Electromagnetic Interference Shielding of Carbon Fibers Oxidatively Brominated in the Liquid-Phase

Polyacrylonitrile carbon fibers (PAN CFs) were oxidatively brominated in the liquid phase. The oxidatively brominated PAN CFs were examined by scanning electron microscopy, and chemical and thermal analysis methods. From the chemical analysis, added bromine amount was 0.31 and 1.37 mmol per
$\mathbf{g}$
of PAN CFs. Two peaks in thermodesorption profiles of HBr, as the product of bromine detachment, confirmed the energetic difference in the attached bromine groups. We found the effect of the liquid phase oxidative bromination on the microwave properties of the resulting PAN CFs. The scattering matrix element
$\boldsymbol{S_{21}}$
, as the parameter of losses, for the PAN CFs with 0.31 mmol of Br per
$\mathbf{g}$
increased 2.5 times in the X-band range relative to that for the pristine PAN CFs and decreased by 10% in the Ka-band range. A higher concentration of the added bromine, 1.37 mmol of Br per gram of PAN CFs, leads to the opposite effect. We suggested the optimal amount of added bromine modifier. But, we found a positive impact from 1.37 mmol of attached Br per
$\mathbf{g}$
of PAN CFs, on the masking properties of the resulting PAN CFs applied to a metal surface. Advanced masking is registered for a wide range of electromagnetic radiation frequencies, as evidenced by a voltage standing wave ratio of about 4.