Clay minerals exfoliated layers

The achievement of a high degree of exfoliation of layered clay minerals in nonpolar rubber matrices, such as NR, is still a major issue. This chapter presents a brief overview of studies of clay reinforcement in NR both in micro and nano scale. Although quite a lot of studies have been reported in the field of NR reinforcement with simple organoclay (OMt), plenty of scope still exists to improve the dispersion of MMT followed by property enhancement. Better dispersion and improvement in dilferent properties was observed in the case of EOMt-filled NR nanocomposites. 

Incorporation of nanofrllers into polymer matrix has been proved to be a powerful tool in order to increase the polymer properties (Lin et al. 201 la, b). It is widely accepted that addition of nanofrller into bio-based matrixes in order to fabricate nano-biocomposite materials could be a powerful solution to improve these properties (Alexandre and Dubois 2000 Bordes et al. 2009 Sinha Ray and Okamoto 2003). Studies on mbular silica-based naturally occurring nanoparticles as reinforcing material is still new (Ismail et al. 2008 Prashantha et al. 2011). Halloysite particles are readily obtainable and are much cheaper than other nanoparticles such as CNTs. More importantly, the unique crystal structure of HNTs resembles that of CNTs, and therefore halloysite particles may have the potential to provide cheap alternatives to expensive CNTs because of their mbular stmcture in nanoscale. Moreover, due to its similarity to other layered clay minerals such as MMT, halloysite has the potential to be further intercalated or exfoliated chemically or physically (Tang et al. 2011). 

Exfoliated nanocomposites In the exfoliated nanocomposites, the individual clay mineral layers are randomly separated in a continuous polymer matrix by an average distance which depends on the clay charge. Generally, the clay content in an exfoliated nanocomposite is much lower than in an intercalated nanocomposite (Ke and Stroeve, 2005 Ray and Okamoto, 2003b). 

Aspect ratios (length/thickness) greater than a thousand are possible [29]. MMT is the most commonly used layered silicate. It is a hydrated alumina-silicate layered clay mineral consisting of an edge-shared octahedral sheet of aluminum hydroxide between two silica tetrahedral layers [6,30]. Highly favorable polymer-surface interactions are essential for thorough clay sheet dispersion [31,32]. Thus, it is conventional to organo-modify these clays with cationic surfactants in order to improve compatibility with the polymer matrix and to faciUtate delamination and exfoliation [3]. 

February 29th) into the calendar to make it match the. solar year. Most work on intercalation compounds has been on synthetic systems in which atoms, ions, or molecules have been inserted between layers of the host material. However, some aluminosilicates that we have encountered above provide useful examples. Thus talc and micas form layered structures with ions between the silicate sheets (Fig. 16.3). Some minerals, including all clays, have water molecules intercalcatcd between the framework sheets. In some, such as vermiculile, the water may rapidly and dramatically be evacuated by heating. The water molecules leave faster than they can ditfuse along the layers—exfoliation occurs. The result is the familiar expanded vermiculile used as a packing material and as a potting soil conditioner. 

Depending on the nature of the components used (layered silicate, organic cation, and polymer matrix) and the preparation method, three types of hybrid PCNs can be obtained [17]. Phase-separated microcomposites (conventional composites) are obtained when the polymer chains are unable to intercalate within the inorganic sheets clay lamellae remain stacked in structures marked as tactoids as in the pristine mineral. Otherwise, when the polymer chains penetrate in between the clay galleries, an intercalative system is obtained. In this case, the nanocomposite shows, at least in principle, a well-ordered multilayer morphology built up with alternating polymeric and clay layers. When clay platelets are randomly dispersed in the polymer matrix and the lamellae are far apart from each other, so that the periodicity of this platelet arrangement is totally lost, an exfoliated structure is achieved. 

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