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 °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 CO 2 in 96.9% and 99.3% yields, respectively. ETFE was also efficiently mineralized to F – (97.6%) and CO 2 (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 –, CO 2 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 CaF 2 .