UV stabilizers and colorants.

UV stabilizers

UV radiation is the radiation having energy in the range 100-72 kcal or corresponds to UV region (280-400 nm).
This radiation have sufficient energy to cleave the polymer linkages resulting in yellowing and embrittlement of polymers.
Polyethylene,PVC,Polystyrene,Polyesters and Polypropylene shows degradation at wavelength 300,310,319,325 and 370 nm of UV radiation respectively.
Thus these degradation demands the use of UV stabilizers such as phenyl salicylate.
Phenyl salicylate in the presence of UV radiation rearranges to form 2,2' dihydroxybenzophenone which act as energy transfer agents i.e they absorb energy to form chelate and then release energy at longer wavelength to give quinone derivatives.

Phenyl salicylate.
The other UV stabilizers are benzotriazole, substituted acrylonitrile, metallic complex and pigments such as carbon black.
The pigments absorb UV radiation and act as screening agents.

Colorants.

Colorants which provide color in polymers are soluble dyes or comminuted pigments.
The polymers such as rubber tires are black in color due to presence of high proportion of carbon black filler.
While some other polymers such as paints are white in color due to presence of titanium dioxide which is the most widely used inorganic pigment.
The pigments are classified as organic and inorganic.
The organic pigments are brighter, less dense and smaller in size than the more widely used, more opaque inorganic pigments/ colorant.
Ultramarine blue is widely used as a pigment.
Carbon black is a widely used organic pigment.
Phthalocyanine blues and greens are present in different shades and are widely used as pigments.
Other organic pigments are azo dye stuffs and acid and base dyes, such as rhodamine red and Victoria blue.
The iron oxides or ocher are widely used pigments.

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