Modification of thermal and rheological behavior of asphalt binder by the addition of an ethylene-methyl acrylate-glycidyl methacrylate terpolymer and polyphosphoric acid

This study evaluated the modification effects of adding ethylene-methyl acrylate-glycidyl methacrylate terpolymer (EMGMA) in the presence of polyphosphoric acid (PPA) to an asphalt binder graded as 50/70 (0.1mm) in the Brazilian penetration grade specification (AC 50/70). The EMGMA terpolymer has been presented as a new alternative to modify asphalt binders properties, as scientific literature is scarce on its usage in this context and also on the role of PPA when used in combination with reactive polymers. The characteristics of the modified binder were analyzed by standard and rheological testing, including Multiple Stress Creep Recovery test (MSCR) and Fourier Transform Infrared Spectroscopy (FTIR) analysis. The MSCR test showed that the modified binder presented lower values of non-recoverable compliances (Jnr) and a higher percent recovery, when compared to the conventional binder. This behavior indicates that addition of EMGMA and PPA in asphalt binders could enhance the resistance to rutting of asphalt mixtures. The statistical evaluation showed that EMGMA had greater influence on the studied properties of Jnr (0.1kPa), MSCR recovery, softening point and elastic recovery at 25°C and that the PPA had also significant influence on these properties. FTIR analysis showed that chemical reactions occurred between the asphalt binder and EMGMA, forming a three-dimensional polymeric network, which promotes improved characteristics274298308sem informaçãosem informaçã

Compatibilization of recycled polypropylene and recycled poly (ethylene terephthalate) blends with SEBS-g-MA

The compatibilization of recycled PP/PET blend with high and low concentration (20 and 5 phr) of elastomer functionalized by maleic anhydride (SEBS-g-MA) was achieved. Recycled polypropylene from plastic industry and recycled PET from post-consumer bottles was used. PP/PET blends: 80:20 w/w, 50:50 w/w and 20:80 w/w were prepared in an internal mixer for mechanical properties, thermal properties, morphology and rheological properties. SEBS-g-MA promoted compatibilization of the PP/PET blends and improved their properties. With an increasing compatibilization level, the refinement of morphology was observed in the PET rich blend. Compatibilized blends showed negative deviation in the PET glass transition temperature related to neat PET, demonstrating that compatibilization was very successful. PET crystallization was accelerated in the blends due to PP presence that enhanced nucleation. It was found that the 50/50/20 blend showed huge potential for textile fiber application and that of 80/20/20 showed more intermediary properties than neat polymers2818491sem informaçãosem informaçã

Influence of clay surfactants polarity on the crystallization and rheological behavior of nanocomposites of PDLLA

The effect of clay hydrophobicity on the cold crystallization and rheological properties of nanocomposites of poly(D,L-lactic acid) (PDLLA) was investigated. Crystallization was evaluated by DSC for isothermal and non-isothermal conditions. The clay modified with a hydrophilic surfactant acts as a nucleating agent, while the clay modified with a hydrophobic surfactant acts in an opposite way. The Avrami and Ozawa parameters showed a three-dimensional spherulitic growth for all samples and the activation energy increased for the hydrophobic clay and decrease for the hydrophilic one. The equilibrium melting point for the PDLLA was found at 161ºC, being slightly altered as function of the surfactant polarity. The rheological behavior was investigated in terms of Isothermal Flow-Induced Crystallization and Structural Recovery. The hydrophobic clay showed to reduce the mobility of chains and retard the chain relaxation, which is attributed to the formation of a network, while the hydrophilic clay increased the chain mobility216FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2011/14250-3; 2012/00227-

Mechanical recycling simulation of polylactide using a chain extender

This work studied the commercial chain extender effectiveness on the mechanical recycling simulation of a pristine PLA using a single‐screw extruder. We processed the material by two extrusion cycles to simulate a recycling process. In the second extrusion, part of the material was processed with chain extender and we evaluated its molecular weight, thermal degradation, melt flow index (MFI), thermal transitions, and mechanical properties. The molecular weight for the extruded neat PLA decreased and the MFI and crystallinity degree increased while the mechanical properties worsened. The onset thermal degradation occurred at lower temperature for the processed material. With the introduction of the chain extender, there was a recovery of properties with the increase in the polymer molecular weight, decrease in the MFI and crystallinity degree, and an improvement in both thermal stability and mechanical properties in relation to recycled PLA without this component37620532060COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPsem informação2014/09883‐

Assessment of percolation threshold simulation for individual and hybrid nanocomposites of carbon nanotubes and carbon black

