Thermal Insulation\nand Flame Retardancy of the Hydroxyapatite\nNanorods/Sodium Alginate Composite Aerogel with a Double-Crosslinked\nStructure

Abstract

As advanced thermal management materials, aerogels have\ngreat research\nvalue in the fields of engineering insulation, pipeline transportation,\nand packaging insulation. The composite interaction of the two-phase\ninterface and the construction of a porous structure have an important\nimpact on the thermal properties. Herein, a novel HANRs/SAB composite\naerogel was prepared using sodium alginate (SA) with hydroxyapatite\nnanorods (HANRs), combined with boric acid crosslinking and freeze\ndrying. In the prepared sample, the calcium ions in HANRs and SA formed\nthe first layer of binding force and the chemical crosslinking of\nsodium alginate with boric acid formed the second layer of strong\nbinding force, which effectively supported the skeleton of the aerogel\nand enhanced the overall mechanical properties. The modulus and maximum\ncompressive strength of the obtained HANRs/SAB aerogel were 2.39 and\n0.75 MPa, respectively, while the bulk density was 0.038–0.068\ng·cm^–3. Based on the prominent physical structure,\nthe as-prepared HANRs/SAB aerogel exhibited good thermal insulation\n(∼35.15 mW·m^–1·K^–1) and outstanding flame retardant performance. Flame-retardant boric\nacid and high-thermal stability HANRs could effectively prevent heat\ntransfer and organic combustion, thus resulting in an extremely low\nsmoke gas release (11.3 m² m^–2). Therefore,\nthe low-cost biopolymer composite aerogel based on a crosslinking\nstrategy has broad application prospects in the field of thermal insulation\nand flame retardancy.