MODES OF DISPERSIVE MIXING AND FILLER AGGLOMERATE SIZE DISTRIBUTIONS IN RUBBER COMPOUNDS

Dispersive mixing experiments in shear and elongational flow regimes w ere carried out in a rotational rheometer and capillary rheometer, res pectively, with values of stress being measured during mixing. Dispers ive mixing was also carried out in an intermeshing internal mixer. Agg lomerate size distributions determined from thin sections of samples t aken at different stages during mixing were compared with distribution s calculated for model fracture and attrition dispersive mixing mechan isms. For the SBR-carbon black compound used in the experiments it was concluded that dispersive mixing occurs by a sub-divisional fracture mechanism in both shear and elongational flow regimes and under condit ions of both low and high stress. Results from the internal mixer expe riments suggest that each rotor revolution brings about disagglomerati on by a fracture mechanism in a relatively small portion of the compou nd, which is then distributively mixed into the bulk of the batch.