MODELING OF VAPOR SORPTION IN POLAR MATERIALS - COMPARISON OF FLORY-HUGGINS AND RELATED MODELS WITH THE ENSIC MECHANISTIC APPROACH

This work focuses on the analysis of organic vapour sorption in polyme r systems strongly deviating from ideality. The sorption of three diff erent types of organics (i.e. alcohol, ether, ester) in polyurethaneim ide block copolymers has been investigated using a microgravimetric te chnique over the entire activity range. For all the polyurethaneimides , sorption increases in the following order: ETBE<EtOH<AcOEt. A furthe r analysis in terms of the Flory-Huggins (FH) theory generally shows a great discrepancy between experimental and calculated sorption values . This quasi-systematic failure could be ascribed to a fairly strong d ependence of FH interaction parameter chi towards penetrant concentrat ion, which cannot be accounted for by the FH theory. A theoretical mod ification of the FH theory, previously reported by Koningsveld and Kle intjens to account for the variation by a three-parameter law, was sho wn to be really efficient for sorption modeling over the entire activi ty range. Despite a systematic divergence for the very low sorption le vels, an empirical modification of the FH theory using a power law chi =a phi(b) could also be an interesting alternative which requires only two parameters for a fairly good modeling for activities higher than 0.1-0.2, Considering the sorption phenomenon as a mechanical anisotrop ic process, the recent ENSIC approach, reported by Favre et al., prove d its striking efficiency allowing the sorption modelling of all the s orption isotherms with a mean correlation coefficient R=0.9983, (C) 19 98 Elsevier Science B.V. All rights reserved.