Compósitos de poliestireno/montmorilonita (PS/MMT) contendo 2,5% em peso de argila foram preparados com dois tipos de argila modificada com sais quaternários de amônio. Também foram preparadas amostras do PS + sal quaternário de amônio, utilizando-se proporção de sal semelhante à usada na modificação da argila. Todas as amostras foram expostas à radiação UV por períodos de até 12 semanas, e em seguida foram realizados testes para avaliar as modificações em massa molar, propriedades mecânicas (tração e impacto), estrutura química (FTIR) e superfície de fratura (MEV) dessas amostras. Os resultados mostraram que compostos metálicos existentes na argila catalisam o processo fotodegradativo do PS e a presença isolada do sal não altera significativamente o comportamento do PS frente à radiação UV.

Composites of polystyrene/montmorillonite (PS/MMT) containing 2.5 wt. (%) clay were prepared with two types of clays modified with quaternary ammonium salts. Were also prepared samples of PS + quaternary ammonium salt, using the same amount employed in modifying the clay. All samples were exposed to UV radiation for up to 12 weeks, and then tests were conducted to evaluate the changes in molecular weight, mechanical properties (tensile and impact), chemical structure (FTIR) and fracture surface (SEM) of these samples. The results showed that metal compounds existing in clay catalyzes the photodegradation process of PS and the presence of salt alone does not significantly alter the behavior of PS under UV.

Este trabalho visa avaliar a influência do tipo de polipropileno no comportamento da blenda polipropileno/poliestireno de alto impacto (PP/HIPS) quando exposta à radiação UV. Foram usados uma resina virgem de PP (PPv) e outra reprocessada (PPrep). Inicialmente, avaliou-se o comportamento individual dos componentes da blenda, HIPS, PPv e PPrep, quando submetidos à radiação UV por até 15 semanas de exposição. As técnicas de caracterização utilizadas para monitorar o desempenho tanto das resinas individualmente quanto das blendas submetidas à radiação UV foram: propriedades mecânicas (tração e impacto), medidas de índice de fluidez (MFI), análise térmica (DSC), espectroscopia no infravermelho (FTIR) e microscopia eletrônica de varredura (MEV). A partir dos resultados com essas técnicas verificou-se que o PPv foi a resina mais afetada pela radiação e consequentemente as blendas preparadas com esse PP também foram mais sensíveis à fotodegradação do que as demais. Em termos de fotoestabilização este resultado mostra-se interessante, já que as blendas PP/HIPS preparadas com uma resina previamente degradada necessitariam de menores teores de aditivos do que esse mesmo tipo de blenda preparada com resina virgem.

The influence from the type of polypropylene on the photodegradation resistance of blends of polypropylene/high impact polystyrene (PP/HIPS) was studied. A virgin polypropylene (PPv) and another sample that suffered prior thermo-mechanical degradation (PPrep) were used. All materials, components of the blends and blends were exposed to UV radiation for up to 15 weeks. They were characterized as a function of time of UV exposure using differential scanning calorimetry (DSC), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The mechanical (tensile and impact) properties and melt flow indexes of the materials were also evaluated. The experimental results revealed that PPv resin and its blends were more sensitive to UV radiation than PPrep and its blends. In terms of photostabilization this finding is very interesting, since PP/HIPS blends prepared with a previously degraded polyolefin would require smaller amounts of additives than the same kind of blends prepared with virgin resin.

In this work, a smectite clay from the State of Paraiba, Brazil, was treated with six different types of ammonium salts, which is an usual method to enhance the affinity between the clay and polymer for the preparation of nanocomposites. The clays, before and after modification, were characterized by X ray diffraction. The conformation of the salts within the platelets of the clay depended on the number of long alkyl chains of the salt. The thermal stability of the clays was also studied. The ammonium salts thermal decomposition was explained in light of their position within the organoclays.

In this work, preliminary results of the use of hydrophobic thin films obtained by plasma deposition to protect grains and seeds are presented: grains coated by the films did not present biological degradation when stored in a saturated water vapor environment, but had their germination accelerated in the presence of water. A model that explains the difference of behavior of the films when exposed to water in vapor form or in liquid form, based on the formation of microchannels within the film that lead to water uptake in seeds, is presented. The model was successfully tested using quartz crystal measurements, which showed that the microchannels within the films can favor the adsorption and permeation of water when the films are immersed in water.

