The influence of the incorporation of nanoparticles (organo-modified montmorillonite Cloisite 30B) in polyamide 6 (PA6) on the transport of small molecules was investigated. Nanocomposites were prepared by melt blending followed by cast extrusion for obtaining film-forming materials. The nanoclay content of the materials was varied from 0 to 5 vol%. Differential scanning calorimetry measurements, electronic microscopy, X-ray diffraction, and rheology were used for characterizing the nanocomposite structure. Because of the presence of nanofillers, a high barrier effect to nitrogen and water was clearly evidenced and mainly attributed to the increase of tortuosity because of the increase of the diffusion pathway generated by impermeable nanofillers. In this study, the high barrier effect was attributed to the very good dispersion of montmorillonite platelets in the PA6 matrix resulting from a twostep melt processing. This peculiar processing has induced a good exfoliation and an orientation parallel to the film surface of lamellar montmorillonite platelets which is clearly demonstrated from transmission electron microscopy analysis. The permeation results were evaluated on the basis of geometrical models proposed by Nielsen and Bharadwaj, and by analyzing the plasticization phenomenon in the case of water permeation involving a concentration-dependence diffusivity correctly approached by an exponential law.
The aim of this work is to study the transport of small molecules through the hybrid systems polyamide 12 (PA12)/organo-modified montmorillonite (Cloisite 30B, C30B) prepared by melt blending, using two blending conditions. The transport mechanisms were investigated by using three probe molecules: nitrogen, water, and toluene. While a barrier effect appears clearly with nitrogen, this effect changes with the amount of fillers for water and disappears for toluene. The reduction of permeability for nitrogen is mainly due to the increase of tortuosity. For water and toluene, the permeation kinetics reveals many concomitant phenomena responsible for the permeation behavior. Despite the tortuosity effect, the toluene permeability of nanocomposites increases with C30B fraction. The water and toluene molecules interact differently with fillers according to their hydrophilic/hydrophobic character. Moreover, the plasticization effect of water and toluene in the matrix, involving a concentration-dependent diffusion coefficient, is correctly described by the law D = D(0)e(gammaC). On the basis of Nielsen's tortuosity concept, we suggest a new approach for relative permeability modeling, not only based on the geometrical parameters (aspect ratio, orientation, recovery) but also including phenomenological parameters deduced from structural characterization and permeation kinetics.
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