This study focused on the mechanical properties of pure sisal, pure glass, and hybrid sisal/glass compression-molded composites, in which various stacking sequences of fiber mat layers were used. It is shown that hybridization originated a material with general intermediate properties between pure glass and pure sisal. However, the importance of controlling the stacking sequence to enhance properties was evident. For instance, to optimize flexural behavior, there must be glass fibers mainly on the top and bottom surfaces. Furthermore, depending on the type of loading and stacking sequence, some hybrid composites may show properties very close to those of pure glass.

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In this study, the short beam strength characteristics of randomly oriented composites were comprehensively investigated. The following parameters were varied: fiber used (curaua or sisal), fiber washing or surface chemical treatment with sodium hydroxide/sodium borohydride, fiber length (from 5 to 60 mm), hybridization with glass fiber and the pre-processing of the polyester resin. The overall fiber volume fraction was kept constant (30 vol.%). In all configurations, the composites containing curaua fiber obtained higher short beam strength than those with sisal. An increase in fiber length yielded higher short beam strength. The optical and electronic micrographs showed mostly horizontal cracks, typical of shear failure. In addition, it was carried out a study of the ASTM D2344 standard regarding the span-to-thickness ratio recommended for testing, the measured strength decreased for higher span-to-thickness ratio for specimens with higher length and width, and the failure mode changed to bending around span-to-thickness >12.

O objetivo deste trabalho é utilizar fibras de algodão como material de reforço em materiais compósitos poliméricos utilizando o poliestireno como matriz e o poli(estireno-co-anidrido maleico) como agente compatibilizante. Os compósitos foram desenvolvidos em uma extrusora dupla-rosca co-rotacional, precedidos de uma pré-mistura em extrusora mono-rosca e moldados por injeção. Os compósitos foram avaliados mediante ensaios mecânicos, térmicos, termo dinâmico-mecânico e de morfologia dos compósitos produzidos. Os ensaios de flexão e tração mostram que a adição de 20% de fibra de algodão faz com que essas propriedades aumentem, sendo esse efeito intensificado em presença de compatibilizante. Observou-se aumento da resistência ao impacto com adição de carga; porém, os compósitos com compatibilizante apresentaram resultados inferiores. A HDT para os compósitos com 20% de fibra de algodão foi de aproximadamente 7 ºC. Por meio do TGA, observa-se que a adição de fibras de algodão desloca o início da perda de massa para temperaturas próximas a 200 ºC. Na análise de DMTA, observa-se que, com a adição da fibra de algodão, ocorre aumento na rigidez e no módulo de armazenamento. As micrografias mostram redução no pull-out das fibras, devido a uma maior adesão fibra/matriz, com a utilização do agente compatibilizante.

The present study addresses the tribological behavior of polyester composites reinforced with a natural fiber (sisal), a synthetic fiber (glass) and their combination (glass/sisal hybrid). The composites were obtained by compression molding with an overall fiber content of 20 or 40 vol%. The composites were rubbed against a steel counterface using a tribometer. Pure sisal composite exhibited superior wear resistance, mainly due to the formation of a concise tribofilm. It also showed the lowest coefficient of friction (CoF) because of the lubricating action of the water present in the natural fiber. Pure glass composite showed the lowest wear resistance due to the strong abrasive effect of the glass fibers. The increase in fiber content lead to an increase in CoF and its effect on wear was complex and discussed throughout the article.

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PolyTech, Prospect CT, USAResumo: Compósitos de PP/argila/PP-g-MA/erucamida contendo 5% (em peso) de argila montmorilonita organofílica (Cloisite 20A), 5 e 15% de PP-g-MA como agente compatibilizante e 0, 0,5% e 1% de cis-13-docosenamida (erucamida) como agente co-intercalante, foram preparados por intercalação no estado fundido. Concentrados de argila e compatibilizantes foram processados em misturador interno e em seguida diluídos com a matriz de polipropileno em extrusora de dupla rosca corrotacional. Os compósitos foram caracterizados através das propriedades mecânicas, difração de raios X e microscopia óptica. Os resultados indicaram o efeito reforçante da argila organofilizada. A presença de co-intercalante aumentou significativamente a distância interlamelar da argila em todos os compósitos, em geral, não afetando notavelmente o comportamento mecânico dos compósitos. Por microscopia óptica foi possível observar o efeito dispersivo do perfil de rosca utilizado, que promoveu a quebra dos aglomerados de argila. Palavras-chave: Polipropileno, nanocompósitos, co-intercalante, propriedades mecânicas. Effect of CIS-13-Docosenamide Cointercalation on the Morphology and Mechanical Properties of Polypropylene/Organoclay CompositesAbstract: PP/organoclay/PP-g-MA/erucamide composites with 5% commercial organo-montmorillonite (Cloisite 20A), 5 and 15% maleated polypropylene as compatibilizer, and 0, 0.5 and 1% erucamide as a co-intercalating agent were prepared by melt intercalation. A masterbatch of compatibilizer and organoclay was compounded in an internal mixer and then diluted in the polypropylene matrix in a corotating twin-screw extruder. The compounds were characterized by x-ray diffraction, optical microscopy and mechanical properties. Results indicate that the organoclay acted as a reinforcer. Addition of the co-intercalating agent significantly increased the interlayer spacing of the clay, without notably affecting the mechanical behavior of the composites. Optical microscopy showed the dispersive effect of the screw profile used, which promoted the breaking of clay agglomerates.