Absorbency properties and electron paramagnetic resonance characterization of polymeric carbon black composites

Sorption kinetics in excess toluene and electron paramagnetic resonance (EPR) experiments on carbon black polymer composites show that these systems exhibit remarkable behaviours. Two types of carbon blacks, having very different primary structures, were used. The swelling ratio expressed as the mass of absorbed solvent divided by the mass of the dry sample in excess toluene has been measured over a wide range of carbon black concentration. The absorbency of these materials is strongly affected by the surface area of the carbon black and is related to the characteristics of the microstructure (porosity and tortuosity). The EPR spectra depend significantly on the structure of the carbon black aggregates. The peak-to-peak amplitudes and the line widths of the EPR spectra are suggested to be significantly affected by the surface area and the morphology of the carbon black. For Y50A samples (low-surface-area carbon black), the experimental observations are explained within the context of a heterogeneous gel: finely dispersed aggregates of submicrometre size dispersed in the polymeric matrix may be considered as additional cross links. For Raven 7000 samples (high-surface-area carbon black), it is suggested that much of the observed behaviour at low concentration can be explained in terms of the agglomerated structure increasing the tortuosity of the material and again by the heterogeneous gel picture for high concentrations.