Reinforcement and degradation mechanisms in polymer/inorganic nanocomposites

This project accomplished the following goals: preparation of polymer/alumina nanocomposites using a single-screw extrusion approach, a systematic investigation of interfacial interactions, the mechanisms for reinforcement, and the thermal degradation and flame retardant mechanisms in polymer nanocomposites. In this work it was found that the stereochemistry of polymer macromolecules and the shapes of nanoparticles are extremely important in determining the interfacial interactions between them. Understanding of the nature of these interactions can result in a comprehensive understanding of reinforcement mechanisms in polymer nanocomposites. It was found that aromatic polymers such as polycarbonate and polystyrene have stronger interfacial interactions with needle or whisker-shaped nanoparticles than with spherical-shaped nanoparticles, while linear aliphatic polymers such as polymethylmethacrylate showed strong interactions with spherical nanoparticles. Other factors affecting the strength of interfacial interactions such as size, surface modification and concentration of nanoparticles were also studied. The thermal stability of polymer nanocomposites was studied to unravel the thermal degradation mechanisms. It was found that the chemical nature of nanoparticles plays a significant role in the thermal decomposition of polymer nanocomposites. For instance, SEM studies of polymer nanocomposites chars revealed that alumina nanoparticles moved to the surface of nanocomposites, while silica nanoparticles stayed in the body of the material, which enhances char formation. The mechanisms for the flammability in polymer/alumina nanocomposites were found to depend on the viscosity of the melt flow of nanocomposites.; FT-IR, MS, and surface free energy characterization for modified alumina surfaces were done. The compatibility of polymer molecules and nanoparticles was studied on the basis of surface free energy. It was shown that modification of the alumina surface with silane coupling agents lowers the values of surface free energy for inorganic nanoparticles to the level of polymer surface free energy, and thus leads to a higher degree of the interfacial interactions between them.