MISCIBILITY OF POLYMER BLENDS WITH ENGINEERING MODELS

The miscibility behavior of polymer blends that do not exhibit strong specific interactions is examined. Phase equilibrium calculations are presented with the van der Waals equation of state and three group-con tribution models (UNIFAC, Entropic-FV, and GC-Flory). Performance of t hese models is also compared. The van der Waals equation of state was recently shown to accurately correlate and predict vapor-liquid and li quid-liquid equilibria for binary polymer/solvent solutions. In this w ork, it is demonstrated that it correlates the upper critical solution behavior of polymer blends with excellent accuracy using the usual mi xing and combining rules and a single temperature- and composition-ind ependent binary interaction parameter. This interaction parameter can be predicted via a generalized expression that uses only the pure comp onent equation-of-state parameters. Using this generalized expression, the upper critical solution temperature can be predicted with an aver age error of less than 45 degrees C. The van der Waals equation of sta te can correlate the lower critical solution behavior of polymer blend s, using an interaction parameter that is a linear function of tempera ture. The UNIFAC and Entropic-FV models, in general, are able to predi ct qualitatively the phase behavior of polymer blends, but quantitativ e predictions of the critical solution temperatures es are not achieve d The GC-Flory equation of state fails to predict the upper critical s olution behavior in polymer blends.