Use of carbon fibril additives to reduce the dc resistivity of elastomer‐based composites

We have prepared insert model solid rocket propellants of two kinds, polycaprolactone (PCP) networks highly (60%) plasticized with triacetin and hydroxyl‐terminated polybutadiene (HTPB) cross‐linked with isophorone diisocyanate, both filled with over 65% NaSO 4 and Al powders as well as traces of fine carbon fibrils 100 Å thick and several micrometers long. Sheets of these dieletric composites were used for dc surface and volume electrical resistivities near room temperature. Addition of less than 1% fibrils in the PCP composites reduces volume resistivity by a factor of 10. The amount required for HTPB is only 0.1% leaving processability unaffected; resistivity reduction rises from one to nearly four orders of magnitude as potential differnce in increased from 10 to 500 V. Addition of fibrils to HTPB composites is a promising candidate for minimizing the incidence of dangerous electric discharge events. © 1995 John Wiley & Sons, Inc.