Synthesis and properties of lightweight flexible insulant composites with a mullite fiber-based hierarchical heterostructure

•Porous fibrous composites with hierarchical heterostructure were fabricated.•The secondary structure of nanowhiskers grew uniformly on the mullite fibers.•The hierarchical structure offered the composites high specific surface area.•The porosity of the obtained nano-porous composites is high, up to 83.2%.•Composites possess a low thermal conductivity of 0.132 W/mK and good elasticity.

A novel mullite fibers-based hierarchical heterostructure were fabricated using a sol–gel method. The porous performs were fabricated by mixing the mullite fibers with the aluminum borate xerogel which is derived from the gelation of Al(OC4H9)3 and boric acid. After calcination, the preforms with different mole ratio of Al/B, transformed into the composites with hierarchical structures of the aluminum borate nanowhiskers/mullite fiber and alumina plate/aluminum borate nanowhiskers/mullite fiber. The formed aluminum borate nanowhiskers showed a uniform distribution on the mullite fibers, and the growth process may follow a self-catalysis mechanism. The fabricated hierarchical mullite fiber-based products possessed low density of 0.448 g/cm3, low thermal conductivity of 0.132 W/mK, high specific surface area of 230.7 m2/g and excellent elastic property with high compression-resilience of 92.7%, and were promising flexible insulant materials for the application in high-temperature heat sealing field.