A tensão interfacial entre polímeros fundidos é um fator chave para a predição da morfologia de blendas poliméricas. Neste trabalho, as teorias de Tomotika e Tjahjadi et al. para medir tensão interfacial entre polímeros fundidos usando o método de fibra quebrante são avaliadas e comparadas. Em particular, foram testadas ambas as teorias para o par de polímeros PP/PS à temperatura de 200 °C. O valor médio de tensão interfacial calculado usando a teoria de Tomotika foi de 5,88 mN/m, e usando a teoria de Tjahjadi et al. foi de 5,66 mN/m.

Interfacial tension between molten polymers is a key factor that helps predicting the morphology of polymer blends. In this work, the theories of Tomotika and Tjahjadi et al. to measure interfacial tension between molten polymers using the breaking thread method are evaluated and compared. In particular, both theories were tested for PP/PS polymer pair at temperature of 200 °C. The average values of interfacial tension calculated using Tomotika´s theory and Tjahjadi et al.´s theory are 5.88 mN/m and 5.66 mN/m, respectively.

Neste trabalho a influência da temperatura, da massa molar (<IMG SRC="/img/revistas/po/v13n1/15069x34.gif" WIDTH=11 HEIGHT=11>n) e da distribuição de massa molar (MWD) na tensão superficial de poliestireno (PS) foi avaliada utilizando o método da gota pendente. A influência da temperatura na tensão superficial de polipropileno isotático (i-PP) e de polietileno de baixa densidade (PELBD) também foi estudada aqui. As teorias de Patterson-Rastogi e Dee-Sauer foram utilizadas em conjunção com a teoria de equação de estado de Flory, Orwoll, e Vrij (FOV) para prever a tensão superficial (gama) utilizando dados de pressão-volume-temperatura (PVT) dos polímeros. Ambas teorias prevêem que a tensão superficial diminui linearmente com o aumento da temperatura e aumenta com a massa molar concordando com os resultados experimentais. Entretanto, ambas teorias subestimam a mudança de entropia de formação de superfície por unidade de área a volume constante para sistemas poliméricos de baixa massa molar e polidisperso e subestimam o efeito da distribuição de massa molar na tensão superficial

In this work, the influence of temperature, molecular weight (<IMG SRC="/img/revistas/po/v13n1/15069x34.gif" WIDTH=11 HEIGHT=11>n) and molecular weight dispersity (MWD) on the surface tension of polystyrene (PS) was evaluated using the pendant drop method. The influence of temperature on the surface tension of isotatic polypropylene (i-PP) and of linear low density polyethylene (LLDPE) was also studied here. Patterson-Rastogi and Dee and Sauer theories were used in conjunction with the Flory, Orwoll, and Vrij (FOV) equation of state to predict surface tension (gamma) using bulk pressure-volume-temperature (PVT) data. Both theories predicted that surface tension decreases linearly with increasing temperatures and increases with molecular weight corroborating the experimental data. However, both theories underestimated the entropy change of surface formation per unit area at constant volume for low molecular weight and polydisperse systems and underestimated the effect of molecular weight dispersity on surface tension.

This work was aimed at producing new polymeric materials using oxygenated organic compounds as main reactants and plasma enhanced chemical vapor deposition (PECVD) as a production technique. The films obtained were analyzed by profilometry, in order to determine the deposition rate, by Infrared Spectroscopy (FTIR) to identify the species deposited and by contact angle measurements to determine the polarity of the surface. For the reactants used, namely ethanol, acetone and 2-propanol, the plasma deposition process was least efficient with ethanol followed by acetone and 2-propanol. With the latter, reproducible thin films were obtained with a high deposition rate (up to 400 Å/min). These films had a high amount of OH and could be wetted by common organic solvents, such as 2-propanol or acetone. The contact angle formed by drops of 2-propanol or acetone aqueous solution on the film produced from 2-propanol varied significantly with the concentration, from 0.9% to 50% by vol., indicating that the film is sensitive to polar solutions.

