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 The use of continuous fibers reinforced polymeric composites has increased substantially in the last year’s due to their high specific mechanical strength compared to other materials. Despite this property, this class of material is susceptible to low, medium, or high energy impacts, which can cause severe damage to composite laminates. One of the most serious damages is delamination, which can lead to partial or total rupture of the structure. In order to minimize this problem, several studies have been carried out in this area. In this context, this work aims to evaluate the influence of aramid reinforcement with bi-directional (2D) and tri-directional (3D) arrangements impregnated with two epoxy resins of different stiffness on the impact strength of composites submitted to the 340 J dart drop test. The impact results showed that the 2D composites had lower impact strength than the 3D ones, with the presence of perforations (when impregnated with the more rigid resin) and delaminations. Delaminations occurred regardless of the epoxy resin used in the impregnation. On the other hand, the 3D composites impregnated with the less rigid epoxy matrix absorbed more energy (3DF: 97.9%) with less deformation and no delamination compared to the 2D laminate (2DF: 96.1%) produced.

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.

Abstract Among the engineering thermoplastics, poly(phenylene sulfide) (PPS) stands out for its excellent properties and mainly for processing at lower temperatures. The requirements requested by industries can be made by improving mechanical strength, weight reduction, and durable components by reinforcing the PPS matrix with fiberglass (FG) and carbon fiber (CF). This review intends to present the most current research related to the physical, mechanical, and thermal properties of PPS and the PPS/FG and PPS/CF composites most currently used by the aerospace, automotive, and energy industries. In addition to presenting the feasibility of mechanical and thermal recycling processes for PPS-based waste to reinsert a high market value thermoplastic into the industrial production cycle, thus contributing to the minimization of waste destined for landfills and incinerated or even improperly disposed of in the environment.

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.

RESUMO O uso de tecidos no processamento de materiais compósitos já é uma realidade, em função das atraentes propriedades mecânicas que esse tipo de reforço confere aos compósitos laminados e à maior facilidade de processamento. No entanto, os compósitos laminados são suscetíveis a falhas por delaminação entre as camadas. Nesse sentido, a utilização de reforços baseados em tecidos multicamadas tridirecionais (tecidos 3D), com filamentos em direções ortogonais, pode contribuir para um melhor desempenho do compósito, com a redução deste tipo de falha. Porém, o acesso a reforços 3D ainda é muito restrito ao nível mundial, devido à complexidade tecnológica envolvida no seu processamento. Nesse escopo, o presente trabalho visa contribuir com a área de processamento de compósitos com a obtenção de um tecido 3D de fibras de aramida, obtido por meio da produção e combinação de 6 camadas de tecido bidirecional, simultaneamente à amarração das referidas camadas por filamentos do urdume, processo esse realizado em uma única etapa. Para isto, um tear convencional foi adaptado e o tecido 3D produzido foi caracterizado por meio de ensaios típicos da área têxtil, como gramatura, densidade linear e espessura, análises por estereoscopia e resistências à tração e ao impacto por queda de dardo. Análises por estereoscopia revelaram detalhes das direções transversal e ortogonal do tecido, que juntamente com os ensaios da área têxtil comprovaram o sucesso da obtenção do tecido 3D, com características físicas condizentes com o arranjo pretendido. Comparativamente, os resultados de resistência à tração mostraram que o tecido 3D possui maior elongação que o tecido 2D comercial e os ensaios de impacto com 40 J mostraram que o tecido 3D resistiu sem perfurar e sem a delaminação das camadas, como vantagens em relação ao tecido 2D.

