Experimental study of the relationship of processing to the morphology in blends of SBR and cis‐polybutadiene with carbon black

Abstract

AbstractThe morphology of carbon‐black‐loaded styrene–butadiene rubber (SBR)/cis‐1,4‐polybutadiene (BR) blends is characterized as a function of mixing energy input. The blends consist of an 80:20 weight ratio of SBR and BR with the incorporation of 20 phr carbon black via three different schemes. These schemes are: (1) free mixing of the three components, (2) mixing of BR–black masterbatch with SBR, and (3) mixing of SBR–black masterbatch with BR. Differential scanning calorimetry (DSC) and electron microscopy (EM) results indicate that the domain morphology is strongly affected by the manner in which the carbon black is introduced into these blends. Some of the features of the blends are as follows: (1) BR, which is the minor rubber component, is always the dispersed phase, and its domain size decreases with increasing energy input during mixing. (2) In the black–rubber masterbatch mixing, the black always stays in the original rubber phase throughout the mixing process. No significant migration of carbon black from one rubber phase to the other is observed. (3) In the free mixing process, the carbon black agglomerates initially line up along the SBR–BR interfaces, and later disperse throughout the SBR matrix with increased mixing. However, the DSC results suggest that the amount of carbon‐black‐free BR is decreasing with increased mixing. This would occur if there is created a carbon‐black‐loaded SBR–BR diffuse interphase. A model is developed to interpret these findings.