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[Display omitted] • Lightweight polybenzoxazine (PBz) aerogels were fabricated by hexamethylene diisocyanate (HDI) modification. • The introduction of HDI formed a covalent-crosslinked structure with the chemical structure of the PBz aerogel. • The HDI-modified PBz aerogel demonstrates a self-extinguishing time of less than 1 s after removal from a 1200 °C flame. The rapid advancement of modern industries has imposed demands on thermal insulators that possess not only low thermal conductivities but also multifunctional properties. Polybenzoxazine (PBz) aerogels with several advantages have garnered considerable research interest in recent years. Nevertheless, PBz aerogels acquired from ambient pressure drying still confront the challenge of exhibiting relatively high densities and thermal conductivities. In this study, to enrich the category and propose practical ideas for overcoming the above plight, hexamethylene diisocyanate (HDI) was selected as an additive to prepare lightweight and efficient thermal-insulating PBz aerogels through chemical modification. Compared with the pristine specimens (0.268 g·cm−3, 0.0387 W·m−1·K−1), the HDI-modified PBz aerogels exhibited lower densities (0.237–0.256 g·cm−3) and thermal conductivities (0.0354–0.0370 W·m−1·K−1). Moreover, the introduction of HDI has been demonstrated to not impact their superior intrinsic flame retardance, despite an observed reduction in the residual char yields in the HDI-modified groups. Given these excellent properties, PBz-HDI aerogels are expected to be promising candidates for thermal insulation and fire resistance applications. [ABSTRACT FROM AUTHOR]

Chitosan aerogels could be applied potentially in thermal insulation for energy-saving buildings, separation/adsorption, and catalysis. However, disadvantages of chitosan aerogels include their hydrophilicity and low insufficient mechanical strength. Here we propose a silica-phase hybriding route to create chitosan/silica hybrid aerogels with a synergistic capability for favourable hydrophobicity and superior mechanical strength, demonstrating an emergent finding (hydrophobicity optimised with the improved mechanical strength). The aerogels exhibit low drying shrinkage (as low as 13.41 %), lightweight (lowest to 0.149 g cm−1), high-efficient thermal insulation (thermal conductivity as low as to 0.024 W m−1 K−1 at room temperature and normal pressure) either under cryogenic (−196 °C) or high-temperature conditions, exceptional fire-retardancy (self-extinguishing in 1.8 s) and environmentally friendly characteristic (initial mineralisation after 10 d). High hydrophobic property (water contact angle up to 142°) of the aerogels were achieved depending upon 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane of vapor deposition, presenting a discovery concerning substantial improvement of mechanical properties (up to 0.188 MPa at 5 % strain, increased by 25 %). Furthermore, we demonstrate that a plausible mechanism for simultaneous hydrophobic and mechanical enhancement is depending upon the modulation of networking skeletons at the nanoscale. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Polybenzoxazine aerogels with excellent thermal insulation property were fabricated by Lewis acid catalysis. • The self-extinguishing performance of PBz aerogels could be obtained apparently. • The aerogels as-prepared possessed a three-dimensional networking structure in the range of 20–140 nm. Polybenzoxazine aerogel is a new polymer aerogel material developed in recent years, which the ring-opening polymerization of benzoxazine monomer under high temperature or HCl could achieve the formation of cross-linked three-dimensional network structure so that to further reduce the cost of preparation. However, HCl as a catalyst has the disadvantages of easy volatilization and corrosion. Here we introduced Lewis acid as the catalyst for fabricating nanoporous polybenzoxazine aerogels with low density and self-extinguishing properties depending upon the evolution law for the influence of the mixed ratio of Lewis acid and hydrochloric acid (volume ratio) on the corresponding aerogels. The results show that PBz aerogels prepared in the mixed acid environment (with n -hexane as the exchange solvent) have a good three-dimensional nanopore network structure, and the pore size distribution is in the range of 20–140 nm. Additionally, the obvious self-extinguishing performance (even exposing to a flame at 1200 °C), low density and excellent mechanical properties are reflected as well, potentially suggesting the broad application prospects in the field of aerospace. [ABSTRACT FROM AUTHOR]