Synthesis and properties of carbon nanofiber reinforced polyimide composite aerogels

4, 4'-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) were used as monomers. Carbon nanofiber (CNF) was used as the reinforcing agent. CNF reinforced polyimide (PI) composite aerogels were prepared with acidified CNF (a-CNF) via sol-gel process followed by freeze-drying technology. The morphologies, thermal insulation, microwave absorption as well as compression properties of PI composite aerogels were characterized. The results show that the volume of PI composite aerogels is shrunk from 45.52% to 35.32%, and the density is decreased from 0.084 g/cm3 to 0.069 g/cm3 with the increase of a-CNF content. The composite aerogels exhibit bigger pore sizes and wider pore size distribution after the introduction of a-CNF as well. CNF in PI matrix play roles for reducing the shrinkage of PI composite aerogels, thereby the thermal conductivity is reduced. Additionally, the reflection loss (RL) of PI composite aerogel with 15%(mass fraction) of a-CNF (15% CNF/PI) reaches -9.7 dB at 8.3 GHz. This is due t