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Phase behavior, density, and crystallization of polyethylene in n-pentane and in n-pentane/CO2 at high pressures

Authors

  • Wei Zhang,

    1. Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
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  • Cigdem Dindar,

    1. Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
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  • Zeynep Bayraktar,

    1. Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
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  • Erdogan Kiran

    Corresponding author
    1. Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
    • Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
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Abstract

The phase behavior and volumetric properties of polyethylene (PE) in solutions of n-pentane and n-pentane/CO2 were studied in a temperature (T) range of 370–440 K at pressures up to 60 MPa. Measurements were conducted with a variable-volume view-cell system equipped with optical sensors to monitor the changes in the transmitted light intensity as the P or the T of the system was changed. Lower-critical-solution-temperature-type behavior was observed for all of the liquid–liquid (L–L) phase boundaries, which shifted to higher pressures in solutions containing CO2. The solid–fluid (S–F) phase boundaries were investigated over a P range of 8–54 MPa and took place in a narrow T range, from 374 to 378 K in this P interval. The S–F phase boundary showed a unique feature in that the demixing temperatures showed both increasing and decreasing trends with P depending on the P range. This was observed in both the PE/n-pentane and PE/n-pentane/CO2 mixtures. The density of these solutions were measured as a function of P at selected temperatures or as a function of T at selected pressures that corresponded to the paths followed in approaching the phase boundaries (S–F or L–L) starting from a homogeneous one-phase condition. The data showed a smooth variation of the overall mixture density along these paths. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2201–2209, 2003

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