WATER SORPTION-DESORPTION KINETICS IN POLY(ETHYLENE NAPHTHALENE-2,6-DICARBOXYLATE) AND POLY(ETHYLENE-TEREPHTHALATE)

Water sorption/desorption experiments were carried out on films (simil ar to 220 mu m thick) of amorphous poly(ethylene naphthalene-2,6-dicar boxylate) (PEN) stored in ambient conditions for different periods of time (0.5-4 years) and of poly(ethylene terephthalate) (PET) with diff erent degrees of crystalinity levels (0-29%) by means of FTIR spectros copy. Water sorption/desorption kinetics follows Fick's law for all sa mples investigated. Water sorption isotherms, obtained from gravimetri c methods, indicate a larger sorption capacity in the case of PEN mate rials. The apparent diffusion coefficients (D) are larger in the case of PET samples. The observed D values decrease with storage time (phys ical aging) of PEN samples and with the crystallinity of PET samples. (C) 1995 John Wiley & Sons, Inc.