ABSTRACT Currently, the presence of spurious microwave radiation is increasing in the environment, which has caused concern due to possible health problems in living beings and electromagnetic interference in electronic systems. To control this problem, studies in the materials area are taking place, aiming to attenuate the spurious radiation and meet requirements of good performance in broadband, low cost and low weight. The present work aimed to study Cu and Ni nanometric films with thicknesses of 65 and 200 nm, deposited on polyethylene terephthalate substrate by magnetron sputtering. Scanning electron microscopy with a field emission gun (FEG-SEM) showed that the films produced have different morphological textures, due to the parameters used in the sputtering process and also the free energy of metals. Impedance spectroscopy measurements showed that the films have low conductivity values, due to the metallic oxides formed on the film surfaces, confirmed by X-ray diffraction, and also to the presence of defects. Electromagnetic characterization (8.2 – 12.4 GHz) showed that the Cu and Ni thin films had low performance, except the Ni_200 nm film, which showed a total shielding efficiency of about 30% in broadband. This result is promising considering the nanometric thickness of the Ni film.

Abstract Prolonged exposure to environmental conditions such as ultraviolet radiation, humidity, and temperature, to which carbon fiber-reinforced thermoplastic polymer components are exposed during their service life, can lead to significant changes in mechanical, physical, and chemicals properties, and can often be irreversible, resulting in premature component failure. This study presents the influence of accelerated weathering exposure times (400 h, 800 h, and 1200 h) on the mechanical, thermal, and structural properties of carbon fiber (CF)/polyamide 6 (PA6) laminates. Analyses of composite surfaces were carried out using microscopy and contact angle measurements, which indicated that the factors of exposure to accelerated only affected the surface of the composites, showing signs of the beginning of degradation. The tensile strength (609 MPa ± 10 MPa) and interlaminar shear strength (27 MPa ± 0.9 MPa) did not present significant changes, showing that the reinforcement, the matrix, and the interface remained stable after exposure to accelerated.

RESUMO A resina furfurílica (RF) é uma bioresina obtida a partir do álcool furfurílico (AF), extraído de fontes renováveis. Essa resina quando curada apresenta excelentes características, como elevada dureza, estabilidade química e boa resistência mecânica, que viabilizam sua utilização em diferentes áreas, destacando-se os setores aeroespacial e de bioengenharia. No entanto, a sua utilização em larga escala ainda é limitada, devido ao difícil controle do seu processo de síntese, pois a reação de policondensação do AF é extremamente exotérmica. O presente trabalho visa contribuir com a área de síntese da RF, por meio do estudo de sua obtenção em meio ácido e em baixa temperatura (∼50 ºC), variando os tempos de reação (1, 2 e 3 h), visando um maior controle da exotermia do meio reacional. O sucesso das sínteses realizadas foi comprovado por análises de espectroscopia na região do infravermelho com transformada de Fourier, que evidenciaram a presença de cetonas e estruturas de acordo com Diels-Alder e de Dunlop e Peters. Medidas de viscosidade apresentaram baixos valores (230 a 470 mPa.s), os quais são concordantes com as baixas massas molares obtidas por cromatografia de permeação em gel ( M ¯ w: ∼800 g/mol). Esses resultados mostram que as condições de síntese utilizadas desfavoreceram cineticamente o avanço da reação; porém, não promoveram picos exotérmicos. As análises termogravimétricas (TGA) das RFs curadas com ácido p-toluenosulfônico (2 e 3%, m/m) mostraram perdas de massa desde o início da análise, devido à presença de água e de frações de baixa massa molar na amostra. Esses resultados são concordantes com as imagens obtidas por microscopia eletrônica de varredura, que mostraram um elevado volume de poros. Resultados relevantes foram observados nas análises de TGA sob atmosfera inerte, com valores elevados de carbono fixo (50–60%), indicando o potencial uso das RFs sintetizadas na área de materiais carbonosos.

ABSTRACT Poly(furfuryl alcohol) (PFA) is a bioresin obtained from furfuryl alcohol (FA) extracted from renewable sources. This resin, when cured, has excellent characteristics, such as high hardness, chemical stability, and good mechanical resistance, which make its use in different areas viable, especially in the aerospace and bioengineering sectors. However, its use on a large scale is still limited due to the difficult control of its synthesis process since the polycondensation reaction of FA is extremely exothermic. The present work aims to contribute to the area of PFA synthesis, through the study of its obtainment in acidic medium and at low temperature (∼50 ºC), varying the reaction times (1, 2, and 3 h), aiming at greater control of the exothermy of the reaction medium. Fourier transform infrared spectroscopy analyses confirmed the syntheses success, which showed the presence of ketones and structures according to Diels-Alder and the Dunlop and Peters. Viscosity measurements showed low values (230 to 470 mPa.s), which are in agreement with the low molar masses obtained by gel permeation chromatography ( M ¯ w: ∼800 g/mol). These results show that the synthesis conditions used kinetically unfavored the progress of the reaction but avoided exothermic peaks. Thermogravimetric analysis (TGA) of the PFAs cured with p-toluenesulfonic acid (2 and 3%, w/w) showed mass losses since the beginning of the analysis due to the presence of water and low molar mass fractions in the sample. These data agree with the images obtained by scanning electron microscopy, which showed a high volume of pores. Relevant results were observed in the TGA analysis under an inert atmosphere, with high values of carbon yield (50–60%), indicating the potential use of synthesized PFAs in the area of carbon materials.

Abstract Polyamide (PA) is a well-known and researched thermoplastic due to its excellent mechanical and physical properties, making it developed in the automotive sector, suitable for lighter vehicles, and, consequently, lower fuel consumption. This review manuscript presents the applications of PA-based materials in the manufacture of vehicle parts, with a description of their processing, a discussion about their thermal properties and the crystallization of polymer structure, the challenges of machining PA-based composite materials, and the feasibility of recyclability. This work aims to revise literature about the use of polyamide 6 (PA6), polyamide 66 (PA66), and polyamide 12 (PA12) and their composites reinforced with fiberglass (FG) and carbon fiber (CF) focused on the potential that these materials have as alternative materials for the automotive industry.