Photo-biodegradation environmental oxidation

Polyethylene oxide) (PEO) is a semicrystalline water-soluble polymer [64, 65], with a crystallinity that is very sensitive to the thermal history of the sample, making this property interesting as an indicator of degradation. Because it is biodegradable and biocompatible, PEO is a good candidate for environmental and medical applications [66-68]. The mechanisms of thermo- and photo-oxidation of PEO have already been investigated [69, 70] on the basis of IR identification of the oxidation products and are summarized in Scheme 10.1. 

A further interesting aspect of heterogeneous photochemistry concerns oil spilled at sea near land, which is subjected to environmental effects such as evaporation, dissolution, photo oxidation, dispersion into the water column and biodegradation. The fate of heavy fuel oil stranded on rock was studied under different environmental conditions [87]. Samples exposed to full or reflected sunlight showed depletion of the larger and more alkylated aromatic hydrocarbons and formation of resins, in agreement with reported laboratory studies on thin films of oil. 

TBBS does not ionize at environmental pHs, is not readily biodegradable, but hydrolyzes in less than 1 day at pH 9 or less. The identified hydrolysis products mercaptobenzothiazole, di(benzothiazoyl2)disulfide, t-butylamine, and benzothiazoleare are non-volatile, with a low potential for bioaccumulation, and are not readily biodegradable. Indirect photo-oxidation by hydroxy radicals is predicted with a half-life estimated at 2.8 hours. Log Pow of 3.9 at room temperature. 

PROBABLE FATE photolysis, extremely slow under environmental eonditions, photo oxidation half-life in air 156.4 days-4.2 yrs, estimated half-life with hydroxyl radicals is 2 yrs oxidation not important hydrolysis not important volatilization volatilization is rapid Iron the water column, however, is probably not important as compared to adsorption, the evapora tion rate from water has a half-life of approximately 8 hrs from a Im deep water column sorp tion strongly sorbed by particulate matter biological processes strongly bioaccumulated fr many organisms, extremely slow biodegradation... 

Abiotic hydrolysis, photo-oxidation and physical disintegration of polymers may enhance the biodegradation rate of polymers by increasing their surface contact area for microbial colonisation or by reducing the molecular weight [113]. In the case of lactic acid homo- and heteropolymers, abiotic hydrolysis is the most important reaction for initiating the environmental degradation... 

The standard ASTM D6954-04 is used for the exposure of plastics that can degrade by a combination of oxidation and biodegradation (87). This standard should permit the comparison and ranking of the overall rate of the environmental degradation of plastics in the course of thermal or photo oxidation. Each degradation stage is independently evaluated to allow a combined evaluation of a polymer s environmental performance. 

The most biodegradable of the commodity polyolefins is polypropylene (PP). Pandey and Singh have recently shown that polypropylene (PP), after removal of antioxidants by solvent extraction, biodegrades much more rapidly than polyethylene by mass loss in compost. PP lost over 60% mass in six months whereas low density polyethylene (LDPE) lost about 10% in the same time. Ethylene-propylene (EP) co-polymers biodegraded at rates intermediate between PP and PE. As expected, prior UV irradiation (photo-oxidation) increased both the rate and extent of the bioassimilation. This is fiilly in accord with the rates of environmental peroxidation of these molecules and it has been shown that PP acts as a sensitiser for the peroxidation of LDPE. ... 

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