ABSTRACT The use of fabrics in the processing of composite materials is already a reality due to the attractive mechanical properties that this type of reinforcement adds to the final material and the greater ease of processing. However, laminated composites are susceptible to failure by delamination between the layers. In this case, the use of reinforcements based on tridirectional multilayer fabrics (3D-fabrics) with filaments in orthogonal directions could better contribute in order to enhance composite performance, reducing this type of failure. However, access to 3D-fabrics is still very restricted worldwide, due to the technological complexity involved in processing. For this purpose, the present work aims to contribute to composite processing area by producing a 3D-fabric with aramid fibers. The fabric was obtained through the production and combination of 6 layers of bidirectional fabric, simultaneously with the bonding of the layers by warp filaments, a process carried out in a single step. For this, a conventional loom was adapted and the 3D-fabric manufactured was characterized by typical tests in the textile industry, as grammage, linear density, and thickness, additionally stereoscopy analysis, tensile and drop tests were assessed. The stereoscopic analysis has revealed details from transversal and orthogonal directions of the fabric, which associated with the textile industry test results proved the success of manufactured 3D-fabric, with physical characteristics consistent with the intended arrangement. Comparatively, the results of tensile strength showed that the 3D-fabric has greater elongation than the commercial 2D-fabric. Under 40 J impact, 3D-fabric withstood without perforation and delamination between layers, an improvement when compared to 2D-fabric.

Pharmaceutical, cosmetic and personal care products are mainly based on emulsions and their rheological behavior can be a critical factor for successful use. Thus, rheological analysis is a promising tool, since the stability, sensory aspects and processing parameters can be assessed. This work presents the rheological analyses of 39 samples of emulsions and the use of data obtained in a tool based on artificial neural networks (ANN), in order to predict the sensory performance of cosmetic emulsions. The storage (G’) and loss (G”) moduli, yield stress and thixotropy were measured experimentally and used in the ANN model. The correlation of the results obtained in the simulations with sensory tests performed with consumers showed accuracy of 60-84%. The reported results demonstrate that the prediction of sensory perception based on rheological analyses offers a very useful strategy for further studies and can support the development of new products in less time.

RESUMO O carbono vítreo reticulado (CVR) é um material carbonoso, rico em átomos de carbono ligados por ligações sp2, obtido pelo tratamento térmico (TT) de carbonização (a pelo menos 1000 ºC, sob atmosfera inerte) de resinas termorrígidas. A sua obtenção pode se dar por diferentes metodologias, usualmente pelo uso de um material de sacrifício, que se degrada durante o TT e gera poros de transporte. Este trabalho teve como objetivo avaliar a influência de diferentes tempos de patamar (2, 8, 12, 24 e 36 h) a 1000 ºC nas características estruturais, morfológicas e condutividade elétrica de amostras de CVR obtidas a partir de uma espuma de poliuretano (PU, material de sacrifício), impregnada com resina furfurílica (PFA). A espuma de PU/PFA foi caracterizada por espectrofotometria de infravermelho com transformada de Fourier (FT-IR) e análises termogravimétricas, as amostras de CVR por difração de raios X (DRX), microscopias óptica (MO) e eletrônica de varredura (MEV), e condutividade elétrica por 2 pontas. Os resultados de FT-IR e DRX confirmam a conversão da espuma de PU/PFA no CVR, com um rendimento de ~44%. As análises de DRX também evidenciam mudanças no ordenamento estrutural das amostras de CVR em função dos diferentes tempos de patamar, devido à provável expulsão de heteroátomos ainda presentes na estrutura do referido material carbonoso. As medidas de condutividade elétrica corroboram com essa observação, com um aumento significativo a partir de 8 h de patamar (de 1,71 x 10-1 para 1,17 x 104 S.cm-1), como uma consequência da diminuição de defeitos na estrutura do CVR. As micrografias mostram a estrutura alveolar da espuma de PU/PFA, rica em poros de transporte, que é preservada no CVR, após a carbonização.

