Nanocompósitos de polietileno/sílica com prata para aplicações antibacterianas

Dois diferentes tipos de nanopartículas de prata (NPAgs) e sílica foram sintetizadas para uso como carga antibacteriana em polietileno. As primeiras NPAgs foram ligadas covalentemente a sílica coloidal (SiAg) através de duas rotas (ácida e básica). As segundas NPAgs foram encapsuladas por sílica pelo método sol-gel (SiAgE). Para as duas cargas a síntese dos nanocompósitos foi realizada através da polimerização in situ de etileno utilizando o sistema catalítico Cp2ZrCl2/MAO (dicloro bis(ciclopentadienil)zircônio IV)/metilaluminoxano (MAO). As SiAg, foram caracterizadas por ICP OES, SAXS e BET determinando a concentração de prata, morfologia e tamanho. Os nanocompósitos (PESiAg) foram caracterizados por DSC, TGA e MEV. O teor de Ag dos mesmos também foi avaliado, assim como a sua atividade frente as bactérias, Staphylococcus aureus, Salmonella spp., Escherichia coli. Todas as amostras apresentaram ação antibacteriana. As SiAgE foram sintetizadas via três rotas de redução da prata: ácido cítrico (R1), glicose (R2) e glicerol (R3). As caracterizações foram através MEV, TGA, DRX, UV-VIS, FT-IR, BET, SAXS e atividade antibacteriana, verificando propriedades estruturais, texturais, morfológicas e antibacterianas. Tanto as cargas (SiAgE) quanto os nanocompósitos (PESiAgE) apresentaram propriedades antibacterianas frente Staphylococcus aureus, Escherichia coli.Two different types of silver nanoparticles (NPAgs) and silica were synthesized for use as antibacterial filler in polyethylene. The first NPAgs were covalently bonded to colloidal silica (SiAg) through two routes (acid and basic). The second NPAgs were encapsulated by silica by the sol-gel method (SiAgE). The nanocomposites were developed by the in situ polymerization of ethylene using the catalytic system Cp2ZrCl2/MAO (dichloride bis (cyclopentadienyl) zirconium IV)/Methylaluminoxane (MAO). The SiAg were characterized by ICP OES, SAXS and BET determining the concentration of silver, morphology and size. PESiAg the nanocomposites (PESiAg) were characterized by DSC, TGA and MEV. The concentration of Ag in the nanocomposites was also evaluated, as well as their bacterial activity against, Staphylococcus aureus, Salmonella spp., Escherichia coli. All samples presented antibacterial action. The SiAgE were synthesized via three silver reduction routes: citric acid (R1), glucose (R2) and glycerol (R3). The characterizations of the nanoparticles were through SEM, TGA, DRX, UV-VIS, FT-IR, BET, SAXS and antibacterial activity, verifying structural, textural, morphological and antibacterial properties. Both the fillers (SiAgE) and nanocomposites (PESiAgE) presented antibacterial properties against Staphylococcus aureus and Escherichia coli

Few layer reduced graphene oxide : evaluation of the best experimental conditions for easy production

This work aimed to produce graphene oxide with few graphene layers, a low number of defects, good conductivity and reasonable amount of oxygen, adequate for use as filler in polymeric composites. Two starting materials were evaluated: expanded graphite and graphite flakes. The method of oxidation used was the Staudenmaier one, which was tested over different lengths of time. No appreciable differences were found among the oxidation times and so the lowest oxidation time (24 h) was chosen as the most adequate. An investigation was also conducted into suitable temperatures for the reduction of graphite oxide. A temperature of 1000 ºC gave the best results, allowing a good quality material with few defects to be obtained. The reduction was also evaluated under inert and normal atmosphere. The best results were obtained when the least modified material, e. g., graphite flakes, was used as a starting material, oxidized for 24h and reduced at 1000 ºC for 30 s in a quartz ampoule under a normal atmosphere

Antimicrobial high-density polyethylene (HDPE)/ZnO nanocomposites obtained by in situ polymerization

