Experimental studies of the relationship of processing to the crack growth of carbon‐black‐loaded SBR—cis‐polybutadiene compounds

Abstract

AbstractThe crack growth of a highly carbon‐black‐loaded SBR—cis‐polybutadiene (BR) blend is investigated as a function of the distribution of carbon black in the individual rubber phases. The blend compound consists of SBR/BR/carbon black/oil = 60/40/85/60 by weight ratio and curatives. A new “old process” is devised to control the carbon black distribution in the individual rubber phases, that is, cross mixing the SBR and BR black master batches with different amounts of carbon black in the SBR and BR patches. The results show that crack growth is very sensitive to the carbon black distribution. A better crack growth resistance compound is seen containing proportionately more carbon black in the major rubber SBR phase. A simple analogy of rubber blends to the rubber‐modified thermoplastics is proposed to interpret these findings. The heat buildup of the blends is also affected by the carbon black distribution. A low heat buildup compound is observed in the system in which more carbon black is in the SBR batch, which is also a better crack growth resistance compound. It is not unexpected that the strength of rubbers decreases with increase of temperature, and so the rate of crack growth becomes faster as heat builds up.