RESUMO O concreto é um material com elevada frequência de utilização em construções brasileiras e em edificações de países ao redor do mundo. Fatores como os custos reduzidos dos materiais, elevado volume de pesquisa e resistência elevada, colaboram para a grande utilização do concreto como material de construção. Entretanto, o concreto tem baixa resistência à tração, fissura facilmente e apresenta pequena capacidade de deformação. O concreto reforçado com fibras (CRF) foi desenvolvido na década de 60 e é um material que apresenta uma boa resposta mecânica em termos de resistência residual após a fissuração da matriz e consequentemente um comportamento mais dúctil do que o concreto sem fibras. Entretanto, o efeito da adição de fibras no concreto restringe-se somente a fase pós-fissuração do processo de carregamento. As fibras não tem efeito no comportamento que antecede a carga de pico. Avanços recentes em nanotecnologia têm possibilitado a produção de nanopartículas, em especial, nanotubos de carbono. Tratam-se de nanopartículas que podem ser utilizadas como reforço da matriz cimentícia para atuar ao nível de sua nanoestrutura. A pesquisa proposta estuda o comportamento de concretos contendo a incorporação de nanotubos de carbono e também de concretos reforçados com fibras de aço (CRFA) juntamente com a adição de nanotubos de carbono. A pesquisa tem o objetivo de avaliar melhorias na resposta dos concretos e dos CRFA, a partir da incorporação das nanopartículas de carbono. Foram realizados ensaios de compressão e de flexão em três pontos em corpos de prova prismáticos entalhados. Foi constatado que os nanotubos de carbono permitem reduzir a absorção de água e melhorar a mobilidade das misturas (de concreto e de CRFA) no estado fresco. Também foram observados aumentos, na resistência à compressão axial e resistências flexionais dos materiais concreto e CRFA quando da adição de nanotubos de carbono.

ABSTRACT Concrete is a material with a high frequency of use in Brazilian constructions and in buildings in countries around the world. Factors such as reduced material costs, high research volume and high resistance, contributed to the wide use of concrete as a building material. However, concrete has low tensile strength, cracking easily and has a low deformation capacity. Fiber reinforced concrete (FRC) was developed in the 1960s and is a material that presents a good mechanical response in terms of residual strength after cracking of the matrix and consequently a more ductile behavior than concrete without fibers. The effect of adding fibers to the concrete is restricted only to the post-cracking phase of the loading process. The fibers have no effect on the behavior that precedes the peak load. Recent advances in nanotechnology have enable the production of nanoparticles, in particular, carbon nanotubes. The nanoparticles can be used to reinforce the cement matrix to act at the level of its nanostructure. The proposed research studies the behavior of concretes containing the incorporation of carbon nanotubes and also of steel fiber reinforced concrete (SFRC) with the addition of carbon nanotubes. The research aims to evaluate improvements in the response of concretes and SFRC, based on the incorporation of carbon nanoparticles. Compression and flexural tests were performed on notched prismatic specimens. It has been found that nanotubes reduce the absorption of water and improve the mobility of mixtures (concrete and SFRC) in the fresh state. Increases in axial compression strength and flexural strengths of concrete and SFRC materials were also observed when adding carbono nanotubes.

Las fibras del seudotallo de plátano (FSP) fueron modificadas mediante epiclorhidrina (EP), anhídrido acético (AA), y su combinación (AA_EP), y con plasma a tres descargas de barrera dieléctrica (DBD) 1, 3 y 6 kW min m-2. Las FSP tratadas y sin tratar fueron caracterizadas mediante espectroscopia infrarroja por la transformada de Fourier (FT-IR), termogravimetría (TGA), microscopía electrónica de barrido (SEM) y pruebas mecánicas de tensión y de humectabilidad. Los espectros FT-IR, las micrografías SEM, y el análisis TGA indicaron pérdidas de lignina, hemicelulosa, impurezas y ceras. Estos efectos en conjunto con las reacciones de grupos OH y -C-C-, con los tratamientos químicos y de plasma respectivamente, incrementaron la hidrofobicidad de las FSP tratadas. Los tratamientos químicos produjeron reacciones de esterificación, eterificación y entrecruzamiento de los grupos OH libres en las FSP, lo que hizo que mostraran mayor rigidez que las expuestas al plasma. Las micrografías SEM mostraron que las FSP expuestas al plasma quedaron con superficie más irregular y rugosa que la de las FSP tratadas químicamente. La humectabilidad de las fibras, medida mediante pruebas de ángulo de contacto, se redujo como consecuencia de ambos tratamientos, característica importante para un relleno en los materiales compuestos.

Banana-plantain pseudo-stem fibers (BPF) were modified using epichlorohydrin (EP), acetic anhydride (AA), and a combination of the two (AA_EP), and three dielectric barrier discharge (DBD), plasma treatments, at 1, 3, and 6 kW min-1 m-2. Untreated and treated BPF samples were characterized via Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), mechanical tensile and wettability tests. The FT-IR spectrum, the SEM images, and the TGA suggest a loss of lignin, hemicellulose, impurities, and waxes. These effects together with the modification of the OH and C-C groups, respectively by the chemical and plasma treatments, increased the hydrophobicity of the treated BPF. The chemical treatments promoted the esterification and crosslinking of the free OH groups in BPF, leading the BPF treated chemically to be more rigid than plasma-treated BPF. SEM images show that plasma-treated BPF have a rougher, more irregular surface than chemical treated BPF. The fiber wettability, measured by the contact angle assay, decreased after both treatments, which is an important characteristic for a filler material in composites.

Chitosan microcapsules containing limonene essential oil as active ingredient were prepared by coacervation using three different concentrations of NaOH (0.50, 1.00, 1.45 wt%) and fixed concentrations of chitosan and surfactant of 0.50 wt%. The produced microcapsules were fully characterized in their morphology and chemical composition, and the kinetic release analysis of the active ingredient was evaluated after deposition in a non-woven cellulose fabric. The concentration of 1.00 and 1.45 wt% clearly show the best results in terms of dimension and shape of the microcapsules as well as in the volatility results. However, at the concentration of 1 wt% a higher number of microcapsules were produced as confirmed by FTIR and EDS analysis. Free microcapsules are spherical in size with disperse diameters between 2 and 12 μm. Immobilized microcapsules showed sizes from 4 to 7 μm, a rough surface and loss of spherical shape with pore formation in the chitosan walls. SEM analysis confirms that at higher NaOH concentrations, the larger the size of the microcapsules. This technique shows that by tuning NaOH concentration it is possible to efficiently control the release rate of encapsulated active agents demonstrating great potential as insect repellent for textiles.