In this study the effects of the dispersion of carboxylated single-walled carbon nanotubes (SWCNT-c) in epoxy matrices using two different routes were investigated. In the first route, SWCNT-c were dispersed in the resin using solvent and tip sonication. In the second route, SWCNT-c were dispersed in the hardener in two different ways: with and without solvent, but both with tip sonication. For comparison purposes, neat epoxy was also prepared using the same curing conditions. The samples were characterized via mechanical and dilatometric testing, raman and FTIR analyses, SEM images, and dilatometric tests. An increase of 88% was found for Young’s modulus in the route with dispersion in the resin aided by solvent. Dispersing the SWCNT-c into the hardener showed a significant increase in some mechanical properties, indicating that this is a possible route for preparing nanocomposites. In addition it was observed that all nanocomposites presented smaller volumetric expansion than neat epoxy.

In this study, carboxylated (SWCNT-c) and pristine (SWCNT) single-walled carbon nanotubes were randomly dispersed in a hardener prior to mixing it with an epoxy resin. The influence of several parameters on the dispersion process were investigated. The produced samples were characterized by infrared spectroscopy, differential scanning calorimetry, dilatometry, dynamic mechanical analysis, scanning electron microscopy and mechanical testing (tensile, flexural and microhardness). The results obtained with the nanocomposites with SWCNT-c suggested that the lowest time and amplitude of sonication improved the mechanical properties. The use of a solvent (acetone) was important to improve dispersion, ultimately increasing microhardness and Young's Modulus up to 32%. Nanocomposites with 0.25 wt. (%) SWCNT-c presented superior mechanical properties compared to those with 0.50 wt. (%) SWCNT. Two simple mathematical models (rule of mixtures and Halpin-Tsai) were used to predict Young's Modulus of the composites yielding results very close to the experimental ones.

Resumo: Neste trabalho são estudados os efeitos da adição de nanotubos de carbono de parede múltipla (NCPM) em uma matriz de Poli(L-ácido láctico) (PLLA). Foras avaliadas duas rotas distintas de dispersão dos NCPM, uma utilizando agitação mecânica em solvente e a outra utilizando sonificação de alta energia em solvente. As propriedades mecânicas destes nanocompósitos foram avaliadas utilizando nanoindentação e microdureza vickers. Através da calorimetria exploratória diferencial foram determinadas as propriedades térmicas dos nanocompósitos (Tg, Tc, Tm e cristalinidade) obtidas. Por último, as propriedades tribológicas foram determinadas através de ensaios de deslizamento do tipo pino sobre disco, onde foram utilizadas diferentes cargas normais. As propriedades mecânicas e térmicas não foram significativamente afetadas pela adição do nanotubos, o que não se repetiu nas propriedades tribológicas, onde tanto o método de dispersão quanto a concentração de NCPM afetaram as propriedades. A micrografia das trilhas de desgaste sugere ainda que o mecanismo atuante foi modificado com a incorporação dos nanotubos, o mesmo pode ter acontecido nas amostras sonificadas. Palavras-chave: Nanotubos de carbono de paredes múltiplas, PLLA, propriedades mecânicas, propriedades tribológicas. Mechanical, Tribological and Thermal Properties of PLLA/MWCNT NanocompositesAbstract: This work studied the effects of the addition of Multiwalled Carbon Nanotubes (MWCNT) to a PLLA matrix. Two distinct methods of preparation were employed: a combination of a solvent/ mechanical stirring and a combination of a solvent/high energy sonication. The mechanical properties of the nanocomposites were determined by nanoindentation and by the Vickers hardness test. Thermal properties of the nanocomposites (T g , T c , T m and crystallinity degree) were determined by DSC. The tribological properties of the nanocomposites were determined by using a pin-on-disc apparatus. Mechanical and thermal properties did not present significant alterations, although tribological properties presented significant changes caused by the method of preparation and different loads. SEM images indicated that the wear mechanism was changed by the addition of MWCNT. Keywords: Multiwalled carbon nanotubes, PLLA, mechanical properties, tribological properties. IntroduçãoA partir do trabalho de Iijima [1] os nanotubos de carbono (NC) têm atraído a atenção da comunidade acadêmica devido as suas propriedades peculiares [2] . Após o primeiro nanocompósito de NC e epóxi [3] , os nanotubos já foram incorporado em mais de 30 matrizes diferentes [4] e o artigo de Iijima foi citado mais de 25 mil vezes [5] . Os NC podem ter uma única parede (NCPS) ou ter paredes múltiplas (NCPM) e essa diferença interfere diretamente nas suas propriedades e nas propriedades obtidas dos nanocompósitos [2] .Além do tipo de NC, outros fatores têm influência nas propriedades finais do nanocompósito. Entre esses fatores pode-se citar o diâmetro, o comprimento e a pureza dos nanotubos de carbono [6] . Além disso...

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