Study of the compatibilization effect of organoclays in immiscible blends of polyamide 6 and low density polyethylene

Orientador: Ana Rita MoralesDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: O trabalho descreve a obtenção de nanocompósitos de polietileno de baixa densidade, poliamida 6, polietileno enxertado com anidrido maleico e montmorilonita organofilicamente modificada com o objetivo de estudar o efeito de compatibilização da argila organofílica nas blendas de polietileno e poliamida. Os compostos foram preparados pelo método de intercalação do fundido em extrusora dupla-rosca e os corpos de prova, obtidos por injeção, foram caracterizados por análise térmica dinâmico-mecânica, microscopia eletrônica de varredura, difração de raios-X, microscopia eletrônica de transmissão, calorimetria exploratória diferencial, análise termogravimétrica e teste mecânicos de resistência a tração e ao impacto. As análises térmicas revelaram uma ligeira queda da estabilidade térmica associada ao efeito de degradação do modificador encontrado na argila; o aparecimento de um novo pico de fusão nas curvas de DSC dos nanocompósitos foi associado à formação de uma nova fase cristalina na poliamida 6, causado pela presença da argila. As análises morfológicas revelaram uma adequada homogeneidade nos nanocompósitos e uma redução dos tamanhos dos domínios das duas fases da blenda, de forma que nenhum aglomerado foi observado, o que mostra que houve uma boa dispersão da argila na matriz. As análises estruturais confirmaram esta boa dispersão através da microscopia eletrônica de transmissão (MET) e da difração de raios-X (DRX), que revelaram que a argila teve suas camadas parcialmente intercaladas e/ou esfoliadas em todos os nanocompósitos estudados, e que esta estrutura encontrada proporcionou uma melhora significativa nas propriedades mecânicas dos compostosAbstract: This work describes the behavior of nanocomposites of polyamide 6 (PA6), low density polyethylene (LDPE) and an organophilic montmorillonite. The compatibilization effect of the orgalophilic clay was studied with and without the presence of a maleic anhydride grafted polyethylene (PE-g-MA). The nanocomposites were prepared by melt intercalation on a twin screw extruder. The samples were prepared by injection molding, and characterized using scanning electron microscopy (SEM), wide-angle X-diffraction (WAXD), dynamic mechanical analysis (DMA), transmission electron microscopy (TEM) and differential scanning calorimeter (DSC). Mechanical properties as tensile strength and impact strength were also evaluated. The thermal analysis showed a slight decrease in thermal stability that was associated with the effect of degradation of the modifier of the clay; the emergence a new melting peak for the Polyamide 6 associated to a new crystalline phase due the clay nucleation effect. The morphologic analysis showed two phases for all systems but a reduction on the particle dimension due the presence of the clay, with low differences by the use of the compatibilizer. Structural analysis confirmed by transmission electron microscopy (TEM) and X-ray diffraction (XRD), which had its clay layers extensive exfoliated, with some small degree of intercalation nanocomposites at all, and that this structure has provided a significant improvement in mechanical properties of compoundsMestradoCiencia e Tecnologia de MateriaisMestre em Engenharia Químic

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 poliméricas.27especial11

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

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

ATLANTIC EPIPHYTES: a data set of vascular and non-vascular epiphyte plants and lichens from the Atlantic Forest

Epiphytes are hyper-diverse and one of the frequently undervalued life forms in plant surveys and biodiversity inventories. Epiphytes of the Atlantic Forest, one of the most endangered ecosystems in the world, have high endemism and radiated recently in the Pliocene. We aimed to (1) compile an extensive Atlantic Forest data set on vascular, non-vascular plants (including hemiepiphytes), and lichen epiphyte species occurrence and abundance; (2) describe the epiphyte distribution in the Atlantic Forest, in order to indicate future sampling efforts. Our work presents the first epiphyte data set with information on abundance and occurrence of epiphyte phorophyte species. All data compiled here come from three main sources provided by the authors: published sources (comprising peer-reviewed articles, books, and theses), unpublished data, and herbarium data. We compiled a data set composed of 2,095 species, from 89,270 holo/hemiepiphyte records, in the Atlantic Forest of Brazil, Argentina, Paraguay, and Uruguay, recorded from 1824 to early 2018. Most of the records were from qualitative data (occurrence only, 88%), well distributed throughout the Atlantic Forest. For quantitative records, the most common sampling method was individual trees (71%), followed by plot sampling (19%), and transect sampling (10%). Angiosperms (81%) were the most frequently registered group, and Bromeliaceae and Orchidaceae were the families with the greatest number of records (27,272 and 21,945, respectively). Ferns and Lycophytes presented fewer records than Angiosperms, and Polypodiaceae were the most recorded family, and more concentrated in the Southern and Southeastern regions. Data on non-vascular plants and lichens were scarce, with a few disjunct records concentrated in the Northeastern region of the Atlantic Forest. For all non-vascular plant records, Lejeuneaceae, a family of liverworts, was the most recorded family. We hope that our effort to organize scattered epiphyte data help advance the knowledge of epiphyte ecology, as well as our understanding of macroecological and biogeographical patterns in the Atlantic Forest. No copyright restrictions are associated with the data set. Please cite this Ecology Data Paper if the data are used in publication and teaching events. © 2019 The Authors. Ecology © 2019 The Ecological Society of Americ

