Study of transport of small molecules through ethylene-co-vinyl acetate copolymers films.: Part B:: CO2 and O2 gases

The transport of gases (pure oxygen and carbon dioxide) through poly(ethylene-co-vinyl acetate) (EVA) of different VA contents. was studied by permeation measurements. Permeabilities, diffusi vi ties. and solubilities were determined for EVA films containing 19, 33, 50 and 70% (w/w) VA. A low density polyethylene LDPE (used as reference with 0% VA) was also studied. The diffusion of oxygen was determined from transient permeation fluxes and the diffusion of carbon dioxide from time-lag permeation. In the case of gas permeation, whatever the VA content of the polymer used, the experimental transient fluxes are characterized by a constant diffusion coefficient for both O-2 and CO2. In terms of gas permeability, compared with water permeability (Part A), these copolymers are characterized by very low coefficients, especially for oxygen. Assuming that D is constant, the O-2 and CO2 solubility coefficient was then deduced and its value is shown to increase proportion ally with the VA content in these rubbery copolymers (whose quantity of crystalline phases decreases and become nil for 70% VA). The H2O/CO2 and H2O/O-2 ideal selectivity a increases with the VA content, in agreement with the increase in average polarity of the copolymer. (C) 2002 Elsevier Science Ltd. All rights reserved.