Crystallization Behavior as a Tool for Assessing the Degree of Dispersion of Elastomer Blends

The present study has demonstrated the suitability of the DSC technique for studying the blending characteristics of unvulcanized unloaded BR-SBR blends. It has been shown that, especially during the initial stages of the blending process, BR-SBR blends can be conveniently characterized in terms of the index M, which can be derived from composition (heat of fusion) measurements on a number of spot samples taken at random from the blend. During the later stages of the blending process, moreover, additional information about the degree of blending can be obtained from the degree of interference of SBR with the crystallization of BR. Furthermore, it has been found that the BR-SBR systems investigated follow an exponential rate law of blending during the early stages of blending, which allows blending processes to be described quantitatively by a single parameter, the rate constant. The approach adopted appears to be useful for a suitable characterization of BR-SBR blends in terms of the degree of blending and also for assessing the influence of blending conditions and the performance of blending equipment. An additional advantage of this method is that it can easily be extended to the characterization of unvulcanized (probably also vulcanized) black-loaded compounds which are difficult to examine by other methods. Finally, it should be noted that this approach is not necessarily restricted to BR-SBR blend systems, but can also be applied to other elastomer systems, (e.g. butadiene rubber and natural rubber, natural rubber and isoprene rubber), blends of thermoplastic materials (e.g. polyethylene and polystyrene), or blends of elastomers and thermoplastics. The only limitation, however, is that one of the components of the blend must be able to crystallize under conditions where the other component, is not.