Kinetics of degradation-induced polymer luminescence: A polyphenylene sulfide/elastomer blend under dry heat exposure

The thermally induced changes of the steady-state photoluminescence of a polyphenylene sulfide/elastomer blend under dry heat exposure are investigated. Two signals, a phenylene fluorescence signal and a degradation-induced luminescence signal are identified and found to exhibit different spectral and kinetic properties. A detailed kinetic analysis of the thermally induced changes reveals, that the phenylene fluorescence signal can consistently be interpreted in terms of a cold crystallization process limited by the viscous flow of the polymeric material with an apparent activation energy of 33 +/- 12 kJ/mol. On the other hand, the changes of the degradation-induced steady-state luminescence signal can be described by a power law kinetics with an apparent activation energy of 113 +/- 25 kJ/mol. The obtained apparent activation energies of the thermally induced material changes and the underlying molecular mechanisms are discussed and related to data available from the literature. In addition to the kinetic analysis of the changes of the degradation-induced steady-state photoluminescence, an equivalent exposure time and temperature can be derived that describe the exposure history of the sample. Furthermore, a relationship between exposure at room temperature and exposure above the glass transition temperature is suggested that, in combination with the density of states model as proposed before, can be used to predict the development of the steady-state luminescence changes over many years of exposure at room temperature. (c) 2017 Elsevier Ltd. All rights reserved.