Thermal separation of plastic components from waste crystalline silicon solar cells: Thermogravimetric characteristics and thermokinetics

Thermal treatment is a mainstream technique to separate plastic components from waste crystalline silicon (c-Si) photovoltaic (PV) modules. In this study, the thermogravimetric analysis (TGA) was conducted for a better understanding of the characteristics of plastic components mainly poly(ethylene-co-vinyl) acetate (EVA) binder and polyfluoroethylene composite membrane (TPT) backsheet in waste c-Si PV panels through thermal treatment at four different heating rates (5-20°C·min-1) under nitrogen and air conditions, respectively. The thermal process of the EVA binder whether in a nitrogen or air atmosphere could be divided into two phases, which were 300-400°C and 400-515°C in nitrogen with the total weight loss reached 99.64%; the two phases in the air were 270-405°C and 405-570°C with the total weight loss was 99.68%. The thermal weight loss of TPT in nitrogen has only one phase occured between 380°C and 520°C, and the weight loss rate is about 83%. There are two weight loss phases in the air atmosphere, which the first phase starts from 265°C to 485°C and the second phase ends at 635°C with a final weight loss reaching 97%. Furthermore, the Kissinger-Akahira-Sunose (KAS) method was chosen to calculate the pyrolysis kinetic parameters. The activation energy for EVA in nitrogen (261.16 kJ·mol-1) was higher than in air (209.04 kJ·mol-1), also the TPT in nitrogen (188.28 kJ·mol-1) higher than in air (172.21 kJ·mol-1). That indicated that the thermal decomposition of EVA binder was accelerated at first phase in nitrogen, but there is little difference in air atmosphere. Moreover, the activation energy of PVF of the TPT backsheet in the first phase was lower than that in the second phase. This study provides the fundamental basis to develop efficient thermal separation for the plastic components EVA and TPT in waste PV panels.Implications: This study mainly aims to explore the thermal separation of plastic components of waste c-Si panels for heating treatment, so that developing an accurate heat treatment approach that is efficient to implement for the separation of secondary raw material i.e., glass and silicon wafer from end-of-life PV panels. Therefore, this research findings have significant implications for providing the basic data support for waste PV panels management recycling standards, specifications, or policy documents.