Catálogo Taxonômico da Fauna do Brasil: setting the baseline knowledge on the animal diversity in Brazil

The limited temporal completeness and taxonomic accuracy of species lists, made available in a traditional manner in scientific publications, has always represented a problem. These lists are invariably limited to a few taxonomic groups and do not represent up-to-date knowledge of all species and classifications. In this context, the Brazilian megadiverse fauna is no exception, and the Catálogo Taxonômico da Fauna do Brasil (CTFB) (http://fauna.jbrj.gov.br/), made public in 2015, represents a database on biodiversity anchored on a list of valid and expertly recognized scientific names of animals in Brazil. The CTFB is updated in near real time by a team of more than 800 specialists. By January 1, 2024, the CTFB compiled 133,691 nominal species, with 125,138 that were considered valid. Most of the valid species were arthropods (82.3%, with more than 102,000 species) and chordates (7.69%, with over 11,000 species). These taxa were followed by a cluster composed of Mollusca (3,567 species), Platyhelminthes (2,292 species), Annelida (1,833 species), and Nematoda (1,447 species). All remaining groups had less than 1,000 species reported in Brazil, with Cnidaria (831 species), Porifera (628 species), Rotifera (606 species), and Bryozoa (520 species) representing those with more than 500 species. Analysis of the CTFB database can facilitate and direct efforts towards the discovery of new species in Brazil, but it is also fundamental in providing the best available list of valid nominal species to users, including those in science, health, conservation efforts, and any initiative involving animals. The importance of the CTFB is evidenced by the elevated number of citations in the scientific literature in diverse areas of biology, law, anthropology, education, forensic science, and veterinary science, among others

Studies of electrical percolation threshold of hybrids polymers nanocomposites of PMMA with carbon nanotubes and carbon black

