Resumo: A tenacificação de termoplásticos vítreos através da adição de partículas de borracha na matriz polimérica é um processo amplamente estudado. Neste trabalho foi avaliada a recuperação das propriedades de poliestireno de alto impacto (HIPS) reciclado através da incorporação de copolímeros estireno-butadieno-estireno (SBS) de estrutura linear e radial. As blendas foram processadas em uma extrusora dupla rosca. Os copolímeros foram adicionados em teores de 5, 10 e 15% em massa. As propriedades avaliadas foram o índice de fluidez, a morfologia e o comportamento frente a ensaios de tração, flexão e resistência ao impacto das blendas formuladas. Em todos os casos, o SBS radial foi mais eficiente na recuperação das propriedades do poliestireno de alto impacto que o SBS linear quando comparadas às propriedades do HIPS reciclado. Palavras-chave: HIPS, reciclagem, tenacificação, copolímero SBS. Recovering Properties of Recycled HIPS Through Incorporation of SBS Triblock CopolymerAbstract: Toughening glassy thermoplastics by blending a rubbery material to the polymeric matrix has been extensively studied. In this work, we evaluated the resulting properties of recycled high impact polystyrene (HIPS), after the incorporation of either radial or linear SBS triblock copolymers. The blends were melt mixed using a twin-screw extruder. The copolymers were added at 5, 10 and 15% weight percent. The investigated properties included the determination of the melt flow index, the morphology and the mechanical behavior according to standard tension, flexion and impact methods of all formulated blends. In all cases, the radial SBS was more efficient in recovering the HIPS properties than the linear SBS, when comparing the properties of the blends with the properties of recycled HIPS. Keywords: HIPS, recycling, toughening, SBS copolymer. IntroduçãoO HIPS (poliestireno de alto impacto -do inglês high impact polystyrene) é uma blenda imiscível de poliestireno (PS), polibutadieno (PB) e uma determinada concentração por enxertia dos dois componentes [1] . O HIPS é obtido pela polimerização in situ do estireno na presença de polibutadieno formando domínios discretos da fase elastomérica dispersos em uma matriz contínua de PS [2] . A polimerização elastômero-estireno gera um produto com maior resistência ao impacto que o poliestireno homopolímero [3,4] e blendas pós-reator de PS e elastômero [3] . O HIPS é também mais resistente a líquidos orgânicos, óleos e graxas que o PS sem adição de PB [4] . Por sua maior tenacidade, o HIPS é amplamente utilizado em aplicações que necessitem maior resistência que o PS não-tenacificado, tais como gabinetes de refrigeradores, eletroeletrônicos, peças de máquinas e veículos, grades de ar-condicionado, saltos para calçados, brinquedos, acessórios para móveis, embalagens de proteção contra choques, utilidades domésticas, entre outros [2,3] . A reciclagem de plásticos é uma prática consolidada e constitui-se uma alternativa real para a redução da demanda por matérias-primas petroquímicas, contribuindo p...

Since epoxy resins are used as composite matrix with excellent results, and silica is one of the fillers most often employed, this study compared the performance of rice husk ash (RHA) as filler in epoxy composites, in replacement for high-purity silica. Composites were molded containing 20%, 40%, and 60% (wt) silica or RHA. Viscosity analysis, infrared spectroscopy (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) as well as mechanical and water absorption tests were carried out to evaluate composites. Glass transition temperature after curing and thermal degradation temperature of all samples analyzed were approximately 140 ºC and 370 ºC, respectively. RHA and silica exhibited similar mechanical and water absorption characteristics, indicating that rice husk ash may be a suitable replacement for silica. SEM imaging showed good filler dispersion and distribution in the polymer matrix, highlighting the more effective adhesion interface between RHA particles and the matrix.

