Closed‐Loop Recyclable Polyhexahydrotriazine Aerogels Derived From PET Waste

Abstract The global plastic waste crisis stems from unsustainable design and a linear economy that leads to massive environmental pollution. Polyethylene terephthalate (PET), widely used in packaging and textiles is one of the primary contributors to this issue. While mechanical recycling of PET results in degraded material quality, chemical recycling offers a promising alternative, enabling the transformation of PET waste into valuable monomers and precursors. In this study, postconsumer PET waste is chemically upcycled into bifunctional aromatic amine that can serve as an effective building block for polyhexahydrotriazine (PHT) aerogels. Additionally, terephthalamide moieties incorporated into the molecular design, enhance the formed network by hydrogen bonding. The resulting PHT aerogels exhibit low density, high mechanical robustness, and outstanding thermal insulation properties. More importantly, these novel PHT aerogels are designed for recyclability, enabling depolymerization under aqueous acidic conditions and efficient monomer recovery in high yield and purity. The recycled monomer can then be immediately reused to produce new aerogels with nearly identical material properties. This work highlights the potential of upcycling plastic waste into sustainable thermally superinsulating materials designed for a circular economy.