Preparation and properties of fiber-reinforced polybenzoxazine composite aerogels based on freeze drying and ambient pressure drying methods

Polybenzoxazine aerogels have gained much attention as a new type of polymeric aerogels in the field of flame resistant materials. Herein, a unique method for the preparation of fiber-reinforced PBa composite aerogels has been reported using polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) as dispersion carriers through freeze-drying for surface modified basalt fibers (Z@BF). Bisphenol-A type benzoxazine (Ba) monomer was used as the matrix, which infiltrated into the carrier for dispersed fibers to obtain a PBa composite gel by sol-gel method. Solvent exchange and ambient drying techniques were used to obtain the final composite aerogel samples. Z@BF formed a double-network structure with the aerogel matrix, which resulted in 55.43% increase in compressive strength, a low volumetric shrinkage (27.46%), and density (0.19-0.21 g cm3) of the prepared aerogel. The addition of Z@BF increased the residual carbon content (59.6% at 800 degrees C) in the aerogel, while reducing the total heat release rate by 36.9% and the peak heat release rate by 60.61%. Besides, the aerogels possessed excellent self-extinguishing property, and the self-extinguishing time was only 1.31 s after flame burning at 1200 celcius for 10 s. The composite aerogels obtained by this combination of atmospheric pressure drying and freeze-drying techniques not only possessed high mechanical strength and excellent flame retardant prop- erties, but also provided a new idea for the preparation of fiber -reinforced PBa aerogels. This would further expand the potential use of PBa aerogels in flame retardant materials.