ABSTRACT The rise of nanotechnology has allowed the development of several inorganic nanoparticles with strong biocidal properties against bacteria, fungi, and viruses. Among them, silver nanoparticles (AgNPs) stand out as one of the most promising antimicrobial nanomaterials. Graphene oxide (GO) is another attractive nanomaterial with antimicrobial properties. Although the antimicrobial effect of AgNPs and GO is known, the development of hybrid materials of GO-AgNPs has considerable interest in various applications since they may exhibit synergistic bactericidal properties that exceed the yields of the individual components. The aims of this work were to evaluate the antimicrobial activity and anti-adhesion properties of AgNPs and GO-AgNPs nanocomposites for potential applications in antimicrobial coatings. The antimicrobial activity was tested by agar diffusion method. It was found that activity varied according to the synthesis procedure of the nanomaterials. Pseudomonas aeruginosa, Bacillus cereus and Kokuria rhizophila were the most susceptible strains. The nanocomposite GO- AgNPs synthetized using the ex-situ method exhibited the highest antibacterial activity against all the assayed strains. Similar results were obtained for bacterial adhesion inhibition tests. Thus, GO-AgNPs nanohybrids could be applied as antibacterial coatings to prevent bacterial biofilm development.

ABSTRACT Mechanical properties in tension, bending, fatigue and lap-shear in two different proportions (0.5%wt and 1%wt) of TRGO (Thermally Reduced Graphite Oxide) doped ARALL (Aramid Aluminium Laminate) were examined. The materials and their failure modes were characterized morphologically by examination through SEM (Scanning Electron Microscopy). Some mechanical properties of ARALL were improved when doped with 0.5% of TRGO, showing a significant increase of fatigue properties, as well as a change in fracture surface morphology. Tension andbending properties showed variable results and further studies should be carried out to arrive to definitive conclusions, while lap-shear testing showed lower shear values. The results were statistically validated through mono-factorial variance analysis. Comparing the present results with previous work on CNT (Carbon Nanotubes) doped ARALL, it can be stated that: (a) TRGO doped ARALL showed improved fatigue properties when compared with non-doped ARALL, but in a less effective way than doping with CNT, (b) TRGO doped ARALL tension properties showed no significant variation as compared with ARALL alone, showing no deleterious influence as in the CNT doping case, (c) TRGO doped ARALL bending properties resulted better than non-doped ARALL, but similar than those obtained when doping with CNT and (d) TRGO decreased the adherence between aramid fiber impregnated L20 epoxy resin and aluminium. These last results are sustained based on observed improvements as a percentage value, without a statistical variance analysis made on CNT doped ARALL.

RESUMEN Se estudiaron las propiedades mecánicas de ARALL (Aramid Aluminium Laminated) al ser reforzado con dos dosificaciones (0.5 y 1% en peso) de TRGO (Thermically Reduced Graphite Oxide), en busca de aumentar las propiedades mecánicas de este material compuesto en tracción, flexión, fatiga y Lap Shear. Los resultados mostraron un aumento en algunas de las propiedades mecánicas de ARALL al ser dopado con TRGO, principalmente en el material que fue reforzado con 0,5%, destacando un cambio en la morfología de fractura de la superficie del aluminio, así como también un aumento significativo de la resistencia a la fatiga del material, tema de gran interés principalmente para el mundo aeronáutico. Otras propiedades como resistencia a la tracción y flexión presentaron resultados variables, siendo necesario un mayor estudio para poder definir el efecto de la cantidad de refuerzo sobre la respuesta entregada por el material estudiado. En el caso de lap-shear, se presentó una disminución en la resistencia al corte de la resina con la dosificación de 0.5% TRGO. Los resultados obtenidos fueron validados estadísticamente mediante el análisis de varianza unifactorial. Al comparar los resultados obtenidos con los de estudios anteriores donde se utilizaron nanotubos de carbono (NTC), se puede concluir que: (a) en fatiga el TRGO se mostró menos efectivo que los NTC en la mejora de vida útil; (b) en tracción el TRGO no presentó variaciones importantes a diferencia de los NTC que disminuyen considerablemente las propiedades mecánicas, (c) en flexión el TRGO no presentó una eficiencia respecto a la obtenida con NTC y (d) el TRGO disminuyó la adherencia de la resina epoxy L20 impregnada con fibra de aramida al aluminio. Estas conclusiones se basan en mejoras porcentuales, ya que no existe un sustento estadístico que respalde los resultados obtenidos en los trabajos que se utilizaron NTC.

ABSTRACT Mechanical properties in tension, bending, fatigue and lap-shear in two different proportions (0.5%wt and 1%wt) of TRGO (Thermally Reduced Graphite Oxide) doped ARALL (Aramid Aluminium Laminate) were examined. The materials and their failure modes were characterized morphologically by examination through SEM (Scanning Electron Microscopy). Some mechanical properties of ARALL were improved when doped with 0.5% of TRGO, showing a significant increase of fatigue properties, as well as a change in fracture surface morphology. Tension andbending properties showed variable results and further studies should be carried out to arrive to definitive conclusions, while lap-shear testing showed lower shear values. The results were statistically validated through mono-factorial variance analysis. Comparing the present results with previous work on CNT (Carbon Nanotubes) doped ARALL, it can be stated that: (a) TRGO doped ARALL showed improved fatigue properties when compared with non-doped ARALL, but in a less effective way than doping with CNT, (b) TRGO doped ARALL tension properties showed no significant variation as compared with ARALL alone, showing no deleterious influence as in the CNT doping case, (c) TRGO doped ARALL bending properties resulted better than non-doped ARALL, but similar than those obtained when doping with CNT and (d) TRGO decreased the adherence between aramid fiber impregnated L20 epoxy resin and aluminium. These last results are sustained based on observed improvements as a percentage value, without a statistical variance analysis made on CNT doped ARALL.

