Elastomer Blend Properties—Influence of Carbon Black Type and Location

Abstract

Abstract Criteria for minimizing hysteresis in carbon-black-filled elastomer blends are: (1) large black unit size, wide distribution, and low structure; (2) higher black loading in the discrete polymer phase (large zones); and (3) polymer of lower hysteresis as the continuous phase (low black loading). Of the different strength properties that were evaluated, tear and fatigue resistance showed the greatest dependence on black location in NR-BR and NR-SBR blends. Both properties were markedly higher for NR-BR, with most of the black in the NR phase. In NR-SBR, tear strength was higher with high loadings of black in the SBR. Fatigue life showed a reverse pattern, but the variations were not as great in this system. Criteria for maximizing tear resistance are: (1) small black unit size, low structure; (2) higher loading of carbon black in the continuous polymer phase ; and (3) the polymer of higher strength as the continuous phase. There may also be optimum levels of polymer zone size and black size distribution which affect tear strength. Optimized performance in a 50:50 NR-BR radial truck tire tread stock was obtained with a wide-distribution N-375 (50:50 N-351-N-110 blend) black with 75% location in the NR phase. This black gave 5–6°C lower heat buildup, equivalent modulus, 35% higher tear strength, and almost double the fatigue life of a conventionally mixed N-220 at essentially equivalent tread wear resistance (−4%). Optimized performance in 50:50 NR-SBR was indicated for a wide-distribution N-231 type (50:50 blend of N-351-N-119) with 75% of the black in the SBR phase. In comparison to conventionally mixed N-234 and N-220, this black gave about 8–10°C lower heat buildup, about 15% lower modulus, and essentially equal tensile, tear, and fatigue properties. Alternatively, a standard N-231 type with 75% location in the NR phase showed about 5–6°C lower heat buildup, about 20% lower modulus, equivalent tensile strength, 60% higher tear resistance, and 75–120% higher fatigue life.