Wang Zhan

The rapid development of science has led to an increasing demand for lightweight and high-performance composite materials. Aiming at the dual requirements of thermal insulation and microwave absorption in the field of aerospace, this paper first clarifies the mechanism of heat insulation and microwave absorption. Secondly, five representative bifunctional aerogel systems are introduced. This paper mainly focuses on the recent research progress of the thermal insulation and microwave absorption bifunctional composite aerogels. Finally, challenges and future perspectives of the current thermal insulation and microwave absorption composite integrated aerogels are discussed.

Gelatin (GA) was used as a reinforced material in the study to enhance the thermal-mechanical properties of the polyimide (PI) aerogel. The effects of the content and the freezing rate on the thermal-mechanical properties of the composite aerogels were investigated. The internal structure and chemical composition of the composite aerogels were analyzed by using characterization methods. Finally, the mechanism of enhancement of thermal-mechanical of the composite aerogels is further discussed. The results show that GA can effectively enhance the thermal-mechanical properties of PI aerogel, and the appropriate freezing rate can form a dense pore structure inside the composite aerogel to reduce the thermal conductivity and improve the mechanical property. Moreover, the thermal runaway protection result demonstrated that the composite aerogel significantly delayed the time of thermal runaway of the lithium battery.

To expand the utilization of bio-based materials as flame retardants in epoxy resin (EP), a green Schiff base structural material (CSV) was synthesized via a one-pot approach employing chitosan and vanillin as the raw materials. Then, the CSV combined with 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO) (the mass ratio between CSV and DOPO was 1:2, written as CSV-DOPO) improved the flame retardancy of the EP. When the amount of CSV−DOPO in the EP was only 3 wt%, the thermogravimetric analysis (TGA) results indicated that the residue of the EP composites was 50.6% higher than that of the EP. The combustion class of the EP/3 wt% CSV−DOPO composites achieved a UL-94 V0 rating and the limit oxygen index (LOI) reached 34.0%. The cone calorimeter test (CCT) showed that the peak heat release rate (PHHR), total heat release (THR), total smoke release (TSP), and peak carbon dioxide production (PCO₂P) of the EP/3 wt% CSV−DOPO composites decreased by 32.3%, 22.0%, 4.6%, and 51.0%, respectively, compared to the EP. The flame-retardancy mechanism was studied by scanning electron microscopy (SEM) and Raman spectra. The quenching effect of phosphorus-containing radicals, the dilution effect of noncombustible gases, and the impeding effect of the carbon layer in the condensed phase contributed collectively to the excellent flame retardancy of the EP/CSV−DOPO composites. Considering the facile preparation method and small addition amount of the flame retardant, the present work provides a convenient solution for the preparation of modified EP with good flame retardancy and heat stability, which is expected to be widely used in industries.