The electrical behavior of thermosetting polymer composites containing metal plated ceramic filler

This paper describes the electrical behavior of a thermosetting system, based on epoxy resin, containing metal plated fillers. Ceramic fillers such as chopped glass fibers and mica flakes were coated with copper by electroless plating and incorporated into an epoxy resin based on di-glycidyl ether of bisphenol A (DGEBA) with tri-ethylenetetramine (TETA) curing agent. The percolation threshold in these systems is obtained at very low copper contents of 0.11-0.44 vol%. The epoxy/copper coated mica system is characterized by an extremely large positive temperature coefficient (PTC) effect, which is not followed by a negative temperature coefficient (NTC) effect. Increasing the copper coated mica concentration raises the PTC temperature of the first temperature cycle, and exposing the material to continuous heating-cooling cycles results in a decrease in the PTC; temperature and an increase of its room temperature resistivity. Inverse relations were found between the coefficient of thermal expansion and the PTC temperature. Accordingly, the mechanism governing the PTC; effect in the epoxy/copper coated mica composite is based on a larger thermal expansion coefficient of the matrix compared with the ceramic filler. POLYM. COW POS., 26:12-19, 2005. (C) 2004 Society of Plastics Engineers