Hindered amine light stabilizers recent developments

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. 

While HALS have been demonstrated to provide super light stabilization, co-additive interactions must also be carefully considered when formulating stabilization packages. Resins, phenohc antioxidants, thioethers, pigments, flame retardants, fillers and external pollutants all are known to interact with HALS under certain conditions. Here some 

Compatibility and mobility within the polymer matrix can have a significant effect on HALS performance. In the case of thick sections (i.e. garden furniture, bumpers) where a suitable HALS mobility toward the surface layers is necessary, it is a general rule to use relatively low molecular weight monomeric types, either alone or in combination with oligomeric HALS. 

Blends of monomeric and oligomeric HALS can partially offset the tendency to lose UV stabilizing activity by combining two different migration rates. Although these blends show improvement over the performance of the two single products, they certcdnly represent a compromise due to the discontinuity in MW distribution and physical characteristics between the two HALS. 

In fibre applications, the high volatility of monomeric HALS such as HALS-1 made it susceptible to loss during post extrusion heat treatments such as tentering. This is presumably related to the relatively high volatility of HALS-1 which is a result of its low molecular weight and 

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Hindered amine light stabilizers an introduction Hindered amine light stabilizers recent developments. 

Hindered amine light stabilizers (HALS), which represent more recent developments in photoreactive compounds and are referred to as scavengers, absorb light above 250 nm and therefore do not act as UV absorbers or quenchers. 

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