Plasticization study on recycled cross-linked EVA encapsulant films from PV module

This study proposes an efficient recycling model for cross-linked EVA materials (X-EVA) collected from retired photovoltaic (PV) modules. The recycled X-EVA raw materials were plasticized by synergistic degradation and lubrication mechanisms. In detail, X-EVA materials experienced chain scission by strong physical shear, with the disruption of the cross-linked network and the creation of active free radicals. The peroxide additives further decomposed to produce peroxyl radicals (RO^•), cleaving X-EVA network into relatively low-molecular-weight aggregates and generating additional active X-EVA radicals (X-EVA^•). Concurrently, polypropylene (PP) in the formulation was activated to a large number of PP-based tertiary carbon radicals (PP^•), permeating the molten system and grafting with X-EVA active chains. Meanwhile, degraded PP acted as an internal lubricant to enhance the melt flow of the recycled composition, namely Circular Recycled EVA (CR-EVA). The melt index (MI) of CR-EVA materials exhibited significantly high flow rate up to 20.5 g/10 min, in contrast to the initial resins (MI < 0.1 g/10 min). Rheological analysis indicated that the CR-EVA materials achieved a critical gel state under low-frequency conditions, as opposed to the virgin X-EVA materials. XPS and FTIR analysis for CR-EVA's extracts verified partial de-crosslinking of X-EVA network and the formation of graft copolymers. The compounds of CR-EVA-modified PP materials were evaluated, exhibiting excellent dispersion and interfacial compatibility. This study provides a novel approach for the value-added recycling of EVA from discarded PV modules.​.