Ice-Templated Anisotropic Flame-Resistant Boron Nitride Aerogels Enhanced through Surface Modification and Cellulose Nanofibrils

High-performance and lightweight fire-resistant structural materials with high thermal insulating and mechanical strength are desired for thermal management in many fields, such as energy-efficient buildings and aerospace. In this work, a fire-resistant aerogel with well-aligned channels, composed with l-glutamine-grafted boron nitride nanosheets (BNNSs-g) and cellulose nanofibrils (CNFs), has been developed with ice-templating methods. The vertical combustion level in the lateral direction of the aerogel reached the highest 5VA level, which is much higher than that of most of the reported aerogels containing CNFs. Additionally, attributed to the excellent mechanical strength of CNFs and the strong interaction between the CNFs and surface-functionalized BNNSs-g, the aerogel possessed excellent mechanical stability. Due to the aligned structure, the thermal conductivity of the aerogel was 28.4 mW m^–1 K^–1 in the lateral direction and 83.3 mW m^–1 K^–1 in the axial direction, demonstrating an anisotropic thermal insulation property. This environmentally friendly, lightweight, thermally insulating, and fire-resistant aerogel, therefore, is promising for reducing thermal loss and increasing environmental safety. The fabrication of anisotropic CNFs/BNNSs-g aerogels could thus guide the development of high-temperature structural materials.