Nanostructured zinc oxide (ZnO) prepared by combustion in solution was used to obtain nanocomposites. The ZnO particles were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), and scanning electron microscopy (SEM), showing crystallite size of 32 nm and a superficial area of 32.6 m2 g–1. Nanocomposites with 1, 3, and 5 wt.% of ZnO in the polymeric matrix were obtained using the in situ polymerization of ethylene with catalytic activities between 1500-1700 kg (molZr h PE)–1. The high-density polyethylene nanocomposites (PEZnO) were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), SEM, and transmission electron microscopy (TEM). The nanocomposites with 1 wt.% ZnO gave excellent mechanical properties, and all were active against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria

Few Layer Reduced Graphene Oxide: Evaluation of the Best Experimental Conditions for Easy Production

This work aimed to produce graphene oxide with few graphene layers, a low number of defects, good conductivity and reasonable amount of oxygen, adequate for use as filler in polymeric composites. Two starting materials were evaluated: expanded graphite and graphite flakes. The method of oxidation used was the Staudenmaier one, which was tested over different lengths of time. No appreciable differences were found among the oxidation times and so the lowest oxidation time (24 h) was chosen as the most adequate. An investigation was also conducted into suitable temperatures for the reduction of graphite oxide. A temperature of 1000 ºC gave the best results, allowing a good quality material with few defects to be obtained. The reduction was also evaluated under inert and normal atmosphere. The best results were obtained when the least modified material, e. g., graphite flakes, was used as a starting material, oxidized for 24h and reduced at 1000 ºC for 30 s in a quartz ampoule under a normal atmosphere

Nanocompósitos de polietileno/sílica com prata para aplicações antibacterianas

Dois diferentes tipos de nanopartículas de prata (NPAgs) e sílica foram sintetizadas para uso como carga antibacteriana em polietileno. As primeiras NPAgs foram ligadas covalentemente a sílica coloidal (SiAg) através de duas rotas (ácida e básica). As segundas NPAgs foram encapsuladas por sílica pelo método sol-gel (SiAgE). Para as duas cargas a síntese dos nanocompósitos foi realizada através da polimerização in situ de etileno utilizando o sistema catalítico Cp2ZrCl2/MAO (dicloro bis(ciclopentadienil)zircônio IV)/metilaluminoxano (MAO). As SiAg, foram caracterizadas por ICP OES, SAXS e BET determinando a concentração de prata, morfologia e tamanho. Os nanocompósitos (PESiAg) foram caracterizados por DSC, TGA e MEV. O teor de Ag dos mesmos também foi avaliado, assim como a sua atividade frente as bactérias, Staphylococcus aureus, Salmonella spp., Escherichia coli. Todas as amostras apresentaram ação antibacteriana. As SiAgE foram sintetizadas via três rotas de redução da prata: ácido cítrico (R1), glicose (R2) e glicerol (R3). As caracterizações foram através MEV, TGA, DRX, UV-VIS, FT-IR, BET, SAXS e atividade antibacteriana, verificando propriedades estruturais, texturais, morfológicas e antibacterianas. Tanto as cargas (SiAgE) quanto os nanocompósitos (PESiAgE) apresentaram propriedades antibacterianas frente Staphylococcus aureus, Escherichia coli.Two different types of silver nanoparticles (NPAgs) and silica were synthesized for use as antibacterial filler in polyethylene. The first NPAgs were covalently bonded to colloidal silica (SiAg) through two routes (acid and basic). The second NPAgs were encapsulated by silica by the sol-gel method (SiAgE). The nanocomposites were developed by the in situ polymerization of ethylene using the catalytic system Cp2ZrCl2/MAO (dichloride bis (cyclopentadienyl) zirconium IV)/Methylaluminoxane (MAO). The SiAg were characterized by ICP OES, SAXS and BET determining the concentration of silver, morphology and size. PESiAg the nanocomposites (PESiAg) were characterized by DSC, TGA and MEV. The concentration of Ag in the nanocomposites was also evaluated, as well as their bacterial activity against, Staphylococcus aureus, Salmonella spp., Escherichia coli. All samples presented antibacterial action. The SiAgE were synthesized via three silver reduction routes: citric acid (R1), glucose (R2) and glycerol (R3). The characterizations of the nanoparticles were through SEM, TGA, DRX, UV-VIS, FT-IR, BET, SAXS and antibacterial activity, verifying structural, textural, morphological and antibacterial properties. Both the fillers (SiAgE) and nanocomposites (PESiAgE) presented antibacterial properties against Staphylococcus aureus and Escherichia coli

