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UV Absorber Definition & Classification
These additives preferentially take in the incident UV radiation and so protect the polymer from the radiation. UV absorbers do not themselves degrade rapidly, however they convert UV energy into hurtless levels of heat energy, which are dissipated throughout the polymer matrix. UV absorbers are limited of their effectiveness because of the physical limitations of the absorption process, and their ability to absorb is ruled by the need for high concentrations of additive and thickness of polymer before enough absorption will happen to retard the photodegradation effectively.
However, high concentrations of additive could be uneconomic and technically limited, while many applications (comparable to polyolefins) are in very thin sections, similar to film and fiber. Benzophenones are good general-purpose UV absorbers for clear polyolefin systems, and can also be utilized in pigmented compounds. Benzotriazoles are used primarily in polystyrene. Each can be utilized in polyesters. Concentrations are usually about 0.25-1.0%
Synonyms of UV absorber
UV absorber agent
UV stabilizer
UV stabilizer agent
ultraviolet absorber agent
ultraviolet light absorber agent
UV Absorber Classification
The primary function of UV absorbers is to absorb UV radiation in the presence of a chromophore (Ch) discovered within the polymer, the purpose is to filter out the UV light that is harmful to the polymer earlier than Ch* has had an opportunity of forming. Above all, a UV absorber should function within the 290 and 350 nm range.The aim of UV absorbers is to soak up harmful UV light and quickly transform it into harmless heat. During this process, the absorbed energy is converted into vibrational and rotational energy of the molecule constituents. For UV absorbers to be efficient, it is essential that this process takes place more rapidly than the corresponding response within the substrate, and that neither the UV absorber nor the polymer it is intended to stabilize is damaged during energy conversion. The most important UV absorbers are:
a) 2-(2-hydroxyphenyl)-benzotriazoles
b) 2-hydroxy-benzophenones
c) hydroxyphenyl-s-triazines
d) oxalanilides
Every of these UV absorber teams will be characterised by a typical absorption and transmission spectrum.
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