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-contribution models (UNIFAC, Entropic-FV, and GC-Flory). Performance of these models is also compared. The van der Waals equation of state was recently shown to accurately correlate and predict vapor-liquid and liquid-liquid equilibria for binary polymer/solvent solutions. In this work, it is demonstrated that it correlates the upper critical solution behavior of polymer blends with excellent accuracy using the usual mixing and combining rules and a single temperature- and composition-independent binary interaction parameter. This interaction parameter can be predicted via a generalized expression that uses only the pure component equation-of-state parameters. Using this generalized expression, the upper critical solution temperature can be predicted with an average error of less than 45 degrees C. The van der Waals equation of state can correlate the lower critical solution behavior of polymer blends, using an interaction parameter that is a linear function of temperature. The UNIFAC and Entropic-FV models, in general, are able to predict qualitatively the phase behavior of polymer blends, but quantitative predictions of the critical solution temperatures es are not achieved The GC-Flory equation of state fails to predict the upper critical solution behavior in polymer blends.