Lee, Minhee2006-07-282006-07-2820002000http://hdl.handle.net/10012/499Extrusion of various polymers and polymer blends was carried out in the presence of supercritical carbon dioxide and the effects of the supercritical CO2 on the viscosity and morphology of polymers and polymer blends were investigated. Various extrusion systems such as single-screw, twin-screw, and twin/single tandem extruders were utilized. In order to ensure a single-phase polymer/CO2 solution, generating high pressure in extruders is essential, and special extruder setups equipped with an CO2 injection device and a secondary die were designed. The solubility of CO2 in polymers and the density prediction of polymer/CO2 solutions were also studied. Effects of supercritical CO2 on the polymer viscosity was mainly studied in polystyrene/carbon dioxide solution system. The viscosity of PS/CO2 solutions was measured on-line using a linear capillary tube die mounted on a single-screw foaming extruder and a wedge die mounted on a twin-screw extruder. The measured solution viscosity was described as a sensitive function of shear rate, temperature, pressure, and CO2 content. In order to mathematically describe the decrease of the shear viscosity due to the dissolved CO2 in the PS melts, several theoretical models were considered. Cross, Carreau, and generalized Cross-Carreau models were employed to describe the shear-thinning behavior of PS/CO2 solutions at various shear rates. The zero-shear viscosity in these models was derived in terms of the temperature, pressure and CO2 content based on the free volume change due to these variables. Various forms of the zero-shear viscosity, including a generalized Arrhenius equation and a WLF equation, were used. The modeling procedure and comparison of the models are presented in detail. The effects of dissolved supercritical CO2 on the viscosity and morphological properties of polyethylene/polystyrene blending systems were also investigated using a twin-screw extruder equipped with a wedge die. A considerable reduction of viscosity was found when CO2 was dissolved in the blend. It was observed that the dissolution of CO2 into PE/PS blends, regardless of the CO2 content used, led to decreased shear thinning behavior. The cell structure of foamed PE/PS blends showed a typical dependence on pressure and CO2 concentration, with higher operating pressures and CO2 content leading to a smaller cell size. Also, it was noted that the size of the dispersed PS phase in the PE/PS blends decreased by increasing the CO2 concentration, and that the dispersed PS phase domains were highly elongated in the direction normal to the cell radius. A twin/single tandem extrusion system was designed for investigating the effects of dissolved supercritical CO2 on the morphological properties of the PE/PS blends. This tandem extrusion system allowed for preferential dissolution of the CO2 into the matrix and/or dispersed polymer phase. By introducing devolatilization to the tandem system, the morphological behaviors of PE/PS blends were investigated on unfoamed filaments. In general, the mixing between two polymers was improved by the dissolution of CO2. The size reduction of the dispersed phase was qualitatively explained using the viscosity ratio of the two polymers and possible effects of the interfacial tension. Reactive extrusion of the polyethylene/polyamide-6/polyethylene-g-maleic anhydride system was performed in the presence of supercritical CO2. Effects of the dissolved CO2 and the polyethylene-g-maleic anhydride (PE-g-MAH) on the viscosity and the blending morphology were investigated in the tandem extrusion system. It was found that the addition of a small amount of polyethylene-g-maleic anhydride to polyethylene/polyamide-6 (PE/PA6) blends causes an increase of blend viscosity, which results from the reaction between PA6 and PE-g-MAH. The reaction was verified by observing an imide peak at 1701cm-1 using FTIR. The size of the dispersed PA6 phase decreased by increasing the concentration of PE-g-MAH concentration. It was found that the injected CO2 affects the size of the dispersed phase when the concentration of PE-g-MAH was low (5 wt%).application/pdf9812113 bytesapplication/pdfenCopyright: 2000, Lee, Minhee. All rights reserved.Harvested from Collections CanadaDoctoral Thesis