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Barrier films

Plastic films are technically defined as thin continuous polymeric materials made in thicknesses of up to 10 mils (0.25 um). Thicker plastic materials are considered sheets.

The large use of polymer-based structures, as for example in food packaging, is mainly due to the possibility to tailor their properties according to the application requirements, and to easily process and conform them into a wide range of sizes. Plastic films are used in packaging to hold contents and to act as printable surfaces  or as barriers.

The term "barrier" indicates the function of the film to seal contents from outside factors that would cause quality degradation, and to preserve original conditions inside. Gas barrier films would slow down or block the permeation through the film of gases like oxygen, nitrogen, carbon dioxide, water vapor, and other gases that have a major impact on the quality of products. Barrier films used in the food industry ensure aroma protection, longer shelf life and less food waste along the value chain.

Barrier polymers can be broadly classified as high barrier, and moderate to low barrier polymers, depending on the degree to which they restrict the passage of gases. The boundaries between these classifications are indicatively based on the effect of the barrier properties on the shelf life of the packaged products. The overall properties of the plastic film depend first and foremost on the nature of the resin used to manufacture the film. 

  • Polyolefins like LDPE, LLDPE, HDPE and PP have good/excellent moisture barrier characteristics and average gas barrier properties.
  • PET has fair/good moisture barrier properties, good gas barrier characteristics and good thermal properties.
  • PVDC has excellent moisture and gas barrier properties and is resistant to grease and oil.
  • EVOH has excellent gas barrier properties, but it loses them when exposed to moisture.

The increasing demand of performance from fresh food packaging requires that films are designed to improve the resins' pristine moisture- and gas-barrier properties. The polymer inherent characteristics can be affected by processing parameters during production but also by ambient conditions associated with storage, transport and end-use of the resulting packaging. High temperatures and humidity strongly affect the degree of permeation of liquids or vapors in the film material, possibly degrading its mechanical properties. Eventually, insufficient barrier properties may render the enclosed product vulnerable to surrounding environmental factors, such as humidity and oxygen. This need for tailored barrier levels has been leading to enhanced film processes and structures. Combining two or more polymers can achieve performance advantages in terms of barrier performance. Multilayer structures can be obtained by co-extrusion, lamination, and coating.

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Barrier films