Hindered amine light stabilizer concentration

Some stabilizers act via cyclic reaction paths and are regenerated, remaining effective at lower concentrations or for longer periods of time than would otherwise occur. This is the case with hindered amine light stabilizers (HALS), an example of which is bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (often known by a commercial name Tinuvin 770), which are especially effective in improving weatherability in polypropylene and other polyolefins. 

Not all antioxidants respond to the OIT test in most cases the phenolic antioxidant concentration can be monitored by measuring the OIT, whereas phosphite antioxidants and hindered amine light stabilizers (HALS) in particular display little response. Because of this, the OIT test is a poor tool for polymer service life predictions as there is no real correlation between the OIT test results and the product s performance in the field. Additional test data such as heat oven aging are often required to supplement the OIT data in order to improve the accuracy of predicting long-term product performance. 

The most recent class of light stabilizer is the Hindered Amine Light Stabilizer (HALS). These materials have been shown to function as radical traps, thus interrupting the radical chain degradation mechanism. The cyclic stabilization mechanism proposed for HALS involves multiple regeneration of the active nitroxyl stabilizer. The surprising performance of HALS at relatively low concentrations supports this non-sacrificial mechanism. 

The second type of UV stabilizer is hindered amine light stabilizers (HALS) that are an extremely efficient stabilizer against the photodegradation process. They are compounds that do not absorb UV radiation, but act to inhibit degradation. Relatively high levels of stabilization are achieved with relatively low levels of concentration because the HALS are not consumed during the stabilization process (unlike primary and secondary antioxidants). 

Effective quenchers are based on nickel complexes (phenolate, dithiocarbamate, di-thiophosphate) and are used almost exclusively in polyolefins at a concentration of 0.2-0.5%. Nickel complexes impart a green coloration to plastic articles and their importance was significantly reduced with the introduction of hindered amine light stabilizers (HALS). 

Typically, a combination of high and low molecular HALS is used to protect polyolefins against light, Fig. 3.10. Depending on the light stability requirement, approx. 0.1 to 0.5% sterically hindered amines are added to polyolefins in exceptional cases (e.g., for polypropylene fibers) HALS concentrations up to 1 % are used [529]. In addition to HALS, benzotriazoles and benzophenones are used [186]. 

---