Abstract Tricomponent epoxy-matrix nanocomposites were prepared by airbrushing multiwalled carbon nanotubes (MWCNT) on glass fiber fabric (GF), aiming to establish a scalable route to produce electromagnetic interference (EMI) materials. The MWCNT deposition on GF by airbrushing was evaluated by scanning electron microscopy (SEM), showing a very reasonable dispersion even at high MWCNT concentrations. Electrical conductivity measurements have shown a maximum of 1.2x10-3 S/cm for GF with 3.4 wt% MWCNT. Electromagnetic shielding response for GF airbrushed with MWCNT and epoxy-matrix nanocomposites were analyzed considering reflection, absorption and transmission mechanisms and have shown an increasing trend as the MWCNT content increases, reaching the best result of 7.6 dB of shielding effectiveness (SE) in X-band spectra for the composite with 3.4 wt% MWCNT. The results showed that the airbrushing process can be a promising and easy route for manufacturing of MWCNT/GF/epoxy nanocomposites.

ABSTRACT In this work, the role of the degree of acetalization of polyvinylbutyral (PVB) on the dynamic mechanical properties of PVB nanocomposites was evaluated. Nanocomposites reinforced with carbon nanoparticles (pristine or oxidized multiwalled carbon nanotubes, graphene oxide and graphene nanoplatelets) were prepared by in situ addition during the synthesis of PVB from polyvinyl alcohol. It was found that the presence of nanoreinforcements during the synthesis considerably alters the degree of acetalization (AD) of PVB (ca. 65 mol% for the neat polymer), which values ranged from 50 to 77 mol%. Dynamic mechanical analyses were used to calculate the storage modulus and other parameters such as: factor C, degree of entanglement and adhesion factor, which were correlated with scanning electron microscopy images. There was a tendency to decrease AD with the increase in the degree of oxidation of the nanoreinforcements, however this contributed to a better dispersion and adhesion of these to the polymer matrix and, consequently, altered positively the nanocomposite properties.

ABSTRACT In this work, polyvinyl butyral (PVB) nanocomposites reinforced with 0.5 to 2.5 wt% of graphene oxide (GO) were synthesized via ‘in situ’ polymerization. PVB was obtained by condensation of hydroxyl groups of polyvinyl alcohol (PVA) with butyraldehyde (BU) Thermogravimetric analyzes (TGA) showed the increase in the thermal conductivity of the nanocomposites compared to PVB. FTIR results showed the conversion of PVA to PVB, but no changes in the spectrum were observed for nanocomposites. Nuclear magnetic resonance spectroscopy (1H NMR) shows a change in the degree of acetalization of PVB with the presence of the nanoparticles. When the increase in the concentration of GO, a decrease in the degree of acetalization of PVB is observed. The differential scanning calorimetry (DSC), show a decrease in Tg values, probably caused by the change of degree of acetalization. The results of the Raman spectroscopy analysis show upshift in the G band up to 20 cm-1, associated with the presence of van der Walls interaction between the GO and PVB and the mechanical compression phenomena of the GO nanoparticles are compressed in the ‘bulk’ of polymer. Thus, it was observed that the ‘in situ’ polymerization process contributed to the formation of a colloid between GO and water used as solvent in the synthesis. The formation of this colloid helped to improve the interfacial interaction between GO and PVB. However, the presence of GO also contributed to change the degree of acetalization of PVB, as it decreased the condensation of some hydroxyl groups of the precursor PVA degree of acetalization.

RESUMO O Grafite natural é uma fonte barata e abundante para obter nanofolhas de grafeno. O método mais eficiente para a produção em grande escala é o método químico, que se baseia na oxidação de grafite natural. Este artigo relata a síntese e caracterização de grafeno obtido pelo método Hummers com algumas modificações. Os resultados indicam um elevado grau de oxidação do grafite, provando que o processo foi eficiente. As análises de microscopia eletrônica de varredura de emissão de campo (FEG), microscopia electrônica de transmissão (TEM), espectroscopia Raman, análise termogravimétrica (TGA) e difração de raios-X revelaram que o grafeno produzido apresentou características similares ao grafeno comercial.

ABSTRACT Natural graphite is an inexpensive and abundant source to obtain graphene nanosheets. The most efficient method for large-scale production is the chemical method, which is based on the oxidation of natural graphite. This paper reports the synthesis and characterization of graphene obtained by the Hummers method with some modifications. The results indicate a high degree of graphite oxidation, proving that the process was efficient. Analyses of field emission scanning electron microscopy (FEG), transmission electron microscopy (TEM), Raman spectroscopy, thermogravimetric analysis (TGA) and X-ray diffraction showed that the graphene produced presented characteristics similar to the commercial graphene.

