Evaluating the Green Solvent d-Limonene for Sustainable Chemical Delamination in Solar Panel Recycling

Abstract

Abstract. The expansion of solar energy has intensified concerns about the end-of-life management of solar panels. High-purity constituent materials can be recovered through chemical delamination, but conventional solvents such as toluene acid and nitric acid and hydrofluoric acids pose substantial environmental and health risks. We evaluate d-limonene, a biodegradable green solvent, for solar panel recycling by investigating its interaction with ethylene–vinyl acetate (EVA), the critical encapsulant layer in solar panels. This study focused on the dissolution and swelling kinetics of EVA samples with varying degrees of cross-linking in d-limonene. Results showed that the EVA dissolution behavior strongly depends on its degree of cross-linking. Linear EVA beads readily dissolved within 2.5 h at room temperature, whereas lightly cross-linked EVA films required elevated temperatures (∼70 °C) for dissolution. The highly cross-linked EVA used in commercial solar panels remained insoluble even at 70 °C, but exhibited substantial swelling. The swelling kinetics showed a linear relationship between the reciprocal swelling rate and time, indicating dominance by stress relaxation in the cross-linked structure. The swelling ratio reached approximately 2 after 90 min at room temperature. At 70 °C, the initial swelling rate increased by approximately sixfold, while the maximum swelling ratio increased marginally. This temperature-accelerated swelling enabled effective delamination and separation of solar panel fragments. Fourier transform infrared spectroscopy showed that characteristic peaks of filtered d-limonene after delamination were identical to those of pristine d-limonene, indicating negligible byproduct formation and allowing solvent reuse after simple filtration.