Exposure to sunlight, and in some cases, even light from artificial sources can have adverse effects on the usefulness of polyethylene products or package contents. UV radiation can break down the chemical bonds in a polymer as well as have adverse effects on packaged food, beverages, pharmaceuticals, and non-perishables. This process called photodegradation will ultimately cause cracking, chalking, and the loss of physical properties such as impact strength, tensile strength, elongation and other properties. It can also alter the chemical composition of packaged goods as well as dyes contained within.
Ultraviolet Absorbers (UVAs)
UVAs slow down the degradation process by absorbing harmful UV radiation and dissipating it as thermal energy This ability results in their widespread use as a UV filter, e.g., protecting what’s behind the package. UVAs are also used synergistically with UV inhibitors for long term weathering applications. There are many non-pigmented applications in today’s market requiring this protection including food, beverage, and non-perishables. A minimum pathway of 6-8 mils is required for UVAs to perform efficiently. UVAs are sacrificial, so the gauge and expected lifespan of the protected product must be considered when making a recommendation. Enough UVA must be present in the reservoir (matrix) to meet the requirements. There are two UVA chemistries which are predominant today.
Hindered Amine Light Stabilizers (HALS)
Hals are the most effective of the light stabilizers (UVIs) for polyolefins. They are available in a wide range of molecular weighs and structures suitable for almost any application. HALS function by trapping free radicals formed during the auto-oxidation process and hindering their proliferation. HALS are colorless, highly efficient at very low concentrations, and may be used from a cyclic process wherein the HALS are regenerated, rather than consumed, during the stabilization process.
The guage of the product, geographic location of exposure, and the chemical environment are the most critical factors in choosing the type and amount of HALS. The chemistries available are differentiated by volatility, migration characteristics and chemical resistance.