We often classify the types of light or UV stabilizers we make according to their action mode: UV absorbers (UVAs) that act by shielding the polymer from ultraviolet light or hindered aminelight stabilizers (HALS) that act by scavenging the radical intermediates formed in the photo-oxidation process.
Hindered Amine Light Stabilizers
Characteristic structure of Hindered Amine Light Stabilizers | Hindered Amine Light Stabilizers (HALS) are extremely efficient stabilizers against light-induced degradation of most polymers. They do not absorb UV radiation, but act to inhibit degradation of the polymer, thus extending its durability. Significant levels of stabilization are achieved at relatively low concentrations. |
HALS’ high efficiency and longevity are due to a cyclic process wherein the HALS are regenerated rather than consumed during the stabilization process. They also protect polymers from thermal degradation and can be used as thermal stabilizer.
Simplified Stabilization Mechanism of Hindered Amine Stabilizers
UV Absorbers
 | The unavoidable presence of catalyst residues in polymers or other chromophores coming from polymerization and processing can initiate the degradation process. UV absorbers (UVA’s) are often used to compete with these contaminant chromophores and preferentially absorb UV light. UV absorbers are since long time well known as stabilizers of transparent or translucent plastics to protect the bulk of thick applications. Color fading of full shade or tint colored plastics with organic pigments can be significantly prolonged by the use of UV absorbers. |
Common UV Absorbers
UV absorbers have the property to convert the energy absorbed from UV light into heat, via a mechanism called keto-enol tautomerism. This heat can then dissipate through the substrate.
Energy dissipation in hydroxyphenyl-benzotriazol UV Absorbers
Thanks to this cyclic mechanism, UV absorbers can remain active during the life-time of the plastic article. Anyway, they are subject to and limited by Lambert-Beer’s law:
Obviously this favors thick plastic articles (high path length b) with high concentrations (c) of very effective (high e) UV absorbers.
In practice, however, the surface of the plastic cannot be completely protected. This is why these UV stabilizers are most of the times used together with products having a different stabilization mechanism (e.g. HALS), thus complementing their stabilization and protection properties.
Products
Related Industries
Adhesives & Sealants
Agriculture
Automotive
Construction & Pipes
Fibers
Packaging
Rubber
|
