Radiation-Curable Gelatin Methacrylates As Novel Oxygen Barrier Layers For Flexible Packaging Materials

One of the major problems in the packaging of foods and similar products is the
protection of the content against oxygen. Good oxygen barrier properties are essential
for achieving a long shelf life for the packaged products. However, most
of the common polymer packaging foils have high gas permeabilities. Better barrier
efficiency can be obtained only with laminates which contain additional barrier
layers against gas transmission. Oxygen barrier layers in flexible laminates
used for food packaging usually consist of special barrier polymers such as
ethylene-vinyl alcohol copolymers (EVOH) or poly(vinylidene chloride) (PVDC).
However, these polymers have several significant drawbacks. They are expensive
and require complex processing technology. Moreover, PVDC is ecologically
acceptable only with restrictions.

An alternative way for obtaining excellent barrier properties is the deposition of
inorganic layers on polymer foils either by evaporation of aluminium or with the
aid of plasmas, e.g. for the generation of SiOX layers. However, these surface
modification processes also require considerable technical efforts ( e.g. high
vacuum ) and expensive materials.

Permeability strongly depends on the intermolecular cohesion of the polymer
chains and is, therefore, influenced by the morphological structure of the polymer.
Good gas barrier properties may be obtained by high degrees of crystallinity
or molecular orientation and a high content of hydrogen bonds. Gelatin meets all
these requirements. It contains large amounts of hydroxyl and amide groups
which are known to be highly efficient with respect to barrier properties due to
their capability of forming hydrogen bonds. Moreover, gelatin may partly adopt
the highly ordered structure of its parent protein collagen (1).

Gelatin shows excellent film forming properties. It can be easily processed by
existing coating technologies. The adhesion properties of gelatin are known for
a long time. Therefore, gelatin may also be used as an adhesive for lamination.
All these features let gelatin become a promising candidate for the development
of oxygen barrier layers (2).