Isopiestic determination of the water activities and prediction of liquid-liquid equilibrium in polyethylene glycol plus hydroxypropyl starch plus water systems

The water activities in aqueous mixtures of polyethylene glycol (PEG) and h ydroxypropyl starch (PES) with different molecular weights, both binary and ternary systems, were measured by using the improved isopiestic method. Th e modified Fitter's model was used to calculate Liquid-liquid equilibrium ( LLE) in PEG/PES aqueous two-phase systems. The model parameters were evalua ted directly from the experimental water activities. Then the phase diagram s of LLE of PEG/PES aqueous two-phase systems with different molecular weig hts were successfully predicted using only one group of model parameters. G ood agreement with the experimental data of tie line was obtained, with mos t of average absolute deviations being less than 1.5 wt.%. (C) 1999 Elsevie r Science B.V. All rights reserved.