Carbon Black Distribution in Elastomer Blends

Abstract A new electron microscope technique permits study of the heterogeneity of elastomer blends and filler distribution therein. Vulcanizates are embedded with a specific monomer system which is subsequently polymerized. Specimens are then sectioned with an ultramicrotome and examined in the electron microscope. Excellent contrast between polymers was obtained in examination of blends of natural rubber with several other elastomers. The homogeneity of these blends is shown to be influenced by mixing procedure and polymer characteristics such as viscosity and various interaction effects. Differences in filler location in elastomer blends can also be detected readily. Carbon black (ISAF) will usually locate preferentially in the polybutadiene in a 50/50 preblend with natural rubber. This affinity is shown to depend on polymer viscosity and can be varied. Investigations with precipitated silica and chemically oxidized ISAF suggest that polarity factors can supersede viscosity considerations and determine filler locations in the blend system. The carbon black content of polybutadiene in 50/50 blends with natural rubber was systematically varied from 7 to 95 per cent. Road wear and tensile strength were highest with most of the carbon black in the polybutadiene. Hysteresis and tear strength were optimized with about 60 per cent of the black in the polybutadiene.