Hindered Amine Light Stabilizers
The ability of hindered amine light stabilizers (HALS or HAS) to scavenge radicals which are produced by weathering, may be explained by the formation of nitroxyl radicals through a process known as the Denisov Cycle. The nitroxyl radical(R-O•) combines with free radicals in polymers:
R-O• + R'• → R-O-R'
Even though HALS are extremely effective in polyolefins, polyethylene and polyurethane, they are ineffective in polyvinyl chloride (PVC). It is thought that their ability to form nitroxyl radicals is disrupted. HALS act as a base and become neutralized by hydrochloric acid (HCl) that is released by photooxidation of PVC. The exception is the recently developed NOR HALS which is not a strong base and is not deactivated by HCl.
Read more about this topic: Stabilizers For Polymers
Other articles related to "amine, hindered amine, hindered":
... there are two common strategies reaction of the alcohol with a silyl chloride with an amine base at room temperature and reaction of the alcohol with a silyl triflate with a hindered amine ... so they can be used to install silyl groups onto hindered positions ... A common hindered base for use with silyl triflates is 2,6-lutidine ...
Famous quotes containing the words light and/or hindered:
“To learn to read is to light a fire; every syllable that is spelled out is a spark.”
—Victor Hugo (18021885)
“Everywhere I am hindered of meeting God in my brother, because he has shut his own temple doors and recites fables merely of his brothers, or his brothers brothers God.”
—Ralph Waldo Emerson (18031882)