UV stabilizers in plastics

UV stabilizers are chemical compounds which are as a protection against aging caused by UV radiation as additives of various materials, such as polymers, are added.

2.1 UV - absorber
2.2 inhibitors

Applications

Plastics

Plastics are subjected to in their use by photolysis photooxidation. This produces various radicals that attack the material. The radicals, the main chains of the polymer are broken up and incorporated various polar compounds, such as peroxides. The consequences of this degradation are loss of color, cracking, and generally negative effects on the physical properties.

Coatings

In paints UV absorbers and radical scavengers are used to improve the weathering resistance. In particular, in clear coats is of importance that the employed UV stabilizers are colorless and are not subject to color change. Because of the tendency to migrate also the base coat with UV stabilizers is equipped in two-layer systems, even though it is already protected from ultraviolet radiation through a stabilized topcoat.

Mechanism

UV - absorber

UV absorber operate on the principle of light absorption ( Lambert- Beer law ). The absorbed amount of UV radiation is a function of the thickness of the irradiated body and the stabilizer concentration. It is distributed as thermal energy.

Nanoscale titanium dioxide in paints can be used as inorganic UV absorbers .. In contrast to the titanium dioxide used as a pigment very fine coarser grades are transparent and cause no turbidity of the paint. Especially not after-treated titanium dioxide pigments, however, are the main component of the Kreidungszyklus and thus a major cause of the injury picture of chalking. Iron oxide pigments contrast, act exclusively as a UV absorber, but can not be used in all applications because of their inherent color.

Inhibitors

Inhibitors do not absorb UV radiation, but act where the degradation takes place, as a hydrogen donor. A hydrogen atom is thereby released into a peroxide radical. They form stable radicals in this reaction, thus acting as radical scavengers.

Types of UV stabilizers,

Organic UV absorbers

Benzophenones
Benzotriazoles
Oxalanilides
Phenyltriazine

Inorganic UV absorbers

Titanium dioxide
Iron oxide pigments
Zinc oxide

HALS ( Hindered Amine Light Stabilizers)

Sebacate tetramethylpiperidine derivatives such as bis (2,2,6,6- tetramethyl-4 -piperidyl)