Efficient-Oxygen Induced Mineralization of Melt-Processable Fluoropolymers in Subcritical and Supercritical Water

Abstract

The decomposition of poly(vinylidene fluoride) (PVDF) and ethylene–tetrafluoroethylene copolymer (ETFE) in subcritical and supercritical water was investigated. Heating PVDF in supercritical water at 380 °C for 6 h with an approximately 5.8-fold molar excess of O2 relative to the fluorine or carbon content in the polymer afforded F– and CO2 in 96.9% and 99.3% yields, respectively. ETFE was also efficiently mineralized to F– (97.6%) and CO2 (98.2%) with an 11-fold molar excess of O2 relative to the fluorine or carbon content of the polymer under the same reaction conditions. The PVDF and ETFE reactivities differed markedly under argon: PVDF formed mainly F–, CO2 formation was suppressed, and a carbon-rich residue formed; in contrast, ETFE was unreactive. This difference suggests that PVDF decomposed via dehydrofluorination in the absence of O2, whereas ETFE did not. Adding stoichiometric Ca(OH)2 to the reaction in the presence of O2 afforded X-ray spectrometrically pure CaF2.