General characteristics of photoluminescence from dry heat aged polymeric materials

Degradation-related polymer luminescence is investigated by means of polarization-sensitive luminescence spectroscopy and anisotropy measurements for different polymers under dry heat ageing conditions. It is found that the spectral development of polymer luminescence with progressive degradation of the polymer is largely independent of the chemical structure and formulation of the polymer. The degradation of the polymer can be categorized into an initial phase with luminescence excited below 300 nm, an intermediate phase with luminescence excited between 300 and 400 nm and a final phase with luminescence excited throughout the full UV/VIS-region. Whereas the properties of the first two phases are consistent with the interpretation as fluorescence originating from individual non-interacting species, the last phase of degradation exhibits luminescence properties, most prominently a high degree of depolarization, consistent with luminescence originating from a density of interacting states that is developed in the process of polymer degradation. A general, polymer independent, model is developed to describe the development of degradation-related polymer luminescence under progressive degradation.