Quantitative Relationship between Mineral Oil Composition and Elastomer-Extender Interaction Parameter

Abstract

Abstract Among the synthetic rubbers, the styrene-butadiene elastomers (SBR) extended with oil have grown more and more important in these last years. These elastomers are obtained by masterbatching an SBR latex of high Mooney viscosity with a mineral oil before coagulation, the oil content normally ranging between 37.5% and 50%. The mineral oil can be classified as predominantly paraffinic, naphthenic, or aromatic according to the ratio of carbon atoms involved in the paraffinic, naphthenic, or aromatic structures. The oil composition greatly affects both the processing and the final-product properties of the extended elastomer. It is well known, for instance, that SBR extended with paraffinic oil is more critical in processing than when extended with naphthenic or aromatic oils, and, on the other hand, that SBR extended with paraffinic oil shows better resistance to the discoloration caused by exposure to light. Leaving the long list of the effects on elastomeric properties of oil composition to the many papers existing on this subject, we prefer to deal here with a very important subject not very much studied on any quantitative basis until now. The oil composition affects many characteristics of the polymer because it brings controllable variation to the physical-chemical interaction between the polymer and the extender, measurable by the Flory-Huggins interaction parameter and strictly related to the more commonly known compatibility meaning. This work deals with the quantitative relationship between the composition of various mineral oils (determined by a well-known method) and their interaction parameters with SBR which greatly affect the main properties of the extended elastomer and which we determine by a swelling measurement of the crosslinked elastomer.