Oxygen, permeability, polymer packaging

No amount of sterilization wiU prevent or even slow autooxidation, and there are only two defenses removal of O2 and addition of inhibitors. Oxygen barriers in food packaging are a major topic in the engineering of polymer films. The barrier properties of various polymers are very important in food applications, and many of these are multilayer polymers that have a thin layer of an impermeable polymer (such as polyacrylonitrile and ionic polymers) on a cheaper but O2-permeable polymer such as a polyolefin, which gives mechanical strength to the fikn. 

To increase the barrier to oxygen, polymer packaging is coated with impermeable layers of metal or silicate glass. Aluminium, if vacuum deposited, is less than a micron thick. Table 11.4 shows that it reduces the permeability of a PET/ PE composite film by a factor of 10. Such collapsible bags are used inside wine boxes, as a method of increasing the shelf life of the partly consumed wine. 

Table 15.7 Oxygen permeability of selected polymers used in food packaging [34] ...

The cross-linked HPC matrix and composites with 10-30% of fibers have similar or even lower oxygen permeabilities than those of most common polymers used in food packaging (LDPE, HDPE, PP and PS), which makes these materials good candidates for that application. 

With the exception of packages for fresh produce, MAP trays or pouches need to be made of materials with low permeability to gases (CO2, Nj, O2). Laminates made of various combinations of polymer as PET, PVdC, PE, and polyamides such as nylons should have low oxygen permeability [175-178]. Respiration in fruits and vegetables leads to a build-up of carbon dioxide that may reduce the rate of respiration and help to prolong the shelf life of the product a reduction in the oxygen... 

The oxygen permeability of silicone materials is just one example of the selective permeability of polymers. The application in the artificial gill is a dramatic one, and the effect is used in many other areas. The selection of materials to package foods is based on the... 

The LLDPE layers provide the bulk of the film body, while the tie layers adhere to both the LLDPE and the oxygen barrier polymer allowing the film to maintain a strong structural foundation. The oxygen barrier layer exhibits low permeability to oxygen to increase shelf-life of the package. 

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