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.

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A brief introduction is given into the theory of radiation scattering by rigid spheroids and deformable random coils dispersed or dissolved in a liquid medium subjected to flow at a well-defined velocity gradient. The theory is limited, in the former instance, to spheroids whose largest dimension does not exceed 13 of the wavelength of the incident radiation. It is shown that the radiation scattering increment produced by flow makes it possible to determine not only the axial ratio, as obtainable by streaming birefringence, but also the numerical values of semimajor and semiminor axis of a spheroid provided two orthogonal components of incident linearly polarized light are used. Essentials of the construction and operation of an apparatus designed for the study of hydrodynamic radiation scattering are described.

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Further insight into the mixing process has allowed a definition of the intermediate objectives of processing, which relate to the different transformations that occur as mixing energy is added to a rubber formulation. These convert the ingredients into a coherent mass with specific flow characteristics and determine the efficiency of the next unit, therefore contributing to overall productivity. The total energy added to the batch is derived from a combination of Banbury, mill, and extruder. These processing units vary in the efficiency with which they achieve the required material transformations. Proper allocation of mixing energy to the most effective equipment, with a knowledge of the total energy required to achieve the desired quality, allows a rational optimization of productivity and product quality. Operating profiles for each unit have been constructed in order to aid in optimizing the process. Using a fixed total energy input, these profiles were used to estimate the productivity of each processing unit. The study shows that in a semicontinuous operation with laboratory-size Banbury, mill, and extruder, the extruder is the primary determinant of overall productivity. The study also shows that maximizing productivity in a single unit will not necessarily lead to the highest productivity along the equipment train. Material properties affect overall productivity in several ways. In this work, carbon black surface area determined the total energy required to attain the desired quality level, the flow rate in the extruder, and the energy required to attain the maximum flow rate. Future studies should focus on the derivation of operating equations for specific equipment and materials. These equations should quantify the interrelationships between the different engineering parameters (such as screw or rotor speeds and Banbury ram pressure), the processing parameters (such as mixing time, fill factor, and temperature), and material variables (such as Mooney viscosity, carbon black morphology, and black and oil loading).