Photostabilization, mechanisms

Hydroxyphenylbenzotriazoles have long been used as photostabilizers of polymers. For further details, see the 1990 review by Rabek fluorescence spectra of these photostabilizers have been the subjects of many publications (see Section 4.01.2.9). There are a great number of commercially available 2-(o-hydroxyphenyl)benzotriazoles. They have been widely used in the photostabilization of polypropylene, polystyrene, polyacrylates. 

S.P. Fairgrieve and J.R. Mac Callum, Hindered amine light stabilizers aproposed photostabilization mechanism, Polym. Degrad. Stab. 1984, 8, 107-121. 

The photostabilization of polymers continues to be a rapidly advancing area of scientific and technological interest. Carlsson and Wileshave written several reviews on photostabilizing mechanisms in polymers, while Swasey has given an updated guide to stabilization, and Reid has discussed the effects of stabilizers in vinyl polymers. Nemzek and Mayo have predicted the service life of polypropylene, and Bredereck has reviewed the photostabilization of PVC. Several comprehensive review articles have appeared. Pospisil has reviewed in considerable depth the photo-oxidation mechanisms of phenolic anti-oxidants, Shlyapintokh has reviewed the kinetics of stabilizer distribution, Vink has... 

Trade name Chemical structure Melting point, °C Recommended use/ photostabilizing mechanism ... 

Fairgrieve SP, Mac CaUum JR. Hindered-amine light stabiUzers a proposed photostabilization mechanism. Polym Degrad Stab 1984 8 107-21. 

PET in comparison to other polymers shows a reasonable degree of lightfastness. Under normal conditions, degradation, resulting in significant losses in mechanical properties, occurs only after long term exposure to terrestrial light. Therefore, little work has been reported on the photostabilization of PET. 

Photostabilizers, regardless of their mechanism of action, have been added as low molecular weight materials at some point in processing. Subsequently, these stabilizers are often lost in further processing due to their volatility or else later migrate to the surface and evaporate. One method which avoids this modifies the polymer to include the quencher as an additional monomer in the polymerization. This paper will describe some recent efforts in our laboratory to pursue this latter approach in the stabilization of poly(ethylene terephthalate). 

Based on luminescence studies, we postulated triplet-triplet energy transfer by electron exchange as the mechanism of photostabilization and we calculated an active quenching sphere with a radius, R0, of 19.7 A for 2,6-ND. Because the value of R0 is larger than 15 A, we postulated that energy migration was occurring. 

The capability to detect such species by ESR spectroscopy provides a means to analyse the mechanisms of polymer breakdown under irradiation (17.19). In addition, certain compounds used to photostabilize polymers against UV radiation act by scavenging the reactive radicals to form more stable radical species (e.g., hindered phenoxy radicals) and thus the performance of these stabilizers can be assessed by ESR methods (12) ... 

Habib MJ, Asker AF. Photostabilization of doxorubicin hydrochloride with radioprotective and photoprotective agents potential mechanism for enhancing chemotherapy during radiotherapy. J Parenter Sci Technol 1989 43 259-261. 

Photostabilization with Ultraviolet Absorbers. Absorption of ultraviolet light in the region 2900-3900 A. (290-390 m/x) results in the yellowing and loss in physical-mechanical properties of most polymers containing aliphatic C—H bonds. This degradation is usually a combination of ultraviolet absorption and oxidative attack (21). 

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... 

The hindered-amine type stabilizer was ineffective, and the zinc acetate dihydrate moderately effective, in protecting the wool fabrics. Further study is needed to determine the mechanisms by which the latter compound imparts photostabilization. 

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. 

Before hand testing of light stabilizing activity of DTIU while introducing it into a polymer as mechanical additive was carried out. Data of Table 24 show that DTIU possesses photostabilizing activity that gives the reason to consider the fact that its condensation with CDA will improve light fastness of the latter. 

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