ABSTRACT Reticulated vitreous carbon (RVC) is a carbon material, rich in carbon atoms linked by sp2 bonds, obtained by the thermal treatment (TT) of carbonization (at least 1000 ºC, under inert atmosphere) of thermoset resins. It can be obtained by different methodologies, usually through the use of sacrifice material, which degrades during TT and generates transport pores. This work aimed to evaluate the influence of different threshold times (2, 8, 12, 24, and 36 h) at 1000 ºC on the structural, morphological, and electrical conductivity characteristics of RVC samples obtained from a polyurethane foam (PU, sacrifice material), impregnated with polyfurfuryl alcohol resin (PFA). The PU/PFA foam was characterized by infrared spectrophotometry with Fourier transform (FT-IR) and thermogravimetric analyzes and CVR samples by X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM), electrical conductivity by 2 points. The FT-IR and XRD results confirm the conversion of PU/PFA foam to RVC, with a carbon yield of ~44%. The XRD analyzes also show changes in the structural ordering of the RVC samples due to the different threshold times, due to the probable expulsion of heteroatoms still present in the carbon material structure. The electrical conductivity measurements corroborate this observation, with a significant increase after 8 h of threshold (from 1.71 x 10-1 to 1.17 x 104 S.cm-1), as a consequence of the decrease of defects in the RVC structure. The micrographs show the alveolar structure of the PU/PFA foam, rich in transport pores, which are preserved in the RVC after carbonization.

RESUMO Atualmente, existe uma demanda na busca por materiais com alta densidade de potência, longo ciclo de vida e baixo impacto ambiental que são em sua maioria utilizados para a produção de supercapacitores, sendo esses considerados fontes promissoras de energia para sistemas eletrônicos. Os tipos de materiais mais promissores para essa aplicação são os baseados em carbono, devido à sua flexibilidade, área superficial e boa estabilidade eletroquímica. Para a produção de materiais carbonosos, o principal precursor utilizado é a poliacrilonitrila (PAN) e suas variações a partir da adição de monômeros, como o acrilato de metila (MA). Geralmente, esses materiais são utilizados em formas de mantas, fios ou nanofibras produzidos a partir de processos de fiação e posteriormente carbonizados para gerar o material carbonáceo. Um dos processos de fiação que tem sido amplamente estudado para a obtenção de nanofibras de carbono é o processo de eletrofiação. Portanto, este trabalho apresenta os resultados obtidos do processo de carbonização de mantas eletrofiadas a partir de solução de PAN homopolímero (PANH) e PAN-co-acrilato de metila 6 % (PA6MA) com dimetilformamida (DMF) com o intuito de obter material para uso em supercapacitores. Os polímeros utilizados foram analisados por DSC para a obtenção dos valores relacionados a faixa de ciclização, sendo possível observar uma melhor estabilidade térmica relacionada as amostras de PAN6MA com faixa de temperatura de 240-312 °C e temperatura máxima do pico exotérmico de 292 °C. As mantas obtidas pelo processo de eletrofiação foram oxidadas a 235°C por 5min e carbonizadas a 900 °C por 5 min. As mantas obtidas, antes e após o processo de carbonização, foram analisadas por MEV apresentando fibras de superfície lisa, dispersas aleatoriamente e de dimensões nanométricas, sendo os valores de diâmetro aproximado de 219 nm para as nanofibras de carbono de PANH (NfcPANH) e 185 nm para as nanofibras de carbono de PAN6MA (NfcPAN6MA). As mantas carbonizadas foram analisadas pela técnica RAMAN e foi possível a obtenção de dados referentes a estrutura carbônica presente nas amostras, onde os valores obtidos demonstraram que as amostras de NfcPAN6MA apresentaram menor valor de grau de cristalinidade medida a partir da relação entre as bandas D e G conhecido como fator ID/IG, sendo o valor obtido igual a 1,06 para as NfcPNA6MA e 1,24 para as NfcPANH, isso demonstra uma maior presença de estruturas grafíticas cristalinas quando comparadas as amostras produzidas a partir da PANH. Para obtenção das características capacitivas foram realizados levantamento das curvas carga/ descarga por análise cronopotenciométrica, foi possível observar as melhores características relacionadas a capacitância específica e estabilidade de ciclagem em baixas correntes aplicadas para as amostras de PAN6MA com valores de capacitância específica de 270,9 F/g, densidade de energia de 30,0 Wh/kg e densidade de potência de 153,5 W/kg. Os resultados obtidos demonstraram que o material apresentou potencial para a aplicação proposta.

