to prepare microwave absorbing composite, and their permittivities and microwave absorbing property of the composites is depended on the content of PANI/MMT and the composition of PANI/MMT when the content of PANI/MMT10%reached to20%, the microwave absorbing performance was improved greatly. PANI-HC1/MMT10%with the flake-like morphology showed better microwave absorbtion than the pristine PANI-HC1with granular particle form, especially in expanding the frequency bandwidth. For the PANI-HCl/MMT10%composite with a thickness of3mm, the peak reflection loss could reach-27dB, and the band with reflection loss below-10dB lay in7.6GHz-12.8GHz. In the same way, as a filler, PANI-DBSA/MMT10%also showed better microwave absorbing performance than PANI-DBSA. With a thickness of8mm, the peak reflection loss of PANI-DBSA/MMT10%could reach-28dB and the band with reflection loss below-10dB lay in10.5GHz-13GHz. The filler of PANI-HC1/MMT10%and PANI-HC1/MMT30%were chosen to mix with glass fiber and epoxy to produce single-layered composite flats. We measured the radar absorbing performance of the single-layered flat composites in arch method The obtained results were similar with the simulated ones. The peak reflection loss could reach-21dB and-19dB, respectively. The band with reflection loss below-10dB respectively ranged from6.6GHz to11.8GHz and from7.8GHz to12.3GHz,confirming the excellent wave absorbing property of PANI-HC1/MMT.The compound PANI/PCFs were prepared from porous carbon fibers PCFs8and PCFs5, respectively in water medium and water/alcohol medium. The size of of PANI particle in the compounds prepared in water/alcohol medium is small and uniformly distributed.The PANI/PCFs compounds as absorber were added to the paraffin with different content. Their permittivities were measured and microwave absorbing property was simulated using software. It was found that the microwave absorbing property of PCFs8is better than PCFs5. The preserved more pores in PCFs8than PCFs5after griding might be attributed to this difference. The microwave absorbing property of PANI/PCFs compounds preceded PCFs. For the PANI/PCFs5/paraffin with12%of PANI/PCFs5which prepared in water medium, the peak reflection loss could reach-15.7dB and the band below-10dB reflection loss ranged from13.1GHz to15.9GHz. The peak reflection loss of the composites where PANI/PCFs5prepared in water/alcohol medium could reach-25.6dB and the bandwidth of reflection loss below-10dB lay in10.6GHz-14GHz. Compared with PCFs8, the microwave absorbing property of PANI/PCFs8composites prepared in two kinds of medium were also improved.