Pristine-layered silicates

K. Okamoto and M. Okamoto also investigated the biodegradability of neat PBS before and after nanocomposite preparation with three different types of OMLF. They used alkylammonium or alkylphosphonium salts for the modification of pristine layered silicates, and these surfactants are toxic for microorganisms [56]. 

Upon replacing the hydrated metal cation from the interlayers in the pristine layered silicates with organic cations such as an alkylammonium or an alkyl-phosphonium, the layered silicate attains a hydrophobic/organophillic character... 

Toughness reduction was also noticed when layered silicate was incorporated in PS. In the related study PS/layered silicate micro- and nanocomposites were produced. Microcomposite was generated by direct melt blending of PS with the silicate. Intercalated nanocomposites were, however, achieved when the pristine layered silicate was swollen in water before adding the related slurry in... 

The clay delamination as well as the development of the silica matrix give rise to an enhancement of the surface area and porosity compared with the pristine layered silicates (Table 14.2). An extraordinary increase (>20 times) in the BET surfece area and in the total pore volume ( 100 times) is observed in the nanoarchitectures prepared from vermiculite, making these materials of potential interest as adsorbents, support of catalysts, and nanofillers of polymers. 

A large number of organoclays can be prepared depending on the chemical structures of surfactants that may be employed to treat pristine layered silicates (e.g., MMT). However, there is only a limited number of organoclays that are commercially available. Table 2 gives a list of six commercial organoclays with their mean... 

Figure 2. XRD spectra of the pristine layered silicate (LS Na-fluorohectorite) and cast TPU nanocomposite containing 10 parts per hundred resin (phr) LS...

Montmorillonite, hectorite and saponite are frequently used pristine layered silicates which are combined with polymeric materials to form nanocomposites... 

The clay was pretreated with MMAO MMAO suspension dried under vacuum thus obtaining a silicate-supported MMAO cocatalyst (DM). Then the Fe" precatalyst suspended in toluene was added to the DM intermediate suspension to preform in situ a layered silicate-immobilized catalyst (DMA/DMB). Homogeneous A and B pristine iron complexes used are both intensely blue colored, after reaction with DM intermediates the color immediately changed to deep, bright orange, as after reaction with MMAO. The intermediates were thoroughly investigated by elemental analysis, TGA, TGA-FTIR, WAXD, and pyrolysis (Table 6.2)P... 

Depending on the nature of the components used (layered silicate, organic cation, and polymer matrix) and the preparation method, three types of hybrid PCNs can be obtained [17]. Phase-separated microcomposites (conventional composites) are obtained when the polymer chains are unable to intercalate within the inorganic sheets clay lamellae remain stacked in structures marked as tactoids as in the pristine mineral. Otherwise, when the polymer chains penetrate in between the clay galleries, an intercalative system is obtained. In this case, the nanocomposite shows, at least in principle, a well-ordered multilayer morphology built up with alternating polymeric and clay layers. When clay platelets are randomly dispersed in the polymer matrix and the lamellae are far apart from each other, so that the periodicity of this platelet arrangement is totally lost, an exfoliated structure is achieved. 

A Japanese patent issued to Sekisui Chemical Co. Ltd." describes cone calorimeter data for polyethylene (PE)-derived nanocomposites in which organically modified layered silicates (OMTs) were combined with a variety of conventional flame retardant additives. The ammonium salt-modified silicate (SBAN-400) was incorporated into the PE compositions at 10 phr (Table 8.10). The PHRR results for the PE nanocomposite materials are 50% lower than the PHRRs for pure PE and PE with 10 phr pristine clay (MMT). These results suggest that without suitable organic treatment of the clay, the addition of MMT has little effect on flame retardant properties. Due to the favorable interactions arising from the organic surface treatment of the clay, the OMT forms a nano-dispersed structure in the PE matrix, while the PE-pristine MMT material is an immiscible or conventional composite. At 10-phr loading levels, where the OMT reduces the PHRR substantially for PE nanocomposite, DB-AO has little effect and APP alone has only a weak effect on PHRR of PE, respectively. Addition of either 15 phr of DB-AO or 15 phr of APP to pure PE decreases the PHRR values by only 10 to 20% from that of pure PE. However, addition of 5 phr of APP to a PE-SBAN N-400 nanocomposite with 10 phr of SB AN N-400 causes a 63% reduction in the PHRR. The addition of 5 phr of phenylphosphate and 10 phr of SB AN N-400 also reduces the PHRR by 60% (Table 8.10). 

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