ABSTRACT Currently, there is a demand in the search for materials with high power density, long life cycle and low environmental impact that are mostly used fot the supercapacitors production, which are considered promising energy power for electronic systems. The most promising types of materials for this application are those based on carbon, due to their flexibility, surface area and good electrochemical stability. For the production of carbonaceous materials, the main precursor used is polyacrylonitrile (PAN) and its variations from the addition of monomers, such as methyl acrylate (MA). Generally, these materials are used in forms of blankets or yarns produced from spinning processes and later carbonized to generate the carbonaceous material. One of the spinning processes that has been widely studied for obtaining carbon nanofibers is the electrospinning process. Therefore, this paper presents the results obtained from the carbonization of electrospun blankets manufactured from solutions of polyacrylonitrile homopolymer (PANH) and poly (acrylonitrile-co-6 % methyl acrylate) (PAN6MA) combined with dimethylformamide in order to obtain material for use in supercapacitors. The polymers used were analyzed by DSC to obtain the values related to cyclization, by that were possible to observe a better thermal stability related to the samples of PAN6MA, with a temperature range of 240-312 ºC and maximum temperature of the exothermic peak of 292 °C. The electrospun mats were oxidized at 235°C per 5 min and carbonized at 90 °C per 5 min. Both pre-carbonization and post-carbonization mats were analyzed by SEM, showing fibers with smooth surface, randomly dispersion and nanometric size, with values of diameter of approximately 219 nm for PANH carbon nanofibers (NfcPANH) and 185 nm for PAN6MA carbon nanofibers (NfcPAN6MA). The carbonized mats were analyzed by RAMAN technique and it was possible to obtain the data related to the carbon structure present in the samples, where the obtained values showed that the mats manufactured from PAN6MA presented the lower value of degree of crystallinity measured from the relationship between bands D and G known as factor ID/IG, the value obtained being equal to 1.06 for NfcPAN6MA and 1.24 for NfcPANH, this shows a higher concentration of crystalline graphitic structures when compared with the samples produced from PANH. To obtain the capacitive characteristic, the load/discharge curves were surveyed by chronopotentiometric analysis, where it was possible to observe the best characteristics related to the specific capacity and low current cycling stability applied to the PAN - co- 6% methyl acrylate sample with specific capacity values of 270.9 F/g, energy density of 30.0 Wh/kg and power density of 153.5 W/kg. The results obtained demonstrated that the material presented potential for the proposed application.

Abstract The aim of this work is to follow the structural variations of polyaniline (PAni) obtained by chemical oxidation on a pre-pilot scale, with different reaction times. Synthesis of PAni is well known, but when it is carried out on a pre-pilot scale, several factors can lead to structural changes and understanding these changes is important to improve controls on the synthesis process. The polymers formed were characterized by spectroscopic techniques (Raman spectroscopy, Fourier Transform Infrared - FTIR and UV-Visible). Degree of oxidation and yield were calculated for each reaction time. The analysis by FTIR, the calculated degree of oxidation and the yield showed significant changes in polymer structure at reaction times of 65 and 80 min. This result was attributed to the excessive oxidation of PAni, with the breaking of its polymer chain. The changes observed in the structure of PAni gave subsidies to the optimization of the process of obtaining polyaniline by chemical synthesis.

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 anhydride-grafted 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.

ABSTRACT: This paper presents a comparative study involving experimental and numerical behaviors of radar absorbing materials (RAM), based on conducting composites of poly(o-methoxyaniline) (POMA) and carbon black (CB). Samples of POMA/CB in epoxy resin matrix were prepared. First, these samples were experimentally characterized by electric permittivity and magnetic permeability measurements in the frequency range of 8.2 to 12.4 GHz. Afterwards, a linear extrapolation of these electromagnetic parameters until 20 GHz was carried out. These amounts were used as parameters for a set of simulations, developed from numerical implementation of theoretical predictions. The main advantage of the performed simulations is to know the behavior of the POMA/CB/epoxy resin as RAM in a wide range of frequencies (8.2-20 GHz), previously to the experimental work. The validation of the simulations with experimental reflection loss measurements showed a good fit and allowed predicting the material behavior as RAM. The results show that the studied RAM presents good return loss values in different frequencies, for example, -32 dB (~99.95% of absorption) at 14.6 GHz and -18 dB at 19.2 GHz, for samples with 7 and 9 mm-thickness values, respectively. The simulation tool used in this study was adequate to optimize the RAM production, contributing to the reduction of development costs and processing time of this kind of material.

