Exfoliation cationic clays

The TEM images and XRD spectra are in good agreement and confirm that cationic pyridinium species can be used for the production of nanocomposites based on both grades of the polyamide. It has been concluded that ready exfoliation of clay layers only occurs with alkyl chain lengths above twelve CH2 units long. 

Combustion Behavior of Polymeric Nanocomposites Based on Cationic Clays Layered silicates dispersed at a nanoscale in a polymeric matrix reduce the maximum rate of heat release up to 50 to 70% with a clay loading of only 5 wt%. The degree of clay dispersion affects the performance observed. On the one hand, a nano-dispersion is necessary, as no significant improvement in terms of the heat of release rate is observed when layered silicates are dispersed in the polymeric matrix at a micro level. On the other hand, exfoliation of clay is not necessary, and intercalated nanocomposites perform as well as delaminated nanocomposites. ... 

Clay minerals or phyllosilicates are lamellar natural and synthetic materials with high surface area, cation exchange and swelling properties, exfoliation ability, variable surface charge density and hydrophobic/hydrophilic character [85], They are good host structures for intercalation or adsorption of organic molecules and macromolecules, particularly proteins. On the basis of the natural adsorption of proteins by clay minerals and various clay complexes that occurs in soils, many authors have investigated the use of clay and clay-derived materials as matrices for the immobilization of enzymes, either for environmental chemistry purpose or in the chemical and material industries. 

Clays are usually cation-exchangeable aluminosilicates, and exfoliated clay particles have a platelet shape with nanoscopic size. Cast protein-clay films on electrodes have been used to immobilize proteins. The Clay/Mb electrode has good electrocatalytic properties for the reduction of oxygen and hydrogen peroxide [236] and the biosensors can also be made based on these properties. 

Polymer clay nanocomposites have, for some time now, been the subject of extensive research into improving the properties of various matrices and clay types. It has been shown repeatedly that with the addition of organically modified clay to a polymer matrix, either in-situ (1) or by melt compounding (2), exfoliation of the clay platelets leads to vast improvements in fire retardation (2), gas barrier (4) and mechanical properties (5, 6) of nanocomposite materials, without significant increases in density or brittleness (7). There have been some studies on the effect of clay modification and melt processing conditions on the exfoliation in these nanocomposites as well as various studies focusing on their crystallisation behaviour (7-10). Polyamide-6 (PA-6)/montmorillonite (MMT) nanocomposites are the most widely studied polymer/clay system, however a systematic study relating the structure of the clay modification cation to the properties of the composite has yet to be reported. 

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