CO2 absorption into a polymer within a multilayer structure, the case of EVA in photovoltaic modules
Résumé
In the objective to develop an efficient circular economy with a low environmental impact in the photovoltaic field, the supercritical CO2 delamination of photovoltaic modules is an interesting alternative way. This paper describes the first phase of this process: the CO2 absorption into poly(ethylene-co-vinyl acetate) (EVA-28) in the photovoltaic multilayer structure. The melting temperature of EVA-28 in CO2 medium was determined by high-pressure differential scanning calorimetry for pressures ranging from atmospheric pressure to 150 bar. This thermodynamic phase equilibrium of the mixture EVA-28/CO2 was determined by the Sanchez-Lacombe EoS modified to take into account the crystallinity and the cross-linking of the polymer. This model was applied with great agreement to swelling experiments for pressures ranging from 60 to 200 bar at temperatures of 60, 75 and 90°C. The diffusion coefficient of CO2 into EVA-28 was determined in the same conditions ranging at 130 bar, from 4 x10$^{-9}$ m$^2$.s$^{-1}$ (60°C) to 7x10$^{-9}$ m$^2$.s$^{-1}$ (90°C). The impact of different interfaces of photovoltaic modules on the CO2 diffusivity into the EVA-28 was studied by an original method of apparent length of diffusion post treatment. This experiment demonstrated a preferential diffusion at the rear side of the cell interface due to an important porosity and at the “backsheet” interface due to favourable interactions