Modeling electrical conductivity of polymer composites with conductive fillers has great applicability to predict conductive materials behavior. In this study, the electrical behavior of simple and hybrid systems prepared from Carbon Black (CB) and Carbon Nanotubes (CNT) was studied. There have been few advances reported in the literature regarding the modeling of hybrid systems, which motivated the development of this study. More specifically, a program was developed with the intention to describe the electric percolation threshold and the effect of synergism between the conductive fillers. Simulation was performed using the Monte Carlo method and Fortran programming language, considering concentration and geometry of conductive fillers to the system in two dimensions. Finally, simulation results were compared with the experimental results and this method proved to be effective in predicting the systems percolation threshold, being an important contribution to predict material behavior, which allows reducing the number of samples to be prepared in an experimental study20616381649CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQsem informaçã

Percolation electrical models applied to conductive polymers composites

O presente artigo apresenta a aplicação e adequação dos modelos de percolação elétrica em trabalhos experimentais e teóricos da literatura para compósitos poliméricos condutores. Foi realizado um levantamento das publicações referentes aos modelos estudados para os diferentes tipos de cargas condutoras mais aplicadas na preparação destes compósitos, tais como pós metálicos, grafite, negro de fumo, nanofibras e nanotubos de carbono. A discussão está apresentada quanto à adequação dos modelos ao comportamento dos compósitos na influência das cargas nas propriedades elétricas de matrizes poliméricas27especial113sem informaçãoThis paper presents the application and adjustment of electrical percolation models in conductive polymer composites. Different models have been proposed for different types of conductive fillers applied in composites preparation, such as metal powders, graphite, black carbon, carbon nanotubes and nanofibers. The discussion was carried out considering the consistency of the model on the behavior of these fillers and their influence on the electrical properties of polymer matricessem informaçã

Single and hybrid organoclay-filled PLA nanocomposites: mechanical properties, viscoelastic behavior and fracture toughening mechanism

Poly (lactic acid) (PLA) nanocomposites based on single and hybrid organic-modified montmorillonites were previously studied in terms of their morphologi-cal, thermal and fire performance. As surfactants of the organoclays influenced thecompatibility between the nanofillers and PLA with different degrees of clay plate-lets dispersion, the present work investigated the effect of these features in themechanical properties of PLA nanocomposites. PLA nanocomposites specimenswere analyzed by dynamic-mechanical-thermal analysis, which pointed outchanges in the viscoelastic behavior of the materials by the incorporation of theorganoclays, namely the increase of the storage modulus due to polymerchains movements rest riction and reinfor cement effects associated with the disper-sion of the nanofillers. Flexural and impact testing showed that hybridorganomontmorillonites containing ester ammonium and ethoxylated amineimproved PLA's ductility, toughness and impact resistance. This behavior wasexplained by the high level of compatibility and interaction between the surfactantsand PLA chains due to the polar groups in their structures. These organoclays cau-sed a transition on PLA's fracture from brittle to ductile in a way that the toughen-ing mechanism was explained by crazing and multi-shear banding induced by theplasticized interfacial region around these organoclaysPostprint (author's final draft

Surveillance of Aedes aegypti populations in the city of Praia, Cape Verde: Zika virus infection, insecticide resistance and genetic diversity.

BACKGROUND: Aedes spp. are responsible for the transmission of many arboviruses, which contribute to rising human morbidity and mortality worldwide. The Aedes aegypti mosquito is a main vector for chikungunya, dengue and yellow fever infections, whose incidence have been increasing and distribution expanding. This vector has also driven the emergence of the Zika virus (ZIKV), first reported in Africa which spread rapidly to Asia and more recently across the Americas. During the outbreak in the Americas, Cape Verde became the first African country declaring a Zika epidemic, with confirmed cases of microcephaly. Here we investigate the prevalence of ZIKV and dengue (DENV) infected Ae. aegypti mosquitoes in the weeks following the outbreak in Cape Verde, and the presence of insecticide resistance in the circulating vector population. Genetic diversity in the mosquito population was also analysed. METHODS: From August to October 2016, 816 Ae. aegypti mosquitoes were collected in several locations across Praia, Cape Verde, the major hot spot of reported ZIKV cases in the country. All mosquitoes were screened by reverse transcription PCR for ZIKV and DENV, and a subset (n = 220) were screened for knockdown insecticide resistance associated mutations in the voltage gated sodium channel (VGSC) gene by capillary sequencing. The mitochondrial NADH dehydrogenase subunit 4 (nad4) gene was sequenced in 100 mosquitoes. These data were compared to 977 global sequences in a haplotype network and a phylogenetic tree analysis. RESULTS: Two Ae. aegypti mosquitoes were ZIKV positive (0.25%). There were no SNP mutations found in the VGSC gene associated with insecticide resistance. Analysis of the nad4 gene revealed 11 haplotypes in the Cape Verdean samples, with 5 being singletons. Seven haplotypes were exclusive to Cape Verde. Several of the remaining haplotypes were frequent in the global dataset, being present in several countries (including Cape Verde) across five different continents. The most common haplotype in Cape Verde (50.6 %) was also found in Africa and South America. CONCLUSIONS: There was low-level Zika virus circulation in mosquitoes from Praia shortly after the outbreak. The Ae. aegypti population did not appear to have the kdr mutations associated with pyrethroid resistance. Furthermore, haplotype and phylogenetic analyses revealed that Cape Verde Ae. aegypti mosquitoes are most closely related to those from other countries in Africa and South America

