UV Absorbers UVA

Ciba Specialty Chemicals Additives for Polyolefins UV Absorbers (UVA)  

High performance UVA with broad food contact clearances 

High performance UVA with enhanced absorption of long wavelength UV radiation 

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UV absorbers (UVA) act by absorbing UV light hence retarding the photolysis of hydroperoxides. Their activity is also associated with hydrogen bonding between the 2-hydroxy group and the carbonyl chromo-phore [22]. Typical examples are based on 2-hydroxy-benzophenones and 2-hydroxybenztriazoIes (e.g., Table lb, AO 23 and AOs 24-26). 

The UV absorber (UVA) class (e.g., 2-hydroxy-benzophenones and benzotriazoles, see AO 23-27 in Table lb) are stable to UV light and have high extinction coefficients in the region 330-360 nm. They operate pri-... 

Most of the UV-absorbers (UVA) used commercially fall into two main classes of compounds, the 2-hydroxybenzophenones, e.g., AO 28, Table 1, and the 2-hydroxybenzotriazoles, e.g., AOs 29-32, Table 1, with the 2-hydroxy group being essential for their activity. These UVAs operate by additional mechanisms too, for example, by removing initiating radicals (e.g., alkoxyl radicals) in a weak chain breaking-donor (CB-D) mechanism.UV absorbers, such as AO 28, also synergize effectively with peroxide decomposers, e.g., metal dithiolates, see Table 4. 

UV absorbers (UVAs) are colorless compounds having high absorption coefficients in the UV part of the terrestrial solar spectrum. They transform the absorbed radiation energy into harmless thermal energy by way of photophysical processes involving the ground state and the excited state of the molecule. Typical UVAs are listed in Tables 9.7 and 9.8. 

Three different classes of compounds form the major and most important commercial categories of photostabilizers for PP. These are based on nickel complexes (those containing sulfur ligands function primarily as peroxide decomposers, PD), UV-absorbers (UVA), e.g. based on 2-hydroxybenzophenone and 2-hydroxyphenylbenztriazole, and sterically hindered amine light stabilizers (HALS). 

Keywords photooxidation, UV absorbers (UVA), outdoor performance, weathering, accelerated weathering, kinetic chain length, photoinitiator, Norrish reactions, peroxide decomposer, hindered amine light stabilizers (HALS), photosensitizer, transition metal complex, UV stabilizer, time-controlled stabilization, reactive antioxidants, polymeric antioxidants. 

Influence of various UV absorbers (UVA-1 = dimer 2-hydroxyphenyl benzotriazole, UVA-2 = 2-hydroxyphenyl triazine) on yellowing in co-extruded double-skin sheets made of polycarbonate (weathering in a weatherometer black standard temperature 55 °C) [529]... 

Butola, B.S., Joshi, M. Photostability of FIDPE filaments stabilized with UV absorbers (UVA) and light stabihzers (HALS). J. Eng. Fibers Fabr. 8, 61-68 (2013)... 

UV absorbers UVAs can strongly absorb UV light and convert the absorbed energy into low-frequency bond vibration or heat, and thereby prevent photodegradation by physical means. The most studied UVAs are hydroxybenzophe-nones and hydroxyphenylbenzotriazoles. 

To retard the phtotodegradation process of WPCs, some additives, such as colorants, antioxidants, UV absorbers (UVAs) and hindered amine fight stabUizers (HALS), are usually incorporated during composite fabrication. These additives either maintain the color stahifily or mechanical properties of WPCs against UV weathering. 

Most known UV stabilizers do not act by a single mechanism but by a combination of mechanisms. Table 7 shows representative examples of different classes of UV stabilizers and their most probable mechanisms of action. It will be shown in the next section that most members of the UV absorber (UVA) class e.g, 2-hydroxybenzophenones and benzotriazoles, see Table 7) operate primarily by absorbing UV light and dissipating it harmlessly as thermal energy (see reaction 6 later) and also act, in part, as radical scavengers. Tinuvin 121, (25) (Table 7) is particularly interesting... 

UV Absorbers (UVA) protect the polymers by absorbing the detrimental UV radiation responsible for their degradation. The protection mechanism exerted by UV Absorbers is based essentially on the absorption of UV radiation and consequent dissipation of the absorbed energy in a manner that does not lead to photooxidation, i.e. dissipation as heat. Hydroxy benzophenones and Hydroxyphenyl benzotriazoles are the UVA structures produced and studied by 3V. The large choice of structures allow them to cover all the application fields of different polymers. 

Hindered amine light stabilizers, HALS, UV absorbers, UVA, polypropylene, PP, polyethylene, HDPE, ABS, weathering. Xenon Are Wealher-ometer, correlation, ontdoor weathering. 

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