Effect of carbon nanofibres dispersion on the microwave absorbing properties of CNF/epoxy composites

Since mid-twentieth century filled polymers have been largely studied for electromagnetic (e.m.) applications, including wave absorbing materials, showing good promise. A certain knowledge was gained in the field of carbon particles filled polymers, even if there is still a lack of understanding the relationship between material microstructure and macroscopic electromagnetic performance. Moreover, the recent discover of carbon nanofibres and nanotubes, with their potentiality, introduces new field of investigation. In this work carbon nanofibers were used to increase permittivity of neat resin, in order to achieve better absorbing performance in the 8–20 GHz range. Carbon nanofibers were chosen as a way of lowering filler content, while increasing the dielectric properties of the resulting composite. Key factor is the nanofiller dispersion process: in this paper two different dispersion methods were used, both employing an organic solvent that was removed either via evaporation or filtration. The resulting microstructures, composed of well dispersed CNF as well as of microaggregates, lead to materials that, on equal filler content, present different dielectric properties and absorbing performance. Microstructures were analyzed by SEM.