Influence of processing and content of vinyl acetate on the properties of Eva/organophilic montmorillonite nanocomposites

O copolímero Etileno Acetato de Vinila (EVA) é uma poliolefina utilizada principalmente em filmes para embalagens, onde a sua flexibilidade, tenacidade, elasticidade e transparência são atributos desejáveis. As propriedades mecânicas, térmicas e de barreira do EVA podem ser melhoradas pela incorporação de cargas inorgânicas. O EVA apresenta polaridade variável de acordo com o teor de Acetato de Vinila, o que promove a viabilidade para obtenção de nanocompósitos com argilas organicamente modificadas, tornando desnecessária a adição de agentes compatibilizantes. Neste trabalho foram preparados nanocompósitos de EVA e montmorilonita organofílica comercial pelo método de intercalação do fundido em um reômetro de torque, com rotores tipo roller, a 150°C durante 10minutos, com monitoramento do torque em função do tempo. A fim de investigar a influência da polaridade do EVA, da concentração da argila e das condições de processamento nas características dos nanocompósitos, variou-se a concentração de Acetato de Vinila (19% e 28%), o teor de argila (2% e 5%) e a velocidade de rotores (60 rpm e 100 rpm). Foram avaliadas a estrutura da argila, a estabilidade térmica e as propriedades mecânicas e de barreira dos nanocompósitos, mediante as técnicas de difração de raios X, análise termogravimétrica, ensaio de tração e análises de taxa de permeabilidade ao oxigênio e ao vapor d’água. A partir dos dados de permeabilidade foi aplicado o modelo de Nielsen para avaliar o grau de esfoliação da argila. Dentre os principais resultados com o planejamento fatorial destacam-se: (a) o aumento da polaridade do EVA aumentou a permeabilidade ao oxigênio e ao vapor d’água dos materiais; (b) o teor de argila não modificou a estabilidade térmica dos nanocompósitos e a estrutura da argila; (c) o aumento da concentração da argila aumentou o módulo elástico, reduziu a deformação de ruptura e reduziu significativamente o coeficiente de permeabilidade ao oxigênio e ao vapor d’água; (d) o fator rotação não implicou em alterações significativas em nenhuma das respostas avaliadas245579586sem informaçãoThe copolymer Ethylene Vinyl Acetate (EVA) is a polyolefin used mainly in packaging films, where its flexibility, toughness, elasticity and transparency are desirable attributes. The mechanical, thermal and barrier properties of EVA can be improved by the incorporation of inorganic fillers. Its polarity varies according to the content of Vinyl Acetate, which allows for nanocomposites to be obtained with organically modified clay, with no need to add compatibilizing agents. In this work nanocomposites of EVA and commercial organophilic montmorillonite were prepared by melt intercalation in a torque rheometer with rotors roller type, at 150°C for 10 minutes, monitoring the torque versus time. The concentration of Vinyl Acetate (19% and 28%), clay content (2% to 5%) and the rotors rotation (60 rpm to 100 rpm) were varied in order to investigate their influence on the characteristics of the nanocomposites. The clay structure, thermal stability, mechanical and barrier properties of the nanocomposites were evaluated by X-ray diffraction, thermal analysis, tensile testing, oxygen and water vapor transmission rates. Based on the permeability data, Nielsen´s model was applied to assess the degree of clay exfoliation. The main results obtained from the factorial design are: (a) increasing the polarity of EVA led to an increase in the permeability to oxygen and water vapor of the material, (b) the clay content did not change the clay structure or the thermal stability of the nanocomposites, (c) increasing the concentration of clay increased the elastic modulus, decreased the elongation at break and significantly reduced the coefficient of permeability for oxygen and water vapor, (d) the rotation factor did not result in significant changes in any of the evaluated responsessem informaçã

Epidemiología básica. Material docente para prácticas en ciencias de la salud

Material docente teórico práctico para apoyar la enseñanza de la epidemiología. Consta de 4 unidades, cada una de ellas con una introducción teórica y unos ejercicios basados en artículos publicados en inglés en revistas científicas