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.