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Resumo: Este estudo apresenta resultados com materiais absorvedores de radiação eletromagnética, MARE, à base de poli(o-metoxianilina) (POMA) e de seus compósitos com negro de fumo (NF) (NF/POMA). A condutividade elétrica dos compósitos NF/POMA foi significativamente maior (0,23-80 S.cm -1 ) que para a POMA (0,017 S.cm -1 ). Medidas de atenuação da radiação eletromagnética de formulações com esses aditivos poliméricos em resina epóxi foram realizadas na faixa de 8,2 a 12,4 GHz. Resultados de refletividade mostram que as composições com o compósito condutivo NF-10%/POMA apresentam os melhores valores de atenuação da radiação eletromagnética (até 99,5% em 11,7 GHz). Palavras-chave: Poli(o-metoxianilina), POMA, MARE, absorvedores de micro-ondas. Application of Poly(o-Methoxyaniline) and its Carbon Black Composites in Microwave AbsorbersAbstract: This study deals with the production of radar absorbing materials (RAM) based on poly(o-methoxyaniline) (POMA) and its conductive composites with carbon black (CB) (CB/POMA). The electrical conductivity of the CB/POMA composite was significantly higher (0.23-80 S.cm -1 ) than for POMA (0.017 S.cm -1 ). The attenuation of the electromagnetic radiation in the range between 8 and 12 GHz was highest for CB/POMA-conductive composites in epoxy resin, reaching up to 99.5% at 11.7 GHz. Keywords: Poly(o-methoxyaniline), POMA, RAM, radar absorbing materials. IntroduçãoOs Materiais Absorvedores de Radiação Eletromagnética (MARE), também denominados de materiais absorvedores de micro-ondas, vêm sendo cada vez mais utilizados nas áreas de eletroeletrônicos, médica, embalagens, aeronáutica, defesa, entre outras, como materiais aplicados na blindagem e no controle de interferência do campo eletromagnético na região de micro-ondas. Dentre os aditivos mais comumente utilizados no processamento desses materiais destacam-se as ferritas, a ferro carbonila, o negro de fumo e os polímeros condutores [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] . Considerando-se os polímeros condutores, vale ressaltar a sua crescente importância na área de MARE, em função de suas interessantes propriedades físicas (eletrônicas), estabilidade química, facilidade de síntese, relativa facilidade de processamento e, principalmente, menor massa específica em relação às ferritas e à ferro carbonila [2,[9][10][11][12][13][14][15][16][17][18] . Os polímeros condutores têm despertado crescentes interesses científicos e tecnológicos nos últimos anos, devido às suas propriedades, em particular, sua condutividade elétrica. Um dos exemplos mais conhecidos refere-se à polianilina (PAni), que está exercendo um papel importante em diferentes desenvolvimentos tecnológicos, devido à sua facilidade de dopagem com ácidos protônicos e sua estabilidade química no estado dopado [2,3,7,[9][10][11] . Nos últimos anos, os derivados da polianilina vêm sendo também investigados visando diferentes aplicações [19][20][21][22][23][24] . Nesse sentido, podem-se mencionar derivados da polianilina resultantes da polimerização d...

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In this work, polyaniline (PANI) in emeraldine-base form, synthesized by chemical oxidation polymerization, was protonated with hydrochloric acid (HCl). Composites based on high-density polyethylene (HDPE) and linear-low density polyethylene (LLDPE) blends with PANI were prepared in molten condition using a torque rheometer. The effect of compatibilizer agent (maleic anhydridegrafted high density polyethylene, HDPE-g-MA) and different contents of PANI on the blends-based composites was also investigated. Thermal, mechanical, and electromagnetic (electric permittivity) measurements and morphological aspects of the composites were evaluated. The addition of PANI content in the composites decreases the degree of crystallinity of HDPE and LLDPE blends, which implies that PANI particles make it difficult for co-crystallization to occur in the HDPE and LLDPE, respectively. On the other hand, the addition of compatibilizer agent in the HDPE and LLDPE blends increased the degree of crystallinity. The complex parameters of permittivity in the frequency range of 8.2 to 12.4 GHz varied as a function of the PANI content in the blend. It was also observed that the compatibilizer agent increased the composite stiffness and decreased the electric permittivity values. This result shows that the increasing rigidity of the molecular structure of the polyethylene matrix hindered the dissipation of the electromagnetic energy in the sample.

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This study involves the preparation of conducting composites based on poly(o-methoxyaniline) (POMA) and carbon nanotubes (CNT) and the evaluation of them as radar absorbing materials (RAM), in the frequency range of 8.2–12.4 GHz (X-band). The composites were obtained by synthesis in situ of POMA in the presence of CNT (0.1 and 0.5 wt% in relation to the o-methoxyaniline monomer). The resulting samples—POMA/CNT-0.1 wt% and POMA/CNT-0.5 wt%—were incorporated in an epoxy resin matrix in the proportion of 1 and 10 wt%. FT-IR analyses show that the POMA was successfully synthesized on the CNT surface. SEM analyses show that the synthesized POMA recovered all CNT surface. Electrical conductivity measurements show that the CNT contributed to increase the conductivity of POMA/CNT composites (1.5–6.7 S·cm−1) in relation to the neat POMA (5.4 × 10−1 S·cm−1). The electromagnetic characterization involved the measurements of complex parameters of electrical permittivity (ε) and magnetic permeability (µ), using a waveguide in the X-band. From these experimental data reflection loss (RL) simulations were performed for specimens with different thicknesses. The complex parameters show that the CNT in the composites increased ε and µ. These results are attributed to the CNT network formation into the composites. Simulated RL curves of neat POMA and POMA/CNT in epoxy resin show the preponderant influence of POMA on all RL curves. This behavior is attributed to the efficient CNT recovering by POMA. RL results show that the composite based on 10 wt% of POMA/CNT-0.5 wt% in epoxy resin (9 mm thickness) presents the best RL results (≈87% of attenuation at 12.4 GHz).

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