Hierarchical microdomains in solution and emulsion polymerized elastomers induced by synthesis and processing and potential effects on properties

The morphology of raw rubber plays a significant role in the degradation processes of rubber. The results of an experimental study involving a unique technique of surface preparation suggests that there is a hierarchy of morphological levels, i.e. those induced by processing and those by emulsion versus solution polymerization. After a micro-level study, the presence of a grain-like structure is found in emulsion polymerized styrene butadiene rubber, ESBR, and absent in solution polymerized styrene butadiene rubber, SSBR, samples. The grain-like structures are roughly spherical in shape and have characteristic sizes of sub-emulsion particles. The rubber particles are examined by SEM, TEM, and AFM micrographs and theological properties. It is found that sub-emulsion particles created during emulsion polymerization remain intact during the processing steps commonly used in the fabrication of rubber articles thus provide a means to understand inherent failure mechanisms. Furthermore, processing induced morphologies, called mixing zones, in filled and gum rubber vulcanizates are found for ESBR and SSBR. In addition to the grain-like structures from the polymerization these mixing zone structures also play a role in the fracture and wear processes. Finally, the length scale at which intrinsic wear particles are formed is compared with those in the processing and polymerization induced morphologies.