Organophilic MMT

TEM photomicrograph of PVDF added with 5 wt% of hydrophilic MMT prepared by melt-extrusion. PMMA-organophilic MMT composites exhibit fine dispersion of nearly individual silicate platelets. (From N. Moussaif and G. Groeninckx, Polymer 44, 7899-7906,2003. With permission.)... 

The incorporation of imidazolium chloride salts between clay layers drastically increased their initial decomposition temperature, whereas no significant improvement was observed in the thermal stability of the intercalated tetrafluoroborate and hexafluorophosphate salts [64]. Apparently this effect was connected with the removal of the anion and depended on its nucleophilicity. Gilman and co-workers reported that the replacement of sodium in natural MMT by l-alkyl-2,3-dimethylimidazolium salts yielded organophilic MMT with a 100 °C improvement in thermal stability (in N2) as compared to the alkylammonium-treated MMT [66]. In Langat et al. s work the initial temperature of decomposition for clays modified with l-hexadecyl-3-(10-hydroxydecyl)-2-methylimidazolium and l-hexadecyl-2-methylimidazolium chloride was also very high - around 370 °C [67]. 

Nanoparticles added to thermoplastic polymers improve the mechanical properties, increase Tg and enhance fire retardancy. Nanoparticles in UPRs bring similar effects [217]. Montmorillonite (MMT) was used to obtain polymer nanocomposites [218]. That general approach was applied to the UPR-layered MMT nanocomposites. The structure of the nanocomposites was investigated by XRD and TEM. Organophilic MMT was applied dodecylammonium-bromide treated MMT was used. A UPR synthesized... 

Wide-angle powder X-ray diffraction patterns of (a) MMT, (b) organophilic/MMT clay, (c) EPCN01 and (d) EPCN03 materials. 

MMT is naturally hydrophilic and must be rendered hydrophobic or organophilic in order for it to be compatible with the polymer matrix. Gel nanocomposite polymer electrolytes were obtained by dispersing organophilic MMT in a PVDF or PVDF-hexafluoropropylene (PVDF-HFP) solution. The composite membranes were obtained by film-casting the film was dried and then the liquid electrolyte was added by swelling. The MMT was exfoliated and, in order to improve MMT delamination, the MMT was sonicated in dimethylformamide (DMF). The filled PVDF membrane shown excellent wettability with the electrolyte solution. Solvent and electrolyte uptake by the filled membrane was considerably greater than that of the unfilled membrane. This increase in electrolyte uptake could explain the improvement in ionic conductivity observed. 

To date, no completely successful preparation of nanocomposites using an anionic polymerization of CL in the presence of organophilized MMT has been described in the specialist literature. During the anionic polymerization, alkylam-monium cations present in the interlayer of the organophilized MMT are substituted by the counteranions of the lactam anion this leads to a decrease in the interlayer distance [92], which in turn hampers the penetration of monomer molecules between the silicate platelets. 

For example, vinyl monomer-montmorillonite intercalate (VM-MMT), able to swell and disperse in organic solvents, was prepared by exchanging the mineral cations of MMT by vinylbenzyltrimethylammonium chloride. The resulting VM-MMT material rendered the mineral organophilic and having polymerizable moieties directly bonded to the lamellar surface of the mineral. Radical polymerization of S between the interlayers of 5,10,25, and 50 wt % of VM-MMT... 

Condesation polymer-MMT based nanocomposites were formed, while polymerizing bifunctional monomers in the presence of organophilic modified clay containing active groups capable of forming a bond between the clay and... 

The effect of high shear mechanical mixing and soni-cation methods on the physical properties of the nanocomposites has been analyzed [84] using modified clays with a quaternary ammonium salt and calcium carbonate [85] and silane-treated clays [31]. Although the nanoclay is usually chemically modified to make it organophilic and compatible with the polymer matrix, untreated MMT was... 

Figure 13.1b and c shows x-ray diffractograms for micro-composites prepared by melt mixing PE with the hydrophilic Na+-MMT and the organophilic Dellite 72T clay, respectively. The mixing was performed in a 0.5 cm DSM micro-extruder at 150°C [40]. It is evident that there is not any indication for either intercalation of the polymer chains or exfoliation of the clay layers with neither the natural clay nor the organophilized one. 

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