Nanocomposites intercalation/exfoliation

Rheology of various polymer layered-silicate nanocomposites - intercalated, exfoliated and end-tethered exfoliated (prepared by in-situ polymerization from reactive groups tethered to the silicate surface), have been performed in a conventional melt-state rheometer in both oscillatory and steady shear modes. These experimental studies have provided insight into the relaxation of polymer chains when confined by the layers of inorganic silicates, as well as the role of shear in orienting the layered nanocomposites. 

Keywords layered fillers, layered silicates, montmorillonite, elastomers, nanocomposites, intercalation, exfoliation, ionic liquids. 

The morphology of rubber-based nanocomposites also seems to change in the presence of compounding ingredients [89, 90]. HNBR, when melt-compounded with organo-modified sodium montmorillonite clays (o-MMTs) prior to sulfur curing, resulted in the formation of nanocomposites with exfoliated or intercalated structures. In stark contrast, under similar conditions HNBR compounded with unmodified sodium montmorillonite clays (NA) formed microcomposites [90]. This was traced to its reactivity with the sulfur in the presence of amine-type organomodifiers. 

Botana et al. [50] have prepared polymer nanocomposites, based on a bacterial biodegradable thermoplastic polyester, PHB and two commercial montmorillonites [MMT], unmodified and modified by melt-blending technique at 165°C. PHB/Na and PHB/ C30B were characterized by differential scanning calorimetry [DSC], polarized optical microscopy [POM], X-ray diffraction [XRD], transmission electron microscopy [TEM], mechanical properties, and burning behavior. Intercalation/exfoliation observed by TEM and XRD was more pronounced for PHB30B than PHB/Na,... 

Indicating the better compatibility between the modified clay and the PHB matrix. An increase in the crystallization temperature and a decrease in spherulites size were observed for PHB/C30B nanocomposites. The intercalation/exfoliation, observed by TEM and XRD patterns were correlated with the higher moduli of the nanocomposites. They have also observed that the burning behavior of PHB/C30B was influenced by the aggregation of the clay mineral particles. 

Fig.1 Schematic illustration of different possible structures of layered silicate polymer composite (a) microcomposite (b) intercalated nanocomposite (c) exfoliated nanocomposite [12]...

Figure 9.2 Types of clay-polymer composites (a) microcomposites, (b) intercalated nanocomposites, (c) intermediate nanocomposites, (d) exfoliated nanocomposites.

Intercalation/exfoliation of biodegradable polymer macromolecules in layered hosts, such as layered silicates, has been proved as an effective method to synthesize polymer layered silicate nanocomposites. Methods like solution intercalation, in-situ synthesis and melt intercalation have emerged as successful methods to prepare biodegradable polymer layered silicate nanocomposites. 

Mainil, M., Alexandre, M., Monteverde, R, and Dubois, P. 2006. Polyethylene organo-clay nanocomposites The role of the interface chemistry on the extent of clay intercalation/exfoliation. Journal of Nanoscience and Nanotechnology 6 337-344. 

In the last decade, considerable progress was observed in the field of PO/compatibil-izer (predominantly on the base of PO-g-MA)/organo-surface-modified clay nanocomposites. Polyethylene (PE), polypropylene (PP), and ethylene-propylene (EP) rubber are one of the most widely used POs as matrix polymers in the preparation of nanocomposites [3,4,6,30-52]. The PO silicate/silica (other clay minerals, metal oxides, carbon nanotubes, or other nanoparticles) nanocomposite and nanohybrid materials, prepared using intercalation/exfoliation of functionalized polymers in situ processing and reactive extrusion systems, have attracted the interest of many academic and industrial researchers because they frequently exhibit unexpected hybrid properties synergisti-cally derived from the two components [9,12,38-43]. One of most promising composite systems are nanocomposites based on organic polymers (thermoplastics and thermosets). 

TEM investigations and TGA analysis under oxidative atmosphere evidenced that the PE-clay nanocomposites were characterized by an intercalated/exfoliated morphology and a higher onset decomposition temperature (Figure 6.14). 

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