Degradation Mechanisms in PET and PECT

Osborn [13] reported work on 25 im (1 mil) thick oriented PET film exposed either to a carbon arc or to fluorescent light sources using inherent viscosity measurements to track the degradation and related them to the number-average 

Stephenson et al. [15] first monitored the tensile properties and determined no damage for photon energies less than 3.2 eV (74kcal/mol or 388 nm) by extrapolation. If this is true, then it implies that photodegradation out to quite 

Investigation turned then to chemical and spectroscopic means to obtain the needed mechanistic understanding. Stephenson et al. [17] looked at gas evolution versus exposure, while Pacifici and Straley [18] used UV fluorescence spectroscopy to identify a photo-oxidation product which was later isolated by Valk et al. [19]. In addition, Valk and co-workers [19-21] isolated a number of additional photolysis products by a combination of hydrolysis and chromatography, Marcotte et al. [22] used ESR to look at radicals generated during degradation, and Day and Wiles [23-26] carried out extensive IR and fluorescence spectroscopic investigations on this subject. 

The end result of these studies showed very clearly that two major processes were important, i.e. photolysis and photo-oxidation. Photolysis reactions were posited to be the result of the well-known Norrish Type 1 and Norrish Type 2 cleavage reactions. As we shall see, the Type 1 cleavage followed by several subsequent reactions can account for many of the observed degradation products. 

The photo-oxidation reactions can take place either on the aromatic rings [18, 25] or the glycol units [11, 25] and lead to many of the rest of the products apparently not accounted for in the pure photolysis reactions. 

---