Transient method of water vapour permeability coefficient determinations for packaging foils.
A concept of transient transmission measurements of the coefficients of water vapour permeability (PH2O) through a packaging foil, based on the analysis of a sorptive sensor reaction inertia, was used to work out the measuring cell, the measuring system and the PH2O measurement method. Measurements were carried out in two phases: the initial phase of stabilization of the water concentration gradient, and the proper phase of measurement — its beginning was determined by the condition of steady-state permeation through the foil. The principles underlying the definition of the beginning of the proper measurement, conversion of the measured signal into relative humidity units, and the determination of the beginning of the sensor intertia analysis have also been developed. The uncertainty of the results obtained by this method was estimated at the significance level a = 0.5. The accuracy of the method, i.e. the maximum relative uncertainty of a single result of τm, was Bpmax = 3% in the case of a 35- μm thick low-density polyethylene foil.
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