Speech more detail should be done with regard to the plastics in the packaging in a modified atmosphere in that the gas retention through more or less easily some polymers than others. Obviously to make effective the change of atmosphere in the package and thus the better preservation of the food there must be the lowest possible exchange of gas between the package and the environment; for this reason we speak barrier film or films consist of polymers with low gas permeability .
The plastic materials that have barrier characteristics are not many, are quite expensive and, at times, does not have the necessary characteristics of weldability and suitability for contact with food. For this reason it resorts to the realization of multi-layer containers and bags, coupling with different techniques (such as lamination or coextrusion) different materials.
The table below shows the oxygen permeability of plastic most common:
Plastic material of the film
|Oxygen permeability of a film of 25 microns thick (Cm3/m2 24h bar)|
|Low density polyethylene (LDPE)||7000-8000|
|High density polyethylene (HDPE)||2800-3000|
|Plasticized polyvinyl chloride (PVC)||6000-9000|
|Polyethylene terephthalate (PET)||45-90|
|Polyamide 6 (PA6)||20-40|
|Polyamide 11 (PA11)||500-1500|
|Polyvinylidene chloride (PVDC)||12-100|
|Ethylene vinyl alcohol (EVOH)||
Obviously the greater the thickness of the packaging and the lower the permeability and instead greater are the dimensions of the packaging and the greater the loss of gas.
Starting from these materials are produced thermoformed trays and film for high, medium or high barrier depending on the product and must contain the length of the retention period required.
* HACCP: Hazard Analysis Critical Control Points