I incorporated rubber into bitumen along with oil, SBS, and SBR; however, despite carefully optimizing the formulation, the rubber did not melt effectively why ??
There are many different grades of rubber. With high molecular weight rubber, the molecules are highly entangled and will not dissolve in solvents as a result. This is only a physical entanglement but the rubber behaves as if it is chemically cross-linked. This entangled rubber will absorb solvent and swell but will not dissolve, similar to how a cotton ball can absorb liquid. The rubber must be run through a two roll rubber mill to line-up the molecules and break any entanglements to be able to dissolve. The rubber does get slightly degraded in the process. The sheets produced can be cut into small pieces and stirred vigorously in solvent. Vigorous stirring is essential to keeping the pieces from sticking together into a solid mass again. The rubber sheets must be used within a few hours or the rubber becomes entangled again. You see the sheets shrink with time. There are grades of crumb rubber that are specially made to not require milling but these still require adequate shearing and cutting action during mixing in order to fully dissolve, usually with a Cowles type of dispersing blade.
