Volume instabilities in capillary flow of pure SBR and SBR compounds

The flow instabilities of pure styrene-butadiene-rubber (SBR) and SBR compounds filled with silica were characterized using capillary rheometry. Above a critical shear stress, volume defects develop, leading to products of unacceptable quality. Unlike other polymers (polystyrene and low density polyethylene), the onset of these defects is concomitant with a transition from no slip (or weak slip) to strong slip conditions. Volume instabilities are affected by the silica content and the type of additive (coating or coupling agents) present in the compounds. A method based on image analysis is proposed to quantify volume defects, which can help to compare the different compounds in terms of extrusion quality.