Polymer-organoclay nanocomposites characteristics

The main uses of montmorillonite stem from its characteristic expansion, and it is used to control viscosity or impart thixotropy to a variety of liquid polymers based on unsaturated polyesters, PVC plastisols, polysulfides, alkyds, etc. It has also been reported to control the melt rheology of thermoplastics and to reinforce polyamides. There has, over the last few years, been enormous industrial and research interest, with many papers and patents, published on montmorillonite, especially as an organoclay as the basis of polymer nanocomposites. Because of the delamination process described above plastic-organoclay nanocomposites have been reported to have very high rigidity, low permeability to fluids, and fire resistance. This subject is covered in more detail in Chapter 10. 

As it is known [4], the parameter x influences essentially on nanocomposites polymer/organoclay properties. One from the most important mechanical characteristics of polymeric materials, namely, elasticity modulus E depends on the value as follows ... 

J. W. Lee, Y. T. Lim, and O. O. Park, Thermal characteristics of organoclay and their effects upon the formation of polypropylene/organoclay nanocomposites. Polymer Bulletin, 45 (2000), 191-8. 

It has been shown that eiystalline phase morphology in nano composites polymer/ organoclay with semiciystalline matrix defines the dimension of fractal space, in which the indicated nanocomposites stractnre is formed. In its turn, this dimension influences strongly on both deformational behavior and mechanical characteristics of nanocomposites. 

The structural analysis of nanocomposites polymer/organoclay flame-resistance was performed within the framework of percolation and multifractal models. The possibility of flame-resistance characteristics prediction on the basis of the indicated approach has been shown. 

The data for nanocomposites polymer/organoclay on the basis of polyamide-6 (PA-6), polyamide-12 (PA-12), polystyrene (PS) and polypropylene (PP), which are listed in table 11.1, were used for the relationships structure-flame-resistance characteristics. The maximum rate of heat release measured with the use of a cone calorimeter according to the standards ASTM 1354-92 and ISO/DIS 13927 [2], the values of which are also listed in Table 11.1, was used as flame-resistance characteristic of the indicated nanomaterials. 

Gatos KG, Thomann R, Karger-kocsis J (2004) Characteristics of ethylene propylene diene monomer rubber/organoclay nanocomposites resulting from different processing conditions and formulations. Polym Int 53 1191... 

Huang W, Han CD (2006b) Dispersion characteristics and rheology of organoclay nanocomposites based on a segmented main-chain liquid-crystalline polymer having side-chain azopyiidine with flexible spacer. Polymer 47(12) 4400 410... 

In this section, we present the dispersion characteristics and rheology of end-functionalized polymers investigated by Zha et al. (2005). In their study, a PS and an SI diblock copolymer were synthesized via anionic polymerization. Then, the chain end of the PS was carboxylated to obtain end-fimctionalized PS-t-COOH, and the chain end of the PI block in the SI diblock copolymer was carboxylated to obtain end-functionalized SI-t-COOH. Subsequently, both PS-t-COOH and SI-t-COOH were neutralized using sodium hydroxide (NaOH) to obtain PS-t-COONa and SI-t-COONa. Each of the end-functionalized polymers was mixed with Cloisite 30B or Cloisite 20A to prepare nanocomposites. Table 12.2 gives sample codes of the eight organoclay nanocomposites prepared. 

Polymer layered-sihcate (PLS) nanocomposites are materials comprised of organoclay platelets dispersed throughout a polymer matrix. Nanocomposite materials have shown enhanced mechanical and thermal properties when compared to their base homopolymers (1). Increased modulus and reduced linear thermal expansion are characteristics that have made polymer nanocomposites desirable materials for the automotive industry (2). 

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