RESUMO Em polímeros autorregeneráveis faz-se uso de cápsulas preenchidas com agentes cicatrizantes, cuja parede rompe em função de estímulo externo, liberando e selando as trincas nos materiais. Assim, esse trabalho teve como objetivo avaliar as possíveis mudanças na morfologia e diâmetro de microcápsulas (MC) de poli(ureia-formaldeído) (PUF) pela variação da concentração de octanol. Medidas de microscopia ótica (MO) e microscopia eletrônica de varredura com efeito de campo (FEGSEM) mostraram que o diâmetro das MC e a rugosidade da parede, associada com a formação de nanocápsulas na emulsão, aumentaram conforme a quantidade de octanol adicionada na síntese aumentou. As curvas termogravimétricas (TG) mostraram que as microcápsulas são mais estáveis termicamente comparadas a trabalhos da literatura. Concluiu-se que o uso do octanol contribui para a obtenção de MC de tamanho mais uniforme e com superfície mais lisa.

ABSTRACT In self-healing polymers, capsules filled with healing agents are used, whose walls rupture as a response to external stimulation, releasing and sealing the cracks in the materials. Thus, this work had as objective to evaluate the possible changes in the morphology and diameter of microcapsules (MC) of poly(urea-formaldehyde) (PUF) by variation of the octanol concentration used in the synthesis. Through the measurements with optical microscopy (OM) and scanning electron microscopy with field effect (FEGSEM), it was verified that the MC diameter and the wall roughness associated with the formation of nanocapsules in the emulsion increased as the amount of octanol added in the synthesis increased. Thermal analysis showed that the microcapsules synthesized this way are more thermally stable compared to those reported in the literature. It was concluded that the use of octanol contributes to obtaining MCs with a more uniform size and smoother surface.

RESUMO Este trabalho tem como objetivo a preparação de mantas compostas por fibras do polímero biodegradável poli(3-hidroxibutirato) -(PHB) por meio da técnica de eletrofiação. Obtiveram-se mantas sob diferentes condições, variando-se o fluxo, a temperatura da solução, a tensão aplicada e a adição de um agente surfactante. O material obtido foi analisado por microscopia eletrônica de varredura (MEV), calorimetria exploratória diferencial (DSC), termogravimetria (TG), difratometria de raios-X (DRX) e viabilidade celular. A caracterização por MEV mostrou que os melhores resultados, apresentando as fibras com diâmetros constantes de 0,77 µm e sem a formação de grãos, foram atingidos nas seguintes condições: concentração da solução de 10% (m/v) em CF/DMF (9/1), fluxo da solução de 5,8 ml/h, tensão de 17 kV e adição de surfactante (dodecilsulfato de sódio, SDS). Os resultados mostraram que as variações de vazão, tensão e a adição de surfactante não influenciam muito o diâmetro médio das fibras, enquanto o aumento da temperatura diminui este parâmetro. No entanto, a adição de um agente surfactante deixa a manta mais densa e com poros interconectados, além de permitir a proliferação celular, sendo então indicada para produção de mantas para uso como arcabouço.

ABSTRACT This work aims the preparing of mats composed of poly (3-hydroxybutyrate) -(PHB) biodegradable polymeric fibers, using the electrospinning technique. Mats were obtained under different conditions: changing the flow and temperature of the solution, tension and the addition of a surfactant to the solution. The obtained material was analyzed by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetry (TG), X ray diffractometry (XRD) and cell viability. The characterization by SEM showed that the best results, presenting fibers with constant diameters of 0.77 μm and without beads formation, were reached under the following conditions: concentration of 10% (m / v) solution in CF / DMF (9/1), solution flow of 5.8 ml/h, 17 kV and addition of surfactant (sodium dodecylsulfate, SDS). The results showed that the variation of the flow, tension and surfactant did not influence the average diameter of the fibers, but the increase of the temperature decreases this parameter. Moreover, the addition of a surfactant increases the density of the blankets and interconnect the pores, allowing cellular proliferation, and, thus. it is indicated for use as scaffolds.

ABSTRACT Epoxy resin is one of the most important polymeric matrixes for diverse uses, such as aeronautical, mobile, electronics and others. Providing a material capable of self-healing microcracks will allow it to have a more reliable and longer use. In order to study this new property of self-healing to an epoxy resin, a Differential Scanning Calorimetry (DSC) study was carried out to measure physical chemical properties such as activation energy, enthalpy of polymerization, order of reaction and pre-exponential factor based on an Arrhenius equation modelling. The materials used are diglycidyl ether of bisphenol A (DGBA) as the core material, triethylenetetramine (TETA) and an aminated polydimethylsiloxane (ADM), as curing agent and poly(urea-formaldehyde) (PUF) as microcapsule wall. Tests were done by dynamic and isothermal DSC of systems containing the resin and microencapsulated curing agent and also the resin with the free curing agent. The results showed the necessity of heating for the cure and the self-healing to be initiated.

