Structure of nanoclays

FIGURE 2.15 Reflective optical micrograph showing the general structure of nanoclay-reinforced syntactic foam. 

Incorporation of modified clays into thermosetting resins, and particularly in epoxy35 or unsaturated polyester resins, in order to improve thermal stability or flame retardancy, has been reported.36 A thermogravimetric study of polyester-clay nanocomposites has shown that addition of nanoclays lowers the decomposition temperature and thermal stability of a standard resin up to 600°C. But, above this temperature, the trend is reversed in a region where a charring residue is formed. Char formation seems not as important as compared with other polymer-clay nanocomposite structures. Nazare et al.37 have studied the combination of APP and ammonium-modified MMT (Cloisite 10A, 15A, 25A, and 30B). The diluent used for polyester resin was methyl methacrylate (MMA). The... 

A strong interaction between the layered nanoclay and the rigid globelike Si02 is due to their different response to shear flow in the melt processing of PPS. Thus, both the exfoliation structure of the nanoclay. 

A good nanoclay dispersion is a prerequisite to obtain a nanocomposite—rather than a microcomposite—structure and therefore to achieve interesting physical properties. During the discussion of various nanocomposite properties, in the remaining part of this chapter, other factors of paramount importance will also need to be taken in account such as the content and orientation of nanoclays, the polymer-filler interaction, the degree of crystallinity, and the crystal morphology of the polymeric phase. 

Very recently, the influence of nanoclay on the morphological and micro-structural changes of NR networks has been reported by Carretero-Gonzalez et al The molecular structure of the polymer network and its morphological... 

Much effort has gone into preparing rubber-clay nanocomposites based on NR as described in the earlier section. However, the dispersion of such nanoclays in non-polar NR matrices was very poor. In this section we would like to outline the preparation and characterization of NR-clay nanocomposites in the presence of certain eompatibilizers added into the system externally. For instance, Teh et al. prepared NR-OMt nanocomposites by a melt compounding method. ENR 25 and ENR 50 were used as compatibilizers. Pristine MMT was modified with oetadecyltrimethylamine and abbreviated as MMT-ODTMA. The amount of organoclay was only 2 phr while the amount of ENR was varied. NR-MMT-ODTMA showed mostly intercalated structure of the... 

The co-continuous structure and the final rheological properties of an immiscible polymer blend are generally controlled by not only the viscoelastic and interfacial properties of the constituent polymers but also by the processing parameters. For example, the effect of plasticizer on co-continuity development in blends based on polypropylene and ethylene-propylene-diene-terpolymer (PP/EPDM), at various compositions, was studied using solvent extraction. The results showed more rapid percolation of the elastomeric component in the presence of plasticizer. However, the same fuUy co-continuous composition range was maintained, as for the non-plasticized counterparts (Shahbikian et al. 2011). It was also shown that the presence of nanoclay narrows the co-continuity composition range for non-plasticized thermoplastic elastomeric materials (TPEs) based on polypropylene and ethylene-propylene-diene-terpolymer and influences their symmetry. This effect was more pronounced in intercalated nanocomposites than in partially exfoliated nanocomposites with improved clay dispersion. It seems that the smaller, well-dispersed particles interfere less with thermoplastic phase continuity (Mirzadeh et al. 2010). A blend of polyamide 6 (PA6) and a co-polyester of... 

Studies involving carbon nanotubes have also shown decrease in the peak heat release rate with no change in the total heat release (Kashiwagi et al. 2002, 2005) with effectiveness equal to or better than exfoliated clay. The level of dispersion of the carbon nanotubes in the polymer matrix was shown to be an important variable (Kashiwagi et al. 2005). Upon combustion, the surface layer was enriched with a protective nanotube network providing a thermal and structural barrier to the combustion process. Continuity of the network was important to achieve optimum performance as very low levels of nanotube incorporation or poor dispersion did not allow a continuous surface network during the combustion process. It is noted that the incorporation of nanoclay and carbon nanotubes often results in slightly earlier... 

Nanoclay is the term generally used when referring to a clay mineral with a phyllosilicate or sheet structure with dimensions of the order of 1 nm thick and surfaces of perhaps 50-150 nm. The mineral base can be natural or synthetic and is hydrophilic. The clay surfaces can be modified with specific chemistries to render them organophilic and therefore compatible with organic polymers. Surface areas of nanoclays are very large, about 750 m /g. When small quantities are added to a host polymer, the resulting product is called a nanocomposite. 

Ingram, S.E., Liggat, J.J., Pethrick, R.A. Properties of epoxy nanoclay system based on diaminodiphenyl sulfone and diglycidyl ether of bisphenol F influence of post cure and structure of amine and epoxy. Polym. Int. 56, 1029-1034 (2007)... 

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