Synthetic layered silicates

However, the field of polymer day silicate has only started to speed up recently, mixing the appropriate modified layered silicate with synthetic layered silicates has long been known (Theng, 1979). The interest in these materials came from two important findings, first has been reported by Toyota research group of a Nylon-6 (N6)/Na-MMT nano-composites (Okada et ah, 1990) where very small amounts of layered silicate loadings resulted in the improvements of thermal and mechanical properties and second the findings of Vaia et ah (1993) about the... 

It is clear that the Wacker cycle in a CuPdY zeolite incorporates the traditional features of the homogeneous catalysis combined with typical effects of a zeolite (303, 310). It also follows that whereas other cation exchangers in principle will show Wacker activity after cation exchange with Cu/Pd ions, the cage and pore architecture will probably be less suitable for Wacker chemistry than those of the faujasite structure. This is the case for fluoro-tetrasilicic mica, a synthetic layer silicate that swells under reaction conditions and allows access to the interlayer space (311). 

Synthetic layer silicates, particularly fluoro-micas, are starting to be exploited where these issues are a real concern. There is also interest in other layered inorganics especially magnesium salts like hydrotalcite, which can be synthesised as very thin plates and for which other forms of modifier attachment are possible. 

Reichert P, Kressler J, Thomaiiii R, Mulhaupt R and Stoppelmaim G (1998) Nano-composites based on synthetic layer silicate and polyamide-12, Acta Polym 49 116-122. 

Figure 3 shows that a part of this synthetic layered silicate (Na-fluorohec-torite) is even exfoliated. One can also see in these TEM pictures the very high aspect ratio of this synthetic LS (clay layers displaced from the view plane). The dynamic-mechanical thermal analysis (DMTA) spectra in Figure 4 display how... 

Polymerization of vinyl monomers intercalating into the montmorillonite (MMT) clay was first reported in the literature as early as 1961. The most recent methods to prepare polymer-layered-siUcate nanocomposites have primarily been developed by several other groups. In general these methods (shown in Fig. 5.1) are able to achieve molecular-level incorporation of the layered silicate (e.g. montmorillonite clay or synthetic layered silicate) in the polymer matrix by addition of a modified silicate either to a polymerization reaction (in situ method), to a solvent-swollen polymer (solution blending), or to a polymer melt (melt blending). Recently, a method has been developed to prepare the layered silicate by polymerizing silicate precursors in the presence of a polymer. ... 

P. Reichert, J. Kressler, O. Thomann, R. Mulhaupt and G. Stdppelmann, Nanocomposites based on a synthetic layer silicate and polyamide 12 , Acta. Polym., 1998, 49, 116-123. 

Smectites are 2 1 charged layered silicates from natural (montmorillonite, hectorite, beidellite, saponite etc.) or synthetic (synthetic fluorohectorites, such as... 

Ahmadi SJ, Huang YD, Li W (2004) Synthetic routes, properties and future applications of polymer-layered silicate nanocomposites. J Mater Sci 39 1919-1925... 

Roy, D.M. and Roy, R., 1954. An experimental study of the formation and properties of synthetic serpentines and related layer silicate minerals. Am. Mineralogist, 39 957-975. 

The growing interest in other categories of nanoparticles, such as synthetic anionic layered silicates, CNTs, nano-oxides or -hydroxides, metallic phosphates, etc., has materialized either through the study of combinations of those nanoparticles with layered silicates or with metal hydroxides or phosphorus FRs. Such combinations are also detailed in Section 12.3. Nevertheless, for some combinations, interpretations of the possible interactions between components are sometimes missing or not completely detailed. 

New trends involve the use of nanoparticles in synthetic fibers. Polymer-layered silicates, nanotubes, and POSS have been successfully introduced in a number of textile fibers, mainly poly-amide-6, polypropylene, and polyester. Although they reduce the flammability of these fibers, but on their own are not effective enough to confer flame retardancy to a specified level. However, in presence of small amounts of selected conventional FRs (5-10 wt %), synergistic effect can be achieved. With this approach fibers having multifunctional properties can also be obtained, e.g., water repellency or antistatic properties along with fire retardancy. Most of the work in this area at present is on the lab scale and there is a potential to take this forward to a commercial scale. 

In the case of mica-type layered silicates it has been recently demonstrated that nanocomposites (both intercalated and delaminated) can be synthesized by direct melt intercalation even with high molecular weight polymers [7-18]. This synthetic method is quite general and is broadly applicable to a range of commodity polymers from essentially non-polar polystyrene, to weakly polar polyethylene terephthalate), to strongly polar nylon. Nanocomposites can, therefore, be processed using currently available techniques such as extrusion, thus lowering the barrier towards commercialization. 

The most common class of pearlescent pigments today is based on thin platelets of mica (see Fig. 15.5). Mica itself is a natural mineral and belongs to the sheet layer silicates. Nacreous pigments are usually based on natural, transparent muscovite and only in some cases on synthetic phlogopite. Muscovite occurs worldwide, but only few deposits are suitable for pigment production. Mica is biologically inert and approved for use as a filler and colorant. 

Almost all these analyses are accompanied only by X-ray powder patterns (sometimes indexed using only the sulphide unit cells) or by insufficient single-crystal X-ray data While most authors assiune that deviations from ideal ratios hydroxide/sulphide are due to various inter-bedded impurities (hydroxides or layer silicates), Dshi et al. from their synthetic work (Mg + A1 and Mg + Cr valleriites powder data only), suggest that the ratios of 2.0 to 2.3 are characteristic of the obtained valleriites and that materials vnth the ideal hydroxide/sulphide ratio contain excess chalcopyiite. 

The dominant class of pearl luster pigments is based on platelets of natural mica coated with thin films of transparent metal oxides [5.122-5.125, 5.127-5.130, 5.137]. The mica substrate acts as a template for the synthesis and as a mechanical support for the deposited thin optical layers of the pearl luster pigments. Mica minerals are sheet layer silicates. Pearl luster pigments are usually based on transparent muscovite mica only some are based on synthetic phlogopite. Although muscovite occurs worldwide, few deposits are suitable for pigments. Natural mica is biologically inert and approved for use as a filler and colorant. 

Synthetic Insoluble Silicates. Insoluble crystalline siUcates, ie, mineral-type compounds, are synthesized from soluble siUcates by precipitation, gelation, ion exchange, and hydrothermal techniques. Hydrothermal treatment of partially neutralized, high mole ratio (m = 12—50), sodium siUcate solutions yields neutral alkaU polysiUcates that exhibit a layered stmcture and high ion-exchange capacity (135,136). These and other lamellar siUcates can be utilized either alone or modified via pillaring (137) as adsorbents and catalysts. 

Farmer, V. C., Krishnamurti, G. S. R., and Huang, P. M., 1991, Synthetic allophane and layer-silicate formation in Si02-Al20j-Fe0-Fe203-Mg0-H20 systems at 23°C and 89°C in a calcareous environment Clays and Clay Minerals, v. 39, p. 561-570. 

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