Resumo: Compósitos de borracha natural (Hevea brasiliensis)-BN/polianilina -PANI, com diferentes composições foram obtidos através da polimerização por emulsão do monômero anilina na presença da BN e do ácido dodecilbenzeno sulfô-nico (DBSA). Filmes finos e homogêneos foram obtidos por prensagem a quente. Os compósitos foram caracterizados por condutividade elétrica, FTIR, UV-vis-NIR, DSC e difração de raios X. Compósito com condutividade elétrica cerca de 14 ordens de grandeza maior que a BN foi obtido. Este alto valor de condutividade é atribuído à formação da PANI no estado dopado no compósito, que foi verificado através das técnicas de UV-vis-NIR e FTIR. Os resultados obtidos com a técnica de DSC e difratometria de raios X indicaram que os polímeros são imiscíveis e que a presença da borracha não altera significantemente a fase cristalina da PANI-DBSA no compósito.Palavras-chave: Polimerização por emulsão, borracha natural, polianilina. Composites of Natural Rubber with PolyanilineAbstract: In this work composites with different compositions were obtained from natural rubber (Hevea brasiliensis) (NR) and polyaniline (PANI) using the emulsion polymerization of aniline in the presence of NR and dodecylbenzenesulfonic acid (DBSA). The samples in film form were obtained by pressing the precipitate at 100 °C for 5 minutes. The composites were characterized by electrical conductivity, Fourier-transform infrared spectroscopy (FTIR), UV-vis-NIR spectroscopy, differential scanning calorimetry (DSC) and X ray diffraction. Composites with electrical conductivity about 14 orders of magnitude higher than NR were obtained. The UV-vis-NIR and FTIR spectra showed that PANI-DBSA was formed in the composites, thus making it responsible for their high conductivity. The DSC thermograms indicated that the two polymers are immiscible and X ray diffraction evidenced that NB does not considerably affect PANI-DBSA crystalline phase in the composite.Keywords: Emulsion polymerization, natural rubber, polyaniline. IntroduçãoOs polímeros intrinsecamente condutores possuem grande potencial para aplicações tecnológicas, devido principalmente a suas propriedades elétricas e óticas. Dentre esses polímeros condutores, destaca-se a polianilina-PANI devido a sua estabilidade química no estado dopado em condições ambientais e também por ser facilmente sintetizada quimicamente [1] . Entretanto, uma das limitações no uso da polianilina tem sido sua processabilidade apresentando baixa solubilidade e infusibilidade. Dentro deste contexto, blendas e compósitos com polímeros convencionais têm atraído muita atenção, uma vez que estes possibilitam a combinação das excelentes propriedades mecânicas e a alta processabilidade, com a condutividade elétrica da polianilina, aumentando o potencial tecnológico destes materiais. A polimerização via emulsão da anilina na presença de um outro polímero em solução [2][3][4][5] , tem sido uma alternativa viável. A vantagem deste método é que ele fornece uma grande quantidade de material que pode ser processado po...
Thermal-oxidative degradation behaviours of raw natural rubber (NR) have been investigated by using thermogravimetry analysis in inert and oxidative atmospheres and the plasticity retention index (PRI). The activation energy E a , was calculated using Horowitz-Metzger and Coats-Redfern methods and compared with PRI. The E a values obtained by each method were in good agreement with each other. The June samples are the least stable rubbers among the studied ones, whereas February samples exhibited the highest values of activation energy, therefore in agreement with the PRI behaviour, which indicates that the thermo-oxidative stability of the June samples are the poorest during the thermo-oxidative degradation reaction. Natural rubber is a product of biological origin, and thus these variations in the values of thermal behaviour and PRI might be related to the genetic differences and alterations of climatic conditions that act directly on the synthesis of non-rubber constituents, which are generally reflected in latex and rubber properties.
This study was undertaken over a 10month period under environmental conditions within the state of Mato Grosso, Brazil, to evaluate the causes of variation in the technological and thermal properties of raw natural rubber (NR) from different clones of Hevea brasiliensis (GT 1, PR 255, FX 3864, and RRIM 600). These clones were chosen to represent good clones available in Brazil. The technological properties of raw NR were evaluated in terms of their dry rubber content (DRC), Wallace plasticity, plasticity retention index (PRI), and Mooney viscosity. The thermal performance was evaluated with the thermogravimetry (TG)/differential thermogravimetry (DTG) technique. There were significant variations (p < 0.01 and p < 0.05) between clones and tappings for all technological properties, except for the percentage DRC among the clones. Of the clones studied, clone PR 255 presented the highest sensitivity to thermooxidation, as measured by its PRI value. The clone type and period of the year did not significantly influence the thermal behavior (TG/DTG under a nitrogen atmosphere) among the four clones evaluated.
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