The influence of the addition of high-impact polystyrene (HIPS) on polypropylene (PP) photodegradation was studied with blends obtained by extrusion with and without styrene-butadiene-styrene (SBS) copolymer (10 wt % with respect to the dispersed phase). The concentrations of HIPS ranged from 10 to 30 wt %. The blends and pure materials were exposed for periods of up to 15 weeks of UV irradiation; their mechanical properties (tensile and impact), fracture surface, and melt flow indices were monitored. After 3 weeks of UV exposure, all of the materials presented mechanical properties of the same order of magnitude. However, for times of exposure greater than 3 weeks, an increasing concentration of HIPS resulted in a better photostability of PP. These results were explained in light of morphological observations. This increase of photostability was even greater when SBS was added to the blends. It was more difficult to measure the melt flow index of the binary PP/HIPS blends than that of PP for low concentrations of HIPS; this was most likely due to energy transfer between the blend domains during photodegradation. This phenomenon was not observed for the ternary blends.

Resumo: 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. Palavras-chave: Polipropileno, poliestireno de alto impacto, blenda, fotodegradação. Influence of the Type of Polypropylene on the Photodegradation of Blends of Polypropylene/High Impact PolystyreneAbstract: 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. Keywords: Polypropylene, high impact polystyrene, blend, photodegradation. IntroduçãoO interesse no estudo das blendas poliméricas tem aumentado a cada ano. Um dos grandes motivos para esse crescimento se dá pela vantagem: 1) tecnológica: as blendas possuem a capacidade de combinar as propriedades de diferentes componentes de modo a obter excelentes propriedades mecânicas, térmicas e químicas, e 2) financeira: o custo de desenvolvimento de uma blenda é menor que o custo de desenvolvimento de um novo polímero. Porém o desenvolvimento de um novo material não se restringe apenas a sua obtenção, é preciso tamb...

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