Ultra-high strength, highly deformable and superhydrophobic polybenzoxazine@cellulose nanofiber composite aerogel for thermal insulation

The poor mechanical properties of aerogels such as low strength and high brittleness are a century problem that has not been solved so far, and the existing structural design, structural composite and structural strengthening methods are far from meeting the requirements. In this study, we prepared a polybenzoxazine@cellulose nanofiber composite aerogel, which solved this problem in a more comprehensive way. Due to the special core–shell separation failure mechanism and the physical adhesion, reversible sacrificial hydrogen bonding force and irreversible chemical bonding force strengthing the interface between cores and shells, the resulting huge energy dissipation mechanism gives the aerogel an ultra-high strength (41.8 MPa at density 0.234 g/cm3). 1D building blocks impart an excellent deformability (fracture strain 83.8 %) and a fatigue resistance (10000 load-unload cycles at 60 % compression strain with almost no plastic deformation). The high-porosity mesoporous interconnected structure (88.7 % and 46.7 nm) results in low thermal conductivities (0.02943 W/(m·K) at 25 ℃ and 0.04846 W/(m·K) at 300 ℃). The resulting nanoscale lotus effect contributes to a superhydrophobicity (hydrophobic angle 162.7°) and a long-term hydrophobic stability (saturated mass moisture absorption rate 0.25 %). These integrated properties make it an ideal thermal insulating material for use in extreme environments, especially those with stringent requirements for integrated mechanical properties and hydrophobic properties.