From waste to new polymeric compounds: recycling of crosslinked EVA, PE, and PU foams for circular economy applications

This thesis work is the result of an internship carried out at SETA polymers S.r.l and focused on the formulation and characterization of new polymeric compounds developed from post-industrial waste, aiming to promote a sustainable and circular approach in the plastic sector. Specifically, composite materials based on expanded cross-linked ethylene-vinyl acetate (EVA) and polyethylene (PE) were obtained by reintroducing the thermoset polymer residues into their respective virgin thermoplastic matrices, whereas polyurethane (PU) residues were exclusively combined with an EVA matrix. Furthermore, given the compatibility between EVA and PE, the combination of EVA residues into a PE matrix was also investigated. These selected post-industrial waste materials were processed through a combined physico-chemical and mechanical recycling approach. The process involved an initial grinding and powdering phase, followed by a specific treatment of the resulting powders and a subsequent reactive extrusion step with the virgin polymer. This well-established yet newly applied process, already patented, has been named REVERSEVA. The formulated compounds were characterized by melt flow index (MFI), hardness, and particle size analysis of the powders, to identify the optimal polymer blends, particularly in terms of processability. To further investigate the matrix–particle interface, which represents the core concept of the material’s functionality, tensile tests and optical microscopy images were performed. The results have shown that, thanks to an effective interfacial adhesion between the phases, it was possible to achieve recycled content levels of up to 45 wt% in the final compounds. Furthermore, for EVA and PE-based compounds, moulding trials were carried out to produce a potential end-use product, corresponding to the same type of item from which the original waste had been derived. The companies involved in this prototyping phase conducted additional laboratory tests on the final products, which confirmed both the quality of the recycled compounds and their reliable performance during subsequent industrial processing, thereby demonstrating their applicability within a circular economy framework.