Eine spektroskopische Methode zur Messung der Ammoniak-Permeabilität in Polymerfilmen

A new spectroscopic method for determining the permeability of ammonia in transparent polymer layers is presented. It is based on the quantitative proof of the ammonia passing the test layer into a sensor layer, containing 4-nitrophenol as an NH₃-sensitive probe, which is placed under the test film. The permeability (P) of the test layer is calculated from the slope of extinction with time in the sensor layer. The lag time (t₁) gives the diffusion coefficient (D). The suitability of this method is confirmed by comparison with literature values. Diffusion coefficients obtained from t₁ correspond well to those obtained by the sorption method. The temperature dependence of P and D in more than five different polymers (CDA, PVB, PVAc, PVC and different polyvinyl alcohols) demonstrates that peculiarities in the temperature dependence of the permeability result from the behaviour of the NH₃-solubility (P/D) which is strongly dependent on the polymer structure.