ABSTRACT
In the twentieth century, incorporation of clays into polymers for improving the technical properties of base polymer revolutionized both research and industrial sectors. The invention of nylon-6/silicate clay nanocomposites by the Toyota research group [1–3] is the inspiration for the development of utilizing mineral clays for advanced products, including aircrafts. Many works have been reported on the incorporation of clays into thermoplastics [4–7], thermosets, and elastomers [8–11]. Nanocomposites are a new class of materials, defined as those with dispersed phase having at least one of the dimensions ranging in 1–100 nm. Nanocomposites are not new to rubber technology, as carbon black (CB) and SiO2 have been used as reinforcing fillers in rubbers over a few centuries now. Compared to conventional macro- or microcomposites, nanocomposites exhibit unique properties with low level of filler loading. At present, clays used are either derived from rocks or synthesized ones, for example, montmorillonite (MMT), kaolinite, sepiolite, and illite. MMT clays are layered aluminosilicates with a layer separation of few nanometers, and it is one of the naturally available nanostructured two-dimensional materials [12]. The compositions of the clays vary from one another. The basic procedure for producing polymer/clay nanocomposite is simply the insertion of polymers in-between clay layers or the polymerization of monomers in-between clay galleries. In general, polymer/clay nanocomposites can be classified into three different types: (1) intercalated nanocomposites, (2) flocculated nanocomposites, and (3) exfoliated nanocomposites. Typically, all these are schematically shown in Figure 3.1 In intercalated polymer composites, chains are inserted into galleries of silicate layers in a crystallographically regular fashion, with a few-nanometer repeat distance in the basal plane. In flocculated nanocomposites, stacked silicate layers are sometimes flocculated due to edge–edge interactions of the clay layers, especially–OH interaction. In exfoliation, complete delamination of individual layers in the polymer matrix, which results from extensive penetration of the polymer within the interlayer spacing, and also the average distance of delaminated layers, depends on the amount of clay loading, and there are no longer sufficient attractions between the silicate layers to maintain uniform layer spacing [13]. The properties of the exfoliated polymer/clay nanocomposites are better than the intercalated ones [14,15]. The modification of clay is more important for improving compatibility between the polymer and the clay. This is because of the fact that generally clays are hydrophilic, but polymers are hydrophobic; due to this, we must modify clays with some organic surfactants. Modified clays exhibit good compatibility with the polymer matrix, leading to better properties compared to unmodified clays [16,17]. Schematic diagram of three different types of the polymer/clay nanocomposite structure. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315371054/19a59aa6-1bb4-4d28-94c7-9f8cac6f3585/content/fig3_1_C.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/> (Reprinted from Prog. Polym. Sci., 28, Sinha Ray, S. and Okamoto, M., Polymer/layered silicate nanocomposites: A review from preparation to processing, 1539–1641, 2003. Copyright 2012 with permission from Elsevier.)
