Photodegradation and Oxidation of Poly ethylene terephthalate PET

Initial investigations of the effects of light on PET were carried out between about 1950 and 1970 [1-8]. These initial experiments showed that the polyester rapidly yellows and embrittles, evolves gases such as CO and CO2, and reduces in solubility after exposure to monochromatic light at wavelengths between 254 nm and 313 nm. Probable reaction schemes are as follows  

Hydrogen abstraction from neighbouring molecules could also occur, leading to various radical species which can then crosslink. 

The first major systematic study of PET photochemical degradation was begun by Day and Wiles in the early 1970s [9-15. Samples were irradiated using carbon-arc and xenon-arc light sources, and their degradation followed by means of tensile properties, intrinsic viscosities, infrared (IR) absorption and fluorescence emission. 

From the data obtained, the authors postulated that there were three potential primary photolytic reactions for PET [13  

In this case the carboxyl radical may then go on to abstract a hydrogen to form an acid chain end, or split off CO2 and additionally form a phenyl radical chain end. 

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