Photochemical Degradation of Polymers

In nintees, the white cloths used to get yelloish after few washes. The washerman was blamed that he did not washes cloths properly. But after some time, the cause was identified. It was due to photodegradation of cloth fibers. Photodegradation of polymers has two contrary features, beneficial as well as non-beneficial. 

The photochemical degradation can occur in two ways after photoinitiation  

The polymers are converted into photo-stable units through photodegradation. 

In order to manufacture environmental friendly qualities of polymers, a photo-active group may be introduced into the polymer. For example, light sensitive polymers are obtained by the co- pol nnerisation of ketonic species with hydrocarbons. The photodegradation of resulting pol nneric material involves. Norrish type II process of the pol mier chain rather than a radical mediated photooxidation. 

Photodisposal of agricultural film or packaging should undergo a sharp and controlable degradation initiated by exposure to UV light. 

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Another explanation was the following. The organomontmorillonite used was a natural montmorillonite that contained iron. Chemical analysis of the clay confirmed the presence of a low amount of iron. It was recalled that iron and, in more general terms, metals are likely to induce the photochemical degradation of polymers. Iron at low concentration had a prooxidant effect that was due to the metal ion of iron that can initiate the oxidation of the polymer by the well-known redox reactions with hydroperoxides [93]. It was concluded that the transition metal ions, such as Fe, displayed a strong catalytic effect by redox catalysis of hydroperoxide decomposition, which was probably the most usual mechanism of filler accelerating effect on polymer oxidation. A characteristic of such catalytic effect was that it did not influence the steady-state oxidation rate, but it shortened the induction time. 

Recent studies have shown that tensile and shear stresses accelerate the rate of the photochemical degradation of polymers. In contrast, compressive stress generally retards the rate of photochemical degradation (3,4). In addition to stress, other factors may affect the rates of polymer photodegradation. These factors include the ... 

R. Chen and D.R. Tyler, Origin of tensile stress-induced rate increases in the photochemical degradation of polymers. Macromolecules, 37(14) 5430-5436, July 2004. 

Photochemical degradation of polymers have both good and bad effect on human life . Give example of each in favour of the thought ... 

There is a substantial literature on the thermal and photochemical degradation of PS and it is well established that polymer properties are sensitive to the manner in which a particular sample of PS is prepared. For example, it has been reported that PS prepared by anionic polymerization shows enhanced stability with respect to that prepared by a radical mechanism.2 10 This has often been attributed to the presence of "weak links" in the latter polymers. However, the precise nature of the "weak links" remains the subject of some controversy. T he situation is further confused by all PS prepared by radical mechanisms often being considered as a class without reference to the particular polymerization conditions employed in their preparation. In many cases the polymers are "commercial samples" with details of the method of preparation incomplete or unstated. 

Accelerate chemical, photochemical, biochemical reactions or processes, e.g. cross-linking or degradation of polymers. Also called promoters, co-catalysts. Refer usually to the cure process in thermosetting resins. 

When similar photolysis of 11 in the presence of MeOD was carried out, again the product whose NMR reveals the resonance due to the Si-H proton was observed. The relative ratio of the Si-H and CH3-0 protons was identical with those of the products obtained in the presence of non-deuterated methanol. The formation of the methoxysilyl group can be understood by the addition of methanol across the silicon-carbon double bonds. H NMR spectra of all photoproducts obtained from the photolyses of 11 in the presence of methanol reveal no resonances attributed to the cyclohexadienyl ring protons. This indicates that the photochemical degradation of the polymer 11 gives no rearranged silene intermediates, but produces... 

The mechanisms of photochemical degradation of a polymer are rather difficult to study as the observed degradation is typically a result of the effect of light on the contaminants in the polymer rather than the pure polymer. Studies typically look for the degradation products, either low molecular weight volatiles or radicals, or work to identify the wavelength of light absorbed by the system via spectroscopic methods. 

Figure 18.12 Effect of fluorescent device exposure on carboxylic acid production in Spectar copolymer as determined by SF4 treatment 1816cm-1, aromatic acid peak 1841 cm1, aliphatic acid peak [11]. Reprinted from Polymer, 41, Grossetete, T., Rivaton, A., Gardette, J.-L., Hoyle, C. E., Ziemer, M., Fagerburg, D. R. and Clauberg, H., Photochemical degradation of poly(ethylene terephtha-late)-modified copolymer, 3541-3554, Copyright (2000), with permission from Elsevier Science...

Kalnins, M.A. (1984). Photochemical degradation of acetylated, methylated, phenylhydrazine-modified and ACC-treated wood. Journal of Applied Polymer Science, 29(1), 105-115. 

SCHEME 3. Photochemical degradation of a polymer with metal-metal bonds along its backbone. 

Photochemical degradation of Iignocellulosic Materials Hon, D. N.-S. Grassie, N. Ed. Developments in Polymer Degradation Applied Science Publishers London, U.K., 1991. 

D.N.-S. Hon, Photochemical Degradation of Liqnocellulosic Materials in Developments in Polymer Degradation - 3... 

A basic requirement of the ESR technique is the presence of molecules or atoms containing unpaired electrons. Such species can be generated in polymeric systems by homolytic chemical scission reactions or by polymerization processes involving unsaturated monomers. These reactions can be initiated thermally, photochemically, or with a free-radical initiator, and, in the case of scission, by mechanical stress applied to the system. Therefore, ESR can be used to study free-radical-initiated polymerization processes and the degradation of polymers induced by heat, light, high-energy radiation, or the application of stress. 

Hon DNS (1982) Photochemical degradation of lignocellulosic materials In Grassie N (ed) Development in polymer degradation 3 Applied Science Publishers, Essex, England, 229-281... 

Horikoshi S, Hidaka H, Serpone N (2001) Photocatalyzed Degradation of Polymers in Aqueous Semiconductor Suspensions V. Photomineralization of Lactam Ring-pendant Polyvinylpyrrolidone at Titania/Water Interfaces,/. Photochem. Photobiol. A ... 

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