Thermal stability/stabilization cationic clays

Cations based on substituted silsesquioxanes have also been intercalated [7]. On heating the ion-exchanged clay minerals water is evolved, but oxycation or oxide pillars keep the siliceous layers apart. These materials have enhanced thermal stability compared with clay minerals expanded with organic cations. Expanded clay minerals cover at least as wide a range of accessibilities to the interlamellar micropore spaces as the zeolites, but the pore characteristics of clay minerals with inorganic pillars need more detailed investigation. 

Many of the different pillaring agents reported in the literature (organic compounds, metal trischelates, organometallic complexes, metal cluster cations, metal oxide sols, polyoxocations, etc.) have drawbacks such as low reactivity or lack of thermal stability, and polyoxocations are by far the most widely employed. Many different polyoxocations (Al, Ni, Zr, Fe, Cr, Mg, Si, Bi, Be, B, Nb, Ta, Mo, Ti, and, more recently, Cu, Ga, and Ce) have been reported in the open and patent literature and clays with multielement or doped pillars also have been claimed [2,8,9,19,20,68-70,73-75]. However, the chemical composition, structure and charge are at present well defined only for the Al-polyoxocation, in which the Keggin ion [Al,304(0H)24(H20)i2] is identified. 

We report here preliminary results of the physicochemical characterization of a composite material obtained by combining the cethyltrimethylammonium cations clay insertion procedure with the room temperature synthesis of mesoporous materials inside of clay layers. The Romanian bentonite, containing 64% montmorillonite was used. The organic cations are incorporated within the interlayer region of the clay, serving to prop of>en the layers and to allow incorporation of the silicon source for MCM-4I synthesis. The obtained materials display a high thermal stability and molecular sieve properties. 

Samakande A, Juodaityte JJ, Sanderson RD, et al. (2008) Novel cationic RAFT-mediated polystyrene/clay nanocomposites synthesis, characterization, and thermal stability. Macromol Mater Eng 293 428 37... 

Natural montroriUonite and organically modified MMT with methyl tallow bis-2-hydroxyethyl ammonium cations located in the silicate gallery (Cloisite 30B) were evaluted in starch-based nanocomposite [232]. It was observed that the TPS/ Cloisite Na-t nanocomposites showed higher tensile strength and thermal stability, better barrier properties to water vapor than the TPS/Cloisite 30B nanocomposites, as well as the pristine TPS, due to the formation of the intercalated nanostructure. Perez et al. [233] compared three different clays (Cloisite Na+, Cloisite 30B and Cloisite 10A) and found the best properties were achieved with Cloisite lOA due to their greatest compatibility with the matrix. 

The definition for catalytic purposes of a zeolite reads as follows a crystalline material with micropores and cation-exchange capacity that is insoluble in water and common organic solvents and has sufficient thermal stability that allows removal of all pore-filling agents present in the as-synthesized materials. This definition is narrower than that of the IZA Constitution, which includes mesoporous solids, metal organic frameworks (MOFs), cationic and anionic clays [3]. 

Corn oil-based polymer resin, prepared by the cationic polymerisation of conjugated corn oil, styrene and divinylbenzene, using boron trifluoride diethyl etherate modifled by Norway fish oil as the initiator with 4-vinylbenzyl triethylammonium cation modified montmorillonite clay (VMMT) nanocomposites were reported. The resultant nanocomposites with 2-3 wt% VMMT exhibited significant around two-fold improvements in tensile modulus, tensile strength and toughness when compared to the pristine polymer. There is an improvement in thermal stability up to 400°C in the nanocomposites. ... 

The thermal stability of some thermosetting nanocomposites obtained by thermal cationic cure of diglycidilether of bisphenol A and y-valerolactone using rare earth metal triflates (trifluoromethanesulfonate) as initiators and containing different types of Cloisite was studied. The addition of clay into the polymeric matrix was found to increase the thermal stability, acting as a superior insulator and mass transport barrier to the volatile products evolved during thermal decomposition [67]. 

Organoclays have also similar effects on polymers thermal stability and in this case the achieved clay dispersion (intercalated-exfoliated) as well as the used modifier can also alter thermal decomposition of polymers. Cationic compounds used for organomodification of MMT have a negative effect in thermal degradation while the exfoliated stmcture due to the finer dispersion of the clay nanoparticles can lead to thermal stabilization than intercalated structure. 

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