APPLICATION OF FLORY-HUGGINS THEORY TO TERNARY POLYMER-SOLVENTS EQUILIBRIA - A CASE-STUDY

The ternary equilibrium data of the following systems: benzene/heptane /NBR at 60 degrees C (system 1), heptane/isooctane/PE at 25 degrees C (system 2), ethanol/water/Ca at 20 degrees C (system 3) and ethanol/wa ter/P(E-co-VAc) at 32 degrees C (system 4), already reported in the li terature, have been used and experimental results compared to predicti ons offered by the Flory-Huggins theory applied to ternary mixtures (o ne polymer and two liquids), with constant interaction parameters and negligible elastic contribution. Polymer-solvent interaction parameter s have been determined from swelling in pure liquid, while liquid-liqu id interaction parameters have been estimated from liquid-vapour equil ibrium data curve fitting. It is shown that the Flory-Huggins theory o ffers reasonable prediction in the case of apolar liquids in an elasto meric matrix (system 1), while approximate isotherm patterns with sign ificant discrepancies, are obtained with apolar liquids in a thermopla stic (system 2). The equilibrium data of polar liquids in either homop olymer or copolymer (systems 3 and 4) can hardly be achieved by Flory- Huggins theory, even when a variable liquid-liquid interaction paramet er is used. Implications in ternary diagram simulations and possible p rediction improvements are discussed.