Description:
Polymer-layered silicate nanocomposites formed from the organically modified clay mineral montmorillonite and related materials have attracted a great deal of technological and scientific interest owing to the promise of greatly improved properties over those of the matrix polymer compared to what can be achieved with conventional fillers. This presentation focuses on two issues: how to achieve high levels of dispersion of the one nanometer thick, high aspect ratio aluminosilicate layers and to what extent the resulting benefits can be explained by conventional composite theories. In essence, the latter raises the question of whether there is an effect of the high surface area, nanoscale filler on the matrix polymer or not, i.e., is there a “nano-effect?” The primary focus will be on nanocomposites formed from polyamides and various polyolefins and some rubber-toughened versions of nylon-6 and polypropylene. The factors that must be addressed to achieve high levels of platelet exfoliation by melt processing will be summarized. The rich morphology of the resulting nanocomposites has been characterized in detail by transmission electron microscopy and particle image analysis. Experimental data for tensile stress-strain, dynamic mechanical, impact strength and thermal expansion behavior as a function of clay content and degree of exfoliation will be presented. Finally, these properties will be compared to the theories of Halpin-Tsai and Mori-Tanaka (also Chow) to address the question of “nano-effects.”