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.