Polymer clay nanocomposites modifying hydrophilic surface

Layered silicates have positive ions present on the surface which makes them hydrophilic and therefore incompatible with many polymers as they are generally hydrophobic [22]. To make bio-nanocomposites, it is necessary to modify the layered silicates by replacing the interlayer cations with cations bearing long alkyl chains, such as alkylphosphonium or alkylammonium [23]. Alkyl ammonium cations are employed to lower the surface energy and enhance the wetting characteristics with the polymer [24]. By incorporating polymers or monomers into the interlayer, this can lead to the formation of a bio-nanocomposite. Different structures can exist for polymer/clay bio-nanocomposites and they are as follows (see Fig. 2) ... 

The nylon-clay nanocomposites were prepared by in situ polymerization in the presence of organically modified, with aminolauric acid, montmorillonite. The reaction between nylon monomer and modified montmorillonite rendered nylon chains end-tethered though aminolauric acid to the silicate surface leading to exfoliated silicates (61). However, not all polymer nanocomposite systems could be produced via in situ polymerization processes because of the chemical sensitivity of polymerization catalysts. Direct melt blending of hydrophilic polymers with montmorillonite in its pristine state or polymers with surfactant-intercalated montmorillonite was found to be possible to deliver polymer intercalated or exfoliated nanocomposites (62,63). 

Nanoclay is the term generally used when referring to a clay mineral with a phyllosilicate or sheet structure with dimensions of the order of 1 nm thick and surfaces of perhaps 50-150 nm. The mineral base can be natural or synthetic and is hydrophilic. The clay surfaces can be modified with specific chemistries to render them organophilic and therefore compatible with organic polymers. Surface areas of nanoclays are very large, about 750 m /g. When small quantities are added to a host polymer, the resulting product is called a nanocomposite. 

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