Abstract This study evaluated the influence of cellulose nanocrystals (CNC) content on the properties of epoxy nanocomposites. The CNC were obtained from microcrystalline cellulose by acid hydrolysis. 4.0, 5.5 and 7.0% of untreated CNC were incorporated into epoxy resin. Sonication was used to disperse the CNC in the resin. The thermal stability, the glass transition temperature and the degree of conversion were reduced as observed by Thermogravimetry and Differential Scanning Calorimetry, respectively. The tensile and bending modulus showed no significant improvement and the impact resistance showed a slight reduction due to the non-uniform dispersion of the CNCs, as observed by Transmission Electron Microscopy. Analysis of Scanning Electron Microscopy showed a change of the fracture mechanism of the epoxy resin: the CNCs increased the elastic modulus by reinforcement, but accelerated the fracture by acting as defects. The Halpin-Tsai model was applied to predict the elastic modulus of the epoxy/CNC system.

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.

Chitosan is soluble in diluted acid solutions and can easily form films by casting. However, residual acid neutralization should be performed for biomedical applications what may compromise physical and mechanical properties of the films. Thus, plasticizers can be added to improve these properties. The aim of this study was to characterize morphological, barrier and mechanical properties, besides evaluate the in vitro cytotoxicity of sorbitol-plasticized and NaOH-Na2CO3 neutralized chitosan membranes for skin substitute application. Scanning electron microscopy, X-ray diffraction, water vapor permeability and mechanical tests were carried out to characterize the obtained membranes. Moreover, Vero cells were used for in vitro cytotoxicity evaluation. In this paper, we report a non-cytotoxic sorbitol-plasticized chitosan membrane with desirable properties for skin substitution, such as flexibility, water vapor permeability and high percentage of elongation.

Neste estudo, foram preparados, pelo método de intercalação do fundido, nanocompósitos de PLA com as argilas organofílicas Cloisite 20A e Cloisite 30B. A influência das argilas no processo de biodegradação do PLA foi avaliada com base no método de respirometria. A incorporação da argila Cloisite 20A praticamente não alterou a curva de mineralização do PLA. O nanocompósito com Cloisite 30B, por sua vez, apresentou um comportamento distinto, indicando um atraso no processo de biodegradação do polímero neste material. As amostras foram caracterizadas pelas técnicas de Difração de Raios X, Análise Termogravimétrica e Calorimetria Diferencial Exploratória. A caracterização dos materiais indicou uma estrutura possivelmente intercalada dos nanocompósitos, bem como a redução da estabilidade térmica e um pequeno aumento no grau de cristalinidade, em relação ao polímero puro.

In this study nanocomposites of PLA and organoclays Cloisite 20A and Cloisite 30B were prepared by melt intercalation. The influence from the organoclays on the biodegradation of PLA was evaluated based on the respirometry method. The incorporation of clay Cloisite 20A did not change the mineralization curve of PLA. The nanocomposite with Cloisite 30B, on the other hand, presented a different behavior, indicating a delay in the polymer biodegradation. The materials were characterized by X-ray Diffraction, Thermogravimetric Analysis and Differential Scanning Calorimetry. The materials characterization indicated nanocomposites with an intercalated structure as well as reduced thermal stability and a slight increase in the degree of crystallinity compared to the pure polymer.

Plastissois reticulados de PVC foram obtidos por meio de espalmagem, na presença de uma resina epóxi polifuncional tipo tetraglicidilmetilenodianilina (TGMDA). A presença de um amino acelerador, baseado numa poliaminoamida comercial, mostrou-se imprescindível para a ocorrência de reticulação das cadeias do PVC. Resultados de grau de reticulação mostraram que só houve formação de gel nas amostras onde o amino acelerador foi utilizado concomitantemente com a resina epóxi, evidenciando uma sinergia entre ambos. Apesar dos resultados de módulo de Young sugerirem a formação de uma rede tridimensional entre as moléculas do PVC e a resina epóxi, a comprovação de uma reação química de reticulação entre o PVC e a resina epóxi não foi possível, devido ao grande numero de moléculas presentes na formulação final. Entretanto, a evidência de que a reticulação de fato ocorreu poderá vir de estudos mais detalhados e o uso de outras técnicas de caracterização complementares, já iniciados.

PVC plastisols, crosslinked in the presence of a polyfunctional epoxy resin, were obtained via spread coating. It was possible to infer that the presence of an amine type accelerator, at least in the conditions used in this study, proved to be essential for crosslinking. The results of reticulation degree showed that gel formation only happened in samples where the amine type accelerator has been used concomitantly with the epoxy resin. The results of Young’s modulus seem to confirm the hypothesis of formation of a three dimensional network between the molecules of PVC and epoxy resin, but it was not possible to confirm a chemical reaction between these two polymers because of the large number of molecules present in the formulation. Evidence that crosslinking actually occurred may come from more detailed studies and the use of complementary characterization techniques, which are underway.

Electrospinning is used to produce fibers in the nanometer range by stretching a polymeric jet using electric fields of high magnitude. Chitosan is an abundant natural polymer that can be used to obtain biocompatible nanostructured membranes. The objectives of this work were to obtain nanostructured membranes based on blends of chitosan and polyoxyethylene (PEO), and evaluate their thermal and morphological properties, as well as their in vitro biocompatibility by agar diffusion cytotoxicity tests for three different cell lines. A nanostructured fibrous membrane with fiber diameters in the order of 200 nm was obtained, which presented a rough surface and thickness ranging from one to two millimeters. The results of the cytotoxicity tests evidenced that the chitosan/PEO membranes are non-toxic to the cells studied in this work. Further, the electrospinning technique was effective in obtaining nanostructured chitosan/PEO membranes, which showed biocompatibility according to in vitro preliminary tests using the cell lines.

This work investigates the reaction parameters of an immobilized lipase in the esterification reaction of n-butanol and butyric acid. Microbial lipase from Candida rugosa was immobilized onto styrene-divinylbenzene copolymer (STY-DVB) and subsequently introduced in an organic medium containing substrates in appropriate concentrations. Heptane was selected as solvent on the basis of its compatibility with the resin and the enzyme. The influence of molar ratio of acid to alcohol, amount of immobilized lipase and temperature on the butyl butyrate formation was determined. The results were compared with those achieved with free lipase and Lipozyme (commercially immobilized lipase) under the same operational conditions.