Polybenzoxazine/Silica Hybrid Aerogels for Thermally Insulating Ablation

Lightweight microablation thermal protection materials are one of the crucial factors contributing to the rapid development of next-generation aircrafts. However, the maintenance of a high mass residual and long-term antioxidant capacity of the matrix after bearing high-temperature aerobic environments remains a major challenge. Herein, we put forward a strategy for constructing polybenzoxazine/silica hybrid aerogels depending on the introduction into silica inorganic phases by different technologic preparation routes, possessing excellent thermal insulation, superior self-extinguishing properties, and outstanding thermal stability. In detail, the mass residual rate of polybenzoxazine/silica aerogels (PSAs) as-prepared could reach up to 40.19%, mainly due to the reinforced networking structure by the introduction of silica that would be preserved well due to the inorganic phase nature in the high-temperature oxidizing environment. The pore size of polybenzoxazine/silica/chitosan aerogels (PSCAs) is mainly distributed within 5–35 nm, which contributes to obtaining a low thermal conductivity (0.037 W m–1 K–1) due to the pore size being smaller than the mean free path of stationary air at normal temperature and pressure. PSAs and PSCAs both exhibit excellent self-extinguishing properties, attributed to the presence of a large number of aromatic ring structures and the introduction of the silica inorganic phase in polybenzoxazine itself. The microscopic morphology, crystalline shape, and Si-related chemical bonding of PSAs did not significantly change after muffle thermal treatment, including the three-dimensional network structure composed of polybenzoxazine and silica. This study provides a kind of approach for designing a thermal protection material matrix with high mass residual and excellent thermal insulation performance in the aerospace field.