Micrography of a Triblend

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Abstract
A micrographic study has been made of a banbury-mixed triblend consisting of natural rubber, neoprene and ethylene-propylene terpolymer, of the composition 50 NR/30 CR/20 EPDM, in a pure gum blend as well as loaded with 35 phr N-330 black. A combination of techniques was used, including phase microscopy and electron microscopy of frozen as well as of embedded sections. Each of the above techniques contributed to the final interpretation of the observed complex phenomena. In the pure gum blend natural rubber forms a continuous phase. Neoprene rubber shows a three dimensional network of large strands of an average width of about three microns. The EPDM is dispersed in small globules throughout the matrix, generally of less than one micron diameter. Three different blends were made in which the carbon black was added to one single elastomer and then cut back with the remaining elastomers. The fourth blend was made by incorporating black in a preblend of the elastomers. A systematic approach to the evaluation of the carbon black distribution in triblends is described and its importance to reinforcement discussed. Problems in measurement of zone sizes are explained. The affinity of the black for the various elastomers is indicated. A major conclusion is that carbon black does not transfer from one elastomer phase to another during mixing. Most of the findings are applicable to all blend systems.

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