Over the last decade, the concept of utilizing nanoparticles to enhance polymer performance has drawn a great deal of research interest. Significant property enhancement can be achieved with a small amount of addition of nanoparticles. Spherical, platelet or tube/fiber like particles have all been used in the fabrication of nanocomposites. In this study, we chose platelet like clay particles to study the particle dispersion and properties of polymer nanocomposites and polymer nanocomposite foams.
Free radical polymerization of methylmethacrylate (MMA) and styrene (St) in the presence of clay nanoparticles were studied in detail. The effect of interactions between the monomer, the initiator and clay surface modification was studied. By careful surface modification of clay surface and choice of initiator, clay particles can be dispersed uniformly at the nanometer scale (exfoliation). Exfoliation was achieved for PS nanocomposites with a clay concentration as high as 20 wt%. For PMMA, although fully exfoliated nanocomposite was only observed for clay concentration of 5 wt%, substantial exfoliation was observed in the 20 wt% nanocomposite.
Nanocomposites were also prepared by extrusion compounding, with or without the aid of CO 2 . The effect of processing conditions on the degree of clay dispersion was studied. The relationships between clay dispersion, surfactant thermal stability and the resulting thermal properties, e.g., thermal stability, dimension stability, fire resistance were investigated.
Novel polymer clay nanocomposite foams were prepared using carbon dioxide as the foaming agent. The role of clay on the foaming process was thoroughly investigated. It was found that clay serves as an efficient nucleation agent. Nucleation efficiency increases as the degree of clay dispersion improves. The exfoliated clay provides the highest nucleation efficiency. Nucleation efficiency can be further improved by tuning the interaction between polymer, CO2 and the surface property of clay nanoparticles. Ultramicrocellular PMMA nanocomposite foam was successfully prepared. Moreover, based on the understanding of clay dispersion and polymer-CO2-clay surface interaction, a new approach to produce microcellular PS nanocomposite foams was demonstrated, which has considerable potential of expanding the commercial applications of microcellular foaming technology.