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 study.

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 structures.

Resumo: Blendas imiscíveis de poliamida 6 e polietileno de baixa densidade foram preparadas com e sem a presença de polietileno enxertado com anidrido maleico como compatibilizante. Montmorilonita organofílica foi incorporada nas blendas por intercalação do fundido. Análises morfológicas e estruturais apresentaram boa dispersão da argila, com a obtenção de estruturas intercaladas e esfoliadas. A separação de fases foi observada nas amostras, e tanto o compatibilizante como a argila causaram redução no tamanho dos domínios. Esta estrutura proporcionou uma melhora significativa nas propriedades mecânicas das blendas, revelando o efeito de reforço causado pela argila. O módulo elástico e a tensão máxima aumentaram em até 300% e 100%, respectivamente. O efeito da compatibilização da argila foi positivo. Pelas análises de DSC pode-se observar o surgimento de um pico na região de fusão da PA6 atribuído à formação de uma nova fase cristalina devido à presença de argila. Palavras-chave: Nanocompósitos, blendas, montmorilonita, polietileno, poliamida. The Effect of Organophilic Montmorillonite on Compatibilization, Morphology and Mechanical and Thermal Properties of PA6/ LDPE BlendsAbstract: Immiscible blends of polyamide 6 and low density polyethylene were prepared with and without maleic anhydride grafted polyethylene used as a compatibilizer. Organophilic montmorillonite was incorporated in the blends by melt intercalation. Morphological and structural analysis showed good clay dispersion with partially exfoliated and intercalated structures. Phase separation was observed and domains size reduction was induced by the clay and the compatibilizer. Improvement on mechanical properties of compounds was observed, showing the reinforcing effect caused by the clay. Elastic modulus and tensile strength have increased up to 300% and 100%, respectively. The clay showed a positive effect on compatibilization. DSC analysis revealed a new melting peak for PA6 assigned to a new crystalline phase due the clay effect.

AesumoO 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. Palavras-chave: compósitos poliméricos, condutividade elétrica, modelos de percolação. AbstractThis 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 matrices.Keywords: polymer composites, electrical conductivity, percolation models. IntroduçãoA incorporação de partículas eletricamente condutoras em uma matriz isolante polimérica é um exemplo importante da modificação de materiais em áreas até então restrita aos metais, tais como, piezo elétricos [1] , adesivos condutivos [2] , roupas e artigos antiestáticos [3] , blindagem eletromagnética [4] e sensores químicos [5] . A esta classe de materiais é dada a denominação de compósitos condutores poliméricos que apresentam muitas vantagens em comparação aos metais, como por exemplo, resistência à corrosão, menor densidade, processabilidade e custo [6] .A adição de cargas eletricamente condutoras, tais como, partículas metálicas [7][8][9] , nanofolhas de grafite [10][11][12] , negro de fumo (NF) [13,14] e nanotubos de carbono (NTC) [15][16][17][18] em uma resina polimérica isolante tem sido o principal recurso para a obtenção de compósitos condutores. Entre estas cargas destacam-se os NTC por seu potencial na obtenção de sistemas nanoestruturados altamente condutores com excelentes propriedades mecânicas [17,18] . A principal questão sobre os nanocompósitos poliméricos condutores está relacionada com a variação da condutividade em função da concentração das partículas condutoras, onde se observa existir uma concentração crítica a partir da qual ocorre um aumento na condutividade do sistema. Este fenômeno pode ser explicado pela teoria da percolação.Vários modelos matemáticos foram desenvolvidos para descrever o fenômeno de percolação e uma revisão abrangente foi feita por Lux 1993 [19] , considerando fatores estruturais micrométricos dos sistemas. Desde então, estes modelos continuam a ser aplicados e discutidos. Mais recentemente, destaca-se a importância de novos materiais obtidos a partir de cargas cujas dimensões são nanométricas.Bauhofer e Kovacs [20] ...

The present study investigated the effects of the mixture of multiwalled carbon nanotubes (MWCNT) and carbon black (CB) on the electrical and dispersion properties of nanocomposites of PMMA polymerized in situ. These systems are named as mixed-carbon-filler filled systems (MCFFS). The electrical conductivity was measured by the four point probe and the dispersion was analyzed by High Resolution Transmission Electron Microscopy (HR-TEM). It has been shown that the addition of MWCNT and CB in PMMA promoted the electrical conductivity of the composite as a percolation critical concentration is reached. The percolation threshold values were 0.2 vol. (%) for MWCNT and 1.5 vol. (%) for CB, showing that this difference for the two fillers was associated with their geometric shapes, aspect ratios and dispersion characteristics. In addition, MCFFS of MWCNT and CB, varying the concentration of each filler were also prepared. For these systems it was applied the Sun model in order to calculate the theoretical values and compare them to the experimental data. It was observed the synergic effect regarding to the electrical percolation threshold concentration. The MCFFS showed lower critical concentrations (considering the sum of each single filler concentration, MWCNT and CB) and similar conductivities as compared to the single fillers. Despite the presence of aggregates, the microscopy analysis showed that both fillers were well dispersed in the polymer matrix, although the dispersion characteristics of the MWCNT were more effective than CB. In the MCFFS the MWCNT act as filaments linking clusters of the CB, what can explain the synergic effect observed for the lower percolation threshold concentration. 978-1-4799-5622-7/$31.00 ©2014 IEEE