Abstract Short fibers are used in thermoplastic composites to increase their tensile and flexural resistance; however, it often decreases impact resistance. Composites with short vegetal fibers are not an exception to this behavior. The purpose of this work is to produce a vegetal fiber reinforced composite with improved tensile and impact resistance in relation to the polymer matrix. We used poly(ethylene-co-vinyl acetate), EVA, to recover the impact resistance of high density polyethylene, HDPE, reinforced with Curauá fibers, CF. Blends and composites were processed in a corotating twin screw extruder. The pure polymers, blends and composites were characterized by differential scanning calorimetry, thermogravimetry, infrared spectroscopy, scanning electron microscopy, tensile mechanical properties and Izod impact resistance. EVA used as impact modifier in the HDPE matrix exhibited a co-continuous phase and in the composites the fibers were homogeneously dispersed. The best combination of mechanical properties, tensile, flexural and impact, were obtained for the formulations of composites with 20 wt. % of CF and 20 to 40 wt. % of EVA. The composite prepared with 20 wt. % EVA and containing 30 wt. % of CF showed impact resistance comparable to pure HDPE and improved tensile and flexural mechanical properties.

Neste trabalho foram desenvolvidos biocompósitos baseados em acetato de celulose e fibras curtas de Curauá tratadas com dióxido de carbono supercrítico. O tratamento das fibras resultou na extração parcial de lignina, sendo este um método interessante pois não resulta em rejeitos químicos. Duas séries de biocompósitos, uma delas plastificada com ftalato de dioctila (DOP) e outra com citrato de trietila (TEC), foram preparadas por extrusão. Para ambas ocorreu a fibrilação e distribuição uniforme das fibrilas. Como conseqüência, os biocompósitos apresentaram maior capacidade calorífica, menor condutividade térmica e maior coeficiente de expansão térmica em comparação ao acetato de celulose plastificado. O tratamento das fibras com CO2 supercrítico intensificou as variações destas propriedades. Dentre os plastificantes, o DOP mostrou-se ligeiramente mais eficiente, resultando em materiais com menores valores de Tg e de módulo de Young. A adição das fibras teve um impacto relativamente baixo sobre o módulo (10%), porém houve uma perda significativa da resistência ao impacto. O conjunto de resultados permite concluir que estes biocompósitos apresentam potencial de aplicação como isolantes térmicos, sendo que os plastificados com TEC apresentam como vantagem o fato de todos seus componentes serem biodegradáveis.

In this work, the effect of pre-processing of short Curaua fibers with supercritical carbon dioxide on the properties of biocomposites with cellulose acetate was studied. The treatment with supercritical CO2 may result in the partial lignin extraction from the fibers. Two series of biocomposites, one plasticized with dioctyl phtalate (DOP) and another with triethyl citrate (TEC), were prepared by extrusion. Fibrilation and uniform distribution of fibers in the cellulose acetate matrix were observed for both biocomposites. As a consequence, the composites showed a higher specific heat, lower thermal conductivity and higher coefficient of thermal expansion than plasticized cellulose acetate. The treatment of the fibers increased such differences. Among the plasticizers, DOP was more efficient, decreasing Tg and Young's modulus of plasticized cellulose acetate. The fiber addition had a relatively low impact on the modulus (10%), however caused a decrease in the impact resistance. Taken together, the results show that these biocomposites are promising as thermal insulators, with the additional advantage of biodegradability of all components in the case of biocomposites plasticized with TEC.

São reportados os testes realizados com dois módulos capazes de realizar análises de reometria capilar e também induzir a orientação molecular (também chamado como auto-reforçamento) de polímeros, os quais foram projetados e montados neste laboratório. Os módulos são acoplados a uma Máquina Universal de Ensaios, a qual é responsável pela realização dos ensaios, sendo o baixo custo o principal atrativo dos módulos. Os resultados obtidos com o módulo de reometria capilar foram comparados com os obtidos num reômetro comercial e apresentaram boa concordância. O auto-reforçamento foi capaz de induzir a orientação molecular e levar a um aumento de aproximadamente 50% nas propriedades de flexão, se comparadas às amostras não reforçadas.

