Nanoclays threshold

Applying a Monte Carlo simulation to the 3D lattice model (Figure 12.19), the authors were able to predict a percolation occurring at a volume fraction of attapulgite of 0.02, or, alternatively, a weight fraction of 3-4 wt%. The slight divergence of this value from the one found for sepiolite nanoclays in PP can be explained by the lower aspect ratio of the latter. In fact, the percolation threshold is inversely proportional to the aspect ratio. 

Work in our own laboratories has shown, however, that in the presence of conventional flame retardants, nanoclays can promote additive and synergistic effects in PA6, PA6,6 Aims that have been used as models for respective fibers. This work has provided evidence that significant reductions in flame retardant additive concentrations may be achievable, as has been noted for other polymers in Section 11.3.1. Normally, minimal flame retardant additive contents of about 15 to 20% w/w are required, which are too high for inclusion in conventional synthetic fibers. This is because for fusible fiber-forming polymers snch as PA6, PA6,6, PET, and polypropylene, flame retardant property trends versns concentration are not linear but follow an S-shaped curve. " This phenomenon is believed to be a consequence of the need to generate a threshold char level having an extended coherence throughout the polymer. It follows that this will... 

Relaxation in Nanocomposites. At concentrations above the percolation threshold polymer/nanoparticle interactions dominate the viscoelastic terminal behaviour of polymer nanocomposites. As has been reported for phenoxy based nanocomposites [8], the analysis of tan 5 relaxation at low frequencies constitutes a reliable rheological method to investigate the strength of phenoxy/nanoclay interactions. Moreover, since coordinates ((o)Max (tan 5)Max)) reflect the blocking effect of nanoparticles on polymer chains, the dependence of (o)Max with nanoparticles volume fraction can be used in the percolation equation X=Xq (volume fraction threshold [Pg.69]

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