Hierarchical construction of a superhydrophobic and superior intrinsically flame-retardant phosphorylated...

The practical deployment of cellulose aerogels in the thermal-insulation fields is severely constrained by their inherent hygroscopicity, flammability, and fragility. Integrating superior flame-retardancy with superhydrophobicity in cellulose-based aerogel remains a significant challenge. Herein, phosphorous-containing microcrystalline cellulose (PMCC) was utilized as an intrinsically flame-retardant bio-based matrix, and a hierarchical organic-inorganic network was engineered via methyltrimethylsilane crosslinking coupled with in situ self-assembly of modified silica (MSiO₂) nanoparticles. The resulting MPMCC-MSiO₂ composite aerogels featured a hierarchically multiscale porous architecture in which MSiO₂ and poly(methylsilsesquioxane) (PMSQ) micro/nanoscale particles were uniformly integrated throughout the coarse three-dimensional pore matrix framework. This configuration of the MPMCC-MSiO₂ aerogel enabled superhydrophobicity across different cross-sections with excellent self-cleaning, achieving water contact angles (WCA) up to 151°. Moreover, the organic-inorganic dual crosslinked network significantly reinforced mechanical performance, delivering compressive moduli of MPMCC-MSiO₂-2 reaching 5.50 MPa, corresponding to enhancements of 491.4% relative to PMCC aerogel. Notably, the limiting oxygen index (LOI) of the MPMCC2-MSiO₂-2 aerogel increased from 36.8% for the PMCC aerogel to 60.0%, attributed to the phosphorus/silicon synergistic flame-retardant effect. The integration of ultra-high flame-retardancy, superhydrophobicity, and structural robustness renders this MPMCC-MSiO₂ bio-based composite aerogel promising for advanced, sustainable thermal insulation applications.