CompÃsitos de Poli (Metacrilato de Metila) / nanofolhas de grafite: preparaÃÃo, caracterizaÃÃo e efeitos radiolÃticos / Nanocomposites of Poly (Methyl Metacrylate)/Graphite nanosheets: Preparation, Characterization and Radiolytic Effects

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Nowadays there is a great interest in the preparation of PMMA/graphite composites, el ther in graphite powder or in nanosheet forms. They are used mainly in the production of conducting composites. In this work graphite nanosheets were obtained by chemical intercalation using H2SO4 and HNO3. After this treatment, the intercalated graphite (GIC) is put into a microwave oven where it expands 75 times, so being called expanded graphite (EG). Next, it is dispersed a 70% alcohol solution, then, it is washed and dried, produting to graphite nanosheets. Two kinds of composites were prepared: PMMA/graphite powder and PMMA/graphite nanosheet with graphite percentages up to 6% and 8% (wt/wt) respectively. The PMMA/graphite nanosheet composites with 0.25% of graphite(wt/wt) presented electrical conductivity in the order of 10-9 S.cm-1, however when irradiated with doses of 30, 60 and 100 kGy, their electrical conductivity change.To values in the order of 10-8 , 10-6 and 10-5 S.cm-1 respectively. The percolation threshold for the PMMA/graphite (nanosheet and powder) composites were 0.22 and 1.66%(wt/wt) respectively. Scannig Electronic Microscopy analyses (SEM) show different morphologies and dimensions of graphite nanosheets. Changes on critical exponent (t) showed dependency with form and concentration of graphite into the PMMA matrix, on the other hand, the diminution of the viscosity- average molar mass during the irradiation process had little influence on the electrical conductivity, because. The of news levels formation of electroconductivity those during the irradiation is independenty of PMMA radiolysis. Those levels contribute to the electrical conductivity observed in the system. FT-IR analyses of the diverse forms of graphite and composites, show that during the chemical intercalation process occurs the introduction of hydroxyl groups (OH). These new chemical groups are fundamental for improving the interactions between graphite filler and PMMA. RMN (1H) analysis made it possible to determine the taticity of the PMMA

ASSUNTO(S)

graphite pmma viscosity spectroscopy nanocompÃsitos condutores, pmma, irradiaÃÃo gama, grafite, espectroscopia, viscosimetria engenharia nuclear gamma irradiation conducting nanocomposite

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