Effect of high-dose electron beam irradiation on thermal decomposition behavior of polytetrafluoroethylene (PTFE)

Abstract

In this study, we investigated the effect of high-dose (>10.0 MGy) irradiation on polytetrafluoroethylene (PTFE) decomposition in the presence of oxygen. To this end, we analyzed the chemical structures of PTFE residues after irradiation and thermal treatment as well as the outgas components during thermal treatment at 50 °C intervals. Thermogravimetric analyses indicated that the residual PTFE powder exhibited an initial decomposition (5% weight loss) at 159 °C, which is 365 °C lower than that of the original unirradiated sample. The initial decomposition temperature decreased at up to 5 MGy and gradually leveled off at above 140 °C. Fourier transform infrared (FT-IR) spectroscopy analysis of the residual PTFE powders indicated that the contents of thermal decomposition at lower temperature ranges were qualitatively related to the extent of the formation of oxidizable PTFE components, such as carbonyl groups. The formation of these components increased as the absorbed doses increased. The oxidized components gradually decreased with increasing thermal treatment temperature and tended to disappear at 470 °C. This demonstrated the effect of the oxidized compounds in the irradiated PTFE on lower temperature decomposition. The analysis of the gas components resulting from the thermal decomposition of the PTFE residuals revealed more detailed chemical information concerning the oxidative components of the irradiated PTFE. At temperatures below 420 °C, approximately 30% of the PTFE residue underwent pyrolysis to yield oxidized fluorocarbon products (CxFyOz) and further decomposed products (CO2). The remaining 70% of the residue thermally decomposed at temperatures above 420 °C, yielding monomer-related products such as C2F4, C3F6, and C4F8. These were identical to the gas products resulting from the thermal degradation of the original PTFE in the same temperature range. These results are indicative of the possibility of recycling and reusing fluorocarbons during irradiation.