Thermal degradation of thermoplastic and thermosetting polymers induced bylaser radiation and its study by FTIR spectroscopy

It is demonstrated that powerful laser radiation causes changes in absorban ce spectra of an epoxy resin, polyethylene and polysulfone. Thin polymer fi lms were located between infrared AgBrCl optical fibers and exposed to the radiation of a CO2 laser. The output of the laser source was varied in the range 0-8.5 W. Absorbance spectra were measured by FTIR spectrometry. It wa s found that characteristic absorbance peaks of polymers decay under the po werful IR light. The apparent dependence of peak magnitude on IR radiation power has been established. The mathematical theory of the observed effect is presented. We suggest that the effect under discussion is caused by the oxygen-free thermal action of IR radiation on the chemical structure of the polymers. We established that the phenomenon of peak disappearance with bo th polymers - thermoplastic (including such engineering polymer as polysulf one) and thermosetting - is of a threshold nature. The proposed method is a valuable instrument for the study of degradation processes in polymers. (C ) 2001 Published by Elsevier Science Ltd. All rights reserved.