Abstract This paper uses a new kinetic modeling and simulations to analyse the effect of temperature on the polystyrene properties obtained by atom-transfer radical polymerization (ATRP). Differently from what has been traditionaly published in ATRP modeling works, it was considered “break” reactions in the mechanism aiming to reproduce the process at high temperatures. Results suggest that there is an upper limit temperature (130 °C), above which the polymer architecture loses the control. In addition, for the system considered in this work, the optimum operating temperature was 100 °C, because at this temperature polymer with very low polydispersity index is obtained, at considerable fast polymerization rate. Therefore, this present paper provides not only a tool to study ATRP processes by simulations, but also a tool for analysis and optimization, being a basis for future works dealing with this monomer and process.

resumo Neste trabalho avaliou-se a atividade antimicrobiana das nanopartículas de prata (AgNPs) incorporadas em membranas de acetato celulose (AC) e blendas de quitosana/poli-óxido de etileno (CTS/PEO) preparadas pelo método de eletrofiação. A formação das AgNPs previamente sintetizadas foi monitorada por UV-Vis e caracterizada por microscopia eletrônica de transmissão (MET). A distribuição de tamanho das AgNPs foi mensurada por espalhamento de luz dinâmico, com tamanho médio em torno de 20 nm. A presença das NPs na superfície das nanofibras eletrofiadas foi observada por microscopia eletrônica com emissão de campo (FEG) e confirmada por MET. A atividade antimicrobiana das membranas nanoestruturadas de AC e CTS/PEO foi avaliada pelo uso de bactérias Gram-positivas, tais como Staphylococcus aureus ATCC 29213 e Propionibacterium acnes ATCC 6919, e Gram-negativas, como Escherichia coli ATCC 25992 e Pseudomonas aeruginosa ATCC 17933. Os resultados microbiológicos mostraram a presença das AgNPs nas membranas de AC e CTS/PEO com significativa atividade antimicrobiana para Escherichia coli e Propionibacterium acnes, respectivamente.

abstract This study examines the antimicrobial activity of silver nanoparticles incorporated into nanostructured membranes made of cellulose acetate (CA) and blends of chitosan/poly-(ethylene oxide, CTS/PEO) and prepared by electrospinning. The formation of chemically synthesized Ag nanoparticles (AgNPs) was monitored by UV-visible spectroscopy (UV-Vis) and characterized by transmission electron microscopy (TEM). The size distribution of the AgNPs was measured by dynamic light scattering (DLS), with an average size of approximately 20 nm. The presence of AgNPs on the surface of electrospun nanofibers was observed by field emission electron microscopy (FEG) and confirmed by TEM. The antimicrobial activity of AgNPs incorporated into nanostructured membranes made of CA and CTS/PEO electrospun nanofibers was evaluated in the presence of both Gram-positive bacteria, such as Staphylococcus aureus ATCC 29213 and Propionibacterium acnes ATCC 6919, and Gram-negative bacteria, such as Escherichia coli ATCC 25992 and Pseudomonas aeruginosa ATCC 17933. Microbiological results showed that the presence of AgNPs in CA and CTS/PEO nanostructured membranes has significant antimicrobial activity for the Gram-positive bacteria Escherichia coli and Propionibacterium acnes.

Este trabalho descreve a síntese e caracterização de nanocompósitos de poliestireno (PS) e hidróxido duplo lamelar (HDL) formado pelos cátions de ZnAl via polimerização in situ. O HDL utilizado neste trabalho foi modificado com uma mistura de dois ânions, laurato e palmitato. Para caracterização da estrutura e morfologia dos nanocompósitos sintetizados, foram realizadas análises por difração de raios X (DRX) e microscopia eletrônica de transmissão (MET). As caracterizações térmicas, mecânicas e de flamabilidade foram realizadas via análise termogravimétrica (TGA), ensaio de flexão e ensaio de flamabilidade, respectivamente. Os resultados obtidos neste trabalho sugerem que os nanocompósitos sintetizados possuem, de uma forma geral, uma morfologia intercalada/esfoliada com melhoras em suas propriedades térmicas e mecânicas, quando comparados com o PS puro. Entretanto, não foi observado melhora na propriedade de flamabilidade.

This work describes the synthesis and characterization of polystyrene (PS) and layered double hydroxide (LDH) nanocomposites formed by ZnAl cations via in situ polymerization. The LDH used in this study was modified with a mixture of two anions: laurate and palmitate. The characterization of structure and morphology for the synthesized nanocomposites was developed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal, mechanical and flammability characterizations properties were carried out via thermogravimetric analysis (TGA), bending test and flammability test, respectively. The results suggest that the nanocomposites have in general intercalated/exfoliated morphology with improvements in thermal and mechanical properties compared to the neat PS. However no significant improvement was observed on the flammability property.

Polystyrene/layered hydroxide salt (LHS) modified with sodium dodecyl sulfate was synthesized by in situ polymerization. The materials synthesized were characterized by gravimetry, X-ray diffraction (XRD), thermogravimetry analyses (TGA), differential scanning calorimetry (DSC) and the flammability test (FT). XRD demonstrated that synthesized nanocomposites in all compositions studied showed poor global dispersion of LHS in polystyrene. TGA showed a slight decrease in thermal stability. DSC curves showed that the glass transition temperature of polystyrene and nanocomposites were similar. The FT showed that the nanocomposite with low load of LHS exhibited good results.