Technical Notebook: Evaluation of liquid farnesene/butadiene rubber in a silica tread

The potential of liquid farnesene/butadiene rubber (LFBR) was evaluated in a silica tread formulation for passenger car radial (PCR) tires. The LFBR was evaluated at 5 phr of LFBR in place of 5 phr of TDAE oil and cure package ratio of 1.05 in the experimental compound. The test plan included Mooney viscosity, MDR cure rheometer, tensile stress strain properties, hardness, dynamic mechanical properties for tire performance predictors, extrusion shrinkage, coefficient of friction—dry, wet, and ice, RTM Friction Tester (MODEL FR-7225) ice coefficient of friction, angle abrader at four severities, physically bound rubber and chemically bound rubber.

The LFBR had the following advantages in a silica tread. LFBR reduced predicted rolling resistance (improved fuel economy) slightly. The bound rubber and chemically bound rubber were increased by LFBR, suggesting improved polymer to filler interaction. LFBR reduced die swell, reduced shrinkage and increased throughput.

The area in which LFBR had the most impact was its dramatic effect on the low-temperature dynamic mechanical properties. LFBR improved predicted winter traction (lower G* at -20°C). LFBR shifted the glass transition temperature slightly to lower temperatures, thereby reducing G* at -20°C. The ice coefficient of friction was directionally better with LFBR by two types of testing: the RTM Friction Tester (MODEL FR-7225) and a Trust Washer Testing Machine per ASTM D 3702.