PET-MMT and PET-PEN-MMT Nanocomposites by Melt Extrusion

Abstract

Polymer nanocomposites have attracted a great deal of interest in the scientific and industrial fields because of remarkable improvements achieved in the physical and mechanical properties at very low filler loadings. For example, the diffusion of gas molecules is largely retarded by the presence of randomly oriented clay particles. These new class of materials can be obtained by means of two main processes: in-situ polymerization of monomers in the presence of nanoparticles and the use of polymer processing techniques such as extrusion [Okamoto, M. 2006 and Suprakas, S. R. 2003]. The use of clay particles to produce nanocomposites is a usual practice; however, clay has to be usually organically modified to induce affinity with the polymer matrix [Kracalik, M. et al 2007; Vidotti, S. E. et al 2007]. The improvement of nanocomposite properties depends on different factors, for example, a good dispersion of clay particles in nano-scale within the polymer matrix. The nanocomposites obtained by melt extrusion require initially, an intercalation process of the polymer macromolecule into the clay galleries and finally clay exfoliation in the polymer matrix. This process is diffusion-controlled and requires long residence times under the pressure buildup produced inside the extruder. However, high residence times or high screw speeds may conduce to polymer degradation. Therefore, optimum process conditions need to be investigated in order to produce high performance nanocomposites. Moreover, it has been found that clay exfoliation may not be a sufficient condition to obtain optimum properties; clay platelets dispersion and polymer-clay interaction are also key features to consider. In this chapter, poly(ethylene terephthalate)-montmorillonite clay (PET-MMT) and poly(ethylene terephthalate)-poly(ethylene naphthalene 2,6-dicarboxylate)-montmorillonite clay (PET-PEN-MMT) nanocomposites were prepared and characterized. Maleic anhydride (MAH) is used as the compatibilizing agent in the blend and its effect is also studied. In both nanocomposite blends, optimum processing conditions were investigated to achieve improved tensile properties. The preparation of the PET-PEN polymer matrix also requires special care since a transesterification reaction between these two polymers is induced by