Methods of processing particulate carbon material, such as graphic particles or agglomerates of carbon nanoparticles such as CNTs are provided. The starting material is agitated in a treatment vessel in the presence of low-pressure (glow) plasma generated between electrodes. The material is agitated in the presence of conductive contact bodies such as metal balls, on the surface of which plasma glow is present and amongst which the material to be treated moves. The methods effectively deagglomerate nanoparticles, and exfoliate graphitic material to produce very thin graphitic sheets showing graphene-type characteristics. The resulting nanomaterials used by dispersal in composite materials, e.g. conductive polymeric composites for electric or electronic articles and devices. The particle surfaces can be functionalized by choosing appropriate gas in which to form the plasma.