Polyurethane adhesives with thermoreversible Diels Alder (DA) bonds offer a sustainable approach to improve recyclability of multilayer packaging. This study evaluates the effect of graphene, used as an internal heater to trigger bond breakage, on the mechanical properties by indentation and shear rheology. Particular attention is paid to their reversibility and cyclability upon thermal heating or IR irradiation. Graphene initially reduces the modulus by disrupting network formation resulting in reduced DA bond incorporation and crosslink density. The intrinsic properties of graphene counterbalance this effect at higher loadings. Rheology shows that graphene accelerates the retro-DA reaction during conventional thermal heating. Indentation tests indicate that IR expo- sure temporarily reduces the mechanical properties, with full recovery after 100 min. Both rheological and indentation methods show improved mechanical properties (modulus and hardness) after the initial retro-DA reaction, which stabilise after further thermal treatments and are related to the formation of a new network structure.

This project has received funding from the Bio Based Industries Joint Undertaking (BBI-JU) under the European Union’s Horizon 2020 research and innovation program under grant agreement Nº 837715. The authors wish to thank the MICIU/AEI/10.13039/501100011033, Spain, for funding under grants PID2019-107710 GB-I00, PID2020- 117573 GB-I00. Project PIE202250E035 (CSIC) is also acknowledged. The TEM-BIOPHYM Service at the IEM-CSIC is acknowledged for granting the use of the rheology facilities.

This article is part of a special issue entitled: POLY-CHAR 2024 published in Polymer

Peer reviewed