Optimized chemical methods for the recycling of multilayered and cross-linked polymers

The growing accumulation of polymeric waste represents a major environmental and industrial challenge. Layered or thermosetting materials are widely used thanks to their superior properties. Mechanical recycling is the simplest approach, but it typically leads to poor mechanical and physical properties. Therefore, chemical and mechano-chemical recycling are employed to recover raw materials necessary for the re-synthesis of new polymers. However, their application at an industrial scale is still limited, mainly due to high energy consumption and the need for complex and expensive equipment. The aim of this work is to explore the possibility of chemically recycling layered materials without prior sorting, such as polyurethane (PU) combined with polyamide 6 (PA6) or polyethylene terephthalate (PET). In addition, the recycling of thermosetting materials with no reactive functional groups, such as crosslinked polyethylene (XLPE)—which cannot be recycled through conventional chemical routes—was also investigated. The first project focuses on the chemical recycling of PU+PA6+PET through glycolysis and hydrolysis. Both conventional and microwave reactors were employed, aiming for rapid depolymerization under mild conditions. The best results were obtained from the hydrolysis approach, where PU was successfully hydrolyzed to obtain high yields of pure polyol, and PA6 depolymerization was achieved at relatively low temperatures. Finally, the combined hydrolysis of PU+PA6+PET confirmed the feasibility of simultaneously recycling different polymers in a single process. The second project investigates the recycling of XLPE through mechano-chemical reactions. In particular, the study aimed to understand whether depolymerization occurs randomly or selectively, using ultracentrifugal milling and reactive extrusion. Furthermore, the possible substitution of XLPE with a new class of materials, namely covalent adaptable networks (CANs), was explored. A two-step synthesis via reactive extrusion was proposed for the preparation of these materials. Together, these studies aim to improve the thermosetting polymer recycling in a more sustainable manner.