Causes & Prevention
Being organically based, polymers are subject to degradation and breakdown through natural oxidation.
Degradation may be initiated or accelerated by numerous factors including ultra-violet light, visible light, ozone, pollutants, manufacturing additives, oxygen, heat, or by carton storage without protective liners.
Antioxidants are used to protect the clear film from the heat of extrusion at the time it is produced, but these will not necessarily protect the material from oxidation during periods of storage and exposure. The stearically hindered phenol antioxidants actually react to UV more so than other shorter term antioxidant additives. Upon request special UVA and UVI inhibitors or hindered amine HALS stabilizer packages, can be added to the extruded film to prevent yellowing when exposed to light.
Stabilizer packages of any sort are eventually consumed or migrate to the surface. The polymer has then lost its protection and the deterioration may proceed rapidly when exposed to the atmospheric factors mentioned.
While film that has yellowed may be quite obvious in roll form due to the density of the viewed material, it may also be invisible to the eye once converted into a flexible package and presents no health or safety concern when used in the normal fashion.