This study aims the synthesis of copolymers of poly (l-lactic acid) and polycaprolactone by ring opening polymerization. The reactions between l-lactide (LLA) and ε-caprolactone (CL) monomers, in 100/0, 95/5, 90/10 and 80/20 LLA/CL mass ratios, were conducted in refluxing toluene, using Stannous octoate as iniciator, methanol as co-iniciator and inert atmosphere (N2). The reaction medium was maintained under stirring at 120 °C for 24 hours. The samples were characterized by carbon-13 and proton nuclear magnetic resonance (C13-NMR and H1-NMR), and gel permeation chromatography (GPC). Monomers were characterized by thermogravimetry (TG). Copolymers were formed only in samples containing 20 wt% ε-caprolactone. NMR spectra of the other samples showed no evidence of CL units. This fact may be associated with the low-temperature volatilization of monomers. The GPC analysis showed that the increase of CL concentration decrease the molecular weight of copolymers.

The aim of this work was the synthesis of hybrid organic-inorganic epoxy-copolysilsesquioxane nanocomposites reinforced with multi-walled carbon nanotubes (MWCNT). Copolysilsesquioxanes oligomers from 3-aminopropyltriethoxysilane (APTES) and phenyltriethoxysilane (PTES) precursors have been synthesized by a sol-gel process and chemically incorporated to an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA). MWCNT (0.25 wt%) was added to the hybrid matrixes with different degrees of condensation. Fourier transform infrared analysis showed that a high degree of cure was achieved, suggesting that the MWCNT did not affect the curing reaction of the hybrid matrixes. Hybrid nanocomposites obtained by sonication technique presented improvement on thermal stability, exhibiting onset degradation temperatures higher than 340 °C under N2. Tensile tests presented Young’s modulus and maximum stress values up to 2.9 GPa and 47 MPa, respectively, indicating that the new hybrid epoxy/MWCNT nanocomposites show a moderate enhancement of the mechanical properties in comparison with the neat epoxy resin.

The aim of this study was to evaluate the effect of different peak wavelengths (450nm, 468nm and 490nm) of experimental LEDs on hardness, elastic modulus, degree of conversion and temperature rise of a microhybrid resin composite – Venus® (Heraeus Kulzer). Hardness and elastic modulus were determined by nanoindentation technique (n=5), degree of conversion was measured by FTIR (n=5) and temperature rise was measured with a thermistor (n=30). Data were submitted to ANOVA and multiple comparisons tests (α=0.05). Mechanical properties and degree of conversion (p<0.001) were superior on the top surfaces of the specimens. 468nm showed the highest mechanical properties values. There was no statistical difference in the degree of conversion (p=0.51) and in temperature rise (p=0.06) among all LEDs. Hardness and elastic modulus were influenced by LED´s wavelength, whereas degree of conversion and temperature rise were not influenced.

As microcápsulas que contêm agentes de cura têm sido utilizadas para desenvolver compósitos poliméricos com propriedades auto regenerativas. Este trabalho tem como objetivo a produção e caracterização de microcápsulas de poli (uréia-formaldeído), PUF, contendo diciclopentadieno, que satisfaz os requisitos para um material de auto cura para resinas epoxídicas. Uma série de microcápsulas de PUF foram sintetizadas utilizando diferentes parâmetros do processo, incluindo o tipo e concentração de surfactante, o método e a velocidade de agitação. As microcápsulas foram caracterizadas por microscopia eletrônica, análise térmica (DSC, TG) e espectroscopia no infravermelho (FTIR). A distribuição do tamanho e o diâmetro médio das microcápsulas foram determinados por difração a laser. Os resultados mostram que os parâmetros do processo afetam diretamente o tamanho e a morfologia das microcápsulas. Pela seleção da taxa de agitação, foi possível produzir microcápsulas com diâmetros entre 1 e 100 µm.

Microcapsules containing curing agents have been used to develop polymer composites with self-healing properties. This work aims the production and characterization of microcapsules of poly (urea-formaldehyde), PUF, containing dicyclopentadiene, which satisfies the requirements for the self-healing of epoxy resins. A series of PUF microcapsules was synthesized using different process parameters, including the type and concentration of surfactant, and the stirring method and speed. The microcapsules were characterized by scanning electron microscopy, thermal analysis (DSC, TG) and infrared spectroscopy (FTIR). The size distribution and the average diameter was determined in a particle size analyzer by laser diffraction. The results show that the process parameters directly affect the size and morphology of the microcapsules. By the selection of the stirring rate, microcapsules were produced in the diameter range of 1-100 µm.

