Polymers and Light, why they need Protection?

Just like many organic materials, polymers can be damaged by certain types of light. When exposed, they undergo chemical reactions that weaken their physical properties, this is called light degradation.
To prevent this, manufacturers mix in special additives called light stabilizers. These stabilizers protect polymers from light damage in two main ways:

UV Absorbers: They absorb harmful ultraviolet rays before they can damage the polymer.
Hindered Amine Light Stabilizers (HALS): They neutralize the reactive molecules (called radicals) that form when light starts breaking down the polymer.

When both types are used together, they work even better, creating a synergistic effect that keeps polymers strong and durable.

What Are Ultraviolet Absorbers and how do they work?

Ultraviolet (UV) absorbers are additives that protect materials from harmful UV rays. They come in different chemical structures, and depending on the structure, they absorb different wavelengths and release the absorbed energy in different ways. The most common type is benzotriazole UV absorbers. They absorb UV light and move to an excited state. Then, they release the energy safely as heat and return to their normal state, thanks to special hydrogen bonds inside the molecule. Other types, like triazine, benzophenone, and salicylate absorbers, use a similar mechanism. However, some absorbers, such as cyanoacrylate types, don’t have these hydrogen bonds. Instead of releasing energy as heat, they release it as light.

Hindered Amine Light Stabilizers (HALS)

HALS are special additives that help plastics resist damage from sunlight. Their main job is to stop the chemical reactions that cause materials to break down when exposed to light.

When sunlight hits plastic, it creates harmful molecules called free radicals. These radicals attack the material and make it age faster. HALS act like “radical catchers”, they trap and neutralize these radicals, keeping the plastic strong and durable. HALS are highly effective for weather-resistant plastics such as polyolefins, styrene resins, and acrylics, including coatings. Some derivatives, like nitroxyl radicals, are also used as oxidative catalysts or polymerization inhibitors. Their main mechanism is radical scavenging, which prevents photodegradation, although the process is complex and difficult to analyse due to the small number of HALS compared to the base material.

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