Abstract
EVOH (Ethylene-Vinyl Alcohol) materials are widely used in automotive applications in multi-layer fuel lines and tanks owing to their excellent barrier properties to aromatic and aliphatic hydrocarbons. These barrier materials are essential to limit environmental fuel emissions and comply with the challenging requirements of fast changing international regulations. Nevertheless, the measurement of EVOH permeability to model fuel mixtures or to their individual components is particularly difficult due to the complexity of these systems and their very low permeability, which can vary by several orders of magnitude depending on the permeating species and their relative concentrations. This paper describes the development of a new automated permeameter capable of taking up the challenge of measuring minute quantities as low as 1 mg/(m 2 .day) for partial fluxes for model fuel mixtures containing ethanol, i -octane and toluene at 50°C. The permeability results are discussed as a function of the model fuel composition and the importance of EVOH preconditioning is emphasized for accurate permeability measurements. The last part focuses on the influence of EVOH conditioning on its mechanical properties and its microstructure, and further illustrates the specific behavior of EVOH in presence of ethanol oxygenated fuels. The new metrology developed in this work offers a new insight in the permeability properties of a leading barrier material and will help prevent the consequences of (bio)ethanol addition in fuels on environmental emissions through fuel lines and tanks.
Highlights
Ethylene-vinyl alcohol (EVOH) copolymers are amongst the best commercial barrier materials used worldwide
To optimize the measurements of the different partial fluxes which could differ by several orders of magnitude for the same experiment, the sensitivity range of the gas chromatograph was adapted to the injected weights
With the small membrane area of 8.4 cm2 of the EVOH films used in this work, the permeate sampling did not induce any significant change in the composition of the model fuel mixture with a minimum circulating feed volume of 150 mL
Summary
Ethylene-vinyl alcohol (EVOH) copolymers are amongst the best commercial barrier materials used worldwide. They are mainly used in packaging applications for their excellent barrier properties to oxygen [1]. The chemical physical properties of EVOH copolymers are highly dependent upon their vinyl alcohol content and the best barrier properties are obtained with high contents in vinyl alcohol The EVOH outstanding barrier performances are highly sensitive to humidity and temperature. In packaging applications, the EVOH barrier material is usually co-extruded with hydrophobic polyolefin layers which protect the barrier layer from humidity
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