Neste trabalho, o efeito da composição da blenda PP/HDPE e da temperatura no comportamento viscoelástico linear e na morfologia destas blendas foi estudado. A tensão interfacial entre PP e HDPE foi avaliada utilizando o espectro de relaxação das blendas, seguindo as análises de Gramespacher e Meissner[1]. Os resultados indicaram que existe uma faixa de composições da blenda PP/HDPE para a qual é possível utilizar as análises de Gramespacher e Meissner[1] na obtenção da tensão interfacial entre polímeros utilizando-se medidas reológicas. A compatibilização da blenda PP/HDPE também foi estudada através de análises morfológicas e da tensão interfacial entre os seus componentes. Três compatibilizantes foram testados: EPDM, SEBS e EVA. Curvas de emulsão relacionando o raio médio da fase dispersa e a tensão interfacial com a concentração de compatibilizante adicionado à blenda foram obtidas. Foi mostrado que o EPDM foi mais eficiente como agente emulsificante para a blenda PP/HDPE que o EVA e o SEBS.

In this paper the influence of composition and temperature on the linear viscoelastic behavior and morphology of PP/HDPE blends was studied. The interfacial tension between PP and HDPE was evaluated using the relaxation spectra of PP/HDPE blends, following Gramespacher and Meissner analysis[1]. The results seemed to indicate that there is a range of compositions for which it is possible to use Gramespacher and Meissner analysis in order to calculate interfacial tension between polymers using small amplitude oscillatory shear measurements. The compatibilization of PP/HDPE blend was also studied through morphological analysis and interfacial tension between its components. Three types of compatibilizers were tested: EPDM, EVA and SEBS. Emulsion curves relating the average radius of the dispersed phase and the interfacial tension to the concentration of compatibilizer added to the blend were obtained. It was shown that EPDM was more efficient as an emulsifier for PP/HDPE blend than EVA or SEBS.

Blends of polypropylene and polystyrene compatibilized with styrene-butadiene-styrene (SBS) or styrene-ethylene/butylene-styrene (SEBS) copolymers were studied. The morphology of these blends was studied by Scanning Electron Microscopy. Emulsion curves relating the average radius of the dispersed phase to the concentration of compatibilizer added to the blend were obtained. The rheological behavior of the blends was studied by small amplitude oscillatory shear, and correlated to the morphological observations. The interfacial tension between the components of the blends was evaluated from the rheological data. In addition, the applicability of time-temperature superposition (TTS) method for PP/PS blend was studied.

In this paper the pendant drop method to measure interfacial tension between molten polymers is reviewed. A typical pendant drop apparatus is presented. The algorithms used to infer interfacial tension from the geometrical profile of the pendant drop are described in details, in particular a new routine to evaluate correctly the value of the radius at the apex of the drop, necessary to the calculation of interfacial tension is presented. The method was evaluated for the possibility of measuring the interfacial tension between polyethylene and polystyrene. It is shown that the method is unsuitable for the measurement of interfacial tension between high density polyethylene and polystyrene due possibly to a too small difference of density between the two polymers. Values of interfacial tension between low density polyethylene (LDPE) and polystyrene (PS) as a function of the molecular weight of PS are presented. It was shown that the interfacial tension between LDPE and PS increased as a function of molecular weight of PS up to values of molecular weight of roughly 40,000 g/mol, value for which entanglements occur.

Dois instrumentos, um deles baseado no princípio da gota pendente e o outro baseado no método da gota girante, para medir a tensão interfacial entre polímeros, são apresentados e comparados aqui. Com ambos instrumentos foi possível visualizar a gota de polímero "on line". Os instrumentos mostraram-se complementares quanto às suas áreas de aplicação. O método da gota pendente deve ser usado quando as quantidades de polímero são limitadas ou quando o polímero mais denso é opaco. O método da gota girante deve ser usado quando a degradação térmica pode ser um problema ou quando o polímero menos denso é opaco.

In this paper two apparatuses, one based on the principle of the pendant drop method and one based on the principle of the spinning drop are presented and compared. With both apparatuses it was possible to view the drop in real time and calculate the interfacial tension on-line. The two equipments were shown to be complementary in their use. The pendant drop method should be used when there are limited quantities of polymer and/or the denser polymer is opaque. The spinning drop method should be used when thermal degradation could be a problem and/or when the lighter polymer is opaque.