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

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 degrees C for 6 h with an approximately 5.8-fold molar excess of O-2 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 O-2 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 O-2, whereas ETFE did not. Adding stoichiometric Ca(OH)(2) to the reaction in the presence of O-2 afforded X-ray spectrometrically pure CaF2.