Organomodified montmorillonite exfoliation

The addition of plasticizer used for the improvement of mechanical properties leads generally to an increase in the oxygen permeability coefficient due to the higher mobility of the polymer chain and higher free volume [102]. On the contrary, the dispersion of nanoclays in PLA makes it possible to divide the permeability coefficient by 2 or 3 depending upon the type of the nanoclays (e.g. organomodified montmorillonite, cloisite 25A or 30B, organomodified synthetic fluorine mica) and exfoliation [129-131]. 

The above technique can be advantageously adapted to a situation where the polymer of interest is not soluble in any solvent, as is the case for polyimides. The polyimide precursor, ie, a poly(amic acid) solution in dimethylacetamide, is prepared and blended to a dispersion of an organomodified montmorillonite in the same solvent. Dimethylacetamide is then gradually removed, and upon heating the poly(amic acid) film at 300°C imder nitrogen atmosphere the polyimide-clay hybrid is obtained. When an ammonium salt of dodecylamine is used in the ion-exchange process, true exfoliation is achieved and fiirthermore the clay platelets align parallel to the film surface (28). 

The morphology of rubber-based nanocomposites also seems to change in the presence of compounding ingredients [89, 90]. HNBR, when melt-compounded with organo-modified sodium montmorillonite clays (o-MMTs) prior to sulfur curing, resulted in the formation of nanocomposites with exfoliated or intercalated structures. In stark contrast, under similar conditions HNBR compounded with unmodified sodium montmorillonite clays (NA) formed microcomposites [90]. This was traced to its reactivity with the sulfur in the presence of amine-type organomodifiers. 

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