Blends of PS with SBR Devulcanized by Ultrasound: Rheology and Morphology

The rheological properties and the morphology of blends of styrene-butadiene rubber (SBR), devulcanizated by ultrasound (dSBR), with polystyrene (PS) were studied. A compatibilizer, a styrene-butadiene block copolymer (SBS) was also added to dSBR/PS blends. The shear viscosity at low and high shear rates, the complex dynamic viscosity and the creep behavior were measured. It was observed that the addition of the dSBR to the PS caused little change in the shear viscosity at high shear rates, decreased the die swell and increased the elastic recovery. The analysis of the dSBR particles in blends after capillary rheometry showed that their shapes were extremely irregular with their sizes decreased and distribution narrowed with increase in the amount of dSBR and the shear rate. The addition of SBS to the blends was found to be more efficient on decreasing the dSBR particle size at the lowest concentration of dSBR. Depending on the dSBR concentration, the dSBR particle sizes in the blends varied between 18 and 6 mm. Thus in order to achieve a toughening of PS by an addition of dSBR, their particle size should be further reduced by changing the devulcanization process conditions.