The current research shows the effect of structural and morphological differences of multilayer carbon nanotubes (CNT) on radar absorbing materials (RAM) performance. Two CNT samples, from different manufacturers, had their morphological and structural aspects investigated by XRD, SEM and SEM-FEG analyses. CNT/epoxy resin based nanostructured composites were prepared and characterized by reflectivity measurements in the X-band. SEM results show the formation of agglomerates in the composites and the XRD patterns show structural differences between the two CNT samples. The best RAM performance (-25 dB) was determined for the nanocomposite based on the CNT with the smallest stacking layers (Lc = 26.9 Å) associated to the longest length of nanofilament (10-20 µm). This characteristic can have contributed to the formation of an interconnected network in the composite favoring electrical conductivity and dielectric properties, with the consequent increase of the wave attenuation.

ABSTRACT: This paper presents the preparation and characterization of carbon fiber felt and activated carbon fiber felt from textile polyacrylonitrile fiber. Carbon fibers are usually related to aircraft manufacturing or high mechanical purposes. Activated carbon fibers are known as excellent adsorbent materials. Despite all advantages, carbon fiber and activated carbon fiber are expensive materials because of their raw material cost. On the other hand, in this study, carbon fiber felt and activated carbon fiber felt were produced from textile polyacrylonitrile fiber, which is cheaper than their precursor, polyacrylonitrile fiber, and can be converted into carbon fiber felt and activated material with high micropore content and surface area. This research describes the transformation of textile polyacrylonitrile fiber in its oxidized form. After that, the oxidized material was transformed in felt and, in the sequence, converted into carbon fiber felt and activated carbon felt. The carbon fiber felt and activated carbon fiber felt were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscope. N2 isotherms were performed to qualify the material obtained for further electrochemical applications. The main result was the conversion dynamics of textile polyacrilonitrile fiber into carbon fiber in felt form and activated carbon fiber in felt with high surface area and high micropores content.

Abstract This work shows the fractographic study of fractured surfaces resulted from tensile tests of thermoplastic composites based on poly(propylene-co-ethylene) (PP-PE) and modified PP-PE copolymers reinforced with continuous carbon fibers (CF). The PP-PE matrix was modified with two agents called AM1 (based on maleic anhydride) and AM2 (containing an elastomeric agent), respectively. Three different laminates - CF/PP-PE, CF/PP-PE(AM1) and CF/PP-PE(AM2) - were manufactured. The best tensile strength and elastic modulus results were determined for the CF/PP-PE(AM1) laminate (507.6 ± 11.8 MPa and 54.7 ± 2.4 GPa, respectively). These results show that the AM1 agent contributed to increase the physicochemical interaction between the CF and the PP-PE matrix. This condition provided a better loading transfer from matrix to the reinforcement. Scanning electron microscopy analyses of the fracture surfaces show the fractographic aspects of the samples and allow evaluating the fiber/matrix-interfacial adhesion. Poor adhesion is observed for the CF/PP-PE and CF/PP-PE(AM2) laminates with the presence of fiber impressions on the polymer rich regions and fiber surfaces totally unprotected of polymer matrix. On the other side, a more consistent adhesion is observed for the CF/PP-PE(AM1) laminate. This result is in agreement with the tensile test data and show the presence of a good interaction between the laminate constituents. The correlation of the mechanical and fractographic results with the curves of complex viscosity versus temperature of the studied polymer matrices shows that the matrix viscosity did not affect the wettability of the reinforcement.