Lightweight, High-Strength, and Anisotropic Structure Composite Aerogel Based on Hydroxyapatite Nanocrystal and Chitosan with Thermal Insulation and Flame Retardant Properties

Advanced thermal management materials with low thermal
conductivity
and robustness have been a research hotspot for energy conservation
and sustainable development. However, the brittleness of inorganic
materials and the high flammability of polymers remain a challenge
for industrial applications. Herein, we demonstrated a novel strategy
to fabricate an organic/inorganic composite aerogel based on a combination
of hydroxyapatite (HAP) and chitosan (CS). The combination of chemical
cross-linking and unidirectional freeze-drying methods can significantly
improve the mechanical properties and thermal stability, and the obtained
anisotropic microstructure has a significant effect on thermal conductivity.
Compared with the uncross-linked HAP-Si/CS composite aerogel, the
cross-linked HAP-Si/CSG composite aerogel has high mechanical strength
(0.82–2.37 MPa) and high specific modulus (41.22–129.20
kN m kg–1). In addition, the as-prepared HAP-Si/CSG
composite aerogel exhibits a lower radial-direction thermal conductivity
(28.16–37.43 mW m–1 K–1) than that of the axial direction. Meanwhile, the composite aerogel
constructed by the HAP nanostructure embedded in the CS sheets better
limits the heat transfer and blocks the combustion of organic compounds,
showing excellent fire resistance. Thus, the biomass-based composite
aerogel will be a sustainable and renewable functional material with
high mechanical properties and thermal insulation, which is further
expected to promote the high-value utilization of biopolymers.