Efficient Mineralization of Fluoroelastomers Using Superheated Water in the Presence of Potassium Hydroxide

Abstract

The mineralization of fluoroelastomers (FKMs) in superheated water in the presence of potassium hydroxide (KOH) was investigated with the aim of developing a methodology for recycling the fluorine element. Two FKMs—an “uncrosslinked FKM”, representing a poly(vinylidene fluoride-co-hexafluoropropylene) (poly(VDF-co-HFP)) copolymer with a VDF/HFP molar ratio of 78/22 and a “crosslinked FKM” consisting of this copolymer (cured by peroxide) and carbon black—were treated. The fluorine content of these FKMs was efficiently transformed into F− ions in the reaction solution using low KOH concentrations (0.10–0.50 M) at 200–250 °C. When the uncrosslinked or crosslinked FKMs reacted with aqueous KOH (0.20 M) at a rather low temperature (200 °C) for 18 h, the fluorine content of these FKMs was completely mineralized (both F− yields were 100%). Although the crosslinked FKM contained carbon black, the fluorine mineralization of the FKM was not inhibited. The addition of Ca(OH)2 to the reaction solutions after the superheated water treatment at 250 °C for 6 h with aqueous KOH (0.50 M) led to the production of pure CaF2, identified using X-ray spectroscopy, with 100% and 93% yields for the uncrosslinked and crosslinked FKMs, respectively.

Microwave-Assisted Oxidative Degradation of Poly(vinylidene fluoride-co-hexafluoropropylene) Copolymers: Preparation, Characterization, and Reaction Mechanism

“…Mizuide et al and Tatsu et al , successfully synthesized LTCFs through oxidative degradation under alkaline circumstances. Subsequent investigations progressively explored the intricate degradation mechanism of the subject. − The oxidative degradation method stands out for its easy preparation process, simple operation, and cost-effectiveness. This, in turn, broadens the range of possibilities for the substance. , Nevertheless, certain limitations, such as prolonged response durations and increased energy usage, need to be addressed.…”