Shear-induced migration of conductive fillers in injection molding

The effect of shear-induced conductive filler migration on surface and volume conductivity of injection molded articles of polystyrene and polypropylene with carbon black was investigated. It was found that the loss of conductivity was most significant when the mean particle concentration was at or slightly above the percolation threshold. The compounds with mean particle concentration well above the percolation threshold showed no loss at all. The conductivity decreased with the increase of shear rate used in molding. The removal of surface layers by excimer laser led to restoration of the conductivity to the value of well-mixed, compression-molded specimens. The thickness of surface layer removed before conductivity was restored was found to be a strong function of the shear rate and the nature of polymer used. Polym. Eng. Sci. 44:2101-2109, 2004. [c] 2004 Society of Plastics Engineers.
INTRODUCTION The commercial success and popularity of conductive polymer compounds are tied to relatively easier control of conductivity by the choice of proper fillers and their contents in compounds. The [...]