Ambient Pressure Drying to Construct Cellulose Acetate/Benzoxazine Hybrid Aerogels with Flame Retardancy, Excellent Thermal Stability, and Superior Mechanical Strength Resistance to Cryogenic Temperature

Cellulose aerogels are highly attractive
candidates in various
applications, such as thermal insulation, adsorption separation, biomedical
field, and as carriers, due to their intrinsic merits of low density,
high porosity, biodegradability, and renewability. However, the expensive
cost of the supercritical drying process and poor mechanical properties
limit their practical applications. Herein, a new method was presented
to fabricate cellulose acetate/benzoxazine hybrid aerogels (CBAs)
with low cost, low drying shrinkage, excellent mechanical properties
under cryogenic condition (−196 °C), outstanding thermal
insulation, flame retardancy, and good thermal stability by ambient
pressure drying. In more detail, the weighted drying shrinkage rate
of CBAs-T2 can be controlled to 6.8% (the average value along the
radial and axial directions), mainly due to the enhanced skeleton,
by introducing polybenzoxazine networking chains. The resultant CBAs-T2
exhibit outstanding mechanical properties at room temperature because
of the presence of the polybenzoxazine hybrid in the cellulose networking
system. CBAs-T2 still have good mechanical properties even after subjecting
them to liquid nitrogen treatment. In addition, the optimal value
of thermal conductivity (0.033 W m–1 K–1) is gained easily because of the uniform cross-linking networking
structure and small pore size. A superior flame retardance of CBAs-T2
is endowed to achieve self-extinguishment after ignition, which is
attributed to the presence of the aromatic ring in the backbone structure.
Moreover, the good thermal stability of CBAs-T2 is attributed to the
fact that polybenzoxazine components could resist the decomposition
of cellulose acetate and inhibit heat release during the combustion
process. Our study would provide a novel method for obtaining biomass
aerogels including the cellulose-based materials system with low drying
shrinkage and superior mechanical properties despite bearing a cryogenic
environment by the low-cost ambient pressure drying approach.