Abstract

With a sharp increase in photovoltaic (PV) installations across the world, PV waste is now a relatively new addition to the e-waste category. From 45,000 tonnes in 2016, the PV waste stream is rapidly increasing and is projected to reach 60 million tonnes by 2050. Backsheets are composite structures made from several material layers of polymer, adhesive, and primer. Widely used PV backsheets can be classified into three core types: (a) KPK (Kynar^®/polyethylene terephthalate (PET)/Kynar^®), (b) TPT (Tedlar^®/PET/Tedlar^®), and (c) PPE (PET/PET/ethylvinylacetate). Kynar^® and Tedlar^® are based on polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), respectively. PPE backsheets are fluorine-free composites made primarily from PET. With increasing focus on the end-of-life (EoL) handling of PV waste, the handling of fluoropolymers, which is largely unexplored, requires closer examination to avoid environmental damage. The aim of this study was to obtain information on the fluorine released from PV backsheet materials into the gas phase during combustion and pyrolysis as EoL pathways. Therefore, several experimental trials were conducted to measure fluorine transfer into the gas phase at 300 °C, 400 °C, 500 °C, and 900 °C (for pyrolysis) and at 750 °C, 850 °C, and 950 °C (for incineration).

Conclusions
… from the experimental analysis presented in this study along with the literature body on the thermal degradation of fluoropolymers, it can be concluded that the EoL [end-of-life] handling of fluorinated PV backsheets is not just challenging but also adds to the formation of other persistent compounds such as fluorocarbons, fluoroacids, furans, and dioxins. Even in hazardous waste incineration plantsthat are  equipped with sophisticated downstream processing, studies show that significant quantities of trifluoroacetate can still be released into the environment. Hence, it can be concluded that although fluoropolymers might have some characteristic attributes such as thermal stability, they still pose risks to both human health and the environment. PPE backsheets on the other hand, are preferable from a recycling and wider the circular economy perspective.

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