Sunlight breaks polymer chains. Without protection, polyolefin film and parts become brittle and chalk within months outdoors.
Two ways to protect
UV absorbers (for example benzophenones and benzotriazoles) absorb UV light and release it as heat; they work best in thicker parts. Hindered amine light stabilisers (HALS) trap the radicals formed by UV and are regenerated, so they protect thin films very efficiently. Many systems combine both.
Choosing the dose
Dosage depends on the polymer, thickness, the required life and the sunlight where the product is used; an Indian summer delivers far more UV than northern Europe. Agricultural films exposed to pesticides containing sulphur or chlorine need HALS grades that resist these chemicals.
Interactions
Some pigments and fillers affect UV performance, and acidic additives can deactivate certain HALS. Test the full formulation in accelerated weathering before field use.
