Polyethylene terephthalate/clay nanocomposites with polyhedral oligomeric silsesquioxane as dispersant

Abstract

Abstract Polyethylene terephthalate (PET)/clay nanocomposite is an attractive high performance material that can be used for demanding applications due to its potential to exhibit superior properties at low clay loadings. However, organoclays do not have the adequate thermal stability to withstand the high temperatures required for processing PET and this limits the complete exfoliation of the organoclays and ultimately the properties and applications of the resultant nanocomposites. In order to overcome the degradation issues of the organic surfactants, the thesis focuses on two approaches, i.e. (1) to incorporate thermal stable polyhedral oligomeric silsesquioxane (POSS) into the PET/clay system to replace conventional organic surfactants, and (2) to completely do away with organic surfactant and prepare PET/clay nanocomposites with surfactant-free clay. In this work, the preparation of PET/clay nanocomposites using POSS compounds either as a surfactant (POSS-imidazolium salt) or a spacer (trisilanolphenyl POSS, Tsp-POSS) was investigated. In particular, the resultant structures and properties of the nanocomposites were evaluated in the areas of the extent of clay dispersion, thermo-mechanical properties and thermo-oxidative properties. In order to facilitate the understanding of the impact of POSS aggregation on the structure of the nanocomposites, a fundamental study on the packing behaviors of the POSSimidazolium surfactants with different molecular rigidities and at various surfactant loadings was carried out. Wide angle X-ray scattering (WAXS), transmission electron microscopy (TEM) and molecular modeling studies established a bilayer packing structure of the POSSimidazolium surfactants within the clay intergalleries. It was found via WAXS and differential scanning calorimetry (DSC) studies that relative flexible POSS-imidazolium surfactants form a two-dimensionally ordered structure in clay, while the more rigid POSSimidazolium surfactants display a disordered packing structure in clay. The relatively rigid