Pyrolysis Kinetic Analysis of Decommissioned Photovoltaic Encapsulation Films

The resource utilization of decommissioned photovoltaic (PV) modules is the final stage of the PV industry chain and a critical step toward achieving sustainable development. Addressing the challenge of removing the encapsulation layer (EVA film) during the recycling process of retired PV modules, this study calculates the acetic acid content using thermogravimetric analysis (TGA) to clarify the thermal stability of EVA films under high-temperature conditions. Based on the thermal weight loss behavior of EVA films at four different heating rates (5C/min, 10C/min, 15C/min, and 20C/min), key parameters such as the onset and completion temperatures of pyrolysis and the temperature at maximum weight loss were determined. The Flynn-Wall-Ozawa method was used to construct a pyrolysis kinetic model, segmenting the pyrolysis reaction into different stages. Linear regression analysis was conducted at nine reaction conversion points to calculate the variation in activation energy across different stages. The results show that the vinyl acetate content in EVA films from decommissioned PV modules is significantly lower than the standard range, indicating reduced thermal stability. The pyrolysis process achieves a mass loss of over 95%, demonstrating the effectiveness of pyrolytic removal. As the heating rate increases, the thermogravimetric curve shifts toward higher temperatures, attributed to temperature lag caused by differences in heat transfer efficiency. According to the kinetic model, EVA pyrolysis can be divided into two stages: the first involving deacetylation and side-chain cleavage, and the second involving main-chain scission. The activation energy in the second stage is significantly higher than in the first, indicating that decomposition of the EVA main chain requires more energy.