IDENTIFICATION OF LUMINESCENT SPECIES CONTRIBUTING TO THE YELLOWING OF POLY(ETHYLENE-TEREPHTHALATE) ON DEGRADATION

Changes in the luminescence of poly(ethylene terephthalate) (PET) degr aded in the absence and presence of oxygen at melt temperatures has be en investigated. On oxidative degradation monomer fluorescence is redu ced, with a concurrent increase in dimer fluorescence at long waveleng ths. This is consistent with main chain breakdown and aggregation of t he terephthalate fragments produced. Longer wavelength fluorescent spe cies have been assigned to hydroxylation of the aromatic rings of PET. Further oxidation of PET degraded in air elicits changes in fluoresce nce and phosphorescence which have been associated with oxidation of h ydroxylated units which exist in equilibrium with quinones by a redox mechanism. Phosphorescence studies on extracts from heavily oxidized P ET have indicated the presence of stilbene quinone type impurities. Th e absence of such changes in the luminescence of PET degraded in nitro gen indicates hydroxylated, quinone and stilbene quinone species arise primarily from oxidation reactions. These species ale suggested to co ntribute to the yellowing of PET on degradation.