Hindered amine light stabilizer regeneration

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. 

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. 

Hindered amine light stabilizers (HALS) were developed as photostabilizers and/or metal deactivators. It was soon determined that the oxime structure functioned as an AO as well. In fact, these AOs are almost self-regenerating so they last for long times. They also serve their original functions, thus they often do double and even triple duty. These additives are responsible for high performance PP used... 

Nitroxyl radicals are formed as intermediates in reactions of polymer stabilization by steri-cally hindered amines as light stabilizers (HALS) [30,34,39,59]. The very important peculiarity of nitroxyl radicals as antioxidants of polymer degradation is their ability to participate in cyclic mechanisms of chain termination. This mechanism involves alternation of reactions involving alkyl and peroxyl radicals with regeneration of nitroxyl radical [60 64],... 

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