Exfoliated clay nanoplatelets

The mechanical properties showed an increase of 0.9 GPa for the storage modulus at 30°C when 5% of exfoliated clay nanoplatelets were added. In contrast, the glass transition temperature, decreases with the addition of the organoclay nanoplatelets (45). 

Biobased epoxy nanocomposites can be reinforced with organo montmorillonite clay and carbon fibers obtained from poly(acryl-onitrile) (45). To get the organically modified clay into the glassy biobased epoxy networks, a sonication technique was used. In this way, clay nanoplatelets were obtained that were homogeneously dispersed and completely exfoliated in the matrix. 

Miyagawa, H., Drzal, L.T., Miyagawa, H., and Carsello, J.A. (2006) Intercalation and exfoliation of clay nanoplatelets in epoxy-based nanocomposites TEM and XRD observations. Polymer Engineering and Science, 46, 452-463. 

Dispersion The degree of dispersion of the nanoplatelets is determined by the degree of delamination of the clay. The fully delaminated (exfoliated) nanocomposite presents much higher values for the tortuosity factor and the aspect ratio in comparison with the partially delaminated (intercalated) nanocomposite. This means that the clay particles that grow as aggregates or books of sheets must be broken up or exfoliated into individual sheets that have a thickness of the order of 1 nm, with lengths and widths of the order of 500 nm. 

Figure 9.6 is a schematic of the various dispersion mechanisms operative in producing nanoplatelets of very high aspect ratio. The nominal size of a dry nanoclay particle is about 8-20 pm. Comprisingthe partide are approximately 1-3 million clay platelets, consisting of bundles of platelets called tactoids. Through a combination of chemistry and processing/shear techniques, the partide is separated into tactoids and the platelets are peeled from the tactoid to become fidly dispersed or exfoliated. 

There are several challenges in the area of rubber nanocomposites. Complete exfoliation and uniform dispersion of nanofillers in rubber matrix still remains to be a challenge. Efficient surfactants have to be designed for the excellent dispersion. In the case of clay filled rubber nanocomposites, the extent of exfoliation-intercalation has not been quantified yet. The orientation of nanoplatelets in rubber matrix by special extrusion is also a major challenge. 

The relatively low cost of graphite in comparison to CNTs makes exfoliated graphite an attractive material (20). The use of graphite nanoplatelets is advantageous because of the chemistry of the graphene and graphene-Uke sheets compared to clay nanoplates. 

These materials, unlike the other nanophase materials described in this chapter, are nano-sized in only one dimension and thereby act as nanoplatelets that sandwich polymer chains in composites. Mont-morillonite (MMT) is a well-characterized layered silicate that can be made hydrophobic through either ionic exchange or modification with organic surfactant molecules to aid in dispersion [5,23]. Polymer-layered silicates may be synthesized by exfoliation adsorption, in situ intercalative polymerization, and melt intercalation to yield three general types of polymer/clay nanocomposites. Intercalated structures are characterized as alternating polymer and siHcate layers in an ordered pattern with a periodic space between layers of a few nanometers [13], ExfoHated or delaminated structure occurs when silicate layers are uniformly distributed throughout the polymer matrix. In some cases, the polymer does not intercalate... 

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