Estudo da obtenção de grafeno a partir de grafite e o seu uso em nanocompósitos poliolefínicos

A obtenção de grafeno a partir do grafite foi avaliada através de dois métodos de oxidação (Staudenmaier e Hummers) e dois métodos de redução (térmica e química com hidrazina). Foi realizada a otimização do método de Staudenmaier (constatado o mais eficiente) avaliando diferentes tempos de reação e temperaturas de redução. Caracterizações dos óxidos reduzidos (DRX, FT-IR, Raman, MEV, MET, CHN e EIE) comprovaram que houve uma diminuição dos tamanhos de cristais, por consequência um menor empilhamento aumentando a condutividade elétrica. Na sequencia esses óxidos (GO) e óxidos reduzidos (RED) foram utilizados como suporte para o catalisador Cp2ZrCl2 em polimerizações in situ de etileno suportadas para a síntese de nanocompósitos. Foram utilizados 15% (p.p-1) de MAO e 2 % Zr/grafite. A quantidade de metal imobilizado no suporte foi quantificada por ICP-OES e mostrou que o suporte em GO foi de 1,31% (p.p-1) e em RED foi de 0,36% (p.p-1) Zr/grafite. Os valores de atividades catalíticas obtidas na presença da nanocarga ficaram na faixa de 30 a 415 quando usado GO e 423 a 780 usando RED. Os percentuais de carga variaram de 1,3 a 17% Grafite/PE. Análises de TGA e DMA, mostraram uma maior estabilidade térmica dos nanocompósitos comparado com o polímero homogêneo. A condutividade elétrica foi avaliada por EIE e mostrou que a introdução do RED fez com que o polímero passa-se de um material isolante para semicondutor. Quando se utilizou GO em um percentual em peso de 2,7% obteve-se uma condutividade elétrica de 1,53x10-12 S.cm-1. Quando empregado o RED observou-se melhor condutividade em todos os percentuais de 3,18 x 10-10 S.cm-1 (2,6% p.p-1) até 1,1 x 10-5 S.cm-1 (1,4% p.p-1).The preparation of graphene from graphite was evaluated by two methods of oxidation (Hummer and Staudenmaier) and two methods of reduction (thermal and chemical with hydrazine). It was performed the optimization of Staudenmaier method (the most efficient) evaluating different reaction times and temperatures of reduction. Characterizations of the reduced oxides (XRD, FT-IR, Raman, SEM, TEM, CHN and EIE) proved that there was a decrease in the size of crystals, consequently, a lower stacking of graphene increasing the electrical conductivity. Following on, these oxides (GO) and reduced oxides (RED) were used as supports for the catalyst Cp2ZrCl2 in the in situ polymerization of ethylene to obtain the nanocomposites. There were used 15 wt.-% of MAO/graphite and 2 wt.-% of Zr/graphite. The amount of immobilized metal on the support was quantified by ICP-OES showing that the efficiency of the support was 1.31 wt.-% Zr/GO and 0.36wt.-% Zr/RED. The values of catalytic activity obtained in the presence of nanocarga were in the range 30-415 when used GO and 423-780 using RED. The load percentages ranged between 1.3 and 17 wt% Graphite/PE. Analysis of TGA e DMA, showed an increase in the thermal stability of the nanocomposites compared to the neat polyethylene. The electrical conductivity was measured by EIE and showed that the introduction of RED makes the polymer to pass from an insulating to a semiconductor material. When GO is used in a percentage by weight of 2.7% the electrical conductivity obtained was 1.53x10-12 S.cm-1. When RED was used it was observed a higher conductivity in all RED percentages from 3.18 x 10-10 S.cm-1 (2.6% wt.- RED/PE) to 1,1 x 10-5 S.cm-1 (1,4% wt.- RED/PE)

Few layer reduced graphene oxide : evaluation of the best experimental conditions for easy production

