Abstract
Decomposition of poly(vinylidenefluoride-ter-hexafluoropropylene-ter-tetrafluoroethylene) terpolymer, a typicalfluoroelastomer with highflexibility and high resistance to permeation of oil and excellent adhesive ability to other materials, in subcritical water (SubCW) was studied as a first example of the decomposition of the terpolymer with the aim of developing a technique to recover thefluorine element. Compared to the commonfluoropolymers such as poly(vinylidene fluoride), the terpolymer was considerably stable in SubCW. 19F NMR spectral analysis of the decomposition products obtained from the reaction at 300 °C was carried out to better understand the decomposition mechanism. When the reaction was performed in SubCW at 300 °C for6 h under argon, only a negligible amount of F−ions (1%) was released. Addition of H2O2 into the reaction system accelerated the mineralization of the terpolymer to form F−and CO2. Apart from these major products, small amounts of malonic acid and CF3H were detected. When this polymer was heated in SubCW at 350 °C with 4.0 M H2O2, both the yields of F−and CO2 reached up to 95%. These features indicate a quasi-complete mineralization of the terpolymer. Furthermore, the reaction in the presence of 4.0 M H2O2and stoichiometric amount of Ca(OH)2at 350 °C for 18 h resulted in the formation of pure CaF2, a raw material for hydrofluoric acid, in 84% yield.