New Methods for Electron Microscopy of Polymer Blends

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Abstract
Two new methods of sample preparation have been developed for electron microscopical examination of polymer blends. The first is an ebonite method where the blend is hardened in a sulfur-sulfenamide-zinc stearate mixture and then microtomed. The second is a cryogenic method where the blend is microtomed in the frozen state and then stained with osmium tetroxide. These methods have been used to examine styrene—butadiene rubber/cispoly (butadiene), natural rubber/ethylene propylene diene monomer rubber, NR/trans Polypentenamer blends, and a NR/starch mixture. Sharp, clear phase differentiation is obtained with all blends studied. SBR/PB blends were obtained when the viscosities of the blended polymers were similar. Similarity of molecular structure, increased milling time, and increased milling temperature also decreased the zone size of the dispersed phase. A three-phase system was observed when a high-styrene SBR was blended with PB ; the third phase consists of block poly (styrene) embedded in the SBR phase. Under all conditions SBR/PB blends were found to be heterogeneous, with no evidence of a single homogeneous phase.

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