Pervaporation, a novel technique for the measurement of vapor transmissionrate of highly permeable films

The moisture vapor transmission rate (MVTR) of poly(ether-block-amide) brea thable films were measured with a set-up based on the ASTM E96 E and SW met hods. These methods led to reliable MVTR for films of low breathability, bu t not for films of high breathability. The latter shows MVTR values varying over a large range when the operating conditions are changed. An analysis of the mass and the heat transfers pointed out the crucial role of the tran sfer resistances in the external phases adjacent to the film. The pervapora tion technique was designed to minimize these mass and heat transfer resist ances using a powerful stirring of the upstream chamber and a good vacuum a pplied on the downstream chamber. The MVTR was determined from the weight o f vapor condensed in a cool trap. The MVTR of films of high breathability w ere reliably determined by this method; their value was much higher than th ose obtained with the ASTM E96 BW method for the same films. The obtained i ntrinsic MVTR data suggest that (i) the film structure: is more ordered at lower thickness, and (ii) the activation energy for water permeation is low , probably due to the high flexibility of polyether segments. The technique was successfully used for the measurement of a very high MVTR film made of poly(vinylalcohol), ca. 120 kg day(-1) m(-2), and for the measurement of t he permeation rate of ethylacetate through a silicone rubber film. (C) 2001 Elsevier Science Ltd. All rights reserved.