Recycling and the end of life assessment of fluoropolymers: recent developments, challenges and future trends

Abstract

Herein, we present the state of the art technology on the recycling, reuse, thermal decomposition (by thermolysis, thermal processing, flash pyrolysis, smoldering, open burning, open-air detonation, and incineration), and the life cycle assessment of fluoropolymers (FPs, ranging from poly(tetrafluoroethylene), PTFE, and poly(vinylidene fluoride), PVDF, to various fluorinated copolymers based on VDF and TFE). FPs are niche specialty polymers endowed with exceptional properties and have found many applications in high-tech industries. However, compared to other polymers, the reuse of FPs is still not well-established and is in its infancy. Accordingly, their recycling has attracted increasing interest, even reaching the pilot stage. In addition, recently, several studies have been reported on vitrimers, which are regarded as polymers ranking between thermosets and thermoplastics. In this case, although many articles have reported to date on the thermal degradation of these technical polymers, intensive efforts have been devoted to avoiding the release of low molar mass oligomers and per- and poly-fluoroalkyl substances (PFAS, and especially polymerisation aids such as perfluorooctanoic acid (PFOA) and its alternatives), while various reports demonstrated the complete decomposition of PTFE, leading to the formation of TFE (and hexafluoropropylene or octafluorocyclobutane to a lesser extent). Incineration is one of only a few technologies that can potentially degrade FPs and completely degrade PTFE and other PFAS from 850 °C. Recent studies on the mineralisation of FPs under subcritical water represent an interesting approach to close the loop of the fluorine chemistry cycle. Because of the high molar masses (several million for PTFE) and thermal, chemical, photochemical, and hydrolytic inertness and biological stability of FPs, it has been clearly evidenced that they satisfy the 13 accepted regulatory assessment criteria to be considered as polymers of low concern.