Supercritical Fluid - Crystal Phase Fractionation of Polymers: Polyethylene-Propane

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Phase equilibrince will be determined for the polyethylene - propane system, including both solid-liquid and liquid-gas phase boundaries, using a view cell (isopleth method). This method was successful in earlier work with unfractionated polyethylene at 100 to 130 degrees centigrade and 9,000 to 11,000 psi. Data will be collected on fractions of high density polyethylene. The effect of agitation during crystallization on polymer morphology will also be examined. The data will be used to design and test a semi-continuous process for the fractionation of high density polyethylene by crystallization from a supercritical fluid. Although polymers have been shown to be fractionable by molecular weight from supercritical fluids, such processes have been based on the coexistence of liquid and gas phases. The process attempted here will be based on solid/supercritical gas coexistence. Advanced polymer technology plays a central role in scenarios for development of advanced engineering materials. One critical aspect of advanced polymer manufacturing is production of polymers with a narrow molecular weight distribution. By economically separating polymer molecules by molecular weight after polymerization this technology becomes another tool for producing advanced materials.