Clay morphological differences between

A synthetic clay [47] produced by Dow Chemical Company demonstrated lower PHRR when compared to montmorillonite in ethylene-vinyl acetate copolymer-clay nanocomposites. The characterization of the synthetic clay is not available. The morphology difference between the synthetic clay and montmorillonite could provide further confirmation of the importance of clay morphology with regard to flame-retardant performance in the cone calorimeter. 

As illustrated in Fig. 1, layered silicate composite structures fall into three different classes (a) microcomposites with no interaction between the clay galleries and the polymer, (b) intercalated nanocomposites, where the silicate is well-dispersed in a polymer matrix with polymer chains inserted into the galleries between the parallel, sihcate platelets, and (c) exfohated nano composites with fully separated silicate platelets individually dispersed or delaminated within the polymer matrix [12]. However, these terms describe only ideal cases and most observed morphologies fall between the extremes. A more detailed nomenclature will be presented later in this review. 

This indicates that the higher dispersion of clay does not guarantee the higher optical transmittance of the prepared system. The existence of additional compatibilizers could affect the matrix properties. The effects include the induced refractive index difference between the original matrix and the dispersed compatibilizers which offset the positive effect from the increased clay dispersion, leading to the lower optical transmittance of compatibilized nanocomposites sometimes. Apparently, the role of compatibilizer types in the competition between the PP and the clay was rather pertinent to the derived morphology. 

In view of the problems associated with the expanding 2 1 clays, the smectites and vermiculites, it seemed desirable to use a different clay mineral system, one in which the interactions of surface adsorbed water are more easily studied. An obvious candidate is the hydrated form of halloysite, but studies of this mineral have shown that halloysites also suffer from an equally intractable set of difficulties (JO.). These are principally the poor crystallinity, the necessity to maintain the clay in liquid water in order to prevent loss of the surface adsorbed (intercalated) water, and the highly variable morphology of the crystallites. It seemed to us preferable to start with a chemically pure, well-crystallized, and well-known clay mineral (kaolinite) and to increase the normally small surface area by inserting water molecules between the layers through chemical treatment. Thus, the water would be in contact with both surfaces of every clay layer in the crystallites resulting in an effective surface area for water adsorption of approximately 1000 tor g. The synthetic kaolinite hydrates that resulted from this work are nearly ideal materials for studies of water adsorbed on silicate surfaces. 

These minerals have different stacking of the silica and alumina layers, as well as, incorporating metal hydrates of Na, K, Mg, Al, or Fe between the silica and alumina layers. Clay minerals can also be characterized according to their morphological features including crystal habit (i.e., plates, rods, or rolled-up platelets) stacked in either a house of cards or blocklike aggregates giving a partide-size distribution. 

The main issue in processing of polymer/clay nanocomposites is to achieve sufficient interaction between the nanofiller and the polymer so as to achieve a favourable morphology. Due to the laminar structure of the most common nanoclays, the morphology of nanocomposites can be classified in three different types depending on the structure of the nanoclays and the interaction with the polymer chains aggregated, intercalated and exfoliated. Figure 8.2 shows the three possible morphologies of a polymer/clay nanocomposite. 

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