Nanoporous Polybenzoxazine Aerogels for Thermally Insulating and Self-Extinguishing Materials in Aerospace Applications

Abstract

Phenolic-based aerogel composites possess particular characteristics, such as low thermal conductivity, light weight, and superior ablative properties, in near-space vehicles. However, their machinability and flammability require further improvement, hampering their application for high-performance thermal protection systems in the aerospace field. Here, we prepare nanoporous polybenzoxazine (PBO) aerogels with outstanding thermally insulating and self-extinguishing properties by an effective-cost ambient pressure drying (APD) approach rather than a conventional high-pressure supercritical drying pattern. The PBO aerogels are prepared by adopting different exchange solvents of tert-butyl alcohol, ethanol, and n-hexane. The results obtained indicate that PBO aerogels (with n-hexane as the exchange solvent) by APD have an optimal three-dimensional nanoporous network structure, a pore size distribution in the range 20−140 nm, an obvious self-extinguishing property (extinguished itself instantly despite exposure to a 1200 °C flame), superior thermal insulation (the cold surface temperature of the sample reached only 36.4 °C after 400 s despite its opposite surface existing at a 65.8 °C atmosphere), and excellent machinable properties (easy-to-form special-shaped sample). PBO aerogels are a great potential candidate material system for thermal protection systems in aerospace applications in the future.

Ambient-Dried, Ultra-high Strength, Low Thermal Conductivity, High Char Residual Rate F-type Polybenzoxazine Aerogel

“…It was found that this aerogel extinguished itself instantly despite exposure to the alcohol lamp (≈660 °C), like that reported by Xiong. 28 All these excellent properties enable the aerogels prepared to be used in aerospace and other fields.…”

“…The currently prepared PBO aerogels are often used as precursors for the preparation of char aerogels . They are also used in thermal insulation, adsorption, supercapacitors, medical hard tissue scaffolds, catalyst carriers, and other fields. − …”

Silicon‐containing polyarylacetylene aerogel with heat resistance and ablative property for high‐temperature insulation

“…Aerogels are highly cross‐linked porous materials whose complex three‐dimensional structures can effectively extend the heat transfer path, thereby affording excellent insulation. These materials have foreseeable advantages in heat insulation applications, such as low density, high porosity, and low thermal conductivity 13,14 . However, the use of common aerogels is usually limited in high‐temperature oxidation extreme environment such as aerospace.…”

Oxazine Ring-Substituted 4th Generation Benzoxazine Monomers & Polymers: Stereoelectronic Effect of Phenyl Substituents on Thermal Properties

“…Polybenzoxazine chemistry has evolved with time and altering the chemical structure of monomers showed profound potential in affecting polymer properties. Interestingly, introduction of additional functionalities besides a reactive oxazine ring in the monomers was helpful in achieving unusual properties and expanded their exploration from conventional to the unconventional domain of applications. − Benzoxazine monomers undergo catalyst-free ring-opening polymerization, albeit demands a very high temperature, which is currently an area of research interest to advance their industrial scalability. To circumvent this problem, two approaches are widely followed.…”