No abstract

IntroduçãoO emprego de compósitos de matriz polimérica reforça-dos por fibras naturais lignocelulósicas vem tendo um crescente desenvolvimento nos últimos anos [1][2][3] . Os grandes atrativos desses materiais incluem o fato das fibras serem biodegradáveis, serem um recurso natural renovável, terem geralmente baixo custo e produzirem menor desgaste nos equipamentos de fabricação quando comparadas com as fibras sintéticas. Dentre as principais fibras vegetais mais estudadas e empregadas em nível mundial como reforço em compósitos de matriz polimérica, destacam-se o sisal e a juta [4,5] . Na Europa, estão sendo aplicados pesados investimentos para o emprego de fibras nativas como o linho e o cânhamo [3] . Entretanto, inúmeras outras fibras vegetais mostram potencialidade de aplicação como reforço em compósitos de matriz polimérica. As fibras de bananeira, por exemplo, são abundantes, tendo uma produção mundial estimada superior a 300.000 toneladas/ ano, além de serem baratas e terem boas propriedades mecâ-nicas [6,7] . Outras fibras que podem ser destacadas são as de coco, rami, piaçava e bucha [7][8][9][10][11][12] . A Luffa cylindrica, vulgarmente conhecida como bucha, é uma planta subtropical, abundante na China, Japão Resumo: Neste trabalho, foi analisado o efeito de um tratamento químico, ou seja, de acetilação de grupos, sobre a estrutura e a morfologia superficial de fibras de bucha (Luffa cylindrica) por meio de FTIR e microscopia eletrônica de varredura. Esse tratamento foi realizado tendo por objetivo aumentar a compatibilidade da bucha com as matrizes poliméricas usualmente empregadas em compósitos. Mostrou-se que o tratamento reduziu a polaridade das moléculas de celulose e removeu a camada superficial das fibras de bucha, expondo a sua estrutura fibrilar interna, com conseqüen-te aumento da área disponível para a adesão. Palavras-chave: Luffa cylíndrica, tratamento superficial, compósitos. Acetylation of Loofah Fiber (Luffa Cylindrica)Abstract: In this work the effect of a new chemical surface treatment on the structure and surface morphology of loofah fibers (Luffa cylindrica) was analyzed, using infrared spectroscopy and scanning electron microscopy. The chemical treatment is aimed at increasing loofah compatibility with the polymeric matrices commonly used in composites. It was shown that the treatment used caused a reduction on the polarity of cellulose molecules, and removed the outer surface layer of loofah fibers, exposing their internal fibrillar structure. As a consequence the treatment promoted an increase on the surface area available to adhesion. Keywords: Luffa cylindrica, surface treatment, composites.Autor para correspondência: José R. M. d'Almeida, Departamento de Ciência dos Materiais e Metalurgia, PUC-Rio, Rua Marquês de São Vicente 225, CEP: 22453-900, Rio de Janeiro, RJ. E-mail: dalmeida@dcmm.puc-rio.br e em outros países da Ásia, bem como em países da Amé-rica Central e do Sul. Sua fruta tem uma sistema vascular que, quando seca, forma uma manta tridimensional natural [11,13] . A ...

A derivatization treatment aimed to reduce the hydrophilic behaviour of sponge gourd (Luffa cylindrica) fibres is described. The effect of the treatment on the chemical composition, surface morphology and thermal stability of the fibres was analysed. FT-IR results show that the polarity of the fibres was reduced, although the acetylation reaction did not go to completion. SEM analysis showed that the surface roughness of the fibres was increased by the treatment due to the removal of the outer surface layer of the fibres, and the thermal analysis showed variations in the fibre thermal behaviour caused by the chemical treatment. In particular, a significant reduction in weight loss was noted in temperatures lower than 100 °C, indicating that the fibres became more hydrophobic after treatment.

Piassava (Attalea funifera) fibers subjected to several surface chemical treatments and as-received raw fibers were compared with respect to their thermal and tensile behaviors. The thermal degradation of the raw fibers was characterized by three main stages that corresponded to water release at low temperatures, decomposition of hemicellulose, and decomposition of a cellulose. Mercerization acted mainly on hemicellulose removal, and there was no change in the hydrophilic behavior of the fibers. The removal of hemicellulose split the fibers into microfibrils and favored the thermal decomposition of a cellulose. The same behavior was observed when the fibers were subjected to mercerization and acetylation. The fibers subjected to only acetylation showed thermal behavior similar to that of the raw fibers. With the acetylation treatment, a minor decrease in the hydrophilic character of the fibers was noted. Despite some differences in the thermal behavior, the tensile strengths of the raw and treated fibers were statistically equal. Complementary Fourier transform infrared and scanning electron microscopy analysis corroborated the thermogravimetric analysis/differential thermogravimetry results.

The surface morphology, thermal behaviour and tensile mechanical properties of raw caroa (Neoglaziovia variegata) fibres have been characterised. The influence of fibre washing with flowing tap water on the surface morphology and thermal properties of these fibres has also been investigated. The results show that gummy tissues are attached to the surface of the raw fibres and that washing leads to the partial removal of these tissues and to the exposure of the inner fibrillar structure of the fibres. Thermogravimetric analysis indicates that fibre thermal degradation is characterised by three main degradation stages corresponding, respectively, to water release at low temperatures, followed by decomposition of hemicellulose and of α-cellulose. Fibre washing produces an increase in the fibre thermal degradation temperature, Tonset, and in the thermal decomposition rate. These characteristics are associated with the removal of gummy tissues and with a decrease in the compactness of the fibres respectively. The tensile properties obtained place caroa as a low-to-medium-strength fibre when compared with other lignocellulosic fibres, but with a strength level similar to that of coir fibres, which, nowadays, are used commercially on a fairly large scale.

No abstract

No abstract

The development of an eco-friendly material that could reduce CO 2 emission and that could aggregate value to a natural fiber, setting man at the countryside and raising the income of populations from poor regions is a challenge. Lignocellulosic fibers are cheap and are a readily available reinforcement, requiring only a low degree of industrialization for their processing. The main drawback of using cement composites reinforced with lignocellulosic fibers is that the fibers can be mineralized inside the alkaline environment. In this work, Portland cement was partially replaced by metakaolinite in order to produce a matrix free from calcium hydroxide, avoiding thus the problem of fiber mineralization. Cement composites reinforced with 2, 4 and 6% of short curaua fibers, were manufactured. The composites were submitted to four pointing bending tests in order to determine their mechanical behavior. The results obtained were compared with those found for cement composites reinforced with sisal fibers.