Thermally reversible prototype adhesive via the furan–maleimide Diels–Alder reaction

Abstract

The development of structural epoxy adhesives with the capacity to bond and de-bond on-demand would open many opportunities for the assembly, inspection, repair, and end of life disposal of structural bonded assemblies. Herein, a reversible cross-linking mechanism enabling bonding and debonding of an epoxy adhesive based on Diels–Alder (DA) chemistry is investigated and demonstrated. The Diels–Alder incorporated multifunctional diamine cross-linker was initially synthesised, followed by forming a covalently cross-linked network with DGEBA epoxy at low temperature (80 °C) that breaks via cleavage of DA adducts at elevated temperature (150 °C). Upon cooling the covalent cross-links reform enabling the epoxy to retain adhesive properties, and the bonding/de-bonding effect was performed over two complete cycles advancing a thermally reversible adhesive based on the retro-DA mechanism. The viscoelastic properties of the prototype adhesive including viscosity, storage and loss modulus were retained after bonding and de-bonding cycles, affirming retro-DA reaction occurs at about 150 °C upon heating cycle and DA reaction upon cooling cycle. Mechanical testing demonstrates maximum of 39.5% reduction in bond strength in debonding cycle, followed by maximum of 100% bond strength in re-bonding cycle with no additional application of the prototype adhesive, revealing excellent adhesive performance.