Photo-oxidative degradation

Protection of polymers against thermal and photo-oxidative degradation is achieved with appropriate stabilizers that ensure the desirable polymer properties throughout the entire service life of the polymer. Compatible and polymeric stabilizers usually give the best protection. In order to avoid migration and evaporation, polymeric stabilizers are used. 

What is mechanical degradation Why is it less commonly encountered relative to thermal and photo-oxidative degradation ... 

The photo-oxidative degradation of polypropylene (PPH) can be largely summarized by the reactions 1 to h ( l,2j. During the... 

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). 

Hiatt, C.W., Haskins, W.T., Olivier, L. (1960) The action of sunlight on sodium pentachlorophenate. Am. J. Trop. Med. Hyg. 9,527-531. Hidaka, H., Nohara, K., Zhao, J., Serpone, N., Pelizzetti, E. (1992) Photo-oxidative degradation of the pesticide permethrin catalyzed by irradiated Ti02 semiconductor slurries in aqueous media. J. Photochem. Photobiol. A Chem. 64, 247-254. 

The presence of extensive backbone scission during photo-oxidative degradation has been demonstrated by molecular weight (Mn) determination, based on solution viscosities. PET with an initial f n of -20,000 decreased to ll+,000 after 600 hr xenon arc irradiation (2 ). PmPiPA with an initial Mn of -1+0,000 decreased to -10,000 after 1+0 hr of xenon arc irradiation ( ). The actual extent of backbone scission is even more startling when it is remembered that degradation has occurred only in the irradiated surface layer (surface layer will be of the order of 1000, i.e., oligomer in each case. 

We have found that this liquid-solid phase system due to efficient sensitized photo-oxidative degradation of dissolved polymer (e.g.polybutadienes). 

The ketonic products can be expected to occur in trace amounts in pure polymers and are also components of the complex photo-oxidation products. Photolytic reactions of these ketones are important both in the very early stages of photo-oxidative degradation and in the continuation of an established photo-degradation reaction. The ketones may affect the source of the photodegradation by contributing to free radical processes, chain scission and energy transfer. 

The UV radiation affects aldehyde groups in polymers in the same way as ketone groups that is, Norrish reactions of type I and II are involved in the photochemical process [116]. These reactions are not very important in the photo-oxidative degradation of polymers, because the aldehyde groups are exclusively found at chain ends namely,... 

When hydrogen peroxide is formed in the photo-oxidative degradation of polymers it is also necessary to take into account the secondary reactions due to its photolysis. 

A number of volatile compounds are obtained apart from the crosslinked products in the final oxidation process. With polyolefines, water, formaldehyde, acetaldehyde, acetone, methanol, hydrogen peroxide, carbon monoxide, and carbon dioxide were identified [Refs. 75, 76, 122, 292, 424, 425, 449, 487, 560, 608]. Table 5 shows the percentage content of particular volatile products formed during the photo-oxidative degradation of polypropylene [122]. 

Photo-oxidized degradation of polymers in solution is highly complicated for the following reasons ... 

In both cases the degradation and photo-oxidative degradation of... 

Rabek found in his investigations of the photo-oxidative degradation of cis-l,4-polyisoprene in solution that benzophenone [496, 502], Michler s ketone (4,4 -bis-(dimethylamino)-benzophenone) [508] and thiobenzo-phenone [494, 495] sensitize the reaction (Fig. 19). In the absence of oxygen benzophenone promotes the formation of microgel. 

The observed photo-oxidative degradation of ci s-l,4-poIyisoprene in benzene solution sensitized by benzophenone may be represented as... 

Dyes are widely known to be active photo-initiators and photosensitizers of the polymerization reaction [489, 503], but the Complete elucidation of their influence on the photo-oxidative degradation of polymers still requires extensive fundamental investigation. 

P. Cerruti, M. Lavorgna, C. Carfagna, and L. Nicolais, Comparison of photo-oxidative degradation of polyamide 6,6 films stabilized with HALS and CuCl2 + KI mixtures, Polymer 2005, 46(13), 4571 1583. 

The photo-oxidative degradation of polypropylene and stabilization by hindered amines has been reviewed. A study has appeared of the effect of P-carotene on the photoreactivity of anthracene in hexane solution and a kinetic scheme has been proposed to account for the photochemical and photophysical processes that occur on irradiation at 365 nm. Quenching rate constants have been determined between /S-carotene and singlet oxygen. Some characteristics have been communicated of the sensitized photo-oxidation of abietic acid contained in a vinyl butyl ether-butyl methacrylate-methacrylic acid copolymer. At 400 nm... 

Photo-oxidative degradation of polymers, especially in the presence of U V radiation. Presence of hydroxyperoxides strongly accelerates this process for PP, PE, PS, etc. Such polymers as PEST, PC, PA, POM sufficiently absorb light to start the degradative process. 

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