Ultrasonically Extruded SBR, BR and Their Blend Filled with Silica after Extrusion

Extrusion of SBR, BR and 50/50 SBR/BR blend without and with ultrasonic treatment at amplitudes 3.5, 5, 7.5 and 10 µm was carried out and their molecular structure was determined. Significant reduction of die pressure was observed during ultrasonic treatment due to the thixotropic effect. Ultrasonic treatment of these rubbers at low amplitudes created molecules of higher molecular weight via long-chain branching. Ultrasonic treatment of SBR at 5 µm created a small amount of gel. In contrast, no gel was generated after similar treatment of BR and SBR/BR blend. However, at high ultrasonic amplitudes gel was formed in rubbers and their blend. Extruded rubbers and blend were compounded with precipitated silica. It was found the formation of branches improved the rubber-filler interaction, as confirmed by the increase of bound rubber content. The filler-filler interaction was also reduced in these compounds, as indicated by study of Payne effect. The improved rubber-filler interaction and reduced filler-filler interaction led to an increase of the modulus at 100% elongation and tensile strength of SBR/silica vulcanizates. Based on the DMA temperature sweep, a lower rolling resistance in BR/silica and SBR/BR/silica vulcanizates is predicted. Ultrasonic treatment of SBR, BR and SBR/BR blends at high amplitudes led to gel formation hindering their mixing with silica.