ESTIMATION OF THE VOLUME RESISTIVITY OF ELECTRICALLY CONDUCTIVE COMPOSITES

The modeling of the electrical conductivity of polymer composites rein forced with conductive fibers is investigated. Existing models general ly can be divided into percolation theories and non-percolation theori es. The basis of the percolation theory is the fact that the conductiv ity of the composite increases dramatically at a certain fiber concent ration called the percolation threshold. This theory can be used to mo del the behavior of the composite or to predict the percolation thresh old itself. Non-percolation theories include terms, which account for microstructural data such as fiber orientation, length, and packing ar rangement. A comparison of experimental data with predictions from the various models reveals that only the percolation theory is able to ac curately model the conductive behavior of an actual composite. Two alt ernative new models, which predict the volume resistivity of a composi te using microstructural data, are evaluated. The first model relates resistivity to the concentration and orientation of the fibers, while assuming perfect fiber-fiber contact. The relationship between resisti vity and fiber concentration predicted by the model is in qualitative agreement with actual data, and predictions of the anisotropy in volum e resistivity compare well with experimental results. The second model accounts for the effect of fiber-fiber contact and fiber length on co mposite resistivity. Predictions are in excellent agreement with exper imental data for polypropylene composites reinforced with nickel-coate d graphite fibers.