The vacuum pyrolysis and thermal degradation in air of irradiated poly(ethylene-co-tetrafluoroethylene) films

摘要

The pyrolytic and thermal degradation mechanisms of poly(ethylene-co-tetrafluoro-ethylene) (ETFE) were investigated in order to understand and help predict the aging characteristics of this material and formulations containing it. Pyrolytic decomposition of γ-irradiated, thermally aged ETFE films in vacuum results in dehydrofluorination, formation of unsaturation, and hydrogen and fluorine migration. Further, pyrolytic random chain scission generates off-gases containing a distribution of ETFE oligomers with one to four repeat units. Also noted was the presence of pyrolytic decomposition products in the unaged, unirradiated ETFE films. The presence of these indigenous decomposition products is evidence that processing/synthesis of these samples involves rapid heating and cooling. Thermal degradation in air of γ-irradiated ETFE films produces carbonyl moieties within the polymer. Also, the oxygen-centered radicals formed as a result of γ-irradiation disappear upon thermal aging. Pyrolytic decomposition was studied with evolved gas analysis using mass spectrometry (EGAMS). The thermal aging processes of ETFE were investigated using a multidisciplinary approach that combined EGAMS, infrared analysis and electron spin resonance. Prior to analysis, the ETFE films were subjected to γ-irradiation followed by thermal aging at 200℃ in air. The thermal aging times were 0, 20, 40, 80 h, and 3 months, and the irradiation doses were 0, 9, 19, and 29 Mrad.