This work aimed to produce graphene oxide with few graphene layers, a low number of defects, good conductivity and reasonable amount of oxygen, adequate for use as filler in polymeric composites. Two starting materials were evaluated: expanded graphite and graphite flakes. The method of oxidation used was the Staudenmaier one, which was tested over different lengths of time. No appreciable differences were found among the oxidation times and so the lowest oxidation time (24 h) was chosen as the most adequate. An investigation was also conducted into suitable temperatures for the reduction of graphite oxide. A temperature of 1000 ºC gave the best results, allowing a good quality material with few defects to be obtained. The reduction was also evaluated under inert and normal atmosphere. The best results were obtained when the least modified material, e. g., graphite flakes, was used as a starting material, oxidized for 24h and reduced at 1000 ºC for 30 s in a quartz ampoule under a normal atmosphere

Polyethylene/reduced graphite oxide nanocomposites with improved morphology and conductivity

Artículo de publicación ISIThe use of graphite and polyolefins as starting materials to prepare nanocomposites is convenient because both are inexpensive and have very different properties, one is conductive and the other is insulating. The formation of nanocomposites can extend the applicability of both commodities. In this work we synthesized nanocomposites of polyethylene (PE) with two types of graphites, graphite oxide (GO) and reduced graphite oxide (RGO), by in situ polymerization using a supported metallocene catalyst. The functional groups on the graphites were used to support the metallocene catalyst by a previous treatment with methylaluminoxane. The nanocomposites were obtained with good catalytic activities and presented excellent morphology and dispersion; their elastic modulus and crystallization temperatures were higher than those of neat PE. However, the nanocomposites PEGO were insulant, whereas PERGO had a conductivity of 1.1 x 10(-5) S cm(-1) with 3.1 wt% filler. This is a significant result compared to the conductivity obtained using non-supported graphite nanosheets where more than 15 wt% of graphite nanosheets are needed to obtain conductivities higher than 10(-7) S cm(-1). This improvement in the percolation threshold was attributed to the good morphology of the PERGO nanocomposites obtained due to the control of the graphitic sheets and the support methodology.CNPq 302902/2013-9 473128/2011-0 FAPERG-PRONEX 09/2009 Department of the Navy Grant N62909-11-1-7069 Millennium Nucleus of Chemical Processes and Catalysis (CPC) NC12008

Synthesis of polyethylene/silica-silver nanocomposites with antibacterial properties by in situ polymerization

Synthesis of polyethylene/silica-silver nanocomposites (PE/SiAg) by in situ polymerization with supported and non-supported catalysts was achieved using the Cp2ZrCl2/MAO catalytic system. Silica-silver nanoparticles (SiAg) were synthesized via two routes (acidic and basic) and characterized to determine the silver content, morphology, and size. The basic route resulted in particles with a lower concentration of silver and with smaller diameters. The polymerizations of ethylene in the presence of the fillers produced high yields of nanocomposites. The catalyst support in SiAg was efficient, although the percentage of Zr effectively immobilized was very low. Polyethylene melting and crystallization temperatures did not change significantly with the addition of the filler. SEM images showed differences in the morphologies between the supported and non-supported catalysis, and between the acidic and basic conditions for SiAg preparation. Two different tests were performed and showed that the nanocomposites inhibited the proliferation of bacteria in contact with the films.Fil: Pavoski, Giovani. Universidade Federal do Rio Grande do Sul; BrasilFil: Kalikoski, Renan. Universidade Federal do Rio Grande do Sul; BrasilFil: Souza, Gustavo. Universidade Federal do Rio Grande do Sul; BrasilFil: Wentz Brum, Luiz Fernando. Universidade Federal do Rio Grande do Sul; BrasilFil: Dos Santos, Cristiane. Universidade Federal do Rio Grande do Sul; BrasilFil: Abo Markeb, Ahmad. Universidade Federal do Rio Grande do Sul; BrasilFil: Dos Santos, João Henrique Zimnoch. Universidade Federal do Rio Grande do Sul; BrasilFil: Font, Xavier. Universidade Federal do Rio Grande do Sul; BrasilFil: Dell'Erba, Ignacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Galland, Griselda Barrera. Universidade Federal do Rio Grande do Sul; Brasi