Azodicarbonamide-derived crosslinkers for debonding on demand polysiloxane adhesives

Adhesives that enable debonding on demand through an external trigger are of great interest for the recycling and repair of bonded components. Among the various external stimuli that enable debonding, heat-induced debonding is particularly popular as it can be easily implemented in many applications. However, thermally activated debonding poses a particular challenge for polysiloxanes (silicones), as they lose their characteristic temperature resistance if the decomposition temperature is too low, whereas the debonding process requires too much energy if extensive heating to high temperature is required. In this work, moisture-curing crosslinkers based on an azodicarbonamide structural motif are used to enable the thermal decomposition of polydimethylsiloxane (PDMS) based adhesives. The crosslinkers decompose readily above 200 °C, thus cleaving the polymer network while simultaneously causing vigorous gas release, which in combination leads to foaming of the PDMS. In this way, the advantages of debonding by gas release and by decomposition of the polymer network are combined. Crosslinker content and debonding temperature are optimized, and the influence of the crosslinkers functionality on mechanical and debonding properties are investigated. An increase in the number of crosslinkable groups improves the mechanical properties and adhesive strength, while the debonding ability deteriorates as a higher crosslink density counteracts the foaming of the silicone. A decline in the silicone's tensile strength of up to 95% and in its tensile lap shear strength on glass by up to 94% can be achieved upon heating to 300 °C for 5 min or 10 min, respectively, enabling quick and simple debonding.