This article is the first one of a series devoted to the study of hydration processes in epoxy resins using infrared (FTIR) spectrometry, with a view to eventually determining the role of ambient H 2 O molecules in the degradation of these resins, particularly when they are exposed to irradiation. The starting experiment consists of recording spectra of thin films of these resins which allows us to propose a preliminary assignment of the bands of interest. The second experiment consists of heating these resins. As the main effect of a temperature elevation is to break hydrogen bonds, the analysis of the corresponding spectra enables us to more precisely assign bands which will be of importance in the hydration process. The third experiment consists of hydrating these resins in a humid atmosphere. The pressure of the water vapor of this atmosphere is directly measured in the IR spectra where the corresponding, extremely narrow bands are easily isolated. The analysis of the spectra obtained, after subtraction of these bands due to water vapor, allows us to determine the interaction configurations of H 2 O molecules which are embedded in the resins, that is, the various ways they establish or accept hydrogen bonds to or from hydrophilic groups.

Functional barriers are multilayer structures deemed to prevent migration of some chemicals released by food-contact materials into food. In the area of plastics packaging, different migration behaviours of mono- and multilayer structures are assessed in terms of lag time and of their influence of the solubility of the migrants in food simulants. Whereas barriers to oxygen or to aromas must prevent the diffusion of these compounds under conditions of use, a functional barrier must also be efficient under processing conditions, to prevent diffusion of substances when the polymer layers are in contact at high (processing) temperatures. Diffusion in melted polymers at high temperatures is much slower for glassy polymers, than in polymers that are rubbery at ambient temperature. To evaluate the behaviour of functional barriers under conditions of use, a set of reference diffusion coefficients in the 40-60 degrees C range were determined for 14 polymers. Conditions for accelerated migration tests are proposed based on worst-case activation energy in the 40-60 degrees C range. For simulation of migration, numerical models are available. The rules derived from the models can be used both by industry (to optimize a material in terms of migration) or by risk assessors. Differences in migration behaviour between mono- and multilayer materials are discussed.

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