Polybenzoxazine Aerogels for Thermal Protection at Extremely High-Temperature/Cryogenic Conditions

Abstract

Polybenzoxazine (PBZ) aerogels are potential thermal insulation and ablative material for thermal protection system in aerospace. However, obtaining the excellent properties of thermal insulation and compression strength remain a formidable challenge at an extreme temperature. Here we proposed a new strategy by optimizing the nanoporous networking structure and pore size distribution to prepare PBZ aerogel (PAs-Fx), which could be self-extinguished in 0.24 s only once departing the outer flame, and the compressive stress of PAs–F10 reached up to 6.62 MPa at the strain of 10%. PAs–F10 presented great advantage in thermal insulation property (although the hot surface existed in the atmosphere at 302.4 °C, the temperature of cold surface remained at only 112.4 °C when heat flow was stable). Even burning the hot surface with 1200 °C outer flames for 30 min, the highest temperature of the cold surface only reached 254 °C at the heat balance state, moreover, the prominent shape-keeping property was confirmed after ultra-high temperature burning. We also found that PAs–F10 has superior compressive strengths which are 5.52 and 9.38 MPa at 10% strain in the conditions of ambient temperatures for 150 and −50 °C, respectively. PAs-Fx could also retain the excellent compression property after treating cryogenically in liquid nitrogen (−196 °C). The work would be a great promise in the application of ablative thermal insulation materials in a great measure in the future.