Decapsulating waste photovoltaic laminated modules using a green solvent terpinolene coupled ultrasound: directional bond cleavage and infinite swelling of EVA

Decapsulation constitutes the critical initial phase in the recycling of waste photovoltaic (PV) laminated modules. Wet decapsulation has emerged as a prominent research focus. However, the underlying removal mechanisms of ethylene-vinyl acetate (EVA) encapsulants remain insufficiently characterized, and the optimal solvent has not been selected. This article introduces a green alternative solvent terpinolene to decapsulate waste PV laminated modules. The decapsulation parameters were optimized. The waste PV laminated modules could be completely decapsulated under the identified optimal conditions: 2 cm × 2 cm specimens treated with 90 wt% terpinolene solvent under 800 W ultrasound agitation for 55 min. This study reveals the decapsulation mechanism: the ultrasonic field caused the water and terpinolene to produce O· and groups containing methylene radicals. The free radicals approached the directional C-C and C-O bonds in the bridging structure and the directional C-C bonds in the backbones of EVA and oxidized them to make them interrupt and to be grafted. EVA molecules were broken into multiple and smaller organic molecules, resulting in a swelling effect and loss of viscosity, thus prompting the laminated modules to decapsulate. We report for the first time the use of the green solvent terpinolene coupled to ultrasonic efficiently decapsulating waste photovoltaic laminated modules. And this study pioneers the discovery of the infinite swelling induced by terpinolene-mediated radical reactions in PV EVA encapsulants. It provides scientific information and key technologies for the decapsulating of waste PV laminated modules, the recycling of materials and the closed-loop development of PV industry.