Modelling the moisture vapour transmission rate through segmented block co-poly(ether-ester) based breathable films

Water permeability is an important property of films used in, for instance, protective clothing or construction applications. There are a number of st andardised test methods available for evaluating the permeability of films. In one class of tests, there is a direct contact between the polymer film and water; in another class of tests there is an air layer between water an d the film. This paper deals with the modelling of water permeability of tw o commercial types of segmented block co-poly(ether-ester). Water transport in the films is modelled assuming a simple Fickian diffusion behaviour, so rption isotherms are described in terms of either a Zimm-Lundberg based clu ster model or Henry's law. Mass transport in the air layer is described in analogy with heat transport for the classical Benard problem. Using this an alysis it is shown that water permeability for both films and for both type s of tests can be predicted as a function of the film thickness. There is a good agreement between the model predictions and the experiment. (C) 2000 Elsevier Science Ltd. All rights reserved.