Aging photochemical

Robinson AL, Donahue NM, Shrivastava MK, Weitkamp EA, Sage AM, Grieshop AP, Lane TE, Pierce JR, Pandis SN (2007) Rethinking organic aerosols semi volatile emissions and photochemical aging. Science 315 1259-1262... 

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). 

Roberts JM, Fehsenfeld FC, Liu SC, et al. 1984. Measurements of aromatic hydrocarbon ratios and NOx concentrations in the rural troposphere Observation of air mass photochemical aging and NOx removal. Atmos Environ 18 2421-2432. 

D. Kotsias, M. Herrmann, A. Zsolnay, R. Bayerle-Pfnur, H. Parlar, F. Korte (1987). Photochemical aging of humic substances. Chemosphere, 16,1463-1468. 

Nearly all photochemical aging processes are influenced by temperature. Considering that a temperature increase of AT = 10 K may double the reaction rate, the increased temperature of the exposed surface is a more important parameter than the temperature of the ambient air. Measurements on differently colored PVC films in outdoor exposure have shown temperature differences between black and white samples of 15 to 25 K, colored samples ranging in-between (Fischer and Ketola, 1994). An example is shown in Figure 5.4 (one example of temperature measurement sequence) and Figure 5.5 ( typical temperature profile). 

The comparison of the evolution of chemiluminescence emission in thermally and photochemically aged PECT and PET indicated the formation of hydroperoxides with different stabilities in the structure of PECT, in the ethylene units as it was observed in PET, and in the cyclohexanedimethylene units. 

El Aidani R, Nguyen-Tri P, Malajati Y, Lara J, Vu-Khanh T. Photochemical aging of an e-PTEE/Nomex membrane used in firefighter protective clothing. Polymer Degrad Stabil 2013 98(7) 1300-10. 

Shape of oxidation kinetic curves in the case of initiation (a) at constant rate (case of radiochemical ageing) thermal ageing) and (c) by unimolecular Per decomposition (case of many photochemical ageings). 

This oxidation mechanism is called a close-loop mechanism , as it produces its own initiator product (Per). The resulting kinetic curves present an induction period followed by a sharp auto-acceleration, preceding a steady state. The auto-acceleration step is much more progressive in its initial phase when Per decomposition is unimolecular (the case for many photochemical ageings) (see Fig. 12.23). 

Miracolo MA, Hennigan CJ, Ranjan M, Nguyen NT, Gordon TD, Lipsky EM, Presto AA, Donahue NM, Robinson AL (2011) Secondary aerosol formation from photochemical aging of aircraft exhaust in a smog chamber. Atmos Chem Phys 11(9) 4135-4147... 

CCN closure studies, where observations of ambient aerosol CCN activity are compared to the CCN concentration predicted via Kohler theory based on the particle size distribution and composition, often show discrepancies that can be attributed to kinetic limitations to droplet growth. Besides affecting cloud properties, kinetic limitations to droplet growth in the atmosphere may also impact the lifetime of aerosol particles. Changes in particle lifetime may influence the aerosol composition due to photochemical aging or heterogeneous processing of the aerosol. 

Hydrolysis sensitive polymers undergo both photochemical aging and hydrolytical degradation under elevated temperatures [650]. 

What is the impact of pollution gases on the photochemical ageing of synthetic fibres Outdoor weathering and laboratory simulation. Climatic and Air Pollution Effects on Materials and Equipment, Seminar Pfinztal, 1999, p. 159- 169... 

Influence of relative humidity on photochemical aging of polyethylene film after 72 hours irradiation time ( 11 MJ/m UV radiation) at 40 °C [87]... 

Arrieta, C., David, E., Dolez, P., Vu-Khanh, T. Hydrolytic and photochemical aging studies of a Kevlar -PBI blend. Polym. Degrad. Stab. 96. 1411-1419 (2011)... 

Arrieta et al. [47] conducted hydrolytic and photochemical aging studies for a Kevlar-Polybenzimidazole (PBI) blend in yam form. UV irradiation was conducted at X, = 340 nm and four different temperatures (50, 60, 70 and 80 °C) between 4 and 31 days. The PBI stracture is given in Fig. 5 [47] (reproduced with kind permission from Elsevier—License no. 3890161358622). 

Fig. 6 Photochemical aging mechanism of Kevlar [47] (Reproduced with kind permission from...

Delor-Jestin, F., Drouin, D., Cheval, P.-Y., Lacoste, J. Thermal and photochemical ageing of epoxy resin—influence of curing agent. Polym. Degrad. Stab. 91, 1247-1255 (2(X)6)... 

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