Ethylene vinyl alcohol (EVOH) is a formal

copolymer In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are som ...

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...

and vinyl alcohol. Because the latter

monomer A monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called polymerization. Classification Chemis ...

mainly exists as its

tautomer In chemistry, tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the reloca ...

acetaldehyde Acetaldehyde (IUPAC systematic name ethanal) is an organic compound, organic chemical compound with the chemical formula, formula , sometimes abbreviated as . It is a colorless liquid or gas, boiling near room temperature. It is one of the most ...

, the copolymer is prepared by polymerization of ethylene and

vinyl acetate Vinyl acetate is an organic compound with the Chemical formula, formula CH3CO2CH=CH2. This colorless liquid is the precursor to polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, and other important industrial polymers. Prod ...

to give the ethylene vinyl acetate (EVA) copolymer followed by hydrolysis. EVOH copolymer is defined by the mole % ethylene content: lower ethylene content grades have higher barrier properties; higher ethylene content grades have lower temperatures for

extrusion Extrusion is a process used to create objects of a fixed cross section (geometry), cross-sectional profile by pushing material through a Die (manufacturing), die of the desired cross-section. Its two main advantages over other manufacturing pro ...

. The

plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...

resin is commonly used as an oxygen barrier in

food packaging Food packaging is a packaging system specifically designed for food and represents one of the most important aspects among the processes involved in the food industry, as it provides protection from chemical, biological and physical alterations ...

. It is better than other plastics at keeping air out and flavors in, is highly transparent, weather resistant, oil and solvent resistant, flexible, moldable, recyclable, and printable. Its drawback is that it is difficult to make and therefore more expensive than other food packaging. Instead of making an entire package out of EVOH, manufacturers keep costs down by coextruding or laminating it as a thin layer between cardboard, foil, or other plastics. It is also used as a hydrocarbon barrier in plastic fuel tanks and pipes.

Industrial production

Because of the high capital cost to build an EVOH plant, and the complexity of making a food grade product, only a few companies produce EVOH:

Kuraray is a Japanese manufacturer of chemicals, fibers and other materials. Their main manufacturing facilities are located in Kurashiki, Okayama. The company's Tokyo administrative offices are located in Otemachi, Chiyoda in the Ote Center Building ...

produces EVOH resin under the name "EVAL," with a 10,000 ton plant in Okayama, Japan; a 58,000 ton plant in the U.S. (near Houston, TX) under its subsidiary Kuraray America; and a 35,000 ton plant in Belgium under its subsidiary EVAL Europe. Nippon Gohsei produces EVOH under the trade name Soarnol. It has production sites in Mizushima, Japan; La Porte, Texas in the USA; and at

Salt End Salt End or Saltend is a Hamlet (place), hamlet in the East Riding of Yorkshire, England, in an area known as Holderness. It is situated on the north bank of the Humber Estuary just outside the Kingston upon Hull, Hull eastern boundary on the A ...

, Hull, England. Chang Chun Petrochemical produces EVOH under the trade name EVASIN. It has a single site in Taipei, Taiwan.

Food packaging

Due to its strong barrier against gasses (especially oxygen), odors and flavours, food packaging manufacturers use EVOH in their packaging structure to extend the shelf life of food products. A downside of EVOH is its relatively high moisture sensitivity, meaning that the barrier capabilities of EVOH decrease in environments with high humidity. As such, EVOH is often applied within a multilayer film. Here, one or more inside layers contain EVOH, but the outside layers consist of a different plastic that is less sensitive to moisture, such as

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bott ...

Medical applications

EVOH is used in a liquid embolic system in

interventional radiology Interventional radiology (IR) is a medical specialty that performs various minimally-invasive procedures using medical imaging guidance, such as Fluoroscopy, x-ray fluoroscopy, CT scan, computed tomography, magnetic resonance imaging, or ultraso ...

, e.g. in

Onyx Onyx is a typically black-and-white banded variety of agate, a silicate mineral. The bands can also be monochromatic with alternating light and dark bands. ''Sardonyx'' is a variety with red to brown bands alternated with black or white bands. ...

. Dissolved in

dimethyl sulfoxide Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula . This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is ...

(DMSO) and mixed with a radiopaque substance, ethylene vinyl alcohol copolymer is used to embolize

blood vessel Blood vessels are the tubular structures of a circulatory system that transport blood throughout many Animal, animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the Tissue (biology), tissues of a Body (bi ...

References

{{reflist Interventional radiology Plastics Packaging materials Copolymers