Montmorillonite clays modification

Recently, interest in clays as acidic catalysts has been quickened by the reported high catalytic activity of a synthetic mica-montmorillonite clay and its nickel-containing analogs. Wright et al. (247) have described the structure, thermal modification and surface acidity of the clay, which they designated SMM for synthetic mica-montmorillonite. 

Polymer clay nanocomposites have, for some time now, been the subject of extensive research into improving the properties of various matrices and clay types. It has been shown repeatedly that with the addition of organically modified clay to a polymer matrix, either in-situ (1) or by melt compounding (2), exfoliation of the clay platelets leads to vast improvements in fire retardation (2), gas barrier (4) and mechanical properties (5, 6) of nanocomposite materials, without significant increases in density or brittleness (7). There have been some studies on the effect of clay modification and melt processing conditions on the exfoliation in these nanocomposites as well as various studies focusing on their crystallisation behaviour (7-10). Polyamide-6 (PA-6)/montmorillonite (MMT) nanocomposites are the most widely studied polymer/clay system, however a systematic study relating the structure of the clay modification cation to the properties of the composite has yet to be reported. 

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. 

Polyurethane/clay-based nanocomposites are already being used for automobile seats and it also exhibit superior flame retardancy. Phenolic resin impregnated with montmorillonite clay was already identified as the resin for manufacturing rocket ablative material with MMT. The nanolevel dispersion of clay platelets leads to a uniform char layer that enhances the ablative performance. The formation of this char was slightly influenced by the type of organic modification on the silicate surface of specific interactions between the polymer and the silicate platelets surface, such as... 

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]. 

Zheng, H., Zhang, Y., Peng, Z., Zhang, Y.J. Inlluence of the clay modification and compatibilizer on the structure and mechanical properties of ethylene-propylene-diene rubber/montmorillonite composites. J. Appl. Polym. Sci. 92, 638-646 (2004)... 

Tonato et al. [20] studied the effect of up to 100 kGy gamma radiation on the properties of organically modified montmorillonite clay-propylene nanocomposites. These workers reported that oxidative degradation under gamma irradiation of poly-propylene-clay nanocomposites causes drastic modification in the structure, morphology, and tensile and thermal properties of the nanocomposites, especially at doses above 20 kGy. 

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

Cationic montmorillonite clays can be modified by ion exchange with ionic liquids. Literature data on their modification by a variety of cations of different molecular weights, including those present in thermally stable phosphonium-based ionic liquids, are presented and compared with data from commercial organoclays. Examples of polyolefin nanocomposites containing IL-modified montmorillonite are also presented. It appears, overall, that the relatively low melt-processing temperatures of the polyolefin composites do not permit full demonstration of the beneficial effects of the thermally stable phosphonium ionic liquid intercalants versus commercial modifiers, which are more prone to thermal... 

TGA is most commonly used for evaluation thermal stability of nanocomposites filled with montmorillonite, clay, or carbon nanotubes. High-resolution TGA is applicable while determining the presence of any excess of surface modification molecules unbound to the surface. It is very important to know this parameter, especially if the nanofiller is to be added to pol5mier at high temperatures. In such a situation, modification molecules may have lower thermal degradation, which will negatively affect the properties of the nanocomposite. The commercially treated filler, in comparison with the second one, clearly exhibits an extra degradation peak at lower temperature, which indicates the presence of modification molecules not bonded with filler surface... 

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... 

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. 

The dispersion and solid-state ion exchange of ZnCl2 on to the surface of NaY zeolite by use of microwave irradiation [17] and modification of the surface of active carbon as catalyst support by means of microwave induced treatment have also been reported [18]. The ion-exchange reactions of both cationic (montmorillonites) and anionic clays (layered double hydroxides) were greatly accelerated under conditions of microwave heating compared with other techniques currently available [19.]... 

A small increase of the (d 001) basal spacing is observed for the Li containing Zr pillared clays. However, the thermal stability of these solids drastically decrease. At high temperature, the collapse of the strucutre is also supported by the decrease of the surface area which is, at 700°C, almost identical to those measured for the montmorillonite. Different hypothesis may be proposed to explain the increase of the interlayer distance at low temperature (i) a better polymerization of the intercalated complex (ii) a modification of the distribution of the pillars (iii) a lower interaction between the pillar and the silica layer. The first hypothesis may easily be eliminated since the small variation of the height of the pillars (less than 1 A) cannot be explained by structural changes of the... 

Sodium bentonite with a cation exchange capacity (CEC) of 75 meq/100 g of clay, supplied by Commercial Minerals Ltd., Australia, was used as starting clay material, to prepare samples for SCD and surfactant treatments. Besides, sodium montmorillonite (Kunipia G), from Kunimine Industrial Company, Japan, was used as the starting clay for samples of pore opening modification. CEC of this clay is 100 meq/100 g of clay. 

Diagenetic modification of expandable clay during burial is an important source of mixed-layer illite-montmorillonite. With increasing depth of burial and increasing temperature the proportion of contracted 10 A layers systematically increases. From about 50°C— 100°C the contracted layers are distributed randomly. At higher temperatures only a few additional layers are contracted but the interlayering becomes more ordered (Perry and Hower, 1970 Weaver and Beck, 1971a). The final product, 7 3 to 8 2, is relatively stable and persists until temperatures on the order of 200°C— 220° C are reached. 

CIL is unavoidable when nanodispersion of any other nanofiller, such as clay or carbon nanotube (CNT) is considered [17,18], Various types of cationic surfactants in the case of montmorillonite (MMT) and reactive interface modifications in the case of CNT have been introduced to ensure... 

Wang, Z.M. Nakajima, H. Manias, E. Chung, T.C. Exfoliated PP/clay nanocomposites using ammonium-terminated PP as the organic modification montmorillonite. Macromolecules 2003, 36, 8919. 

Illite and montmorillonite are similar in structure and differ slightly from kaolinite in this regard. The first two are composed of two silicon-oxygen layers per octahedral layer containing iron, magnesium and aluminum and in kaolinite the ratio of tetrahedral and octahedral layers is 1. In clays thermal modification occurs at lower temperature than silica because the bonds formed between the Al, Fe, and Mg atoms and oxygen are weaker than the Si-0 bonds. 

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. 

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