Antioxidants and UV Absorbers

Ultraviolet inhibitors or antioxidants may be incorporated into recording sheets in the form of a solution or dispersion (23). In order to increase the effect of preventing color changes, an ultraviolet inhibitor and an antioxidant may be used in combination. 

When a dispersion is used, a dispersant, e.g., sodium hexameta-phosphate, may be used. Also, the particle surface may be chemically modified by a sol-gel method to elevate the affinity for the liquid medium or the dispersibility. 

Allophanate Methyl allophanate Biuret Dimethyl biuret Tetramethyl biuret L-Ascorbic acid 2-(2H-Benzotriazole-2-yl)-4,6-ditertpentylphenol Decanedioic acid, bis(2,2,6,6-tetramethyl-l-(octyl-oxy)-4-piperidinyl)ester Bis (l,2,2,6,6-pentamethyl-4-pi-peridinyl)-[[3,5-bis(l,l-dimethyl-ethyl)-4-hydroxyphenyl]methyl]butylmalonate Tinuvin 328 Tinuvin 123 Tinuvin 144 

Specific examples of benzotriazole and benzophenone UV absorbers are given in Table 3.14. 

2-(2 -Hydroxy-5 -methylphenyl)benzotriazole 2-(3-ferf-Butyl-5-methyl-2-hydroxyphenyl)-5-chlorobenzotriazole, 2-(2 -Hydroxy-3, 5 -di-ferf-butylphenyl)benzotriazole 2-(2 -Hydroxy-5 -ferf-octylphenyl)benzotriazole 2-(2 -Hydroxy-3 -ferf-butyl-5 -methylphenyl)-5-chlorobenzotriazole 2-(2 -Hydroxy-3, 5 -di-ferf-butylphenyl)-5-chlorobenzotriazole 2-(2 -Hydroxy-3, 5 -di-ferf-aminophenyl)benzotriazole 2-2 -Hydroxy-3 -(-3 ,4 ,6 -tetrahydrophthalimidemeth-yl)-5 -methyl- phenylbenzotriazole 

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Cyclohexadienones and quinone methides from phenolic antioxidants and UV absorbers... 

Stabilizers are intended to prevent degradation reactions (in the broadest sense) of plastics during processing (heat stabilizers against thermal decomposition) and in practical use (antioxidants and UV absorbers to protect against light and aging). They are added in amounts of 1 %. See Chapter 24 for their protection mechanisms. 

Costabilizers enhancing light stability antioxidants and UV absorbents... 

Three polymers, listed in Table 26.6, were selected for further work in which the effect on ITV of fillers, antioxidants and UV absorbers was to be examined. The effect of fillers was explored in the fluorine containing copolymer, the silicone copolymer and polyethylene polyethylene was selected for antioxidant and UV absorber study because of the three it is the most susceptible to oxidation. These results showed that there was a general deterioration compared with pure polymers, although hydrated alumina showed some benefit in polyethylene and silicone rubbers. However such results were not general - alumina hydrate for example deteriorates the performance of fluorine copolymers. The following tables summarize these effects. (Tables 26.6, 26.7, 26.8). 

Kirkbright and co-workers [86] carried out a study of the general feasibility of the fluorimetric or phosphorimetric determination of stabiliser compounds after their extraction from polymers with organic solvents. They examined the fluorescence and phosphorescence characteristics of 29 common antioxidants and UV absorbers in an organic solvent medium at room temperature and -200 °C, respectively, and they report the fluorescence and phosphorescence spectral characteristics in a mixture of diethylether, isopentane, ethanol and chloroform and the calibration data phosphorescence detection limits and phosphorescence life-times. 

Figure 4.4 Separation of antioxidants and UV absorbers at 250 °C. Peaks 1 - Topanol OC, 2 - Polygard, 3 - Irganox 1010, 4 - Tinuvin P, 5 - Nonox DCP, 6 - Nonox DCP, 7 - Polygard, 8 - Tinuvin 326, 9 - Tinuvin 327, and 10 - Santonox R Reproduced from Denning and Marshall, RSC [6]...

Polymer additives - mould release agents, plasticisers, antioxidants and UV absorbers, with molecular weights extending beyond 1000 - are generally unsuitable for GC or liquid chromatographic (LC) analysis because of their low volatility, lack of chromophore or thermal instability. 

The material from which plastic objects are made is rarely a pure polymer. Usually it contains a lot of additives plasticizers for the control of T, antioxidants and UV absorbers for extension of life-... 

For outdoor applications of stabilized PVC, phosphites, antioxidants, and UV absorbers are also added to produce synergetic effects. 

Antioxidants and UV absorbers (see Section 11.2) are also used as secondary PVC stabilizers [67]. They become necessary, since double bonds created in degraded PVC can absorb radiation in the ultraviolet range which energy is high enough to produce more dehydrochlorination. Furthermore, these radiations could decompose peroxides or hydroperoxides formed or already present in PVC and induce radical promoted oxidation of the polymer chains [68,69]. The wavelength range that may produce these undesired effects is believed to go from 310 to 400 nm [79-82]. UV absorbers used for PVC are mainly benzo-triazol, benzophenone derivatives, zinc oxide, and titanium oxide. 

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