(368h) Optimizing Composition and Solar Light Conditions for the Reversible Diels-Alder Reaction in Titanium Nitride Nanoparticle-Laden Epoxy

Thermoset polymers such as epoxy resins have been used extensively in coatings, structural, electronics, and adhesive applications. Unlike thermoplastic polymers, the end-of-life products of these polymers cannot be repaired or recycled simply by applying heat as this will cause the material to be damaged rather than melt. We synthesized a reversible epoxy containing Diels-Alder adducts that is capable of depolymerizing at higher temperatures and repolymerizing at lower temperatures, allowing the epoxy to become recyclable. Additionally, photothermal plasmonic titanium nitride nanoparticles are incorporated to the epoxy matrix. When irradiated with solar light, the nanoparticles will induce heating at the nanoscale that is rapidly delivered to the Diels-Alder adducts, causing quick depolymerization in a specific area if desired. These epoxy composites were irradiated with different levels of light intensity from a solar simulator; light intensity was varied at different levels ranging from 2.445 mW/cm² to over 500 mW/cm². Reversible epoxies/nanoparticle composites containing different wt.% of TiN nanoparticles (0, 0.2, 0.5, and 0.7 wt.%) were tested for their light absorbance as well as photothermal efficiency. Optical microscopy is used to study the in situ melting of the epoxy composites under solar simulator. Both the nanoparticle loading as well as the light intensity were optimized to determine the optimal conditions for melting, which is important for the reprocessing and recycling of the epoxy. Results indicate that solar light concentrated with a lens can produce sufficient intensity to melt TiN nanoparticle-laden epoxy. In some cases, the sample showed signs of melting after 10 seconds of exposure to light, and at a temperature around 90ËšC. Such findings suggest that this procedure could be increased from the laboratory scale and used to extend the lifetime or recycle products.