Minimal aramid nanofiber interfacial densification enables mechanically robust and fire-safe cellulose nanofiber aerogels

Cellulose nanofiber (CNF) aerogels are promising sustainable porous materials, but their mechanically weak sheet-like networks and intrinsic flammability limit practical deployment under demanding conditions. Herein, we report a minimal-polymer interfacial densification strategy that uses only approximately 2 wt% aramid nanofibers (ANFs) to reinforce and fire-protect CNF aerogels. Through an in situ sol–gel–coating process, the ANF sol is converted into a compact interfacial coating on CNF sheets, yielding a hierarchical ANF–CNF–ANF sandwich skeleton that stabilizes weak inter-sheet junctions while preserving the ultralight porous structure. This optimized skeleton endows the aerogel with a compressive strength of 219 kPa and a modulus of 618 kPa, corresponding to 2.6- and 15-fold improvements over pristine CNF aerogel, respectively, while maintaining a low thermal conductivity of 37.1 mW m −1  K −1 . The ANF-modified aerogel also exhibits self-extinguishing behavior, an increased limiting oxygen index, and reduced heat and smoke release, demonstrating improved fire resistance. This study provides a facile minimal-polymer interfacial engineering route for developing mechanically robust, fire-safe, and thermally insulating bio-based aerogels.