Interactions between water and EVOH food packaging films

The transport of water in four EVOH copolymers commonly used in high barrie r food packages was characterized through permeation (continuous flow) and gravimetric experiments at different relative humidities and 23 +/- 2 degre es C. Water sorption isotherms were fitted with the D'Arcy and Watts' equat ion. From these data, the value of the solubility coefficient (S, as define d by Henrys law) was determined and was found constant within a 0.2-0.75 wa ter activity (a(w)) range. Water uptake at the same a(w) increased as the E VOH ethylene content decreased. The permeability coefficient (P) for water through EVOH was determined as a function of water activity. The permeabili ty was constant within the range of 0.3-3.75 a(w) and decreased with EVOH e thylene content. At high relative humidities (a(w) > 0.75) the value of per meability increased by up to two orders of magnitude. In this range, the hi gher the ethylene content the lesser the value of P.