Clay-polymer nanocomposites properties

In this chapter, the methods of producing clay-polymer nanocomposites are discussed in detail. The influence of clay reinforcement on the mechanical, thermal and physical properties of thermoplastic and thermosetting polymers is also discussed. This chapter also comprises of processing techniques of polymer nanocomposites using nanoparticles hke Al O, CaCO, TiO, ZnO and SiO as reinforcements. These materials have the potential to alter tribological, electrical and optical properties considerably. 

Clay-polymer nanocomposites, a new class of hybrids, came into the purview of researchers after their invention by the Toyota research group [7,8]. They found dramatic improvement in tensile properties of polymers by adding clay in small weight fractions. In continuation of this, other researchers have used various techniques to develop polymer nanocomposites with clay as reinforcement after proper organic treatment. 

The impact strength of clay-polymer nanocomposites either increases, decreases or remains unaltered by the nano-clay incorporation. The impact strength is not altered much by the presence of nano-clay, as reported elsewhere [21]. A special co-intercalation type of organoclay was used. In another study, an improvement in impact property is noticed while incorporating nano-clay in PP matrix [58]. The Izod impact strength of PP and CPN is shovm in Figure 9.37. 

The decrease in permeability and enhanced gas barrier property of clay-polymer nanocomposites makes them viable for packaging application. 

The flammability behaviour of clay-polymer nanocomposites could be restricted by incorporating the nano-clay as reinforcement in limited volume fraction. The heat release rates also are found to be diminished substantially by nano-clay incorporation. The flammability resistance can be enhanced by the incorporation of nano-clay platelets without compromising other properties [114]. This improvement in flammability resulted in development of Wire Cable jacket material [115]. 

In addition to the rapidly expanding field of exfoliated clay-polymer nanocomposites (see Nanocomposites, Polymer-Clay), direct intercalation of macromolecules into inorganic layered materials with retention of the layered nature is also an excellent way of constructing nanocomposites with original properties. The synthetic pathways have to overcome large entropic barriers. 

As stated in the introduction, this study is part of a more general project that deals with the synthesis, characterization, materials properties investigation, and molecular modelling of clay-polymer nanocomposites. This section presents die experimental and theoretical approaches used in this work. 

In nanoparticle-polymer composites, thermal stability is one of the most important property enhancements. Recently, some theoretical efforts have been made to predict the thermal stability of such composites. For example, FEM and the theory of Chow have been used to predict the thermal expansion of clay-polymer nanocomposites. The results indicate that it is possible to considerably reduce and eventually match the thermal expansion of metal and polymer parts by dispersing a small amount of exfoliated muscovite mica platelets into a polymer matrix. Moreover, reduction is controlled by the product of aspect ratio and volume fraction of the platelets. 

Since the 1990 s, clay polymer nanocomposites (CPN) have aroused a great scientific interest, not only because they have better properties in relation to the traditional polymer composites, but also because nanoclays are relatively cheap materials. Furthermore, the existing polymer processing techniques can be easily adapted to the use of this type of nanoadditive. 

Provided in this chapter is an overview on the fundamentals of polymer nanocomposites, including structure, properties, and surface treatment of the nanoadditives, design of the modifiers, modification of the nanoadditives and structure of modified nanoadditives, synthesis and struc-ture/morphology of the polymer nanocomposites, and the effect of nanoadditives on thermal and fire performance of the matrix polymers and mechanism. Trends for the study of polymer nanocomposites are also provided. This covers all kinds of inorganic nanoadditives, but the primary focus is on clays (particularly on the silicate clays and the layered double hydroxides) and carbon nanotubes. The reader who needs to have more detailed information and/or a better picture about nanoadditives and their influence on the matrix polymers, particularly on the thermal and fire performance, may peruse some key reviews, books, and papers in this area, which are listed at the end of the chapter. 

Zhang, J., Jiang, D. D., and Wilkie, C. A. Thermal and flame properties of polyethylene and polypropylene nanocomposites based on an oligomerically-modified clay, Polym. Degrad. Stab. (2006), 91, 298-304. 

Most of the previous studies on flame retardation of polymer nanocomposites are focused on the relationship between macroscopic morphologies of chars and the flammability properties. Fang et al. studied the relationship between evolution of the microstructure, viscoelasticity and graphitization degree of chars and the flammability of polymers during combustion (68). The flame retar-dancy of ABS/clay /MWNTs nanocomposites was strongly affected by the formation of a network structure. Flammability properties... 

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