In this study, the thermal, dynamic-mechanical and tribological behavior of nanocomposites of a photocurable epoxy-acrylate resin and multiwalled carbon nanotubes (MWCNT) are investigated. A route consisting of a combination of sonication, mechanical and magnetic stirring is used to disperse 0.25-0.75 wt. (%) MWCNT into the resin. Two photocuring cycles using 12 hours and 24 hours of UV-A radiation are studied. The storage modulus, the loss modulus and the tan delta are obtained by dynamic mechanical analysis. Thermal stability is investigated by thermogravimetry, morphology by transmission electronic microscopy (TEM) and tribological performance using a pin-on-disk apparatus. The results indicate an increase in stiffness and higher ability to dissipate energy, as well as a shift in the glass transition temperature for the nanocomposites. The addition of nanofillers also decreased friction coefficient and wear rate of the nanocomposites but did not change the observed wear mechanisms.

O grafite é a fonte mais abundante e de baixo custo para obtenção de grafeno. Para sua produção e aplicação em nanocompósitos em escala industrial, o método de redução do óxido de grafite (OG) tem sido o mais utilizado. A oxidação do grafite promove a introdução de grupos funcionais na sua estrutura lamelar que causam o afastamento dos planos cristalinos do grafite, produzindo assim o OG. Sua redução pode ser realizada tanto por métodos químicos quanto térmicos, a qual remove parcialmente os grupos funcionais introduzidos na oxidação, fazendo com que a estrutura grafítica seja também parcialmente reestabelecida. Várias matrizes poliméricas estão sendo utilizadas na produção de nanocompósitos com grafeno, dentre elas as resinas epoxídicas. Um dos desafios é proporcionar a dispersão total do nanoreforço na matriz e promover uma forte adesão interfacial matriz/nanoreforço para se obter melhores propriedades finais. Portanto, o objetivo deste trabalho foi caracterizar as propriedades morfológicas, mecânicas e térmicas de nanocompósitos de matriz epoxídica à base de éter diglicidílico do bisfenol A (DGEBA) com reforços produzidos a partir do grafite natural, sendo estes o grafite sonificado (GS), OG e o OG expandido (OGE) na concentração de 0,1% m/m. O sistema contendo o OGE se mostrou o mais promissor na melhoria das propriedades mecânicas de sistemas com resina epoxídica, uma vez que apresentou um incremento de ~37% na resistência à tração. Não foram observadas alterações significativas na estabilidade térmica dos nanocompósitos, indicando que não se formam redes de percolação na concentração de reforço estudado.

Graphite is the cheapest and the most abundant source to obtain graphene. For its production and application in nanocomposites in industrial scale, reduction of the graphite oxide (GO) has been the most used method lately. Graphite oxidation promotes the insertion of functional groups in its layers which lead to an increase in graphite interlayer distance, producing GO. The GO can be reduced either by chemical or thermal methods, which partially removes the functional groups inserted during oxidation, partially reestablishing the graphitic structure. Several polymer matrices have been utilized to produce graphene nanocomposites, including the epoxy resins. One of the challenges to produce polymer nanocomposites is the total dispersion of the nanofillers into the matrix and a strong matrix/nanofillers interfacial adhesion to obtain enhanced final properties. Therefore, the aim of this work was the characterization of morphological, mechanical and thermal properties of epoxy matrix based on diglycidyl ether of bisphenol-A (DGBEA) nanocomposites with reinforcements produced from natural graphite, such as sonicated graphite (SG), GO and expanded GO (EGO) at the concentrations of 0.1 wt%. The most promising system to enhance mechanical properties of epoxy resin nanocomposites was the EGO system, since it showed an increase of ~37% in tensile strength. The results showed no significant change on thermal stability of the nanocomposites indicating the absence of a percolation network with the amount of reinforcement studied.

Arc discharge is the most practical method for the synthesis of single wall carbon nanotubes (SWCNT). However, the production of SWCNT by this technique has low selectivity and yield, requiring further purification steps. This work is a study of purification of SWCNT by heat treatment in an inert atmosphere followed by supercritical fluid extraction. The raw arc discharge material was first heat-treated at 1250 °C under argon. The nanotubes were further submitted to an extraction process using supercritical CO2 as solvent. A surfactant (tributylphosphate, TBP) and a chelating agent (hexafluoroacetylacetone, HFA) were used together to eliminate metallic impurities from the remaining arc discharge catalysts. Analysis of Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) showed an efficient removal of iron and cobalt (>80%). The purified nanotubes were further analyzed by TGA and Raman spectroscopy.