Antioxidants photostabilization

The timescale for these processes to occur is dependent on the type of polymer, the content of added materials, plasticizers and additives such as antioxidants, photostabilizers, thermostabilizers, etc), filling and reinforcing materials such as particles and fibers, etc. 

Additives (pigments, dyes, thermal stabilizers, antioxidants, photostabilizers, etc.). 

Additives such as antioxidants and photostabilizers of low-molecular weight face two major problems (1) they may evaporate during high temperature moulding and extrusion process or (2) they may migrate to the surface of the plastic and get extracted. There are, in general, three ways of overcoming these problems. 

Antioxidants and photostabilizers may need to be added to treated books to avoid future acid generation in book papers. 

Photoantioxidants are typified by the class of HAS which although were developed for photostabilization of polyolefins, also possess thermal antioxidant properties. They are generally assumed to function as primary antioxidants in that they scavenge radicals and in particular, peroxy radicals. 

Plastics have to be stabilized to withstand chemical and physical stresses during different phases of their lifetime. Stabilizers protecting plastics against particular degradation processes were developed and commercialized by various companies. According to their principal activity mechanisms, polymer stabilizers are conventionally classified as antioxidants, photoantioxidants, photostabilizers, heat stabilizers and... 

Anthrone forms in polyphosphoric add a polycondensate 117 having semiconducting and paramagnetic properties. Compound 117 was tested as thermo-and photostabilizer of PS. It was concluded [149] that the antioxidant properties are due to the ability of 117 to form CTC with R and ROj radicals. 

It should be pointed out that in selecting a photostabilizer, whether it is a light absorber, antioxidant, or a synergist, one should take into consideration... 

Hydroxy-4-n-octoxybenzophenone is an effective photostabilizer for a variety of plastic systems. It may be used in food packaging materials as an antioxidant and stabilizer and in addition may be used as a stabilizer in petroleum wax. When used in packaging materials, it prevents UV-radiation from reaching the stored product and increases the stability of the container. 

Sodium metabisulfite and thiourea have been shown to be the best antioxidants for photostabilization of sulfacetamide solutions. Sodium editate has also a stabilizing effect on sulfacetamide solutions. The activity of antioxidants in preventing the photodegradation of sulfacetamide solutions appears to depend on their redox potentials. The lower is the redox potential of antioxidant the higher is the stabilization effect (125). 

As with thermal stabilizers, photostabilizers must satisfy basic chemical and physical requirements (see the section titled ""Antioxidant permanence effects of chemical and physical factors ). In addition, they must be photo-stable, i.e., stable to UV-light, to withstand continuous periods of UV-exposure, without being prematurely destroyed or effectively transformed into sensitizing products. There are essentially three classes of compounds that are categorized as photostabilizers/ photoantioxidants UV-absorbers and pigments, peroxide decomposers including nickel complexes, and sterically hindered amine light stabilizers. 

Al-Malaika, S. Desai, P. Scott, G. Mechanisms of antioxidant action photostabilization of polypropylene using dithiophosphoryl compounds— effects of alkyl substituents. Plast. Rubber Proces. Appl. 1985, 5 (1), 15-18. 

Polymer systems, however, contain some other additives, e.g. antioxidants to avoid the thermal oxidation during processing, and it would be very interesting to know whether the concentration of the N-oxyl radicals can be influenced by other additives present in the polymer. The formation and nature of N-oxyl radicals, and the influence of a hindered phenolic antioxidant on the concentration of N-oxyl radicals, as well as on the photostabilizing activity of the HALS compound, were investigated. 

The interaction and subsequent oxidative behavior under UV light exposure of nanocomposite using poly(styrene) (PS) as polymer and LDH organomodified by a monomer surfactant as filler were recently investigated [115]. The photooxidation study revealed that the hybrid nanofiller did not modify the photooxidation mechanism of PS. The same products of oxidation were observed with the same proportions. A slightly higher oxidation rate was observed in the case of the sample with 5% of filler. The advantage of this system was its ability to be tailored in order to limit/ control eventual interactions with photostabilizers and antioxidants. 

U.V. Stabilizers.—Many of the papers discussed in preceding sections contain discussion of the nature and mechanism of u.v. stabilizers. A brief survey of antioxidants and stabilizers used in the plastics industry has appeared,28 and some new photostabilizers, including a polymeric u.v. absorber and a surface-grafted antioxidant, have been proposed.280 The mechanism of nickel chelate stabilizers has been further discussed,281 and the diffusion of and loss of light stabilizers in poly(olefins) described.282 As part of an attempt to understand the transformations of stabilizers during the ageing of polymers, the photooxidation of 2,6-di-t-butyl-4-methylphenol sensitized by Methylene Blue has been studied.283 U.v. light protection by sunscreens, with mechanisms of interest to the polymer field, has been described.284... 

The photostabilizing role (in PP and other polymers) and the antioxidant mechamsms of UV absorbers based on hydroxybenzophenones... 

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