A study of the barrier properties of ethylene vinyl alcohol copolymers using gas chromatography

Abstract

Ethylene vinyl alcohol copolymer (EVOH) is one of the most commonly used barrier materials in a broad range of applications. Its outstanding gas barrier properties have already been widely investigated for oxygen (O2). However, EVOH is also gaining more attention as a barrier material against other gases and organic substances such as aromas, flavours, fuels, chemicals and even as a functional barrier. The objective of the research is to determine the barrier properties of EVOH against a selection of gases, i.e. O2 and nitrogen (N2) in varying conditions of relative humidity and temperature, and organic substances such as mineral oil saturated hydrocarbons (MOSH), mineral oil aromatic hydrocarbons (MOAH) and other non-intentionally added substances (NIAS). The permeation of the gases was determined by an online permeation setup based on the equal pressure method and consists of a permeation system connected to a gas chromatography (GC)-based detection system. A similar setup with GC-mass spectrometry (MS) was used for the organic substances. Additionally, an off-line method using a spiked donor taped on barrier and receptor were used to perform experiments modelling mineral oil migration from cardboard into foodstuff with EVOH acting as a functional barrier. The concentration of the mineral oil components was analysed by GC-MS. The research shows that EVOH is a multi-functional barrier against both gases such as O2 and N2, as well as a functional barrier against mineral oils. Three grades containing 32, 44 and 48 mol% ethylene show good O2 and N2 barrier properties and outperform other polymers such as polyethylene (PE), polypropylene (PP) and polyamide 6 (PA 6) by several orders of magnitude. Moreover, only 3 m EVOH containing 27 or 32 mol% ethylene is required as functional barrier against mineral oils and other NIAS migrating from paperboard to protect foodstuff with a shelf-life of over 2 years.