Liquid–Liquid Equilibrium of Aqueous Biphasic Systems Containing Ethylene Oxide–Propylene Oxide Block Copolymers and Maltodextrins

Abstract

This work presents liquid–liquid phase equilibrium data of ternary systems formed by aqueous mixtures of ethylene oxide–propylene oxide block copolymers and maltodextrin. Phase diagrams were obtained for five copolymers (with EO ratios ranging from 20 % to 80 % and molar masses ranging from 1900 g·mol–1 to 8400 g·mol–1) and three maltodextrins (with number averaged molar masses of 990 g·mol–1, 1500 g·mol–1, and 3000 g·mol–1) at 298.2 K and 308.2 K. The main factor influencing the phase diagrams is the ratio between ethylene oxide and propylene oxide chain sizes. The size distribution of maltodextrin was studied through gel permeation chromatography, and the size distribution of some equilibrium phases was also determined. Maltodextrin was found to partition unevenly between equilibrium phases, with larger molecules being excluded from the polymer-rich phases. The phase equilibrium was modeled using the UNIQUAC equation and with the consideration that maltodextrin can be represented by six pseudocomponents. It was verified not only that the model can adequately describe the phase equilibrium but also that the uneven distribution of maltodextrin molecules can be qualitatively assessed.