FLOW METHOD FOR STUDY OF GAS-TRANSPORT IN POLYMERS - APPLICATION TO THE STUDY OF OXYGEN, NITROGEN, AND CARBON-DIOXIDE PERMEATION THROUGH CELLULOSE-ACETATE MEMBRANES

Transient permeation of oxygen, nitrogen, and carbon dioxide through c ertain cellulose acetate (CA) dense membranes made from solutions in d ioxane and dioxane-added ethanol were studied by the flow method. In o rder to explain the overshoots for transient permeation rates in the l atter case, a new model is proposed. It postulates a time-dependence s olubility coefficient, in the form of a series of exponential terms, w hich is combined in Fick's second law and solved. The model fits well the obtained permeation kinetics, leading to values of the diffusion, and permeation coefficients, and the structure change-related time. Th e overshoots are explained by the formation of unstable structure from dioxane-ethanol solvent mixtures, a memory effect of aggregated chain s, which undergoes consolidation upon gas penetration. The stable stat e which results from the consolidation process is the same as that of membranes obtained from pure dioxane solutions. (C) 1994 John Wiley an d Sons, Inc.