Reactions of poly(vinylidene fluoride)[PVDF], poly(vinylidene fluoride-co-hexafluoropropylene) [poly(VDF-co-HFP)] copolymer, and poly(vinylidene fluoride-co-perfluoromethyl vinyl ether) [poly(VDF-co-PMVE)] copolymer in subcritical water were performed with the aim to develop a technique for recycling fluorine element. By addition of KMnO 4 to the system, quasi-complete mineralization of PVDF was achieved at a rather low temperature (250 °C). When PVDF was reacted for 18 h in the presence of KMnO 4 (158 mM, corresponding to a 1.6-fold molar excess relative to both fluorine and carbon atom contents of PVDF), the fluoride ions (F − ) yield reached 100%, and the amount of remaining total organic carbon decreased to 2% of the carbon atoms in the initial PVDF. Poly(VDF-co-HFP) and poly(VDF-co-HFP) copolymers also showed quasi-complete mineralizations under the same conditions. During the reactions, MnO 4 − was modified into MnO 2 . Compared to the previous method using H 2 O 2 , the reaction temperature that allows a complete mineralization was reduced by 50 °C.

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The decomposition of functional fluoropolymers poly­[vinylidene fluoride-co-2-(trifluoromethyl) acrylic acid] copolymers, [poly­(VDF-co-MAF)], in superheated water was investigated as the first example of the decomposition of these copolymers aimed at recycling the fluorine element. Such statistical copolymers were prepared from the conventional radical copolymerization of VDF and MAF in two different feed molar ratios leading to different VDF/MAF molar ratios (90/10 and 58/42 molar percentages). Their degradation was achieved in the presence of two oxidizing agents. By the use of KMnO4 (25–158 mM), these poly­(VDF-co-MAF) copolymers efficiently generated F– ions and resulted in low total organic carbon (TOC) content in the reaction solutions. Specifically, when the copolymer containing a 90 mol % VDF was treated with aqueous KMnO4 (158 mM) at 250 °C for 6 h, the F– yield reached 83% and the remaining amount of TOC decreased to 4% of the carbon atom amount in the initial copolymer. Likewise, for the same treatment of the other copolymer (58 mol % VDF), the F– yield reached 90% while the remaining TOC ratio was 4%. Compared to KMnO4, H2O2 induced a lower copolymer mineralization. Adding Ca­(OH)2 to the solutions from superheated water treatment with KMnO4 and a subsequent washing procedure gave pure CaF2.

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