Supercritical carbon dioxide (CO_2) is of interest as a physical blowing agent in the manufacture of plastic foam and as a plasticizer to reduce melt viscosity during processing. The combined effects of concentration (C) of dissolved CO_2, pressure (P), and temperature (T) on the rheological properties of the melt were determined to achieve optimum processing conditions. Linear and branched polypropylenes and their blends were chosen. A high-pressure sliding plate rheometer, in which the shear deformation, T, P, and C are all uniform, was used. It was possible to use shift factors for T, P and C to obtain a master curve.
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