DIFFUSION AND SORPTION OF CO2 IN POLY(ETHYLENE-TEREPHTHALATE) AND POLY(ETHYLENE NAPHTHALATE)

Measurements have been made of the solubilities and effective diffusio n coefficients at 25 degrees C for carbon dioxide in random and uniaxi ally oriented samples of poly(ethylene terephthalate) and poly(ethylen e naphthalate) (PET and PEN). Most measurements were made using a doub le-sided experiment in which the penetrant entered both sides of the s ample simultaneously and the concentration was monitored as a function of time by means of infrared spectroscopy. Pressures of carbon dioxid e from 0.125 to 5 atmospheres were employed. Finite difference modelin g was used to determine concentration-dependent diffusion coefficients from the effective diffusion coefficients measured directly and to co mpare the results with the dual-mode and gas-polymer matrix models. Th e results could be fitted slightly better by the dual-mode model than by the gas-polymer matrix model, although the latter also provided a r easonable fit to the data. There was, however, no observed change in t he spectrum of the absorbed carbon dioxide with concentration, as woul d be expected if it existed in two distinct states within the polymer, as required by the dual-mode model. No definite conclusion can thus b e drawn about the applicability of the two models to the systems studi ed. (C) 1996 John Wiley & Sons, Inc.