Application of FTIR spectroscopy to determine transport properties and water–polymer interactions in polypropylene (PP)/poly(ethylene-co-vinyl alcohol) (EVOH) blend films: Effect of poly(ethylene-co-vinyl alcohol) content and water activity

This paper reports the use of FTIR spectroscopy along with gravimetric analysis to simultaneously study water sorption, transport properties and water–polymer interactions in PP/EVOH films at 25 °C, as a function of EVOH content and water vapour activity. The results indicate the existence of two different mechanisms, below (dual-mode) and above a critical concentration value close to the clustering limit activity. Several spectroscopically distinguishable “types” of sorbed water molecules with different diffusion rates have been detected, and their evolution as a function of the penetrant concentration followed. The main changes in the water structure take place from the clustering limit activity onwards. Significant differences both in the state of water and diffusion sequence of free/bound water have been found between 90/10 PP/EVOH films and blends with EVOH content ≥20%, suggesting not only composite-dependence but also morphology-dependence.