REDONDO (Reversibly Designed Cross linked Polymers) is a Horizon Europe project that aims to produce recyclable, reversibly cross-linked polyethylene. Indeed, cross-linked polyethylene is a difficult to recycle material. REDONDO aims at achieving a fully reversible cross-linking process that will enable the production of sustainable-by-design cross-linked polyethylene and that can further be applied to other cross-linked polymers.

Polyethylene is the most widely used plastic. Cross-linked PE (PEX) exhibits significantly improved properties, notably in terms of thermal stability, chemical resistance and structural integrity. As a result of cross-linking, PEX can be used in a number of applications for which PE naturally lacks required properties related to temperature, strength, chemical resistance, etc.. PEX has now a wide range of applications, such as insulation material for electric wires and cables and in the production of pipes for hot and cold-water and heating systems (PEX accounts for 60% of plastic pipes), replacing potentially toxic materials, such as poly(vinyl chloride) or copper (for pipes). However, due to the existence of cross-links, PEX cannot be melted and recycled/reused and is generally downcycled as a filler in other thermoplastic blends.

REDONDO aims to achieve a fully reversible cross-linking process, that will enable the synthesis of reversibly cross-linked polyethylene (rPEX), that will be inherently recyclable and thus sustainable-by-design. Additionally, innovative biobased/green additives will be used to confer to rPEX novel/improved properties. Overall, rPEX will obtain significant added value due to its recyclability and its lower toxicity, compared to the use of traditional PVC-based polymeric materials or expensive and non-recyclable PEX.