Modeling Vapor Solubility in Semicrystalline Polyethylene

The solubility of vapors within semicrystalline polyethylenes produced in the gas phase process is examined. Experimentally measured solubilities of ethylene, 1-butene, isobutane, isopentane, 1-hexene, and n-hexane as a function of temperature, pressure, and vapor composition are reported for a series of semicrystalline linear low density polyethylenes, and a model for predicting these results is presented in detail. This paper demonstrates that conventional thermodynamic methods, which accurately predict polymer phase behavior in fluid systems, fail to account for a critical concept associated with semicrystalline polymers; the elastic constraint. Through application of a simple thermodynamic model addressing this effect, vapor solubility in such systems can be accurately predicted using a limited number of adjustable parameters.