PACKAGING TECHNOLOGY AND SCIENCE VOL 8 zyxwv 73-83 (1995) A Mathematical Model for the Prediction of Water Vapour Transmission Rate at Different Temperature and Relative Humidity Combinations Lucian0 Piergiovanni", Patrizia Fava and Antonio Siciliano DISTAM, Department of Food Science and Microbiology, University of Milan, via Celoria 2,201 33 Milan, Italy A simple mathematical procedure for the estimation of water vapour trans- mission rate under different conditions is presented and discussed. The ASTM dynamic and gravimetric methods were used for measuring the water vapour transmission rate of four thin plastic films (PET 19pm. PVC 16pm, EVA 15pm and LDPE 23pm) under 38 different conditions of temperature and relative humidity and the corresponding permeance values were drawn. On the basis of the Clausius Clapeyron's relationship between temperature and water vapour pressure, a simple equation was derived for a rapid transfor- mation of water vapour transmission rate data. The mathematical procedure was applied to the data collected for the four thin films and good agreement was found between observed and predicted values for the PET and LDPE films, while for the PVC and EVA films the equation developed led to an over- estimate of water vapour transmission at the lower temperatures. zyx Keywords: WVTR; plastic films; modelling; shelf-life zyxw INTRODUCTION zyxwvu Gas and water vapour permeation through plastic materials is a diffusion phenom- enon influenced by several factors, depending both on the chemical nature of the material and on environmental conditions. A major role is played by temperature, which affects permeability according to the well known Arrhenius equation zy [K, = zyxwv Kpo exp(-E,/RT)], where the permeability constant (K,) is an exponential function of temperature and of the apparent energy of activation for permeation zy (Ep), the latter deriving from the energy of activation for diffusion (Ed) and the heat of *Author to whom correspondence should be addressed. Research supported by the National Research Council of Italy. Special Project RAISA, Subproject 4, Paper no. ??. CCC 0894-3214/95/020073-11 zyxwvut 0 1995 by John Wiley & Sons, Ltd. Received 5 December 1994 Accepted 31 January 1995