| Supercritical carbon dioxide (scCO2) has been widely studied as an environmentally friendly alternative to organic solvents in many applications. This thesis will describe specific routes for both melt and solid-state processing of polymers in scCO2-mediated environments. The primary goal is to analyze the influence of scCO2 on the final properties of polymers as well as to design novel processing routes using scCO2 that could allow access to well-defined structures and novel materials, and processing of "intractable" polymers.; Most of the fiber-drawing studies of polymers in scCO2 have focused on permeable conditions, where the plasticization process of scCO 2 dominates the interaction and the effect of the imposed hydrostatic pressure is negligible.1--3 In this thesis, the interactions of scCO2 with solid state polymers under non-permeable conditions are investigated through the drawing behavior of highly crystalline, highly oriented, polymorphic fibers (UHMWPE) within this environment. The high-pressure environment appears to stabilize the crystal structure of the fiber, which in this case is the major component. As a consequence, scCO2-treated samples display a constant mechanical and thermal response compared to air-drawn samples that show significant temperature dependence in their behavior.; In addition, the interactions of scCO2 with polymers in the melt are analyzed by designing a modified processing system that allows to process polymers in scCO2. Using this system, the foaming process of polyethylene in scCO2 is studied, and scCO2-assisted polymer processing is then applied to high molecular weight polymers, including fluoropolymers and high molecular weight polyolefins, as a novel processing-route. The success of this method is based on the effect of scCO2 on the melting behavior of semicrystalline polymers, along with its large plasticizing properties observed primarily in fluoropolymers.; Finally, the feasibility of preparing polymer-clay nanocomposites by this route using a variety of approaches is also studied. The use of polymers with controlled hydrophilicity, as well as the introduction of chemically designed hydrophilic polymers or compatibilizers that enhance the interaction between the polymer and the clay have been used to understand the effect of scCO2 on the melt intercalation process as well as on the final structure and morphology of these systems. |
