Abstract
Diffusion coefficients for water in amorphous poly(ethylene furanoate) (PEF) and poly(ethylene terephthalate) (PET) were studied at 35 °C over the entire water activity range. PEF exhibits a ∼5× reduction in diffusion coefficient averaged over the entire concentration interval compared to PET. Fickian diffusion was observed for water in both polyesters up to ∼0.6 activity, after which the presence of non-Fickian relaxations required treatment using the Berens–Hopfenberg modeling framework. Penetrant plasticization at high activity was found for both PEF and PET, as evidenced by a positive correlation between diffusion coefficient and increasing water concentration. Arrhenius interpretation of diffusion coefficients measured at 15, 25, 35, and 45 °C allowed calculation of the activation energies of diffusion for PEF and PET, which were similar at 47.1 ± 2.8 kJ/mol and 46.4 ± 3.0 kJ/mol, respectively. This study complements prior work pertaining to the equilibrium water sorption properties in both polyesters, and subsequently provides a detailed investigation of the water diffusion process in these materials.
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