RESUMEN Se estudiaron las propiedades mecánicas de ARALL (Aramid Aluminium Laminated) al ser reforzado con dos dosificaciones (0.5 y 1% en peso) de TRGO (Thermically Reduced Graphite Oxide), en busca de aumentar las propiedades mecánicas de este material compuesto en tracción, flexión, fatiga y Lap Shear. Los resultados mostraron un aumento en algunas de las propiedades mecánicas de ARALL al ser dopado con TRGO, principalmente en el material que fue reforzado con 0,5%, destacando un cambio en la morfología de fractura de la superficie del aluminio, así como también un aumento significativo de la resistencia a la fatiga del material, tema de gran interés principalmente para el mundo aeronáutico. Otras propiedades como resistencia a la tracción y flexión presentaron resultados variables, siendo necesario un mayor estudio para poder definir el efecto de la cantidad de refuerzo sobre la respuesta entregada por el material estudiado. En el caso de lap-shear, se presentó una disminución en la resistencia al corte de la resina con la dosificación de 0.5% TRGO. Los resultados obtenidos fueron validados estadísticamente mediante el análisis de varianza unifactorial. Al comparar los resultados obtenidos con los de estudios anteriores donde se utilizaron nanotubos de carbono (NTC), se puede concluir que: (a) en fatiga el TRGO se mostró menos efectivo que los NTC en la mejora de vida útil; (b) en tracción el TRGO no presentó variaciones importantes a diferencia de los NTC que disminuyen considerablemente las propiedades mecánicas, (c) en flexión el TRGO no presentó una eficiencia respecto a la obtenida con NTC y (d) el TRGO disminuyó la adherencia de la resina epoxy L20 impregnada con fibra de aramida al aluminio. Estas conclusiones se basan en mejoras porcentuales, ya que no existe un sustento estadístico que respalde los resultados obtenidos en los trabajos que se utilizaron NTC.

Background: The antimicrobial activity of copper (Cu+2) is recognized and used as an antimicrobial agent. Aim: To evaluate the antimicrobial activity of copper against microorganisms obtained from chronic cutaneous wound infections. Material and Methods: Five chemical products that contained copper particles in their composition were tested (zeolite, silica, acetate, nitrate and nanoparticle of copper). The antimicrobial activity against antibiotic resistant strains usually isolated from chronic cutaneous wound infections was determined for two of the products with better performance in copper release. Results: The minimal inhibitory and minimal bactericidal concentrations of copper acetate and nitrate were similar, fluctuating between 400-2,000 µg/ml. Conclusions: The studied copper salts show great potential to be used to control both gram positive and gram negative, antibiotic resistant bacteria isolated from wound infections.

The present study reports the propylene polymerization using four different metallocene catalysts: rac-Et(Ind)2ZrCl2 (I); rac-Et(2-Me-Ind)2ZrCl2 (II); rac-Me2Si(Ind)2ZrCl2 (III) and Ph2C(Flu)(Cp)ZrCl2 (IV) in the presence of Metilaluminoxane (MAO) as cocatalyst. The polymerization carried out using different conditions of temperature, catalyst concentration, cocatalyst/catalyst ration and monomer concentration. The study was made with the aid of a statistical model of experimental planning. It was observed that the type of catalyst, and the experimental conditions of reaction have a significative influence in the catalytic activity and the properties of polymers obtained. Elevated values of activity were found at temperature of 70 C with catalysts I and III. Catalyst III produced polypropylenes with highest isotacticity. With catalyst IV were obtained syndiotactics polymers

En este trabajo se reporta el estudio de la polimerización de propeno utilizando los catalizadores metalocenos: dicloruro de etilenbisindenil circonio IV racémico, rac-Et(Ind)2ZrCl2 (I); dicloruro de etilenbis(2-metil-indenil) circonio IV racémico, rac-Et(2-Me-Ind)2ZrCl2 (II); dicloruro de dimetilsililbisindenil circonio IV racémico, rac-Me2Si(Ind)2ZrCl2 (III) y dicloruro de difenilmetilindeno ciclopentadienil 9-fluorenil circonio IV, Ph2C(Flu)(Cp)ZrCl2 (IV) en presencia de metilaluminoxano (MAO) como cocatalizador. Las polimerizaciones fueron realizadas a diferentes condiciones de temperatura, concentración de catalizador, razón molar cocatalizador/catalizador y concentración de monómero. Este estudio fue elaborado con la ayuda de un modelo estadístico de planeamiento experimental. Se observó que tanto el tipo de catalizador, como las condiciones de reacción estudiadas tienen una influencia en la actividad catalítica y en las propiedades de los polímeros obtenidos. Valores elevados de actividad fueron encontrados con los catalizadores I y III a una temperatura de polimerización de 70 C. Con el catalizador III se obtuvieron los polipropilenos de mayor isotacticidad. El catalizador IV produjo polímeros sindiotácticos