Diffusion barriers with nanocomposites

The arrangement of the layers themselves also has an impact. The self-extinguishing properties of these materials, for instance, have been described qualitatively. A protective char layer forms and acts as a diffusion barrier to further combustion. Likewise, before the advents of nanocomposites, models of the barrier properties of glass-ribbon reinforced composites foreshadowed the increased tortuosity arguments often heard with regard to nanocomposite barrier properties. Improvements on these first approximations of bar-... 

Previous work by Sancaktar and Kuznicld (2006) also showed reduction in water uptake in nanoclay/epoxy composites, specifically when stressed to stagger the clay layers with the action of strain that squeezed the layers to a smaller interlayer distance, thus producing a more effective barrier against water diffusion into the nanocomposite adhesive. This trend was not observed in the unfilled epoxy system, in which barrier properties were not affected by stressing below the yield point. 

It is generally accepted that thermal stability of polymer nanocomposites is higher than that of pristine polymers, and that this gain is explained by the presence of anisotropic clay layers hindering diffusion of volatile products through the nanocomposite material. It is important to note that the exfoliated nanocomposites, prepared and investigated in this work, had much lower gas permeability in comparison with that of pristine unfilled PE [12], Thus, the study of purely thermal degradation process of PE nanocomposite seemed to be of interest in terms of estimation of the nanoclay barrier effects on thermal stability of polyolefin/clay nanocomposites. 

This silicate morphology may act as an cfBcient barrier to oxygen diffusion towards the bulk of the polymer. Surface polymer molecules trapped within the silicate are thus brought to a close contact with oxygen to produce the thermally and oxidative stable charred material providing a new char-layered silicate nanocomposite acting as an effective surface shield... 

Stabilizing effect of A50°C (Fig.4 b) of PP-MAPP-Cloisite 20A over neat PP calculated with the maximum rate of mass loss can be explain by means of the barrier effect of the silicate nanolayers which operate in the nanocomposite level against oxygen diffusion, shielding the polymer from its action. 

Barrier properties. At a high aspect ratio which can be achieved in nanocomposites (with exfohated clay) significant decreases in permeability are predicted and observed in practice (Hollaway and Hackman, 2004). The barrier properties of polymers can be significantly altered by inclusion of inorganic platelets with sufficient aspect ratio to alter the diffusion path of the penetrant molecules. 

Slavutsky et al. (2014) prepared starch/cellulose nanocrystals (CNCs) films and their water barrier properties were studied. The measured film solubility, contact angle, and water sorption isotherm indicated that reinforced starch/CNC films have a lower affinity to water molecules than starch films. Permeability, dififusivity, and solubility coefficients indicated that the permeation process was controlled by the water diffusion and was dependent on the tortuous pathway formed by CNC incorporation. The decrease in surface hydrophilicity and the improvement in water vapor barrier properties with the addition of CNC showed that these nanocomposites present excellent potential as a new biomaterial for application in food packaging and conservation. 

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