Effect of incorporation of conducting carbon black as filler on melt rheology and relaxation behaviour of ethylene-propylene-diene monomer (EPDM)

The effect of incorporation of different doses of extra conducting carbon black filler on melt rheology and relaxation behaviour of curative-free elastomer from ethylene-propylene-diene monomer (EPDM) system at 190 and 200°C, was studied using a constant shear rate plate and cone viscometer. Melts of both unfilled EPDM and carbon black filled EPDM compounds showed pseudoplastic or shear thinning flow behaviour. Increasing carbon black loading caused a monotonic increase in the pseudoplastic character of EPDM. Higher incorporation of carbon black as filler, commonly imparted a decreasing trend in rupture shear rate (Dr) and in shear hysteresis loss upto the rupture point; however, other rheological parameters, such as, limiting shear viscosity (ηL), rupture shear viscosity (ηr), yield stress (τ0) and relaxation time (tR) followed increasing trends with increasing filler loading. The trends of changes of different rheological property parameters with increasing carbon black phr have been explained on the basis of developing trends in clustering of filler particles ultimately leading to filler networking. Carbon black filler-induced structural modification of the elastomer chain segments mostly through physical interactions including occlusion within the pores of the filler particles and partly through chemical anchorage of the elastomer chain molecules or segments thereof on the surface of the conducting carbon black filler particles, utilizing the traces of functional groups (OH, CO, COOH, etc.) present in them, may also explain the observed effects.