Orientador: Ana Rita MoralesTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: A modificação de matrizes poliméricas isolantes em semicondutoras ou condutoras pela incorporação de cargas de carbono é amplamente difundida. O Negro de Fumo (NF) é a carga condutora mais utilizada e os Nanotubos de Carbono são considerados uma alternativa pelas suas propriedades diferenciadas. Neste trabalho estudou o comportamento destas cargas em nanocompósitos de PMMA obtidos por polimerização in situ. Para a análise da condutividade elétrica dos materiais resultantes foi considerada a teoria da percolação aplicando-se o modelo do volume excluído, que prevê a ocorrência de uma concentração crítica conhecida como o limiar de percolação. O trabalho foi dividido em etapas. Primeiramente foram estudadas as condições de dispersão e de polimerização para a obtenção dos nanocompósitos, obtendo-se as curvas de percolação da condutividade elétrica dos nanocompósitos e determinando o limiar de percolação para os sistemas com Nanotubos de carbono de paredes múltiplas (NTCPM) e NF de alta estrutura. Considerando-se a hipótese de que a combinação de cargas condutoras com diferentes geometrias pode apresentar efeitos diferentes da soma das cargas individuais, investigou-se o efeito da mistura NTCPM e NF em comparação com nanocompósitos das mesmas cargas individuais. Foram encontrados valores de condutividade próximos ao de semicondutores, e limiares de percolação de quase 8 vezes menor para NTCPM em relação ao NF. Para os sistemas híbridos, ou seja, sistemas de misturas das cargas, o limiar de percolação ocorreu para concentração total abaixo dos valores dos nanocompósitosos com as cargas unitárias, indicando o efeito de sinergismo. Por análise de microscopia eletrônica de transmissão observou-se que, morfologicamente, os NTCPM atuaram como filamentos ligando os agregados de NF, o que pode explicar o efeito observado para a menor concentração necessária para a percolação. A modelagem da condutividade elétrica de compósito polimérico com uma carga condutora é muito importante e pode prever o comportamento condutivo dos materiais. Para os sistemas híbridos pouco tem se avançado com relação à modelagem, e isto motivou a segunda parte deste trabalho, quando se levantou a hipótese de que é possível o desenvolvimento de um programa capaz de simular o limiar de percolação e o efeito de sinergismo, utilizando-se o método de Monte Carlo e programado em linguagem Fortran. A simulação foi feita levando-se em consideração a geometria das cargas condutoras para o sistema em duas dimensões. Este método mostrou-se eficaz na previsão do limiar de percolação dos sistemas híbridos e simples sendo uma importante contribuição para a previsão do comportamento de materiais o que permite a redução da quantidade de amostras a ser preparadas num estudo experimentalAbstract: The insulating polymer matrices modification with conductive carbon fillers is widely known. Carbon black is the most used conductive filler and Carbon Nanotubes are considered an important alternative because of its unique properties. The present work studied these fillers behavior in PMMA nanocomposites obtained by in situ polymerization. The electrical conductivity of the materials was analyzed considering the percolation theory by the excluded-volume model, which predicts the critical concentration known as the percolation threshold. The work was divided into steps. First, the nanocomposites dispersion and polymerization conditions were studied, obtaining the percolation curve of the electrical conductivity and determining the percolation threshold for carbon nanotube multi-walled (MWCNT) and high-structure carbon black (CB) nanocomposites. Aiming the hypothesis that conductive fillers combination with different geometries could provide different effect than the additive one, the present study analyzed the effect of the MWCNT and CB mixture on the electrical and dispersion properties of nanocomposites, comparing with individual fillers nanocomposites. The conductive value founded near the semiconductor and percolation threshold 8 times lower for NTCPM that for NF. Hybrid nanocomposites, the percolation threshold achieved total concentration below the singles fillers nanocomposites, showing the synergism effect. From the Transmission Electronic Microscopy, we could notice that, morphologically, the MWCNT acted as filaments linking clusters of the CB, what can explain the lower concentration required for the percolation threshold. Modeling of the electrical conductivity of carbon-filler-filled polymer composites is very important for predicting the conductive behavior of the materials and for material design. There are only few works related to modeling hybrid systems and this motivated the second part of this study considering the hypothesis that could be possible the prediction of the percolation threshold and the synergism effect by a simulator based on the Monte Carlo method programed in FORTRAN. This method demonstrated to be efficient in predicting the hybrid fillers and single fillers systems percolation, which can allow a decrease in the number of samples in an experimental studyDoutoradoCiencia e Tecnologia de MateriaisDoutor em Engenharia Químic

Modelos de percolação elétrica aplicados para compósitos poliméricos condutores

Resumo 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 poliméricas

Electrical percolation, morphological and dispersion properties of MWCNT/PMMA nanocomposites

Nanocomposites of poly (methyl methacrylate) (PMMA) and carbon nanotubes have a high potential for applications where conductivity and low specific weight are required. This piece of work concerns investigations of the level of dispersion and morphology on the electrical properties of in situ polymerized nanocomposites in different concentrations of multi-walled carbon nanotubes (MWCNT) in a PMMA matrix. The electrical conductivity was measured by the four point probe. The morphology and dispersion was analyzed by Transmission Electron Microscopy (TEM) and Small Angle X-ray Scattering (SAXS). The correlation between electrical conductivity and the MWCNT amount, presented a typical percolation behavior, whose electrical percolation threshold determined by power law relationship was 0.2 vol. (%) The exponent t from the percolation power law indicated the formation of a 3D network of randomly arranged MWCNT. SAXS detected that the structures are intermediate to disks or spheres indicating fractal geometry for the MWCNT aggregates instead of isolated rods. HR-TEM images allowed us to observe the MWCNT individually dispersed into the matrix, revealing their distribution without preferential space orientation and absence of significant damage to the walls. The combined results of SAXS and HR-TEM suggest that MWCNT into the polymeric matrix might present interconnected aggregates and some dispersed single structures171127132CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQsem informaçã