The rheological properties of chlorosulfonated polyethylene (CSM) loaded with conductive carbon black filler were measured using capillary rheometer at three different temperatures (110, 120, and 130 degrees C) and four different shear rates (12.26, 24.52, 61.3, and 122.6 s-1). The effect of filler and plasticizer [dioctyl phthalate (DOP)] loading on melt flow properties of CSM was also studied. The viscosities of all samples decrease with shear rate indicating their pseudoplastic or shear thinning nature. The higher shear viscosity is observed for the CSM loaded with higher filler content, which may be due to inhibition of the polymer chain motion by the filler particles. With increasing filler loading the extrudate swell clearly decreased, which is attributed to the limitation of the elastic recovery of the polymer chains by filler particulates. Further, the reduction in die-swell ratio with increase in plasticizer loading indicates a reduction in melt elasticity compared with the composite containing no DOP. The dependence of shear viscosity on temperature obeyed the ArrheniusEyring expression, and the activation energy (E?) decreased with increasing shear rate. Extrudate swell is a non-linear function of shear rate. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012