Multiple percolation in a carbon-filled polymer composites via foaming

This article describes an investigation into the effects of foaming on the electrical conductivity for a carbon-filled cyclic olefin copolymer (COC) composite incorporating both chopped carbon fibers (cCF) and carbon black (CB). Foamed and solid samples were injection molded and then analyzed for cell size, fiber length, fiber orientation, and electrical conductivity. Foamed samples exhibited higher electrical conductivity in the through-plane direction for materials containing only CB or composites containing both filler types, and reduced electrical conductivity in the cCF-filled composites. The increased electrical property gained by foaming was attributed to multiple percolation with CB aggregates forming more effective conductive clusters and networks in the continuous polymer phase during growth of the gas domains. A mechanism for the phenomenon was proposed based on these experimental observations.