New Studies of Carbon—Rubber Gel

Abstract High resolution electron micrographs of undistorted carbon—rubber gel were obtained by ultramicrotomy of frozen unvulcanized SBR compounds which were subsequently extracted with benzene to remove any soluble rubber. The remaining black and rubber form a 3-dimensional, meshlike network which is larger than the size of primary units of the black itself. The networks for different blacks indicate considerable compaction which increases in the direction of lower structure and surface activity (e.g., normal vs. graphitized carbon black). Removal of the soluble rubber from the carbon—rubber gel network produces visible gaps between the black units which diminish in size as the black loading increases. Soluble rubber is also removed from many regions of the black surface indicating that there is no uniform layer of surface-bonded rubber. The swollen carbon—rubber gel networks are readily dispersible in good solvents using ultrasonic energy. In the process, a high percentage of the rubber is solubilized and removed from the black surface. GPC analyses of this soluble rubber from the gel indicate higher molecular weight in comparison to the soluble portion removed by benzene extraction.