The materials used to form modified atmosphere packs must provide a barrier
to the exchange of gases between the pack and the ambient atmosphere.
However, the gas barrier properties of the packaging materials differ for
different types of packaging and differing commercial functions of the packs.
Bulk and master packagings which are expected to contain product for only a
day or two are often laminates composed of a strong material with limited gas
barrier properties, such as nylon, and a sealable layer of a material such as
polyethylene. Such materials may have nominal oxygen transmission rates of
more than 100 cc/m2
/24h/atm under stated conditions of humidity and
temperature. However, films used for modified atmosphere packs usually have
oxygen transmission rates between 10 and 100cc O2/m2
/24h/atm, while
packagings designed to contain product for the longest possible times are likely
to be composed of materials with oxygen transmission rates less than 10 cc/m2
/
24/atm (Jenkins and Harrington, 1991).
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