Thermomechanical Characterization of Recyclable Diels-Alder Epoxies with TiN Nanoparticle Loading

Typically, epoxy products are non-recyclable and difficult to remove. Recyclable epoxies were crosslinked by a Diels-Alder (DA) reaction between maleimide and furan functional group containing adducts (synthesized from polyetheramines and epoxide precursors). Epoxy variants studied include different architectures (4-arms or 6-arms) and different stoichiometric ratios of furan to maleimide. Titanium nitride (TiN) nanoparticles with significant visible light absorption were added for local, instant triggering of the rDA reaction by a high-intensity light source. Epoxies showed calorimetric glass transition temperatures in the range 0 to 30°C depending on molecular composition. High-temperature (~120°C) endothermic peaks corresponding to the rDA reaction were observed. In addition to the low temperature glassy phase, rheometry detected a rubbery plateau at moderate temperature followed by a rapid decrease in modulus indicative of liquid behavior. This high temperature (above ~140°C) decrease is a consequence of the rDA reaction depolymerizing the network. Lowering the temperature regenerates the network with a return of glassy and rubbery plateaus upon reheating. The incorporated TiN filler (<1wt%) slightly increased the modulus of the epoxies and permits localized heating.