Volume resistivity of carbon-fibre-filled epoxy-resin under shear flow

Abstract

The volume resistivity of carbon-fibre-filled epoxy-resin samples under shear flow was investigated by a rheometer with double cylindrical sample cells. The outer and inner cells were also used as electrodes. Effects of shear rate and fibre content on the resistivity were investigated. These results were compared with those of carbon-fibre-filled silicone-oil samples. The volume resistivity showed a minimum value at a characteristic shear rate. In order to explain the experimental results, the shear rate indicating minimum resistivity was assumed to be a characteristic shear rate, where carbon fibre formed the densest network structures. When the shear rate was lower than the characteristic value, the resistivity decreased with increasing shear rate, due to the increase in frequency of forming and breaking up of electrical networks made by the fibres. The resistivity increased with increasing shear rate, when it exceeded the characteristic value because of fibre alignments parallel to the electrode. These assumptions were confirmed using epoxy-resin samples filled with carbon fibres, whose volume resistivity can be measured over a wide range of shear rate. The maximum volume fraction of fibres for epoxy-resin samples was greater than that for silicone-oil systems because of the difference between the viscosity of epoxy resin and that of silicone oil. © 1998 SCI.