Silicate platelets, delaminated

As illustrated in Fig. 1, layered silicate composite structures fall into three different classes (a) microcomposites with no interaction between the clay galleries and the polymer, (b) intercalated nanocomposites, where the silicate is well-dispersed in a polymer matrix with polymer chains inserted into the galleries between the parallel, sihcate platelets, and (c) exfohated nano composites with fully separated silicate platelets individually dispersed or delaminated within the polymer matrix [12]. However, these terms describe only ideal cases and most observed morphologies fall between the extremes. A more detailed nomenclature will be presented later in this review. 

Nano-clay composites contain very thin, high aspect ratio, alumino-silicate platelets, derived from the stacks present in the parent clay. Two types of stmcture can be recognised, intercalated and delaminated. In the intercalated form, the stacks of platelets are still present, but with polymer chains present between clay platelets, pushing them apart. In the delaminated form, the original stacks are no longer present, and the platelets are fully dispersed. 

Figure 19.4 shows the HRTEM images of the hsv fibres and injection-moulded nanocomposites. Overall, the relative thickness and dispersion of the layered-silicates in the PP matrices are consistent with the XRD trend. For example, the highly delaminated silicate platelets observed in the PPEX matrix are manifested as a level plateau in its XRD spectmm an indication of full exfoliation. The observed smaller lateral dimension of layered-silicates in the hsv matrix relative to their corresponding Isv fibres would corroborate the more repressed XRD peaks seen for the hsv fibres. This further suggests the influence of extensional flow deformation on the exfoliation of layered-silicate. 

Mica is a generic name to describe a group of complex hydrous potassium aluminate silicate materials, differing in chemical composition, but sharing a unique laminar crystalline structure. In nature, mica develops in a book-like form. The individual platelets can be delaminated into very thin high aspect ratio particles that are tough and flexible. Of the commercially important forms, muscovite and phlogopite are used as reinforcements for plastics. 

Nanocomposite technology using small amounts of silicate layers can lead to improved properties of thermoplastic elastomers with or without conventional fillers such as carbon black, talc, etc. Mallick et al. [305] investigated the effect of EPR-g-M A, nanoclay and a combination of the two on phase morphology and the properties of (70/30w/w) nylon 6/EPR blends prepared by the melt-processing technique. They found that the number average domain diameter (Dn) of the dispersed EPR phase in the blend decreased in the presence of EPR-g-MA and clay. This observation indicated that nanoclay could be used as an effective compatibilizer in nylon 6/EPR blend. X-ray diffraction study and TEM analysis of the blend/clay nanocomposites revealed the delaminated clay morphology and preferential location of the exfoliated clay platelets in nylon 6 phase. 

Well-dispersed nanocomposites with potential property improvements as to mechanical properties, heat resistance, dimensional stability, barrier and flame retardation, consist of delaminated platelets distributed homogeneously in the polymer. In these new polymer materials the silicate layers of the clay are separated at the nm scale. Degree of delamination and dispersion are commonly studied by XRD... 

---