Equilibrium Water Sorption in Poly(ethylene furanoate) Compared to Poly(ethylene terephthalate)

Recent introduction of poly(ethylene furanoate) (PEF), which is a bio-based, performance-enhanced furanic analog to poly(ethylene terephthalate) (PET), has sparked widespread investigation into previously un-reported fundamental properties of this polymer. The current work examines equilibrium water sorption properties in amorphous PEF and PET at 35°C over the entire water activity range. PEF exhibits a largely increased equilibrium water sorption uptake of ~1.7X compared to PET at unit activity, resulting from substitution of the non-polar phenyl ring in PET with the polar furan ring in PEF. Both polyesters exhibit dual-mode sorption up to ~0.6 activity, after which deviation is observed via a noticeable upturn in concentration vs. activity for both polyesters. Excellent agreement is found between three independent sorption measurement techniques, thereby providing a consistency check for the reported data. Supplementary characterization techniques are utilized to provide a more detailed understanding of the morphological changes induced by the increased sorption at unit activity.