Ethylene vinyl alcohol

Ethylene Vinyl Alcohol (EVOH), also known as ethylene-vinyl alcohol copolymer, is a formal copolymer of ethylene and vinyl alcohol. The material is primarily used in the creation of barrier properties in various packaging materials. EVOH is known for its excellent barrier to oxygen, making it a popular choice for food packaging to extend shelf life by preventing oxidation. This article will delve into the properties, applications, and production of EVOH, along with its significance in the medical field.

Properties

EVOH is characterized by its exceptional gas barrier properties, particularly against oxygen, which surpasses most other polymers. This characteristic is attributed to the dense packing of the polymer chains due to the polar hydroxyl groups of vinyl alcohol. EVOH also exhibits good resistance to organic solvents, oils, and fuels. However, it is relatively sensitive to moisture, as its barrier properties can decrease significantly with increased humidity. The material also has good clarity and gloss, along with excellent flex-crack resistance, making it suitable for flexible packaging applications.

Applications

Packaging

The primary application of EVOH is in the packaging industry, where it is used as a barrier layer in multi-layered packaging materials. These include food packaging for products such as meat, cheese, and snack foods, as well as in non-food applications like fuel tanks and cosmetic containers. The oxygen barrier properties of EVOH help in preserving the freshness, flavor, and color of the packaged goods.

Medical

In the medical field, EVOH is utilized in the manufacturing of medical devices and packaging. Its barrier properties are beneficial in creating sterile packaging for medical and pharmaceutical products, ensuring their safety and efficacy. EVOH can also be used in the production of some medical devices where barrier properties are crucial.

Other Applications

Beyond packaging, EVOH finds applications in agriculture for films that require selective permeability to gases, in the automotive industry for fuel system components, and in construction for gas barrier layers in pipes and underfloor heating systems.

Production

EVOH is produced by copolymerizing ethylene and vinyl alcohol. The process involves the polymerization of ethylene and vinyl acetate, followed by the hydrolysis of vinyl acetate groups to vinyl alcohol. The ethylene content in EVOH can vary, typically between 27% to 44%, which affects the material's properties, including its barrier performance and flexibility. The production process and the composition of the copolymer are carefully controlled to achieve the desired properties for specific applications.

Environmental Impact

EVOH is considered to have a moderate environmental impact. While it is not biodegradable, it is recyclable, and efforts are being made to improve the recyclability of EVOH-containing materials through mechanical and chemical recycling methods. The use of EVOH in packaging can also contribute to reducing food waste by extending the shelf life of perishable goods.

Conclusion

Ethylene Vinyl Alcohol copolymer stands out for its exceptional barrier properties, especially against oxygen, which makes it invaluable in packaging applications requiring extended shelf life and preservation of product quality. Its use in the medical field further underscores its importance in maintaining the sterility and efficacy of medical products. As technology advances, the applications of EVOH are expected to expand, highlighting the ongoing need for materials that combine performance with sustainability.