Scalable Liquid‐Phase Exfoliation of h‐BN for Solar‐Reflective and Thermally Stable Polymer Aerogels

Efficient materials for temperature‐resistant barriers are crucial for future energy‐conscious applications. Aerogels, with their porous structure and tunable composition, represent a promising class of materials for advanced heat barriers, achieving optimal thermal insulation and solar radiation reflection under extreme conditions. In this study, composite aerogels are fabricated using three polymer matrices polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and hydroxyethyl cellulose (HEC) reinforced with exfoliated hexagonal boron nitride (h‐BN) nanosheets. The h‐BN flakes are synthesized using a high‐pressure homogenizer (HPH) to obtain stable, homogeneous dispersions within the polymer matrix. Varying the h‐BN content from 0 to 50 wt% induces a transition from open, interconnected porous networks to densely packed structures, strongly affecting optical, thermal, and mechanical performance. The PVA‐based aerogel with 20 wt% h‐BN shows the best overall performance, achieving 95.5% solar reflectance and an ambient surface temperature reduction of ≈10 °C under 1 sun. CMC and HEC aerogels also exhibit enhanced solar reflectance and thermal stability. Compression testing reveals mechanical strengths up to 200 kPa while maintaining thermal stability to 250 °C. These results highlight HPH‐assisted h‐BN exfoliation and polymer hybridization as an effective route to lightweight, scalable, and high‐performance aerogels for next‐generation energy‐efficient barriers.