Organically modified montmorillonite system

A series of five nanocomposite elastomer systems were prepared for this study incorporating 0, 1, 2, 4 and 8% (on total resin mass) of the organically modified montmorillonite clay Cloisite 6A. The appropriate level of Cloisite was dispersed in a starting resin blend of OH terminated PDMS (M -77,000 and Mn -550 g mol in a 3 1 ratio) by a combination of mechanical mixing and ultrasonic processing to give a nano-dispersion of clay platelets. The blend was subsequently crosslinked with a stoichiometric level of tetrapropoxysilane (TPOS) in the presence of 5% diphenylmethylsilanol (DPMS) chain terminator and 5% tin(II) 2-ethylhexanoate catalyst, cured in an open mould at 65°C for twenty minutes, then removed from the mould and post cured for a further fifteen hours at 65°C to give an elastomeric mat. 

The effect of nanostructured and organically-modified montmorillonite fillers on the overall behavior of reinforced systems has also been explored [54]. In order to obtain relevant data and, furthermore, to reveal possible mechanisms... 

Kajtna and Sebenik described the synthesis of pressure-sensitive adhesives based on polyacrylates by suspension polymerization. The monomers used were 2-ethylhexyl acrylate (2-EHA) and ethyl acrylate (EA), and dibenzoyl peroxide (DBF) was used as initiator. Surface-active agents [modified ester of sulfocarboxylic acid (SCA) and ethoxylated oleyl alcohol (EOA)], chain transfer agent (w-dodecanethiol) (CTA) and suspension stabilizer [poly(vinyl alcohol) (PVA)] were also used. Various organically modified montmorillonites were used as fillers. It was observed that the kinetics of suspension polymerization were independent of the presence of the montmorillonite in the system, as shown in Figure 1.8. 

On the other hand, Bhattacharya et al. have reported the plasticization effect of organically modified layered silicates on dynamic mechanical properties [13]. In this work, nanocomposites of SBR have been prepared using various nanofillers like modified and unmodified montmorillonite, SP, hectorite etc. It has been observed that the Tg shifts to lower temperature in all the nanocomposites, except for systems from hectorite and NA. This is due to the fact that clay layers form capillaries parallel to each other as they become oriented in a particular direction. Due to wall slippage of the unattached polymer through these capillaries, the Tg is lowered, which could be even more in the absence of organo-modifiers [13]. A similar type of plasticization effect is also noted in the case of the low... 

A detailed study of the interaction of hydrocarbons with cetyl trimethyl ammonium bromide modified montmorillonite has been done using Raman spectroscopy [82]. The quaternary salt was observed to be in a liquid-like state and it was concluded that interaction of organic compounds in this system is best classified as absorption. 

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. 

Research efforts on filled polymer blends have been more focused on nanopartide-filled systems [42, 43]. One usual observation is the same as those with microscopic fillers - polar nanofillers localize in more polar phases [44—53]. In cases where both phases are polar or nonpolar, the filler particles have been observed to be expelled from both phases in the blend [54—56]. Selective localization of nano-sized partides has been an interesting topic of research. We discuss some of the results here. Gahleitner et al. [57] observed a preferential localization of clay particles in PA6 droplets in PA6/PP blends. Recall that day, espedally montmorillonite, is highly polar in both its pristine and various organically modified forms [58-62]. Similarly, Wang et al. [63] reported selective localization of clay particles in maleic anhydride grafted ethylene-propylene-diene (EPDM-MA) rubber droplets in poly(trimethylene terephthalate)/EPDM-MA blends. Selective localization of fillers other than clay particles has also been reported. Eor instance, Ou and Li [64] observed that toluene diisocyanate modified titania particles selectively localized in PA6 droplets in PP/ PA6/titania blends. 

The nylon-clay nanocomposites were prepared by in situ polymerization in the presence of organically modified, with aminolauric acid, montmorillonite. The reaction between nylon monomer and modified montmorillonite rendered nylon chains end-tethered though aminolauric acid to the silicate surface leading to exfoliated silicates (61). However, not all polymer nanocomposite systems could be produced via in situ polymerization processes because of the chemical sensitivity of polymerization catalysts. Direct melt blending of hydrophilic polymers with montmorillonite in its pristine state or polymers with surfactant-intercalated montmorillonite was found to be possible to deliver polymer intercalated or exfoliated nanocomposites (62,63). 

Na-montmorillonite (MMT) was purified by dispersion of crude clay into deionized water and separation of non-colloidal impurities. To obtain cation exchange process, the purified MMT was swollen in deionized water for 24 h agitation at room temperature and a certain quantity of 1-octadecylamine was added. The system was maintained at around 68 °C for about 4 h and then filter and repeatedly washed with deionized water. The product was then dried, crushed, and sieved with 325-mesh to obtain organically modified montorillonite (OMMT). The main objective for the modification of nanoclay montmorillonite consists in or-ganophilization of clay in order to improve the compatibility with epoxy resin blends. Otherwise, the polymer and the clay will form a separate phase system with a low interface among the various components. 

Un-OH can also be copolymetized with propene on a MAO-pretreated glass surface by Et(Ind)2ZrCl2. Parts of the resulting copolymer are chemically bonded to the surface, as shown by extraction experiments, scanning electron microscopy (SEM) microscopy as well as Fourier transformation infrared spectroscopy (FUR) analysis. Similar results were reported for the copolymerization of ethene with Un-OH by the same catalyst system on the organically modified silicate montmorillonite (OMMT) resulting in PE-Un-OH/OMMT nanocomposites which consist of well-exfoliated OMMT dispersions and controlled degrees of PE functionalization. ... 

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