Lightweight, covalent-crosslinked, and ambient-dried polybenzoxazine aerogels for fire resistance and thermal insulation

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 thermalinsulating PBz aerogels through chemical modification. Compared with the pristine specimens (0.268 g center dot cm- 3, 0.0387 W center dot m- 1 center dot K- 1), the HDI-modified PBz aerogels exhibited lower densities (0.237-0.256 g center dot cm-3) and thermal conductivities (0.0354-0.0370 W center dot m- 1 center dot 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.