Clays dispersion mechanisms, schematic

Figure 9.6 Schematic of the different clay dispersion mechanisms.

Figure 6.2 Schematics of various clay dispersion mechanisms [26]. With permission from Wiley-VCH.

Figure 9.6 is a schematic of the various dispersion mechanisms operative in producing nanoplatelets of very high aspect ratio. The nominal size of a dry nanoclay particle is about 8-20 pm. Comprisingthe partide are approximately 1-3 million clay platelets, consisting of bundles of platelets called tactoids. Through a combination of chemistry and processing/shear techniques, the partide is separated into tactoids and the platelets are peeled from the tactoid to become fidly dispersed or exfoliated. 

Beyond this traditional class of polymer-filler composites, two types of nanocomposites can be obtained. Intercalated structures are formed when a single (or sometimes more) extended polymer chain is intercalated (sandwiched) between the silicate layers. The result is a well-ordered multilayer structure of alternating polymeric and inorganic layers. Exfoliated or delaminated structures are obtained when the silicates are completely and uniformly dispersed in the continuous polymer matrix. The delamination configuration is of particular interest because it maximizes the polymer-clay interactions, making the entire surface of the layers available for the polymer. This should lead to the most significant changes in mechanical and physical properties. A schematic of the types of possible structure formations in PC composites is depicted in Fig. 13.2. 

The process of organizing clay using ammonium ions has a considerable impact on production cost. In order to omit this expensive process, silicate layers of clay (sodium-type montmorillonite) were uniformly dispersed in a water slurry and mixed with a molten resin. This method is shown schematically in Fig. 1.16. The clay slurry was injected into a twin-screw extruder by a pump, and water was removed under reduced pressure. In this process, a nylon nanocomposite with uniformly dispersed silicate layers was fabricated successfully. This method simplified the clay organization process, allowing nanocomposites to be obtained at low cost. Table 1.8 shows the mechanical properties of this nanocomposite. The heat distortion temperature was somewhat lowered because the bonding between clay and nylon was not ionic bonding. 

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