Modelling of vapour 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 polymer systems strongly deviating from ideality. The sorption of three different types of organics (i.e. alcohol, ether, ester) in polyurethaneimide block copolymers has been investigated using a microgravimetric technique over the entire activity range. For all the polyurethaneimides, sorption increases in the following order: ETBE<EtOH<AcOEt. A further 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 dependence of FH interaction parameter chi towards penetrant concentration, which cannot be accounted for by the FH theory. A theoretical modification of the FH theory, previously reported by Koningsveld and Kleintjens to account for the variation by a three-parameter law, was shown to be really efficient for sorption modeling over the entire activity range. Despite a systematic divergence for the very low sorption levels, 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 anisotropic process, the recent ENSIC approach, reported by Favre et al., proved its striking efficiency allowing the sorption modelling of all the sorption isotherms with a mean correlation coefficient R=0.9983, (C) 1998 Elsevier Science B.V. All rights reserved.