The swelling mechanism of ethylene-vinyl acetate polymer in different solvents via molecular dynamics and experimental studies

Abstract

Ethylene-vinyl acetate (EVA) film is the predominant encapsulation material in crystalline silicon photovoltaic modules, the efficient and eco-friendly processing of which is essential for the recycling of the modules. Among the various existing techniques, the chemical approach uses solvents to induce swelling and dissolution on the EVA film to facilitate the separation of distinct layers. This method demonstrates the potential for achieving low-energy consumption and minimal-damage retrieval of the diverse materials within the components. Nonetheless, the mechanism underlying the swelling of the EVA polymer and the consequent delamination of various layers remains elusive, hindering the proper choice of solvents. In this study, the swelling behaviors of the EVA polymer in water, ethanol, and D-limonene solvents were analyzed via molecular dynamics (MD) simulations. The influence of intermolecular interactions on the swelling degree of the EVA polymers had been examined to determine the dominant factors leading to the discrepancies in the diffusion state of EVA in different solvents. The molecular electrostatic potential (MEP) maps were utilized to explain the differences in interactions from a molecular structure perspective. Furthermore, the results of MD simulations were experimentally verified by solvent-immersion experiments and testing methods. Based on the results, the swelling mechanism of the EVA polymer in the selected solvents was proposed and illustrated, providing theoretical support for chemically-driven photovoltaic module recycling processes.