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 properties, of water, methanol, toluene, fuel C (50/50 toluene and iso-octane) and oxygenated fuels (fuel C+10% ethanol and fuel C+15% methanol) in 32 mol% ethylene-vinyl alcohol (EVOH) copolymer has been carried out by sorption (weight uptake) and/or permeation (weight loss) measurements, Alcohol-containing fuels are aimed at reducing toxic emissions and are envisaged to replace standard fuels. Large-scale water- and methanol-induced polymer plasticization was suggested by large solvent uptakes and confirmed by the observation of a considerable depletion in the glass transition temperature (T-g) as measured by differential scanning calorimetry and dynamic mechanical analysis. Polymer plasticization is somewhat larger in the presence of methanol. The barrier performance of EVOH to toluene, and consequently to fuel C, is outstanding (better than 0.01 g mm/m(2) day) at 21 degreesC and 40 degreesC under dry conditions, but deteriorates significantly for fuel containing methanol. This is caused by the selective loss of methanol, a severe plasticizing 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 Science Ltd, All rights reserved.