High oleic soybean oil and hydrogenated soybean oils having a different degree of unsaturation were investigated as bio-based plasticizers for ethylene-propylene-diene monomer (EPDM) rubber filled with carbon black and vulcanized with sulfur. The plasticizing effect of the oils with different unsaturation levels was studied by dynamic mechanical analysis (DMA) while the variation in crosslink density of EPDM rubbers was investigated by the equilibrium solvent swelling method. The linear thermal expansion coefficient (LTEC) at different temperatures for EPDM rubbers formulated with different oils was examined by thermomechanical analysis (TMA). The oil with the highest level of unsaturation demonstrates the greatest plasticizing effect but interacts with vulcanizing sulfur lowering crosslink density and deteriorating the mechanical properties of the EPDM rubber. Hydrogenated oil with all-saturated fatty acid chains shows no decrease in crosslink density, improvements in the mechanical properties of rubber but is less effective as a plasticizer for EPDM. The results of tensile testing for EPDM rubbers formulated with different concentrations of soy-based oils were studied, correlated, and discussed. The properties of soy-based EPDM rubbers compared to the properties of EPDM rubbers formulated with petroleum-based paraffinic oil.

Soybean oils having less unsaturation than conventional soybean oil (SBO) were studied as sustainable plasticizers for ethylene‐propylene‐diene monomer (EPDM) rubber compounds vulcanized with peroxide. In EPDM formulations, part of the petroleum‐based paraffinic oil (PO) was replaced with soy‐derived plasticizers such as high oleic soybean oil (HOSO), partially hydrogenated soybean oil (PHSO), and completely hydrogenated soybean oil (HSO). The mechanical and viscoelastic properties of EPDM rubbers formulated with soy‐derived plasticizers were studied and compared with the properties of PO‐based rubber. Torque rheometry was used to study the vulcanization process and the properties of the vulcanized rubber compounds were evaluated using tensile testing, compression testing, dynamic mechanical analysis, and solvent swelling experiments. The equilibrium swelling test and examination of gel fraction demonstrated the incorporation of soy‐based process aids into the rubber network during vulcanization. It was found that soy‐derived plasticizers could partially substitute for the petroleum‐based plasticizer in EPDM compounds with minimal impact on properties. An additional benefit of the use of hydrogenated SBO is the increase of crosslink density in vulcanized rubber indicating enhanced peroxide efficiency.

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