Degradation Monitoring of Hindered Amine Light Stabilizer Doped Polymers

Polycarbonate (PC) is the most widely used aromatic polymer in various industrial applications. It is a condensation polymer in which benzene rings plus quaternary carbon atoms form bulky stiff molecules that promote rigidity and strength. The bulky chains crystallize with great difficulty, so the polymer is normally amorphous with excellent characteristics such as optical clarity, heat stability and mechanical resistance. The fluorescence and fluorescence excitation spectra of pure and doped PC depending on hindered-amine light stabilizers (HALS: Tinuvin 770 and Tinuvin 123) concentration and different processing conditions have been studied. Non-processed PC has no emission band in the visible range but processed PC with additives show visible fluorescence bands between 400–470 nm. It suggested that PC undergoes a kind of degradation process which lead to the fluorescence emission caused by the transitions from the new distortion-related localized states (defect states) created by processing and the additives. Such defects lead also to the emergence of a new band in the excitation and emission spectra at lower energies, where the symmetry of the bands break near. The intensity of these bands drastically depends on the sample treatment where the luminescence intensity quantitatively characterizes the concentration of defect radicals. An increase in screw speed resulted in an increase in specific mechanical energy (SME), higher SME led to a remarkable macromolecular degradation. The fluorescence spectroscopy of pure and doped polycarbonate (PC) depending on hindered-amine light stabilizers (HALS: Tinuvin 770 and Tinuvin 123) concentration and different processing conditions have been shown that pure non-processed PC has no emission band in the visible range but have an absorption band at 290 nm. Processing under excessive conditions is most likely to produce chains and general degradation which leads to a fluorescence emission. Processed PC with additives shows visible fluorescence bands between 400–470 nm. The intensity of these bands drastically depends on the sample treatment where the luminescence intensity quantitatively characterizes the concentration of defect radicals. PC becomes considerably yellow discolored with higher concentration of Tinuvin 770 or Tinuvin 123 and the PC gets more brittle (higher degradation grade).

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