Closed-Loop Recyclable Polyhexahydrotriazine Aerogels Utilizing N,N-Dimethyl Lactamide as a Green Solvent

Organic aerogels, known for their lightweight, highly porous structure, and ultralow thermal conductivity, have shown great potential in thermal insulation, chemical absorption, and energy storage. However, most aerogels to date pose environmental concerns, as their permanently cross-linked scaffold makes recycling back to the original monomers virtually impossible. Additionally, the use of toxic solvents in aerogel fabrication raises further environmental and health concerns, challenging their sustainable application. Moreover, the development of next-generation organic aerogels requires the design of recyclable materials with improved mechanical properties. In response to these challenges, this study demonstrates the synthesis of chemically recyclable polyhexahydrotriazine (PHT) aerogels based on an amide containing aromatic diamine, utilizing N,N-dimethyl lactamide, a nontoxic and label-free solvent, as gelation medium. Hansen solubility parameters provide key insights into how solvent choice influences the morphology and properties of PHT aerogels. The resulting PHT aerogels exhibit low bulk density (≈63 mg cm^-3), high porosity (≈96%), excellent thermal insulation properties (≈17 mWm^-1 K^-1), and enhanced mechanical performance, all while being closed-loop recyclable. This work highlights the importance of solvent selection in tuning aerogel properties and demonstrates a green route for fabricating sustainable, high-performance thermal insulating materials.