Aging photooxidative

Sama T. et al., Loss of melanin from human RPE with aging possible role of melanin photooxidation, Exp. Eye Res.,16, 89, 2003. 

For photochemical aging, it is well known that photooxidation affects only a thin superficial layer directly exposed to solar radiation - a few dozens of micrometers in the case of epoxies (Bellenger and Verdu, 1983). Thus the aging mode cannot control the material s lifetime in most cases (composites, adhesives), except for applications such as, for example, varnishes of automotive bodies (Bauer et ah, 1992). 

Once in the atmosphere, OAs can also undergo a wide range of physical and chemical aging processes under atmospheric conditions. OA components can react with atmospheric photooxidants (e.g., OH, NO3, and 03), acids (e.g., H2S04 and HN03), water, and UV radiation, forming for instance more polar and hygroscopic products than the precursor material. These atmospheric transformation processes can also occur at the surface layers of BC or EC (Poschl, 2005). 

Phenomenology of the thermal decomposition, 765 Phonon model, 646 Photochemical degradation, 779 Photo-doping, 341 Photooxidation, 781, 783 Physical ageing, 438 Physical constants of solvents, 904 Physical data of simple gases, 657, 658 Physical properties of polymers, 920 Physical quantity, 52 Pilling, 881 tester, 881... 

The materials analyzed were blends of polystyrene (PS) and poly(vinyl methyl ether) (PVME) in various ratios. The two components are miscible in all proportions at ambient temperature. The photooxidation mechanisms of the homo-polymers PS and PVME have been studied previously [4,7,8]. PVME has been shown to be much more sensitive to oxidation than PS and the rate of photooxidation of PVME was found to be approximately 10 times higher than that of PS. The photoproducts formed were identified by spectroscopy combined with chemical and physical treatments. The rate of oxidation of each component in the blend has been compared with the oxidation rate of the homopolymers studied separately. Because photooxidative aging induces modifications of the surface aspect of the material, the spectroscopic analysis of the photochemical behavior of the blend has been completed by an analysis of the surface of the samples by atomic force microscopy (AFM). A tentative correlation between the evolution of the roughness measured by AFM and the chemical changes occurring in the PVME-PS samples throughout irradiation is presented. 

UV spectra of 95 (R = H) films did not changed after 400 h of accelerated aging at 300-400 nm. Some surface photooxidation observed after 500 h was attributed to the presence of tertiary C—H bonds in the copolymer. This consideration was confirmed by testing the relevant 5-isopropenyl derivative 95 (R = CH3) the respective copolymer remained photostable for KKIO hu... 

The photooxidation and photodegradation of polymers continues to attract some interest but is not as widespread as in previous years. Review articles have appeared dealing with poly(2,6-dimethyl-l,4-phenylene oxides) , photocatalyst fibres, polymers with azo links and accelerated weathering specifications. Other articles of interest include the design of an integrating sphere for repeatability in polymer ageing and the use of FTIR for monitoring the photostability of clearcoats . 

Effect of dyes of different class on light ageing of PA is studied more detailed in the work [83]. It appeared that dyes, used by the authors, sensibilize PA photooxidation according to radical mechanism, however the total action of the dye may be stabilizing owing to shielding effect, and in some cases according to the mechanism of antioxidant action. 

The task of light stabilization is the increase of light stability of polymer materials in the process of photooxidative ageing. Different light stabilizers are used to execute this task. 

This chapter reports the results of the literature that concerns the photooxidation of polymer nanocomposites. The published studies concern various polymers (PP, epoxy, ethylene-propylene-diene monomer (EPDM), PS, and so on) and different nanofillers such as organomontmorillonite or layered double hydroxides (LDH) were investigated. It is worthy to note that a specific attention was given to the interactions with various kinds of stabilizers and their efficiency to protect the polymer. One of the main objectives was to understand the influence of the nanofiller on the oxidation mechanism of the polymer and on the ageing of the nanocomposite material. Depending on the types of nanocomposite that were studied, the influence of several parameters such as morphology, processing conditions, and nature of the nanofiller was examined. 

The susceptibility of LDPE with HMW-HALS-2 to chemical hydrolysis, photooxidation and composting was studied by Haider and Karlsson [114]. In this case, it was shown that nonconsumed stabilizer remained in the polymeric matrix after aging in compost, while a large loss of stabilizer was found in water at pH 5. 

Thermooxidative and Photooxidative Aging of Polypropylene Separation of Heptane-Soluble and -Insoluble Fractions... 

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