Permeation of water, methanol, fuel and alcohol-containing fuels in high-barrier ethylene-vinyl alcohol copolymer

A comprehensive study of the permeation rate, and other transport propertie s, of water, methanol, toluene, fuel C (50/50 toluene and iso-octane) and o xygenated fuels (fuel C+10% ethanol and fuel C+15% methanol) in 32 mol% eth ylene-vinyl alcohol (EVOH) copolymer has been carried out by sorption (weig ht uptake) and/or permeation (weight loss) measurements, Alcohol-containing fuels are aimed at reducing toxic emissions and are envisaged to replace s tandard fuels. Large-scale water- and methanol-induced polymer plasticizati on was suggested by large solvent uptakes and confirmed by the observation of a considerable depletion in the glass transition temperature (T-g) as me asured by differential scanning calorimetry and dynamic mechanical analysis . Polymer plasticization is somewhat larger in the presence of methanol. Th e barrier performance of EVOH to toluene, and consequently to fuel C, is ou tstanding (better than 0.01 g mm/m(2) day) at 21 degreesC and 40 degreesC u nder dry conditions, but deteriorates significantly for fuel containing met hanol. This is caused by the selective loss of methanol, a severe plasticiz ing agent, that permeates faster. In spite of this, the barrier performance of EVOH to oxygenated fuels is still outstanding, and only slightly worse than that to fuel C, if ethanol is added to fuel C. (C) 2001 Elsevier Scien ce Ltd, All rights reserved.