The results obtained with a capillary rheometer and die-drawing module, designed and assembled in our laboratory, are presented. The modules were connected to a universal stress-strain equipment, which is responsible for the movements and the data acquisition. The results obtained with the capillary module, assembled in this work, were comparable to those obtained with a commercial equipment. The low cost is one of the main advantages of the reported equipment. The die-drawing method was also capable of inducing a molecular orientation and enhancing the flexural properties of a polymer material in comparison to the non-reinforced sample.

A simple experiment for the preparation of transparent conducting glass electrodes by deposition of pure and fluorine doped SnO2 films is described. This procedure was tested in the undergraduate inorganic course at IQ-UNICAMP. The success in achieving a conducting layer was easily checked using the standard probes of a volt-ohm meter. The optical transmittance and thickness were studied by UV-vis spectrophotometry. To discuss the experimental results we place significant emphasis on molecular orbital and energy band model theories. The undergraduate students can also discuss the concepts related to the electronic properties of solids and to interesting new materials, such as transparent conducting films, which are the subject of significant current research and technological applications.

Solid municipal waste contains a large volume of polymers and its final disposal is a serious environmental problem. Consequently, the recycling of the principal polymers present in the solid waste is an alternative. In this review we describe the mechanical and chemical recycling of polymers and the energy recovery from plastic wastes. Polymer recycling involves not only the development of processing technologies, but also the solution of many chemical and analytical problems. The technological, economical and social aspects of polymer recycling are also considered.

Descrevemos neste trabalho as causas e o mecanismo do embranquecimento de peças de polipropileno isotático injetado. Para isto foram injetados corpos de prova e placas com e sem estabilizantes. As amostras foram envelhecidas por exposição ambiental e em equipamento de envelhecimento acelerado (Weatherometer). Foi feito o acompanhamento visual das peças para que pudessem ser caracterizadas quando começassem a embranquecer. A caracterização foi feita através de espectroscopia FT-IR por reflectância, Microscopia eletrônica de varredura, Microfluorescência de raios-X, Reflectância de luz e Microanálise de energia dispersiva (EDS) da superfície. Os espectros de infravermelho mostraram o aparecimento de diversos produtos de degradação como cetonas, aldeídos, ácidos carboxílicos, ésteres, perésteres e alfa-cetoésteres. Quando as amostras começaram a embranquecer foi verificada a formação de fissuras superficiais e o aumento da reflectância de luz para todos os comprimentos de onda do espectro. Concomitantemente foi verificado que a composição de superfície não é alterada pelo envelhecimento. A superfície não apresenta grande quantidade de partículas de TiO2 expostas. Conclui-se que o embranquecimento das peças é devido ao fissuramento superficial que aumenta a quantidade de luz refletida na superfície e não pela migração do pigmento.

We studied in this work the whitening mechanism in injection molded polypropylene (PP), a problem usually manifested in car parts and particularly in car bumpers. For the development of this work we had samples (plaques and test samples) with and without antioxidants and ultraviolet stabilizers. These samples had been already aged by natural and artificial (Weatherometer equipment) exposure. In the natural aging samples were collected when the material started to whiten, after 3190, 4320 and 6190 h of exposure. In the artificial aging samples were collected after 415, 515 and 3000 h of exposure. The samples were characterized by visual observation, infrared spectroscopy, scanning electron microscopy, surface total light reflectance and titanium mapping in the samples cross section by X-ray microfluorescence and X-ray difraction of the TiO2 used in the formulation. When the samples start to whiten we observe the evolution of surface fissures which increase the surface roughness. This is followed by an increase in the total light reflection by the surface for all wavelengths. We observed that titanium is almost homogeneously distributed along samples cross section. In addition, we did not observe high concentration of exposed TiO2 on the surface. We conclude that the whitening phenomenon is a consequence of surface fissures evolution, which provides higher surface roughness and is followed by a higher surface diffuse light reflectance.