Water sorption in poly(ethylene furanoate) compared to poly(ethylene terephthalate). Part 1: Equilibrium sorption

- Water sorption properties in PEF and PET were studied at 35 °C from 0 to 1 activity.
- Dual-mode sorption occurred at activity <0.6 and swelling at activity >0.6.
- PEF exhibits an increased water sorption capacity of ∼1.8× compared to PET.
- The effective enthalpy of water sorption is reported for both polyesters.
- The current work is the first detailed study of equilibrium water sorption in PEF.

Equilibrium water sorption properties of amorphous poly(ethylene furanoate) (PEF) and amorphous poly(ethylene terephthalate) (PET) were studied at 35 °C over the entire water activity range. PEF exhibits a largely increased equilibrium water sorption capacity of ∼1.8× averaged over the entire concentration range compared to PET, 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 the onset of swelling produces a noticeable upturn in concentration vs. activity for both polyesters. Excellent agreement was observed between three independent sorption measurement techniques, thereby providing a consistency check for the reported data. Sorption measurements performed at 15, 25, 35, and 45 °C allowed estimation of the effective enthalpy of water sorption for both polyesters, which were similar to the enthalpy of condensation for pure water. The current work demonstrates the importance of structure on sorption and transport properties in these two important polyesters.

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