This study evaluates the thermal, morphological and mechanical behavior of polypropylene (PP) composite with different natural fibers. The fibers used were wood, sugarcane, bamboo, babassu, coconut and kenaf with and without coupling agent. The thermal, morphological and mechanical properties were evaluated, and a composite PP+GFPP (glass fiber) was used as reference. The interaction at the interface fiber-polymer matrix was studied by scanning electron microscopy (SEM) at the fractured surface of the composites, as expected the presence of maleic anhydride (MA) as coupling agent increasedthe interaction at the interface. The influence of natural fiber in the degree of crystallinity of the composites was evaluated by DSC analysis. The samples of PP+GFPP and PP+(PP-MA)+WF (wood flour) showed better temperature stability. PP+GF also presented superior flexural modulus. The thermal dynamic mechanical behavior was evaluated by DMA, a decrease in storage modulus with increasing temperature was observed, the PP+GF and the composite containing maleic anhydride and sugarcane fiber showed higher modulus. The natural fiber biocomposites studied, consistently presented lower flexural modulus and tensile strength than the reference composite, with and without the use of coupling agent. As expected the use of natural fibers lowered the density compared to the reference material.

The geometry of the title compounds in the ground state and in the first excited singlet state have been investigated using AM1 semi-empirical molecular orbital calculations. The data obtained have been employed in a comparative study of the HAM/3 and the INDO/S-CI computational methods for electronic spectra simulation. AM1 results show that the most stable forms of the studied structures are H-bonded structures-enol and keto tautomers for the ground state and first excited singlet state, respectively. Concerning spectroscopic results, INDO/S-CI yields numerical values of excitation energy that better agree with experimental data, while HAM/3 better describes the distribution and relative intensities of the absorption/emission bands.Compounds showing excited state intra-molecular protontransfer reactions (ESIPT) have been declared efficient sources of tuneable stimulated emission 1-3 as well as stabilisers against UV radiation, 4,5 giving rise to renewed interest among photophysicists. 6-19 Their common feature is an unusual very fast proton transfer (Scheme 1), even at low temperatures, from Paper 6/08094D

Resumo:No presente trabalho a polissulfona bisfenol-A (PSU) foi sulfonada com o agente de sulfonação trimetil silil cloro sulfônico [(CH 3 ) 3 SiSO 3 Cl], em solução homogênea de dicloroetano. A reação de sulfonação foi confirmada por titulação ácido-base e análises FTIR. As membranas híbridas foram obtidas por vazamento da solução polimérica da polissulfona bisfenol-A sulfonada (SPSU) e sílica precipitada Tixosil ® 333 em N-N-dimetilacetamida (DMAc), e a formação das ligações cruzadas foi estudada por irradiação. Foram utilizadas doses totais de 5 a 30 kGy de radiação gama, oriunda de uma fonte de 60 Co. A absorção de água foi determinada pela variação percentual da massa da membrana seca e hidratada em água deionizada a 40 e 60 °C. A condutividade protônica das membranas na forma ácida foi obtida pela técnica da espectroscopia de impedância ac utilizando um potenciostato/galvanostato. As membranas híbridas reticuladas por irradiação apresentaram condutividade protônica próxima de 10 -1 S.cm -1 a 100% RH e 80 °C. O desempenho eletroquímico, as estabilidades térmica e mecânica, e o baixo custo tornam a membrana SPSU híbrida reticulada um possível substituto da membrana Nafion nas células a combustível que usam eletrólito polimérico. Palavras-chave: Membrana híbrida, condutividade protônica, irradiação gama, ligações cruzadas. Study of Cross-linking Reactions Induced by Gamma Rays in Hybrid Membranes of Bisphenol-A-Polysulfone and Precipitated SilicaAbstract: In this work the bisphenol-A-polysulfone (PSF) was sulfonated using trimethyl silyl chlorosulfonate [(CH 3 ) 3 SiSO 3 Cl] as a mild sulfonating agent in a homogeneous solution of dichloroetane. The sulfonation reaction was confirmed by acid-base titration and FTIRspectroscopy analysis. The hybrid membranes were obtained by casting the sulfonated bisphenol-A-polysulfone (SPSF) and precipitated silica Tixosil ® 333 solutions in N-N-dimethylacetamide. Cross-linking in the hybrid membranes was obtained by irradiation, with doses ranging from 5 to 30 kGy using gamma ray from a 60 Co source. The water uptake and the swelling of the membranes were estimated by measuring the change in weight between dry and wet conditions. The conductivity of the membranes in acid form was measured with the ac impedance technique using a PGSTAT30 frequency response analyzer. The hybrid cross-linked membranes have conductivity close to 10 -1 S.cm -1 at 100% RH and 80 °C. Electrochemical performances, thermo-mechanical stability and low cost make this cross-linked SPSF hybrid membrane an attractive material for fuel cells using a proton exchange membrane.