Photothermal Enhancement Effects of Plasmonic Nanoparticles on Diels-Alder Reactions towards The Development of Solar Light Enhanced Recyclable Epoxy

Thermosets are suitable candidates for vast range of applications such as in adhesives, electronics, automotives, aerospace, and household devices due to their superior mechanical properties, high chemical resistance, and thermal stability. However, irreversible crosslinking of thermosets poses problems for their recycling. We have developed light mediated recyclable epoxy incorporating thermo-reversible covalent adaptable network (Diels–Alder (DA) reactions) into it and mixing that with refractory plasmonic titanium nitride (TiN) nanomaterials. Plasmonic TiN nanomaterials can absorb broad spectrum visible light to generate localized heat to drive Diels-Alders reactions enabling reversible polymerization and depolymerization. Nanoparticles loading and their dispersion in the polymer matrix is optimized to maximize their photothermal efficiency. It was found that these nanoparticles can absorb visible light to drive the Diels–Alder (DA) reactions efficiently to reversibly liquefy the epoxy for reprocessing. We used in situ FTIR to study the kinetics of Diels Alder reactions driven by photothermal effects and compared that with conventional heat driven reaction kinetics. One of our key findings is that the kinetics of Diels-Alder reactions are significantly different with light induced photothermal heat generation in comparison to conventional heating even though the bulk temperature of the sample is similar. This indicates the local heat generation around the nanoparticles and the interaction of reactants with nanoparticles may affect the Diels-Alder reactions differently than the bulk heating. Further studies are being done to understand the exact mechanisms behind the photothermally induced Diels-Alder reactions.