Analysis MethodThe effect of ethylene content on the interaction between ethylene-vinyl alcohol copolymers and water: (I) Application of FT-IR spectroscopy to determine transport properties and interactions in food packaging films

A simultaneous analysis of the transport properties of water through extruded food packaging films made of ethylene-vinyl alcohol copolymers (EVOH) with various ethylene contents, i.e. ranging from 26 to 48 mol% of ethylene, and of water polymer interactions have been carried out using fourier transform infrared spectroscopy (FT-IR). This study is part of a more extensive project, the overall aim of which is to demonstrate the capabilities of the FT-IR technique to test transport properties in high barrier plastic films of interest in food packaging applications. A characterization of solvent uptake (water sorption isotherms), diffusion and permeability coefficients as a function of ethylene content and relative humidity has been carried out across the above composition regime. From the results, an unreported Langmuir contribution was found at low relative humidity conditions for the copolymers, which could be responsible for the unusual trend in oxygen permeability reported earlier for these materials. Furthermore, a distribution of water molecules with different hydrogen bonding strengths and different diffusion rates was encountered, which suggests that the interaction and transport properties of moisture in these polymers is far from being a simple and homogeneous process.