Water sorption/desorption kinetics in poly(ethylene naphthalene‐2,6‐dicarboxylate) and poly(ethylene terephthalate)

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Abstract
Water sorption/desorption experiments were carried out on films (∼ 220 μm thick) of amorphous poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN) stored in ambient conditions for different periods of time (0.5‐4 years) and of poly(ethylene terephthalate) (PET) with different degrees of crystalinity levels (0‐29%) by means of FTIR spectroscopy. Water sorption/desorption kinetics follows Fick's law for all samples investigated. Water sorption isotherms, obtained from gravimetric methods, indicate a larger sorption capacity in the case of PEN materials. The apparent diffusion coefficients (D) are larger in the case of PET samples. The observed D values decrease with storage time (physical aging) of PEN samples and with the crystallinity of PET samples. © 1995 John Wiley & Sons, Inc.