Experimental Investigations for Recycling and Characterisation of EVA, PVF and PET Polymers from Waste Photovoltaic Modules

Abstract

Photovoltaic (PV) modules are highly efficient and non-polluting power generators associated with solar energy. Recently, PV has attracted incessant attention due to its potential application in alternative energy generation. The rapid growth of the photovoltaic industry will lead to a sharp increase in the waste that is generated from PV panels. The most common silicon solar cells (close to 90% of the PV market) have a 20–30 years lifespan on average. The amount of PV e-waste will rise to globally 60–78 million tons and degraded PV modules to produce 10% of all electronic waste by the 2050 year are predicted [1]. However, electro-waste can be successfully used as a source of secondary materials.In this study, a unique procedure for recycling waste PV modules that differed from previous investigations was developed [2,3]. The first stage in recycling PV modules was to remove the aluminium frame and junction box, 18 %wt. and 1 %wt. of the module, respectively, which is typically done mechanically. The following stage was crucial, involving a mechanical-thermal method to remove the tempered glass, that accounts for 70 %wt. of the PV module. As a result, only 11 %wt. of the initial mass of the PV to the further stage of chemical delamination was subjected, which reduces the amount of solvents used. Among the aromatic and cyclic hydrocarbons, the solvents that best swelled the ethylene vinyl acetate, EVA encapsulate and allowed separation of the PV module were selected. In the next stages of the research, optimal conditions for the swelled EVA were selected. The effects of temperature, mixing and ultrasound on the separation time of different fractions were investigated. After the separation process of the laminated PV modules, a fraction of crushed silicon cells, metal ribbons (busbar, tabbing), EVA copolymer and backsheet was obtained. Silicon cells require further thermal treatment, pyrolysis to remove EVA copolymer contaminants. The metals can be recovered by chemical methods proposed in the literature [4]. The backsheet was separated from the EVA copolymer and was formed from polyethylene terephthalate, PET and polyvinylidene fluoride PVDF polymer layers. The purity of the recovered polymers were determined by analytical chemistry, FTIR spectroscopy, ED-XRF X-ray fluorescence spectroscopy and elemental analysis. Physiochemical properties were measured using the DSC calorimetry in order to determine the basic parameters of the material, i.e. the temperature of glass transition. The presented research techniques allow to fully characterize the recovered materials and indicate the direction of further development, as well as determine reuse in new photovoltaic modules.This work sheds a new light on safety of environment and safe use of electronic waste materials that are properly separated and treated. Xu, Y.; Li, J.; Tan, Q.; Peters, A.L.; Yang, C. Global Status of Recycling Waste Solar Panels: A Review. Waste Manag. 2018, 75, 450–458.Xu, X.; Lai, D.; Wang, G.; Wang, Y. Nondestructive silicon wafer recovery by a novel method of solvothermal swelling coupled with thermal decomposition. Chem. Eng. J. 2021, 418, 129457.Tembo, P.M.; Heninger, M.; Subramanian, V. An Investigation of the Recovery of Silicon Photovoltaic Cells by Application of an Organic Solvent Method. ECS J. Solid State Sci. Technol. 2021, 10, 025001Zante, G.; Rivera, R. M.; Hartley, J.M.; Abbott, A. P. Efficient recycling of metals from solar cells using catalytic etchants. J. Clean. Prod. 2022, 370, 133552.