Polymers: Ethylene vinyl alcohol
Ethylene vinyl alcohol (EVOH) is a copolymer of ethylene and vinyl alcohol monomers, as shown in the diagram above. It is a thermoplastic material well known for its gas barrier properties (specifically oxygen, nitrogen, and carbon dioxide), allowing for its usage in packaging.
Other properties of EVOH include oil and water resistance, transparency, flexibility, high chemical resistance, a lack of odor, and little to no toxicity when incinerated. However, EVOH also has many less than favorable properties, including the fact that its gas barrier properties weaken when exposed to moisture, and EVOH is thus often combined or layered with other materials which are more impenetrable to moisture. Because of these layers, EVOH is also difficult to recycle, and, even on its own, is not usually considered biodegradable (though the combination of EVOH with polyvinyl alcohol has better degradation properties).
EVOH’s combination of properties lends to its application in packaging, primarily food packaging in order to preserve the shelf life of the contents such as fresh produce, however other applications of this copolymer also include other packaging applications (such as medical), piping, and hydrogen fuel cells.