Solvent-Assisted Intercalation

Burnside and Giannelis discussed the nanostructure-property relationships in polydimelhylsiloxane/LS nanocomposites. The solvent uptake in this nanostruc-tured silicon rubber was dramatically decreased when compared to conventional composites. Both swelling behavior and modulus were related to the excess amoimt of bonded rubber formed in the nanocomposites compared to conventional composites. 

The conditions for dispersing clay nanolayers into both cis-1,4-polyisoprene (IR) and epoxidized natural rubber (ENR) have been reported. The incorporation of the clays into these elastomers was achieved by mixing the components in a standard internal mixer/mixing mill (melt compounding) or by mixing their dispersions produced in toluene or methyl ethyl ketone solvents (solution Intercalation). X-ray diffraction studies indicated the intercalation of IR and ENR into the silicate interlayers, followed by exfoliation (delamination) of the silicate layers. The reinforcing effect strongly depended on the extent of dispersion of the silicate layers. 

Solvent-assisted techniques my be Important also in the future. The reason behind this prediction is an interesting finding with melt compounded LS-reinforced, sulfur-cured rubbers. In such systems, considerable confinement (reaggregation) and even full deintercalation have been noticed. This was believed to be the result of chemical reactions with the participation of the original surfactant of the The solvent-assisted techniques offer some possibilities to circumvent the above problems observed in melt intercalation. The confinement and deintercalation of LS can probably be hampered due to the solvent molecules being also intercalated . 

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Chapter 5 Layered Silicate/Rubber Nanocompositres 2.2 Solvent-Assisted Intercalation... 

Solvent-assisted intercalation is also the method of choice in difficult to process polymers like PEA. Ghiang and Wu used this technique to prepare PIA-LDH nanocomposites by dispersing LDH modified with an end group-modified PLA in order to get a fully biodegradable material. Even with 1.2% organomo-dified LDH an increase in storage modulus could be achieved. 

Other methods to prepare nanocomposites include a solvent-assisted process, whereby a cosolvent is employed to help carry the monomer into the galleries and is subsequently removed from the polymer system, and direct polymer melt intercalation methods, which involve the direct addition of nanoclays to a polymer melt under shear conditions atelevated temperatures, allowing their direct exfoliationintothepolymer[5]. 

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