Photodegradation behavior

Based on the different pathways for breakdown available the photodegradation behavior can be generally classified as belonging to one of four categories ... 

G. A.V. Timoteo, G.J.M. Fechine, M.S. Rabello, Stress cracking and photodegradation behavior of... 

Torimoto, T., Y. Okawa, N. Takeda, and H. Yoneyama, Effect of activated carbon content in TiOj-loaded activated carbon on photodegradation behaviors of dichloro-methane. J. Photocham. Photohiol. A. 103 (1997) 153-157. 

Ikada, E., 1997. Photodegradation behaviors of aliphatic polyesters. Photo- and bio-degradable polyesters. J. Photopolym. Sci. Technol. 10, 265—270. 

Hwang, D.K., Shul, Y.G., Chu, Y.H. Photodegradation behavior of the polycarbonate/Ti02 composite films under the UV irradiation in ambient air condition. Polym. Compos. 36, 1462-1468 (2015)... 

Xu, J., Shi, W., Gong, M., Yu, F., Yan, L. Preparation of poly(methyl methacrylate-co-maleic anhydride)/Si02-Ti02 hybrid materials and their thermo- and photodegradation behaviors. J. Appl. Polym. Sci. 97(4), 1714-1724 (2005)... 

Figure 40.16 Mixed oxide inorganic UV protective coatings prepared by epoxy assisted sol-gel procedure used for protection of a colored surface, (a) Photodegradation behavior, (b) Unprotected and protected coatings.

Water, methanol, and n-hexane do not influence the photooxidation of PVC (43), but the photodegradation is accelerated by ferric chloride (70,71) and certain other compounds containing iron (70,71,72). Purification of the polymer might be expected to enhance its photostability by removing deleterious impurities such as iron compounds that are derived from metal equipment. This type of result was obtained in one recent study (58) but not in others (30,59). In contrast, the photo-oxidative degradation of PVC should be enhanced by admixture of the polymer with materials that are unusually susceptible to photooxidation themselves. Such behavior has been observed for impact-modified PVC containing polybutadiene-based polyblends (69,73). 

Photophysical Processes and Photodegradation of Poly(ethylene terephthalate-co-2,6-naphtha1enedi carboxyl ate) Copolymers. We have recently reported the photophysical processes and the photo-degradative behavior of Doly(ethylene terephthalate-co-2,6-naphthalenedicarboxyl ate), PET-2,6-ND, copolymer yarns containing 0.5 - 4.0 mole percent 2,6-naphthalenedicarboxyl ate, 2,6-ND (1) and the parent naphthalenedicarboxyl ate monomer, Figure 3 and 4. 

Fig. 16.17 Representative plot of the behavior of sulfa drugs obtained from photolysis on a turntable apparatus, under four Pyrex-filtered 175-W medium-pressure Hg-vapor lamps. Photodegradation of sulfamethazine in deionized H O ( ) and enhanced photodegradation in natural lake water ( ). Reprinted with permission from Boreen AL, Arnold WA, McNeil K (2005) Triplet-sensitized photodegradation of sulfa drugs containing six-membered heterocyclic groups identification of an S02 extrusion photoproduct. Environ Sci Technol 39 3630-3638. Copyright 2005 American Chemical Society...

The photodegradation rate dependence on phenol concentration in the TiOi/F system shows a plateau in the 3 X IO " M to 3 X 10 M range, whereas for naked TiO2, a maximum is reached around 2 X 10 M of phenol followed by a decrease. This behavior is rationalized by the possibility of reductive back reactions of intermediates formed after the first oxidation step. The presence of fluoride could limit the occurrence of this detrimental effect, reducing the interaction of the formed intermediates with the surface. Moreover, also the change of the oxidation pathway changes the amount of the products. 

Some of the topics addressed here have been reviewed by other authors. Studies of photoinduced processes (direct or indirect) of chlorophenols carried out before 1998 have been covered comprehensively [8] this work will only cursorily be treated here. A detailed overview of the photochemical behavior of phenylurea herbicides was in press at the time of writing this article [9]. The related subject of the photodegradation of pharmaceuticals in the aquatic environment has been reviewed very recently [10]. 

Four papers have appeared on the photodegradation of PCBs on sediments [118-121]. Tang and Myers, for example, have carried out a study to model the behavior of PCBs on sediments confined in disposal facilities [ 118, 120]. In their glass aquariums the authors found PCB levels decreased by 40% over a 5-month span. Unfortunately, they were unable to pin point the source of the loss. Tang and Meyers believed the loss was due to a combination of volatilization, photo degradation and biodegradation. 

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