Decreased oxygen permeability of EVOH through molecular interactions

Poly(ethylene-co-vinyl alcohol) of 48 mol% ethylene content was modified with N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)- isophthalamide (Nylostab SEED) to decrease the oxygen permeability of the polymer. The additive was added in a wide concentration range from 0 to 10 wt%. The structure and properties of the polymer were characterized with various methods including differential scanning calorimetry, X-ray diffraction, mechanical testing, optical measurements and oxygen permeation. Interactions were estimated by molecular modeling and infrared spectroscopy. The results showed that oxygen permeation decreased considerably when the additive was added at less than 2.0 wt% concentration. The decrease resulted from the interaction of the hydroxyl groups of the polymer and the amide groups of the additive. The dissolution of the additive in the polymer led to decreased crystallinity, but also to decreased mobility of amorphous molecules. Stiffness and strength, but also deformability increased as a result. Above 2 wt% the additive forms a separate phase leading to the deterioration of properties. The success of the approach represents a novel way to control oxygen permeation in EVOH and in other polymers with similar functional groups capable of strong interactions.