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The water content of paper and its time dependence are of great importance for the use of paper and cardboard as packaging materials. The physical process of water sorption and the mechanisms of water "binding" in paper, as fundamental principles of the kinetics, are discussed. Water exists in up to four different "states" (i.e. domains of mobility) in paper: the first layer at the primary sites on the surface of the fibers; the multimolecular layers, with less "binding" energy, on these inner surfaces; condensed water in the voids; and dissolved water in the cellulose fibers. All these "states" influence the shape of the sorption isotherm and correspond to a different water content and to different transport mechanisms. The various types of water "binding" on paper were studied by measuring the transversal relaxation rate, T2, using a pulsed Nuclear Magnetic Resonance spectrometer (minispec pc 120). In addition, a non-destructive, fast method of determining the water content in packaging materials with NMR spectroscopy is described.

Various lipids, present as thin films on polar filter paper supports, were evaluated for resistance to the transmission of water vapor (rH2O) and oxygen (rO2). Beeswax exhibited the largest r(H2O), followed in order by fully-hydrogenated soy-rapeseed oil, stearyl alcohol, acetylated monoglycerides, hexatriacontane, tristearin, and stearic acid. Most of the lipids exhibited negative activation energies, E, for resistance to transmission of water vapor and positive Es for resistance to transmission of oxygen. The type of lipid support (hydrophobic or hydrophilic) also influenced E for resistance to water vapor transmission. Differences in r(H2O) for the various lipids, comparative r(H2O) and r(O2) values, and the temperature dependence of these values can be explained, in part, by the degree of hydrophilicity of the lipid molecule. Tempering at 48 degrees C of stearyl alcohol caused a substantial decrease in its permeability to oxygen and water vapor. The polymorphic form of a blend of fully-hydrogenated soybean and rapeseed oil had a moderate influence on its permeability to oxygen and water vapor. This information will be useful for formulating lipid-containing films with controlled barrier properties to the passage of water vapor and oxygen.