Chemical modification montmorillonite

The present study makes an attempt to increase mesoporosity within the pillared structure of montmorillonite and to study the catalytic property of the resulting material. Enhancement of mesoporous areas has been observed in a smectite seunple pillared by aluminium polyoxy cations by chemical modification in presence of varied amounts of a nonionic surfactant. The effeet of the enhaneement in mesoporous areas on the pillar density and the deaetivation of the pillared materials in a typical alkylation reaction has been studied. 

Chemical modification with different amounts of tween-80, a nonionic surfactant, was foimd to enhance the mesoporous area in pillared montmorillonite samples. Deactivation of the modified clays in the vapour phase catalysis of alkylation of toluene by methanol showed that the pillar density and the rate of deactivation could be controlled by the amount of surfactant used during the preparation of pillared samples. Presence of surfactant within the gallery affects the distribution of pillars perhaps during washing and dehydration. This offers a method to suppress deactivation in pillared samples to catalyze organic reactions. 

Miy Miyagawa, H., Drzal, L. T. The effect of chemical modification on the fracture toughness of montmorillonite clay/epoxy nanocomposites. J. Adhesion Sci. Technol. 18 (2004) 1571-1588. 

The chemical modification of the clay can be studied with the help of Fourier transform infrared spectroscopy (FTIR). In FTIR spectra of co-treated and mono-treated clays, the transmittance bands at 2922 cm and 2854 cm correspond to asymmetric and symmetric stretching vibration of methylene groups (Figure 9.5). Carbonyl stretching shows a band at 1715 cm. Both the mono-treated and co-treated montmorillonites have the absorbance bands of methylene, which is due to the successful tethering of octodecylammonium and aminoimdecanoic acid to the clay platelets [24]. 

Due to the brittleness of starch materials, plasticizers are commonly used. A frequently utilized low weight hydroxyl compoxmd is glycerol. Another effective plasticizer is water, although not the best because it evaporates easily. Still, starch-based materials readily absorb water and this may result in significant changes in the mechanical properties. Different routes have been explored in order to improve the mechanical properties and water resistance of starch materials. These are chemical modifications to the starch molecule, blends with polymers such as polycaprolactone [61], or reinforcement with different types of cellulose-based fillers, such as ramie crystaUites [62], and timicin whiskers [63], or montmorillonite clay particles [64]. 

Table 5.1 Material compositions used in chemical modification of natural montmorillonite clay (Na-MMT) [46]...

We alluded earlier to the variety of structural modifications which may he observed in sheet silicates. Clearly it is a matter of considerable in jortance to he able to determine if, for example, the aluminium content within a clay arises p a ely from octahedral substitution (as in montmorillonite) or whether there is some tetrahedral component (as in heidellite). a1 MASNMR readily provides the necessary answers. Figvire 1 illustrates the a1 spectrum for a synthetic heidellite material with Na as charge balancing cation. Aluminium in two distinct chemical environments is observed, with chemical shifts corresponding to octahedrally and tetrahedrally co-ordinated aluminium. 

Wu et al. [129] prepared biodegradable polyQactic acid) (PLA)/organically modified montmorillonite (m-MMT) nanocomposites by solution blending, the most critical part of this process being the modification of the MMT. The MMT was first treated with hexadecyltrimethyl-ammonium bromide (CTAB) cations, and then modified with biocompatible and biodegradable chitosan. As the chemical similarity between m-MMT and PLA was improved, the m-MMT became well separated in the PLA matrix. 

Figure 1.20 Schematic of the nitroxyl-based organic cation modification of montmorillonite surface and generation of PS nanocomposite. Reproduced from Ref [44] with permission from American Chemical Society.

A. Vazquez, M. Ldpez, G. Kortaberria, L. Martm, and I. Mondragon, Modification of montmorillonite with cationic surfactants Thermal and chemical analysis including CFG determination. Applied Clay Science, 41 (2008), 24—36. 

Y. Yang, Z.-K. Zhu, J. Yin, X.-Y. Wang, and Z.-E. Qi, Preparation and properties of hybrids of organo-soluble polyimide and montmorillonite with various chemical surface modification. Polymer, 40 (1999), 4407-14. 

The first study [31] surveyed a wide range of different quaternary ammonium ion modifications of montmorillonite with Tyril 100 (manufactured by Dow Chemical Co.). Tyril 100 is polystyrene with approximately 25 wt.% acrylonitrile and a weight-average molecular... 

Greesh et al described an interesting study on the effect of clay surface modification on the microstructure and properties of polymer-clay nanocomposites synthesized by using free radical emulsion polymerization. Copolymers of styrene and butyl acrylate were synthesized in the presence of montmorillonites modified with various surface modifiers in order to relate their chemical structure, degree of interaction within the clay gallery surface... 

Isomerization and oligomerization of olefins are important reactions in chemical industry and they have been studied extensively in acidic IL systems. For purpose of easy catalyst separation and recovery, the supported chloroaluminate IL-phase catalyst was applied in endo-tetrahydrodicyclopentadiene isomerization. Scheme 2.26 [108]. As a typical operation, sodium montmorillonite (Na-MMT) was first transformed to l-hexadecyl-3-methyl-imidazolium (HDMI) montmorillonite (I-MMT) through ion exchange with [HDMIjCl and used as the support. Subsequently, chloroaluminate IL [HDMIjCl was supported onto the I-MMT by impregnation ([HDMIjCl-AlClj/I-MMT). Under optimized reaction conditions, >99% yield to exo-tetrahydrodicyclopentadiene was obtained over [HDMIjCl-AlClj/I-MMT catalyst at 50 °C in 2 h. The conversion of endo-tetrahydrodicyclopentadiene was 82.7% when Na-MMT was used as the support directly without IL modification. 

Because of the poor thermal stability of alkyl ammonium modifiers, various other cationic surfactants have recently been proposed for clay modification. In this work, we prepared hexadecyl pyridinium (CiePy), dioctadecyl imidazolium (2Ci8lm), and tributyl hexadecyl phosphonium (3C4C16P) modified montmorillonites (MMT). The chemical structures of the corresponding intercalants are illustrated in Table 1. The properties of the organoclays obtained will be compared to those of Cloisite 20A, a commercial clay modified with a dimethyl... 

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