Morphological alterations induced by temperature and humidity in ethylene-vinyl alcohol copolymers

The morphologies of a number of high barrier ethylene−vinyl alcohol food packaging films with different ethylene contents have been evaluated by simultaneous WAXS/SAXS, FT-IR, DSC, and Raman spectroscopy. This rather descriptive pioneering study was aimed at the understanding of the morphological changes that occur in these polymers as a result of temperature, humidity, and combination of temperature and humidity treatments. From the results, the temperature effect was, as expected, found to improve polymer crystalline morphology, leading to a higher, denser, and more stable crystallinity. Lower ethylene content copolymers underwent partial solid−solid phase transition toward a more thermodynamically stable monoclinic morphology upon sufficient annealing. On the other hand, moisture sorption was found to result in melting of ill-defined crystals, particularly for the lowest ethylene content copolymers. This water sorption-induced crystal melting process has not been reported before and was seen to be larg...