Carbon fibers brominated with bromine cold plasma and liquid bromine for shielding applications: effect of the bromination method on microwave absorption characteristics

Brominated polyacrylonitrile-based carbon fibers (PAN CFs) were obtained by bromination with low-temperature bromine plasma and liquid bromine. The brominated PAN CFs with different bromine concentrations demonstrated different thermal stability and carbon surface oxidation. Besides, the bromination changes the microwave properties of PAN CFs in the X and Ka bands. The magnitude of losses S21 and the voltage standing wave ratio (VSWR) showed complex dependencies on the bromine concentration and the bromination method used. Typically, adding more bromine degrades the shielding properties but improves the VSWR in the Ka-band.