Gas barrier properties of poly(?-caprolactone)/clay nanocomposites: Influence of the morphology and polymer/clay interactions

Synthesis and Characterization of Aliphatic-aromatic Random Copolyester/clay Nano-biocomposites

Aliphatic-aromatic biodegradable random copolyester, poly (butylene sebacate-co-butylene isophthalate) (PBSeI) was synthesized by a two step direct melt polycondensation method. This copolyester was characterized by solubility studies, viscosity measurements, infrared, 1H-NMR, 13C-NMR and thermal data. However, to be a real alternative to classical synthetic polymers and find applications, the thermal properties of biodegradable polymers have to be improved. Synthesis of nano-biocomposites, which are obtained by incorporation of nanofillers into a biomatrix, is an interesting way to create polymers with characteristic properties. In the present study, the nano-biocomposites were synthesized by dispersing different weight percentages (1, 3 and 5%) of organo-modified montmorillonite clay (OMMT) into the biodegradable polyester matrix by the solvent intercalation method. Structural characterization and thermal analysis were carried out to better understand, the relationship between the structuring of the nanofillers and the properties of nano-biocomposites. The X-ray diffraction patterns obtained for the systems confirmed the nanodispersion of the OMMT-clay in the polyester networks. The scanning electron microscopy and high resolution transmission electron microscopy analyses showed that there was no phase separation between the two components which confirmed the compatibility of polyester with the organo-modified clay system. The results show that clay incorporation improved the thermal properties of PBSeI due to the exfoliated structure of the nanocomposites formed, and thus may increase the applicability of this biodegradable polymer in different fields.

Obtenção de membranas microporosas a partir de manocompósitos de poliamida 6/argila nacional. Parte 1: influência da presença da argila na morfologia das membranas

Membranas poliméricas foram produzidas a partir de nanocompósitos de poliamida 6 e argila constituída de silicatos em camadas, utilizando a técnica de imersão-precipitação. A argila foi modificada organicamente com os sais quaternários de amônio, Dodigen e Cetremide. Foram obtidos nanocompósitos de poliamida 6 com argila sem tratamento (MMT) e com argila tratada (OMMT). Os nanocompósitos obtidos foram avaliados por DRX e MET, apresentando estrutura com predominância de lamelas de argila esfoliadas na matriz polimérica. As membranas produzidas pelo método de inversão de fases foram caracterizadas por DRX e MEV. A difração de raios X das membranas confirmou os resultados para os nanocompósitos anteriormente preparados. A superfície da matriz observada por MEV apresentou poros irregulares. Já para as membranas com os nanocompósitos observou-se maior quantidade e melhor distribuição dos poros, indicando que a presença da argila alterou a morfologia da membrana. As fotomicrografias das seções transversais dessas membranas mostraram uma estrutura morfológica assimétrica, constituída de uma pele, onde os poros são muito pequenos ou inexistentes, e uma camada porosa com poros de tamanho e distribuição uniformes.

Micromechanical modeling and characterization of the effective properties in starch-based nano-biocomposites

The aim of this work was to predict the effective elastic properties of starch-based nano-biocomposites. Experiments (materials elaboration, morphological characterization and determination of mechanical properties) were conducted on both the pristine matrix (plasticized starch) and the matrix filled with montmorillonite nanoclay. Aggregated/intercalated and exfoliated nano-biocomposites were produced and mechanically tested under uniaxial tension to understand the effect of montmorillonite morphology/dispersion on the stiffness properties of starch-based nano-biocomposites. Micromechanical models, based on the classical bounds and the Mori-Tanaka approaches, were developed taking into consideration the influence of the clay concentration, the exfoliation ratio, the relative humidity and the storage time (ageing). Predicted results are in a good agreement with our experiments and show that the micromechanical model can be used as an indirect characterization technique to quantify the exfoliation/aggregation degree in the plasticized starch/clay nano-biocomposites.

Influence of the intercalated cations on the surface energy of montmorillonites: Consequences for the morphology and gas barrier properties of polyethylene/montmorillonites nanocomposites

Organically modified montmorillonites obtained by cation exchange from the same natural layered silicate were studied. The surface properties of the pristine and a series of organically modified clays were determined by inverse gas chromatography and the water adsorption mechanisms were studied by a gravimetric technique coupled with a microcalorimeter. A significant increase of the specific surface area, a decrease of the water adsorption, and a decrease of the dispersive component of the surface energy were observed when the sodium cations of the natural montmorillonite were exchanged for a quaternary ammonium. Slighter differences in surface properties were observed, on the other hand, between the different types of organically modified montmorillonites. Indeed, similar dispersive components of the surface energy were determined on the organoclays. Nevertheless, the specific surface area increased in the range 48-80 m(2)/g with increasing d-spacing values and the presence of specific groups attached to the quaternary ammonium, such as phenyl rings or hydroxyl groups, led to some specific behaviors, i.e., a more pronounced base character and a higher water adsorption at high activity, respectively. Differences in interlayer cation chain organization, denoted as crystallinity, were also observed as a function of the nature of the chains borne by the quaternary ammonium. In a later step, polyethylene-based nanocomposites were prepared with those organically modified montmorillonites. The clay dispersion and the barrier properties of the nanocomposites were discussed as a function of the montmorillonite characteristics and of the matrix/montmorillonite interactions expected from surface energy characterization.